US20030095115A1 - Stylus input device utilizing a permanent magnet - Google Patents

Abstract

A stylus that operates utilizing magnetic fields, wherein a permanent magnet is disposed within a passive stylus that is detectable by a plurality of magnetic sensors that remove the magnetic field of the stylus from the earth's relative magnetic field to thereby obtain vectors that are used in a triangulation equation to determine the location of the stylus in two or three dimensions, depending upon the number of magnetic sensors that are used, wherein one set of magnetic sensors can be used as a reference for earth's magnetic field, and wherein each of the magnetic sensors includes a polarizing coil to change direction of sensitivity, a null coil and a flipping coil.

Description

BACKGROUND
• 1. Cross Reference[0001]
• This application claims priority to a co-pending application Ser. No. 09/993,394, filed Mar. 22, 2002.[0002]
• 2. The Field of the Invention[0003]
• This invention relates generally to input devices for electronic information devices. More specifically, the present invention provides a sensing system and a stylus that is operable in two or three dimensions, and which is utilized to provide input such as lines that represent movement of the stylus within a field of operation, or cursor control for computers and portable information appliances such as laptops, PC tablets, personal digital assistants (PDAs) or other types of electronic appliances such as mobile telephones.[0004]
• 3. Background of the Invention[0005]
• The state of the art of input devices utilizing a stylus is generally characterized by digitizing tablets or a touchpad. A digitizing tablet is generally a large surface that is used to input data with a stylus that is coupled to the tablet or touchpad. For example, a cable connects the stylus to the tablet, and movement of the stylus is detected or tracked as it moves across the surface of the tablet. The movement is typically portrayed as lines on a display.[0006]
• The basis of operation for most stylus-based tablets is reliance upon electromagnetic sensors. A magnetic field is formed by electric current that is flowing in a loop. The pen has a coil that picks up this magnetic field and sends it back to a convertor that determines the X and Y position from this data. This type of pen generally requires a tether between the pen and a base device to transfer the data, or the use of an active pen that is battery powered and generates some type of signal that is detectable by the touchpad.[0007]
• It would therefore be an advantage over the prior art to provide a pen or stylus-based system for data input or cursor control which does not require a tethered stylus or an active pen. It would also be advantageous if the stylus did not require an internal power source to operate.[0008]
• The prior art also describes using a stylus with personal digital assistants (PDAs). When a stylus requires pressure in order to be detectable, the writing surface of the PDA can be damaged. In addition, the writing area for the stylus is typically very small. It is also difficult to use a stylus when there is no visual feedback or “inking trail” to show the writer what has been written. Inking can also be difficult if there is a delay between stylus movement and the appearance on a display screen of what is being written.[0009]
• Accordingly, it would be an advantage over the prior art to provide an off-screen inking surface to prevent damage to a PDA screen. It would also be an advantage to provide a larger writing surface for the PDA, as well as visual feedback that is rapid.[0010]
• The prior art also fails to teach any type of stylus which can operate without making contact with a surface that can detect the presence of the stylus. In other words, the surface being written on is some surface that is capable of detecting the stylus. Accordingly, it would be an advantage to be able to detect and track movement of a stylus on a surface, where the surface is not a stylus detection surface.[0011]
• The prior art also teaches that some type of sensing surface must be used with a stylus. Accordingly, it would be an advantage over the prior art to provide a stylus which does not require any sensing surface in order to be detectable. It would also be an advantage to therefore enable a stylus to be detectable as it moves within three dimensions.[0012]
• Another aspect to be addressed is the ability to turn writing on and off. Typically, this type of function has required a sensitive surface, possibly a tether from the pen to another device, or an active pen. Accordingly, it would be an advantage over the prior art to provide a stylus that can be actuated to turn on and off writing on an associated display, where the stylus is a passive device that does not write on a special sensing surface, and is not physically tethered to another device.[0013]
• A final aspect of the invention is the ability to implement a stylus for use in a very small area. Consider the mobile telephone user that wants to input and email message and send it. It is a tedious and time consuming task with state of the art input options on cell phones. It would be an advantage over the prior art to provide a very small keyboard that is actuated by the stylus so that it can be used in mobile situations, and with relatively small devices.[0014]
SUMMARY OF INVENTION
• It is an object of the present invention to provide a passive stylus that operates in two or three dimensions.[0015]
• It is another object to provide a passive stylus that only requires a permanent magnet disposed therein.[0016]
• It is another object to provide a passive stylus that can provide signals indicative of touchdown and pressure.[0017]
• It is another object to provide a passive stylus that can provide “start” and “stop” writing signals to a display device, wherein the signals are actuated by normal writing movements and actions.[0018]
• It is another object to provide a passive stylus that can include an inking cartridge that provides real inking of the stylus on paper when used off-screen.[0019]
• It is another object to provide a passive stylus that can operate in three dimensions by providing a sufficient number of sensors to provide a three dimensional detection volume.[0020]
• It is another object to provide a passive stylus that increases magnetic field strength to thereby function as an indicator of a changing signal.[0021]
• It is another object to provide a passive stylus that rotates a permanent magnet stored within a pen body to thereby change polarity and provide a digital “on” and “off” signal.[0022]
• It is another object to provide a passive stylus that can detect rotation of the stylus.[0023]
• It is another object to provide a passive stylus that can be turned over to perform an erasing function on a display device.[0024]
• It is another object to provide a passive stylus that can be incorporated into a mechanical pencil as well as with an inking cartridge.[0025]
