Research On Two-degree-of-freedom Linear Motion Platform Actuated By Ultrasonic Motor And Its Driving Control System

Speed control of linear motion platforms is needed in many cases.Among many driving methods of the linear motion platform,the linear ultras onic motor has inherent advantages in some applications due to its high torque density,self-locking and non-electromagnetic interference.In this work,a set of two-degree-of-freedom(two-DOF)linear motion platform actuated by ultrasonic motor and its drive and control system were developed,and the experimental research on the closed loop control of the velocity of the motion platform was carried out.A two-DOF linear motion platform was designed and fabricated.According to the requirement of the velocity control of the two-DOF linear motion platform,the ultrasonic motor operating in bending hybrid modes was selected as the actuator for the motion platform.On the basis of an existing ultrasonic motor operating in bending hybrid modes,the end cap of it was improved so as to apply a fixed constraint to the motor better.The consistency of the resonance frequencies of working modes was verified by finite element modal analysis.Two ultrasonic motors were fabricated,and their vibration modes and impedance characteristics were tested.With the impedance parameters,inductances for impedance matching were calculated.The impedance matching effect was verified by an experiment,which was used as a basis for power supply design.According to the needs of the velocity control of the motion platform,the input and output performance requirements of the ultrasonic power supply were clarified,and the design task of the ultrasonic power supply was analyzed and the realization scheme of each part was determined.Th en,the DC voltage regulator circuit and the half-bridge inverter circuit,two main parts in the scheme,were designed and simulated.Aiming at the need of these two parts,a control circuit and a set of control program were designed.On this foundation,the power supply was fabricated and its output was tested.In order to verify that the power supply had the ability to output a square wave voltage with a sufficiently high amplitude or a low amplitude,a square wave with an amplitude of ±80 V and a square wave with amplitude of ±2 V were output.In addition,it showed that the power supply had enough output power to apply a voltage up to ±180 V in amplitude for the motor.Besides,the amplitude of output voltage was adjusted by the sine law of 10 Hz,which proved that it was able to be adjusted quickly.The velocity characteristics of the linear motion platform were tested.The relationship between the velocity of the paltform and the frequency of the excitation voltage was measured.For the velocity-frequency relationship,the frequency range corresponding to the relatively high velocity included modal frequencies in vibration modes test,which proved that the motors had good driving ability when working under the designed vibration mode.A frequency corresponding to the relatively high velocity was selected as the excitation voltage frequency in other velocity experiments.The velocity-voltage amplitude relationships of two degrees of freedom were measured.It is reasonable to control voltage amplitude in the closed-loop velocity control experiment,because both the two velocity-voltage amplitude curves showed a linear relationship within a wide range of voltage amplit ude.A closed-loop velocity control system for the two-degree-of-freedom linear motion platform was built.The velocity control of two degrees of freedom was studied through experiments.The research on velocity control focused on the step velocity control and the sinusoidal velocity control for low target velocity.In the velocity step control experiment with a target value of 50 mm/s,the velocity error was within ±2.5 mm/s,the risetime is 27 ms.When the target value was set as 5 mm/s,the velocity error was within ±1 mm/s after stabilization.In the sinusoidal velocity control experiment,the target velocity was set varying according to the sine rule of amplitude of ±20 mm/s and frequency of 0.5 Hz,1 Hz,1.5 Hz and 2 Hz in turn.The phase lags were 0.72°,1.44°,2.16° and 2.88°,respectively.And the amplitude errors were 2.03%,2.34%,2.5% and 2.19%,respectively.Velocity control experiments showed that the velocity control system for the proposed two-DOF platform had the capability of step and sinusoidal low target velocity control.