Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1986-01-22
1988-03-29
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356 5, G01N 2186
Patent
active
047345870
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optoelectric distance measuring apparatus wherein short light pulses emitted by a light source such as a laser diode, and reflected by a target object are received by a photodiode, respectively one optical switch being arranged in an optical transmitting guide as well as receiving guide for the formation of a short path for reference signals, and wherein the electric pulse signals provided by the photodiode are fed to a time discriminator controlling the gate time of a quartz oscillator, the clock pulses of the latter being gated to a counter, this time discriminator being connected to an offset voltage; a differentiating member is connected in front of the negative pulse input, and a delay line is connected in front of the positive pulse input of this discriminator.
In a conventional optoelectric rangefinder as described, for example, in the EP Publication No. 0076232, a determination is made, on the one hand, of the transit time of the light pulses (target pulses) emitted by the laser diode, reflected by a target object, and received by the photodiode and, on the other hand, of the transit time of the reference pulses emitted by the laser diode but passing by way of the optical switches and the short path to the photodiode, and evaluated for range-finding. In this process, the first-arriving reference pulse triggers, after an optoelectric transformation in a time discriminator, a gate time signal which is cut off by the later-arriving target pulse passing via the target object. During the controlled gating time, the clock pulses (150 MHz) continuously generated by a quartz oscillator are gated through a counter. The counted pulses are fed in groups to a processor determining, by sorting and mean value formation, the distance to be detected. In order to elmininate errors caused by fluctuations in the supply voltage and in the temperature, an addition value is formed for the time discriminator with the use of auxiliary pulses. This measuring procedure permits only the counting out of whole meter steps in various threshold value ranges and makes possible the measurement on the order of magntiude of centimeters and millimeters only with the aid of a disadvantageous mean value formation from a plurality of individual measurements. Although DOS No. 2,908,854 also discloses a device having an accuracy lying in the millimeter range, this can be done only by means of the sampling method utilized for transforming the pulses into the LF range wherein the curve shape is reconstructed from many scanned amplitude samples; this is effected in a very complicated way and furthermore merely in a very narrow measuring range since the time transformation can be performed only during the so-called rapid sawtooth voltage.
In cases where a time discriminator is used in distance measuring devices of this type for the processing of the electric pulse signals, there is the disadvantage that an exact determination of their time sequence is greatly impaired by varying amplitudes; in other words, a change in amplitude causes a corresponding shift in time of triggering the derived signal. The problem in connection with time discriminators resides in the identification of signals of varying amplitudes with respect to their exact location in time. The rising flank is to be maximally short in order to fix this time determination very exactly. The errors of the conventional cicuits are due, above all, to the fact that, on account of the finite rising time, the time discriminators employed respond with differing delays. In order to compensate for this effect, the conventional circuits utilize a so-called constant-fraction trigger using, for identification of the point in time, a signal predominantly a differentiated signal, derived from the signal proper. For this purpose, for example, a differentiated pulse is applied to the negative input of a voltage comparator, and the pulse proper is applied to the positive input. The negative voltage at the input of the voltage comparator can be created, for example, by a
REFERENCES:
patent: 4181431 (1980-01-01), Chaborski
patent: 4297642 (1981-10-01), Baldwin et al.
patent: 4521107 (1985-06-01), Chaborski et al.
patent: 4553836 (1985-11-01), Meirer et al.
"A Leading-Edge Time Pickoff Circuit", Nuclear Instruments and Methods, No. 67, North-Holland Publishing Co., 1969, by S. Kinbara et al., pp. 261-266.
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