GB2187570A

GB2187570A - Apparatus for measuring distance

Info

Publication number: GB2187570A
Application number: GB08705094A
Authority: GB
Inventors: Roger Bennison
Original assignee: Rabone Chesterman Ltd
Current assignee: Rabone Chesterman Ltd
Priority date: 1986-03-06
Filing date: 1987-03-05
Publication date: 1987-09-09
Also published as: ZA871558B; GB8605508D0; GB8705094D0

Abstract

The apparatus comprises means for projecting a first beam of light towards a surfaces whose distance is to be measured, an arrangement for directing a second beam towards to surface along a path inclined to the first beam path, means for varying the inclination of one path relatively to the other and an arrangement for indicating the relative inclination. One embodiment comprises a laser source (1) whose light beam is split by a beam splitter (4) into a fixed beam (5) and a movable beam (6) whose inclination relative to the fixed beam (5) is variable by means of a pivotally mounted reflector (8). By measuring the degree of pivotal movement of the reflector (8) required to bring into coincidence areas of light projected on to a surface by the first and second beams, the distance to the surface can be obtained. Alternatively (Fig. 5), two laser sources may be used, one (33) being fixed in position while the other (35) is variable in inclination. <IMAGE>

Description

SPECIFICATION Improvements in or relating to apparatus for measuring distances This invention relates to apparatus for measuring distances.

Many known forms of apparatus for measuring distances are unsuitable for use when the distance to be measured is relatively small and others are suitable for use only in daylight conditions.

Many known forms are also heavy and not easily portable.

It is an object of the present invention to provide apparatus for measuring distances that is especially suited to the measurement of relatively short distances and can be used under conditions of darkness and semi-darkness.

According to the present invention, apparatus for measuring distances comprises means for projecting a first beam of light towards a surface whose distance from an observation point is to be measured, an arrangement for directing a second beam of light towards the object along a path that is inclined to the path of the first beam, means for varying the inclination of one beam relatively to the other, and an arrangement for indicating the relative inclination.

The invention also provides means for projecting a beam of coherent light towards an object whose distance is to be measured, an arrangement for directing a second beam of coherent light towards the object along a path that is inclined to the path of the first beam, means for varying the inclination of one beam relatively to the other, and an arrangement for indicating the relative inclination.

The coherent light is provided by one or more lasers. A single laser may be used, beam splitting being employed to divide the output of the laser into the first and second beams.

The or each laser may be a continous wave laser or it may pulsed at a frequency high enough to create the visual impression of continuous wave operation.

The or each laser may be a low-powered ruby laser, or a gas laser for example a helium-neon or helium-cadmium laser.

The inclination of the second beam may be varied by means of a pivotally mounted reflector.

The invention also provides a method of measuring the distance of an object comprising the steps of directing a first beam of light towards the object and producing a first visual area of light thereon, directing a second beam of light towards the object along a path that is inclined with respect to the path of the first beam to produce a second area of light on the object, bringing the areas of light into alignment and deriving the distance from the relative inclinations of the first and second beams at which alignment of the first and second areas occurs.

Preferably, the inclination of only one of the other beams is variable.

Alternatively, the inclination of both beams may be variable.

By way of example only, embodiments of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is a schematic layout of a first embodiment illustrating its method of operation, Figure 2 is a perspective view of a handheld form of the first embodiment, Figure 3 is a front elevation of a second embodiment, Figure 4 is a side elevation of the second embodiment, and, Figure 5 is a schematic diagram showing part of the internal mechanism of the second embodiment.

Basically, the invention provides means for projecting a first beam of light towards an object whose distance is to be measured, an arrangement for directing a second beam of light towards the object along a path that is inclined relatively to the path of the first beam, means for varying the relative inclination of the beams, and an arrangement for measuring the relative inclination.

Preferably, both beams of light are beams of coherent light. The beams may be provided by separate low-power laser or a single laser may be used in conjunction with a beam splitter for dividing into two parts the beam of coherent light emitted by the laser. Typically, lasers with an output of about 1 mw are used so that special precautions to protect the eyes of a user are not needed.

