GB2173369A

GB2173369A - Determining position

Info

Publication number: GB2173369A
Application number: GB08603688A
Authority: GB
Inventors: Barry James Goreham
Original assignee: LASERFIX Ltd
Current assignee: LASERFIX Ltd
Priority date: 1985-02-14
Filing date: 1986-02-14
Publication date: 1986-10-08
Also published as: GB8503812D0; GB8603688D0

Abstract

A laser beam with a straight line cross-section is caused to rotate with its straight line section at a known non-zero angle to the horizontal. As it rotates it crosses at least three light detectors spaced in the vertical direction. The extent of rotation of the beam is indicated by pulse transmitted to the detector station. The time of transit of the beam across the various detectors is also counted by these pulses. By suitable calculation, the distance, elevation and azimuth of the sensors from the source of the beam can be calculated. <IMAGE>

Description

SPECIFICATION Method and apparatus for determining position 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 a 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.

It is also known, and described in detail in British Patent No. 2 090 096 to provide position sensing apparatus comprising 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 a 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 angular displacement 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.

Such apparatus usually relies upon a laser beam with a cross section shaped as a V or an X, rotating in a horizontal plane and crossing a group of sensors arranged vertically. As the different limbs of the V or X cross the sensors pulses are received, and from the relative spacing of these pulses at different sensors can be calculated (e.g. for electronic means programmed with a suitable algorithm) the distance of a given sensor above or below the reference plane, and the distance from the axis of rotation. By a further refinement the extent of rotation of the beam is measured by counting of suitable observable pulses, e.g. by a digitised disc giving a suitable counting signal to the electronic calculation; from this the angular displacement from a datum direction can be calculated. Thus, declination, distance, and azimuth are all available using one machine and one operator.

The present invention is related to this earlier invention referred to above, and for that reason all of the disclosure therein is incorporated herein by way of reference.

The present invention is based upon the realisation that a beam of different effective shape can be used in such equipment to give pulses from a suitable array of sensors from which distance and declination can be differently calculated, and which can be combined with a pulse count based on the rotation so as to give a reading for azimuth.

Thus, to utilise for contrast and comparison the terminology of the earlier application, there is provided, according to one aspect of the invention, position sensing or determining apparatus comprising generating means for generating a beam of radiation; rotation means for rotating the beam to define a reference plane, the beam having an effective single known angle to the reference plane; at least three radiation sensors spaced known distances apart and iying in a direction at a different known angle to the reference plane: and means for determining the relative angular displacements of the beam as it passes 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.

Preferably there are three sensors, arranged in a line at right angles to the reference plane, which is itself preferably horizontal. Preferably moreover the three sensors are equispaced. Thus the beam should be at an angle other than 90 to the reference plane; a preferred angle is 45 , but this is not essential.

According to a further aspect, there is provided position determining apparatus comprising: as a first part: a laser source which provides a beam of light; rotatable optical means for converting the beam to a beam rotating about a vertical axis, the beam having an effective straight line section at a known angle to the horizontal; a divided circle rotatable with the optical means; a fixed reading head which provides pulses corresponding to the divisions of the divided circle; and transmission means to transmit the pulses; and as a second part: at least three light detectors spaced in the vertical direction; receiving means to receive the transmitted pulses; counting means associated with each light detector to count said pulses, occurring in the intervals between successive detectors detecting the rotating beam; and calculating means to calculate from the counted pulses at least one of the distance of a light detector from the reference plane and the distance of a light detector from the axis of rotation of the beam.

There is also provided a method of determining position comprising generating a beam of radiation; rotating the beam to define the reference plane, the beam having an effective straight line sectional shape at a known angle to the horizontal; receiving the beam at three positions spaced at a known distance apart and lying at a different known angle to the reference plane; determining the angular displacement between the positions along those edges which pass across each sensor; and from the displacements determining at least one of the distance of one reception position from the reference plane and the distance of the reception positions from the axis of rotation.

For example a fan-shaped beam of visible radiation may be rotated about a vertical axis to define a horizontal reference plane, the beam having an effective section a straight line at a known angle e.g. 45" to the horizontal.

By "effective section" is meant that the beam for measurement, as sorted and calculated by the subsequent calculating means e.g. a microprocessor, is a straight line. Of course, the beam itself may, and in practice will always, diverge or fan out so that the straight line section is long enough to sweep the sensors wherever they are relatively located.

In theory a beam of any non-zeroangle to the horizontal could be used but in practice 45" is preferred. Two permanent beams with limbs intersecting as an X or V can be provided each limb being treated as a separate effective straight line beam to give a cross checking of results; thus the method of the present invention could, by a suitable change of algorithm, on a calculating means, be carried out with the equipment of the prior art invention although not utilising the X or V for its original function. Moreover, flashing or intermittent use of either of the limbs of an X or V-section beam, or the use of spaced limbs, or the use of parallel straight lines, could all be envisaged e.g. as checking devices for the readout.