• It is another object to provide a passive stylus that can be utilized with a small keypad, wherein the keypad detects contact of the passive stylus with keys on the keypad.[0026]
• It is another object to provide an active stylus that provides a signal to a display device to thereby provide pressure information so as to be able to draw with varying degrees of shading.[0027]
• In a preferred embodiment, the present invention is a stylus that operates utilizing magnetic fields, wherein a permanent magnet is disposed within a passive stylus that is detectable by a plurality of magnetic sensors that subtract the magnetic field of the stylus from the earth's relative magnetic field to obtain vectors that are used in a triangulation equation to determine the location of the stylus within a writing area.[0028]
• In a first aspect of the invention, each pair of magnetic sensors provides a vector, wherein two pairs provides vector information for two dimensions, and three pairs provide vector information for three dimensions.[0029]
• In a second aspect of the invention, the three pairs of magnetic sensors are disposed in three of four corners in the plane of a virtual rectangle.[0030]
• In a third aspect of the invention, one of the three pairs of magnetic sensors functions as a reference for earth's magnetic field.[0031]
• In a fourth aspect of the invention, each of the magnetic sensors includes a polarizing coil to change direction of sensitivity, a null coil and a flipping coil.[0032]
• In a fifth aspect of the invention, a “start” and “stop” signal generated by the passive stylus are detectable by the magnetic sensors by rapid movement of a permanent magnet within the stylus body.[0033]
• These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings.[0034]
DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a top elevational view of magnetic field sensors set out in sets to provide an area of sensitivity that is two dimensional when two sets are used, and three dimensional when three sets are used.[0035]
• FIG. 2A is an example of an area of sensitivity of the present invention.[0036]
• FIG. 2B is an example of another area of sensitivity of the present invention.[0037]
• FIG. 2C is an example of another area of sensitivity of the present invention.[0038]
• FIG. 3 is a profile cut-away view of a stylus.[0039]
• FIG. 4 is circuit diagram of a magnetic field sensor.[0040]
• FIG. 5 is schematic diagram of components of the present invention.[0041]
• FIG. 6 is a profile cut-away view of two views of a stylus showing an alternative embodiment.[0042]
• FIG. 7 is a profile cut-away view of an alternative embodiment of a stylus.[0043]
• FIG. 8 is a profile cut-away view of an alternative embodiment of a stylus.[0044]
• FIG. 9 is a close-up view of the drive coils of FIG. 9.[0045]
• FIG. 10 is a profile cut-away view of an alternative embodiment of a stylus.[0046]
• FIG. 11 is a cross-sectional profile view of another embodiment of a passive stylus.[0047]
• FIG. 12 is a cross-sectional profile view of the passive stylus of FIG. 11.[0048]
• FIG. 13 is a close-up cross-sectional view of the passive stylus of FIG. 11, with the stylus actuated to write on a display.[0049]
• FIG. 14 is a block circuit diagram that can be used to determine the degree of pressure being applied by a stylus tip on a writing surface.[0050]
• FIG. 15 is a circuit diagram of a transmitter utilized in an active stylus that is performing pressure sensing described in FIG. 14.[0051]
• FIG. 16 is a see-through view of the components in an improve tilt stack pen embodiment.[0052]
• FIG. 17A is a top view of three round magnets.[0053]
• FIG. 17B is a profile view of the magnets in FIG. 16A.[0054]
• FIG. 17C is a profile view of the magnets being rotated.[0055]
• FIG. 17D is a profile view of the magnets being rotated.[0056]
• FIG. 17E is a profile view of the magnets having completed a rotation of 180 degrees.[0057]
• FIG. 18 is a see-through perspective view of an assembled stylus using the magnets of FIG. 17.[0058]
• FIG. 19 is a perspective view of half of the housing for the three magnets.[0059]
• FIG. 20 is a perspective view of a lever arm that is pushed by the pen tip, causing the first magnet to rotate.[0060]
• FIG. 21 is a perspective view of a holder for the first magnet.[0061]
• FIG. 22 a first circuit diagram that illustrates the layout of a sensor system that can be utilized in the present invention.[0062]
• FIG. 23 a first circuit diagram that illustrates the layout of a sensor system that can be utilized in the present invention.[0063]
• FIG. 24 a first circuit diagram that illustrates the layout of a sensor system that can be utilized in the present invention.[0064]
• FIG. 25 a first circuit diagram that illustrates the layout of a sensor system that can be utilized in the present invention.[0065]
DETAILED DESCRIPTION
• Reference will now be made to the drawings in which the various elements of the present invention will be given numerical designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the claims which follow.[0066]
• The presently preferred embodiment of the invention is a plurality of magnetic sensors that are capable of determining a location and orientation of a passive stylus that generates a magnetic field without using a power source. In the presently preferred embodiment, the plurality of magnetic sensors are directionally sensitive devices. For example, the magnetic sensors can be a magnetic field sensor such as one sold having part number KMZ51 from Philips Semiconductors. However, any similar magnetic sensor can be substituted and create the same results. It is noted that the magnetic file sensor KMZ51 is relatively inexpensive, and is thus desirable for the applications herein.[0067]
• In the presently preferred embodiment, the magnetic field sensors are disposed in pairs, stacked one on top of the other or arranged side-by-side, and separated by a non-conductive material such as PC board when they are stacked. Each pair of magnetic field sensors provides a vector to the stylus. Thus, two pairs of magnetic field sensors are sufficient to provide two vectors, and thus determine the location of the stylus in two dimensions.[0068]
• In an alternative embodiment, a third magnetic field sensor is added to each pair, thus making two groups of three magnetic field sensors each. The third magnetic field sensor provides up-down sensitivity to give the configuration three-dimensional sensitivity.[0069]
• It is noted that in the preferred embodiment, three magnetic field sensor sets will be arranged so as to have a straight line between them. For example, FIG. 1 shows a first magnetic sensor set[0070]10, and a second magnetic sensor set12, each set comprised of threemagnetic field sensors8. The directional sensitivity of each of themagnetic field sensors8 is identified by thearrows14. Note that the dot representing anarrow14 in each set10,12 indicates that sensitivity is directed out of the page. The approximate area of sensitivity is identified by dottedline16.