Fig. 1 shows schematically a particular arrangement using a single laser indicated by block 1 that is housed in a container 2. Also located within the container 2 and positioned in the path of a beam 3 of coherent light from the laser 1 is a beam splitting mirror 4. The mirror divides the beam 3 in equal proportions 5, 6 of which proportion 5 passes out of the container through an aperture 7 in a wall thereof.

The mirror 4 is so located in the container 2 that the proportion 6 is directed towards a reflector 8 at right angles to the direction of the proportion 5 of the beam 3. The reflector 8 deflects the proportion 6 through a slot 9 in the wall of the container 2.

The reflector 8 is mounted for pivotal movement about an axis 10 and is equipped with means for indicating very accurately the inclination of the reflector.

Mounted externally of the container 2 is a control operation of which by a user rotates the reflector 8 about its pivotal axis. The control may be a knob directly mounted upon a shaft upon which the reflector 8 is also mounted or it may comprise a slow motion drive, for example a worm drive that enables the user to rotate the reflector very accurately.

The indicating means shown diagrammatically at 11 may comprise a vernier type scale that enables rotational movement of the reflector to be measured to a required degree of accuracy depending upon the range of distances for which the apparatus is designed.

For example, for distances from 1 metre up to say 100 metres, measurement to an accuracy of 1' of arc is needed.

Preferably, however, reflector 8 is fitted with a shaft encoder that electronically scans a scale movable with the reflector. The output of the encoder may be fed to a visual display of alpha-numeric form via a device for converting the output into required units of length, i.e. feet and/or metres and sub-multiples thereof.

The device is preferably a microcprocessor having storage facilities and programmed to enable a user to store measured distance and to perform calculations involving the measured distances. The microprocessor may have an output port for transferring stored distances to a computer or to a printer for providing a print-out of the stored measurements.

The container may be a hand-held unit 12, for example that shown in Fig. 2. The unit is of generally rectangular form when seen in end and side views and has a slot 13 towards one end that is contoured to provide a grip by means of which the user is able to grasp the unit.

The unit 12 has a front wall with the aperture 7 and slot 9. External of the unit and conveniently located upon a side wall 14 thereof is a control knob 15 by means of which the user is able to rotate the reflector 8. Located within the unit is the microprocessor adapted to energise a display 16 which is preferably a liquid crystal display.

The knob 15 may also operate on ON/OFF switch for the laser contained within the unit or a separate ON/OFF switch may be provided. The laser is a low power ruby laser, for example or it may be a low power helium neon laser and is powered by batteries located within the unit.

Buttons 17 on the unit allow the user to select the particular units in which a length is to be displayed, to store the values of measured distances and to output stored measurements to other equipment as described above.

In use, the laser 1 is energised and the user directs beam 5 towards the object whose distance is to be measured so that the beam impinges on the object providing a visible area of light. The user then rotates the knob 15 to direct beam 6 towards the object and brings the area of light from beam 6 into accurate alignment, i.e. coincidence, with that from beam 5. The distance to the object is then derived from the equation X=Y tan A where X is the distance to the object, Y is the distance between the centres of the beam splitter 4 and the reflector 8 and A is the angle of inclination with respect to the vertical of the beam 6.

The container 12 may be of a configuration that a user can hold against his body to give a greater degree of stability than may be possible with the hand-held design of Fig. 2. The configuration may incorporate a carrying strap or straps which the user can place over his head to support the container. In such a case, the control knob may be on the front or on the side of the container and the display may be on the upper surface thereof in a location in which it is readily visible to the user.

Figs. 3 and 4 are, respectively, front and side elevations of a second embodiment of the invention in which two light sources in the form of lasers are used. The lasers are housed within a carrying case 18 provided with a carrying handle 19 and a front wall 20 with a window 21 adjacent the lower edge of the wall. Projecting through the wall 20 adjacent the upper edge thereof is the operating lever member 22 of an ON/OFF switch mounted behind the wall 20 inside the case 18.

