IEEE TRANSACTIONS MANUSCRIPT 1
Finite-Time Trajectory Tracking Control of a Class
of Nonlinear Discrete-Time Systems
Zhuo Wang, Member, IEEE, Renquan Lu, Member, IEEE, Furong Gao, and Hong Wang, Senior Member, IEEE
Abstract—This paper studies how to control a class of nonlin-
ear discrete-time systems, to completely track any given bounded
expected trajectories in finite time. For this problem, we develop
some constructive control methods for both the total output case
as well as the partial output case. Some of these control methods
can design the tracking instant when the trajectory tracking is
just accomplished, but cannot guarantee the monotonic decrease
of the norm of the tracking error before that instant. The other
control methods not only can determine the tracking instant after
which the (partial) output trajectory coincides with the expected
trajectory, but also can make the norm of the tracking error
decrease monotonically before that instant. In the mean time,
for the partial output case, the rest part of the system output is
bounded for all the time. Then, we give some simulation examples
to demonstrate the effectiveness of these control methods. Among
these examples, a permanent magnet linear motor system is
employed to illustrate the practicability.
Index Terms—Bounded expected trajectories, finite-time tra-
jectory tracking, nonlinear discrete-time systems, partial output
trajectory, total output trajectory.
I. INTRODUCTION
I
N control theory and control engineering, trajectory track-
ing is one of the most important subjects to be extensively
studied for both linear/nonlinear continuous-time systems and
discrete-time systems [1], [2], [3]. The objective of these
studies is to make the system state/output track a prescribed
trajectory. The trajectory tracking has so far been investigated
can be divided into two categories: the asymptotic trajectory
tracking [4], [5], [6] and the finite-time trajectory tracking [7],
[8], [9]. The asymptotic trajectory tracking is generally in the
Lyapunov’s sense [5], [6], [10], [11], that the norm of the
tracking error decreases monotonically as time increases, and
the system state/output will converge to the expected trajectory
as time tends to infinity. Besides, it is often required that
the system model has smooth dynamic characteristics [12],
[13], such as the continuous partial derivatives. However, it is
impractical to wait for an infinitely long time, thus people need
to introduce a prescribed accuracy (usually referred to as the
maximum tolerable tracking error), and consider the trajectory
This work was supported in part by Guangzhou Scientific and Technological
Project under Grant 12190007, NSFC-On-Line Quality Measurement Instru-
ment for Injection Molding under Grant 61227005, and Guangdong Scientific
and Technological Project under Grant 2012B090500010.
Z. Wang and F. Gao are with Fok Ying Tung Graduate School, Hong Kong
University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
(e-mail: zwang8381@foxmail.com, Kefgao@ust.hk).
R. Lu is with Institute of Information and Automation, Hangzhou Dianzi
University, Hangzhou 310000, China (e-mail: rqlu@hdu.edu.cn).
H. Wang is with the Control Systems Centre, University of Manchester,
Manchester M60 1QD, U.K. (e-mail: hong.wang@manchester.ac.uk).
tracking is accomplished when the accuracy requirement is
satisfied.
The finite-time trajectory tracking, on the other hand, is
quite a different problem. It is concerned with how to design
a tracking instant when the trajectory tracking is accomplished,
and how to make the tracking error keep zero from that instant
on. In this sense, the finite-time trajectory tracking is superior
to the asymptotic trajectory tracking regardless of the system
requirements, since it has higher tracking precision, faster
convergence rate, and can determine the exact time when the
trajectory tracking is accomplished. In engineering practice,
there are some precise tracking tasks need to be done in
finite time, due to the resource limitation or the standard of
workmanship, etc. For example, in the areas of shipbuilding
and car manufacturing, it has become very common that the
industrial robot precisely cuts materials along the preset edge
or welds workpieces along the preset welding seam [14], [15].
When launching aircraft, the aircraft is supposed to enter
the predesigned trajectory in finite time, and subsequently,
flies along this trajectory precisely [16], [17]. In astronomical
observation area, the attitude precision and the flying precision
along the predesigned trajectory of spacecrafts (such as Hubble
Space Telescope), will directly affect the observation of the
far-away stars [18], [19]. In this circumstance, the study and
investigation of finite-time trajectory tracking problems have
important significance in theory and practice.
Up to now, most of the existing works on finite-time
trajectory tracking are about the control design problem, and
some typical control schemes have been proposed for it. Such
as the backstepping methods [10], [19], [20], the sliding mode
methods [18], [21], [22], and the neural network methods [23],
[24]. Despite the merits of these control methods, they have
some shortcomings: they can only deal with some particular
systems with specific structures or dynamic characteristics, but
cannot control a general class of systems; they can only drive
the system state/output to track some particular trajectories,
but not to track arbitrary bounded trajectories; they can only
accomplish the trajectory tracking within a finite time horizon,
but cannot determine the exact tracking instant when the
state/output trajectory begins to coincide with the expected
trajectory. In this situation, further researches need to be
conducted. The study on these problems is necessary to reveal
the essential role of finite-time trajectory tracking control.
In this paper, we will conduct research on the finite-time
output trajectory tracking control problem for a class of
nonlinear discrete-time systems. We will develop control laws
in a constructive way, for both the total output case and the
partial output case of these systems. Our control methods