Machine Guiding System

Abstract

Determining the instantaneous position of a rotating machine moving at high speed along a trajectory path by impinging a fine light beam of generally flat form which rotates about an axis parallel to the direction of light propagation onto a plurality of detectors carried by the rotating machine in a plane perpendicular to the trajectory axis and measuring the time intervals separating the generated signals.

Description

The present invention relates to a system and a method of guiding moving bodies, or to a system permitting a moving body to self-establish the information concerning its position in relation to a predetermined trajectory.

The invention is applicable to any mobile machine, such as a land vehicle or marine vessel, a drilling vehicle or an aircraft, such as an airplane or propelled rocket, or even to ballistic missiles.

The present invention is preferably applicable to moving bodies carrying means enabling them to change their trajectory, but this invention can also be applied to moving bodies which do not have such means but which, for any particular purpose, have systems which need to receive at any moment data concerning the position of the moving body with respect to a given trajectory.

There are known systems which make it possible to determine the position of a machine or to guide the movement of a machine by means of a light beam. Certain of them use rotating eccentric beams which strike detectors placed on the machine with the measurement of the variations in luminous intensity making it possible to calculate approximately the displacement of the machine in relation to the axis of rotation of the light beam. One such system, described in the article "Optical Guidance of Vehicles," published in the journal "Measurement and Control," Mar., 1964, does not permit accurate results to be obtained and can in fact only be applied to slow vehicles, such as machines used in public works.

It is also known from French Pat. No. 1,466,437 (granted the Dec. 12, 1966), to provide a projectile guiding system which comprises means for obtaining a guiding "light channel" by means of four flat laser beams.

The known systems do not resolve the problems which arise in a satisfactory manner, because they are all based on measurements of luminous intensity or of detection of modulation of a light wave.

The present invention has for its object to provide a guiding system in which the efficiency is not a function of any variations in the luminous intensity of a beam.

The system according to the present invention comprises a light beam emitter of the laser type, capable of emitting a beam of generally flat form which rotates about an axis parallel to the direction of propagation of the light waves, and a plurality of light ray detectors disposed on a machine in a plane substantially perpendicular to this axis. The relative disposition of the detectors preferably defines a regular polygon and the measurement of the time intervals separating the pulses produced by the detectors scanned by the said rotating beam determines the position of the machine in relation to the axis, which thus constitutes a reference trajectory.

According to one feature of the present invention, the detectors are arranged in such a manner as to supply a calibrated electric pulse when they detect the passage of the light beam, and the machine comprises an electronic data processing arrangement which measures the time intervals between the pulses emitted by the detectors, and the electronic arrangement is connected to the means for controlling modification in trajectory of the machine.

According to another feature of the invention, the machine comprises four detectors disposed at the apices of a square, the trajectory-modifying means being such that the machine receives a movement pulse directed parallel to the tangent to the circle passing through the four detectors at the point where the detector lies which has sent the first pulse of the series of four pulses forming a measurement sequence.

The invention will now be made clear by the detailed examination of one embodiment of the invention, given as a nonlimiting example, in which the machine is a flying missile of the ground-to-air or ground-to-ground type.

The invention will be described by reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of a ground-to-ground engagement, according to the system of the present invention;

FIG. 2 is a section of the laser beam used in the system of FIG. 1;

FIG. 3 is a diagrammatic view of a missile provided with photonic detectors arranged according to the invention;

FIG. 4 is a schematic representation of various relative positions of the missile and of the propagation axis of the laser beam;

FIG. 4a represents the diagram of electric pulses supplied by the detectors for the positions of the missile of FIG. 4;

FIG. 5 is a schematic view of a similar representation to that of FIG. 4;

FIG. 5a is a schematic representation of various relative positions of the missile and of the propagation axis of the laser beam;

FIG. 6 is a schematic view of a calculation of the intensity of the intensity of the movement pulse;

FIG. 7 is a schematic representation of a missile including a detector system;

FIG. 8 is a schematic representation of a missile including means for communicating with the ground; and

FIG. 9 is a schematic representation of an optical system for use with the present invention.

As shown in FIG. 1, a laser emitter 11, located in the vicinity of a firing point, sends a laser beam 12 in the direction of the target 13, towards which missile 10 is directed. The cross section 20 of the beam 12, that is, its section through a plane P perpendicular to the axis of propagation, is represented in FIG. 2. The cross section 20 is preferably narrow and elongated and, bearing on the trace 0 in the plane P of the beam propagation axis, turns about this axis in the plane P at a constant angular velocity w.sub.o.

As one example, this beam has a length D of several meters and a mean width d of a few centimeters, preferably smaller than 10 centimeters.

