Geometrical instruments – Gauge – Movable contact probe – per se
Patent
1996-07-11
1998-05-26
Fulton, Christopher W.
Geometrical instruments
Gauge
Movable contact probe, per se
33556, G01B 520
Patent
active
057550387
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a touch probe which, for example, may be mounted on the movable arm of a coordinate positioning machine such as a machine tool or coordinate measuring machine for the purpose of enabling the machine to determine the position of a surface. One known form of touch probe is a "touch trigger probe", which includes a fixed structure, such as a housing, by which the probe is supported on the movable arm, and a stylus holder carrying an elongate stylus having a sensing tip at its free end. The stylus holder is located in a rest position relative to the fixed structure, from which it may be displaced when a force is applied to the stylus; the stylus holder returns to a rest position after the force has been removed. In use, the movable arm of the machine is driven until the sensing tip of the stylus is brought into contact with an object whose position is to be measured. Contact between the sensing tip and the object causes the emission of a trigger signal from an interface processing circuit connecting the probe to the machine control. The trigger signal is used to instruct the machine control to record the position of the movable arm, and to arrest movement of the movable arm.
2. Description of the Related Art
It is known to sense contact between the sensing tip of the stylus and the surface under inspection by employing one or more sensors in the probe which generate an output signal when subject to tension or compression. These sensors may for example be piezoelectric, as shown for example in U.S. Pat. Nos. 4,177,568, 4,364,180, 4,455,755, 5,435,072, WO86/03829, or may be strain gauges as shown in U.S. Pat. Nos. 4,462,162, 4,813,151 or 5,339,535.
SUMMARY OF THE INVENTION
The present invention provides an alternative touch probe. According to the present invention a touch probe for use on a coordinate positioning machine having an arm and a base movable relative to each other comprises: a first location by at least one first connecting element, and at a second location, axially spaced from the first location, by at least one second connecting element; end thereof, the stylus holder having at least one second engagement element, said first and second engagement elements being mutually engageable to provide a rest location for said stylus holder; thereby to urge said first and second engagement elements into said mutual engagement, the stylus holder being deflectable against the action of the biasing means, thereby to cause disengagement of said first and second engagement elements, when a force is applied to the sensing tip, and said first and second engagement elements being re-engageable under the action of the biasing means when said applied force is removed, thereby to return said stylus to a rest location; signals responsive to changes in relative displacement of said fixed structure and said load member due to deformation of one or more of said connecting elements; wherein sensors is such that when a force is applied to said sensing tip at least one of said sensors generates a signal indicative of strain in at least one of said connecting elements prior to disengagement of said first and second engagements elements.
Such a probe may be adopted to function either as a two or three dimensional probe.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present invention will now be described, by way of example, and with reference to the accompanying drawings in which:
FIG. 1 is a section through an embodiment of probe according to the present invention; and
FIG. 2 is a perspective view of a part of the probe illustrated in FIG. 1.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to FIG. 1, a touch probe includes a strain-sensitive sensing module 10, and a stylus module 12 releasably connectable to the sensing module 10. The stylus module 12 is magnetically retained on the sensing module 10 (to enable exchange of one stylus module 12 for another) by means of permanent magnets 24A, 24B, provided on the sensing module 10 and
REFERENCES:
patent: 5083379 (1992-01-01), Enderle et al.
patent: 5339535 (1994-08-01), McMurtry et al.
patent: 5345689 (1994-09-01), McMurtry et al.
patent: 5435072 (1995-07-01), Lloyd et al.
Fulton Christopher W.
Renishaw plc
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