Patent Description:
Coordinate measurement machines serve to, among other things, measure points in a three-dimensional space. Coordinate measuring machines trace the measuring points in Cartesian coordinate space (x, y, z), for example. Coordinate measuring machines typically consist of a stand and a tracing system. The stand may serve as a reference point relative to which the tracing system moves in the space in a measurable manner. The 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.

For the measurement to be useful, it must be accurate. Very high accuracy, however, is difficult to achieve because of factors such as temperature and load conditions. Particularly in portable coordinate measuring machines, warping of the arm caused by thermal changes or by changes in loads has a negative effect on the measurement's accuracy. Consequently, in terms of their performance, conventional portable coordinate measuring machines were not nearly as accurate as conventional, non-portable type coordinate measuring machines.

Accuracy Improvements may be available. Conventionally, however, such improvements came accompanied by significant increases in mass and/or weight of the coordinate measuring machine. Conventional portable coordinate measuring machines of improved accuracy were bulky and heavy. These are undesirable characteristics for coordinate measuring machines, particularly portable coordinate measuring machines. Moreover, processes for constructing and assembling coordinate measuring machines' joints, particularly long joints, with the required precision to obtain accurate measurements have not been available.

<CIT> discloses a portable coordinate-measuring machine comprising a multi-jointed manually-positionable measuring arm for measuring a volume and a controller that acts as an electronic interface between the arm and a host computer. Additionally, a number of end effector probes are provided that fulfill functions other than measurement only.

<CIT> discloses a portable articulated arm coordinate-measurement machine. An articulated arm is provided having a plurality of arm segments. Each arm segment includes an angular encoder for producing a signal corresponding to an angle of rotation. A shaft rotates which about an axis is attached to an inner portion of a first and second bearing. A patterned disk is attached to the shaft. A housing is attached to an outer portion of the first and second bearing. A read head is attached to the housing in proximity to the patterned disk which produces an electrical signal in response to an angle of rotation. The patterned disk and the first arm segment supported for rotation about the axis by only the first and second bearing. A circuit receives the electrical signal and provides an angle and data corresponding to a position of the probe.

<CIT> discloses an articulated coordinate measuring arm having swivelling joints which are unlimited by an end-stop. Power and signals are transmitted through a swivelling joint using a multi-conductor electrical slip-ring subassembly. Joint position transducer signal conditioners are closely located to the joint position transducers. Rigid transfer members connecting the joints comprise a freely rotating shaft mounted within an outer sheath, wherein both shaft and sheath extend substantially the length of the transfer member, and the shaft outer diameter approaches that of the sheath inner diameter.

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

In a first aspect of the invention according to claim <NUM> or claim <NUM>, the CMM includes rotary joints whose shaft has no portion with a diameter larger than the inner diameter of the joint's bearings and/or whose housing has a bearing engaging port that has no portion with a diameter narrower than the outer diameter of the joint's bearings.

In another aspect of the invention at least one of the rotary joints includes a rotary damper operably coupled to the shaft and the housing and configured to provide controlled damping of rotational movement of the shaft about the axis of rotation.

In another aspect of the invention rotary damping is built into at least one of the rotary joints to provide controlled damping of rotational movement of the shaft about the axis of rotation.

In another aspect of the invention at least one of the rotary joints includes a rotary damping mechanism configured to provide controlled damping of rotational movement of the shaft about the axis of rotation, and a circuit operably connected to the at least one transducer and configured to output a speed and direction signal corresponding to the speed of the rotational movement of the shaft about the axis of rotation based on the angle signal and time, the circuit further configured to compare the speed signal to a predetermined speed threshold to determine whether the rotational movement occurred at excessive speed resulting in excessive torque.

In another aspect of the invention at least one of the rotary joints includes a rotary damping mechanism configured to provide controlled damping of rotational movement of the shaft about the axis of rotation, and at least one strain gauge operably coupled to at least one of the shaft and the housing and configured to sense strain on the 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 that may be used to correct the location of the measurement probe based in part on the strain signal.

In another aspect of the invention in at least one joint of the plurality of joints a) the shaft that engages the inner diameter of at least one of the first bearing and the second bearing and b) the port of the housing that engages the outer diameter of at least one of the first bearing and the second bearing are fabricated of steel.

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 that is in contact with the inner or outer of a bearing of the first joint or the inner or outer race of a bearing of the second joint.

In another aspect of the invention all structural portions of at least one of the plurality of rotary joints are fabricated of steel.

In another aspect of the invention any structural portions of the CMM including the plurality of arm segments and the plurality of rotary joints are fabricated of a controlled expansion alloy lighter in weight than steel and having a thermal expansion coefficient matching that of steel or stainless steel in the range of between of <NUM> to <NUM>/m°C at <NUM>.

In another aspect of the invention the measurement probe includes a handle mechanically but not electrically operably coupled to the first end, the handle rotatably coupled to the first end to rotate about a central axis of the measurement probe, the handle including a wireless transmitter, and at least one switch operably connected to the wireless transmitter and configured to, when activated, cause the wireless transmitter to transmit a wireless signal that causes the CMM to take a measurement.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various example systems, methods, and so on, that illustrate various example embodiments of aspects of the invention. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. One of ordinary skill in the art will appreciate that one element may be designed as multiple elements or that multiple elements may be designed as one element. An element shown as an internal component of another element may be implemented as an external component and vice versa. Furthermore, elements may not be drawn to scale.

<FIG> illustrate perspective views of an exemplary coordinate measuring machine (CMM) <NUM>. <FIG> illustrates a cross-sectional view of the exemplary CMM <NUM>. CMM <NUM> includes an articulated arm <NUM>, a base <NUM>, and a measurement probe <NUM>. The articulated arm <NUM> is attached at one end to the base <NUM> and at the other end to the measurement probe <NUM>. The base <NUM> may include, for example, a magnetic holder <NUM> to attach the arm <NUM> to, for example, a working surface. Articulated arm <NUM> includes two arm segments <NUM>, <NUM> and a number of rotary joints <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The CMM <NUM> may also include an on-arm switch assembly <NUM>.

The overall length of articulated arm <NUM> and/or the arm segments <NUM>, <NUM> may vary depending on its intended application. In one embodiment, the articulated arm may have an overall length of about <NUM> inches. This arm dimension provides a portable CMM which is well suited for measurements now accomplished using typical hand tools such as micrometers, height gages, calipers and the like. Articulated arm <NUM> could have smaller or larger dimensions.

The rotary joints generally include two types of joints, swivel joints <NUM>, <NUM>, <NUM>, <NUM> and hinge joints <NUM>, <NUM>, <NUM>. The swivel joints <NUM>, <NUM>, <NUM>, <NUM> are positioned generally axially or longitudinally along the arm <NUM>. The hinge joints <NUM>, <NUM>, <NUM> are positioned generally at <NUM>° to the swivel joints or <NUM>° to the longitudinal axis of the arm <NUM>. The swivel and hinge joints are generally paired up as shown in <FIG> but the joints may be arranged in other configurations. Because of the multiple rotary joints, the arm <NUM> is manually-positionable meaning that a user is free to manually move the probe <NUM> to virtually any position within a radius anchored at the base <NUM> of the CMM <NUM>. Each of these joints are generally shown in <FIG>.

In general, the magnetic holder <NUM> of the base <NUM> attaches the CMM <NUM> to a working surface, the base <NUM> includes the swivel joint <NUM>, which attaches to the hinge joint <NUM>, which attaches to the swivel joint <NUM>, which attaches to the hinge joint <NUM>, which attaches to the swivel joint <NUM>, which attaches to the hinge joint <NUM>, which attaches to the swivel joint <NUM>, which attaches to the measurement probe <NUM>.

<FIG> illustrates an exploded view of exemplary base <NUM> and swivel joint <NUM>. <FIG> also illustrates the base enclosure 4a, which has mounted thereon a battery receptacle <NUM>. The CMM <NUM> is portable and, therefore, may be operated on battery power from a battery (not shown) installed to the CMM <NUM> via the receptacle <NUM>. The CMM <NUM> may also include a power jack <NUM> to which a power adapter may be connected to power the CMM <NUM>.

