Counter balance for coordinate measurement device

A portable articulated arm coordinate measurement device is provided. The coordinate measurement device includes a base and an articulated arm portion having at least one arm segment. A biasing member is coupled on a first end to the base and on a second end to the articulated arm portion. The first end of the biasing member is movable between a first position and a second position. An adjuster is coupled between the base and the biasing member. The adjuster is coupled to move the first end of the biasing member from the first position to the second position.

BACKGROUND

The present disclosure relates to a coordinate measuring machine, and more particularly to a portable articulated arm coordinate measuring machine having an adjustable counterbalance system.

Portable articulated arm coordinate measuring machines (AACMMs) have found widespread use in the manufacturing or production of parts where there is a need to rapidly and accurately verify the dimensions of the part during various stages of the manufacturing or production (e.g., machining) of the part. Portable AACMMs represent a vast improvement over known stationary or fixed, cost-intensive and relatively difficult to use measurement installations, particularly in the amount of time it takes to perform dimensional measurements of relatively complex parts. Typically, a user of a portable AACMM simply guides a probe along the surface of the part or object to be measured. The measurement data are then recorded and provided to the user. In some cases, the data are provided to the user in visual form, for example, three-dimensional (3-D) form on a computer screen. In other cases, the data are provided to the user in numeric form, for example when measuring the diameter of a hole, the text “Diameter=1.0034” is displayed on a computer screen.

An example of a prior art portable articulated arm CMM is disclosed in commonly assigned U.S. Pat. No. 5,402,582 ('582), which is incorporated herein by reference in its entirety. The '582 patent discloses a 3-D measuring system comprised of a manually-operated articulated arm CMM having a support base on one end and a measurement probe at the other end. Commonly assigned U.S. Pat. No. 5,611,147 ('147), which is incorporated herein by reference in its entirety, discloses a similar articulated arm CMM. In the '147 patent, the articulated arm CMM includes a number of features including an additional rotational axis at the probe end, thereby providing for an arm with either a two-two-two or a two-two-three axis configuration (the latter case being a seven axis arm).

The articulated arm may be of a variety of lengths, typically between two feet and four feet for example. To ease the use of the arm, a counter balance arrangement may be coupled to a fixed base to offset the torque applied by the weight of the articulated arm. The counter balance allows the articulated arm to be moved by the user with little effort and prevents the articulated arm from falling if released by the user. Unfortunately, in some circumstances the counter balance may apply too much, or too little torque due to differences in components, tolerances, configurations, and accessories of the articulated arm. As a result, rather than moving freely, the articulated arm may sag or resist movement depending on whether too little or too much counter balance is applied.

Accordingly, while existing articulated arms are suitable for their intended purposes what is needed is an AACMM having an improved adjustment and calibration of a counter balance for the articulated arm.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, a portable articulated arm coordinate measurement device (AACMM) for measuring coordinates of an object in space is provided. The AACMM includes a base. A manually positionable articulated arm portion is provided having an opposed first end and second end, the arm portion being rotationally coupled to the base, the arm segment including a plurality of connected arm segments, each of the arm segments including at least one position transducer for producing a position signal. A measurement device is attached to the first end. An electronic circuit is provided for receiving the position signals from the transducers and for providing data corresponding to a position of the measurement device. A rotation assembly is coupled to the second end to the base, the rotation assembly having a first axis of rotation and a second axis of rotation substantially perpendicular to the first axis of rotation. A biasing member is operably coupled between the rotation assembly and the second end to apply a force to the second end about the second axis of rotation the biasing member having at least one projection thereon. An adjuster having a threaded portion is arranged to engage the at least one projection, wherein the force applied by the biasing member to the arm portion changes in response to movement of the adjuster.

In accordance with another embodiment of the invention, another AACMM is provided. The AACMM includes a base. A manually positionable articulated arm portion is provided having an opposed first end and second end, the arm portion including a plurality of connected arm segments, each of the arm segments including at least one position transducer for producing a position signal. A measurement device is attached to the first end. An electronic circuit is provided for receiving the position signals from the transducers and for providing data corresponding to a position of the measurement device. A biasing member is operably coupled between the base and the second end, the biasing member having at least one projection movable between a first position and a second position. An adjuster having a threaded portion is operably coupled between the base and the biasing member, wherein the threaded portion is engaged to the at least one projection to move the at least one projection between the first position to the second position.

