US20100328272A1 - Optical system, an analysis system and a modular unit for an electronic pen - Google Patents

Abstract

A modular unit is designed for an electronic pen. The modular unit comprises a carrier with a receiver for a writing implement, a printed circuit board, a two-dimensional radiation sensor mounted on the printed circuit board, and an imaging unit which defines an image plane. The carrier, the printed circuit board, and the imaging unit are joined together with the imaging unit facing the radiation sensor to locate the image plane at the radiation sensor. A radiation source, such as an LED or a laser diode, may be arranged on the printed circuit board or mounted in a holder on the imaging unit. The imaging unit may be implemented as a boresight unit for controlling the spatial origin of radiation transmitted towards the radiation sensor. The boresight unit may comprise a radiation-transmitting channel, an imaging lens, and a redirecting mirror in the channel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application claims the benefit of Swedish patent application No. 0303351-1 and U.S. provisional patent application No. 60/529,118, both filed on Dec. 15, 2003, as well as Swedish patent application No. 0401802-4 and U.S. provisional patent application No. 60/586,083, both filed on Jul. 8, 2004, which all are hereby incorporated by reference.
FIELD OF THE INVENTION
• The present invention relates to an optical system, which is arranged to irradiate an object and to transmit an image of the object to an image plane. The invention also relates to an analysis system including such an optical system, and to a modular unit for an electronic pen.
BACKGROUND ART
• In the ever increasing demands on mobility of society of today, it is popular to provide small and portable devices having imaging capability. The optical systems of the above type are thus implemented in handheld imaging devices, such as handheld scanners and electronic pens. In order to restrict the overall size of such a handheld device, it is desirable to make the optical system compact.
• The optical system typically comprises an irradiating system including a radiation source for providing the irradiation of the object, and an imaging system including a two-dimensional radiation sensor for recording. an image of the object. For handheld devices, the spatial orientation between the optical system and the object, which typically is a plane surface, such as a paper, may vary substantially. For example, during the process of writing with an electronic pen, the pen will frequently be held at varying angles to the paper. Thus, the spatial orientation of the paper also varies in relation to the radiation sensor and the radiation source. As the angle varies, the relation between the radiation sensor and the writing surface will be changed. This sets demands on an imaging system to adequately image the viewed part of the object for different angles between the pen and the paper.
• Further, demands are set on the radiation source to irradiate the object properly. These demands are accentuated when the radiation source and the radiation sensor are arranged at positions that relate to the object in different ways, such as being arranged at different distances to the object and forming different angles to the object. In these cases, the radiation source needs to emit radiation in a sufficiently large solid angle in order to ensure that the viewed object area is irradiated irrespective of orientation changes between the handheld device and the object.
• WO 03/001358 discloses an electronic pen, in which a camera unit, a light source and a writing implement are carried by a common mounting part which is arranged at the front end of the pen. This design aims at controlling the mutual location of relevant components in the pen. However, the assembly of this electronic pen is not entirely satisfactory. Further, the electronic pen still involves relatively long tolerance chains between the components of the camera unit and the light source, as well as an electrical coupling between the camera unit and a printed circuit board that may increase the manufacturing cost, decrease the durability of the pen, and introduce manual assembly steps in the production.
• WO 03/025658 discloses an optical component which is designed to enable an irradiating system and an imaging system to share optical axis. Thus, irrespective of its orientation in relation to the object, the radiation source will irradiate the area of the object being imaged by the radiation sensor.
• U.S. Pat. No. 5,939,702 discloses an optical reader, in which an emitter and a photodiode are mounted on a circuit board and a light pipe is used for communicating light between an external device, such as a paper having optical data, and the emitter and the photodiode. This optical reader forms merely a pointing means and provides no possibility of optical detection while using a writing functionality. Further, the optical reader is only capable of point detection and requires the reader to be moved for obtaining one- or two-dimensional data. Moreover, the emitter and the photodiode uses the same light pipe, which may cause the photodiode to detect light that comes directly from the emitter and has not interacted with the external device.
SUMMARY OF INVENTION
• It is a general object of the invention to provide an enhanced optical system.
• It is a specific object of the invention to provide an optical system that is able to image an irradiated object with tolerance to varying orientations and distances between the optical system and the object. It is a further object of the invention to provide an optical system that may be implemented in a compact form. It is also an object of the invention to at least partly relieve or solve the above-mentioned problems.
• These and other objects of the invention that will appear from the following description are fully or at least partly achieved by an optical system according toclaim1, an analysis system according toclaim20, modular units according toclaims21 and38, a sensor boresight unit according toclaim29, an optical component according toclaim34, and an electronic pen arrangement according to claim49. Embodiments of the invention are defined in the dependent claims.
• According to one aspect of the invention, it relates to an optical system, which comprises an irradiating system which has an optical axis within said irradiating system and includes a radiation source, and an imaging system which has an optical axis within said imaging system and includes a two-dimensional radiation sensor, said imaging system being arranged to provide an image of an object being irradiated by said irradiating system, wherein said radiation source and said two-dimensional radiation sensor are mounted on a common substrate, and wherein said optical axis of the irradiating system and said optical axis of the imaging system are non-coinciding within said systems.
• This aspect provides for an optical system with a well-defined spatial relationship between the radiation source and the two-dimensional radiation sensor. This enables a short tolerance chain for defining the possible variation of the relationship between the irradiated area and imaged area on the object. Thereby, requirements on design tolerances and/or assembly tolerances may be relaxed, whereby the yield in serial production may be increased. Alternatively, the required solid angle to be irradiated may be reduced or the variation in orientation allowed in use between a device incorporating the optical system and the object may be increased. This is possible, since the variation due to tolerances in the relationship between the irradiated area and the imaged area is reduced. Reducing the solid angle implies that the power fed to the radiation source may be reduced, whereby battery lifetime may be increased.
• The radiation source and the radiation sensor being mounted on a common substrate may be implemented by mounting the radiation source and the radiation sensor on a common printed circuit board (PCB). This enables cheap and simple connection of the source and the sensor to electronics for controlling their function and analysing the acquired image information.
• An optical axis of a system forms a symmetry line for propagation of radiation in relation to the system. The optical axis extends within and between components of the system, and further extends beyond the components of the system to one or more objects imaged or irradiated by the system. In the context of the present application, the terms “optical axis within the irradiating system” and “optical axis within the imaging system” implies the optical axis as defined only within the components of the respective systems. Thus, these terms do not include the optical axis outside and beyond the components of the respective systems. Further, the definition that the optical axes are “non-coinciding within said systems” implies that the optical axes do not overlap or cross each other at any point within the systems.
• The provision of non-coinciding optical axes of the irradiating system and the imaging system, within the systems provides a possibility to optimize irradiating optics and imaging optics to their respective purpose. Further, the risk of leakage of radiation directly from the radiation source to the radiation sensor may be reduced.
• As mentioned above, depending on the orientation between a device incorporating the optical system and the object, different areas of the object will be imaged. At a certain orientation between the device and the object, a planar object may be arranged at the object plane of the imaging system. However, when the orientation is changed, the planar object will not lie in the object plane of the imaging system. The imaging system may still image the planar object by a depth of field of the imaging system allowing deviations from the object plane.
• The irradiating system may be arranged to redirect radiation from the radiation source, and the imaging system may be arranged to redirect radiation from the irradiated object towards the radiation sensor. This implies that the radiation source and the radiation sensor may be arranged on a substrate that extends in a direction substantially along a longitudinal axis of an elongate device, wherein the area to be imaged and irradiated is at a short end of the device. Such a device may be an electronic pen or a bar code reader. Thus, this arrangement may be suitable if the radiation source and the radiation sensor are to be mounted on e.g. a common PCB in an electronic pen.
• The optical axis within the irradiating system and the optical axis within the imaging system may run essentially in parallel to each other. This ensures that the optical axes will be non-coinciding within the systems. Further, optical components of the irradiating system and optical components of the imaging system may be arranged without interfering with each other.
• The optical axis within the irradiating system and the optical axis within the imaging system may further run essentially parallel to the common substrate. Thus, the substrate will not interfere with the optical path of the irradiating and imaging systems.
• Moreover, the optical axis within the irradiating system and the optical axis within the imaging system may define a plane which is essentially parallel to and at a distance from the common substrate. In one such arrangement, the optical axes of the irradiating and imaging systems are arranged side by side over the common substrate. Thereby, the height of the irradiating system and the imaging system over the common substrate may be minimized, and the diameter of an electronic pen including the optical system may be kept small.
• The irradiating system may further comprise a radiation guide for guiding radiation from the radiation source towards the object. The radiation guide may guide the direction of emitted radiation from the radiation source in order to direct it correctly towards the object. Further, there is a control of the emitted radiation, reducing the spreading of stray radiation. The radiation guide may comprise a mirror above the common substrate over the radiation source to provide the redirection of radiation from the radiation source.
• The radiation guide may comprise metallized non-exit surfaces. Thus, surfaces of the radiation guide not intended for output of radiation may be metallized to prevent leakage of radiation. This further enhances control of stray radiation from the radiation source and enhances control of the distribution of the emitted radiation.
• It should be noted that, as used herein, “stray radiation” implies either radiation that does not give the radiation sensor information on the imaged area, since it may not originate in this area, or radiation which has passed or leaked directly from the radiation source to the radiation detector without having interacted with the object to be imaged.
• Further, the radiation guide may present an inclined radiation-redirecting exit surface. This implies that a normal axis of the exit surface is inclined to the optical axis within the irradiating system. This provides a redirection of the radiation emitted from the radiation source towards the object. Thus, the exit surface may be inclined so as to direct the emitted radiation to create an irradiated area that better corresponds to an imaged area at the object.
