Geometrical instruments – Gauge – Internal
Patent
1992-01-21
1993-04-27
Haroian, Harry N.
Geometrical instruments
Gauge
Internal
335421, 335551, G01B 728
Patent
active
052050475
DESCRIPTION:
BRIEF SUMMARY
Technical Field
The present invention relates to a method for checking dimensions of a mechanical part by means of a checking head including a casing, at least a feeler movable with respect to the casing and adapted to contact a surface of the part, and transducer means for providing a signal responsive to the position of the feeler, the method comprising the steps of controlling a mutual displacement between the checking head and the part so as to obtain a first mutual sliding motion between the feeler and the surface of the part, towards a portion to be checked, along a determined path; detecting a first passage of the feeler at the portion to be checked; and detecting the signal provided by the transducer means in correspondence with said first passage.
The invention also regards an apparatus for automatically checking linear dimensions of a mechanical part, with a checking head comprising a casing, at least a feeler movable with respect to the casing and transducer means for providing a signal responsive to the position of the feeler with respect to the casing, driving means for obtaining a first mutual displacement between the checking head and the part along a determined path, processing and control means connected to the transducer means and the driving means for controlling said mutual displacements, and for performing a first detection and processing of the signal of the transducer means.
BACKGROUND ART
Dimensional checkings performed by contacting mechanical parts--by means of heads having feelers contacting the surface of the part--involve sliding motions between the feeler and the surface for arranging the feeler in correspondence with a portion to be checked. In particular, these checkings can be carried out in dynamic way , i.e. the position of the movable feeler can be measured during said sliding motions, that may be manually or automatically controlled. For example, in connection with dynamic checkings it may be foreseen to detect, by means of mechanical or electric datums, the passage of the feeler along a predetermined portion to be checked, or to locate this portion depending on the output signals of the head during the sliding motions.
A simple manual checking of this type is carried out by a plug gauge, for example like that described in the U.S. Pat. No. 4 884 346, that is inserted into a hole, the diameter of which must be checked, and advanced up to a depth defined by a flange. During the advance two feelers slide on the hole surface, resiliently urged by a spring and by the structure of the arm-set, that also comprises transducer means.
A similar device, in which the transducer means are obtained by strain gages, is described in international application WO-A-89/03507, and can be used for checkings of automatic type, according to a method corresponding to the prior art portion of claim 1, in which the plug gauge is arranged on a slide and is displaced by it from a rest position to a measurement position.
In addition to plug gauges for internal dimensions like those mentioned above, there are many known devices and instruments with gauging heads of contacting type featuring sliding motions between feelers and surfaces. As an example only, it is possible to mention snap gauges for external diameters used in apparatuses like that described in international application WO-A-89/04455, featuring feelers that are displaced into contact with cylindrical external surfaces and caused to slide on said surfaces towards portions to be checked, located by mechanical datums.
In each of the above mentioned cases, the positioning of the feeler (or the feelers) on a surface of the part takes place through a sliding motion of the feeler on the surface along a determined direction or path. It is evident that the friction arising through said sliding motion, although limited in view of the particular shape and material of the feeler, cannot be eliminated. The resulting strains transmitted to the elements of the gauging heads can cause malfunctions due to flexures in the movable arm-set and/or stra
REFERENCES:
patent: 4167066 (1979-09-01), Cooper et al.
patent: 4884346 (1989-12-01), Cook
patent: 5083384 (1992-01-01), Possati et al.
Haroian Harry N.
MARPOSS Societa' per Azioni
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