Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller

Development of Novel Compound Controllers to Reduce Chattering of Sliding Mode Control

The robotics and dynamic systems constantly encountered with disturbances such as micro electro mechanical systems (MEMS) gyroscope under disturbances result in mechanical coupling terms between two axes, friction forces in exoskeleton robot joints, and unmodelled dynamics of robot manipulator. Sliding mode control (SMC) is a robust controller. The main drawback of the sliding mode controller is that it produces high-frequency control signals, which leads to chattering. The research objective is to reduce chattering, improve robustness, and increase trajectory tracking of SMC. In this research, we developed controllers for three different dynamic systems: (i) MEMS, (ii) an Exoskeleton type robot, and (iii) a 2 DOF robot manipulator. We proposed three sliding mode control methods such as robust sliding mode control (RSMC), new sliding mode control (NSMC), and fractional sliding mode control (FSMC). These controllers were applied on MEMS gyroscope, Exoskeleton robot, and robot manipulator. The performance of the three proposed sliding mode controllers was compared with conventional sliding mode control (CSMC). The simulation results verified that FSMC exhibits better performance in chattering reduction, faster convergence, finite-time convergence, robustness, and trajectory tracking compared to RSMC, CSMC, and NSFC. Also, the tracking performance of NSMC was compared with CSMC experimentally, which demonstrated better performance of the NSMC controller

Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller

Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller

Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller

A Lower Extremity Exoskeleton: Human-Machine Coupled Modeling, Robust Control Design, Simulation, and Overload-Carrying Experiment

A robust H∞ control method and switched control algorithm for hydraulic actuator presents in human-machine coordinated motion to solve the motion delay of lower extremity exoskeleton. After the characteristic parameters synthesis of human limb and exoskeleton linkage, the human-machine coupled motion model is constructed to estimate the appropriate hydraulic pressure, which is considered as a structural uncertainty in hydraulic model. Then the robust controller is designed to improve the robust stability and performance under the structural and parametric uncertainty disturbances. Simulation results show that, in walking mode, this robust controller can achieve a better dynamic response and aid-force efficiency than PID controller. Then, according to gait divisions of person’s limb motion, the switched control algorithm is designed to reduce the delay of exoskeleton tracking person. Finally, the experimental results show that the human-machine coordinated walk with bearing 60 kg load and squat action with no external load are realized effectively by this proposed method

Optimization of Sliding Mode Control using Particle Swarm Algorithm for an Electro-hydraulic Actuator System

The dynamic parts of electro-hydraulic actuator (EHA) system are widely applied in the industrial field for the process that exposed to the motion control. In order to achieve accurate motion produced by these dynamic parts, an appropriate controller will be needed. However, the EHA system is well known to be nonlinear in nature. A great challenge is carried out in the EHA system modelling and the controller development due to its nonlinear characteristic and system complexity. An appropriate controller with proper controller parameters will be needed in order to maintain or enhance the performance of the utilized controller. This paper presents the optimization on the variables of sliding mode control (SMC) by using Particle Swarm Optimization (PSO) algorithm. The control scheme is established from the derived dynamic equation which stability is proven through Lyapunov theorem. From the obtained simulation results, it can be clearly inferred that the SMC controller variables tuning through PSO algorithm performed better compared with the conventional proportionalintegral-derivative (PID) controller

PSO-Tuned Pid Sliding Surface Of Sliding Mode Control For An Electro-Hydraulic Actuator System

It is well known that the control engineering applications are widely implemented in the industrial fields through the assistance of the Electro-Hydraulic Actuator (EHA) system. The EHA system is commonly exposed to the parameter variations, disturbances, and uncertainties, which are caused by the changes in the operating conditions including supply pressure, total moving mass, and friction. Thus, due to the changes and uncertain operating conditions, an optimization to the system’s controller is necessary in order to obtain a more robust system performance. This thesis presents the optimization on the Proportional- Integral-Derivative (PID) sliding surface of the Sliding Mode Control (SMC) scheme by using Particle Swarm Optimization (PSO) algorithm, applied to EHA system particularly for positioning tracking control. The EHA system is modelled according to the theories of the physical law, which taking into account the effect of nonlinearities, uncertainties, and disturbances occurred in the system. A robust control strategy is then formulated based on the control laws of the SMC, where the design of the sliding surface is integrated with the PID controller. The proposed control strategy is designed based on the EHA system that is subjected to the nonlinear characteristics and model uncertainties. Then, the PSO, which is based on the inspiration of the swarming behaviour has been utilized to seek for the optimum PID sliding surface parameters. The conventional tuning technique for the PID controller, which is known as Ziegler-Nichols (ZN) has been used to obtain the initial value of the PID sliding surface. Finally, the comparison has been made by applying the obtained parameters through the ZN and PSO tuning technique to the conventional PID controller and the PID sliding surface of the SMC. The findings indicate that the proposed robust SMC with PSOPID sliding surface is preserved to ensure the actuator robust and stable under the variation of the system operating condition, which produce 26% improvement in terms of robustness characteristic that gave a better positioning tracking performance and reduced the controller effort as compared to the conventional PID controller