Joint for coordinate measurement device

An articulating joint for a coordinate measurement machine can include an improved optical encoder. The optical encoder can have an encoder hub and a read head that are rotatable with respect to each other based on movement of the articulating joint about an axis of rotation of the joint. The encoder hub has a read surface. The read surface can be an outer surface of a generally cylindrical segment. The read head can be positioned such that a read direction defined by the read surface is generally perpendicular to the axis of rotation of the articulating joint.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates to measuring devices, and more particularly, to articulated arm coordinate measurement machines for measuring the coordinates of three-dimensional objects.

2. Description of the Related Art

Rectilinear measuring systems, also referred to as coordinate measuring machines (PCMM's) and articulated arm measuring machines, are used to generate geometry information. In general, these instruments capture the structural characteristics of an object for use in quality control, electronic rendering and/or duplication. One example of a conventional apparatus used for coordinate data acquisition is a portable coordinate measuring machine (PCMM), which is a portable device capable of taking highly accurate measurements within a measurement sphere of the device. Such devices often include a probe mounted on an end of an arm that includes a plurality of transfer members connected together by joints. The end of the arm opposite the probe is typically coupled to a moveable base. Typically, the joints are broken down into singular rotational degrees of freedom, each of which is measured using a dedicated rotational transducer. During a measurement, the probe of the arm is moved manually by a user to various points in the measurement sphere. At each point, the position of each of the joints must be determined at a given instant in time. Accordingly, each transducer outputs an electrical signal that varies according to the movement of the joint in that degree of freedom. Typically, the probe also generates a signal. These position signals and the probe signal are transferred through the arm to a recorder/analyzer. The position signals are then used to determine the position of the probe within the measurement sphere. See e.g., U.S. Pat. Nos. 5,829,148 and 7,174,651.

As mentioned above, the purpose of PCMM's is to take highly accurate measurements. Accordingly, there is a continuing need to improve the accuracy of such devices.

SUMMARY OF THE INVENTION

In one embodiment, a coordinate measuring machine is disclosed. The coordinate measurement machine comprises a first transfer member, a second transfer member, and an articulating joint assembly. The articulating joint assembly rotatably couples the first transfer member to the second transfer member and defines an axis of rotation. The articulating joint comprises a housing, a shaft, and an encoder assembly. The shaft is rotatable relative to said housing. The encoder assembly comprises a read head coupled to one of said housing and said shaft; and an encoder hub attached to the other of said housing and said shaft, the encoder hub having a read surface. The encoder read head and the read surface of the encoder hub define a read direction of the encoder assembly. The read direction is transverse to the axis of rotation of the articulating joint.

In another embodiment, an optical encoder is disclosed. The optical encoder comprises a housing, a shaft, an encoder hub, and a read head. The shaft is rotationally coupled to the housing and defines an axis of rotation. The encoder hub is disposed on the shaft. The encoder hub defines a read surface. The read head is rotationally fixed with respect to the housing. A read direction defined by the position of the read head with respect to the read surface is transverse to the axis of rotation of the shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates one embodiment of a coordinate measuring machine (PCMM)10. In the illustrated embodiment, the PCMM10comprises a base20, a plurality of substantially rigid, transfer members24,26, and28, a coordinate acquisition member30, and a plurality of articulation members40,42,44,46,48,50connecting the rigid transfer members24,26,28to one another. Each articulation member is configured to impart one or more rotational and/or angular degrees of freedom. The articulation members40,42,44,46,48, and50allow the transfer members24,26,28of the PCMM10to be aligned in various spatial orientations thereby allowing fine positioning of a coordinate acquisition member30in three-dimensional space.

The position of the rigid transfer members24,26,28and the coordinate acquisition member30may be adjusted manually, or using, robotic, semi-robotic, and/or any other adjustment method. In one embodiment, the PCMM10, through the various articulation members40,42,44,46,48,50, is provided with six rotary axes of movement. However, there is no strict limitation to the number or order of axes of movement that may be used, and, in other embodiments, a PCMM can have more or fewer axes of movement.

