Manual three dimensional coordinate measuring machine

A manual three dimensional coordinate measuring machine has a probe manually movable along three orthogonal coordinate axes, X, Y and Z, and a Z axis member supporting the probe. The size and shape of a workpiece is determined by displacements along the three axes from a predetermined origin when the probe contacts the workpiece. The manual coordinate measuring machine further includes a slide ring positioned at the bottom side of the Z axis member and at least one elastic member. The slide ring is movable in an arbitrary direction relative to the Z axis and along the Z axis. The slide ring is held at a predetermined position in the plane and along the Z axis by the at least one elastic member. The at least one elastic member allows the slide ring to move in the plane or along the Z axis by elastic deformation of the at least one elastic member in response to a force which is larger than a predetermined value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to coordinate measuring machines. In particular, 
this invention relates to a manual or floating-type coordinate measuring 
machine having a probe which is movable along three orthogonal coordinate 
axes, X, Y and Z. The probe is provided on a Z axis member, which is 
manually movable along the three coordinate axes. The size and shape of a 
workpiece is determined by the displacements along the three axes from a 
predetermined origin as the probe contacts the workpiece. 
2. Description of the Related Art 
Manual three dimensional coordinate measuring machines (CMM) are known. 
Such CMMs have a probe which is manually movable along three orthogonal 
coordinate axes, X, Y and Z, by an operator. The probe is provided on a 
tip or bottom of the Z axis member. The size and shape of a workpiece is 
determined by the displacement of the probe along the three axes from a 
predetermined origin as the probe contacts the workpiece. 
The structure of such manual three dimensional coordinate measuring 
machines is simpler than that of automatically driving coordinate 
measuring machines. Automatic CMMs are automatically movable along three 
axes by means of driving mechanisms provided for these axes. The manual 
CMMS, on the other hand, have probes which are rapidly movable toward a 
given direction or place by the hand of the operator. Manual CMMs, 
however, are prone to problems during manual operation, including: (i) 
force being applied to the tip of the Z axis member to deflect the tip; 
and (ii) the forces applied to the tip during operation vary from operator 
to operator. Due to these problems, the accuracy of manual CMMs decreases 
because each operator moves the Z axis member with his own velocity or 
acceleration. Additionally, in manual three dimensional coordinate 
measuring machines which use air bearings as sliding mechanisms for the 
three axes, the accuracy decreases due to the gap variation in the air 
bearings. 
A mechanism for decreasing the deflection of the Z axis member is described 
in Japanese Unexamined Patent Publication No. 54-107763. In the manual CMM 
described in this reference, the bottom of the Z axis, which is provided 
with a probe or sensing element, has a pair of blade springs provided 
parallel to the Z axis. The tops of the blade springs are fixed to the Z 
axis. The bottoms of the blade springs can be displaced in the X axis. A 
handling flange is provided at the bottom of the parallel blade springs. 
An X axis movement sensor, comprising two limit switches, and opposed to a 
respective one of the blade springs for sensing movement of the blade 
springs and a Y axis movement sensor having the same configuration are 
provided perpendicular to the Z axis. Mechanisms for imparting auxiliary 
forces are provided on two axes. 
In operation of the manual CMM described in this reference, air is jetted 
in the reverse direction of movement detected by the movement sensors to 
impart a thrust smaller than the frictional resistance in the detected 
direction. When the probe is moved in the X axis and Y axis directions 
while holding the handling flange, the blade springs are displaced toward 
such directions to jet air in the reverse direction of the movement. Thus, 
hysteresis errors due to the deflections in the X and Y directions can be 
eliminated and the accuracy can be improved. 
Because the configuration set forth above, however, requires the X axis and 
Y axis movement sensors each having a pair of parallel blade springs and 
the mechanisms for imparting the auxiliary forces, the structure of this 
apparatus is complicated and the deflection further increases due to the 
increased weight of the apparatus provided for each axis. Furthermore, 
because two X axis and two Y axis movement sensors must be provided 
perpendicular to the Z axis, the structure is further complicated. 
Moreover, because the configuration set forth above eliminates hysteresis 
errors due to the X axis and Y axis deflections formed when the Z axis 
moves, (in other words, formed by movement from the static state) the 
moving direction must be detected before the Z axis moves in the X axis or 
Y axis direction. Thus, the parallel blade springs of each movement sensor 
must be displaced by a small force. However, when the Z axis moves with a 
great deflection of the blade springs, the probe can contact the 
workpiece. Thus, the forces applied to the tip of the Z axis member vary 
from operator to operator and the measured accuracy remains low. 