The swivel joint <NUM> may include housing <NUM>, shaft <NUM>, bearings <NUM>, <NUM>, encoder printed circuit board (PCB) <NUM>, encoder disk <NUM>, and slip ring <NUM>. The swivel joint <NUM> may also include dust covers 42a-c and various hardware such as the threaded studs 44a-c and screws 47a-c. Swivel joints in general are discussed in detail below in reference to swivel joint <NUM>.

<FIG> illustrates partial exploded views of exemplary swivel joint <NUM> while <FIG> illustrates partial cross-sectional views of swivel joint <NUM>. Each of the figures illustrates only the ends of the swivel joint <NUM>; the middle portion of the swivel joint not illustrated corresponds to the arm segment <NUM>. The swivel joint <NUM> will be used here to describe swivel joints <NUM>, <NUM>, <NUM>, <NUM> in general even though the swivel joints may not be identical. The swivel joints <NUM> and <NUM> are very similar. Swivel joint <NUM> is also similar to swivel joints <NUM> and <NUM> except that, as described below, swivel joint <NUM> has a shorter shaft. At least some of the components of swivel joint <NUM> are substantially similar to components discussed in detail above in reference to swivel joint <NUM> and thus these similar components are identified in <FIG> and <FIG> with the same reference designators as in <FIG>.

The swivel joint <NUM> may include housings <NUM>, <NUM>, shaft portions 50a, 50b, and 50c, bearings <NUM>, <NUM>, encoder PCB <NUM>, encoder disk <NUM>, and slip ring <NUM>. The bearings <NUM>, <NUM> are preferably steel or stainless steel ball bearings. The shaft portions 50a and 50c may be operably attached to the ends of the shaft portion 50b to form a shaft assembly <NUM> as described in detail below. The shaft portion 50b, being relatively long may be fabricated of rigid yet relatively lighter material such as, for example, carbon fiber, aluminum, etc. as well as from steel. The shaft portions 50a and 50c, however, may be fabricated of steel to match the material from which the bearings <NUM>, <NUM> are fabricated. Similar to the relatively long shaft portion 50b, the tube <NUM> within which the shaft portion 50b resides may be fabricated of the same rigid yet relatively light material as shaft portion 50b as well as from steel. The swivel joint <NUM> may also include covers 62a-b and various hardware such as the snap rings 64a-c.

At one end of the swivel joint <NUM>, the housing <NUM> has a surface 48a that operably attaches to one end of the tube <NUM> of the corresponding arm segment (arm segment <NUM> in the case of swivel joint <NUM>). The housing <NUM> also has a shaft connecting portion 48c that operably connects the swivel joint <NUM> to the previous hinge joint (see <FIG>). In the case of swivel joint <NUM>, the shaft connecting portion 48c connects the swivel joint <NUM> to the shaft of the hinge joint <NUM>. At the other end of the swivel joint <NUM>, the housing <NUM> has a surface 49a that operably attaches to a second end of the tube <NUM> of the corresponding arm segment (arm segment <NUM> in the case of swivel joint <NUM>). The housing <NUM> also has a port 49b within which an end of the shaft assembly resides, particularly shaft portion 50a. Assembly of the tube <NUM> to the housing ends <NUM> and <NUM> is described in more detail below.

As may be best seen in <FIG>, at one end of the swivel joint <NUM>, the inner diameter <NUM> of the port 48b of the housing <NUM> engages (e.g., fixedly attaches to) the outer diameter or outer race of the bearing <NUM>. The port 48b of the housing <NUM> may, for example, be glued to the outer diameter or outer race of the bearing <NUM>. The shaft portion 50c, for its part, has an outer diameter <NUM> that engages (e.g., is fixedly attached to) the inner diameter or inner race of the bearing <NUM>. The shaft portion 50c may, for example, be glued to the inner diameter or inner race of the bearing <NUM>. At the other end of the swivel joint <NUM>, the inner diameter <NUM> of the port 49b of the housing <NUM> engages (e.g., fixedly attaches to) the outer diameter or outer race of the bearing <NUM>. The port 49b of the housing <NUM> may, for example, be glued to the outer diameter or outer race of the bearing <NUM>. The shaft portion 50a, for its part, has an outer diameter <NUM> that engages (e.g., is fixedly attached to) the inner diameter or inner race of the bearing <NUM>. The shaft portion 50a may, for example, be glued to the inner diameter or inner race of the bearing <NUM>. The shaft assembly <NUM>, therefore, rotates about the axis of rotation a of the bearings <NUM> and <NUM> and the housings <NUM> and <NUM>.

The PCB <NUM> of the swivel joint <NUM> has installed thereon at least one transducer configured to output an angle signal corresponding to an angle of rotation of the shaft assembly <NUM> relative to the housing <NUM>, <NUM> about the axis of rotation a. Each transducer comprises an optical encoder that has two primary components, a read head <NUM> and the encoder disk <NUM>. In one embodiment, two read heads <NUM> are positioned on PCB <NUM>. In the illustrated embodiment, the encoder disk <NUM> is operably attached to an end of the shaft assembly <NUM> (e.g., using a suitable adhesive) spaced from and in alignment with read heads <NUM> on PCB <NUM>, which is operably attached to the housing <NUM> (e.g., using a suitable adhesive). The locations of disk <NUM> and read heads <NUM> may be reversed whereby disk <NUM> may be operably attached to housing <NUM> and read heads <NUM> rotate with shaft assembly <NUM> so as to be rotatable with respect to each other while maintaining optical communication. Encoders are commercially available from, for example, Celera Motion under trade names such as MicroE encoders. Each PCB <NUM> may additionally include a processor for receiving and processing angle signals received from the read heads <NUM>, and a transceiver and connector <NUM> for connecting the PCB <NUM> to the communication bus of the CMM <NUM> and/or other wiring as will be discussed hereinafter. Each of the PCB <NUM> may also include a temperature sensor connected to the processor to provide for thermal compensation due to room temperature variation.

The cover 62b operably attaches to the housing <NUM> to cover and seal the PCB <NUM> and encoder disk <NUM> from dust contamination. The cover 62a operably attaches over the cover 62b and portions of the housing <NUM> and tube <NUM> for cosmetic appearance. The cover 62b has the opening <NUM> from which the shaft connection portion 48c of the housing <NUM> protrudes to operably connect the swivel joint <NUM> to the hinge joint <NUM>.

Swivel joint <NUM> (as well as other joints in CMM <NUM>) may have unlimited rotation, meaning that it may rotate <NUM>° about its axis of rotation a. Thus, slip ring <NUM> is used and provides unlimitedly rotatable electrical connections to swivel joint <NUM>. Shafts used herein in swivel joints such as the shaft <NUM> of base swivel joint <NUM> and the shaft assembly <NUM> of swivel joint <NUM> may be hollow (i.e., have an axial opening <NUM>). Shafts used herein in hinge joints such as the shaft <NUM> of hinge joint <NUM> described below may also be hollow and may also include an aperture <NUM> (see <FIG>). Back to <FIG> and <FIG>, as illustrated, the housing cover 62a has the opening <NUM>, the cover 62b has the opening <NUM>, and the housing <NUM> has the opening 48d which aligns with the aperture <NUM> of the shaft <NUM> of the hinge joint <NUM>. Thus, communication bus wiring may enter the swivel joint <NUM> from the aperture <NUM> of hinge joint <NUM>, through the opening 48d, through the opening <NUM>, the opening <NUM> and connect to PCB <NUM>, which connects to the slip ring <NUM>. From the slip ring <NUM>, wiring may travel through the axial opening <NUM> of the shaft <NUM> to the next hinge joint. Such wiring is shown diagrammatically below.

Conventionally a shaft used in a joint for a coordinate measuring machine had one or more shoulders or flanges extending radially outwardly from the axis of the joint beyond the surface of the shaft that engages the inner diameter or inner race of the bearing. These shoulders or flanges were deemed necessary to retain the shaft axially in place in relation to the rest of the joint particularly the joint's bearings. Similarly, conventionally a housing used in a joint for a coordinate measuring machine had one or more shoulders or flanges extending radially inwardly towards the axis of the joint beyond the surface of the housing that engages the outer diameter or outer race of the bearing. These shoulders or flanges were deemed necessary to retain the housing axially in place in relation to the rest of the joint particularly the joint's bearings. See, for example, <FIG>, <NUM>, <NUM>, and <NUM> of <CIT> in which both shafts and housings have shoulders or flanges to retain the shafts and housings axially in place in relation to the bearings.

