Ultra-light and ultra-accurate portable coordinate measurement machine

Abstract

To provide a portable coordinate measuring machine (CMM) including an articulated arm having a rotary joint.SOLUTION: Each of rotary joints 12, 14, 16, 18, 20, 22 and 24 includes a bearing, a shaft configured to engage with an inside diameter of the bearing and rotate about a rotational axis of the bearing, a housing having at least one port engaging with at least one outside diameter of the bearing, and at least one transducer configured to output an angular signal corresponding to a rotational angle of the shaft relative to the housing around the rotational axis. The shaft has no section having a diameter greater than an inner diameter of the first bearing or the second bearing, or the at least one port of the housing has no section having a diameter smaller than an outer diameter of the first bearing or the second bearing.SELECTED DRAWING: Figure 1A

Description

background

[0001] FIELD OF THE DISCLOSURE

[0001] The present disclosure relates generally to coordinate measuring machines, and more particularly to high-precision, ultra-lightweight, portable coordinate measuring machines.

[0002]

[0002] Coordinate measuring machines are useful, among other things, for measuring points in three-dimensional space. A coordinate measuring machine traces measurement points in, for example, Cartesian coordinate space (x, y, x). A coordinate measuring machine typically consists of a stand and a tracing system. The stand may act as a reference point, while the tracing system moves in space in a measurable manner relative to the reference point. A tracing system for a portable coordinate measuring machine may include an articulated arm attached to the stand at one end and a measurement probe at the other end.

[0003]

[0003] Measurements must be accurate to be usable. However, very high accuracy is difficult to achieve due to factors such as temperature and load conditions. In particular, in portable coordinate measuring machines, arm deflection due to thermal changes or load changes adversely affects measurement accuracy. Therefore, in terms of their performance, conventional portable coordinate measuring machines have not been as accurate as conventional non-portable types of coordinate measuring machines.

[0004]

[0004] Improved accuracy is sometimes available. However, traditionally, such improvements have been accompanied by a significant increase in the mass and / or weight of the coordinate measuring machine. Traditional portable coordinate measuring machines with improved accuracy have been bulky and heavy. These are undesirable characteristics for a coordinate measuring machine, especially a portable coordinate measuring machine. Furthermore, processes for constructing and assembling coordinate measuring machine joints, especially long joints, with the precision required to obtain high-precision measurements have not been available. Summary of the Invention

[0005]

[0005] The present disclosure provides a portable coordinate measuring machine (CMM) that is more accurate than prior art coordinate measuring machines. Surprisingly, the CMM disclosed herein is lighter and less bulky.

[0006]

[0006] In a first aspect of the present invention, the CMM includes a rotary joint, the shaft of which has no portion with a diameter larger than the inner diameter of the joint's bearing, and / or the housing of the rotary joint has a bearing engaging portion, the bearing engaging portion having no portion with a diameter narrower than the outer diameter of the joint's bearing.

[0007]

[0007] In another aspect of the present invention, at least one rotary joint includes a rotary damper operably coupled to the shaft and housing and configured to provide controlled damping of rotational motion of the shaft about the axis of rotation.

[0008] In another aspect of the invention, rotational damping is incorporated into at least one rotary joint to provide controlled damping of rotational motion of the shaft about the axis of rotation.

[0009]

[0009] In another aspect of the invention, at least one rotary joint includes a rotational damping mechanism configured to provide controlled damping of the rotational movement of the shaft about the axis of rotation, and circuitry operatively connected to the at least one transducer and configured to output speed and direction signals corresponding to the speed of the rotational movement of the shaft about the axis of rotation based on the angle signal and time, the circuitry being configured to compare the speed signals with a predetermined speed threshold to determine whether the rotational movement is occurring at an excessive speed and resulting in excessive torque.

[0010] In another aspect of the present invention, at least one rotary joint has a rotation damping mechanism. and at least one strain gauge, the rotational damping mechanism configured to provide controlled damping of rotational movement of the shaft about the axis of rotation, the at least one strain gauge operatively coupled to at least one of the shaft and the housing and configured to sense strain in at least one of the shaft and the housing due to rotational movement of the shaft about the axis of rotation, and output a strain signal usable to modify the location of the measurement probe based in part on the strain signal.

[0011]

[0011] In another aspect of the present invention, in at least one of the plurality of joints, a) a shaft that engages with the inner diameter portion of at least one of the first bearing and the second bearing, and b) a portion of the housing that engages with the outer diameter portion of at least one of the first bearing and the second bearing are made of steel.

[0012]

[0012] In another aspect of the invention, a first joint from the plurality of joints is attached to a second joint from the plurality of joints by a steel structure, which contacts the inside or outside of a bearing of the first joint or the inner or outer ring of a bearing of the second joint.

[0013] In another aspect of the invention, all of the structural portions of at least one of the plurality of rotary joints are fabricated from steel.

[0014]

[0014] In another aspect of the invention, any structural portion of the CMM, including multiple arm segments and multiple rotary joints, is fabricated from a controlled expansion alloy that is lighter in weight than steel and has a thermal expansion coefficient that matches the thermal expansion coefficient of steel or stainless steel in the range of 9.9 to 18 μm / m°C at 25°C.

[0015]

[0015] In another aspect of the present invention, the measurement probe includes a handle operably coupled to the first end mechanically rather than electrically, the handle rotatably coupled to the first end so as to rotate about a central axis of the measurement probe, the handle including a wireless transmitter and at least one switch, the at least one switch operably connected to the wireless transmitter and configured to, when actuated, cause the wireless transmitter to transmit a wireless signal that causes the CMM to take a measurement.

[0016]

[0016] In another aspect of the present invention, the electrical circuit includes a serial communication circuit that eliminates the need for dedicated input wires to receive analog signals and other angle signals from other transducers in the CMM, and the electrical circuit is configured to output a concentration of the angle signal and other angle signals to provide information corresponding to the position of the measurement probe relative to the base.

[0017] In another aspect of the invention, the shaft may include an intermediate portion and first and second end portions fixedly attached to the ends of the intermediate portion. The first and second end portions may be concentric to within 0.0001 inches. The first end portion engages with the inner diameter of the first bearing, and the second end portion engages with the inner diameter of the second bearing. The shaft is configured to rotate about the axis of rotation of the first and second bearings. The end of the first housing has an inner diameter that engages with the outer diameter of the first bearing, and the end of the second housing has an inner diameter that engages with the outer diameter of the second bearing. The end of the first housing and the end of the second housing may be concentric to within 0.0005 inches. Therefore, the first and second bearings may be preloaded to eliminate play.

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various example systems, methods, and the like, illustrating various exemplary embodiments of aspects of the present invention. It will be understood that the boundaries of elements depicted in the drawings (e.g., boxes, groups of boxes, other shapes) represent one example of a boundary. Those skilled in the art will understand that an element can be designed as multiple elements, or multiple elements can be designed as one element. An element shown as an internal component of another element can be implemented as an external component, and an element shown as an external component can be implemented as an internal component. Furthermore, elements need not be drawn to scale. [Brief explanation of the drawings]

[0019] [Figure 1A] FIG. 1A illustrates a perspective view of an exemplary coordinate measuring machine (CMM). [Figure 1B] FIG. 1B illustrates a perspective view of an exemplary coordinate measuring machine (CMM). [Figure 1C] FIG. 1C illustrates a perspective view of an exemplary coordinate measuring machine (CMM). [Figure 1D] FIG. 1D illustrates a cross-sectional view of the exemplary CMM of FIGS. 1A-1C. [Figure 2] FIG. 2 illustrates an exploded view of an example base and pivot joint of the CMM of FIGS. 1A-1D. [Figure 3A] FIG. 3A illustrates a partially exploded view of an example pivot joint of the CMM of FIGS. 1A-1D. [Figure 3B] FIG. 3B illustrates a cross-sectional view of an example pivot joint of the CMM of FIGS. 1A-1D. [Figure 3C] FIG. 3C illustrates the process of assembling the housing end to the outer tube of an exemplary swivel joint. [Figure 3D] FIG. 3D illustrates the process of assembling the housing end to the outer tube of an exemplary swivel joint. [Figure 3E] FIG. 3E illustrates the process of assembling the shaft and bearings to the outer tube of an exemplary swivel joint. [Figure 4] FIG. 4 illustrates an exploded view of an example pivot joint of the CMM of FIGS. 1A-1D. [Figure 5A] FIG. 5A illustrates an exploded view of the hinge joint of the CMM of FIGS. 1A-1D. [Figure 5B] FIG. 5B illustrates a cross-sectional view of the hinge joint of the CMM of FIGS. 1A-1D. [Figure 6A] FIG. 6A illustrates a cross-sectional view of the example hinge joint of FIGS. 1A-1D including a rotational damper. [Figure 6B] FIG. 6B illustrates an exploded view of the exemplary instrumented rotational damper assembly of FIGS. 1A-1D. [Figure 6C] FIG. 6C illustrates an exploded view of the exemplary uninstrumented rotational damper assembly of FIGS. 1A-1D. [Figure 7A] FIG. 7A illustrates a perspective view of an exemplary measurement probe of the CMM of FIGS. 1A-1D. [Figure 7B] FIG. 7B illustrates a perspective view of an exemplary alternative measurement probe of the CMM of FIGS. 1A-1D. [Figure 8] FIG. 8 illustrates a perspective view of an exemplary on-arm switch assembly of the CMM of FIGS. 1A-1D. [Figure 9] FIG. 9 illustrates a block diagram of exemplary electronics for the CMM of FIGS. 1A-1D. [Figure 10A] FIG. 10A illustrates a timing diagram of exemplary electronics for the CMM of FIGS. 1A-1D. [Figure 10B] FIG. 10B illustrates a timing diagram of exemplary electronics for the CMM of FIGS. 1A-1D. [Figure 10C] FIG. 10C illustrates a timing diagram of exemplary electronics for the CMM of FIGS. 1A-1D. [Figure 10D] FIG. 10D illustrates a timing diagram of exemplary electronics for the CMM of FIGS. 1A-1D. [Figure 10E] FIG. 10E) illustrates a timing diagram of exemplary electronics for the CMM of FIGS. 1A-1D. [Figure 10F] FIG. 10F illustrates a timing diagram of exemplary electronics for the CMM of FIGS. 1A-1D. [Figure 11A] FIG. 11A illustrates an exemplary trajectory plot showing shaft rotation for a conventional long arm joint. [Figure 11B] FIG. 11B illustrates an exemplary trajectory plot showing shaft rotation for a long arm joint of a CMM of the present disclosure.

