Patent GB-1273161-A (GB)
Title: Image motion and change transducers and systems controlled thereby
Inventor: BOLSEY EMIL JACK
IPC: G03B15/00
Filed: 1969-05-05
Abstract: 1,273,161. Image comparison. E.J.BOLSEY. 5 May, 1969 [27 May, 1968], No. 22768/69. Heading H4D. General.-The invention is generally concerned with the comparison of the results of two time spaced scans of the same or different radiant images and is stated to have the following applications:-(a) Tracking for an air to ground missile, (b) Automatic bomb sight, (c) Automatic aircraft landing, (d) Acoustic torpedo guidance, (e) comparison of stereo photographs, (f) Positioning a workpiece, (g) Pattern recognition, (h) Automatic variation of focal length of a lens to keep its field of view constant. (i) Automatic variation of radial position of a slot in a scanning disc to keep the field of view constant, (j) Velocity/Height ratio for a photoreconnaissance aircraft to enable movement of the image at the film so as to remove blurring, (k) Control of altitude of photographic satellite. Of these applications, only (a), (h) and (j) are described in detail. Missile tracking, Figs. 3 and 5.-The missile is initially carried by an aircraft which aims itself and the missile towards the target before firing the missile. The missile conical scans the area ahead of it and compares the video signal result with a reference produced (i) by a similar scanning system 90A<SP>1</SP>, 90<SP>1</SP>, 91<SP>1</SP>, 92<SP>1</SP>, Fig. 5, in the aircraft during the airing procedure, or (ii) by scanning a photograph of the target. Only (i) is described in detail, wherein, the scan may be produced by a rotating prism and a fixed aperture, Figs. 1 and 2 (not shown), or a slit in a rotating disc, 90A or by a commutator arrangement sweeping over a disc of insulated photo-sensitive segments (Figs. 8, 9, not shown). The missile scanning system, together with pitch, roll and yaw gimbal controls, all housed in the missile nose, is shown in Fig. 3. Before firing the missile, the a.g.c. controlled output of aircraft photomultiplier 90<SP>1</SP> (or photo-cell), is fed, via an umbilical connection and switch 140 in the "aim" position, to a Schmitt trigger 94 for conversion to a two level or binary signal. The binary signal is fed as a first reference to one track of 3-track memory 97 rotating in synchronism with the disc 90A via the enabled one of the recording amplifiers 95, 96. One of the tracks of the memory produces synchronizing signals and these are fed to the aircraft where they are phase compared with those being produced by a 1-track memory 131 rotating with the disc 90A<SP>1</SP>. The result of the comparison is used to control motor 138 and thus bring the scanning discs 90A and 90A<SP>1</SP> into synchronism. When the aircraft has been aimed at the target, switch 140 is connected to "fire" and the missile fired. The video signal from the missile scanner assembly is converted by Schmitt trigger 94 and compared with the reference signal from memory 97 by feeding the two signals to a pair of balanced modulators 100, 101, the reference signal being read out through the enabled one of read amplifiers 98, 98<SP>1</SP> and delay units 102, 103 being inserted in the reference signal path for modulator 100 and in the "real time" signal path for modulator 101, to enable the determination of the sense of the roll &c. displacements. Since the yaw and pitch axes are orthogonal, the modulator's outputs are detected in synchronous detectors 110 and 110<SP>1</SP> with respect to orthogonal signals derived from the sync. signals. The yaw and pitch outputs of the detectors 110<SP>1</SP> and 100 respectively are fed, via dalance amplifiers and A.C./D.C. converter to respective yaw and pitch mount torques 117, 118 (see also Fig. 3) and flight control surfaces. The roll signal is directly produced from the modulator and the degree of roll used to control torques 119. After a while the aircraft produced reference is no longer sufficiently like the real time signal to give useful correlation, e.g., the missile is now much nearer the target, and the reference signal track in the memory must be updated. The degree of correlation is detected by "automatic re-record inertial switching control circuitry" receiving the outputs of the balanced modulators. The lack of correlation limit necessitating re-referencing is set by 171. A pulse is then sent enabling one of the record amplifiers 95, 96 to record the real time video signal as the new reference. Figs. 11 and 13 show the