Patent GB-1064649-A (GB)
Title: Video tracker
IPC: G01S3/786
Filed: 1964-11-26
Abstract: 1,064,649. Semi-conductor circuits; television tracker; television. BARNES ENGINEERING CO. Nov. 26, 1964 [Dec. 5, 1963], No. 48105/64. Headings H3T, H4D and H4F. [Also in Division G3] In a television system for automatically tracking a moving target, the target is automatically centred within a " window " generated electronically in the television raster. In the embodiment of Fig. 1 a television camera (12) feeds video signals A to a monitor display (25), and the signals for generating a window 92 are derived from the horizontal and vertical synchronizing pulses of the raster. Manual controls permit adjustment of the size of window 92 to totally enclose a target. Video signals from camera (12) are also fed to a processing channel (13) for driving vertical and horizontal error signals dependent upon the displacement of the centroid of the target 94 from the centre of the window 92. These error signals vary the timing of the window generating signals so as to move the window 92 within the field of view of the camera (12) to maintain the target 94 central in the window 92 and may also be used to operate servo driven azimuth and elevation-controls of a camera mounting for automatic target-tracking. Electronic window generator (Figs. 3 and 4).- A generator (102) synchronized with the television line scan by horizontal synchronizing pulses (S) produces a sawtooth output (T) whose frequency, D.C. level, linearity and amplitude may be adjusted by controls (108), (110), (112), (114) respectively. Waveform (T) is applied to a trigger circuit in which a tunnel diode (116) conducts at a reference level (b), set by resistors (118), (120), (122), to give a waveform (N) comprising a negative-going step function corresponding to the centre of the window 92. Waveform (T) is clamped to a fixed reference level, to give a waveform (V) by a clamp circuit (138) which is keyed by negative pulses (U) obtained by differentiating waveform (N). Waveform (V) is applied to two parallel trigger circuits (144), (146) with differing pre-determined reference levels (c), (h), producing output waveforms (O and P) which have negative-going steps corresponding to the left-hand (" early ") and right-hand (" late ") edges of the window 92. " Early " and " late " horizontal gating pulses (Q and R) are derived from waveforms (O) and (P) respectively, e.g. by using bi-stable circuits (30), (32) (Fig. 1). Similar circuitry to the above produces " early," " centre," and " late " vertical gating pulses from the frame synchronizing pulses of the televison raster. The horizontal and vertical gating waveforms are summed in a circuit (34) and passed to a video amplifier (16) driving the monitor display (25) to produce the window 92. Control (114) varies the slope of the sawtooth waveform (T) to alter the width of the window 92 without shifting the window centre. A similar control varies the height of the window. Video-processing.-Keying pulses B, corresponding to the centre of window 92 and derived from the coincidence of the " centre " vertical and " centre " horizontal pulses, are applied to an input (166) of a keyed clamp circuit (46) (Fig. 5). The video signals A, applied to an input (160), are clamped to a " target reference level " (ground) by a transistor (164) whose base is tied to ground during the occurrence of the keying pulses B, giving a video waveform C which is applied to inputs (170) and (172) of a threshold circuit (Fig. 6). Signals E below the target reference level are passed by transistor (174), inverted by transistor (178), and applied to a mixer (182) in which they are combined with waveform D comprising signals above the target reference level passed by transistor (176). The output F, from mixer (182) is clipped to give a waveform G from which all video signals occurring outside the window 92 are subsequently eliminated by a gate (58) (Fig. 1). To produce the error signals, the resultant video pulse, J, is combined with the horizontal gating pulse Q by a gate (60) to give a positive pulse K. Pulse J is also inverted and combined with gating pulse R in a gate (64) to give a negative pulse L. During a frame scan the successive pulses K and L are integrated (waveform M) on a capacitor (70). As the relative widths of pulses K and L depend on the horizontal displacement of the target 94 from the centre of the window 92, the final voltage across capacitor (70) at the end of a frame scan will be positive or negative according to the direction of the target displacement and constitutes a horizontal error signal. The error signal is applied at the end of a frame scan to a transistor stage (130) for varying the reference level (b) of the tunnel diode trigger circuit (116) so as to cause a horizontal shift of the window 92 in the direction which reduces the error signal. The error signal may also be applied to the servo-driven azimuth control of the camera mounting. A similar error signal for the vertical direction is derived from the combination of pulse J with the vertical gating pulses.