Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1990-12-24
1992-08-25
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356349, 356363, G01B 902
Patent
active
051413175
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for optoelectronically making distance and angle measurements wherein a beam is directed at a pregiven incident angle onto an object to be measured.
BACKGROUND OF THE INVENTION
An electrooptical precision distance and angle measuring arrangement is known from the corporate paper "Hewlett-Packard Journal", No. 3, Apr. 1983. In this arrangement, the distance information is obtained via the Doppler effect. A laser is provided which supplies two optical beams having different frequencies and different polarizations. The superposed beams reach a first optical receiver as well as a beam splitter which deflects one of the two beams and transmits the other beam. The beam deflected by the beam splitter impinges on two deflecting mirrors and returns to the beam splitter. This beam traverses a predetermined optical path. The beam transmitted by the beam splitter having the other frequency likewise impinges on two deflecting mirrors and is returned to that particular location in the beam splitter at which the deflected returned beam impinges. The return beams are superposed in the beam splitter and are incident upon a second optical receiver.
The two deflecting mirrors in the beam path of the beam transmitted by the beam splitter are movably mounted. With a movement, the optical distance traversed by the transmitted beam is increased or decreased. The movement leads to an increase or reduction of the frequency of the reflected beam (Doppler effect).
The first optical receiver supplies an output signal having a frequency proportional to the frequency difference of the two beams generated by the laser. The second optical receiver supplies an output signal having a frequency proportional to the frequency difference of the two beams generated by the laser and is reduced or increased by the Doppler frequency. The two output signals are applied to a frequency counter which determines the difference of the two signals with the result being the Doppler frequency which is a measure of the velocity of the moving deflecting mirrors. The traversed path or angle is determined from the velocity.
SUMMARY OF THE INVENTION
According to the method of the invention for optoelectronically measuring distances and angles, a first beam and a second beam are directed onto the object at pregiven incident angles with the second beam having a phase modulation compared to the first beam. At least one component of each of the two beams impinges upon the same point of incidence on the object. At the point of incidence of the two beams, a diffraction and an interference take place because the surface of the object always has a roughness which has the effect of an optical diffraction grating.
The diffracted beam components interfere and are applied to a first optical sensor. A phase change of the sensor output signal with reference to the phase of a reference signal is evaluated as a measure for the distance traversed by the object being measured or the angle traversed by the object being measured. With these steps, in combination with a constant distance between the object being measured and the measuring arrangement, the influence of environmental conditions such as air pressure, humidity and temperature on the measuring result is reduced. Further advantages are the high resolution of the measuring result as well as the stability of the inertia-free and contact-free measuring method.
A further reduction of the environmental influences is obtained if the angle of incidence of the first beam directed onto the object is determined as being equal to the negative angle of incidence of the second optical beam likewise directed onto the object being measured and if the first optical sensor is aligned in the vertical direction to the surface of the object being measured with the angles of incidence of the two beams lying on opposite sides of the vertical. With this measure, both beams traverse optical distances of the same length and environmental influences have the same effect in both beam
REFERENCES:
patent: 3891321 (1975-06-01), Hock
patent: 4710026 (1987-12-01), Magome et al.
patent: 4940330 (1990-07-01), Dopheide et al.
patent: 5000573 (1991-03-01), Suzuki et al.
Paper of R. C. Quenelle et al entitled "A New Microcomputer-Controlled Laser Dimenstional Measurement and Analysis System", Hewlett-Packard Journal, No. 3, pp. 3 to 13, Apr. 1983.
"Follow-Up-Type Laser Doppler Velocimeter Using Single-Mode Optical Fibers"; Sasaki et al, Applied Optics, Apr. 1990, pp. 1306-1308.
Bollhagen Heins-Erdam
Drabarek Pawel
Ottesen Walter
Robert & Bosch GmbH
Turner Samuel A.
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