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Intelligent Control and Automation, 2012, 3, 390-403 http://dx.doi.org/10.4236/ica.2012.34043 Published Online November 2012 (http://www.SciRP.org/journal/ica) Stable Adaptive Fuzzy Control with Hysteresis Observer for Three-Axis Micro/Nano Motion Stages Lih-Chang Lin, Bor-Yih Chang, Biing-Der Liaw Department of Mechanical Engineering, National Chung Hsing University, Taichung, Chinese Taipei Email: [email protected] Received July 31, 2012; revised August 31, 2012; accepted September 7, 2012 ABSTRACT This paper considers the analytical dynamics with simplified Dahl hysteresis model for a three-axis piezoactuated micro/ nano flexure stage. An adaptive controller with nonlinear dynamic hysteresis observer is proposed using Lyapunov sta- bility theory. In the controller, a fuzzy function approximator with parameters update law is included to compensate for the identification inaccuracy, model uncertainty, and flexure coupling effects. Simulation results are used to demon- strate the control performance. Keywords: Micro/Nano Stage; Adaptive Fuzzy Control; Hysteresis Observer; Fuzzy Function Approximator 1. Introduction Recently, control of micro/nano stages considering the piezoactuator hysteresis effects has found great interests in the literature. Effective ultrafine-resolution trajectory tracking performance of stages is limited by the intrinsic hysteretic behavior of the piezoceramic material and the structural vibration of the devices [1]. Many efforts were trying to decrease the hysteresis ef- fect of piezoactuators. Newcomb and Flinn [2] found that the relationship between the extension of a piezoceramic actuator and its applied electric charge has significantly less hysteresis nonlinearity than that between deforma- tion and applied voltage. Furutani et al. [3] proposed an induced charge feedback control for the piezoactuators. The approach needs measurement of the induced charge and a specially designed charge drive amplifier, and will cause an increase in the response time of the actuator. In order to linearize the control system, many re- searches focused on the inverse feedforward compensa- tion based on some inverse hysteresis model. Several models have been suggested for describing the complex hysteretic behavior, for example, the Preisach model in Ge and Jouaneh [4,5], Yu et al. [6], and Liu et al. [7], the generalized Preisach model in Ge and Jouaneh [8], the dynamic Preisach model in Yu et al. [9]; the general- ized Maxwell elasto-slip model in Goldfarb and Celano- vic [10]; the variable time-relay hysteresis model in Tsai and Chen [11]; the Prandtl-Ishlinskii (PI) model (a sub- class of the Preisach model) in Ang. et al. [1] and Has- sani and Tjahjowidodo [12]; the Duhem model in Ste- panenko and Su [13]; the polynomial approximation method in Croft and Devasia [14]; and the Jiles-Atherton model in Dupre et al. [15]. Ge and Jouaneh [5] proposed a PID feedback control using the classical Preisach model for the hysteresis. Song et al. [16] proposed a cascaded PD/lead-lag feedback controller based on a linear model for the piezoactuator with hysteresis being compensated via the feedforward cancellation using the inverse classical Preisach model. Recently, Maslan et al. [17] presented a discrete-time transfer function and its inverse for a highly nonlinear and hysteretic piezoelectric actuator, and traditional PID controller and PID with active force control were considered. To mitigate the effects of the unknown hysteresis, Wang et al. [18] suggested a model reference control for linear systems with unknown input hysteresis using an inverse KP (Krasnosel’skii-Pokrovskii) hysteresis model [19]. Hwang et al. [20] proposed a neural-network non- linear model for learning the hysteretic behavior of a piezoelectric actuator, and suggested a discrete-time va- riable-structure control for enhancing the nonlinear mo- del-based feedforward control performance. Based on the learned nonlinear model of piezoelectric actuator systems in [20], Hwang and Jan [21] proposeed a controller in- cluding a nonlinear inverse control and a discrete neuro- adaptive sliding mode control using a recurrent neural network to compensate for the residue dynamic uncer- tainty. Wai and Su [22] presented a supervisory genetic algorithm (SGA) control system for a piezoelectric ce- ramic motor. The controller consists of a GA control to search an optimum control effort online via gradient de- scent training process and a supervisory control to stabi- lize the system states around a predefined bound region. Copyright © 2012 SciRes. ICA

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Page 1: Stable Adaptive Fuzzy Control with Hysteresis Observer for …file.scirp.org/pdf/ICA20120400011_96201248.pdf ·  · 2013-12-24Department of Mechanical Engineering, National Chung

