Three dimensional coordinate measuring apparatus

A novel, portable coordinate measuring machine comprises a multijointed (preferably six and/or seven joints) manually positionable measuring arm for accurately and easily measuring a volume, which in a preferred embodiment, comprises a sphere ranging from six to eight feet in diameter and a measuring accuracy of 2 Sigma +/-0.003 inch. In addition to the measuring arm, the present invention employs a controller (or serial box) which acts as the electronic interface between the arm and a host computer. Additionally, a number of end effector probes are provided that fulfill functions other than measurement only.

BACKGROUND OF THE INVENTION 
This invention relates generally to three dimensional coordinate measuring 
machines (or CMM's). More particularly, this invention relates to a new 
and improved three dimensional CMM which is portable and provides improved 
accuracy and ease of use. 
It will be appreciated that everything in the physical world occupies 
volume or space. Position in a space may be defined by length, width and 
height which, in engineering terms, is often called an X, Y, Z coordinate. 
The X, Y, Z numbers represent the dimensions of length, width and height 
or three dimensions. Three-dimensional objects are described in terms of 
position and orientation; that is, not just where an object is but in what 
direction it points. The orientation of an object in space can be defined 
by the position of three points on the object. Orientation can also be 
described by the angles of alignment of the object in space. The X, Y, and 
Z coordinates can be most simply measured by three linear scales. In other 
words, if you lay a scale along the length, width and height of a space, 
you can measure the position of a point in the space. 
Presently, coordinate measurement machines or CMM's measure objects in a 
space using three linear scales. These devices are typically non-portable, 
expensive and limited in the size or volume that can be easily measured. 
FARO Technologies, Inc. of Lake Mary, Fla. (the assignee of the present 
invention) has successfully produced a series of electrogoniometer-type 
digitizing devices for the medical field. In particular, FARO 
Technologies, Inc. has produced systems for skeletal analysis known as 
METRECOM.RTM. and systems for use in surgical applications known as 
SURGICOM.TM.. Electrogoniometer-type devices of the type embodied in the 
METRECOM and SURGICOM systems are disclosed in U.S. Pat. Nos. 4,670,851, 
5,251,127 and 5,305,203, all of which are assigned to the assignee hereof 
and incorporated herein by reference. 
While well suited for their intended purposes, the METRECOM and SURGICOM 
electrogoniometer-type digitizing systems are not well suited for general 
industrial applications where three dimensional measurements of parts and 
assemblies are often required. Therefore, there is a continuing need for 
improved, accurate and low cost CMM's for industrial and related 
applications. 
SUMMARY OF THE INVENTION 
The above-discussed and other problems and deficiencies of the prior art 
are overcome or alleviated by the three dimensional measuring instrument 
(e.g., electrogoniometer) of the present invention. In accordance with the 
present invention, a novel, portable coordinate measuring machine 
comprises a multijointed (preferably six or seven joints) manually 
positionable measuring arm for accurately and easily measuring a volume, 
which in a preferred embodiment, comprises a sphere preferably ranging 
from six to twelve feet in diameter (but which may also cover diameters 
more or less than this range) and a measuring accuracy of preferably 2 
Sigma +/-0.0003 inch (and optimally 2 Sigma +/-0.001 inch). In addition to 
the measuring arm, the present invention employs a controller (or serial 
box) which acts as the electronic interface between the arm and a host 
computer. 
The mechanical measuring arm used in the CMM of this invention is generally 
comprised of a plurality of transfer housings (with each transfer housing 
comprising a joint and defining one degree of rotational freedom) and 
extension members attached to each other with adjacent transfer housings 
being disposed at right angles to define a movable arm preferably having 
five, six or seven degrees of freedom. Each transfer housing includes 
measurement transducers and novel bearing arrangements. These novel 
bearing arrangements include prestressed bearings formed of 
counter-positioned conical roller bearings and stiffening thrust bearings 
or alternatively, standard duplex bearings for high bending stiffness with 
a low profile structure. In addition, each transfer casing includes 
physical visual and audio endstop indicators to protect against mechanical 
overload due to mechanical stressing. 
The movable arm is attached to a base or post which includes (1) a 
temperature monitoring board for monitoring temperature stability; (2) an 
encoder mounting plate for universal encoder selection; (3) an EEPROM 
circuit board containing calibration and identification data so as to 
avoid unit mixup; and (4) a preamplifier board mounted near the encoder 
mounting plate for transmission of high amplified signals to a remote 
counter board in the controller. 
As in the prior art METRECOM system, the transfer casings are modular 
permitting variable assembly configurations and the entire movable arm 
assembly is constructed of one material for ensuring consistent 
coefficient of thermal expansion (CTE). Similarly as in the METRECOM 
system, internal wire routing with rotation stops and wire coiling 
cavities permit complete enclosure of large numbers of wires. Also 
consistent with the prior an METRECOM system, this invention includes a 
spring counterbalanced and shock absorbed support mechanism for user 
comfort and a two switch (take/accept) data entry device for allowing high 
precision measurements with manual handling. Also, a generalized option of 
the type used in the prior art METRECOM system is provided for the 
measurement of variables in three dimensions (e.g., temperature may be 
measured in three dimensions using a thermocouple attached to the option 
port). 
The use of a discrete microprocessor-based controller box is an important 
feature of this invention as it permits preprocessing of specific or 
integrated controller calculations without host level processing 
requirements. This is accomplished by mounting an intelligent preprocessor 
in the controller box which provides programmable adaptability and 
compatibility with a variety of external hosts (e.g., external computers). 
The serial box also provides intelligent multi-protocol evaluation and 
autoswitching by sensing communication requirements from the host. For 
example, a host computer running software from one manufacturer will 
generate call requests of one form which are automatically sensed by the 
controller box. Still other features of the controller box include serial 
port communications for standardized long distance communications in a 
variety of industrial environments and novel analog-to-digital/digital 
counter boards for simultaneous capture of every encoder (located in the 
transfer housing) resulting in highly accurate measurements. 
Efficient on-site calibration of the CMM of the present invention is 
improved through the use of a reference ball positioned at the base of the 
CMM to obviate potential mounting complications to system accuracy 
evaluation. In addition, the CMM of this invention includes means for 
performing a volummetric accuracy measurement protocol on an interim 
basis, preferably using a novel cone ballbar device. 
