Geometrical instruments – Gauge – Having a movable contact probe
Patent
1997-11-10
1999-07-06
Bennett, G. Bradley
Geometrical instruments
Gauge
Having a movable contact probe
33560, G01B 2104
Patent
active
059183780
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an inspection system for use on a coordinate positioning machine such as a coordinate measuring machine or inspection robot, for example.
A prior art inspection system on a coordinate measuring machine is illustrated in FIG. 1. The coordinate measuring machine includes an arm 10, movable in three linear directions x,y,z relative to a table 12, upon which a part W to be inspected is supported. Displacement of the arm in each of the x,y,z directions is measured by three corresponding encoders, each of which includes a scale 14 and a readhead (not shown). Each encoder generates an incremental output whose instantaneous value is displayed on a counter 16, so that the counters 16 of the x,y, and z encoders may be thought of as displaying the instantaneous positional coordinates of the movable arm 10 relative to an origin, or datum. Movement of the arm of the machine along each of the x,y and z axes is performed by x,y and z servos (which incorporate the x,y and z encoders), and the servos are controlled by means of a machine control unit 18, either on the basis of software containing a pre-programmed sequence of manoeuvres which the user requires the machine to perform, or the instantaneous control of an operator by means of a joystick (not shown).
The movable arm 10 carries a touch probe 20 having an elongate stylus 22 with a spherical sensing tip 24 provided at its free end. The probe 20 is mounted to the arm 10 via an articulating probe head 26 which may rotate the probe 20 about substantially perpendicular rotational axes D and E. In use, the machine control 18 operates the servos of the x,y and z axes, and, where appropriate, the D and E axes of the probe head 26 to drive the movable arm 10 of the machine so that the sensing tip 24 of the probe 20 comes into contact with a surface S of a part W to be measured. Contact between tip 24 and the surface S causes the emission of a signal to a probe interface unit 30, which then sends a step change, or "trigger" signal to the machine control 18. Upon receipt of the trigger signal, the machine control records the values of the x,y and z counters in order to obtain an indication of the position of the surface S, and also arrests the movement of the movable arm 10.
For added flexibility, a probe-changing magazine 40 is provided, which contains a plurality of different types of inspection probe, suitable for a number of different inspection tasks. The exchange of one probe for another first of all involves the machine control driving the movable arm 10 to a position where the probe 20 which is currently carried on the probe head 26 is positioned in one of the ports 50 of the magazine 40, whereupon an actuating mechanism provided within the magazine 40 disengages the probe 20 from the probe head 26. The arm is then driven to a further port 50 where the probe head 26 may acquire a different probe, engagement of the new probe with the probe head 26 once again being performed by the actuating mechanism within the probe changing magazine 40. Such a probe-changing magazine is known for example from EP 142373.
Yet further flexibility is provided in respect of one type of probe (which, in FIG. 1, is carried on the probe head 26) which includes an electronic retaining module 60, and a stylus module 70 releasably magnetically mounted thereon to enable the exchange of one stylus module 70 for another of a plurality of alternative stylus modules supported in a stylus changing magazine 80. The exchange of stylus modules is performed in a manner similar to that of a probe, with the important exception that the movement of the movable arm 10, powered by the respective x,y,z servos, is used to couple and uncouple the stylus modules 70 from the electronic retaining modules 60. To this extent, the exchange of stylus modules may be regarded as "passive", in that the magazine 80 does not play a role in coupling or uncoupling stylus modules 70. Probes of this type, and the automated "passive" exchange of stylus modules are known from U.S. Pat. No. 5,505,0
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Renishaw Electrical Limited Sales Brochure, "Autochange Flexible Probe System for Coordinate Machines", published Aug. 1984.
Hellen Graham A.
McMurtry David R.
Sullivan Jonathan S.
Bennett G. Bradley
Renishaw plc
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