These conventional shafts and housings were manufactured by machining in order to produce the shoulders or flanges. But even the most advanced machining processes were limited in the precision they could impart to such machined shafts and housings. These parts were, therefore, significantly limited by the precision of the machining process. This was a problem since, as discussed in the Background section of the present application, accuracy is important for coordinated measuring machines.

As best seen in <FIG>, the shaft portions 50a and 50c have no portion whose diameter is larger than the inner diameter or inner race of the bearings <NUM>, <NUM>. No portion of the shaft portion 50a has a larger diameter than the outer diameter <NUM>, which engages the inner diameter or inner race of the bearings <NUM>. No portion of the shaft portion 50c has a larger diameter than the outer diameter <NUM>, which engages the inner diameter or inner race of the bearings <NUM>. Similarly, the port 48b, which engages the outer diameter or outer race of the bearing <NUM>, has no portion whose diameter is smaller or narrower than the outer diameter of the bearing <NUM>. The port 49b, which engages the outer diameter or outer race of the bearing <NUM>, has no portion whose diameter is smaller or narrower than the outer diameter of the bearing <NUM>. Therefore, it may be said that the shaft assembly <NUM> and housings <NUM> and <NUM> are shoulderless as that term is defined herein. The shaft portions 50a and 50c have no portion extending radially outwardly from the axis a of the joint <NUM> beyond the surfaces <NUM>, <NUM> that engage the inner diameters or inner races of the bearings <NUM>, <NUM>. Similarly, the housings <NUM>, <NUM> have no portion extending radially inwardly towards the axis a of the joint <NUM> beyond the surfaces <NUM>, <NUM> of the housings <NUM>, <NUM>, respectively, that engage the outer diameters or outer races of the bearing <NUM>, <NUM>.

Instead of shoulders or flanges, the shaft portions 50a and 50c may have grooves <NUM>, <NUM> machined or otherwise formed thereon. The snap rings 64b-c may engage the grooves <NUM>, <NUM> to retain the shaft assembly <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>. Similarly, the housing <NUM> may have a groove <NUM> machined or otherwise formed thereon. The snap ring 64a may engage the groove <NUM> to retain the housing <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>. In one embodiment, instead of or in addition to the combination of the grooves <NUM>, <NUM> and the snap rings 64b-c to retain the shaft <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>, the shaft <NUM> may be fixedly attached to the inner diameters or inner races of the bearings <NUM>, <NUM> by use of an adhesive. Similarly, in one embodiment, instead of or in addition to the combination of the groove <NUM> and the snap ring 64a to retain the housing <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>, the surface <NUM> of the housing <NUM> may be fixedly attached to the outer diameter or outer race of the bearing <NUM> by use of an adhesive.

Shoulderless shafts and housings such as those illustrated in <FIG> and <FIG> may be manufactured by grinding and honing processes that may be an order of magnitude more precise than machining process used to manufacture the shouldered or flanged shafts and housings of the prior art. The shoulderless shafts and housings disclosed herein may thus be significantly more precisely built resulting in significant improvements in the precision of measurements that may be achieved at the joint <NUM> and similar joints of the CMM <NUM>. In part because of the shoulderless shafts and housings disclosed herein, the CMM <NUM> achieves significantly better accuracy than prior art portable coordinate measurement machines.

The swivel joint <NUM> of arm segment <NUM> is a relatively long joint as compared to, for example, joint <NUM> as may be appreciated from <FIG> and <FIG>. The bearings <NUM> and <NUM> are located far apart. The shaft <NUM> has three parts, the middle portion 50b having end portions 50a and 50c attached to the ends of the middle portion 50b far apart from each other. The outer tube <NUM> is long with housing ends <NUM> and <NUM> spaced far apart from each other. Such relatively long joints, and particularly long joints with multi-portioned shafts, have conventionally not been able to be constructed such that joint rotation remains precise, particularly when compared to shorter, single-portion shaft, joints.

<FIG> illustrates an orbit plot showing typical behavior of rotation of a conventional long arm's shaft measured as prescribed by Orton (<NPL>). The technique measures, not only angular position of the shaft, but also horizontal and vertical motion of the shaft. See also <CIT>. Notice on the orbit plot of <FIG> that horizontal and vertical displacement of the conventional shaft during rotation is about <NUM> microns from center. Moreover, notice that the horizontal and vertical displacement of conventional shafts during rotation is non-circular and inconsistent from one rotation to the next, varying as much as approximately <NUM> microns. In actuality, horizontal and vertical displacement of conventional shafts (and particularly long, multi-portion shafts) during rotation is typically even larger than <NUM> microns from center, non-circular, and varies from rotation to rotation even more than <NUM> microns. This shaft displacement from center negatively affects accuracy of measurements taken by conventional coordinate measuring machines. At least part of the problem causing such undesirable displacement from center is that, up to this point, there has not been a process for constructing and assembling long, multi-portion shaft, joints with the required precision.

<FIG> and <FIG> illustrate an exemplary process for assembling the outer tube <NUM> of the exemplary swivel joint <NUM> to the housing ends <NUM> and <NUM>. As shown in <FIG>, a fixturing tube FT may be used to promote precision in assembling the outer tube <NUM> to the housing ends <NUM> and <NUM>. The fixturing tube FT may, for example, be precisely grinded to near perfect dimensions so that it is cylindrical to within one tenths of thousands of an inch (<NUM>"). Its outer diameter is concentric to within one tenths of thousands of an inch (<NUM>"). The housing ends <NUM> and <NUM> may be glued to respective ends of the tube <NUM> and the fixturing tube FT may be used to precisely fix the housing ends <NUM> and <NUM> in place relative to each other while the glue cures. As seen in <FIG> (a halfway cross-sectional view), the housing ends <NUM> and <NUM> may be fixed to the tube <NUM> with the fixturing tube FT inside the assembly. The inner walls <NUM> and <NUM> of the housing ends <NUM> and <NUM> may be made to fit tightly (very tightly, almost interference) against the walls FTa and FTb of the very precise fixturing tube FT. Once the glue has cured, the fixturing tube FT may be removed from the assembly. The fixturing tube FT may be oiled to aid in its removal. Using this process, the housing ends <NUM> and <NUM> may be made to be concentric (i.e., their inner diameters share the same axis a) to within five tenths of thousands of an inch (<NUM>"). Other methods that may be used to achieve similar results may include internal grinding of the housing ends <NUM> and <NUM> once affixed to the assembly including the tube <NUM>.

<FIG> illustrates an exemplary process for assembling the shaft assembly <NUM> and the bearings <NUM> and <NUM> to the assembly including the outer tube <NUM> and the housing ends <NUM> and <NUM>.

First, as described above, the shaft ends 50a and 50c may be attached to the shaft portion 50b to form the shaft assembly <NUM>. To promote precision, the shaft ends 50a and 50c may be first machined oversized by a few thousands of an inch. That is, the shaft ends 50a and 50c may be first made to be wider (larger outer diameter) than their final desired diameter. The shaft ends 50a and 50c may then be glued to the two ends of the long shaft portion 50b using, for example, v-blocks on a granite table. Next the shaft assembly <NUM> may be grinded at the two ends 50a and 50c so that the two ends are concentric (i.e., their outer diameters share the same axis a) to within one tenth of thousands of an inch (<NUM>").

