Optimization design of compliant constant-force mechanism for apple picking actuator

Abstract

Low-destructive picking method is part of the key technologies for fruit-picking robots. To reduce the picking-induced fruit bruising during the clamping process, this paper realizes the constant output force required for low-destructive fruit clamping by setting the compliant mechanism on the end-effector and optimizing the mechanical characteristics of the compliant mechanism. Firstly, based on the shape function, the nonlinear ordinary differential equations of buckling deformation of compliant beams are established with boundary conditions. Secondly, the above boundary value problem is re-described as the initial value problem by using the shooting method, and the initial value optimization solution is combined with the genetic algorithm. Then, the sequence quadratic programming method is implemented to optimize the shape function of the beam to achieve constant force output within a certain deformation range. Taking apple picking as an example, the initial shape parameters of the compliant mechanism are set and the constant clamping force is obtained at about 7.9N. The above method is verified by the nonlinear finite element simulation, the force-displacement experiment and the apple clamping test. The compliant mechanism can provide the required grasping force and the successful grasping rate is about 95.3%. By properly adjusting the parameters of the compliant beam, the algorithm can also meet the requirements of constant force clamping for different types of fruit. The research provides a reference for the effective application of the compliant mechanism in low-destructive fruit-picking.