US20110112786A1 - Cmm with improved sensors - Google Patents

Abstract

A method of operating an articulated arm CMM is provided. One or more coordinates on an object can be measured with the articulated arm CMM. At least one of the encoders can then be at least partially powered-off. The encoder can then be powered on and one or more coordinates on the same object can be measured without recalibrating the encoder.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims the priority benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/259,105 (filed Nov. 6, 2009), the entirety of which is hereby expressly incorporated by reference herein.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to articulated arms and coordinate measurement, and more particularly to coordinate measurement machines.
• 2. Description of the Related Art
• Rectilinear measuring systems, also referred to as coordinate measuring machines (CMMs) and articulated arm measuring machines, are used to generate highly accurate geometry information. In general, these instruments capture the structural characteristics of an object for use in quality control, electronic rendering and/or duplication. One example of a conventional apparatus used for coordinate data acquisition is a portable coordinate measuring machine (PCMM), which is a portable device capable of taking highly accurate measurements within a measuring sphere of the device. Such devices often include a probe mounted on an end of an arm that includes a plurality of transfer members connected together by joints. The end of the arm opposite the probe is typically coupled to a moveable base. Typically, the joints are broken down into singular rotational degrees of freedom, each of which is measured using a dedicated rotational transducer. During a measurement, the probe of the arm is moved manually by an operator to various points in the measurement sphere. At each point, the position of each of the joints must be determined at a given instant in time. Accordingly, each transducer outputs an electrical signal that varies according to the movement of the joint in that degree of freedom. Typically, the probe also generates a signal. These position signals and the probe signal are transferred through the arm to a recorder/analyzer. The position signals are then used to determine the position of the probe within the measurement sphere. See e.g., U.S. Pat. Nos. 5,829,148 and 7,174,651, which are incorporated herein by reference in their entireties.
• Generally, there is a demand for such machines with a high degree of accuracy, high reliability and durability, substantial ease of use, and low cost, among other qualities. The disclosure herein provides improvements of at least some of these qualities.
SUMMARY OF THE INVENTIONS
• In one embodiment, a method of operating an articulated arm CMM is provided. One or more coordinates on an object can be measured with the articulated arm CMM. At least one of the encoders can then be at least partially powered-off. The encoder can then be powered on and one or more coordinates on the same object can be measured without recalibrating the encoder.
• In another embodiment, an articulated arm CMM can include an articulated arm with a plurality of articulated arm members, a coordinate acquisition member at a distal end, and a base at a proximal end. Further, at least one of the articulation members can include an absolute encoder.
• In a further embodiment, an articulated arm CMM can include an articulated arm and a tilt sensor. The articulated arm can include a plurality of articulated arm members, a measuring probe at a distal end, and a base at a proximal end. The tilt sensor can be rigidly connected to the base such that the tilt sensor can detect a tilting angle of the base.
• In a further embodiment, a method of operating an articulated arm CMM is provided. One or more coordinates can be measured with an articulated arm CMM. While these are measured, the tilt of the articulated arm CMM can also be measured. When the measured tilt exceeds a threshold value, the articulated arm CMM or an external device can compensate the measured coordinates for the tilt, provide a signal regarding the tilt to the user, and/or flag measured coordinates taken during the tilt.
BRIEF DESCRIPTION OF THE DRAWINGS
• Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention, in which:
• FIG. 1 is a perspective view of an articulated arm;
• FIG. 1A is an exploded view of the articulated arm ofFIG. 1;
• FIG. 2 is a perspective view of a transfer member of the articulated arm ofFIG. 1 with its associated articulation members;
• FIG. 2A is a perspective view of the transfer member ofFIG. 2 with a cover portion removed;
• FIG. 2B is an enlarged perspective view of the transfer member ofFIG. 2A;
• FIG. 2C is an enlarged cross-sectional view of the articulation members ofFIG. 2
• FIG. 2D is an enlarged cross-sectional view of the transfer member ofFIG. 2B;
• FIG. 2E is a partially exploded side view of the transfer member and articulation members ofFIG. 2;
• FIG. 3 is a perspective view of a counterbalance system of the articulated arm ofFIG. 1;
• FIG. 3A is an exploded view of the counterbalance system ofFIG. 3;
• FIG. 3B is a side view of the counterbalance system ofFIG. 3 in a first position;
• FIG. 3C is a side view of the counterbalance system ofFIG. 3 in a second position;
• FIG. 4 is a perspective view of a handle of the articulated arm ofFIG. 1;
• FIG. 5 is a perspective view of a base and a feature pack of the articulated arm ofFIG. 1;
• FIG. 6 is a plan view of a demonstrative embodiment of an encoder;
• FIG. 7 is a screen shot from an embodiment of calibration software associated with an articulated arm;
• FIG. 7A is a perspective view of an articulated arm in wireless communication with a computer; and
