Patent GB-1521270-A (GB)
Title: Distance detecting apparatus
IPC: G01C3/06
Filed: 1976-06-08
Abstract: 1521270 Automatic focusing HONEYWELL Inc 8 June 1976 [15 July 1975] 23517/76 Heading H4D An apparatus for measuring the distance between the apparatus and an object, first and second optical means 6, 7, Fig. 1, produce first and second images respectively of the object on first and second radiation detectors 4, 5, each including an array of elements 9, 10, 11, 12, 13, 14, 15, 16, each responsive to radiation to produce an electrical signal. Scanning means 22-28 cyclically varies the relative position of one of said optical means 7 and its respective detector 5, with a signal processor 8 comparing the electrical signal from each element of one array with that from a corresponding element of the other array to produce a resultant signal and summing said resultant signals to produce an output signal which exhibits a predetermined characteristic each time the radiations on said arrays are in best correspondence. A circuit determines in each cycle the instant and the relative position of said one optical means and its detector at which said characteristics is exhibited whereby to measure said object distance. The apparatus is described as applied to automatically focusing a camera lens 1 by a continuous comparison of its position as indicated by an electro mechanical transducer with said relative position. The signal processor 8 (Fig. 2, not shown) of the kind disclosed in Specification 1,521,268, gives a dip in its output 146, Fig. 3, when the images on the two detectors are in maximum correlation. A slope change detecting circuit 54-59, 64, 67, 68 converts this to a pulse 147 which sets the # output 140 of bi-stable 66. Lens 7 is moved, via lever 26, by a cam 25 rotated by a motor 22, also rotating a disc 31 carrying a magnet 32. A fixed coil 33 produces a pulse 138 when the lens 7 is at far right (equivalent to infinity). Camera lens 1 is focused by a rackpinion 38, 39 moved by a bidirectional motor 34. Pinion shaft 35 carries a disc 40 with a coil 41 which, when swept by magnet 32, produces a pulse 145 via slip rings 42 setting the # output 139 of bistable 62. Bi-stables 62 and 66 are both reset by the 'reference position' pulse 138 such that the difference in the durations of the set states of the bistables (139, 140) indicates the degree of out of focus of the camera lens 1. A logic circuit 75,76, 77, 79, determines the amount and sense of the duration difference, Fig. 3 showing an output 141 from gate 75 only (as against none from gate 77, 142), which output causes appropriate drive pulses 144 on one of lines 99, 102 for activating the motor 34 and moving the lens 1 into focus. The module arrangement 3, Fig. 6 described in Specification 1,521,268, may be used, the detectors 4, 5 and the processing circuit 8 being incorporated in an integrated circuit 158. Mirror 166, scanning the image over detector 5 is moved by a double cam set 25, 170. Only the scan from left to right is used. A switch 174 part carried by lens 1 and part by cam 170 is closed for part of each cycle of 170, the length of the part being greatest when the lens 1 is at the infinity position. The switch gives the output pulse 203, Fig. 7. The output, 202 of the processing circuit is fed to coincidence logic circuit 188-199 together with the pulse 203, such that when there is no overlap, e.g. at 204, 205 with lens 1 too far out, a drive signal is generated bringing the lens in, and vice versa for overlap (206). The stable, just overlap 207 state, is hunted, at focus. Switch 174 may be replaced by a photo-electric set-up, Fig. 8 (not shown). The lens I may be coupled to the wiper of a potentiometer, Fig. 9 (not shown), to give an analogue signal which is compared with a ramp voltage generated from the output of the processing circuit, the comparison giving the lens 1 drive signal.