Development of a novel variable-curvature soft gripper used for orientating broccoli in the trimming line

Abstract

Orientating the broccoli plays an important part in the trimming line, which helps reduce the redundant stalk length and provides accurate throughput data for sale. However, this work is still manual with high labor intensity and low work efficiency, and current grippers show limitations in replacing manual operations, which need the ability to self-adaptively grasp broccoli without damage and guide them upright. This study presented a novel pneumatic variable-curvature soft gripper (VCSG) for orientating broccoli, which mainly comprised three soft variable-curvature fiber-reinforced bending actuators (VCFRBAs). The VCFRBAs can generate additional lifting forces to help guide the broccoli upright, thus orientating the broccoli. A design concept was built for the VCFRBA, and an analytical model and finite element method (FEM) were proposed to evaluate the bending deformation of VCFRBA, achieving a good match with a root mean squared error of below 5.8°. Step response tests of VCFRBA showed a response time of 0.35 s, hysteresis tests demonstrated a hysteresis error of less than 10 %, and durability tests in 5,000 cycles showed two error bands of both less than 5 %, indicating a fast response, good repeatability, and good durability, respectively. Single actuator force experiments demonstrated the VCFRBA can generate a clamping force of 1.13 N with an additional lifting force of 1.38 N when grasping under the pressure of 0.2 MPa. Furthermore, a maximum pull-off force of 35.06 N was measured for the VCSG at this pressure. Results of grasping experiments showed a 100 % success rate without damage when the VCSG grasped broccoli positioned upright, and broccoli can still be securely and self-adaptively grasped and guided upright when grasping them inclinedly. Further orientating tests suggested that the VCSG had a good performance with an 85 % success rate. These results demonstrate that the proposed VCSG has a good ability to orientate the broccoli self-adaptively without complex operations. This study showcases a novel VCSG, providing a unique solution to orientating broccoli in the trimming line.