• FIG. 8 is a flow diagram of a method of operating an articulated arm.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIGS. 1 and 1A illustrate one embodiment of a portable coordinate measuring machine (PCMM)1 in accordance with the present invention. In the illustrated embodiment, the PCMM1 comprises abase10, a plurality ofrigid transfer members20, a coordinateacquisition member50 and a plurality of articulation members30-36 that form “joint assemblies” connecting therigid transfer members20 to one another. The articulation members30-36 along with thetransfer members20 and hinges (described below) are configured to impart one or more rotational and/or angular degrees of freedom. Through the various members30-36,20, the PCMM1 can be aligned in various spatial orientations thereby allowing fine positioning and orientating of the coordinateacquisition member50 in three dimensional space.
• The position of therigid transfer members20 and the coordinateacquisition member50 may be adjusted using manual, robotic, semi-robotic and/or any other adjustment method. In one embodiment, the PCMM1, through the various articulation members30-36, is provided with seven rotary axes of movement. It will be appreciated, however, that there is no strict limitation to the number of axes of movement that may be used, and fewer or additional axes of movement may be incorporated into the PCMM design.
• In the embodiment PCMM1 illustrated inFIG. 1, the articulation members30-36 can be divided into two functional groupings based on their associated motion members operation, namely: 1) thosearticulation members30,32,34,36 which are associated with the swiveling motion associated with a specific and distinct transfer member (hereinafter, “swiveling joints”), and 2) thosearticulation members31,33,35 which allow a change in the relative angle formed between two adjacent members or between the coordinateacquisition member30 and its adjacent member (hereinafter, “hinge joints” or “hinges”). While the illustrated embodiment includes four swiveling joints and three hinge joints positioned as to create seven axes of movement, it is contemplated that in other embodiments, the number of and location of hinge joints and swiveling joints can be varied to achieve different movement characteristics in a PCMM. For example, a substantially similar device with six axes of movement could simply lack the swivel joint30 between the coordinateacquisition member50 and theadjacent articulation member20. In still other embodiments, the swiveling joints and hinge joints can be combined and/or used in different combinations.
• As is know in the art (see e.g., U.S. Pat. No. 5,829,148, which is hereby incorporated by reference herein) and depicted inFIG. 2D, thetransfer members20 can comprise a pair of dual concentric tubular structures having an inner tubular shaft20arotatably mounted coaxially within an outer tubular sheath20bthrough a first bearing mounted proximately to a first end of the member adjacent and a second bearing located at an opposite end of the member and which can be positioned within thedual axis housing100. Thetransfer members20 operate to transfer motion from one end of the transfer member to the other end of the transfer member. Thetransfer members20 are, in turn, connected together with articulation members30-36 to form joint assemblies.
• The hinge joint, in turn, is formed, in part, by the combination of ayoke28 extending from one end of a transfer member (seeFIG. 1A), the rotational shaft extending through thearticulation members31,33,35 and thearticulation members31,33,35 themselves, which rotate about the rotational shaft to form a hinge or hinge joint.
• Each hinge or swiveling joint has its own dedicated motion transducer in the form of anencoder37 which can be seen inFIG. 2C. Advantageously, both the hinge and swiveling joint encoders are positioned at least partially, and more preferably, entirely within thedual axis housing100 within the respective articulation members30-36.
• In various embodiments, the coordinateacquisition member50 comprises a contact sensitive member55 (depicted as a hard probe inFIG. 1) configured to engage the surfaces of a selected object and generate coordinate data on the basis of probe contact. In the illustrated embodiment, the coordinateacquisition member50 also comprises a non-contact scanning and detection component that does not necessarily require direct contact with the selected object to acquire geometry data. As depicted, the non-contact scanning device comprises a non-contact coordinate detection device (shown as a laser coordinate detection device/laser scanner) that may be used to obtain geometry data without direct object contact. The non-contact scanning device can include a camera or otheroptical device70, which functions in conjunction with a laser not depicted herein. It will be appreciated that various coordinate acquisition member configurations including: a contact-sensitive probe, a non-contact scanning device, a laser-scanning device, a probe that uses a strain gauge for contact detection, a probe that uses a pressure sensor for contact detection, a device that uses an infrared beam for positioning, and a probe configured to be electrostatically-responsive may be used for the purposes of coordinate acquisition. Further, in some embodiments, a coordinateacquisition member50 can include one, two, three, or more than three coordinate acquisition mechanisms.
• Further description of certain embodiments of a coordinate acquisition member that can be used with the embodiments described herein can be found in U.S. patent application Ser. No. 12/487,535, filed 18 Jun. 2009 and entitled ARTICULATING MEASURING ARM WITH LASER SCANNER, which is incorporated by reference herein in its entirety. As depicted in said reference, the coordinate acquisition member can include a modular laser scanner that can attach to the main body of the coordinate acquisition member (which can also include a touch probe). The modular features can allow various other coordinate detection devices to be used with the coordinate acquisition member. Additionally, other coordinate acquisition members can be used, as is generally know by those of skill in the art.
• Advantageously, as depicted inFIGS. 2-2C, the articulation members30-36 form a dual-axis housing100. The dual-axis housing100 can be a single monoblock housing, a housing comprising multiple pieces bonded together (e.g. by welding, adhesive, etc.), or otherwise. As depicted, the dual-axis housing100 can be coupled to thetransfer members20 and comprise part of hinge and swivel joints, corresponding to the second and third axes of rotation from thebase10. As noted above, separately functionalrotational encoders37 and associated electronics for measuring a position of the transfer members and hinge and swivel joints (as are generally known by those of skill in the art) can be positioned in thearticulation members34 and35 (as well as the articulation members30-33 and36, depicted in other figures).
