Geometrical instruments – Gauge – Coordinate movable probe or machine
Reexamination Certificate
1999-11-22
2001-07-03
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Gauge
Coordinate movable probe or machine
C033S504000, C033S0010DD, C901S048000, C901S025000, C074S490050
Reexamination Certificate
active
06253458
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates generally to three dimensional coordinate measuring machines (CMM's). More specifically this invention relates to an arm and counterbalance mechanism for use on a CMM which provides increased reliability and adjustability.
2. Description of the Prior Art
It is well known in the art to utilize a CMM to measure objects in a space in terms of their X, Y, and Z coordinates commonly referring to length, width and height, respectively. Advancement in the art has led to lightweight portable CMM's well suited for general industrial applications. Such a CMM is disclosed in U.S. Pat. No. 5,402,582 which is commonly assigned to the assignee hereof and incorporated herein by reference.
One of the above mentioned advancements in the art of portable CMM's is a light weight multi-jointed manually positionable measuring arm, shown generally in
FIG. 1
at
10
. Measuring arm
10
is comprised of a plurality of transfer housings
12
(with each transfer housing comprising a joint and defining one degree of rotational freedom) and extension members
14
attached to each other with adjacent transfer housings being disposed at right angles to define a movable arm
10
preferably having multiple degrees of freedom. At one end of arm
10
is attached a base
20
. At the end of arm
10
opposite base
20
is attached a probe
15
.
Referring to
FIG. 2
, the measuring arm
10
of the prior art further comprises a torsional spring
16
positioned in a joint
22
near base
20
of measuring arm
10
. The torsional spring
16
provides a counter balance force to offset the weight of the arm and ease manipulation thereof by an operator. An air piston shock absorber
18
is mounted on base
20
of arm
10
in intimate contact with joint
22
such that piston
18
is fully compressed when arm
10
is in rest position, as is shown. Piston
18
is fully decompressed and awaiting retraction of arm
10
when said arm is fully extended. Air piston
18
absorbs the shock load accompanying the spring coiled retraction of arm
10
by exerting a force opposite to said retraction.
The base
20
of CMM arm
10
of the prior art is typically mounted in the horizontal plane. Referring again to
FIG. 2
, the recoiled torsional spring
16
generates a compensating torque at the base
20
of the arm
10
in a direction
24
to considerably reduce the weight of the arm
10
, said weight acting in a direction
26
when arm
10
is extended. Such alignment allows for a counterbalanced use of the arm
10
when base
20
is mounted in the horizontal plane as described herein above. However, there are many applications of CMM's where it is advantageous to mount the arm perpendicular to or inverted to the above discussed original mounted horizontal plane. For instance, it is often desired in the art to mount the arm
10
to a wall or to a ceiling to facilitate a particular use of the CMM. This mounting naturally changes the direction
26
of the weight of the arm
10
relative to said arm. The compensating torque
24
, however, created by torsional spring
16
remains the same. Thus, the effect of the arm's spring coiled counterbalancing mechanism is diminished. Without the aid of the counterbalancing mechanism, use of the arm
10
may be cumbersome.
Prior art CMM arms, as discussed above, do not readily allow multiple applications requiring changability of a single CMM. For instance, a single CMM may be used by a variety of operators who may require different counterbalancing forces to effect a proper movement of the machine. Different end probes may be required for various application and alternative mountings may be necessary. The CMM arms of the prior art do not readily allow adjustability of the counterbalancing mechanism to compensate for the change in forces acting upon the arm associated with use of various mountings and end probes.
The positioning of the torsional spring counterbalance of the prior art CMM arm causes a high overhung load. As discussed herein above the counterbalance mechanism is positioned in a joint near the base of the arm. Such positioning creates a substantial moment arm from the neutral axis of joint previous to the mechanism. The majority of the weight of the measuring arm acts on this moment arm and creates a considerable load on the joint and on the base thereby reducing operability and increasing stress on the base assembly of the CMM arm.
Thus the need has arisen for a CMM arm with a mechanism which allows for the counterbalanced use of the arm in a variety of mountings, with a variety of end probes which prevents overhang stress on the base of the arm and provides ease in changability.
SUMMARY OF THE INVENTION
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the present invention. A novel counterbalance mechanism for use with a multi-joint manually positionable measuring arm of a three dimensional coordinate measurement system provides a reversible and adjustable counterbalancing force to offset the weight of the arm and facilitate its movement. An exemplary counterbalance device comprises a ratchet mechanism to select the direction of counterbalance assistance allowing for the mounting of the arm on a horizontal plane, a wall or a ceiling. In one embodiment, the exemplary counterbalance mechanism further comprises a compression spring which adjustably biases a cable and a system of intermeshing gears to provide varying levels of counterbalancing force. Alternatively, a second embodiment of the exemplary counterbalance mechanism comprises a cam assembly around which a member is rotated and counterbalanced by an internal compression spring. The counterbalance mechanism of the present invention acts within the plane of the joint minimizing the moment arm created by the joint and allowing for low overhung loads transmitted from the arm to the base. The mechanism of the present invention is readily adjustable to accommodate a variety of uses and mounting positions.
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.
REFERENCES:
patent: 5768792 (1998-06-01), Raab
patent: 5794356 (1998-08-01), Raab
patent: 5829148 (1998-11-01), Eaton
patent: 5890300 (1999-04-01), Brenner et al.
patent: 5926782 (1999-07-01), Raab
patent: 5978748 (1999-11-01), Raab
patent: 6131299 (2000-10-01), Raab et al.
patent: 6134506 (2000-10-01), Rosenberg et al.
patent: 6151789 (2000-11-01), Raab et al.
Bodjack John A.
Raab Simon
Cantor & Colburn LLP
Faro Technologies Inc.
Guadalupe Yaritza
Gutierrez Diego
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