• Unfortunately, a stylus cannot be detected when it is disposed along the[0071]straight line18 that lies directly between the first and second magnetic sensor sets10,12. To be detectable, it is preferable in an alternative embodiment to include athird set20 of magnetic field sensors. This third set20 makes detection of a stylus in three dimensions much simpler, and also eliminates the “blind spot” represented byline18.
• It is noted that in the alternative embodiment of three[0072]sets10,12,20 of three magnetic field sensors each, the sets are preferably arranged as three corners of a square or rectangle. This area is represented byarea16.
• It is important to recognize that the area of sensitivity can be varied according to the desired placement of the magnetic field sensor sets. This means that the area of sensitivity is a relative area that is based upon the needs of the application. For example, if the application is for a cursor control input device, then the area of[0073]sensitivity22 could be as shown in FIG. 2A relative to three magnetic field sensor sets24, or as in FIG. 2B or2C. What is important to realize is that the area of sensitivity is very approximate, and will extend beyond the sharply defined lines of the figures. However, it is the practical realization that some arbitrarily defined area must be selected to give a user a feel for the area to operate in to write, draw, or cause cursor movement in a defined area on a computer screen when that is the application of a stylus and sensors.
• FIG. 3 illustrates that the presently preferred[0074]stylus30 is a generally pen-like object, having apermanent magnet32 disposed near thetip34 thereof. Thestylus30 preferably has a magnetic field whose strength is approximately equal to that of the earth's magnetic field.
• In order to understand operation of the[0075]stylus30, it must be considered in context with an understanding of the operation of the magnetic field sensors. Each magnetic field sensor of the preferred embodiment includes a polarizing coil. The polarizing coil allows a user to swap the direction in which a magnetic field sensor is sensitive. This feature enables a user to cancel out offsets, drift, etc. Generally, a user will only swap directions in order to occasionally “zero-out” the magnetic field sensor, but will generally not perform this operation before every measurement. The magnetic field sensors generally have good bandwidth, from about 1 volt DC to about 1 MHZ.
• As shown in FIG. 4, the magnetic field sensor is essentially a[0076]bridge40, which also includes anulling coil42 and a flippingcoil44. In order to get a good dynamic range, it is best to avoid flipping before each measurement because as the magnetic field grows higher and higher, it starts saturating the magnetic field sensor. At that point, the magnetic field sensor begins to lose linearity.
• Accordingly, the preferred magnetic field sensor includes the[0077]nulling coil42. The output of adifferential amplifier46 is fed back into thenulling coil42. This allows obtaining a “zero” magnetic field on the magnetic field sensor, to thereby increase gain immensely while maintaining linearity.
• It is important to realize that if the sensor system is to be accurate, the sensor system should not try to maintain a linear circuit. Instead, the user should select a null point, and then feed a linear DAC into it to maintain a null point. That provides the sensor system with a tremendous dynamic range. By using the[0078]nulling coil42, it is possible to maintain linearity and better range.
• It is also noted that the range of the magnetic field sensor is a function of several factors. An analog-to-digital (A/D) converter used in the presently preferred embodiment is 14 bits. This A/D convertor is sufficient to obtain an area of sensitivity that is approximately 8.5 by 11 inches, or a regular sheet of paper. This area of sensitivity is obtained when the sets of magnetic fields sensors are separated by approximately 4 or 5 inches. Using a 16 bit A/D converter would obtain an even greater range, and thus provide a larger area of sensitivity.[0079]
• Assume that a sensor system is operated in the configuration as shown in FIG. 1, with three[0080]sets10,12,20 of three magnetic field sensors. When the sensor system is first turned on, the system will be assumed to be stationary and coupled to a desktop computer or other stationary device. The first action is to calibrate the sensor system so that it can determine its position relative to the earth's magnetic field. This information is preferably stored in a driver, RAM or other memory device. This information is used for sensitivity and correction factors. Each magnetic field sensor set10,12,20 provides a vector to a stylus that is disposed within the identified area ofsensitivity16. It is important to determine an absolute vector, then subtract out a calibration vector.
• If all of the magnetic field sensor sets[0081]10,12,20 give vectors that are parallel to each other, then it is assumed that there is no magnet within the area ofsensitivity16. Because the earth's magnetic field is also known, that is also subtracted out to thereby obtain a null space within the sensor system's field of sensitivity.