Intelligent Control and Automation, 2012, 3, 390-403 http://dx.doi.org/10.4236/ica.2012.34043 Published Online November 2012 (http://www.SciRP.org/journal/ica)

Stable Adaptive Fuzzy Control with Hysteresis Observer for Three-Axis Micro/Nano Motion Stages

Lih-Chang Lin, Bor-Yih Chang, Biing-Der Liaw Department of Mechanical Engineering, National Chung Hsing University, Taichung, Chinese Taipei

Email: [email protected]

Received July 31, 2012; revised August 31, 2012; accepted September 7, 2012

ABSTRACT

This paper considers the analytical dynamics with simplified Dahl hysteresis model for a three-axis piezoactuated micro/ nano flexure stage. An adaptive controller with nonlinear dynamic hysteresis observer is proposed using Lyapunov sta- bility theory. In the controller, a fuzzy function approximator with parameters update law is included to compensate for the identification inaccuracy, model uncertainty, and flexure coupling effects. Simulation results are used to demon- strate the control performance. Keywords: Micro/Nano Stage; Adaptive Fuzzy Control; Hysteresis Observer; Fuzzy Function Approximator

1. Introduction

Recently, control of micro/nano stages considering the piezoactuator hysteresis effects has found great interests in the literature. Effective ultrafine-resolution trajectory tracking performance of stages is limited by the intrinsic hysteretic behavior of the piezoceramic material and the structural vibration of the devices [1].

Many efforts were trying to decrease the hysteresis ef- fect of piezoactuators. Newcomb and Flinn [2] found that the relationship between the extension of a piezoceramic actuator and its applied electric charge has significantly less hysteresis nonlinearity than that between deforma- tion and applied voltage. Furutani et al. [3] proposed an induced charge feedback control for the piezoactuators. The approach needs measurement of the induced charge and a specially designed charge drive amplifier, and will cause an increase in the response time of the actuator.

In order to linearize the control system, many re- searches focused on the inverse feedforward compensa- tion based on some inverse hysteresis model. Several models have been suggested for describing the complex hysteretic behavior, for example, the Preisach model in Ge and Jouaneh [4,5], Yu et al. [6], and Liu et al. [7], the generalized Preisach model in Ge and Jouaneh [8], the dynamic Preisach model in Yu et al. [9]; the general- ized Maxwell elasto-slip model in Goldfarb and Celano- vic [10]; the variable time-relay hysteresis model in Tsai and Chen [11]; the Prandtl-Ishlinskii (PI) model (a sub- class of the Preisach model) in Ang. et al. [1] and Has- sani and Tjahjowidodo [12]; the Duhem model in Ste- panenko and Su [13]; the polynomial approximation

method in Croft and Devasia [14]; and the Jiles-Atherton model in Dupre et al. [15]. Ge and Jouaneh [5] proposed a PID feedback control using the classical Preisach model for the hysteresis. Song et al. [16] proposed a cascaded PD/lead-lag feedback controller based on a linear model for the piezoactuator with hysteresis being compensated via the feedforward cancellation using the inverse classical Preisach model. Recently, Maslan et al. [17] presented a discrete-time transfer function and its inverse for a highly nonlinear and hysteretic piezoelectric actuator, and traditional PID controller and PID with active force control were considered.

To mitigate the effects of the unknown hysteresis, Wang et al. [18] suggested a model reference control for linear systems with unknown input hysteresis using an inverse KP (Krasnosel’skii-Pokrovskii) hysteresis model [19]. Hwang et al. [20] proposed a neural-network non- linear model for learning the hysteretic behavior of a piezoelectric actuator, and suggested a discrete-time va- riable-structure control for enhancing the nonlinear mo- del-based feedforward control performance. Based on the learned nonlinear model of piezoelectric actuator systems in [20], Hwang and Jan [21] proposeed a controller in- cluding a nonlinear inverse control and a discrete neuro- adaptive sliding mode control using a recurrent neural network to compensate for the residue dynamic uncer- tainty. Wai and Su [22] presented a supervisory genetic algorithm (SGA) control system for a piezoelectric ce- ramic motor. The controller consists of a GA control to search an optimum control effort online via gradient de- scent training process and a supervisory control to stabi- lize the system states around a predefined bound region.

