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To improve motion accuracy through functional electrical stimulation (FES) of forearm muscles, feedback control laws are applied to the index finger’s metacarpophalangeal (MP) joint. This paper introduces a proxy-based super-twisting algorithm (PSTA) for precise servo control of MP joints via FES. The PSTA combines first-order sliding mode control with a second-order super-twisting algorithm, effectively preventing windup during FES saturation and ensuring robust, accurate control. An implicit Euler method minimizes numerical chattering in the digital implementation. Experiments with Arduino and volunteers confirm the algorithm’s effectiveness.

Abstract This paper addresses the exploitation of vector based contraction theory to synchronize the motion of agents in multiagent systems. The convergence analysis of the agents using this theory provides a flexible frame as the components of a vector distance norm follow less stringent conditions than classical contraction analysis. The key feature is that it encompasses the formulation of some comparison system, as a result, the problem of convergence analysis of a complex multiagent system reduces to the convergence analysis of a much simpler comparison system. Hence, despite the nonlinearities, the methods of designing consensus controls remain simple as compared to the existing literature. We address four different cases: 1) consensus of third‐order dynamics multiagent systems subjected to acceleration and input constraints; 2) consensus of multiagent systems with heterogeneous nodes under communication imperfections; 3) synchronization of multiagent systems with connected and disconnected switching topologies; 4) synchronization in networked systems with time‐varying couplings. Moreover, an effective synchronization control scheme for a class of multiagent systems with underactuated agent dynamics is developed using the method of aggregation of comparison systems. Finally, simulation results are illustrated that show the validity of the mathematical results.

Abstract This paper proposes a distributed artificially delayed output feedback‐based leader–follower and leaderless consensus control for the uncertain general linear multiagent systems (MASs) with an arbitrary relative degree. Based on the measured relative output and their delayed information with respect to neighbours, two distributed controllers are designed, which relaxes the requirement of all relative states information of agents. Through the Lyapunov–Krasovskii functional, linear matrix inequalities (LMIs) are formulated, and these LMIs are feasible for arbitrary small delays selected by the user. Delay‐dependent sufficient conditions are provided to guarantee the asymptotic convergence of nominal error systems and ultimately uniform boundedness in the case of a perturbed error system, using the input to state stability (ISS) theory. Finally, the efficacy of the proposed method is illustrated through numerical examples.

Abstract This paper addresses a quantized feedback hands‐off control for a class of nonlinear systems. Here, [K,KL] sector is constructed with the suitable choice of control‐Lyapunov function. With adjustment policy of quantization parameters, the quantized feedback hands‐off control can force the states of the nonlinear feedback system to the interior of a continuous‐time [K,KL] sector infinite time and the Lyapunov‐candidate function decreases automatically inside the designed sector. Finally, the effectiveness of the proposed method is illustrated by numerical examples.

High voltage gain DC-DC converter is a prime requirement for renewable applications, in particular for PV. Though numerous DC-DC converter is available for increasing the voltage gain, the passive elements requirement is higher which reduces the compactness, consequently, increases the cost of the system. To address this issue, a high gain DC-DC converter is reported recently. However, the number of passive elements is quite high which increases the size. To reduce the number of passive elements and maintain the same number of semiconductor devices, in this paper, a new switched inductor arrangement is proposed which is named as switched inductor double switch DC-DC converter (SL-DS-DC). Moreover, the proposed converter has a higher gain as compared to the recently reported converter. The proposed converter is analyzed in steady state and a comparative analysis is presented to prove the suitability. Finally, the proposed converter is validated experimentally.

This paper investigates the problem of nonsmooth feedback stabilization for the higher order uncertain chain of integrators. For achieving the specified goal, the integral term of classical Proportional-Integral (PI) controller is replaced by an integral of the discontinuous function. Replacing this integrator, the overall control becomes absolutely continuous rather than discontinuous as in the first order sliding mode control. With this proposed scheme, the property of invariance concerning the matched Lipschitz uncertainty is still preserved. The main technical contribution of the paper is a sound and non-trivial Lyapunov analysis of the closed loop system controlled by nonsmooth PI controller. The effectiveness of the proposed controller is illustrated with the help of numerical simulation on the magnetic suspension system.

Visual servoing (VS) is a technique which uses feedback information obtained from a camera to control the motion of a robot. With respect to approaches that rely on feature-based perception processes to recover the relative pose between the target and the robot, direct visual servoing (DVS) does not require pose estimation, nor featur extraction, tracking and matching, but uses the images as a whole feature directly. Set-based DVS (SDVS) algorithms are based on theory of mutation analysis of shapes or sets and these algorithms have been proposed by researchers recently. However, the computational efficiency for SDVS is relatively slow. In this paper, we proposed a family of novel fast algorithms to improve computing efficiency of SDVS. Simulation results demonstrate the validation of our algorithms as well as the computation efficiency advantage over other SDVS work.

