Chae-Cheon Cheong

Moving switching surfaces for robust control of second-order variable structure systems

Abstract Most of the switching surfaces proposed so far for a variable structure control system (VSCS) have been determined independently of initial conditions. The VSCS with these typical switching surfaces may be sensitive to parameter variations and extraneous disturbances during the reaching phase. To overcome this drawback, we propose a new switching surface which is initially designed to pass arbitrary initial conditions, and subsequently move towards a predetermined switching surface by rotating or/and shifting. We call it a moving switching surface (MSS). Using the MSS a low sensitivity system is obtained through shortening the reaching phase. Furthermore, the system robustness is guaranteed during whole intervals of control action by eliminating the reaching phase. To illustrate the advantages of the proposed method, a simple second-order linear system subjected to external disturbance is considered as a preliminary example followed by a two-link manipulator.

Force tracking control of a flexible gripper featuring shape memory alloy actuators

Abstract This paper presents a robust force tracking control of a flexible gripper using shape memory alloy (SMA) actuators. The governing equation of a partial differential form for the flexible gripper is derived by employing Hamilton’s principle, and a state-space control model is obtained by retaining a finite number of vibration modes. In the formulation of the control model, time constant of the SMA actuator is treated as uncertain parameter. This is adopted due to the fact that the SMA actuator has different time constant at the heating and cooling stage, respectively. The H ∞ -controller is then synthesized by treating the uncertain parameter as coprime factor. The specifications of stability margin and steady state error to achieve robust performance are imposed, and the first-order reference model is augmented to avoid excessive overshoot. After analyzing the robust stability of the system using the singular value plot, the controller is experimentally realized and force tracking control responses for step and sinusoidal force trajectories are presented in time domain to demonstrate the effectiveness of the proposed methodology.

Comparison of Field-Controlled Characteristics between ER and MR Clutches

This paper presents torque control characteristics of ER (electro-rheological) and MR (magneto-rheological) clutches. As a first step, Bingham properties of ER and MR fluids are experimentally distilled under the shear mode. A nondimensional model of the clutches is established for reasonable comparison. Two clutches have the same principal design parameters such as outer radius of the disc and electrode gap size. Following the manufacturing of two clutches on the basis of the nondimensional model, field-dependent torque levels are experimentally evaluated. A PID (proportional-integral-derivative) controller is then designed and experimentally realized to achieve desired torque. Both regulating and tracking torque control responses of the two clutches are evaluated and compared. In addition, control durability for torque tracking is undertaken to provide a practical feasibility of the proposed clutches.

Active Vibration Control of Intelligent Composite Laminate Structures Incorporating an Electro-Rheological Fluid

This paper addresses an active vibration control of intelligent composite laminate structures containing an electro-rheological (ER) fluid. Firstly, complex shear modulus of the ER fluid itself is obtained as a function of imposed electric fields and excitation frequencies through a rotary oscillation test. By incorporating the measured complex modulus with a conventional sand wich beam theory, elastodynamic properties of the structures are then predicted. Subsequently, an experimental investigation is undertaken in order to identify modal characteristics such as damped natural frequencies, damping ratios, and mode shapes of the structures. As for the validation of the modeling methodology, the comparison between the predicted elastodynamic properties and the measured ones is performed. Characteristics of the ER fluid actuator explicitly representing the relationship between elastodynamic properties and imposed electric fields are also inferred. A control system model is then formulated by combining the actuator characteristics into a phenomenological governing equation of a finite element form. Based on the field-dependent frequency responses of the structures, an active control algorithm for accomplishing desired responses of the tip deflection is established. In addition, in order to validate the proposed control strategy, the measured desired responses by means of an experimental implementation are compared with the predicted ones through the proposed model in the frequency domain. Finally, the effectiveness of the proposed control model for avoiding resonance to variable disturbances is evaluated by presenting the controlled tip deflection of the employed composite structures with respect to control gain in the time domain.

Feedback control of tension in a moving tape using an er brake actuator

Abstract A feedback controller for a moving tape tensioning system which uses an ER (electro-rheological) brake actuator is presented.Firstly, an arabic gum-based ER fluid is composed and its static yield stress is obtained by applying electric fields to the fluid domain.An appropriate size of ER brake is manufactured, and its dynamic characteristic is experimentally identified.After formulating a governing equation of motion for the feedback tension control system, a sliding mode control algorithm is formulated to achieve a desired level of tension.Both simulation and experimental work are undertaken on the tension regulating and tracking controls in order to demonstrate the efficiency and feasibility of the proposed method.

