Patent GB-841849-A (GB)
Abstract: 841,849. Electric correspondence control. INDUCTOSYN Ltd. May 4, 1956 [Sept. 26, 19551, No. 13863/56. Class 40 (1). In a machine-tool the nominally straight guide-members 4 by means of which, for example a carriage 6 is moved with respect to a bed 2 are corrected for unwanted curvature which displaces a cutting tool at a point P of the carriage from a desired position by providing two linear position measurement transformers 9, 9<SP>1</SP>. The transformers each of which is constructed as described in Application No. 13275/56, are identical and each comprises a member 10, 10<SP>1</SP> and a member 12, 12<SP>1</SP>. The members 10, 10<SP>1</SP> are fixed to the bed of the machine-tool parallel to each other and to the guide members 4 and the members 12, 12<SP>1</SP> are fixed to the carriage parallel to each other and so that they are above the members 10, 10<SP>1</SP>. The members 10, 10<SP>1</SP> each have an insulating support 11, 11<SP>1</SP>, one surface of which supports a winding 14, 14<SP>1</SP>, alternate conductors of which carry current in opposite directions. The members 12, 12<SP>1</SP> each have a similar insulating support 13, 13<SP>1</SP>, but each has two windings 16, 16<SP>1</SP> and 18, 18<SP>1</SP>; alternate conductors in each winding also carry current in opposite directions and the spacing of alternate conductors of each winding is the same as that of the conductors in the windings 14, 14<SP>1</SP>; the spacing of the conductors of one winding relative to those of the other winding is, however, such that when each conductor of one winding is directly above a respective conductor of the winding 14 or 14<SP>1</SP> the conductors of the other winding are mid-way between the conductors of the windings 14 or 14<SP>1</SP>. The windings 16 and 16<SP>1</SP> are connected in series with each other and the windings 18, 18<SP>1</SP> are similarly connected in series and they are supplied from a generator 20 which positions two in-phase output voltages, one for each winding. The amplitude of the voltage for windings 16, 16<SP>1</SP> depends upon the cosine of the desired position between three adjacent conductors of the windings 14 or 14<SP>1</SP> if the distance between such conductors is considered to be 360 electrical degrees and the amplitude of the voltage for windings 18, 18<SP>1</SP> similarly depends upon the sine of the desired position. The amplitude of the voltage induced in the winding 14 by the windings 16 and 18 varies in amplitude as the carriage is moved relative to the bed and there is a position between each pair of conductors at which the voltage induced is zero; the voltage induced by the windings 16<SP>1</SP> and 18<SP>1</SP> in the winding 14<SP>1</SP> similarly varies and when there is no curvature in the guide members is zero at the same position of the carriage as that at which the voltages in winding 14 is zero. Corresponding ends of the windings 14, 14<SP>1</SP> are connected together and to earth and the other ends of the windings are connected to the ends of a potentiometer 22. The voltage from the two transformer windings 14, 14<SP>1</SP> appears between the tap 24 of the potentiometer and earth and is used to control a motor 7 which drives a lead-screw 8 for moving the carriage. When the guide-members are straight the voltages supplied by the two transformer windings 14, 14<SP>1</SP> are in parallel and after initial coarse positioning of the point P to be between two adjacent conductors of each winding, the motor 7 drives the carriage until the output from the windings 14, 14<SP>1</SP> is zero; the point P is then in a known position. The voltages produced by the windings 14, 14<SP>1</SP> when the guide-members are curved are additive since the members 12, 12<SP>1</SP> move relatively in opposite directions about the point P with respect to the members 10, 10<SP>1</SP> and the transformers and potentiometer then act as a Wheatstone bridge circuit and the motor 7 is driven until the output between the tap 24 and earth is zero; if the tap 24 is correctly positioned the point P will then be in the desired position. The tap 24 is adjusted so that the signals from the windings 14 and 14<SP>1</SP> are in proportions inversely related to the distances of the centre lines C, C<SP>1</SP> of the transformer from the projection of the point P in the plane defined by the centre lines. Thus if the point P was immediately above the centre line C<SP>1</SP> the tap 24 would be at one end of the potentiometer so that the output of the winding 14 was shortcircuited. In a modification instead of using a single potentiometer each winding has its own potentiometer and one side of each winding is earthed. The output voltage is taken between earth and a terminal connected through respective resistors to the potentiometer taps. In a modification of this latter embodiment step-up transformers are interposed between the windings 14, 14<SP>1</SP> and the two potentiometers and each transformer secondary is earthed at a point which is one-third of the number of turns from an end of the winding. With this arrangement the point P on the carriage can be between the centre lines C, C<SP>1</SP> of the transformers 9, 9<SP>1</SP> or outside of them.