GB2148650A - Surveying - Google Patents

Abstract

The system comprises the optical beacon and cooperating sensor array 13, 14, 15 of GB 2090096, which transmits and receives a specially shaped light beam at a reference and a remote location respectively, is modified by the addition of a tilt sensor at the beacon. The tilt information can be transmitted to the remote location by radio if required. Alignment of the beacon is obviated thereby. <IMAGE>

Description

SPECIFICATION Surveying apparatus and method This invention relates to levelling devices, and in particular, to levelling devices for use with remote data processing apparatus. It find application in apparatus employing a rotatable laser beam to generate a reference plane used for surveying.

Current rotating laser beam levels incorporate means for controlling the orientation of the platform carrying the rotatable optical unit of the beam transmitter. One system uses a mirror pendulum to maintain a vertical axis of rotation of the laser beam. Such devices are very sensitive but all have a bulky mechanical construction and, furthermore, operate only over a limited angular range. Another system uses a servosystem with a pair of glass vials containing a liquid. The vials, which act as sensors, are arranged in a bridge circuit which produces an error signal when they depart from the horizontal.

In our co-pending UK Patent Application No. 2 090 096A (Reference No. 120842) we describe apparatus employing a table laser beam for levelling purposes. A laser beam with a "V" or "X" sectional shape defines a reference plane and is rotated about a vertical axis. The leading and trailing edges of the beam are detected by photosensor at a remote receiving station. A digitiser disc coupled to the laser beam rotating means provides an indication of the angular position of the laser beam and this is used to modulate a radio signal for remote telemetry at the receiving station. As a result of these combined features, once set up, the laser source can operate as an unattended beam, all measurements can be made and data processing carried out at the receiving station.This means that the survey can be carried out by a single person rather than the two operators which were required with earlier systems.

In order to make the necessary calculations, the receiving station is provided with a computer which carries out the determination of height and range.

This apparatus may advantageously be modified to introduce corrections for misorientation of the laser beam, thereby eliminating the need for elaborate levelling devices at the transmitting station.

Accordngly, the present invention provides apparatus for sensing position comprising means for generating a beam of radiation having leading and trailing edges which are straight and diverge from one another, means for rotating the beam about an axis to define a reference plane, a plurality of remote radiation sensors placed at a receiving station to determine the distance between leading and trailing edges of the rotated beam, means for determining the angular position of the beam, telemetry means for transmitting to said receiving station a signal dependent on said angular position, correcting means for periodically determining the difference between the measured position of the beam and its intended position at the same instant.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows in schematic form a surveying instrument similar to that described in British Patent Application 2 090 096, but incorporating telemetry apparatus in accordance with the present invention.

Figure 2 shows in more detail the laser beam generating apparatus of the embodiment of Fig. 1.

Figure 3 illustrates a device for determining the orientation of the laser beam axis, and Figure 4 is a block diagram showing one method of transmitting data from the laser beam generator to the receiving station.

Referring now to Fig. 1 of the drawings, a beacon unit comprising a laser source 1 is mounted on a tripod 2. Also mounted on the tripod is a carrier comprising a base 3, support bars 4 and an upper mount. The base carries a beam expander 5 through which a beam from the laser source passes to a rotatable optical unit 6 on an axle 7 which is rotated by a motor 8. The axle 7 also carries an encoder disc 9 from which is derived a signal which provides an indication of the angular position of the axle and its associated beam transmission apparatus. The optical unit 6 transmits a beam of light 10 in a direction orthogonal to its axis of rotation and defines a reference plane as it rotates. The beam is received by a modified surveyor's staff 11 which carries a moveable cursor 1 2 bearing three equispaced photo-detectors 13, 14, 1 5.

The beacon unit also includes a radio transmitter 1 6 which sends a modulated signal to a receiver 1 7 on the staff 11. Rigidly coupled to an axle mounting plate 1 8 is a tilt sensing device 1 9 comprising a pair of vials, mounted orthogonally to one another and including transducers which provide signals dependent on the tilt of the axle mounting plate. These tilt signals, together with the orientation signal from the encoder disc modulate the radio signal from the transmitter 1.

The receiver 1 7 demodulates the signal and passes tilt and orientation dependent signals to a microprocessor unit 20 which calculates the degree of tilt corresponding to the direction of the receiving staff from the beacon.

Fig. 2 illustrates the beacon unit in greater detail. An optical unit comprises a laser source 1 coupled to a carrier 3 by means of a kinematic mount 21. A beam from the laser source is split by means of a half-silvered mirror 22 and shaped by front-silvered mirror 23 and lenses 24 all of which are mounted on an axle 7 which also carries an encoder disc 9. The axle rotates in a bearing box 25 which is ridigly coupled to an upper mounting plate 18, an extension of which carries a mount 1 9 for pair of tilt sensors 26 (Fig. 3).

The interconnection of the various units is shown in block diagrammatic form in Fig. 4.

Output signals from the encoder 9 and tilt sensors 26 modulate a radio transmitter 1 6.

The separate signals are derived in a receiver 1 7 which passes them as control signals to a microprocessor unit 20 used also for calculating levels.

In the embodiment described, a pair of vials is used as tilt sensors. Alternative, sensors such as a pendulum or gyroscopes may be used. Furthermore, if the tilt sensor is mounted on the encoder disc, a single sensor may be used as the orientation is derived simultaneously with the measurement of the angular position.

In another arrangement tilt correction is applied before the orientation signal is transmitted. The output from the orientation measuring vials is used to calculate a beam angle datum corresponding to the degree of tilt in the direction of a specified staff. A correction-factor is calculated and applied to the pulses which are transmitted. Under these circumstances it would not be necessary to apply correction at the staff. This method could also be extended to cover corrections for systematic errors in the set-up of this apparatus.

Claims (7)

1. Apparatus for sensing position comprising means for generating a beam of radiation having leading and trailing edges which are straight and diverge from one another, means for rotating the beam about an axis to define a reference plane, a plurality of remote sensors placed at a receiving station to determine the distance between the leading and trailing edges of the rotated beam, means for determining the position of the beam, telemetry means for transmitting to said receiving station a signal dependent on such angular position, correcting means for periodically determining the difference between the measured position of the beam and its intended position at the same instant.

2. Apparatus as claimed in Claim 1 having a transducer adapted to produce a signal dependent on the angular displacement of the axis of the rotating beam from a reference axis.

3. Apparatus as claimed in Claim 2 wherein the transducer incorporates a pair of vials.

4. Apparatus as claimed in Claim 2 wherein the transducer incorpoates a pendulum.

5. Apparatus as claimed in Claim 2 wherein the transducer incorporates a gyroscope.

6. Apparatus as claimed in any one of the preceding claims 2 to 5 incorporating microprocessor means for determining a tilt connection signal from the output signal of said transducer.

7. Apparatus for sensing position substantially as herein described with reference to the accompanying drawings.