Position Tracking Control of a Smart Flexible Structure Featuring a Piezofilm Actuator

A position tracking control of a smart flexible structure with a piezofilm actuator is presented. A governing equation of motion for a smart cantilevered beam is derived via Hamiltons principle, and a reduced-order control model is subsequently obtained through a modal analysis. Uncertain system parameters such as frequency variations are included in the control model. A sliding-mode control theory, which has inherent robustness to system uncertainties, is adopted to design a position tracking controller for the piezofilm actuator. Using the output information from a tip displacement sensor, a full-order observer is constructed to estimate state variables of the control system. Tracking control performances for desired position trajectories represented by sinusoidal and step functions are evaluated by undertaking both simulation and experimental works. Nomenclature A i = cross-sectiona l area of the composite beam A 2 = cross-sectional area of the piezofilm b = width of the composite beam (or piezofilm) di = magnitude of the disturbance d3i = piezoelectric strain constant E\ = elastic modulus of the composite beam EI = elastic modulus of the piezofilm e = tracking error of the tip displacement / = external disturbance g = gradient of the sliding surface hi = thickness of the composite beam hi = thickness of the piezofilm // = generalized mass /i = area moment of inertia of the composite beam 72 = area moment of inertia of the piezofilm k = discontinuity gain of the sliding-mode controller L = length of the composite beam (or piezofilm) qi = generalized modal coordinate R = observer matrix s = sliding surface t = time variable Tk = kinetic energy V = control input voltage Vp = potential energy x = spatial variable in the axial direction Xj = state variable Xj = estimated state variable ydt = desired tip displacement yt = actual tip displacement Pi = weighting factor of the natural frequency deviation Yi = weighting factor of the damping ratio deviation s = boundary layer width of saturation function f/ = damping ratio Pi = density of the composite beam p2 = density of the piezofilm , = mode shape function o)i = natural frequency

PERFORMANCE ANALYSIS OF AN ENGINE MOUNT FEATURING ER FLUIDS AND PIEZOACTUATORS

Conventional rubber mounts and various types of passive or semi-active hydraulic engine mounts for a passenger vehicle have their own functional aims on the limited frequency band in the broad engine operating frequency range. In order to achieve high system performance over all frequency ranges of the engine operation, a new type of engine mount featuring electro-rheological(ER) fluids and piezoactuators is proposed in this study. A mathematical model of the proposed engine mount is derived using the bond graph method which is inherently adequate to model the interconnected hydromechanical system. In the low frequency domain, the ER fluid is activated upon imposing an electric field for vibration isolation while the piezoactuator is activated in the high frequency domain. A neuro-control algorithm is utilized to determine control electric field for the ER fluid, and H∞ control technique is adopted for the piezoactuator Comparative works between the proposed and single-actuating(ER fluid only or piezoactuator only) engine mounts are undertaken by evaluating force transmissibility over a wide operating frequency range.

Performance Evaluation of a Mixed Mode ER Engine Mount Via Hardware-in-the-Loop Simulation

This paper proposes a new type of an ER (electro-rheological) engine mount which has a mixed mode as fluid working mode (the combination of shear and flow modes). As a first step, a mixed mode ER engine mount, which is applicable to a medium-sized passenger vehicle, is designed and manufactured by incorporating Bingham model of the ER fluid. The vibration isolation performance of the ER engine mount with different intensity of electric fields is evaluated in the frequency domain and compared with that of conventional hydraulic type engine mount. Subsequently, a full car system installed with the proposed ER engine mounts is constructed and modeled by considering engine excitation forces. After deriving its governing equations of motion, HIh control algorithm is formulated by taking into account the semi-active actuating condition. The vertical engine displacement and body acceleration are evaluated via hardware-in-the-loop simulation (HILS) at various engine excitation frequencies.

Position control of an ER valve-cylinder system via neural network controller

Abstract A system of position control which uses a single-rod cylinder activated by an electrorheological (ER) valve is presented. Following the manufacture of a silicone oil-based ER fluid, a Bingham property of the ER fluid is first tested as a function of electric field in order to determine operational parameters for the ER valve.The ER valve with multi-channel plates is then designed and manufactured. Subsequently, pressure drops of the ER valve are evaluated with respect to the number of electrodes as well as the intensity of the electric fields. The ER valve—cylinder system is formulated and governing equations of motion for the system are derived. From the state-space model for the governing equations, a neural network control scheme is synthesized to achieve the position control of the cylinder system.Both regulating and tracking control responses are experimentally evaluated and presented in order to demonstrate the effectiveness of the proposed methodology.

control of structure-borne noise of a plate featuring piezoceramic actuators

This paper addresses active structural acoustic control of a flexible plate using piezoelectric actuators. The analytical model of a thin plate with simply supported boundary conditions is derived from Hamiltons principle and a control model represented by the transfer function is obtained. Optimal locations of the piezoelectric actuators are found such that it minimizes the radiated sound power at the farfield. With optimally designed actuators, an controller is designed by using the loop shaping design procedure to achieve robust acoustic control of the proposed system subjected to parameter variations and external disturbances. Control performance and robustness are presented in both frequency and time domains in order to demonstrate the effectiveness of the proposed approach. In addition, the comparison between the proposed robust controller and the conventional adaptive Filtered-x LMS algorithm is undertaken.