[0020] Detailed Description

[0021]

[0033] 1A-1C illustrate perspective views of an exemplary coordinate measuring machine (CMM) 1. FIG. 1D illustrates a cross-sectional view of the exemplary CMM 1. The CMM 1 includes an articulated arm 2, a base 4, and a measurement probe 6. The articulated arm 2 is attached to the base 4 at one end and to the measurement probe 6 at the other end. The base 4 may include, for example, a magnet holder 5 for mounting the arm 2, for example, to a working surface. The articulated arm 2 includes two arm segments 8, 9 and a number of revolute joints 12, 14, 16, 18, 20, 22, and 24. The CMM may include an on-arm switch assembly 10.

[0022]

[0034] The overall length of the articulated arm 2 and / or arm segments 8, 9 may vary depending on its intended use. In one embodiment, the articulated arm may have an overall length of approximately 48 inches. This arm size provides a portable CMM that is well suited for measuring machines accomplished using typical hand tools such as micrometers, height gauges, calipers, etc. The articulated arm 2 may have smaller or larger sizes.

[0023]

[0035] The rotational joints generally include two types of joints: swivel joints 12, 16, 20, and 24, and hinge joints 14 and 18. The swivel joints 12, 16, 20, and 24 are generally axially or longitudinally positioned along the arm 2. The hinge joints 14, 18, and 22 are generally 90° relative to the swivel joints or the longitudinal axis of the arm 2. The swivel and hinge joints are paired as shown in FIGS. 1A-1D, but may be arranged in other configurations. Because of the multiple rotational joints, the arm 2 is manually positionable, meaning that a user can manually move the probe 6 to virtually any position within a radius anchored to the base 4 of the CMM 1. Each of these joints is shown schematically in FIGS. 2-6A.

[0024]

[0036] Generally, magnet holder 5 on base 4 mounts CMM 1 to a working surface, base 4 includes pivot joint 12, pivot joint 12 is attached to hinge joint 14, hinge joint 14 is attached to pivot joint 16, pivot joint 16 is attached to hinge joint 18, hinge joint 18 is attached to pivot joint 20, pivot joint 20 is attached to hinge joint 22, hinge joint 22 is attached to pivot joint 24, pivot joint 24 is attached to measurement probe 6.

[0025]

[0037] Figure 2 illustrates an exploded view of an exemplary base 4 and pivot joint 12. Figure 2 also illustrates a base enclosure 4a, which has a battery receptacle 26 mounted on top of it. Because the CMM 1 is portable, it can operate on battery power from a battery (not shown) that is installed on the CMM 1 via the receptacle 26. The CMM 1 may also include a power jack 25, to which a power adapter can be connected to provide power to the CMM 1.

[0026]

[0038] Pivot joint 12 may include a housing 28, a bearing 30, bearings 32, 34, an encoder printed circuit board (PCB) 36, an encoder disk 38, and a slip ring 40. Pivot joint 12 may also include dust covers 42a-42c and various hardware such as threaded studs 44a-c and screws 47a-c. Pivot joints in general are described in more detail below with reference to pivot joint 16.

[0027]

[0039] FIG. 3A illustrates a partially exploded view of an exemplary pivot joint 16, and FIG. 3B illustrates a partial cross-sectional view of the pivot joint 16. Each of these views illustrates only the end of the pivot joint 16; the intermediate portion of the pivot joint, not shown, corresponds to arm segment 8. Here, pivot joint 16 is used to generally describe pivot joints 12, 16, 20, and 24, even though the pivot joints are not identical. Pivot joints 16 and 20 are very similar. Also, pivot joint 24 is similar to pivot joints 16 and 20, except that pivot joint 24 has a shorter shaft, as described below. Because at least some of the components of pivot joint 16 are substantially similar to those previously described with reference to pivot joint 12, these similar components are identified in FIGS. 3A and 3B with the same reference numerals as in FIG. 2.

[0028]

[0040] The pivot joint 16 may include housings 48 and 49, shaft sections 50a, 50b, and 50c, bearings 32 and 34, an encoder PCB 36, an encoder disk 38, and a slip ring 40. The bearings 32 and 34 are preferably steel or stainless steel ball bearings. The shaft sections 50a and 50c may be operably attached to opposite ends of the shaft section 50b to form a shaft assembly 50, as described in more detail below. The relatively long shaft section 50b may be fabricated from a stiff yet lightweight material (e.g., carbon fiber, aluminum, etc.), as well as steel. However, the shaft sections 50a and 50c may be fabricated from steel to match the material from which the bearings 32 and 34 are fabricated. Like the relatively long shaft section 50b, the tube 60 containing the shaft section 50b may be fabricated from a stiff yet lightweight material, as well as steel, as well. Swivel joint 16 may also include various hardware such as covers 62a-62b and snap rings 64a-64c.

[0029]

[0041] At one end of the pivot joint 16, the housing 48 has a surface 48a that operably attaches to one end of the tube 60 of the corresponding arm segment (arm segment 8 in the case of the pivot joint 16). The housing 48 also has a shaft coupling portion 48c that operably connects the pivot joint 16 to the preceding hinge joint (see FIGS. 1A-1D). In the case of the pivot joint 16, the shaft coupling portion 48c connects the pivot joint 16 to the shaft of the hinge joint 14. At the other end of the pivot joint 16, the housing 49 has a surface 49a that operably attaches to the second end of the tube 60 of the corresponding arm segment (segment 8 in the case of the pivot joint 16). The housing 49 also has a port 49b within which the end of the shaft assembly, specifically shaft portion 50a, is located. The assembly of the tube 60 to the housing ends 48, 49 will be described in more detail below.

[0030]

[0042] As best seen in FIG. 3B , at one end of the swivel joint 16, the inner diameter of the port 48 b of the housing 48 engages (e.g., is attached and fixed to) the outer diameter or outer ring of the bearing 32. The port 48 b of the housing 48 may, for example, be glued to the outer diameter or outer ring of the bearing 32. The shaft portion 50 c has, as part thereof, an outer diameter that engages (e.g., is attached and fixed to) the inner diameter or inner ring of the bearing 32. The shaft portion 50 c may, for example, be glued to the inner diameter or inner ring of the bearing 32. At the other end of the swivel joint 16, the inner diameter of the port 49 b of the housing 49 engages (e.g., is attached and fixed to) the outer diameter or outer ring of the bearing 34. The port 49 b of the housing 49 may, for example, be glued to the outer diameter or outer ring of the bearing 34. Shaft portion 50a has, as part thereof, an outer diameter 71 that engages (e.g., is attached and secured to) an inner diameter or inner race of bearing 34. Shaft portion 50a may, for example, be glued to the inner diameter or inner race of bearing 34. Thus, shaft assembly 50 rotates about the axis of rotation of bearings 32, 34 and housings 48, 49.

[0031]

[0043] The PCB 36 of the pivot joint 16 has at least one transducer mounted thereon, configured to output an angular signal corresponding to the angle of rotation of the shaft displacement 50 relative to the housings 48, 49 about the axis of rotation a. Each transducer comprises an optical encoder having two main components: a read head 68 and an encoder disk 38. In one embodiment, the two read heads 68 are located on the PCB 36. In the illustrated embodiment, the encoder disk 38 is operably attached (e.g., with a suitable adhesive) to one end of the shaft assembly 50, which is spaced apart and aligned with the read head 68 on the PCB 36, which is operably attached (e.g., with a suitable adhesive) to the housing 48. The locations of the disk 38 and read head 68 may be reversed, such that the disk 38 is operably attached to the housing 48 and the read head 68 rotates with the shaft assembly 50 and can rotate relative to each other while maintaining optical communication. Encoders are commercially available from Celera Motion, for example, under the trade name "MicroE" encoder. Each PCB 36 may further include a processor for receiving and processing angle signals received from the readhead 68, a transceiver and connector 93 for connecting the PCB 36 to a communication bus of the CMM 1, and / or other wiring, as described below. Each of the PCBs 36 may include a temperature sensor connected to the processor to provide thermal compensation for room temperature variations.

[0032]

[0044] Cover 62b is operably attached to housing 48 to cover and seal PCB 36 and encoder disk 38 from dust contamination. Cover 62a is operably attached over cover 62b and a portion of housing 48 and tube 60 for aesthetic purposes. Cover 62b has an opening 63 through which shaft connecting portion 48c of housing 48 protrudes to operably connect swivel joint 16 to hinge joint 14.

[0033]

[0045] Pivot joint 16 (and other joints of CMM 1) may have unlimited rotation, meaning that it can rotate 360° around rotation axis a. Therefore, slip ring 40 is used to provide an unlimited rotation electrical connection to pivot joint 16. Pivot joints, such as the shaft of base pivot joint 12, and shafts used herein, such as shaft assembly 50 of pivot joint 16, may be hollow (e.g., may have axial opening 51). Shafts within hinge joints used herein, such as shaft 80 of hinge joint 18 described below, may also be hollow and may include hole 81 (see FIG. 5B). Returning to FIGS. 3A and 3B, as shown, housing cover 62a has opening 63, cover 62b has opening 61, and housing 48 has opening 48d, which aligns with the hole in shaft 80 of hinge joint 18. Thus, communication bus wiring may enter pivot joint 16 through hole 81 in hinge joint 14, pass through opening 48d, through opening 63, through opening 61, and connect to PCB 36 which connects to slip ring 40. From slip ring 40, the wiring may travel through opening 51 in shaft 50 to the next hinge joint. Such wiring is shown diagrammatically below.

