The generation and variation of forces necessary to achieve a training stimulus is often realized in sports and rehabilitation equipment by manually adjustable masses or by complex motor-brake systems. This leads to heavy and unwieldy systems, which cannot be used flexibly, and in addition to high costs. The main objective of this paper is to prove that pseudoelastic shape memory alloys (SMA) are potentially suitable for use in sports and rehabilitation equipment and offer additional value in the area of training flexibility combined with high training resistance. Therefore, the properties of pseudoelastic SMAs for this application were investigated. These multifunctional materials offer the potential for special elastic and sensory properties. The pseudoelastic effect is based on stress-induced martensite formation, which allows high elastic deformations. During this phase transformation, the mechanical stress passes through a plateau. The stress plateau can be moved by changing the temperature of the SMA. The determination of properties of pseudoelastic SMAs with different alloy compositions was carried out according to the specifications of “VDI 2248: Product Development with Shape Memory Technology”. With a functional model based on the material tests, which replaces a commercially available force clamping device, the monitoring of force, displacement and temperature changes can be realized by the integrated sensor technology. This paper presents the methodology, experiments and findings for the use of pseudoelastic SMAs in sport and rehabilitation devices. It concludes with prospects to commercial application.

In this paper, a shape memory alloy (SMA) based handling system is presented. The gripping system consists of two different actuator systems based on SMA wires. The first one is a reconfigurable end-effector with four independent gripping arms. The second SMA actuator system is a bi-stable SMA actuated vacuum suction cup, of which one is mounted on each of the four arms of the end-effector. While the four independently adjustable gripping arms of the end-effector allow for an adaption to different workpiece geometries like a flat shaped workpiece or a round shaped, spherical workpiece, integrated SMA driven brake mechanisms enable an energy free position holding of the end-effector components. This means that an electric current is only required when the end-effector arms need to be rearranged. This results in a versatile, adaptive and energy-efficient handling system that can replace mostly pneumatically driven state-of-the-art systems in production and assembly industry. No manual adjustment of the gripping system or even exchanging is needed, if an assembly line switches between products with different work piece geometries as a result. The gripping unit is controlled using an external microcontroller and can be mounted on a robot for diverse handling purposes.

Brake squeal phenomenon poses serious challenges to the automotive industry due to its technical complexity and the pressing need for mitigating its undesirable effects. More importantly, brake squeal causes significant customer dissatisfaction and adversely affects the subjective quality of the vehicles. These effects have substantial economic impact on the automotive industry. Furthermore, it is essential to properly treat the brake squeal problems in order to avoid unexpected catastrophic failure of the brake system. In this paper, it is proposed to mitigate the brake squeal problems by providing the brake pads with piezoelectric patches which are shunted by properly tuned electric networks. The shunted piezoelectric pads offer a unique ability to convert the mechanical energy induced by the brake squeal into electrical energy which can be dissipated into the network in order to enhance the damping and stability characteristics of the brake system. Accordingly, it is envisioned that the proposed approach would enable the disc brake systems to operate over broad ranges of operating parameters without experiencing the adverse effects of brake squeal. The proposed system is modeled by a simple two Degree-Of-Freedom ( DOF ) disc brake model. The structural DOF are integrated with the constitutive model of the shunted piezoelectric network in order to predict the threshold of brake squeal. The stability limits of the proposed brake system are established as a function of the design parameters of the shunted piezoelectric network. Numerical examples are presented to demonstrate the effectiveness of the proposed system in expanding the operating range of the brake system without experiencing squeal problems. Application of the proposed system to a distributed disc brake system model is a natural extension of the present work.