In the embodiment of PCMM10illustrated inFIG. 1, the articulation members40,42,44,46,48,50can be divided into two functional groupings based on their operation, namely: 1) those articulation members40,44, and48which allow the swiveling motion associated with a specific transfer member (hereinafter, “swiveling joints”), and 2) those articulation members42,46, and50which allow a change in the relative angle formed between two adjacent members or between the coordinate acquisition member30and its adjacent member (hereinafter, “hinge joints”). While the illustrated embodiment includes three swiveling joints and three hinge joints positioned as to create six axes of movement it is contemplated that in other embodiments, the number of and location of hinge joints and swiveling joints can be varied to achieve different movement characteristics in a PCMM. For example, a substantially similar device with seven axes of movement could simply have an additional swivel joint between the coordinate acquisition member30and articulation member50.

The coordinate acquisition member30can comprise a contact sensitive member or hard probe32configured to engage surfaces of a selected object and/or generate coordinate data on the basis of probe contact as is known in the art. Alternatively, the coordinate acquisition member30can comprise a remote scanning and detection component that does not necessarily require direct contact with the selected object to acquire geometry data. In one embodiment, a laser coordinate detection device (e.g., laser camera) can be used to obtain geometry data without direct object contact. It will be appreciated that in various embodiments of PCMMs, various coordinate acquisition member30configurations can be used including: a contact-sensitive probe, a remote-scanning probe, a laser-scanning probe, a probe that uses a strain gauge for contact detection, a probe that uses a pressure sensor for contact detection, a probe that used an infrared beam for positioning, and a probe configured to be electrostatically-responsive. Each of these can be used for the purposes of coordinate acquisition.

With continued reference toFIG. 1, in various embodiments of the PCMM10, the various devices which may be used for coordinate acquisition, such as the probe32, may be configured to be manually disconnected and reconnected from the PCMM10such that a user can change coordinate acquisition devices without specialized tools. Thus, a user can quickly and easily remove one coordinate acquisition device and replace it with another coordinate acquisition device. Such a connection may comprise any quick disconnect or manual disconnect device. This rapid connection capability of a coordinate acquisition device can be particularly advantageous in a PCMM10that can be used for a wide variety of measuring techniques (e.g. measurements requiring physical contact of the coordinate acquisition member with a surface followed by measurements requiring only optical contact of the coordinate acquisition member) in a relatively short period of time.

In the embodiment ofFIG. 1, the coordinate acquisition member30also comprises buttons66, which are configured to be accessible by a user. By pressing one or more of the buttons66singly, multiply, or in a preset sequence, the user can input various commands to the PCMM10. In some embodiments the buttons66can be used to indicate that a coordinate reading is ready to be recorded. In other embodiments the buttons66can be used to indicate that the location being measured is a home position and that other positions should be measured relative to the home position. In other embodiments the buttons may be used to turn on or off the PCMM10. In other embodiments, the buttons66can be programmable to meet a user's specific needs. The location of the buttons66on the coordinate acquisition member30can be advantageous in that a user need not access the base20or a computer in order to activate various functions of the PCMM10while using the coordinate acquisition member30. This positioning may be particularly advantageous in embodiments of PCMM having transfer members24,26, or28that are particularly long, thus placing the base20out of reach for a user of the coordinate acquisition member30. In some embodiments of the PCMM10, any number of user input buttons (e.g., more or fewer than the three illustrated inFIG. 1), can be provided, which may be placed in various other positions on the coordinate acquisition member30or anywhere on the PCMM10. Other embodiments of PCMM can include other user input devices positioned on the PCMM or the coordinate acquisition member30, such as switches, rotary dials, or touch pads in place of, or in addition to user input buttons.

With continued reference toFIG. 1, in some embodiments, the base20further comprises magnetic attachment mounts60that can attach the base20to a metallic work surface. The magnetic attachment mounts60can desirably be selectively engaged so that a user can position the PCMM10on to a work surface then engage the magnetic attachment mounts60once the PCMM10has been placed in a desirable position. In other embodiment, the base20can be coupled to a work surface through a vacuum mount, bolts or other coupling devices. Additionally, in some embodiments, the base20can comprise various electrical interfaces such as plugs, sockets, or attachment ports62. In some embodiments, attachment ports62can comprise connectability between the PCMM10and a USB interface for connection to a processor such as a general purpose computer, an AC power interface for connection with a power supply, or a video interface for connection to a monitor. In some embodiments, the PCMM10can be configured to have a wireless connection with an external processor or general purpose computer such as by a WiFi connection, Bluetooth connection, RF connection, infrared connection, or other wireless communications protocol. In some embodiments, the various electrical interfaces or attachment ports62can be specifically configured to meet the requirements of a specific PCMM10.