• To facilitate assembly of the dual-axis assembly, the dual-axis housing100 can include aremovable back cover102, shown removed inFIG. 2A. As depicted, theremovable cover102 can cover an opening in thehousing100 generally axially aligned with anadjacent transfer member20 mounted to the housing. Further, in some embodiments thecover102 can be configured so as not to bare any significant load of the CMM1. Accordingly, it may be desirable to form thecover102 of a less rigid material that can also serve as a shock absorber. As depicted, thecover102 can be positioned at an “elbow” position of the arm1. During some activities the “elbow” positions may be more likely to abruptly contact an external, hard surface that could damage the arm1. Advantageously, acover102 formed of a shock absorbent material can protect the arm1 from such damage. Even further, in some embodiments the material of thecover102 can also serve to promote enhanced sealing with the material of the dual-axis housing100. The dual-axis housing100 can comprise a rigid material, and thecover102 can comprise a more flexible material that can conform to the edges of the housing when mounted thereto, creating an enhanced seal.
• Theremovable back cover102 can provide a general sealing of the interior of the dual-axis housing100 from the external elements, protecting theencoders37 positioned within the housing. When thecover102 is removed theseparate encoder37 associated with thearticulation member34 can be exposed and inserted/removed from the dual-axis housing100 into a swivel-receivingportion104 generally axially aligned with the depicted transfer member20 (as depicted inFIG. 2E). In the illustrated embodiment, the encoders associated with thearticulation members34 and35 are separate components from thetransfer members20. That is, the encoder and transfer member are two separate and distinct components that are connected together but can rotatably operate apart from each other. The same principle can also be applied to the other articulation members30-33 and36. That is, thetransfer members20 can operate separately from the articulation members30-36 that form a joint or joint assembly as described above and operate to measure rotation.
• Additionally, additional electronics can be inserted/removed while thecover102 is removed, as depicted inFIG. 2B. As shown, the dual-axis housing100 can provide a receiving portion for a printedcircuit board38 that can hold additional electronics. In some embodiments, the additional electronics can perform additional signal processing such as digitizing an analog signal from the encoders. In some embodiments, such digitization can be performed prior to passing the signal to slip rings or other rotatable electronic connections. Further, in some embodiments the additional printedcircuit board38 can facilitate forming the physical electronic connection between both encoders within the dual-axis housing100.
• Further, in the depicted dual-axis housing100 theseparate encoder37 associated with thearticulation member35 can be inserted/removed independent of theback cover102. To facilitate this insertion/removal, the dual-axis housing100 can have a hinge-receivingportion106 oriented perpendicularly from a primary plane of the housing. The hinge-receivingportion106 can have anopen end108, into which theencoder37 can enter, and a substantiallyclosed end110 against which the encoder can abut to define a position for the encoder. Once theencoder37 has been inserted, acap piece112 can then be inserted to secure the encoder within the hinge-receivingportion106.
• As depicted inFIG. 2C, theencoder37 can include anencoder disk38aand a read head38b. Theencoder disk38acan have a pattern on its surface that can be measured by the read head38b. For example, in some embodiments theencoder disk38acan have an optical pattern including varying colors, transparent and opaque portions, or other visible variations; and the read head38bcan include an optical measuring device such as a camera. In some embodiments thedisk38acan have a defined pattern of lines on the disk similar to a bar code such that any image of the disk by the read head can define an absolute rotational angle, as further discussed below. As another example, theencoder disk38acan have varying magnetic portions and the read head38bcan measure a corresponding magnetic field. The varying patterns on theencoder disk38acan be measured by the read head38bto indicate a rotational position, or a change in rotational position of the encoder disk relative to the read head. In turn, as depicted, the read head38bcan be rotationally fixed with thehousing100 and theencoder disk38acan be rotationally fixed to anencoder shaft39 that is rotatably mounted within the housing. Thus, rotation of theshaft39 relative to thehousing100 can cause a corresponding relative rotation between thedisk38aand read head38bthat can be measured. However, it will be clear from the description herein that the apparatus can vary. For example, in some embodiments the read head38bcan be rotatably mounted to thehousing100 and theencoder disk38acan be rotatably fixed.
• In the depicted embodiment, the encoder associated with thearticulation member35 can mount with an adjacent transfer member, not shown inFIG. 2, via a fork joint on the transfer member and theencoder shaft39. Said fork joint can be similar to that depicted at the end of the depictedtransfer member20 opposite the dual-axis housing100, with ayoke28 that can mount to theencoder shaft39 rotatably mounted within thehousing100. The forks of theyoke28 can mount about the ends of the dual-axis housing100 and its contained encoder to form ahinge articulation member35. Accordingly, both encoders in the dual-axis housing100 can be inserted/removed independently of one another from the single housing. Notably, in other embodiments the form of the dual-axis housing100 can vary. For example, in some embodiments the dual-axis housing100 can form two swivel-receivingportions104, or two hinge-receivingportions106, as opposed to one of each.
