Patent GB-816133-A (GB)
Title: Improvements relating to the control of machine tools
Inventor: SPENCER ROLF EDMUND
IPC: G05B19/4105
Filed: 1954-10-01
Abstract: 816,133. Programming of machine tools; copy-milling. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 21, 1955 [Oct. 1, 1954], No. 28289/54. Class 83 (3). [Also in Group XXXVIII] An attachment for a copying machine comprises means for deriving signals from a dimensional record 37 such as a pulse, or an analogue, code on a punched or magnetic tape, a member, such as a striking plate 23, adapted to cooperate with the sensing element 21 of the copying machine, and means 26 for displacing the member in response to the signals to cause the member to describe a master which can be reproduced by the copying machine. The copying- machine table 2 is rotated by a motor 4 on a slide 1 traversed by a screw 10 beneath a fixed cutter 7. The screw 10 is rotated by a motor 11 controlled by a sensing head having two coils 14, 15 and a centre energizing coil 17. The sensing head co-operates with, and follows the movement of, an armature 19 connected to the spindle 20 of the sensing element 21. In a modified sensing head, displacement of the element 21 tilts a reflector to cause a light beam to be reflected into one or other of two photo-electric cells. The striking plate 23 is formed on a tube 24 moved by the screw 26 rotated by a servomotor 33 according to instructions recorded, (a) as the successive radii of the locus of the cutter axis 8, taking into account the radius of the sensing element; or (b) as the lifts of a cam at successive angular displacements. The instructions are taken from the record 37 and are passed through temporary stores 40-43 and quadratic interpolators 47, 48, which may be as described in Specifications 796,993, [Group XXXVIII], and 796,994, [Group XXXVI]. Instead of interpolating the radius of the locus as a function of angle, the radius and angle may be interpolated separately as functions of time or ordinate number, the servomotor 4 then being controlled by the angleinterpolating means. Other, such as rectangular, co-ordinates may be used, and the control may be in three dimensions. So that the actual dimensions of the profile to be cut can be recorded, instead of the locus of the cutter axis, the angle of the striking plate may be varied in accordance with the rate of change of dimensions. This reduces the error which, if the plate were not angled, would be caused by the milling cutter 90, Fig. 5, taking up a position 91 as it passes from a point A to a point B, the angle ## representing the angle between two successive output studs of the quadratic interpolating means. The angle of the .plate 92, Fig. 6, is varied by controlling a rod 96 passing through the screw 93 (26 in Fig. 1), the rod having an extension 100 bearing against an abutment on the striking plate 92. The nut 94 is controlled by the servomotor 33 of Fig. 1 and is coupled to rotate a nut 95 engaged by the screw 96. Differential motion is imparted to the nut 95 through a gear 99 rotated by a servomotor 102 to control the angle # of the plate, so that its tangent a/k = #R/R## to approximate the condition of Fig. 5, the constant k, which is the distance from the pivot point to the abutment of the plate, being made representative of the constant ##. Compensating for difference in form, between cutter and tracer.-To compensate for a difference d in the radii of the cutter and roller 110 (21), the striking-plate is advanced or is tilted at an angle # to the vertical, the roller then being displaced vertically along the plate a distance c = d/tan #. Specifications 805,391 and 807,643, [both in Group XXXVIII], also are referred to.