Patent GB-1391669-A (GB)
Title: Position-measuring transformer
IPC: G01D5/20
Filed: 1972-06-29
Abstract: 1391669 Displacement transducers INDUCTOSYN CORP 29 June 1972 [15 March 1972] 30381/72 Heading G1N [Also in Division H 1] A position-measuring transformer has first, 2, and second, 6, relatively movable windings, the second winding being formed of two seriesconnected winding sections comprising continuous printed conductors inductively coupling to the first winding and arranged so that an unwanted coupling component in the first winding section cancels out an unwanted coupling component in the second winding section. Constant Coupling Cancellation. As shown in Fig. 1, member 6 has a first winding section having active conductor portions 18-1 to 18-6 and end portions 16-1 to 16-6. The second winding section has active portions 19-1 to 19-6 and end portions 17-1 to 17-6. The portions 18-and 19- conduct in the same direction, but the end portions 16- and 17- conduct in opposite directions so that their coupling to the reference winding 2 is zero. Quadrature Compensation. Fig.7 shows series connected winding sections C and B forming a sine winding, and series-connected winding sections A and D forming a cosine winding. Each pair of windings exhibits cancellation of constant coupling, and it is shown that if the angles α 1  and α 2  between the windings are the same then the use of two windings for each phase member ensures that the coupling signals are exactly in quadrature even when α 1  and α 2  are not exactly 90 degrees. The winding sections may be placed in four separate layers, or the sine windings may be in one layer, with the cosine windings in another. Further accuracy can be obtained by placing resistors across one or more of the winding sections. For example, a resistor across winding section A reduces the coupling of that section and reduces the angle between the sine and cosine windings; a resistor across winding section D increases the angle. Coupling Equalization and Harmonic Cancellation. It is stated that if the active conductor portions have a width twice that of the width of the spaces between them, then errors due to coupling of the third harmonic of the fundamental frequency are obviated. Alternatively, since the magnitude of coupling is dependent on the conductor to space width ratio, this ratio can be made smaller for the winding sections furthest from the reference member so that the magnitude of coupling is the same for all winding sections. As described the ratios for the winding sections C and A, and for the winding sections B and D are made the same, and are arranged so that the average ratios for the sine winding C and B and for the cosine winding A and D are both 2 to 1, allowing cancellation of third harmonic errors. Further coupling equalization or line balancing may be achieved by placing a resistor across the sine or cosine winding and thereby reducing that winding's coupling to the reference member. Construction and Arrangements. A four layer linear transformer may be made by printing the sections B and D on either side of a metal, glass or plastics base and sticking this on to a base by means of an adhesive insulating layer. A similar laminate with sections C and A is stuck on top with another adhesive, insulating layer. An electrostatic shield is placed on top. A multi-cycle, twophase rotary transducer, Fig.20 (not shown) is described in which the active conductors are wedged-shaped, but the spaces are made rectangular. A four-layer, single cycle rotary transducer, Figs.24-29 (not shown) has each winding section in the form of a spiral. Two laminates are placed face to face, and identical spirals are printed on their exposed faces. The laminates then swop positions and are rotated through 90 degrees, and identical spirals printed on their newly exposed faces. The four spirals are then correctly orientated to provide single-cycle sine and cosine windings. Space-phase compensation in 3 or N- phase systems may also be provided. For an N- phase system the transducer includes N windings each having N winding sections arranged in N pattern which are shifted relative to each other by approximately 360/N degrees.