Geometrical instruments – Gauge – Movable contact probe – per se
Patent
1993-09-13
1994-08-02
Fulton, Christopher W.
Geometrical instruments
Gauge
Movable contact probe, per se
33556, G01B 1103, G01B 503
Patent
active
053333888
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to probes, such as are used with co-ordinate measuring and similar machines, to indicate a touch to an object.
BACKGROUND OF THE RELATED ART
In co-ordinate measuring and similar machines an object is measured by relative motion between a probe and an object in a controlled manner, usually from a datum, until a "touch" of the object is indicated by the probe. The co-ordinates of the touch position are recorded. By such repeated actions the dimensions of the object can be determined.
The aim of such measurements is to achieve precision to better than one micron with a repeatability of half a micron or less. Accordingly it is clear that the "touch" action must be very responsive and free from error. Probes to achieve such touch action usually use a light, thin stylus with a ball-end of hard material to touch the object. The touch action deflects the stylus in a mounting in the probe and the occurrence of the deflection of the stylus is sensed to cause the co-ordinates to be recorded.
Known probes provide good results in many measurements but in some measurements errors arise which cannot be compensated by corrections to the recorded co-ordinates. One cause for such errors is that deflections of the stylus in different directions requires different amounts of deflection before sensing occurs. Another cause is that an electromechanical switch operated by the stylus is used for the sensing action and the making or breaking of the switch is not consistent because of arcing or corrosion at the switch contacts. Probes used hitherto have electrical or mechanical connections to the stylus.
UK Patent Number GB 2,220,748A describes a probe with an external constraining means and a sensing arrangement consisting of a mirror on the stylus to deflect light away from a detector on deflection of the stylus.
SUMMARY OF THE INVENTION
According to the invention there is provided a probe for position-determining apparatus and the like having a housing and in the housing a sensing space and an aperture to the sensing space, a stylus extending out of the sensing space through the aperture, a stylus-support means at the aperture and means for constraining the stylus In low-friction engagement with the support means and generally towards a neutral axis while permitting position-determining displacement on the support means. The stylus is linked to the constraining means through a lever arrangement including a first lever element extending sideways from and around the stylus and a second lever from the first lever to transfer stylus displacement to the constraining means and constraint from the constraining means to the stylus. The lever arrangement includes an abutment engageable by the second lever.
The probe stylus has a spherical surface in the support means and the support means provides only localized contact to the spherical surface. The localized contact is formed by balls. Conveniently the stylus includes the spherical surface and the balls are housed around the aperture.
The stylus has a uniformly extending collar as the first lever. The constraining means is inside the housing and acts on the stylus collar first lever through a follower second lever engageable with the abutment held in the housing. Preferably the constraining means is arranged to urge the second lever onto the abutment against the resistance of the first lever to maintain the low-friction engagement with the stylus on the neutral axis. Conveniently this produces pre-stress. The the abutment is around the inside of the housing, which is circular, and the second lever is circular to fit on the abutment and the first lever is circular and is inside the abutment and, when in the natural position, level with or just above the level of the abutment and the second lever.
The parts of the probe may be arranged to retain their relationship and to not rotate relatively about the neutral axis. The sensing space may include means to send out radiation of a sensing means and means to collect radiation for a sensing
REFERENCES:
patent: 4177568 (1979-12-01), Werner et al.
patent: 4352246 (1982-10-01), Hauert
patent: 4477976 (1984-10-01), Suzuki
patent: 4941266 (1990-07-01), Bissegger et al.
Patent Abstracts of Japan, vol. 8, No. 144 (P-284) (1581), Jul. 5, 1984 & JP, A, 59-43302 (Mitsutoyo Seisakusho K. K.) Mar. 10, 1984.
Butler Clive
Shams Iden
British Technology Group Limited
Fulton Christopher W.
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