Moreover, in a modification, the angularity of the straight section could be replaced by polarisation of the light, with suitable sensors and equivalent calculations.

The nature of the calculation to be made differs fundamentally from and is not obvious in view of that calculation utilised in the earlier invention.

The new calculation can be effected by a suitable algorithm programmed into a calculator which is permanently part of, or associated with, the equipment. This combination therefore constitutes another aspect of the invention. Moreover, in that the prior art equipment described in GB Patent 2 090 096 (which uses a compound beam instead of a single beam) can nonetheless be equipped with electronic selector and calculation means, programmed as above (i.e. programmed differently from any calculator used in the prior art) for operation on one straight line portion of the compound beam, the present invention extends to such a combination.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a general highly schematic view of a prototype two part land surveying instrument according to the invention, Figure 2 shows sensors mounted on a staff to intercept a rotating beam generated by the equipment of Fig. 1, Figures 3 to 5 are diagrams of possible arrangements of beam and sensors, Figures 6 and 7 are diagrams relevant to calculation of angle, azimuth and inclination using the arrangement of Fig. 3, Figure 8 shows the use of a tapered beam each edge being capable of use in accordance with the present invention, and Figure 9 shows in diagrammatic form an optical arrangement of a further variant of the invention.

In Fig. 1 a first part of a land surveying instrument comprises a tripod 10 supporting a laser 12 which is arranged to emit its beam vertically upwards and which can be plumbed by a plumb line 14. The tripod 10 supports a carriage consisting of a base 16, three narrow vertical support bars 18 and an upper part 20. The base 16 carries a beam expander 22 through which the vertical beam from the laser 12 passes to a rotatable optical unit 24 which is rotated via axle 26 by a motor 28, the axle also carrying a divided circle or digitiser disc 30. The motor 28 is supported by the upper part 20 which also carries a radio antenna 32. In operation the beam from laser 12 is modified by the optical unit 24 to give a beam of laser light 33 of the required effective straight line cross sectional shape which is rotated to sweep out a horizontal plane. As the beam is rotated, the digitiser disc 30 provides a digital signal related to the angular position and this signal is used to modulate a radio frequency signal emitted by the antenna 32.

Fig. 2 shows a surveyor's staff 34 on which slides a cursor 36 carrying three equispaced light sensors 38, 40, 42, a radio frequency receiver 44 and an electronic circuit 46 which includes a microprocessor. In use, the modulated RF signal is received by receiver 44 and the pulse signals are supplied to the circuit 46 which includes several pulse counters (not illustrated separately).

The light sensors 38, 40, 42 provide start and stop signals to the circuit 46 as the laser beam sweeps over them, and the counters are operated in accordance with these signals.

Some relative configurations of sensor arrangement and beam angle which may be used in the present invention are as shown in Figs. 3 to 5.

Fig. 3 shows a preferred configuration of sensors and beam angle. The instrument rotates about a vertical axis X-X and a beam of light B of straight line section emitting by the instrument thus travels in a horizontal path around the instrument as it rotates. The beam itself diverges while maintaining its straight-line section, the divergent i.e. fan beam thus occupying a plane. This plane lies at an angle 6450 to the horizontal. Three equispaced sensors Si, S2 and S3 are arranged in a straight line A-A which lies parallel to and in the same plane as the rotation axis X-X, thus defining angles 0 and r as shown which are both equal to 90".

Fig. 4 shows a further simple expedient, less preferred than that of Fig. 5. The line of sensors A-A is at an angle to the vertical of 0=45 , whereas the slit beam is vertical i.e. 6=900. The angle r is still 90". This embodiment could be achieved by mounting the sensors on a block accurately at 45" to a vertical staff.

Fig. 5 shows a more complex case where neither 0 nor 6=450. Both the beam and the sensor line are at angles to the horizon. Angle T is however still 90".

Various further modifications are possible and will be apparent to the man skilled in the art.

Thus, although 6 or 0 are preferably 45 , they are not necessarily so. Moreover, the three sensors need not be equispaced provided that their different spacings are known. Also, the angle z can be varied from 90" (i.e. in practical terms the sensors can be tilted towards or away from the beam generator by a known angle). It may even be possible to work with sensors in other than a straight line (again, provided that they are spaced out along the "staff" direction, and their configuration is known). Also, the beam could be solid with a straight edge, or could be of a single cross-section other than a straight line, provided it was of known geometry.