Copyright © 2012 SciRes. ICA

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L.-C. LIN ET AL. 391

Recently, Ronkanen et al. [23] presented a two-input (velocity and voltage) one-output (current) feedforward backpropagation network to model the inverse nonlinear velocity-current relation of a piezoelectric actuator, and then introduced a feedforward charge control scheme.

Other analytical types of nonlinear differential hys- teresis models include the simplified Dahl model used in Lyshevski [24], Sun and Chang [25], Sain et al. [26], and the Bouc-Wen model in Low and Guo [27], Chen et al. [28], and Gomis-Bellmunt et al. [29]. Chen et al. [28] proposed an H∞ almost disturbance decoupling robust control based on the Bouc-Wen hysteretic model. Shieh et al. [30] proposed an adaptive displacement control for a piezopositioning mechanism with the LuGre (hysteretic) friction model suggested by De Wit et al. [31]. Gu and Zhu [32] suggested a new mathematic model to describe the frequency-dependent and amplitude-dependent hys- teresis in a piezoelectric actuator using a family of ellip- ses. These analytical hysteresis models will be much easier for precision positioning control design.

In this work, we consider the precision control of a three-axis piezoactuated micro/nano stage. An adaptive controller with simplified Dahl model-based hysteresis variables observer is designed using the Lyapunov stabil- ity theory. In the adaptive controller, a fuzzy function approximator with parameters update law is included to compensate for the identification inaccuracy, model un- certainty, and flexure coupling effects. Simulation results are used for illustrating the possible control performance.

2. Dynamic Model for a Three-Axis Micro/Nano Motion Stage

The dynamic model for a single-axis piezoactuated flex- ure stage with analytic simplified Dahl hysteresis model is as below [24]:

2 31 2mx k x k x k x k x 3x u fk u k f (1)

1

fx

f x x fk

(2)

where x is the output displacement of the flexure stage; is the mass of the flexure mover; m xk

,k kk

is the damping coefficient; 1 , 2 and 3 are the stiffness constants; u is the input voltage of the piezoelectric actuator; u is the input gain;

k

f is the hysteresis variable; f and govern the scale and the shape of the hysteresis loop.

k fxk

Consider a

Figure 1. Three-axis flexure stage.

2 31 2 3x u f Mx K x K x K x K x K u K f (3)

xyz three-axis flexure micro/nano stage (P-517.3CL, Physik Instrumente, PI) [33] driven by pie- zoelectric actuators shown in Figure 1. The hysteresis phenomena and the coupling effects among the three axes induced by the flexure structure, can be taken into account via the following complete matrix-vector model:

1fv f x K x f

T

(4)

x y zx

2 2 2 2 ;T

x y z

is the output displacements vector; where

x

3 3 3 3 ;T

x y z

x

diag ;x y z x

T

x y zD D D

diag , ,T

x y z x y zm m m u u u

is used to consider the coupling effects among the axes and the model uncertainty;

M u

1 1 1 1diag , diag ,x x y z x y zk k k k k k

K K

2 2 2 2 3 3 3 3diag , diag ,x y z x y zk k k k k k

K K

, diag ,T

x y z u ux uy uzf f f k k k

f K

, , ,diag , diag .f fx fy fz fv fx x fx y fx zk k k k k k

K K

For ease of numerical simulation and implementation, the system parameters in SI units could be scaled in terms of more suitable units: displacement in nm, mass in g, time in ms, and input voltage in mV. After scaling, the scaled models keep the same forms as Equations (3) and (4). The parameters of the stage are identified, based on input/output data pairs via genetic algorithms by Chang [34], and are given as follows:

30.2903 10 g; 249.27g ms;x y x ym m k k

2 21 1 4.579 10 g ms ;x yk k

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L.-C. LIN ET AL. 392

3 2g nm ms ;2 2 1.6958 10x yk k

9 2 2g nm ms ;3 3 8.6767 10x yk k

3 2m mV ms ; 0.4716 10 g nux uyk k

2 2g ms ;3.6339 10k k fx fy

2 218.783 10 g ms ;fz zk k 3 2 1.8344 10 g ms ;

2 2ms ;2 1.9910 10 g nmzk

7 2 2g nm ms ;3 2.4296 10zk

3 2nm mV ms ;

4 110 nm

1 4 110 nm .

x x

0.4653 10 guzk

1 1, , 1.6242fx x fx yk k

, 4.9758fx zk

After defining the state vector as 1 , 2 x x

, the stage’s dynamic model can be written in the follow- ing vector state equations:

1 2

1 2 32 3

x x

x M K x K x K x K x2 2 1 1

1 1

12

x

u f

f

fv

M K u M K f

A Bu B f

f x k x f

(5)

where

1 2 31 1 2 3x

2A M K x K x K x K x

1 1, f u fB M K B M K

1x 1 2x x

1 1x ν

1 1 d e x x

x

1 1 1d d e x x ν x

3. Stable Fuzzy Approximator-Based Adaptive Control for Micro/Nano Stages

3.1. Control Design Using Backstepping Method

Based on the nonlinear dynamics model (5), this subsec- tion considers the backstepping-based stable control law design for the three-axis flexure stage.