The inner snap rings 64b and 64c may be installed to shaft assembly <NUM> at grooves <NUM> and <NUM>, respectively. The inner races or inner diameters 32a and 34a of the bearings <NUM> and <NUM> may be press fitted to the shaft assembly <NUM> until they are against snap rings 64b and 64c and glued to the shaft assembly <NUM>. Outer snap ring 64a may be installed to the end housing <NUM> at the groove <NUM>. The assembly including the shaft assembly <NUM> and the bearings <NUM> and <NUM> may be inserted into the assembly including the tube <NUM> and the end housings <NUM> and <NUM>. Glue may be used to adhere the outer races 32b and 34b of the bearings <NUM> and <NUM> to the inner diameters <NUM> and <NUM> of the end housings <NUM> and <NUM>. Then a preload (e.g., <NUM> or 10lb weight) may be applied to the outer race 32b of bearing <NUM> to remove play between the inner and outer races of the bearings <NUM> and <NUM>. In <FIG>, the preload PREL is applied to the outer race 32b of bearing <NUM> using the preload application tools PLT1 and PLT2, which ensure that the preload is applied only to the outer race 32b and not the inner race 32a. The preload PREL is applied to the outer race 32b until the glue has cured and then removed. Application of the preload PREL results in removing play from the bearing assembly.

Conventional processes for constructing and assembling long (and particularly multi-portion shaft) joints did not allow for the precision necessary to effectively preload the bearings to remove play, which caused excessive horizontal and vertical displacement of the conventional shaft during rotation. Attempts to preload such imprecise conventional long joints to remove play would result in either excessive deformation of the bearings, jamming, grinding, excessive wear, etc. (i.e., the joints would not be usable or perform unsatisfactorily) or insufficient preloading resulting in excessive shaft displacement from center during rotation.

<FIG> illustrates an orbit plot showing typical behavior of rotation of a long arm <NUM> including the multi-portion shaft joint <NUM> as measured as prescribed by Orton. Notice that, on the orbit plot of <FIG>, horizontal and vertical displacement of the shaft <NUM> during rotation has been significantly reduced to within <NUM> microns from center. Moreover, notice that the horizontal and vertical displacement of the shaft <NUM> during rotation is remarkably circular and consistent from one rotation to the next. This is a significant improvement from the measured displacement exemplarily shown on <FIG> for the conventional long joint. This significant improvement in displacement from center drastically improves accuracy of measurements taken by the CMM <NUM> when compared to conventional coordinate measuring machines. The process described above for constructing and assembling the long joint <NUM> including the multi-portion shaft <NUM> provides the required precision to achieve such significant improvements.

<FIG> illustrates an exploded view of an exemplary swivel joint <NUM>. Swivel joint <NUM> is similar to swivel joints <NUM> and <NUM> described above except that swivel joint <NUM> has a shorter shaft <NUM> whose length corresponds to the distance between swivel joint <NUM> and probe <NUM> being shorter than the distance between, for example, swivel joint <NUM> and hinge joint <NUM>. Thus, the probe <NUM> rotates about the axis a of the swivel joint <NUM> and the swivel joint <NUM> detects the angle of rotation of the probe <NUM>, which is attached to the end of the swivel joint <NUM>.

<FIG> illustrates an exploded view of exemplary hinge joint <NUM> while <FIG> illustrates a cross-sectional view of hinge joint <NUM>. The hinge joint <NUM> will be used here to describe hinge joints <NUM>, <NUM>, <NUM> in general even though the hinge joints may not be identical. At least some of the components of hinge joint <NUM> are substantially similar to components discussed in detail above in reference to swivel joints <NUM> and <NUM> and thus these similar components are identified in <FIG> and <FIG> with the same reference designators as in the previous figures.

The hinge joint <NUM> may include housing <NUM>, shaft <NUM>, bearings <NUM>, <NUM>, encoder PCB <NUM>, and encoder disk <NUM>. The housing <NUM> has an opening 78b to which the shaft of the previous swivel joint (shaft <NUM> of swivel joint <NUM> in the case of hinge joint <NUM>) connects. The hinge joint <NUM> may also include covers 82a-c and various hardware such as the snap rings 64a-c and cap <NUM>.

As may be best seen in <FIG>, the housing <NUM> has ports <NUM> that engage (e.g., fixedly attach to) the outer diameters or outer races of the bearings <NUM>, <NUM>. The ports <NUM> of the housing <NUM> may, for example, be glued to the outer diameter or outer race of the bearings <NUM> and <NUM>. In the embodiment of <FIG> and <FIG> the housing <NUM> has two ports <NUM>. The shaft <NUM>, for its part, has an outer diameter <NUM> that engages (e.g., is fixedly attached to) the inner diameter or inner race of the bearings <NUM>, <NUM>. The shaft <NUM> may, for example, be glued to the inner diameter or inner race of the bearings <NUM>, <NUM>. The shaft <NUM>, therefore, rotates about the axis of rotation b of the bearings <NUM><NUM> and the housing <NUM> of the hinge joint <NUM>.

Similar to the swivel joints discussed above, the PCB <NUM> of the hinge joint <NUM> has installed thereon at least one transducer configured to output an angle signal corresponding to an angle of rotation of the shaft <NUM> relative to the housing <NUM> about the axis of rotation b. Each transducer comprises an optical encoder that has two primary components, a read head <NUM> and the encoder disk <NUM>. In the illustrated embodiment, two read heads <NUM> are positioned on PCB <NUM>. In the illustrated embodiment, the encoder disk <NUM> is operably attached to an end of the shaft <NUM> (e.g., using a suitable adhesive) spaced from and in alignment with read heads <NUM> on PCB <NUM>, which is operably attached to the housing <NUM> (e.g., using a suitable adhesive). The locations of disk <NUM> and read heads <NUM> may be reversed whereby disk <NUM> may be operably attached to housing <NUM> and read heads <NUM> rotate with shaft <NUM> so as to be rotatable with respect to each other while maintaining optical communication.

The cover 82b operably attaches to the housing <NUM> to cover and seal the PCB <NUM> and encoder disk <NUM> from dust. The covers 82a and 82c operably attach to each other at one end of the shaft <NUM> and the cap <NUM> caps to the opposite end of the shaft <NUM> to protect the bearings.

Communications bus wiring may enter the hinge joint <NUM> from the axial opening <NUM> of the shaft <NUM> of the previous swivel joint through the openings 78b, 78c of the housing <NUM>. The wiring may then connect to the PCB <NUM> and depart the hinge joint <NUM> through the axial opening 80a and the aperture <NUM> of shaft <NUM>. Such wiring is shown diagrammatically below.

As discussed above, conventionally a shaft used in a joint for a coordinate measuring machine had one or more shoulders or flanges extending radially outwardly from the axis of the joint beyond the surface of the shaft that engages the inner diameter or inner race of the bearing. These shoulders or flanges were deemed necessary to retain the shaft axially in place in relation to the rest of the joint particularly the joint's bearings. Similarly, conventionally a housing used in a joint for a coordinate measuring machine had one or more shoulders or flanges extending radially inwardly towards the axis of the joint beyond the surface of the housing that engages the outer diameter or outer race of the bearing. These shoulders or flanges were deemed necessary to retain the housing axially in place in relation to the rest of the joint particularly the joint's bearings. See, for example, <FIG>, <NUM>, <NUM>, and <NUM> of <CIT> in which both shafts and housings have shoulders or flanges to retain the shafts and housings axially in place in relation to bearings.

These conventional shafts and housings were manufactured by machining in order to produce the shoulders or flanges. But even the most advanced machining processes were limited in the precision they could impart to such machined shafts and housings. These parts were limited by the precision of the machining process and, as discussed in the Background section of the present application, accuracy is important for CMM.

As best seen in <FIG>, the shaft <NUM> has no portion whose diameter is larger than the inner diameter or inner race of the bearings <NUM>, <NUM>. No portion of the shaft <NUM> has a larger diameter that the outer diameter <NUM>, which engages the inner diameters or inner races of the bearings <NUM>, <NUM>. Similarly, the ports <NUM>, which engage the outer diameters or outer races of the bearings <NUM>, <NUM>, have no portion whose diameter is smaller or narrower than the outer diameter of the bearing <NUM> or the outer diameter of the bearing <NUM>. Therefore, it may be said that the shaft <NUM> and housing <NUM> are shoulderless as defined herein i.e., <NUM>) the shaft <NUM> has no portion extending radially outwardly from the axis b of the joint <NUM> beyond the surface <NUM> of the shaft <NUM> that engages the inner diameters or inner races of the bearing <NUM>, <NUM>, and <NUM>) the housing <NUM> has no portion extending radially inwardly towards the axis b of the joint <NUM> beyond the surface <NUM> of the housing <NUM> that engages the outer diameters or outer races of the bearing <NUM>, <NUM>.

