GB2249683A

GB2249683A - Optical system for the remote determination of position and orientation

Info

Publication number: GB2249683A
Application number: GB9023625A
Authority: GB
Inventors: John Malcolm Morrison
Original assignee: GEC Ferranti Defence Systems Ltd
Current assignee: Leonardo MW Ltd
Priority date: 1990-10-31
Filing date: 1990-10-31
Publication date: 1992-05-13
Anticipated expiration: 2010-10-31
Also published as: GB2249683B; GB9023625D0

Abstract

To determine the position of a helmet in a cockpit to enable weapon's aiming to be determined from the position of the pilot's head, a pair of fan shaped beams (scan 1, scan 2) alternately intercept all four photo-sensitive strips A-D arranged in an upright fashion and equally angularly spaced apart on the rear of the pilot's helmet (Fig. 1), (as seen in the straight ahead looking position). The outputs (Fig. 3) of the photo-sensors depend upon the position at which it is illuminated by the light beam, and sufficient information is provided by the outputs of the four photo-sensors for both fan beams in order to enable the position of the helmet in the cockpit to be determined. <IMAGE>

Description

OPTICAL SYSTEM FOR THE REMOTE DETERMINATION OF POSITION AND ORIENTATION This invention relates to an optical system for the remote determination of position and orientation. The invention is especially concerned with determining the position and orientation of a helmet in a cockpit of an aircraft or helicopter. This is done to control aiming systems of weapoons which are aimed in accordance with the direction in which the pilots head is pointing, and also because a head-up display is sometimes reflected via a combiner mounted on the helmet or via the visor itself, and the display may need to depend on the direction in which the head is pointing.

The invention provides an optical system for the remote determination of the position and orientation of a helmet in a cockpit, comprising at least four spaced apart photo-sensitive strips, the output from which is dependent upon the position along the strip at which it is illuminated, and means for generating at different times two fan shaped light beams, the centre planes of which are inclined relative to each other and which each intercept the photo-sensitive strips simultaneously.

The two lines of inter-section of the beams with the photo-sensitive strips give sufficient information for the position and orientation of a helmet to be determined.

The two fan shaped beams may be generated using cylindrical lenses with their axes inclined to each other, and the light source may be a pair of laser diodes which alternately illuminate the photo-sensitive strips, or a single laser diode which alternately illuminates the strips at different inclinations.

An optical system for the remote determination of the position and orientation of a helmet in a cockpit of an aircraft will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of the helmet; Figure 2 is a rear view of the helmet; Figure 3 shows schematically the output of the photosensitive strips when illuminated by one of the fan shaped beams; Figure 4 is an optical diagram in schematic form of a means for generating the fan shaped light beams; and Figure 5 is an optical diagram in schematic of an alternative means for generating the two fan shaped light beams.

Referring to Figures 1 and 2, four photo-sensitive strips A-D are arranged on the pilots helmet. The strips are upright when the pilot is looking in the straight ahead position and the angular displacement from one strip to the next as seen by the light generating means are equal to each other. The photo-sensitive strips are illuminated by a fan shaped beam 1 produced by an optical system 3 from a laser diode 2.

Referring to Figure 3, the centre plane of the fan shaped beam 1 lies either in the direction marked scan 1 or in the direction marked scan 2, but in either case extends over all four photo-sensors.

The output of the photo-sensors is dependent upon the position along the strip at which it is illuminated. If the strip is illuminated near the lower end, the output is low and if it is illuminated at the upper end its output is high. Thus, the output produced by the sensors A-D for the illumination by the fan beam marked 'scan 1' is as shown in figure 3.

It will be apparent that the information from the output from the photo-sensors for the two scans is sufficient to determine the position and orientation of the helmet. This is because upward and downward displacements of the helmet would change the output values of the sensors for both fan shaped beams, whereas side to side movement of the helmet would move the point of inter-section of the fan shaped beams to one side or other of its central position.

Processing means is able to calculate the position of the helmet in the cockpit.

The means for generating the two fan shaped beams from the photodiode 2 are illustrated in figure 4. Light from the laser diode 2 is focused into a parallel cylindrical beam by means of a lens 5 where it is split into two paths by means of a beam splitter 6. A transmitted path passes through a cylindrical lens 7 orientated to produce one of the fan beams (scan 1 or scan 2), and the reflected beam is incident via a mirror 8 on another cylindrical lens 9 orientated to produce the other fan shaped beam (scan 2 or scan 1) so that there is angle alpha between the two fan shaped beams. The reflected beam is recombined with the transmitted beam by means of a mirror 10 and a combiner 11.

In order to switch alternatively between the beams, electro-optic switches 12 and 13 are provided, with are either transparent to allow the fan beam to pass or opaque to block and allow the other fan beam to pass.

An alternate method of producing the two fan beams is shown in figure 5, in which two laser diodes 14 and 15 are provided, these being imaged by means of lenses 16 and 17 onto cylindrical lenses 18 and 19 and the outputs being combined by means of a mirror 20 and a beam splitter 21.

The axes of the cylindrical lenses 18 and 19 are inclined to each other at an angle alpha to produce the required fan beams. This time, in order to project one beam at a time onto the photo-sensitive strips, the photodiodes are driven with the illustrated square wave drive forms so that one photodiode is on while the other one is off and visa versa.

In order to make the beams fan shaped the cylindrical lenses are diverging so that the lines into which the incoming cylinder of radiation is focused increases in length the further away from the cylindrical lens.

The photo-sensitive strips may be linear photodetector arrays, and may conveniently be formed from amorphous silicon. The provision of four strips means that at least three will be visible at any one time, since it is possible that one will be obscured if the pilot turns his head. It would however be possible to provide more that four such strips.

Claims

1. An optical system for the remote determination for the position and orientation of a helmet in a cockpit, which comprises at least four spaced apart photo-sensitive strips the output from which is dependent upon the position along the strip at which it is illuminated, and means for generating at different times two fan shaped light beams, the centre planes of which are inclined relative to each other and which each intercept the photo-sensitive strips simultaneously.

2. An optical system as claimed in claim 1, in which a pair of cylindrical lenses with their axes inclined is provided to produce the two fan shaped light beams.

3. An optical system as claimed in claim 1 or 2, in which the means for generating the light beams comprises a pair of diodes arranged to be alternately illuminated.

4. An optical system as claim in any one of claim 1 to 3, in which the means for generating the two fan shaped light beams comprises a single diode in combination with a beam splitter and electro-optic means for switching between the two parts of the beam so divided.

5. An optical system for the remote determination for the position and orientation of a helmet in a cockpit substantially as herein described with reference to the accompanying drawings.

6. A method for the remote determination of the position and orientation of the helmet in a cockpit, in which two fan shaped light beams, the centre of planes of which are inclined relative to each other alternately intercept at least four spaced apart photo-sensitive strips on the helmet, the output of which is dependent along the position along the strip at which it is illuminated.