SUMMARY OF THE INVENTION 
This invention thus provides a manual three dimensional coordinate 
measuring machine having a simplified structure and an improved 
measurement accuracy which is not dependent on the operator. 
This invention further provides a manual three dimensional coordinate 
measuring machine which enables a manual operation, such that when a probe 
contacts a workpiece, the acceleration is suppressed to at most a 
predetermined value just before the probe contacts the workpiece. 
This invention also provides a manual three dimensional coordinate 
measuring machine which achieves a highly accurate measurement by 
automatically eliminating data obtained when the probe contacts the 
workpiece at too large an acceleration. 
In the manual three dimensional coordinate measuring machine constructed in 
accordance with this invention, a probe is provided on a Z axis member and 
is manually movable along three orthogonal coordinate axes, X, Y and Z. 
The size and shape of a workpiece is determined by the displacements along 
the three axes from a predetermined origin as the probe contacts the 
workpiece. The manual CMM includes: 
a slide ring provided at a bottom side of a Z axis member, the slide ring 
movable in an arbitrary direction relative to the Z axis, the slide ring 
held at a predetermined position relative to the Z axis; and 
at least one elastic member holding the slide ring at the predetermined 
position relative to the Z axis and allowing the slide ring to move in an 
arbitrary direction relative to the Z axis by elastic deformation of the 
at least one elastic member in response to a force larger than a 
predetermined value. 
The bottom side of the Z axis member also includes a position lower than 
the bottom end of the Z axis member provided by, for example, positioning 
a probe adaptor at the bottom end of the Z axis member, as well as the 
bottom section of the Z axis member. 
According to this structure, the probe contacts the workpiece to generate a 
measurement while the operator holds the slide ring and moves the probe 
along three coordinate axes. When the probe moves along the X axis and Y 
axis and a force larger than a predetermined value acts on the slide ring, 
in, for example, a plane (XY plane) perpendicular to the Z axis, the at 
least one elastic member is elastically deformed. The operator holding the 
slide ring can perceive the deformation of the at least one elastic member 
as a motion of the slide ring. Because the probe can contact the workpiece 
while the velocity of the probe decreases, the at least one elastic member 
is elastically deformed. This elastic deformation suppresses the 
acceleration to at most a predetermined value just before the probe 
contacts the workpiece. Therefore, a force acting on the slide ring (or a 
force relative to the Z axis) can be readily maintained at a predetermined 
value or less. Therefore, the variation in the measurement accuracy 
dependent on the operator can be decreased. Further, the structure is 
simplified by the combination of the slide ring with the at least one 
elastic member. 
In the manual three dimensional coordinate measuring machine described 
above, the slide ring is preferably provided at the bottom of the Z axis 
and at the periphery of the probe adaptor which detachably holds the 
probe. The at least one elastic member is preferably provided between the 
slide ring and the probe adaptor. By this structure, the slide ring can be 
attached to the Z axis member without any additional work and the probe 
can be detachably held on the Z axis member of an existing manual three 
dimensional coordinate measuring machine. Thus, the machine can be 
fabricated with a low cost. 
In the manual three dimensional coordinate measuring machine described 
above, an annunciating means is preferably provided to announce when a 
predetermined amount of movement of the slide ring has occurred. By this 
structure, the probe contacts the workpiece while the operator watches the 
annunciating means to determine when the slide ring has moved the 
predetermined amount. 
In the manual three dimensional coordinate measuring machine described 
above, an error preventing means is also preferably provided to cancel 
recording the displacements of the three coordinates based on a touch 
signal. The error preventing means determines when the probe has contacted 
the workpiece at too great an acceleration by measuring whether the slide 
ring has moved a second predetermined amount. By this structure, the data 
is automatically discarded when the probe contacts the workpiece at a 
substantial acceleration, resulting in an improvement in the measurement 
accuracy. 