As shown in FIG. 3, the missile carries four light detectors indicated at 1 to 4, placed at the four apices of a square, of which the plane is perpendicular to the missile axis and of which the center is on the axis. The trace of this axis in the plane of the square formed by the detectors is designated by .OMEGA. in FIG. 3. The detectors will preferably be placed at the ends of four ailerons of the missiles and staggered by 90.degree..

In general, the missile turns on itself during its flight at an angular velocity w.sub.10.

The angular velocity w.sub.o of rotation of the laser beam is preferably chosen to be very much higher than the angular velocity w.sub.10 of rotation of the missile 10 about its axis, so as to be able to assume that this latter remains relatively stationary in rotation during one revolution of the laser beam.

The detectors 1 to 4 are arranged in such manner that each emits a calibrated electric pulse every time that they detect the passage of the laser beam.

The guiding principle according to the invention is as follows:

With the missile following its trajectory in the direction towards the target, the rotation laser beam scans the detectors and, during one revolution of the beam, the four detectors each receive, one after the other, a certain quantity of light and each emits an electric signal one after the other and in the same order.

FIG. 4 represents diagrammatically, in a plane perpendicular to the axis of the laser emitter, the trace 20 of the laser beam, the four detectors 1, 2, 3 and 4 at the apices of a square, the trace 0 of the laser emitter axis and the trace .OMEGA. of the missile axis.

It is clearly shown in FIG. 4 that, with the laser beam turning about the point 0, the first detector which receives the signal is that which is on the arc AB of the circle C passing through the detectors, seen from the point .OMEGA. at a right angle, and such that A, B and 0 are aligned.

In the case of FIGS. 4 and 5, it is the detector 1 which first intercepts the beam.

FIG. 4a represents, as a function of time t, the diagram of the pulses supplied by the four detectors during several passages of the laser beam, on the hypothesis that w.sub.10 is very small as compared with w.sub.o.

If the missile was placed exactly on the trajectory of the laser ray, that is to say, if the trace 0 was inside the square formed by the detectors 1, 2, 3 and 4, the pulses would be regularly spaced and distributed in the order 1, 2, 3, 4 (see FIGS. 5 and 5a).

In the case of FIG. 4, it is clearly seen that consideration of the time intervals separating the signals of one measuring sequence or the signals of several measuring sequences makes it possible to determine the relative position of the missile in relation to the trace 0; in actual fact, the circle C having a constant diameter, the measurement of an angle, such as 104 or 103, permits of calculating the distance 0.OMEGA..

On the other hand, it is pointed out that the identification of the detector which supplies the first signal of a measuring sequence makes it possible to determine with a good approximation the direction of the spot where is situated the trace 0 in relation to the trace .OMEGA. of the missile. Actually, it can be seen that, in the case of FIG. 4, the tangent 1a to the point 1 of the circle C is pointed parallel to the direction .OMEGA.0 with an error smaller than 45.degree..

Whatever may be the position of the missile relative to the trace 0 of the beam, the direction of the movement to be given to the missile in order to return it to its perfect trajectory as materialized by the axis 12 is substantially that of the tangent to the circle C at the point where is situated the detector giving an electric pulse terminating the largest of the time intervals between pulses in a given measuring sequence. This rule is valid, even if the trace 0 of the beam is inside the circle C passing through the four detectors, as is shown by FIGS. 5 and 5a which illustrate this case.

Referring to FIGS. 7 and 8, if the missile has an electronic arrangement which permits of measuring (with time measure means 15) the different time intervals and the direction control means 14 permitting the trajectory to be modified, it is possible to elaborate a control signal for a modification of the trajectory, tending to bring the missile back towards the perfect trajectory materialized by the beam 12. According to the invention, the missile comprises an electronic arrangement for measuring (with time measure means 15) and comparing (with comparator 16) the time intervals separating the pulses supplied by the detector 1, 2, 3 and 4 during one or more revolutions of the beam.

The information concerning the distance .OMEGA.0 is obtained by measuring the intervals separating the signals from one another, while the direction according to which the trajectory is to be corrected is obtained by the comparison of the various time intervals, which permits identifying the detector which has supplied the signal terminating the largest of the four time intervals corresponding to one revolution of the light beam.

In a modified embodiment, in which a measuring sequence is limited to the reception of four successive electric pulses, the electronic arrangement for comparison of the intervals can be omitted.

In actual fact, if it is known to extract a sequence of four signals (either by extracting this sequence from a series of measurements, or by using an emitter which would only make the beam turn for one revolution), it is known that the maximum time interval separating two pulses is T/4, T being the period of revolution of the revolving beam. Consequently, if there are considered four consecutive signals of the same sequence, defining three time intervals, or even if these three intervals are small than T/4 and it is the first signal which determines the start of a sequence, or even if one of the intervals and one only will be greater than T/4, then in this case it is the signal terminating this time interval which is to be a commencement of sequence.

