RESUMO
Legged robots have shown great adaptability to various environments. However, conventional walking gaits are insufficient to meet the motion requirements of robots. Therefore, achieving high-speed running for legged robots has become a significant research topic. In this paper, based on the Spring-Loaded Inverted Pendulum (SLIP) model and the optimized Double leg-Spring-Loaded Inverted Pendulum (D-SLIP) model, the running control strategies for the double flying phase Bound gait and the Rotatory gallop gait of quadruped robots are designed. First, the dynamics of the double flying phase Bound gait and Rotatory gallop gait are analyzed. Then, based on the "three-way" control idea of the SLIP model, the running control strategy for the double flying phase Bound gait is designed. Subsequently, the SLIP model is optimized to derive the D-SLIP model with two touchdown legs, and its dynamic characteristics are analyzed. And the D-SLIP model is applied to the running control strategy of the Rotatory gallop gait. Furthermore, joint simulation verification is conducted using Adams virtual prototyping and MATLAB/Simulink control systems for the designed control strategies. Finally, experimental verification is performed for the double flying phase Bound gait running control strategy. The experimental results demonstrate that the quadruped robot can achieve high-speed and stable running.
RESUMO
The electro-hydraulic servo system (EHSS) drives the hydraulic quadruped robot, which has the advantages such as high load capacity, fast response velocity, and powerful motion ability. EHSS of single leg consists of three sets of hydraulic drive unit (HDU), which is the joint driver. As a result, HDU control is the fundamental control of the hydraulic quadruped robot, and it controls the robot's motion performance directly. In order to improve the control accuracy and adaptability to different working conditions of impedance control for HDU, a composite control method combining sliding mode control (SMC) and model-based linear extended state observer (MLESO), which is called SMC-MLESO, is designed in this paper. Firstly, the chattering problem of SMC is improved by designing a novel composite reaching law and adding total disturbance to sliding mode control law. Secondly, the parameters of sliding mode surface are calculated by the optimal control. The parameters of MLESO are calculated by the bandwidth of the controller. And the known model of the system is added to observer to reduce the influence of sensor noise. Finally, comparative experiments show that SMC-MLESO has a good control effect. The maximum error of using SMC-MLESO is 0.101 mm and the biggest change of the maximum error is 36.5% under different working conditions, which is better than PI+Gcp and PI+Gcp+Gfp(The two controllers were designed by the author's previous research, which was published by Journal of the Franklin Institute).
RESUMO
Hydraulic drive mode enables legged robots to have excellent characteristics, such as greater power-to-weight ratios, higher load capacities, and faster response speeds than other robots. Nowadays, highly integrated valve-controlled cylinder, called hydraulic drive unit (HDU), is employed to drive the joints of these robots. However, various robot control issues exist. For example, during the walking process of legged robots, different obstacles are encountered, making it difficult to control such robots because the load characteristics of the ends of their feet change with the environment. Furthermore, although the adoption of HDU has resulted in high-performance robot control, the hydraulic systems of these robots still have problems, such as strong nonlinearity, and time-varying parameters. Consequently, robot control is very difficult and complex. This paper proposes an improved second-order dynamic compliance control system, impedance control, for HDU. The control system is designed to rectify the issues affecting the impedance control accuracy of the dynamic compliance serial-parallel composition between the HDU force control inner loop and the impedance control outer loop. Specifically, it consists of a compliance-enhanced controller and a feedforward compensation controller for the force control inner loop. Furthermore, the dynamic compliance composition of the inner and outer HDU control loops is rearranged. The results of experiments conducted indicate that the proposed method significantly improves the control accuracy compared to that of traditional force-based impedance control.