The above-discussed and other features and advantages of the present 
invention will be appreciated and understood by those skilled in the art 
from the following detailed description and drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 1, the three dimensional measuring system of the 
present invention generally comprises a coordinate measuring machine (CMM) 
10 composed of a manually operated multijointed arm 12 and a support base 
or post 14, a controller or serial box 16 and a host computer 18. It will 
be appreciated that CMM 10 electronically communicates with serial box 16 
which, in turn, electronically communicates with host computer 18. 
As will be discussed in more detail hereinafter, CMM 10 includes 
transducers (e.g., one transducer for each degree of freedom) which gather 
rotational positioning data and forward this basic data to serial box 16. 
Serial box 16 provides a reduction in the overall requirements of host 
computer 18 to handle certain complex calculations and provides certain 
preliminary data manipulations. As shown in FIG. 2, serial box 16 is 
intended to be positioned under the host computer 18 (such as the notebook 
computer shown in FIG. 2) and includes EEPROMS which contain data handling 
software, a microcomputer processor, a signal processing board and a 
number of indicator lights 20. As mentioned, basic transducer data is sent 
from CMM 10 to serial box 16. Serial box 16 then processes the raw 
transducer data on an ongoing basis and responds to the queries of the 
host computer with the desired three-dimensional positional or 
orientational information. 
Preferably, all three components defining the three dimensional measuring 
system of this invention (e.g., CMM 10, serial box 16 and host computer 
18) are mounted on either a fixed mounting surface using a rigid plate 
and/or a standard optical measurement instrument thread followed by 
mounting on a known and standard theodolite mobile stand such as shown at 
22 in FIG. 3. Preferably, theodolite stand 22 comprises a part no. MWS750 
manufactured by Brunson. Such a mobile stand is characterized by a stable 
rolling platform with an extendable vertical tower and with common 
attachments and locking mechanisms. As shown in FIGS. 2 and 3, support 
base 14 of CMM 10 is threaded or otherwise attached onto a vertical 
support member 24 of stand 22 while serial box 16/host 18 is supported on 
a shelf 26 pivotally connected at a first joint 28 to an arm 30 which is 
pivotally connected to a second joint 32. Connecting member 34 
interconnects joint 32 to a swivel connection 36 attached to a cap 38 
mounted over the top of member 24. 
Referring now to FIGS. 1 and 4-9, CMM 10 will now be described in detail. 
As best shown in FIG. 5, CMM 10 comprises a base 14 connected to a first 
set of two transfer housings including a first transfer housing 40 which, 
in turn, is connected to a second transfer housing 42 (positioned 
transverse to housing 40). A first extension member 44 is rigidly attached 
to a second set of two transfer housings including a third transfer 
housing 46 transversely attached to a fourth transfer housing 48. First 
extension member 44 is positioned perpendicularly between transfer 
housings 42 and 46. A second extension member 50 is aligned with an 
rigidly attached to transfer housing 48. Rigid extension member 50 is 
rigidly attached to a third set of two transfer housings including a fifth 
transfer housing 52 transversely attached to a sixth transfer housing 54. 
Fifth transfer housing 54 has attached thereto a handle/probe assembly 56. 
In general (and as will be discussed in more detail hereinafter), position 
sensing transducers are mounted in each of the six transfer housings 40, 
42, 46, 48, 52 and 54. Each housing is comprised of bearing supports and 
transducer compartments which are made to then cylindrically attach to 
each other using 45.degree. angled attachment screws (FIG. 6). At the base 
14 is a counterbalanced spring device 60 for support of arm 12 in its 
standard vertical configuration (FIG. 8). 
Turning now to FIGS. 6 and 7, a detailed description will be made of a 
transfer housing and its internal components. It will be appreciated that 
FIG. 6 is an exploded view of a transfer housing, while FIG. 7 shows an 
enlarged view of the transversely oriented and attached transfer housings 
(e.g., housings 46 and 48). Each housing includes an internal carrier 62 
and an external casing 64. Mechanical stability between internal carrier 
62 and external casing 64 is provided by two counter-positioned (e.g., 
oppositely disposed) conical roller bearings 66, 68 positioned to compress 
against their respective conical races, 70, 72. Conical races 70 and 72 
are permanently affixed into the external transfer casing 64. Carrier 
includes a shaft 122 extending therefrom and terminating at threading 74. 
Conical bearings 66, 69 are preferably made from hardened steel while 
races 70, 72 are also made from hardened steel. 
A second preferred alternative bearing arrangement will be discussed 
hereinafter after the first preferred embodiment is fully described herein 
for reasons of clarity. 
During assembly of transfer casing 48, a compressional force is applied 
using a nut 73, which is tightened to a specific torque on threads 74, 
providing a prestressed bearing situation resulting in no motion other 
than axial rotation under typically applied loads. Because of the 
necessity of a low profiled or such an arm during manual handling and the 
attendant reduction in the overall stiffness, it is preferable and, in 
fact required in certain applications, to also install a thrust bearing 76 
at the interface between carrier 62 and casing 64. Thrust bearing 76 
provides further mechanical stiffening between carrier 62 and casing 64 of 
the transfer housing. Thrust bearing 76 comprises five elements including 
thrust adjustment ring 300, flat annular race 302, roller bearing and cage 
304, annular race 306 and opposing thrust cover 308. Thrust bearing 76 is 
adjusted through a series of set screws 78 and provides for high bending 
stiffness. The transducer, (preferably an encoder 80 such as is available 
from Heindenhain under the designation Mini-Rod, part no. 450M-03600), is 
mounted to a universal mounting plate 82 for mounting into the transfer 
casing. Universal mounting plate 82 is important in satisfying possible 
component availability problems such that a change in manufacture of 
transducer 80 and, hence, the change in mounting screw configuration can 
be accommodated through modifications in the mounting plate 82. Mounting 
plate 82 is shown in FIG. 6A as a triangular shaped plate having rounded 
corners. FIG. 6A also depicts threaded members 88 and 90, a pin 86 and a 
coupler 84 (all of which are discussed hereinafter). 
High accuracy rotational measurements using encoders 80 require that there 
should be no loads applied to the encoders and that motion of the transfer 
casing be accurately transmitted to the encoder despite small 
misalignments of the axis of the transfer casing and axis of the encoder. 