• The radiation guide may also be mounted on the common substrate. This distinctly defines the position of the radiation guide of the irradiating system in relation to the radiation source, whereby the tolerance chain of the irradiating system is kept short. The tolerance of the irradiating system defines a deviation from a nominal position of the irradiated area on the object. Thus, keeping the tolerance chain short may result in a better control of the irradiated area on the object.
• The imaging system may further include a sensor boresight unit for controlling a spatial origin of radiation transmitted towards the radiation sensor. The sensor boresight unit thus controls the area viewed by the sensor. It will therefore define the boresight of the sensor. The sensor boresight unit of the imaging system may be a separate unit from the radiation guide of the irradiation system. The sensor boresight unit also provides control of stray radiation, preventing it from being detected by the radiation sensor.
• The sensor boresight unit may also be attached to the common substrate. This defines the position of the sensor boresight unit of the imaging system in relation to the radiation sensor, whereby the tolerance chain of the imaging system is kept short. The opto-mechanical tolerances of the imaging system define a deviation from a nominal position of the imaged area on the object. Thus, keeping the tolerance chain short may result in a better control of the imaged area on the object.
• Further, where the sensor boresight unit and the radiation guide are both mounted on the common substrate, the spatial interrelationship of these parts may also be well-defined, whereby a short tolerance chain is obtained for the relationship between the imaging and irradiating systems. This implies that the relationship between the imaged and irradiated areas on the object may be adequately controlled.
• The sensor boresight unit may comprise a mirror for redirecting radiation from the object towards the radiation sensor. The mirror is suitably arranged over the substrate on which the radiation sensor is mounted and above the radiation sensor to reflect radiation from the object directly onto the radiation sensor.
• The sensor boresight unit may further comprise a lens for creating an image of adequate image quality on the radiation sensor. The lens provides focus of the object plane onto the radiation sensor. The depth of field of the imaging system is suitably arranged to view an object placed in or near the object plane such that a sufficient image quality may be obtained for allowed changes to the optical set-up causing the object to move away from the object plane.
• The sensor boresight unit may comprise an optical component, which is arranged to transmit radiation towards the radiation sensor, wherein the optical component comprises a mirror for redirecting radiation from the object towards the radiation sensor, and a lens for creating an image of adequate image quality on the radiation sensor. In this way, the sensor boresight unit comprises few components, whereby tolerance chains of the production of the optical system are shortened. This implies that the allowed variation in the relationship between the irradiated area and the imaged area due to assembly tolerances is reduced. As mentioned above, reduced tolerance chains imply that the irradiated area may be reduced and, thus, that the power fed to the radiation source may be reduced. This also gives fewer problems with stray radiation since the emitted power is reduced.
• The sensor boresight unit may further comprise an aperture stop, which may be arranged in front of the optical component. The aperture stop may be used for adjusting the depth of field of the imaging system. Decreasing the size of an opening of the aperture stop will increase the depth of field of the imaging system.
• The optical component presents outer surfaces at least part of which may be covered with a material arranged to reduce internal reflections in said outer surfaces. The cover material may have optical properties adapted to provide that the majority of radiation impinging the cover material from the inside of the optical component will not be reflected back into the optical component. Thus, the cover material may have a refractive index that is matched to the refractive index of the material of the optical component, whereby radiation incident on the cover material will be transmitted into the cover material. Additionally or alternatively, the cover material may provide for absorption of radiation that impinges the walls from the inside of the component. This reduces stray radiation caused by internal reflections or scattering in the optical component. The cover material has suitably a large absorption coefficient for radiation wavelengths acquired by the sensor. Further, the cover material may also be selected to prevent radiation from entering the optical component through the cover material. For instance, this may be achieved by the cover material absorbing or reflecting the radiation impinging it from outside the optical component. This would provide an effective block for radiation incident upon the optical component through other surfaces than an entrance surface.
• The optical component may be implemented as a solid optics component formed by a unitary body. The solid optics component may be formed of a plastic material, such as polymethylmethacrylate (PMMA), polycarbonate (PC), Zeonex®, polystyrene, nylon, or polysulfone.
• The sensor boresight unit may alternatively comprise a housing, providing an internal channel, which is arranged to transmit radiation towards the radiation sensor, wherein a mirror for redirecting radiation from the object towards the radiation sensor and a lens for creating an image of adequate image quality on the radiation sensor are mounted in the housing. This implementation of the lens and the mirror implies that the imaging optics is constituted of separate conventional components, whereby manufacture and quality control is easily implemented. Further, the housing may be structured to be suited for attachment to the common substrate.
• The sensor boresight unit may further comprise an aperture stop arranged in the housing. The aperture stop may be formed as a part of inside surfaces of the housing. In this way, the housing may hold all components of the imaging system controlling the radiation path towards the radiation sensor.
• The housing presents inside surfaces at least part of which may be arranged to reduce specular reflection of radiation. The inside surfaces may comprise a material which absorbs radiation, and specifically absorbs radiation wavelengths that are acquired by the sensor. The inside surfaces of the housing may also or alternatively be rough or have an appropriate texture in order to avoid specular reflections. This reduces stray radiation to the radiation sensor caused by internal reflections or scattering in the housing. Still further, the inside surfaces may be provided with one or more radiation traps, which attenuate received radiation by one or more reflections inside the trap, and/or one or more controlling surfaces which reflect impinging radiation away from the radiation sensor, optionally into a radiation trap.
• According to another aspect of the invention, it relates to an analysis system, which comprises an optical system according to the invention, a PCB implementing said common substrate, and an image processor for analysing image information received from the radiation sensor, wherein the optical system is supported by and the image processor is mounted on the PCB.
• The optical system being supported by the PCB implies that the spatial positions of the components of the optical system are defined by their relation to the PCB, even though each component does not need to actually be mounted on or attached to the PCB. For example, a sensor boresight unit of the optical system need not be attached to the PCB. The arrangement of the optical system being supported on a PCB provides a well-defined spatial relationship between components of the optical system. Thus, a compact arrangement for the acquiring of images and the processing of the images may be provided. Further, the analysis system readily provides control of the radiation source, which is mounted on the PCB, and further provides simple and inexpensive connection of the radiation sensor to an image processor.
• According to a further aspect of the invention, it relates to a modular unit for an electronic pen having a writing implement, said modular unit comprising a carrier, and an analysis system according to the invention being mounted on the carrier, said carrier having means for receiving said writing implement in order to position the writing implement in relation to the analysis system within the electronic pen.
• This arrangement of a modular unit provides a possibility to test the quality of the analysis system before the electronic pen is finally mounted by inserting the modular unit into an outer shell of the electronic pen. Thus, defects in the analysis system may be detected at an earlier stage in production, whereby fewer steps need be made for defective products. This speeds up and improves the production process.
• Since the analysis system is mounted on the carrier and the carrier provides a means for receiving a writing implement, the spatial relationship between the analysis system and the writing implement is defined by the design of the carrier. This implies that the imaged area and the irradiated area are accurately defined in relation to a pen point of the writing implement in contact with the object. Further, the mutual mounting on the carrier of the analysis system and the writing implement implies that the modular unit provides a short tolerance chain of the relation of the imaged and irradiated areas to the pen point.
• The term “modular unit” should be construed as a unit that may be assembled and which is not held together by pieces that do not form part of the unit. In this case, the modular unit for the electronic pen forms an integral unit before final assembly of the electronic pen.
• The modular unit suitably has a dimension allowing the modular unit to be mounted inside the electronic pen. Thus, in the assembly of the electronic pen, the modular unit may be arranged within the outer shell of the electronic pen.
• The PCB of the analysis system may be mounted on the carrier for mounting the analysis system on the carrier. Thus, the position of the PCB may be fixed by the carrier. This implies that the insertion of the modular unit into the outer shell of a pen need not comprise securing the PCB to the shell.
• The carrier may have an elongate shape which extends, when the modular unit is incorporated in an electronic pen, in a longitudinal direction of the electronic pen. Hereby, the carrier may provide possibility to fix the position of several components of the pen along the longitudinal shape of the pen.
• The modular unit may further comprise a contact sensor which is mounted on the carrier. The contact sensor may detect when the writing implement is pressed against a writing surface. This detection may activate the optical system to irradiate and image the writing surface, which forms the object. The contact sensor's functionality may be obtained by components arranged integrated on the carrier or may, alternatively, be obtained by a contact sensor unit that is mounted on the carrier.
• The modular unit may also comprise means for forming attachment to an outer shell part of the electronic pen. Thus, the modular unit is prepared for installation in the pen shell. The means for forming attachment could be a hook or pin for engaging the outer shell part or a slot or recess for receiving a protrusion from the outer shell part.
• Further, the modular unit may comprise a vibrator unit, which is mounted in the carrier. The vibrator unit may by vibration provide feedback to the user e.g. when the electronic pen fails to appropriately image the writing surface.
• Moreover, the modular unit may comprise a wavelength filter mounted on the carrier. The wavelength filter may be arranged such that the radiation from the object passes the wavelength filter before being detected by the radiation sensor. Thus, undesired wavelengths for the analysis to be performed by the analysis system may be filtered out.
• According to a still further aspect of the invention, it relates to a modular unit for an electronic pen having a writing implement, said modular unit comprising a carrier with a receiver for the writing implement, a PCB, a two-dimensional radiation sensor mounted on the PCB, and an imaging unit which defines an image plane, wherein the carrier, the PCB, and the imaging unit are joined together with the imaging unit facing the radiation sensor to locate the image plane at the radiation sensor.
• The carrier provides for control of the location of the writing implement. The carrier can be manufactured with adequate precision in a separate manufacturing step.
