Patent GB-913977-A (GB)
Title: Trigonometric store for converting digital entered angles into analog voltages
IPC: H03M1/00
Filed: 1961-06-27
Abstract: 913,977. Electric selective-signalling systems. CINCINNATI MILLING MACHINE CO. June 27, 1961 [Aug. 30, 1960], No. 23197/61. Class 40 (1). In a system for producing a voltage corresponding in amplitude to the sine or cosine of a selected angle of first transformer provides voltages corresponding to the sines of a desired sequence of angles at a plurality of tappings and a switching network applies an adjacent pair of these voltages across a second transformer which effects a linear interpolation between the selected tappings. As described, three ten-position switches 1SS, 2SS and 3SS, corresponding respectively to increments of 36 degrees, 3.6 degrees and 0.36 degrees, are selectively positioned to produce on leads 81 and 106 voltages corresponding to the sine and cosine of the selected angle. These voltages are then used in a conventional servo-system 72, 86, 107 to position a slide 93 of a machinetool and it is so arranged that an angular increment of 36 degrees corresponds to a linear increment of 0.01 of an inch. The production of the sine voltages is as follows. Two transformers 15 and 21 together produce voltages at a series of terminals A, B ... L, corresponding to the sines of the angles 90, 72, 54 ... -72, - 90 degrees. The first ten-position switch selects a pair of adjacent tappings, in accordance with the number of increments of 36 degrees in the selected angle, and connects them across a winding 29 of a second transformer. Thus the voltage at the top end of winding 29 will represent sin# where # is the setting of the first switch 1SS, shown as 180 (i.e. 5 X 36) in the drawing, and the voltage at the bottom end will represent sin(# + 18). The winding 29 is linearly divided by five tapping points one of which is selected by the second switch 2SS (which represents increments of 3.6 degrees). Thus the voltage picked-off by the second switch, shown on contact 4 in the drawing, will represent sin(5 Î 36 + 4 Î 3.6). On the same core as the winding 29 is a second winding 30, there being a 5 to 1 step-down ratio between the windings and the winding 30 is linearly divided ten tapping points one of which is selected by the third switch 3SS, and the voltage picked-off from this winding is added, in series, with that selected by the second switch. Thus, as shown in the drawing, a voltage representing sin(5 x 36+4x3.6+2x0.36) is produced on lead 81. The system, as described so far, will only function correctly if the setting of the second switch 2SS is from 0 to 4 since the total voltage across winding 29 represents only 18 degrees and a setting of 9, for example, of switch 2SS calls for 9 x 3.6 degrees which is larger than 18 degrees. This difficulty is overcome by a relay 2CR controlled by a further bank of switch 2SS (Fig. 2, not shown) and it results in voltages representing sin(# + 18) and sin(# + 36) being applied across winding 29, when switch 2SS is in positions 5 to 9, instead of voltages sin# and sin(# + 18) as above. Thus the voltage produced by a setting of say 5, 9, 2, of the switches 1SS, 2SS, 3SS will produce a voltage of sin{5 Î 36 + 18 + 9 - 5 Î 3.6+2Î0.36} which is the required voltage. A similar circuit using a transformer 36 produces the cosine voltage.