Study On Loading Force Control Of Sheet Metal Pure Bending Test

For the processing and forming process based on bending deformation,such as roll bending,the bending test results are often better than that of the tensile test to characterize the mechanical properties of the material bending,so the pure bending test is very important to determine the mechanical properties of materials.When the pure bending moment is loaded,the loading trajectory of the clamping end of the sheet metal is uncertain.In order to further study the pure bending loading of the sheet metal,the process control of the pure bending experiment is realized by controlling the running trajectory of the clamping end of the sheet metal.From the Angle of displacement loading,based on the metal bending testing machine,and impedance control theory,a method of internal force control of metal deformation is proposed in this study,To achieve the ideal pure bending force state of the plate only by pure bending moment.In order to solve the problem of jitter of loading element caused by flexible deformation during loading,fuzzy variable impedance control method based on dynamic model compensation is used to obtain the pure bending motion path of plate.The main work is as follows:Firstly,the loading principle of the testing machine is analyzed.The testing machine carried out free bending loading on the plate specimen in the way of displacement loading.In order to obtain the motion mapping relationship of the driving end to end loading mechanism,the closed-loop vector method is adopted to obtain the kinematic relationship of the testing machine mechanism.Secondly,taking into account of the problem of jitter of loading element caused by flexible deformation during loading of specimen,it is necessary to calculate the theoretical input torque to carry out feedforward control of motor current loop.Therefore,the closed-chain hybrid dynamic model of plate specimen during loading process is established based on Lagrange equation method and Newtonian Euler method,and through the optimization and decoupling of plate internal forces,the control internal force required by the plate specimen is obtained.Then,by referring to the idea of impedance control strategy,a model mechanism is proposed to approximate the microdeformation of tension and compression generated during plate bending into the position correction of loading element.This model mechanism can realize the pure bending loading trajectory design based on displacement control.Considering the elastoplastic deformation of loading specimens,two kinds of force control strategies are introduced: Direct adaptive stress control method(MRAC method)and fuzzy variable impedance control method based on dynamic model feedforward are theoretically derived and analyzed,and the conventional impedance control method and MRAC method are simulated to demonstrate the effectiveness of impedance control method and direct adaptive stress control method.Finally,experiments are carried out on MRAC method and fuzzy variable impedance control method based on dynamic model feedforward to realize pure bending loading process.The experimental results show that the fuzzy variable impedance control method based on the dynamic model can control the tension pressure of bending plate.Two kinds of galvanized iron sheets of the same thickness with different hard and soft materials were used in the experiment.The experimental results show that the tensile pressure of the two plates in the process of bending deformation is less than 2.4 N,which basically meets the requirements of pure bending loading,indicating that the fuzzy variable impedance force control algorithm is effective,and the pure bending loading trajectory suitable for 0.8 mm thick galvanized plate is obtained.