Design and test of a contact mechanics model for papaya picking

Objective For stably picking papaya without damage.

Method A clamping plan of papaya was designed by means of three-finger clamping symmetrically and wringing, and the equilibrium equation of contact force was constructed. On the basis of force screw theory, the clamping stability was analyzed. The picking contact mechanics model was formulated, and a picking test for papaya was conducted.

Result There were no obvious deformation, crack or indentation on the surfaces of papaya samples. The pulp at the clamping position had no obvious color change or bruise after leaving for 24 hours at room temperature. The maximum clamping force was far less than the pressure limit on the transverse diameter of ripe papaya at the elastic deformation stage. Papaya mass and torque moment were correlated closely with transverse diameter, vertical diameter, stalk length and diameter of the twisted stalk. Mass multiple linear regression analysis achieved extremely significant level, and twist torque linear regression analysis reached significant level. There were good trend consistency between theoretical clamping forces and the measured clamping forces. The measured clamping forces were higher than theoretical values, but the maximum deviation was less than 20%.

Conclusion The picking scheme can stably clamp papaya without mechanical damage. The papaya picking contact mechanics model is correct and practical. The research can provide a basis for designing papaya picking end-effector and controlling clamping force.