With continued reference toFIG. 1, in some embodiments, the base20of the PCMM10can also include a self contained power source64such as a battery. Embodiments of PCMM10having a self contained power source can be easily moved to various locations that do not have easy access to a power source such as an AC power outlet, allowing enhanced flexibility in the operating environment of the PCMM10. In one embodiment, the self-contained power source64can be a lithium-ion rechargeable battery that can provide power to the PCMM for periods of use away from a power outlet. In other embodiments, the self-contained power source64can be other types of rechargeable batteries such as nickel cadmium, nickel metal hydride, or lead acid batteries. In other embodiments, the self-contained power source64can be a single use battery such as an alkaline battery.

With continued reference toFIG. 1, the transfer members24,26, and28are preferably constructed of hollow generally cylindrical tubular members so as to provide substantial rigidity to the members24,26, and28. The transfer members24,26, and28can be made of any suitable material which will provide a substantially rigid extension for the PCMM10. As will be discussed in greater detail below, the transfer members24,26, and28preferably define a double tube assembly so as to provide additional rigidity to the transfer members24,26, and28. Furthermore, it is contemplated that the transfer members24,26, and28in various other embodiments can be made of alternate shapes such as those comprising a triangular or octagonal cross-section.

In some embodiments, it can be desirable to use a composite material, such as a carbon fiber material, to construct at least a portion of the transfer members24,26, and28. In some embodiments, other components of the PCMM10can also comprise composite materials such as carbon fiber materials. Constructing the transfer members24,26,28of composite such as carbon fiber can be particularly advantageous in that the carbon fiber can react less to thermal influences as compared to metallic materials such as steel or aluminum. Thus, coordinate measurement can be accurately and consistently performed at various temperatures. In other embodiments, the transfer members24,26,28can comprise metallic materials, or can comprise combinations of materials such as metallic materials, ceramics, thermoplastics, or composite materials. Also, as will be appreciated by one skilled in the art, many of the other components of the PCMM10can also be made of composites such as carbon fiber. Presently, as the manufacturing capabilities for composites are generally not as precise when compared to manufacturing capabilities for metals, generally the components of the PCMM10that require a greater degree of dimensional precision are generally made of a metals such as aluminum. It is foreseeable that as the manufacturing capabilities of composites improved that a greater number of components of the PCMM10can be also made of composites.

With continued reference toFIG. 1, some embodiments of the PCMM10may also comprise a counterbalance system80that can assist a user by mitigating the effects of the weight of the transfer members26and28and the articulating members44,46,48, and50. In some orientations, when the transfer members26and28are extended away from the base20, the weight of the transfer members26and28can create difficulties for a user. Thus, a counterbalance system80can be particularly advantageous to reduce the amount of effort that a user needs to position the PCMM for convenient measuring. In some embodiments, the counterbalance system80can comprise resistance units (not shown) which are configured to ease the motion of the transfer members26and28without the need for heavy weights to cantilever the transfer members26and28. It will be appreciated by one skilled in the art that in other embodiments simple cantilevered counterweights can be used in place or in combination with resistance units.

In the embodiment illustrated inFIG. 1, the resistance units are attached to the transfer member26to provide assisting resistance for motion of the transfer members26and28. In some embodiments, the resistance units can comprise hydraulic resistance units which use fluid resistance to provide assistance for motion of the transfer members26and28. In other embodiments the resistance units may comprise other resistance devices such as pneumatic resistance devices, or linear or rotary spring systems.

With continued reference toFIG. 1, the position of the probe32in space at a given instant can be calculated if the length of each transfer member24,26, and28and the specific position of each of the articulation members40,42,44,46,48, and50are known. The position of each of the articulation members40,42,44,46,48, and50can be measured as a singular rotational degree of motion using a dedicated rotational transducer, which will be described in more detail below. Each transducer can output a signal (e.g., an electrical signal), which can vary according to the movement of the40,42,44,46,48,50in its degree of motion. The signal can be carried through wires or otherwise transmitted to the base20of the PCMM10. From there, the signal can be processed and/or transferred to a computer for determining the position of the probe32in space.

