Researches On Linear Piezoelectric Inchworm Motor Based On Triangle Displacement Amplifier

Piezoelectric inchworm motor is widely used in the field of micro-driving platform and scanning electron microscope(SEM) because of high force, low s peed and high precision. With rapid development of spaceflight project, the linear and low speed driver without electromagnetic interference is demanded in some aerocrafts. Inchworm motor could satisfy the working condition. For now most of piezoelectric inchworm motors need electric energy for load position. In addition, most driving power supplies are large and heavy. Therefore the application of piezoelectric inchworm motor is limited in aerospace craft. For reducing the weight and electric energy, researches on inchworm motor self-locking without electric energy and its special driving power supply have great value for aerospace craft.Based on the driving principle of inchworm motor, a new self-locking piezoelectric inchworm motor without electric energy and its design principle are proposed. The working principle of the motor is introduced and its configuration is designed. The inchworm motor is comprised of driving part, clamping part and guide. In order to amplify the displacement of clamping part and enhance the extent of releasing guide, a triangle displacement amplifier configuration is applied. The resonance frequency models of driving part and clamping part are established based on the energy method. In order to establish the relationship between driving part(or clamping part) and PZT stack, the PZT stack is assumed to be an active spring. It shows that the respond speed of driving process is higher than that of resuming process.The stiffness and natural frequencies of driving part and clamping part are calculated by mathematical models and FEM(Finite Element Model) in different configuration parameters respectively. The application scopes of mathematical models and the deviations between the FEM results and analytic calculations have been analysed. A designing process of the inchworm motor is proposed according to design principle. The configuration parameters of prototype are calculated by mathematical models. Then the prototype has been manufactured. According to the configuration parameters, the relationship between deformation and preload is concluded by FEM. The displacement of clamping part influenced by stiffness equilibrium is simulated by FEM. A structure of stiffness equilibrium has been proposed and calculated.A special driving power supply for inchworm motor including flyback boost circuit, signal generation circuit and half-bridge chopping circuit has is designed and manufactured based on the working principle and control strategy of inchworm motor. The output voltage of flyback boost circuit can be adjusted continuously from low direct voltage to high direct voltage. The Micro Control System(MCS) is selected to generate control signal which drives the chopper circuit to chop the output voltage of flyback boost circuit. It boosts volt age together and chops the output voltage respectively. There is no power frequency transformer. The driving power supply has advantages of small volume, light weight, simplification and high efficiency.The testing system for performances of the prototype is established. The performances of the prototype have been tested in stiffness equilibrium and non-equilibrium condition including clamping force, no load characteristic a nd load characteristic. The clamping force and performance influenced by preloads have been revealed. When the stiffness of clamping part is not equal, the rotary displacement is increasing and the horizontal displacement is decreasing, the extent of releasing guide is low. It increases the residual clamping force between clamping part and guide. When the prototype is working, the performance of inchworm motor is poor because of the interference between the clamping parts by residual force. When the stiffness is equal, the horizontal displacement of the clamping part increases, the guide can be fully released and the performance of inchworm motor increases dramatically after equilibrium. The maximum velocity and driving force of the inchworm motor are 1.49 mm/s and 7N respectively which satisfy the technical requirements of the aerocraft.