IL123064A - Optical tracking system - Google Patents

Description

OPTICAL TRACKING SYSTEM "03w mnO riDi a 1 123,064/2 The present invention relates to an optical pointer system and method for scanning and tracking a moving target in an extended field of regard.

Reconnaissance systems are, in general, required to search and acquire visible objects in the field of view located in front of them. These systems have two major components: the electro-optical sensor/emitter and the pointer device. The pointer device has to cover this wide field of view and to transfer the light energy to and from the scene and to and from the sensor/emitter, while the sensor/emitter receives/creates the energy and detects/creates the image for various applications and users.

Coverage of the wide field of view is usually achieved by means of moving the optical line of sight (LOS). Two methods may be applied to this end: movement of the whole sensor/emitter on a gimbaled system and movement of LOS alone, using a pointer, while the sensor/emitter remains static.

The first of the above-mentioned methods is widely used in stabilized observation systems and also in radar systems, and has the following main limitations: 1) The gimbal system is usually a big, heavy and complex device, as it has to carry the entire sensor/emitter. Therefore, the rate of motion is limited and the velocities and accelerations that can be achieved by the gimbal, are relatively low. 2) This method requires the incorporation of a complex interface between the rotating part and the stationary part, which interface must transfer electronic signals from the sensor/emitter to the users. Also, in some cases, cooling media, either gaseous or liquid, must be transferred to the rotating part in order to cool the sensor/emitter. 2 123,064/2 The second of the above-mentioned methods of moving the LOS usually involves, reflective or refractive elements, which are located between the sensor and the scene. In this method, the rotation movement is applied only on the reflective or refractive elements, while the sensor is stationary. The main limitation in this method is that the field of regard (FOR), which is the region scanned by the LOS, is small. Another problem, commonly called "image tilt", is that the image rotates around the center of the LOS during its movement.

When trying to extend this method to a large FOR, a new problem is encountered, commonly known as "singularity point". A singularity point appears when, in order to move the LOS from one point in the field to a second, close, point, a very large movement is required of the rotating axis. For a tracking system which is expected to follow continuously after a moving target, passing such a point is liable to cause loss of the target. Therefore, the existence of such a point is unacceptable in a tracking system.

It is therefore one of the objects of the present invention to provide an optical pointer system and method that are based on a stationary sensor having a narrow field of view, which is extended to become an at least hemispherical field of regard that is not afflicted by singularity points and that is capable of very high angular accelerations and angular velocities.

According to the invention, the above object is achieved by providing an optical pointer system for tracking a moving target in a hemispherical field of regard, said system comprising a bench member rotatable about a first axis and mounting, at least indirectly, a dual-axis scanning mirror and at least one first and second folding mirror stationary relative to said bench member, and a gimbal member mounted on said bench member for rotation about a second axis, in which gimbal member said 3 123,064/2 scanning mirror is mounted for rotation together with said gimbal member about said second axis and, without said gimbal member, about a third axis, whereby the respective rotational movements of said axes are controlled and coordinated in such a way that electromagnetic radiation from and to a target moving in said hemispherical field of regard is maintained.

The invention further provides a method for tracking a moving target in a hemispherical field of regard, comprising providing a bench member rotatable about a first axis and mounting, at least indirectly, a dual-axis scanning mirror and at least one first and second folding mirror stationary relative to said bench member, and a gimbal member mounted on said bench member for rotation about a second axis, in which gimbal member said scanning mirror is mounted for rotation together with said gimbal member about said second axis and, without said gimbal member, about a third axis, controlling and coordinating respective rotational movements of said axes in such a way that electromagnetic radiation from and to a target moving in said hemispherical field of regard is maintained, thereby a narrow field of view is extended to become an at least hemispherical field of regard that is not afflicted by singularity points.

