Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1989-08-24
1992-03-17
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
250561, 356376, G01J 120, G01N 2186
Patent
active
050971190
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an instrument for determining the focal distance of a test are from a reference area.
BACKGROUND
An instrument of this type is disclosed in DE-OS 35 36 700. This equipment enables surfaces of a test object to be measured to a high degree of accuracy on very small surface contours.
For many applications it would be desirable to be able to use a device of this kind under non-laboratory conditions, and even when the test piece and/or the equipment is subjected to vibrations or jolts.
THE INVENTION IN GENERAL
The present invention enables a device to be developed still further, so that even under the above-mentioned conditions of use it will be possible to measure even the smallest surface contours of a test piece.
The instrument of this invention is equipped with a regulating circuit which quickly controls errors in a test signal caused by vibrations and shocks. This correction is effected roughly speaking in that two nested control loops are used, whereby the outer control loop is provided with an integral action controller and there has a relatively large time constant, whereas the internal control loop is provided with a proportion-derivative controller and therefore has a small time constant. The outer control loop derives the control value for the inner control loop from the output signal of the opto-electrically working measured distance and from the actual position of the precision optics or the output signal of an acceleration sensor, and the inner control loop receives as the actual value the directly measured position of the precision optics. In the error signal, which supplies the inner control loop for driving the servo mechanism, are thus contained signal portions which are susceptible to vibrations and jolts and have such a phase length that an additional force is applied on the servo drive, which actively compensates the reaction of the precision optics to the vibrations and jolts.
The design of the apparatus in accordance with the invention also eliminates disturbances which are brought on by electrical irradiations.
With my instrument the control of vibrations and jolts is effected by having a reference optics exactly identical to the measuring optics, which is also linked up with a signal channel identical to the signal channel of the measuring optics. Whereas however the measuring optics is directed on the test area having micro unevenesses, the reference optics works with an ideal flat reference area which is fixed vis-a-vis the instrument housing. Thus the output signals of the signal channel associated with the reference optics are directly a measure for vibration and shock induced signal portions in the signal channel associated with the measuring optics. Thus if the outputs of the two signal channels are collated by differentially a vibration and shock-compensated measuring signal is obtained. The design of the actual measuring instrument and the reference device is exactly the same optically, mechanically and electrically, down to the difference between the test area and the reference area, a broad-band balancing of the vibrations and shocks is thus obtained, because both the systems react in exactly the same way to these external disturbances. The development of my invention ensures that the acceleration sensor used to determine the vibrations and shocks reacts to the latter exactly the same as the measuring optics.
The development of my invention ensures that the measuring optics and the mass-body optics and also the electro-magnetic unit associated with them may have exactly the same design. Only the external circuitry of these electro-magnetic units are different: In the measuring optics the coil serves as a driving coil, and in the mass-body optics as an induction coil.
The working speed of an instrument for accurate determination of the distance of a test point lying on a test area from a reference area is a function of the gradient of the characteristic curve of the detector. Obviously the detector generates an output signal for a given distance o
REFERENCES:
patent: 4611317 (1986-09-01), Takeuchi et al.
patent: 4641020 (1987-02-01), Iwai
patent: 4674882 (1987-06-01), Dorman et al.
patent: 4703468 (1987-10-01), Baba et al.
patent: 4737920 (1988-04-01), Ozawa
patent: 4806777 (1989-02-01), Ulbers et al.
patent: 4891798 (1990-01-01), Shinkai
patent: 4899327 (1990-02-01), Bates et al.
Messinger Michael
Nelms David C.
Philpitt Fred
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