GB2114770A - Telemetry device - Google Patents

Abstract

A telemetry device for measuring the distance of an object comprises a telescopic arm (2) having at one end a first emitter (3) and at the other end a second emitter (9). The two emitters (2, 9) transmit beams (6 and 10) towards an object T and means (15, 16, 18) are provided for adjusting and measuring the angular position of the second emitter (9). The distance of the object T is read from the display 18 when the beams (6 and 10) are seen to intersect at the object. The two beams may originate from a single laser beam, which is split in a beam splitter 5 (Fig. 2, not shown). <IMAGE>

Description

SPECIFICATION Telemetry device for measuring the distance of an object by direct intersection of coherent light beams This invention relates to telemetry devices and has as its subject matter a telemetry device, characterised in that it comprises: a casing having a straight arm; a first coherent light emitter disposed at one end of the arm and adapted to transmit a first radiation beam perpendicuiar to the arm towards an object whose distance from the casing it is required to measure; a second coherent light emitter disposed at the other end of the arm and angularly orientable relatively to the arm and adapted to transmit a second radiation beam towards the object; and means for measuring the angular position of the second emitter relatively to the arm in the state in which the first beam and the second beam intersect at the object.

The invention can therefore provide a rugged, functional and low-cost telemetry device which is very convenient and effective to use in cases such as, for instance, measurement of distances at the site of a road accident or the like.

In cases of this kind distances are usually measured by means of measuring tapes which are particularly time-consuming when a large number of measurements have to be made and which may be difficult or dangerous to use, for instance, when measurements have to be carried out on a road carrying heavy traffic. The device according to the invention not only makes it possible to carry out a large number of measurements rapidly but also enables the actual measurement operations to be carried out in convenient and safe conditions, there being no need for the measurer to have access to the objects of whose position it is required to determine.

Use of the device according to the invention is also very advantageous as compared with optical, radar or laser beam telemetry devices such as are used for military purposes. Such devices are normaily very expensive, may be very bulky and are often unselective at short distances; in the particular case of radar appliances they can often detect the position just of metal articles and nothing else.

The advantages provided by the invention will become apparent from the purely exemplary and non-limitative description given hereinafter with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a device according to the invention, shown in use for measuring the distance of an object; Figure 2 is a plan view, with parts broken away, ofthe device shown in Figure 1, and Figure 3 is a view in block schematic form of one of the elements shown in Figure 2.

Referring to Figure 1, an oblong casing 1 has a straight tubular arm 2 near one of its corners.

The arm 2 is telescopically extensible from a retracted position (not shown), in which the arm 2 is received substantially completely in the casing 1, so that the device is very compact and readily transportable, into an operative position which is shown in Figure 1 and in which the arm 2 projects out of the casing 1.

Disposed in the casing 1 is a laser source 3, preferably a HeNe laser which emits coherent radiation in the visible range (approximately 632.8 nm).

The laser source 3 is energized by a power pack 4 and has at its output a beam splitter 5 which is disposed at one end of the tubular arm 2.

The splitter 5 sub-divides the radiation from the laser 3 into a first beam 6, which issues from the casing 1 through an aperture 7 perpendicularly to the arm 2, and an auxiliary beam 8, which is propagated in the arm 2 towards a metal mirror 9 disposed at the other end of the arm 2.

The mirror 9 is rotatable around an axis perpendicular to the plane identified by the first beam 6 and the arm 2.

The mirror 9, which is at a distance b from the beam splitter 5 in Figure 1, produces by deflection of the auxiliary beam 8 a second coherent light beam 10 which issues from the arm 2 through an aperture 11, forming angle B, indicated in Figure 1, with the axis of the arm 2.

The angle B can be varied by rotation of the mirror 9.

As shown in Figure 2, the mirror 9 can be rotated by means of a d.c. motor 1 2 connected to the mirror 9 through a transmission comprising reduction gearing 13 and a worm 1 3a meshing with peripheral toothing of a disc rigidly secured to the mirror 9.

The motor 12, which is connected by means (not shown) to a supply battery 14, can be run to either end by the operation of two buttons 1 5, 16 disposed on the top surface of the casing 1.

