GB2101948A - Air combat simulator - Google Patents

Abstract

A simulator comprising a simulator pilot's cockpit, a steerable image projector (6) adjacent the cockpit, means for supplying image generating signals to the projector, a display screen (5), and means for steering the image projector. The image projector comprises a first wide angle projection device and a second narrow angle projection device mounted on a common steerable support, the image field of the second device lying within the image field of the first. The support is steered in dependence upon orientation of the pilot's field of view relative to the screen such that the image field of the second projection device is substantially centred relative to the centre of the pilot's field of view. Image signals are supplied to the first projection device representative of all images including for example aircraft targets which are to be displayed at least outside the image field of the second projection device, and image signals and supplied to the second project device representative of details of images such as targets within the image field of the second project device. <IMAGE>

Description

SPECIFICATION Simulator The present invention relates to a simulator, and in particular to a simulator capable of providing a wide angle visual display to an observer of a scene relative to which the observer is moving. Such a simulator may be used for air combat and ground attack training.

Conventional air combat simulators comprise a fixed projector which projects a low definition wide angle image of the earth and sky, and a steerable projector which superimposes a high definition target image on the earth/sky image. The images are projected onto a front projection screen which extends over all the field of view of a pilot operating the simulator. The fixed projector can comprise a pair of hemispherical transparencies (one for the sky, the other for the earth) which together define a sphere. A point light source is positioned within the sphere which is gimbal-mounted to provide pitch and roll cues to the pilot. The point source is moved up and down to simulate the change in horizon position with height above the earth.There is no provision for the introduction of the translation effects due to flying over the earth terrain, nor of the perspective change which occurs with change of height. Thus the pilot does not receive height and speed cues.

The principle of the known projector is to provide a background image using one projector and then to 'paint' target details on that background. As in air combat simulation the target must be movable relative to the background one of the projectors must be movable relative to the other. Since a practical projector has a limit to the number of resolvable scene elements it can project, and a high resolution target is required, the target projector can only project an image covering a relatively small angle which is steered around the large field of view available out of the cockpit windows by pointing the optical axis of the target projector in the direction required to portray the target.

Given the requirement for large relative angular movement between the projectors of the known simulator, the projectors must be spaced apart by a distance of the order of several tens of centimetres.

In addition, the projectors must be located so as to avoid the pilot seeing them, and so as not to project shadows of either themselves or the pilot's cockpit structure onto the screen. Ideally both the projectors would be located at the same position as near as possible to the pilot's head to avoid mutually incompatible distortions. As in fact they must be spaced apart by a distance which is significant in proportion to the pilot/screen distance considerable distortion is inevitable. In an all round view system no location of the projectors is satisfactory as they must then obstruct at least a portion of the pilot's view.

If a second target is to be displayed, the problems outlined above become even more acute as this requires a steerable third projector spaced from each of the other two, thus increasing the shadowing/ intrusion problems. This is a particularly serious problem as combat aircraft generally fly in pairs.

In one known system which attempts to display two targets, a target projector is mounted at each side of the pilot's position. The target projectors can swivel and a single target circling the pilot has to be passed from one projector to the other. By allowing the projectors to cover overlapping areas of the screen, it is possible to display two targets simultaneously, but it is very difficult to keep two targets accurately displayed in all parts of the screen at all times due to the problem of knowing which projector to hand over to at any particular time.

In the case of ground attack training simulators it is again highly desirable to provide a wide angle image. Although targets are not moving rapidly relative to the background scene as in the case of air combat it is nevertheless importantforthe pilot to be able to see details of the terrain over which he flys to assess his position, speed and height. This requires a high resolution image not previously achievable in a wide angle projection system.

It is an object of the present invention to overcome or substantially reduce the problems referred to above.