The angular transfer errors are well known to those skilled in the art 
from the published encoder literature. Communicating with encoder 80 is a 
coupler 84 such as is available from Renbrandt under the designation 
B1004R51R. An extension shaft 86 is utilized for ultimately connecting 
encoder 80 to the transfer casing 64. Shaft 86 is attached both to coupler 
84 and to the end of carrier 62 at threading 74 using set screws 88, 90 
(see FIG. 7). In accordance with an important feature of this invention, 
an electronic preamplifier board 92 is positioned in close proximity to 
encoder 80 and is mounted (via screws 94) on the inside of cap cover 96. 
Cap cover 96 is attached to casing 64 via screw 97. A transition housing 
98 interconnects cap cover 96 to casing 64 via screw 97 and screws 100. 
Sealing of the transfer housing to the environment is accomplished at the 
joint using an O-ring groove 102 in which is mounted a standard rubber 
O-ring groove 104. A rotational endstop 106 (to be discussed hereinafter), 
is best shown in FIG. 6B and comprises a square shaped metal housing 
having an opening therethrough which is mounted onto casing 64 using bolt 
108 threaded through the opening of the housing. Wire pass through 
grommets to stop abrasion over long term use are mounted on both carrier 
62 and casing 64 at 110 and 112. A location pin 114 is received by a 
complimentary shaped recess 116 in carrier 62 for the purpose of 
maintaining relative orientation of two adjacent transfer casings. 
Referring to FIG. 7, for environmental and other reasons, it is important 
that all wire be completely hidden from sight and, therefore, contained 
within the arm 12. FIG. 7 depicts two assembled transfer housings 46, 48 
mounted perpendicularly to each other and demonstrating the passage of 
wires. It will be appreciated that during use of CMM 10, the encoder 
information from encoder 80 is passed to its processor board 92 through 
wire 118 which is then amplified and passed through the arm by machined 
passageways 120. Wire 118 then passes through a channel 120 in the shaft 
122 of the internal carrier 62 of the transfer casing 46 and through a 
grommetted hole 124 at which time it passes into a large cavity 126 
machined on the external casing 64 of transfer housing 46. Cavity 126 
permits the coiling of the wire strands during rotation of the transfer 
casing and is configured so as not to produce any wire abrasion and a 
minimum of wire bending. However, because the wire limits the overall 
ability to fully rotate, an incomplete spherical groove 128 is created in 
which is positioned an endstop screw, 130 which limits the full rotation, 
in this case to 330.degree.. A second preferred alternative end stop 
design which permits 660.degree. of rotation will be discussed hereinafter 
after the first preferred embodiment is fully described herein for reasons 
of clarity. It will be appreciated that the pass through channel 120 and 
wire coiling cavities 122 are subsequently repeated in each transfer 
casing allowing the wires to progressively make their way down to the 
connector mounted at the base 14, resulting in no exposed wiring. 
Turning now to FIG. 8, the construction of the aluminum arm as well as the 
various bearings and transducers results in an accumulated weight of 
approximately 10 to 15 pounds at the probe handle assembly 56 of CMM 10. 
Under normal circumstances, this would create a significant amount of 
fatigue during use and, hence, must be counterbalanced. Weight 
counterbalances are not preferred since they would significantly increase 
the overall weight of the device when being considered for 
transportability. Therefore, in a preferred embodiment counterbalancing is 
performed using counterbalance device 60 which comprises a torsional 
spring 132 housed in a plastic casing 134 and mounted at transfer housing 
42 at base 14 for providing a lift for arm 12. Coiled torsional spring 132 
can be mounted in a variety of positions affecting the overall pretension 
and, hence, may be usable on a variety of lengths and weights of arms 12. 
Similarly, due to the weight of arm 12 and the effect of the recoiled 
spring, significant shock loads may occur when repositioning the arm to 
the storage position. To prevent significant shocking of the arm upon 
retraction, air piston shock absorber 134 is also configured into plastic 
housing 142 of counterbalance spring device 60. This results in an 
absorption of the shock load and slow relaxation into the rest position. 
It will be appreciated that FIG. 8 depicts the shock absorber 134 in a 
depressed configuration while FIGS. 16-18 depict shock absorber 134 in a 
fully extended position. 
In FIGS. 9A and 9B, top and bottom views of probe handle assembly 56 are 
shown. Probe handle assembly 56 is meant to be held as either a pencil or 
pistol grip and possesses two switches (items 150 and 152 in FIG. 9A) for 
data taking, a connector (item 154 in FIG. 9B) for the attachment of 
optional electronics and a threaded mount 156 for receiving a variety of 
probes. Because the CMM 19 is a manual measurement device, the user must 
be capable of taking a measurement and then confirming to CMM 10 whether 
the measurement is acceptable or not. This is accomplished through the use 
of the two switches 150, 152. The from switch 150 is used t trap the 
3-dimensional data information and the back switch 152 confirms its 
acceptance and transmits it to the host computer 18. On the back of the 
switch enclosure 158 (housing 150, 152) is connector 154 which possesses a 
number of voltage lines and analog-to-digital converter lines for general 
attachment to a number of options such as a laser scanning device or touch 
probe. 
A variety of probes may be threaded to handle assembly 56. In FIG. 10A, 
hard 1/4 inch diameter ball probe 158 is shown while in FIG. 10B, a point 
probe 160 is shown. Both probes 158, 160 are threadably mounted to mount 
156 (using male threaded member 157), which in turn, is threadably mounted 
to probe housing 58. Mount 156 also includes a plurality of flat surfaces 
159 for facilitating engagement and disengagement of the probes using a 
wrench. 
Six additional preferred alternative probe designs will be described 
hereinafter after the rest of the elements of the first preferred 
embodiment of CMM 10 have been fully discussed for reasons of clarity. 
Turning now to FIGS. 11 and 12, a description of the controller or serial 
box 16 now follows. FIG. 11 shows the front panel face 162 of the 
controller or serial box 16. Front panel 162 has eight lights including 
power indicator light 164, error condition light 166, and six lights 20, 
one for each of the six transducers (identified as items 1-6) located in 
each transfer housing. Upon powering up, power light 164 will indicate 
power to the arm 12. At that time, all six transducer lights will indicate 
the status of each of the six transducers. In a preferred embodiment of 
this invention, the transducers are incremental digital optical encoders 
80 and require referencing. (In a less preferred embodiment, the 
transducers may be analog devices). Hence, upon start up, each of the six 
joints (e.g., transfer housings) must be rotated to find the reference 
position at which time the six lights shall turn off. 