First consider the subsystem, . Let

(6)

where 1 is a virtual input. Define the tracking error signal as

ν

(7)

where d is the desired trajectory for the three-axis mo- tion. Differentiating Equation (7), we have

(8)

Considering the Lyapunov function candidate

1 1 1 1

1

2TV e P e

3 3

(9)

where 1 P R

1 1 1 1 1 1 1T T

dV e P e e P ν x

1 1d

is symmetric and positive definite, and differentiating Equation (9), we have

(10)

Thus, we can choose the virtual input as

ν x κe (11)

with positive definite feedback gain matrix

1 2 3diag κ κ κκ

1 1 1 1 0TV

,

such that

e Pκe

1lim ( ) 0,t

t

(12)

and e

1 2

2 f

that is, the subsystem is asymptoti-

cally stable. Further, the actual whole nonlinear system is consid-

ered:

x x

x A Bu B (13)

f

After introducing new error signal

2 2 1, e x ν

1 1 2 1

22 2 1 2 1

d

f d

(14)

we can obtain

e x x e κe

e x ν A Bu B f x κe κ e (15)

Then by considering the Lyapunov function candidate as

1 2 2 2

1 1

2 2T T

sV V + e P e e Pe

1 2

TT T

(16)

where e e e , 1 2diag ,P P P 3 32, P R

is symmetric and positive definite, and taking the time derivative of Equation (16), we have

1 1 2 1

22 2 2 1

Ts

Tf d

V

e P e κe

e P A Bu B f x κe κ e

1 2 12 1 2 1 12

s

d f

u u

B x κe κ e A B f P P e

1 1 1 2 2 2T T T

sV e Pκe e P κe e PΚe

diag[ ]

(17)

Thus we can choose the nonlinear control law as fol- lows:

(18)

and obtain

(19)

where Κ κ κ .

ΚIf further choose I 0 with , then we can

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L.-C. LIN ET AL. 393

have

2 0sV e

TsV e P (20)

and lim 0t

t

e 0. Thus, the equilibrium point e

f

of

the closed-loop system is exponentially stable. The internal state variables can also be shown to

be bounded. Consider the Lyapunov function

1

2T

fV f f (21)

By choosing the class- K functions

1 2f f 1

2Tf f f f ,

then since

2f f f f f1 V , (22)

we know that fV is positive definite, decrescent, and radially unbounded [35]. Differentiating Equation (21) and substituting in the internal dynamics

12 ,fv

k x ff x (23)

we have

12 fv

T TfV f f f x k x f

2 dt tx x

0d xlim 0ft

V

0 0x

0f

(24)

Since limt

if the desired trajectory satisfies , then we can have Thus, f is bounded and the overall .

closed-loop system is stable. Let the output vector 1 , 2 , we can obtain

the system’s zero dynamics as follows: x

(25)

That is, the hysteresis variables will become constants when the flexure mover returns to the origin and remains there.

In order to further enhance the system’s active damping capability, we can introduce a nonlinear damping term

s

TV

e

0 B

where into the control law (18). That is, the control law can be modified as

TT

1 22 1

2 1 1

1 12 1 1 2 2

ˆ ˆ 2

ˆ ˆ ˆ ˆ

ˆ ˆ

T

sa s

u d

f x

E u

Vu u

e

K M x κe κ e

M K f K x K x

P P e M K P e

1 2 32 3

1

ˆ ˆ

ˆu

K x K x

K

1ˆ ,

(26)

where M ˆ ,fˆ ,u

ˆ , 1ˆ , 2

ˆ , 3ˆK K K K K and x K are the

nominal matrices for 1,M ,fK ,uK ,xK 1,K 2 ,K and

3K , respectively, obtained by substituting in the esti- mated parameters, and E represents the discrepancy due to the estimate error. Let t E u be the integral uncertainty, we can further design a fuzzy func- tion approximator fs