According to the present invention, there is provided a simulator comprising a simulator pilot's cockpit, a steerable image projector located adjacent the cockpit, means for supplying image generating signals to the projector, a display screen positioned to direct light emitted by the projector to a pilot station within the cockpit, and means for steering the image projector, characterised in that the steerable image projector comprises a first wide angle projection device and at least one second narrow angle projection device mounted on a common steerable support, the image field of the second device lying within the image field of the first device, the steering means comprises means for sensing the orientation of the pilot's field of view relative to the display screen and means for steering the support such that the image field of the second projection device is substantially centred relative to the centre of the pilot's field of view, and the signal supplying means comprises means for supplying to the first projection device signals representative of all images which are to be displayed at least outside the image field of the second projection device, and means for supplying to the second projection device signals representative of details of images which are to be displayed within the image field of the second projection device.

The means for sensing the orientation of the pilot's field of view may comprise means for sensing the orientation of the pilot's head.

Thus objects such as target aircraft which are near the periphery of the pilot's field of view are displayed in relatively low definition as part of the wide angle image. As soon as the target moves to the central region of the pilot's field of view, either as the result of the pilot turning his head, or as a result of relative movement between the pilot and the target, the second projection device projects a detailed image of the target. Peripheral vision is such that the low definition of the target when it is not in the central region of the pilot's field of view is not perceived.

The first projection device may produce an image subtending an angle of 160% whereas the second projection device may produce an image subtending an angle of only 30 .

The fact that the projectors move together on a common support means that neither one of them can move so as to obstruct the lightfrom the other.

This can be contrasted with prior art equipment where shadowing and mutual interference is inevitable with wide angle displays.

When it is desired to project a second target, a third projection device having a relatively narrow angle of projection may be provided on the same steerable support. Alternatively the third projection device could be used to increase flexibility in colour, origin of information, coded signals,orfireburst effects for example. Tasks may be divided between the second and third projection devices.

The first low definition projector may be a single black and white projection tube. The second high definition projector may be composed of three projection tubes, each projecting a primary colour, so as to give a full colour high definition display.

(Three tubes cannot be used with a wide angle lens on each since each colour projection lens would then form a shadow in the other two colours). Such a system would then give a full colour target in a monochrome surround or may be used to portray a high resolution ground scene for ground attack training, again with a monochrome surround for peripheral vision. A projector assembly thus formed would have four tubes in all. A further projector may be added as an optional extra to extend the system capability.

Known air combat image projectors are target directed, the pilot being expected to move his head in response to the known target position. In the present invention, the projector is pilot's head orientation directed and this enables a visual search task to be carried out under more realistic conditions than can be achieved with existing simulators.

A study of pilot's head and eye movements has shown that the eyes are usually close to the skull axis, with maximum excursion of the order of 30 to 35 degrees off axis. Certainly it is difficult to fixate on an object out of the corner of one's eye although one can artificially force oneself to do so. There is, therefore, sound reason to suppose that the eye position when observing a distant target will be close to the skull axis.

The high definition second projector may be gimbal-mounted on the support to provide a limited amount of relative movement between the high and low definition images. This would provide extra flexibility but at the cost of having to control the relative motion. However if there are two second projectors, one steerable relative to the first projector, the steerable second projector could be used to provide great detail in a very small (i.e. distant) target.

Assuming the two projectors are rigidly mounted relative to each other, then if the target or high definition second projection device projects an image which subtends + 30 degrees at the pilot's eye, this should suffice. If the target is in the mid distance so it subtends a small angle then it will be projected as a small high definition target, but can be anywhere within the t 30 degree pyramid. If a very high definition target is required for long range identification or tracking, then raster shrink may be employed to keep the number of raster lines forming the target at a reasonable level.If the raster shrink were performed about the optical axis of the projector, as is done on conventional air combat projectors in order to provide an electronic zoom to multiply the effect of the optical zoom lens usually fitted, then the target projector would require local pointing control so as not to lose the target if it is off axis. To avoid this problem, the raster shrink may take place about the target centroid so that a target following an off axis radial will get smaller (or larger) without having one side chopped off by the edge of the raster.

