Optics: measuring and testing – By configuration comparison – With photosensitive film or plate
Patent
1984-01-03
1985-12-31
Rosenberger, R. A.
Optics: measuring and testing
By configuration comparison
With photosensitive film or plate
350 691, G01B 1108
Patent
active
045617783
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to apparatus for measuring the dimensions of cylindrical objects, by means of a scanning laser beam.
Apparatus for measuring the diameter of cylindrical objects, such as axles, tubing, piping and the like are known to the art. The objects are measured with the aid of a laser beam, which co-acts with a rotating mirror or prism. A lens sights the beam, the beam is sighted onto the objects by means of a lens, such, that said beam sweeps over the object being measured in mutually parallel paths.
An apparatus for measuring the dimensions of an object with the aid of a laser beam is described in Swedish Published Patent Application No. 7812400-5 (Publication No. 414,225). In this apparatus the beam is directed from a light source onto a rotating mirror, from where it passes through a lens located a focal-length distance from the centre of rotation of the mirror, and impinges upon an object to be measured, from where the beam is reflected against said mirror to a light detector. Arranged to rotate with the mirror is a pulse-emitter which, together with the light detector, controls a data processor, which determines the sensed dimension of the object.
The problem associated with known measuring apparatus of this kind is that horizontal and vertical displacement of the object to be measured always results in measuring errors. Calibration of the measuring apparatus is namely only applicable for a certain given position of the object being measured. The measuring error caused by displacement of said object on one direction (the Y-direction) can be eliminated by also measuring the position of the object in this direction and by using this information to correct the measurement value with the aid of a suitable microprogram. On the other hand, it is not possibly by means of the measuring apparatus to register movement of the object to be measured in a direction (X-direction) perpendicular to the first mentioned direction.
The beam transmitted by the measuring apparatus shall move with rotation of the mirror, so that the beam constantly lies parallel with the object axis of the system. This is difficult to achieve, however, because all objectives having spherical surfaces exhibit lens errors, which result in measuring errors. It is possible to eliminate such errors, by using lenses having aspherical surfaces, or by using lens combinations which are finally corrected against spherical aberration. Such objectives having large apertures are extremely difficult to manufacture, however, and are also extremely expensive.
The object of the present invention is to eliminate the aforedescribed difficulties.
This is achieved by means of an apparatus for measuring the dimensions of cylindrical objects with the aid of a scanning laser beam, which is directed from a source of laser light onto a rotating mirror and through a first lens located a focal-length distance from the centre of rotation of the mirror, the beam being arranged to sweep over one side of the object and to be reflected by the rotating mirror to a light detector arranged to control a data processor which determines and indicates the sensed dimension, the apparatus being mainly characterized by means arranged to direct the beam towards and to sweep over the other, opposite side of said object alternating with the sweep over said first side of said object, the data processor being arranged to formulate the mean value of the measuring values sensed on said first and said second side of the object, and in that the mirror is reflective on both sides thereof and the laser beam, during one half of a revolution of said mirror is arranged to be directed by said mirror through a first system of fixed mirrors onto said first lens so as to sweep across one side of the object; in that the beam is arranged to be directed towards the detector via a second lens which is located on the opposite side of the object to be measured and a second system of fixed mirrors via the rotating mirror; and in that the beam during the subsequent half revolution of the
REFERENCES:
patent: 4007992 (1977-02-01), Petrohilos et al.
patent: 4381152 (1983-04-01), Riech et al.
patent: 4521113 (1985-06-01), Kuwabara et al.
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