From the upper surface 23 of the case 18 adjacent the junction of wall 20 with that surface extends a hollow tube 24. The tube 24 terminates at its distal end in a reflector head 25. Inside the head 25 is an inclined mirror 26 (Fig. 5), the mirror beiing mounted at an angle of 45O so as to reflect a beam of light directed along the tube outwardly from the latter through a window 27 that faces forwardly of the case 18.

The tube 24 is firmly secured to the case 18 in a manner that permits the tube 24 to be removed if required. The lower end of the tube 24 seats centrally over an aperture in the upper surface of the case.

The reflector head 25 is removable from the tube 24 and is held in place by an internally threaded ring 28 that screws over the lower threaded external surface of the head 25. Location marks on the head and tube ensure accurate repositioning of the head after removal.

The upper surface 23 has a further aperture closed by a window 29. A dial indicated diagrammatically at 30 in Fig. 4 is visible through the window 27.

Mounted upon a shaft that extends through that one, 31, of the side walls of the case 18 that is seen in Fig. 4 is an adjusting handle 32.

Mounted on a suitable mounting plate (not shown) within the case 18 is a first, fixed laser 33 orientated to direct a beam of coherent light centrally along the tube 24 and on to the mirror 26. Laser 33 is also able to direct a beam of coherent light downwardly away from tube 24 and through a normally closed window (not shown) in the lower wall 34 of the case 18.

A second laser 35 is pivotally mounted upon the mounting plate referred to above, the axis of rotation being indicated at 36.

Laser 35 is orientated in such manner as to direct a beam of coherent light through the window 21 in the front wall 20 of the case 18.

Secured to the laser 35 is a cam follower 36 spring biassed into contact with a cam 37 formed on or attached to one face of a pinion 38 which is one pinion in a gear train comprising further pinions 39....45. Pinion 45 meshes with a gear wheel 46 on a driving shaft of the dial 30. Handle 32 is mounted upon the common shaft of pinions 41 and 42.

Thus, rotation of the handle 32 in the correct direction will point laser 35 about axis 36 and so vary the inclination to the horizontal of the axis of the laser and also of the beam of coherent light emerging therefrom. Rotation of the handle will also operate the dial 30.

Also housed within the case 18 is a power pack for both lasers. The pack comprises a battery located within a battery compartment access to which is provided by a door in the side wall of the case 18. Associated with that door is a safety switch in series with the ON/OFF switch mentioned above and which de-energises the power pack when the door is opened and the ON/OFF switch is also in its 'ON' position and re-energises it when the door is closed.

In use, a user aims the beam emerging from window 27 at the surface whose distance from the observation point is to be measured, thereby producing a disc of light on the surface. The handle 32 is then rotated until the beam of light from the laser 35 emerging from window 21 impinges on the surface to produce a disc of light thereon that is aligned with the first mentioned disc of light. Because the two beams of light do not lie in the same vertical plane, as can be inferred from Fig. 3 which shows that the vertical centre line of window 21 is slightly to the right of the plane containing the longitudinal axis of the tube 24 and which passes centrally through the mirror 26, it is not possible to secure actual registration of one light disc with the other.The discs of light can, however, be brought into side-by-side alignment and when that occurs, the dial 30 shows the distance from the observation point to the surface. The dial, the gear train and the cam may be such that the distance is indicated directly in desired units, for example centimetres.

However, in a further embodiment of the invention, the reflector head 25 is mounted upon the tube 24 in a manner such that the head is rotatable about the longitudinal axis of the tube. Thus, having brought the discs of light into accurate side-by-side alignment, a slight rotation of the reflector head 25 will bring the discs into complete registration and overlap. If as a result, the side-by-side alignment is found not to be completely accurate a further slight rotation of handle 32 will suffice to give the desired complete registration.

By removing the reflector head 25 before a measurement is taken, a beam of light may be projected upwardly on to an overhead surface to identify accurately the location from which the measurement is taken. Alternatively, the normally closed window in the lower wall 34 of case 18 may be uncovered to permit light from laser 33 to shine downwardly on to the ground beneath the case 18.

Although case 18 may be hand held during use, it is preferred to mount the case on a tripod or other transportable support. The tripod has an adjustable mounting that enables a user to pivot the case about a vertical axis so as to swing the laser beam about that axis. In addition, the mounting may also permit tilting of the case to produce a downward or upward inclination of the beams.