The equipment for sensing the pilot's head orientation may be of any suitable type. The general principles of one type of such equipment may be appreciated from British Patent Specification No. 1 489 758.

The wide angle projector will only produce low definition imagery, and therefore preferably it should not be allowed to project imagery in the central region in which the high definition image will appear or the result will be a low definition image.

Thus, in general, a target should only be projected by the first projector when it falls outside the field of view of the second projector. In practice it is desirable to perform a "fade" from one projectorto the other in the region near the edge of the zone covered by the second projector.

If as is preferred the imagery is computer generated, problems arise because of computational delays as a new image cannot be produced for a period of for example lOOms and an existing image must be deflected relative to the projection devices when the pilot moves his head to maintain that image in the correct spatial position. Accordingly a predictor can be provided which at the beginning of each computational period feeds to the image generator a predicted orientation for the projection devices at the end of the computational delay. This minimises the amount of image deflection required at the start of the period for which an image is displayed, as it is only necessary to correct for differences between the actual and predicted orientations.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates the general structure of an air combat simulator according to the invention; and Figures 2 and 3 illustrate features of the control system for a simulator according to the invention.

Figure 1 shows an air combat simulator comprising a cockpit 1 which from the position of a pilot sitting in a seat 2 is identical to the cockpit of the aircraft-being simulated. The cockpit is mounted on a rigid base 3, access to the cockpit being via ladder 4.

Simulators for commercial aircraft include a full motion system which tilts the cockpit as appropriate in response to the manipulations of the cockpit controls. A full motion system is not fitted to air combat simulators for various reasons, for example the view point within the simulator changes, high acceleration forces cannot be sustained, etc. It is however usual to fit a buffet system to shake the pilot's seat and possibly the cockpit frame to simulate a high acceleration manoeuvre. Ag-suit is also normally worn by the pilot.

A screen 5 extends over the pilot's entire possible field of view. The screen 5 is not fully reflective (a mirror) but may be partially reflective so as to provide a gain. A gain of less than 10 is preferred as the screen structure and imperfections show up as brighter areas if a higher gain is used.

Mounted above and behind the pilot's head outside his field of view is a projection device 6 comprising four cathode ray tube projectors mounted so as to be fixed in position relative to each other on a support pivotal about vertical and horizontal axes so as to be able to follow the pilot's head in pitch and yaw. The projection device is supported by a strut 7 which is rigid with the structure of the simulator. A device (not shown) monitors the orientation of the pilot's head and steers the projection device such that the pilot's field of view is centred relative to the image projected.

The relative positions of the projector assembly and the pilot should be such that the assembly presents no obstruction to a pilot looking upwards, and the assembly is positioned accordingly. The projector assembly could be mounted on a horizontal platform behind and above the pilot.

One of the four projectors produces a low definition monochrome 160 image, the other three a high definition full colour 30 image. All the projectors move together in response to movements of the pilot's head. If a target moves into a position in which the pilot's peripheral vision can pick it up, the target is initially low definition monochrome. After detecting the target, the pilot turns his head towards it and the projectors move with this head movement.

This projector movement is fed to the image generation equipment in such a way that it does not itself cause movement of the target image across the screen, so that relative to the field of view of the projectors the target moves towards the centre of view. As soon as the target is positioned within the 30 image, it is shown in high definition colour. This gives a highly realistic impression to the pilot.

The 160 image provides a low brightness background to which a brighter and lighter image is added. To avoid blurring of the high definition target image, the target is only projected by the 160 projector so long as the target is outside the 30 image.

The means by which the images projected on the screen are stabilised in space as the pilot's head moves will now be described with reference to Figures 2 and 3.

Referring initially to Figure 2, the pilot's head orientation is determined by sensor 8 which provides projector orientation control signals 9 to a projector support drive device 10 controlling the position of projectors 11. Thus the projectors 11 are driven so that their fields are always centred on the centre of the pilot's field of view. The projector orientation is determined by a sensor 12 from an output 13 of the projector support drive 10 and signals from the sensor 12 are applied to an image generator 14 which provides an image drive output signal 15 to the projectors 11.

