Controlling bending deformation of a shape memory alloy-based soft planar gripper to grip deformable objects

Abstract

Integrating flexible sensors into a soft finger is a common approach to control the deformation of the finger. However, adding sensors, especially sensors with a degree of stiffness, sacrifices the overall compliance of the finger structure and increases the complexity of fabrication and control. This study provides an alternative approach, without the need for integrated sensors, to control the deformation of a shape memory alloy (SMA)-based soft planar gripper for grasping deformable objects. The gripper consists of one soft finger which is an SMA-based hinge actuator capable of producing hinge-like bending deformation. The soft finger can automatically achieve the desired deformation by introducing a closed-loop PID control system. A camera as a vision sensor, instead of integrated flexible sensors, was used to detect the bending deformation of the soft finger in real-time. With the feedback from the camera, the PID controller was implemented in a microcontroller with designed external circuits, to enable the soft finger to reach any targeted bending angle within its deformation range, according to the size of the manipulated object. As a demonstration, the soft planar grippers with the desired deformation were eventually used to grip deformable objects, including flowers and a panicle. Without the need for material characterization and analytical models, the proposed method can also be extended to other soft planar grippers based on different actuation techniques.