Design Of End-effector Of Litchi Picking Robot And Study On Derogative Strategy Of Picking-and-placing

Litchi is special fruit of southern China,its cultivated area and yield are ranked the top of the world.Picking is an important part of Litchi production.W hen using robot to pick litchi,it can improve picking efficiency and working conditions,also it can reduce picking cost.However,the litchi which is thin、fleshy and high water content is prone to mechanical damage after being subjected to external force.In order to develop the litchi picking robot and reduce the mechanical damage in picking-and-placing,this paper carries on the simulation optimization design of the picking robot’s end-effector of the important part.Also,the method of experiment and simulation are used to study the derogative strategy of litchi’s picking-and-placing.The following are the main completion of research work:1)Study on shear characteristics of litchi fruiting cane.The clamping-and-shearing experiment device is built near the actual picking condition and the shear experiment of different cutting edge forms and shear velocities of litchi fruiting cane are executed.The results indicated that the higher the shear velocity,the lower the peak shear force of litchi fruiting cane,the smoother the cross-section of the shear-cut mouth;the peak shear force and shearing power of the arc blade cutter are less than the straight blade cutter,and the cross-section of shear-cut mouth is smoother.Although,with the increase of shear velocity,the difference of the shear performance of 2 kinds of cutters on the litchi fruiting canes decrease;the straight blade cutter is more convenient than the arc blade cutter to reach the cutter shear point position.2)Study on design of litchi picking end-effector of clamping-and-shearing integration.Combining with the picking method of litchi fruit and the shear characteristics of the litchi fruiting cane,the global design of the clamping-and-shearing integrated litchi picking end-effector is carried out.It includes the detailed design of the constituent modules and control system.The structure of the shear module of the end-effector is analyzed and the shear mechanics model is constructed.Also,the force closure a nalysis of the design form of the clamping fingers is carry out and the mechanical model of the stable clamping force of litchi fruiting cane is constructed.3)Study on simulation optimization of end-effector and its performance test.The finite element analysis on the components of the end-effector is execute.Meanwhile,the kinematics and dynamics simulation based on ADAMS are carried out.The simulation results indicated that the clamping-and-shearing movement is stationary;the action of clamping-and-shearing the litchi fruiting cane is less time consuming and efficient when picking;the clamping force precedes the shear force,therefore the clamping fingers can be used to preload in picking.According to the optimized results,the physical prototype of end-effector which is manufactured is used for performance test.The test results indicated that the Anti-blocking interference ability of end-effector is moderate,but it has reasonable load capacity,also it can effectively and steadily clamp the litchi fruiting cane.The average picking success rate of the physical prototype is 84%,the average cut-clamp of a single string of fruit is 2 sec.At last,according to the performance test results,further topology optimization of the end-effector’s key parts and structure improvement of clamping and shearing module are execute.4)Study on experiment of derogative strategy of litchi’s picking-and-placing.Using the “Huai Zhi” litchi as the research object,the effects of different drop collision conditions and stacking conditions on the weight loss rate and the browning index of the litchi damage are analyzed and researched by the damage experiments of drop collision and stacking placement.Then,the picking-and-placing of litchi’s derogative strategy is obtained.The results of drop collision test indicated that the litchi’s damage of collision contact material for the PVC is greater than the corrugated paperboard.Within the experiment range,it is beneficial to reduce the maximum starting height of the robotic picking-and-placing for the impact damage of litchi: storage 2 days with 60 cm and storage 7 days with 30 cm when the placement device was made of PVC;storage 2 days with 75 cm and storage 7 days with 45 cm when the placement device was made of corrugat ed paperboard;storage 2 days with 90 cm and storage 7 days with 60 cm when the placement device covered with litchi.The results of stacking test indicated that the litchi’s damage of placing container material for the plastic material is greater than the corrugated material,the EPS foam material is the smallest.It is beneficial to reduce the maximum stacking layers of the the litchi’s stacking damage: the plastic material is 8 layers,corrugated material is 8 layers,EPS foam material is 10 layers when storage 2 days;the maximum layer of all materials are reduce to 6 layers below(excluding layer 6th).5)Finite element analysis of litchi drop collision and stacking damage.First,the mechanical parameters of litchi components are determined.Second,the mechanical model of the stacking placement of the bottom litchi is deduced,also the drop collision and stacking finite element model of litchi are constructed.Third,the drop collision and stacking placement process of litchi are simulated.Last,the e ffects of different drop collision and stacking conditions on litchi’s damage are analyzed by equivalent stress cloud image.The simulated results indicated that the internal equivalent stress of litchi’s pericarp and pulp are maximal and the damage is fastest when the collision contact material is PVC,second is the corrugated paperboard and litchi is the smallest.The internal equivalent stress of the bottom litchi pericarp is maximal and the microscopic rupture damage is achieved faster when the placing container material is plastic,second is the corrugated material and the EPS foam material is the smallest.The results of predicting the impact damage of litchi under 3 kinds of collision contact material and the stacking damage of bottom litchi under 3 kinds of placement containers are consistent with the results of the damage index analysis of 2 days after the drop collision and stacking experiment.