• The provision of the radiation sensor on the PCB allows for a simple and durable construction, which can be manufactured in a cost-effective way. For example, the radiation sensor can be attached to and tested together with the PCB in a separate manufacturing step. The imaging unit may be of simple and durable construction and can be manufactured with adequate precision in a separate manufacturing step. The imaging unit may be the above-mentioned sensor boresight unit. The joining of the carrier, the PCB, and the imaging unit allows for a modular unit with adequate control of opto-mechanical tolerances which, i.a., affect the mutual relation between the tip of the writing implement and the image recorded by the radiation sensor. Further, such a modular unit may be subject to quality tests before final assembly of the electronic pen, thereby allowing for defects to be detected at a relatively early stage in production.
• The modular unit may comprise a radiation source for illuminating an object plane defined by the imaging unit. In one embodiment, the imaging unit comprises a holder for carrying the radiation source. This results in a simple and durable construction providing a short tolerance chain between the radiation source and the imaging unit. Further, the radiation source is kept in a close relationship to the imaging unit, whereby the above-mentioned effects of pen orientation on the relationship between imaged and irradiated areas on a writing surface is minimized.
• In one embodiment, the imaging unit is supported by the PCB. Thereby, the PCB may define the position of the imaging unit. However, the imaging unit need not be actually mounted or attached to the PCB. The sensor boresight unit may, for example, be attached directly to the carrier while being supported by the PCB. Since the PCB at least partly defines the position of the imaging unit, a short tolerance chain between the imaging unit and the radiation sensor may be obtained.
• According to still another aspect of the invention, it relates to a sensor boresight unit for transmitting radiation from an object to a radiation sensor, said sensor boresight unit comprising a housing, which provides an internal channel that changes direction at a turn within said housing and further provides a radiation entrance end and a radiation exit end of said channel, a lens, which is mounted in the internal channel at said radiation entrance end of said housing, and a mirror, which is mounted in the housing at said turn of the internal channel for redirecting radiation along the change of direction of the internal channel.
• According to yet another aspect of the invention, it relates to an optical component for transmitting radiation from an object to a radiation sensor, said optical component being formed by a solid body defining a radiation path within the body, said solid body comprising a radiation entrance surface for receiving radiation into said radiation path, said entrance surface including a lens element, a radiation exit surface, a tubular part for transmitting radiation in the radiation path along a longitudinal axis of the tubular part, and a mirror surface at an end of the tubular part opposite the entrance surface, wherein a normal of the mirror surface is slanted to the longitudinal axis of the tubular part such that the radiation path is redirected in the mirror surface towards the radiation exit surface of the solid body.
• Both these last-mentioned aspects of the invention respectively provide devices for transmitting of radiation from an object to a radiation sensor. This transmitting of radiation may advantageously be used in an imaging system for collecting radiation from the object and redirecting the radiation towards a radiation sensor. Thus, these devices respectively enable positioning of the radiation sensor more freely in relation to the object to be imaged by the radiation sensor.
• According to a still further aspect of the invention, it relates to an electronic pen arrangement, comprising a writing implement, an optical system which is designed to generate an image of a writing surface on which the pen is operated, said image including part of the writing implement, and a processing unit which is designed to derive data indicative of a position, based upon a position-coding pattern in said image and based upon the location of said part in the image.
• By designing the optical system to include part of the writing implement in the recorded images, the processing unit is capable of accurately relating a decoded position, given by the position-coding pattern, to the actual writing position, i.e. the position of the point of contact between the writing implement and the writing surface. Thus, the processing unit may be self-calibrating with respect to any variation, over time or between pens, in the location of the image to the actual writing position. In one embodiment, the processing unit is arranged to calculate, based upon the image, the spatial orientation of the pen and a decoded position. Knowing the position, the spatial orientation and the location of the aforesaid part in the image, the processing unit may calculate the actual writing position. During normal operation of the pen arrangement, the processing unit need not derive the location of the part in the images; instead the calculation of the actual writing position may be based on a calibration parameter which has been derived, in a preceding calibration step, from the location of the part in one or more images. In one embodiment, the electronic pen arrangement is unitary, with the writing implement, the optical system and the processing unit being incorporated in a pen device. In another embodiment, the writing implement and the optical system are incorporated in a pen device, whereas the processing unit is located in a separate device.
• Other objects, advantages and features of the invention are set out in the following detailed description of the invention, in the attached claims and in the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention will now be described in further detail with reference to the accompanying schematic drawings, which by way of example only illustrate embodiments of the invention.
• FIGS. 1aand1billustrate angles defining an orientation of an electronic pen in relation to a writing surface.
• FIG. 2 illustrates relations between contact point, imaged area and irradiated area for an optical system of the electronic pen.
• FIG. 3 is a side view of the electronic pen.
• FIG. 4 is a perspective view of a modular unit in an electronic pen, where the outer shell of the pen has been removed.
• FIG. 5 is a perspective view of components of a modular unit for the electronic pen before being assembled.
• FIG. 6 is a perspective view of the components of the modular unit ofFIG. 5 after being assembled.
• FIG. 7 is a side view of an ink cartridge and illustrates the effect of a radial gap between the ink cartridge and a receiving bore of the pen.
• FIG. 8 is a perspective view of an analysis system comprising an optical system and a processor.
• FIG. 9 is a side view of an imaging system of the optical system.
• FIG. 10 is a sectional view of an embodiment of the imaging system.
• FIG. 11 is a sectional view of another embodiment of the imaging system.
• FIG. 12 is a side view of an embodiment of an irradiating system of the optical system.
• FIG. 13 is an exploded perspective view of another embodiment of a modular unit for an electronic pen.
• FIG. 14 is a perspective view of a component included in the modular unit ofFIG. 13.
• FIG. 15 is a front view of the component inFIG. 14.
• FIG. 16 is a top plan view of the component inFIG. 14.
• FIG. 17 is a sectional view taken along the line A-A inFIG. 16.
• FIG. 18 is a bottom plan view of the component inFIG. 14.
• FIG. 19 is a bottom perspective view of the component inFIG. 14.
• FIG. 20 is a sample image taken with an electronic pen according to the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
• Referring now toFIGS. 1-4, the parts and components of an electronic pen and the functionality of the pen will initially be summarily described. Although the invention is not restricted to its use in an electronic pen, an embodiment of the invention as used in an electronic pen will illustrate the features and functionality that may be obtained according to at least some aspects of the invention.
• It should be apparent to the skilled person that features, advantages and objectives described only in connection with a particular embodiment below may be equally applicable to the other embodiments as disclosed below.
Designing an Optical System for an Electronic Pen
• InFIGS. 1a-b,anink cartridge8 of anelectronic pen1 is shown. Theink cartridge8 comprises apen point9, which will contact awriting surface14, when a user is writing. The writingsurface14 comprises a pattern, which carries information on the writingsurface14. The pattern may encode a position on thesurface14 or general information regarding what the writing pertains to. This may be used for calculating the movement of thepen point9 and/or for registering if writing is made in a special area on a paper, such as a check box or a date in a calendar. In order to decode the pattern on the writing surface, thepen1 comprises an imaging system15 (FIG. 4) for imaging an area on thesurface14. Using the imaged area, thepen1 may determine the position of thepen point9 on thesurface14. Theimaging system15 comprises a focusing lens for obtaining a sufficiently sharp image of the imaged area. Further, in order for theimaging system15 to adequately image the area on thesurface14, this area should be irradiated by a radiation source.
• When a user writes, the orientation of theink cartridge8 in relation to thesurface14 will vary. Ideally, an area centred on thepen point9 is imaged, to minimize any variations in the relation between the imaged area and thepen point9 resulting from the varying pen orientation. However, this may be difficult to achieve, since the optical axis of theimaging system15 would then have to be placed coinciding with the longitudinal axis of theink cartridge8. Further, theink cartridge8 and thepen point9 may then obscure the imaged area. Thus, theimaging system15 is arranged to image an area adjacent to thepen point9. Thereby, the relation between the imaged area and thepen point9 will depend on the orientation between theink cartridge8 and thesurface14, as will be explained below.
• InFIGS. 1a-b,the orientation between theink cartridge8 and the writingsurface14 is illustrated. This orientation may be described by using three angles. As shown inFIG. 1a,theink cartridge8 forms an inclination angle θ, which is defined as the tilt angle between the longitudinal axis A of theink cartridge8 and the normal of thesurface14. The inclination angle θ may vary substantially during writing. Further, as shown inFIG. 1a,thepen1 may be rotated around the longitudinal axis A. Since theimaging system15 is not arranged on this axis, such a rotation will affect the relation between an imaged area and thepen point9. The rotation of thepen1 around the longitudinal axis A is called a skew angle Φ. Moreover, as shown inFIG. 1b,thepen1 may be rotated in relation to the pattern on thesurface14. This rotation around the normal of thesurface14 is called a pattern rotation angle α.
• Referring now toFIG. 2, the effects of differing inclination angle θ between theink cartridge8 and the writingsurface14 is illustrated. Three different writing surfaces WS₀, WS₋₄₅, WS₄₅are shown to illustrate differing inclination angles, namely θ=0°, θ=−45°, and θ=45°, respectively, between theink cartridge8 and the writingsurface14. As shown inFIG. 2, thesurface14 is arranged at different positions along an optical axis C of the imaging system depending on the inclination angle θ. Thus, the distance between a radiation sensor of the imaging system15 (FIG. 4) and the imaged area on the writingsurface14 will also depend on the inclination angle θ. The inclination angles θ that are allowed during writing define a range of distances between the imaged area and the radiation sensor, at which the radiation sensor should detect the imaged area with an adequate sharpness over relevant parts of the imaged area for decoding the pattern on thesurface14. This range of distances is called the depth of field requirement FD of theimaging system15. As seen inFIG. 2, this necessary depth of field FD is proportional to the distance D in a reference plane, which in this case is the plane of the writing surface at inclination angle θ=0, between the contact point P, i.e. thepen point9, and the optical axis C of theimaging system15. In order to provide a large depth of field, theimaging system15 should have a high f-number, which results in low amounts of radiation being passed to the radiation sensor. If luminosity is critical, it may therefore be desirable to keep the optical axis offset or distance D to a minimum.
• Theimaging system15 images an area on thesurface14, which is the field of view of theimaging system15. Since the absolute magnification (|m|) of an object onto an image plane in the radiation sensor is inversely proportional to the distance between the object and the lens of theimaging system15, the absolute magnification of the field of view will increase with increasing inclination angle θ between theink cartridge8 and thesurface14. The field of view that is imaged onto an active area on the radiation sensor is smaller at a larger absolute magnification. Theimaging system15 should image an area on thesurface14 which holds sufficient amounts of information for decoding a pattern on thesurface14. The field of view should therefore be large enough to allow imaging of a decoding area DA. Thus, an upper limit of the absolute magnification is set in order for the field of view to include a decoding area DA. Further, a lower limit of the absolute magnification is set in order to enable discrimination of the smallest relevant details of the pattern. Also, by keeping the necessary depth of field FD as small as possible, the variation in the magnification of the imaged area is minimized.
