Page 352 - Mechatronics for Safety, Security and Dependability in a New Era

Ch68-I044963.fm Page 336 Tuesday, August 1, 2006 8:30 PM
Ch68-I044963.fm
336
336 Page 336 Tuesday, August 1, 2006 8:30 PM
from the road, is attached at the lower part of the hydraulic actuator and is driven by a hydraulic motor.
The amount of disk eccentricity is set to 5 mm. Each displacement of the body mass and wheel is
detected by position sensors, while cylinder pressure is detected by a pressure sensor. These signals
are transmitted to a computer through an A/D converter and thus the control input u to the valve is
calculated so that the vibration of the car body can decrease in the minimum level.

PREVIEW CONTROL METHOD WITH ADAPTIVE DIGITAL FILTER

In our advanced work, we adopted a sky-hook control method to confirm that the active suspension
system using the digital valve has adequate control performance almost equivalent to the conventional
5
one composed of a pressure control valve' '. Thus, the method of preview control using an ADF is
adopted in this study as the more effective controller for robustly decreasing vibration. Figure 6 shows
the schematic diagram of the preview control using an ADF.

\ Preview distance: L K ~~- i
(a) Vehicle model (b) Block diagram

Figure 6: Preview control using an ADF

We assumed that the displacement of the road surface in the forward of an automobile can be detected
before T ci seconds by using some sort of sensor. (In the experiment, we actually used the displacement
of the eccentric disk (in Fig.5) which is detected one period before. Here, road displacement x rp and
x
body displacement i, are considered as an input signal and a error signal, respectively. The road
x
displacement x rp is compensated by the ADF using error signal h. In this method, the LMS £east
Mean Square) algorithm is used for renewal of the ADF's coefficients. The formula for the renewal of
the filter coefficients is

(1)
where W k is the filter coefficient, ju is a step size, s k is the error signal {=x b), and X k is the input
signal (=x rp).
Equation of motion for the active suspension:
px\, + c p(x hp -x lp) + k p(x hp-x rp) = 0. (2)

In the preview control part, x hp is calculated using the above equation (2). Thus, the control input
is obtained as . The valves are controlled after the system delay time i is compensated
F AnF c pre • x bp
for. Here,