Lin Liu

Sun Yat-Sen University | SYSU

This paper addresses the trajectory tracking problem for a class of uncertain manipulator systems under the effect of external disturbances. The main challenges lie in the input constraints and the lack of measurements of joint velocities. An extend‐state‐observer is utilized to estimate the velocity signals; then, a neural‐network‐based adaptive c...

Objective: Although there have been studies conducted on the instantaneous remote center of motion (RCM) mechanism, the general closed-loop control method has not been studied. Thus, this paper fills that gap and employs the advantages of this mechanism to develop a novel injection system. Methods: The injection prototype involves the instantane...

The cascade impedance control (CIC) is a well-known architecture framework for rehabilitation exoskeleton with compliant joint (e.g., a series elastic actuator). The cascaded position–torque–velocity control loop of the CIC system can deal with specific issues, such as stiction or the accuracy of output impedance. In this article, the control loops...

This paper presents an integration of two significant targets, i.e., reducing the output impedance and the vibration at the trajectory tracking, into one variable stiffness actuator (VSA) system. The VSA is operated within the cascade impedance control framework, in which the inner torque control loop is designed with the unknown input observer (UI...

Active lower limb exoskeletons are increasingly used in rehabilitation therapy. An important aspect and ongoing research topic in developing such assistive devices is safe human–machine interaction. Another major challenge in the control of exoskeletons is determining the subject's intention to move for providing cooperative assistance. To address...

We present a framework for achieving a robust stability test of the variable stiffness actuator (VSA) exoskeleton programmed with the gain scheduling-based variable impedance control (GSVIC). In this brief, the focused impedance control framework involves the cascaded position torque control loop, in which both control loops are closed, and the ind...

This paper investigates a closed-loop torque-controlled variable stiffness actuator (VSA) combined with a disturbance observer for enhancing low output impedance. We implement the generalized extended state observer (GESO) for conveniently testing the stability of the time-varying VSA system. In our application, the GESO is also required to serve t...

Compliant actuators have been increasingly used for active joints in lower-limb exoskeletons or orthoses because they help to guarantee a safe human interaction. One example of such compliant motors is the variable stiffness actuator (VSA). The design of a torque controller for such an actuator is a crucial task in order to provide patients with ph...

Variable stiffness actuators help to guarantee a safe human interaction when it is used as the active joints in lower-limb exoskeletons. Therefore, we designed a unilateral exoskeleton consisting of a mechanical-rotary variable impedance actuator (MeRIA) assisting the human knee. In this paper, a first walking trial with a healthy, human subject ha...

We present a novel application of the variable stiffness actuator (VSA)-based assistance/rehabilitation robot-featured impedance control using a cascaded position torque control loop. The robot follows the adaptive impedance control paradigm, thereby achieving an adaptive assistance level according to human joint torque. The feedforward human joint...

We present a nonlinear feedback controller design for a variable stiffness actuator, that will force the closed-loop system to a stable limit cycle. The controller design synthesis allows for an inherent selection of limit cycle parameters, such as frequency and magnitude. The controller is based on the central pattern generator (CPG), that is a co...

Variable impedance actuators are widely used in tasks with an interaction between human and machine. In this paper, a mechanical-rotary variable impedance actuator (MeRIA), designed for knee or hip joint of a lower limb exoskeleton, is investigated. In the torque control loop of the MeRIA, a zero-torque controller is designed to achieve a low outpu...

Series elastic actuators decouple stiff motors and gear trains from the load by an mechanic elastic element. This elastic element can be used as torque sensor, acts as an energy storage, decouples the actuator from exogenous high frequency excitation and contributes towards shock resistance and safety in human–robot interaction scenarios. A series...

A Variable Stiffness Actuator (VSA) is an inherently parameter-dependent system due to the controllable stiffness element. Within the torque-controlled framework, the VSA is distinguished from the classical Series Elastic Actuator (SEA). A frozen torque controller can directly determine the SEA performance with a fixed-stiffness spring selection. H...

In many applications for industry and everyday life electromagnetic actuators have become the standard for mechatronic systems. Actuators with a serial compliance (fixed or variable spring rate) in the actuation system are currently investigated. Further methods for interaction monitoring are required due to the specific resulting dynamics. The int...

Variable stiffness actuators were introduced to decouple an otherwise stiff actuator from the load by an adjustable elasticity. This variable elastic element can be used as torque sensor, acts as an energy storage, decouples the actuator for exogenous high frequency excitation inputs and contributes towards shock resistance and safety in human-robo...

To realize different tasks in human-robotic interaction, various mechanical variable stiffness actuators are being investigated. A mechanical-rotary impedance actuator (the MeRIA) is presented that is based on the controllable effective length of a mechanical bending bar, which can be implemented into an orthosis for future research on rehabilitati...

In this paper we describe a synthesis procedure for the design of output feedback controllers subject to a strictly positive real constraint. The procedure addresses the minimisation of the H2-norm, in the absence of assumptions typically made for the standard H2-control problem. In order to impose the additional strictly positive real constraint o...

We present a new decentralised control design involving an adaptive friction compensator for the electro-pneumatic adaptable impedance actuator (EPAIA). EPAIA consists of a brushless direct current (BLDC)-motor and a rotational pneumatic actuator, where the latter serves as an adaptable compliant element in series to the gear train. The decentralis...