[0034]

[0046] Shafts used in coordinate measuring machine joints traditionally have one or more shoulders or flanges that extend radially outward from the axis of the joint beyond the surface of the shaft that engages the inner diameter or inner ring of the bearing. These shoulders or flanges have been considered necessary to hold the shaft in a predetermined axial position relative to the rest of the joint, particularly the bearing of the joint. Similarly, housings used in coordinate measuring machine joints traditionally have one or more shoulders or flanges that extend radially inward toward the axis of the joint beyond the surface of the housing that engages the outer diameter or outer ring of the bearing. These shoulders or flanges have been considered necessary to hold the housing in a predetermined axial position relative to the rest of the joint, particularly the bearing of the joint. See, for example, Figures 10, 12, 14, and 16 of U.S. Pat. No. 8,607,467 (incorporated herein by reference in its entirety). Here, both the shaft and the housing have shoulders or flanges that hold the shaft and housing in a predetermined axial position relative to the bearing.

[0035]

[0047] These traditional shafts and housings were manufactured by machining to produce a shoulder or flange. However, even the most advanced machining processes were limited in the precision that could be imparted to such machined shafts and housings. As a result, these parts were significantly limited by the precision of the machining process. This is problematic because, as discussed in the background section of this application, precision is critical to coordinate measuring machines.

[0036]

[0048] As best seen in FIG. 3B , shaft portions 50a, 50c have no portion with a diameter larger than the inner diameter or inner race of bearings 32, 34. No portion of shaft portion 50a has a diameter larger than the outer diameter that engages with the inner diameter or inner race of bearing 34. No portion of shaft portion 50c has a diameter larger than the outer diameter that engages with the inner diameter or inner race of bearing 32. Similarly, portion 48b that engages with the outer diameter or outer race of bearing 32 has no portion with a smaller or narrower diameter than the outer diameter of bearing 32. Portion 49b that engages with the outer diameter or outer race of bearing 34 has no portion with a narrower or narrower diameter than the outer diameter of bearing 34. Therefore, shaft assembly 50 and housings 48, 49 are shoulder-less, as that term is defined herein. Shaft portions 50a, 50c do not have portions that extend radially outward from the axis a of joint 16 beyond surfaces 67, 71 that engage the inner diameters or inner races of bearings 32, 34. Similarly, housings 48, 49 do not have portions that extend radially inward toward the axis a of joint 16 beyond surfaces 65, 69 of housings 48, 49 that engage the outer diameters or outer races of bearings 32, 34, respectively.

[0037]

[0049] Instead of a shoulder or flange, shaft portions 50a, 50c may have grooves 72, 73 machined or otherwise formed therein. Snap rings 64b-c may engage with grooves 72, 73 to hold shaft assembly 50 in place axially relative to joint 16 and bearings 32, 34. Similarly, housing 49 may have groove 74 machined or otherwise formed therein. Snap ring 64a may engage with groove 74 to hold housing 49 in place axially relative to joint 16 and bearings 32, 34. In one embodiment, instead of or in addition to the combination of grooves 72, 73 and snap rings 64b-c to hold shaft 50 in place axially relative to the rest of joint 16 and bearings 32, 34, shaft 50 may be attached and secured to the inner diameter or inner race of bearings 32, 34 using an adhesive. Similarly, in one embodiment, instead of or in addition to the groove 74 and snap ring 64a combination, the shaft 71 may be attached and secured to the outer diameter or outer ring of the bearing 34 by using an adhesive to hold the housing 49 in place axially relative to the rest of the joint 16 and bearings 32, 34.

[0038]

[0050] 3A and 3B may be manufactured by grinding and honing processes that are orders of magnitude more accurate than the machining processes used to manufacture prior art shouldered or flanged shafts and housings. As such, the shoulderless shafts and housings disclosed herein are made with significantly greater precision, resulting in significant improvements in the measurement accuracy achievable with joint 16 and similar joints of CMM 1. In part because of the shoulderless shafts and housings disclosed herein, CMM 1 achieves accuracy significantly greater than prior art portable coordinate measuring machines.

[0039]

[0051] Pivot joint 16 of arm segment 8 is a relatively long joint, as can be seen in FIGS. 1A-1D and 3A, compared to, for example, joint 14. Bearings 32, 34 are spaced far apart. Shaft 50 has three parts, with intermediate section 50b having end sections 50a, 50c attached to opposite ends of intermediate section 50b that are spaced far apart. Outer tube 60 is long, and housing ends 48, 49 are spaced far apart. Because such relatively long joints, especially those with multi-section shafts, could not be conventionally constructed, rotation of the joint remains precise, especially when compared to shorter, single-section shaft joints.

[0040]

[0052] FIG. 11A is a graph of the chromatographic data of Orton (PA Orton et al., 2004), which is incorporated herein by reference in its entirety. Automatic Self-Calibration of an IncrementalMotion Encoder11A illustrates a trajectory plot showing typical behavior of a conventional long-arm shaft rotation measured as specified in [Publication ID: 11A ], IEEE Instrument and Measurement Technology Conference, Budapest, Hungary, May 21-23, 2001, at 1614. This technique measures not only the angular position of the shaft, but also the horizontal and vertical motion of the shaft. See also U.S. Patent No. 5,596,189, issued January 21, 1997, which is incorporated herein by reference in its entirety. Note in the trajectory plot of FIG. 11A that during rotation, the horizontal and vertical displacement of the conventional shaft is approximately 20 microns from the center. Further, note that during rotation, the horizontal and vertical displacement of the conventional shaft is not circular, is inconsistent from one rotation to the next, and varies by approximately 5 microns. In fact, during rotation, the horizontal and vertical displacement of conventional shafts (especially long, multi-section shafts) is typically greater than 20 microns from the center, is non-circular, and varies by more than 5 microns from rotation to rotation. Such shaft deviation from center adversely affects the accuracy of measurements taken by conventional coordinate measuring machines. At least part of the problem causing the undesirable deviation from center is that, until now, there has been no process for constructing and assembling long, multi-part shafts, joints, with the required accuracy.

[0041]

[0053] 3C and 3D illustrate an exemplary process for assembling the outer tube 60 to the housing ends 48, 49 of the exemplary swivel joint 16. As shown in FIG. 3C, a retaining tube FT may be used to increase precision in assembling the outer tube 60 to the housing ends 48, 49. The retaining tube FT may be precision ground to near perfect dimensions, for example, to within 1 / 10,000 of an inch (0.0001 inch), and its outer diameter may be concentric to within 1 / 10,000 of an inch (0.0001 inch). The housing ends 48, 49 may be glued to the respective ends of the tube 60, and the retaining tube FT may be used to precisely secure the housing ends 48, 49 in place relative to each other while the adhesive cures. As seen in FIG. 3D (half cross-section), the housing ends 48, 49 may be secured to the tube 60 using the retaining tube FT inside the assembly. The inner walls 65, 69 of the housing ends 48, 49 may be made to fit snugly (very tight, almost like a mating surface) against the very precise walls FTa, FTb of the retainer tube FT. Once the adhesive has cured, the retainer tube FT may be removed from the assembly. To facilitate removal, the retainer tube FT may be oiled. Using this process, the housing ends 48, 49 can be made concentric (i.e., their inner diameters share the same axis a) to within 5 parts per million. Another method that can be used to achieve a similar result may include internally grinding the housing ends 48, 49 once they are attached to the assembly including the tube 60.

[0042]

[0054] FIG. 3E illustrates an exemplary process for assembling the shaft assembly 50 and bearings 32, 34 into an assembly that includes the outer tube 60 and housing ends 48, 49.

[0043]

[0055] First, shaft ends 50a, 50c may be attached to shaft portion 50b to form shaft assembly 50, as described above. For precision, shaft ends 50a, 50c may first be machined oversized by a few thousands of an inch. That is, shaft ends 50a, 50c may first be made wider (with a larger outer diameter) than their final desired diameter. Shaft ends 50a, 50c may then be glued to the two ends of long shaft portion 50b, using, for example, a V-block on a granite table. Shaft assembly 50 is then ground at two ends 50a, 50c to make them concentric within 0.0001 inches (1 / 10,000 of an inch) (i.e., their outer diameters share the same axis a).

[0044]

[0056] The inner snap rings 64b, 64c may be installed in the shaft assembly 50 at the grooves 72, 73, respectively. The inner rings or bores 32a, 34a of the bearings 32, 34 may be press-fit onto the shaft assembly 50 until they contact the snap rings 64b, 64c and are glued to the shaft assembly 50. The outer snap ring 64a may be installed in the end housing 49 at the groove 74. The assembly including the shaft assembly 50 and the bearings 32, 34 may be inserted into the assembly including the tube 60 and the end housings 48, 49. Adhesive may be used to glue the outer rings 32b, 34b of the bearings 32, 34 to the bores 65, 69 of the end housings 48, 49. A preload (e.g., a weight of 5 or 10 pounds) may then be applied to the outer ring 32b of the bearing 32 to remove any play between the inner and outer rings of the bearings 32, 34. 3E, a preload PREL is applied to the outer ring 32b of the bearing 32 using preload tools PLT1 and PLT2, which ensure that the preload is applied only to the outer ring 32b and not the inner ring 32a. The preload PREL is applied to the outer ring 32b until the adhesive cures and is then removed. Application of the preload PREL removes play from the bearing assembly.

