Optics: measuring and testing – Range or remote distance finding – With photodetection
Patent
1981-05-29
1984-04-10
Buczinski, S. C.
Optics: measuring and testing
Range or remote distance finding
With photodetection
356 4, 356152, G01C 310, G01C 308
Patent
active
044418094
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the determination of position with respect to a reference point or reference plane and will usually be applied in the field of land surveying, but other applications are also possible.
In land surveying it is known to make measurements of height, distance and angular position with respect to a known reference point using three separate instruments.
For example, in one instrument a laser beam is rotated to sweep out a horizontal reference plane which is located at a distant point either by a self-seeking sensor which can travel vertically on a portable staff held by an operator or by use of the human eye. Height above or below this plane can then be read from a scale and recorded manually by the operator. Subsequently, the distance and angular position of the location are measured by, respectively, an electromagnetic distance meter and theodolite, and recorded manually. While the laser-based instrument can be operated by one man, the other two devices must be operated by two people.
In one embodiment of apparatus according to the present invention, all three measurements can be made by one operator using a single two-part instrument.
According to the invention, position sensing apparatus comprises generating means for generating a beam of radiation; rotation means for rotating the beam to define a reference plane, the beam having an effective sectional shape such that a leading edge and trailing edge are straight and diverge from each other on at least one side of the reference plane; at least two radiation sensors spaced a known distance apart in a direction parallel to the axis of rotation of the beam; and means for determining the distances between the leading and trailing edges at the positions along those edges which pass across each radiation sensor, whereby the distance of each sensor from the reference plane and the distance of the sensors from the axis of rotation can be determined.
For example, a beam of visible radiation may be rotated about a vertical axis to define a horizontal reference plane, the beam having an actual section which is "V" shaped or which forms a multiplication cross.
Consider the case of a V-shaped beam of visible radiation, for example from a laser source, sweeping across two vertically-spaced sensors. The distance between the leading and trailing edges of the beam is greater at the upper sensor than at the lower sensor. If a measure is made of these distances, the distance of either sensor from the horizontal reference plane and of their distance from the axis of rotation can be calculated.
The beam cross section may comprise two thin arms each defining one side of the "V" and constituting respectively the leading and the trailing edge (although each thin arm will have its own leading and trailing edge), or the beam section may be fan shaped, forming effectively a solid inverted triangle. Alternatively, a beam section in the shape of a multiplication cross may be used.
When two thin arms are used to provide the leading and trailing edges, they may be closely adjacent so that if the beam cross section is examined a "V" or "X" shape is visible. Alternatively, in certain circumstances the trailing edge may be rotated 180.degree. behind the leading edge.
In many circumstances it will be an acceptable approximation to measure not the distance between the edges at each sensor but the angle subtended by that distance at the axis of rotation, provided the angle is small, e.g. 5 degrees or less. This measurement can be achieved by further providing means to generate a train of pulses, each pulse corresponding to an equal subdivision of the 360.degree. rotation of the beam, and pulse counting means for counting the number of pulses generated between passage of the leading and trailing edges of the rotating beam at each sensor.
A further measurement is also possible. By providing means for generating a reference pulse at a fixed angular position with respect to rotation of the beam, and pulse counting means for counting the number of pulses generated between
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patent: 3469919 (1969-09-01), Zellner
patent: 3620626 (1971-11-01), Daly
patent: 3714657 (1973-01-01), Lapeyre
patent: 4218834 (1980-08-01), Robertsson
patent: 4268167 (1981-05-01), Alderman
Dudley James R.
Gorham Barry J.
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