Electrorheological Actuator Research Articles

Fabrication, Experiment, and Simulation of a Flexible Microvalve-Integrated Microarm for Microgrippers Using Electrorheological Fluid

Because of the power density advantages of fluid power systems, many researchers have developed microactuators using homogeneous electrorheological (ER) fluids (ERFs) for applications to various micromachines. An ER valve, as a critical component of the ER actuator, can control ERF flow by the apparent viscosity increase resulting from the applied electric field without any mechanical moving parts. Hence, it is adequate for the miniaturization of a fluidic microactuator. However, it is not easy to integrate rigid ER valves into soft microrobots. To overcome these limitations, we developed a novel elastic ER microarm using flexible ER valves (FERVs) in this study. Each microarm consists of an FERV, a movable chamber, and a displacement constraint element, so that it bends with the inner pressure controlled by the FERV. We proposed and developed a micro-electromechanical system fabrication process for the FERV, movable chamber, and displacement constraint element. By utilizing the proposed method, we successfully fabricate a FERV-integrated microarm. The characteristics of the FERV were experimentally clarified. In addition, the bending motion of the FERV-integrated microarm was demonstrated by experiments and verified by finite-element method simulation. This ER microarm was shown to be feasible for an ER microgripper composed of multiple microarms.

A compact and compliant electrorheological actuator for generating a wide range of haptic sensations

Robust haptic devices that can convey the entire spectrum of human touch perception are necessary to afford realistic haptic experiences. For vivid and immersive interaction, a combination of both tactile and kinesthetic information must be presented to users. While vibrotactile feedback has become ubiquitous in today’s handheld devices, traditional kinesthetic actuators present significant challenges to miniaturization. Moreover, only limited success has been achieved in developing haptic actuators capable of conveying both tactile and kinesthetic sensations for small consumer electronics. Therefore, this study presents a compact actuator based on electrorheological (ER) fluid for generating a wide range of concurrent kinesthetic and tactile feedback. The design focus for the proposed actuator is to activate multiple operating modes of ER fluid to maximize the force generated by the actuator within a given small size constraint. To this end, the design incorporated two ground electrodes (a stationary ring electrode and a movable electrode attached to a spring element) for tuning the fluid’s yield stress in both flow and squeeze modes. After fabricating a prototype actuator, testing was performed with a dynamic mechanical analyzer (DMA) and an accelerometer to evaluate its ability to produce a wide range of kinesthetic feedback, as well as distinct vibrotactile feedback up to the limit of human perception. The results of kinesthetic testing indicate that the actuator can generate large forces (6.2 N maximum at 4 kV) at rates greater than the just-noticeable difference, indicating that the actuator can convey a wide range of kinesthetic sensations. Tactile evaluation using DMA and the processed acceleration response demonstrated that the actuator can generate both low and high frequency (up to 300 Hz) vibrotactile sensations at perceivably high intensity.

Extending the operation range of electrorheological actuators for vibration control through novel designs

Electrohydraulic actuators with electrorheological fluids were lately introduced for active vibration decoupling. They are suited especially for active isolation of heavy machines and apparatuses. Compared to conventional electrodynamic or hydraulic actuators, these electrorheological systems have considerable advantages because of very high force density and broad frequency range. However, the potential of the electrorheological technology does not remain used up to now completely. In this study, new designs are introduced, which extend the operation borders of the electrorheological actuators for vibration decoupling by utilization of hydrostatic as well as to hydrodynamic forces. The theoretically determined dynamic behaviors of the new actuator principles form the basis for the choice and adaptation of the electrohydraulic systems to special vibration isolation problems and show the advantages to conventional hydraulic actuators.

