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使用鲁棒扩展H∞滤波的移动机器人定位
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2021-02-23
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在本文中,提供了一种新颖的方法,可使用基于内部和外部传感器的自主导航来精确定位移动机器人。 开发了一种新的鲁棒扩展H∞滤波器来处理机器人的非线性运动学模型和非线性距离测量,以及过程和测量噪声。 所提出的滤波器依赖于两步预测校正结构,该结构类似于卡尔曼滤波器。 仿真结果证明了该方法的有效性。
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Mobile robot localization using
robust extended H
‘
filtering
Fuwen Yang
1
, Zidong Wang
2
*
, Stanislao Lauria
2
, and Xiaohui Liu
2
1
School of Information Science and Engineering, East China University of Science and Technology, Shanghai, People’s
Republic of China
2
Department of Information Systems and Computing, Brunel University, Uxbridge, UK
The manuscript was received on 14 April 2009 and was accepted after revision for publication on 3 August 2009.
DOI: 10.1243/09596518JSCE791
Abstract: In this paper, a novel methodology is provided for accurate localization of a mobile
robot using autonomous navigation based on internal and external sensors. A new robust
extended H
‘
filter is developed to deal with the non-linear kinematic model of the robot and
the non-linear distance measurements, together with process and measurement noises. The
proposed filter relies on a two-step prediction–correction structure, which is similar to a
Kalman filter. Simulations are provided to demonstrate the effectiveness of the proposed
method.
Keywords: autonomous m obile robot, localization, robust extended H
‘
filtering, navigation
1 INTRODUCTION
Localization is one of the fundamental problems for
autonomous navigation of mobile robots. The
knowledge about the position and orientation of a
robot is useful in different tasks, such as office
delivery and obstacle avoidance, for example. In the
past, a variety of approaches for mobile robot
localization have been developed. They mainly differ
in the techniques used to represent the belief of the
robot about its current position, and in the type of
sensor information that is used for localization. For
the robot to be really autonomous, only on-board
sensors must be used to perform localization. This
prevents the robot from using direct configuration
measurements, and calls for suitable numerical
processing of the data provided by the sensor
equipment. The on-board sensors allow two differ-
ent kinds of localization: relative and absolute. The
former is realized through the data provided by
sensors measuring the dynamics of variables inter-
nal to the vehicle. One of the common methods used
to estimate the current position is dead reckoning
using internal sensors [1, 2], such as optical incre-
mental encoders, which are fixed to the axis of the
driving wheels or to the steering axis of the vehicle.
At each sampling instant the position is estimated on
the basis of the encoder increments along the
sampling interval. A drawback of this method is that
the errors of each measure are cumulative. The error
in dead reckoning increases as the robot travels. This
heavily degrades the position and orientation esti-
mates of the vehicle, especially for long and winding
trajectories [3].
Absolute loc alization is performed by processing
the data provided by a proper set of sensors
measuring some parameters of the environment in
which the vehicle is operating. External sensor
devices, such as a laser scanner or sonar, are
generally used for this purpose. They are fixed to
the vehicle and measure the distance with respect to
parts of the known environment [2, 4]. They are also
widely utilized for the guidance of autonomous
vehicles for obstacle avoidance in unknown envir-
onments [5, 6]. The main drawback of absolute
measures is their dependence on the characteristics
of the environment. Possible changes to environ-
mental parameters may give rise to an erroneous
interpretation of the measurements provided by the
localization algorithm.
*Corresponding author: Department of Information Systems and
Computing, Brunel University, Uxbridge, Middlesex UB8 3PH,
UK.
email: Zidong.Wang@brunel.ac.uk
1067
JSCE791 Proc. IMechE Vol. 223 Part I: J. Systems and Control Engineering
In order to obtain an accurate localization for a
mobile robot, an efficient method is to fuse together
relative and absolute measurements using sensors of
different natures. For this purpose, the localization
problem has been extensively studied in the robotics
literature (see, for instance, references [7–11], and the
references therein). The mainstream approach for
robot localization is Bayesian estimation, which is
based on stochastic assumptions about the process
and measurement errors, and is aimed at construct-
ing the posterior density of the current robot state,
conditioned on all available measurements. In parti-
cular, when the process and measurement error
processes are assumed Gaussian, the Bayesian ap-
proach results in the classical extended Kalman
filtering (EKF) framework (see references [12–14]).
However, in robotics applications, the distribution of
the sensor and process noise is generally multimodal
and imprecisely known, and the non-linearities of the
system may seriously degrade the EKF performance.
These limitations have been recognized in the
literature, and several schemes have been proposed
to overcome them. Notably, an adaptive EKF ap-
proach for online estimation of the noise statistics has
been proposed in references [9], [10], and [15], and
joint Bayesian hypothesis testing and Kalman filtering
have been proposed in reference [16]. A probabilistic
confidence set approach has been presented in
reference [11], which is optimal over a certain class
of noise distributions. A Monte Carlo approach,
where the noise density is represented by means of
a set of randomly drawn samples, is proposed in
reference [17]. The key idea of particle-filter-based
methods is to approximate the densities through
samples (particles) according to the posterior dis-
tribution over robot poses [17]. The particle repre-
sentation therefore, can provide universal density
approximators without the assumption of Gaussian
distribution and can adapt to the available computa-
tional resources by controlling the number of sam-
ples. The Markov-chain-Monte-Carlo-based method
provides a posterior distribution estimation over
robot poses [18]. Piecewise constant functions are
used instead of Gaussians to approximate the
distribution. However, the computation of the piece-
wise constant representation is very demanding.