In accordance with an important feature of the present invention, during 
usage, should any of the transducers approach its rotational endstop 106 
from within 2 degrees, a light and an audible beep for that particular 
transducer indicates to the user that the user is too close to the end 
stop; and that the orientation of the arm should be readjusted for the 
current measurement. The serial box 16 will continue to measure but will 
not permit the trapping of the data until such endstop condition is 
removed. A typical situation where this endstop feature is necessary is 
the loss of a degree of freedom by the rotation of a particular transducer 
to its endstop limit and, hence, the applications of forces on the arm 
causing unmeasured deflections and inaccuracies in the measurement. 
At any time during the measurement process, a variety of communication and 
calculation errors may occur. These are communicated to the user by a 
flashing of the error light and then a combination of lights of the six 
transducers indicating by code the particular error condition. It will be 
appreciated that front panel 162 may alternatively utilize an alphanumeric 
LCD panel giving alphanumeric error and endstop warnings. 
Turning to FIG. 12, the rear panel 168 of serial box 16 includes a variety 
of standard PC connectors and switches including a reset button 170 which 
resets the microprocessor; an AC input fan 172 for air circulation; a 
connector 174 for a standard PC AT keyboard, connector 176 for an optional 
VGA board for monitoring of the internal operations of serial box 16, 
connector 178 for receiving the variety of signal lines for the CMM data, 
and connector 180 for the standard RS232 connector for the host 18. 
Serial box 16 is responsible for monitoring the temperature of the CMM and 
in real time modifying the kinematics or mathematics describing its motion 
according to formulas describing the expansion and contraction of the 
various components due to changes in temperature. For this purpose, and in 
accordance with an important feature of this invention, a temperature 
monitoring board 182 (which includes a temperature transducer) is 
positioned at the location of the second joint 42 on the interior of a 
cover 184 (see FIGS. 4 and 5). CMM 10 is preferably constructed of 
aircraft grade aluminum externally and anodized. Preferably, the entire 
arm 12 is constructed of the same material except for the mounting screws 
which are stainless steel. The same material is used throughout in order 
to make uniform the expansion and contraction characteristics of arm 12 
and make it more amenable to electronic compensation. More importantly, 
the extreme degree of stability required between all parts through the 
large temperature range requires that there be no differential thermal 
expansion between the parts. As mentioned, the temperature transducer 182 
is preferably located at transfer housing 42 because it is believed that 
this location defines the area of highest mass and is therefore the last 
area to be stabilized after a large temperature fluctuation. 
Referring now to FIG. 13, the overall electronic schematic layout for CMM 
10 and serial box 16 is shown. Six encoders 80 are shown with each encoder 
having an amplifier board 92 located in close proximity to it for the 
minimization of noise on signal transfer. An option port 154 is shown 
which is a six pin connector available at the handle 56 for the attachment 
of a variety of options. Two control buttons 150 and 152 for indicating to 
serial box 16 the measurement process, are also shown. 
The temperature transducer is associated with a temperature circuit board 
182 which is also located in arm 12 as shown in FIG. 13. In accordance 
with still another important feature of this invention, the temperature 
board 182 comprises an EEPROM board. The EEPROM is a small computerized 
memory device (electrically erasable programmable read only memory)and is 
used to contain a variety of specific calibration and serial number data 
on the arm (see discussion regarding FIGS. 19-21). This is a very 
important feature of this invention which permits high quality control of 
CMM 10 and importantly, precludes the inadvertent mixup of software and 
arms. This also means that the CMM arm 12 is a stand alone device not 
requiring specific calibration data to reside in controller box 16 which 
may need to be separately serviced and/or switched with other machines. 
The electronic and pulse data from the arm electronics is then transmitted 
to a combined analog-to-digital converter/digital counting board 186 which 
is a paired set comprising a 12 bit analog to digital converter and a 
multi channel 16 bit digital counter. Board 186 is positioned on the 
standard buss of the controller box. The counting information is processed 
using the core module 188 (comprising a commercially available Intel 286 
microprocessor such as a part number CMX-286-Q51 available from Ampro) and 
programs stored on an EEPROM also residing in the controller box. 
Subsequent data is then transmitted through the serial communication port 
189. 
The microprocessor-based serial box 16 permits preprocessing of 
calculations specific to CMM 10 without host level processing 
requirements. Typical examples of such preprocessor calculations include 
coordinate system transformations; conversion of units; leap-frogging from 
one coordinate system to another by using an intermediary jig; performance 
of certain certification procedures, including calculations of distance 
between 2 balls (such as in ANSI B89 ballbar); and outputting data in 
specific formats required for downloading to a variety of hosts and user 
programs. 
The serial box is configured to communicate with a variety of host formats 
including PC, MSDOS, Windows, Unix, Apple, VME and others. Thus, the 
serial box processes the raw transducer data on an ongoing basis and 
responds to the information requests or polling of the host computer with 
the desired three dimensional positional or orientational information. The 
language of the serial box is in such a form that drivers or computer 
communication subroutines in microprocessor 188 are written in the 
language of the host computer so as to drive the serial port and 
communicate with CMM 10. This function is designated the "intelligent 
multiprotocol emulation and autoswitching" function and works as follows: 
A variety of host programs may be installed on the host computer. These 
host programs will poll the serial port with a variety of requests to 
which the serial box must respond. A number of protocols have been 
preprogrammed into the serial box to respond to polls or inquiries on the 
serial port for a variety of different, popular softwares. A polling 
request by a software requires a specific response. The serial box will 
receive the polling request, establish which protocol it belongs to, and 
respond in the appropriate manner. This allows transparent communication 
between CMM 10 and a wide variety of application software such as computer 
aided design and quality control softwares, e.g., AutoCad.RTM. from 
Autodesk, Inc., CADKEY.RTM. from Cadkey, Inc., and other CAD programs; as 
well as quality control programs such as GEOMET.RTM. from Geomet Systems, 
Inc. and Micromeasure III from Brown and Sharpe, Inc. 
The three dimensional CMM of the present invention operates as follows. 