In some embodiments of PCMM10, a rotational transducer for each of the articulation members40,42,44,46,48., and50can comprise an optical encoder. Various embodiments of optical encoder are discussed in more detail below with reference toFIGS. 3-6. In general, an optical encoder measures the rotational position of an axle by coupling its movement to a pair of internal hubs having successive transparent and opaque bands. In such embodiments, light can be shined through or reflected from the hubs onto optical sensors which feed a pair of electrical outputs. As the axle sweeps through an arc, the output of an analog optical encoder can be substantially two sinusoidal signals which are 90 degrees out of phase. Coarse positioning can be determined through monitoring a change in polarity of the two signals. Fine positioning can be determined by measuring an actual value of the two signals at a specific time. In certain embodiments, enhanced accuracy can be obtained by measuring the output precisely before it is corrupted by electronic noise. Thus, digitizing the position information before it is sent to the processor or computer can lead to enhanced measurement accuracy.

As will be described in detail below, in the illustrated embodiment, the articulation members40,42,44,46,48, and50can be divided into two general categories, namely: 1) articulation members40,44,48, which allow swiveling motion of a transfer member24,26,28and are thus sometimes referred to as “swivel members”40,44,48herein and 2) articulation members42,46and50, which allow for change in the relative angle formed between two adjacent members and are sometimes referred to herein as “pivot or hinge members”42,46,50.

While several embodiment and related features of a PCMM10have been generally discussed herein, additional details and embodiments of PCMM10can be found in U.S. Pat. Nos. 5,829,148 and 7,174,651, and the entirety of these patents are hereby incorporated by reference herein. While certain features below are discussed with reference to the embodiments of PCMM10described above, it is contemplated that they can be applied in other embodiments of PCMM such as those described in U.S. Pat. Nos. 5,829,148 or 7,174,651, or some other pre-existing PCMM designs, or PCMM designs to be developed.

Referring now toFIG. 2, a cross-sectional view of a transfer member26and articulating member44is illustrated. While this view illustrates a single transfer member28in the PCMM10, other transfer members24,28of the PCMM10can have similar construction. The transfer member26preferably comprises a distal end98and a proximal end99. As described herein, the terms distal and proximal are used to describe relative ends of the PCMM10and its associated components with the base20being the proximal end and probe32being the distal end (SeeFIG. 1). The terms distal and proximal are meant only to simplify description and are in no way intended to limit the scope of the technology described herein.

Beginning with the tubular assembly illustrated inFIG. 2, the transfer member26preferably comprises an inner shaft102and an outer housing104. The inner shaft102is preferably configured to be rotated independently of the outer housing104so as to provide rotational freedom for the transfer member26. The inner shaft102can desirably rotate on a first bearing118and also on, preferably, a compliant bearing133that are positioned at opposite ends of the inner shaft102and the outer housing104. This configuration is particularly advantageous in that the bearings118and133are located relatively far apart so as to provide a very stable rotating interface between the inner shaft102and the outer housing104. In the illustrated embodiment, the bearings118,133are desirably press fit so as to provide a secure rotating interface between the inner shaft102and the outer housing104. Furthermore, in some embodiments, it may be preferable to appropriately preload the bearings118,133so that any unwanted axial movement of the inner shaft102relative to the outer housing104is minimized. In other embodiments, the bearings can be positioned at different locations to provide a rotating interface between the inner shaft102and the outer housing104. In still other embodiments more or fewer than two bearings118,133can provide a rotating interface between the inner shaft102and outer housing104of the transfer member26. For example, a single bearing positioned on the proximal end can provide the rotating interface. In some embodiments, the second bearing133is a compliant bearing including an O-ring135extending therearound. In some embodiments, a bearing120of the encoder assembly128can be a compliant bearing, and the two bearings118,133of the transfer member26can be rigid bearings. In some embodiments, bushings can be substituted for bearings.

