Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1985-11-20
1988-03-15
Rosenberger, R. A.
Optics: measuring and testing
By polarized light examination
With light attenuation
356 28, G01P 336
Patent
active
047309296
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for the contactless measurement of the relative movement of an object in relation to a scannable pattern, a scanning beam being generated which scans the pattern along a scanning path over a portion of the pattern which moves with the object, in order to generate a scanning signal from a series of scanning pulses corresponding to pattern structure elements on the pattern portion.
In the case of a known method of this type (P. Kreutzer, Richtungserkennung bei beruhrungsloser Geschwindigkeitsmessung mit optischen Gittern, Zeitschrift Feinwerktechnik und Messtechnik 83 (1975), No. 7, pp. 330 to 332, Carl Hanser Verlag, Munich), the pattern is scanned through an optical scanning system rigid with the housing; therefore, the scanning path corresponds to the path of movement of the object relative to the pattern. By means of a plurality of photo receivers disposed behind a grid, a plurality of scanning signals are generated from the superposition of which it is possible to ascertain the sign of the direction of movement of the object relative to the pattern.
The object on which the invention is based lies in indicating a method of the type mentioned at the outset, by means of which it is possible to ascertain the angle between a reference direction rigid with the object and the direction of relative movement of the object in relation to the scannable pattern.
This problem is resolved in that
(a) the scanning beam is so pivoted and/or displaced parallel with and along a curved guide path rigid with the object that the scanning path results essentially as a superposition of the scanning movement along the guide curve upon the relative movement of pattern and object, the movement of the scanning beam along the guide curve occurring to a guide angle function which indicates the time curve of the momentary angle (guide angle) between a reference direction rigid with the object and the radial beam leading from the centre point of curvature of the guide curve to the scanning beam,
(b) and in that there is derived from the scanning signal a density signal which indicates the time curve of the reciprocal value of the time interval between the momentary scanning pulse and the preceding scanning pulse, possibly averaged out over an averaging period which is small in relation to the scanning time needed to move the scanning beam along the guide curve, and
(c) in that the phase location of the density signal in relation to the guide angle function is determined which corresponds to the angle between the reference direction and the direction of movement of the pattern in relation to the object.
The method according to the invention is based on the knowledge that during scanning of the scanning pattern along a scanning path being a superposition of the relative movement of object and pattern and the movement of the scanning beam along the curved guide curve which is rigid with the object, a specific scanning signal results wherein the time interval between successive scanning pulses depends in predetermined manner upon the angle between the radial beam and the direction of relative movement of object and pattern. If this absolute angle amounts for example to 90.degree., which in the case of a circular guide curve means that the momentary direction of movement of the scanning beam along the guide curve extends parallel with the direction of relative movement, then a scanning signal is obtained with particularly rapidly or particularly slowly consecutive scanning pulses according to whether, at the time, the scanning beam is moving along the guide curve in opposition to or together with the pattern. In this case, the density signal assumes a maximum or a minimum as the case may be. With an absolute angle of 0.degree., the result is an average value of the density signal to which, in the case of a uniform movement of the scanning beam along a partial or complete circle, a reversal point of the substantially sinusoidal density signal corresponds. Consequently, from the phase location of the densit
REFERENCES:
patent: 2772479 (1956-12-01), Doyle
patent: 3045232 (1962-07-01), Mercer
patent: 3059521 (1962-10-01), Clemens et al.
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patent: 3950099 (1976-04-01), Malueg
Optische Sensoren zur Beruhrungslosen und Schlupffreien weg- und Weschwindigkeits-Messung an Landfahrzeugen, pp. 2-4.
Richtungserkennung Bei Beruhrungsloser Geschwindigkeitsmessung Mit Optischen Gittern, pp. 2-4.
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