1ˆ + K

to compensate for its effect. The modified control law can be written as follows:

1 22 1

1 2 32 1 1 2 3

1 12 1 1 2 2

ˆ

ˆ ˆ 2

ˆˆ ˆ ˆ ˆ ˆ ˆ

ˆ ˆ

u d

f x

u fs

u z,θ

K M x κe κ e

M K f K x K x K x K x

P P e M K P e

ˆ

(27)

f is the observed hysteresis vector for where f , z is the input vector of the controller, and is the pa- rameters vector to be updated for the fuzzy compensator. Here

ˆ tθ

ˆ ˆdiag , , , diag , , ,x y z u ux uy uzm m m k k k M K

ˆ ˆdiag , diag ,f fx fy fz x x y zk k k k k k

K K

1 1 1 1 2 2 2 2ˆ ˆdiag , diag ,x y z x y zk k k k k k

K K

3 3 3 3ˆ diag

and

x y zk k k K

are used in Equation (27). The hysteresis observer and the fuzzy compensator design will be considered in the sequel.

3.2. Hysteresis Observer Design

Since the hysteresis variables are difficult to measure for feedback, a nonlinear observer can be suggested as:

1ˆ ˆ , 0, , ,i i i i oi fi oifii

f x x f k e k i x y zk

ˆ

(28)

where if are the estimated hysteresis variables, fi are the observer’s input variables to be defined later in the derivation of the stable control law and parameters update law, and are the input gains. Define es- timate errors as

e

0oik

ˆi i if t f t f t ,

we have

1, 0, , ,i i i oi fi oi

fii

f x f k e k i x y zk

(29)

And Equation (29) can be written in the following vector form:

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L.-C. LIN ET AL. 394

f o ff K f + K e

T

zt f t

(30) 1,1 1,2 1,3 1 ,T

e e e

where

x yt f t ff

is the estimate error vector, and

=diagf fxxx k yK fyy fzzk z k

,ox oy ozk k k

T

fy fzt e t

, , and

,

diago K

f fxt e t ee .

3.3. Fuzzy Function Approximators Design

This subsection will construct the fuzzy function ap- proximators using T-S fuzzy systems to compensate for the modeling errors and coupling effects among the three axes. The tracking errors 1, 1, 1,x y z are chosen respectively as the input variable of the fuzzy approxi- mator for each axis, and the compensating voltage of each axis is the output variable. In the universe of dis- course of each input variable, five fuzzy sets are defined as in Figure 2. The rule base of the fuzzy approximator for the i-th ( i ) axis is considered as follows: Rule j: If is

e e e

1, 2,31,ie jA

Then

, , 1,1 , 1,2 , 1,3 ,i j i j i j i j i j

s

, 1,2, ,5e d j y a e b e c (31)

where jA are the fuzzy sets defined over the universe of discourse of each input variable 1,i , , stands for the

e 1, 2,and 3i x , y, and axis, respectively. z

Using singleton fuzzifier, product inference engine, and center average defuzzifier [36], the mapping of the fuzzy approximator for the i-th axis is

5

1,3i, j i, jc e + d

1,1 1,21

5

1

i, j i, j i, jj

i

i, jj

a e +b e +

y =

(32)

where , 1,i j j iA e is the degree of firing of the j-th rule’s antecedent. Let

Figure 2. Membership functions for each axis.

ψ

T

, , , , , ,i j i j i j i j i ja b c d

θ

,1 ,2 ,5 ,1 ,2 ,5μ μ μ TT T T T T T

i i i i i i iy

then

ψ ψ ψ θ θ θ

,1 ,2 ,5μ μ μTT T T

i i i i

(33)

Defining the regressor vector

φ ψ ψ ψ

,1 ,2 ,5

TT T Ti i i i

and the unknown parameter vector

θ θ θ θ

Ti iy

,

Equation (33) can be written as

i

ˆfs f

(34)

And the fuzzy approximators for the three axes can be written in the vector form as

1 2 3diag ,T T Tf

(35)

where

1 2 3ˆ ˆ ˆ ˆ .

TT T T

T

f fx fy fze e e

3.4. Derivation of Parameters Update Law and Stability of Overall System

In this subsection, the input signals

e

of the hysteresis observer, and the parameters update laws of the fuzzy function approximators will be selected in the stability consideration of the overall adaptive feedback control system for a three-axis piezoelectric flexure stage.

