RESUMEN
This paper investigates the pre-pressure's influence on the key performance of a traveling wave ultrasonic motor (TRUM) using simulations and experimental tests. An analytical model accompanied with power dissipation is built, and an electric cylinder is first adopted in regulating the pre-pressure rapidly, flexibly and accurately. Both results provide several new features for exploring the function of pre-pressure. It turns out that the proportion of driving zone within the contact region declines as the pre-pressure increases, while a lower power dissipation and slower temperature rise can be achieved when the driving zones and the braking zones are in balance. Moreover, the shrinking speed fluctuations with the increasing pre-pressures are verified by the periodic-varying axial pressure. Finally, stalling torque, maximum efficiency, temperature rise and speed variance are all integrated to form a novel optimization criterion, which achieves a slower temperature rise and lower stationary error between 260 and 320 N. The practical speed control errors demonstrate that the proportion of residual error declines from 2.88% to 0.75% when the pre-pressure is changed from 150 to 300 N, which serves as one of the pieces of evidence of the criterion's effectiveness.
RESUMEN
A ring-shaped traveling wave ultrasonic motor with a suspension stator is proposed for improving output power density. Piezoelectric stacks working in d33 mode are involved in the stator, whereas piezoelectric plates employed in classic ring-shaped traveling wave motors often work in d31 mode. Spring-mass systems are used to suspend the stator from the base that supports the motor and provide preload force. The volume of piezoelectric material and the power density of the motor can be easily increased through the suspension structure. Large vibration amplitude of the stator can be generated on the coupling surface. Simulink analysis and finite element analysis are conducted to verify the theory and determine the optimum parameters of the suspension stator with four piezoelectric stacks. The maximum free vibration amplitude of 4.25⯵m of the stator is observed, which is nearly 4.7 times of that without suspension. The prototype can work at a maximum no-load speed of 62â¯rpm and produce a stall torque of 49.5â¯mNâ¯m under a driving signal of 30â¯Vpp when the mass block is 0.30â¯g. Furthermore, the higher output power can be expected because more extra stacks can be added in this suspension structure.
RESUMEN
Elastic wave quality determines the operating performance of traveling wave ultrasonic motor (TWUM). The time-variant circumferential force from the shrink of piezoelectric ceramic is one of the factors that distort the elastic wave. The distorted waveshape deviates from the ideal standard sinusoidal fashion and affects the contact mechanics and driving performance. An analytical dynamic model of ring ultrasonic motor is developed. Based on this model, the piezoelectric parametric effects on the wave distortion and contact mechanics are examined. Multi-scale method is employed to obtain unstable regions and distorted wave response. The unstable region is verified by Floquét theory. Since the waveshape affects the contact mechanism, a contact model involving the distorted waveshape and normal stiffness of the contact layer is established. The contact model is solved by numerical calculation. The results verify that the deformation of the contact layer deviates from sinusoidal waveshape and the pressure distribution is changed, which influences the output characteristics directly. The surface speed within the contact region is averaged such that the rotor speed decreases for lower torque and increases for larger torque. The effects from different parametric strengths, excitation frequencies and pre-pressures on pressure distribution and torque-speed relation are compared.
RESUMEN
A simple control strategy with acceptable control performance can be a good choice for the mass production of ultrasonic motor control system. In this paper, through the theoretic and experimental analyses of typical control process, a simpler intelligent PID speed control strategy of TWUM is proposed, involving only two expert rules to adjust the PID control parameters based on the current status. Compared with the traditional PID controller, this design requires less calculation and more cheap chips which can be easily involved in online performance. Experiments with different load torques and voltage amplitudes show that the proposed controller can deal with the nonlinearity and load disturbance to maintain good control performance of TWUM.