Upon power up, the microprocessor 188 in the serial box 16 undergoes start 
up self-checking procedures and supplies power through the instrument port 
to arm 12 of CMM 10. The microprocessor and software residing on EEPROM 
182 determines that upon initial power up none of the encoders 80 have 
been initialized. Hence, the microprocessor 188 sends a signal to the 
display board lighting all the lights 20, indicating a need to be 
referenced. The user will then mechanically move the arm which will cause 
the transducers to individually scan their range, at which time a 
reference mark is passed. When the reference mark is passed, the digital 
counter board 186 responds by trapping its location and identifying to the 
front display board 20 that the transducer has been referenced and the 
light is extinguished. Once all transducers have been referenced, the 
system establishes serial communication with the host and waits for 
further instruction. Pressing of the front or back button of handle 56 
will initiate a measurement process. Pressing the front button 150 will 
trap the current transducer readings. Pressing the back button 152 will 
indicate to the microprocessor that these values are to be translated into 
dimensional coordinates and issued through the serial port to the host 18. 
The host 18 and the serial box 16 will then continue to react to each 
other's serial line requests. 
Turning now to FIGS. 19, 20 and 21 subsequent to assembly of CMM 10, the 
device is optimized or calibrated by altering the program software to 
account for any measured imperfections in assembly or machining. This 
initial calibration is an important feature of this invention and is 
accomplished in two stages. First, a variety of dimensional measurements 
are made which include positions, orientations and dimensions throughout 
the entire volume of the device. Subsequently, an optimization software 
program is used to determine the actual misalignments exiting at each of 
the joint axes and, hence, adjusting the kinematic formulas describing the 
motion of the arm. The general result is that imperfect machining and 
assembly is rendered perfect through the identification of those 
imperfections and their inclusion in the kinematics of the device. 
Referring to FIGS. 19 and 20A-E, due to the huge amount of data and the 
requirement that it be accurately and easily obtained, a calibration and 
testing jig is shown at 320. Jig 320 is comprised of a large granite plate 
322 to which is attached two spaced towers 324, 326 which can rotate 360 
degrees in the horizontal plane. The CMM 10 is mounted on tower 326 and 
the adjustable dimensional testing jig 320 is mounted on the other tower 
324. Jig 320 is mounted on an extendable vertical arm 328 which is 
vertically displaceable within an opening 330 through tower 324. Arm 328 
is shown in a fully extended position. 
Still referring to FIGS. 19 and 20, the adjustable dimensional testing jig 
320 is comprised of three basic components: a 24 inch bar 332 on which is 
found a set of precision balls 334, a series of holes 336 positioned along 
its length, and a 24 inch precision step gauge 338 (shown in detail in 
FIGS. 20A-E) Arm 332 is used to measure the positions of the holes, steps 
and balls in a variety of positions for the testing jig and in all areas 
of the volume of the arm as shown in FIG. 21. This data is then optimized. 
In summary, the important optimization procedure can be described as 
follows. Standard test jig 320 with predetermined positions and 
orientations of objects is measured by arm 10. The data is then processed 
through a multi-variable optimization program created to provide the 
relative misalignment and dimension of all major components of the arm. 
Optimization is performed, at which time a calibration file is produced 
containing the overall characteristics of the arm. These overall 
characteristics and subsequent transducer readings are combined in a 
variety of kinematic formulas which will generate the X, Y and Z values in 
an absolute coordinate system. 
In order to further optimize performance, a novel reference ball 192 
extends laterally from a detachable mount 194 attached to base 14 of CMM 
10 (see FIGS. 14 and 15). By locating reference ball 192 at base 14, ball 
92 represents the absolute origin of the device (0, 0, 0) corresponding to 
the X, Y and Z axes. Because of the known position of reference ball 192, 
positioning of the tips, as shown in FIG. 15, allows the present invention 
to determine the coordinates of the digitizer tip 158 in relationship to 
the last link of CMM 10. Knowledge of this position allows CMM 10 to 
determine the position of the center of that ball when making subsequent 
measurements. In a general sense, this means that a variety of different 
probes may then be attached depending on the particular application and 
each can be calibrated against the reference ball. 
Because of the portable nature of the present invention, it will be 
subjected to significant mishandling and repositioning in a variety of 
environments. Therefore, the present invention includes a protocol by 
which the user may establish a degree of volummetric accuracy prior to 
using a device according to a convenient maintenance schedule. Volummetric 
accuracy is defined, according to ASME ANSI B891.1.12 (1989) standard, as 
the ability of a device to measure a fixed length which is positioned in 
its working volume in a variety of orientations. FIG. 16 shows the 
capability of this invention to do this using a first ballbar approach 
while FIGS. 17 and 18 depict a second ballbar approach. 
FIG. 16 shows a standard ballbar 196 at each end of which is positioned a 
precision spherical ball 198, 200 which are mounted respectively into two 
magnetic sockets 202 and 204. Socket 202 is located at base 14 of CMM 10 
and socket 204 is located at probe handle 56. As arm 12 is moved about, 
the sockets 202, 204 and balls 198, 200 rotate to accommodate this 
movement and CMM 10 is required to measure the fixed distance between the 
center of ball 200 and socket 204 at the handle 56 and the center of ball 
198 at the base. Remembering, of course, that socket 202 at base 14 
represents the 0, 0, 0 coordinate of CMM 10, calibration software in 
control box 16 then calculates the vector length from the 0, 0, 0 to the 
center of the ball at the probe and this length, which, of course, is 
unchanging during the test, must measure constantly throughout the entire 
volume through multiple configurations and rotations of the handle and 
other joints. 
It will be appreciated that the socket 204 at the handle, may tend to be 
inconvenient and inconclusive when wanting to verify the accuracy of a 
particular probe on the handle. Hence, in accordance with an important 
feature of this invention, a novel cone socket ballbar as shown at 206 in 
FIG. 17 is used. Cone socket ballbar 206 includes a cone 208 at one end 
and two balls 210, 212 at the other end. The cone and balls are 
interconnected by a bar 207 having an angled portion 209 with then angle 
.alpha. preferably comprising 20 degrees. Ball 212 is attached to a mount 
211 which extends laterally from bar 207. A ball probe 158 or point probe 
160 is positioned in cone socket 208 and ball 210 can be mounted in the 
standard magnetic socket 202 of base 14 of CMM 10. As in the calibration 
method of FIG. 16, a number of positions of the ball and bar and joint 
positions are measured and the distance between cone socket 208 and ball 
210 must remain constant. It is the nature of the positioning of ball 
socket 202 that the user will not be able to reach on the far side of the 
machine (position shown by Item 214). To this end, ball 212 is used as 
shown in FIG. 18. This allows the user to position cone ballbar 206 so as 
to reach on the reverse far side of CMM 10 in order to measure the 
distance between the center of ball 212 and the center of cone socket 208. 
