Geometrical instruments – Gauge – Movable contact probe – per se
Patent
1995-10-17
1997-06-03
Fulton, Christopher W.
Geometrical instruments
Gauge
Movable contact probe, per se
33556, 33572, G01B 7012, G01B 5012
Patent
active
056342802
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to measuring probes of the kind having a stylus attached to a stylus carrier which is supported in a rest position in a housing when no external force is acting on the stylus, and which is movable from the rest position when a force is applied to the stylus. Such force is applied to the stylus for example, when the probe is moved to bring the stylus into contact with a workpiece on a machine. The probe includes signalling means to provide a signal to the machine indicating that the stylus has been deflected by the workpiece. Such probes are known as touch trigger probes.
One example of such a probe is described in our U.K. Patent No. 1,445,977. It is a characteristic of the probe described in this patent that the force required to tilt the stylus from its rest position is not the same for all directions.
Attempts have been made to eliminate this characteristic, for example, as described in U.S. Pat. No. 4,477,976 (Kuroda) by mounting the stylus for pivoting on an annular surface surrounding the probe axis. However, because of the poor lateral constraint which is provided in this probe when the stylus is tilted from its rest position, detection of stylus deflection has to take place before the loss of accuracy due to sideways movement of the stylus holder becomes significant and affects the accuracy of the measurement.
Other examples of touch trigger probes which provide a more nearly uniform force to deflect the stylus are described in U.S. Pat. No. 4,763,421 (Heidenhain) and our U.S. Pat. No. 4,155,171.
In both of these designs the stylus support comprises a ring of ball bearing elements resting on a similar number of counterbearing elements.
One object of the present invention is to provide a support for the stylus of a touch trigger probe in which the force required to tilt the stylus from its rest position is substantially equal in all directions.
Another object of the present invention is to provide a support for the stylus of a touch trigger probe which provides lateral constraint for the stylus, once it is tilted from its rest position and until it reaches its signalling position.
According to the present invention a measuring probe comprises: the fixed member, fixed member, the movable member being deflectable from the rest position against the action of the bias means when an external force is applied to the stylus and being returnable to the rest position when the external force is removed, and deflected from the rest position, the fixed and movable members and concentric with said axis, the elements in at least one of the rings having curved surface portions, surface portions of each element in one of the rings contact two adjacent elements in the other ring, and additional support surfaces are provided on one of the members which are contacted by curved surface portions of the elements on the other member.
The support elements may take any convenient form but in a preferred embodiment of the invention each ring of support elements comprises a ring of balls arranged so that each ball in a ring is confronted by and contacts two adjacent balls in the other ring.
The additional surfaces may be provided in any convenient form but in the preferred embodiment they are formed as parts of an annular surface.
In one preferred embodiment the rings of balls have sufficiently different pitch circle diameters that they rest substantially side-by-side within the probe when the stylus is in the rest position. The plane of the ring of balls on the movable member is slightly higher than the plane of the ring of balls on the fixed member. The annular surface is formed on the movable member and contacts the tops of the balls on the fixed member.
In another preferred embodiment, the pitch circle diameters of the two ball rings are only slightly different, and the planes of the two ball rings are axially spaced, so that the ball rings rest more nearly on top of one another. In this embodiment the additional annular surface is formed on the fixed member and is contacted by the balls on t
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patent: 4270275 (1981-06-01), McMurtry
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patent: 4763417 (1988-08-01), Ernst
patent: 4763421 (1988-08-01), Feichtinger
patent: 4897929 (1990-02-01), Ernst et al.
patent: 5299361 (1994-04-01), Fiedler
patent: 5319858 (1994-06-01), Coy
Harding Andrew J.
Hellier Peter K.
Fulton Christopher W.
Renishaw plc
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