Battery 14 also provides the power for the laser 3 and of the other electrical facilities of the telemetry device.

When the device is positioned as shown in Figure 1, with the casing 1 oriented so that the first beam 6 strikes an object T, for instance, the side of a vehicle, at a distance dfrom the casing, by operation of the buttons 1 5, 1 6 and observation of the light traces produced by the beams 6 and 10 on the object T, the mirror 9 can be oriented into a position in which the second beam 10 intersects the first beam 6 at the object T.

Consequently, the distance dcan be expressed in accordance with basic trigonometric formulae as d = b.tg B.

Since the distance d between the splitter 5 and the mirror 9 is known and calibrated, a signal indicating?the distance d can be produced by means of a potentiometric detector 1 7 which is rigidly secured to the shaft carrying the worm 1 3a and which is therefore sensitive to the angular position of the mirror 9.

The detector 17 can be such, for instance, that is resistance varies in proportion to the tangent of the angle B between the second beam 10 and the arm 2. A detector having this kind of variation can be embodied as a wire or metal layer device or as a device of the kind in which the deposit of resistive material is produced by means of a technology similar to that used for logarithmic and anti-logarithmic potentiometers.

The detector output signal goes to a display unit 18 disposed on the top surface of the casing 1; the display unit 1 8 has, for instance, measurement scales enabling direct determination of the distance din dependence upon the signal level.

Preferably, and as shown in Figure 3, the detector 1 7 is linear. The detector output signal then goes to a processing circuit 1 9 comprising an amplifier 20 and an analog-digital converter associated with a time base oscillator 22.

The signal thus converted is supplied to arithmetical circuit 23 (trigonometric chip), of a kind conventional in minicomputers, which is adapted to prepare from the digitalized signal a data item corresponding to the product of the distance b by the tangent of the angle B in accordance with the trigonometric relation hereinbefore recalled.

This item, which corresponds to the value of distance d, is supplied to the display unit 1 8 which is of the light segment type.

Very advantageously, the function of the processing unit 1 9 can be taken over at least to some extent by a microprocessor which also makes it possible, if so required, to perform further processing operations on the data relating to the measured distances d.

Conveniently, the device according to the invention can have an optical unit (not shown) for observing coincidence between the light traces produced by the two beams 6, 10 on an object T far away from the device, in order to ensure accurate intersection of the two beams.

For long-range use any spread of the beams 6, 10 can be compensated for by the use of collimators.

The effects of this invention also of course cover the models achieving similar useful effects by means of the same innovative concept, such as devices in which the mirror 9 is rotated manually or in which the mirror 9 is replaced by another laser source, and devices in which the arm 2 has disconnectable eiements making it possible to increase the distance b serving as measurement base.

Claims (8)

1. A telemetry device comprising a casing having a substantially straight arm; a first coherent light emitter disposed at one end of the arm and adapted to transmit a first radiation beam perpendicular to the arm towards an object whose distance from the casing it is required to measure; a second coherent light emitter disposed at the other end of the arm and angularly orientable relatively to the arm and adapted to transmit a second radiation beam towards the object; and means for measuring the angular position of the second emitter relatively to the arm in the state in which the first beam and the second beam intersect at the object.

2. A device according to Claim 1, characterised in that the arm is telescopic.

3. A device according to Claim 1 or 2 characterised in that the first emitter comprises a laser source having associated with its output a beam splitter which sub-divides the radiation from the laser source to produce the first beam and an auxiliary beam; and the second emitter comprises an orientable mirror which reflects the auxiliary beam.

4. A device according to Claim 3 characterised in that the arm is tubular and the auxiliary beam is propagated therein.

5. A device according to any of the previous claims, characterised in that the measuring means comprise a potentiometric detector whose resistance varies in proportion to the tangent of the angle between the second beam and the arm.

6. A device.a'ccording to any of Claims 1 to 4, characterised in that the measuring means comprise a potentiometric detector and a processing circuit connected thereto to produce a signal indicating the tangent of the angle between the second radiation beam and the arm.

7. A device according to Claim 6 characterised in that the processing circuit comprises a microprocessor.

8. A device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.