Measuring and testing – Vibration – Sensing apparatus
Patent
1989-08-07
1991-10-22
Williams, Hezron E.
Measuring and testing
Vibration
Sensing apparatus
73661, 73662, 33556, 33561, 33573, 33503, 318572, G01B 1504
Patent
active
050584332
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the inspection of workpieces on position-determining apparatus such as a coordinate measuring machine, inspection robot or machine tool.
DESCRIPTION OF PRIOR ART
It is well known to mount a touch trigger probe on such a machine to allow workpiece inspection. The probe is moved in three dimensions by the machine to touch various pre-determined points on the workpiece surface. When a surface is touched by a stylus of the probe, it generates a trigger signal which is taken back to a control of the machine and used to "freeze" the outputs of measuring devices such as scales and readheads which show the position in space of the probe at the time of contact. The control can then read the coordinate values of the position.
A known type of such probe, such as shown in U.S. Pat. No. 4,702,013, contains a sensor which is sensitive to acoustic vibrations. The sensor may for example detect the acoustic shock wave which is generated when the stylus of the probe hits a workpiece surface, and generate a trigger signal as a result. One possible disadvantage of this type of arrangement is that the acoustic shock wave may occasionally be insufficient to generate the trigger signal, for example if the probe is moving very slowly when it contacts the workpiece surface, or if dirt or grease on the workpiece surface at the point of contact reduces the amplitude of the wave. One result of this disadvantage is that there is a certain minimum recommended speed at which the probe stylus should contact the workpiece surface, so as to ensure triggering, and this makes it difficult to probe internal surfaces of the workpiece such as small bores where there is insufficient space to accelerate the probe to the desired minimum speed.
SUMMARY OF THE INVENTION
The present invention proposes that the surface to be probed should be vibrated. Upon contact between the probe stylus and the surface, these vibrations are transmitted to the stylus so that they can be detected by the probe sensor.
Stated more particularly, one aspect of the invention provides position-determining apparatus comprising:
a probe;
a support for a workpiece;
means for providing relative movement between the probe and the workpiece support;
vibration-sensitive means associated with the probe for determining contact between the probe and a workpiece; and,
means for vibrating the workpiece; whereby upon contact between the probe and the workpiece, vibrations are transmitted from the workpiece to the probe for detection by the vibration-sensitive means.
A preferred method of vibrating the surface to be probed is by vibrating the bed or table on which the workpiece is mounted with a suitable vibration transducer. Means may be provided to decouple the probe so that it does not receive such vibrations through the structure of the machine in which it is mounted. More than one frequency of vibration may be provided. The frequency and/or amplitude of vibration may be varied.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic diagram of a coordinate measuring machine (CMM), and
FIGS. 2, 3 and 4 are partial schematic diagrams of modifications to FIG. 1.
DESCRIPTION OF PREFERRED EMBODIMENTS
The CMM shown in FIG. 1 comprises a bed or table 10, for example of granite, and a bridge or gantry 12. The bridge or gantry 12 is movable in the direction of a Y axis on air bearings 14. A carriage 16 is movable in the direction of an X axis on the bridge or gantry 12 on further air bearings (not shown). The carriage 16 carries a quill 18 which is movable in the direction of a Z axis, also on further air bearings (not shown). At its lower end, the quill 18 carries a touch trigger probe 20.
The movements of the carriage 16, bridge or gantry 12 and quill 18 in the X, Y and Z directions respectively are effected by drive motors 22 under the control of a computer numerical control 24 of the CMM. Means for measuring these
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Quantelec leaflets, (1) High-Power Transducer Bolt Clamped Langevin Type and (2) High-Power Transducers Bolt Clamped Langevin Type.
Lloyd Peter G.
Wilson David
Finley Rose M.
Renishaw plc
Williams Hezron E.
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