Hakan Elmali

Robust output tracking control of nonlinear MIMO systems via sliding mode technique

The robust output tracking control problem of general nonlinear multi-input multi-output (MIMO) systems is discussed. The robustness against parameter uncertainties and unknown disturbances is considered. A second order sliding mode control (SMC) technique is used to establish the desired tracking. Input/output (I/O) linearization, relative degree, minimum phase and matching condition concepts are reviewed. Some earlier SMC strategies which are restricted to the systems in canonical form are extended to a much broader class of nonlinear dynamics. It is also shown that for unperturbed dynamics, the sliding phase of the SMC applications have a direct correspondence to the I/O linearization operations. Interesting parametric flexibilities emanate within the formation of the second order SMC, designating the “s dynamics” and the “error dynamics” segments as frequency domain filters. However, a critical impasse is posed in the off-line selections of the design parameters. A set of example cases is presented for a spacecraft attitude control problem. These examples manifest that the proposed control strategy is tunable to a desired response despite the disturbances and uncertainties.

Sliding mode control with perturbation estimation (SMCPE): a new approach

Abstract Sliding mode control (SMC) of a general class of nonlinear control systems is considered in this work. The conventional SMC technique requires knowledge of the upperbounds of disturbances and modelling uncertainties to assure robustness. However, this may not be easy to obtain. As a remedy, an estimation process for these dynamic perturbations is employed jointly with the SMC technique. This new methodology, sliding mode control with perturbation estimation (SMCPE), offers a robust feedback control with much lower gains than its conventional counterparts against slowly varying perturbations. This resolves one of the problematic issues which has caused concern over the years of development of SMC applications. An interesting perspective of selecting the cut-off frequency for s dynamics is presented with a novel upperbound argument. Much desirable tracking fidelity is arrived through SMCPE in the computer simulation studies for a two-link manipulator. A companion approach to SMCPE, the discrete equ...

Implementation of sliding mode control with perturbation estimation (SMCPE)

Experimental verification of a recently developed algorithm, sliding mode control with perturbation estimation (SMCPE), is performed, a two-axes planar SCARA type robot is used as the test platform. The controller is a PC-based microprocessor with transducer and actuator interfaces. The objective of trajectory tracking is achieved by directly controlling the joint torques, despite the modeling deficiencies and unknown disturbances. Two major practical issues are considered. One of them is the measurement noise and the other is the hard/software limitations on the control loop closure speed. Both of these issues affect the parametric selections with the SMCPE algorithm. A sample test result is presented, to compare the performance of SMCPE with the classical SMC.

Active Vibration Control of Distributed Systems Using Delayed Resonator With Acceleration Feedback

The Delayed Resonator (DR) and Dual Frequency Fixed Delayed Resonator (DFFDR) are newly introduced control techniques for active vibration absorption. Both methods propose a delayed position feedback within the absorber section of the structure to impart ideal resonance features to the absorber. When installed on an oscillating primary body, they form notch filters at their resonance frequencies attenuating the response of the primary structure. The DR absorber is shown to be real-time tunable to time varying disturbance frequencies. In this article, a number of new issues are considered. First, the basic theory is modified for acceleration feedback instead of position, which was originally proposed for the DR methodology. Second, the new absorption methods are implemented on distributed parameter structures which are under high frequency excitation (around 1 KHz). Stability of the combined structure is studied on a reduced order multi-degree-of-freedom primary structure together with the DR absorber. Experimental tests are conducted on a steel beam to verify the analytical findings. Piezoelectric actuators are used both to generate harmonic disturbances and to implement the control. The correspondence observed between the theoretical and experimental results is encouraging. The efficiency of the DR and DFFDR absorption techniques is demonstrated.

Sliding Mode Control With Sliding Perturbation Observer

This work introduces a new robust motion control algorithm using partial state feedback for a class of nonlinear systems in the presence of modelling uncertainties and external disturbances. The effects of these uncertainties are combined into a single quantity called perturbation. The major contribution of this work comes as the development and design of a robust observer for the state and the perturbation which is integrated into a Variable Structure Controller (VSC) structure. The proposed observer combines the procedures of Sliding Observers (Slotine et al, 1987) with the idea of Perturbation Estimation (Elmali and Olgac, 1992). The result is what is called Sliding Perturbation Observer (SPO). The VSC follows the philosophy of Sliding Mode Control (SMC) (Slotine and Sastry, 1983). This combination of controller/observer gives rise to the new routine called Sliding Mode Control with Sliding Perturbation Observer (SMCSPO). The stability analysis shows how the algorithm parameters are scheduled in order to assure the sliding modes of both controller and observer. A simplified form of the general design procedure is also presented in order to ease the practical applications of SMCSPO. Simulations are presented for a two-link manipulator to verify the proposed approach. Experimental validation of the methodology is also performed on a PUMA 560 robot. A superior control performance is obtained over some full state feedback techniques such as SMC and Computed Torque Method.

