| Robots can replace human beings to perform tasks that are heavy,boring,dangerous,etc.The tasks to be completed are different,and the types of robots are also different.To meet the requirements of large load and the adaptability to non-structural environments,hydraulic driven robot came into being.The joint drive of these robots uses a highly integrated servo valve to control the servo cylinder(Hydraulic driving unit).In order to make the foot robot joint have compliance to alleviate the rigid impact of the external environment,the hydraulic drive unit needs to compliant control.Position-based impedance control(Abbreviated position impedance control)is a typical compliant control method.For robotic hydraulic drive unit,position impedance control methods are studied to improve the tracking performance and steady-state accuracy of the system.The main research tasks include:(1)In order to improve the position impedance control performance of the robotic hydraulic drive unit,based on the modern control theory and using the state variables that can fully characterize the system characteristics,the state feedback control method is studied.Using the basic equations of the hydraulic system and the mathematical model of the sensor,the state space expression of the position impedance control system is established.Based on the state space expression,the system is analyzed for its observability,controllability and stability,and the system simulation model is built.The linear quadratic optimal control is used to obtain the state feedback matrix of the system.The full-dimensional state observer is used to obtain the state variables of the system.Utilize the desired steady-state error to zero to obtain the input transform amplifier.Finally,the state feedback control of the system is achieved.(2)In order to restrain the influence of the load force on the control performance of the robotic hydraulic drive unit,combining the structural characteristics of the hydraulic drive unit,the feedforward disturbance rejection control method is studied.Based on the state space expression of the position impedance control system,considering the load force of the system,the state space expression including the load force is established.Based on the state space expression including the load force,the equivalent input that produces the same output result as the load force is obtained through equivalent calculation,and then the effect of suppressing the load force interference is obtained by subtracting the equivalent input at the system input end.(3)In order to improve the control performance of the robotic hydraulic drive unit in a typical periodic motion gait,the plug-in repetitive control method is studied based on the internal model principle.Analyze the advantages and disadvantages of the existing multiple repetitive control methods,select the plug-in repetitive control method,design the low-pass filter and dynamic compensator(system model identification using least square method)separately,and form the insert-type repetitive controller for positional impedance control system.(4)In order to verify the effectiveness of the three control methods,namely state feedback control,feedforward disturbance rejection control and plug-in repetitive control,the hydraulic drive unit performance test bench and the robot single leg test bench are used to carry out experimental research on the position impedance control of the hydraulic drive unit.For the positional impedance control experiment of a single hydraulic drive unit,under different sinusoidal loading conditions with different frequencies and amplitudes,the impedance control performance at different input positions is studied,and the experimental control effects of the three control methods were quantitatively given.For the one-legged double-joint position impedance control experiment of the robot,the impedance control performance of different input positions on the single leg is studied under the no-load and loading conditions of the foot. |
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