Abstract:
A portable articulated arm coordinate measuring machine (AACMM) is provided including a manually positionable articulated arm having opposed first and second ends. The arm includes multiple connected arm segments. Each arm segment has a longitudinal axis. Each arm segment includes a generally tubular core, an outer sleeve surrounding at least a portion of a length of the core, and at least one position transducer for producing a position signal. The outer sleeve is a cylindrical tube having a first portion at a first end and a second portion that extends from the first portion to an opposite end. The first portion is coupled to an end of the core. The first portion is shorter than the second portion and the second portion is configured to move relative to the core.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Design Application No. 29/412,903, filed Feb. 9, 2012 and U.S. Design Application No. 29/379,170, filed Nov. 16, 2010 the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to a coordinate measuring machine and, more particularly, to an arm of a portable articulated coordinate measuring machine. 
     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 (e.g. machining) or production 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. Alternatively, the data may be provided to the user in numeric form, for example, when measuring the diameter of a hole, the text “Diameter=” is displayed on a computer screen. 
     Arm portions of AACMMs may be susceptible to twist due to temperature changes. Twisting of a portion of an arm segment may cause a coupled encoder to rotate, thereby generating an angle error and reducing the accuracy of the machine. Such a twisting may be caused for example by a patterned composite material on an outer region of the arm segment, the outer region having a non-uniform pattern. In general, such twisting effects cannot be removed by measuring temperatures, especially since temperature sensors are ordinarily located in the interior of the arm segments. A method is needed to minimize twisting of the arm segments. 
     SUMMARY 
     According to one embodiment of the invention, a portable articulated arm coordinate measuring machine (AACMM) is provided including a manually positionable articulated arm having opposed first and second ends. The arm includes a plurality of connected arm segments. Each arm segment has a longitudinal axis. Each arm segment includes a generally tubular core, an outer sleeve surrounding at least a portion of a length of the core, and at least one position transducer for producing a position signal. The outer sleeve is a cylindrical tube having a first portion at a first end and a second portion that extends from the first portion to an opposite end. The first portion is coupled to an end of the core. The first portion is shorter than the second portion and the second portion is configured to move relative to the core. The portable AACMM also includes a measurement device attached to a first end. An electronic circuit receives the position signal from the at least one transducer and provides data corresponding to a position of the measurement device. 
     According to another embodiment of the invention, a portable AACMM is provided including a manually positionable articulated arm having opposed first and second ends. The arm includes a plurality of connected arm segments. Each arm segment has a longitudinal axis and includes a core surrounded by an outer material and at least one position transducer for producing a position signal. The outer material includes a plurality of first fibers arranged orthogonally to a plurality of second fibers. The plurality of first fibers and the plurality of second fibers are oriented relative to a longitudinal axis of the arm segment. The AACMM also includes a measurement device attached to a first end of the AACMM and an electronic circuit. The electronic circuit receives a position signal from the at least one position transducer and provides data corresponding to a position of the measurement device. 