Instead of shoulders or flanges, the shaft <NUM> may have grooves <NUM> machined or otherwise formed thereon. The snap rings 64b-c may engage the grooves <NUM> to retain the shaft <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>. Similarly, the housing <NUM> may have a groove <NUM> machined or otherwise formed thereon. The snap ring 64a may engage the groove <NUM> to retain the housing <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>. In one embodiment, instead of or in addition to the combination of the grooves <NUM> and the snap rings 64b-c to retain the shaft <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>, the shaft <NUM> may be fixedly attached to the inner diameters or inner races of the bearings <NUM>, <NUM> by use of an adhesive. Similarly, in one embodiment, instead of or in addition to the combination of the groove <NUM> and the snap ring 64a to retain the housing <NUM> axially in place in relation to the rest of joint <NUM> and the bearings <NUM>, <NUM>, the ports <NUM> of the housing <NUM> may be fixedly attached to the outer diameters or outer races of the bearings <NUM>, <NUM> by use of an adhesive.

Joints for prior art coordinate measurement machines were manufactured mostly of aluminum or other lightweight materials. See, for example, <CIT> which discloses a coordinate measurement machine in which joints are constructed of cast or machined aluminum components, lightweight stiff alloy or composite, or fiber reinforced polymer. The reference makes clear that relatively low weight is very important for the proper functionality of the disclosed coordinate measurement machine. A problem with such prior art coordinate measurement machines was that their aluminum (or similarly lightweight material) construction, which has a significantly different thermal expansion coefficient from that of the joint's bearings, causes variation in the joint's rigidity over temperature. This reduces accuracy of measurements taken over the operating temperature range.

The present invention takes an approach that may seem counterintuitive. In one embodiment, structural elements of the joints of the arm <NUM> may be fabricated of steel matching the material from which the bearings <NUM>, <NUM> are fabricated. Structural elements in this context refer to housings <NUM>, <NUM>, <NUM>, and <NUM>, shafts <NUM>, <NUM>, and <NUM>, and shaft portions 50a and 50c. These are the structural elements that are in contact with the inner or outer race of the ball bearings <NUM>, <NUM>. The housing <NUM> also attaches a swivel joint to the next hinge joint. Steel in this context includes stainless steel and has a thermal expansion coefficient in the range of between of <NUM> to <NUM>/m°C at <NUM>. The use of relatively heavy steel for the structural elements of the joints of the arm <NUM> may seem somewhat counterintuitive because, as discussed above, one of the important features of the CMM <NUM> is that it must be lightweight. Steel is significantly heavier that the materials used by prior art coordinate measurement machines such as aluminum. Structural elements matching the material (i.e., steel) from which the bearings <NUM>, <NUM> are fabricated, however, would have the same (or nearly the same) thermal expansion coefficient (i.e., would expand or contract with temperature at the same rate) as the bearings <NUM>, <NUM>. This minimizes variation in the joint's rigidity over temperature and thus maintains accuracy of measurements taken over the operating temperature range of the CMM <NUM>.

In another embodiment, structural elements of the joints of the arm <NUM>, other structural elements such as shaft portion 50b, tubes <NUM>, etc. and even non-structural elements of the CMM <NUM> may be fabricated of a controlled expansion alloy lighter in weight than steel but having a thermal expansion coefficient matching that of chrome steel or 440C stainless steel (i.e., in the range of between of <NUM> to <NUM>/m°C at <NUM>). A commercially available example of such controlled expansion alloy is Osprey CE sold by Sandvik AB of Sandviken, Sweden. Structural elements fabricated from materials matching the thermal expansion coefficient (i.e., would expand or contract with temperature at the same rate) of the bearings <NUM>, <NUM> minimize variation in the joint's rigidity over temperature and thus maintain accuracy of measurements taken over the operating temperature range of the CMM <NUM>. The significantly thinner arm segments <NUM> and <NUM> fabricated from rigid yet relatively light material such as, for example, carbon fiber or controlled expansion alloy combined with structural elements (and even non-structural elements) fabricated from controlled expansion alloy result in a CMM <NUM> that is significantly lighter and significantly more accurate over the operating temperature range than prior art coordinate measuring machines.

<FIG> illustrates a cross-sectional view of exemplary hinge joint <NUM>. Hinge joint <NUM> is very similar to hinge joint <NUM> described above. Hinge joint <NUM> is also similar to hinge joints <NUM> and <NUM>, a significant difference being that the hinge joint <NUM> includes a rotary damper assembly. In the illustrated embodiment of <FIG>, the rotary damper assembly is an instrumented assembly 90a as described in detail below. To ease the use of the arm <NUM>, a counter balance arrangement in the form of the rotary damper assembly 90a may be provided to offset the torque applied by the weight of the articulated arm. The counter balance prevents the articulated arm <NUM> from falling down rapidly due to its own weight if the user releases it.

Conventionally, portable coordinate measuring machines used coil springs or torsion springs to counter balance the weight of the arm. See, for example, <CIT> and <CIT>. Another conventional counter balance systems included a piston or linear actuator assembly forming a gas shock counterbalance. See, for example, <CIT>. Each of these conventional counter balance solutions had problems with adjustment and calibration of the counter balance. Also, these conventional counter balance solutions were generally bulky and heavy, two undesirable characteristics for portable coordinate measuring machines.

<FIG> illustrates an exploded view of the exemplary rotary damper assembly 90a. The assembly 90a includes the rotary damper <NUM> which may be a commercially available rotary damper such as WRD dampers manufactured by Weforma Dämpfungstechnik GmbH of Stolberg, Germany. In one embodiment, the rotary damper <NUM> is a unidirectional rotary damper that provides controlled damping of rotational movement of the shaft about the axis of rotation in one direction of rotation. The assembly 90a may also include damper hub <NUM>, damper sleeve <NUM>, and torque sensor shaft hub <NUM>, which together form an Oldham coupling. The assembly 90a may also include torque sensor shaft <NUM>. The assembly 90a may also include spacer <NUM>, mount <NUM>, and hardware such as bolts 107a-d and 108a-d. The mount <NUM> has four threaded apertures 110a-d and four non-threaded apertures 111a-d.

As best seen in <FIG>, the damper assembly 90a comes together by first coupling a portion of the torque sensor shaft <NUM> to the shaft <NUM> of the hinge joint <NUM>. A portion of the torque sensor shaft <NUM> may be inserted in and fixedly attached to (e.g., by using adhesive) the axial opening 80a of the shaft <NUM>. The mount <NUM> is coupled to the housing <NUM> of the hinge joint <NUM> by inserting the bolts 108a-d through the apertures 111a-d and threading them into threaded openings in the housing <NUM>. The rest of the components of the rotary damper assembly 90a are then stacked in order: the shaft hub <NUM> on the shaft <NUM>, the damper sleeve <NUM> on the shaft hub <NUM>, the damper hub <NUM> on the damper sleeve <NUM>, and the damper hub <NUM> on the shaft <NUM> of the rotary damper <NUM>. The spacer <NUM> is sandwiched between the rotary damper <NUM> and the mount <NUM> by threading the bolts 107a-d to the threaded apertures 110a-d of the mount <NUM>. Thus, the rotary damper <NUM> is operably coupled to the shaft <NUM> and the housing <NUM>.

The rotary damper <NUM> provides controlled damping of rotational movement of the shaft <NUM> about the axis of rotation b. The amount of torque output to control damping provided by the rotary damper <NUM> may be preadjusted and precalibrated to tight specifications. Thus, the rotary damper assembly 90a alleviates problems with adjustment and calibration of counter balance that were typical to conventional counter balance solutions for portable coordinate measuring machines such as coil springs, torsion springs, and pistons. Also, the rotary damper assembly 90a provides a counter balance solution that is generally more compact and lighter in weight when compared to conventional counter balance solutions such as coil springs, torsion springs, and pistons.

A potential issue that arises, particularly with use of a rotary damper to provide controlled damping of rotational movement, is that a user may apply excessive torque to the arm <NUM> when moving it. The excessive force may effectively bend portions of the arm <NUM> affecting the ability of the CMM <NUM> to accurately detect the position of the measurement probe <NUM>. Measurements taken under these conditions, in which the user essentially moves the arm too fast, may be inaccurate. The present disclosure provides two potential solutions to this potential issue.

