GB2249449A

GB2249449A - Optical system for the remote determination of position and orientation

Info

Publication number: GB2249449A
Application number: GB9023628A
Authority: GB
Inventors: John Malcolm Morrison
Original assignee: GEC Ferranti Defence Systems Ltd
Current assignee: Leonardo UK Ltd
Priority date: 1990-10-31
Filing date: 1990-10-31
Publication date: 1992-05-06
Anticipated expiration: 2010-10-31
Also published as: GB9023628D0; GB2249449B

Abstract

To determine the position of a pilot's helmet in a cockpit, four upwardly extending photo-sensitive strips A-D are provided on the helmet, and those are scanned by a beam 4 produced from a laser diode which scans across the strips in turn in a horizontal direction. The output of each strip is dependent upon the position of illumination along it such that relative timings and outputs from the strips as the beam crosses them gives sufficient information for the position of the helmet to be calculated. <IMAGE>

Description

OPTICAL SYSTEM FOR THE REMOTE DETERMINATION OF POSITION AND ORIENTATION This invention relates to optical systems for the remote determination of position and orientation, and especially such systems for determining the position and orientation of a helmet in a cockpit of an aircraft or helicopter. This is done to control aiming systems of weapons which are aimed in accordance with the direction in which the pilot's 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 depend on the direction in which the head is pointing.

The invention provides an optical system for the remote determination of position and orientation of a helmet in a cockpit, comprising at least four spaced apart photo-sensitive strips mounted on the helmet, the output of which is dependent upon the position along the strip at which it is illuminated, and means for producing a light beam for scanning each of the strips in turn.

The position and orientation of the helmet can be determined from the magnitudes and relative timings of the outputs from the strips crossed by the beam.

The photo-sensitive strips may be mounted in an upright fashion on the rear of the pilot's helmet, and may be spaced apart so that a light beam scanning from side to side traverses equal angles in going from one strip to the next. The scanning may conveniently be provided by a laser diode in conjunction with a galvanometer mirror or a rotating mirror polygon i.e. a drum, the periphery of which is provided with mirrored facets equally inclined to each other.

An optical system for the remote determination of position and orientation of a helmet in a cockpit constructed in accordance with the invention 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; and Figure 3 shows in schematic form the output of the photo-sensitive strips.

Referring to Figures 1 and 2, the helmet is provided with four photo-sensitive strips A-D, which are vertical when the pilot is looking in the straight ahead position.

The photosenstive strips are repeatedly scanned by a narrow beam 1 emanating from a photodiode 2 which is repeatedly scanned by means of a rotating faceted mirror 3 to traverse the helmet from left to right in a horizontal straight line.

The beam rapidly returns to the left hand side of the helmet after the end of the scan and so on for subsequent scans.

The photo-sensitive strips are arranged so that they are equally angularly spaced with respect to the scanning beam.

Each of the photo-sensitive strips is a single axis rectangular photodetector strip, which may be of amorphous silicon. An electrical signal is produced as output from the strip when it is illuminated by the scanning beam. If the strip is illuminated in the centre, then half the signal which would have been obtained had the strip been illuminated at its upper end, is obtained.

Referring to figure 2, a reference photodiode 4 is mounted in a fixed position in the cockpit to the left of the helmet in line with the scanning beam from the photodiode. This produces an output when illuminated.

Referring to figure 3, the outputs of the photo-sensitive strips A-D and of the reference photodiode 4 are shown for various positions of the helmet. With the pilot looking straight ahead, and the helmet thus horizontal, each sensor produces a pulse of amplitude half the maximum possible and equally spaced in time. In the next line down, the pilot has rotated his head to the left and, while the outputs of the photo-sensitive strips are unchanged, they are delayed relative to that of the datum pulse and also the strip 4 has been obscured altogether. In the next line down, the pilot has looked down while still maintaining an ahead position. This results in the sensor strips B and C as being cut at a lower position, resulting in a lower amplitude output and the sensor strips A, D being cut nearer the upper end, which results in a higher amplitude output.The timings of the outputs nevertheless are in syncronism with those for the first line, since the helmet is in the straight ahead position. In the next line down the helmet remains in the ahead position, so that the sensor strip outputs are in line with the first line, but the sensor strip A is now cut nearer its lower end and the strip D is cut near its upper end (corresponding to a tilt to the right), and the outputs of the sensor strips therefore increase progressively from A-D. In the next line below, the helmet has been subject to a tranlational move forward but no other tilting or rotation, and this means that the outputs are all the same as for the first line, but the relative timings are changed, corresponding to the fact that the angles subtended at the scanning beam between successive sensor strips is now reduced. In the final line, the sensor strips maintain time syncronism with those for the first row, but the amplitude is either lower corresponding to the pilot's head moving vertically upwards or higher corresponding to the pilot's head moving vertically downwards.

The outputs of the photo-sensitive strips A-D are fed to processing means, and the position of the helmet in all six possible degrees of freedom can be extracted.

Claims

1. An optical system for the remote determination of 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 a light beam for scanning the strips in turn.

2. An optical system as claimed in claim 1, in which the light beam is generated by means of a laser diode.

3. An optical system as claimed in claim 1 or 2, in which the photo-sensitive strips are arranged such that they extend vertically when the helmet is pointing in the straight ahead position.

4. An optical system as claimed in claim 3, in which the angle subtended by successive strips at the scanning beam is equal.

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

6. A method for the remote determination of position and orientation of a helmet in a cockpit in which a light beam scans at least four spaced apart photo-sensitive strips cn the helmet, the output of which is dependent upon the position along the strip at which it is illuminated.