Patent GB-818861-A (GB)
Title: Improvements relating to contour machining systems
Inventor: BOND HAROLD WILLIAM
IPC: G05B19/4105
Filed: 1955-09-19
Abstract: 818,861. Electric analogue calculating systems; resistor networks. BRITISH THOMSON-HOUSTON CO. Ltd. Sept. 27, 1956 [Sept. 19, 1955; Oct. 18, 1955], Nos. 26745/55 and 29719/55. Class 37. Apparatus for producing a curve 2 (Fig. 1) conforming approximately with a series of discrete coplanar points a-f on a contour 1, the distance of each point from an axis y being defined by the magnitude of a voltage Va-Vf respectively, comprises a potentiometer P (Fig. 3) connected between voltage sources Va- Vf representing the points, the voltage between a common terminal T1 and the slider t as it moves between the tapping points on the potentiometer defining the straight line 2 joining adjacent points. A more accurate interpolation for a curve with not more than one inflection is produced by considering the points in groups of three, the voltage of the middle point being compared with the average voltage of the two outer points, and algebraically adding a non- linear fraction of the difference to the voltage at the slider t. As shown (Fig. 5) a linear interpolation between three points represented by voltages Vk, Vl, Vm as obtained by slider t. Equal resistors R1, R2 are also connected in series between voltages Vk, Vm, and the centre point, whose voltage is the average of Vk, Vm, is fed in opposition to the voltage Vl of the middle point to an amplifier AMP whose output is led through a high resistance R3 to the tap St of a potentiometer SP whose outer ends and centre point are short-circuited. The voltage at the tap St is algebraically added to that from the tap t of the linear interpolator to give at T1, T2 a non-linear interpolation which more closely approximates to the curve through the three points. Where the contour is defined by more than three points, these may be considered three at a time, the non-linear correction to the linear interpolating voltage being the algebraic sum of two non-linear voltages which are fractions of the non-linear voltages as derived in Fig. 5 from e.g. points a, b, c and b, c, d, the fractions varying as the potentiometer taps move from e.g. b to c. As shown (Fig. 6), the non-linear component for the first two sections of the contour, defined by voltages V1, V2, V3, is obtained from potentiometer SP1, and for the second and third sections, defined by voltages V2, V3, V4, is obtained from potentiometer SP2. For the section between V2, V3 a proportion, initially maximum, of the output from SP1 is tapped off potentiometer PP1, and added to a proportion, initially minimum of the output of SP2 tapped off potentiometer PP2. Sliders t, St1, St2, t1, t2 are mechanically linked to move together. When slider t reaches the tapping point V3, the switch Sw changes over from points 1, 2, 3 and 2, 3, 4 to 2, 3, 4 and 3, 4, 5, and so on. The invention is described as for use in copy milling or the like, and may be used for three-dimensional work. The voltages representing the distances of the points from the axis are obtained from an electrical feeler gauge associated with a profile cam, or directly set up in accordance with design data, and can be recorded on magnetic or punched tape for subsequent conversion to a voltage.