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Hydraulic Control Systems

The discrete cosine transform (DCT), introduced by Ahmed, Natarajan and Rao, has been used in many applications of digital signal processing, data compression and information hiding. There are four types of the discrete cosine transform. In simulating the discrete cosine transform, we propose a generalized discrete cosine transform with three parameters, and prove its orthogonality for some new cases. A new type of discrete cosine transform is proposed and its orthogonality is proved. Finally, we propose a generalized discrete W transform with three parameters, and prove its orthogonality for some new cases. Keywords: Discrete Fourier transform, discrete sine transform, discrete cosine transform, discrete W transform Nigerian Journal of Technological Research , vol7(1) 2012

On discrete cosine transform

This paper presents and experimentally demonstrates a control methodology that provides transparency and stability robustness in bilateral telemanipulator systems. The approach is based upon a previously published method that structures the human-manipulators-environment system in a manner that enables the application of frequency-domain loop-shaping methods. This paper reformulates the human-manipulator interaction described in the previously published work, and experimentally demonstrates the approach on a single degree-of-freedom telemanipulation system. Experimental measurements indicate significant improvements offered by the method in both the stability robustness and transparency of the human-manipulators-environment system. Finally, experimental results are presented that demonstrate the robustness in the transparency to significant changes in the environment dynamics.

Loop shaping for transparency and stability robustness in bilateral telemanipulation.

This article presents a novel control scheme that primarily provides a solution to the problem of simultaneously performing stable trajectory tracking and variable impedance control (VIC) of flexible-joint robots. The existing asymptotically stabilizing tracking controllers for compliant robots rely upon several model-based terms and their derivatives. Contrarily, the proposed minimally model-based trajectory tracking control scheme requires knowledge of only the gravitational torque vector model. Although interaction and tracking performance enhancements are achievable through VIC, its operation introduces energy injections, thereby impacting closed-loop stability/passivity. Existing VIC passivity preservation techniques deal exclusively with rigid-joint robots. To this end, the proposed method introduces the minimally model-based trajectory tracking variable impedance control scheme, which ensures passivity/stability when applying VIC to flexible-joint robots. Numerical and experimental results corroborate the controllers’ efficacy in terms of realizing VIC interaction and tracking tasks, thus enabling flexible-joint robots to stably replicate biologically inspired behaviors.

Minimally Model-Based Trajectory Tracking and Variable Impedance Control of Flexible-Joint Robots

Gait phase estimation is important technology in controlling the exoskeleton robot to assist elderly walking. Several kinds of Gait estimation methods have been proposed, however, the previously proposed methods were mainly aiming at one kind of walking task, e.g., level ground walking. There are only a few studies aiming at continuous gait phase estimation during continuous multilocomotion tasks. In this article, we design a continuous gait phase estimator based on adaptive oscillator (AO) network. In order to overcome the problem that the traditional AO does not converge or converges slowly when the gait task is switching, a new structure of gait phase estimator, including a gait tasks classifier, an AO reset, a peak detector, and a model-based (MB) transition gait phase estimator is designed to improve the performance of AOs network. The switching unit is designed to reorganize the output gait phase. Considering the stabilization of the sensors in continuous multilocomotion tasks, the gait tasks classifier only utilizes the angle of hip joints. The results show that the constructed classifier has similar performance to other gait tasks classifiers and requires minimum sensing sources. The continuous gait phase estimation results during continuous multilocomotion tasks show that the proposed method has better performance than the traditional AO and the AO network with self-designed reset.