In accordance with another embodiment of the invention, another AACMM for measuring coordinates of an object in space is provided. The AACMM includes a base. A manually positionable articulated arm portion is provided having an opposed first end and second end, the arm portion including a plurality of connected arm segments, each arm segment including at least one position transducer for producing a position signal. A measurement device is attached to the first end. An electronic circuit is provided which receives the position signals from the transducers and provides data corresponding to a position of the measurement device. A rotation assembly is rotationally coupled to the second end to the base about a first axis of rotation and a second axis of rotation, the second axis of rotation being substantially perpendicular to the first axis of rotation. A biasing member is arranged within the rotation assembly and having a third end operably coupled to the second end, the biasing member having a fourth end opposite the third end, the fourth end being movable between a first position and a second position. An adjusting member is operably coupled for rotation to the base and operably coupled to the fourth end, wherein the fourth end moves between the first position and the second position in response to a rotation of the adjusting member.

DETAILED DESCRIPTION

Portable articulated arm coordinate measuring machines provide manufacturers and others with a convenient and flexible way to obtain high quality, high precision measurements of parts, components and objects. To provide this flexibility, the AACMM may have a multi-segmented arm having many degrees of freedom. Embodiments of the present invention provide advantages in offsetting the weight of the multi-segmented arm allowing the operator to make measurements with less effort and higher reliability. Embodiments of the present invention also provide advantages in providing a counter balance that is adjustable to compensate for differences in weights, tolerances and accessories associated with the multi-segmented arm.

FIGS. 1A and 1Billustrate, in perspective, a portable articulated arm coordinate measuring machine (AACMM)100according to various embodiments of the present invention, an articulated arm being one type of coordinate measuring machine. As shown inFIGS. 1A and 1B, the exemplary AACMM100may comprise a six or seven axis articulated measurement device having a measurement probe housing102coupled to an arm portion104of the AACMM100at one end. The arm portion104comprises a first arm segment106coupled to a second arm segment108by a first grouping of bearing cartridges110(e.g., two bearing cartridges). A second grouping of bearing cartridges112(e.g., two bearing cartridges) couples the second arm segment108to the measurement probe housing102. A third grouping of bearing cartridges114(e.g., three bearing cartridges) couples the first arm segment106to a base116located at the other end of the arm portion104of the AACMM100. Each grouping of bearing cartridges110,112,114provides for multiple axes of articulated movement. Also, the measurement probe housing102may comprise the shaft of the seventh axis portion of the AACMM100(e.g., a cartridge containing an encoder system that determines movement of the measurement device, for example a probe118, in the seventh axis of the AACMM100). In use of the AACMM100, the base116is typically affixed to a work surface.

Each bearing cartridge within each bearing cartridge grouping110,112,114typically contains an encoder system (e.g., an optical angular encoder system). The encoder system (i.e., transducer) provides an indication of the position of the respective arm segments106,108and corresponding bearing cartridge groupings110,112,114that all together provide an indication of the position of the probe118with respect to the base116(and, thus, the position of the object being measured by the AACMM100in a certain frame of reference—for example a local or global frame of reference). The arm segments106,108may be made from a suitably rigid material such as but not limited to a carbon composite material for example. A portable AACMM100with six or seven axes of articulated movement (i.e., degrees of freedom) provides advantages in allowing the operator to position the probe118in a desired location within a 360° area about the base116while providing an arm portion104that may be easily handled by the operator. However, it should be appreciated that the illustration of an arm portion104having two arm segments106,108is for exemplary purposes, and the claimed invention should not be so limited. An AACMM100may have any number of arm segments coupled together by bearing cartridges (and, thus, more or less than six or seven axes of articulated movement or degrees of freedom).