     According to another embodiment of the invention, a method is provided for forming an arm segment for a portable AACMM including forming a generally hollow cylindrical core having a longitudinal axis from a first material. The first material includes a plurality of first fibers arranged orthogonally to a plurality of second fibers. A tubular sleeve is formed from a second material. The second material includes a plurality of third fibers arranged orthogonally to a plurality of fourth fibers. The plurality of third fibers and the plurality of fourth fibers are in a desired orientation relative to the axis. The core is inserted into the sleeve and a first end of the sleeve is fastened to a first end of the core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings, exemplary embodiments are shown which should not be construed to be limiting regarding the entire scope of the disclosure, and wherein the elements are numbered alike in several FIGURES: 
         FIG. 1 , including  FIGS. 1A and 1B , are perspective views of a portable articulated arm coordinate measuring machine (AACMM) having embodiments of various aspects of the present invention therewithin; 
         FIG. 2 , including  FIGS. 2A-2D  taken together, is a block diagram of electronics utilized as part of the AACMM of  FIG. 1  in accordance with an embodiment of the present invention; 
         FIG. 3 , including  FIGS. 3A and 3B  taken together, is a block diagram describing detailed features of the electronic data processing system of  FIG. 2  in accordance with an embodiment of the present invention; 
         FIG. 4  is a perspective view of an end of an arm segment according to an embodiment of the present invention; 
         FIG. 5  is a top view of a portion of an arm segment according to an embodiment of the present invention; 
         FIG. 6  is a perspective view of a portion of an arm segment according to an embodiment of the invention; 
         FIG. 7  is a perspective view of a portion of an arm segment according to an embodiment of the invention; and 
         FIG. 8  is a perspective view of a portion of an arm segment according to an embodiment of the invention; 
         FIG. 9  is a cross-sectional view of an arm segment according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  illustrate, an exemplary portable articulated arm coordinate measuring machine (AACMM) according to various embodiments of the present invention, and articulated arm being one type of coordinate measuring machine. AACMMs are used in a variety of applications to obtain measurements of objects. The AACMM  100  may include a six or seven axis articulated measurement device having a probe end  401  that includes a measurement probe housing  102  coupled to an arm portion  104  of the AACMM  100  at one end. The arm portion  104  comprises a first arm segment  106  coupled at a first end  106   a  to a second arm segment  108  by a first grouping of bearing cartridges  110  (e.g. two bearing cartridges). A second grouping of bearing cartridges  112  (e.g. two bearing cartridges) couples the second arm segment  108  to the measurement probe housing  102 . A third grouping of bearing cartridges  114  (e.g. three bearing cartridge) couples the second end  106   b  of the first arm segment  106  to a base  116 . A bearing cartridge, as used herein, allows a component coupled to the bearing cartridge to move independently about an axis. When combined into a group  110 ,  112 ,  114 , the bearing cartridges may form a hinge and swivel type of connector such that an adjoining component is independently movable about two axes. It should be appreciated that bearing cartridges may be grouped together in different configurations to a form a connector movable about a single axis or a plurality of axes. The measurement probe housing  102  may comprise the shaft of an additional axis of the AACMM  100  (e.g. a cartridge containing an encoder system that determines movement of the measurement device, for example a probe  118 , of the AACMM  100 .) In this embodiment, the probe end  401  may rotate about an axis extending through the center of measurement probe housing  102 . In use of the AACMM  100 , the base  116  is typically affixed to a planar work surface. 
     Each bearing cartridge within each bearing cartridge grouping  110 ,  112 ,  114  typically contains an encoder system (e.g. an optical angular encoder system). The encoder system provides an indication of the position of the respective arm segments  106 ,  108  and the corresponding bearing cartridge groupings  110 ,  112 ,  114  that together provide an indication of the position of the probe  118  with respect to the base  116 . A portable AACMM having multiple axes of articulated movement, such as six or seven for example, provides advantages in allowing the operator to position the probe  118  in a desired location within a  360  degree area about the base, while providing an arm portion  104  that may be easily maneuvered by an operator. It should be appreciated that the illustrated arm portion  104  having a first arm segment  106  coupled to a second arm segment  108  is for illustrative purposes only and the claimed invention should not be so limited. An AACMM  100  according to the invention may include 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 probe  118  is detachably mounted to the measurement probe housing  102 , which is connected to the bearing cartridge grouping  112 . A handle  126  is removable with respect to the measurement probe housing  102  by way of, for example, a quick connect interface. The handle  126  may be replaced with another device (e.g. a laser line probe, a bar code reader, etc. . . . ), thereby providing advantages in allowing the operator to use different measurement devices with the same AACMM  100 . In one embodiment, the probe housing  102  houses a removable probe  118 , which is a contact measurement device and may have any number of different tips that 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). The handle  126  may be replaced with the LLP using a quick-connect interface. Other types of measurement devices may replace the removable handle  126  to provide additional functionality. Examples of such measurement devices include, but are not limited to, one or more illumination lights, a bar code scanner, a projector, a paint sprayer, or a camera. 
     As shown in  FIGS. 1A and 1B  the AACMM  100  includes the removable handle that provides advantages in allowing accessories or functionality to be changed without removing the measurement probe housing  102  from the bearing cartridge grouping  112 . As discussed in more detail below, with respect to  FIG. 2 , the removable handle may also include an electrical connector that allows electrical power and data to be exchanged with the handle and the corresponding electronics located in the probe end  401 . 