• However, to keep the necessary depth of field FD as small as possible, the field of view should be arranged next to the tip of theink cartridge8. Thus, there is a risk that the field of view becomes partly obscured by the tip of theink cartridge8. If theink cartridge8 obscures a large part of the field of view, the imaged area of thesurface14 may not be large enough to enable decoding of the pattern. This implies that the distance D should not be designed too small. If an angle between the optical axis C and the longitudinal axis A (FIG. 2) of theink cartridge8 is increased while keeping the distance D constant, the obscuration of the tip of theink cartridge8 in the field of view may be reduced. However, a greater angle also implies that the optical axis C is further apart from the longitudinal axis A inside thepen1, resulting in a larger radius of thepen1.
• As briefly mentioned above, at least the relevant parts of the imaged area, i.e. the decoding area DA holding the pattern to be decoded, should be irradiated. This may easily be ensured, if an optical axis I of an irradiatingsystem13 is arranged coincident with the optical axis C of theimaging system15. However, if the optical axes C, I of the imaging and irradiatingsystems15,13 are arranged to coincide, optical components on the coinciding optical axes need to be adapted to perform functions of both the imaging and irradiatingsystems15,13. This may result in loss of radiation in the optical components. On the other hand, if the optical axes C, I are arranged not to coincide (FIG. 2), the relation between the imaged area and the irradiated area will depend on the angles between theink cartridge8 and the writingsurface14. Then, the design of the pen needs to arrange the irradiatingsystem13 such that the irradiated area always includes the relevant parts of the imaged area for all allowed angles between theink cartridge8 and the writingsurface14. The irradiatingsystem13 should irradiate the decoding area DA properly, for example with sufficiently uniform radiation of a sufficient magnitude (irradiance). The uniformity may be defined by the largest difference in irradiance and/or the irradiance gradients within the decoding area DA.
• The accumulated decoding areas DA for all allowed angles between theink cartridge8 and thesurface14 define a space that is to be irradiated. As described above, this space depends on the design of thepen1, i.e. on the distance D, the decoding area DA, the angle between the optical axis C and the longitudinal axis A of theink cartridge8 and the allowed angles between theink cartridge8 and thesurface14. Thus, the irradiatingsystem13 should be arranged to emit radiation in such a large solid angle γ that it covers the space to be irradiated. Placing the optical axis I of the irradiatingsystem13 close to the optical axis C of theimaging system15 implies that the required solid angle γ is kept relatively small. The properties of the irradiatingsystem13 needed for obtaining the required solid angle γ could be designed by calculating the irradiation pattern using a ray-tracing program.
• Above, the effects of differing inclination angles θ have been explained. Further, differing skew angles affect the requirements on depth of field FD and the irradiated space. Again, increasing the distance D implies that a larger depth of field FD and a greater irradiated space are needed when varying skew angles are allowed.
• When the pattern rotation angle α is changed, the encoded pattern viewed by theimaging system15 will be changed. This needs to be accounted for in calculation of the position of thepen point9 on thesurface14. Allowing all pattern rotation angles α implies that the required size of the imaged area of the writing surface is essentially defined by a circle formed by rotating the decoding area DA over 360°. However, varying the pattern rotation angle α will not affect the size of the area being imaged, the distance of the imaged area to the radiation sensor or the distance D.
Effect of Tolerances
• Thepen1 is designed with nominal parameters, such as sizes and relative mounting angles and distances, for all components of thepen1. This design gives a nominal value of the distance D. However, in manufacturing thepen1 tolerances to the nominal parameters should be allowed. Tolerance chains add up to set requirements on allowed largest value of the distance D. This largest value sets the requirement on the depth of field FD of theimaging system15. Further, tolerance chains add up to define possible needed irradiated spaces.
• In designing thepen1, the above-explained parameters of the imaging and irradiatingsystems15,13 should be considered. If the nominal distance D between thepen point9 and the optical axis C of theimaging system15 in the reference plane is decreased, the nominal depth of field FD may be reduced. This implies that an opening of an aperture stop in theimaging system15 may be increased allowing more radiation to reach the radiation sensor. Thus, the power of the radiation source may be reduced, whereby battery lifetime of thepen1 is increased. The decreased distance D may alternatively be used to allow the pattern on the writingsurface14 to comprise smaller details, while theimaging system15 is unchanged. The decrease in the nominal distance D may as a further alternative be used for allowing larger differences in the angles between theink cartridge8 and the writingsurface14, while keeping the nominal depth of field FD constant. Further, the decrease in the nominal distance D may be used for allowing larger tolerances in individual components of thepen1 or in the assembly of the components.
• These parameters, i.e. the nominal distance D, the nominal depth of field FD, the scale of the details on the writingsurface14, the allowed variation in the angles between theink cartridge8 and thesurface14, and the allowed tolerances may be varied in several different ways, wherein a change in the requirement of one parameter may cause changes in the requirements of one or more of the other parameters.
• With insufficient control of the tolerance chain, the distance D may thus for some pens be so great that theimaging system15 is not capable of supplying useful images to the processor16 (FIG. 4). This may be solved by constructing theimaging system15 with a great nominal depth of field by decreasing the opening of an aperture stop and/or decreasing the focal length of an imaging lens. This, however, may cause an undesirable restriction on the amount of radiation that can be transferred to the radiation sensor.
• The presently preferred embodiments are designed to handle decoding areas DA of approximately 3-5 mm. The distance D is suitably set in the range of about 2-4 mm, and the necessary depth of field FD is suitably set in the range of about 2.5-10 mm, preferably in the range of about 4-8 mm, and most preferably in the range of about 6.5-7.5 mm. Preferably, the optical system is designed to allow for a symmetric range of inclination angles θ, for all skew angles Φ, so as to allow the user to grip and write with the pen at any skew angle. Preferably, the range of allowable inclination angles comprises about ±30°, and preferably about ±40°, and most preferably ±45°. Preferably, the imaging system is designed with a length of the optical axis C, from the writing surface to the radiation sensor at θ=0° and Φ=0°, in the range of about 15-60 mm, preferably about 30-45 mm. At the lower limit, the imaging system may require an undesirably small aperture stop and exhibit significant image aberrations, e.g. distortion. At the upper limit, the imaging system may take up significant longitudinal and radial space in the pen and/or require an optically redirecting element at the front end of the pen.
Embodiments
• Below, some embodiments of imaging and irradiating systems within apen1 will be described, illustrating ways of designing thepen1 to meet the above-mentioned requirements.
• Thepen1 inFIG. 3 has abody2 with aforward portion2aand a cap3 with a clip4. Theforward portion2ais formed by a projecting end of acarrier5, as illustrated inFIG. 4, which is arranged to extend within ahollow casing6 towards a rear portion7 of thepen1.
• Anink cartridge8 with apen point9 is inserted into areceiver10 in thecarrier5, as illustrated inFIGS. 5-6. Thereceiver10 provides a throughbore10ain theforward portion2aof thepen1 and alongitudinal groove10baligned therewith. Theink cartridge8 is slid into thereceiver10 and may be replaced by a user. Between theink cartridge8 and thereceiver10 there is a certain radial play.
• Returning now toFIG. 4, a printed circuit board (PCB)12 is mounted on thecarrier5 to extend parallel to theink cartridge receiver10. Anoptical system11 is attached to thePCB12. Theoptical system11 comprises an irradiatingsystem13 for emitting and directing radiation towards an object, which is typically a writing surface, such as a paper, on which the user writes using thepen1. Theoptical system11 further comprises animaging system15 for collecting and detecting radiation from the object in order to record images of the object. The irradiating and optical systems operate under the control of theprocessor16 on thePCB12, which processor may implement an image processor that receives and analyses the recorded images.
• Thepen1 further comprises a means for providing power to theprocessor16, theoptical system11 and any other parts of thepen1 that need electric power. The means for providing power may be abattery21 or a flexible cord (not shown) for connection to an external source of power. Thepen1 may further comprise a means (not shown) for enabling connection to an external computer unit for transfer of recorded images or information from theprocessor16. The means for enabling connection to an external computer unit may be a wireless transmitter/receiver, a cradle connector (docking station) or any kind of wire connection, such as a USB-connector.
• When thepen1 is not used, the cap3 is normally arranged over theforward portion2aof thepen1 to protect thepen point9 and other components thereat. The clip4 can then be used to fix thepen1, for instance, in a shirt pocket. When thepen1 is to be used, the cap3 is removed and the processing circuitry of thepen1 is set in a standby mode, wherein thepen1 is sensible for activating actions. Techniques for sensing cap removal and selectively activating controlling electronics of the pen are further disclosed in Applicant's publications US 2002/0175903 and WO 03/069547, which are herewith incorporated by reference.
• Thepen1 further comprises acontact sensor arrangement17, which is mounted in a contactsensor receiving pocket18 on the carrier. Thecontact sensor arrangement17 is installed at the distal end of thereceiver groove10b.Thecontact sensor arrangement17 receives a rear end of theink cartridge8, when inserted into thereceiver10. When thepen point9 is pressed against a writingsurface14, theink cartridge8 will be pressed towards acontact sensor19 attached to a wall of thepocket18. The detection of a sufficient pressure via thecontact sensor19 is used to fully activate the controlling electronics, such as theprocessor16, and thereby also activating the irradiatingsystem13, theimaging system15, etc. If the output signal of the contact sensor represents the amount of exerted pressure, a pressure value may be associated to the corresponding image recorded at the same time, for example to be used in subsequent rendering of electronic pen strokes.
• In the embodiment ofFIGS. 5-6, the rear end portion of theink cartridge8 is inserted. and press fitted into aninsert22, which is movably arranged in thepocket18. Thecontact sensor19 is attached to a wall in the space defined by thepocket18. The space is defined so that theinsert22 can move towards and away from thecontact sensor19, but simultaneously so that theinsert22 cannot move out of thepocket18. Theinsert22 is designed to hold various makes of similar ink cartridges, which makes it possible to use exchangeable ink cartridges for ordinary ball point pens. Theinsert22 ensures good contact with thecontact sensor19 when thepen point9 of theink cartridge8 is pressed against the writingsurface14 and reduces the risk of ink possibly leaking out damaging thecontact sensor19. The design of thepocket18 causes theinsert22 to stay in place when anink cartridge8 is removed from thepen1 to be exchanged. The radial play between theink cartridge8 and thereceiver10 ensures that theink cartridge8 can be removed from thepen1 with minor resistance only. When mounting anew ink cartridge8, thereceiver10 ensures that theink cartridge8 is correctly positioned in the interior of thepen1.
