1. INTRODUCTION
Recently, researches on a combined system of a
mobile robot and an inverted pendulum system, the
mobile pendulum robot system are quite actively
conducted. The mobile pendulum robot has not only a
certain level of difficulty to control, but also practicality
of the real world applications. Segway is the popular
commercial product of human carriers that carries
humans to the desired destination. Segway is suitable
for the place where human traffic is frequent so that
narrow turn is necessary such ac airport lobbies or
where to move short distance [1].
JOE is a small two-wheeled inverted pendulum robot
system which is somewhat difficult to control since the
normal friction force is not large due to light weight of
the pendulum [2]. Other mobile inverted pendulum
robot systems have been designed and controlled[3-9].
The gyro sensor drift problem of the mobile inverted
pendulum system has been proposed[5]. In our previous
researches, a similar mobile pendulum robot system has
been built and controlled to follow desired trajectories
while balancing by a neural network controller [10].
To make the mobile inverted pendulum robot
system work well, accurate sensing of current state of
the system becomes more important and has to be done
before control.
Manuscript received May 1, 2008. This work was supported by the
Ministry of Commerce, Industry, and Energy (MOICE) and Korea
Industrial Technology Foundation (KOTEF) through the Human
Resource Training Project for Regional Innovation, Korea.
H. j. Lee is with the intelligent systems and emotional engineering
laboratory(ISEE), the Mechatronics Engineering Department,
Chungnam National University, Daejeon, 305-764 KOREA (e-mail:
noogo82@naver.com).
S. Jung, is with the intelligent systems and emotional engineering
laboratory(ISEE), Chungnam National University, Daejeon, Korea
305-764(Tel: +82-042-821-6876, e-mail: jungs@cnu.ac.kr).
The balancing angle of the pendulum can be measured
by a gyro sensor or a tilt sensor. In [10], an expensive
commercial gyro sensor has been used to measure the
pendulum angle and controlled since the gyro sensor has
the fast response.
To replace with a low cost gyro sensor, a drift
problem of the gyro sensor has to be compensated with
the help of the tilt sensor. The gyro sensor shows the
fast response, but suffers from drift due to accumulated
errors by integration to obtain angle information from
acceleration. Meanwhile, the tilt sensor has a good
steady state response, but has a slow response and
suffers from noise in high frequency response.
Therefore, combining the gyro sensor and the tilt sensor
together by considering different frequency responses is
required. The complementary filter compensates for
those defects and has been used for different frequencies
to obtain accurate angle information [3]. The Kalman
filter with neural network has been used to model the
gyro sensor drift[11,12].
In this paper, the mobile pendulum robot system is
controlled with low cost sensors such as a gyro sensor
and a tilt sensor to measure the balancing angle of the
inverted pendulum system. The highpass filter is
designed for the gyro sensor and the lowpass filter is
designed for the tilt sensor. This forms the
complimentary filter. Then the Kalman filter is designed
to estimate the angle based on filtered sensor data.
Experimental studies of balancing and position control
of the mobile inverted pendulum robot system are
conducted to validate the proposed estimation method.
2. KINEMATICS OF MOBILE INVERTED
PENDULUM ROBOT
The mobile pendulum robot system is a combined
Gyro Sensor Drift Compensation by Kalman Filter to Control
a Mobile Inverted Pendulum Robot System
Hyung-Jik Lee
1
and Seul Jung
2
1
Department of Mechatronics Engineering, Chungnam National University, Deajoen, Korea
(Tel : +82-42-821-7232; E-mail: hjlee81@cnu.ac.kr)
2
Department of Mechatronics Engineering, Chungnam National University, Deajoen, Korea
(Tel : +82-42-821-6876; E-mail: jungs@cnu.ac.kr)
Abstract: In this paper, a sensor fusion technique of low cost sensors such as a gyro sensor and a tilt
measure the balancing angle of the inverted pendulum robot system accurately is implemented. The complimentary
filter consisting of the lowpass filter for the gyro sensor and the highpass filter for the tilt sensor are used based on the
frequenc
y response characteristics of those sensors. The Kalman filter is used to estimate the angle based on filtered
sesnor data. Experimental studies of balancing and position control of the mobile inverted pendulum robot system are
conducted to validate the proposed estimation method.
Keywords: Inverted pendulum, Kalman filter, complementary filter, gyro drift
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