Design,Modeling And Performance Analysis Of Constant-Force Gripper

The gripper is a common end-effector in the fields of modern industrial production,bioengineering,medical science and so on.The target objects operated have various characteristics,including some fragile,non-rigid and Bio-cell objects which are easily damaged in the process of gripping.In order to avoid damage to the target during the clamping process,it is of great theoretical and practical significance to design a clamper with constant force clamping function.Based on the compliant constant force mechanism,three kinds of clampers with constant force clamping function are designed in this paper.The theoretical modeling and performance optimization of the designed clamps are carried out.The main contents are as follows:Aiming at the problem that the constant force of the traditional constant force clamp can not be adjusted,a clamp with adjustable constant force is designed based on the compliant constant force mechanism.Constant force clamp mainly includes magnifying module and constant force module.The magnifying module is composed of two L-type magnifying mechanism in series.According to the principle of positive and negative stiffness combination,the constant force module is connected by bistable beam and trapezoidal beam in parallel.The clamping constant force can be adjusted by changing the pre-tightening of trapezoidal beam.A theoretical model reflecting the force-displacement relationship of the gripper is established by combining the pseudo-rigid body method with the elliptic integral method.The force-displacement relationship of the gripper is obtained by finite element analysis.The results verify the correctness of the theoretical model.Based on the theoretical model,the structural parameters of the gripper are optimized to expand the scope of constant force clamping and improve the stability of constant force.The experimental results show that the constant force clamp has the function of constant force clamping.The constant force range is 1.3mm,the constant force range is 1.3N without pretension,and the constant force range after pretension is 2N.The correctness of the design idea and the effectiveness of the optimization method of the constant force clamp are illustrated.Aiming at the problem that the traditional constant force clamp has only one constant force clamping range,a clamp with two constant force clamping ranges is designed.In order to realize the function of constant force clamping range of two segments of gripper,the same positive stiffness structure and different negative stiffness structure are connected respectively by using the principle of combination of positive stiffness and negative stiffness,so that the stiffness of the whole mechanism is close to zero.The positive stiffness structure of gripper adopts composite beam structure,which has linear force-displacement relationship and constant stiffness;the negative stiffness 1 structure is a bistable beam,and the negative stiffness 2 structure is a parallel structure of bistable beam and trapezoidal beam;the function of connecting composite beam and two negative stiffness structures is realized by setting transfer rods.The experimental results show that the constant force gripper has two clamping ranges,the first one is 0.4-5.4 mm,the constant force is 7N,the second one is 1.2-4.4 mm,and the constant force is 15 N.In order to ensure the stability of the clamping force,the BP neural network prediction model is established based on the experimental data,and the change of the clamping force is predicted.The correctness of the BP neural network prediction model is verified by comparing with the experimental results.In order to solve the problem that the clamp can not have two constant force ranges in a single clamping process,a clamp with two continuous constant force ranges was designed based on a compliant constant force mechanism.Through theoretical analysis and design of the structure with positive and negative stiffness,a clamp with two consecutive constant force ranges is obtained.The positive stiffness structure adopts a composite beam structure with constant positive stiffness,which combines two negative stiffness structures with the same negative stiffness value in series,so that the clamp has two constant force ranges after parallel connection with the positive stiffness structure.The pseudo-rigid-body method is used to model the composite beam,and the interpolation method is used to model the force-displacement relationship of the gripper.According to the theoretical model,the influence of structural parameters on the constant force performance of the clamp is studied,and its sensitivity is analyzed.The prototype is manufactured and tested.The results show that the designed gripper has two continuous constant force clamping ranges.The first one is 0.4-5 mm,and the constant force is 7.5 N.The second one is 7.8-10.5 mm,and the constant force is 32 N.The results prove the validity of the design idea and the correctness of the model.