A 10-kV Linear Current-Mode Power Amplifier for Capacitive Actuators

High-voltage linear pulse amplifiers with current output are advantageous for driving piezoelectric or electrorheological actuators because the inherent current ripple of switched-mode power converters can be avoided. The new amplifier provides output voltages up to 10 kV with an output current of 200 mA. Low quiescent currents of 0.6 mA minimize static power loss. Nested feedback loops are applied to ensure symmetrical voltage division among cascaded output insulated-gate bipolar transistors (IGBTs) in half-bridge configurations. Optical isolated output stages control the load current. Local current controllers at the power IGBTs enhance linearity and allow for quasi-complementary circuit design without high-voltage small-signal transistors.The symmetrical rise and fall times of 80 μs are achieved, together with the pulse peak power of more than 1 kW.

Model validation of the output reciprocating dynamic responses of a twin electro-rheological (ER) clutch mechanism

Abstract Electro-rheological (ER) fluid devices are becoming more popular in the industrial applications. This is due to the fast speed of response and large output dynamics of the ER actuators. The usefulness of this ER dynamic response is considered in the material winding processes where fast output bi-directional responses are essential. Therefore in the present paper, an ER twin clutch mechanism is proposed. This clutch mechanism consists of two identical clutches that rotate in opposite directions. But the bi-directional output dynamics of the clutch mechanism is not well understood due to its non-validation in the past. The main aim of this paper is to model the reciprocating responses of the clutch mechanism and then perform model validation with the measured test results. The close agreements between the modeled and experimental data indicate that the ER output angular velocity and displacement responses’ models of the clutch mechanism are validated. These validated models can then be used to predict accurately the reciprocating output responses of the twin ER clutch mechanism for future research studies.

Time series analysis of electrorheological actuator with double driving discs

An electrorheological(ER) actuator with double driving discs rotating at the same speed in the opposite directions was designed for studying the electrorheological torque experiments. The dynamic model of the disc transmission system consists of the linear part between the output angle and the electric torque, and the nonlinear part between the electric torque and the applied field strength dependent on the ER fluids. Using only the output sampled torque signals, an autoregressive model, the auto-spectral density function, the autoregressive(AR) bispectrum and the slices of the bispectra, taken to analyse the torque dynamic response, are obtained when a zero mean and non-Gaussian white noise interferes with the rotary disc system. The method for AR model order selection based on bispectral cross correlation is proposed and employed to determinate the model order. The experimental and theoretical results show that the time series analysis method and the parametric bispectrum might be helpful to establish the dynamic model of an ER actuator and to quantitatively analyse the torque response.

Dynamic characteristics and optimization design for disc-shape electro-rheological actuator

A disc-shape electro-rheological actuator was developed. The torque generated by a pair of rotary discs consists of two components: the torque from the viscosity of electro-rheological fluid(ERF) and the torque owing to the field-dependent yield shear stress. The former contributes to the viscous power loss. Changing the application of electric field between the two discs, the output torque of ER actuator can be controlled to amplify the torque of input signal to overcome the load and friction. Relationships between the main structure parameters, the dynamic characteristics of the device, the physical properties of ERF and the torque transmission, range of speed regulation, power loss, stiffness of system were discussed. A multi-object programming model was set up for the optimization design. Experimental simulations with step and pulse signals were presented.

Modeling and Control of an Electrorheological Actuator

This paper deals with the modeling and nonlinear control of an ER (electrorheological) actuator consisting of a double-rod cylinder and four ER valves in a full-bridge configuration. Basically, we have to face two difficulties within the controller design: First of all, the ER effect is inherently nonlinear and secondly, the ER full-bridge provides more control inputs than necessary for solving the primary control task. We will show that these additional degrees-of-freedom can be exploited to circumvent undesirable operation and to optimize the overall closed-loop performance. Furthermore, the nonlinearities of the mathematical model will be systematically included in the controller design. Measurement results performed on an experimental test-stand will demonstrate the feasibility of the proposed strategy.