The projector orientation sensor 12 monitors the projector orientation directly rather than being driven in parallel with the projector drive by the head orientation sensor. This means that the true projector position is taken into account when generating the image to be projected even though the projector orientation cannot follow the measured head orientation instantaneously due to inertia in the system.

The image generator preferably provides computer generated image (C.G.I.) information to the projectors. Currently available CGl equipment has a throughput delay or computation period of approximately 100 milliseconds and therefore the content of the image projected during any 1 00ms time slot is based on data gathered 1 00ms before the beginning ofthattimeslot. Rapid pilot head movements can occur in the 100ms period between the beginning of a computational period and the replacement of the image generated as a result of the computation.It is necessary therefore if a highly realistic display is to be obtained to displace the image relative to the image fields of the projectors to take account of projector movements occurring during the computation period and also to stabilise the position of the image despite movements of the projectors during the period for which an image is displayed. The desirability of displacing a head-directed image to compensate for the throughtput delay is further explained in British Patent Specification 2041562 which also describes techniques for achieving the necessary displacement.

Referring now to Figure 3, an embodiment of the invention comprising more sophisticated image stabilisation circuits will be described. Components common to Figures 2 and 3 bear the same reference numerals.

As described above the image should be displaced relative to the projector fields of view to take account of head and projector movements occurring during the throughput delay period during which the image is generated and during the period of display of each image. The embodiment of Figure 3 seeks to predict the likely head movement which will occur during the computational period so as to minimise the displacement which is necessary.

The embodiment of Figure 3 comprises a predictor 16 interposed between the sensor 12 and image generator 14. The predictor monitors the projector orientation and its angular rate of movement and supplies to the image generator signals representative of a predicted orientation to which the projectors will have moved in 100ms time assuming the projectors continue to move at the same angular rate. The image generator 14 then produces image information which will be suitable for projection without any displacement relative to the projector fields if the projectors have moved to the predicted orientation during the 100ms computational period.

The outputs of the projector orientation sensor 12 and the predictor 16 are supplied to a correction computation circuit 17 which compares the predicted orientation with the actual orientation at the end of a computational period. The circuit 17 provides an output to a correction circuit 18 which causes the displacement of the image relative to the projector fields to an extent sufficient to compensate for the difference between the predicted and actual orientations. Thus the degree of image deflection necessary at the start of a period during which an image is projected is minimised.

As the image is being projected the output of the sensor 12 changes with continuing movement of the projectors. The output of the correction computation circuit 17 is thus changed and the correction circuit 18 adjusts the deflection of the image as appropriate to maintain the image in the correct position relative to free space.

Alternatively, the angular velocity of the projector may be integrated during the display output period and the result subtracted from the projector deflection sygnals so as to maintain the image orientation constant in free space as the projector swings.

Detailed circuitry for the various components shown in Figure 3 will not be illustrated herein as these components are well known to engineers experienced in the field of flight simulators. Brief details of some of these components are however given below to indicate features of one embodiment of the Figure 3 arrangement.

In this one embodiment, the projector support drive 10 comprises conventional servo drives for the yaw (x) and pitch (y) axes of the projectors, separate control paths for these two axes existing throughput the entire system. The projector orientation sensor comprises appropriate optical angle encoders providing a digital output. The encoders are of the type comprising transparent discs bearing a plurality of circulartracks each of which is arranged to cooperate with a light source and sensor. A first track is obscured over a 180 arc, the next over alternate 90; arcs, the next over alternate 45' arcs and so on until the angle subtended by the alternate arcs is less than the required resolution.The light sensor associated with each track provides an output which is either "on" or "off", the plurality of outputs defining a binary number uniquely representative of the angular position.

The predictor 16 incorporates a simple mocroprocessor operating in accordance with well known algorithms.

