Patent GB-1207157-A (GB)
Title: Machine control tracing system
IPC: B23Q35/128
Filed: 1967-09-29
Abstract: 1,207,157. Template followers. SFM CORP. Sept. 29, 1967 [March 3, 1967], No.44502/67. Heading G3N. [Also in Divisions G1 and H3] A photo-electric-tone follower as of circularly  scans a line recognizes code marks extending from one side of the line. The follower may control the movements relative to a workpiece of a machine tool and in response to one or more code marks perform an auxiliary operation such as gradually coming to a stop. An indication is given to an operator that the follower is following the line. In Figs. 1 and 2 a photo-multiplier 12 scans a line pattern 9 by a rotating disc 27 having an eccentrically located aperture. A tube 18 in which the disc is fixed is rotated within the follower head 10 by a motor 33 and contains a magnet 35 which forming the rotor of a generator having quadrature windings 34, 35 connected to gates 77, 78 in a control unit 14. Pulses from the photo-multiplier generated by scanning the leading and trailing edges of the line (leading and lagging being with reference to the direction of movement of the head) pass to a circuit 57 which is set according to whether a dark line upon a light background or vice versa, is being scanned so as to always deliver negative pulses to a Schmidt trigger 60. The trigger feeds two monostable tandem connected multivibrators 62 and 67 both being set by a leading edge pulse but 62 being re-set about 300 degrees of scan later, thereby rejecting the trailing edge pulse, and 67 being re-set 180 degrees after the leading edge pulse. Multivibrator 67 via amplifiers 70, 71 controls the gates 77 and 80 so that signals from the generator 34 pass through on the first half of the scan but pass through inverted during the second half. There portions of signal are capacitively integrated and of the modulation at 86 provide A.C. drive signals to the co-ordinate servomotors 3 and 4 of the work table, or alternatively the photo-electric and work heads. Upon scanning a code mark 200 Fig.6 a Schmidt trigger to pulse appears upon line 211 Fig. 5 to pass through gate 210 previously conditioned by multivibrator 201 which was set by multivibrator 67 in response to the leading edge pulse and re-set by timing circuit 202 180 degrees of scan later. The gate output sets a multivibrator 216 which operates via a filter a relay (R) 223 and also passes to an active filter 229 whose output is proportional to the distance of the code mark from the axis of the scan. This output is compared with a voltage from divider 230 having the magnitude the filter output has when the axis is co-incident with the mark. The modulated difference now drives the x-axis servomotor 3 over contacts of relay 233 Fig.1 so that the head, which is assumed for simplicity to be non-moving in the X direction only, gradually comes to a stop with the scan axis coincident with the code mark. In an alternative arrangement also shown in Fig. 5, relay (R) 223<SP>1</SP> operates in response to the scanning a second mark in the same scanning cycle as the first the associated gate 210<SP>1</SP> being conditioned when multivibrator 216 is set by the first code mark pulse. The repeated setting of monostable circuit 62 Fig.2 maintains a relay 65 operated, via a transistor circuit 64, where contacts indicate that the line is being followed.