A Computer‐controlled Profile Milling Machine: A Description of the E.M.I. System of Electronic Machine Tool Control

ONE of the first computer‐controlled machine tools to be put to work on a production basis was recently demonstrated at the Norwich works of Laurence Scott & Electromotors Ltd. The tool is a precision copy miller manufactured by Research Engineers Ltd., on which the master cam has been replaced by a control unit designed and made by E.M.I. Electronics Ltd., Hayes, Middlesex. On the original machine the workpiece and master cam are carried on two turntables mounted on one carriage which slides on the machine bed in a direction parallel to the line joining the axes of the turntables. The turntables rotate in synchronism and the master cam bears upon a cam follower, which actuates a servo‐mechanism to move the carriage in such a way that the extension of the plunger carrying the follower roller remains constant. This is achieved by the plunger turning a mirror so that a light source is reflected on to one of two photo‐electric cells. Each cell operates a relay which starts the motor driving the carriage feed screw in such a direction as to bring the light beam back between the cells. Thus the reflected light spot is kept oscillating between the two cells, the proportions of the mirror linkage being such that the corresponding carriage movements are within the required accuracy, in this case ±·0002 in.