• When the stylus is introduced into the null space (field of sensitivity), the threshold for the presence of the stylus is simply a determination that the vectors are no longer parallel. By subtracting out the magnetic field of the permanent magnet disposed within the stylus from the earth's relative magnetic field, the user obtains two vectors that point to the stylus. By triangulation, the location of the stylus is then determined.[0082]
• FIG. 5 is a schematic diagram of the presently preferred sensor system. As shown, a[0083]MUX50 goes to all themagnetic field sensors8 of the three magnetic field sensor sets10,12,20. The signal from theMUX50 goes to an A/D converter52, which is then passed to aCPU54. The presently preferred embodiment utilizes an A/D converter card disposed in a slot of a personal computer. The input to the A/D converter52 is accessed by a program executing on the personal computer to process a triangulation formula to thereby provide stylus position determination. A good example of an A/D converter with adequate properties is an 8051 processor.
• Some details on triangulation methods are useful to an understanding of implementing the present invention. Triangulation is usually done in one of two ways, neither of which is adequate for the present invention. The first method will not work because when either an x or y sensor has a value close to zero, it becomes for difficult to determine accurate coordinates. Furthermore, if the user is inclining the stylus, incorrect coordinates are again given.[0084]
• The second method requires an alternating signal from the source of a fixed frequency and uses two sensors at a fixed distance from each other. This method is not useful for tracking the stylus of the present invention because the magnetic sensors look at non-alternating magnetic fields and frequency information is not available.[0085]
• Thus, the present invention looks to the circular-triangulation method. This method uses a knowledge of how magnetic fields drop off in distance. As a magnetic source moves away from it's sensor, the sensor records a value that is proportional to the inverse cube of the distance between the source and sensor. This information enables a hypothetical circle to be drawn around the sensor at a radius that is calculated from the sensor value and the inverse-cube formula. This circle projects all the possible points the stylus can be on.[0086]
• A second sensor at a fixed distance away projects another circle of a different radius. The circles intersect in at most two points, with one of the points being behind the sensors in a non-drawing area, which means that this point can be eliminated as a solution. The remaining point's coordinates are thus calculated by solving for the intersection of the two circles and using the positive solution as the coordinates of the stylus.[0087]
• This method has the advantage of only requiring two x or two y sensors separated at a distance, as opposed to the four sensors required for the angle methods described above.[0088]
• Advantageously, changes in the pen's angle with respect to the writing surface do not influence the calculation of the stylus' coordinates if two x and y sensors are used at each sensing location. A decrease in x from one set of sensors will be compensated for by an increase in the corresponding y from that set. The magnitude between the two sensors can be determined as the square root of (x{circumflex over (2)}+y{circumflex over (2)}). This eliminates angle disturbances because of low x and y values, and eliminates the effects of pen angle with respect to a writing surface.[0089]
• This method also allows for increased distance because of the use of raw sensor magnitudes instead of angles calculated from these magnitudes. The same concept can be applied to electromagnetic fields, which lose energy in their fields by the inverse of the distance-squared, as opposed to inverse of distance-cubed for magnetic dipoles. Spheres can be drawn from each antenna to the source and the solution of the source's coordinates is found be solving for the intersection of the spheres. By triangulating electromagnetic sources with this method, dependence on the angle that the object is facing with respect to the antennas of the magnetic sensors can be eliminated.[0090]
• The[0091]stylus30 used with the presently preferred and alternative embodiments has been described as a passive device with apermanent magnet32 disposed therein. However, the present invention also teaches alternative designs for the stylus that include modifications to the passive configuration, and the addition of active elements that enable the user to do more than just determine the location thereof.
• For example, to enhance the passive stylus, it can be advantageous to alter the strength of the magnetic field generated by the stylus. If this change in strength can be detected, the stylus is able to provide more input information to a receiving device. An embodiment that provides a changing magnetic field relies on applying pressure to a stylus tip.[0092]
• In FIG. 6, the increased pressure pushes a[0093]stylus tip60 inwards until the firstpermanent magnet62 makes contacts with a secondpermanent magnet64. The magnetic field of the combinedpermanent magnets62,64 is larger than the individual magnets, and this increase in magnetic field strength is detectable. Releasing pressure on thestylus tip60 enables aspring66 to push thepermanent magnets62,64 apart, returning the magnetic field strength to an initial state. This is all done without the use of a power source.
• In an alternative embodiment, it is possible to introduce active elements that go beyond the basic stylus design above. For example, FIG. 7 is an alternative embodiment of an[0094]active stylus70. In this embodiment, the inner detail of thestylus70 is illustrated to show that apermanent magnet72 is oriented in a first orientation when at rest. Shown here, the south pole of the magnet is toward the stylus tip. When pressure is applied to thestylus tip74, arod76 pushes on thepermanent magnet72, causing it to rotate. The rotation reverses the polarity of thepermanent magnet72, causing the south pole to be on the opposite side, away from thestylus tip74. Thus, the stylus again provides a signal to an input device. The signal could be a digital1 changing to a digital0, or vice versa. Thespring78 pushes therod76 back towards thestylus tip74 and thus causes the permanent magnet to rotate back to an original orientation when pressure is removed from the stylus tip.