As illustrated inFIGS. 1 and 2, both the inner shaft102and the outer housing104comprise generally cylindrical members. This generally cylindrical construction can be advantageous because it offers construction simplicity, rigidity, light weight, and space inside for a printed circuit board which will be discussed in greater detail below. Also, as shown inFIG. 2, the generally cylindrical shape allows concentric mounting of an inner shaft102having an outer diameter approaching the inner diameter of the outer housing104, thereby increasing rigidity while maintaining low weight and a sleek profile. In some embodiments, the outer diameter of the inner shaft102is desirably at least 50%, and more preferably at least 75% of the inner diameter of the outer housing104. In some embodiments the inner shaft102and outer housing104can comprise alternate shapes. For example, in some embodiments, the inner shaft102can comprise a solid shaft as opposed to a tubular member. Furthermore, in other embodiments the inner shaft and outer housing104can comprise substantially polygonal cross-sectional profiles such as an octagonal shape, a triangular shape, or a square shape.

With continued reference toFIG. 2, the inner shaft102can desirably comprise an inner tubular member106that comprises a first end cap110and a second end cap112. Furthermore, the outer housing104can comprise an outer tubular member108, a first end cap114and a second end cap116. The assembly of the inner and outer tubular members106,108can form the transfer member26. The transfer member26thus formed can provides a substantially rigid structure defining a reach distance for the PCMM10.

In some embodiments, the end caps110,112,114,116can provide precision machined bearing surfaces for the bearings118and133. Further, the end caps110,112,114,116can provide precision concentricity to the articulating member44. In some embodiments, it is preferable that the end-caps110,112,114,116are bonded to the tubular members106and108in such a way that the resulting inner shaft102and outer housing104are precisely and accurately balanced. One method of assuring this balance involves allowing an adhesive agent such as a glue or epoxy to cure while the bonded assembly is being rotated. Other suitable securing methods may be used to secure the end caps110,112,114, and116to the tubular members106and108. In some embodiments of PCMM, such suitable securing methods can also comprise mechanical fastening means such as a threaded interface, a plurality of screws or bolts, press fit (such as interference fit), thermal fit, tapered fit, or any combinations thereof.

In some embodiments, when the end caps110,112,114, and116are bonded to the tubular members106in108using an adhesive agent such as a glue or epoxy, portions of the interior surface of the inner tubular member106and the outer tubular member108may be scored, wire brushed, or otherwise grooved to provide a more positive bonding surface for the adhesive agent. Likewise, corresponding surfaces of the end-caps110,112,114, and116may be scored in place of or in addition to tubular member scoring.

In some embodiments, it can be desirable that the end caps110,112,114,116comprise a different material than the inner and outer tubular members106,108. Thus, in some embodiments, precision machined metallic end caps can be used together with carbon fiber tubular members106,108. In these embodiments, the metallic end caps110,112,114,116can provide precision bearing mounting surfaces while the carbon fiber tubular members106,108can achieve beneficial thermal growth properties. In other embodiments it may be preferable to construct the entire inner shaft102and the outer housing104of a single material, such as carbon fiber.

In the embodiment illustrated inFIG. 2, the first end cap110of the inner shaft102, comprises mounting holes122positioned radially around the end cap110. The mounting holes122can be used to attach another articulating member, such as the articulating member46to the transfer member26. The mounting holes122can also be used to attach an extending member to the articulating member26so as to provide additional range of movement or reach to the PCMM10. For example, in one embodiment, a pair of transfer members28can be coupled to each other to extend the reach of the device. The illustrated arrangement of the mounting holes122is particularly advantageous in that a relatively large number of fasteners can be used to secure an additional articulating member or an additional extension number thus providing a substantially secure and concentric attachment.

FIG. 3illustrates a detail view of the articulating member44ofFIG. 2. With reference toFIG. 3, a cover piece124can be coupled to the second end cap116of the outer housing104. The cover piece124can extend proximally so as to accommodate internal components of the articulating member44which reside towards a proximal end of the articulating member44. In the illustrated embodiment, a slip ring assembly126and an encoder assembly128are housed within the cover124. The slip ring assembly126, in some embodiments, can be substantially similar to the slip ring assembly described in U.S. Pat. No. 5,829,148 issued on Nov. 3, 1998. In other embodiments, different slip ring assemblies can be housed with the encoder assembly128. In still other embodiments, no slip ring assembly126is present. Embodiments of the encoder assembly128will be described in detail below.

