Design of berry compliant clamping mechanism with variable stiffness based on gradient lattice structure

Objective According to the clamping performance requirements of berries in picking, sorting and other links, to apply the berry clamping mechanism simultaneously driven with high stiffness and clamped nondestructively with low stiffness at the end of the robot, and effectively promote the application of agricultural robot in the field of berry production.

Method Taking small tomato clamping mechanism as an example, a design method of berry compliant clamping mechanism with variable stiffness was proposed based on gradient lattice structure by introducing the theory of multi-level topology optimization. And an optimization model of this method was developed, which realized the design of an integrated compliant clamping mechanism that constructed from single material and had gradient distribution of stiffness.

Result A prototype of compliant clamping mechanism weighing about 45 g was fabricated by Polyjet additive manufacturing technology. The results of performance test of clamping Maoming ‘Millennium’ small tomatoes showed that when the driving load at the input end of the sample of the clamping mechanism was 11.00−14.56 N, the compression ratio of the small tomato was 0.90%−1.91%, and the mechanical damage degree was 0.

Conclusion The optimized compliant clamping mechanism with variable stiffness can effectively grip the fragile berries nearly nondestructively, and provide a feasible method for the design of automatic clamping equipment for berry picking and sorting.