Investigation of mechanical and electrical characteristics of selfsensing pneumatic torsional actuators

Soft pneumatic actuators are one of the most promising actuation for soft robots,and great achievements have been obtained.But it remains challenging to endow sensing capabilities to pneumatic actuators,especially for the sensing ability originating directly from the actuator architecture.Herein,a self-sensing pneumatic torsional actuator(SPTA)is designed based on the electromagnetic induction effect and magnetically responsive materials.The SPTA can generate feedback voltage and current with the deformation,in which the sensing function comes from its inherent structure.To investigate the mechanical and electrical characteristics,an experimental platform and a finite element model are established,respectively.We find that the torsion angle and output torque increase in nonlinear with the actuating pressure.The maximum torsion angle is 66.35°,which is 84.34%of that for the actuator fabricated by pure rubber.The maximum output torque(24.9 N mm)improves by 23.19%compared with the actuator made by pure rubber.As regards the electrical characteristics,the maximum feedback voltage and current are 2.90μV and 29.50 nA when the SPTA is actuated by a pressure of−40 kPa.We also demonstrate that the relationship between the torsion angle and the magnetic flux change is approximately linear.Finally,the number of turns of wires,magnetic powders contents,and magnetic direction on the feedback voltage and current are studied.Results show that the feedback voltage and current can be enhanced by increasing the number of turns and magnetic powders contents.We envision that the SPTA would be promising for soft robots to realize their accuracy control and intelligentization.

Piezoelectric d_(15) shear-response-based torsion actuation mechanism:An exact 3D Saint-Venant type solution

This paper is concerned with the detailed analysis of the behavior of a piezoceramic bi-morph torsion actuator using the d_(15)-effect.The bi-morph actuator is made of two oppositely polarized adjacent piezoceramic prismatic beams.The mathematical analysis is based on the Saint-Venant torsion theory;a formulation of the electromechanically coupled problem in terms of a stress function and of the electric potential is derived,which represents an exact solution of a specific three-dimensional problem;in particular,for the case when the axial stress and the axial component of the electric displacement vector are independent of the axial coordinate.The resulting boundary-value problem in the cross-section is solved using the method of finite differences.Solutions for the actuated rate of twist are presented and compared to three-dimensional electromechanically coupled finite element solutions using ABAQUS®for the case of a cantilevered bi-morph actuator.A very good agreement is found.

Piezoelectric d_(15) shear response-based torsion actuation mechanism:an experimental benchmark and its 3D finite element simulation

An experimental benchmark is proposed for piezoelectric,direct-torsion actuation using mono-morph piezoceramic d_(15)shear patches.This is reached by designing and assembling an adaptive plate having two identical composite faces sandwiching a core made of connected six oppositely polarized(OP)piezoceramic d15 shear patches along the length.An electronic speckle pattern interferometry system was used to measure the static tip deflection of the adaptive sandwich composite plate that was mounted in a cantilever configuration and actuated in torsion by progressively applied voltages on the piezoceramic shear core electroded major surfaces.Then,the effective rate of twist was post-processed and proposed as an evaluation criterion for smart composites under piezoelectric torsion actuation.For verification of the experimental results,the proposed experimental benchmark was simulated using three-dimensional piezoelectric finite elements(FE)within ABAQUS®commercial software.The comparison of the obtained experimental and simulation results showed reasonable agreement,but the slight nonlinear experimental response was not confirmed by the linear FE analysis.The experimentally proved torsion actuation mechanism,produced by OP piezoceramic d15 shear patches,can be applied actively to prevent torsion in many applications,such as in wind turbines,helicopter blades,robot arms,flexible space structures,etc.