Consider the following Lyapunov function candidate,

1 1

1 11 1 1 2 2 2

1 1

2 21 1 1 1

2 2 2 2

T Ta s o

T T T To

V V

Γ

Γ

+ θ θ + f K f

e P e + e P e + θ θ + f K f

Γ ˆ .

(36)

where is symmetric and positive definite, θ θ θ

1 11 1 1 2 2 2

1 1 2 1

22 2 2 1

1 1

ˆ

ˆ+

T T T Ta o

T

Td

T To f o f

V

Γ

e P e e P e θ θ f K f

e P e κe

e P A Bu x κe κ e

θ Γ θ f K K f K e

Taking the time derivative, we have

(37)

After substituting in Equations (30) and (17), Equation

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L.-C. LIN ET AL.

ICA

395

ˆ ˆ ,M I + εI

1 1ˆ ,m M M + ε I

1 2 3

Copyright © 2012 SciRes.

(37) becomes (38). Let

1 1u u

M K K

where

diag

ε

and

1 2 3 m m m m=diag

Iˆf f +

ˆ ˆ ˆ[ ]Tx y z

ε

are the error matrices, is the identity matrix. Since , where f

ˆ f f ff ,

we have

ˆ

f

f f f

ˆˆ ˆ

ˆ

f f f

K f K f K f f K f

K K f K f

1

1 12 2

1 1

ˆ

ˆ ˆ

Ta o f

u u

T T

,

and Equation (38) can be written as

1 1 1 2 2 2

2 2

12 2

2 2

ˆ ˆ ˆ

ˆˆ ˆ

ˆ ˆ

T T

T

Tf f

u f

V

e Pκe e P κe

f K K f

e P M K M

e P M K f e

e P M K Φ θ

K P e

f

θ Γ θ

(39)

where is defined as (40). Choosing the input vector of the hysteresis observer

fe1

2 2ˆ ˆT T

as:

f fe e P M K

12 2

ˆ ˆf f

e K M P e

11 1 1 2 2 2

1 12 2 2 2

1 12 2

ˆ ˆ ˆ ˆ

ˆ ˆˆ ˆ

T T Ta o f

Tu u

T Tu f

V

(41)

That is,

(42)

we can obtain

e Pκe e P κe f K K f

e P M K M K P e

e P M K Φ θ θ Γ θ

(43)

By further representing the uncertainty as:

12 2

ˆ ˆ ,Tu

e P M K

and substituting

ˆf f f f Φ θ Φ θ + θ Φ θ +Φ θ

11 1 1 2 2 2

1 12 2 2 2

1 12

12 2

ˆ ˆ ˆ ˆ

ˆˆ ˆ

ˆ ˆ

T T Ta o f

Tu u

T Tu f

Tu f

V

Γ

2

e Pκe e P κe f K K f

e P M K M K P e

e P M K Φ θ θ θ

e P M K Φ θ

in Equation (43), we have

(44)

Thus, we can choose the parameters adaptation law of the fuzzy approximators as:

1 02 2

ˆ ˆˆ ˆT

Tu

Γ

fθ e P M K Φ θ θ (45)

If further choose κ I , η I f

, and assume the approximation error fs Φ θ ω θ be bounded, i.e., ω W , then we can obtain

11 1 1 2 2 2

21 1

2 2 2 2 2 2

1

0 0

ˆ ˆ ˆ ˆ

ˆ

22

2

T T Ta o f

T Tu u

T Ts o f

T

V

W

WV

4

0

e P e e P e f K K f

e P M K P e e P M K

θ θ

f K K f θ θ

θ θ θ θ

1 2 32 1 1 2 3

1 1 2 2 3 12 1 2 1 1 2 3 2 1 1

1 2 1 12 2 2 1

ˆˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ

ˆˆ ˆ

a f x

u u d f x

T T Tu fs d o f f

1

K f K x K x K x K x

K M x κe κ e M K f K x K x K x K x P P e

M K P e x + κe κ e θ Γ θ f K K f + f e

(46)

1 1 2 1 2 2+

T TV

e P e κe e P M

M K

(38)

2 32 1 1 1 2 2 3 3

2 3 2 12 1 1 2 3 2 1 2 1 1

1 2 3 1 1 12 1 1 2 3 2 2

ˆ ˆ ˆ ˆ

ˆˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ ˆ

f f x x

m f x d

f x u u u f

K f K K x K K x K K x K K x

K x K x K x K x ε x 2κe κ e εP P e

f K x K x K x K x ε M K M K P e ε M K Φ θ

2 2ˆ ˆ

T

1e P M K

ε K f

(40)

ˆˆ ˆ+εM K

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L.-C. LIN ET AL. 396

Letting θ 2d

0 0T θ θ

class-

2

Wd

4

θ θ (47)

and defining K functions:

1 1

2e sV Te e Pe ,

and 1f f f

1To fK K f ,

Equation (46) can be rewritten as

1 12a e f

V e f

2T d

θ θ (48)

Hence, when 11 2e d e

or

or 11f

d f 0aV

, , and

, ,

and thus the overall adaptive control system is boundedly stable.