The correction computation circuit 17 comprises a digital subtractorfollowed buy a multiplier to give an output signal with the correct scaling matching the deflection sensitivity of the projectors. It also contains memories and subtractors to compute the angular velocities, and integrators to integrate the velocity in each axis to provide signals which can be subtracted from the image generator deflection sygnals to cancel the effect of projector rotation during the picture display period.

The correction circuit 18 is designed to match the type of display generation system being used. If the display is calligraphic rather than raster based, an adder is provided for each of the x and y coordinates, the content of the adders being dependent upon the output of the correction computation circuit. The adders are arranged to vary the sweep signal in the scanning circuit controlling the beam position in the projectortube.

The above arrangement can be used for both calligraphic and raster based displays, but in the case of raster based displays it is possible to displace the projected image more easily by adjusting the timing ofthesynchronising pulses which must be present. It will be appreciated that in projectors of the type used in this sort of application varying the synchronising pulses does not upset the operation of the EHT generator, as would be the case with standard television receivers, because such projectors are provided with independent dedicated EHT supplies.

Claims (13)

1. A simulator comprising a simulator pilot's cockpit, a steerable image projector located adjacent the cockpit, means for supplying image generating signals to the projector, a display screen positioned to direct light emitted by the projectorto a pilot station within the cockpit, and means for steering the image projector, characterised in that the steerable image projector comprises a first wide angle projection device and at least one second narrow angle projection device mounted on a common steerable support, the image field of the second device lying within the image field of the first device, the steering means comprises means for sensing the orientation of the pilot's field of view relative to the display screen and means for steering the support such that the image field of the second projection device is substantially centred relative to the centre of the pilot's field of view, and the signal supplying means comprises means for supplying to the first projection device signals representative of all images which are to be displayed at least outside the image field of the second projection device, and means for supplying to the second projection device signals representative of details of images which are to be displayed within the image field of the second projection device.

2. A simulator according to claim 1, wherein the means for sensing the orientation of the pilot's field of view comprises means for sensing the orientation of the pilot's head.

3. A simulator according to claim 1 or 2, wherein the first projection device produces an image subtending an angle of 160;, and the second projection device produces an image subtending an angle of 30;.

4. A simulator according to any preceding claim, wherein the first projection device is a single black and white projection tube, and the second projection device comprises three projection tubes, each projecting a primary colour, so as to give a full colour display.

5. A simulator according to any preceding claim, wherein the second projection device is gimbalmounted on the support to provide a limited amount of relative movement between the first and second projection devices.

6. A simulator according to any preceding claim, comprising means for shrinking the raster of the second projection device to increase the definition of an image displayed by that device.

7. A simulator according to claim 6, wherein the raster shrink takes place about the centroid of an object an image of which is displayed within the image field of the second projection device.

8. A simulator according to any preceding claim, comprising means for preventing the projection of images by the first projection device inside the field of view of the second projection device.

9. A simulator according to any preceding claim, comprising at least one further projection device mounted on the support.

10. A simulator according to any preceding claim, characterised in that the means for supplying image generating signals to the projection devices comprises means for sensing the orientation of the projection devices, an image generator responsive to the sensing means for producing image drive signals appropriate to the sensed orientation of the projection devices, and means for supplying the image drive signals to the projection devices.

11. A simulator according to claim 10, wherein the means for supplying image generating signals produces image drive signals after a predetermined delay, characterised in that a predictor is provided between the orientation sensing means and the image generator, the predictor being responsive to the output of the orientation sensing means to provide to the image generator signals representative of a predicted orientation to which the projection devices are expected to have moved after the said predetermined delay, and a correction circuit is provided to deflect the image produced by the projection devices by an amount related to the difference between the actual and predicted orientations of the projecting devices.

12. A simulator according to claim 11, with angular rate integrators to supply signals to the projector deflection circuit to move the image with respect to the projector as the projector rotates during the display output period so as to provide an image which is stable in free space.

13. A simulator substantially as hereinbefore described with reference to the accompanying drawings.