Probe for checking linear dimensions

Details Probe for checking linear dimensions Probe for checking linear dimensions

1991-10-18

1994-04-05

Cuchlinski, Jr., William A.

Geometrical instruments

Gauge

Movable contact probe, per se

33561, G01B 503, G01B 703

Patent

active

052993604

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The invention relates to a probe for checking linear dimensions of workpieces on machine tools or measuring machines, comprising a support casing that defines a first reference surface with circular symmetry; a movable structure including a second reference surface with circular symmetry, and an arm carrying a feeler for touching the surface of the workpiece to be checked, the movable structure being apt to assume a central position in which at least one portion of the movable structure is substantially arranged along a longitudinal geometrical axis; detection means for providing a signal depending on the position of the movable structure; and thrust means located between the support casing and the movable structure for biasing the first and second reference surfaces towards each other; and in which said portion of the movable structure can accomplish limited translation displacements along said longitudinal geometrical axis and limited rotational displacements about geometrical axes lying in any whatever direction perpendicular to the longitudinal geometrical axis direction.
2. Background Art
Contact detecting and measuring heads or probes are used on coordinate measuring machines and machine tools, more specifically, machining centres and lathes, in order to accomplish checkings on machined--or to be machined--workpieces, tools, machine tables, etc. Generally, these heads comprise a movable arm carrying one or more feelers and a detection circuit with one or more switches or position transducers.
In the case of contact detecting probes, the touch of the feeler on the workpiece causes, after a possible prestroke, the switching of the detection circuit that in turn controls the reading of transducers associated with the machine slides and that provide measuring values with respect to a reference position or point. The essential requirements of these heads are repeatability--i.e. the correspondence between determined positions of the feeler and the switching of the detection circuit, or, in the case of the measuring heads, the signal values of the transducers in the heads -, sturdiness, small overall dimensions and limited costs.
According to the degrees of freedom of the movable arm-set, and consequently to the displacements that the feeler can accomplish, there can be distinguished heads with one or more axes.
Referring, for the sake of simplicity, to contact detecting heads equipped with a movable arm and an associated feeler that in rest conditions are aligned along a longitudinal geometrical axis of the head, in the major part of the applications there are used omnidirectional heads--sometimes improperly referred to as "3-axis" heads--in which the feeler can accomplish displacements along the longitudinal geometrical axis as well as displacements along any whatsoever transversal direction (perpendicular to the longitudinal axis). Normally the transversal displacements are not plain translations, but rotational movements of the movable arm-set about transversal geometrical axes.
Most of the known probes are anisotropic as far as the switching of the detection circuit--occurring as a consequence of transversal displacements of the feeler--is concerned. In other terms, as the direction of the transversal displacement varies, the switching of the circuit occurs in correspondence with different eccentricities of the feeler with respect to the longitudinal geometrical axis.
U.S. Pat. No. US-A-4477976 discloses contact detecting heads according to the prior art portion of claim 1, that have a structure for reducing, at least in part, the anisotropy as the transversal measurement direction changes These heads comprise an annular plate secured to the head casing and having an annular shaped projection, and a plane annular flange secured to the movable arm-set that comprises the arm carrying the feeler.
The casing and the movable arm-set carry a pair of electrical contacts that are arranged, in rest condition, according to the longitudinal geometrical axis of the head. The rest co

REFERENCES:
patent: 3520063 (1970-07-01), Rethwish et al.
patent: 4187614 (1980-02-01), Abiru et al.
patent: 4288925 (1981-09-01), McMurtry
patent: 4477976 (1984-10-01), Suzuki
patent: 4523382 (1985-06-01), Werner et al.
patent: 4549356 (1985-10-01), Ernst
patent: 4941266 (1990-07-01), Bissegger et al.

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