The case 18 will be of a water and gas tight construction and all openable doors/flaps will be fitted with suitable seals.

Instead of using a direct gear drive to translate the pivotal movement of the pivotally mounted laser into distance, a shaft encoder may be used.

The embodiment may also be provided with a temperature sensor responsive to ambient temperatures and means for compensating a measured distance for dimensional changes in the embodiment resulting from changes in ambient temperature.

The use of coherent light produces very sharply defined areas of light uon the object.

The use of optically visible radiation enables the apparatus to be used under conditions of little or no natural light, for example it is particularly suitable for use in mines where lighting is poor or non-existent.

Obviously, the described apparatus is usable only when the areas of light can be observed sufficiently clearly to enable the accurate registration referred to above to be effected but this is usually so where the distances involved are of the values indicated above.

For very short distances, conventional light sources may be used in conjunction with collimating means to produce narrow, substantially non-divergent beams of light.

Claims

1. Apparatus for measuring distance comprising means for projecting a first beam of light towards a surface whose distance from an observation point is to be measured, an arrangement for directing a second beam of light towards the surface along a path that is inclined to the path of the first beam, means for varying the inclination of the path of one beam relatively to that of the other beam, and an arrangement for indicating the relative inclination.

2. Apparatus as claimed in claim 1 in which the first and second beams are beams of coherent light.

3. Apparatus as claimed in claim 2 in which the source of the first and second beams is a single laser.

4. Apparatus as claimed in claim 2 and comprising first and second lasers for producing the first and second beams.

5. Apparatus as claimed in claim 3 and further comprising a beam splitter for splitting the output of the single laser into the first and second beams and which includes a reflector for directing the second beam towards the surface.

6. Apparatus as claimed in claim 5 in which the reflector is pivotally mounted in such manner as to vary the inclination of the path of the second beam relatively to that of the first beam.

7. Apparatus as claimed in claim 6 in which the means for varying the inclination comprises an arrangement for varying the inclination of the reflector.

8. Apparatus as claimed in claim 4 in which the second laser is pivotally mounted in such manner as to vary the inclination of the path of the scond beam relatively to that of the first beam.

9. Apparatus as claimed in claim 8 in which the means for varying the inclination comprises an arrangement for varying the pivotal orientation of the second laser.

10. Apparatus as claimed in claim 7 or 9 in which the arrangement is operatively coupled to the means for indicating the relative inclination.

11. Apparatus as claimed in claim 10 in which the arrangement comprises a cam and follower mechanism and a gear train for driving the cam, the gear train also actuating the indicating means.

12. Apparatus as claimed in any one of the preceding claims in which the indicating means includes a shaft encoder actuated by the means for varying the inclination of the second beam.

13. Apparatus as claimed in any one of the preceding claims in which the arrangement is such that the indicating means indicates the distance of the surface.

14. Apparatus as claimed in claim 2 or claim 4 or in any preceding claim dependent upon claim 2 or claim 4 in which the first beam is directed towards the surface by a beam reflector.

15. Apparatus as claimed in claim 14 in which the beam reflector is spaced from the second laser.

16. A portable case or container including apparatus as claimed in any one of the preceding claims.

17. A case or container as claimed in claim 16 in which the case or container includes a wall with first and second apertures through which the first and second beams respectively are directed towards the surface.

18. A case or container as claimed in claim 17 in which the case or container includes a part extending away from the case or container, and in which a beam reflector is located in a position adjacent the distal end of the part for directing the first beam towards the surface.

19. A case or container as claimed in claim 18 in which the beam reflector is mounted in a reflector head adjustable in position relatively to the part in a manner such as to vary the direction of the first beam towards the surface.

20. A case or container as claimed in any one of the claims 16-19 in conjunction with a supporting structure including a mount for the case or container which is provided with means for varying the orientation of the case or container relatively to the structure.

21. Apparatus substantially as herein described with reference to and as illustrated by Figs. 1 and 2 or Figs. 3, 4 and 5 of the accompanying drawings.