Geometrical instruments – Gauge – Movable contact probe – per se
Patent
1984-07-05
1986-03-25
Stearns, Richard R.
Geometrical instruments
Gauge
Movable contact probe, per se
33169R, G01B 728
Patent
active
045774161
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a tracing sensor, comprising a housing at which a support member is arranged, a sensor pin carrier resting on the support member by way of a bearing which is disposed all around a central longitudinal axis and designed for securing at least one sensor pin, and a spring means tending to hold the sensor pin carrier in an inoperative position in which it rests on the support member by way of the entire bearing yet permitting the sensor pin carrier to tilt, under the influence of an external force acting on the sensor pin, about a transverse axis extending transversely of said force and of the longitudinal axis and also permitting the emission of a signal caused by such tilting.
The sensor pin carrier of a known tracing sensor of this kind (journal "Industrie-Anzeiger", no. 27 of Apr. 2, 1982/104th year, page 20) has three radial arms which are offset with respect to one another by angular distances of 120.degree. each within the housing in a plane normal to the central longitudinal axis. At their ends they each comprise a contact piece. In the inoperative position these contact pieces abut against the support member and together form a bearing for the sensor pin carrier, on the one hand, while they are connected, on the other hand, to a circuit each adapted to be closed by the support member. The spring means consists of a central helical compression spring which is held between an axial spike provided at the inner end of the sensor pin carrier, with respect to the housing, and an opposed front end wall of the housing.
Good measuring accuracy cannot be maintained with this known tracing sensor over longer periods of use because the contact pieces cannot be of such character, either in configuration or choice of material, as to correspond in optimum fashion to the demands to be met on the one hand as component parts of the bearing and, on the other hand, as electric switching elements. If the contact pieces are designed as dot-shaped seats or sharp edged blades of hard material, as would be desirable for a high-quality bearing, contact is not established reliably and more or less burnoff loss occurs in operation, depending on the level of the electrical voltage applied. Hereby, again the bearing properties become poorer. On the other hand, if the contact pieces are made of precious metal in consideration of their electrical properties, they become softer than component parts of a dot or blade support are allowed to be at strict accuracy requirements.
These problems become even more acute when the known tracing sensor in operation is exposed to forces acting on the sensor pin in the direction of the longitudinal axis and causing the sensor pin carrier to be lifted with its three stellate arms simultaneously from the support body. In this raised condition the sensor pin carrier remains to be supported only by the axial helical spring which exerts a force of reaction that is not exactly axial on the sensor pin carrier even if the deviations from a configuration and arrangement coaxial with the longitudinal axis are only minute, as cannot be avoided in practice. Under predetermined load, therefore, the sensor pin carrier will adopt a position that cannot be predetermined accurately and in which one or the other of its contact pieces will establish a more or less uncertain electrical connection with the support member, at any rate, an electrical connection which is not reproducible with sufficient accuracy. In this manner measuring results may be pretended which not only are inaccurate but even lack any detectable relationship with reality.
It is, therefore, the object of the invention to develop a tracing sensor such that it will provide accurate and reproducible measuring results during a long lifetime.
This object is met, in accordance with the invention, with a tracing sensor of the kind recited initially in that the spring means comprises an elastic disc which is disposed substantially vertically with respect to the longitudinal axis and in the center of which the sensor pin carrier is
REFERENCES:
patent: 4203225 (1980-05-01), Nilsson
patent: 4270275 (1981-06-01), McMurtry
patent: 4279080 (1981-07-01), Nakaya
patent: 4443946 (1984-04-01), McMurtry
Flocks Karl W.
Neimark Sheridan
Starobin A. Fred
Stearns Richard R.
Traub GmbH
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