GB1240362A - Digital plotter - Google Patents

Abstract

1,240,362. Graphical plotter. ELECTRONICS ASSOCIATES Inc. 29 April, 1969 [30 April, 1968; 3 Dec., 1968], No. 21733/69. Heading G4H. In graphical plotting apparatus, with coefficients x 0 , y 0 ; x 1 , y 1 ; x 2 , y 2 ... through which the pen is to pass an interpolation curve fitting technique is used, the path to be followed by the pen being defined by with the constants being found by applying a set of constraints on the characteristic of the curve. The optimum command velocity for any segment is found by determining the curvature of the end points of the segment, selecting the larger k max and choosing a velocity to plot the calculated maximum curvature. The distance necessary to get from zero to maximum velocity and vice versa is obtained from the equation length v 0 = 0 and v = v max . A dummy data point is created such that the length of curve from the dummy position to the required stop position is equal to the stop length. A general purpose computer generates the values a x a y . . . c y , z s , v c and they are fed either directly or by way of a magnetic tape stage to the control system (Figs. 3, 4). In operation a binary coded representation of V c is fed to a digital differential analyser 3 together with a signal representing the actual plotter speed v to feed a signal v - v c to detector 19 from which an acceleration or deceleration signal is derived. A digital differential analyser 1 receives positive or negative clock pulses, in accordance with whether acceleration or deceleration is required, and the difference signal v - v c to feed a signal dv to a digital differential analyser 2. This sums the increments dv to generate the actual velocity signal v for comparison with the command velocity and also generates a signal dz = #dvdt. This is fed to a first series of digital differential analysers 24, 25, 26 which also receive the constants a x , b x , c x to generate a signal The incremental signals dx are summed in a store 31 and compared with the actual x position to control the motor 37 positioning the x plotter. Similar circuitry also controls the y plotter. A counter 17 is preset to the value of the curve length z x and is decremented by the signal delta z.