One of the most severe problems encountered with the use of the CMM 
(portable coordinate measuring machine) in accordance with the present 
invention is that the stand or base on which the arm is mounted through a 
loading plate may not be entirely stable with respect to the item which is 
being measured. This is caused by the fact that the loading plate to which 
the base of the arm is mounted may not be entirely stable with respect to 
the item being measured because the measured item is fixed to a separate 
mounting table or is pan of a larger assembly. This instability can 
adversely affect the high accuracy of the CMM. To resolve this problem, 
strut supports are provided which are mounted at the one end to threaded 
holes aimed radially outward from the base loading plate and at the second 
end are fitted with universal clamps (i.e., C-clamps). The strut support 
is provided with an adjustment screw to adjust the length of the strut to 
properly reach the measured item. The strut is intended to be used in 
pairs preferably by means of an identical strut on the opposite side of 
the base loading plate. 
Referring now to FIG. 22, the details of the strut and its use will be 
described. The base 14 of the measuring arm 10 is mounted into base plate 
38 of a theodolite stand 22 or other suitable rigid plate in a known 
manner. Base plate 38 has threaded holes 400 of a suitable known size 
extending outwardly in at least two places directly opposite each other. 
Strut 402 is generally comprised of four elements. There are two arm 
elements 404, an adjustment screw 406 and a universal clamp 408 (i.e., 
C-clamps) as shown. Of course, instead of a C-clamp as shown, any number 
of adaptable attachment devices could be used such as magnetic clamps and 
suction clamps. As shown in FIG. 22, an item 410 to be measured by the 
three dimensional measuring arm 10 is mounted to a second mounting plate 
412 or is otherwise rigidly fixed. Thus both base plates 38 and 412 are 
held rigidly in relation to one another and instability is reduced to an 
absolute minimum. 
Three basic arm configurations in accordance with the present invention of 
three dimensional coordinate measuring apparatus or CMM's have been 
developed to meet a wide range of needs and conditions. Two of these arm 
configurations allow for six degrees of freedom. A third arm configuration 
allows for seven degrees of freedom. These three arm configurations 
represent three preferred embodiments of the present invention. Each 
embodiment has advantages for different functions and/or measuring 
conditions as dictated by the objects being measured or function or 
operation being performed. FIGS. 3 and 23A-C describe each of these 
configurations. Also reference to FIG. 3 should also be made. FIGS. 23A-C 
are diagrammatic representations of degrees of freedom allowed in CMM 10. 
The support base 14 allows two degrees of freedom as indicated by the 
rotational arrows 421 and 422. 
CMM 10 may be compared to the arm configuration of the human body as 
consisting of elements such as a shoulder which would be equivalent to 
support base 14, The elbow element, 444, 50 is the equivalent of the elbow 
of the human arm and the handle/probe assembly 56 is equivalent to the 
human wrist. The design FIG. 23A which has two degrees of freedom 
represented at the shoulder, elbow and wrist (designated 2-2-2) is more 
easily able to probe into difficult to reach areas. On the other hand, the 
FIG. 23B design which has two degrees of freedom at the shoulder, one 
degree of freedom at the elbow and three degrees of freedom at the wrist 
has the following advantages. The provisions of three degrees of rotation 
(2-1-3 design) at the end effector (wrist) allows full orientation and 
positioning of an object or non-axial probe. Each of the two 
configurations discussed heretofore (FIGS. 23A and B) have very specific 
advantages as already described. The third preferred arm configuration 
(FIG. 23B) has the combined advantages of the two arm configurations 
discussed above by providing seven degrees of freedom (a 2-2-3 
configuration). This third preferred arm configuration provides the 
combined advantages of reach and positioning of the 2-2-2 design and the 
full end effector orientation capabilities of the 2-1-3 design. 
As previously stated, all three configurations have two degrees of freedom 
at the shoulder (support base 14). In FIG. 23A, the two degrees of freedom 
of the elbow are designated by the rotational arrows 424, 426 and finally 
the two degrees of freedom at wrist (or effect element) assembly 56 are 
designated by the rotational arrows 428, 430. In FIG. 23B, the one degree 
of freedom of the elbow segment is designated by the rotational arrows 
434, 436, and 438. Lastly, in. FIG. 23C, the two degrees of freedom of the 
elbow segment are designated by the rotational arrows 444, 446 and 448. 
Of course, it should be noted that each degree of freedom adds to the cost 
and/or weight of the CMM. That is one of the reasons for offering the 
three different configurations in accordance with the present invention to 
accommodate the various needs of different requirements (measuring or 
processes) that may be needed without increasing the cost of CMM except as 
is required. 
FIGS. 24A and 24B are diagrammatic representations of two preferred means 
in accordance with the present invention for interconnection of the signal 
paths between the CMM 10 (coordinate measuring machine), or controller or 
serial box 16 and the host computer 18. In FIG. 24A (also refer to FIG. 
1), CMM 10 is electronically connected to serial box 16 by known cabling 
means 460 and again serial box 16 is connected by known cabling means 462 
to host computer 18. This method of interconnecting the CMM 10, controller 
or serial box 16 and the host computer 18 is and has proven quite 
satisfactory for innumerable applications of the present invention. 
However, there are applications presently known and envisioned in the 
future where distance or environmental or other conditions would make 
wireless telemetry the only or preferred method for interconnecting the 
signals between CMM 10, serial box 16 and host computer 18. This is 
accomplished in accordance with the present invention by the means shown 
in FIG. 24B. The circuitry and components are miniaturized and mounted 
directly on port base 14 of device 10 designated as 464. Miniaturized 
serial box 464 includes a telemetry device 466 which is provided with 
means capable of transmitting telemetry signals 468 which are received by 
a telemetry receiver 470 mounted on host computer 18. Thus, items 10 and 
18 are freed of the need to use cabling 460, 462, 
FIGS. 25A and 25B depict two preferred bearing designs. The bearing design 
of FIG. 25A has hereinbefore been described in complete detail as depicted 
in FIGS. 6 and 7. To summarize, a pair of counter positioned layered 
bearings with inner race 480 and outer race 482 are positioned around a 
shaft and preloaded using a nut 484. The preloading is determined entirely 
by the amount of torque applied to the nut 484. This design is quite 
satisfactory for many applications and has been used with considerable 
success. However, under certain conditions and applications it is 
difficult to maintain consistent loading parameters. In these cases, a 
second preferred alternative embodiment of the bearing design is provided 
in accordance with the present invention. 
