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

A soft-bodied robot made of smart soft composite with inchworm-inspired locomotion capable of both two-way linear and turning movement has been proposed, developed, and tested. The robot was divided into three functional parts based on the different functions of the inchworm: the body, the back foot, and the front foot. Shape memory alloy wires were embedded longitudinally in a soft polymer to imitate the longitudinal muscle fibers that control the abdominal contractions of the inchworm during locomotion. Each foot of the robot has three segments with different friction coefficients to implement the anchor and sliding movement. Then, utilizing actuation patterns between the body and feet based on the looping gait, the robot achieves a biomimetic inchworm gait. Experiments were conducted to evaluate the robot's locomotive performance for both linear locomotion and turning movement. Results show that the proposed robot's stride length was nearly one third of its body length, with a maximum linear speed of 3.6 mm s(-1), a linear locomotion efficiency of 96.4%, a maximum turning capability of 4.3 degrees per stride, and a turning locomotion efficiency of 39.7%.

https://iopscience.iop.org/article/10.1088/1748-3182/9/4/046006/pdf

Locomotion of inchworm-inspired robot made of smart soft composite (SSC)

Shape memory alloy (SMA) wire-based soft actuators have had their performance limited by the small stroke of the SMA wire embedded within the polymeric matrix. This intrinsically links the bending angle and bending force in a way that made SMA-based soft grippers have relatively poor performance versus other types of soft actuators. In this work, the use of free-sliding SMA wires as tendons for soft actuation is presented that enables large increases in the bending angle and bending force of the actuator by decoupling the length of the matrix and the length of the SMA wires while also allowing for the compact packaging of the driving SMA wires. Bending angles of 400° and tip forces of 0.89 N were achieved by the actuators in this work using a tendon length up to 350 mm. The tendons were integrated as a compact module using bearings that enables the actuator to easily be implemented in various soft gripper configurations. Three fingers were used either in an antagonistic configuration or in a triangular configuration and the gripper was shown to be capable of gripping a wide range of objects weighing up to 1.5 kg and was easily installed on a robotic arm. The maximum pulling force of the gripper was measured to be 30 N.

/pdf/long-shape-memory-alloy-tendon-based-soft-robotic-actuators-pnnzol0iw4.pdf

Long Shape Memory Alloy Tendon-based Soft Robotic Actuators and Implementation as a Soft Gripper

Curved shape memory alloy-based soft actuators and application to soft gripper

Compliant bistable mechanisms are a class of mechanical systems that benefit from broth compliance, allowing easy manufacturing on a small scale, and bistability, which provides two passive and stable positions. These properties make them first-class candidates not only for microswitches but also several other robotic appliances. This paper investgates the actuation of a simple bistable mechanism, the bistable buckled beam. It is pointed out that the position of the actuation has a significant impact on the behavior of the system. A new model is proposed and discussed, with experimental validations to compare central and offset loading, highlighting the strengths of each.

Bistable Buckled Beam: Modeling of Actuating Force and Experimental Validations

This paper presents a design of an active knee and leg muscle exerciser using a shape memory alloy (SMA) rotary joint actuator. This active exerciser is designed for a paraplegic to exercise his or her knee and leg muscles. The exerciser is composed of a lower extremity orthosis or a knee brace, an SMA rotary joint actuator, and an electronic control unit. The lower extremity orthosis and knee brace are commercially available. The analysis model of the SMA rotary joint actuator is introduced and the design formulas are derived. A quasi-static analysis of the SMA rotary joint actuator is assumed in this design. The actuating component of the SMA rotary joint actuator is a bundle of lengthy SMA wires which are wrapped on several wrapping pulleys. A constant force spring is incorporated in this actuator to provide the SMA wires with a bias force to maintain a recoverable initial position of the actuator. A prototype of the active knee and leg muscle exerciser is designed, and an electronic control unit in the prototype provides users with a means of adjusting forward rotation speed and cycle time of the exerciser.

