Patent GB-840002-A (GB)
Title: Course plotter
Inventor: FRANK ROBERT LEE
IPC: G01S5/10
Filed: 1957-06-27
Abstract: 840,002. Photo-electric control. SPERRY RAND CORPORATION. June 27, 1957, No. 20402/57. Class 40 (3). [Also in Groups XX and XL (c)] Relates to a system as described in Specification 840,003 for automatically positioning a carriage 10, Fig. 1, over a chart 18 having spaced position lines a, b, c, d, e marked thereon such that an index 17 on the carriage is located between the lines b and c and along a locus p, p<SP>1</SP> parallel to the direction of movement of the carriage at a distance x from the line b which is predetermined fraction x/y of the distance y between the lines b and c, the said predetermined fraction x/y being given by the angular position of an input control shaft 38 ; alternatively the index 17 may record on a second adjacent chart representing the same area as the chart 18. When the position lines on the chart correspond to position lines in space defined by a Loran radio navigation system, the shaft 38 is controlled in accordance with the output of a Loran receiver to make a complete revolution as the craft carrying the receiver moves from one position line, e.g. b, to an adjacent position line c and according to the present invention when the craft moves to a point whose distance from a position line is less than a predetermined value the system interpolates between points spaced midway between the position lines instead of interpolating between the position lines themselves as described in Specification 840,003 so that the carriage moves continuously in accordance with the movement of the craft as it crosses a position line. As described a segment s, s<SP>1</SP> of the line p, p<SP>1</SP> at least equal to twice the greatest spacing between two adjacent position lines is scanned as described in Specification 840,003 by a phototube, Fig. 2 (not shown), mounted on the carriage 10 to produce (1) recurrent groups of scan pulses b, c, d, A, Fig. 3, corresponding in time to the lines b, c, d; and (2) reference pulses D, Fig. 3, corresponding to the position of the index 17. The scan pulses A are slightly delayed at 24 to give a corresponding series B of pulses b<SP>1</SP>, c<SP>1</SP>, d<SP>1</SP> which trigger a primary sawtooth generator 25 giving an output C which is sampled (1) in a gate circuit 29 by the reference pulses D to give a D.C. voltage I proportional to the distance of the index 17 from the chart line b, and (2) in a gate circuit 26 by pulses F corresponding to the c pulses to give a D.C. voltage G proportional to the distance y between the lines chart b and c; each F pulse is produced by gating the A pulses in a coincidence gate 31 by the output pulse E from a bi-stable multivibrator 30 which is turned on by each reference pulse D and turned off by the succeeding pulse F. The voltage G is applied to a circular potentiometer 34 whose continuously rotatable slider 35 is controlled by the input shaft 38 to give an output H proportional to the distance x of the craft from the space position line b. The voltages H and I are applied to a relay 42 and filter 48 to give an A.C. error signal K which controls a servomotor 50 to adjust the position of the carriage 10 until the voltages H and I are of equal amplitude. According to the present invention the signals C and H are only applied to their utilization circuits 29 and 42 when the angular position of the input shaft 38 is within limits corresponding to values of the fraction x/y between “ and ¥, this being effected by relays 40 and 46 controlled by a relay winding 66 whose energization is controlled by a rotary switch 62 ganged to the input shaft 38. An output from the sampling gate 26 is also applied to a potential divider 55, 56 giving a bias voltage Q, C, Fig. 3, of amplitude equal to half that of the voltage G, the bias voltage being applied together with an output C from the primary sawtooth generator 25 to a comparator 57 and pulse generator 58 to give a pulse series N corresponding to the pulse series A but delayed relatively thereto by half the time interval between the b and c pulses. The pulse series N trigger an auxiliary sawtooth generator 59 to give an output O corresponding to waveform C but delayed relatively thereto by half the time interval between the b and c pulses. The potentiometer 34 is also provided with an additional slider 60 diametrically opposite to the slider 35 and producing an output P proportional to the distance of the craft from a point midway between the space position lines b and c. When the craft approaches the position line c within a distance of a quarter of the separation between the lines b and c (reference pulses now shown as waveform D<SP>1</SP>), the relays 40 and 46 operate to select the signals O and P in place of C and H. The resultant output I<SP>1</SP> from the sampling gate 29 is now proportional to the distance of the index 17 from a point on the chart 18 midway between the lines b and c and the carriage is now controlled in accordance with any difference in amplitude between the voltages P and I<SP>1</SP>. This mode of operation continues until the craft has crossed the position line c (corresponding values of D and I shown as D<SP>11</SP> and I<SP>11</SP> in Fig. 3) and reached a point whose distance from the line c is a quarter of the separation between the lines c and d when the switch 62 operates to restore the first mode of operation, the resultant voltages G, H and I being then related to the interval between the lines c and d. Thus the carriage 10 continuously follows the movement of the craft as it crosses a position line. Alternatively the outputs C and O from the primary and auxiliary sawtooth generators 25 and 59 may be applied to separate sampling gates each similar to the sampling gate 29, the outputs from the two sampling gates being selected by the relay 40 and the magnitudes of the signals G, G<SP>1</SP>, H, H<SP>1</SP>, I, I<SP>1</SP> may be represented by electrical frequencies, digital code signals or mechanical displacements or rotations.