GB2194702A - Determining angular location - Google Patents

Abstract

The device, which is suitable for measuring angular deviation in railway tracks, or the angular position of a distant object with respect to a vehicle, comprises at the measuring station a laser source L, a reflector M which is rotatable or oscillatable at a positively monitored rate, a first laser detector D1 for detecting a beam direct from the reflector M, a second laser detector D2 for detecting a beam from a retroreflector R on the target, and a timer for timing the time between detection by detector D1 and by detector D2. This time is indicative of the angular position of retro- reflector R with respect to source L. <IMAGE>

Description

SPECIFICATION Remote measurement device The present invention is concerned with remote measurement devices, which are suitable for measuring angular deviations in railway tracks, for measuring the range end orientation from a vehicle to a stationery or moving object, for use in surveying, and the like.

According to the present invention, there is provided a remote measurement device, which comprises: (a) a laser source; (b) a reflector for reflecting a laser beam from said source; (c) means for rotating or oscillating said reflector at a positively monitored rate; (d) a first laser detector, which is arranged to detect a beam reflected from said reflector, and which is fixedly mounted relative to a fixed mounting for said reflector; (e) a second laser detector which is arranged to detect a beam from a retroreflector on a distant target, which second detector is fixedly mounted relative to said fixed mounting; and (f) means for timing the minimum time lag between detection of a reflected beam by said first detector and detection of a reflected beam by said second detector.

The laser source is typically an He/Ne laser source, although other conventional laser sources may be used (for example, a semiconductor or carbon dioxide laser). Since the divergence of the laser beam is generally responsible for the limiting accuracy of the device according to the invention, it is desirable for the laser source to be collimated, for example, by means of a collimating telescope system. Since, furthermore, the light intensity is diluted because of the rotation or oscillation of the reflector, it is preferred for the telescope system to have cylindrical optics.

The reflector is typically a rotating or oscillating planar mirror; the latter is preferably rotated or oscillated at a rate of 50 to 200 cycles per second, typically about 100 cycles per second. In any case, the rate of rotation or oscillation should be positively monitored at a desired level employing, for example, a shaft encoder.

The timing means preferably comprises an electronic clock, which typically has a count rate of 10 to 30 MHz (e.g. about 16 MHz).

The clock is generally "zeroed" in each cycle of rotation or oscillation of the reflector by means responsive to such rotation or oscillation. This may be for example, a laser detector (typically a photodiode) or a shaft encoder.

When a laser detector is used, the latter is in fixed disposition and arranged so that the clock is reset in each cycle when the reflected beam from the rotating or oscillating reflector reaches the detector. When a shaft encoder is used, the latter is arranged to ensure that the clock is reset when a predetermined count is reached (for example, indicative of a complete revolution of the reflector).

In operation of the device according to the invention, a pulse reflected from the reflector to the first detector (which is typically a photodiode) starts the electronic clock. As the reflector rotates (or oscillates), it reaches a position where it directs a pulse at the distant retroreflector; the latter reflects the pulse to the second detector which is aligned with the reflector. The reception of the pulse by the second detector then stops the clock. The second detector is preferably fixed relative to the fixed mounting for the reflector.

The retroreflector is such that it reflects the pulse substantially along its line of incidence on the retroreflector; the latter is typically an isosceles triangular prism arranged so that the incident beam is substantially normal to the base of the triangle, and then undergoes total internal reflection by the other two sides in succession, the beam being directed back through the base substantially normal thereto.

The divergence of the retroreflector beam from the incident beam is preferably no more than the separation between the first and second detectors.

The elapsed time between detection of the reflected beam by the first detector and detection of the reflected beam by the second detector can be used for a variety of purposes, as follows: (i) in surveying, for measuring distance and angles between fixed points; (ii) for measuring of distance, direction, and angles between a fixed point and a moving vehicle (such as a ship or a helicopter); and (iii) for measuring of distance, direction and angles between moving vehicles.

In connection with the latter, the device according to the invention may be mounted on one railway vehicle and the retroreflector mounted on a further railway vehicle unconnected to the first-mentioned vehicle. Such an arrangement will now be described with reference to Figures 1 and 2 of the accompanying drawings, in which: Figure 1 is a schematic illustration of the operation of an exemplary remote measuring device according to the invention; and Figure 2 is a schematic block diagram of the electronic control of the device of Figure 1.