     In various embodiments, each grouping of bearing cartridges  110 ,  112 ,  114  allows the arm portion  104  of the AACMM  100  to move about multiple axes of rotation. As mentioned, each bearing cartridge grouping  110 ,  112 ,  114  includes 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 segments  106 ,  108 . The optical encoder system detects rotational (swivel) or transverse (hinge) movement of, e.g., each one of the arm segments  106 ,  108  about the corresponding axis and transmits a signal to an electronic data processing system within the AACMM  100  as 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 AACMM  100  itself (e.g., a serial box) is required, as disclosed in commonly assigned U.S. Pat. No. 5,402,582 (&#39;582). 
     The base  116  may include an attachment device or mounting device  120 . The mounting device  120  allows the AACMM  100  to 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 base  116  includes a handle portion  122  that provides a convenient location for the operator to hold the base  116  as the AACMM  100  is being moved. In one embodiment, the base  116  further includes a movable cover portion  124  that folds down to reveal a user interface, such as a display screen for example. 
     In accordance with an embodiment, the base  116  of the portable AACMM  100  contains 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 AACMM  100  as 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 AACMM  100  without the need for connection to an external computer. 
       FIG. 2  is a block diagram of electronics utilized in an AACMM  100  in accordance with an embodiment. The embodiment shown in  FIG. 2A  includes an electronic data processing system  210  including a base processor board  204  for implementing the base processing system, a user interface board  202 , a base power board  206  for providing power, a Bluetooth module  232 , and a base tilt board  208 . The user interface board  202  includes a computer processor for executing application software to perform user interface, display, and other functions described herein. 
     As shown in  FIG. 2A , the electronic data processing system  210  is in communication with the aforementioned plurality of encoder systems via one or more arm buses  218 . In the embodiment depicted in  FIGS. 2B and 2C , each encoder system generates encoder data and includes: an encoder arm bus interface  214 , an encoder digital signal processor (DSP)  216 , an encoder read head interface  234 , and a temperature sensor  212 . Other devices, such as strain sensors, may be attached to the arm bus  218 . 
     Also shown in  FIG. 2D  are probe end electronics  230  that are in communication with the arm bus  218 . The probe end electronics  230  include a probe end DSP  228 , a temperature sensor  212 , a handle/LLP interface bus  240  that connects with the handle  126  or the LLP  242  via the quick-connect interface in an embodiment, and a probe interface  226 . The quick-connect interface allows access by the handle  126  to the data bus, control lines, and power bus used by the LLP  242  and other accessories. In an embodiment, the probe end electronics  230  are located in the measurement probe housing  102  on the AACMM  100 . In an embodiment, the handle  126  may be removed from the quick-connect interface and measurement may be performed by the laser line probe (LLP)  242  communicating with the probe end electronics  230  of the AACMM  100  via the handle/LLP interface bus  240 . In an embodiment, the electronic data processing system  210  is located in the base  116  of the AACMM  100 , the probe end electronics  230  are located in the measurement probe housing  102  of the AACMM  100 , and the encoders are located in the bearing cartridge groupings  110 ,  112 ,  114 . The probe interface  226  may connect with the probe end DSP  228  by any suitable communications protocol, including commercially-available products from Maxim Integrated Products, Inc. that embody the 1-wire® communications protocol  236 . 
       FIG. 3  is a block diagram describing detailed features of the electronic data processing system  210  of the AACMM  100  in accordance with an embodiment. In an embodiment, the electronic data processing system  210  is located in the base  116  of the AACMM  100  and includes the base processor board  204 , the user interface board  202 , a base power board  206 , a Bluetooth module  232 , and a base tilt module  208 . 
     In an embodiment shown in  FIG. 3A , the base processor board  204  includes the various functional blocks illustrated therein. For example, a base processor function  302  is utilized to support the collection of measurement data from the AACMM  100  and receives raw arm data (e.g., encoder system data) via the arm bus  218  and a bus control module function  308 . The memory function  304  stores programs and static arm configuration data. The base processor board  204  also includes an external hardware option port function  310  for communicating with any external hardware devices or accessories such as an LLP  242 . A real time clock (RTC) and log  306 , a battery pack interface (IF)  316 , and a diagnostic port  318  are also included in the functionality in an embodiment of the base processor board  204  depicted in  FIG. 3 . 
