**6. Conclusions**

This chapter reviews the recent developments and achievements on PMP piezoelectric actuators. Combined with stepping motion principle, the PMP piezoelectric actuator acquires the capabilities on long working stroke and relatively large output capability, which breaks through the long-standing obstacles on micrometric working stroke of single piezoelectric element. In addition, some novel flexure-based hinge mechanisms are introduced to enhance the performances of the parasitic type motion, which not only extend the motion displacement in one step but also improve the motion stability in long working stroke. In addition, the underlying potential issues, i.e. backward motion and contact force, are investigated to understand the nature of the mechanism. By utilizing theoretical analysis and FE simulation, novel structures and driving strategies are applied to suppress the backward motion and improve the motion speed by adjusting interfacial interaction. These prototypes demonstrate better performances than previous parasitic type actuators, verifying the feasibility of the proposed methods. However, further studies should be conducted for improving the performances and overcoming current issues to satisfy the increasing demands for precision positioning and related applications.