[0045]

[0057] Conventional processes for constructing and assembling long (especially multi-section shaft) joints do not allow the precision necessary to effectively preload bearings to eliminate play, which results in excessive horizontal and vertical displacement of conventional shafts during rotation. Attempting to preload such imprecise conventional long joints to eliminate play can result in excessive bearing deformation, jamming, grinding, excessive wear, etc. (i.e., the joint will be unusable and perform poorly), or insufficient preload can result in excessive shaft deflection off center during rotation.

[0046]

[0058] FIG. 11B illustrates a trajectory plot showing typical behavior of the rotation of a long arm 8 including a multi-section shaft joint 16, measured as defined by Orton. Note that in the trajectory plot of FIG. 11B, the horizontal and vertical displacements of the shaft 50 during rotation are significantly reduced to within 1.5 microns from the center. Furthermore, during rotation, the horizontal and vertical displacements of the shaft 50 are significantly circular and consistent from one rotation to the next. This is a significant improvement from the measured displacements shown illustratively in FIG. 11A for a conventional long joint. This significant improvement in the offset from the center dramatically improves the accuracy of measurements made by the CMM 1 when compared to a conventional coordinate measuring machine. The above-described process for constructing and assembling a long joint 16 including a multi-section shaft 50 provides the precision necessary to achieve such significant improvement.

[0047]

[0059] 4 illustrates an exploded view of an exemplary pivot joint 24. The pivot joint 24 is similar to the pivot joints 16, 20 described above, except that the pivot joint 24 has a short shaft 50, the length of which corresponds to the distance between the pivot joint 24 and the probe 6, which is shorter than the distance between, for example, the pivot joint 16 and the hinge joint 18. As such, the probe 6 rotates about the axis of the pivot joint 24, the pivot joint 24 detects the angle of rotation of the probe 6, and the probe 6 is attached to the end of the pivot joint 16. See FIGS. 1A-1D.

[0048]

[0060] Figure 5A illustrates an exploded view of an exemplary hinge joint 18, while Figure 5B illustrates a cross-section of the hinge joint 18. Here, hinge joint 18 is used to generally describe the characteristics of hinge joints 14, 18, and 22, even though the hinge joints may not be identical. Because at least some of the components of hinge joint 18 are substantially similar to components previously described with reference to pivot joints 12 and 16, the same reference numerals designated in the previous figures are used to identify these identical components in Figures 5A and 5B.

[0049]

[0061] Hinge joint 18 may include a housing 78, a shaft 80, bearings 32, 34, encoder PCB 36, and encoder disk 38. Housing 78 has an opening 78b to which the previous pivot joint (shaft 50 of pivot joint 16 in the case of hinge joint 18) connects. Hinge joint 18 may also include covers 82a-c and various hardware such as snap rings 64a-c and cap 66.

[0050]

[0062] As best seen in FIG. 5B , the housing 78 has a port 87 that engages with (e.g., is attached to and fixed to) the outer diameter or outer ring of the bearings 32, 34. The port 87 of the housing 78 may, for example, be glued to the outer diameter or outer ring of the bearings 32, 34. In the embodiment of FIGS. 5A and 5B , the housing 78 has two ports 87. The shaft 80 has an outer diameter 85 at a portion thereof that engages with (e.g., is attached to and fixed to) the inner diameter or inner ring of the bearings 32, 34. The shaft 80 may, for example, be glued to the inner diameter or inner ring of the bearings 32, 34. As such, the shaft 80 rotates about the rotation axis b of the housing 78 and bearings 32, 34 of the hinge joint 18.

[0051]

[0063] Similar to the pivot joint described above, the PCB 36 of the hinge joint 18 has at least one transducer mounted thereon, the at least one transducer configured to output an angular signal corresponding to the angle of rotation of the shaft 80 relative to the housing 78 about the axis of rotation b. Each transducer comprises an optical encoder having two main components: a read head 68 and an encoder disk 38. In the illustrated embodiment, two read heads 68 are positioned on the PCB 36. In the illustrated embodiment, the encoder disk 38 is operably attached (e.g., using a suitable adhesive) to the end of the shaft 80, which is aligned with and spaced from the read head 68 on the PCB 36, and the PCB 36 is operably attached (e.g., using a suitable adhesive) to the housing 78. The locations of the disk 38 and read head 68 may be reversed, whereby the disk 38 is operably mounted in the housing 78 and the read head 68 rotates with the shaft 80, allowing them to rotate relative to each other while maintaining optical communication.

[0052]

[0064] Cover 82b is attached to housing 78 to cover and seal against dust over PCB 36 and encoder disk 38. Covers 82a, 82c are operably attached to one end of shaft 80, and cap 66 covers the opposite end of shaft 80 to protect the bearings.

[0053]

[0065] Communication bus wiring may enter hinge joint 18 from axial opening 51 in shaft 50 of the previous pivot joint, through openings 78b, 78c in housing 78. The wiring may then be connected to PCB 36 and leave hinge joint 18 through axial opening 80a and hole 81 in shaft 80. Such wiring is shown diagrammatically below.

[0054]

[0066] As previously mentioned, shafts used in coordinate measuring machine joints traditionally have one or more shoulders or flanges extending radially outward from the axis of the joint beyond the surface of the shaft that engages the inner diameter or inner ring of the bearing. These shoulders or flanges have been considered necessary to hold the shaft in a predetermined axial position relative to the rest of the joint, particularly the bearing of the joint. Similarly, housings used in coordinate measuring machine joints traditionally have one or more shoulders or flanges extending radially inward from the axis of the joint beyond the surface of the housing that engages the outer diameter or outer ring of the bearing. These shoulders or flanges have been considered necessary to hold the housing in a predetermined axial position relative to the rest of the joint, particularly the bearing of the joint. See, for example, Figures 10, 12, 14, and 16 of U.S. Pat. No. 8,607,467. Here, both the shaft and the housing have shoulders or flanges to hold the shaft and housing in a predetermined axial position relative to the bearing.

[0055]

[0067] These conventional shafts and housings were manufactured by machining to produce shoulders or flanges. However, even the most sophisticated machining processes are limited in the precision they can impart to such machined shafts and housings. Precision is important to CMMs because these parts are limited by the precision of the machining process, as discussed in the background section of this application.

[0056]

[0068] As best seen in FIG. 5B , shaft 80 has no portion whose diameter is larger than the inner diameter or inner race of bearings 32, 34. No portion of shaft 80 has a larger diameter than the outer diameter that engages the inner diameter or inner race of bearings 32, 34. Similarly, portion 87 that engages the outer diameter or outer race of bearings 32, 34 has no portion with a smaller or narrower diameter than the outer diameter of bearing 32 or the outer diameter of bearing 34. As such, shaft 80 and housing 78 do not have shoulders as defined herein, i.e., 1) shaft 80 has no portion that extends radially outward from axis b of joint 18 beyond surface 85 of shaft 80 that engages the inner diameter or inner race of bearings 32, 34, and 2) housing 78 has no portion that extends radially inward toward axis b of joint 18 beyond surface 87 of housing 78 that engages the outer diameter or outer race of bearings 32, 34.

[0057]

[0069] Instead of a shoulder or flange, the shaft 80 may have a groove 72 machined or otherwise formed therein. The snap rings 64b-c may engage with the groove 72 to hold the shaft 80 in place axially relative to the bearings 32, 34 and the rest of the joint 18. Similarly, the housing 78 may have a groove 74 machined or otherwise formed therein. The snap ring 64a may have the groove 74 to hold the housing 78 in place axially relative to the bearings 32, 34 and the rest of the joint 18. In one embodiment, instead of or in addition to the groove 72 and snap ring 64b-c combination, the shaft 80 may be attached and secured to the inner diameter or inner race of the bearings 32, 34 using an adhesive to hold the shaft 80 in place axially relative to the bearings 32, 34 and the rest of the joint 18. Similarly, in one embodiment, instead of or in addition to the groove 74 and snap ring 64a combination, the port 87 of the housing 78 may be attached and secured to the outer diameter or outer ring of the bearings 32, 34 using an adhesive to hold the housing 78 in place axially relative to the bearings 32, 34 and the rest of the joint 18.

[0058]

[0070] 5A and 5B can be manufactured by grinding and honing processes that are an order of magnitude more accurate than the machining processes used to manufacture prior art shouldered or flanged shafts and housings. Therefore, the shoulderless shafts and housings disclosed herein can be constructed with significantly greater precision, resulting in significant improvements in the accuracy of measurements achievable with joint 18 and similar joints of CMM 1. In part because of the shoulderless shafts and housings disclosed herein, CMM 1 achieves significantly better accuracy than prior art portable coordinate measuring machines.

[0059]

[0071] Prior art coordinate measuring machine joints have mostly been fabricated from aluminum or other lightweight materials. See, for example, U.S. Pat. No. 8,607,467, which discloses coordinate measuring machines in which joints are constructed from cast or machined aluminum components, lightweight, stiff alloys or composites, or fiber-reinforced polymers. This reference makes clear that relatively light weight is crucial to the proper functioning of the disclosed coordinate measuring machines. A problem with such prior art coordinate measuring machines has been that aluminum (or similar lightweight material) structures, which have significantly different thermal expansion coefficients than the joint's bearings, cause the joint's stiffness to vary with temperature. This reduces the accuracy of measurements made over the operating temperature range.

