GB2249684A

GB2249684A - Optical system for the remote determination of position and orientation

Info

Publication number: GB2249684A
Application number: GB9023627A
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: 1992-05-13
Anticipated expiration: 2010-10-31
Also published as: GB9023627D0; GB2249684B

Abstract

To determine the position and orientation of a helmet in a cockpit to enable weapons aiming to be determined from the position of the pilot's head, at least two light sources on the pilot's helmet are imaged onto a pair of position sensitive detectors 11 and 12, the first (11) of which is transparent, and which provide x and y electrical signals corresponding to the position in the area of the position sensitive detector of the light spot. The use of sequential detectors enables the determinations of the direction lines of the sources. It is not necessary for the images to be focussed on each detector, the use of one focussing means 13 thereby being possible, Fig. 4. <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 the 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 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 two light sources mounted on the helmet, and means for imaging light sources onto a second position sensitive detector via a first, transparent, position sensitive detector, each position sensitive detector comprising a photo-sensitive layer arranged to provide an electrical signal dependent on the position of the light spot on the respective layer.

The outputs of the two position sensitive detectors enable the position and orientation of the helmet to be determined within the cockpit.

There may be three or more light sources e.g. LEDs mounted on the helmet and, in this case, a single position sensitive detector is sufficient to enable the position of the helmet to be known given the relative positions of the light sources on the helmet (our co-pending patent application P/8521/GEF). However the provision of the transparent position sensitive detector enables the position that has been determined to be checked, and also simplifies the calculations since the angle of the incident beam can be determined directly by comparison of the electrical signals from the two position sensitive detectors.

It is not necessary for the light sources to be imaged to a point on the position sensitive detectors, and a spot having a finite area would still give accurate results.

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 or example, with reference to the accompanying drawings, in which: Figure 1 shows, partly schematically, the optical arrangement of the system; Figure 2 is a perspective view of one of the position sensitive detectors (not shown to scale); Figure 3 is a front view of one of the position sensitive detector shown in Figure 2; Figure 4 shows one possible optical arrangement; Figure 5 shows another possible optical arrangement; Figure 6 shows another possible optical arrangement; and Figure 7 shows another possible optical arrangement.

A pilot's helmet has two LEDs mounted on the rear, and means to image those LEDs onto two position sensitive detectors 11, 12. The light beam strikes the latter because the former is transparent. From the outputs of the position sensitive detectors, and from a knowledge of the spacing of the LEDs on the helmet, it is possible to work out the position and orientation of the helmet.

Each position sensitive detector comprises a p layer 1 and an n layer 2 on either side of the intrinsic layer 3 (Figures 2 and 3). Electrodes 4, 5 on top of the p layer and electrodes 6, 7 underneath the n layer provide a current output from which the position of a light spot on the detector, from left to right, and from front to rear, respectively can be determined. The detector responds to radiation in the 700 - 1100 micron band, and the position of the spot of radiation can be determined to an accuracy of + 200 microns with a resolution of 6 microns. Thus, the electrodes 4, 5 thus enable the x co-ordinate of the light spot to be determined i.e. the co-ordinate parallel to the conductor 6, and the electrodes 6, 7 provide the y co-ordinate of the light spot. The detector 11 differs from the detector 12 in that the detector 11 is transparent.

The optical arrangement is shown in Figure 4, the imaging means being constituted by a lens 13. It will be noted that the incident radiation is not focussed to a point on the detector 11, because the nature of the detector is such that it gives an equally accurate reading of position for an out of focus spot as it would to a focussed point of light. The point of focus is actually between the position sensitive detectors 11 and 12.

An alternative arrangement shown in Figure 5 does focus the radiation to a spot on detector 11 and further imaging means 14 focus the emerging radiation onto the position sensitive detector 12.

The optical path may be folded to assist in packaging in considerations for example as shown in Figure 6, where the second position sensitive detector is arranged at right angles to the first position sensitive detector, a 900 prism 16 being used to bend the radiation passing through the first position sensitive detector and focussed by the lens 15 through 90 onto the second position sensitive detector 12. In an alternative arrangement shown in Figure 7, the lens 15 is placed after the prism 16 rather than before it to provide an alternate packaging arrangement.

In all the arrangements described, the angle of the incoming beam from the LED after imaging can be readily determined by subtracting the x co-ordinates of the light spot as it strikes the first position sensitive detector from those of the light spot when it strikes the second position sensitive detector, bearing in mind the known separation between the two position sensitive detectors.

The light sources are illuminated sequentially.

Variations may of course be made without departing from the scope of the invention. Thus, for example, other forms of light source mounted on the helmet may be used in place of LEDs. Further, to provide redundancy and to assist in the situation where the pilot turns his head and risks obscuring one of the light sources, further light sources may be provided. "Light" as used herein is not limited to visible light but includes infra-red.

Claims

1. An optical system for the remote determination of the position and orientation of a helmet in a cockpit, comprising at least two light sources mounted on the helmet, and means for imaging light sources onto a second position sensitive detector via a first, transparent, position sensitive detector, each position sensitive detector comprising a photo-senstive layer arranged to provide an electrical signal dependent on the position of the light spot on the respective layer.

2. An optical system as claimed in claim 1, including means for calculating the position of'the helmet using the angle of the beams from the imaged light sources determined from the pairs of output signals from the position sensitive detector that relate to the position of the light spot in orthogonal directions in the plane of the position sensitive detector.

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

4. A method of determining remotely the position and orientation of a helmet in a cockpit comprising imaging at least two light sources on the helmet onto a second position sensitive detector via a first transparent position sensitive detector, each position sensitive detector comprising a photo-sensitive layer arranged to provide an electrical signal dependent on the position of the light spot on the layer.