4. Results and Discussion

In this section computer simulation will be used to illus- trate the performance of the proposed adaptive fuzzy control with hysteresis observer for a three-axis flexure stage. Triangular uncertainties for the x, y, and z axes ( x y z ) shown in Figure 3 are selected in the simulation. The desired trajectories for the x, y, and z axes are selected as follows (t in ms):

D D D

0 1000 2000 3000 4000 5000 6000 7000 8000t (ms)

8000

6000

0

-2000

-4000

-6000

-8000

4000

2000

ms2 )

Dx (

nm/

(a)

0 1000 2000 3000 4000 5000 6000 70t (ms)

00 8000

8000

6000

4000

2000

0

-2000

-4000

-6000

-8000

Dy (

nm/m

s2 )

(b)

0 1000 2000 3000 4000 5000 6000 700t (ms)

0 8000

6000

4000

2000

0

-2000

-4000

-6000

Dz (

nm/m

s2 )

(c)

Figure 3. Triangular uncertainties for the x, y, and z axes. (a) Dx, (b) Dy, (c) Dz.

Copyright © 2012 SciRes. ICA

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L.-C. LIN ET AL. 397

π 2 nm5000 5000sin 2π 1000

d dx t y t

t

π 2 nm

3000 3000sin 2π 1000dz t t

Controller parameters are selected as follows:

1 diagP

,P I

15 15 50 ,

30.5 ,

2 3 κ I

30.4 , Iη 1 2 3diag , , ,Γ Γ Γ Γ

7 4 5 5

7 4

5 5 7

0 10 10 10

10

10 10

5 4 5

7 5

4 5 7

10 10

10

10 10

5 5 4

7 5

5 4 7

10 10

10

10 10

3ˆ, 0.1 and 0 0, , , .o i i x y z K I θ

, , and

4 5 5diag 10 10 10 1 1Γ

7 4 5 5

5 5 7 4

10 10 10 10 10

10 10 10 10 10

5 4 5 72 diag 10 10 10 10 10 Γ

7 5 4 5

4 5 7 5

10 10 10 10 10

10 10 10 10 10

5 5 4 73 diag 10 10 10 10 10 Γ

7 5 4 4

5 4 7 5

10 10 10 10 10

10 10 10 10 10

The simulation results are shown in Figure 4. From Fig- ures 4(a)-(c), we know that the tracking performances are very good. The tracking errors of x- and y-axes are within –2.5 nm - 2.2 nm, and the tracking error of z-axis is within ±2 nm. From Figures 4(d)-(f), the hysteresis- variable estimate errors of x- and y-axes are within ±0.5 nm, and the estimate error of z-axis is within ±1 nm. The control voltages x y z are shown in Figure 4(g), and the fuzzy compensation voltages ,fs x , ,fs y

u u u , and

,fs z are shown in Figure 4(h). And the parameters update processes of the function approximators for x-, y-, and z-axes are shown in Figures 4(i)-(k), respectively. The parameters of the first and fifth rules are not updated since the tracking errors are small and they are nearly not fired. Although the persistent exciting of the system sig- nals of this considered simulation case are not sufficient enough to let the other parameters converge to constants, the adaptive control system can guarantee the tracking control performance to be still very good.