From the time intervals separating the electric pulses, an electronic arrangement 17 is able to establish a signal of which the amplitude is a function of the distance of the trace .OMEGA. of the missile axis from the trace 0 of the beam axis. Actually, by referring to FIG. 6, showing the relative position of the missile (represented by its four detectors positioned at the points A, B, C and D and by the point .OMEGA.) and of the beam 12, it is seen that the distance 0.OMEGA. can be easily expressed as a function of the angles .theta..sub.1 =2.pi./Tt.sub.1, where t.sub.1 is the time interval separating the electric pulses due to the passage of the beam onto the detectors A and B, and .theta..sub.2 =2.pi./Tt.sub.2, t.sub.2 being the time interval separating the electric pulses due to the passage of the beam onto the detectors B and C, T being the period of revolution of the beam.

Actually, if D is the diameter of the circle passing through A, B, C and D, the following relationships exist: OA.sup.2 +OB.sup.2 -2 OA.sup.. OBcos.theta..sub.1 =D.sup.2 /2 OB.sup.2 +OC.sup.2 -2OB.sup.OA OCcos.theta..sub.2 =D.sup.2 /2 OA.sup.2 +OC.sup.2 -2OA .sup.. OCcos(.theta..sub.1 +.theta..sub.2)=D.sup.2 0.OMEGA..sup.2 =1/2(OA.sup.2 +OC.sup.2 -D.sup.2 /2)

Electronic arrangements 15, 16, 17 of conventional type are known which are capable of establishing a signal proportional to 0.OMEGA. from the measured values t.sub.1 and t.sub.2. These electronic arrangements comprise in known manner shaping and calibrating means for the electric pulses supplied by the detectors, means for measuring 15 and for comparing 16 time intervals separating these pulses and calculating members 17 functioning as an analogue or digital system.

As mentioned in the introduction to the present specification, the system according to the invention is applicable to a large number of particular cases. The data given by the detectors can be elaborated to a greater or lesser extent by means on board the moving body (see FIG. 7), and can be transmitted by radio (emitter 18) or any other transmission means to fixed control systems or monitors 19 which, in their turn, transmit orders to receiver 21 on the moving body (see FIG. 8).

According to a preferred modification of the invention, illustrated in FIG. 7, the moving body comprises means for processing this data and for using it directly for controlling the functioning of means which permit the trajectory of the moving body to be modified.

In the case of a flying machine, equipped with a propulsion unit, or of a ballistic missile following a predetermined trajectory, the trajectory-modifying means can be ailerons or systems known as "jet deflectors."

The data processing systems 17 on board the machine can easily calculate the distance of the machine from the trace 0 of the light beam axis and the direction in which the point 0 is situated in relation to a fixed direction of the machine, this direction being the tangent 1a defined with reference to FIGS. 4 and 5.

Thus, the system according to the invention has the advantage of permitting a correction of trajectory in a direction associated with a detector identified by the control circuit of the machine, whatever may be the position of the machine rotating about itself, and it is thus unnecessary to have on board the machine a vertical reference, as for example, a gyroscopic arrangement.

The trajectory correction control signal can be established after a certain number of revolutions of the light beam, and this makes it possible to obtain a signal which takes into account possible errors and which can also take into account slow variations of the trajectory. In other words, the signal can be different, according to the case where the distance between the machine and the theoretical trajectory is constant, or the case where the spacing between the machine and the theoretical trajectory varies continuously in one direction or the other.

If a trajectory correction is made with each revolution of the light beam, there will be obtained a data rhythm 1/T, T being the revolution period of the beam, and it is possible with advantage to choose a frequency of revolution having a value from 10 to 500 c.p.s. preferably 100 c.p.s.

As the trajectory correction is carried out by movement pulses imparted to the machine, the calculation of the distance of the latter from its perfect trajectory then makes it possible to adjust the value of this pulse, which can, for example, be proportional to this distance.

In a modification, the movement pulse is chosen to be inversely proportional to the time separating the first pulse from the last pulse during one revolution of the beam. This method is less accurate than the foregoing, but it is easier to carry into effect.

The flat revolving laser beam can be obtained in various ways: for example, by focusing on a slot of suitable dimensions, turning about the optical axis of the laser at a speed of rotation equal to the desired speed of rotation of the beam, or revolving arrangements are even known which comprise special prisms, such as the Wollaston prisms, the slot remaining movable. Such known devices are generally shown by element 22 in FIG. 9.

