Adaptive Fault Tolerant Control For Direct Drive NC Rotary Table System With Actuator Saturation

Numerical control machine technology is a typical representative in the field of industrial process. However, the traditional NC rotary table cannot provide the basic conditions for introducing new technology because of the structural defects in the traditional NC rotary table. The direct drive NC table technology reduces transmission links to zero from the motor to the rotary table, which provides favorable conditions for implementing a high performance control method in NC rotary table systems. As an ideal driving mode, direct drive technology has been applied into the field of multi-axis CNC machine tools. However, the simplified structure of the direct drive NC rotary table provides the hardware conditions for the ultra precision machining. In practice, the external disturbance, the system malfunction and the saturation problem have a serious impact on the normal operation of NC rotary table systems. Therefore, the direct drive NC rotary table proposes higher requirements on the control ability of controller.In this paper, the NC rotary table system is considered as the research object and the permanent magnet torque motor is used to drive the NC rotary table directly. According to the structure characteristics of the direct drive NC rotary table, the mathematical model of the NC rotary table system is established. In order to improve the fault tolerance ability and anti disturbance ability of the NC rotary table in the case of actuator saturation, adaptive fault-tolerant H_? controllers are designed by using linear matrix inequality theory and fault tolerant control technology based on adaptive method in two cases of state feedback and dynamic output feedback, respectively. Trough the way of estimating the failure rate r of actuator online, the adaptive fault-tolerant H_? controller gain is adjusted in real time. The NC rotary table system fault is compensated actively and the stability of system is improved so as to ensure that the system still has good ability of disturbance tolerance when faults occur.The NC rotary table system is simulated by MATLAB. The performance indexes of the NC rotary table system are compared under the fixed gain control strategy and the adaptive fault-tolerant H_? control strategy. The results show that the NC rotary table system with external disturbances is more stable for adaptive fault-tolerant H_? control strategy. The following conclusion is obtained: the robustness of the direct drive NC rotary table system is more robust when adaptive fault-tolerant H_? controller is used. The control method is suitable for the direct drive system.