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, 123,064/2 no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a general perspective view of the pointer system according to the invention; Fig. 2 is a partially cross-sectional view of the pointer system, indicating the three axes of rotation as well as the positions, relative to each other, of the optical components of the device; Fig. 3 schematically illustrates the reaction of the line of sight (LOS) to tilt of the scanning mirror about the elevation axis C and the resulting movement of the LOS along meridian lines of the hemispherical FOR; Fig. 4 illustrates the reaction of the LOS to rotation of the bench about the roll axis A, as a result of which the LOS moves along the latitudinal lines of the hemispherical FOR, and Fig. 5 illustrates the reaction of the LOS to rotation of the scanning mirror about the azimuth axis B, as a result of which the LOS moves in a direction perpendicular to that induced by rotation of the scanning mirror about axis C.

Referring now to the drawings, there is seen in the perspective drawing of Fig. 1 a stationary main drive unit 2, comprising a high resolution rotary encoder and a motor which, being per se known, are of the commercially available kind and need not be gone into in any detail, a substantially hollow body 4, also known as "bench", which carries all optical components of the device and which is driven by main drive unit 2, having an angular range of 360°. The optical components are seen to better advantage in Figs. 2 and 3. A second drive unit 6, with an angular range of ±10°, rotates a gimbal 8 mounting a dual-axis scanning mirror 10, which is rotated about 123,064/2 what is in this drawing a vertical axis by a third drive unit 12 with an angular range of +22.5°. The entire system is aligned with an electromagnetic radiation producing and/or responsive device 14, e.g., a sensor and/or an emitter, such as a laser source.

Fig. 2 shows the three axes of rotation of the drive: axis A, the "roll" axis about which rotates bench 4 when driven by drive unit 2; axis C, the elevation axis of scanning mirror 10 driven by drive unit 12, and axis B, the azimuth axis of scanning mirror 10 which is mounted in a gimbal 8 affixed to the output shaft of drive unit 6, which shaft defines axis B. Axes A and B are co-planar, and axes B and C are mutually perpendicular.

Further seen are two ray-folding mirrors, a front folding mirror 18 and a rear folding mirror 20, both of which are fixedly mounted in bench member 4 and can only move together with bench member 4, while scanning mirror 10, which also moves together with bench member 4, has two additional axes of rotation: axis C defined by pivots 22 (of which only one is visible in Fig. 2), and axis B, which is the axis of rotation of gimbal 6.

The operation of the pointing device according to the invention 2' is best understood with reference to Figs. 3 to 5. These drawings represent device 14, folding mirrors 18 and 20, and scanning mirror 10 facing a hemispherical FOR defined by imaginary semi-circular (meridian) and circular lines, representing lines of longitude 24 and latitude 26, respectively. Of special interest is the region between 80° and 90° latitude, for reasons to be explained further below.

Fig. 3 shows the effect on the LOS of rotating scanning mirror 10 about axis C, representing the pre-rotation position of scanning mirror 10 by faint outlines and the post-rotation position thereof 10' by bold lines. It is seen that rotation of scanning 6 123,064/2 mirror 10 about axis C causes the original LOS 28 (dash-dotted lines) to be deflected, as indicated by the new, dashed lines LOS 30. Path 32, traced by the deflected LOS, is seen to follow a meridian or longitudinal line.

Fig. 4 shows the effect on the LOS of rotating bench member 4, including all mirrors, about axis A, the "roll" axis of the device. The original positions of mirrors 18, 20 and 10 are again represented by faint lines and the post-rotation positions thereof, 18', 20', 10', by bold lines. It is seen that rotation of bench member 4 about axis A causes the original LOS 28 (dash-dotted lines) to be deflected, as indicated by the new, dashed lines LOS 30. Paths 32 traced by the deflected LOS are seen to follow lines of latitude.

Fig. 5 shows the effect on the LOS of rotating gimbal 6 (see Fig. 2) about the azimuth axis B of scanning mirror 10. It is seen that rotation of gimbal 6 about axis B causes the original LOS 28 to be deflected, as indicated by the new, dashed lines LOS 30. Paths 32 traced by the deflected LOS are seen to be perpendicular to the path traced due to rotation about axis C (Fig. 3).

Drive units 2, 6 and 12 advantageously consist of motors controlled by rotary encoders which, in their turn, are computer-controlled and coordinated to ensure the optimal course of the LOS, depending on the tracking task and the position of the target in relation to the pointer device.