The probe118is detachably mounted to the measurement probe housing102, which is connected to bearing cartridge grouping112. A handle126is removable with respect to the measurement probe housing102by way of, for example, a quick-connect interface. The handle126may be replaced with another device (e.g., a laser line probe, a bar code reader), thereby providing advantages in allowing the operator to use different measurement devices with the same AACMM100. In exemplary embodiments, the probe housing102houses a removable probe118, which is a contacting measurement device and may have different tips118that physically contact the object to be measured, including, but not limited to: ball, touch-sensitive, curved and extension type probes. In other embodiments, the measurement is performed, for example, by a non-contacting device such as a laser line probe (LLP). In an embodiment, the handle126is replaced with the LLP using the quick-connect interface. Other types of measurement devices may replace the removable handle126to provide additional functionality. Examples of such measurement devices include, but are not limited to, one or more illumination lights, a temperature sensor, a thermal scanner, a bar code scanner, a projector, a paint sprayer, a camera, or the like, for example.

As shown inFIGS. 1A and 1B, the AACMM100includes the removable handle126that provides advantages in allowing accessories or functionality to be changed without removing the measurement probe housing102from the bearing cartridge grouping112. As discussed in more detail below with respect toFIG. 2, the removable handle126may also include an electrical connector that allows electrical power and data to be exchanged with the handle126and the corresponding electronics located in the probe end.

In various embodiments, each grouping of bearing cartridges110,112,114allows the arm portion104of the AACMM100to move about multiple axes of rotation. As mentioned, each bearing cartridge grouping110,112,114includes corresponding encoder systems, such as optical angular encoders for example, that are each arranged coaxially with the corresponding axis of rotation of, e.g., the arm segments106,108. The optical encoder system detects rotational (swivel) or transverse (hinge) movement of, e.g., each one of the arm segments106,108about the corresponding axis and transmits a signal to an electronic data processing system within the AACMM100as described in more detail herein below. Each individual raw encoder count is sent separately to the electronic data processing system as a signal where it is further processed into measurement data. No position calculator separate from the AACMM100itself (e.g., a serial box) is required, as disclosed in commonly assigned U.S. Pat. No. 5,402,582 ('582).

The base116may include an attachment device or mounting device120. The mounting device120allows the AACMM100to be removably mounted to a desired location, such as an inspection table, a machining center, a wall or the floor for example. In one embodiment, the base116includes a handle portion122that provides a convenient location for the operator to hold the base116as the AACMM100is being moved. In one embodiment, the base116further includes a movable cover portion124that folds down to reveal a user interface, such as a display screen.

In accordance with an embodiment, the base116of the portable AACMM100contains or houses an electronic data processing system that includes two primary components: a base processing system that processes the data from the various encoder systems within the AACMM100as well as data representing other arm parameters to support three-dimensional (3-D) positional calculations; and a user interface processing system that includes an on-board operating system, a touch screen display, and resident application software that allows for relatively complete metrology functions to be implemented within the AACMM100without the need for connection to an external computer.

The electronic data processing system in the base116may communicate with the encoder systems, sensors, and other peripheral hardware located away from the base116(e.g., a LLP that can be mounted to the removable handle126on the AACMM100). The electronics that support these peripheral hardware devices or features may be located in each of the bearing cartridge groupings110,112,114located within the portable AACMM100.

FIG. 2is a block diagram of electronics utilized in an AACMM100in accordance with an embodiment. The embodiment shown inFIG. 2includes an electronic data processing system210including a base processor board204for implementing the base processing system, a user interface board202, a base power board206for providing power, a Bluetooth module232, and a base tilt board208. The user interface board202includes a computer processor for executing application software to perform user interface, display, and other functions described herein.

As shown inFIG. 2, the electronic data processing system210is in communication with the aforementioned plurality of encoder systems via one or more arm buses218. In the embodiment depicted inFIG. 2, each encoder system generates encoder data and includes: an encoder arm bus interface214, an encoder digital signal processor (DSP)216, an encoder read head interface234, and a temperature sensor212. Other devices, such as strain sensors, may be attached to the arm bus218.