Magnetorheological fluid is a special smart fluid which can show different rheological properties under different magnetic flux densities due to its magnetically sensitive structure. This makes the fluid able to be manipulated and semi-actively controlled for various applications such as dampers, clutches and brakes. To provide an effective damping it is necessary to create an appropriate control algorithm. In order to design a structure with magnetorheological fluid and to get an idea for a control approach, the physics of the fluid motion has to be modelled. Computational Fluid Dynamics is an effective tool to model any fluid behaviour or any fluid involved structure. For magnetorheological devices, despite number of numerical models available in the literature, a befitting model is not yet presented. In this study a mapped rheological model is proposed and used in a magnetorheological damper simulation. The results are compared with other models and experimental data. It is shown that the new mapped model is effective and better than old approaches. It also showed a good agreement with the experimental data.

Compared to clinic-based systems, rehabilitation robots designed for home use could enable increased accessibility and intensity of therapy for stroke survivors. To move upper extremity rehabilitation robots from the clinic to the home, the designs must become smaller, lighter, and less complex. One path to reducing the size of the robot’s hardware is to replace conventional actuators with smaller designs utilizing the unique properties of smart materials. As a first step towards reducing the size of upper extremity rehabilitation robots, this paper presents results from a characterization study of a prototype electrorheological fluid. The fluid’s dynamic yield stress was first measured using a modified controlled stress rheometer. A testbed was then developed to analyze the mechanical performance of a custom brake filled with the fluid. System parameters measured included braking torque at varying electric field strengths as well as the fluid’s speed of response. Maximum torque output was 4.80 N-m at an electric field strength of 3 kV/mm. Experimental results also indicate that the fluid’s activation and relaxation times will enable sufficient control bandwidth for the desired application. However, non-linear effects, such as field-dependent hysteresis, are significant and may require compensation from the controller supervising interaction between the robot and patient.

Magneto-rheological fluids (MRF) are commonly applied in MRF brakes and vibration damping. The apparent viscosity dependence with respect to the magnetic field has been addressed in detail in the state of the art. The aim of this paper is to experimentally study the vibration effects on the particle chain-like structures and, as a consequence, the shear stress variation applied to the fluid. Three vibration configurations have been applied to a ferromagnetic cylinder rotating between two magnetic poles filled with MRF a “Z-vibration” where the generated displacement is along the rotation axis of the shearing cylinder, a “θ-vibration”, tangential to the cylinder, and an “R-vibration”, normal to the cylinder surface. First we focus on the vibration mode characterisation in free air, and then when plunged in the fluid. In a second step, we measure the reactive torque generated on the clutch under different magnetic field intensities with different rotation speeds and vibration amplitudes. It appears that the “R-vibration” configuration is providing the most influence, up to 20% of torque reduction observed at moderate B field. The “Z-vibration” and the “θ-vibration” configurations respectively have less influence on the torque, nevertheless vibrations always tend to decrease the corresponding yield stress in the MRF.

The magnetorheological Brake (MRB) is an electromechanical brake in which smart magnetorheological (MR) fluids have been utilized to generate the required braking torque. The purpose of this study is to design optimize a real-size MRB for automobile applications considering geometrical, material and magnetic circuit parameters. The mathematical equations governing the system’s braking torques are derived. The dynamic range of a disk-type MRB expressing the ratio of generated toque at on and off states has been formulated as a function of the rotational speed, geometrical and material properties, and applied electrical current. The magnetic circuit analysis of the proposed MRB is performed to find the relation between magnetic field intensity and the applied electrical current as a function of the MRB geometrical and material properties. Finally, a multidisciplinary design optimization problem has been formulated to identify the optimal brake geometrical parameters to maximize the dynamic range of the MRB under weight, size and magnetic flux density constraints. The optimization problem has been solved using combined Genetic Algorithm and Sequential Quadratic Programming techniques. The optimal design is then compared with those available in the literature.