[0060]

[0072] The present invention takes an approach that may seem counterintuitive. In one embodiment, the structural elements of the arm 2 joints may be fabricated from steel, which is compatible with the material from which the bearings 32 and 34 are fabricated. In this context, structural elements refer to the housings 28, 48, 49, and 78, shafts 30, 50, and 80, and shaft portions 50a and 50c. These structural elements contact the inner and outer rings of the ball bearings 32 and 34. The housing 48 also attaches the pivot joint to the subsequent hinge joint. In this context, steel includes stainless steel, which has a thermal expansion coefficient at 25°C ranging from 9.9 to 18 μm / m°C. While the use of relatively heavy steel for the structural elements of the arm 2 joints may seem somewhat counterintuitive, this is because, as previously mentioned, one of the key features of the CMM 1 is that it must be lightweight. Steel is significantly heavier than the material (aluminum) used by prior art coordinate measuring machines. However, structural elements that are compatible with the material (i.e., steel) from which the bearings 32, 34 are made will have the same (or nearly the same) coefficient of thermal expansion (i.e., expand or contract with temperature at the same rate) as the bearings 32, 34. This minimizes variation in joint stiffness with temperature, thereby maintaining the accuracy of measurements made over the operating temperature range of the CMM 1.

[0061]

[0073] In other embodiments, the structural elements of the arm 2 joints, shaft portion 50b, other structural elements such as tube 60, etc., and even nonstructural elements of the CMM 1 may be fabricated from a controlled expansion alloy that is lighter in weight than steel but has a thermal expansion coefficient that matches that of chrome steel or 440C stainless steel (i.e., within the range of 9.9 to 18 μm / m°C at 25°C). A commercially available example of such a controlled expansion alloy is Osprey CE, sold by Sandvik AB of Sandviken, Sweden. Structural elements fabricated from a material that matches the thermal expansion coefficient of the bearings 32, 34 (i.e., expands or contracts at the same rate with temperature) minimizes variations in joint stiffness with temperature, thereby maintaining the accuracy of measurements made over the operating temperature range of the CMM 1. For example, significantly thinner arm segments 8, 9 fabricated from a stiff but relatively lightweight material such as carbon fiber or a controlled expansion alloy combined with structural elements (and even nonstructural elements) would result in a CMM 1 that is significantly lighter and significantly more accurate over the operating temperature range than prior art coordinate measuring machines.

[0062]

[0074] FIG. 6A illustrates a cross-sectional view of an exemplary hinge joint. Hinge joint 22 is very similar to hinge joint 18 described above. Hinge joint 14 is also similar to hinge joints 18 and 22, with the notable difference being that hinge joint 14 includes a rotational damper assembly. In the illustrated embodiment of FIG. 6A, the rotational damper assembly is an instrumented assembly 90a, as described in more detail below. To facilitate use of arm 2, a counterbalance device in the form of rotational damper assembly 90a may be provided to offset torque applied by the weight of the articulated arm. The counterbalance prevents articulated arm 2 from rapidly dropping due to its own weight once the user releases articulated arm 2.

[0063]

[0075] Traditionally, portable coordinate measuring machines have used coil or torsion springs to offset the weight of the arm. See, e.g., U.S. Pat. Nos. 6,904,691 and 8,001,697, each of which is incorporated herein by reference in its entirety. Other traditional counterbalance systems include piston or linear actuator assemblies that form gas shock counterbalances. See, e.g., U.S. Pat. No. 8,402,669, each of which is incorporated herein by reference in its entirety. Each of these traditional counterbalance solutions has had problems with adjusting and calibrating the counterbalance. Additionally, these traditional counterbalance solutions have been generally bulky and heavy, two undesirable characteristics for portable coordinate measuring machines.

[0064]

[0076] FIG. 6B illustrates an exploded view of an exemplary rotational damper assembly 90a. Assembly 90a includes a rotational damper 92, which may be a commercially available rotational damper such as a WRD damper manufactured by We forma Dampfungstechnik GmbH of Stolberg, Germany. In one embodiment, rotational damper 92 is a one-way rotational damper that controls the damping of rotational motion of a shaft about an axis of rotation in one direction of rotation. Assembly 90a may include a damper hub 94, a damper sleeve 96, and a torque sensor shaft hub 98, which together form an Oldham coupling. Assembly 90a may also include a torque sensor shaft 100. Assembly 90a may also include hardware such as a spacer 102, a mount 104, and bolts 107a-d and 108a-d. Mount 104 has four threaded holes 110a-d and four unthreaded holes 111a-d.

[0065]

[0077] As best seen in FIG. 6A , the damper assembly 90a is assembled by first coupling a portion of the torque sensor shaft 100 to the shaft 80 of the hinge joint 14. The portion of the torque sensor shaft 100 may be inserted into the axial opening 80a of the shaft 80 and secured (e.g., by using an adhesive). The mount 104 is coupled to the housing 78 of the hinge joint 14 by inserting bolts 108a-d into holes 111a-d and threading them into the threaded holes in the housing 78. The remaining components of the rotational damper assembly 90a are then stacked in order: shaft hub 98 on shaft 100, damper sleeve 96 on shaft hub 98, damper hub 94 on damper sleeve, and damper hub 94 on shaft 93 of the rotational damper 92. Spacer 102 is sandwiched between rotational damper 92 and mount 104 by threading bolts 107a-d into threaded holes 110a-d in mount 104. Rotational damper 92 is thus operatively coupled to shaft 80 and housing 78.

[0066]

[0078] Rotational damper 92 provides controlled damping of the rotational motion of shaft 80 about axis of rotation b. The torque output that controls the damping provided by rotational damper 92 may be pre-tuned and pre-calibrated to exacting specifications. As such, rotational damper assembly 90a alleviates the problems associated with counterbalance adjustment and calibration that are typical of conventional counterbalance solutions for portable coordinate measuring machines, such as coil springs, torsion springs, and pistons. Rotational damper assembly 90a also generally provides a more compact and lighter weight counterbalance solution compared to conventional counterbalance solutions, such as coil springs, torsion springs, and pistons.

[0067]

[0079] A potential problem that arises, particularly with the use of a rotational damper to provide damping control of the rotational motion, is the user applying excessive torque when moving the arm 2. Excessive force can effectively bend portions of the arm 2, affecting the ability of the CMM 1 to accurately detect the position of the measurement probe 6. Measurements taken under conditions where the user moves the arm substantially too quickly may be inaccurate. The present disclosure provides two solutions to this potential problem.

[0068]

[0080] In the embodiment of FIGS. 6A and 6B, the rotational damper assembly 90a is instrumented to directly detect excessive torque at the joint 14. The mount 104 has webbing or spokes 104a-d that connect an outer ring of the mount 104, which includes threaded holes 110a-d, to an inner ring of the mount 104, which includes unthreaded holes 110a-d. Mounted on at least some of the spokes are strain gauges 98. Similarly, the torque sensor shaft 100 has webbing or spokes 100a-d that connect the torque sensor shaft 100 to the torque sensor shaft hub 98. Mounted on at least some of the spokes 100a-d are strain gauges 106. The rotational damper assembly 90a includes a torque sensor PCB 112 having electronics mounted thereon that receive signals from the strain gauges 106.

[0069]

[0081] Torque applied to joint 14 is transmitted through spokes 100a-d and spokes 104a-d. Such torque manifests itself as rotational strain in spokes 100a-d and spokes 104a-d. Thus, by measuring strain in spokes 100a-d and spokes 104a-d, gauges 106 effectively sense strain in shaft 80 and housing 78 of joint 14 due to rotational movement of shaft 80 about axis of rotation b. In this sense, strain gauges 106 are operatively coupled to shaft 80 and housing 78. The strain gauges output strain signals that can be used by circuitry within PCB 112 within CMM 1 or other circuitry external to CMM 1 (e.g., a processor within the corresponding joint's PCB 36) to detect and describe the torque applied to joint 14.

[0070]

[0082] The strain measured by the gauges 106 corresponds to the amount of torque applied to the joint 14. Therefore, the measured strain also corresponds to the amount of bending or flexing of the portion of the arm 2. The measured strain may therefore be related to the amount and nature of bending or flexing of the arm 2, and this information may be taken into account when making measurements using the CMM 1 to compensate for excess torque. Thus, in an instrumented embodiment of the rotational damper assembly 90, the electrical circuitry in the PCB 112 (or a processor in the corresponding joint PCB 36 that receives the angle signal from the readhead 68) may receive the strain signals (or amplified strain signals) from the strain gauges 106, convert those signals to a corresponding bending or flexing of the arm 2 due to the torque applied to the arm 2, and calculate measurements at the measurement probe 6 that take into account the corresponding bending or flexing of the arm 2. For example, the PCB 112 may include an amplifier that amplifies the analog signals from the strain gauges 106 and an analog-to-digital converter that converts the amplified analog signals to digital signals that are provided to the processor in the corresponding joint PCB 36. The processor may look up a table or calculate the amount and direction of bending or flexion of arm 2 corresponding to the location and amplitude of the measured strain. Thus, by measuring the strain in spokes 100a-d, spokes 104a-d, CMM 1 can accurately detect the position of measurement probe 6, regardless of whether a user applies excessive torque to arm 2.

[0071]

[0083] In an alternative embodiment, when either the strain signal or the concentration of the strain signal exceeds a certain strain threshold, it may be determined that too much torque has been applied to joint 14. Based on that determination, CMM 1 may not be able to take measurements until a certain amount of time (e.g., 2-10 seconds) has passed. This is to allow any portions of arm 2 that may have bent due to excessively applied torque to return to their original shape.

[0072]

[0084] FIG. 6C illustrates an exemplary rotational damper assembly 90b that is not instrumented. Unlike the rotational damper assembly 90a of FIGS. 6A and 6B, the rotational damper assembly 90b is not instrumented to directly detect excessive torque. In this embodiment, the angle signal output by the read head 68 may be used to generate a velocity signal, which may be used as a proxy for applied torque. The torque applied to the arm 2 to move it generally corresponds to the speed at which the arm 2 moves. As previously mentioned, excessive torque applied to the arm 2 corresponds to a user moving the arm too quickly. Therefore, excessive applied torque may be indirectly detected at the joint in the form of a relatively high (i.e., too high) rotational speed. The read head 68 outputs an angle signal corresponding to the relative rotational angle of the joint. The rate at which the measured rotational angle changes corresponds to the rotational speed of the joint. Detecting the rotational speed at the joint is a good proxy for detecting applied torque. In this embodiment, the angle signal output by the readhead 68 may be used to generate a velocity signal by calculating the rate at which the measured rotational angle changes. A processor on the PCB 36 (or elsewhere) may measure the velocity signal (e.g., degrees per second) using a high-resolution timer (e.g., 12.5 ns resolution) that measures one period of the encoder's quadrature signal. When the velocity signal exceeds a certain rotational speed threshold, a determination is made that the applied torque is too great. Based on that determination, the CMM 1 may not be able to take any further measurements until a certain amount of time (e.g., 2-10 seconds) has passed. This is to allow any portions of the arm 2 that may have bent due to excessively applied torque to return to their original shape.