Also shown inFIG. 2are probe end electronics230that are in communication with the arm bus218. The probe end electronics230include a probe end DSP228, a temperature sensor212, a handle/LLP interface bus240that connects with the handle126or the LLP242via the quick-connect interface in an embodiment, and a probe interface226. The quick-connect interface allows access by the handle126to the data bus, control lines, and power bus used by the LLP242and other accessories. In an embodiment, the probe end electronics230are located in the measurement probe housing102on the AACMM100. In an embodiment, the handle126may be removed from the quick-connect interface and measurement may be performed by the laser line probe (LLP)242communicating with the probe end electronics230of the AACMM100via the handle/LLP interface bus240. In an embodiment, the electronic data processing system210is located in the base116of the AACMM100, the probe end electronics230are located in the measurement probe housing102of the AACMM100, and the encoder systems are located in the bearing cartridge pairs110,112,114. The probe interface226may connect with the probe end DSP228by any suitable communications protocol, including commercially-available products from Maxim Integrated Products, Inc. that embody the 1-Wire® communications protocol236.

FIG. 3is a block diagram describing detailed features of the electronic data processing system210of the AACMM100in accordance with an embodiment. In an embodiment, the electronic data processing system210is located in the base116of the AACMM100and includes the base processor board204, the user interface board202, a base power board206, a Bluetooth module232, and a base tilt module208.

In an embodiment shown inFIG. 3, the base processor board204includes the various functional blocks illustrated therein. For example, a base processor function302is utilized to support the collection of measurement data from the AACMM100and receives raw arm data (e.g., encoder system data) via the arm bus218and a bus control module function308. The memory function304stores programs and static arm configuration data. The base processor board204also includes an external hardware option port function310for communicating with any external hardware devices or accessories such as an LLP242. A real time clock (RTC) and log306, a battery pack interface (IF)316, and a diagnostic port318are also included in the functionality in an embodiment of the base processor board204depicted inFIG. 3.

The base processor board204also manages all the wired and wireless data communication with external (host computer) and internal (display processor202) devices. The base processor board204has the capability of communicating with an Ethernet network via an Ethernet function320(e.g., using a clock synchronization standard such as Institute of Electrical and Electronics Engineers (IEEE) 1588), with a wireless local area network (WLAN) via a LAN function322, and with Bluetooth module232via a parallel to serial communications (PSC) function314. The base processor board204also includes a connection to a universal serial bus (USB) device312.

The base processor board204transmits and collects raw measurement data (e.g., encoder system counts, temperature readings) for processing into measurement data without the need for any preprocessing, such as disclosed in the serial box of the aforementioned '582 patent. The base processor204sends the processed data to the display processor328on the user interface board202via an RS485 interface (IF)326. In an embodiment, the base processor204also sends the raw measurement data to an external computer.

Turning now to the user interface board202inFIG. 3, the angle and positional data received by the base processor is utilized by applications executing on the display processor328to provide an autonomous metrology system within the AACMM100. Applications may be executed on the display processor328to support functions such as, but not limited to: measurement of features, guidance and training graphics, remote diagnostics, temperature corrections, control of various operational features, connection to various networks, and display of measured objects. Along with the display processor328and a liquid crystal display (LCD)338(e.g., a touch screen LCD) user interface, the user interface board202includes several interface options including a secure digital (SD) card interface330, a memory332, a USB Host interface334, a diagnostic port336, a camera port340, an audio/video interface342, a dial-up/cell modem344and a global positioning system (GPS) port346.

The electronic data processing system210shown inFIG. 3also includes a base power board206with an environmental recorder362for recording environmental data. The base power board206also provides power to the electronic data processing system210using an AC/DC converter358and a battery charger control360. The base power board206communicates with the base processor board204using inter-integrated circuit (I2C) serial single ended bus354as well as via a DMA serial peripheral interface (DSPI)356. The base power board206is connected to a tilt sensor and radio frequency identification (RFID) module208via an input/output (I/O) expansion function364implemented in the base power board206.

Though shown as separate components, in other embodiments all or a subset of the components may be physically located in different locations and/or functions combined in different manners than that shown inFIG. 3. For example, in one embodiment, the base processor board204and the user interface board202are combined into one physical board.