• Generally, a stylus does not need to provide “Z” to an input device. However, “Z” orientation is useful when using an electronic paintbrush because it provides an infinite range of pressure values.[0095]
• The next alternative embodiment of an active stylus is shown in FIG. 8. The[0096]stylus80 is shown having acoil configuration82 near thetip84 of the stylus. Thecoil configuration82 comprises threecoils86,88,90 disposed about asphere92 as shown in close-up in FIG. 9. Thecoils86,88,90 are drive coils having three different frequencies, from 250 KHz to 1 MHZ. Each of the magnetic field sensor sets would be tuned to be sensitive to a different drive coil. In this way, the sensor system would not only be able to track the location of each drive coil in three dimensions, but it would also enable the detection of rotation. The only drawback to this embodiment is that the drive coils would require power to drive them at the required frequencies. However, the tradeoff is obtaining not only XYZ position, but pitch, roll, and yaw. Thus, the sensor system would have six (6) degrees of freedom. It is noted that it would be possible to transmit the signals from eachcoil86,88,90 to another device, such as a personal digital assistant (PDA), because each coil functions as an antenna of its own signal, thus providing a wireless connection.
• Accordingly, the present invention enables the use of static magnetic fields instead of dynamic fields. This fact provides a way to use permanent magnets that do not require power when using the basic features of the invention, and only requires power when trying to do provide more features to the user.[0097]
• FIG. 10 is provided as an illustration of another means for increasing magnetic field strength. The[0098]stylus tip100 is coupled to apermanent magnet102 and to a cylindrical coil104 (shown in cross-section). When thespring106 is compressed by thetip100 until making contact with anothercylindrical coil108, the magnetic field strength is increased.
• FIG. 11 is a cross-sectional profile view of an alternative embodiment of a[0099]passive stylus110 in an exploded view. Thispassive stylus110 provides “start” and “stop” signals to the magnetic sensors through a novel use of a tilting magnet. The components of thepassive stylus110 are aplastic housing112 or other material that will not interfere with magnetic fields. Thehousing112 has a plastic orferrous housing cap114 that can be removed in order to replace anink cartridge116. Theink cartridge116 includes an interference fit threadedferrous component118 with thehousing112. The threadedferrous component118 is threaded in order to couple theplastic housing cap114 to theplastic housing112. Aspring120 is disposed between the interference fit threadedferrous component118 and the inside of theplastic housing cap114. Above theinterference fit118 are disposed circularceramic magnets122 that have a hole through the middle for theink cartridge116 to pass through. The number ofceramic magnets122 depends upon the sensitivity of the magnet sensors that are being used to detect the location of the ceramic magnets. More or stronger magnets will improve detection of thepassive stylus110.
• On the top of the[0100]ink cartridge116 is disposed aplastic actuator124. This plastic actuator is used to more uniformly push on therare earth magnet126. Whereas the top of the ink cartridge might be dented or otherwise made irregular, theplastic actuator124 presents a consistent interface to themagnet126. Between theplastic actuator124 and therare earth magnet126 are disposed aceramic trigger magnet128, and aferrous washer130 with pitched ID. The last two components are aferrous cylinder132 that extends along most of the length of theplastic housing112, and aplastic housing cap134 that is screwed into theplastic housing112.
• FIG. 12 is a cross-sectional profile view of the[0101]passive stylus110 shown in FIG. 11, but put together in an operable mode.
• Operation of the[0102]passive stylus110 is novel in its system for enabling the magnetic sensors to determine when a user wants to begin writing on a display, and to stop writing. A user will begin to write with thepassive stylus110. After gentle and nominal pressure is applied, as when a person presses down on paper to write with ink, thepassive stylus110 actuates the “start” signal, indicating that an associated display device is to begin “inking” or writing on a display.
• This “start” signal is generated by the pressure on the[0103]ink cartridge116. This pressure causes theink cartridge116 to move approximately {fraction (1/16)} to ⅛ of an inch upwards into theplastic housing112. Theink cartridge116 is coupled to theplastic actuator124, which is turn moves through a whole in theceramic trigger magnet128, and then partially into the pitched ID of theferrous washer130. Movement of theink cartridge116 is stopped because of theplastic actuator124 that cannot move past theceramic trigger magnet128 when alower shelf136 meets the bottom138 of the ceramic trigger magnet.
• FIG. 13 is provided as a close-up view of how the above-described process will appear when the user is writing. The figure shows the[0104]plastic housing112, therare earth magnet126 that is now in an upright position, theferrous washer130 with the pitched ID, theceramic trigger magnet128, and theplastic actuator124. Atip140 of theplastic actuator126 is pushing up on a bottom surface of themagnet126. Themagnet126 is now resting on asmall lip142 of theferrous washer130.
• It may not be obvious why tipping the[0105]rare earth magnet126 from an inclined position to an upright position will provide a “start” signal. However, the magnetic sensors that are tracking the position of thepassive stylus110 are also detecting therare earth magnet126. When therare earth magnet126 is at rest in the inclined position shown in FIGS. 11 and 12, themagnet126 is actually being held in place by magnetic attraction to theferrous washer130. The force required to break therare earth magnet126 free is relatively small, approximately 80 to 100 grams of force. However, when therare earth magnet126 breaks free, it accelerates rapidly and moves to the upright position to which it is also magnetically attracted on thelip142 of theferrous washer130. Even though the distance moved by therare earth magnet126 is very small, it is very detectable. Fortunately, the movement is also very rapid, which is the key to distinguishing this movement from ordinary movement of thepassive stylus110 when writing. This movement is so fast that it will not be accidentally caused through normal use of the stylus.
