Patent GB-979631-A (GB)
Title: Improvements relating to the automatic control of machine tools
Inventor: WHITEMORE GERALD
IPC: G05B19/4105
Filed: 1960-02-25
Abstract: 979,631. Electric analogue calculating. ELECTRIC & MUSICAL INDUSTRIES Ltd. Feb. 21,1961 [Feb. 25, 1960],No.6559/60. Heading G4G. [Also in Division G3] In an automatic control apparatus suitable for controlling the relative displacement of a cutter and a workpiece according to a desired outline, there is included a source of a signal which varies to represent the value of a first coordinate which, in association with a corresponding second co-ordinate, defines the outline, and an arrangement for generating component signals representing resolved parts of a dimension of the cutter in the directions of the said co-ordinates. An arrangement responding to the source signal and to the component signals derives signals for controlling the relative displacement of the cutter and the workpiece, taking account of the cutter dimension, and the arrangement for generating the component signals includes a means for selectively variably adjusting the component signals in response to the operation of the deriving arrangement so that the compensation for the cutter dimension can be varied between zero and the correct value during the description of a portion of the outline. The system may be used to correct the outputs from two quadratic interpolators I x  and I y , which are of the type described in Specification 796, 994, receiving alternating voltages representing the values of x and y co-ordinates respectively of three points P, Q, R and providing interpolated values between these points at the studs of the selectors S x , S y . Coupled to the interpolator transformers are secondary windings 11,12,15,16 which are disposed so as to apply voltages representing dx/dT, dy/dT to the stator windings 13,17 of a resolver 14. This is explained in Specification 849,091. T is the interpolation variable with respect to which both x and y are expressed parametrically, and is represented by the position of the shaft 20, to which the various selectors of the apparatus are ganged. The resolver 14 carries two rotor windings 21,22 connected through amplifiers 23, 24 to the motor 25 in such a way as to maintain the sensitivity of the servo system formed by these components and the shaft 26 at a substantially constant value. (This is fully described in Specification 863,114). A second resolver 27 is attached to the shaft 26, and carries rotor windings 30, 31, from which are obtained the voltages representing the compensations required in the x and y co-ordinate directions for the dimensions of the cutter, which are added to the voltages produced from the interpolator, at the wipers 9 and 10. The appropriate voltages are produced in the windings 30, 31 if a voltage representing r, the radius of the cutter, is fed to the stator winding 28. The shaft 26 takes up an angular position 6, where # = tan<SP>-1</SP> (dy/dT / dx/dT), by virtue of the servo action described above, and hence the voltage injected into the winding 30 will be representative of - r sin tan<SP>-1</SP>(dy/dT / dx/dT)]  and the voltage injected into the winding 31 will be representative of r cos [tan<SP>-1</SP>dy/dT / dx/dT)]  Thus the voltages obtained at the outputs 32, 33 represent the x and y co-ordinates of points on the outline to be cut, compensated for the size of the cutter, which outputs are used to control the positional servo mechanism operating the displacement of the workpiece relative to the cutter. The radius for which compensation is required is set up by the wiper 8 on the winding 5, which is connected through the switch A (when in the appropriate position), to an alternating current input applied at terminals 1 and 2. When it is desired not to compensate for the dimensions of the cutter initially, but to bring in the compensation during the first span of the cut, the switch A is arranged to respond to a programme which sets the switch to the position A2. The wiper 7 on a potentiometer 3 ganged to the shaft 20 then gradually brings in the full compensating voltage during the first half of an interpolator span. The switch A then moves to the position A3 after this half span. If at a later time it is desired to remove the compensation, the programme is arranged to move the switch to the position A4 during the second half of an interpolator span and the wiper 7 operates so as to remove the voltage applied at the terminals 1 and 2. At the end of the half span the switch A is moved from position A4 to A1 so as to maintain zero input to the transformer 5. The Provisional Specification describes a more elaborate arrangement of transformers than that shown at 5 for setting up a voltage proportional to the cutter radius, further details of which are given in Specification 846,381.