In the embodiment of <FIG> and <FIG>, the rotary damper assembly 90a is instrumented to directly detect excessive torque at the joint <NUM>. The mount <NUM> has webbing or spokes 104a-d that connect the outer ring of the mount <NUM> which include the threaded apertures 110a-d to the inner ring of the mount <NUM> which include the non-threaded apertures 111a-d. Installed on at least some of the spokes 104a-d are strain gauges <NUM>. Similarly, the torque sensor shaft <NUM> has webbing or spokes 100a-d that connect it to the torque sensor shaft hub <NUM>. Installed on at least some of the spokes 100a-d are strain gauges <NUM>. The rotary damper assembly 90a also includes a torque sensor PCB <NUM> which has installed thereon electronics that receive signals from the strain gauges <NUM>.

Torque applied to the joint <NUM> is transmitted through the spokes 100a-d and 104a-d. Such torque manifests itself as rotational strain on the spokes 100a-d and 104a-d. Thus, by measuring strain at the spokes 100a-d and 104a-d, the gauges <NUM> effectively sense strain at the shaft <NUM> and the housing <NUM> of the joint <NUM> due to the rotational movement of the shaft <NUM> about the axis of rotation b. In that sense, the strain gauges <NUM> are operably coupled to the shaft <NUM> and the housing <NUM>. The strain gauges output strain signals that circuitry in the PCB <NUM> or another circuit (e.g., the processor in the corresponding joint's PCB <NUM>) in or external to the CMM <NUM> may use to detect and account for torque applied to the joint <NUM>.

Strain measured by the gauges <NUM> corresponds to an amount of torque applied to the joint <NUM>. The measured strain, thus, also corresponds to an amount of bending or flexing of portions of the arm <NUM>. The measured strain, therefore, may be correlated to an amount and nature of bending or flexing of the arm <NUM> and that information, in turn, may be taken into account when taking measurements with the CMM <NUM> to compensate for excessive torque. Thus, in this instrumented embodiment of the rotary damper assembly <NUM>, an electrical circuit in the PCB <NUM> (or the processor in the corresponding joint's PCB <NUM> that receives the angle signals from the read heads <NUM>) may receive the strain signals (or amplified strain signals) from the strain gauges <NUM>, convert those signals to corresponding bending or flexing of the arm <NUM> due to torque applied to the arm <NUM>, and calculate the measurement at the measurement probe <NUM> taking into account the corresponding bending or flexing of the arm <NUM>. For example, the PCB <NUM> may include amplifiers to amplify the analog signals from the strain gauges <NUM> and analog to digital converters to convert the amplified analog signals to digital signals that may be provided to a processor of the PCB <NUM> of the corresponding joint. The processor may look up on a table or calculate an amount and direction of bending or flexing of the arm <NUM> corresponding to the location and amplitude of the measured strain. Therefore, by measuring strain at the spokes 100a-d and 104a-d, the CMM <NUM> can accurately detect the position of the measurement probe <NUM> regardless of a user applying excessive torque to the arm <NUM>.

In an alternative embodiment, when any of the strain signals or an agglomeration of the strain signals exceeds a certain strain threshold, a determination may be made that too much torque has been applied to the joint <NUM>. Based on that determination, the CMM <NUM> may disable the taking of measurements until after a certain amount of time (e.g., two to ten seconds) has passed. This is to allow for any portions of the arm <NUM> that may have bent due to the excessive applied torque to return to its original shape.

<FIG> illustrates an exemplary non-instrumented rotary damper assembly 90b. Unlike the rotary damper assembly 90a of <FIG> and <FIG>, the rotary damper assembly 90b is not instrumented to directly detect excessive torque. In this embodiment, the angle signal output by the read heads <NUM> may be used to generate a speed signal that may be used as a proxy for applied torque. Torque applied to the arm <NUM> to move it generally corresponds to the speed at which the arm <NUM> moves. As stated above, excessive torque applied to the arm <NUM> essentially corresponds to the user moving the arm too fast, at too much speed. Therefore, excessive applied torque may be indirectly detected at the joints in the form of relatively high (i.e., too high) rotational speed. The read heads <NUM> output the angle signal that corresponds to the relative angle of rotation of the joint. The rate at which the measured angle of rotation 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 read heads <NUM> may be used to generate a speed signal by calculating the rate at which the measured angle of rotation changes, the speed signal. A processor in the PCB <NUM> (or anywhere else) may measure the speed signal (e.g., degrees per second) using a high resolution timer (e.g., <NUM> ns resolution) measuring the period of one of the encoder's quadrature signals. When the speed signal exceeds a certain rotational speed threshold, a determination is made that too much torque has been applied. Based on that determination, the CMM <NUM> may disable the taking of measurements until after a certain amount of time (e.g., two to ten seconds) has passed. This is to allow for any portions of the arm <NUM> that may have bent due to the excessive applied torque to return to its original shape.

The assembly 90b is similar to assembly 90a of <FIG> and <FIG>. The assembly 90b may include the rotary damper <NUM>. The assembly 90b may also include the damper hub <NUM>, damper sleeve <NUM>, shaft hub <NUM> (together forming an Oldham coupler), and shaft <NUM>. The assembly 90b may also include spacer <NUM>, mount <NUM>, and hardware such as bolts 107a-d and 108a-d. The spacer <NUM> is similar to the spacer <NUM> except that it does not need to hold the PCB <NUM>. The mount <NUM> has four threaded apertures 110a-d and four non-threaded apertures 111a-d. The mount <NUM> is similar to the mount <NUM> except that it does not need the webbing or spokes 104a-d.

The damper assembly 90b comes together by first coupling a portion of the torque sensor shaft <NUM> to the shaft <NUM> of the hinge joint <NUM>. A portion of the torque sensor shaft <NUM> may be inserted in and fixedly attached to (e.g., by using adhesive) the axial opening 80a of the shaft <NUM>. The mount <NUM> is coupled to the housing <NUM> of the hinge joint <NUM> by inserting the bolts 108a-d through the apertures 111a-d and threading them into threaded openings in the housing <NUM>. The rest of the components of the rotary damper assembly 90b are then stacked in order: the shaft hub <NUM> on the shaft <NUM>, the damper sleeve <NUM> on the shaft hub <NUM>, the damper hub <NUM> on the damper sleeve <NUM>, and the damper hub <NUM> on the shaft <NUM> of the rotary damper <NUM>. The spacer <NUM> is sandwiched between the rotary damper <NUM> and the mount <NUM> by threading the bolts 107a-d to the threaded apertures 110a-d of the mount <NUM>. Thus, the rotary damper <NUM> is operably coupled to the shaft <NUM> and the housing <NUM>.

In one embodiment (not shown), instead of an add-on rotary damper assembly such as the assemblies 90a and 90b, rotary damping is built into the hinge joint <NUM>. In this embodiment, a combination of a) the first bearing <NUM> or the second bearing <NUM> with b) the shaft <NUM> or the housing <NUM> provides controlled damping of rotational movement of the shaft <NUM> about the axis of rotation b.

<FIG> illustrates a perspective view of an exemplary measurement probe 6a. Probe 6a includes a housing <NUM> that has an interior space for housing PCB <NUM> and a handle <NUM> that has an interior space for housing PCB <NUM>. The housing <NUM> and the handle <NUM> are shown in <FIG> transparent for illustration purposes. Housing <NUM> operably couples to the swivel joint <NUM> (see <FIG>). Thus, the probe 6a rotates about the axis a of the swivel joint <NUM> and the swivel joint <NUM> detects the angle of rotation of the probe 6a about the axis a.

The measurement probe 6a may also include a probe stem assembly <NUM> having a probe connector <NUM> at one end and a probe <NUM> at the other end. The probe connector <NUM> connects to the housing <NUM> and the PCB <NUM>. The probe stem assembly <NUM> may be a touch trigger assembly which triggers the capture of the position of the probe <NUM> when the probe <NUM> touches an object. The PCB <NUM> receives such a trigger signal and transmits it as described below. The probe stem assembly <NUM> may also house electronics such as, for example, an integrated circuit (e.g., EEPROM) having stored therein a serial number to uniquely identify a probe stem assembly <NUM> upon installation to the CMM <NUM>.

