Patent GB-960242-A (GB)
Title: Improvements in or relating to electrical computers for performing arithmetical operations, especially in navigation apparatus
IPC: G06F7/548
Filed: 1960-05-02
Abstract: 960, 242. Electric analogue calculating, electric digital calculators. GENERAL PRECISION Inc. May 2,1960 [April 30, 1959], No. 15460/60. Headings G4A and G4G. An electrical computer for performing arithmetical operations on input signals representing mathematical values comprises means converting an input signal into a digital signal coarsely approximating the input value to an accuracy limited by digit interval size, and an electric analog interpolation signal representing the value which must be added to the approximate digital signal valve to represent the exact input value; digital computer circuitry performing an arithmetical ope - ration on the digital signal; electric analog computer circuitry performing the equivalent arithmetical operation on the analog signal, and means for combining the results of the two arithmetical operations into a unitary electric analog output signal. Such a computer may have two distinct channels responsive to latitude and longitude navigational signals for comparison of inputs representing the latitude and longitude of a vehicle, with inputs representing those of a selected fixed station, which may be simulated by circuit means. General. In Fig. 1, input signals V N , V E  representing the rectangular velocity components of a real or simulated vehcile referred to rectangular N-S and E-W co-ordinates are fed to a latitude/ longitude computer 100 together with initial starting point latitude and longitude signals L 0 , # 0  from initial location means 102, to drive shafts 120, 122 to represent angularly the true latitude and longitude L, # of the vehicle. Utilization device 146 coupled to shafts 120, 122 may plot the vehicle position on a globe or spherically projected chart, and utilization device 140 responsive to rotation of shafts 136, 138 representing cartesian variables X, Y referred to the N or S pole as origin may produce a polar plot of the vehicular position. Shafts 120, 122, operate a relative position computer 104 also receiving approximate digital and interpolative analog signals from devices 106, 108, .... 110, representing the latitudes and longitudes L 1 , # 1 , L 2 , # 2 ,.... L n , # n , of corresponding actual or simulated fixed stations S 1 , S 2 .... S n  to produce computed accurate analog signals at terminals 125, 126; 127, 128; 129, 130; representing the latitudinal and longitudinal differences between the vehicle and the several stations. By multuplication of the longitudinal difference signals by the cosine of the vehicle latitude; signals proportionally representing differences of distance between the vehicle and the stations may be obtained. Latitude-longitude computer. Fig. 2a shows a computer initially operating in subpolar regions between latitudes 70 degrees wherein rectangular velocity component V N , is applied to terminal 112, over switch SP 1  in position S to the input of latitude servomechanism 200 (Fig. 2b not shown) of conventional form operating as a velocity or integrating servomechanism; the output shaft 208 making 1 revolution for <SP>1</SP>/ 600  minute of latitude being geared to counter type latitude indicator 212 and output shaft 120 with a step down ratio of 12,000: 1. Component V E  on terminal 114 is applied over input resistor R 2  to modifying circuit 220 comprising an amplifier U 2  with cosine potentiometer feedback ovee R 1  adjusted in accordance with latitude by shaft 222 over gearing 223 from latitude output 120, to produce an output  VE sec L applied over switch SP 3  in position S to longitude servomechanism 202 (Fig. 2e not shown) similar to latitude servomechanism 200, whose input shaft 224 rotates once per <SP>1</SP>/ 150  minute of longitude, and is geared to drive counter type longitude indicator 228 and output shaft 122 at 3,000: 1 reduction to make 1 revolution per 20 minutes longitude. It is shown that where X and Y are orthogonal co-ordinates of vehicle position referred to a geographical pole as origin, in sterographic polar projection, where X, Y are the orthogonal co-ordinates of polar sterographic projection about Greenwich Meridian as Y axis; L is latitude, A is longitude and k is the chart constant. X and Y servomechanisms 204, 206 (Figs. 2c, 2d not shown) are slaved to the L, # servosystems 200, 202. Potentiometer R 4  driven by shaft 222 produces an output proportional to tan 90-L/2 which is fed over switch SP5 in position S to energize resolver R 5  in opposite polarities, and drive is applied over shaft 244 geared to longitude shaft 122 to make 1 revolution per 360 degrees longitude. The outputs over wipers 238, 240 represent equations (1) and (2) above, and are applied to summing amplifiers U 5 , U 6  over resistors R 6 , R 7 . The outputs are applied over S terminals of switches SP 6 , SP 7  and SP 8 , SP 9  respectively to X and Y servomechanisms 204, 