Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1997-05-12
1998-10-27
Allen, Stephone B.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
25055938, 356 306, 356 407, G01B 1126, G01C 308
Patent
active
058280570
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of the type which is mentioned in the introduction to claim 1 and an arrangement for carrying out the method.
Target seeking systems, with or without subsequent target following, are more and more common in, for example, laying out work. A distance measuring instrument is automatically rotatable horizontally and vertically. A target is looked for with electromagnetic radiation, preferably light in the infrared or visible wavelengths, emitted from a target seeking and target following unit on the distance measuring instrument. After an indication that the electromagnetic radiation has reached a detected target, the instrument can, if necessary, be held directed towards it. This target seeking and target following unit is preferably separate in relation to the measuring system of the distance instrument. The target can be equipped with a reflector. Detection takes place when the unit receives electromagnetic radiation reflected from the target. The instrument is in that case positioned in a suitable place in the region of which the topography is to be measured.
The reflectors on the target are preferably at least one cube comer prism, which gives a reflected beam in the opposite direction to the transmitted beam and which is placed on a setting-out pole against which the measuring is to take place, which is placed by an operator at chosen positions.
The advantage of such systems is that they can be operated by only one operator through the seeking system of the instrument automatically looking for and focusing its beam on the reflector.
A problem of such systems, however, is that there are other reflectors than the target reflector in the surroundings. It is not desirable to measure these but the instrument can become focused on them. Examples of such reflectors can be traffic signs, vehicle number plates, bicycle reflectors and the like.
The object of the invention is to achieve a method for automatic target seeking and possibly target following, for example for a distance measuring instrument, where all reflectors are ignored, except the one or those which is/are placed on a target.
This object is achieved with a method with the characteristics given in claim 1. Further characteristics, developments and an arrangement for performing the method are given in the other claims.
In order to ignore all other reflectors than the reflectors on the target, a combination of polarizing and controllable polarization modulating arrangements placed in the path of the electromagnetic beam to and from the instrument are used. One of these arrangements is placed according to the invention on each target reflector. Preferably at least one polarizing and/or controllable polarization modulating arrangement is placed in the path of the electromagnetic beam on the instrument. The controllable polarization modulating arrangement is controllable to alternately change the polarization direction of the beam. A check of the discovered reflector is performed by testing if the received beam alternately changes at the same rate as the polarization changes on the controlled polarization modulating arrangement. Only targets are accepted which give different signal strengths at the same rate as the received beam.
The polarization modulating arrangement and/or at least one of the polarizing arrangements are preferably placed on the target seeking and target following unit either on its light emitting side or light receiving side. Each target the instrument discovers during its search for a correct target is checked for its degree of reflection of incoming beams while the polarization is alternatively changed by the polarization modulating arrangement, which is for example a Pockels cell, a unit with controllable liquid crystals or the like. The polarization modulating arrangement can be part of a combined polarizing and polarization modulating arrangement and in that case can also have a continuous change between different polarization planes and can, for example, be made of a continuously rotating
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Hertzman Mikael
Naslund Anders
Allen Stephone B.
Spectra Precision AB
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