Variable impedance actuators: A review <s> Eddy Current Dampers <s> When a conductive material experiences a time-varying magnetic field, eddy currents are generated in the conductor. These eddy currents circulate such that they generate a magnetic field of their own, however the field generated is of opposite polarity, causing a repulsive force. The time-varying magnetic field needed to produce such currents can be induced either by movement of the conductor in the field or by changing the strength or position of the source of the magnetic field. In the case of a dynamic system the conductor is moving relative to the magnetic source, thus generating eddy currents that will dissipate into heat due to the resistivity of the conductor. This process of the generation and dissipation of eddy current causes the system to function as a viscous damper. In a previous study, the concept and theoretical model was developed for one eddy current damping system that was shown to be effective in the suppression of transverse beam vibrations. The mathematical model developed to predict the amount of damping induced on the structure was shown to be accurate when the magnet was far from the beam but was less accurate for the case that the gap between the magnet and beam was small. In the present study, an improved theoretical model of the previously developed system will be formulated using the image method, thus allowing the eddy current density to be more accurately computed. In addition to the development of an improved model, an improved concept of the eddy current damper configuration is developed, modeled, and tested. The new damper configuration adds significantly more damping to the structure than the previously implemented design and has the capability to critically damp the beam 's first bending mode. The eddy current damper is a noncontacting system, thus allowing it to be easily applied and able to add significant damping to the structure without changing dynamic response. Furthermore, the previous model and the improved model will lie applied to the new damper design and the enhanced accuracy of this new theoretical model will he proven. <s> BIB001 </s> Variable impedance actuators: A review <s> Eddy Current Dampers <s> We describe the design of an eddy current brake for use as programmable viscous damper for haptic interfaces. Unlike other types of programmable brakes, eddy current brakes can provide linear, programmable physical damping that can be modulated at high frequency. These properties makes them well suited as dissipative actuators for haptic interfaces. We overview the governing physical relationships, and describe design optimization for inertial constraints. A prototype haptic interface is described, and experimental results are shown that illustrate the improvement in stability when simulating a stiff wall that is made possible using programmable eddy current dampers. <s> BIB002 </s> Variable impedance actuators: A review <s> Eddy Current Dampers <s> A novel eddy current damper is developed and its damping characteristics are studied analytically and experimentally. The proposed eddy current damper consists of a conductor as an outer tube, and an array of axially magnetized ring-shaped permanent magnets separated by iron pole pieces as a mover. The relative movement of the magnets and the conductor causes the conductor to undergo motional eddy currents. Since the eddy currents produce a repulsive force that is proportional to the velocity of the conductor, the moving magnet and the conductor behave as a viscous damper. The eddy current generation causes the vibration to dissipate through the Joule heating generated in the conductor part.An accurate, analytical model of the system is obtained by applying electromagnetic theory to estimate the damping properties of the proposed eddy current damper. A prototype eddy current damper is fabricated, and experiments are carried out to verify the accuracy of the theoretical model. The experimental test bed consists of a one-degree-of-freedom vibration isolation system and is used for the frequency and transient time response analysis of the system. The eddy current damper model has a 0.1 m s−2 (4.8%) RMS error in the estimation of the mass acceleration. A damping coefficient as high as 53 Ns m−1 is achievable with the fabricated prototype.This novel eddy current damper is an oil-free, inexpensive damper that is applicable in various vibration isolation systems such as precision machinery, micro-mechanical suspension systems and structure vibration isolation. <s> BIB003 </s> Variable impedance actuators: A review <s> Eddy Current Dampers <s> Electromagnetic drives are subjected to an inherent inertia-torque tradeoff that fundamentally limits transparency: the higher the torque, the higher the inertia. We describe a dual-stage design that is not subjected to this tradeoff and that is able to approach perfect transparency for human users. It comprises a large, proximal motor and a small, distal motor to reproduce the transients. The two stages are coupled by a viscous clutch based on eddy currents that, without contact, accurately transforms slip velocity into torque. Such a system can, in general, be controlled to achieve a variety of objectives. Here, we show that an advanced, discrete-time, RST polynomial pole-placement controller can achieve near-perfect transparency. Experimental validation evaluated the human ability to detect small haptic details when using this drive and compared it with when using a conventional, single-motor interface. <s> BIB004
Eddy Current Dampers (ECDs, see Fig. 11d ) are magnetic devices composed of a conductive material moving through a magnetic field. Eddy currents are induced and create a damping force that is proportional to the relative velocityq r between the material and the magnetic field: The coefficient D depends, ultimately, on the geometry of the conductor, represented by r, and of the magnet, denoted by d, their gap, h, the magnetic flux, B and the specific conductivity of the conductor σ. These devices can be realized with both permanent magnets or electromagnets. In both cases there is the possibility to design a device whose damping can be adjusted BIB003 BIB002 [97] BIB004 . In one case, the damping coefficient can be controlled by varying the intensity of the magnetic field, in the other case, by modifying the geometry of the conductor, or the gap between the conductor and the magnets (the effectiveness is shown in BIB001 ). Albeit electromagnetic ECD are not composed of mobile parts, they have the disadvantage of consuming power while maintaining a fixed damping value. This class of devices, being fluid-free and contact-free, is not affected by typical troubles due to oil (e.g., the need of seals against leakage), and by frictional wear. Still, they present the disadvantage of requiring a gearbox because of their low damping torque.