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Friction is an important parameter to ensure the stable working of inertial actuators. It is usually regulated by adjusting the normal pressure, which will inevitably lead to wear due to the solid-to-solid contact and consequently a degradation of the output performance. This paper proposes to generate friction with magnetorheological fluid (MRF) whose shearing stress could be adjusted by the magnetic induction from an electromagnet. An inertial actuator prototype with a two fixed-end beam asymmetric structure and a MRF friction regulation unit is fabricated to verify the feasibility of electromagnet controlled MRF in friction regulation. COMSOL and MATLAB/Simulink are used for modal analysis and dynamic analysis of the proposed actuator. Experiments are conducted to evaluate the performance of the actuator. Experiment data show that the step displacement of the actuator is dramatically affected by the magnetic induction and reaches a peak value at 8.4 mT. Under the square wave excitation signal of 25 V, 7 Hz, the minimum step displacement is 0.1 µm with a rollback rate of 0.92 at a magnetic field of 19.5 mT, the maximum step displacement is 2.53 µm with a rollback rate of 0 at a magnetic field of 8.4 mT.

A walking-type piezoelectric actuator based on the parasitic motion of flexure mechanisms is proposed in this paper. With the help of the parasitic motion of the asymmetrical flexure mechanism, the conventional walking-type piezoelectric actuator with four piezoelectric elements and four input signals is simplified to be with only two piezoelectric elements with two input signals. The finite element method has been utilized to quantitatively investigate the parasitic motion of the asymmetrical flexure mechanism. A series of experiments have been carried out to investigate the working performance (stepping performance, speed performance, and load performance) of the proposed walking-type piezoelectric actuator. The results indicate that the minimum stepping displacement is L = 0.18 µm, under the condition of U = 30 V and f = 1 Hz. In addition, the maximum motion speed is V s = 39.78 µm/s in the case that U = 100 V and f = 20 Hz. This paper confirms the feasibility of the utilization of parasitic motion in the simplification and design of the walking-type piezoelectric actuators. INDEX TERMS Piezoelectric, actuator, walking type, flexure hinge, nano-positioning.

A piezoelectric inertial actuator for magnetorheological fluid (MRF) control using permanent magnet is proposed in this paper. The stable linear motion of the actuator with high controllability is obtained by integrating the piezoelectric vibrator and MRF control structures. The magnetic field distribution between yoke teeth is analyzed by finite element analysis. Laser displacement measuring and scanning vibrometer systems are built to test the output performance of the proposed actuator. The experimental results show that the actuator with MRF control structure has good controllability, with a minimum step displacement of 0.0204 µm and maximum moving speed and a load of 31.15 µm/s and 800 g, respectively.The experiments confirm that the MRF control structure can be used to control the piezoelectric actuator with high controllability and increase the stability of output displacement.