     The base processor board  204  also manages all the wired and wireless data communication with external (host computer) and internal (display processor  202 ) devices. The base processor board  204  has the capability of communicating with an Ethernet network via an Ethernet function  320  (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 function  322 , and with Bluetooth module  232  via a parallel to serial communications (PSC) function  314 . The base processor board  204  also includes a connection to a universal serial bus (USB) device  312 . 
     The base processor board  204  transmits 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 &#39;582 patent. The base processor  204  sends the processed data to the display processor  328  on the user interface board  202  via an RS485 interface (IF)  326 . In an embodiment, the base processor  204  also sends the raw measurement data to an external computer. 
     Turning now to the user interface board  202  in  FIG. 3B , the angle and positional data received by the base processor is utilized by applications executing on the display processor  328  to provide an autonomous metrology system within the AACMM  100 . Applications may be executed on the display processor  328  to 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 processor  328  and a liquid crystal display (LCD)  338  (e.g., a touch screen LCD) user interface, the user interface board  202  includes several interface options including a secure digital (SD) card interface  330 , a memory  332 , a USB Host interface  334 , a diagnostic port  336 , a camera port  340 , an audio/video interface  342 , a dial-up/cell modem  344  and a global positioning system (GPS) port  346 . 
     The electronic data processing system  210  shown in  FIG. 3A  also includes a base power board  206  with an environmental recorder  362  for recording environmental data. The base power board  206  also provides power to the electronic data processing system  210  using an AC/DC converter  358  and a battery charger control  360 . The base power board  206  communicates with the base processor board  204  using inter-integrated circuit (I2C) serial single ended bus  354  as well as via a DMA serial peripheral interface (DSPI)  35 . The base power board  206  is connected to a tilt sensor and radio frequency identification (RFID) module  208  via an input/output (I/O) expansion function  364  implemented in the base power board  206 . 
     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 in  FIG. 3 . For example, in one embodiment, the base processor board  204  and the user interface board  202  are combined into one physical board. 
     Referring now to  FIGS. 4 and 5 , an exemplary arm segment  108  of arm  104  of the AACMM  100  is illustrated in more detail. Each arm segment  106 ,  108  includes a generally cylindrical hollow core  500  made from a suitably rigid material such as, but not limited to, a carbon-fiber composite material for example. A carbon-fiber composite material may be selected because of its low coefficient of thermal expansion (CTE) and its high stiffness. The core may alternatively be made from an extruded or woven synthetic material or metal. In one embodiment, the tubular core  500  of each arm segment  106 ,  108  is manufactured by wrapping at least one layer of an impregnated carbon-fiber composite material around a mandrel rotatable about a longitudinal axis X. In other embodiments, the core  500  may be made by other materials such as but not limited to extrude or woven synthetic materials or metals. 
     An outer material  550  is positioned adjacent the exterior surface  506  of the core  500  to enhance the aesthetic appeal of each arm segment  106 ,  108 . The outer material  550  may include at least one layer of a composite material, such as an aluminum coated glass fiber epoxy prepreg for example. In one embodiment, the outer material  550  is Texalium® manufactured by Hexcel Corporation. In some embodiments, the absolute value of the coefficient of thermal expansion (CTE) of the material in the outer layer is much larger than the CTE of the composite material of the inner core  500 .  FIGS. 6 and 7  show the composition of the outer material  550  in detail. The outer material  550  includes a plurality of first fibers  560  oriented in a first direction and a plurality of second fibers  562  oriented in a second, different direction. In one embodiment, the first direction and the second direction are orthogonal to one another. The fibers  560 ,  562  of each layer of the outer material  550  may be arranged in any number of orientations, including but not limited to, a woven configuration, a braided configuration, or a unidirectional configuration for example. In one embodiment, one of the plurality of first fibers  560  and the plurality of second fibers  562  of the outer material  550  is oriented generally coaxially with the longitudinal axis X (see  FIG. 6 ). In such embodiments, the other of the plurality of first fibers  560  and the plurality of second fibers  562  is oriented cylindrically, such that the fibers extend in a direction around the periphery of the tubular outer material  550  and the longitudinal axis X. In another embodiment, illustrated in  FIG. 7 , the plurality of first fibers  560  and the plurality of second fibers  562  may be arranged such that both the first fibers  560  and the second fibers  562  are oriented at a generally 45 degree angle to the longitudinal axis X. 
