SUMMARYA scheme for bilateral control of hydraulic actuators is developed and experimentally evaluated in this paper. The control laws are derived based on Lyapunov's feedback control design technique. Owing to the discontinuity originating from a sign function in the control laws, the control system is non-smooth. First, the existence, continuation, and uniqueness of Filippov's solution to the system are proven. Next, the extensions of Lyapunov's stability theory to non-smooth systems and LaSalle's invariant set theorems are employed to prove the asymptotic stability of the control system. Effectiveness of the proposed controller is verified by simulation and experimental studies. It is shown that beside stability, the system has good transparency in terms of position and force exchanges between the master and slave actuators.

In this paper, we present experimental results of implementing five bilateral control schemes, widely used for electro-mechanical systems, to a hydraulic actuator. The goal is to investigate the applicability of each control scheme to a hydraulic actuator and compare their performances on a common system. The considered schemes are ‘force reflection’, ‘position error’, ‘shared compliant control’, ‘force reflection with passivity’ and ‘four channels architecture’ schemes. The evaluation is conducted in terms of position tracking, force tracking, and fidelity of perceived stiffness by the operator. It is shown that force reflection and four channels architecture control schemes perform best in terms of both position tracking and force tracking during interaction with an environment emulated by different springs. Position error scheme, on the other hand, exhibits good position tracking capability, but cannot track environmental force encountered at the master site. It, however, produces a feel to the operator, based on position error between the slave and the master arms, which is potentially desirable during unconstrained motion control of the actuator.

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A control scheme for teleoperation of hydraulic actuators, using a haptic device, is developed and experimentally evaluated in this paper. In the control laws, the position error between the displacement of the haptic device and the hydraulic actuator movement is used at both master and slave sides to maintain good position tracking at the actuator side while providing a haptic force to the operator. Lyapunov’s stability theory and LaSalle’s invariant set theorems are employed to prove the asymptotic stability of the system. It is shown that beside stability, the system performs well in terms of position tracking of the hydraulic actuator and providing a feel of telepresence to the operator. Proposed controller only needs system’s pressures and displacements that are easy to obtain via on-line measurements. Additionally, the controller does not need any information about the parameters of the system. These characteristics make the controller very attractive from the implementation view point.