Application potential of magnetic field driven new actuators

Most of the magnetic field driven actuators can be classified as electromagnetic, electrodynamic, magnetostrictive or magnetorheological (MR). While the first two mentioned have been known for a long time and are widely distributed, the actuators of the latter two groups have been gaining importance only in the last few years. In this paper, the principle, design and structure of magnetostrictive and MR actuators are presented. Typical examples illustrate their application potential which is clarified further by comparing the properties of their dual alternatives, namely, electrostrictive/piezoelectric and electrorheological actuators.

Compensator-based position control of an electrorheological actuator

This paper addresses the question of whether compensator-based controllers can be used to successfully control the position of a model scale robot arm attached to the output shaft of an electrorheological (ER) actuator, with a view of recommending the actuator for robotic applications and providing an alternative control strategy to proportional plus integral plus derivative, (PID), control. An ER actuator is a device that uses a ‘smart’ material, called an ER fluid or suspension, as a coupling medium between the prime mover running at a constant speed and a load. Three compensator-based controllers—the phase-lag, the phase-lead and lead-lag compensators—were designed and implemented on the ER actuator-arm system. The phase-lead and phase-lag compensators gave reasonable performance. The lead-lag compensator, on the other hand, was impossible to implement.

PWM Flow Rate Control of ER Valve and its Application to ER Actuator Control

The PWM (Pulse Width Modulation) control of ER valve consisting of two parallel electrodes has been investigated to continuously control the flow rate of an electrorheological (ER) suspension containing sulfonated polymer particles in silicone oil. PWM wave voltages are applied to the electrodes of the ER valve. It is possible to control continuously the flow rate by changing the duty ratio of the PWM wave from 1 to 0, where the duty ratio of 1 corresponds to the state to stop the flow. A miniature bellows actuator driven by a pair of PWM controlled ER valves has been developed, and the control characteristics of the actuator have been investigated. The duty ratios of both ER valves have been proposed to be changed alternately in proportion to the control voltage V to control the flow rate into and out of the bellows chamber, and also an overlap duty ratio D ov at V=0V has been introduced. The introduction of the overlap duty ratio D ov was found to be very important to smoothly control the actuator and to improve the control performance.

Active vibration control system of smart structures based on FOS and ER actuator

An active vibration control system based on fiber optic sensor (FOS) and electrorheological (ER) actuator is established in this paper. A new intensity modulated fiber optic vibration sensor is developed following the face coupling theory. The experimental results show that this new type of intensity modulated fiber optic vibration sensor has higher sensitivity in measuring the vibration frequency. At the same time, experimental investigations are focused on evaluating the dynamic response characteristics of a beam fabricated with ER fluid. It is noted that the most significant change in the material properties of ER fluid is the change of material stiffness and damping which varies with the electric field intensity imposed upon the ER fluid. Finally, the structural vibration of the smart composite beam based on ER fluid, fiber optic sensor and piezoelectric transducer has been monitored and controlled actively utilizing a fuzzy-logic algorithm.

Robot torque and position control using an electrorheological actuator

An electrorheological (ER) clutch driven from a constant speed motor provides a steady torque independent of shaft angle and can be controlled by control of the applied field. Such an actuator avoids the ‘cogging’ variation in torque observed in d.c. servo-motors and is thus well suited to robot control applications, particularly in view of the very rapid time response of ER clutches (≍ 10−3 s). However, the relationship between applied field and torque is difficult to model, being both non-linear and time varying. Whereas the non-linearity can be shown to be relatively small, the time-varying characteristic has remained a problem. In most controlled plants, a non-linear or time-varying characteristic can be mitigated by providing a closed control loop around the plant. A PID (proportional plus integral plus derivative)-based torque controller was developed and tested. This was shown to be stable with at least critical damping and to exhibit low steady state error. Design of the controller was facilitated by the identification of the open-loop transfer function of the ER actuator. The ER actuator with torque feedback was used to position a small robot link. A second PID control loop responding to the error in the link position and tuned using the standard Ziegler and Nichols method was designed and tested. A steady state error of less than 0.75 mm was achieved with a 2 per cent settling time of 2.0 s. Finally, the link position was controlled using a single-loop controller with no torque feedback and a similar steady state error achieved with a 2 per cent settling time of 1.4 s. It is argued that the ER torque actuator is ideally suited to the actuation of robot joints where precise smooth movement is required.