Design of a knee and leg muscle exerciser for paraplegics using a shape memory alloy rotary joint actuator

Presented is a novel design of a composite linear actuator utilizing a parallel array of contractile shape-memory alloy (SMA) wires. The fiber bundle of SMA wires is either circumscribed inside a helical compression spring with flat heads or are in parallel with a number of helical compression springs, end-capped by two parallel circular plates with embedded electrodes to which the ends of the SMA wires are secured. Thus, the wires can be electrically heated and subsequently contracted to compress the helical compression spring. Upon cooling the SMA wires expand and allow the helical compression spring to tightly stretch them to their initial length. Design details are first fully described. Steps involved in the fabrication of a number of these composite SMA actuators are then elaborated on. A number of interesting heat transfer phenomena are observed. In essence the dynamic behavior of the actuator depends on the interaction between the current supplied to the wires and the rate of heat transfer from the wires due to convection and radiation. A design model is finally presented for the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs, hyperelastic springs such as rubberlike materials, or nonlinear springs such as air. The fiber bundle is assumed to consist of a parallel array of contractile fibers made from contractile shape-memory alloy (SMA) wires. The proposed model considers the temperature- induced contraction of the fibers due to resistive heating of the shape-memory wires. Results of both dynamic computer simulation and dynamics of a prototype model built in our laboratory indicate a fairly good comparison.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design and modeling of a novel fibrous shape memory alloy (SMA) actuator

Presented in this paper is a new design approach for a bias force type of shape memory alloy (SMA) rotatory joint actuator, which uses an SMA contractile wire as an actuating element. A quasi-static analysis is assumed and a coefficient of variation of bias stress, fi, is introduced to give a quantitative expression of a variation of bias stress in terms of a working stress range of the SMA wire. The effects of this coefficient on the load efficiency and the bias spring's parameters of a bias force SMA rotatory joint actuator are described. The use of this coefficient,B leads to a simple design procedure. An example design case is carried out by using this design procedure to demonstrate its usefulness. This paper does not cover an analysis of thermal response history of a designed actuator. The design approach described in this paper will provide a practical and convenient method for use in design of bias force SMA rotatory joint actuators for design requirements of maximum loads and maximum displacements.

A New Design for a Rotatory Joint Actuator Made with a Shape Memory Alloy Contractile Wire

Presented are a number of novel designs for large-motion shape-memory alloy (SMA) actuators that may minimize the performance constraints associated with such actuators. Shape-memory alloy (SMA) actuators suffer from two performance constraints, namely small strains (epsilon) , such that (epsilon) <EQ 6%, and heat transfer problems in computer- controlled ohmic heating of contractile SMA fiber bundles to induce contraction and/or expansion type linear actuators. Intelligent material systems and structures have become important in recent years due to some potential engineering applications. Accordingly, based on such materials, structures and their integration with appropriate sensors and actuators, novel applications, useful for a large number of engineering applications have emerged. In the present paper a number of conceptual designs and their respective mathematical models are presented for large motion SMA actuators. The dynamic modeling is preceded by a model of a small motion SMA linear actuator. This model considers the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs or hyperelastic springs such as rubber-like materials. The proposed theory presents a description of such processes for resilient shape-memory alloy fiber bundles. We consider the fiber bundle of SMA to be either in a serial configuration with a linear tension spring or a parallel configuration circumscribed inside a helical compression spring with flat heads or in parallel with a number of helical compression spring, end-capped by two parallel circular plates with embedded electrodes to which the ends of the SMA fibers are secured. Thus, the fibers can be electrically heated and subsequently contracted to either expand the tension spring or compress the helical compression spring back and forth. Design details are first described. In essence the dynamic behavior of the actuator depends on the frictional interference effects as well as the interaction between the current supplied to the wires and the heat transfer from the wires. Further, a mathematical model is presented to simulate the electro-thermomechanics of motion of such actuators. The proposed model takes into account all pertinent variables such as the strain (epsilon) , the temperature of the fibers T(t) as a function of time t, the ambient temperature T0, the martensite fraction (xi) , the helical compression spring constant k, the frictional effect and the coefficient of friction (mu) and the overall heat transfer coefficient h. Numerical simulations are then carried out and the results are compared with experimental observations of a number of fabricated systems.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design, Modeling and Performance Evaluation of A Novel Large Motion SMA Actuator

A new design for shape memory alloy rotatory joint actuators using shape memory effect and pseudoelastic effect is presented. In this design, one SMA wire works with its shape memory effect, while the other SMA wire works with its pseudoelastic effect. The pseudoelastic type of SMA wire provides the shape memory type of SMA wire with bias force, and therefore, the bias spring in a bias force type of SMA actuator can be eliminated. A quasi-static analysis of this type of actuators is performed which incorporates a varying load torque. General stress-strain relation and stress- temperature relation of the shape memory effect wire and a formula for an equivalent spring rate of the pseudoelastic wire are derived. Liang and Rogers' model for shape memory materials is used for the analysis. An experimental method to obtain the equivalent spring rate is also described. Design formulas for a simplified design are derived based on the quasi-static analysis of the actuator.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design for shape memory alloy rotatory joint actuators using shape memory effect and pseudoelastic effect

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