【正文】 of spindle speeds, cutting tools, and other functions. 黃石理工學(xué)院 畢業(yè)設(shè)計（論文）外文文獻(xiàn)翻譯 5 The machine control unit (MCU) consists of the electronics and control hardware that reads and interprets the program of instructions and convert it into mechanical actions of the machine tool or other processing equipment. The processing equipment is the ponent that performs metal process. In the most mon example of numerical control, it is used to perform machining operations. The processing equipment consists of the workable and spindle as well as the motors and controls needed to drive them. Types of NC There are two basic types of numerical control systems: point to point and contouring. Point to point control system, also called positioning, are simpler than contouring control system. Its primary purpose is to move a tool or workpiece from one programmed point to another. Usually the machine function, such as a drilling operation, is also activated at each point by mand from the NC program. Point to point system are suitable for hole machining operations such as drilling, countersinking, counterboring, reaming, boring and tapping. Hole punching machines, spotwelding machines, and assembly machines also use point to point systems. Contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different velocities. Because the tool cuts as it travels along a prescribed path, accurate control and synchronization of velocities and movements are important. The contouring system is used on lathes, milling machines, grinders, welding machinery, and machining centers. Movement along the path, or interpolation, occurs incrementally, by one of several basic methods. There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a contouring type NC system. They include linear interpolation, circula