Transfer Function Identification of an Electro-Rheological Actuator

A fluid clutch utilising an Electro-Rheological (ER) suspension provides a controlled torque coupling between input and output through the control of the applied electric field. If the input is driven at constant speed the device can be considered as an ER torque actuator and thus be used to drive robot links or other mechanisms requiring precise positioning. Such an ER torque actuator can replace a DC servo-motor in robotic applications with the benefits of low time constant and smooth output torque unaffected by cogging (i.e. variation in torque of a DC motor as the magnetic reluctance of the armature-stator path changes with rotation). Although the ER actuator has many benefits, it suffers from a non-linear and time varying relationship between input voltage and output torque. These undesirable characteristics can be mitigated by providing a local closed loop controller around the system. The design of such a controller requires a knowledge of the relationship between the applied voltage and output torque; i.e. the transfer function of the actuator. This transfer function has been determined by observing the response of an ER torque actuator in the frequency domain. It is shown that a linear transfer function model reasonable represents the actuator behaviour, that the actuator is a stable second order system and that the time constant of the clutch studied is sufficiently short to hold considerable promise for robotic applications. Furthermore, the maximum torque capability is shown to be sufficient for many medium scale industrial robots.

Development of Micro Actuator Using ER Fluid

In recent years, a great deal of research has been done in the area of micro electro mechanical systems (MEMSs). Among the elements of micro machines, the micro actuator is very important. In this paper, a fluiddriven micro actuator using an electro-rheological (ER) fluid is discussed. The proposed actuator consists of micro valves, a piston and a cylinder. These ER micro valves do not require mechanical parts because they form chain clusters like bridges between the electrodes. As a result, the ER actuator can be driven at 75Hz and generate 60gf.

Modeling and control of an electrorheological device for structural control applications

This paper presents some of the results of an experimental and analytical study of a controllable electrorheological (ER) device configured to induce an adjustable amount of dynamic shear force in response to an applied voltage. Maps of the force-deformation characteristics of the aluminosilicate based ER material are developed over a relatively wide frequency range, and approximating analytical expressions are obtained for the force-deformation-frequency-voltage characteristics of the material. Subsequently, an evaluation is made of the efficiency of using online control of an electrorheological actuator to emulate the operation of an optimally tuned auxiliary mass damper attached to a primary system subjected to arbitrary dynamic environments. It is shown through numerical simulation studies that the proposed parameter control algorithm provides an efficient means for the online control of the primary system under a wide range of excitations. An experimental study is presented in which an ER device is used, in conjunction with a small laboratory building model, as a semiactive element in an online structural control approach using pulse control techniques.

ER Fluid Applications to Vibration Control Devices and an Adaptive Neural-Net Controller

This article describes several applications of electro-rheological (ER) fluid to vibra tion control actuators and an adaptive neural-net control system suitable for the controller of ER ac tuators. ER fluid is a kind of colloidal suspension, and has a notable characteristic feature in that its apparent viscosity can be controlled in response to applied electric field strength. Viscosity can be varied in a wide range and the response time is very short, as short as several milliseconds. Accord ing to previous studies, one promising application is a controllable damper. In the present article, four applications are proposed: a shock absorber system for automobiles, a squeeze film damper bearing for rotational machines, a dynamic damper for multi-degree-of-freedom structures and a vibration isolator. Furthermore, an adaptive neural-net control system, composed of a forward model network for structural identification and a controller network, was introduced for the control system of these ER actuators. As an example study of intelligent vibration control systems, an experi ment was conducted in which the ER dynamic damper was attached to a beam structure and con trolled by the present neural-net controller so that the vibration in several modes of the beam was reduced with a single dynamic damper.