# A Systematic Literature Review of Various Control Techniques for Active Seat Suspension Systems
## 5 Type of Suspension Systems
### Integrated Active Seat Suspension with Vehicle Suspension  
In the last few decades, the majority of studies have been developed to integrate the seat suspension with the vehicle suspension to provide high performance in the ride comfort since design strategies of control force can be implemented in both the seat and vehicle suspensions taking into the account the road disturbance that can be applied direct to the vehicle wheels rather than to the cabin floor [60; 61]. Additionally, the seat suspension system normally integrated with the vehicle model can be evaluated for the seat performance considering different features such the tire deflection and suspension stroke [62]. There are three types of vehicle suspension model, namely: full, half and quarter vehicle suspension models. For the most recent studies, the quarter vehicle suspension model has been extensively used to examine the vertical vibration of the human body due to the simple mathematical model that includes all essential parameters. However, the quarter vehicle suspension model cannot provide a clear information about the pitch and roll motions like the half and full vehicle suspension models do. In [14; 63], the researchers have integrated the active seat suspension with the quarter car suspension and considered a driver human body as a four degree of freedom (DOF). Robust \(H_{\infty}\) control method has been implemented with both the state and static feedback controllers [14]. The active seat suspension and the vehicle suspension have been controlled separately, and the results  
Figure 5: Multiple DOF active seating suspension system [49]. of the separate controls have been compared with those of the integrated seat and vehicle suspension system [63; 64]. It was shown that integrated control system has better ride comfort performance than the separate control systems. However, it is difficult to implement the active suspension vehicle with the active seat suspension in the real application due to the high cost, control design algorithm complexity and vehicle energy consumption. Figure 6 shows the active quarter suspension model with active seat suspension system. Table 2 summarizes the current work in active seat suspension in multiple vibration directions. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**References** & \begin{tabular}{c} **Type of Actuator** \\ **System** \\ \end{tabular} & \begin{tabular}{c} **Degree of Freedom** \\ \end{tabular} & \begin{tabular}{c} **Summary** \\ \end{tabular} \\ \hline \multirow{4}{*}{[48]} & \multirow{4}{*}{Pneumatic actuator} & Vertical and lateral & \begin{tabular}{c} Decoupled controllers were designed in \\ the frequencies between 0.5 and 1 Hz. \\ Experimentally measured vibration \\ amplitude reduction in a single direction \\ is 70\%. Reduction of 20\% is evident when \\ the lateral and vertical vibration controls \\ are integrated \\ \end{tabular} \\ \hline \multirow{4}{*}{[50]} & \multirow{4}{*}{Linear actuator + Air spring} & Vertical and lateral & \begin{tabular}{c} Dynamic feedforward Controller (DFC) \\ and Hybrid Vibration Control (HVC) \\ were used. Experimentally measured \\ vibration amplitude reductions in the \\ vertical direction are 39\% and 36\% using \\ HVC and DFC, respectively. No reduction \\ in the lateral direction was observed. \\ \end{tabular} \\ \hline \multirow{4}{*}{[51]} & \multirow{4}{*}{Hydraulic actuator} & Vertical and \
\begin{tabular}{c} Fast Fourier Transform (FFT) analysis \\ based on ISO 5007. \\ The results showed that the active seat \\ suspension is stable in the frequency \\ range of 0–5 Hz. \\ \end{tabular} \\ \hline \multirow{4}{*}{[49]} & \multirow{4}{*}{Rotary servo motors} & Vertical and roll motion &
\begin{tabular}{c} Two decoupled controllers were \\ implemented. Experimentally measured \\ vibration amplitude reductions in \\ FW-RMS are 29.8\% in health evaluation \\ and 23.6\% in ride comfort. \\ \end{tabular} \\ \cline{1-1} \cline{3-5}  & & & \\ \hline \hline \end{tabular}
\end{table}