GB1413045A - Computing device for interpolation - Google Patents

Abstract

1413045 Interpolating HITACHI Ltd 21 Feb 1973 [21 Feb 1972] 8498/73 Heading G4A In an interpolation device where the values of a function Z=f(x, y) at predetermined points (x n , y m ) are stored in a memory 12 (Fig. 5) at addresses given by the values x n , y m , the value z p =f(x p , y p ) at an intermediary point in the area banded by stored points (x i , y i ), (x i , y j ), (x j , y i ) and x j , y i ) is determined by entering the values x p , y p into counters 10, 11 the upper orders of which used to address the memory and incrementing the lower orders of counter 11 to their full count each time counter 10 is incremented until a full count has been-applied to the lower orders of counter 10. The memory being addressed at each incremental pulse. Each time the memory 12 is addressed by the counters, adder circuit 14 adds the read-out values of z (which are appropriately sealed) to the sum of the previously read-out values held in register 15 so that at the end,of the read out register 15 holds the value z p . With the point (x p , y p ) having the position relative to the boundary points shown in Fig. 4 the first pulse applied to-counter 11 results in the value z ii =f(x i , y i ) being read from memory 12 into register 13 for addition. At the sixth pulse the upper orders of counter 11 are stepped to a count of y j so that the value z ij =f(x i , y j ) is read out until after n pulses counter 8, simultaneously incremented with counter 11, reaches its full count to increment counter 10 and reverse the direction of count in counter 11. This process is repeated until the memory has been addressed once for each square in the area bounded by the points A2; A4; A6; (x p , y p ), so that the values z ii , z ij , z ji and z jj are added for each square in the areas bounded by (x j , y p ), (x j , y j ), (x p , y j ), (x p , y p ); (x j , y j ), A5, A6, (x p , y j ); A2, A3, (x j , y j ), (x j , y p ); A3, A4, A5 (x j , y j ) respectively. The apparatus may be used for calculation of the ignition advance angle in an internal combustion engine in which case the variables x, y are derived in digital form from sensors 1, 2 and represent the speed of rotation of the engine and the vacuum pressure in the intake manifold. The value zp is compared with the instantaneous position of the engine piston held in a register 17, a comparator 16 producing an output at equality to trigger the ignition. It may also be used to control the fuel injection valve of a fuel injection internal combustion engine. In a modification (Fig. 7, not shown) the memory (12) is addressed from a counter (11) in combination with one of two counters (10, 10<SP>1</SP>) receiving inputs-representing the partial vacuum in the intake manifold of an engine from a sensor (1) or the throttle opening of an engine from a second sensor (1<SP>1</SP>). Counter (11) is controlled from a sensor (2) measuring the rotational speed of the engine so that in one cycle the quantity of fuel to be injected is measured and in the next cycle the ignition advance angle is calculated.