With continued reference toFIG. 3, in the illustrated embodiment, the encoder assembly128comprises a read head130, an encoder hub132, a housing131, encoder shaft137and a bearing120mounted between the housing131and encoder shaft133. In some embodiments, the bearing120can be a compliant bearing. In these embodiments, both bearings118,133of the transfer member28can be rigid. The encoder hub132can be mounted on the encoder shaft137, which, in turn, can be inserted into the second end cap112of the inner shaft102. A hub mounting portion134extends proximally from the encoder hub132. The hub mounting portion134can comprise a tapered portion over which the encoder hub132can mount. In the illustrated embodiment, the encoder hub132preferably comprises a tapered recess138which closely matches a tapered portion136of the hub mounting portion134. In some embodiments, this matched tapered fit can rotationally fix the encoder hub132to the encoder shaft137. In other embodiments, it is desirable that the encoder hub132is further and/or alternatively attached to the hub mounting portion134with fasteners or an adhesive agent in addition to the tapered fit. The taper mounted design advantageously allows for the eccentricity between the hub and the axis to be minimized during mounting of the encoder hub132to the encoder shaft137. However, in other embodiments, the encoder hub132could be mounted directly to the encoder shaft137using bolts, adhesive, press fit or temperature fit with or without a taper interface. While in the illustrated embodiment, the encoder hub132is rotationally fixed to encoder shaft137, in other embodiments, the encoder hub132can be directly mounted to the inner shaft102, the end cap112and/or another intermediate member.

In some embodiments, it is preferable that the encoder assembly128can be a light emitting diode (LED) encoder design. A reflective LED encoder design can provide particular advantages in that the light is reflected back to the read head130instead of being passed through gratings of the encoder hub132. This reflective arrangement simplifies the encoder assembly128so as to not require an additional light source to pass light through optical demarcations or grating of the encoder hub132. In other embodiments, a laser light source can be used. In other embodiments, the encoder can be a magnetic encoder rather than an optical encoder, and the encoder hub can include a magnetic pattern disposed thereon. In some embodiments of the encoder assembly128the encoder hub132is a RESR Taper Mounted Encoder hub as produced by Renishaw of the UK. Furthermore, in some embodiments the read head130is a type RGH35 also produced by Renishaw of the UK. These aforementioned devices are strictly examples of a read head and an encoder hub that can be used with one embodiment of the PCMM10. In other embodiments, any suitable read head130or encoder hub132can also be used.

With continued reference toFIG. 3, in the illustrated embodiment, the read head130and the encoder hub132are arranged such that a read surface140of the encoder hub132is on a radially outer surface of the encoder hub132and the read head132is positioned radially outwards of the read surface140. In some embodiments, the read head130can be attached to a bracket162, which secures the read head130in a relatively stable position relative to the encoder hub132. In some embodiments, the bracket162may be also used to secure the slip ring assembly126and/or a printed circuit board which will be discussed in greater detail below. In other embodiments, the read head130, slip ring assembly126, and printed circuit board can each be retained by separate brackets, or can be retained by mounting features formed in the surface of the cover124.

In a preferred embodiment of the encoder, a read direction of the encoder assembly128is substantially perpendicular to the rotation axis RA of the articulating member, and the optical demarcations or gratings on the read surface are parallel to the rotation axis RA of the encoder assembly. This orientation of read direction is in opposition of a “disc style encoder” in which the read direction is parallel to a rotation axis RA of the encoder assembly128and gratings are arranged perpendicular relative to the rotation axis RA of the encoder assembly128. As noted below, in other embodiments, other read head and read surface arrangements can be made. In the illustrated embodiment, optical demarcations or gratings on the read surface140are preferably parallel to a rotation axis RA of the encoder assembly128. In some embodiments, the demarcations can be placed directly on the shaft137, eliminating the need for a separate hub or disk. In some embodiments, the optical demarcations are not substantially parallel to the rotation axis RA (e.g., the optical demarcations could be transverse to the RA). In some embodiments, a read direction of the encoder assembly128is transverse to the rotation axis RA of the articulating member44. In the illustrated embodiment, the read direction of the encoder assembly128is substantially perpendicular to the rotation axis RA of the articulating member. It is contemplated that still other embodiments of encoder assembly can include various combinations of read direction configuration and optical demarcation orientation. For example, it is contemplated that some embodiments, an encoder can have a read direction that is transverse to the rotation axis RA and optical demarcations that are not substantially parallel to the rotation axis RA (e.g., the optical demarcations could be transverse to the RA).

