| The processing requirements of micro array structure and freeform surface put forward higher requirements for fast tool servo(FTS)technology.Due to the limitation of the motion mode and structural form of the traditional single piezoelectric ceramic FTS,the stroke and working frequency cannot meet the application requirements at the same time.In this paper,a novel coaxial double piezoelectric ceramics opposite driving FTS is proposed to overcome the limitations of traditional single piezoelectric ceramic FTS.Through the research on the principle analysis,structural design,servo control,performance test and machining experiment of the new double piezoelectric ceramics FTS system,the key technologies,such as the design of flexible hinges with small feed stiffness and large off-axis stiffness,the collaborative servo control of double piezoelectric ceramics,and the processing of typical micro array structure,is developed.The high performance FTS device is developed to provide effective technical support for the processing of micro array structure and freeform surface.Main research contents :(1)Structure design and analysis of coaxial double piezoelectric ceramics FTS.The working principle and motion model of the new FTS are studied.The key technology of small feed stiffness and large off-axis stiffness flexible hinge design is broken through,and the stiffness calculation model of flexible hinge is established.FTS mechanical structure with feed stiffness less than 3N/μm and off-axis stiffness greater than 88N/μm is developed.(2)Servo control of coaxial double piezoelectric ceramics FTS.The nonlinear effect,amplitude attenuation,phase delay and cooperative motion of FTS servo control of coaxial double piezoelectric ceramics are analyzed.The modified Bouc-Wen model,modified Prandtl-Ishlinskii model,rate-dependent hysteresis model and modified particle swarm optimization algorithm are studied.PID servo control method based on modified Prandtl-Ishlinskii inverse model is used to compensate the hysteresis nonlinear error of piezoelectric ceramics,and the relative hysteresis error is reduced to 0.1%.The amplitude attenuation and phase delay of piezoelectric ceramics are compensated by zero phase controller.The cross-coupling controller is used to suppress the synchronization error of the double piezoelectric ceramics.Finally,with the composite control algorithm,the error of the double piezoelectric ceramic cooperative motion(frequency 1～200Hz,amplitude 15μm)is less than 5.093 %.(3)Performance evaluation of coaxial double piezoelectric ceramics FTS.The natural frequency and linearity test scheme of coaxial double piezoelectric ceramic FTS are designed.The first-order natural frequency of the new FTS is more than 850 Hz and the linearity is less than 0.436%.The experiment of machining typical micro array structure by the new FTS is completed,in which the roughness Ra of sine ray and two-dimensional sine wave surface are 6.83 nm and 7.49 nm,and the PV value error of the actual measurement surface are 4.91% and 3.95%,The obtained results verifies the processing ability of the new FTS system. |
