Systems & Control Letters 61 (2012) 1069–1078
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Systems & Control Letters
journal homepage: www.elsevier.com/locate/sysconle
Stabilization of an Euler–Bernoulli beam with input delay in the boundary
control
✩
Ying Feng Shang, Gen Qi Xu
∗
Department of Mathematics, Tianjin University, Tianjin 300072, China
a r t i c l e i n f o
Article history:
Received 12 April 2011
Received in revised form
7 July 2012
Accepted 24 July 2012
Keywords:
Euler–Bernoulli beam
Input delay
Feedback control
Exponential stability
a b s t r a c t
In this paper, we consider a cantilever Euler–Bernoulli beam with controller delay. Suppose that the
output of the boundary controller is of the form αu(t) + βu(t − τ ), where u(t) is the controller input. It
is well known that a system with a collocated feedback control law is exponentially stable if β = 0, and
it is unstable with the same control law when α = 0. In the present paper, we shall design a dynamic
controller that makes the system stabilize exponentially for any |α| = |β| and τ > 0. Furthermore, we
discuss the stability of the system for |α| = |β|.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
It is well known that a cantilever Euler–Bernoulli beam with
input delay in the boundary control is described by (see [1])
w
tt
(x, t) + w
xxxx
(x, t) = 0, 0 < x < 1, t > 0,
w(0, t) = w
x
(0, t) = w
xx
(1, t) = 0,
w
xxx
(1, t) = αu(t) + βu(t − τ ),
w(x, 0) = w
0
(x), w
t
(x, 0) = w
1
(x),
u(θ) = f (θ ), θ ∈ (−τ , 0),
(1.1)
where α, β ∈ R with |α| + |β| = 0 are the controller constants,
τ > 0 denotes the delay time, and u(θ) = f (θ ), θ ∈ [−τ , 0] is a
bounded measurable function. If β = 0 and α > 0, which means
that the controller has no delay, the system can be exponentially
stabilized by u(t) = w
t
(1, t); see [2,3]. However, such a feedback
law no longer stabilizes the system if the controller has full delay,
i.e., β = 0 and α = 0; for a similar result, we refer to [4,5]. When
α > 0 and β ∈ R, the relationship between α and β concerning the
stability of this system is discussed in [1]. The result in [1] shows
that a system with the same feedback control law is exponentially
stable when α > |β| and unstable when |β| > α > 0. When
α = |β|, the system is asymptotically stable for τ ∈ ∪
k
{τ >
0, f
k
(τ ) = 0}, where f
k
(x) is a real function defined by [1, Formula
(15), Theorem VI.2].
✩
This research was supported by the National Science Natural Foundation in
China (NSFC–61174080).
∗
Corresponding author. Tel.: +86 2281831255.
E-mail addresses: xugq_2001@yahoo.com, gqxu@tju.edu.cn (G.Q. Xu).
In the past five years, a similar issue has been studied exten-
sively for wave equations. In 2006, Xu et al. [6] discussed the sta-
bility of one-dimensional wave equations with partial time delay
in the boundary feedback control. Using a detailed spectral analy-
sis, they proved that the wave equation is exponentially stable if
α > β > 0, but the system is unstable for 0 < α < β. Nicaise
and Pignotti [7] extended this result to multi-dimensional wave
equations with a delay term in the boundary or internal feedbacks.
Nicaise and Valein [8] obtained similar results for one-dimensional
wave networks with delay in the nodal feedbacks. In 2009, Ben-
hassi et al. [9] characterized the stabilization of a class of abstract
second-order evolution equations with delay for α > β > 0. The
results mentioned above show that α > β > 0 is a criterion of sta-
bility of a system with delay damping. However, we see from [1]
that, for practical control systems, the coefficients α and β are de-
termined by the controller; this represents an inherent property of
the controller. Usually one cannot determine whether α > β holds
or not. Therefore, how to design an anti-delay control law for any
α, β ∈ R with |α|+|β| = 0 is an important task. We note that this
issue has not been discussed until now. In the present paper, we
propose a dynamic feedback law to stabilize system (1.1) for any
α, β ∈ R with |α| = |β|.
The idea of the dynamic control strategy in this paper comes
from the classical Smith predictor. Suppose that the full state of the
system is measurable, and that y(t) is the observation value of the
endpoint velocity of (1.1), which has no time delay. It is well known
that, if the output feedback law u(t) = y(t) is adopted, system (1.1)
is unstable for α = 0 and β = 0. Since the state of the system is
measurable, the classical Smith predictor can give an estimate of
the future state of the system. It should be pointed out that the
0167-6911/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.sysconle.2012.07.012