Referring now toFIGS. 4-11, an embodiment of AACMM100having an adjustable counter balance system is shown. The AACMM100includes a first rotation assembly402that includes a pair of bearing cartridges402disposed between the base116and the first arm segment106. The first rotation assembly402is configured to rotate about a first axis404and a second axis406. In one embodiment, the first axis404is substantially perpendicular to the second axis406. The first axis404is defined by a rotary bearing cartridge405(FIG. 7) disposed within the base116that allows communications and power conduits to pass from the first arm segment106into the base116.

The first rotation assembly402includes a first portion408and a second portion410. The first portion408is fixed relative to the second axis406. The first portion408includes a first housing member412and a second housing member414. The second housing member414includes a projection416having a stop member418. In the exemplary embodiment, the stop member418is an elastomeric material that dampens the impact of the second portion410when the first arm segment106is rotated to a position substantially co-linear with the first axis404. As will be discussed in more detail herein, a counter balance assembly is at least partially positioned within the first portion408.

The second housing member414includes a first opening434(FIG. 7) that is sized to receive a shaft436. The second housing member414further includes a second opening438(FIG. 9) sized to receive a biasing member, such as torsion spring440for example. In the exemplary embodiment, the first opening434and second opening438are substantially co-linear. A third opening442is arranged in the second housing member414adjacent to the second opening438. As will be discussed in more detail herein, the third opening442is disposed to intersect the second opening438to allow at least one projection444arranged on one end of the torsion spring440to engage a worm gear446. In one embodiment, the at least one projection444includes a plurality of projections that form gear teeth. In the exemplary embodiment, the torsion spring440has 28-30 teeth disposed over an arc length of 140 degrees. In the exemplary embodiment, the worm gear446has single thread and a pitch diameter of approximately 0.45 inches and a length of approximately 1 inch. The worm gear446is retained in position by the force applied by torsion spring440.

It should be appreciated that while embodiments describe the gear teeth being disposed on the end of the torsion spring, the claimed invention should not be so limited. In one embodiment, the torsion spring is comprised of two counter wound torsion springs with gear teeth formed about a middle portion.

The gear teeth444are configured to rotate the end of the torsion spring440in response to the rotation of the worm gear446. The gear teeth444and worm gear446cooperate to form an adjuster assembly for the torque applied to the first arm segment106. It should be appreciated that the rotation of the worm gear446causes the end of the torsion spring440to move or rotate in a manner that results in a change in the torque being applied by the torsion spring440.

In one embodiment, a first bore opening448extends from one end of the third opening442. The first bore opening448is sized to receive a tool (not shown) that couples to rotate the worm gear446. In another embodiment, the second housing member414includes a wall450. In this embodiment, a second bore opening452is arranged co-linearly with the bore opening448to allow access of the tool to the worm gear446.

The second portion410is disposed between the first portion408and the first arm segment106. The second portion includes a third housing member420and a fourth housing member422. The second portion410rotates about the second axis406. A projection424having a surface426extends from the third housing member420. The projection424is arranged such that the surface426contacts the stop member418when the first arm segment is rotated to a position substantially co-linear with the first axis404(the “initial position”). In the exemplary embodiment, the second portion410may rotate at least 165 degrees relative to the initial position. The section portion410further includes a tapered portion428that couples to the first arm segment106. A projection430extends from the tapered portion428. A bracket432is coupled to the projection430. The bracket432is configured to support the second arm segment108when the first arm segment106and the second arm segment108are positioned in parallel.

The third housing420is coupled to a second shaft454. The second shaft454has an outer portion470, an intermediate portion472and an inner portion474. The outer portion470has a diameter that is sized to engage and couple to the third housing420. The outer portion470transitions to the intermediate portion472at a lip476. In the exemplary embodiment, the lip476provides a stopping feature against which a corresponding feature on the third housing420contacts. The diameter of the intermediate portion is sized to receive the inner diameter of the torsion spring440. The second shaft454tapers from the intermediate portion472to the inner portion474. The inner portion474has a diameter that is less than the inner diameter of the torsion spring440to provide clearance to accommodate changes in the inner diameter of the torsion spring440as the first arm segment106is rotated.