• Placing theencoders37 into a single housing can provide numerous advantages over prior art assemblies with separate housings. For example, the combined housing can reduce the number of parts and joints required, and thus also reduce cost and assembly time. Further, the accuracy of the device can improve from the elimination of deflection, misalignment, or other problems with multiple components. Additionally, removal of the additional housing can allow a more compact combined joint assembly, allowing the arm to be better supported and have less weight. As shownFIG. 1A, ayoke28 of the next or proceedingtransfer member20 can be coupled to the bearing shaft extending throughdual axis housing100 to form the hinge joint.
• Although depicted as enclosing the second and third axes from the base, a similar dual-axis housing100 can be used with other combinations of articulation members, such as the fourth andfifth articulation members32,33. Further, the dual-axis housing can provide additional advantages not explicitly discussed herein. However, it should be noted that in other embodiments of the inventions described herein, the articulation members30-36 can each have a separate housing.
• It should be appreciated that the dual-axis housing or joint assembly described above can be used in other types of CMMs and need not be used in combination with the additional embodiments described below.
• FIGS. 3 and 3A depict animproved counterbalance system80. As depicted, thecounter balance system80 can include apiston assembly84 forming a gas shock counterbalance. A nitrogen charged gas spring can connect between points separated by apivot88 aligned with an articulation member such as the second-closest-to-the-base articulation member35. As depicted, the connection point nearer the base10 can be closer to thepivot88 than to the base. This results in a counterbalance design where the gas shock is in a predominantly horizontal position when the second linkage is in a horizontal position, as depicted inFIG. 3C. The predominantly horizontal position of the gas shock can be further promoted by the position of the connection point further from the base. As depicted, the connection point further from the base can be positioned at approximately the mid-point of thetransfer member20 supported by thecounterbalance system80. Further, as depicted thepiston assembly84 can include alock86 that can increase the resistance against movement of the piston, thus preventing additional rotation of the alignedarticulation member35. In one embodiment the lock is implemented with a lever on thelock86, pushing on a pin that opens and closes an aperture within the gas shock. The opening and closing of the aperture either allows or prevents the flow of gas within the piston.
• Thisimproved counterbalance system80 can provide a number of advantages. For example, this design can allow the first axis of rotation from the base (associated with articulation member36) to be shorter, reducing associated deflection. Additionally, this reduced length can be accomplished without a reduced angular span of rotation about thepivot88. Theimproved counterbalance system80 can also reduce the number of parts required, as the locking mechanism and the counterbalance mechanism can be integrally combined into a single system. Further, thepiston assembly84 can damp the motion about thepivot88. This reduces the chance of damaging the CMM when a user tries to move the arm while it is still locked. However, it should be noted that in other embodiments of the inventions described herein, a different counterbalance system can be used, such as a weight provided on a back end of atransfer member20. Further, in other embodiments of the inventions described herein, a different locking mechanism can be used, such as a rigid physical stop. It should be appreciated theimproved counterbalance system80 described above can be used in other types of CMMs and need not be used in combination with the additional embodiments described above and below the preceding section.
• FIG. 4 depicts animproved handle40. Thehandle40 can include one or moreintegrated buttons41. The handle can connect to the axis with bolts, snaps, or clamps. Additionally, thehandle40 can includeelectronics44 included within its interior. Advantageously, providing theelectronics44 in thehandle40 can further separate the electronics from rotational encoders and other components that may lose accuracy when heated. In some embodiments thehandle40, or theelectronics44 therein, can be thermally isolated from the remainder of the arm. Additionally, when thehandle40 is removable and includes theelectronics44, it can form a modular component similar to the feature packs (described below). Thus, a user can change the functionality by changing thehandle40, and accordingly also changing theelectronics44 and thebuttons41 that control the electronics. A plurality ofhandles40 with different functionalities can thus be provided in a CMM system to provide modular features to the CMM. Again, it should be noted that in other embodiments of the inventions described herein, a different handle can be used, or alternatively there can be no distinct handle. Additionally, the handle can contain a battery to power the arm, the scanner or both.
• It should be appreciated theimproved handle40 described above can be used in other types of CMMs and need not be used in combination with the additional embodiments described above and below the preceding section
• Additionally or alternatively, in some embodiments a CMM arm1 can be at least partially controlled by motion of the arm itself, as depicted inFIG. 8. For example, whereas some commands or instructions may be triggered by the pressing of a button, pulling a lever, turning a dial, or actuating some other traditional actuation device in some embodiments, in other embodiments the same or different instruction can be triggered by a specific motion or position of the CMM arm1, which can be detected by theencoders37. As a more specific example, in some embodiments the CMM arm1 can be instructed to enter a sleep mode when the arm is placed in a generally folded or retracted position, such as that depicted inFIG. 1. The CMM arm1 can then perform that instruction. Similarly, the CMM arm1 can be reawakened by a rapid movement, or movement into a more extended position. Other combinations of instructions, motions, and positions are possible.
