Patent GB-1442685-A (GB)
Title: Target apparatus for use with a light-beam gun
IPC: G01D5/26
Filed: 1973-07-30
Abstract: 1442685 Target apparatus TOSHIBA ELECTRONIC SYSTEMS CO Ltd 30 July 1973 [3 Aug 1972] 36174/73 Heading F3C [Also in Division A6] A target apparatus for use with a light beam gun which can discharge a light beam, comprises a target means upon which said light beam can impinge, an optical system for focusing the light beam, a television image pick-up tube having a light beam receiving surface upon which focused light from the optical system can fall, said tube providing an image signal corresponding to a landing position of a light beam on said target means and a display means responsive to said image signal for indicating the light beam landing position on the target means. In an embodiment an electronic target apparatus comprises a light beam landing section or target 11 having a transparent screen 12 and a Fresnel lens 14, the latter being fitted either to the back or the front of the screen 12. A television image pick-up tube 13, having an optical member (not shown) for focussing the beam, is positioned a distance behind the lens 14 which distance is substantially equal to the focal length of the lens. The screen 12 has a target pattern as shown in Fig. 2 and receives a light beam from a laser gun 15, Fig. 1. The beam impresses a spot image which is focused by the lens 14 and is received by the image pickup tube 13. The output side of the latter is electrically connected to a television receiving set 17 through a video amplifier 16. Consequently the target pattern and the bright landing spot of light beam are read-out by known electric scanning to constitute input signals to the video amplifier 16 and amplified thereby to be indicated as a visible image on the television receiving set 17. The output side of the amplifier 16 is also connected to a circuit 18, the output of which is connected to an X-Y plotter 19. Accordingly an image signal amplified by the amplifier 16 is also supplied to the detecting circuit 18. The latter generates signals indicating the position of the light spot in the X and Y directions from a scanning line bearing the spot image on the scanning line. These position signals actuate the X-Y plotter 19 so as to indicate the light beam landing spot by plotting. The Fresnel lens increases the amount of input light to the television pick-up tube 13. In a modification an image of target circles on the screen 12 and an image of a light spot are read by the known electric scanning to form image signals. The latter are passed from the image pick-up tube 13 to a video amplifier 16, Fig. 5, so as to be amplified and then to a low pass filter 21 and mixer 53. The low pass filter eliminates noises overlapping the image signals to provide a signal having the wave form 71, Fig. 6. A level detector 22, Fig. 5, derives out a signal having a wave form 72, Fig. 6, corresponding to the largest amplitude of the wave form 71. An output signal from the level detector 22 is differentiated by a differentiator 23 into a wave form 73 and in the next stage into a wave form 74 by a clipper 74. The pulses of wave form 74 rises near the intermediate point of a signal having a wave form 72 representing the largest amplitude of the wave form 71 constituting the image signal of the spot image. Accordingly, rectangular output pulses 75 having a wave form produced by a wave form shaper 25 corresponds to the central point of the light beam landing position. The output pulses 75 are supplied as start pulses to a subtracting counter 31 for detecting the light beam landing position in the horizontal direction and also a subtracting counter 41 for detecting the light beam landing position in the vertical direction. The subtracting counters 31, 41 are supplied by a synchronizing pulse generator 26 with pulses having repetition frequencies nf H  and mf V  respectively. The generator 26, which is actuated in synchronization with electric scanning, consists of a horizontal driving pulse generator 27, a vertical driving pulse generator 28 and pulse generators 29, 30, the generators 27, 28 co-operating in the scanning of the image pick-up rube. The pulse generator 29 multiplies n-fold the repetition frequency f H  of an output pulse from the horizontal driving pulse generator 27 to generate a pulse having a frequency nf H , where n represents a value determined by the horizontal resolving capacity of the subject target apparatus to detect the light beam landing position. The pulse generator 30 multiplies m-fold the repetition frequency f V  of an output pulse from the vertical driving pulse generator 28 to generate a pulse having a frequency of mf V , where m denotes a value defined by the vertical resolving capacity of the subject target apparatus to detect the spot image. The subtracting counter 31 commences subtraction upon receipt of an output pulse from the waveform shaper 25 and stops subtraction upon receipt of an output pulse from the horizontal driving pulse generator 27. Counters 32 and 42 count pulses having numbers nf H  and mf V  for each period of the horizontal and vertical scanning respectively and are supplied with output pulses from the pulse generators 29 and 30. When a comparator 33 detects the exact time at which an output pulse from the subtracting counter 31 coincides with that from the counter 32, then the light beam landing position HT 1  in the horizontal direction, Fig. 7, can be detected; Similarly an output from a comparator 43 represents the light beam landing position VT 1  in the vertical direction. The counters 29 and 30 maintain data stored therein until they are supplied with a clear signal consisting of a signal denoting the commencing time of shooting which is delivered from, for example, the laser gun 15. Outputs from the comparators 33 and 43 are converted into pulses having widths HT 2  and VT 2  respectively by monostable multivibrators 34 and 44. Where, therefore, signals obtained by logically operating the pulses HT 2  and VT 2  by an AND gate 52 and signals derived from the video amplifier 16 are combined by a mixer 53, and the resulting composite signal is supplied to cathode ray tube after being amplified by a T.V. display driven 60, then it is possible to display, as shown in Fig. 7, both target pattern and light beam landing position at the same time. Output signals from the subtracting counters 31 and 41 are converted into analog signals by D-A converters 35 and 45 and supplied to mixers 36 and 46. The mixers 36 and 46 are supplied with signals of several cycles by a low frequency oscillator 50. An output signal from the mixer 36 represents the X axis and an output signal from the mixer 46 denotes the Y axis. An output signal from the oscillator 50 is supplied to the mixer 36 after being shifted about radian by a phase shifter 51. Thus the X-Y plotter 19 which is supplied with signals representing the X and Y axes can draw a light beam landing position with a circle having the prescribed size.