[0073]

[0085] Assembly 90b is similar to assembly 90a of FIGS. 6A and 6B. Assembly 90b may include a rotational damper 92. Assembly 90b may also include a damper hub 94, a damper sleeve 96, a shaft hub 118, and a shaft 120 (together forming an Oldham coupler). Assembly 90b may also include hardware such as a spacer 122, a mount 124, and bolts 107a-d and 108a-d. Spacer 122 is similar to spacer 102, except that it does not require support for PCB 112. Mount 124 has four threaded holes 110a-d and four unthreaded holes 111a-d. Mount 124 is similar to mount 104, except that it does not require webbing or spokes 104a-d.

[0074]

[0086] The damper assembly 90b is assembled by first coupling a portion of the torque sensor shaft 120 to the shaft of the hinge joint 14. The portion of the torque sensor shaft 120 may be inserted into the axial opening 80a of the shaft 80 and attached and secured (e.g., by using an adhesive). The mount 124 is coupled to the housing 78 of the hinge joint 14 by inserting bolts 108a-d into holes 111a-d and threading them into the threaded openings of the housing 78. The remaining components of the rotational damper assembly 90b are then stacked in order: shaft hub 118 on the shaft 120, damper sleeve 96 on the shaft hub 118, damper hub 94 on the damper sleeve 96, and damper hub 94 on the shaft 93 of the rotational damper 92. A spacer 122 is sandwiched between the rotational damper 92 and the mount 124 by threading bolts 107a-d into the threaded holes 110a-d of the mount 124. To that end, rotary damper 92 is operatively coupled to shaft 80 and housing 78 .

[0075]

[0087] In one embodiment (not shown), instead of an add-on rotational damper assembly such as assemblies 90a, 90b, rotational damping is incorporated into hinge joint 18. In this embodiment, the combination of a) first bearing 32 or second bearing 34 and b) shaft 80 or housing 78 provides controlled damping of rotational motion of shaft 80 about axis of rotation b.

[0076]

[0088] FIG. 7A illustrates a perspective view of an exemplary measurement probe 6a. The probe 6a has a housing 126 having an interior space for accommodating a PCB 130 and a handle 128 having an interior space for accommodating a PCB 125. In FIG. 7A, the housing 126 and the handle 128 are shown as transparent for purposes of illustration. The housing 126 is operatively coupled to a pivot joint 24 (see FIGS. 1A-1D). As such, the probe 6a rotates about the axis of the pivot joint 24, and the pivot joint 24 detects the angle of rotation of the probe 6a about axis a.

[0077]

[0089] Measurement probe 6a may also include a probe stem assembly 136 having a probe connector 138 at one end and a probe 140 at the other end. Probe connector 138 is connected to housing 126 and PCB 130. Probe stem assembly 136 may be a touch-trigger assembly that initiates capture of the position of probe 140 when probe 140 touches an object. PCB 130 receives and transmits such trigger signals, as described above. Probe stem assembly 136 may also contain electronics, such as an integrated circuit (e.g., EEPROM) having a serial number stored therein to uniquely identify probe stem assembly 136 installed on CMM 1.

[0078]

[0090] Handle 128 may include two switches, a take switch 131 and a confirm switch 132. These switches may be used by an operator to take a measurement (take switch 131) and confirm that measurement (confirm switch 132) during operation. Handle 128 is generally shaped to resemble a human grip, making it more ergonomic than at least some prior art probes. Handle 128 may also house a switch PCB on which switches 131 and 132 are mounted. Switch PCB 134 is electrically coupled to PCB 125, which hosts components for processing signals from switches 131 and 132. In one embodiment, PCB 125 includes a wireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of an electrical connection to the CMM1's communication bus) that wirelessly transmits the take and confirm signals associated with switches 131 and 132 to, for example, a host PC that typically controls CMM1. Wireless transmission of the take and acknowledge signals associated with switches 131 and 132 significantly simplifies the construction and wiring of probe 6a.

[0079]

[0091] Measurement probe 6a may also include an option port 142 to which optional devices, such as a laser scanner (not shown), may be connected. Option port 142 provides a mechanical connection for optional devices supported by measurement probe 6a. Option port 142 may also provide an electrical connection for optional devices that interface with the communication bus of CMM 1.

[0080]

[0092] FIG. 7B illustrates a perspective view of an exemplary alternative measurement probe 6b. Probe 6b is similar to probe 6. However, probe 6b includes a different housing 127 and handle 129. Unlike probe 6, the housing 127 of probe 6b includes a connecting portion 143 that can be directly connected to hinge joint 22. Therefore, when probe 6b is used, the pivot joint 24 is not used. The housing 127 and probe stem assembly 136 do not rotate about axis a. The housing 127 and probe stem assembly 136 are fixed about axis a. The handle 129, on the other hand, includes a connecting portion 144 that couples to the housing 127 so that the handle 129 can rotate. Therefore, the handle 129 rotates about axis a. Like the handle 128 of probe 6, the handle 129 has an interior space that accommodates the PCB 125. PCB 125 may include a wireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of an electrical connection to the communication bus of CMM 1) that wirelessly transmits take and acknowledge signals associated with switches 131, 132 to, for example, a host PC that typically controls CMM 1. Thus, handle 129 is rotatably coupled to arm 2 for rotation about axis a, but importantly, handle 129 is not electrically coupled to arm 2 as signal transmission is achieved wirelessly.

[0081]

[0093] Probe 6b represents a significant advancement in the field of coordinate measuring machines because it alleviates the need for seven true axes of rotation. CMM 1, as illustrated in FIGS. 1A-1D, includes seven true axes of rotation (i.e., axes associated with joints 12, 14, 16, 18, 20, 22, and 24). The inclusion of seven true axes of rotation makes CMM 1 relatively complex and expensive. Rotatable handle 129, mechanically and wirelessly connected to arm 2 and thus eliminating the need for seven joints 24, alleviates the need for seven "true" axes because handle 129 allows for rotation of handle 129 as needed for hand positioning without the complexity of seven sets of bearings, transducers, electronics, etc.

[0082]

[0094] FIG. 8 illustrates a perspective view of an exemplary on-arm switch assembly 10. The switch assembly 10 includes a housing 146 that mounts (e.g., clamps) the switch assembly 10 to arm segment 8 or, alternatively, arm segment 9. The housing 146 has an interior space for accommodating a PCB. Like probes 6, 6b, the switch assembly 10 may include two switches, a take switch 131 and a confirm switch 132, that an operator may use during operation to take a measurement (take switch 131) and confirm that measurement (confirm switch 132). The location of the switches 131, 132 on the on-arm switch assembly 10, and more importantly, on the arm 2 instead of the handle of probe 6, allows the operator to actuate the switches 131, 132 while moving and positioning the measurement probe 6 with one hand and supporting the arm with the other. Prior art coordinate measuring machines required the operator to position the measurement probe and activate the measurement switch on the probe with the same hand, which is not ergonomic. The on-arm switch assembly 10 represents a significant advancement in the field of coordinate measuring machines because it provides a significantly more ergonomic solution compared to conventional coordinate measuring machines.

[0083]

[0095] The on-arm switch assembly 10 may also house a switch PCB 134 to which the switches 131, 132 are mounted, and the on-arm switch assembly 10 may include a PCB that incorporates the functionality of both the PCB 130 and the switch PCB 134. In one embodiment, the PCB in the on-arm assembly 10 electrically connects to a communication bus of the CMM 1. In another embodiment, the PCB in the on-arm assembly 10 includes wireless (e.g., WiFi, Bluetooth, etc.) transmitters (instead of an electrical connection to a communication bus of the CMM 1) that wirelessly transmit take and acknowledge signals associated with the switches 131, 132.

[0084]

[0096] FIG. 9 illustrates a block diagram of exemplary electronics for the CMM 1. The CMM 1 may include external communication interfaces such as a universal serial bus (USB) 150 or wireless (Wi-Fi) 152. The CMM 1 may also include an internal communication bus (e.g., RS-485) 154. As previously described, the various joints or axes of the CMM 1 each include a PCB 36 having at least one transducer mounted thereon, the transducer configured to output an angle signal corresponding to the rotational angle of the joint. Each PCB 36 may include a processor 70 for receiving and processing the angle signals from the transducers and / or the strain signals from the PCB 112 of the rotational damper assembly 90. The PCB 36 may also include a transducer 156 that interfaces with the bus 154. The PCB 130 of the measurement probe 6 may carry signals from the touch-trigger probe 140 and may also connect to the communication bus 154. The bus 154 may also be connected to the option port 142 of the measurement probe 6 to communicate with / control optional devices, such as a laser scanner integrated into the option port 142. The PCB 125 of the handle 128 may wirelessly transmit take and acknowledge signals associated with the switches 131, 132.

[0085]

[0097] The bus 154 may terminate at a main PCB 158, which is preferably located on the base 4 of the CMM 1. The main PCB 158 includes its own main processor 160 and transceiver 162 for connecting to the bus 154. The main PCB 158 receives angle signals from the transducers within the CMM 1 and outputs a collection of the received angle signals via USB 150 or Wi-Fi 152 to a host PC, which may calculate the position of the measurement probe 6 based on this information and other information related to the CMM 1 (e.g., arm segment locations, lengths, etc.). The internal bus 154 may be compliant with RS485.