Referring to Figure 1, there is shown a trailing vehicle T having thereon a laser source L, and a mirror M arranged to rotate clockwise (in the direction of arrow A). On rotation of the mirror M, a pulse first illuminates a photodiode detector DO and then a photodiode detector D1.

Referring to Figure 2, the output from detector DO is processed by a microcomputer, the output of which resets a display to zero; the output from detector D1 is processed by a microcomputer to produce an output which starts an electronic clock (such as a 16 MHz clock).

After the detector D1 has been illuminated (referring again to Figure 1), the scanning mirror then directs the laser beam towards a retroreflector R on leading vehicle V which returns the light to photodiode detector D2 which, in practice, is generally immediately above, or adjacent to, mirror M.

Referring again to Figure 2, the output from the detector is processed by a microcomputer, which stops the clock; the elapsed time is processed by the microcomputer to produce a display which is indicative of an angular deviation or a distance.

With reference to a display of angular deviation, if retroreflector R moves to the right (Figure 1), the clock will run for an extended period, while if retroreflector R moves-to the left the clock will run for a shorter period. The time duration is therefore indicative of the relative angular movement between vehicles T and V.

When a display of angular deviation is desired, this may be calculated as follows: If the rate of rotation of the mirror is f revolutions per second, then the angular frequency is 360f degrees per second.

If the elapsed time between starting of the electronic clock (by detector D1) and stopping of the clock (by detector D2) corresponds to n pulses of the clock, and the clock frequency is c, then the angular deviation will be n x (360f)/c.

For example, if a clock with a frequency of 1MHz is used, with a mirror rotating at 100 Hz, and the number of pulses of the clock is detected as 100, this corresponds to an angular deviation of (100 x 10-6 x 100 x 360) ; that is, 3.6 .

In practice the laser source, the photodiodes, the rotating mirror plus all associated electronics can be on the trailing vehicle T with the leading vehicle V having the retroreflector R only. This technique requires no electrical connection between the two vehicles.

In an alternative arrangement, the retroreflector may be on the trailing vehicle, with the laser source, the photodiodes, rotating mirror and associated electronics on the leading vehicle.

While the invention has been described primarily with reference to measurement of angular deviation between railway vehicles (and hence angular deviation of the track), it may be used for many other purposes. For example, when used in surveying, the device according to the invention may be associated with a device provided with two retroreflectors which may be located remotely relative to the first-mentioned device.

Claims (8)

1. A remote measurement device; which comprises (a) a laser source; (b) a reflector for reflecting a laser beam from said source; (c) means for rotating or oscillating said reflector at a positively monitored rate; (d) a first laser detector, which is arranged to detect a beam reflected from said reflector, and which is fixedly mounted relative to a fixed mounting for said reflector; (e) a second laser detector which is arranged to detect a beam from a retroreflector on a distant target, which second detector is fixedly mounted relative to said fixed mounting; and (f) means for timing the minimum time lag between detection of a reflected beam by said first detector and detection of a reflected beam by said second detector.

2. A remote measurement device according to claim 1, in which the laser source is provided with collimating means.

3. A remote measurement device according to claim 1 or 2, in which said rotating or oscillating means includes a shaft encoder for positively monitoring the rate of rotation or oscillation of said reflector.

4. A remote measurement device according to any of claims 1 to 3, which is further provided with means for resetting the timing means in each cycle of rotation or oscillation.

5. A remote measurement device according to any of claims 1 to 4, in which said second laser detector is fixed relative to the fixed mounting for the reflector.

6. A remote measurement system comprising a device according to any of claims 1 to 5, and a retroreflector which is such that it can reflect a laser beam substantially along its line of incidence on the retroreflector.

7. A system according to claim 6, in which said device is mounted on a first railway vehicle and said retroreflector is mounted on a further railway vehicle unconnected to the first-mentioned vehicle.

8. A remote measurement device according to claim 1, substantially as described herein with reference to the accompanying drawings.