An articulated finger driven by single-mode piezoelectric actuator for compact and high-precision robot hand

In this paper, a novel finger driven by single-mode piezoelectric actuator for a compact and high-precision robot hand is proposed. Three piezoelectric actuators are articulated by two sets of connecting elements to form the finger. The finger utilizes a single model of the piezoelectric actuator to generate friction force to drive the joint. Without the difficulty to adjust for the coincidence of modal frequencies, the design of the piezoelectric actuator has fewer restrictions on size and structure; thus, the finger has a compact structure. The bidirectional motion of the joint is achieved by changing the temporal phase difference of two excitation signals applied on the two adjacent piezoelectric actuators. In addition, due to the characteristics of piezoelectric drive, such as power cut self-locking and quick response, the finger has a high resolution to realize micromanipulation for high precise movement. In our design, the first order longitudinal vibration mode of the piezoelectric actuator is used to generate the friction force. By using a finite element model, the geometric parameters of the piezoelectric actuator are obtained. A prototype of the finger is fabricated and experimentally investigated, the size (111 × 10 × 10 mm) is approximately 1.5 times that of a human middle finger, and the weight is 0.11 kg. The experimental results indicate that the angular speed of the prototype reaches 6.6 rad/s, the resolution is 20 mrad, and the startup and shutdown response times are 26 ms and 7 ms under a voltage of 400 V_pp, respectively. The fingertip force is 0.27 N under a voltage of 400 V_pp. The proposed finger has a compact size and simple structure with a high resolution (20 mrad).