• Likewise, the release of pressure off the[0106]ink cartridge116 will enable the stronger attraction of therare earth magnet126 to be in the inclined position to occur. The amount of force is approximately 45 to 50 grams, but can be varied as desired, as can the actuation force. The rare earth magnet is trying to be in the inclined position because thelip142 is small as compared to the broader surface of the pitched ID of theferrous washer130.
• The movement of the[0107]ink cartridge116 that is necessary to send the start and stop signals is barely detectable, enabling thepassive stylus110 to function well as a normal inking pen. The movement of the rare earth magnet as it snaps into an actuated upright position, and then snaps back to the released inclined position does not interfere with use of the stylus. Furthermore, various methods of dampening any outward indication of this motion is possible by modifying theplastic housing112.
• Another aspect of the present invention is to provide pressure sensing utilizing an active stylus. Varying degrees of pressure applied to the stylus tip are difficult to detect with the magnetic sensors. Accordingly, a resistive rubber is used to detect pressure. The rubber changes resistance for small changes in compression. The force of the stylus' ink cartridge on a writing surface is used to compress the rubber against the case of the stylus. This change in resistance is used to change the frequency of an RC oscillator. This information is then sent to a frequency modulated transmitter. The data is transmitted to a receiver on a controller board. A microcontroller on the controller board determines the frequency of the signal, or the change from a given frequency, to thereby determine the degree of pressure that is being applied to the stylus tip on a writing surface. Ultimately, the pressure data can be displayed in two different ways. Either the width of line being drawn can be varied, or an inking gray scale is displayed on a computer display.[0108]
• The resistive rubber acting as a pressure transducer for the present invention is operating in the circuit described in FIG. 14. FIG. 14 shows the[0109]resistive rubber150 coupled to anRC circuit152. For example, a 555 chip can receive inputs from theresistive rubber150. Output from theRC circuit152 is sent to anRF modulator154 for transmission viaantenna156. Output from theRF modulator154 is utilized to determine the degree of compression of theresistive rubber150, and thus the degree to which pressure is being applied. A conversion table can be used to relate the amount of pressure being applied to a value for the width of a line being drawn, or the shade of gray that should be applied.
• A resistive rubber that can be used in the present invention is sold under the brand name of ZOFLEX ZF40(™).[0110]
• FIG. 15 is provided as an example of a circuit that can be utilized to transmit the pressure data from the stylus to the controller board. This is a sample only, and should not be considered limiting. However, it is noted that this type of transmitter can be disposed within the space limitations of a stylus.[0111]
• It is noted that the present invention has many applications, especially with mobile appliances such as cell phones, digital phones, PDA's and other similar electronic appliances that need simple yet efficient ways of inputting data to an electronic device.[0112]
• Another aspect of the invention is the ability to detect very small and precise positioning of the passive stylus. This enables the passive stylus to be used in a very small area that is defined as a keyboard. The keys of the keyboard are actuated by the small tip of the passive stylus. For example, consider a small keyboard that is coupled to a mobile telephone. The keyboard contains the magnetic sensors of the present invention, and can determine what key is being touched by a tip of the passive stylus. This detection ability can enable rapid input of text to a mobile phone, for example, to send email messages.[0113]
• By providing the keyboard with its own memory, the keyboard could also be provided with a small display screen, such as one line of text on an LCD display. The keyboard could then even be used when not attached to the mobile telephone, for example, to take notes during a call. Afterward when the keyboard is attached to the mobile telephone, the memory of the keyboard is uploaded or synchronized with the memory in the mobile telephone, so that a user can input data that has been stored by the keyboard. For example, a user can take notes on the keyboard while talking on the mobile telephone. After the conversation is over, the user attaches the keyboard to the mobile telephone, and uploads whatever data was typed into the keyboard memory into the memory of the mobile telephone. Typically, this action is performed in order to send the data in an email message from the mobile telephone.[0114]
• However, the keyboard does not have to be used apart from the mobile telephone. The keyboard can be used when attached to the mobile telephone. The user may be able to take advantage of the larger display of the mobile telephone, or just continue to use the built-in LCD display of the keyboard. This may depend on the visibility of the LCD display when the keyboard is attached to the mobile telephone.[0115]
• Two additional stylus embodiments have been developed which are an improvement over the previous embodiments. The first new stylus embodiment has much in common with the earlier designs. Before describing the embodiment shown in FIG. 16, it is useful to understand that the algorithms being used in a two sensor system work best when there is a single magnetic dipole being seen in the stylus. But a single magnet creates weaker magnetic field lines. Thus, a balance has been reached, where a small stack of[0116]magnets170 is used. The stack ofmagnets170 is large enough so that their signal can be tracked over a larger area, but small enough that the critical tilting of the stack ofmagnets170 is still detectable within the stylus.
• Another factor in the design is the diameter of the[0117]stylus body172. If thestylus body172 has a large diameter, the stack ofmagnets170 can tilt further within the stylus, which is more detectable by the sensor system. But alarge stylus diameter174 is not desired because it can become too large to feel comfortable in the average user's hand. Accordingly, thestylus diameter174 must be balanced against the height of the stack ofmagnets170, which must be balanced against the need for a detectable tilt of the stack of magnets when changing from a non-inking mode, to an inking mode, and back again. Furthermore, the stack ofmagnets170 has been moved as close as possible to the inkingend176 of thestylus172. This is helpful to the sensor system.
