Multiple degrees of freedom (DOFs) motion manipulation of various objects is a crucial skill for robotic systems, which relies on various robotic hands. However, traditional robotic hands suffer from problems of low manipulation accuracy, poor electromagnetic compatibility and complex system due to limitations in structures, principles and transmissions. Here we present a direct-drive rigid piezo robotic hand (PRH) constructed on functional piezoelectric ceramic. Our PRH holds four piezo fingers and twelve motion DOFs. It achieves high adaptability motion manipulation of ten objects employing pre-planned functionalized hand gestures, manipulating plates to achieve 2L (linear) and 1R (rotary) motions, cylindrical objects to generate 1L and 1R motions and spherical objects to produce 3R motions. It holds promising prospects in constructing multi-DOF ultra-precision manipulation devices, and an integrated system of our PRH is developed to implement several applications. This work provides a new direction to develop robotic hand for multi-DOF motion manipulation from micro scale to macro scale.
Stick-slip rotary piezoelectric actuators (SRPAs) are commonly used nowadays. However, most of them achieve high velocity by high exciting frequency, which causes the problems of wide power-source passband requirement and the wear of actuators. Moreover, their further applications are limited, due to the poor motion stability caused by the backward motion. To solve the problems, the stick-slip process is analyzed with kinematics, indicating that the large step contributes greatly to SRPAs for achieving high velocity under low operating frequency and backward motion elimination. Then a large-step SRPA is proposed, fabricated, and tested. The experiments show that under the sawtooth signal with 100 V and 400 Hz, the prototype can reach a maximum velocity of 1.854 rad/s, benefiting from the large step (above 4.636 mrad). While other works require the exciting frequency of several kilohertz to reach the same level of velocity. Additionally, by increasing the step, the backward ratio decreases from 14.43% to 8.89% at the frequency of 1 Hz, and the minimum no-backward frequency decreases from 120 Hz to 60 Hz. The results indicate the effectiveness of the large step for solving the problems, which is significant for the design of SRPA.
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