An arrangement of intereset is to put five sensors in the form of a quincunx, or so as to define a V-shape with preferably 90" included angle. As a beam, preferably vertical, traverses such an arrangement it gives signals for each arm of the notional V, or for each diagonal of the quincunx of sensors. Thus, provided they are carried accurately on a mounting block, that block itself need not be accurately set up in the field: an angular misplacement in one direction will be compensated by an equal and opposite misplacememmt of the other notional sensor group.

A yet further arrangement, to give only two of the three quantities involves rotating the beam in a vertical reference plane. Provided that the beam still intercepts at least three sensors of known spacing and position range and declination can be calculated. A horizontal beam could transverse three sensors in a 45" line, or vice versa, the beam moving in each case vertically i.e.

"down the wall" (or "up the wali").

Further, a beam rotated about an axis at a known angle to the horizon, with the same sensorinterception characteristics as defined above, could be used.

Figs. 6 and 7 show how, using the system of Fig. 3, distance, azimuth and declination can be calculated. The calculation is as follows: The vertical angle c=a+B (since 45" angle) A-h h tan (I'= ; tan n?= R R

From (1) h2-Ah+R2=AR cota (3) From (2) h2+Ah+R2=AR cot ss (4) R=2h Subtract (3) from (4) gives ------- (5) cotfi-cota Substituting for R is equaton (3) 4h2 2th cota h2Ah+ = (cotfi-cota)2 (cotp-cota) which after reduction gives (cot ss-cotα) h=# ------ (6) (cotss-cotα)+4 In the special case where h=0 i.e. a=ss, R=Acotss.

azimuth=latched angle count value at B cell a-2 =n,2--ATN (h/R) Horizontal angle displacement of the beam during rotation must be described by the source continuously including a fixed datum direction or zero. Alternatively, it may be possible to modulate the beam so as to provide an absolute encoding of direction for the sweeping beam.

Fig. 8 shows how a single wedge-shaped beam, the edges of which are detected by an array of photocells could be used. A tapered beam provides two-edge detection between beams of known inclinations to the horizontal. In fact transit-time measurements of the beam across the array of photocells could be used to generate both height and horizontal range information; the former by ratio and the latter by difference.

In a still further embodiment as shown in Fig. 9, a single inclined fan beam is produced by a pentaprism in combination with a fanning lens and is rotated about a vertical axis through the source, in an arc which includes the photocell array. This gives in effect the inclination of a single beam reversed on successive scans. In the succeeding reversal of the arc the optical train is mechanically linked to a DOVE prism which reverses the inclination of the fan beam. Such reversal of the beam inclinations can occur in successive arcs or successive full cycles of rotation. This feature copies with any non-verticality of the photocell array.

Claims

1. Position determining apparatus comprising generating means for generating a beam of radiation; rotation means for rotating the beam to define a reference plane, the beam having an effective single straight line section at a known angle to the reference plane; at least three radiation sensors spaced known distances apart and lying in a direction at a different known angle to the reference plane: and means for determining the relative angular displacements of the beam as it passes 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.

2. Position determining apparatus as claimed in claim 1 comprising three sensors arranged in a line at right angles to the reference plane.

3. Position determining apparatus as claimed in claim 2 in which the three sensors are equispaced.

4. Position determining apparatus as claimed in claim 1, 2 or 3 in which the angle of the beam is at 45".

5. Position determining apparatus comprising: as a first part: a laser source which provides a beam of light; rotatable optical means for converting the beam to a beam rotating about a vertical axis, the beam having an effective straight line section at a known angle to the horizontal; a divided circle rotatable with the optical means; a fixed reading head which provides pulses corresponding to the divisions of the divided circle; and transmission means to transmit the pulses; and as a second part: at least three light detectors spaced in the vertical direction; receiving means to receive the transmitted pulses; counting means associated with each light detector to count said pulses, occurring in the intervals between successive detectors detecting the rotating beam; and calculating means to calculate from the counted pulses at least one of the distance of a light detector from the reference plane and the distance of a light detector from the axis of rotation of the beam.

6. A method of determining position comprising generating a beam of radiation; rotating the beam to define the reference plane, the beam having an effective straight line-sectional shape at a known angle to the horizontal; receiving the beam at three positions spaced at a known distance apart and lying at a different known angle to the reference plane; determining the angular displacement between the positions along those edges which pass across each sensor; and from the displacements determining at least one of the distance of one reception position from the reference plane and the distance of the reception positions from the axis of rotation.

7. A method as claimed in claim 6 in which a fan shaped beam of visible radiation is rotated about a vertical axis to define a horizontal reference plane, the beam having an effective section and a straight line at a known angle to the horizontal.

8. A method as claimed in claim 7 in which the angle is 45".

9. A method as claimed in claim 7 or 8 in which two beams with limbs intersecting as an X or as a V are provided, each limb beam being treated as a separated effective straight line to give a cross checking of results.

10. A method as effective in claim 9 in which the two straight limbs are flashed intermittently.