[0086]

[0098] Prior art coordinate measuring machines configured to use an RS485 internal bus incorporated dedicated capture and trigger wires to transmit capture and trigger signals, respectively. See U.S. Pat. No. 6,219,928, incorporated herein by reference in its entirety. The capture signal is a synchronous signal generated by the master controller in an RS485 configuration. The trigger signal is an asynchronous signal generated by a device attached to the articulating arm, such as a touch-trigger probe accessory (e.g., Renishaw TP20). A dedicated trigger wire travels from the probe to the master controller at the base of the articulating arm. The trigger signal traveling through the dedicated trigger wire interrupts the master controller. An interrupt service routine in the master controller generates a synchronous capture signal to capture the angle signal from the encoder.

[0087]

[0099] Note that there are no dedicated capture or trigger wires in Figure 9. Instead, the bus 154, from the perspective of the main PCB 158, includes a pair of bidirectional wires 164, 166 (AB pair, half duplex) or two pairs of unidirectional wires (AB pair, full duplex).

[0088]

[0100] Despite the use of steel for the structural elements of the joints as described above, arm 2 remains relatively lightweight in part because many of its components (e.g., shafts, bearings, housings, arm segments, etc.) are smaller than those of prior art coordinate measuring machines. For example, compare the shaft, housing, and arm segments of CMM 1 disclosed herein with the corresponding components of the coordinate measuring machine disclosed in U.S. Patent No. 8,607,467. The small components of CMM 1 have significantly less mass and are therefore significantly lighter than their prior counterparts. Smaller components may be used in part in CMM 1 because the amount of wire used to carry signals within CMM 1 has been significantly reduced compared to prior art coordinate measuring machines. Prior art coordinate measuring machines required significant space within the shaft, housing, arm segments, etc., for routing wires. Due to the placement of electronics as illustrated in FIG. 9 and timing signals as described below, CMM 1 requires significantly less wiring, which contributes to its light weight.

[0089]

[0101] FIG. 10A illustrates an example timing diagram for the example electronics of FIG. 9 during operation. During operation, main processor 160 may send capture commands (via wires 164, 166) to processors 70 of encoder PCBs 36 at predetermined intervals (e.g., 960 microseconds). As seen in FIG. 10A, each processor 70 receives a capture command. In response, an interrupt service routine in processor 70 generates an internal capture pulse with a fixed, calibrated latency between encoder PCBs 36. As shown in FIG. 10A, the internal capture pulse is active low (or active high, as shown in some of the other example timing diagrams) and may have a typical length of, for example, 5 microseconds.

[0090]

[0102] FIG. 10B illustrates another example timing diagram for the example electronics of FIG. 9 during operation. During operation, main processor 160 may send capture commands (via wires 164, 166) to each of the processors 70 on encoder PCB 36 at predetermined intervals (e.g., 960 microseconds). As seen in FIG. 10B, each processor 70 receives its capture command. At (1), the first encoder processor 70 enables a serial line interrupt 8 data bytes or 11 μs (8*11 bits / data byte*125 ns / bit) after receiving its capture command. At (2), the second encoder processor 70 enables a serial line interrupt 7 data bytes or 9.625 (~9.63) μs after receiving its capture command, and similarly for the third through sixth encoder processors. At (7), the seventh encoder processor 70 enables a serial line interrupt two data bytes or 2.75 μs after receiving its capture command. At (8), the option port processor 70 enables a serial line interrupt one data byte or 1.375 (∼1.38) μs after receiving its capture command. Then, at (9), the main processor 160 sends a read data command to the first encoder processor 70, a hardware interrupt is generated on the rising edge of the start bit, and the interrupt service routine in processor 70 generates an internal capture at approximately 0.19 μs. As shown in FIG. 10B, the internal capture pulse is active high (or active low, as shown in some of the other example timing diagrams) and may have a typical length (e.g., 4 μs).

[0091]

[0103] 10C illustrates another example timing diagram for the example electronics of FIG. 9 in operation. As shown in FIG. 10C, the processor 70 can begin an internal capture 1.38 microseconds after receiving the last capture command. This method may have larger errors than some of the previously described methods, primarily due to clock errors introduced by the use of a different processor 70.

[0092]

[0104] 9 in operation. As shown in FIG. 10D, in a dual-pair (AB pair and YZ pair, full-duplex) serial configuration, once a capture command is received by the encoder processors 70, each processor 70 enables the serial line interrupt. The main processor 160 then sends a read data command to the first encoder processor 70, a hardware interrupt is generated on the falling edge of the start bit, and the interrupt service routine in processor 70 generates an internal capture in approximately 0.19 μs.

[0093]

[0105] Figure 10E illustrates another exemplary timing diagram for the exemplary electronics of Figure 9 in operation. As shown in Figure 10E, in a dual pair (AB pair and YZ pair, full duplex) serial configuration, once a capture command is received by the encoder processors 70, each processor 70 can immediately begin internal capture, typically with a delay of 1.63 microseconds. This method is less accurate than some of the methods previously described due to variations in the clock frequency of the processors 70.

[0094]

[0106] As shown in Figure 10F, in PCB 130, the interrupt service routine for a capture instruction saves and resets the interval timer / counter. For example, an asynchronous trigger from a touch-trigger probe accessory captures and saves the value of the interval timer / counter. In a subsequent capture instruction (n+1), the interval timer / counter is saved and reset.

[0095]

[0107] To find the position of probe 6 at the time of the asynchronous trigger, the vector difference between position (n) and position (n+1) can be multiplied by a ratio where the asynchronous trigger acquisition value is divided by the acquisition value of the (n+1) position and added to the vector of position (n). In an alternative embodiment, the asynchronous trigger may have a fixed calibration latency, which may be subtracted from the asynchronous trigger acquisition value to arrive at the true position. In another embodiment, an asynchronous trigger port (not shown) at the base of the arm may be used to start an internal timer / counter within main processor 160.

[0096]

[0108] Therefore, by accounting for and correcting for the latency in each PCB 36, the CMM 1 electronics can make accurate measurements without having dedicated capture and trigger wires.

[0097] definition

[0098]

[0109] The following includes definitions of selected terms used herein. These definitions include various examples or component forms that fall within the scope of the terms and may be used in implementations. Examples are not intended to be limiting. Both singular and plural forms of terms may be included within the definitions.

[0099]

[0110] As used herein, an "operably connected" or "operably coupled," or a connection where entities are "operably connected" or "operably coupled," is a connection where the components are connected to function as intended. An operably connected connection may be a direct connection or an indirect connection, where an intermediate component or components cooperate or are otherwise part of a connection or are between the operably connected components. In the context of signals, an "operably connected" or a connection where components are "operably connected" is a connection where signals, physical communications, or logical communications can be sent and received. Typically, an operably connected connection includes a physical interface, an electrical interface, and a data interface, but it should be noted that an operably connected connection may include different combinations of these or other types of connections sufficient to enable operative control. For example, two components may be operably connected by being able to communicate signals to each other directly or through one or more intermediate components, such as a processor, operating system, logic, software, or other component. Any logical or physical communication channel can be used to create an operational connection.

[0100]

[0111] As used herein, a "signal" includes, but is not limited to, one or more electrical or optical signals, analog signals, digital signals, data, one or more computer or processor instructions, messages, bits or bitstreams, or other means capable of being received, transmitted or detected.

[0101]

[0112] To the extent the term "include" or "comprising" is used in the detailed description or claims, it is to be interpreted in an inclusive manner, similar to the term "comprising," as if that term were used as a transitional term in a claim. Furthermore, to the extent the term "or" is used in the detailed description or claims (e.g., A or B), it is intended to mean "A or B, or both." When an applicant wishes to indicate "only A or B, but not both," the term "only A or B, but not both" is used. Therefore, the use of "or" herein is inclusive, not exclusive. See Bryan A. Garner, A Dictionary of Modern Legal Usage 6 24 (2nd ed., 1995).

[0102]

[0113] Although embodiments of the systems, methods, etc. have been illustrated by way of illustration and described in considerable detail, it is not the applicant's intention to restrict or limit the scope to such detail. Of course, it is not possible to describe every conceivable combination of components or methodologies for purposes of describing the systems, methods, etc. described herein. Additional advantages and modifications will be readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details, representative apparatus, and illustrative examples shown and described. Therefore, the present application is intended to embrace alternatives, modifications, and variations that fall within the scope of the appended claims. Moreover, the foregoing description is not intended to limit the scope of the present invention. Rather, the scope of the present invention is to be determined by the appended claims and their equivalents.

Claims

1. In a portable coordinate measuring machine (CMM), a manually positionable articulated arm having a first end and a second end, the articulated arm including a plurality of arm segments and a plurality of rotary joints, the first end including a connector configured to couple to a measurement probe, and the second end including a base; At least one of the rotary joints includes a first bearing and a second bearing; a shaft engaged with an inner diameter portion of the first bearing and an inner diameter portion of the second bearing, the shaft configured to rotate about an axis of rotation of the first bearing and the second bearing; a housing having at least one port that engages with at least one of the outer diameter of the first bearing and the outer diameter of the second bearing; at least one transducer configured to output an angle signal corresponding to an angle of rotation of the shaft relative to the housing about the axis of rotation; Including, the shaft has two ends that are concentric within one ten-thousandth of an inch (0.0001 inch); A CMM wherein the at least one port in the housing does not have a portion narrower than the outer diameter of the first bearing or the outer diameter of the second bearing.

2. the at least one rotary joint includes a rotary damper, the rotary damper operatively coupled to the shaft and the housing to provide controlled damping of rotational movement of the shaft about the axis of rotation; or 2. A CMM according to claim 1, configured to provide rotational damping incorporated into said at least one rotary joint to provide damping control of rotational movement of said rotary axis.