5. Conclusion

In this work, a stable adaptive control law with nonlinear dynamic hysteresis observer for a three-axis flexure stage

0

4

3

1

0

-1

-2

-3

-4

2

e 1,x (

nm/m

s2 )

1000 2000 3000 4000 5000 6000 7000 8000t (ms)

(a)

0 1000 2000 3000 4000 5000 6000 7000 8000t (ms)

4

3

2

1

0

-1

-2

-3

-4

e 1,y (

nm/m

s2 )

(b)

Copyright © 2012 SciRes. ICA

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L.-C. LIN ET AL. 398

0 1000 2000 3000 4000 5000 6000 700t (ms)

0 8000

4

3

2

1

0

-1

-2

-3

-4

e 1,z (

nm/m

s2 )

(c)

0 1000 2000 3000 4000 5000 6000 700t (ms)

0 8000

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

-1

(d)

0 1000 2000 3000 4000 5000 6000 70t (ms)

00 8000

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

-1

(n

m)

(e)

0 1000 2000 3000 4000 5000 6000 70t (ms)

00 8000

1.5

1

0.5

0

-0.5

-1

-1.5

-2

(nm

)

(f)

Copyright © 2012 SciRes. ICA

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L.-C. LIN ET AL. 399

0 1000 2000 3000 4000 5000 6000 7000t (ms)

8000

15000

10000

5000

0

-5000

15000

10000

5000

0

-5000

3

2

1

0

-1

0 1000 2000 3000 4000 5000 6000 7000t (ms)

8000

0 1000 2000 3000 4000 5000 6000 7000t (ms)

8000

u z (

mV

)

u y (

mV

)

u x

(m

V)

×104

(g)

0 1000 2000 3000 4000 5000 6000 700t (ms)

0 8000

0 1000 2000 3000 4000 5000 6000 700t (ms)

0 8000

0 1000 2000 3000 4000 5000 6000 700t (ms)

0 8000

20

10

0

-10

-20

20

10

0

-10

-20

20

10

0

-10

-20

(mV

)

(m

V)

(m

V)

(h)

Copyright © 2012 SciRes. ICA

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L.-C. LIN ET AL. 400

0 5000 10000 0 5000 10000 0 5000 10000 0

t (ms) t (ms) t (ms) 5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0

t (ms) t (ms) t (ms) 5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0

t (ms) t (ms) t (ms) 5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0

t (ms) t (ms) t (ms) 5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0

t (ms) t (ms) t (ms) 5000 10000t (ms)

1

0

-1

0

-5

-10

4

2

0

-2

10

5

0

1

0

-1

1

0

-1

0

-0.1

-0.2

0.04

0.02

0

-0.02

0.2

0.1

0

1

0

-1

1

0

-1

0

-0.1

-0.2

0.04

0.02

0

-0.02

0.2

0.1

0

1

0

-1

1

0

-1

0

0.5

0

0.5

0

-0.5

-1

0.1

0.5

0

1

0

-1

(i)

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms)

5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0

5000 10000t (ms) t (ms) t (ms) t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms)

5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms)

5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0

t (ms) t (ms) t (ms) 5000 10000t (ms)

1

0

-1

0

-5

-10

4

2

0

-2

10

5

0

1

0

-1

1

0

-1

0

-0.1

-0.2

0.04

0.02

0

-0.02

0.2

0.1

0

1

0

-1

1

0

-1

0

-0.1

-0.2

0.04

0.02

0

-0.02

0.2

0.1

0

1

0

-1

1

0

-1

1

0.5

0

0.5

0

-0.5

-1

0.1

0.5

0

1

0

-1

(j)

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L.-C. LIN ET AL.

Copyright © 2012 SciRes. ICA

401

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms)

5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms)

5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms)

5000 10000t (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms) t

5000 10000 (ms)

0 5000 10000 0 5000 10000 0 5000 10000 0 t (ms) t (ms) t (ms)

5000 10000t (ms)

1

0

-1

0

-5

-10

4

2

0

-2

10

5

0

1

0

-1

1

0

-1

0

-0.1

-0.2

0.04

0.02

0

-0.02

0.2

0.1

0

1

0

-1

1

0

-1

1

0.5

0

0.5

0

-0.5

-1

0.1

0.5

0

1

0

-1

1

0

-1

0

-0.1

-0.2

0.04

0.02

0

-0.02

0.2

0.1

0

1

0

-1

(k)

Figure 4. Control results. (a) x-axis, (b) y-axis, (c) z-axis tracking errors; Hysteresis es erro ) timate rs, (d xf y; (e) f ; (f) zf ;

ages , yu and zu ,fs , y and ; Param process

(i) x-axis; (j) y-axis; (k) z-axis. is proposed. Fuzzy function approximators are included in the control law to compensate for the identification inaccuracy, model uncertainty, and flexure coupling ef- fect. The stability of the overall closed-loop system is guaranteed using the Lyapunov theory. Simulation re- sults are shown to illustrate the effectiveness of the sug- gested control approach. In the future study, actual im- plementation can be considered for the development of a precision stage for testing the control performance.

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