Comparison of Passive Seat Suspension with Different 

Configuration of Seat Pads and Active Seat Suspension

Bertrand Valero, Farid Amirouche 

University of Illinois at Chicago, IL

Alan Mayton, Christopher Jobes 

NIOSH, PRL Pittsburgh, PA 

ABSTRACT 

 Exposure to vibration induced in and around 

underground m in e ’s e xp lo ra tio n is a m a jo r co n ce rn to 

vehicles operators. Most of these drivers over time 

develop serious spinal musculoskeletal and discs 

problems causing low back injuries. The first purpose of 

this paper is to analyze the performance and dynamic 

response of driver/operator when subjected to different 

levels of vibration due to rough road conditions depicted 

in a mine field. The second purpose of the paper is to 

quantify the energy transmission in the presence of seat 

padding with special characteristics and active 

suspension. Using experimental testing data collected 

at NIOSH/PRL (National Institute for Occupational 

Safety and Health/ Pittsburgh Research Laboratory) 

along with model simulation algorithms developed at the 

University of Illinois at Chicago we investigated how 

acceleration transfer functions as well as absorbed 

power affects the different parts of the body. To this end, 

we used a previously validated human model which 

includes the head, torso segments and legs. The 

connective forces between body segments were 

modeled through modal analysis techniques from 

previous experimental data at the UIC Vehicle 

Technology Laboratory. The absorbed power and 

energy transmitted to the body are used as an index 

measure to assess the viability of the different seat 

p a d d in g ’s and active seat suspension control strategies. 

INTRODUCTION 

 Whole body vibration can affect not only 

comfort, working efficiency and performance, but also 

health and safety. Operators of mine vehicles are in 

particular subject to high levels of vibrations under very 

constraining conditions. The vehicle operator often is

more confined to a less space than in normal cars or 

vehicles and the seats are not equipped with a 

suspension system. Injury statistics from the Mine Safety 

and Health Administration (MSHA) showed incidences 

of exposure to whole-body vibration (WBV). Sources of 

vehicle vibrations are generally divided into two classes: 

Road roughness 

On-board sources 

 In the case of heavy vehicles, an effective 

vehicle handling requires a significant torque on the 

fro n t a xle w h ich cre a te s vib ra tio n s in th e d rive r’s se a t. 

Improving the ergonomics of the seat can lessen the 

adverse effects of vehicle vibration. Adding a secondary 

su sp e n sio n m e ch a n ism to th e d rive r’s se a t o f h e a vy 

vehicles is another solution that was found to reduce the 

vibration induced by the seat [Tong et al]. 

 The initial step in optimizing the seat 

suspension is to identify the spring and damping 

coefficients that provide the best performance. This 

technique usually is limited to the input profile used. The 

optimization helps identify the stiffness of the spring. 

Through identification of natural frequencies yet the 

damping leads to values where insufficient damping 

provides poor resonance control and good isolation at 

high frequencies. On the other hand, excess damping 

results in a good resonance control and poor high 

frequency isolation. 

 In a skyhook suspension configuration, the seat 

is attached to a fixed point in the sky through a damper. 

The response of this virtual configuration shows an 

almost complete elimination of the trade-off between 

resonance control and high frequency isolation as 

observed in a passive suspension system. The Semiactive suspension designs with a variable damping rate 

can emulate the principle of a skyhook suspension 

configuration. These control ideas are explored further 

in this paper. 

METHOD 

Using Simulink/Matlab a simulation was created to 

reproduce the behavior of the suspension design. The 
experimental results collected were used to validate the 

simulation. It is important to note that the simulation is a 

based on the real control algorithm used in controlling 

the actual suspension. 

 Meanwhile, the Pittsburgh Research Laboratory 

(PRL)/NIOSH were experimenting with a new padding 

for mine vehicles o p e ra to r’s se a t. In o rd e r to va lid a te th e 

new design, field testing was conducted using passive 

suspension. The acceleration of the vehicle chassis and 

the seat were collected. 

 The acceleration for the NIOSH seat was then 

fed into a lump-mass model of the human body where 

the RMS (Root Mean Square) accelerations and 

absorbed power of the body were computed and used to 

evaluate the new ergonomic padding design. 

 Furthermore, the acceleration of the chassis 

was fed into the UIC seat with semi-active suspension 

simulation. The acceleration of the seat obtained was 

then used as an input for the human body model. Thus, 

providing the HBV needed for comparing the 

performance of the new ergonomic seat padding with 

the active suspension design. 

Figure 1: Scheme of the method used 

SEAT VIBRATION 

L e t’s co n sid e r th e e q u a tio n o f m o tio n fo r a n id e a l 

skyhook suspension: 

.. . . .

( ) ( ) 0 m x C x y C x K x y       SK

The equation is composed of three different terms: 

Inertia force: 

..

mx

Spring force: 

K x y ( )

Damper force: 

. . .

