A novel single-unit morphable piezoelectric stick-slip actuator with active contact regulation

Abstract Piezoelectric stick-slip actuators experience significant backward motion at low operating frequencies due to reduced inertial effects. Addressing this challenge through active contact force regulation, without introducing additional functional units or increasing power consumption, is crucial for practical positioning applications. This paper presents a compact, single-unit stick-slip actuator featuring a morphable end-effector driven by the sequential activation of a low-power macro fiber composite (MFC) and a piezoelectric stack. This concept enables active modulation of the end-effector and bearing interface, thereby altering the contact trajectory to suppress backward motion. A finite element model is developed to analyse the static and dynamic performance of the design and guide actuator development. Experimental results reveal a 3.9 times improvement in stepping angle at 1 Hz with MFC activation at an optimal phase shift of 165°. Moreover, under an increased preload of 2.2 N at 10 Hz, a 2.8 times enhancement of stepping angle is observed, highlighting its robustness under loading conditions. The actuator also demonstrates the capability to sustain vertical loads exceeding 3 kg, with a maximum torque capacity of 23.2 N·mm. Furthermore, the prototype achieved a maximum tested rotational speed of 160.4 mrad s ⁻¹ at 350 Hz and a resolution of 9.1 µ rad. Overall, this research introduces a new design paradigm for actively controlled, morphable piezoelectric stick-slip actuators, laying the foundation for compact, high-performance positioning systems with enhanced design flexibility.