Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1986-01-22
1988-04-12
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250227, H01J 314
Patent
active
047376244
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optoelectric distance measuring apparatus with an optical measuring probe wherein short light pulses emitted by a laser diode are conducted via an emitting lightguide and emitted by a lens, and the light signals reflected by a target object are received and transmitted to a photodiode by way of a receiving lightguide; the photodiode feeds the thus-formed electric pulse signals to a time comparator, which latter controls the gate signals of a clock generator, the clock pulses of which are gated to a counter.
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 rangefinding. In this process, the first-arriving reference pulse triggers, after an optoelectric transformation in a time comparator, 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 to 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 the conventional measuring devices of this type, respectively a separate lens is provided for the emitting optic and receiving optic. These lenses, arranged in juxtaposition at the device, have the drawback that the light pulse, directed from the emitting lens toward an uncooperative target object is not reflected into the receiving lens at distances below about 2 m. Only at a distance of more than 2 m there begins an overlapping of the optical emitting and receiving channels, lens-shaped in cross section, but the partial overlapping existent in the proximate range leads to considerable measuring errors. These double-lens measuring devices are thus unsuitable for smaller distances. There is also the additional disadvantage that the emitting and receiving optic is located directly at the housing of the appliance, which housing also contains the components for producing the light pulses, for converting the received light signals into electric pulse signals, and for the processing and evaluation of the electric pulse signals. Considerable difficulties are also encountered due to the inhomogeneous phase front of the light pulses emitted by the laser diode and transmitted via an emitting lightguide, consisting of glass fiber, to the transmitting lens.
In contrast to the above, the invention is based on the object of fashioning an optoelectric range finder of the type described above so that a maximally accurate distance measurement is possible also at close range.
This object has been achieved according to this invention by providing the measuring probe with a double face mirror extending along the optical axis of the lens up to the ends of the emitting lightguide and receiving lightguide lying approximately in the zone of the focal point.
On account of this arrangement, the optical transmitting and receiving channels lie directly side-by-side in the lens zone, separated merely by the plane of an extremely thin mirror, so that one half of the lens is associated with the emitting channel and the other half with the receiving channel. The emitting lightguide and receiving lightguide, terminating in the zone of the focal point, permit measuring up to the lens. The optoelectric rangefinding is thus also maximally suited for level indication of tank vessels, bulk containers, and the like. Also, the edges of the emitting and receiving lobes do not overlap; rather, overlapping takes place at the location of both lobes having the broadest cross section and therefore is representative for the phase transit time
REFERENCES:
patent: 4029391 (1977-06-01), French
patent: 4249076 (1981-02-01), Bergstrom et al.
patent: 4325638 (1982-04-01), Takeda et al.
patent: 4329017 (1982-05-01), Kapany et al.
patent: 4549504 (1986-06-01), Coursolle et al.
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