• For example, in some embodiments the CMM arm1 can enter into different data acquisition modes depending on its general orientation. Varying the data acquisition mode by position can be advantageous where the CMM arm1 regularly measures products that require different data acquisition modes along different parts of a product.
• Further, in some embodiments the arm can enter into different data acquisition modes depending on its speed of movement. For example, an operator of the CMM may move the CMM slowly when a critical point will soon be measured. Thus, the CMM can increase its measurement frequency, accuracy, or other characteristics when the arm is moving slowly. Additionally, the CMM can be toggled between a mode where the arm is used as a computer mouse and a measurement mode with a quick movement of one of the last axes (embodiments of an associated computer further described below).
• As with the previous embodiments, it should be appreciated that these features related to control of the arm can be used in other types of CMMs and need not be used in combination with the additional embodiments described above and below the preceding section.
• FIG. 5 depicts a set of feature packs90 that can connect with thebase10 via adocking portion12. Thedocking portion12 can form an electronic connection between the CMM arm1 and thefeature pack90. In some embodiments thedocking portion12 can provide connectivity for high-speed data transfer, power transmission, mechanical support, and the like. Thus, when connected to a docking portion, afeature pack90 can provide a modular electronic, mechanical, or thermal component to the CMM arm1, allowing a variety of different features and functionality such as increased battery life, wireless capability, data storage, improved data processing, processing of scanner data signals, temperature control, mechanical support or ballast, or other features. In some embodiments this modular functionality can complement or replace some modular features of thehandle40. The modular feature packs can contain connectors for enhanced functionality, batteries, electronic circuit boards, switches, buttons, lights, wireless or wired communication electronics, speakers, microphones, or any other type of extended functionality that might not be included on a base level product. Further, in some embodiments the feature packs90 can be positioned at different portions of the CMM arm1, such as along a transfer member, an articulation member, or as an add-on to thehandle40.
• As one example, afeature pack90 can include a battery, such as a primary battery or an auxiliary battery. Advantageously, in embodiments where thepack90 is an auxiliary battery the CMM can include an internal, primary battery that can sustain operation of the CMM while the auxiliary battery is absent or being replaced. Thus, by circulating auxiliary batteries a CMM can be sustained indefinitely with no direct power connection.
• As another example, afeature pack90 can include a data storage device. The available data storage on thefeature pack90 can be arbitrarily large, such that the CMM can measure and retain a large amount of data without requiring a connection to a larger and/or less convenient data storage device such as a desktop computer. Further, in some embodiments the data storage device can transfer data to the arm, including instructions for arm operation such as a path of movement for a motorized arm, new commands for the arm upon pressing of particular buttons or upon particular motions or positions of the arm, or other customizable settings.
• In examples where the feature pack includes wireless capability, similar functionality can be provided as with a data storage device. With wireless capability, data can be transferred between the CMM and an external device, such as a desktop computer, continuously without a wired connection. In some embodiments, the CMM can continuously receive commands from the auxiliary device. Further, in some embodiments the auxiliary device can continuously display data from the arm, such as the arm's position or data points that have been acquired. In some embodiments the device can be a personal computer (“PC”) and the feature pack can transmit arm coordinate data and scanner data wirelessly to the PC. Said feature pack can combine the arm data and scanner data in the feature pack before wireless transmission or transmit them as separate data streams.
• In further embodiments, the feature packs can also include data processing devices. These can advantageously perform various operations that can improve the operation of the arm, data storage, or other functionalities. For example, in some embodiments commands to the arm based on arm position can be processed through the feature pack. In additional embodiments, the feature pack can compress data from the arm prior to storage or transmission.
• In another example, the feature pack can also provide mechanical support to the CMM. For example, the feature pack can connect to thebase10 and have a substantial weight, thus stabilizing the CMM. In other embodiments, the feature pack may provide for a mechanical connection between the CMM and a support on which the CMM is mounted.
• In yet another example, the feature pack can include thermal functionality. For example, the feature pack can include a heat sink, cooling fans, or the like. A connection between the docking portion and the feature pack can also connect by thermally conductive members to electronics in thebase10 and the remainder of the CMM, allowing substantial heat transfer between the CMM arm and the feature pack.
• Further, as depicted inFIG. 1, in some embodiments the feature packs90 can have a size and shape substantially matching a side of the base10 to which they connect. Thus, thefeature pack90 can be used without substantially increasing the size of the CMM, reducing its possible portability, or limiting its location relative to other devices.
