# A Systematic Literature Review of Various Control Techniques for Active Seat Suspension Systems
## 9 Our Contributions
### Research Gaps and Research Questions  
Based on the previously published research papers, various vehicle seating suspension structures have been proposed and illustrated in detail in the above sections. However, these structures have a common shortcoming, which is that the seat suspension designs are either expensive or difficult to implement in real commercial vehicles because the size of the seat suspension structures are huge. Therefore, our team are going to design an innovative seat structure which can be practically implemented at a low cost. The detailed seat suspension design structure will be presented in our future work.  
In terms of the control algorithms of active seat suspension, to the authors' best knowledge, the Model Predictive Controller (MPC) technique has not been applied in the active seat suspension system, which encourages the authors to bring the method up for study and implement the method into the vehicle seat suspension system.  
System-state estimation and disturbance observers are the core feature of the active seat suspension because they can reduce the number of sensors needed to provide information about the system performance measurements. However, some observers require a mathematical model of high complexity, which is hard to understand. Thus, choosing a more accurately estimation observer for the real model is essential for our research direction.  
Based on the above comprehensive research gaps, the following questions are raised:  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Controller Type** & **Advantages** & & **Disadvantages** \\ \hline \(H_{\infty}\) & \(\bullet\) High stability & \(\bullet\) High level of mathematical complexity & \(\bullet\) Large control efforts \\ \hline \multirow{3}{*}{Preview controller} & \(\bullet\) Guarantee good vibration & \(\bullet\) Costly & \(\bullet\) Consumes energy \\  & \(\bullet\) attenuation performance in the & \(\bullet\) Takes longer time to estimate the & \\  & vertical direction & & road condition \\ \hline \multirow{2}{*}{Sliding mode controller} & \(\bullet\) Ensure high stability in presence of the disturbances and noise. & \(\bullet\) Chatter problem, which leads to system damage. \\ \hline \multirow{3}{*}{Adaptive controller} & \(\bullet\) Robust controller. & \(\bullet\) The reference model is critical & \\  & \(\bullet\) Provide high periodic vibration & \(\bullet\) Parameter variation & \\  & attenuation performance & & \\ \hline \multirow{3}{*}{Active Force Control} & \(\bullet\) Efficient to reduce the disturbances & \(\bullet\) High force could easily damage the system \\  & \(\bullet\) Simple design & & \\ \hline \multirow{3}{*}{PID} & \(\bullet\) Simple. & \(\bullet\) Diffident tuning methods for each process & \\  & \(\bullet\) Easy-to-implement. & \(\bullet\) Difficult to achieve a fast response with & \\ \cline{1-1}  & \(\bullet\) Low cost control strategies. & & small overshoot. \\ \cline{1-1}  & \(\bullet\) Highly effective. & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of cons and pros of the control types used in the active seat suspension.  
1. What innovative seat suspension structure should be used to implement the actuator and control algorithm within?
2. What type of MPC can be used to improve the driver comfort for active seat suspension system?
3. How can the Kalman filter be used to estimate the disturbances for active vibration seating system?