This second preferred alternative embodiment of the bearing design is 
depicted in FIG. 25B. In FIG. 25B, a pair of bearings (usually called 
duplex bearings) 486 which are usually radial ball bearings and which are 
preground to permit very specific preloading replace the conical bearings 
of FIG. 25A. The preloading is preset by the use of fixed spacers 488, 490 
and these fixed spacers 498, 490 are tightened down completely by a nut 
492. The difference between the duplex bearing casing are accommodated and 
the amount of preload is predetermined by deformations in the transfer 
casing at the time of tightening nut 492. An advantageous feature of this 
second preferred embodiment is that the nut 492 can be tightened as much 
as possible without any damage of overloading the bearings 486 along the 
shaft 494. 
As hereinbefore discussed, with reference to FIGS. 10A-B, a ball probe 158 
and a point probe 160 were described and of course are satisfactory for 
their intended use in accordance with this invention. Six additional probe 
embodiments in accordance with the present invention will be discussed in 
detail by referring to FIGS. 26A-F and FIGS. 9A-B. FIGS. 9A-B are front 
and rear side elevation views of probe handle assembly 56. 
Referring first to FIGS. 26A-C, an adapter 500 is fitted onto the end 
effector of probe handle assembly 506. Probe 508 which is either of a 
different size and/or configuration has a relatively longer depth bore 510 
and the bore is designated as 572. Both probes 502 and 508 have a male 
thread 514 sized to match the female thread 516 at the end of adapter 500. 
Because of the dirty and rigorous environment of the industrial 
applications in which it is necessary and desirable to use these probes, 
the use of electrical contacts are often too problematic. To overcome this 
problem, a probing shaft 518 extends downwardly from a transducer 520 
which in turn is connected to the internal circuitry through wiring 522 
which connects the probe signal to the rest of the CMM 10 through the 
probe handle assembly 56. Any number of probes thus can be automatically 
identified through this invention, thus preventing any errors that would 
result from manually selecting the wrong probe. In this way, a number of 
probes can be used that would be difficult to identify with the human eye. 
Of course, many other applications can be made of this automatic probe 
identification system. It should be noted that probing shaft 518 is of a 
slightly smaller diameter than the bores 504, 512. Arrow 524 represents 
the axial motion of probing shaft 518. 
Turning now to FIGS. 26D and 26E, another embodiment of a probe in 
accordance with the present invention is generally shown at 530. Marking 
probe 530 is comprised of mounting system 532, a clamp 534 and a marking 
pen 536. Mounting stem 532 has a shank 538 which is suitably sized to 
enter a bore 540 for either a press fit into bore 540, or may be welded or 
otherwise suitably fastened to clamp 534. The other end of shank 538 of 
mounting stem 532 has a suitably sized male thread 542 to be threaded into 
the female bore 544 of the probe handle assembly 56. FIG. 26E is a 
cross-section of clamps 534 taken along line 26E--26E at the center line 
of marking pen tightening set screw 546. Note that space 548 allows for 
secure tightening of marking pen tightening set screw 546. The arrow 550 
indicates the direction in which mark 552 is being made. It should be 
noted that in this manner, the marking probe 530 can be used with a wide 
variety of marking implements to create highly accurate lines and/or other 
operations with the benefit of the inherent accuracy of the CMM 10 of this 
present invention. 
A third additional preferred embodiment of a probe in accordance with the 
present invention is shown in FIG. 26F and is generally shown at 560. 
Automatic punch probe 560 is comprised of a standard recoil punch probe. 
The mounting portion 562 of punch probe 560 has a male thread 564 which is 
sized to be threaded into female thread 566 of probe handle assembly 56. 
Internally, automatic punch probe 560 contains a recoil spring and trigger 
assembly 568 which allows the positioning of the punch point 570 along the 
axial direction as shown by arrows 572. Positioning the automatic punch 
probe 560 in the desired location and then pushing the punch point 570 in 
the axial direction 572 toward the probe handle assembly 56 will thus 
actuate a spring release (which is part of the recoil spring and trigger 
assembly 568) and penetrate a punch prick point without the use of a 
hammer and therefore achieve location within the high accuracy limits of 
CMM 10 equal to or close to those accuracy limits that are possible with 
the same CMM 10 when used only for measurements. 
Turning now to FIG. 26G, a fourth additional preferred embodiment of a 
probe in accordance with the present invention and known as a force 
sensing probe will now be described. Basically, this force sensing probe 
may be equipped with a variety of end tips (ball tip, points tip, flat 
bottom tips, etc.) which are attached to probe body 582. The force sensing 
probe is generally shown at 580. A spherical end tip 584 is shown in FIG. 
26G. At the top of the force sensing probe 580 is a male mounting thread 
586 which is sized to threadably attach to female thread 588 of probe 
handle assembly 56. The force sensitive probe 580 has internally mounted 
strain gauges 590 preferably of the readily available and known standard 
resistive type (such as those manufactured by Omega Engineering, Inc. of 
Stamford, Conn.), and is connected to the circuitry through connector 592, 
cable 594 and finally to a suitable connector 596 to connect to the option 
port 154 of probe handle 56. When the end tip 584 comes in contact with a 
surface to be measured, the associated forces that develop deform the 
probe body 582 causing electrical changes in the strain gauges 590, which 
in turn, automatically trigger the signals through the cabling 594 which 
thence, is fed through the option port 154 of probe handle assembly 56 and 
then through the circuitry of CMM 10 through the serial box 16 and the 
host computer 18. It should be noted that strain gauge technology is well 
established and known in the art. While there is a variety of other 
methodologies for measuring strain, experience in the art has demonstrated 
that the methodology discussed herein is the preferred methodology. 
FIG. 26H depicts a fifth additional preferred embodiment of a probe in 
accordance with the present invention, this probe being known as a drill 
mounting probe. The drill mounting probe is generally shown at 600. Drill 
mounting probe 600 is compromised of mounting stem 602, body 604 and 
rotary assembly and shaft 606 laterally displaced from mounting stem 602. 
Mounting stem 602 is sized at one end to be installed via press fitting 
into base 608. 
