Measuring and testing – Vibration – Sensing apparatus
Patent
1981-05-01
1983-08-09
Kreitman, Stephen A.
Measuring and testing
Vibration
Sensing apparatus
G01H 1300
Patent
active
043971881
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to measuring apparatus and in particular to devices for measuring linear dimensions. More specifically, it concerns a piezoelectric resonant contact sensor.
BACKGROUND ART
A contact sensor is one of the main assemblies of a coordinate measuring machine, which determines to a large extent its accuracy, versatility and degree of automation. The error introduced by the contact sensors is one of the fundamental errors of the coordinate measuring machine. It may be a predominant error in measuring small dimensions by the use of precision coordinate measuring machines. The known contact sensors utilized with automated and distant-reading precision coordinate measuring machines do not meet present-day requirements for accuracy, sensitivity and versatility. Disadvantages of the prior art sensors are low stability in determining the moment at which the measured surface is contacted in a desired direction, a varying amount of absolute displacement of the control lug of the sensor from the initial to the response position, a changing measuring force required to make a contact in different directions of measuring parametric deviations of a given part, and low accuracy with which the contact lug returns to the initial position after signal reproduction.
Known in the art is an electrocontact probe (cf. British Pat. No. 1,445,977, Cl. G01B 7/02, "Izermitelnaya Technika", August 1976) comprising a rod with a contact lug secured to a flange. The flange is centered in an enclosure by the use of three rollers disposed within the flange at an angle of 120.degree. in a plane perpendicular to its axis and conjugated with three prisms formed by three pairs of support balls. The balls are installed within the enclosure of the probe in a manner providing isolation therefrom. The support balls and the rollers centering the flange simultaneously act as contacts of a series-connected electrical circuit. In measurement, after the contact lug touches the measured surface there occurs spatial displacement of the flange with respect to the enclosure whereby one or several contacts of the electrical circuit make. The circuit break indicates the moment at which the contact lug contacts the measured surface.
Disadvantages of the aforesaid electrocontact probe are inadequate accuracy in fixing the moment at which the contact lug contacts the measured part and unequal measuring forces in different measuring directions. These disadvantages are generally attributed to the fact that said forces are used to overcome a longitudinal force pressing the flange with the rod to the enclosure when the measuring direction coincides with the rod axis or to overcome a moment set up by said force pressing the flange to the enclosure in measuring parameters of a given part in other directions. The moment occurs due to a difference between the arms from the point at which the contact lug contacts the measured surface and from the point of application of the force pressing the flange to the flange turning axis when the electrical circuit is broken. The probe error is dependent upon great frictional slipping forces occurring between the balls and the rollers during small displacements of the flange with respect to the enclosure as the contacts break. Furthermore, the probe has only one measuring rod, a limitation substantially reducing a measuring accuracy and efficiency of the coordinate measuring machine in measuring parameters of intricately shaped parts. Also, the probe is less versatile. During parametric measurements, great forces displacing the rod with the contact lug are required to break the electrical circuit, a limitation causing considerable measuring errors.
Also known in the art is a piezoelectric resonant contact sensor comprising an enclosure with a piezoelectric vibration exciter and a contact lug arranged in a manner providing an acoustic contact between said lug and the piezoelectric vibration exciter whose one electrode is grounded, while the other electrode receives sine-wave el
REFERENCES:
patent: 4246795 (1981-01-01), Sigg et al.
patent: 4294121 (1981-10-01), Inoue
Bansevichus Ramutis J.
Gapshis Vladas-Algis A.
Kasparaitis Albinas J.
Perfilov Viktor V.
Ragauskas Alvidas J.
Experimentalny Naucho-Issledovatelsky Institut Metallorezhuschik
Kreitman Stephen A.
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