scanning details and circuitry respectively of an apparatus which though generally applicable to detecting any change in an image, is especially suitable for the missile tracking applications. Lens 20 focuses the target etc. on to a slit 23 in a rotating drum 21. Optics inside the drum direct the scanned circle to the photomultiplier 32. The circumference of the drum is used to magnetically record on two tracks. Video signals are recorded on and read from track 37 and sync. signals are recorded and read from track 38. To establish the initial reference, switch 144 is moved to the left such that the video signal produced by the photomultiplier and converted by bi-stable 143 to the binary form V 2 , Fig. 14, is stored on track 37. Thereafter until a new reference is required, switch 144 is returned to the shown position. V 2  is now read out of the track 37 to appear at the inputs of differential amplifier 152 and delay 149 whilst the next scan is producing video signal V 1  which is fed to delay 148 and differential amplifier 151. The amplifier 151, 152 produce half the difference of the signals applied to them i.e., 151 gives ([V 1  - V 2 ]/2) and 152 gives ([V 1 -V 2 <SP>1</SP>]/2). Oppositely poled output full wave rectifiers 153, 154 give signals V 3 , V 4 , which sum to give V 5  at output terminal 39. The presence of negative pulses in V 3  indicate that V 2  lags V 1  and positive pulses indicate that V 2  leads V 1 . The state of mismatch of the signals and original scans is given at output 44 produced by rectifying and then low pass filtering V 5 . The average time difference between pulses in V 1  and V 2  is given at output 41 obtained by low pass filtering V 5 . Pitch and yaw type signals are produced at outputs 42 and 43 by synchronously detecting V 6  with sync. signals from track 38, a 90 degree phase shifter 157 being added at the input of synchronous detector 158. Automatic variation of focal length, Fig. 15.- The image scanned is viewed through the lens to be varied 20a. A system 168 similar to that described, produces a signal representing the degree of mismatch of a real time scan with a reference scan. This is fed to one input of a synchronous detector 169. A low frequency (2H 3 ) oscillator 163 feeds the detector and also one input of a D.C. differential servo-amplifier 164 feeding a servomotor 165. The lens 20a focused by the servomotor thus oscillates and changes the size of the image. A 2H 3  component thus occurs in the mismatch signal, in phase or antiphase with the output of the oscillator depending on the sense of change of size of the image. Detector 169 thus produces a signal of sign representing this sense and which is fed to servo amplifiers 164 to drive the motor and lens to regain the previous image size. Velocity/height ratio detection, Figs. 19, 20, 21 and 22.-The object is to cause the camera image axis to move from A to B as the aircraft moves from position I to II, such that blur in any photograph is reduced. When the rearward angle has increased to b, the camera image axis moves forward to A<SP>1</SP> to commence photography of a new section of ground. Movement of the camera image axis may by lateral movement of the camera lens 20b, Fig. 21, or by pivotal movement of a mirror 210, Fig. 22. In the circuitry of Fig. 20 an output from photomultiplier a.g.c. circuit 226 can be used as a camera exposure control signal. The remainder of the circuitry is mainly as already described, delay sensor 230 containing the delay lines and balanced modulators. A "degree of correlation signal" 230A indicates the photographic visibility and can be used to control the camera exposure. It also determines whether a reference value of aircraft velocity &c. is worthwhile storing. Integrating servo amplifiers 233/235 controlling the lens/mirrors controlling motors 236/238, comprise diode circuits giving non- linear characteristics such that when the circuit is started up and correlation errors are large the integration times are short and the servo response rapid. In the arrangement of Fig. 21 the output of block 276, representing Fig. 13 and giving the movement L of the aircraft is integrated at 279, 283, 284. A servo amplifier 281 controls motor 282, which by means of cam causes the movement of lens 20b with velocity V. A tacho generator 285 feeds a signal representing V to the input of the servo amplifier where it is added to L and Ldt signals. The input signal (L+ # Ldt+V) to the servo amplifier thus gives high gain for accurate tracking but also stable damping.