Research On Structure Design And Drive Control Of Pneumatic Variable Stiffness

Because the traditional rigid drive has the advantages of high accuracy,strong load,and high linearity,the traditional mechanical drive mostly uses rigid drive.However,in the fields of service,medical care,entertainment,and unmanned operations,due to the complex working environment,variable human-computer interaction or limited carrying energy,the traditional rigid drive cannot meet the requirements in flexibility,safety,and energy saving.There are elastic elements in the variable stiffness drive system,so it can reduce the mechanical,impact and other injuries suffered by humans in carriers such as service robots and rehabilitation robots.At the same time,the variable stiffness actuator can use the elastic body to store energy and release it at a suitable position,which can save energy.In this paper,based on the large size,high weight,complex structure,many mechanical contacts,low efficiency and other shortcomings of the existing variable stiffness actuator,a pneumatic variable stiffness actuator is developed based on the compressibility of gas.And establish a model,carry out simulation,design control system,design adaptive variable stiffness and experimental verification.The research includes the following:(1)Modeling.Analyze the mathematical principle of the pneumatic variable stiffness actuator,establish the relationship between the pneumatic spring stiffness and the angle difference,and establish the mathematical relationship between the compression of the variable stiffness mechanism and the pneumatic spring stiffness.At the same time,MATLAB was used to verify the correctness of the mathematical model,and the performance curves of the input shaft and the output shaft’s rotation angle difference and stiffness,rotation angle difference and torque,and rotation angle difference and energy storage were obtained.(2)Control system research.Research the mathematical models of motors,elastic elements and transmission shafts.After fully studying the mathematical model of the motor and the elastic load,a feedforward PID controller with speed and position as the target is established.At the same time,MATLAB/Simulink is used to simulate the feedforward PID controller under various working conditions.It also optimizes the position tracking effect and response speed of the transmission system.At the same time,the influence of temperature,backlash and other unfavorable factors on the system was verified.(3)Adaptive variable stiffness analysis.Analyze the influence of different stiffness on energy consumption during the reciprocating motion of the pneumatic variable stiffness actuator.And establish the relationship between stiffness and energy consumption,and thus design an adaptive variable stiffness controller based on the gradient descent method,so that the pneumatic variable stiffness actuator can take the single-cycle energy consumption as the optimization goal in different working conditions,and automatically adjust the stiffness of pneumatic variable stiffness actuator.(4)Environment construction and experimental verification.Establish the 3D model and prototype production of the pneumatic variable stiffness actuator.An experimental environment including torque sensors and encoders has been built.The experimental data of the pneumatic variable stiffness actuator under various working conditions such as sine tracking,step response and slope tracking are obtained.Verify the consistency between the prototype and the theory.