Piezo robotic hand for motion manipulation from micro to macro

Abstract

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.

Fig. 1. Classifications and problems of the existing robotic hands, as well as the piezo robotic hand (PRH) inspired by in-hand motion manipulation.

a Classifications of typical robotic hands according to their structure features, driving principles, and transmission mechanisms. b Several typical problems of the existing robotic hands. c Our work to solve the problems of current robotic hands: a unique PRH inspired by in-hand manipulation of the human hand, which is available for motion manipulation with advantages of high adaptability, multi-DOF, high resolution, large load, and excellent electromagnetic compatibility.

Fig. 2. Structural configurations of the PRH and multi-dimensional motions of the piezo finger induced by deformations of the actuation part.

a Prototype and overall structure of the PRH. b Components of single piezo finger. c Deformations of the actuation part, including 2D lateral bending motions along the x-axis and y-axis, as well as 1D longitudinal extending motion along the z-axis. d Photos of the actuation part and piezo fingers. e Multi-dimensional motions of the piezo fingers, which are induced by the deformations of the actuation part. f Simulated multi-dimensional motions of the piezo finger by the finite-element method. g Influences of the number of piezo rings and exciting voltage on the response displacement.

Fig. 3. Several typical functionalized hand gestures of the PRH, which are planned to manipulate various objects.

a and b show gesture 1 and gesture 2, in which all fingers bend along positive and negative directions of the X-axis, respectively. c and d indicate gestures 3 and 4, in which all fingers bend along positive and negative directions of the Y-axis, respectively. e and f represent gestures 5 and 6, in which all fingers bend along the clockwise and anticlockwise tangent direction of the circumscribed circle of their distribution position in the top view, respectively. g shows gesture 7 for grasping operation. h Micro photos of four fingertips.

Fig. 4. Mechanisms and characteristics of manipulating a plate.

a Diagram of the periodical saw-tooth exciting signal. b–d Processes of manipulating plate to produce one displacement step in a single period: linear motion along X_p axis (labeled as LX_p), linear motion along Y_p axis (labeled as LY_p) and rotary motion around the Z_p axis (labeled as RZ_p). e–g Motion of the plate under different exciting voltages: bidirectional motions of LX_p, LY_p, and RZ_p DOFs, respectively. h Relationship between the manipulating velocity and the exciting voltage. i–k Motion of the plate under different frequencies: bidirectional motions of LX_p, LY_p, and RZ_p DOFs, respectively. l Relationship between the manipulating velocity and the exciting frequency. m Photos of manipulating the plate with carrying loads of 0, 7.38, and 14.76 kg. n Motion manipulation characteristics carrying different loads: the manipulating velocity versus carrying the load. o–q Manipulating velocity versus the exciting voltage of LX_p, LY_p, and RZ_p DOFs carrying loads of 0, 7.38, and 14.76 kg, respectively. Note: the error bars represent the measurement deviation of five repeated tests.

Fig. 5. Manipulation experiments of various objects and promising application scenarios of our PRH.

a The selected ten typical manipulated objects. b Photos of manipulating three flatbed plates P₁–P₃. c Photos of manipulating three typical cylindrical objects C₁–C₃. d Photos of manipulating four typical spherical objects S₁–S₄. Note: the details about shapes, materials, and dimensions of these objects are listed in Supplementary Table 2. e Using the PRH to manipulate plate for constructing 2L + 1R micro/nano motion platform, which can serve for defect detection in semiconductor manufacturing and micro observation in biomedical fields. f Using the PRH to manipulate cylindrical objects for constructing 1L + 1R posture adjustment device, which can carry the imaging device to achieve focusing. g Using the PRH to manipulate spherical objects for constructing 3R motion scanning platform, which can carry the camera to achieve visual scanning. Note: the complete experimental records are presented in Supplementary Movie 8. h The packed PRH is stalled on a 6-DOF mechanical arm to extend manipulation DOFs and implement in-situ motion manipulation. i Diagram of the packaged PRH installing four levers and needles on the fingertips for grasping tasks. j Experimental setup for grasping a small sphere and gravel. k Video sequences for grasping small spheres and gravel from Supplementary Movie 10.

Fig. 6. Characteristic summary and comparison of the PRH.

a Characteristics of the PRH summarized from three aspects: (i) structures and principles; (ii) fundamental characteristics; (iii) manipulation characteristics. b Quantitative characteristic comparison of the PRH and other robotic hands. c Main advancements of this work compared with other robotic hands.