Patent GB-1215341-A (GB)
Title: Improved tracer
IPC: B23Q35/12
Filed: 1968-01-16
Abstract: 1,215,341. Template followers. ANDREW ENGINEERING CO. Jan.16, 1968. [Feb.27, 1967] No.2357/68. Heading G3N [Also in Division G1] In a photo-electric line follower system, producing signals to control the displacement of a workpiece with respect to a tool, the proportional relationship between the size of the shape to be produced and of the line pattern followed can be selected and the control signals can be modified to compensate for differences between the shape produced and the pattern, due to the working reach of the tool. The line follower head 31, Fig.1, and Fig. 12 (not shown) comprises a light source and one end of a bundle 42 of optic fibres. The head is movable in two directions at right angles. The Y axis servomotor 35 moves the head along track 30 which is itself movable in the X-axis direction by servomotor 35. In this way the head can follow a line 26 drawn on a transparent panel 23. Cross lines 27 are provided for locating the tool or stopping the workpiece. The optic fibre bundle conducts an image to a photo-electric system locating within casing 15a and producing control signals for movement of a workpiece mounted on bed 16h, through X and Y axis servomotors 21, 20. The image I, Fig. 8, at the lower end of light guide 44 is split up for direction to two photo-cell pairs 80, 81 by a beamsplitting prism 79. Each photo-cell pair comprises two semi-circlar shaped cells connected in a bridge arrangement and arranged to sense the orientation of a minute section of the line being received at a particular instant. The cellpair 80 is used during forward movement of the head and pair 81 during reverse movement. A further cell arrangement 83 senses the cross lines 27. The output of the all pair 80 or 81 is used to operate reversible motor 59 to rotate the photo-electric head with respect to the axis of the end of the light guide 42., to maintain a balance between the cells in the photo-cell pair. This continuous orientation of the head 45 causes movement of a crank-pin 47, Fig.6, which is transmitted through discs 48,49 and slides 50, 51 to ball and disc integrators 52, 53 which are driven by a reversible motor 54. The output of the integrators feeds gear trains 55, 56, the wheels of which are in fixed proportions to one another. The rotations and speeds of the individual gears are sensed by synchro control transformers 57a-g, 58a-g, Figs. 10, 11 (not shown). A particular synchro control transformer can be selected by a multi position switch to provide a desired proportioned reduction in the shape to be produced compared to the size of the original drawn pattern. The synchro control transformers co-operate with synchro transmitters sensing the rotation of screws 33, 34 for the line follower head and 18, 19 of the workpiece displacement mechanism to control the servomotors 35, 36 and 20, 21, which drive these screws. Manually operable synchro differential transmitters are provided to allow control of the servomotors 20, 21 for initial setting up of the workpiece with respect to the tool. The compensation to allow for the working reach of the tool, which may be a revolving tool, grinding tool, or flame cutting torch, is effected by use of tool offset rotor 60, Fig. 6 (and detailed in Fig. 5), (not shown). A manual control dial is provided to cause movement of slide 64 and thus the distance between the axis of pin 65 and the axis of the rotor, which distance is equal to the radius or reach of the tool. The rotor is rotated by the same motor 59 which orientates the photo-electric head 45. Any rotation of the rotor is sensed by synchro differential transmitters 72, 73 X and Y vectors. These transmitters are connected in the servomotor 20,21 control circuits so as to modify the drive instructions for screws 18,19. Instead of the arrangement of Fig. 8, alternative photo-electric systems use an image-rotating prism mounted on a disc rotatable by motor 59 Fig. 13 and 14 (not shown), in one a fixed beamsplitting prism and two fixed pairs of cells being used, and in the other simply a fixed arrangement of four sector shaped cells with non-responsive dividing areas.