This paper presents a comprehensive treatment of the complex motion control systems in the Sliding Mode Control (SMC) framework. The single and multi degrees of freedom (DOF) plants and applications ...to haptics and functionally related systems are discussed. The proposed algorithms are based on the application of the equivalent control observer and the convergence term that guaranty stability of the closed loop in a Lyapunov sense and enforces the sliding mode on selected manifolds. Presented SMC design leads to a solution that easily could be modified to include majority of the algorithms presented in the literature.
In the operation of large-scale manufacturing equipment, accurate tracking of the desired trajectory and overall motion synchronizations are the keys to ensuring the products' high quality. These ...multi-axis plants are highly coupled nonlinear systems with a range of uncertainties (parametric uncertainties, unmodelled dynamics, cross-coupling between axes, and external disturbances). That makes the control design for such systems a challenging task. In this paper, a Lyapunov-based design for motion tracking and/or cross-coupling synchronization control for multi-axis systems is proposed. The aim is to develop a general framework for the design of motion tracking and/or cross-coupling synchronization. The proposed design is based on a specific structure of the generalized control error and design of control which enforces a predefined form of the Lyapunov function time derivative. The structure of the generalized error allows the application of the same controller design procedure for motion tracking and/or cross-coupled synchronization control in either configuration or operation space. In the proposed design compensation of uncertainties and the convergence of the generalized error are treated separately. The compensation for the uncertainties is realized by the application of an unknown input observer within the controller structure. That yields efficient compensation of the projection of the system uncertainties to the generalized error. In ensuring the desired convergence and stability the Lyapunov function time derivative is used as a design parameter. It could be selected so that closed-loop dynamics exhibits asymptotic or finite-time convergence. The proposed design results in a simple easy-to-implement controller structure with a small number of design parameters. The details of the design procedure and the proposed controller are evaluated in simulation and experiments for a coupled 4-axis system.
This paper presents a comprehensive overview of the application of Variable Structure Systems (VSSs) with Sliding Mode (SM) methods in motion control systems. Our aim is to give implementable sliding ...mode design solutions for complex motion systems, actuators and supply converters. This paper provides a frame for further study of sliding mode applications in motion control systems.
When a complex task has to be performed by multiple systems, it imposes functional dependencies between the states and/or outputs of the systems. These functional dependencies create a system of’ ...virtually’ interconnected subsystems, even though they may be physically separated. The component subsystems within the overall system we call ‘functionally related systems’. This paper deals with motion control design for functionally related systems. The design is based on identifying functions. The control design is then performed by projecting the system dynamics into the function space. The main goal is to obtain unit control distribution matrix in the function space and enforce a desired dynamics for each of the identified functions.
This paper investigates the bilateral teleoperation with the possibility of continuously variable scaling during real-time operation. The algorithm proposed for this purpose provides the operator ...with the ability to change the scaling gains of force and velocity loops during operation. The controllers are derived to enforce exponentially decaying error dynamics on systems which have inner loop disturbance compensation. The proposed architecture assumes the scale factors as continuous functions of time which have continuous derivatives that are also included in the mathematical derivation. Unlike the existing studies, the presented framework allows real-time adaptation of scaling gains, which provides the user with the ability to conduct coarse and fine motion in the same operation. The Lyapunov stability proof of the proposed method is made and the margins of the controller gains are identified for practical operation. Furthermore, the operational accuracy is enhanced by the application of a PD force control loop which is also new for scaled bilateral teleoperation. The realization of PD loop is made using an
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filter to differentiate the force signal. The algorithm is validated on a setup consisted of two single DOF motion control systems. In order to provide a complete analysis, a wide range of experiments are made, velocity and force scales having sinusoidal patterns with different amplitudes and frequencies. Moreover, comparison with a classical bilateral control architecture is made to highlight the flexibility of the proposed control method. The efficacy of the proposed approach is solidified by the successful tracking responses obtained from these experiments.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
This paper offers a new approach for specifying the waveforms of driving voltages for a Piezo LEGS motor. A novel idea of coordinate transformation to define the waveforms of driving voltages, based ...on the motor static model, is presented. This transformation defines driving voltages according to the desired motion of the motor legs in the x- and y-directions. The approach allows a user to first define force acting on the motor rod in the y-direction and define the rod's x-direction trajectory profile. Waveforms of the driving voltages are subsequently defined to meet these requirements. The proposed approach also enables the possibility of defining the desired step shape for the motor and, according to that definition, producing driving voltages. Based on the given coordinate transformation, a simple method for Piezo LEGS motor control, identified as virtual time control, is presented. This method results in overshoot-free high precision positioning.
