# Development of a Magnetorheological Damper with Self-Powered Ability for Washing Machines
## 1 Introduction  
Semiactive suspension systems have been widely used in the field of vibration control [1]. Since the 1990s, magnetorheological (MR) dampers have been promisingly studied for these systems due to their attractive features such as high damping force, good adaptability, continuous controllability, and high reliability. MR dampers can be increasingly applied in industrial environments of civil structures [2], automobiles [3], and precision machines [4]. One of the particularly interested applications of MRdampers is to attenuate vibration of washing machines. The distribution of the laundry in the washing drum is often out of balance causing the vibration of washing machines. It is found that during spinning process, the washing machine usually experiences the first resonance at quite low frequency, around 100-200 rpm [5; 6; 7]. This resonance comes from the rigid vibration mode of the washing drum. When the spindle speed exceeds 1000 rpm, such as in spinning stage, resonances can appear at the rear and side frame panels bringing about noises, uncomfortable feelings, and the shortening of the washing machine life span. The dampers in conventional suspension systems could provide passive damping forces to well eliminate the vibration at low frequency of resonance but raise the force transmissibility at high excitation frequencies because the damping coefficient could not be changed. Therefore, to effectively mitigate the vibration of washing machines at low frequency of resonance while it is still well isolated at high excitation frequencies, semiactive suspension systems that can continuously control the damping coefficient such as MR dampers-based vibration control systems should be employed (Figure 1). Although several studies on MR dampers have been performed to control the vibration of washing machines [8; 9], optimal design of these MR dampers was not considered. [PERSON] et al. [10] conducted optimal design of a small MR damper in flow-mode for washing machines. The results showed that size of the optimized MR damper is well fit for integration in washing machines to replace conventional ones. The maximum damping force was up to 150 N, which is greater than expected damping force for MR damper (from 80 to 100 N). However, off-state force of the damper was quite high, around 25 N. Later, [PERSON] et al. [11] proposed a new shear-mode configuration of MR damper for washing machines. The optimal results indicated that the proposed shear-mode MR damper was able to generate a damping force of about 120 N with much smaller off-state force, around 10 N. It was also pointed out that the proposed damper can be well installed in washing machines to replace conventional dampers. In addition, no bobbin for coils is used, which facilitate the manufacturing. However, no experimental works was conducted in this research. Recently, [PERSON] et al. [12] performed a research on optimal design of MR dampers for front-loaded washing machines, considering expected damping forces, assembly space, power consumption, and cost as an extension of study carried out by [11]. In addition, experimental works on performance characteristics of the damper and effectiveness of implementation of the damper in a prototype washing machine was also implemented. The research results showed a good correlation between the experimental performance and theoretical simulation. Similarly, [PERSON] and [PERSON] [13] developed a MR sponge damper for washing machines with design optimization of geometric parameters; however, stability and lastingness of the sponge are considerable issues. Although the above semiactive systems can well solve the problem of washing machine vibration control, they require auxiliary equipment such as sensors, control units, and power sources to enable the operation. This makes the systems more complicated and difficult for maintenance with high production cost.