• The next embodiment is a substantial departure from the tilting stack of magnets shown in the previous embodiment. In this new embodiment shown in a top view in FIG. 17A, three[0118]magnets200,202,204 are separated some distance that allows them to rotate without touching each other, but to still be close enough to have a strong magnetic attraction. Themagnets200,202,204 are disks having the same height and diameter. Height and diameter can be varied, even within the same pen if the mechanical structure within the stylus compensates. To operate properly, they are also aligned coaxially alongcommon axis206. Coaxial alignment is critical for the algorithms currently in use because the magnets will appear as a single magnetic dipole.
• This new embodiment operates on the principle of using magnetic attraction between magnets to enable the on/off inking and non-inking signal from a stylus. Consider three magnets which are coaxially aligned, but are spaced apart. Three magnets are used to increase the strength of the magnetic field lines of the stylus. However, two magnets could be used, as well as more than three. The[0119]magnets200,202,204 are free to rotate alongparallel axes208,210,212.
• FIG. 17B is a profile view of the same set of magnets as shown in FIG. 17A, but the profile view is necessary to see the rotation of the magnets.[0120]
• FIG. 17C is a profile view of the[0121]magnets200,202,204, where thefirst magnet200 is beginning to be rotated. If rotated slowly, it is easy to see that thesecond magnet202 begins to rotate in a somewhat delayed fashion because of the inescapable effects of friction between a magnet casing or holder, and the physical pins being used as the axis along which the magnet is turning. Thethird magnet204 rotates in a more pronounced delayed manner.
• FIG. 17D shows that when the[0122]first magnet200 is turned (rotated about an axis) some amount greater than 90 degrees, thefirst magnet200 will then rapidly continue the movement, if unimpeded, until it has turned a full 180 degrees because of the attraction to thesecond magnet202 which is also being caused to turn. Thus, by turning thefirst magnet200, thesecond magnet202 also turns in order to maintain attraction between the North and South poles of themagnets200,202. Thethird magnet204 will likewise be caused to turn because of the rotation of thesecond magnet202. If thefirst magnet200 is turned very rapidly, the second andthird magnets202,204 also turn very quickly so as to be virtually simultaneous. Slowly turning thefirst magnet200 results in a delay down the line of magnets. Yet, once thefirst magnet200 is turned beyond 90 degrees, it rapidly snaps over if movement is unimpeded, along with the second andthird magnets202,204. FIG. 17E shows that themagnets200,202,204 have completed rotation 180 degrees, and form a single magnetic dipole.
• This embodiment requires all of the magnets to operate about[0123]parallel axes206,208,210. The space between the magnets must be large enough to allow free rotation, and small enough to enable strong attraction between the magnets that results in the rapid “snapping” rotation. It is this rapid rotation that is recognized by the magnetic sensors as a signal for a change of state between inking and non-inking. It is also an advantage that the magnets are changing polarity by 180 degrees. The change in magnetic field lines is more recognizable to the sensors than the change in the field lines from a stack of tilting magnets.
• The reason for trying to make the motion of the magnets rapid is because it desirable to have a signal that is recognizable to the sensor system and virtually instantaneous so that the on/off inking action of the stylus can occur without any visible delays. This is one of the advantages of using an active instead of a passive stylus. The active stylus can transmit a signal, such as an RF signal, that travels virtual instantaneously to a sensor system, and inking can be turned on an off rapidly. But a passive stylus must try to make its inking signal as rapid as possible without using power from an electrical source. Of course, the passive stylus does not need to have a battery replaced.[0124]
• FIG. 18 is a see-through profile view of the assembled components of this stylus embodiment to be described hereinafter.[0125]
• FIG. 19 is a perspective view of one half of the[0126]housing220 for the magnets within a stylus body. The view illustrates theholes222,224,226 for the axis pins of themagnets200,202,204. The other half of the housing would have the other corresponding holes for the other axis pins.
• A mechanism must be in place to push on the[0127]first magnet200 so that it is caused to rotate. In this embodiment, pushing down on a stylus tip (not shown) will cause a lever arm to push against a magnet casing (FIG. 21). FIG. 20 shows thelever arm230 that is pushed upward in the stylus to cause the casing of thefirst magnet200 to rotate. In order for thefirst magnet200 to rotate back 180 degrees when the user is no longer pushing on the stylus tip and therefore does not want to ink, thelever arm230 compresses a spring (not shown) within the stylus body. When the user removes the stylus tip from a writing surface, the spring pushes the lever arm down toward the stylus tip, which pulls the casing of thefirst magnet200 and causes the first magnet to rotate. Back to its original position.
• FIG. 21 is a perspective view of a[0128]magnet casing240 in which thefirst magnet200 is disposed. The twoaxis pins242,244 about which thefirst magnet200 rotates within thecasing240 are shown. The cut-away246 in thecasing240 enables thelever arm230 to push on the casing and cause it to rotate. The casings for the second andthird magnets202,204 do not have the cut-away246. They simply rotate about their axis pins.