( ) C x y C x   SK 

If we consider a configuration with only one damper 

connecting the two bodies, the equation of motion would 

be similar to a passive suspension system case: 

.. . .

m x C x y K x y      V( ) ( ) 0

And the three terms become: 

Inertia force: 

..

mx

Spring force: 

K x y ( )

Damper force: 

. .

( ) C x y V 

 The damping coefficient CV is adjusted in order 

to reach a damping force that matches the one given by 

the skyhook model this is achieved when: 

. . . . .

.

. .

( ) ( ) SK V

SK

V

C x C x y C x y

so

C x C C

x y

   

 

DESCRIPTION OF THE PROPOSED SUSPENSION 

DESIGN 

Figure 2: scheme of the proposed suspension design 

 The seat suspension is a scissors-type 

suspension forming an 'X' that opens and closes when 

the seat moves up and down. The seat is bolted to a 
platform that is driven by the system actuator. The 

platform corresponds to the chassis in real vehicle and 

depicts the input vibration to the seat. A bladder is 

mounted onto the crossing members as a safety 

precaution to prevent the bottom and top platforms of 

the support from colliding. 

 The actuator consists of a piston inside of a 

cylinder. Both sides of the piston are connected through 

a valve controlled by a motor. The proposed design is a 

pneumatic suspension which requires air pressure to be 

adjusted to achieve the required actuation vibration 

force. 

 The signals of two accelerometers placed on top 

of the suspension and onto the chassis are used as 

input by a control algorithm that returns a position for 

the valve in order to determine the right damping 

coefficient to minimize the vibration at the seat interface. 

The digital valve can be positioned at infinite number of 

positions between the fully close and fully open cases. 

In the current algorithm we have selected three 

scenarios where we can have the valve open either at 2, 

3, or 4 positions, depending on the control strategy 

adapted. 

EXPERIMENTAL TESTING 

 The seat suspension was tested using a singleaxis MTS®

 shaker at the PRL NIOSH Vibration Testing 

Laboratory, Pittsburgh PA. The test protocol consisted 

of a sinusoidal vibration sweep of amplitude ±10mm and 

a frequency range of 1 to 4 Hz at 0.1 Hz intervals. A 

test weight of 40 kg was used to simulate seated vehicle 

operators. 

 Different control strategies were tested under 

the same input: 

 The pressure inside the suspension piston was 

set to 45, 60, and 85 PSI. The control strategies have 

been evaluated for each pressure, leading to a total of 

12 different configurations of the suspension design that 

were tested. 

 The acceleration of the shaker and the seat pan 

was measured and used to calculate the ratio of the 

seat pan RMS acceleration to the shaker table RMS 

acceleration (i.e., transmissibility ratio). This ratio is 

commonly used to measure of how effective the seat 

suspension is and how much vibration we were able to 

cancel during the process. 

 The results show a reduction of the peak at the 

resonance for all the control strategies when the 

pressure inside the actuator increases. We also saw a 

direct correlation between the ability of having higher 

options in damping selection via the different positions 

of the valves and the resonance peak. The results 

clearly indicate how dual valves are not reliable. 

SIMULATION OF THE PROPOSED SUSPENSION 

DESIGN 

 

 A model of the proposed suspension design 

was developed using MATLAB® and Simulink®. The 

simulation is based on the control code developed for 

the experimental set up. The control is performed in 

exactly the same fashion. Input of the accelerometer 

placed on the chassis is given. Displacement, velocity, 

and acceleration of the seat are computed according to 

the control strategy and mechanical characteristics of 

the system. The acceleration of the seat is then fed back 

in the simulation as an input from the accelerometer 

placed on the seat. 

 The parameters for the simulation are: 

control strategy 

pressure inside the system 

Figure 3 shows the results obtained from both the 

experiment as well as the simulation under the same 

conditions. The correlations between the two are 

extremely close. Our main thrust is to be able to account 

for every component in the active suspension system 

including motor control and shaft that drives the valve as 

well as the encoder and feedback mechanism to set the 

right pressure in the piston/actuator. While the 

transmissibility can be approved further the lower 

pressure provided better results. 

1 1.5 2 2.5 3 3.5 4

0

0.5

1

1.5

2

2.5

frequency in Hz

transmissibility

exp 45 PSI 4 levels

exp 60 PSI 4 levels

simultation 60 PSI 4 levels

simultation 45 PSI 4 levels

Figure 3: Transmissibility of the suspension obtained 

though experimental and simulated data 

HUMAN BODY VIBRATION 

The displacement of the seat is applied to the 

extremities of the spring and the dashpot connecting the 

lower torso to the seat. Our multibody model computes 

the acceleration of each body segment and its 

corresponding RMS (Root Mean Square) acceleration. 

The body segments dynamics is estimated at each step 

in time and the connective forces are evaluated. 