Estimating reliable signal component and its derivatives from noisy feedback signal is important in control systems. Toward this problem, this article presents a new model-free variable gain sliding mode tracking differentiator for derivative estimation of noisy signals by modifying a Levant and Yu’s sliding mode tracking differentiator. Specifically, different from Levant and Yu’s TD, the new TD employs an additional variable that contributes to overshoot reduction. In addition, the new TD adaptively changes its gains for improving the tracking and filtering performances. Moreover, the new TD only uses previous output values and it does not require input signal model in advance. The advantages of the new TD over previous TDs are confirmed through numerical examples.

Noise reduction is one of the important issues for feedback control systems. Toward this problem, this paper proposes a new sliding mode filter, which is an improvement of Lv et al. ’s parabolic sliding mode filter. The proposed filter employs a first-order derivative feed-forward term for increasing both tracking and noise attenuating performances. Its discrete-time algorithm is derived by applying the implicit-Euler discretization, and it realizes exact convergence without producing chattering in discrete-time implementation. The effectiveness of the proposed filter is evaluated through an open-loop and a closed-loop numerical examples.

Switched boost inverter (SBI) is a high gain converter that uses the concept of Z-source inverter but with a reduced number of passive elements. The analysis and operation of SBI are already reported for continuous and discontinuous input current but these converters operate in the restricted range of duty cycle and load variation. In a certain duty cycle situation, the converter shows inadvertent behavior and the inductor current tends to become equal to the AC load current. This phenomenon creates a ripple in dc link voltage which causes increased THD at the output AC voltage. Moreover, the DC link capacitor undergoes higher voltage stress. In this paper, the duration for which this peculiar phenomenon lasts is termed as non-zero discontinuous current mode (NZ-DCM) of operation. The analytical expression during NZ-DCM is derived and analyzed in terms of peak to peak ripple inductor current. To overcome NZ-DCM, the authors propose a modified SBI which consists of an extra active switch antiparallel across the diode. The simulation and experimental results pertaining to the adverse effect of NZ-DCM and its mitigation in the form of the conventional and modified SBI are presented in this paper.

In this paper, we concerned to achieve an asymptotic stabilization of a generalized nonlinear system with significant uncertainties by rendering a relatively lesser amount of control. Here, a combined control consist of Hands-Off control and an adaptive sliding mode control is allowed to adjust the movement of the system state to the interior of [K, KL] sector and compensate the unknown disturbance, respectively. The adaptation methodology consists of a low-pass filter to filter-out the high-frequency component and searches for minimum possible value to cancel the effect of the unknown disturbance throughout the dynamical system. Finally, a design example is shown with the simulation results for [K, KL] sector design.

EMI has remained a limiting factor in driving the SiC MOSFETs to its maximum potential and achieving a trade-off between EMI and switching losses is a major challenge for the designers. In this paper, an inductor-less, discontinuous current source gate driver (DCSD) is proposed. Exclusion of inductor results in a compact footprint and easy integration in IC form. The absence of predriver for proposed DCSD reduces the complexity of the driver, making it easier to control and implement. In addition, very low propagation delay is attained with the proposed DCSD which allows SiC MOSFETs to switch at higher switching frequencies with low losses. The proposed DCSD is compared with a commercially available reference gate driver for SiC MOSFET, and the results are analyzed and validated with hardware prototype. A better trade-off between switching losses and EMI is obtained with the proposed driver, where during turn-off, a 65% reduction in dVds/dt and 45% reduction in dId/dt is achieved at the cost of 33% increase in the total switching loss.

The coupled inductor based Z-source converter produces higher voltage gain with lower number of components count. In this paper, a new two winding mutually coupled inductor based Z-source DC-DC converter is proposed to boost the voltage gain. The proposed converter utilizes reduced number of passive elements count to produce higher voltage gain specially in lower duty cycle range. Moreover, the coupled inductor winding are arranged in auto-transformer fashion to maximize the effective turns ratio. Therefore, minimum number of winding turns are used for realizing the higher gain. The proposed converter draws continuous input current and has common grounding which are attractive features for hybrid electric vehicle powered by renewable sources. Furthermore, the voltage stress across the different components is reduced for the proposed converter. The operation, steady state analysis and comparative analysis is presented for the proposed converter. Finally, an experimental setup of 215 W is designed and tested to show the feasibility of the proposed converter.

This paper proposes an alternative implementation for a continuous terminal algorithm (CTA) proposed by Torres-Gonzalez et al. The original CTA is a continuous version of the twisting algorithm (TA), which mitigates the chattering by integrating the signum functions with increased relative higher order. However, the discrete-time version of CTA resulting from conventional explicit discretization method still suffer from some magnitude of chattering. The chattering is obvious when the gains of CTA and the time-step sizes are set large. We propose an implicit Euler integration method, which totally suppresses the chattering and keeps the properties of the continuous version of CTA, such as finite time convergence and high accuracy. The efficiency of this discrete-time implementation is illustrated by comparing it to the conventional explicit method.

