Designing and Manufacturing a New Type of Variable Friction Dampers with Electromagnetic Actuator

Structural vibrations caused by earthquakes, wind or other factors can be controlled by various methods. The conceptual approach of structural control includes changes in member stiffness, structural mass and damping to deal with forces passively, semi-actively and actively. Until today, a number of these structural control methods have been successfully used and researchers are promoting methods to increase their applicability and scope by improving performance.
In recent years, researches have significantly been focused on the development and expansion of structural control methods and equipment. Also, in the last three decades, many efforts have been made to transform the conceptual approaches of structural control into usable and practical technologies in structures. It has been clarified that the structural control is one of the important and key points in the design of new structures and a suitable solution for improving structures against wind and earthquake loads. However, until today, most of the existing programs and strategies have led to the use of passive mass dampers or isolation of vibrations from the base. Over the past years, various control equipment and algorithms have been proposed, each of which has its own advantages according to the required performance and the part used.
Semi-active control systems are a separate and emerging example, similar to active control systems. In this control system, the required external energy is much less compared to the energy controlled by the structure. Basically, the semi-active control system does not introduce external energy into the structural system, so the output band of the structure's seismic response is guaranteed [1].
The resistive force or energy dissipation is determined by the internal mechanism of the system members based on the feedback of external or internal sensors. Therefore, this system has combined the advantages of passive and active control systems. Studies have clearly shown that the use of semi-active control equipment and systems has been significantly better than passive control systems in reducing the seismic response of structures, and this system has the ability and potential of this has the ability to perform at the same level or even better than active control systems [2].
In this study, the use of electromagnetic force in the friction damper has been considered and a controllable friction damper has been introduced. In this damper, electric current changes are used to change the force perpendicular to the sliding surfaces of the friction plates. In this method, by using powerful electric magnets that require little electrical energy and by controlling the intensity of the passing current, the function of the friction damper is controlled. For this purpose, taking into account the magnetic behavior of the material and using computer modeling, in addition to validating the analytical results, the behavior of this electromagnet was analyzed parametrically and the test results confirmed the proper behavior and controllability of this damper. To change the force perpendicular to the surface of the electromagnets, using electronic circuits, the current passing through them was changed from zero to 1.5 amps, and the maximum force produced by the damper reached about 1200 N. The electric power needed to create the maximum power capacity was measured to be 8.5 watts. Also, the response time of power generators to current changes was measured to be maximum 56 milliseconds to reach the maximum capacity and 68 milliseconds to reset the damper force. The results of this study showed that this type of power 
generator has the ability to be used in the direction of semi-active structural control. The analytical and experimental results of electromagnets showed that the maximum tension perpendicular to the surface that this type of power generator can create is around 10 kg/cm [22].