It is also possible to achieve this by means of an afocal system 23 having two cylindrical lenses intersecting at 90.degree. such that the system is afocal in all directions, but with a variable ratio thus producing a beam of flat form. This afocal system is driven so as to rotate about its axis. It is advantageous for the detectors to receive, apart from adsorption, the same quantity of light with the passage of the beam, whatever may be the distance of the laser emitter from the machine. In order to effect a correct quantitative correction, it is necessary for the divergence of the beam to be adjustable so that the section of the beam through a plane perpendicular to its propagation axis at the location where the machine is situated is constant. It is possible to provide the laser beam emitter with a device by which it is possible to obtain a divergence variable as a function of time, knowing the speed of displacement of the machine. This can be achieved by using an afocal arrangement as described above, provided with means for continuously achieving derangement by displacement of the lenses or by relative rotation of these lenses upon reception of orders from conventional ranging or control means. It is also possible to obtain arrangements having variable divergence by using gas lenses by which it is possible to vary the focal lengths by acting on the pressure of the gas or on the nature of the gas.

The invention is not in any way limited to the embodiment described and illustrated, which has only been given by way of example. In particular, without departing from the scope of the invention, it is possible to introduce modifications as regards detail, to change certain arrangements or to replace certain means by equivalent means.

Claims

What is claimed is:

1. A system to establish data concerning the instantaneous position of a moving machine relative to an instantaneous theoretical trajectory materialized by a light beam, comprising: a light beam emitter capable of emitting a fine beam of generally flat form which emitter rotates about an axis parallel to the direction of propagation of the light waves, three detectors disposed on the moving machine and in a plane substantially perpendicular to said axis, means for measuring the time intervals separating the signals produced by the detectors when they are successively scanned by the rotating light beam, and means for determining the sequence of the excitation of said detectors, the sequence of excitation and the time intervals being indicative of the instantaneous position of the machine relative to the axis of the revolving light beam.

2. The system as claimed in claim 1 wherein said spaced detectors disposed on said moving machine define a polygon.

3. The system as claimed in claim 2 wherein said polygon is a square.

4. The system as claimed in claim 1 in which said light beam emitter comprises a laser.

5. The system as claimed in claim 1 in which said measuring means is carried by the moving machine.

6. The system as claimed in claim 1 further comprising calculating means for calculating the distance of the axis of the moving machine relative to the axis of rotation of the light beam as a function of the time interval values.

7. The system as claimed in claim 6 wherein said calculating means is installed at a fixed position, remote from said moving machine and said system further includes wireless communicating means carried by said calculator means and said moving machine, whereby the values of said time intervals are transmitted from said moving machine to said calculator means and control signals are transmitted from said calculator means back to said moving machine.

8. The system as claimed in claim 1 further including calculating means for calculating from the signals emitted by the detectors, the amplitude and direction of the correction to be applied to the trajectory of the moving machine, the amplitude of the correction to the trajectory of the moving machine being substantially inversely proportional to the time interval separating the first signal from the last signal applied by the detectors during one revolution of the light beam.

9. The system as claimed in claim 1 wherein the machine comprises a moving body being rotated about an axis substantially parallel to that of the light beam and wherein the rotational speed of said beam is substantially larger than the rotational speed of said machine.

10. The system as claimed in claim 1 in which said light beam emitter comprises a laser focused on a revolving slot.

11. The system as claimed in claim 1 further comprising a Wollaston prism for achieving rotation of said light beam.

12. The system as claimed in claim 1 further comprising an afocal optical system for rotating said light beam, said afocal optical system including cylindrical lenses intersecting at 90.degree..

13. The system as claimed in claim 1 in which said light beam emitter comprises an afocal optical system with means providing a continuously variable divergence as a function of the distance of the moving body from the emitter.

14. The system as claimed in claim 1 wherein said light beam emitter comprises at least one gas lens of variable focal length.

15. The method of guiding a moving body in relation to a rectilinear theoretical trajectory path, said method comprising: emitting a fine light beam of relatively flat form to define the trajectory path, rotating the body about an axis parallel to the direction of propagation of the light rays, intercepting the light beam successively by at least three detectors disposed on said moving body in a plane substantially perpendicular to the axis of said light beam, with the detectors being distributed in said plane in accordance with a regular polygon, measuring the sequence of excitation of said detectors and the time intervals separating the successive signals emitted by the detectors, and modifying the trajectory of the moving body in response to the sequence of excitation and the value of said time intervals.

16. The method of guiding a moving body in relation to a rectilinear theoretical trajectory path as claimed in claim 15 further comprising the steps of: comparing the time intervals in order to identify the detector which has been excited by the light beam after the longest time interval, calculating the distance of the center of gravity of the polygon from the axis about which the light beam is rotating as a function of the value of said time intervals, and modifying the trajectory of the moving body by imparting to it a movement pulse, the direction of which is substantially that of the tangent to the circle in which are inscribed the detectors at the point at which the identified detector is situated and in which the amplitude is a direct function of the distance of the moving body from said axis.