Handle <NUM> may include two switches, namely a take switch <NUM> and a confirm switch <NUM>. These switches may be used by the operator to take a measurement (take switch <NUM>) and to confirm the measurement (confirm switch <NUM>) during operation. The handle <NUM> is generally shaped to resemble a person's grip, which is more ergonomic than at least some prior art probes. The handle <NUM> may also house a switch PCB <NUM> to which the switches <NUM> and <NUM> may mount. Switch PCB <NUM> is electrically coupled to PCB <NUM> hosting components for processing signals from the switches <NUM> and <NUM>. In one embodiment, the PCB <NUM> includes a wireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of an electrical connection to the communication bus of the CMM <NUM>) that wirelessly transmits take and confirm signals associated with the switches <NUM> and <NUM> to, for example, a host PC that generally controls the CMM <NUM>. Wireless transmission of the take and confirm signals associated with the switches <NUM> and <NUM> significantly simplifies construction and wiring of the probe 6a.

The measurement probe 6a may also include an option port <NUM> to which optional devices such as, for example, a laser scanner (not shown) may be connected. The option port <NUM> provides mechanical connections for the optional devices to be supported by the measurement probe 6a. The option port <NUM> may also provide electrical connections for the optional devices to interface with the communication bus of the CMM <NUM>.

<FIG> illustrates a perspective view of an exemplary alternative measurement probe 6b. The probe 6b is similar to the probe <NUM>. The probe 6b, however, includes a different housing <NUM> and handle <NUM>. Unlike the probe <NUM>, the housing <NUM> of the probe 6b includes a connecting portion <NUM> that may connect directly to the hinge joint <NUM>. Thus, when the probe 6b is used, the swivel joint <NUM> is not used. The housing <NUM> and the probe stem assembly <NUM> do not rotate about the axis a. The housing <NUM> and the probe stem assembly <NUM> are fixed about the axis a. The handle <NUM>, on the other hand, includes a connecting portion <NUM> that rotatably couples the handle <NUM> to the housing <NUM>. Thus, the handle <NUM> rotates about the axis a. Like the handle <NUM> of probe <NUM>, the handle <NUM> has an interior space for housing PCB <NUM>. The PCB <NUM> may include a wireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of an electrical connection to the communication bus of the CMM <NUM>) that wirelessly transmits signals such as, for example, take and confirm signals associated with the switches <NUM> and <NUM>. Thus, the handle <NUM> is rotatably coupled to the arm <NUM> to rotate about the axis a but, importantly, the handle <NUM> is not electrically coupled to the arm <NUM> because signal transmission is accomplished wirelessly.

The probe 6b is a significant advance in the coordinate measuring machine field because it alleviates the need for seven true axes of rotation. The CMM <NUM> as illustrated in <FIG> include seven true axes of rotation (i.e., axes associated with joints <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>). Including seven true axes of rotation results in a relatively more complex and expensive CMM <NUM>. The rotatable handle <NUM>, mechanically and wirelessly (but not electrically) connected to the arm <NUM> and thus not requiring the seventh joint <NUM>, alleviates the need for a "true" seventh axis because it permits the handle <NUM> to rotate as needed for hand position without the complexity of a seventh set of bearings, transducers, electronics, etc..

<FIG> illustrates a perspective view of an exemplary on-arm switch assembly <NUM>. Switch assembly <NUM> includes a housing <NUM> that has opening <NUM> to mount (e.g., clamp) the switch assembly <NUM> to the arm segment <NUM> or, alternatively to the arm segment <NUM>. The housing <NUM> has an interior space for housing a PCB. Similar to the probes <NUM> and 6b, the switch assembly <NUM> may include two switches, namely a take switch <NUM> and a confirm switch <NUM> that may be used by the operator to take a measurement (take switch <NUM>) and to confirm the measurement (confirm switch <NUM>) during operation. The position of the on-arm switch assembly <NUM>, and more importantly of the switches <NUM> and <NUM>, on the arm <NUM> instead of in the handles of the probe <NUM> allow for the operator to move and position the measurement probe <NUM> with one hand and to actuate the switches <NUM> and <NUM> with the other hand while supporting the arm. Prior art coordinate measurement machines required operators to position the measurement probe and actuate measurement switches in the probe with the same hand. This is not ergonomic. The on-arm switch assembly <NUM> is a significant advance in the coordinate measuring machine field because it provides a significantly more ergonomic solution as compared to prior art coordinate measurement machines.

The on-arm switch assembly <NUM> may also house a switch PCB <NUM> to which the switches <NUM> and <NUM> may mount or the on-arm switch assembly <NUM> may include a PCB that incorporates the functionality of both PCB <NUM> and switch PCB <NUM>. In one embodiment, the PCB in the on-arm switch assembly <NUM> electrically connects to the communication bus of the CMM <NUM>. In another embodiment, the PCB in the on-arm switch assembly <NUM> includes a wireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of an electrical connection to the communication bus of the CMM <NUM>) that wirelessly transmits take and confirm signals associated with the switches <NUM> and <NUM>.

<FIG> illustrates a block diagram of exemplary electronics for the CMM <NUM>. The CMM <NUM> may include external communication interfaces such as a Universal Serial Bus (USB) <NUM> and wireless (Wi-Fi) <NUM>. The CMM <NUM> may also include an internal communication bus (e.g., RS-<NUM>) <NUM>. As discussed above, the various joints or axis of the CMM <NUM> each includes a PCB <NUM> which has installed thereon at least one transducer configured to output an angle signal corresponding to an angle of rotation of the joint. The PCB <NUM> may each include a processor <NUM> for receiving and processing angle signals from the transducers and/or strain signals from the PCB <NUM> of the rotary damper assemblies <NUM>. The PCB <NUM> may also include a transceiver <NUM> to interface with the bus <NUM>. The PCB <NUM> of the measurement probe <NUM>, which may carry signals from the touch trigger probe <NUM>, may also connect to the communication bus <NUM>. The bus <NUM> may also connect to the option port <NUM> of the measurement probe <NUM> to communicate/control optional devices such as, for example, a laser scanner installed to the option port <NUM>. The PCB <NUM> of the handle <NUM> may wirelessly transmit take and confirm signals associated with the switches <NUM> and <NUM>.

The bus <NUM> terminates at a main PCB <NUM> preferably located at the base <NUM> of the CMM <NUM>. The main PCB <NUM> includes its own main processor <NUM> and transceiver <NUM> for connecting to the bus <NUM>. The main PCB <NUM> receives the angle signals from the transducers in the CMM <NUM> and output an agglomeration of the received angle signals via the USB <NUM> or the Wi-Fi <NUM> to a host PC such that the host PC may calculate the position of the measurement probe <NUM> based on this information and other information relating to the CMM <NUM> (e.g., location, length of arm segments, etc.) The internal bus <NUM> may be consistent with RS485.

Prior art coordinate measuring machines configured to use an RS485 internal bus incorporated dedicated capture and trigger wires to transport capture and trigger signals, respectively. See, for example, <CIT>. A capture signal is a synchronous signal generated by a master controller in the RS485 arrangement. A trigger signal is an asynchronous signal that is generated by devices attached to the articulated arm such as a touch trigger probe accessory (e.g., Renishaw TP20). The dedicated trigger wire travels from the probe to the master controller in the base of the articulated arm. The trigger signal that travels through the dedicated trigger wire interrupts the master controller. An interrupt service routine in the master controller generates a synchronous capture signal to capture angle signals from the encoders.

Note that in <FIG> there are no dedicated capture or trigger wires. Instead the bus <NUM> includes, from the main PCB <NUM>'s point of view, a pair of bidirectional wires <NUM> and <NUM> (A-B Pair, half duplex) or two pairs of unidirectional wires (A-B Pair and Y-Z pair, full duplex).

