Abstract
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 the hydraulic drive unit (HDU), is employed to drive the joints of these robots. However, there are some common problems in the HDU resulted from hydraulic systems, such as strong nonlinearity, asymmetry dynamic characteristics between positive and negative moving directions of the piston rod, and time-varying parameters. It is difficult to obtain the desired control performance by just using classical control methods such as the traditional PID control. In this paper, a position controller that combines fuzzy terminal sliding mode control (FTSMC) and time delay estimation (TDE) is proposed, in which FTSMC adopts a compound reaching law which combines the tangent function and the exponential reaching law. Moreover, the fuzzy control is introduced to adjust the parameters of the reaching law in real time to improve the adaptability of FTSMC. Based on FTSMC, the external uncertain disturbance of the HDU position control system is estimated by TDE, which ensures the simplicity of system modeling and the normal application of FTSMC. Finally, the control effects of the controller combining FTSMC and TDE are verified on the HDU performance test platform and the load simulation experiment platform. The experimental results show that the proposed controller greatly improves the system position control performance and has a strong disturbance rejection ability and a good adaptability under different working conditions. The above research results can provide an important reference and experimental basis for the inner loop of compliance control of legged robots.
Highlights
In recent years, robots have been more and more widely used in various industries and have become a hot spot of research, which attracts lots of scholars’ attention
The introduction of the hydraulic drive unit (HDU) brings the advantages of the hydraulic system and brings some common problems of the hydraulic system, such as strong nonlinearity, asymmetry dynamic characteristics of positive and negative
E block diagram of the HDU position closed-loop control system is shown in Figure 2, and the deduction is shown in Appendix
Summary
Robots have been more and more widely used in various industries and have become a hot spot of research, which attracts lots of scholars’ attention. E legged bionic robot takes the legged animals as the bionic object, which has the characteristic of discontinuous support. E advantages of small size and large output power make legged robots being widely used in the military and civilian field such as the transportation of military materials, antiterrorism or antiexplosion tasks, deep-sea exploration, and automobile assembly. Each leg of this kind of robots has several degrees of freedom (DOFs) controlled by highly integrated valve cylinders, which is known as theHDU [6, 7].
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