This paper presents a novel Magentorheological (MR) brake with permanent magnets. The proposed MR brake can generate a braking torque at a critical rotation speed without an external power source, sensors, or controllers, making it simple and cost-effective device. The brake system consists of a rotary disk, permanent magnets, springs and MR fluid. Permanent magnets are attached to the rotary disk via springs, and they move outward through grooves with two different gap distances along the radial direction of the stator due to centrifugal force. Thus, the position of the magnets is dependent on the spin speed, and it can determine the magnetic fields applied to MR fluids. Proper design of the stator geometry gives the system unique torque characteristics. To show the performance of an MR brake system, the electromagnetic characteristics of the system are analyzed, and the torques generated by the brake are calculated using the result of the electromagnetic analysis. After the simulation study, a prototype brake system is constructed and its performance is experimentally evaluated. The results demonstrate the feasibility of the proposed MR brake as a speed regulator in rotating systems.

Current prosthetic legs rely on technology that is inefficient. Electric motors used today require high amounts of current to operate. Prostheses utilizing smart materials, including magnetorheological fluid (MRF), require less power to operate effectively. In this study, the MR fluid knee was designed for above the knee amputees. The design was in the family of MR fluid brake/clutch as it provides simple design and good MR fluid uniformity. However, this MR knee design is different from any existing MR brake, featuring a novel non-circular rotor. Three fourths of the rotor, considered circular, has the same radius, and the remaining quarter has a varying radius to provide a variable gap size between the rotor and stator. This feature allows the MR fluid to experience a stronger magnetic field as the knee rotates, resulting in a variable braking torque. At this stage of research, the first working prototype of the proposed MR fluid knee was built and tested to determine the braking torque profile. Corresponding theoretical models were also created. The calculated torque was used to predict the performance of the MRF knee. The experiments has been conducted to examine the MRF knee performance and to compare with the theoretical model. The knee was expected to use less power to operate and provided the necessary braking torque required by an average male human body. An improved design was planned for weight reduction and optimization to allow the commercialization of the MRF knee.

The paper presents the conceptual design, modeling and prototyping of a novel rotary motor based on shape memory alloy (SMA) wires. The basic architecture of the device capitalizes on a SMA wire wound around a low-friction cylindrical drum. The backup force to the SMA wire is provided by a beam spring which generates a nearly-constant force tangential to the drum. The electrical activation of the wire produces a contraction of the wire, hence a rotation of the drum fitted to the shaft through an overrunning clutch (free wheel). Thanks to the overrunning clutch, during the backup phase (recoiling of the wire), the drum rotates backward while the shaft does not move. Spurious backward movements of the shaft are contrasted by a second overrunning clutch linking the shaft to the frame. The paper presents a model for the quasi-static simulation of the motor and the experimental characterization of a prototype device featuring three active drums, a rotary sensor and an angular brake to apply the external load.

The viscous losses at high rotational speeds in idle mode represent a major drawback for an energy-efficient operation of MRF brakes and clutches. In this paper, an innovative concept is presented that allows a complete torque-free idle mode of the mentioned actuators by the use of a MR-fluid control. Using magnetic forces, the MR-fluid control is capable to increase the efficiency and lifetime of MRF based actuators for torque transmission. An approach of designing actuators using the investigated MR-fluid control is applied which considers in detail the required magnetic excitation systems for enabling a MRF movement in the shear gaps. A clutch is presented and simulations of the transient switching behavior are performed. Measurements of a realized clutch underline the functionality and efficiency of those actuators. Additionally, further approaches for a shear gap design are introduced that increase the maximum torque capacity. By the use of a micro-grooved structure for the MR-fluid control, a torque-to-volume ratio can be achieved that is in the order of typical MRF actuators for torque-transmission with completely filled shear gaps.

A challenge that is opposed to a commercial use of actuators like brakes and clutches based on magnetorheological fluids (MRF), are durable no-load losses, because a complete torque-free separation due to the permanent liquid intervention is inherently not yet possible. In this paper, the necessity of reducing these durable no-load losses will be shown by measurements performed with a MRF brake for high rotational speeds of 6000min −1 . The detrimental high viscous torque motivates the introduction of a novel concept that allows a controlled movement of the MRF from an active shear gap into an inactive shear gap, enabling a complete separation of the fluid engaging surfaces. This behavior is modeled by the use of the ferrohydrodynamics and simulations are performed for different transitions between braking and idle mode. Images of high speed video capturing, showing the motion of MRF induced by a magnetic field, are presented for the validation of the modeling approach. Measurements performed with a realized proof-of-concept actuator show that the viscous induced drag torque can be reduced significantly.

