Optics: measuring and testing – Range or remote distance finding – With photodetection
Patent
1982-11-23
1985-11-12
Buczinski, S. C.
Optics: measuring and testing
Range or remote distance finding
With photodetection
356 6, 372 10, G01C 325, G01C 300
Patent
active
045524556
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to a method and apparatus for functionally testing a laser rangefinder.
BACKGROUND
Rangefinders, based on measuring the time taken for a light pulse from a laser in a rangefinder to reach an object, the distance to which is to be measured, and return to the instrument after reflection by the object, are tested for correct function and precision using a known measuring distance. Testing can therefore only be carried out at places which are specially arranged for the purpose.
It is further known that a laser of the passive Q-switched laser type can transmit more than one light impulse when the laser excitation voltage is higher than normal. This is a drawback with this type of laser, since normally it is only desired to transmit one light pulse at each measuring occasion.
SUMMARY OF INVENTION
In the method and apparatus according to the present invention, the property which is otherwise regarded as a drawback of the passive Q-switched laser has been taken advantage of, namely that it transmits two light pulses when the laser excitation voltage is raised above the normal value.
Each transmitted light pulse is reflected in a mode known per se to the rangefinder receiver, the first such pulse starting time measurement and the second one stopping it in the same way as a light pulse reflected from a remote object would also do.
In order that the excitation voltage to the laser can be raised during testing, a voltage divider in a control circuit controlling the excitation voltage is adapted for switching by a switch especially arranged for testing.
By utilizing the invention, correct functioning of the flashlamp and light receiver of a rangefinder can be tested, as well as circuits for measuring and indicating distance.
The invention is not intended for testing the precision of the distance measurement, since such testing still requires specially prepared measuring distances.
BRIEF DESCRIPTION OF DRAWING
In the accompanying drawing, the sole FIGURE is a diagram schematically illustrating the components and circuitry, of a preferred embodiment of the invention.
DETAILED DESCRIPTION
An example of a laser rangefinder in accordance with the invention is described below with reference the associated drawing. The rangefinder laser is of the passive Q-switched type.
The rangefinder laser, not shown, is adapted to transmit a short light pulse when it is struck by a light flash from the rangefinder flashlamp 1. Energy for the flashlamp is supplied by charging a capacitor C1 in series with the flashlamp 1. A choke L is also connected in series with these components.
The capacitor C1 is connected to a high-voltage generating unit 2 for the charging of the capacitor, the unit 2 being disposed for receiving a D.C. supply via terminals 3. The output of a regulating amplifier 4 is connected to the high-voltage unit for controlling its output voltage. A constant reference voltage is connected to one input terminal 4a of the amplifier, and to a second input thereof is connected a junction 4b in a voltage divider comprising three resistors R1, R2 and R3. The voltage divider is connected between the pole with the high voltage U and the other grounded pole of the high-voltage unit. A switch 5 is coupled across the resistor R3, which is nearest the grounded side of the voltage divider, for short-circuiting the resistor 3 when closed.
A pulse transformer 6, in this connection called a triggering transformer, has one winding connected to one of the poles of the flashlamp 1. The second winding of the transformer is included in a circuit where the winding is in series with a capacitor 7 and a thyristor 8. The thyristor is adapted to be made conductive by a voltage pulse on a terminal 9 connected to the thyristor 8. The capacitor 7 is intended for charging by a D.C. source connected to terminals 10.
The described apparatus is made ready for actuating the laser in the rangefinder to give one or more light pulses by direct voltage being applied to the terminals 3, so that the capacitor C
REFERENCES:
patent: 3601488 (1971-08-01), Plessis-Robinson
patent: 4182570 (1980-01-01), Courrier et al.
Johansson Karl H.
Severinsson Anders S.
Buczinski S. C.
Issing Gregory C.
Telefonaktiebolaget LM Ericsson
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