# A Systematic Literature Review of Various Control Techniques for Active Seat Suspension Systems
## 1 Introduction  
Drivers of heavy trucks experience the whole body vibration (WBV) because they spend most hours driving for a long distance, which will result in discomfort of the diver [1]. Various elements can affect the ride comfort of the driver such as the road roughness, vehicle suspension system and seat suspension system [2]. In addition, the noise and vibration generated from internal combustion engines play a minor effect on the drivers' discomfort as well [3]. As a result, human body subjected to the vibration can suffer from adverse health effects such as fatigue, back pain, motion sickness, nervous disorders, spline fracture [4].  
Researchers in the field of WBV have classified the vibration assessment measures into three categories namely: the mechanical impedance, apparent mass and seat to head transmissibility [5; 6; 7]. These function categories are used to assess the human body subjected to the vibration. The mechanical impedance is defined as the periodic excitation force at a certain frequency divided by the resulting vibration velocity [8]. The apparent mass is expressed as the periodic excitation force at a certain frequency over the resulting vibration acceleration. The seat to head transmissibility is known as the response motion of the head divided by the response motion of the seat floor or seat base. The vibration acceleration data from experimental measurement is extensively used to analyze the WBV [9].  
In the recent studies, various approaches were proposed to improve the ride comfort and avert the fatigue risks associated to the human body. Some researchers have improved the vehicle suspension system to reduce the input vibration into the human body [10; 11; 12], while others focus on enhancing the vehicle seat suspension design [13]. Similarly, few studies integrated both the vehicle suspension systemand seat suspension system to isolate vibration transmitted to human body [14; 15]. On the other hand, reducing the vibration transmitted through vehicle cabin suspension system was investigated [16]. In this paper, the main interest will be directed toward the seat suspension system and its control methods and implementations. The main contribution of this paper is in providing a systematic review about the active vibration control of seating suspension systems including their actuation system structures and control algorithms.  
The advantage of the work is identification of the research gaps and clarification of the future research questions. The paper is organized as follows: Section 1 provides the overview about the biodynamic model of seat suspension system combined with human body. Section 2 presents the source of vibration that can transmitted to the human body. Section 3 shows the ride comfort evaluation methods. Section 4 addresses the type of suspension systems and analyses the importance of the integrated seat suspension with vehicle suspensions. Section 5 studies the actuator types used in the active seat suspension. Section 6 demonstrates the overview of the existing active seat suspension structure design. Section 7 evaluates the recent control methods applied in the active seat suspensions. Section 8 will identify research gap and research questions. Finally, Section 9 will conclude this review.