Effect of Electromagnetic Damping on System Performance of Voice-Coil Actuator Applied to Balancing-Type Scale

Changing a time-varying magnetic field induces an electromotive force (EMF) in non-magnetic conductive materials, resulting in an eddy current across the conductor. Thus, electromagnetic damping can be used as viscous damping. This study theoretically and experimentally investigates the electromagnetic damping characteristics of a bobbin-wounded coil with an attached cantilever beam floating over a permanent magnet; the beam is balanced by electromagnetic force compensation (EMFC) instead of applied weight. System identification is carried out for the mass (m), damping coefficient (c), and spring constant (k) values. The presence of a back EMF seen in either conductive or non-conductive material responses in the experiments includes the step input and corresponding output responses to measure the electromagnetic damping force with and without a voice-coil actuator (VCA). The results were validated using bobbins of conductive (aluminum) and non-conductive (plastic) materials. The experimental results for the conductive material show that the electromagnetic damping force is 10 times greater than that of the non-conductive material; the opposite was true in the case without a VCA, where the force was almost zero for the non-conductive material. In conclusion, conductivity is directly related to the electromagnetic damping force, which affects the performance of a VCA.

Mathematical modeling and parametric study of magnetic negative stiffness dampers

This article presents mathematical modeling and parametric study of a type of magnetic negative stiffness dampers. A magnetic negative stiffness damper uses the interaction forces and movement of magnets inside a conductive pipe to achieve inverse force–deformation response and create frequency dependent damping. One advantage of magnetic negative stiffness dampers over other conventional dampers is that they do not add stiffness to the system and hence will not increase the force in the structural members to which the magnetic negative stiffness damper is attached. Using nonlinear regression analysis, simple formulas to describe the magnetic force and electromagnetic damping of a specific type of magnetic negative stiffness dampers are derived. A parametric study is then performed to show that maximum negative stiffness is obtained when the height-to-diameter (aspect) ratio of the magnets is in the range of 0.3–0.4, and for design applications upper bound values for the clear spacing-to-radius ratio and aspect ratio of the magnets are determined to be 3 and 2, respectively. The highest value of damping coefficient is found to correspond to a magnet aspect ratio of 1.6, and for design purpose the pipe wall thickness should be set equal to the height of the magnet. Based on a pushover analysis of three frames modeled as single-degree-of-freedom systems, it is found that the frame with the magnetic negative stiffness damper experiences lower base shear at the expense of a slightly higher residual drift. The effect of base shear reduction is more pronounced when the target displacement is small.

Rotational speed control of magnetic coupling with variable damping method

Permanent Magnetic Coupling (PMC) is used in underwater vehicle to transmit torque from the motor to propeller without leakage and friction. Output rotational speed stability of PMC is an important index indicating the PMC output makes smaller vibration. To improve the stability of the output rotational speed, PMC dynamic characteristic was analyzed based on Lagrange equation in this paper. The dynamic characteristic was indicated by the angular phase generated by the master rotor and the slave rotor. The angular phase varied with the damping coefficient, torsional rigidity and rotational inertia of PMC. These parameters' influence on the angular phase was analyzed and the results revealed the rules between these parameters and the angular phase. Based on the rules, a variable damping method was proposed to control the angular phase. The angular phase changed smoothly with this method that was used to design a variable damping controller based on electromagnetic damping effect principle. This method was verified by theoretical calculation and finite element analysis (FEA). Finally, a novel variable damping PMC was designed to improve the output rotational speed stability of PMC.

Analysis and Numerical Evaluation of H∞ and H2 Optimal Design Schemes for an Electromagnetic Shunt Damper

The electromagnetic coupling effect can generate electromagnetic damping to suppress disturbance, which can be utilized for vibration serviceability control in civil engineering structures. An electrodynamic actuator is used as a passive electromagnetic damper (EMD). Ideally, the EMD is assumed to be attached between the ground and the structure. The kinetic energy of the vibrating structure can be converted to electrical energy to activate the electromagnetic damping. To induce appropriate damping, the two terminals of the damper need to be closed and cascaded with a resonant shunt circuit as an electromagnetic shunt damper (EMSD). In this study, an resistance–inductance–capacitance (RLC) oscillating circuit is chosen. For determination of optimal circuit components and comparing against the tuned mass damper (TMD), existing H∞ design formulae are applied. This work extends this with a detailed development of an H2 robust optimization technique. The dynamic properties of a footbridge structure are then selected and used to verify the EMSD optimal design numerically. The vibration suppression performance is analytically equivalent to the dynamic characteristic of the TMD and has feasible installation and better damping enhancement. To further evaluate the potential application of the EMSD, multi-vibration mode manipulation via connecting multiple RLC resonant shunt circuits is adopted. The multiple RLC shunt circuit connecting to EMD is an alternative to the single mode control of a traditional TMD. Therefore, the EMSD can, in principle, effectively achieve suppression of single and multiple vibration modes.

Characteristics and Analysis of an Eddy Current Shock Absorber Damper Using Finite Element Analysis

In the paper a model is developed for a proposed eddy current damper using finite element analysis. Several damper configurations are studied and its characteristics are analyzed. The steady state performance for the configurations is compared to reach a design with an acceptable performance for the eddy current damper. Furthermore, the proposed designs performance are compared with the traditional damper performance. It was found that the best two designs to achieve the targeted performance were to have an iron core damper or an iron core with an aluminum sleeve. Those two designs are economical and simple while achieving acceptable performance when compared to traditional dampers and other electromagnetic damping systems.