Research On Force/position Hybrid Control Of Three-dimensional Stress Loading Testing Machine

High-pressure forming is an advanced processing technology in today’s manufacturing industry that enables the production of shaped hollow components.In the process of high pressure forming,the mechanical properties of the material,the geometric parameters of the pipe and the loading path have an effect on the forming quality of the component.Forming defects and wall thickness distribution characteristics of the pipe are closely related to different stress loading paths.Therefore,using a testing machine capable of simulating high pressure loading environment to study the performance of different materials under high pressure is very important for molding quality and process.This topic takes a three-dimensional stress loading tester as the research object,analyzes the problems in the loading process and causes,and studies its control system.The test pipe has complex force under the triaxial stress composite loading of axial force,internal pressure and external pressure.The three-dimensional stress is closely related to the load.In this paper,the formula between the three-dimensional stress and the loading force are deduced.The deformation trend of the pipe is analyzed by ABAQUS,and the variable stiffness and disturbance problems encountered in the loading process are summarized.Understanding the motion characteristics of the system is the basis for formulating the control strategy.Therefore,according to the structural principle of the power mechanism of each channel,a mathematical model was deduced for the thrust cylinder and the internal and external superchargers.And a single channel was built using Simulink software to analyze the response characteristics of system position control and force control.In addition,this paper also uses AMESim software to build a composite loading model,simulate the problems summarized in the deformation process,which is to help confirm the control strategy.In this paper,the robot’s flexibility control experience is used to introduce the forcebased impedance control into the thrust cylinder system,which achieves the purpose of coping with the elongation of the pipe and increasing the sealing force.In addition,there is a problem of tracking deviation in impedance control,and an adaptive control law is deduced so that the thrust cylinder achieves desired position tracking under force control.Through the choice of different control methods,the testing machine can have different degrees of flexibility.The loading mechanism of the testing machine was improved for the test efficiency,and a control program was written to implement the control strategy.The one-direction and multi-direction loading tests on the testing machine were conducted through the debugging of the parameters.Finally,the process analysis and application were discussed.