These and other features and advantages of this invention are described in 
or apparent from the following detailed description of the preferred 
embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first preferred embodiment of this invention is shown in FIGS. 1 to 3. As 
shown in FIG. 1, the manual three dimensional coordinate measuring machine 
includes a stand 1, a table 2 provided on the stand 1 for supporting a 
workpiece W, a gate type column 3 which is movable between the front and 
rear of the table 2, i.e., along the Y coordinate axis, an X axis slider 4 
which is movable between the left and right sides of an X axis beam 3B of 
the gate type column 3, i.e., along the X coordinate axis, a Z axis 
spindle 5 functioning as a Z axis member which is vertically movable along 
the X axis slider 4, i.e., along the Z coordinate axis, and a probe 7 
which is detachably positioned at the bottom of the Z axis spindle by a 
probe adaptor 6. A balancer 8 is provided for balancing the weight of the 
Z axis spindle 5. 
Air bearings are provided between the table 2 and both legs 3A of the gate 
type column 3, between the X axis beam 3B and the X axis slider 4, and 
between the X axis slider 4 and the Z axis spindle 5. Thus, the gate type 
column 3, the X axis slider 4 and the Z axis spindle 5 can be manually 
moved by exerting only a slight force. When the probe 7 contacts the 
workpiece W while moving along one or more of the three orthogonal 
coordinate axes, i.e., the X, Y and Z axis, the displacements of these 
axes from a predetermined origin are input from a displacement detector 
(not shown) by a displacement recording device (not shown) in response to 
a touch signal. The size and shape of the workpiece W is then determined 
based on the recorded displacement data. 
As shown in FIGS. 2 and 3, the probe adaptor 6 comprises a cylinder body 
11. Flanges 12 and 13 are monolithically formed with the body 11 and have 
a larger diameter than the body 11. A holding hole 14 is formed on the 
center of the body 11 and extends between the flange 12 to the flange 13. 
A bolt (not shown) detachably holds the probe 7 to the probe adaptor 6. An 
annular slide ring 15 is provided on the outside of the Z spindle 5 so 
that the slide ring 15 can move in any direction in a plane (such as the 
XY plane) relative to the Z axis and along the axis of the Z axis spindle 
5 (i.e., along the Z axis). The travel limits of the slide ring 15 in the 
XY plane and along the Z axis direction are set to a value which the 
operator can perceive by hand. That is, the operator can perceive the 
movement of the slide ring 15 when moving the Z axis spindle by holding 
the slide ring in his/her hand. This value is, for example, 2 mm. 
A number of compressed coil springs 16 are provided between the inside of 
the slide ring 15 and the outside of the body 11. The coil springs 16 act 
as elastic members. Preferably, 4 coil springs 16 are provided at 
intervals of 90 degrees around the body 11 and slide ring 15. The coil 
springs 16 hold the slide ring 15 at a predetermined position in the XY 
plane. The coil springs 16 allow the slide ring 15 to move in the XY plane 
by elastic deformation due to a force larger than a predetermined value. 
The force can be applied to the slide ring 15 in an arbitrary direction in 
the XY plane. Further, a number of compressed coil springs 17 are provided 
between the top end of slide ring 15 and the flange 12 and between the 
bottom end of slide ring 15 and the flange 13. The coil springs 17 also 
act as elasic members and are also at intervals of 90 degrees around the 
flanges 12 and 13 and slide ring 15. The coil springs 17 hold the slide 
ring 15 at a predetermined position along the Z axis. The coil springs 17 
allow the slide ring 15 to move in the Z axis by elastic deformation due 
to a force larger than a predetermined value. The force can be applied to 
the slide ring 15 along the Z axis. 
In the first preferred embodiment, the operator lets the probe 7 contact 
the workpiece W while holding the slide ring 15 with one hand and manually 
moving the probe 7 along the X axis and the gate type column 3 along the Y 
axis. When moving the probe 7, if the velocity or acceleration of the 
probe 7 exceeds the predetermined value, a force higher than the 
predetermined value acts on the slide ring 15. Thus, the compressed coil 
springs 16 and 17 are elastically deformed. For example, when a force 
higher than the predetermined value acts on the slide ring in an arbitrary 
direction in the XY plane, one or more of the compressed coil springs 16 
are elastically deformed. 
When this occurs, the operator holding the slide ring 15 perceives the 
movement of the slide ring 15. Thus, the operator can control the force 
when the probe contacts the workpiece W by reducing the velocity of the 
probe 7. This ensures that the compressed coil springs 16 and 17 
elastically deform just before the probe contacts the workpiece W. 