The study presents an experimental investigation into the trade-offs between field-on versus field-off rheological characteristics of magnetorheological (MR) fluids. This is relevant in a particular application in prosthetic devices where field-off characteristics are of equal importance to the field-on rheological characteristics. The paper introduces a biomechanical prosthetic knee joint that uses an MR fluid to actively control its rotary stiffness while an amputee walks. The knee is a synergy of artificial intelligence, advanced sensors and MR actuator technology. The knee joint is equipped with an MR rotary brake, utilizing the fluid in direct-shear mode. The MR fluid has response time in the order of milliseconds, making it possible to vary the knee’s stiffness in real-time, depending on sensors data. The field-on characteristics of the employed MR fluid define the rigidness of the knee joint while the field-off characteristics define its flexibility in the absence of a magnetic field. Five MR fluid compositions are prepared, each with a different solid loading ranging from 0.25 to 0.35, by volume. All fluids employ a commercially available carbonyl iron powder and a base fluid. The MR fluids are experimentally evaluated in a rheometer, where both field-off and field-on characteristics are measured. An MR fluid figure of merit function is introduced which is used to rate the selected MR fluids for a potential application in the MR prosthetic knee. An MR fluid composition is sought with the highest ratio between the field-on shear yield stress and the off-state viscosity. The research shows the off-state viscosity to decrease faster than the field-on shear yield stress when reducing the solid loading from 0.35 to 0.25. This suggests that an optimum solid loading exists with regards to the defined merit function. The off-state viscosity of suspensions is known to be exponentially dependent on solid loading while the field-on shear-yield stress is known to sub-quadratically dependent on solid loading. Field-on and field-off models are presented from literature. The models compared to the experimental data and used to theoretically predict the optimum solid loading with regards to field-on shear yield stress and off-state viscosity. As a result of the experimental and the theoretical analysis, a prominent MR fluid composition is selected for a potential application in the MR prosthetic knee. This has been shown to help in the development of prosthetic devices and furthering the success of an MR prosthetic knee joint.

Shape Memory Alloys (SMAs) have essential advantages compared to conventional actuators, in particular their high power density and their silent mode of operation. However, this material has not gained acceptance in technical applications yet. The main reasons are the missing simulation tools and a lack of knowledge of materials as well as the companies’ uncertainty how to handle SMAs. The resetting of the SMA element to generate a repeatable movement is often a defined problem. In this context reset springs made of steel are conventional solutions although their characteristics are a disadvantage. To reach a high level of power output and hence a high degree of efficiency, a reduction of the pre-load is necessary. A solution for this problem is an adaptive resetting. One main possibility to generate an adaptive resetting is given by the agonist-antagonist principle where two SMA-elements work against each other. Here the reset force can be applied if necessary. The advantage of this type of design is that a conventional return spring or a mechanical brake for clamping the position (electrically operated) is not necessary. Another possibility for adaptive resetting is to change the spring characteristics of a pseudoelastic SMA-element by heating. The aim of this study is to show the properties of the agonist-antagonist design and the other concepts. It also provides methods and the knowledge to support the development process of such resetting principles. The development of these methods is based on the analysis of different designs and requirements. Based on the results, instructions for the conception of adaptive resetting systems have been created.

Shape Memory Alloy actuators offer solutions to many common actuation problems especially where space or weight is limited. However, practical applications for SMA actuators in the automotive industry are still relatively few. The design of a novel automotive mirror actuator is outlined. The actuator utilizes a spherical joint and a passive friction brake to translate the linear motion of SMA wires into the angular rotation required for the mirror. A simple and effective variable structure controller is developed for the control of the mirror actuator and experimental results are obtained showing the controller is effective with small perturbations.