Abstract:In order to achieve high efficiency and low damage recovery of white asparagus, an end effector was designed for selective harvesting of white asparagus, and a calculation method of driving force was derived. In order to drive the end effector to complete the action of earth, shear, clamping and pulling, the control parameters such as driving force, shear force and clamping force must be described quantitatively. Firstly, aiming at the problem of driving force, DEM simulation was used to establish the end-effector-soil discrete element model, the process of end-effector and soil was studied, and the driving force of end-effector was analyzed. Secondly, the shearing force of the end-effector was analyzed from the cutting of white asparagus and soil. The interaction model of white asparagus-end-effector-soil was established by universal testing machine and DEM. The shearing strength of white asparagus was determined by means of universal testing machine. And the shearing force of cutting the soil was determined from the DEM simulation, and the range of shearing force parameters of end-effector was determined. Thirdly, the process of the end-effector holding the white asparagus was simulated by the universal testing machine. And the compressive strength of white asparagus was determined, and the clamping force required by the end-effector in the soil was analyzed from the DEM simulation, and the range of the clamping force parameters of the end-effector was determined. Finally, the parameters range of the driving force FRT>195N, the shear force FJQ>1.8N, and the clamping force FJC<13N were determined. According to the parameters of the end-effector, a few combinations of parameters were selected for field harvesting test. The results showed that the recovery rate of white asparagus was more than 99% and the damage rate was less than 3% under the conditions with driving force of 200N, shear force of 2N and the parameters of clamping force of 11N. The damage rate was within acceptable range, which was accorded with the requirements of low damage of white asparagus, and provided theoretical support for selective harvesting of white asparagus and low damage recovery.
