Patent GB-946772-A (GB)
Title: Improvements in or relating to electrostatic capacitance resolvers
IPC: G01D5/241
Filed: 1960-04-25
Abstract: 946,772. Capacitors. CONTINENTAL ELEKTROINDUSTRIE A.G., [trading as CONTINENTAL ELEKTROINDUSTRIE A.G. ASKANIA-WERKE]. April 25, 1960 [April 29, 1959], No. 14456/60. Heading HIM. [Also in Division G1] An electrostatic capacitance resolver for converting the angular position of a rotatory shaft into a correspondingly phase variable alternating voltage comprises two relatively rotatable insulating members separated by an air gap, which are provided with angular metal coatings coaxial with the rotary axis which are divided by insulating patterns on one member to provide two pairs of driving electrodes, the electrodes of each pair mating one with the other with the part electrodes of one pair offset angularly with regard to the electrodes of the other pair; so that each driving electrode forms with the coupling electrode a capacitative coupling variable with the relative rotation of the members, whereby on application to each pair of driving electrodes of respective alternating voltages of identical frequency but mutual phase displacement a sinusoidal constant alternating voltage appears on the coupling electrode formed on the other insulating members, whose phase angle varies linearly with the relative angular position of the two members; the driving and coupling electrodes comprising sets of associated electrically connected mating part electrodes located annularly of the rotational axis with their insulating boundaries constituted by radial lines and by arcuate lines whose centre of curvature coincides with the rotational axis, and the output voltage appearing between a set of such coupling electrodes. In Fig. 1, a shaft 1 rotated, e.g. in accordance with the vertical deflection of a kinetheodolite carries a mounting 4 for a glass rotor plate 5 with a metal coating 6 spaced from a glass stator plate 8 having a further metal coating 9; the coatings being divided by insulating patterns into a pair of mating electrodes on plate 5 and two pairs of mating electrodes on plate 8. An oscillator 10 energizes a bridge phase shifter 11 to apply quadrature voltages over lines 12, 14 and 13, 15 to the respective pairs of electrodes on plate 8, while a voltage divided from the pair of electrodes on plate 5 is connected over slip rings 16, 17 to phase comparator 20<SP>1</SP> receiving a reference voltage from phase shifter 11 over line 15<SP>1</SP>. The phase difference is indicated digitally at 21<SP>1</SP> and is stored for recording at predetermined times by printer 22, or for operation of electronic calculators, as a measure of the shaft angular rotation. Stator 8 (Fig. 2) is coated, e.g. with copper or aluminium which is selectively removed to leave concentric annular conducting surfaces 25, 26 of equal area insulated from each. other by circular grooves 21, 22. Each surface is divided into mating electrically separate electrode areas by grooves 27, 28 respectively of stepped form consisting of radial and arcuate portions; the electrodes 29, 30 of surface 25 having terminals 29<SP>1</SP>, 30<SP>1</SP> interconnected to lines 13, 15 and the electrodes 31, 32 of surface 26 being interconnected to lines 12, 14 over similar terminals. The arcuate patches of the steps are similar and those of electrodes 29<SP>1</SP>, 30<SP>1</SP> are offset  cycle or 90 degrees phase angle with respect to electrodes 31, 32 energized in quadrature with respect to electrodes 29, 30. Rotor 6 (Fig. 3) has a similar metallic coating which is selectively removed to leave annular surface 42 divided into two mating electrically separate electrode areas 44, 45 by groove 43 having terminals 44<SP>1</SP>, 45<SP>1</SP> interconnected to the slip rings (Fig. 1). It is shown by an extended mathematical analysis that, if for the stator portion shown in Fig. 4 the angular spacings of adjacent radial portions of grooves 27, 28 are given by α<SP>1</SP> st  and α<SP>11</SP> st  and the angular spacing of alternate radial portions is given by γ<SP>1</SP> st  and for the rotor portion shown in Fig. 5, the respective angular spacings are given by α<SP>1</SP> R  and α<SP>11</SP> R  and the alternate angular spacing by γ<SP>1</SP> R , the phase angle of the output signal represents the shaft angular rotation to a high degree of accuracy if angles α<SP>1</SP> R  and α<SP>11</SP> R  are adjusted to differing critical values which may be calculated. Alternatively, the angular spacings α<SP>1</SP> st  and α<SP>11</SP> st  may be unequal and correspondingly adjusted to critical values. The stepped electrode elements of areas 44, 45 (Fig. 3) may be interconnected in electrically separate groups over angles of e.g. 60 degrees, the groups of electrodes 44 being offset by a critical angle with respect to the groups of the electrode 45 (Figs. 4b, 5a, not shown). The electrode elements of the stator may be similarly grouped and angularly offset. The angular spacings α<SP>1</SP> st , α<SP>11</SP> st , α<SP>1</SP> R  and α<SP>11</SP> R  of the stator and rotor electrodes may each or all be varied round the stator and rotor peripheries. The insulating grooves may be cut by a dividing machine in the first instance, and successive stator and rotor plates may be reproduced photochemically or photomechanically therefrom. Since the output phase angle varies n times (n being half the number of mating electrodes of elements 29, 30, 31, 32, 44 and 45) for one revolution of the rotor relatively to the stator, the phase angle only indicates the shaft rotation relatively to the nearest point at which the phase angle is 0 or 2 #, so that an additional coarse indicating device (which may be a similar resolver) must be associated with the above device to position the indication with relation to a fixed datum.