206 operating as positional systems in the S switch position and as velocity systems in the P switch position; to produce the required X, Y co-ordinates according to the equations; which may be applied over shafts 136, 138 to utilization device 140 (Fig. 1). As the vehicle navigates into the polar region of latitude > 70 degrees, all the SP switches change over to the P position by energisation of coil 207 in response to a rotary voltage relay switch 248 operated by shaft 222. Velocity signals V N , V E  are applied in opposed polarities to energize resolvers R 11  and R 10 , having sin and cos sliders 250, 251 and 252, 253 driven by shaft 244 revolving once per 360 degrees change of longitude. The outputs of 251, 252 are summed over resistors R 13 , R 12  and amplifier U 11  while those of 250, 253 are summed over resistors R 14 , R 15  and amplifier U 12 ; both having feedback paths over cosine potentiometers R 16 , R 17  whose sliders are driven by shaft 222 in accordance with latitude, and further feedback paths are provided over resistors R 18 , R 19  to produce output signals given by differentiating equations 1 and 2 i.e. on leads 258, 260 applied to servosystems 204, 206 connected for velocity operation in the polar navigation condition (Figs. 2c, 2d not shown) yielding true output values of X, Y representing the vehicular position on a stereographic polar chart, since up to the time of switchover to polar navigation servomechanisms 204, 206 are slaved to servomechanisms 200, 202. Corresponding signals are applied to slave the latitude and longitude servosystems 200, 202 connected to operate positionally (Fig. 2b, 2e not shown) so that shafts 208, 224 are rotated in correspondence with the vehicular latitude and longitude. For this purpose, resolver R 5  is disconnected from slider 236 by switch SP5 and connected to the output of servosystem 204 for opposed energization with X signals while resolver R22 is connected to the output of servosystem 256 for opposed energization with Y signals, the resolvers being driven from shaft 244. Signals from sliders 238, 264 are summed over resistors R 6 , R 23  and amplifier U 5 , while potentials from sliders 240, 262 are summed similarly at R 7 , R 24  and amplifier U 6  to develop signals representing the transformation equations of vehicular position from rectangular to polar co-ordinates, viz. where X and Y are functions of L and # as given in equations and the polar system is defined by the tangent of half the co-latitude as the radius vector and the longitude as the vectorial angle with a base e.g. the Greenwich Meridian. The output from summation amplifier U 5  is applied over P positions of switches SP 6 , SP 1  to servomechanism 200 and a positional follow up signal of tan 90-L/2 is derived from potentiometer R 4  driven from shaft 222 for application to the input thereof. Similarly the output from summation amplifier U 6  is applied over P position of switches SP 8 , SP 3  and modifying circuit 272 to servomechanism 202; the circuit 272 comprising an amplifier U 14  with feedback potentiometer R 25  driven from shaft 222 to produce a signal proportional to exhibiting a constant sensitivity per degree of longitude, so that the servomechanism sensitivity is independent of longitude. Latitude and longitude servomechanisms 200, 202 thus follow X, Y servomechanisms 204, 206 during polar operation. Gear-boxes 210, 226 in the outputs of servosystems 200, 202 are variable by clutches operated from relay 207 to give ratios of 12,000:1 for sub polar operation and 20:1 for polar operation. Initial co-ordinates of vehicular position L 0 # 0  are set manually into the computer (Figs. 2b, 2e servosystems 200, 202 over changeover switches (not shown) disabling the normal servo operation, and simultaneously energising relay 207 to place the system in the polar mode of operation. The computing system may be arranged for A.C. operation, and minor modifications are set forth. The instantaneous vehicular latitude and longitude outputs L, # may operate plotting means and relative position computing means, and may also be utilized to supply compass error signals as functions of latitude and longitude to simulated polar gyro systems. Servomechanisms 200, 202 and associated variable gearing 210, 226 are each replaceable-by separate positional and velocity servosystems with outputs interconnected through fixed gears by a differential, the systems being switchably selected for the nonpolar and polar modes of navigation, (Figs. 3a, 3b not shown). Relative position computer. (Fig. 4). Input latitude and longitude channels respond to the rotation of latitude and longitude input shafts 120, 122 (Fig. 1), the shaft 120 being geared to encoder 402 expressing 180 degrees latitude divided into e.g. 512 zones each expressed by e.g. 9 digit binary code, and to a potentiometric transducer 404 whose range of variation corresponds to a digital change in the least significant digit of encoder 402 so that the digital code represents a coarse zon