The preferred configuration of read direction described above can be particularly advantageous in that the circumference that the demarcations are placed on is greater than it would be for a disc style encoder of the same diameter. This increased circumference can yield a larger number of demarcations per revolution, thus increasing the resolution of the axis. This fine resolution is achieved in part because the read surface148is placed on a radially outer surface of the encoder hub132, thus providing a relatively large readable surface area on the encoder hub132. Thus, in some embodiments of optical encoder assembly128having optical demarcations on the read surface140of the encoder hub132, there are a greater number of optical demarcations. This fine resolution is particularly advantageous in a PCMM10because the greater the resolution that can be achieved by the encoder assembly128, the greater the accuracy of the measurement that can be achieved by the PCMM10.

In a “disc style encoder”, the read head and the encoder disc are arranged in a direction such that they can be detrimentally affected by thermal expansion. In these disc-style encoders, the inner shaft102and the bracket162could change in dimensions by differing amounts under certain conditions in response to temperature variations, causing the read head to move closer to or further away from the grating. This thermal response by the disc-style encoder could greatly affect the accuracy of readings by the encoder under certain thermal conditions. However, in the embodiments of encoder assembly128described above, the read surface140and read head130are positioned such that the read direction is perpendicular to the rotation axis RA. Thus, the change in encoder signal due to temperature variations is greatly reduced. This improved thermal response can in part be attributed to the fact that if thermal expansion does take place it is less likely to affect the distance between the read head130in the encoder hub132because the read head130and the encoder hub132are located on surfaces which are generally thermally similar. Furthermore, if thermal expansion were to take place, it is likely that the encoder hub132would simply displace laterally relative to the read head130, thus minimally affecting the accuracy of the encoder assembly128as compared to thermal expansion which may influence the distance between the read head130and the encoder hub132.

While a particular configuration of read head130and encoder hub132is illustrated, other embodiments are contemplated. In one embodiment, the encoder hub132can be externally mounted with respect to the housing124. This external mounting arrangement allows for easy setup and alignment of the encoder hub132to the hub mounting portion134. In another embodiment both the encoder hub132and read head130can be located outside of the cover124for easy alignment of the read head130to the encoder hub132. In yet another embodiment, the encoder hub132may be surrounded by a portion of the cover124, but the read head130is external to the cover124. In yet another embodiment both the read head130and the encoder hub132are internal to the cover124.

In various other embodiments, it can be desirable to use an encoder assembly128which comprises multiple read heads130. For example, in some embodiments, the encoder assembly128may comprise three read heads130positioned at approximately 120° intervals around the encoder hub132such that the read heads130read the read surface140at multiple locations. This arrangement of read heads130may be particularly advantageous if any eccentricity is present in the encoder hub132as the multiple read heads130can cross check one another and reduce any inaccuracy produced by eccentricity of the encoder hub132. Furthermore, it is also contemplated that in one embodiment of the encoder assembly128, multiple read heads130can be included while data may be collected from only one read head130at any given time. In various embodiments, any number of read heads130can be used with the most common being 1, 2, 3, or 4.

With continued reference toFIG. 3, the second end cap116of the outer housing104preferably is also attached to a mounting clamp142that provides a mounting location for the articulating member44to mount to another articulating member assembly. The mounting clamp142can comprise a mounting base148, which, in some embodiments, can be integrally formed with the end cap116. The mounting base148preferably extends from the articulating member44and is attached to a face plate146by fasteners144. The face plate146and the mounting base148can define a mounting hole150which is configured to attach to an axle of another articulating member assembly as described in greater detail below.