3. The at least one rotary joint a rotational damping mechanism configured to provide controlled damping of rotational motion of the shaft about the axis of rotation; a circuit operatively connected to the at least one transducer and configured to output a speed signal and a direction signal corresponding to a speed of the rotational movement of the shaft about the axis of rotation; The CMM of claim 1 , comprising:

4. The at least one rotary joint a rotational damping mechanism configured to provide controlled damping of rotational motion of the shaft about the axis of rotation; at least one strain gauge operatively coupled to at least one of the shaft and the housing and configured to sense strain in at least one of the shaft or the housing due to the rotational movement of the shaft about the axis of rotation and output a strain signal; The CMM of claim 1 , comprising:

5. At least one of the plurality of joints a) the shaft engaging the inner diameter of at least one of the first bearing and the second bearing, and b) a portion of the housing engaging the outer diameter of at least one of the first bearing and the second bearing are made of steel; or a first joint from the plurality of joints is attached to a second joint from the plurality of joints by a steel structure that contacts the interior or exterior of the bearing of the first joint or the inner or outer ring of the bearing of the second joint; or The CMM of claim 1 , wherein all of the structural portions of at least one of the plurality of rotary joints are fabricated from steel.

6. 2. A CMM as described in claim 1, wherein any structural parts of the CMM including the arm segments and rotary joints are fabricated from a controlled expansion alloy that is lighter than steel and has a thermal expansion coefficient that matches that of steel or stainless steel within the range of 9.9 to 18 μm / m°C at 25°C.

7. The measurement probe includes a handle, the handle being non-rigidly mechanically coupled to the first end for movement and rotatably coupled to the first end for rotation about a central axis of the measurement probe, the handle comprising: a radio transmitter; at least one switch operatively connected to said wireless transmitter, said switch, when activated, causing said wireless transmitter to transmit a wireless signal corresponding to a CMM taking a measurement; The CMM of claim 1 , comprising:

8. 2. A CMM as described in claim 1, comprising an electrical circuit configured without dedicated input wires for receiving angle signals and other signals from other transducers within the CMM, the electrical circuit configured to output a concentration of the angle signals and the other signals to provide information corresponding to the position of the measurement probe relative to the base.

9. In a portable coordinate measuring machine (CMM), a manually positionable articulated arm having a first end and a second end, the articulated arm including a plurality of arm segments and a plurality of rotary joints, the first end including a connector configured to couple to a measurement probe, and the second end including a base; At least one of the rotary joints is a first bearing and a second bearing; a shaft engaged with an inner diameter portion of the first bearing and an inner diameter portion of the second bearing, the shaft configured to rotate about a rotation axis of the first bearing and the second bearing; a housing having at least one port that engages with at least one of the outer diameter of the first bearing and the outer diameter of the second bearing; at least one transducer configured to output an angle signal corresponding to an angle of rotation of the shaft relative to the housing about the axis of rotation; Including, The shaft has two ends, including a first end that engages the inner diameter of the first bearing and a second end that engages the inner diameter of the second bearing, the two ends being concentric within ten thousandths of an inch (0.0001 inch).

10. At least one of the rotary joints is 10. The CMM of claim 9, including a rotational damper operatively coupled to the shaft and the housing and configured to provide controlled damping of rotational movement of the shaft about the axis of rotation.

11. A CMM according to claim 9, wherein rotational damping is incorporated into at least one of said rotary joints to provide controlled damping of rotational movement of said shaft about said axis of rotation.

12. At least one of the rotary joints is a rotational damping mechanism configured to provide controlled damping of rotational motion of the shaft about the axis of rotation; a circuit operatively connected to the at least one transducer and configured to output a velocity signal corresponding to a velocity of the rotational movement of the shaft about the axis of rotation based on the angle signal and time; Including, 10. A CMM as claimed in claim 9, wherein the circuitry is further configured to compare the speed signal with a predetermined speed threshold to determine whether the rotational movement is occurring at an excessive speed or as a result of excessive torque.

13. At least one of the rotary joints is a rotational damping mechanism configured to provide controlled damping of rotational motion of the shaft about the axis of rotation; at least one strain gauge operatively coupled to at least one of the shaft and the housing and configured to sense strain in at least one of the shaft and the housing due to the rotational movement of the shaft about the axis of rotation and to output a strain signal; Including, The CMM comprises:

10. The CMM of claim 9, including circuitry configured to calculate a location of the measurement probe based in part on the strain signal.

14. 10. The CMM of claim 9, wherein in at least one of the plurality of joints: a) the shaft that engages with the inner diameter of at least one of the first bearing and the second bearing; and b) the port in the housing that engages with the outer diameter of at least one of the first bearing and the second bearing are made of steel.

15. 10. The CMM of claim 9, wherein a first joint from the plurality of joints is attached to a second joint from the plurality of joints by a steel structure, the steel structure contacting the inside or outside of a bearing of the first joint or the inside or outside of a bearing of the second joint.

16. 10. The CMM of claim 9, wherein all structural parts of at least one of said plurality of rotary joints are fabricated from steel.

17. 10. A CMM as described in claim 9, wherein any structural part of the CMM including the arm segments and rotary joints is fabricated from a controlled expansion alloy, which is lighter in weight than steel and has a thermal expansion coefficient that matches that of steel or stainless steel within the range of 9.9 to 18 μm / m°C at 25°C.

18. The measurement probe is a handle operatively mechanically (but not electrically) coupled to the first end, the handle rotatably coupled to the first end for rotation about a central axis of the measurement probe, the handle comprising: a radio transmitter; at least one switch operatively connected to the wireless transmitter, the at least one switch configured, when actuated, to cause the wireless transmitter to transmit a wireless signal that causes the CMM to take a measurement; 10. The CMM of claim 9, comprising:

19. 10. A CMM as described in claim 9, comprising an electrical circuit including a serial communication circuit configured without a dedicated input wire to receive the angle signal and other angle signals from other transducers within the CMM, the electrical circuit configured to output a concentration of the angle signal and the other angle signals to provide information corresponding to the position of the measurement probe relative to the base.

20. In a portable coordinate measuring machine (CMM), a manually positionable articulated arm having a first end and a second end, the articulated arm including a plurality of arm segments and a plurality of rotary joints, the first end including a connector configured to couple to a measurement probe, and the second end including a base; At least one of the rotary joints is a first bearing and a second bearing; a shaft engaged with an inner diameter portion of the first bearing and an inner diameter portion of the second bearing, the shaft configured to rotate about a rotation axis of the first bearing and the second bearing; a housing having at least one port that engages with at least one of the outer diameter of the first bearing and the outer diameter of the second bearing; at least one transducer configured to output an angle signal corresponding to an angle of rotation of the shaft relative to the housing about the axis of rotation; Including, A CMM wherein the at least one port in the housing does not have a portion narrower than the outer diameter of the first bearing or the outer diameter of the second bearing.

21. 21. The CMM of claim 20, wherein the at least one rotary joint includes a rotary damper operatively coupled to the shaft and the housing and configured to provide controlled damping of rotational movement of the shaft about the axis of rotation.

22. 21. A CMM according to claim 20, wherein rotational damping is incorporated into said at least one said rotary joint to provide controlled damping of rotational movement of said shaft about said axis of rotation.

23. The at least one rotary joint is a rotational damping mechanism configured to provide controlled damping of rotational motion of the shaft about the axis of rotation; a circuit operatively connected to the at least one transducer and configured to output a velocity signal corresponding to the velocity of the rotational motion of the shaft about the axis of rotation based on the angle signal and time; Including, A CMM according to claim 20, wherein the circuitry compares the speed signal with a predetermined speed threshold to determine whether the rotational movement is occurring at an excessive speed or as a result of excessive torque.

24. The at least one rotary joint is a rotational damping mechanism configured to provide controlled damping of rotational motion of the shaft about the axis of rotation; at least one strain gauge operatively coupled to at least one of the shaft and the housing and configured to sense strain in at least one of the shaft and the housing due to the rotational movement of the shaft about the axis of rotation and to output a strain signal; Including, The CMM comprises:

21. A CMM according to claim 20, including circuitry configured to calculate a location of the measurement probe based in part on the strain signal.

25. At least one of the plurality of joints 21. The CMM of claim 20, wherein a) the shaft that engages with the inner diameter of at least one of the first bearing and the second bearing, and b) the port in the housing that engages with the outer diameter of at least one of the first bearing and the second bearing are made of steel.

26. 21. The CMM of claim 20, wherein a first joint from the plurality of joints is attached to a second joint from the plurality of joints by a steel structure, the steel structure contacting the inside or outside of a bearing of the first joint or the inner or outer ring of a bearing of the second joint.

27. 21. A CMM according to claim 20, wherein all of the structural parts of at least one of the plurality of rotary joints are fabricated from steel.

28. A CMM as described in claim 20, wherein any structural parts of the CMM including the arm segments and rotary joints are fabricated from a controlled expansion alloy that is lighter in weight than steel and has a thermal expansion coefficient that matches that of steel or stainless steel within the range of 9.9 to 18 μm / m°C at 25°C.

29. The measurement probe includes a handle operatively mechanically (but not electrically) coupled to the first end, the handle rotatably coupled to the first end for rotation about a central axis of the measurement probe, the handle comprising: a radio transmitter; at least one switch operatively connected to the wireless transmitter, the at least one switch configured, when actuated, to cause the wireless transmitter to transmit a wireless signal that causes the CMM to take a measurement; 21. The CMM of claim 20, comprising:

30. 21. The CMM of claim 20, including an electrical circuit configured without dedicated input wires for receiving angle signals and other signals from other transducers within the CMM, and configured to output a concentration of the angle signals and the other angle signals to provide information corresponding to the position of the measurement probe relative to the base.

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