Study On A Novel Flexible Gripper And Its Performance For Rice Dumplings

As a traditional food in China,the market demand for rice dumplings is increasing in recent years.However,the traditional production method of rice dumplings has a low degree of automation and high labor costs,and it is difficult to meet the current development requirements.As a new type of mechanical arm end effector,the flexible gripper can replace manual operations to complete packaging tasks such as sorting,filling,and combination of rice dumplings,and can grasp it without damage.Up to now,the existing flexible gripper has problems such as poor adaptability and difficulty in grasping stably when it is used for grasping rice dumplings.In this dissertation,a fingertip-enhanced flexible gripper is developed according to the geometric characteristics of the rice dumplings and the requirements of the grasping method,and its manufacturing process,bending deformation characteristics and grasping performance are also studied.The main work contents are as follows:（1）The three-dimensional structure for four-cornered rice dumplings which is taken as grasping object in this study is simplified.The damage pressure limit of the rice dumplings is determined by the compression damage experiment method so as to the non-destructive grasping requirements of the flexible gripper are then determined.As a result,a flexible gripper fingertip grasping scheme,a 3-finger pneumatic flexible gripper,was finally adopted.Therefore,a multi-cavity flexible finger with a fingertip reinforcement structure and a flexible gripper fixing connector are designed.SJ3113 type silica gel is selected as the flexible finger material,and the finger forming mold is 3D printed and the flexible finger is then produced by the soft lithography method.（2）The optimum ratio of SJ3113 silica gel material is determined by uniaxial tensile experiments,and the hyperelastic constitutive model and its parameters are also determined.Secondly,a mathematical model of flexible finger bending deformation is established by using the virtual work principle method combined with the material strain energy density function according to the assumption of piecewise constant curvature.Then,taking the finger bending angleφas the performance index,the orthogonal experiment is used to explore the influence of the finger airbag wall thickness a₁,the cavity height h₂,the connecting layer thickness h₃,and the confining layer thickness e on the bending performance.The results show that the influence degree of these structural parameter of finger onφis a₁>h₃>e>h₂.Based on the results of the orthogonal experiment,the main structural parameters of the finger are further optimized by the single-factor experiments,and the optimal structural parameters of the finger are finally determined as a₁=3 mm,h₃=5 mm,e=3 mm.The bending properties and mechanical properties of different phalangeal fingers are also compared.The results show that the bending performance of the fingers increases significantly with the increase of the number of phalanges,but the fingertip force decreases gradually with the increase of the number of phalanges.（3）The flexible gripper pneumatic drive system and experimental test platform are built to test the bending performance,mechanical properties of different knuckle fingers and the correctness of the flexible finger bending deformation mathematical model and finite element simulation.According to the performance index of rice dumplings,the structure parameters of the flexible gripper fingers are optimized,and the grasping performance of the flexible gripper is further evaluated experimentally.The results show that the flexible gripper with4-knuckle fingers,fingertip reinforcement structure parameters of m=9 mm,n=7 mm,α=80°,and the finger surface feature of barb type performs best.The better grasping performance for rice dumplings is still available for different specifications and non-ideal grasping positions,and it can withstand severe shaking when the air pressure is in the range of 70～80 k Pa.Therefore,it also preforms the better grasping stability.The fingertip-enhanced flexible gripper designed in this study can grasp rice dumplings efficiently and stably without damage.The gripper can be used as a novel tools and methods for automatic sorting,filling,combined packaging and other production links of rice dumplings,and it can also be provided reference for the application of flexible grippers in the food packaging industry.