Even with the use of steel for the structural elements of the joints as described above, the arm <NUM> remains relatively lightweight partly because many of its components (e.g., shafts, bearings, housings, arm segments, etc.) are smaller than those of prior art coordinate measuring machines. Compare, for example, the shafts, housings, and arm segments of the CMM <NUM> disclosed herein to corresponding elements of the coordinate measuring machines disclosed in <CIT>. The smaller components of the CMM <NUM> have significantly less mass and are, thus, significantly lighter than their prior art counterparts. Smaller components may be used in the CMM1 in part because the amount of wires to carry signals within the CMM <NUM> has been significantly reduced when compared to prior art coordinate measuring machines. Prior art coordinate measuring machines needed significant space within shafts, housings, arm segments, etc. to route wires. Because of the arrangement of the electronics as described in <FIG> and the timing signals as described below, wiring may be significantly reduced in the CMM <NUM>, which contributes to its light weight.

<FIG> illustrates an exemplary timing chart of the exemplary electronics of <FIG> in operation. In operation, the main processor <NUM> may send (via wires <NUM> and <NUM>) a capture command at predetermined intervals (e.g., <NUM> microseconds) to the processors <NUM> of the encoder PCB <NUM>. As seen in <FIG>, each processor <NUM> receives the capture command. In response, an interrupt service routine in the processor <NUM> generates an internal capture with a fixed calibrated latency among encoder PCB <NUM> of, for example, <NUM> microseconds. As shown in <FIG>, the internal capture pulse may be active low (or activate high as shown in some of the other exemplary timing diagrams) and have a typical length of, for example, <NUM> microseconds.

<FIG> illustrates another exemplary timing chart of the exemplary electronics of <FIG> in operation. In operation, the main processor <NUM> may send (via wires <NUM> and <NUM>) capture commands at predetermined intervals (e.g., <NUM> microseconds) to each of the processors <NUM> of the encoder PCB <NUM>. As seen in <FIG>, each processor <NUM> receives their capture command. At (<NUM>) the first encoder processor <NUM> enables the serial line interrupt <NUM> data bytes or <NUM> (<NUM> * <NUM> bits/data byte * <NUM> ns/bit) after receiving its capture command. At (<NUM>) the second encoder processor <NUM> enables the serial line interrupt <NUM> data bytes or <NUM> (~<NUM>) µs after receiving its capture command and so on for the third to sixth encoder processors <NUM>. At (<NUM>) the <NUM>th encoder processor <NUM> enables the serial line interrupt <NUM> data bytes or <NUM> after receiving its capture command. At (<NUM>) option port processor <NUM> enables the serial line interrupt <NUM> data byte or <NUM> (~<NUM>) µs after receiving its capture command. Next, at (<NUM>), the main processor <NUM> sends a read data command to the first encoder processor <NUM>, a hardware interrupt is generated on the falling edge of the start bit, and an interrupt service routine in the processor <NUM> generates an internal capture in about <NUM>. As shown in <FIG>, the internal capture pulse may be active high (or active low as shown in some of the other exemplary timing diagrams) and have a typical length of, for example, <NUM> microseconds.

<FIG> illustrates another exemplary timing chart of the exemplary electronics of <FIG> in operation. As shown in <FIG>, the processor <NUM> could initiate an internal capture <NUM> microseconds after receiving the last capture command. This method may have a larger error than some of the methods described above mostly due to clock errors introduced by the use of different processors <NUM>.

<FIG> illustrates another exemplary timing chart of the exemplary electronics of <FIG> in operation. As shown in <FIG>, in dual pair (A-B pair and Y-Z pair, full duplex) serial configuration, once the capture command is received by the encoder processors <NUM>, each processor <NUM> enables the serial line interrupt. Next, the main processor <NUM> sends a read data command to the first encoder processor <NUM>, a hardware interrupt is generated on the falling edge of the start bit, and an interrupt service routine in the processor <NUM> generates an internal capture in about <NUM>.

<FIG> illustrates another exemplary timing chart of the exemplary electronics of <FIG> in operation. As shown in <FIG>, in dual pair (A-B pair and Y-Z pair, full duplex) serial configuration, once a capture command is received by the encoder processors <NUM>, each processor <NUM> can immediately initiate an Internal Capture with a typical latency of <NUM> microseconds. This method is less precise than some of the methods described above due to the variation in clock frequency of processors <NUM>.

As shown in <FIG>, on PCB <NUM> the interrupt service routine for capture command (n), stores and resets an interval timer/counter. The asynchronous trigger from, for example, the touch trigger probe accessory captures and stores the value of the interval timer/counter. On the subsequent capture command (n+<NUM>), the interval timer/counter is stored and reset.

To find the position of the probe <NUM> at the time the asynchronous trigger, the vector difference between positions (n) and (n+<NUM>) may be multiplied by the ratio of the asynchronous trigger captured value divided by the (n+<NUM>) position captured value and added to the position (n) vector. In an alternative embodiment, the asynchronous trigger may also have a fixed calibrated latency, which may be subtracted from the asynchronous trigger captured 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 trigger an internal timer/counter in the main processor <NUM>.

Thus, by accounting and correcting for latency at each PCB <NUM>, the electronics of the CMM <NUM> may take accurate measurements without requiring dedicated capture and trigger wires.

The definitions include various examples or forms of components that fall within the scope of a term and that may be used for implementation.

As used herein, an "operable connection" or "operable coupling," or a connection by which entities are "operably connected" or "operably coupled" is one in which the entities are connected in such a way that the entities may perform as intended. An operable connection may be a direct connection or an indirect connection in which an intermediate entity or entities cooperate or otherwise are part of the connection or are in between the operably connected entities. In the context of signals, an "operable connection," or a connection by which entities are "operably connected," is one in which signals, physical communications, or logical communications may be sent or received. Typically, an operable connection includes a physical interface, an electrical interface, or a data interface, but it is to be noted that an operable connection may include differing combinations of these or other types of connections sufficient to allow operable control. For example, two entities can be operably connected by being able to communicate signals to each other directly or through one or more intermediate entities like a processor, operating system, a logic, software, or other entity. Logical or physical communication channels can be used to create an operable connection.

"Signal," as used herein, includes but is not limited to one or more electrical or optical signals, analog or digital signals, data, one or more computer or processor instructions, messages, a bit or bit stream, or other means that can be received, transmitted, or detected.

To the extent that the term "includes" or "including" is employed in the detailed description or the claims, it is intended to be inclusive in a manner similar to the term "comprising" as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term "or" is employed in the detailed description or claims (e.g., A or B) it is intended to mean "A or B or both". When the applicants intend to indicate "only A or B but not both" then the term "only A or B but not both" will be employed. Thus, use of the term "or" herein is the inclusive, and not the exclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage <NUM> (2d.

Claim 1:
A portable coordinate measurement machine "CMM" (<NUM>) comprising:
a manually-positionable articulated arm (<NUM>) having first and second ends, the articulated arm including a plurality of arm segments (<NUM>, <NUM>) and a plurality of rotary joints (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), the first end including a connector configured to connect to a measurement probe (<NUM>) and the second end including a base (<NUM>);
wherein at least one of the rotary joints includes:
first and second bearings (<NUM>, <NUM>);
a shaft (<NUM>, <NUM>, <NUM>) that engages an inner diameter (32a) of the first bearing and an inner diameter (34a) of the second bearing, the shaft configured to rotate about an axis of rotation of the first bearing and the second bearing;
a housing (<NUM>, <NUM>, <NUM>, <NUM>) having at least one port (48b, 49b, <NUM>) that engages at least one of an outer diameter of the first bearing and an outer diameter of the second bearing; and
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,
wherein the at least one port of the housing has no portion whose diameter is narrower than the outer diameter of the first bearing or the outer diameter of the second bearing and/or the shaft has no portion whose diameter is larger than an inner diameter of the first bearing or an inner diameter of the second bearing; and.
wherein a first joint, from the plurality of joints, is attached to a second joint, from the plurality of joints, by a structure that is in contact with the inner or outer race of a bearing of the first joint or the inner or outer race of a bearing of the second joint, the structure fabricated from steel, stainless steel, or a controlled expansion alloy lighter in weight than steel and having a thermal expansion coefficient matching that of steel or stainless steel in the range of between of <NUM> to <NUM>/m°C at <NUM>.