Additionally, the deflection of the Z axis spindle 5 along the X and Y 
axes and the deflection of the X axis beam 3B along the Y axis can be 
suppressed. Thus, because the floating variations of the X axis slider 4 
and the gate type column 3 are limited, a high accuracy measurement can be 
achieved. 
The structure of the slide ring 15 and the compressed coil springs 16 and 
17 is significantly simplified compared to the conventional device. In 
particular, the structure for allowing the slide ring 15 to move along the 
XY plane and the Z axis is extremely simplified compared with the prior 
art structure set forth above which has two movement sensors with parallel 
blade springs at intervals of 90 degrees. Furthermore, as the slide ring 
15 is positioned on the outside of the probe adaptor 6 and is detachably 
held to the Z axis spindle 5, no additional working is required for 
attaching the slide ring 15 to the Z axis spindle 5. Accordingly, the 
probe adaptor can be used for any existing manual three dimensional 
coordinate measuring machine with a reduced cost. 
FIGS. 4 and 5 show a second preferred embodiment in accordance with this 
invention. The second preferred embodiment of the apparatus includes an 
annunciation circuit 21 for indicating a predetermined movement of the 
slide ring 15. It also includes an error preventing circuit 31 for 
determining when to discard the displacements along the three coordinates 
recorded when the probe contacts the workpiece. 
As shown in FIG. 4, the annunciation circuit 21 includes a first fixed 
contact 22A provided on the periphery of the body 11 of the probe adaptor 
6. A second fixed contact 22B is provided on the bottom face of the flange 
12. A third fixed contact 22C is provided on the top face of the flange 
13. Similarly, a first moving contact 23A, a second moving contact 23B and 
a third moving contact 23C are provided on the interior, top and bottom 
faces of the slide ring 15, respectively. One or more of the moving 
contacts 22A-C contact their respective fixed contacts 23A-C when the 
slide ring 15 moves in the XY plane and/or the Z axis by the predetermined 
displacement. The annunciation circuit 21 further includes an LED driver 
circuit 24 and an LED 25. The LED 25 is positioned at the bottom of the Z 
axis spindle and emits light when one or more of the moving contacts 23A-C 
connect to their respective fixed contacts 22A-C. 
As shown in FIG. 4, the error preventing circuit 31 includes a first fixed 
contact 32A provided on the periphery of the body 11 of the probe adaptor 
6. A second fixed contact 32B is provided on the bottom face of the flange 
12. A third fixed contact 32C is provided on the top face of the flange 
13. Similarly, a first moving contact 33A, a second moving contact 33B and 
a third moving contact 33C are provided on the inner, top and bottom faces 
of the slide ring 15, respectively. One or more of the contacts 33A-C 
contact their respective fixed contacts 32A-C when the slide ring 15 moves 
in the XY plane and/or the Z axis by the predetermined displacement. The 
error preventing circuit 31 further includes a touch signal interface 
circuit 34 and a counter 35. The touch signal(s) generated when at least 
one of the moving contacts 33A-C connect to their respective fixed 
contacts 32A-C are input to the touch signal interface circuit 34. The 
touch signal interface circuit 34 generates a latch command to the counter 
35 when the probe 7 contacts the workpiece W, unless the touch signal is 
generated. In this case, the touch signal cancels the latch command to the 
counter 35 when one or more of the moving contacts 23A-C and 32A-C contact 
the corresponding ones of the fixed contacts 22A-C and 32A-C. 
With the above configuration, the annunciation circuit 21 and error 
preventing circuit 31 are triggered by a movement meeting or exceeding the 
predetermined value in either the XY plane and/or the Z axis. For example, 
sufficient upward movement of the slip ring 15 connects the second moving 
contacts 23B to the second fixed contacts 22B (as shown in upper left 
portion of FIG. 4). It will also cause the second moving contact 33B to 
contact the second fixed contact 32B (as shown in upper right portion of 
FIG. 4). Likewise, sufficient downward movement of the slide ring 15 will 
force the moving contacts 23C and 33C to contact the fixed contacts 22C 
and 32C, respectively. Similarly, with sufficient movement in the XY 
plane, the moving contacts 23A and 33A (on either side of FIG. 4) move to 
contact fixed contacts 22A and 32A (on either side of FIG. 4). 