• It is conceivable to essentially eliminate the radial play between thecartridge8 and thereceiver10, in order to tighten the relationship between thepen point9 and theimaging system15. However, since thepen point9 generally has a non-zero radial extension, the part of thepen point9 being in actual contact with the writingsurface14 will vary with the inclination angle and the skew angle of thepen1. This causes an inaccuracy in the determination of the pen point location on the writingsurface14. A ballpoint pen typically has a pen point (roller ball) with a diameter of about 0.5 mm. For inclination angles of ±45°, the above inaccuracy is about 0.35 mm, which is large enough to be visible if the handwriting is reproduced against a ruled background that represents the writing surface. It is possible to calculate a compensation value to minimize this inaccuracy, if the geometry of thepen point9 is known, as well as the instant inclination and skew angles. However, it has been found that these inaccuracies instead can be lowered by careful design of the total radial play.FIG. 7 shows theink cartridge8 at two extreme inclinations: +45°(solid lines) and −45° (dashed lines). As can be seen, the actual contact point remains essentially constant. This may be achieved by the size of a radial gap RG being set equal to the effective diameter of the area that is defined by the location of the contact point on thepen point9, at the extreme pen inclination angles for a zero radial play embodiment, as projected onto a plane perpendicular to the longitudinal axis of theink cartridge8. In practice,_the radial gap RG is set to about 40-90% of the effective diameter, to take into account that thepen point9 generally sinks into the writingsurface14 during writing.
• The mounting of thecontact sensor arrangement17 in the pocket18 (FIGS. 4-5), which has a well-defined position on thecarrier5, minimises risk of mutual misalignment of theink cartridge8 and thecontact sensor arrangement17. Such misalignment may interfere with the axial motion of theink cartridge8, so that an arbitrary delay is introduced in the contact sensor's detection of the pen's contact with the writing surface. Furthermore, such misalignment may cause wear on theinsert22 and/or thecontact sensor19. The mounting of thecontact sensor arrangement17 on thecarrier5 may also reduce the pen's susceptibility to mechanical shocks.
• Thecarrier5 may also be effective in protecting the electronic circuits of the pen against electrostatic discharge (ESD), in the form of over-voltage discharges or sparks over small insulating gaps, e.g. air gaps, between conductive members in thepen1. ESD may cause serious damage to the electronic circuits and/or latch-up thereof. The problem of ESD may be enhanced in electronic pens, since electrical charge may travel into or out of thepen1 via theink cartridge8, which is often made of metal. In the embodiment ofFIGS. 4-6, all such small gaps between the cartridge/contact sensor and thePCB12 are effectively eliminated by thereceiver10 and thepocket18 being located on one side ofcarrier5, and the electronic circuitry (PCB12,processor16, etc) being located on an opposite side of thecarrier5. The carrier material is continuous, i.e. there are no through holes, at least not in the surfaces defining thereceiver10 andpocket18.
• Further, mounting thecontact sensor arrangement17 on thecarrier5 provides the possibility of testing this functionality of thepen1 before thepen1 is finally assembled. Thus, the final assembly need not be made if defects are detected to the functionality of thepen1.
• It should also be appreciated that other types of sensors may be used to activate thepen1 when thepen point9 is pressed against a writing surface. For instance, part of an open electric circuit (not shown) may be arranged in the position of thecontact sensor19. In this case, theinsert22 is provided with conductive pins or a conductive sheet which, as thepen point9 is being pressed against the writing surface, contacts and closes the electric circuit. Alternatively, an optical or magnetic detector can be used to sense the motion of theink cartridge8. Aforesaid WO 03/69547 describes a contact sensor that may be used in connection with the present invention.
• Thepen1 further comprises avibrator20, which is attached to a rear end wall of thecarrier5. Thevibrator20 is connected to control equipment on thePCB12. Thevibrator20 may vibrate for giving feedback to the user. For instance, when thepen1 has detected that the user has ticked a checkbox, thevibrator20 may vibrate for signalling to the user that thepen1 has correctly detected that the checkbox was ticked. Further, when thepen1 detects an error, thevibrator20 may vibrate continuously, for example when thepen1 does not recognize a pattern on thesurface14 which it expects to recognize.
• Thecarrier5 and the parts mounted on thecarrier5, such as thePCB12, theoptical system11, thecontact sensor arrangement17, thevibrator20, and theink cartridge8 form a modular unit for thepen1. This modular unit can be tested for functionality and resistance to certain outer conditions without the need for final assembly of thepen1. This provides that defective modular units may be discarded or corrected before final assembly of thepen1. Further, the arrangement of all these parts in one modular unit provides the possibility that the modular unit is delivered by a subcontractor to a pen manufacturer or pen dealer. The pen manufacturer/dealer need then merely package the modular unit with a battery and any other desired or needed parts in an outer shell or casing before marketing thepen1. It may also be conceivable that the battery forms a part of the modular unit. In either case, the modular unit may provide the basic functionality of thepen1.
• When a user writes with the activatedpen1, an area on the writing surface adjacent or around thepen point9 is irradiated by the irradiatingsystem13 of theoptical system11. Theimaging system15 of theoptical system11 records images of an irradiated area of thesurface14 adjacent thepen point9, and theprocessor16 calculates the position of thepen1 based on the images. Here, a specific position-coding pattern (not shown) on thesurface14 may be used, for instance of the type as described in U.S. Pat. No. 6,570,104, U.S. Pat. No. 6,674,427, US 2001/0038349, US 2003/0066896, U.S. Pat. No. 5,477,012 and U.S. Pat. No. 6,330,976. With the aid of the pattern on the writing surface, the position of thepen1 can at any moment be determined, and in this way the user's writing can be recorded.
• In order to achieve good image quality, the area imaged by theimaging system15 needs to be properly irradiated by the irradiatingsystem13. This is achieved, as explained above, by the irradiatingsystem13 emitting radiation in a solid angle γ that covers a space formed by the possible positions of the imaged area dependent on e.g. the angles between thepen1 and the writing surface and the tolerances in the components of thepen1.
• Referring now toFIGS. 8-12, an analysis system will be described. The entire analysis system is shown inFIG. 8, whereas parts of the analysis system are shown in detail inFIGS. 9-12. The analysis system comprises thePCB12, on which theprocessor16 is arranged and on which theoptical system11 is mounted. The analysis system may be used for irradiating an object and imaging the thus-irradiated object. The recorded images may be analysed in theprocessor16, which is connected to theimaging system15 on thePCB12. Thus, the analysis system provides an analysis functionality, which may be used in differing optical analysis applications. The analysis system is particularly suitable for use in handheld devices, wherein an object is to be analysed based upon images of the irradiated object. The analysis system will below be described in relation to the application of the analysis system in an electronic pen, but it should be emphasized that the scope of protection of the present application is in no way limited to this use of the analysis system. It may, for instance, be applied in a bar code reader instead.
• The analysis may be achieved in each specific application by programming theprocessor16 to perform image analysis. Theimage processor16 may perform pre-processing of the images, and optionally extract information from the images, whereas an external computer unit may calculate coordinates on the writingsurface14, based upon the pre-processed images or the extracted information, as the case may be. Alternatively, theimage processor16 performs all processing on the information in the images. Alternatively, all or parts of theimage processor16 may be integrated in the radiation sensor24. In one embodiment, theimage processor16 is implemented as an application-specific integrated circuit (ASIC).
• The analysis performed is highly dependent on the application of the analysis system and the needed information from the recorded images. Therefore, in the following description, referring now toFIGS. 9-12, theoptical system11 of the analysis system will be described in detail, whereas the function of theprocessor16 will be only briefly discussed.
• As shown inFIG. 8, the irradiatingsystem13 and theimaging system15 are arranged adjacent to each other. Thus, the effect of varying angles between thepen point9 and the writingsurface14 on the relationship between the irradiated area and the imaged area is kept low.
• Theoptical system11 may, as shown inFIG. 8, be mounted on thePCB12. This is a rigid and simple assembly of theoptical system11.
• Referring now toFIG. 9, the imaging system will be schematically described. The imaging system comprises a two-dimensional radiation sensor24. The two-dimensional radiation sensor24 may be an electro-optical image sensor, such as a CCD or a CMOS sensor. The radiation sensor24 may be arranged in a package25 that is soldered to thePCB12. Alternatively, a sensor chip may be attached directly to thePCB12, for example via wedge or ball bonding. The radiation sensor24 is connected through thePCB12 to theimage processor16 for control and analysis.
• The imaging system further comprises a sensor boresight unit orimaging unit26 for directing radiation onto the radiation sensor24. In the embodiment ofFIG. 9, theboresight unit26 is mounted on thePCB12 surrounding the radiation sensor24. Theboresight unit26 has asensor pocket27 to receive the package25 with the sensor24. Thus, only radiation that propagates through theboresight unit26 will reach the sensor24. Theboresight unit26 comprises amirror28, which is arranged above the sensor24. Themirror28 is arranged to reflect radiation from the writing surface onto the sensor24, and to redirect the optical axis of the imaging system accordingly. The mirror surface need not be planar, but a slightly curved mirror surface is also conceivable.
• The redirection of radiation by themirror28 allows the sensor24 to be mounted on thePCB12, which extends away from the writing surface in a direction substantially perpendicular thereto. The radiation is redirected essentially 90° in themirror28, so that the optical axis of the imaging system in the optical path upstream of themirror28 is essentially parallel with the surface of thePCB12. Thus, thePCB12 will not obscure the field of view of theimaging system15. The optical axis of the imaging system upstream of themirror28 may be somewhat inclined, typically by less than about 15°, preferably by less than about 10°, and most preferably by about 3°-8°, to the longitudinal axis of the ink cartridge, so that the imaging system will view an area of the writing surface close to the pen point.
• Theboresight unit26 further comprises alens29 upstream of themirror28 in the optical path. Thelens29 is arranged to focus radiation from the writing surface onto the sensor24 via themirror28. Thelens29 is arranged in theboresight unit26 such that the distance between thelens29 and the sensor24 is shorter than the distance between thelens29 and the writing surface, whereby the imaged area on the writing surface is increased. Theboresight unit26 should provide such demagnification that a sufficient area of the writingsurface14 is imaged on the sensor24 to determine the position of thepen point9. The imaged area may, however, not be demagnified to such a degree that the features required for decoding cannot be distinguished in the recorded image.
• Theboresight unit26 also comprises anaperture stop30. Theaperture stop30 reduces the amount of radiation passed towards the sensor24. If an opening of theaperture stop30 is increased, more radiation is passed towards the sensor24, but the depth of field of theimaging system15 is simultaneously decreased.
• In one embodiment, shown inFIG. 10, the lens and the mirror are implemented in oneoptical component31. Theoptical component31 is a solid optics component denoted herein as an imaging prism. Theimaging prism31 may be produced of a plastics material, such as polymethylmethacrylate (PMMA), polycarbonate Zeonex®, polystyrene, nylon, or polysulfone. Theprism31 has a base32 to be attached to thePCB12, e.g. by gluing, snapping, clamping or ultrasonic welding. Thesensor pocket27 is arranged in thebase32. The surface inside thepocket27 of theprism31 may be planar or slightly curved and forms aradiation exit surface33 towards the radiation sensor. Theprism31 further has amirror surface34 which is arranged above thepocket27 and inclined in relation to thebase32. Themirror surface34 is metallized on the outside for providing a reflective surface. Thus, the radiation incident on themirror surface34 from within theprism31 will be reflected in themirror surface34. Alternatively, a glass mirror is glued to theprism31 by means of optical glue. Theprism31 also has an essentiallytubular part35 which extends from themirror surface34 and is at least partly supported by thebase32. Thetubular part35 extending from themirror surface34 is slightly inclined towards the geometrical plane of thebase32. Thereby, the optical axis may be tilted to the longitudinal axis of theink cartridge8, whereby theimaging system15 may image an area close to thepen point9. The proximate end of thetubular part35 extends beyond thebase32. This end forms anentrance surface36 of theprism31. Theentrance surface36 includes a lens surface and is arranged to receive radiation from the object plane. The lens surface may be formed by any suitable refractive means, such as a curvature of thesurface36 and/or Fresnel zones in thesurface36.
