GB2105545A

GB2105545A - Attitude indication by horizon sensing

Info

Publication number: GB2105545A
Application number: GB08223422A
Authority: GB
Inventors: Brian Frederick Luff
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1981-08-26
Filing date: 1982-08-13
Publication date: 1983-03-23
Also published as: FR2512199A1; DE3231182A1

Abstract

The present invention provides an horizon viewing, attitude indication system for an aerial vehicle. The system includes a pair of oppositely directed optical means (1, 2) mounted on an aerial vehicle body (3) for horizon viewing, and photodetector means which may comprise a pair of photodetector arrays (5, 6), wherein the optical means are arranged to focus an image of the horizon on, or scan an image of the horizon over, the the photodetector output means output signals are indicative of vehicle roll attitude. The horizon location is detected by a sudden change in the output of the photodectector means. <IMAGE>

Description

SPECIFICATION Improvements in or relating to horizon viewing attitude indication systems The present invention relates to attitude indication systems for aircraft, projectiles or other aerial vehicles, and particularly, though not exclusively relates to attitude indication systems for use in unmanned vehicles which are being flight tested.

A common method of determining the attitude of a missile entails the analysis of kinetheodolite and high speed camera records. The method includes film reading and checking which are labour intensive and costly processes.

It is especially difficult to get accurate measurements of, for example, missile roll using kinetheodolite techniques. Contrasting patterns on the body of a missile have been used to enhance such techniques but accurate roll measurements, particularly at ranges of greater than 1 km, are not sufficiently accurate for many purposes.

The present invention provides an on-board attitude indication system which, under sufficiently clear horizon conditions, gives improved vehicle measurement compared with the above-described method.

According to the present invention an horizon viewing, attitude indication system for an aerial vehicle includes a pair of oppositely directed optical means mounted on the vehicle for horizon viewing, and photodetector means, wherein the optical means are arranged to focus an image of the horizon on, or to scan an image of the horizon over, the photodetector means, and wherein the photodetector means output signals are indicative of vehicle roll attitude.

According to one aspect of the invention the photodetector means comprises a pair of linear arrays of photodetectors, one array associated with each optical means which is arranged to focus an image of the horizon on its associated array of photodetectors, and readout means for reading from the arrays output signals corresponding to light patterns on the arrays which are indicative of vehicle roll attitude.

According to a further aspect of the invention the photodetector means may comprise two photodetectors, one associated with each optical means which is arranged to scan an image of the horizon over its associated photodetector.

Systems in accordance with the invention may further include a coincidence detector connected to receive signals from the readout means or the photodetector means for indicating whether said signals have substantially coincident stepped waveforms, and/or may further include averaging means for averaging the signals from the readout means to indicate an average value of vehicle roll attitude, and/or may further include means for indicating when only one of said signals has a stepped waveform.

Embodiments of the invention will now be described by way of example only, with reference to the drawings of which: Figure 1 is a side view of an attitude indication system installed in a missile body.

Figure 2 is a schematic circuit diagram of the attitude indication system of Figure 1.

Figure 3 shows idealised video signal waveforms which indicate different roll positions of the missile.

Figure 4 is a schematic arrangement of a further attitude indication system.

Figure 5 is a graph of photodetector output against time for a missile flying over the sea.

Figure 1 shows a section of a missile body 3 having a pair of lenses 1,2, mounted in apertures on opposite sides of the body 3. The lenses 1, 2, focus the images of distant scenes onto a linear arrays of photodiodes 4, 7 respectively, as indicated by the dotted lines in Figure 1, to produce corresponding video signals.

In good conditions where the contrast between the earth and sky produces a well-defined horizon, an image of the horizon can be focussed on the array. A scan of the array output from one end to the other produces a signal having a single 1 step waveform. The arrays, 4, 7, each comprise photodiode arrays containing a linear set of 128 diodes, and have associated scanning units 5, 6, respectively. The scanning units are driven by a circuit 8, which is shown in Figure 2, and which produces attitude indication and confidence signals shown as Flag 'A' and 'B' in Figure 1. The output from each of the scanning units is a video signal of which example waveforms are shown in Figure 3.

