Contact probes

Geometrical instruments – Gauge – Movable contact probe – per se

Patent

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Details

33559, 33558, G01B 503

Patent

active

053456904

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to contact probes for use on position determining apparatus such as coordinate measuring machines, measuring robots or machine tools.


DESCRIPTION OF PRIOR ART

One type of contact probe is known as a touch-trigger probe. Such a probe has a workpiece-contacting stylus extending from a housing. The stylus is supported in a rest position by support elements within the housing, and is urged into the rest position by a bias means such as a spring, so as to be deflectable out of the rest position when the stylus contacts a workpiece. The probe also contains means for detecting when the stylus contacts the workpiece, to produce a trigger signal. In use, the machine into which the probe is mounted moves the probe relative to the workpiece. When the trigger signal is generated, the machine reads the instantaneous X,Y,Z coordinates of the probe. By repeating this process at various points of contact on the workpiece surface, it is possible to make very precise measurements of the dimensions of features of the workpiece. It is also known to support the stylus via such support elements in analogue or measuring probes, in which a transducer measures the amount of stylus deflection.
Usually, the support elements are arranged so as to form a kinetic support, e.g. as described in U.S. Pat. No. 4,153,998 (McMurtry), which ensures that the rest position of the stylus is very precisely defined. In that patent, the contact with the workpiece is detected and the trigger signal produced by the breaking of electrical contact between the kinematic support elements. However, in recent years probes have been produced which can generate the trigger signal more quickly at the instant of contact, for example by using strain gauges to detect the minute amounts of strain produced in components of the probe when the stylus starts to be deflected by the workpiece; or piezoelectric elements which can detect either such strain or a shock wave generated by the contact between the stylus tip and the workpiece. Examples are shown in U.S. Pat. No. 4,462,162 (McMurtry), No. 4,813,151 (Hajdukiewicz et al), No. 4,702,013 (McMurtry) and No. 4,177,568 (Zeiss) . It is also known to use other detection means such as photoelectric sensors and capacitance sensors. A probe for a programmable manipulator, using semiconductor capacitance sensors, is shown in European Patent Application No. EP-159781-A (EMI).
However, such probes are complex to assemble and therefore expensive.


SUMMARY OF THE INVENTION

Preferred embodiments of the present invention make use of the techniques developed for the manufacture of integrated circuits, and provide the stylus support elements of a probe on such a circuit. Such circuits may be mass produced at relatively low cost, and assembling them into probes can be less complex (and therefore cheaper) than existing stylus support mechanisms.
The present invention provides a contact probe for use on position determining apparatus, comprising:
a relatively fixed member for attachment to the apparatus;
a relatively movable member for carrying a workpiece-contacting stylus;
mutually engageable support elements on the fixed member and the movable member respectively, for supporting the movable member on the fixed member;
bias means for biasing said engageable elements into engagement, the movable member being deflectable against the action of the bias means;
a sensing element for providing an output signal when the stylus is in contact with a workpiece; and
an integrated circuit or circuit board within the probe, at least one of said support elements being integrated onto the integrated circuit or circuit board.
Preferably said sensing element is also integrated onto the integrated circuit. Other circuitry associated with the sensing element may also be integrated onto the integrated circuit, e.g. for processing the signals produced by the sensing element or for temperature compensation.
The integrated circuit may be either a monolithic or hybrid integrated circuit. Alternatively, a

REFERENCES:
patent: 4153998 (1979-05-01), McMurtry
patent: 4177568 (1979-12-01), Werner et al.
patent: 4462162 (1984-07-01), McMurtry
patent: 4702013 (1987-10-01), McMurtry
patent: 4734994 (1988-04-01), Cusack
patent: 4813151 (1989-03-01), Hajdukiewicz et al.
patent: 4859817 (1989-08-01), Cassani

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