Patent GB-1304376-A (GB)
IPC: G06K15/22
Filed: 1970-03-02
Abstract: 1304376 Measuring position electrically BENDIX CORP 2 March 1970 [10 March 1969] 9811/70 Heading G1N [Also in Divisions G3, G4, H1 and H3] A position measuring arrangement comprises a pair of superposed grid elements 40, 44, each consisting of a plurality of parallel straight conductors whose ends are linked to form a continuous winding, the conductors of one being perpendicular to those of the other, and a cursor device in inductive relationship with both windings. As shown in Figures 2 and 3, the conductors may be printed on a backing of glass or epoxy resin, and the cursor may be a circular winding 34 embedded in a block of clear plastics material 36 which has cross hair pattern 38. The diameter of the loop is equal to an odd multiple of the spacing between parallel conductors. In the embodiment of Figure 1 two further grid elements 42, 46 are provided similarly arranged to the ones above them but having their windings displaced, perpendicular to the direction of conductors, by half a spacing. A 3 MHz signal from a clock source 21 is divided by 1000 by a counter 22, filtered, and amplified to provide a sinusoidal 3KHz signal to the cursor 14, and voltages are induced in the grid element windings. As the cursor is moved perpendicularly to the conductors 50 of grid element 40 (the "Y" direction) the maximum amplitude of the signal induced therein will vary sinusoidally with cursor displacement completing a full cycle over a distance of two conductor spacings. The maximum amplitude of the signal in element 42 will vary similarly but displaced by ¢ a grid spacing. If this signal is subjected to a 90 degree phase shift at 84 and the two signals are combined in amplifier 86 the phase of the resulting sinusoidal voltage shifts linearly and in direct proportion to the displacement of the cursor. Figures 6-10 (not shown). This signal is squared by a zero-cross detector 90 and applied to a phase comparator logic 92 which is also supplied with a reference signal from a counter 96. When the two signals are in phase 3MHz pulses from clock 21 are transmitted through logic 94 to counter 96 which changes the sign of its output signal after every 500 pulses received, thereby providing a 3KHz reference signal. If the input signal just leads this reference signal the switching logic operates to cause the counter 96 to change polarity after 499 pulses and thereby advance the reference signal. At the same time, the count in a count register 104 is increased. The reference and input signals are therefore kept in step, and the count register 104 gives an accurate measure of cursor displacement which is displayed at 108. The accuracy is 1/500 of the spacing between conductors. The arrangment of grids 44, 46 is associated with identical circuitry to provide a measure of displacement in the "X" direction. In operation, the gird arrangement is placed over or under the surface to be measured, the cursor is placed at a suitable reference point and the counters 104 are cleared. The cursor is then moved to a point of interest and the output displays are read.  Figure 12 Embodiment. In the embodiment of Figure 12 excitation signals are supplied to the grids not the cursor, and a different phase identifying arrangement is used. Several cursors can be operated independently. Two 3KHz signals in quadrature are supplied to the two "Y" axis grids, and two 4KHz signals in quadrature to the "X" axis grids. The induced signal in the cursor is then passed to two apparatuses 118, 120 for identification of the Y and X displacements respectively. In apparatus 118, the 3KHz signal is obtained via a filter 130. Again, the phase of this signal is dependent of Y displacement of the cursor. This signal is passed to a phase sensitive dimodulator 136 which also receives a 3KHz reference signal from a counter 138 (similar to counter 96 in Figure 1) supplied with a 3MHz clock signal. The phase relation between the summation and reference signals determines the level of output from the demodulator, no output obtaining with a 90 degree phase difference. As the cursor moves to vary the summation signal phase, the output of the demodulator 136 controls a voltage controlled oscillator 140 to supply pulses to the counter 136 to add to the clock pulses and vary the phase of the reference, signal. The V. C.O pulses are also supplied to a count register 143 whose total measures the cursor displacement in the Y direction. Similar apparatus provides the X displacement on a register 150. Further cursors 14 and their output equipment are disclosed. In a further embodiment Figure 13 (not shown) the cursor comprises two inductive loops mounted in a single rectangular holder, the loops being supplied with 3KHz and 4KHz signals respectively. Signal processing and phase identifying apparatuses similar to that disclosed in Figure 1 are used and the resulting outputs provide measures of (a) the movement of the cursor and (b) its angular rotation.  Figure 14 Embodiment. A further embodiment Figure 14 discloses a different means of determining the X and Y displacements of a cursor which is supplied with an excitation signal. For the Y displacement the induced signal from the grid 40 is fed to a primary winding 220 of a mechanical resolver 221, and the signal from the quadrature grid 42 is fed to winding 224. It is shown that the amplitude of the voltage induced in a rotor 226 is given by K sin (y/d, 360-#) where y is the cursor displacement d is the conductor spacing and # is the rotor angle. If the rotor is caused to rotate as the cursor is moved so that # = y/d360, no rotor output will obtain. Amplifier 228, motor 230, and gearing 232 operate to effect this, the result of rotation being shown on an output device 234, which may be a shaft encoder, potentiometer or mechanical counter. X displacements are measured similarly. Plotting device. Fig.15 discloses a plotting device in which the arrangement of Fig.1 is modified so that the cursor 238 has a pen attached thereto and conventional mechanical drives 250, 254 are provided. The count register output for each of the X and Y directions (indicative of cursor position) is fed together with command signals from a computer 260 to a digital error register 258, or 266, the errors being fed through D-A converters to amplifiers supplying the motor drives 250 and 254. A further plotting device is also disclosed Fig. 16, (not shown) in which the signal processing arrangement of Fig. 12 and the comparator, mechanical drive and computer arrangement of Fig. 15 are utilized. The difference lies firstly in the grid structure 276 wherein only the two grids 40 and 44 are used see Fig. 2, these being fed with 3KHz and 4KHz signals respectively and secondly in the cursor structure which holds three loops 284, 286, 288 and a pen 282, the loops 286 and 288 being each an odd multiple of conductor spacings away from loop 284 in the X direction and Y directions respectively. These loops act as "quadrature" loops to the loop 284, in distinction to the "quadrature" windings of previous examples. The operation is otherwise as previously described.