In circuit 8 of Figure 2, the video signals from the scanning units 5, 6, are input via signal conditioners 12, 14, respectively, to control the operation of gates, 19, 20, respectively. Clock pulses from a drive unit 9 are passed through gate 1 9 to a counter 21 until an edge is detected in the video signal from conditioner 12 whereupon the gate is closed. Similarly, counter 22 counts clock pulses input via gate 20 controlled by the signal from conditioner 14. The counter state is then a function of the horizon image on the corresponding array. An end-of-scan pulse generated by the drive unit 9 resets the counters 19, 20. An averaging circuit 23 averages the count signals from the counters 21, 22 and outputs the averaged count.A signal, shown as 'Flag B' in Figure 2, which is indicative of horizon detection by only one of the arrays, is produced when the averaging circuit is inhibited by a signal from a hold circuit 24. The hold circuit 24 has inputs from the signal conditioners 12, 14, and produces the inhibit signal for the averaging circuit 23 wherever there is detection of an horizon edge in only one of the video signals from conditioners 12, A coincidence detector 13 receives signals from the signal conditioners 12, 14, and produces an output signal, shown as 'Flag A' in Figure 2, when coincident horizon edges are detected, and simultaneously produces an inhibit signal for closing the gates 1 9, 20. Clock pulses from the drive unit 9 are passed through a gate 10 to a counter 11 until an edge is detected in the signal from the coincidence detector 13 whereupon the gate 10 is closed. The state of counter 11 is then a function of coincident horizon images on the arrays. The counter 11 is reset by the end-of-scan signal from the drive unit 9.

Figure 3 shows three sets of array output waveforms for a single scan T, for a pair of arrays A, B, corresponding to arrays 4 and 6 of Figure 1.

All three sets show coincident horizon detection at the points marked 'h'. The upper set indicates level flight, the middle set indicates that the missile has rolled in a clockwise direction from level flight and the bottom set an anticlockwise roll.

Figure 5 shows a graph of the output, 0, of the photodetectors 28, 29, of the system of Figure 4 when overflying the sea. One scan cycle from to to t2 is shown. The output from to to t1 corresponds to light reflected from the surface of a moderate sea, and from t, to t2 corresponds to light from the sky. Filtering of the sea signal and pulse shaping circuitry produces an output corresponding to the chain-dotted line p in Figure 5 from the output signal, 0.

Figure 4 shows a further embodiment of the invention. A scanning rotor 25 has fourteen plane reflective surfaces and is mounted on a shaft 36 driven by an electric motor 32 so as to revolve about an axis B-B which is inclined at an angle of 300 to the roll axis AA of a missile (not shown).

The end of the shaft 36 remote from the motor 32 carries an optically encoded disc 33 which has an associated readout head 34 with an output on a line 35 indicative of shaft angular position. The rotor scans images of distant scenes produced by lenses 26 and 17 onto photodiodes 28, 29 respectively. The outputs from the photodiodes 28,29, are transmitted via lines 30 and 31 to a signal processing circuit (not shown) which is similar to that shown in Figure 2 and indicates average values of roll attitude and includes horizon coincidence detection as described for the previous embodiment.

Claims

1. An horizon viewing, attitude indication system for an aerial vehicle including a pair of oppositely directed optical means mounted on the vehicle for horizon viewing, and photodetector means, wherein the optical means are arranged to focus an image of the horizon on, or to scan an image of the horizon over, the photodetector means, and wherein the photodetector means output signals are indicative of vehicle roll attitude.

2. An horizon viewing, attitude indication system as claimed in claim 1 wherein the photodetector means comprises a pair of linear arrays of photodetectors, and wherein each of the optical means is arranged to focus an image of the horizon on an associated one of the arrays of photodetectors, and readout means for reading from the arrays output signals corresponding to light patterns on the arrays which are indicative of vehicle roll attitude.

3. An horizon viewing, attitude indication system as claimed in claim 1, wherein the photodetector means may comprise two photodetectors, and wherein each of the optical means is arranged to scan an image of the horizon over an associated one of the photodetectors.

4. An horizon viewing, attitude indication system as claimed in claim 2, further including a coincidence detector connected to receive signals from the readout means for indicating whether said signals have substantially coincident stepped waveforms.

5. An horizon viewing, attitude indication system as claimed in claim 3, further including a coincidence detector connected to receive signals from the photodetector means for indicating whether said signals have substantially coincident stepped waveforms.

6. An horizon viewing, attitude indication system as claimed in claim 3, further including a coincidence detector connected to receive signals from the photodetector means for indicating whether said signals have substantially coincident stepped waveforms.

7. An horizon viewing, attitude indication system as claimed in claim 2 or claim 4 further including averaging means for averaging signals from the readout means to indicate an average value of vehicle roll attitude.

8. An horizon viewing, attitude indication system as claimed in claim 3 or claim 5 further including averaging means for averaging signals from the photodetectors to indicate an average value of vehicle roll attitude.

9. An horizon viewing attitude indication system for an aerial vehicle substantially as described herein with reference to the drawings.