Research On Impedance Control Based On Force Servo For Leg Of Hydraulic Legged Robot

Legged robot has broad application prospects in military operations, earthquake rescue, field exploration and other fields due to its strong adaptive capacity to complex terrains and harsh environment. The hydraulic drive has good dynamic performance, large power density and anti-electromagnetism interference capability so that it can meet the growing requirements of legged robot on load ability and movement performance. Contacting with the environment is inevitable to legged robot because of walking, and its stability will be seriously affected by high rigidity position control. So it is an urgent need to implement the leg compliance control for the legged robot. Therefore, this paper focuses on the leg variable impedance control of the legged robot based on the hydraulic force servo control. The main contributions focus on the following research contents:Based on the model analysis of hydraulic drive unit, mathematical model and simulation of force servo control system are established. Moreover, the transfer function of the system is obtained by linearization of the nonlinear element in force servo, and the stability of the system is also analyzed. On the basis, the velocity compensation model is proposed according to the definition of redundant force and proved effectiveness with analysis of its transfer function. In addition, the single leg impedance control model is built and analyzed on the basement of establishment and analysis to impedance control model on force.To study the hydraulic force servo control characteristics, the design of double hydraulic cylinder experimental platform is designed. Multi-threaded task is created with the use of embedded QNX system, and the force servo control algorithm as well as its specific application form on the thread is given. Furthermore, modeling and simulation on the experimental platform are conducted, and the effectiveness of PI control with velocity compensation control algorithm is proved through the simulation and experiment.The experimental platform of single leg is built to study the characteristics of impedance control on force based on the hydraulic force servo. The hardware and software design of experimental platform is completed, and the impedance control algorithm based on the force servo is simplified through fitting to make it easy to use in the control program. The impedance control experiment is tested on single leg, and the effectiveness of algorithm of impedance control based on force servo on the joint and single leg is proved through the joint and single leg impedance control experiment respectively. The experimental results show that this algorithm can achieve the goal of variable impedance control, and can also realize the active compliance in the case of impact.