• Again, the feature packs90 can be used in combination with each other and the other features described herein and/or can be used independently in other types of CMMs.
• Additionally, in some embodiments the CMM arm1 can include anabsolute encoder disk95, a demonstrative embodiment depicted inFIG. 6. Theabsolute encoder disk95 can include a generally circular, serialized pattern that can be embodied in reflective and non-reflective materials, translucent and non-translucent materials, alternating magnetic properties, or the like. The serialized pattern can allow a read head to determine a unique position on the encoder by only reading a limited portion of the encoder's coded surface. In some embodiments, the serialized pattern can resemble a bar code, as depicted inFIG. 6. The pattern can be non-repetitive along a viewing range of an associated read-head. Thus, an image or other data collected by the read-head from theencoder disk95 can yield a pattern unique from any other position on the encoder, and therefore be associated with a unique angular position. Each encoder can consist of a single serialized disk that is read by one or more read-heads that can be, e.g., CCD imagers. The use of two or preferably four CCD imagers can improve the accuracy of the encoder by measuring the eccentricity of the axis and subtracting out the eccentricity from the angle measurement. Further, the angle accuracy can be improved by averaging the measurements of the multiple CCD imagers.
• In prior art encoders an incremental and repetitive surface was often used, in which the coded surface only indicates incremental steps and not an absolute position. Thus, incremental encoders would require a return to a uniquely identified home position to re-index and determine the incremental positions away from the home position. Advantageously, some embodiments of anabsolute encoder disk95 can eliminate the required return to a home position. This feature of a CMM can also be used in combination with the other features described herein and/or can be used independently in other types of CMMs.
• Advantageously, theabsolute encoder disk95 can improve functionality of a CMM arm1 that enters a sleep mode. Entering sleep mode can reduce the power consumption of a CMM arm1. However, if enough systems are shut down during sleep mode then incremental encoders may “forget” their position. Thus, upon exiting sleep mode incremental encoders may need to be brought back to the home position prior to use. Alternatively, incremental encoders can be kept partially powered-on during sleep mode to maintain their incremental position. Advantageously, with anabsolute encoder disk95 the encoders can be completely powered off during sleep mode and instantly output their position when power is returned. In other modes, the absolute encoder can read its position at a lower frequency without concern that it may miss an incremental movement and thus lose track of its incremental position. Thus, the CMM arm1 can be powered-on or awakened and can immediately begin data acquisition, from any starting position, without requiring an intermediary resetting to the “home” position. In some embodiments absolute encoders can be used with every measured axis of rotation of the CMM. This feature of a CMM can also be used in combination with the other features described herein and/or can be used independently in other types of CMMs. For example, as described above, this sleep mode can be induced by movement into a particular position. As a further example, theencoder disk38acan be anabsolute encoder disk95.
• Additionally, in some embodiments the CMM arm1 can be associated with calibration software. Generally, calibration of a CMM arm can be performed by positioning the distal end of the CMM arm (e.g. the probe) at certain predefined and known positions, and then measuring the angular position of the arm. However, these calibration points often do not define a unique arm orientation, but instead can be reached with a plurality of arm positions. To improve the effectiveness of the calibration procedure, software can be included that indicates a preferred or desired CMMarm calibration position1a, including the distal point as well as the orientation of the rest of the arm. Further, in some embodiments the software can also show the arm's current position1bin real time as compared to the desiredposition1a, as depicted inFIG. 7. Even further, in some embodiments the software can highlight portions of the arm that are out of alignment with the desiredposition1a.
• As depicted inFIG. 7A, the calibration software can be included on a separate, auxiliary device such as acomputer210 coupled to adisplay220 and one ormore input devices230. Anoperator240 may plan a calibration procedure using system thecomputer210 by manipulating the one ormore input devices230, which may be a keyboard and/or a mouse. Thedisplay220 may include one or more display regions or portions, each of which displays a different view of the CMM arm1 in its current position, and optionally a desired calibration position (as described above). Each of these displays may be linked internally within a program and data oncomputer210. For example, a program running on acomputer210 may have a single internal representation of the CMM arm's current position in memory and the internal representation may be displayed in two or more abstract or semi-realistic manners ondisplay220.
• In various embodiments, thecomputer210 may include one or more processors, one or more memories, and one or more communication mechanisms. In some embodiments, more than one computer may be used to execute the modules, methods, and processes discussed herein. Additionally, the modules and processes herein may each run on one or multiple processors, on one or more computers; or the modules herein may run on dedicated hardware. Theinput devices230 may include one or more keyboards (one-handed or two-handed), mice, touch screens, voice commands and associated hardware, gesture recognition, or any other means of providing communication between theoperator240 and thecomputer210. Thedisplay220 may be a 2D or 3D display and may be based on any technology, such as LCD, CRT, plasma, projection, et cetera.