Furthermore, the work associated with each body 

segment is evaluated. Integrating further the work 

against time, we obtain the absorbed power for each 

body segments. 
EXPERIMENTAL DATA 

A team from PRL/NIOSH Vibration Testing Laboratory 

conducted a study regarding a new cabin design for a 

mine vehicle e n title d : “D e sig n Im p ro ve m e n ts in O p e ra to r 

Cab Seat and Vibration Considerations for Low-Coal 

S h u ttle C a r H a u la g e in U n d e rg ro u n d M in e s” A S M E 

2005. Different loads for the vehicle were considered 

and various seat models were studied. The 

accelerations of both chassis and seat were monitored 

for different operators/drivers. 

Experimental data from the above study was used as 

input to the current human model/driver. We used data 

obtained for a single operator driving a low coal shuttle 

with three different seat designs for the purpose of 

illustrating the effects of padding on the operator. The 

seat with the padding characteristics which provided 

best performance was selected. 

To take advantage of the active suspension developed 

we used the experimental displacements for the chassis 

and provided that as an input to the simulation 

developed to emulate the new seat-suspension design. 

The same control strategies of the suspension were 

investigated against experimental results obtained using 

new seat pads. 

 

RESULTS 

 Using the results from the human body model, 

we plotted the RMS acceleration, absorbed power for 

the legs, lower torso, mid-torso, upper torso, and head 

for all 3 different seat designs: a current commercialized 

seat (Seat 1 in the graph) and two seat designs 

proposed by NIOSH (Seat 2A and Seat 2B in the graph). 

 From the results shown in Figure 4 we see that 

the RMS acceleration for the new padding designs 

compared to the seat design from the market, seat 2B 

provided the best response. Yet, considering the 

absorbed power, the new designs reduction was seen 

only at the upper torso only. 

 

 

RMS acceleration of the bodies against the seat

0

1

2

3

4

5

6

seat legs lower torso middle torso upper torso head

Body

rms acceleration (m.s^2)

Seat 1

Seat 2A

Seat 2B

Absorbed power against seat

0

0.5

1

1.5

2

2.5

3

3.5

4

legs lower torso middle torso upper torso head

Body

Absorbed power (W)

Seat 1

Seat 2A

Seat 2B

Figure 4: rms acceleration and absorbed power for a 

passive suspension with different seat pads 

 The second series of graph (Figure 5) show the 

human body response when the semi active suspension 

was employed. We plotted the RMS acceleration and 

the absorbed power for different control strategies and 

configurations of the seat suspension. 

 In all the configurations and for all the strategies 

the addition of the active suspension translates into a 

significant reduction of the RMS acceleration and 

absorbed power for each body component. 

0

0.5

1

1.5

2

2.5

3

Absorbed power 

(W)

legs lower

torso

middle

torso

upper

torso

head

body

Absorbed power for the ON/OFF control strategy for different 

pressures

60 PSI

NIOSH exp (Seat 2A)
0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

rms acceleration 

(m.s^2)

seat legs lower

torso

middle

torso

upper

torso

head

body

RMS accelerations for the 4 level control strategy for different 

pressures

60 PSI

NIOSH exp (Seat 2A)

Figure 5: rms acceleration and absorbed power for an 

active suspension with different seat pads 

There are two conclusions that can be drawn 

from this study. One is that padding can indeed help 

diminish the energy being transmitted to the body this is 

supported by examining both the RMS values as well as 

the power absorption at different body levels from 

padding simulation. Second, we have demonstrated that 

active suspension can lead to even better results and 

hence it should be considered as the ultimate mean to 

achieve low energy transmission. The cost associated 

with padding is a lot cheaper than the active suspension 

and if the difference is kept below 50% it may not justify 

the cost of an active suspension. This work needs 

further investigation and additional padding materials 

need to be investigated to address the advantages and 

disadvantages of both systems. 

REFERENCES 

1. F.Amirouche, Computational Methods in Multibody 

Dynamics. Practice Hall, 1993 

2. F. Amirouche, Advanced Topics in Seat Suspension 

Design and Human Body Vibration Control. SAE 

Seminars, 1998 

3. F. Amirouche, L. Palkovics and J. Woodrooffe, 

Optimal driver seat suspension design for heavy 

trucks, International Journal of Vehicle Design, 

1992. 

4. A. Mayton, F.M.L. Amirouche, Design Improvements 

in Operator Cab Seat and Vibration Considerations 

for Low-Coal Shuttle Car Haulage in Underground 

Mines , ASME 2005 

5. A. Mayton, F.M.L. Amirouche, Design Improvements 

in Operator Cab Seat and Vibration Considerations 

for Low-Coal Shuttle Car Haulage in Underground 

Mines , ASME 2005 

CONTACT 

Farid Amirouche 

Professor and Director 

Biomechanics Research Laboratory 

University of Illinois at Chicago 

Email: amirouch@uic.edu

312-996-3601