• All surfaces of theimaging prism31 except for theentrance surface36 and theexit surface33, and optionally themirror surface34, may be covered with a radiation-transfer material. The radiation-transfer material has a refractive index that is sufficiently matched to the refractive index of the prism material, such that the major part of any radiation within the prism impinging on these covered surfaces is transmitted into the radiation-transfer material instead of being reflected back into the prism. The radiation-transfer material may also be selected to absorb the relevant wavelengths, typically with an absorbance of at least 0.5, to prevent the transferred radiation from spreading within the pen casing. The provision of a radiation-transfer material on the outside of the imaging prism prevents stray radiation from reaching the radiation sensor. Since an effective prevention of internal reflections in the prism is provided, the surfaces of the prism may be arranged close to the desired optical path in the prism. Thus, the prism may have a small size. The radiation-transfer material may also be selected to prevent radiation from entering the prism through other surfaces than the entrance surface. In one embodiment, the radiation-transfer material is a black paint.
• Further, there is provided anotch37 in thebase32. Thisnotch37 forms a barrier in front of the radiation sensor as seen from theentrance surface36 and provides that radiation is not allowed to impinge on the radiation sensor directly from theentrance surface36 without interacting with themirror surface34.
• In this embodiment, theboresight unit26 consists of theprism31 and anaperture stop38. Theaperture stop38 may be implemented as a cap to be mounted over thetubular part35 of theimaging prism31 at theentrance surface36. Theaperture stop38 has anopening39 to be arranged in front of theentrance surface36 to allow radiation into theprism31. Theaperture stop38 may be formed in plastics material and be glued or snapped onto theprism31. Theaperture stop38 may alternatively be provided by masking a part of theentrance surface36 that should not transmit radiation, e.g. with the radiation-transfer material used for the other surfaces of theprism31.
• In another embodiment, shown inFIG. 11, the boresight unit is implemented as ahousing40 containing the needed optical components. Radiation is propagated in achannel41 formed in thehousing40. Thehousing40 has essentially the same shape as theimaging prism31 and thus a similar optical path is formed within thehousing40. Abase42 of thehousing40 may have a large surface towards thePCB12. Further, thehousing40 may be formed in a material optimal for strongly attaching thehousing40 to thePCB12 by e.g. gluing, snapping, clamping or ultrasonic welding. Thehousing40 has anopening43 in the base42 forming the sensor pocket, which is open into thechannel41.
• Amirror44 is attached by e.g. gluing to cover an opening in thehousing40 above theopening43 in thebase42. Thehousing40 may provide slots (not shown) for receiving themirror44 and defining the position of themirror44. Thehousing40 further provides atubular part45 of thechannel41 extending from themirror44. Thehousing40 may have a thick base wall which forms the lower inside surface of thechannel41. At an end of thetubular part45, inside walls of thehousing40 may haveradial protrusions46 for reducing the diameter of thechannel41 and effectively forming anaperture stop47. Theaperture stop47 may be arranged a short portion into thechannel41 of thehousing40. Thehousing40 further comprises an outer opening for receiving radiation from the writingsurface14. Alens48 may be attached in thehousing40 upstream of theaperture stop47, for example by means of gluing, crush ribs, ultrasonic welding, form fitting, snap fitting, etc.
• As an alternative (not shown), the lens may be attached in thechannel41 downstream of the aperture stop. Typically, the lens is slid in the channel into a predefined position, e.g. into abutment with the aperture stop. Such downstream mounting may reduce the influence of assembly tolerances on the distance between the lens and the radiation sensor, since any deviations in the position of the lens from predefined position will counteract any deviations in the positions of the mirror to the holder and the holder to the radiation sensor. Similar advantages may be attained by mounting the mirror from the inside of the channel.
• The aperture stop may alternatively be arranged as a separate component, which is inserted into and attached to thehousing40. Alternatively, the aperture stop may be provided by means of a cap that is arranged over the front end of thehousing40. Such a cap may also include thelens48.
• Thehousing40 may be formed in a radiation-absorbing material for absorbing stray radiation. The inner surface of thehousing40 may also or alternatively be coated with a radiation-absorbing material. The inner surface of thehousing40 may be roughed or textured to reduce specular reflections. Alternatively or additionally, the inner surface Of thehousing40 may have one or more controlling surfaces that direct specular reflections away from theopening43. The downstream walls of theprotrusions46 forming theaperture stop47, i.e. the walls facing themirror44, may be tapered away from the mirror. Thereby, reflections in these protrusion walls are steered into the walls of thehousing40. These protrusion walls may also be roughed or textured.
• The position-coding pattern on the writing surface may be printed to be visible in the near infrared wavelength band. Further, the ink from thepen1 may be chosen in order not to be visible in the near infrared wavelength band such that it will not interfere with the information of the position-coding pattern. In order not to image wavelengths in the visible region, an infrared filter23 (FIG. 4) may be arranged in front of the lens of theimaging system15. Theinfrared filter23 may absorb all wavelengths shorter than the near infrared wavelengths. Theinfrared filter23 will then absorb undesired radiation from sunlight and external illumination. By placing theinfrared filter23 in front of thelens29 of theimaging system15, theinfrared filter23 may also serve as a protective window or shielding plate.
• The function of an infrared filter may be implemented anywhere in theimaging system15. Thus, the infrared filter may alternatively be arranged in thehousing40 or be integrated in theprism31 by the material of theprism31 being highly absorptive to wavelengths shorter than the near infrared wavelengths. Alternatively or additionally, the infrared filter may be integrated in the lens, the mirror, the radiation sensor or the package (cf.25 inFIG. 9).
• FIG. 12 illustrates the irradiatingsystem13 ofFIG. 8 in more detail. The irradiating system comprises aradiation source50 which is arranged to emit radiation. Thesource50 is typically a light-emitting diode (LED) or a laser diode that emits radiation in a limited wavelength band. Thesource50 may be mounted in a throughhole51 in thePCB12 and be electrically connected thereto. The irradiatingsystem13 further comprises aradiation guide52 for directing the radiation to the desired area on the writing surface. Theguide52 may be formed in one piece of a plastic material, such as PMMA, polycarbonate, Zeonex®, polystyrene, nylon, or polysulfone.
• Theguide52 is mounted to thePCB12 over the throughhole51. Theguide52 comprises abase surface53 which may be attached to thePCB12 by e.g. gluing. Thebase surface53 may comprise aflange54 for providing a larger attachment area to thePCB12, for example if needed to withstand a mechanical shock caused by the pen being dropped to the floor. Theflange54 is arranged merely for securing attachment of theguide52 and not for transmitting radiation from thesource50. Theguide52 may further comprise guidance pins or holes (not shown) for controlling the positioning of theguide52 in relation to thePCB12 and/or theadjacent boresight unit26 of theimaging system15.
• Theguide52 comprises asource receiving pocket55, which is to be arranged over the throughhole51 in thePCB12. Thepocket55 has aplanar entrance surface56 at its base and radiation from thesource50 enters theguide52 through thisentrance surface56.
• Theguide52 further has amirror surface57 which is arranged above thesource receiving pocket55 and inclined in relation to thebase surface53. Themirror surface57 is metallized on the outside to provide a reflective surface. The radiation is redirected essentially 90° in themirror surface57, so that the optical axis of the irradiatingsystem13 in the optical path downstream of themirror surface57 is essentially parallel with the surface of thePCB12. Thus, thePCB12 will not obscure the irradiating of the writing surface by means of the irradiatingsystem13. The optical axis of the irradiatingsystem13 downstream of themirror surface57 may be somewhat inclined, typically by less than about 15°, and preferably by less than about 10°, to the longitudinal axis of the ink cartridge so that the irradiatingsystem13 will irradiate an area of the writing surface close to the pen point.
• Theguide52 forms an essentially tubular shape for guiding the radiation after its reflection in themirror surface57. The radiation exits theguide52 through anexit surface58, which is provided at an end of the tubular shape. All surfaces except theentrance surface56 and theexit surface58 may be metallized, whereby radiation is controlled to exit only through theexit surface58. Any internal radiation impinging on other walls will thus be reflected back into theguide52.
• The tubular shape of theguide52 may have an essentially constant cross-section. The cross-section of the tubular shape may be designed to yield a desired shape of the irradiated area. Further, the longer the tubular shape is, the more uniform the emitted radiation of theguide52 will be. However, it may be sufficient to keep the tubular shape so short that most of the emitted radiation will only have been reflected once before exiting theguide52. The minimum width of the cross-section of the tubular shape in a direction parallel to the PCB surface is mainly determined by the size of thesource receiving pocket55. The cross-section of the tubular shape should be kept as small as possible to keep the radial size of thepen1 down, while the emitted radiation should irradiate a sufficiently large area. To this end, the tubular shape of theguide52 may be designed with an asymmetrical cross-section.
• As illustrated inFIGS. 8 and 12, theexit surface58 of theguide52 is angled to the longitudinal axis of the tubular shape of theguide52 so that the radiation is redirected in theexit surface58 towards the writing surface to be irradiated. The redirection of radiation in theexit surface58 implies that an optical axis of the irradiatingsystem13 beyond theguide52 converges with the optical axis of theimaging system15 towards the writing surface. The redirection of the optical axis of the irradiatingsystem13 in theexit surface58 may be needed, since the optical axis of the irradiatingsystem13 in the tubular shape of theguide52 is essentially parallel to the optical axis of theimaging system15 in thetubular part35 of theprism31 or in thechannel41 of thehousing40. Typically, the angle between the optical axes of the imaging and irradiating systems is less than 15°.
• Theexit surface58 of theguide52 may be planar. Alternatively, theexit surface58 may be curved to provide a surface power for controlling the size of the irradiated area.
• Since thesource50 and the radiation sensor24 are arranged close to each other on thePCB12, there is a need for preventing leakage of radiation directly from thesource50 to the radiation sensor24. Some features of theoptical system11 mentioned above serve to hinder such leakage. Thus, theguide52 of the irradiatingsystem13 is metallized for preventing radiation to escape from other surfaces than theexit surface58. Further, theprism31 or thehousing40 may be painted or coated by a non-transmitting material to prevent radiation from entering theprism31 orhousing40 through other surfaces than the entrance surface.
• Since it is not uncommon for the radiation sensor24 to be transparent from its backside, it may be important to ensure that radiation is not transmitted through thePCB12 from thesource50 to the radiation sensor24. To minimize any direct leakage of radiation from thesource50 into thePCB12, the throughhole51 in thePCB12 may be metallized. Further, one or more layers of copper may be arranged in thePCB12 to reduce radiation propagation in the PCB. Further, non-transmitting glue may be used in attaching theprism31 or thehousing41 to thePCB12. Thereby, radiation is prevented from propagating in the interface between theprism31 or thehousing40 and thePCB12.