With reference toFIG. 4, a proximal end of the articulating member44is illustrated with the cover124removed for clarity. In some embodiments, the articulating member44preferably also comprises a processor such as a printed circuit board160operatively coupled to the encoder assembly128. The printed circuit board160preferably can be used to process an electronic signal generated by the encoder assembly128. In some embodiments, the printed circuit board160can be used to convert an analog signal generated by the encoder assembly128to a digital signal. The printed circuit board160can be operatively coupled to a processor or other computer via a wired or wireless link and can transmit the digital signal to the processor or computer. In the illustrated embodiment, the printed circuit board is desirably located proximally of the encoder hub132and is further supported by the bracket162. In some embodiments, the bracket162can be also configured to support the slip ring assembly126and/or the read head130(seeFIG. 3). The location of the printed circuit board160, as illustrated inFIG. 4can be particularly advantageous in that it provides a relatively out-of-the-way position for the printed circuit board such that the operation of the encoder assembly128and the slip ring assembly126are not impeded by the printed circuit board160. Furthermore, in the illustrated embodiments, the printed circuit board160is housed within the cover124, thus providing protection from bumping or contamination. In other embodiments, other positions for the printed circuit board160may also be employed, such as that illustrated inFIG. 5described in greater detail below.

FIG. 5, illustrates the articulation member or hinge member46ofFIG. 1decoupled from the transfer member26and the transfer member28. The articulation member46can comprise a housing yoke202supporting a shaft204. In some embodiments of PCMM10, the shaft204can be clamped by a mounting clamp associated with the articulating member48, similar to the mounting clamp142of the articulating member44(FIG. 3). The housing yoke202can desirably support the shaft204at two locations so as to provide an exposed region of the shaft202. This exposed region of the shaft204can be clamped by the mounting clamp142. In the illustrated embodiments, the housing yoke202extends downwards to a mounting member206comprising mounting holes208As illustrated, the mounting holes208configured to mate with the holes122of the transfer member26(seeFIG. 2). In some embodiments, a cover210is attached to one external side of the housing yoke202. The cover210is configured to house internal workings of the articulating member46. In some embodiments, an encoder assembly is housed within the cover210.

FIG. 6is an illustration of a cross-sectional view of the articulating member46ofFIG. 5. In some embodiments, the articulating member46comprises bearings216,218which support opposing ends of the shaft204so as to provide a smooth rotational interface for the shaft204relative to the housing yoke202. In some embodiments, the shaft204can include an encoder mount portion220. In some embodiments, the mount portion220can be formed to a tapered mount portion222configured to receive an encoder hub224. The encoder hub224can comprises a tapered recess226which is sized and shaped to closely receive the tapered mount portion222of the shaft204.

Similar to the encoder assembly illustrated inFIG. 3above with respect to a swiveling articulation member, the encoder assembly212illustrated inFIG. 6comprises an encoder hub224and a read head230. The encoder hub224can comprise a read surface228that is located on a radially outer surface thereof. Furthermore, the read head230can be mounted to the housing yoke202. The read head can be configured to read optical demarcations on the read surface228of the encoder hub224.

Once again, the arrangement of the encoder hub224and the read head230can be particularly advantageous in that the read surface228is located on the encoder hub224such that a relatively large number of optical demarcations can be placed on the encoder hub with relatively large spacing between adjacent demarcations. Thus, relatively fine resolution can be achieved by the encoder assembly212. Furthermore, in some embodiments, the optical demarcations can be oriented such that they are substantially parallel to a rotation axis RA2of the encoder assembly212. Furthermore, similar to the encoder assembly128described above with respect toFIG. 3, the relative positioning of the encoder hub224and the read head230can orient the read direction of the optical encoder assembly212transversely to the rotational axis RA2of the encoder assembly212. In some embodiments, the read direction of the encoder assembly212can be substantially perpendicular to the rotation axis RA2.

With continued reference toFIG. 6, a printed circuit board214can extend below the mounting member206. The printed circuit board214preferably can be used to process an electronic signal generated by the encoder assembly212. In some embodiments, the printed circuit board214can be used to convert an analog signal generated by the encoder assembly128to a digital signal. The printed circuit board214, like the printed circuit board160, can be operatively coupled to a processor or other computer via a wired or wireless link and can transmit the digital signal to the processor or computer. One particular advantage of the location of the printed circuit board214is that when the articulating member46is assembled with the transfer member26(FIG. 1), the printed circuit board214will preferably extend within the transfer member26. Thus, the transfer member26can provide a protective covering for the printed circuit board214. This covering arrangement can be particularly advantageous in that the transfer member26achieves a dual purpose by acting as both a protective member and a structural member of the PCMM10.