This paper introduces a novel control approach for Doubly-Fed Induction Generator (DFIG) operating in island mode based on the cascaded control structure with disturbance estimation. The control of ...the DFIG is a challenging task due to its inherent nonlinearity, fast dynamics, and unpredictable disturbances acting on the system. The proposed control structure involves a nominal controller for plant and disturbance observer (DOB) in each of the inner and outer control loop. The first-order disturbance observers are designed to estimate the time-varying and unknown disturbances. With disturbance estimation, the nominal linear dynamics is obtained in both loops. This enables the same approach for designing controllers for the inner and outer loop which significantly simplifies implementation. The controllers are designed based on the demanded error dynamics and ensure stable operation of the system, while proposed DOBs estimate disturbances including external load. Finally, the effectiveness and quality of the proposed control structure were verified through numerical simulations in terms of external disturbances rejection and closed-loop tracking performance.
This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected ...inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration of total utility power. However, restrictive grid codes require that renewable sources connected to the grid must support stability of the grid under grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a proportional current controller with a first-order low-pass filter disturbance observer (DOb). The proposed controller establishes independent control on positive, as well as negative, sequence current components under asymmetrical grid voltage conditions. The approach is independent of parametric component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb. A numerical simulation model of the overall power system was implemented in a MATLAB/Simulink (2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover, a set of simulation results provided in the article matches the developed theoretical background for its feasibility.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In this paper, control of piezostage using sliding-mode control (SMC) method is presented. Due to the fast dynamics of the piezostage and since high accuracy is required the special attention is paid ...to avoid chattering. The presence of hysteresis characteristics represents main nonlinearity in the system. Structure of proposed SMC controller is proven to offer chattering-free motion and rejection of the disturbances represented by hysteresis and the time variation of the piezostack parameters. In order to enhance the accuracy of the closed loop system, a combination of disturbance rejection method and the SMC controller is explored and its effectiveness is experimentally demonstrated. The disturbance observer is constructed using a second-order lumped parameter model of the piezostage and is based on SMC framework. Closed-loop experiments are presented using a proportional-integral-derivative controller and sliding-mode controller with disturbance compensation for the purpose of comparison
This study experimentally and numerically investigates the effects of the nozzle/needle distance (clearance) and supply pressure on single phase compressible gas flow in a micro orifice with needle ...restriction, which play important roles in many engineering applications such as cryogenic cooling and MEMS (microelectromechanical systems) device cooling. Nitrogen was used as the working fluid at supply pressures ranging from 10 to 50 bars, while the conical needle draft angle was 15°. The nozzle/needle distance (clearance) was changed from 100 µm to 500 µm. From the experimental point of view, the load provided by the working fluid over the needle was measured by a load sensor. For the numerical analysis, six turbulence models and three wall treatments were considered in numerical simulations. The effect of micro restriction on high-pressure micro-gas flows was further assessed by numerical modeling. It is evident from the results that the utilized turbulence model has a considerable effect on the computed results. The k–ε standard and Spalart–Allmaras models were found to be not suitable for modeling micro-scale gas flows with restriction. On the other hand, the k–ε realizable and k–ω SST models exhibit the best performance in predicting the results.
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