• Moreover, where the shielding plate23 (FIG. 4) is arranged in front of the imaging system, radiation emitted from theradiation guide52 may, by reflection in theplate23, be directed into the entrance surface of theimaging system15. To avoid this, theimaging system15 may be arranged to receive radiation that has passed through an area of theplate23 that does not coincide with the area of theplate23 that is irradiated by the irradiatingsystem13. Further, theplate23 may be anti-reflection coated on one or both surfaces. Still further, theplate23 may be angled such that reflections from the emitted radiation are deflected away from theimaging system15.
• In all of the above embodiments, the radiation source of the irradiating system may be mounted in any position directly on the carrier, on the PCB or on another component of the modular unit. However, the radiation source should preferably be kept in a close relationship to the imaging system, so as to minimize the effects of the pen orientation on the relationship between the imaged and irradiated areas on the writing surface.
• In one embodiment, illustrated inFIGS. 13-19, the radiation source is mounted in a holder on an outer surface of the sensor boresight unit or imaging unit, which in turn is supported by the PCB. Thereby, a short tolerance chain and, consequently, a well-defined relationship is obtained between the irradiating system and the imaging system. Further, by attaching the radiation source to the boresight unit, the radiation source may be brought sufficiently close to the object plane of the imaging system for the radiation guide to be omitted. By dispensing with the radiation guide, the complexity and cost of the optical system may be reduced.
• The embodiment ofFIGS. 13-19 will now be described in some more detail, with emphasis being put on features, functions and advantages that differ from the previously described embodiments. In particular, it is to be noted that the above discussion on the irradiating system is not applicable to the embodiment described below.
• Thecarrier70 and the PCB72 do not differ in essence from the embodiment described in relation toFIG. 4. Thus, thecarrier70 may comprise mounting compartments74-77 for, i.a., a writing implement with a pen point (compartment74), a contact sensor for the writing implement (compartment75), a vibrator for user feedback, a battery for powering the processor and any further electronic components, a plurality of LEDs for user feedback (compartment76), a transparent front plate for protecting the interior of the pen (compartment77). The PCB72 carries theradiation sensor78, aprocessor80 and further electronic equipment (not shown).
• The optical system includes theboresight unit82, theradiation sensor78 and the irradiatingsystem84.
• Theboresight unit82 contains animaging lens86, anaperture stop88, and a redirectingmirror90. Theboresight unit82 defines an object plane, an image plane, an optical axis, and a depth of field in the object plane. Theboresight unit82 is a unitary component which may be manufactured in one piece or assembled from separate elements. Thus, as an alternative to the embodiment illustrated inFIGS. 13-19, the boresight unit may be based on solid optics similarly to the boresight unit ofFIG. 10. The following description is equally applicable to such an alternative embodiment.
• The boresight unit is designed to be mounted on the PCB72, with a given relation to thesensor78 thereon. The PCB72, in turn, is designed to be mounted on thecarrier70. Aholder92 is integrated with theboresight82 unit to provide for mounting of theradiation source94, in this case an LED, but alternatively a laser diode. Integrating theholder92 in theboresight unit82 may minimize the influence of assembly tolerances on the relative location of the field of view and the illuminated area on the writing surface. In an alternative embodiment (not shown), the holder is a separate part which is attached to the body of the boresight unit.
• Thesource94 is electrically connected to the PCB72 via a pair of connectingpins94′ (truncated inFIGS. 13-19), to be supplied with power under the control of theprocessor80. Thepins94′ are guided by means of a pair of guiding tracks formed in theholder92 and adownstream projection95. The tracks in theprojection95 are curved to provide for forming of thepins94′. During assembly, thepins94′ are arranged in the tracks and bent towards the PCB72 before being fixed thereto, suitably by being soldered in corresponding receiving holes (not shown) in the PCB72. It has been found that the fixation of thepins94′ to the PCB72 produces desirable clamping forces between theboresight unit82 and the PCB72.
• The boresight unit B2 has a bottom surface with aradiation outlet96, which is adapted to face the surface of the PCB72 in suitable alignment with thesensor78, and a proximate end with aradiation inlet98 facing the shielding plate (cf. holder77 inFIG. 13). Theoutlet96 is dimensioned with clearance to thesensor78. Thus, one and the same boresight unit may accommodate sensors/-packages of different type and/or geometry. In this embodiment, as well as in the other embodiments disclosed herein, the image plane defined by the boresight unit is located at, and in a predefined spatial relation to, the radiation sensor.
• As shown inFIGS. 17-18, a radiation path is defined between theinlet98 and theoutlet96 and is confined within theboresight unit82. Theimaging lens86 is accommodated in a front pocket in abutment with theaperture stop88. A channel is defined to extend from theaperture stop88 to theoutlet96. The channel also connects to aradiation trap104 which is defined in the side wall portion facing away from theholder92. The trap is designed as a channel wall recess which collects and attenuates any impinging radiation. In particular, thetrap104 is positioned and designed for any source radiation that is reflected into the boresight unit by the shielding plate mounted in the holder77 (FIG. 13). Further, abarrier wall106 is formed upstream of theoutlet96, to block radiation from impinging on thesensor78 without interacting with themirror90. To attenuate such blocked radiation, a bottomwall radiation trap108 is formed upstream of thebarrier wall106. Also, asecondary radiation trap104′ is formed in the side wall downstream of thebarrier wall106. Although not shown on the drawings, further radiation traps may be formed in the top wall portion and/or in the side wall portion facing the holder. It has been found that radiation traps are particularly important for reduction of stray light within the boresight unit when it is desired to minimize the diameter of the internal channel.
• The bottom surface has two projecting guidingpins110,112, which cooperate with corresponding guidingholes110′,112′ in the PCB72 to define the placement of theboresight unit82 on the PCB72.
• In the embodiment ofFIGS. 13-18, theboresight unit82 is fixed to the PCB72 by deformation of asupplementary fixation pin114 in a corresponding throughhole114′ in the PCB72. Alternatively or additionally, fixation may be achieved by deformation of one or both of the guiding pins110,112. Alternatively or additionally, use may be made of external clamping fixtures and/or welding, gluing, form fitting, press fitting, snap fitting, etc.
• Further, the PCB72 is fixed to thecarrier70 by deformation of supplementary fixation pins116,118 on thecarrier70 in corresponding throughholes116′,118′ in the PCB72. Alternatively or additionally, use may be made of external clamping fixtures and/or welding, gluing, form fitting, press fitting, snap fitting, etc.
• Thus, an analysis system is formed by the combination of theboresight unit82, thesource94 and the PCB72 which carries thesensor78 and theprocessor80.
• Likewise, a modular unit is formed by the combination of the analysis system and thecarrier70. The modular unit may be connected to one or more shell parts forming an outer casing of the pen, by means of one ormore connectors120 on thecarrier70, which may be designed to engage a corresponding connector on the shell part(s). Alternatively or additionally, use may be made of external fixtures, gluing, press fitting, etc.
• The electronic pens as described herein may allow for determination of a position from an image of a position-coding pattern on the writing surface, the determination being carried out by the internal processor of the pen or by an external processor, e.g. as described in any one of US 2002/0044138, US 2002/0048404, US 2003/0053699, US 2003/0118233, US 2003/0122855, US 2003/0128194, U.S. Pat. No. 6,667,695, U.S. Pat. No. 6,674,427, U.S. Pat. No. 6,732,927, WO 04/097723, and references therein. The determination may also involve using the distance D (FIG. 2) to relate the position decoded from the imaged pattern to the actual writing position, i.e. the position of the contact point P (FIG. 2) on the writing surface. For instance, the processor can be arranged to calculate, based upon an image, the spatial orientation (e.g., inclination angle θ and skew angle Φ) of the pen and a position, and, knowing the position, the spatial orientation and the distance D, to calculate the writing position. However, deviations from the nominal value of the distance D may introduce systematic errors in the calculated writing position.
• To mitigate the effects of these deviations, the optical system/modular unit may be designed to image an area of the writing surface that is partly obscured by the ink cartridge. The tip of the ink cartridge may consist of a ball held by a cone leading up to the cylindrical body of the ink cartridge. The edge between the cone and the cylindrical body of the ink cartridge may then form an obscuration edge in the recorded images, although any other part of the tip may form such an obscuration edge. The obscuration edge may be nominally placed in the image such that the tolerance chain of components of the pen keeps the obscuration edge placed within the image. Thus, the obscuration edge may always be detectable in the images. Thereby, the position of the obscuration edge in the recorded images could be used for calibrating the distance D for individual pens. It should be noted that the distance D is a vector in the reference plane and the calibration is therefore made in two dimensions.FIG. 20 shows an example of such an image of a position-coding pattern P, in which the obscuration edge is visible (a reference point on the obscuration edge being indicated by R).
• It should be emphasized that the embodiments described herein are in no way limiting and that many alternative embodiments are possible within the scope of protection defined by the appended claims.
• For instance, the above writing implement can be, instead of an ink cartridge, a fountain pen unit, a pencil unit, a felt pen unit, a magnetic head for cooperation with a selectively magnetisable base, a heating head for cooperation with a heat sensitive base, an electronically controlled ink jet unit, a miniaturized laser printer unit etc. It may even be conceivable that the writing implement will not leave any trace of its path along the writing surface, and the writing that is detected by the imaging system and the image processor will not be visible to the eye. In this case, the writing implement may be e.g. a stylus or a pointed bar or rod.
• Further, in the above description, a lens is described in several different occasions. In such cases, the lens may be implemented as a single optics component exhibiting a lens function or alternatively as a compound lens or a lens package.
• Likewise, the above-mentioned printed circuit board (PCB) is intended to encompass other equivalent structures, such as thick film hybrids of metal or ceramic material, or wire wraps.
• In an alternative embodiment, the boresight unit is supported by the PCB without being directly attached thereto. More specifically, the PCB with the radiation sensor rests on one side of the carrier, with at least one through hole in the PCB being aligned with a corresponding receiving bore in the carrier. The boresight unit, which has at least one protruding guiding pin, is fitted onto the PCB with the guiding pin passing the through hole and being fixed in the receiving bore of the carrier, to thereby adequately line up the boresight unit, the radiation sensor, and the carrier. As an alternative or addition, there may be provided at least one corresponding guiding pin on the carrier for cooperation with a receiving bore on the boresight unit, via a through hole in the PCB. Further, the base of the boresight unit may have at least one control surface for abutment on at least one corresponding control surface on the PCB and/or the radiation sensor. As mounted, the boresight unit may be pressed against the PCB, to thereby minimize any variations in the position of the boresight unit in the normal direction of the radiation sensor. The boresight unit may be fixed to the carrier by means of external clamping fixtures and/or by means of welding, gluing, form fitting, press fitting, snap fitting, etc, for example via the guiding pins.
• In yet another alternative embodiment, the boresight unit is arranged to be supported directly by the carrier instead of by the PCB. Thus, the carrier comprises means for supporting the boresight unit, as well as means for supporting the PCB. These means may be implemented as cooperating pins and bores, form fits, snap fits, welding surfaces, gluing surfaces, etc.