This paper presents a new quick-response sliding mode tracking differentiator (new TD) for feedback control of mechatronic systems. The new TD is an extension of Jin et al.’s sliding mode tracking differentiator (TD-J) by employing an exponential reaching term for balancing the trade-off between noise attenuating efficiency and convergence speed. The discrete-time algorithm of the new TD is derived by using the implicit-Euler discretization and an equivalent between a set-valued signum function and a saturation function, and it does not produce chattering, which has been one major challenge of implementing sliding mode technique in discrete-time. Simulations and experiments are conducted for validating the effectiveness of the new TD.

Micro-electro-discharge machining (μEDM) plays a significant role in miniaturization. Complex electrode manufacturing and a high wear ratio are bottlenecks for μEDM and seriously restrict the manufacturing of microcomponents. To solve the electrode problems in traditional EDM, a µEDM method using liquid metal as the machining electrode was developed. Briefly, a liquid-metal tip was suspended at the end of a capillary nozzle and used as the discharge electrode for sparking the workpiece and removing workpiece material. During discharge, the liquid electrode was continuously supplied to the nozzle to eliminate the effects of liquid consumption on the erosion process. The forming process of a liquid-metal electrode tip and the influence of an applied external pressure and electric field on the electrode shape were theoretically analyzed. The effects of external pressure and electric field on the material removal rate (MRR), liquid-metal consumption rate (LMCR), and groove width were experimentally analyzed. Simulation results showed that the external pressure and electric field had a large influence on the electrode shape. Experimental results showed that the geometry and shape of the liquid-metal electrode could be controlled and constrained; furthermore, liquid consumption could be well compensated, which was very suitable for µEDM.

Metabolic cost during walking is positively linked to exercise intensity. For a walking assistive device, one of the major aims should be the maximization of wearers’ metabolic benefits for different walking situations. Toward this goal, this paper experimentally evaluates the influence of an authors’ soft robotic suit, which has been developed to assist hip flexion for energy-efficient walking of elderly persons in daily life activities, on metabolic cost reduction in the long-distance level and inclined walking. Experiment results show that, for a 79-year-old healthy male subject, the robotic suit significantly reduced metabolic cost in the condition of the robotic suit worn and powered on compared with the condition of worn but powered off.

As a walking assistive device for elderly persons, one of the major aims should be to improve and rehabilitate gait characteristics after long-term repeated use of the device. However, most of the existing research on walking assistive devices only emphasize their immediate effects, and there is limited research indicating the long-term effects. To address this gap, this paper experimentally validates the effects of our soft wearable robotic suit on gait characteristics of elderly persons after repeated use of the device for six weeks. Experimental results on four elderly subjects (age = 74.8 ± 5.0 year) show that, after six weeks of gait rehabilitation training by the robotic suit, the gait characteristics of the subjects were improved, leading to an increased walk ratio with an average of 9.8% compared with the initial state. The results of this research will benefit the potential use of the robotic suit in gait training and rehabilitation for elderly persons and also will be useful to the establishment of practical guidelines that maximize the training and rehabilitation effectiveness of the robotic suit.

This paper quantitatively evaluates the performance of an adaptive-gain parabolic sliding mode filter (AG-PSMF), which is for removing noise in feedback control of mechatronic systems under different parameter values and noise intensities. The evaluation results show that, due to the nonlinearity of AG-PSMF, four performance measurements, i.e., transient time, overshoot magnitude, tracking error and computational time, vary widely under different conditions. Based on the evaluation results, the paper provides practical tuning guidelines for AG-PSMF to balance the tradeoff among the four measurements. The effectiveness of the guidelines is validated through numerical examples.

In feedback control of mechatronic systems, sensor signals are usually noisy and uncertain because of measurement errors and environmental disturbances. Such uncertainty and noise of feedback signals may cause instability of the controlled systems. This paper presents a new model-free discrete-time sliding mode filter for effectively removing noise by balancing the tradeoff between the filtering smoothness and the suppression of delay. The presented filter is an extension of a sliding mode filter (Jin et al. Real-time quadratic sliding mode filter for removing noise. Adv. Robot., 2012) by including an adaptive gain, of which value is determined in a similar way to that of a first-order adaptive windowing filter (Janabi-Sharifi et al. Discrete-time adaptive windowing for velocity estimation. IEEE Trans. Control Syst. Technol., 2000). The effectiveness of the presented filter is validated through numerical examples and experiments.

Nonsmooth mechanical systems, which are mechanical systems involving dry friction and rigid unilateral contact, are usually described as differential inclusions (DIs), that is, differential equations involving discontinuities. Those DIs may be approximated by ordinary differential equations (ODEs) by simply smoothing the discontinuities. Such approximations, however, can produce unrealistic behaviors because the discontinuous natures of the original DIs are lost. This paper presents a new algebraic procedure to approximate DIs describing nonsmooth mechanical systems by ODEs with preserving the discontinuities. The procedure is based on the fact that the DIs can be approximated by differential algebraic inclusions (DAIs), and thus they can be equivalently rewritten as ODEs. The procedure is illustrated by some examples of nonsmooth mechanical systems with simulation results obtained by the fourth-order Runge-Kutta method.