Experimental Comparison of Delayed Resonator and PD Controlled Vibration Absorbers Using Electromagnetic Actuators

The Delayed Resonator (DR) is a recent active vibration absorption technique which uses time delayed position feedback generating ideal resonance feature in a passive vibration absorber. This objective can also be achieved using proportional and derivative (PD) control as well as other more sophisticated routines such as LQR, sliding mode control. In this paper, DR technique is compared with PD, a widely adopted control strategy. Actuator dynamics is taken into account in analyzing the system. An analytical comparison is presented which is followed by an experimental validation of the findings using a single-degree-of-freedom primary structure and an absorber with electromagnetic actuator. Both analytical and experimental results show that the DR and PD implementations can be equally effective in suppressing undesired oscillations. The latter, however, requires a velocity observer, which is an additional complexity beyond the DR feedback structure.

Theory and implementation of sliding mode control with perturbation estimation (SMCPE)

A novel approach, sliding mode control with perturbation estimation (SMCPE), is presented to remove the restrictions of SMC about the a priori upperbound knowledge for the perturbations and to improve the tracking performance. It does not require the a priori knowledge of the upper bounds of the uncertainties and it offers much better tracking accuracies. However, SMCPE requires that the control loop speeds be reasonably faster than the perturbation dynamics. The success of SMCPE applications is closely related to the precision of the state measurements. Experimental justifications are presented from the applications of SMCPE on a SCARA-type Hitachi robot.<<ETX>>

Analysis and Design of Delayed Resonator in Discrete Domain

The delayed resonator (DR) is a new active vibration absorption technique that uses time-delayed partial state feedback to generate ideal resonance on a passive vibration absorber. It has many attractive features such as real-time tunability, ease of implementation, and total suppression of vibration for tonal frequency disturbances. The DR controller has been developed in continuous domain until now. In this paper, discrete domain analysis is presented. Simulation results indicate an expected dependency of stability on the sampling period for this active control strategy. A major advantage of discrete domain analysis is the reduction of characteristic roots from infinite to finite numbers and consequent simplicity in the analysis and design of the controller. It is shown that discrete domain control design for DR yields better vibration suppression considering the sampled control structure in implementations.

The Centrifugal Delayed Resonator as a Tunable Torsional Vibration Absorber for Multi-Degree-of-Freedom Systems

The centrifugal delayed resonator (CDR) is a novel active vibration absorption technique for elim inating undesired torsional oscillations in rotating mechanical structures. The key idea is to reconfigure the dynamics of a damped centrifugal pendulum arrangement so that it mimics an ideal real-time tunable ab sorber. This objective is achieved by applying a control torque based on proportional position feedback with variable gain and time delay. Theoretical fundamentals of the technique are explained, its implementation on a multi-degree-of-freedom primary structure is presented, stability of the controlled system is discussed, and real-time tuning ability is elaborated upon and demonstrated via simulations. The strengths of the CDR control consist of complete vibration elimination of the fundamental frequency component of torsional oscil lations at the location where the absorber is attached to the rotating structure, automatic tuning to time-varying frequencies, decoupling of the feedback control from the mechanical and dynamic properties of the rotating structure, relatively simple implementation of the control algorithm, and fault-tolerant performance in the case of control failure.

Tracking control of a rotating flexible beam using modified frequency-shaped sliding mode control

The purpose of this study is to improve a robust control strategy using frequency-shaped sliding surfaces. The control objective is the trajectory tracking of a flexible beam attached to a rigid hub. A compensator is introduced in sliding mode through a frequency-shaped performance index with prescribed degree of stability. This procedure yields desirably fast trajectory tracking without exciting the unmodelled dynamics (UD). It also offers a methodology to resolve this trade-off. Simulation results show that regarding the excitation of UD, the proposed control structure exhibits superior characteristics among peer sliding mode strategies.