Claims (17)

1-50. (canceled)

51. An imaging unit for transmitting radiation from an object to a radiation sensor, said imaging unit being designed to control a spatial origin of radiation reaching the radiation sensor, said imaging unit comprising:

a housing having an internal channel, a radiation entrance end, and a radiation exit end, wherein radiation is transmitted in the internal channel from the radiation entrance end of the housing to the radiation exit end of the housing;

a lens mounted in the internal channel at said radiation entrance end of said housing;

a mirror associated with said housing and configured to redirect radiation within the internal channel such that radiation transmitting through the internal channel is redirected towards the radiation exit end of the housing; and

a holder for receiving a radiation source, said holder being associated with an outer part of the housing.

52. The imaging unit according toclaim 51, wherein the holder is integrated with the outer part of the housing.

53. The imaging unit according toclaim 52, wherein the holder comprises at least two arms extending from the housing and configured to receive the radiation source there between.

54. The imaging unit according toclaim 51, wherein said lens defines an image plane at said radiation exit end.

55. The imaging unit according toclaim 54, further comprising at least one pin configured to be inserted into a corresponding hole on a printed circuit board on which a radiation sensor is mounted, the one pin causing the imaging unit to be aligned with the printed circuit board to locate the image plane on the radiation sensor.

56. The imaging unit according toclaim 51, wherein said lens defines an image plane at said radiation exit end, and said housing further comprises a barrier included in said internal channel, the barrier configured to screen said image plane from said radiation entrance end.

57. The imaging unit according toclaim 56, wherein said housing further comprises at least one radiation trap included between said barrier and said radiation entrance end.

58. The imaging unit according toclaim 51, wherein said housing further comprises an aperture stop included in said internal channel.

59. An imaging unit for transmitting radiation from an object to a radiation sensor, said imaging unit being designed to control a spatial origin of radiation reaching the radiation sensor, said imaging unit including a solid body including a radiation path, said solid body comprising:

a tubular part having a first end and a second end, and defining the radiation path between the first and second ends of the tubular part such that radiation is transmitted along the radiation path along a longitudinal axis of the tubular part;

a radiation entrance connected to the first end of the tubular part and configured to receive radiation entering said radiation path, said radiation entrance including a lens element;

a base of the solid body having a sensor pocket and a radiation exit; and

the second end of the tubular part including a mirrored portion formed at an angle with respect to the longitudinal axis of the tubular part such that the mirrored portion is configured to redirect radiation, transmitted along the radiation path, towards the radiation exit.

60. The imaging unit according toclaim 59, wherein the solid body further comprises:

an outer part external to the tubular part; and

a holder connected to the outer part and configured to receive a radiation source, wherein the holder is a separate component that is attached to the outer part.

61. The imaging unit according toclaim 59, wherein the solid body further comprises:

an outer part external to the tubular part and associated with a holder configured to receive a radiation source.

62. The imaging unit according toclaim 60, wherein the holder comprises at least two arms configured to receive the radiation source there between.

63. The imaging unit according toclaim 59, wherein said lens element defines an image plane at said radiation exit.

64. The imaging unit according toclaim 63, further comprising at least one pin configured to be inserted into a corresponding hole on a printed circuit board on which a radiation sensor is mounted, the one pin causing the imaging unit to be aligned with the printed circuit board to locate the image plane on the radiation sensor.

65. The imaging unit according toclaim 59, wherein said lens element defines an image plane at said radiation exit, and said solid body further comprises a barrier included in said tubular part to screen said image plane from said radiation entrance.

66. The imaging unit according toclaim 59, further comprising:

an aperture stop formed on said radiation entrance.

Images