Study On Apple Non-destructive Picking Based On Biological Yield Point

China is the country whose apple production is the largest in the world.At present,apple picking mainly depends on human labor,but the labor intensity and labor costs are getting higher and higher.With the continuous progress of science and technology and its close integration with agricultural production,the picking robot will become an important technology to replace manual operations as well improve efficiency and ensure picking quality.Achieving nondestructive fruit picking is a key link of the robotic picking operations,which directly affects picking efficiency and fruit quality.Therefore,research on the structure of the picking actuator and the corresponding control algorithm appears to be particularly important.First of all,this paper researched the mechanical properties of the fruit closely related to the picking.The horizontal and vertical apple compression experiments were carried out on the electronic universal testing machine,and a large amount of experimental data was obtained,then using the 3σcriterion to eliminate accidental errors.Afterwards,the SPSS software was applied to do correlation analysis,and found that apple varieties or size did not affect the mechanical properties,while the loading rate was significantly related to the mechanical properties of the fruit.By analyzing the data of apple compression experiments,it was found that when the apple reached the biological yield point,the external force was 7N,and the grip force was controlled to not exceed this threshold.Then,through the experiments of apple skin friction characteristics,the solid rubber was selected as the material attached to the surface of the picking manipulator.Afterwards,the apple finite element model was established,then comparing the simulation results with the apple compression data,which verified the accurateness of this model.At last,the nonlinear finite element simulation analyzed the deformation distribution and internal stress change of the contact model between the apple and fingers,and determined the curved finger as the style of the picking manipulator with a curvature radius of48 mm.Based on the simplified apple picking geometric model,rotation was used as the picking method and the maximum rotation angle of the picking robot was deduced.Besides,the FSR402 pressure sensor was used to monitor the pressure on the picking manipulator,then calibrating the pressure sensor by weight statically loading to obtain the corresponding relationship between pressure and voltage,and the sensor was placed in the center of the manipulator.The manipulator was controlled by steering gears,and the Arduino UNO control board was used as the control system to achieve apple picking.Through fifty apple picking experiments,it was found after statistics that the success rate was 92% and the average picking time was 8s,especially,the picking force was about 2N,which was less than fruit damage threshold,meaning it would not cause mechanical damage to the fruit and met the design requirements for nondestructive apple picking.