Semiactive control devices have received significant attention in recent years because they offer the adaptability of active control devices without requiring the associated large power sources. Magnetorheological (MR) dampers are semiactive control devices that use MR fluids to produce controllable dampers. They potentially offer highly reliable operation and can be viewed as fail-safe in that they become passive dampers should the control hardware malfunction. To develop control algorithms that take full advantage of the unique features of the MR damper, models must be developed that can adequately characterize the damper's intrinsic nonlinear behavior. Following a review of several idealized mechanical models for controllable fluid dampers, a new model is proposed that can effectively portray the behavior of a typical MR damper. Comparison with experimental results for a prototype damper indicates that the model is accurate over a wide range of operating conditions and is adequate for control design an...

Phenomenological model for magnetorheological dampers

This tutorial/survey paper: (1) provides a concise point of departure for researchers and practitioners alike wishing to assess the current state of the art in the control and monitoring of civil engineering structures; and (2) provides a link between structural control and other fields of control theory, pointing out both differences and similarities, and points out where future research and application efforts are likely to prove fruitful. The paper consists of the following sections: section 1 is an introduction; section 2 deals with passive energy dissipation; section 3 deals with active control; section 4 deals with hybrid and semiactive control systems; section 5 discusses sensors for structural control; section 6 deals with smart material systems; section 7 deals with health monitoring and damage detection; and section 8 deals with research needs. An extensive list of references is provided in the references section.

Structural control: past, present, and future

Control of civil engineering structures for earthquake hazard mitigation represents a relatively new area of research that is growing rapidly. Control systems for these structures have unique requirements and constraints. For example, during a severe seismic event, the external power to a structure may be severed, rendering control schemes relying on large external power supplies ineffective. Magnetorheological (MR) dampers are a new class of devices that mesh well with the requirements and constraints of seismic applications, including having very low power requirements. This paper proposes a clipped-optimal control strategy based on acceleration feedback for controlling MR dampers to reduce structural responses due to seismic loads. A numerical example, employing a newly developed model that accurately portrays the salient characteristics of the MR dampers, is presented to illustrate the effectiveness of the approach.

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Modeling and Control of Magnetorheological Dampers for Seismic Response Reduction

MR fluid, foam and elastomer devices

Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201707035

Soft Robotic Grippers.

An electrorheological material comprising a carrier fluid and an atomically, polarizable particle component. The atomically polarizable particle component has a crystalline lattice structure which allows atoms to shift position with respect to each other in response to the application of an electric field. The electrorheological materials are subjected to an alternating current electric field at a frequency of at least 500 Hz. The materials exhibit substantial electrorheological activity over a broad temperature range.

Method for activating atomically polarizable electrorheological materials

Magnetorheological thixotropic materials

An electrorheological material containing a particle component and a carrier fluid. The carrier fluid has a dielectric constant between about 3.0 and 7.5 and an observed conductivity less than about 1.00 x 10-7 S/m. The carrier fluid can be a silicone copolymer, a hindered ester compound or a cyanoalkylsiloxane homopolymer. The electrorheological materials exhibit substantial electroactivity over a broad temperature range.

High strength, low conductivity electrorheological materials

The concept of using electrorheological (ER) fluids as inks originated with the design of several electroviscous recording devices some 25 years ago.1,2 The colored, ER active pigments used in these early inks included carbon black, copper phthalocyanine derivatives (Skyline Blue & Monstral Green B), flavanthrone (Indofast yellow toner), quinacridone (Quindo Magenta), 3,4,9,10-bis(n,n′-(p-methoxyphenyl)-imido)perylene (Indofast Brilliant Scarlet toner), and 1,2,5,6-di-(c,c′-diphenyl)thiazole anthraquinone. In addition to utilizing colored pigments in an ink, the possibility of coloring conventional ER fluids (i.e., those prepared by W. Winslow3, etc.) through the addition of dyes also was suggested.1,4 Examples of the oil soluble dyes used to colorize known ER fluids included Oil Yellow AB, Oil Red, Oil Blue G Extra and Oil Black.

ER Fluid Inks: A Rainbow of Possibilities

An electrorheological material containing a carrier fluid, an electrorheologically active particle and a colorant additive which can be classified as a dye, an insoluble pigment, an A-type soluble pigment, or a B-type soluble pigment. The incorporation of these colorant additives in accordance with the invention does not dramatically affect the viscosity, dynamic yield stress, static yield stress, current density or response time exhibited by the electrorheological material. The colorant-containing electrorheological material is useful for creating aesthetic visual effects in a variety of applications.

Keith D. Weiss

Papers

Method for activating atomically polarizable electrorheological materials

Magnetorheological thixotropic materials

High strength, low conductivity electrorheological materials

ER Fluid Inks: A Rainbow of Possibilities

Colorant-containing electrorheological materials