In this paper, an alternative to an adaptive EKF
approach, called the robust extended H
‘
filtering
method, is proposed. It combines the data provided
by internal and external sensors to estimate the
robot’s position. The advantage of the robust ex-
tended H
‘
filtering technique is that it can consider
non-linear systems with unknown process noises and
measurement noises. It is suitable for use on the
kinematic model of the robot and data obtained from
sensors. The techniques proposed here are superior
to the EKF techniques proposed in the literature [19],
for the estimation of robot localization by considering
the linearization error and non-Gaussian noises in
process and measurement. The main novelty of the
proposed robust extended H
‘
filtering technique is its
ability to tolerably estimate robot localization in an
unknown environment. The computation of the
robust extended H
‘
filtering method is similar to the
EKF. It can be implemented online.
The remainder of this paper is organized as
follows. In section 2, the kinematics of the mobile
robot are described and the scheme of absolute
measurements is provided. A novel robust extended
H
‘
filtering algorithm is developed in section 3 for
handling non-linear processes and measurements,
and unknown noises. In section 4 a numerical
simulation is provided to demon strate the effective -
ness of the proposed algorithm. Some concluding
remarks are provided in section 5.
Notation
The notation X > Y (respectively, X . Y) where X and
Y are symmetric matrices, means that X 2 Y is positive
semi-definite (respectively, positive definite). The
superscript T stands for matrix transposition. By
f
k
kk
2
R
, we denote the product f
T
k
Rf
k
. It is denoted that
Gramian matrix R
x
5 ^x, x&, where ^x, x& stands for the
inner product of x,i.e.^x, x& 5 xx
T
, and x is a vector.
2 KINEMATICS OF THE MOBILE ROBOT AND
THE ABSOLUTE MEASUREMENT
Consider a unicycle-like mobile robot with two
driving wheels, mounted on the left and right-hand
sides of the robot, with their common axis passing
through the centre of the robot (see Fig. 1). Localiza-
tion of this mobile robot in a two-dimensional space
requires knowledge of the coordinates of the mid-
point between the two driving wheels and of the
angle between the main axis of the robot and the
direction. The kinema tic model of the unicycle robot
is described by the following equations
_
xxtðÞ~vtðÞcos h tðÞ
_
yytðÞ~vtðÞsin h tðÞ
_
hh tðÞ~v tðÞ
8
>
<
>
:
ð1Þ
where
1068 Fuwen Yang, Zidong Wang, Stanislao Lauria, and Xiaohui Liu
Proc. IMechE Vol. 223 Part I: J. Systems and Control Engineering JSCE791
vtðÞ~
v
R
tðÞzv
L
tðÞ
2
ð2Þ
v tðÞ~
v
R
tðÞ{v
L
tðÞ
d
ð3Þ
where x(t) and y(t) are the coordinates of the main
axis midpoint between the two driving wheels, h(t)is
the angle between the robot forward axis and the x-
direction, v(t) and v(t) are, respectively, the dis-
placement and angular velocities of the robot, v
R
(t)
and v
L
are, respectively, the right and left displace-
ment velocities of the robot, and d is the distance
between the two wheels of the robot. The encoders
placed on the driving wheels provide a measur e of
the incremental angles over a sampling period. The
odometric measures are used to obtain an estimate
of the displacement and angular velocities, respec-
tively, which are assumed to be constant over the
sampling period. If zero-order hold on v(t) and v(t)
is assu med, then the above system is discretized
with sample time and expressed in linear form as
x
k z1
~x
k
zDTv
k
cos h
k
y
k z1
~y
k
zDTv
k
sin h
k
h
kz1
~h
k
zDTv
k
8
>
<
>
:
ð4Þ
Let
z
k
~
x
k
y
k
h
k
2
6
4
3
7
5
ð5Þ
and
u
k
~
DTv
k
DTv
k
:~
u
1, k
u
2, k
ð6Þ
equation (4) can be rew ritten as
z
kz 1
~f z
k
, u
k
ðÞ ð7Þ
where
f z
k
, u
k
ðÞ~z
k
z
u
1, k
cos h
k
u
1, k
sin h
k
u
2, k
2
6
4
3
7
5
ð8Þ
The distance and angle to the marker M are
treated as the measurements (see Fig. 2). The
azimuth y with respect to the x-axis and the distance
from the robot’s planar Cartesian coordinates (x, y)
to the marker (x
M
, y
m
) at a time instant k can be
related to the current syst em state variables x
k
, y
k
,
and h
k
as follows
d
k
~
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
x
m
{x
k
ðÞ
2
z y
m
{y
k
ðÞ
2
q
ð9Þ
y
k
~h
k
{arctan
y
m
{y
k
x
m
{x
k
ð10Þ
Let
m
k
~
d
k
y
k
ð11Þ
equation (4) can be rew ritten as
m
k
~g z
k
ðÞ ð12Þ
Fig. 1 The mobile robot
Fig. 2 The coordinate frame for the mobile robot
Mobile robot localization using robust extended H
‘
filtering 1069
JSCE791 Proc. IMechE Vol. 223 Part I: J. Systems and Control Engineering
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