     The cross-section of exemplary arm segment  108 , illustrated in  FIG. 4 , is formed by wrapping the outer material  550  around the carbon fiber core  500 , for instance before the core  500  is removed from the mandrel. In a first embodiment, outer material  550  is bonded to the outer surface  506  of the core  500  by applying pressure from a vacuum and heat to the arm segment  108 . The outer material  550  is wrapped around the core  500  such that the plurality of first fibers  560  and the plurality of second fibers  562  are in a desired orientation relative to each other and to the longitudinal axis X. By arranging the fibers  560 ,  562  in the outer material  550  orthogonally and by orienting them relative to the longitudinal axis X the torsional effects are minimized and restricted. As such, the outer material  550  is less likely to twist relative to the core  500  in response to a temperature change. The resulting torque placed on the encoders  214 ,  216 ,  234  of the arm  104  due to a change in environmental temperature is reduced or eliminated, thus improving the accuracy of the AACMM  100 . 
     As shown in  FIG. 8 , the outer material  550  may alternatively be formed as a separate component  570 , such as a tubular sleeve or shell for example, that slidably engages the core  500 . The sleeve  570  may extend over a portion of, or alternatively, over the entire length of an inner core  500 . In embodiments where the outer material  550  is a sleeve  570 , the external surface  506  of the core  500  is smoothed, giving the core  500  a uniform outer diameter. The outer material sleeve  570  has an inner diameter larger than the outer diameter of the core  500  to create a loose fit. The outer material sleeve  570  may include a first portion  574  adjacent a first end  572  and a second portion  576  extending from the first portion  574  to adjacent a second, opposite end  578 . In one embodiment, the first portion  574  of the sleeve  570  is coupled to a first end  502  of the core  500  (see  FIG. 5 ) and the second portion  576  of the sleeve  570  is configured to move freely relative to the core  500  (see  FIG. 9 ). By coupling only the first portion  574  of the sleeve  570  to the core  500 , torsional forces from the sleeve  570  are imparted to the core  500  only at the location where the sleeve  570  and core  500  are coupled, rather than over the full length of the core  500 . In one embodiment, the sleeve  570  is coupled to the end  502  of the core  500  opposite, not adjacent, a bearing cartridge  110 ,  112 ,  114 . The first portion  574  of the sleeve  570  may be coupled to the first end  502  of the core  500  such as with a fastener, a weld, an adhesive, diffusion bonding, ultrasonic welding or any other known connection means. In one embodiment, the first portion  574  extends a predetermined length from the end  572  of the sleeve  570  wherein the first portion  574  is substantially smaller than the remaining portion of the sleeve  570 . In the embodiment of  FIG. 1 , the sleeve  570  on arm segment  108  is coupled to the composite core of the arm segment  108  near the bearing cartridge pair  112 . The sleeve on the arm segment  106  is coupled to the composite core of the arm segment  106  near the bearing cartridge pair  110 . The short segment  107  has an outer sleeve that covers a metallic element such as aluminum or steel. It should be appreciated that the location of the coupling of the sleeve  570  to the core  500  may be reversed or a combination thereof. 
     Forming the outer material  550  as a sleeve  570  separate from the core  500  further isolates the core  500  of an arm segment  106 ,  108  from the twisting of the outer material  500  caused by a non-orthogonal fiber orientation. The sleeve  570  also isolates the core  500  from torque induced by a user while operating the AACMM  100 , thereby further improving the accuracy of the machine. In addition, the sleeve  570  may be removably connected to the core  500  to allow for easy replacement if the outer material sleeve  570  is damaged. The color of the sleeve  570  may also be modified to correlate with a desired model of the AACMM  100 . 
     While the invention has been described with reference to example embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. 
     Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.