In the second preferred embodiment, when the slide ring 15 moves by the 
predetermined value while moving the probe 7, the LED 25 in the 
annunciation circuit 21 is turned on. Thus, the operator can let the probe 
7 contact the workpiece W while moving the slide ring to avoid turning on 
the LED 25. Accordingly, the force acting on the slide ring 15 is 
suppressed to the predetermined value or less. Thus, the measurement 
accuracy can be securely improved. 
Even if the probe 7 contacts the workpiece W when the LED 25 is turned on, 
storing or recording the displacements of the three axes is prevented by 
the error preventing circuit 31. Thus, recording a measurement having an 
essential error can be prevented. 
It should be appreciated that the shape of the contacts 22A-C, 23A-C, 32A-C 
and 33A-C can be any shape that will ensure the electric circuit is 
clearly closed by contact between the corresponding contacts. As 
illustrated, the contacts are hemispherically shaped. However, the shapes 
of the contacts are not limited to this shape. For example, the contacts 
may extend along the circumference of the slide ring 16 and the body 11. 
Futhermor, the cross-sectional shape of the contacts can be square, 
rectangular, trapezoidal, or any polyagonal shape. Furthermore, the 
contacts may be completely annular so as to extend completely around the 
slide ring 15, and the body 11 and the flanges 12 and 13. It should be 
appreciated that contacts 23B and 33B, 22B and 32B, 23C and 33C, and 22C 
and 32C will be located concentrically on their respective surfaces of the 
adapter or slip ring 15. 
Each of the annunciating circuit 21 and the error preventing circuit 31 has 
a simplified configuration as set forth above. Further, the fixed contacts 
22A-C and the moving contacts 23A-C of the annunciating circuit 21 and the 
fixed contacts 32A-C and the moving contacts 33A-C of the error preventing 
circuit 31 can be replaced with common contacts. For example, the fixed 
contacts 32A-C and the moving contacts 33A-C can be omitted. In this case, 
the fixed contacts 22A, 22B and 22C and the moving contacts 23A, 23B and 
23C can be connected to both the touch signal interface 34 and to the LED 
driver circuit 24. This results in an even further simplified circuit 
configuration. 
FIGS. 6 and 7 show a third preferred embodiment of this invention. In this 
third preferred embodiment, the slide ring 15 moves only in the XY plane 
relative to the spindle Z-axis. The probe adaptor 6 includes two members, 
a ring mounting body 41 and probe holding member 43. The ring mounting 
member 41 has a body 11 and a flange 12. The probe holding member 43 has a 
flange 13 and a holding hole 14. The probe holding member 43 is attached 
to the bottom face of the ring mounting member 41 with two bolts 42. The 
probe adaptor 6 is mounted to the bottom face of the Z axis spindle 5 with 
three bolts 44. 
The ring mounting member 41 has four spring holding holes 45 for holding 
the compressed coil springs 16. A clamping screw 46 is screwed into the 
probe holding member 43 to clamp the shank of the probe 7 inserted into 
the holding hole 14. The probe holding member 43 is also provided with a 
connector case 47 for passing wire from the probe 7 the Z axis spindle 5. 
According to the third preferred embodiment, deflection of the Z axis 
spindle in the XY plane and deflection of the X axis beam 3B in the Y 
direction can be reduced due to the movement of the slide ring 15 in only 
the XY plane. As in the second preferred embodiment, the annunciation 
circuit 21 and the error preventing circuit 31, as described above, can be 
provided between the adaptor 6 and the slip ring 15. 
Although this invention has been described in its preferred forms, it 
should be understood that this invention is not limited to the preferred 
forms outlined above. Changes and variations may be made to these 
described preferred forms without departing from the spirit or scope of 
this invention. 
For example, the slide ring 15 can be directly attached to the bottom of 
the Z axis spindle 5, differing from the embodiments set forth above in 
which the probe adaptor 6 is provided between the slide ring 15 and the 
bottom of the Z axis spindle 5. 
The plan view of the slide ring 15 may be a shape other than circular, for 
example, square, etc. The compressed coil springs 16 and 17 functions can 
be replaced with blade springs, rubber members, wire springs and the like. 
As shown in FIG. 8, when using a wire spring 51, the wire spring 51 is 
spirally coiled along the periphery of the body 11 of the probe adaptor 6. 
One end of the wire spring 51 is attached to the probe adaptor 6, while 
the other end of the wire spring 51 is attached to the slide ring 15.