• The communication among the various components ofsystem200 may be accomplished via any appropriate coupling, including USB, VGA cables, coaxial cables, FireWire, serial cables, parallel cables, SCSI cables, IDE cables, SATA cables, wireless based on 802.11 or Bluetooth, or any other wired or wireless connection(s). One or more of the components insystem200 may also be combined into a single unit or module. In some embodiments, all of the electronic components ofsystem200 are included in a single physical unit or module.
• The enhanced capabilities of the calibration software can allow the operator to refer simply to the live images on the display and position the live image over the desired image which reduces the need for manuals or additional training documentation which slows down the calibration process. Additionally, new calibration technicians can be trained accurately and quickly with the aid of the aforementioned display. The data acquired from these methods of calibration can be more repeatable and more accurate due to, e.g., increased consistency of articulations. In addition to positioning of the CMM in the correct pose, thecalibration artifact120 should be positioned in the correct location within the arm's volume of reach. When the display shows a true3 dimensional image, the position of the calibration artifact in 3D space can also be correctly displayed, further ensuring that the correct volume of measurement is measured.
• These calibration features of a CMM can also be used in combination with the other features described herein and/or can be used independently in other types of CMMs. For example, in some embodiments the calibration process can utilize commands based on the position and motion of the CMM (as discussed above). In some embodiments, during calibration holding the arm still for an extended period of time can indicate to the calibration software that the arm is in the desired position. The software can then acknowledge its processing of this command with a change in display, sound, color, etc. This result can then be confirmed by the operator with a rapid motion of the arm out of said position. The calibration software can then indicate a next calibration point, or indicate that calibration is complete. In addition this functionality can be extended to the operator as well. One example is during the calibration of the probe the software can display the required articulation pose that the CMM should be in as well as the actual pose that it is in. The operator can then move the CMM until it is in the correct position and record a position or it can be recorded automatically. This simplifies the process for the user and improves the accuracy of the data taken. Different methods can be presented depending on the type of probe that is sensed to be present such as laser line scanner, touch trigger probe, etc.
• Even further, in some embodiments the CMM arm1 can include a tilt sensor. In some embodiments the tilt sensor can have an accuracy of at least approximately 1 arc-second. The tilt sensor can be included in thebase10, afeature pack90, or in other parts of the CMM arm1. When placed in the base10 or thefeature pack90, the tilt sensor can detect movement of the CMM arm's support structure, such as a table or tripod on which the arm sits. This data can then be transferred to processing modules elsewhere in the arm or to an external device such as a computer. The CMM arm1 or the external device can then warn the user of the movement in the base and/or attempt to compensate for the movement, for example when the tilt changes beyond a threshold amount. Warnings to the user can come in a variety of forms, such as sounds, LED lights on thehandle40 or generally near the end of the arm1, or on a monitor connected to the arm1. Alternatively or additionally, the warning can be in the form of a flag on the data collected by the arm1 when tilting has occurred. This data can then be considered less accurate when analyzed later. When attempting to compensate for the movement, in some embodiments the tilting and its effects on position can be partially measured and accounted for in the calibration process. In further embodiments, the tilting can be compensated by adjusting the angular positions of the articulation members accordingly. This feature of a CMM can also be used in combination with the other features described herein and/or can be used independently in other types of CMMs.
• In further embodiments, a trigger signal is sent from the arm to the scanner upon each measurement of the arm position. Coincident with the arm trigger the arm can latch the arm position and orientation. The scanner can also record the time of receipt of the signal (e.g. as a time stamp), relative to the stream of scanner images being captured (also, e.g., recorded as a time stamp). This time signal data from the arm can be included with the image data. Dependent on the relative frequency of the two systems (arm and scanner) there may be more than one arm trigger signal per scanner image. It might not be desirable to have the arm running at a lower frequency than the scanner, and this usually results in the arm and scanner frequencies being at least partially non-synchronized. Post-processing of the arm and scanner data can thus combine the arm positions by interpolation with the scanner frames to estimate the arm position at the time of a scanner image. In some embodiments, the interpolation can be a simple, linear interpolation between the two adjacent points. However, in other embodiments higher-order polynomial interpolations can be used to account for accelerations, jerks, etc. This feature of a CMM can also be used in combination with the other features described herein and/or can be used independently in other types of CMMs.
• The various devices, methods, procedures, and techniques described above provide a number of ways to carry out the invention. Of course, it is to be understood that not necessarily all objectives or advantages described may be achieved in accordance with any particular embodiment described herein. Also, although the invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and obvious modifications and equivalents thereof. Accordingly, the invention is not intended to be limited by the specific disclosures of preferred embodiments herein.

