Intelligent Control of the Linear Motor Direct Drive Feed System for CNC Machine Tools

The linear feed system directly driven by a linear motor is more and more widely used in high speed CNC machine tools. In this linear ¿direct drive¿ feed system, all mechanical transmission elements are eliminated. The linear motor¿s primary and secondary parts are assembled into the worktable and the machine bed respectively to directly drive the worktable. Compared with traditional ball screw transmission system, the direct drive feed system has compact structure, high positioning precision, excellent acceleration and deceleration performance, and wide speed range. It also has no transmission error and reverse backlash. At the same time, simplified mechanical structure is very suitable for close-loop control. However, as a result of the linear motor mounted into the structure of machining tool feed system, outside disturbances, such as worktable inertia, variety of moving mass and cutting force, will affect system¿s performance dramatically. In this paper, a typical structure of a linear direct drive feed system is introduced. The model of the linear direct drive feed system is established. An intelligent solution to solve the problem caused by variety of moving mass is presented. In this intelligent control system, a dynamic mass identifier is designed to identify the variety of dynamic moving mass, and a mass compensator is connected with the system to optimize the system¿s performance online according to the identified mass disturbance. The effect of online mass identifier and compensator on the direct drive feed system is simulated. Experiment is performed and measured results shows the mass identifier and compensator are very effective.