Of course, any known method such as welding may be used to install mounting 
stem 602 into body 604. Mounting stem 602 has a male thread 610 at its 
upper end sized to fit the female mounting thread 612 of probe handle 
assembly 56. Rotary assembly 606 is comprised of a shaft 614, an assembly 
nut 620, a pair of bearings 616 and chuck 618. Shaft 614 is sized at one 
end to be received by the chuck of a standard drill or other rotary 
portable power source 622 known to the industry. Body 604 is substantially 
of rectangular shape and is sized to adequately support the rotary power 
source described above and is preferably made of aluminum. Assembly nut 
620, shaft 614, the pair of bearings 616 and chuck 618 can be assembled in 
any number of known ways. The bearings 616 are preferably of the ball 
bearing type. Chuck 618 is sized to handle any desired size drill bit or 
other tool (i.e., countersink, etc.). The rotary direction of the drill is 
the same as the direction of the power source 622 as shown by rotary arrow 
624 shown between power source 622 and rotary assembly 606 and rotary 
arrow 626 shown below drill bit 628. The resulting holes or other 
operations again, with the use of the discussed probe, are within the high 
accuracy limits of CMM 10. 
A sixth additional preferred embodiment of a probe in accordance with the 
present invention is known as a contact probe and is depicted 
schematically in FIG. 26I and generally shown at 650. A cable 652 is 
connected at one end through a connector 654 to the option port 154 of the 
probe handle assembly 56. The other end of cable 652 is terminated in an 
alligator clip or other suitable termination 656 to make contact with the 
metallic object 658 to be measured or other desired functions to be 
performed. A voltage is applied to cable 652. Grounding occurs as a result 
of contact by the end probe 660 (shown in solid lines when retracted and 
dotted lines when extended) contact with the object 658. As a result of 
this contact with object 658 the voltage V drops to the potential of 
ground and the software in the analog to digital converter (A to D) 659 
has been designated to consider the grounding of cable 652 through the A 
to D device to be identical to the actuation of the buttons 150, 152 of 
the probe handle assembly 56. This option port 154 is connected through 
the cable 652 and the termination 656 to the object 658 which is metallic 
or conductive. In this manner, the probe 660 is grounded when probe 660 
comes into contact with the conductive object 658. Grounding the cable 652 
and reducing the voltage V to ground level results in a grounding signal 
being sent through the A to D device and software to actuate the probe 
handle assembly 56. Therefore, any time the end probe 660 contacts the 
object 658, the result is equivalent to a probe handle assembly 56 switch 
actuation. This is an ideal set up for scanning metallic objects and 
eliminates the tiring need to constantly activate the switch on the probe 
handle assembly 56. A further advantageous feature of this contact probe 
650 of the present invention is that because the contact switch actuation 
occurs at the first instance of the probe tip 660 touching the object 658, 
any additional or subsequent movement involving the object 658 are 
obviated or precluded and the initial measurements are therefore clear of 
any extraneous impulses. 
Referring back again to FIG. 7 and the heretofore detailed discussions 
concerning the ability to rotate the various transfer casings of the arm 
where there is provided an incomplete spherical groove 128 and an end stop 
screw 130 which protects the elements of the arm by limiting the full 
rotation and individual set of transfer casings to a maximum of 
330.degree.. This arrangement is completely satisfactory for a 
multiplicity of uses for the CMM 10. However, as will now be discussed, a 
second preferred embodiment of the present invention allows for 
660.degree. of rotation instead of just 330.degree. of rotation of each 
transfer casing set. 
This novel mechanism includes the creation of two incomplete circular 
grooves in the two halves of the transfer case in which is placed an arc 
shaped shuttle which is free to transfer through the respective two 
grooves aforementioned and provide a hard stop at the incomplete groove 
ends after a full 660.degree. of rotation. Referring now to FIGS. 27A-27E, 
a transfer case set is shown schematically at 700. FIG. 28A is a top view 
of the arch shaped shuttle and FIG. 28B is a side elevation view of the 
arc shaped shuttle used in this second preferred design that allows a full 
660.degree. of rotation in any set of transfer cases of the present 
invention. Matching channels are machined to a suitable depth in the 
shoulder of the transfer case shaft and the mating shoulder of the 
transfer case housing sized to accommodate the shuttle 701 (see FIGS. 29A 
and 28B). In one example, shuttle 702 is preferably 0.246" in height and 
the inside radius is preferably 1.042 and the outside radius is preferably 
1.187" with the length of shuttle 702 representing a 20.degree. arc at 
these radii shuttle 702 is made preferably of plastic material. X arc 
represents the 30.degree. stop arc in transfer case housing shoulder and Y 
represents the 30.degree. stop arc in the transfer case shaft shoulder. 
Groove 504 in the transfer case housing is sized to accommodate one half 
of the elevation height of shuttle 702 and suitably finished so that the 
shuttle 702 freely travels in the groove 704 of the transfer casing 
housing (see FIG. 27B) and the groove 706 of the transfer case shaft (see 
FIG. 27C). Shuttle 702 is depicted by cross-hatching in FIGS. 27B-27E. As 
can be seen in FIGS. 27B and 27C, shuttle groove is free to travel from 
the P position adjacent to the X stop segment in FIG. 27B (representing 
the shuttle groove in the transfer case shoulder housing) and the P 
position adjacent to the Y stop segment in FIG. 27C (representing the 
shuttle groove in the transfer case shaft shoulder) 330.degree. to the P1 
position adjacent to the X stop segment in FIG. 27B and the P1 position 
adjacent to the Y stop segment in FIG. 27C. As seen in FIG. 27D, shuttle 
702 is now rigidly fixed between segment Y and segment X as seen in FIG. 
27D after counter clockwise rotation of 330.degree.. In FIG. 27E, the 
transfer case assembly is thus allowed to rotate an additional 330.degree. 
in a clockwise direction. It should be noted that the shuttle 702 is 
designed to have a shear strength to protect the elements of the CMM 10 
from deformation should the arm be moved beyond the 660.degree. provided 
by this invention as a safety precaution. Not shown is a window slot 
provided for easy replacement of the shuttle 702. 
While preferred embodiments have been shown and described, various 
modifications and substitutions may be made thereto without departing from 
the spirit and scope of the invention. Accordingly, it is to be understood 
that the present invention has been described by way of illustrations and 
not limitation.