# A Systematic Literature Review of Various Control Techniques for Active Seat Suspension Systems
## 7 Active Seating Suspension System Structure Design  
Various active seating suspension system structures have been implemented for vibration control. The most popular structure mechanism is the scissor structure which takes in a x shape. It was designed with air spring as shown in Figure 7[68]. The bottom plate of the seat base was fixed to the cabin floor and the top plate was connected to the seat chassis. The air spring was placed inside the inner scissor structure while the shock absorber linked the top and bottom plates of the seat base.  
The seating suspension system structure shown in Figure 8 consists of a scissor structure mechanism, a hydraulic absorber and a pneumatic spring. The air flow inflates the air to the pneumatic spring through two valves that are controlled using a control signal. Hence, the air pressure is always changing inside the air spring generating an active force to drive the seat in the vertical direction [69].  
Figure 7: Scissor structure of active seating suspension system [64].  
Another structure of the active seating suspension system proposed consists of two linear electric motors, which can slide independently along the vertical and lateral directions [50]. The vertical linear motor was placed in the backrest of the seat while the lateral linear motor was placed under the seating surface as illustrated in Figure 9. The air spring was implemented in the vertical direction to achieve the desired seat level.  
The seating suspension system consists of passive and active suspension systems [70]. The passive suspension system consisting of the coil spring and adjustable damper to support the driver body and seat pan. The active suspension system is composed of two parallel linear actuators to generate the active control force. Two bar lever mechanisms were used to support the seat pan. The seat can move vertically through the linear sliders placed at the seat rail as shown in Figure 10 [70].  
The following seating suspension system structure consists of three active mounts and one vibration exciter where three accelerometers are used to measure the acceleration of the human body as illustrated in Figure 11 [71]. The seat was supported with three passive springs. At the middle of the seat base, the vibration exciter was placed to produce a displacement out as a real road profile.  
A seating suspension system structure that is mainly used to eliminate the vibration in the vertical and pitch directions for an agriculture tractor was implemented in [51]. The active seating suspension system with a scissor structure mechanism was driven by a hydraulic actuator in the vertical direction. The hydraulic damper was used in parallel with the hydraulic actuator to absorb the shock during operation. Another actuator was attached to the upper frame with a tilting platform to control to the pitch motion as seen in the Figure 12.  
Figure 8: Active seating suspension system structure [69].  
Figure 9: CAD model of active seating suspension system [50].  
Figure 11: Structure of active seating system [71].  
Figure 12: Active seating suspension system scheme [51].  
Figure 10: Mechanical design of active seating suspension system [70].