The second shaft454has a substantially hollow interior portion that is disposed about the first shaft436. The second shaft454is coupled to the first shaft436by a pair of bearings456,458, such as a ball bearing or a roller bearing for example. The bearings456,458allow the rotation of the second portion410relative to the first portion408about the second axis406. Additional components, such as spacers478, collars480and washers482may also be included to provide the desired spacing and support of the assembly. In one embodiment, an optical encoder assembly464is coupled to the second shaft454and arranged to measure the rotational movement between the first shaft436and the second shaft454.

The torsion spring440is disposed about the shafts436,454. In the exemplary embodiment, the torsion spring includes a first end460adjacent the worm gear446and a second end462coupled to the second portion410. In the exemplary embodiment, the second end462is coupled to the fourth housing member422by at least one fastener466(FIG. 6). The fastener466couples the second end462to the second portion410such that when the first arm segment106is rotated about the second axis406a torque is applied to the first arm segment106by the torsion spring440. The torsion spring440is selected to substantially counter balance the weight of the arm portion104when the arm segments106,108are articulated to the desired position. In the exemplary embodiment, the torsion spring440is configured to provide a torque level that allows the first arm segment to remain at a desired angular position without sagging (e.g. moving downward under the force of gravity) or springing back (e.g. towards the initial position) when the operator releases the measurement device102.

It should be appreciated that variations in the manufacturing processes of the components of the arm portion104may result in the torque produced by the torsion spring440being either too large (causing spring back) or too small (causing sagging). To compensate for the variations in components, the AACMM100includes an adjuster that provides means for changing the torque. In the exemplary embodiment, the adjustment of the torque is provided by rotating the worm gear446within the third opening442by inserting a tool through the first bore opening448and engaging a feature468on the end of the worm gear446. The feature468may be any suitable feature appropriate to engage a tool such as but not limited to a straight slot, a Philips slot, a Frearson slot, a hexagon socket, an Allen socket, a star socket, or a Torx socket for example. By rotating the worm gear446clockwise or counter-clockwise, the first end460of the torsion spring440will be moved from a first position to a second position.

As the first end460is moved, the torque applied by the torsion spring440on the second portion410and thus the first arm segment106will increase or decrease. This provides advantages in adjusting the counter balancing torque to the components within a particular arm portion104. In the exemplary embodiment, the torque may be adjusted from 0 ft-lb to 63 ft-lb over the range 70 degrees of rotation of the worm gear446and gear teeth444engagement. In one embodiment, the calibration of the torsion spring440is performed during the manufacturing assembly and a cap or plug (not shown) is inserted into the first bore opening448or second bore opening452to prevent tampering. In one embodiment, a set screw is used to lock the worm gear446to prevent movement.

Another embodiment of an adjuster assembly is shown inFIG. 12. In this embodiment, the second housing member414has a substantially hollow interior portion484defined by walls450,486and488. Arranged within the interior portion484is a threaded member490, such as a threaded rod for example. The threaded member490is coupled for rotation between the walls450,486. The threaded member490may include a feature (not shown), similar to feature486for example, that allows the user to insert a tool to rotate the threaded member. A collar492is coupled to the threaded member490. The collar492includes an internal thread that engages the threads of the threaded member490such that when the threaded member490is rotated, the collar492translates along the longitudinal axis of the threaded member490. An arm494extends between the collar492and the torsion spring440. The arm494may be a separate member from or integral with the torsion spring440. As such, when the collar translates along the threaded member, the first end460of the torsion spring440moves from a first position to a second position. As described above, the movement of the first end460allows the calibration of the torque output of the torsion spring440to provide the desired level of counter balance.

It should be appreciated that while embodiments of the invention describe an adjuster that is manually adjusted, the claimed invention should not be so limited. In one embodiment, a motor such as a stepper motor is coupled to rotate the adjuster. In one embodiment, the stepper motor is coupled with a controller that adjusts the torque of the torsion spring based on the position of the arm.