# Review on Seat Suspension System Technology Development
###### Abstract
Complex head-neck-torso models studying both vertical motion and rotation of the seated human body were proposed in [36; 37; 38; 39]. However, the multiple-DOF modelling in 3D space, in particular, when studying the multiple-DOF vibrations, has not been investigated to date [40]. In addition, the model parameters should be modelled in terms of various driver bodies and postures. So, real-time classification of model parameters should be extended [41]. An innovative seating solution is vital to reach a comfortable ride, and therefore reduce driver exhaustion, by effectively decreasing undesired vibrations [42]. Vehicle seating systems have been used to reduce vibration transferred from road disturbances. However, vibrations from the driver of vehicles and machine tools have not been fully studied for most of the currently available seating systems because these vibrations may come from various directions rather than just from vertical and fore-and-aft motions [43]. Furthermore, the driver is the most significant vehicle occupant when the physical and psychological effects of vehicle vibration on the body are considered, especially in the case of commercial vehicles [44]. A driver's biodynamic responses to vehicle vibration should be focused when designing seating systems. However, combining a human body biodynamic model with a seating system design has also not been fully discussed in research to date [45]. In studies on seating systems, Because the frequency range plays a vital role in vehicle ride comfort, the head acceleration or a rigid driver and passenger body acceleration usually is considered as a performance index to evaluate ride comfort [46]. However, neither a sprung mass acceleration nor rigid body acceleration can accurately show human bio-dynamical characteristics. Studies [47; 48; 49] show that it is essential to involve a complex biomechanical model of the human body in a seated position to get a good insight into ride comfort as an essential parameter when designing a seating suspension. It is seen in preliminary work towards this purpose that developing an integrated model that incorporates the vehicle chassis suspension, the seating system, and a human body model, and designing an integrated control system, will be important in attempts made to promote human ride comfort and safety [50; 51]. Therefore, the multiple-DOF vibration reduction seating system together with the human-in-the-loop control strategy will be an innovative seating solution. The Whole Body Vibration in terms of the body frame \(x\)-\(y\)-\(z\) is described in Figure 2, where the three translational vibrations are along the \(x\), \(y\), and \(z\) axes; the three rotational vibrations, which are also described as roll, pitch, and yaw motions, are around the three axes. It can be noticed that the most sensible frequencies for humans are close to those of translational vibration along the \(x\) and \(y\) axes, and those of the three rotational vibrations; however, the translational vibration amplitudes along the \(z\)-axis are larger than the vibration amplitudes in other DOFs at the sensitive frequencies [52]. This implies that when designing a multiple-DOF seat suspension, the yaw vibration control, which would have the weakest impact on ride comfort comparing with the vibration in other DOFs, could be neglected in order to decrease the complexity of the seat suspension configuration; the translational vibration along the \(z\)-axis could be decoupled from other DOFs in order to clarify the vibration control [53]. The simple vehicle seat form contains an isolation system and a seat frame, as given in Figure 2. Various techniques which have been applied in seating system designs by different researchers are explained in the following sections.