The development and design of electrical control-gear for machine tools

The paper deals with some of the technical considerations of the design and application of control gear to machine tools. The application of electrical control to machine tools is compared with other orthodox types of control gear, and the choice of electrical control gear is discussed with particular reference to the frequency of operation. Design of components (in particular, contactor design) is given due consideration, and the paper also shows how design may be based on results obtained from experimental work and past experience. After a note on complex schemes of control, the need for incorporating reliable interlocks is stressed, especially electrical interlocks involving auxiliary switches. Thesupply voltage is shown to have its importance, and low-voltage control circuits are compared withthose operating from line voltage. Speed control is next treated, with some regard to the application of electronics. The importance of motor protection is stressed, with particular reference to protection by h.r.c. fuses. Electricbraking, especially the d.c. injection method, is dealt with in some detail. Types of timing devices are described, and the electrical timer is compared with mechanical and thermal types. After discussing d.c. supply and its advantages over a.c. supply in connection with motor speed control, future developments in design of control gear and its application are reviewed.