Thus, a target moving in the hemispherical FOR at latitudes of up to 80° will be tracked by the appropriate rotation about axes A and C only. However, when the target to be tracked is within the latitudinal zone of between 80° and 90°, the above-discussed problem of the singularity point would emerge. For example, assuming that the target was located at a latitude of 85° and was moving along a 7 123,064/2 meridian from a point Pj to a point P2, the distance between which could be very small, to move the LOS from point P! to point P2 would still require a rotation of bench member 4 about axis A that would take long enough to lose the target. In other words, the presence of a singularity point would severely interfere with the rapid response to target movement of the LOS. To overcome this problem, tracking is here effected mainly by motion about axes B and C, while movement about axis A is reduced to a much slower rate, merely sufficient to be ready to continue the smooth movement of the LOS, the moment the target leaves this zone and moves into latitudes below 80°.

It is thus seen that drive units 2, 6 and 12 are controlled and coordinated in such a way that electromagnetic radiation, e.g., light, reflected from a target moving in the hemispherical FOR, is captured by scanning mirror 10 and is continuously reflected via folding mirrors 18 and 20 into device 14 which is coaxial with axis A.

The coordinated movement produced by drive units 2, 6 and 12, and the avoidance of singularity points facilitated by this coordination, make it possible to obtain very high angular accelerations and angular velocities.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (11)

8 123,064/3 WHAT IS CLAIMED IS:

1. An optical pointer system for tracking a moving target in a hemispherical field of regard, said system comprising: a bench member rotatable about a first axis and mounting, at least indirectly, a dual-axis scanning mirror and at least one first and second folding mirror stationary relative to said bench member, and a gimbal member mounted on said bench member for rotation about a second axis, in which gimbal member said scanning mirror is mounted for rotation together with said gimbal member about said second axis and, without said gimbal member, about a third axis, said second and third axes being mutually perpendicular, whereby the respective rotational movements of said axes are controlled and coordinated in such a way that electromagnetic radiation from and to a target moving in said hemispherical field of regard is maintained.

2. The optical pointer system as claimed in claim 1 further comprising an electromagnetic radiation producing and/or responsive device disposed in said system, coaxial with said first axis.

3. The optical pointer system as claimed in claim 2, wherein said device is a sensor.

4. The optical pointer system as claimed in claim 2, wherein said device is an emitter.

5. The optical pointer system as claimed in claim 4, wherein said emitter is a laser. 9 123,064/3

6. The optical pointer system as claimed in claim 1 , wherein said first and second axes are co-planar.

7. The optical pointer device as claimed in claim 1, further comprising: first drive means for rotating said bench member about said first axis; second drive means for rotating said scanning member and said gimbal member about said second axis, and third drive means for rotating said scanning member about said third axis.

8. A method for tracking a moving target in a hemispherical field of regard, comprising: providing a bench member rotatable about a first axis and mounting, at least indirectly, a dual-axis scanning mirror and at least one first and second folding mirror stationary relative to said bench member, and a gimbal member mounted on said bench member for rotation about a second axis, in which gimbal member said scanning mirror is mounted for rotation together with said gimbal member about said second axis and, without said gimbal member, about a third axis, said second and third axes being mutually perpendicular, controlling and coordinating respective rotational movements of said axes in such a way that electromagnetic radiation from and to a target moving in said hemispherical field of regard is maintained, thereby a narrow field of view is extended to become an at least hemispherical field of regard that is not afflicted by singularity points.

9. The method as claimed in claim 8, further comprising the step of disposing an electromagnetic radiation producing and/or responsive device coaxially with said first axis, so as to cause said scanning mirror to reflect said electromagnetic radiation via said first and second folding mirrors into said device. 10 123,064/3

10. An optical pointer system according to claim 1, substantially as hereinbefore described and with reference to the accompanying drawings.

11. A method for tracking a moving target in a hemispherical field of regard according to claim 8, substantially as hereinbefore described and with reference to the accompanying drawings. For the Applicant WOLFF, BREGMAN AND GOLLER