• Some comments about algorithms used by the sensor system to detect the stylus are useful to discuss in more detail to enable those skilled in the art to practice the invention. Several algorithms have been implemented, each with its advantages and disadvantages.[0129]
• The first algorithm to be developed is the angular triangulation method that used vectors. The problem with this method is that when an angle becomes small, the error in the equations increases rapidly. Thus, when the stylus is near one of the sensors, the error increases to the point that determination of the position of the stylus tip becomes very inaccurate. The method works well when the stylus stays away from the sensors, and remains between them. This method is also very sensitive to pen tilt because there is very little if any 3D capability in the equations.[0130]
• The next method uses Maxwell's equations. An element of the equations is a magnetic constant for the magnets being used in the stylus. This magnetic constant is the dipole moment. The dipole moment is fixed as a constant in the equations to make them easier to use. But the value is only an estimate. This next method can be referred to as the magnitude method. The magnitude method generates an equation for a circle, the center of the circle being the location of the sensor, and the stylus tip being defined as a point on the circle. Two sensors means that equations for two circles are generated that must intersect. The two equations are solved for two unknowns to determine the location of the stylus tip. Advantageously, there are some 3D elements in the equations that make this method less sensitive to tilting of the pen. In addition, when the stylus gets too close to one of the sensors, the equations for the other sensor become highly accurate and can compensate for errors. But when the stylus is closer than one half inch to a sensor, the equations begin to break down. This is because the circles are supposed to intersect, and because this method uses estimates in Maxwell's equations, it is sometimes the case where one circle is completely within another circle. With no intersection, the equations fail completely. This method also does not work well when the stylus is tipping toward the sensors.[0131]
• The next method is a modification of the magnitude method. In this case, the method includes mathematical compensation for when the stylus is tipped toward the sensors. Otherwise, the method is the same.[0132]
• The next method is a substantial increase in complexity over the previous methods, but it yields surprisingly more accurate results. This method will be referred to as the field line method, or the 3D dipole triangulation method, and it also uses two equations to solve two unknowns. This method uses the full 3D equations of Maxwell. The full equations are more difficult to solve because they require more steps. In this method, the equations are trying to determine the shape or surface of the field lines of the stylus in order to determine the location of the stylus tip. In other words, the algorithm is trying to find a best fit curve. Because the equations are not closed, an iterative answer is obtained in a method similar to a binary search that closes in on the correct values. In this embodiment, the algorithm utilizes approximately 50 iterations at most to close in on the solution to the equations.[0133]
• This embodiment has used a neural net as well as a Fourier series to solve the equations. The more elements used in the Fourier series, the faster the solution is reached. The tradeoff is the number of calculations that must be performed. Using a neural net, the algorithm finds a best case approximation of the field lines to create a function that describes them. The algorithm converges on a solution using a gradient descent.[0134]
• Unfortunately, this method can often get trapped in a local minima. However, it is possible to simply throw out these wrong answers using an error checking routine. In other words, if the stylus tip location suddenly jumps to a new one that is beyond a certain distance, the answer is thrown out and recalculated using new data. It should be realized that there is no approximation in this method. It can be used to find the location of the stylus tip down to a very small margin of error. While the algorithm may take 50 iterations, it sometimes gets lucky and finds the correct answer earlier as well. This method can give the 3D location of the stylus tip, and handles any type of stylus tipping.[0135]
• Alternatively, this method can use the last calculated position as a beginning point for the next set of calculations. If the calculations get trapped in a local minima, then they can be thrown out and the position can be determined without using the last known position.[0136]
• The last method is similar, but relies on three sensors instead of two sensors used in the algorithms above. Three sensors will increase the cost of the system, but the equations become extremely simple. With three sensors, the system now has the intersection of three planes at the stylus tip. Thus, the algorithm is the planar method that doesn't use Maxwell's equations. Instead, the algorithm utilizes linear algebra to find the intersection of three planes. This method is not iterative, and is of a closed form.[0137]
• It is observed that these methods all assume that the Z plane is fixed as the writing surface. This works well when the user writes, for example, in front of a PDA or laptop. But when the user wants to write on an LCD screen of the laptop and have the inking appear, compensation must be used to fix the Z plane a certain distance above the assume writing surface. The LCD screen of the laptop or PDA would have to be level. This may be a calibration issue that is used to solve this distance problem.[0138]
• FIGS. 22, 23,[0139]24, and25 are provided as detailed schematic circuit diagrams that illustrate the sensor system in great detail.
• It is noted that by turning the stylus upside down, the permanent magnet(s) in the stylus change polarity. This change in polarity can be detected as a relatively slow movement, not interpreted to be a signal indicating inking and non-inking. The software can use this to erase what was written in the vicinity of the erasing end of the stylus.[0140]
• It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention. The appended claims are intended to cover such modifications and arrangements.[0141]

Claims (1)

What is claimed is:

1. A passive stylus system for providing input to an electronic appliance, wherein the passive stylus utilizes a permanent magnet to provide location information to a magnetic sensor system, said passive stylus comprising:

a passive stylus including at least one permanent magnet;

a magnetic sensor system for detecting a location of the at least one permanent magnet disposed within the passive stylus, wherein the magnetic sensor system further comprises a plurality of magnetic sensors that are capable of (1) detecting the at least one permanent magnet, (2) determining a location of the at least one permanent magnet relative to a reference point, and (3) transmitting the location of the at least one permanent magnet; and

a display system, wherein the display system utilizes the location of the at least one permanent magnet to display data on the display system that represents movement of the passive stylus within a field of operation.

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