Locomotion Mode Identification and Gait Phase Estimation for Exoskeletons During Continuous Multilocomotion Tasks

This paper addresses the trajectory tracking problem for constrained high dynamic electro-hydraulic actuator in the presence of time-varying parameters, high frequency external load interference, measurement noise and some unmeasurable states. An adaptive robust optimal control scheme is proposed for the electro-hydraulic actuator in legged robot. The framework of our presented scheme is based on a linear time-varying model predictive controller (LTV-MPC) embedded with a multi-scale online estimator (MEKF). With fast- varying and slow- varying time scales, the MEKF part is used not only for measurable states filtering and unmeasurable states estimation, but also for time-varying parameters and external load interference estimation, which will be integrated into the mpc model in real time. The LTV-MPC part is a trajectory tracking controller designed by constrained MPC with an approximate high-precision real-time model and a rapidly solved cost function, which guarantees that the input and output constraints are satisfied during the receding horizon and optimal control process. Finally, with a series of highly dynamic conditions, the comparison experiment results show that the proposed controller has a simple design process, strong adaptive robust performance and trajectory tracking performance, which verifies the effectiveness of the control scheme.

/pdf/model-predictive-trajectory-tracking-control-of-electro-48x4ku1jua.pdf

Model Predictive Trajectory Tracking Control of Electro-Hydraulic Actuator in Legged Robot With Multi-Scale Online Estimator

The body weight support method of exoskeletons is useful for the rehabilitation of patients with lower limb dyskinesia and performance augmentation of elders. Rather than enhancing the human joint strength directly, the body weight support exoskeleton provides assistance by supporting part of the human body weight and thus releasing the burden experienced by human legs. This paper proposes a two-level hierarchical control method aiming to achieve task-free and strong system robustness. A scale force control method, which can be simply described as making the supporting force of the robot several times the magnitude of a human leg, is developed as the high-level controller. The low-level controller is designed as a fuzzy cerebellar model articulation controller (CMAC)-based adaptive control to enhance the system robustness. The proposed method is applied to a squat movement and a single leg stance movement and is simulated in a combined simulation environment. The results show that the exoskeleton can always provide improved support according to the foot reaction force that is controlled by the user and that the system handles model errors and external disturbances well.

/pdf/fuzzy-cmac-based-adaptive-scale-force-control-of-body-weight-1ukpfsgn1h.pdf

Fuzzy CMAC-Based Adaptive Scale Force Control of Body Weight Support Exoskeletons

This paper focus on the modelling and control of a hydraulically-actuated biologically-inspired articulated robotic leg. The leg has two hydraulically-actuated degrees of freedom (DoF), the hip and knee joints, and a passive spring DoF, the ankle joint. After a brief description of the prototype leg, the paper developed a nonlinear model of the leg, including its kinematics and dynamics. Subsequently, an actively compliant control architecture based on outer virtual compliant leg model and inner torque controller was designed to achieve a spring-damper like touchdown dynamics behavior. Lastly, both a Pushdown experiment and a Dropdown experiment were carried to verify the designed controller. The result confirmed that a hydraulically-actuated robot articulated leg can successfully emulate virtual passive components through proper mechanical design and actively compliant control under dynamic situations.

Active compliance control for a hydraulically-actuated articulated robotic leg

Motion Planning for a Bounding Quadruped Robot Using iLQG Based MPC

considering the perturbation and disturbance of electro-hydraulic servo force control system for foot robot with single joint actuator. Firstly, the dynamic nonlinear model of electro-hydraulic servo actuator is deduced, secondly, the model is locally linearized by using the input/output feedback linearization theory to improve the control accuracy of the nonlinear system. By analyzing the zero dynamic stability of the system, the validity of the linearized model is proved theoretically. Thirdly, the sliding mode variable structure control is designed to compensate the external disturbance and uncertainty, the boundary layer method is added to suppress the high frequency jitter of the system. Finally, the feedback linearized sliding mode control rate of the original nonlinear system is summarized. The comparative simulation experiment between the proposed algorithm and PID are respectively carried out, results show that the algorithm can effectively improve the force tracking control accuracy and achieve a good tracking effect, with a strong robustness to external interference and system parameters perturbation.

Electro-hydraulic Servo Force Control of Foot Robot Based on Feedback Linearization Sliding Mode Control

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