Claims (19)

1. A method of operating an articulated arm CMM comprising:

measuring one or more coordinates on an object with an articulated arm CMM;

at least partially powering off at least one encoder in the articulated arm CMM;

powering on said at least one encoder; and

measuring one or more coordinates on said object after powering on said encoder without re-indexing said encoder.

2. The method ofclaim 1, wherein the step of powering off comprises fully powering off said encoder.

3. The method ofclaim 1, further comprising the step of putting the CMM in a sleep mode.

4. The method ofclaim 1, further comprising the step of combining the measured coordinates from before and after the powering off step into a single data set representing the measured object.

5. An articulated arm CMM comprising:

an articulated arm comprising a plurality of articulated arm members, a coordinate acquisition member at a distal end, and a base at a proximal end;

wherein at least one of the articulation members comprises an absolute encoder.

6. The articulated arm CMM ofclaim 5, wherein the at least one absolute encoder is configured to enter a sleep mode during which it does not measure its position.

7. The articulated arm CMM ofclaim 6, wherein the at least one absolute encoder is powered off during said sleep mode.

8. The articulated arm CMM ofclaim 5, wherein the at least one absolute encoder is configured to enter a mode in which it reads position at a lower frequency.

9. The articulated arm CMM ofclaim 5, wherein the absolute encoder comprises a non-repeating pattern.

10. The articulated arm CMM ofclaim 9, wherein the pattern comprises varying reflective properties.

11. The articulated arm CMM ofclaim 9, wherein the pattern comprises varying translucent properties.

12. The articulated arm CMM ofclaim 9, wherein the pattern comprises varying magnetic properties.

13. The articulated arm CMM ofclaim 5, wherein the arm comprises a plurality of measured axes of rotation and at least one absolute encoder for each measured axis of rotation.

14. The articulated arm CMM ofclaim 5, wherein the absolute encoder consists of more than one readhead.

15. An articulated arm CMM comprising:

an articulated arm comprising a plurality of articulated arm members, a measuring probe, at a distal end, and a base at a proximal end:

a tilt sensor rigidly connected to the base such that the tilt sensor can detect a tilting angle of the base.

16. The articulate arm CMM ofclaim 15, wherein the arm provides a signal to a user when the tilt of the base changes beyond a threshold amount.

17. The articulated arm CMM ofclaim 15, wherein the arm or an external device compensates the data for tilting sensed by the tilt sensor.

18. The articulated arm CMM ofclaim 15, wherein the arm or an external device flags data taken while the tilt of the base has changed beyond a threshold amount.

19. A method of operating an articulated arm CMM comprising:

measuring one or more coordinates with an articulated arm CMM;

continuously measuring the tilt of the articulated arm CMM; and

when the measured tilt exceeds a threshold value, performing an action selected from the group consisting of compensating the measured coordinates for the tilt, providing a signal regarding the tilt to a user, and flagging the measured coordinates taken during the tilt.

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