Simplified Nonlinear Control for Planar Motor based on Singular Perturbation Theory

The Transactions of The Korean Institute of Electrical Engineers.
2015.
Feb,
64(2):
289-296

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/)which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited

- Received : December 29, 2014
- Accepted : January 29, 2015
- Published : February 01, 2015

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In this paper, we propose the nonlinear control based on singular perturbation theory for position tracking and yaw regulation of planar motor. Singular perturbation theory is characterized by the existence of slow and fast transients in the system dynamics. The proposed method consists of auxiliary control to decouple error dynamics. We develop model reduction with control input. Also, we derIve decoupled error dynamics with auxiliary input. The controller is designed in order to guarantee the desired position and yaw regulation without current feedback or estimation. Simulation results validate the effect of proposed method.
Planar motor
Several feedback control methods were developed have been studied to improve the position tracking and yaw regulation performance. An adaptive control is used for minimization of ripple and analyzing the control performance
[1]
,
[2]
. A PD/PID controllers is designed in conjunction with commutation and delay compensation schemes
[3]
,
[4]
. These methods require the current feedback and position feedback. Position and yaw feedback can be clearly measured by laser interferometer. Alternately, measurements of currents can be corrupted by pulse width modulation switching noise. Thus, low pass filters and current observer are used to reduce the noise
[5]
. However, the use of the filters cause the phase lag in the current tracking. The use of the current estimation increases complexity of implementation and the computation time. Therefore, using only X, Y position feedback, the control method without current measurement is key work.
In this paper, we propose a simplified nonlinear control for planar motors based on singular perturbation theory to improve the position tracking and yaw regulation performance using only X, Y position and yaw feedback. Since mechanical and electrical dynamics are generally slow and fast in the planar motor, respectively, the singular perturbation theory can be applied to the position tracking control of planar motor. In practically all well designed planar motors, we can put the inductance, L, into the small scalar parameter of singular perturbation system
[9]
. We design the input voltage, which includes auxiliary input, in order to transform to the three single-input single-output systems at the complex nonlinear multi-input multi-output system. The origin of boundary layer system is globally exponentially stable. The nonlinear controller is designed so as to guarantee stability of the simplified single-input single-output (SISO) system for each motion. We mathematically prove that the origin of tracking error dynamics is globally exponentially stable. Simulation results are performed to evaluate the performance of the proposed method.
where
and x and y are the position [m] of the center of the motor on the platen. xv and yv are the velocity [m/s] of the center of the motor on the platen.
θ
is the yaw [rad] rotation and
θ_{v}
is the yaw rate of the center of the motor on the platen.
and
are phase currents [A] in phase A and B of the forcer
X
_{1}
,
X
_{2}
,
Y
_{1}
and
Y
_{2}
.
and
are input voltages [V] in phase A and B of the forcer
X
_{1}
,
X
_{2}
,
Y
_{1}
and
Y
_{2}
, and
d_{x}
,
d_{y}
and
d_{θ}
are unknown constant load forces [N] and torque [ N·m].
r_{x}
and
r_{y}
are the distance from where
x^{d}
and
y^{d}
are desired positions of X and Y axes,
and
are desired velocities,
θ^{d}
and
are the desired yaw and yaw rate. We have added the additional integral term of the mechanical errors,
e_{zx}
,
e_{zy}
and
e_{zθ}
, into the mechanical subsystem to decrease of the position errors. The desired currents,
will be defined.
From (1) and (2), we can derive the tracking error dynamics of the position and yaw as follows
We define the desired currents and desired torque in order to simplify tracking error dynamics of the position and yaw as follows
Then, the tracking error dynamics of the position and yaw are rewritten as
In the following theorem, we propose the nonlinear controller based on singular perturbation theory for position tracking of planar motor and prove the globally exponential stability.
Theorem 1:
Consider planar motor dynamics (1). Suppose that the auxiliary control law and control law are given by
where
k
_{x1}
,
k
_{x2}
,
k
_{x3}
,
k
_{y1}
,
k
_{y2}
,
k
_{y3}
,
k
_{θ1}
,
k
_{θ2}
and
k
_{θ3}
are positive numbers. Then
e_{x}
,
e_{y}
,
e_{θ}
,
e_{xv}
,
e_{yv}
and
e_{θv}
are globally exponentially stable.
Proof:
Substitute the control laws,
and
,of (7) into the current error dynamics. In order to make the singular perturbation model of a dynamical system, the derivatives of the current error dynamics are multiplied by a small positive parameter
L
. Thus, the singular perturbation model becomes
We can obtain the quasi-steady states at inductance L = 0 as follows
To move the equilibrium point to zero, let us define
y
_{ax1}
, ⋯,
y
_{by2}
as
Then, the dynamics of
y
_{ax1}
, ⋯,
y
_{by2}
are given by
Thus, we can obtain the boundary-layer system as follows
where
is a new time variable. Since
R
is always positive parameter, the equilibrium point
y
_{ax1}
, ⋯,
y
_{by2}
= 0 of the boundary-layer system (12) is globally exponentially stable. From the definition, we can obtain
as follows
Substituting quasi-steady-state
of (9) into the tracking error dynamics of the (13) results in the reduced-order model as
From the auxiliary control law (6), the mechanical tracking error dynamics results in the reduced-order model. The load forces and load torque perturbation, denoted by
d_{x}
,
d_{y}
and
d_{θ}
are assumed to be zero for all analysis purposes as
Since each error dynamics are decoupling, We can put the reduced tracking error dynamics into the matrix form respectively as follows
where
Decoupled error dynamics are linear state equations. The controllability matrix of the error dynamics is given by
Since each controllability matrix is full rank, we design control law in order to move left half plane at all eigenvalues of tracking error dynamics as follows
Then, the dynamics of
e_{xv}
,
e_{yv}
and
e_{θv}
are given by
Therefore, The origin of reduced order error dynamics,
e_{m}
= 0, is globally exponentially stable.
Remark 1:
If the unknown disturbances,
d_{x}
,
d_{y}
and
d_{θ}
, are non-vanishing perturbation, the proposed method guarantees uniformly ultimately boundedness of the tracking error dynamics.
λ_{x}
= [−11.37 −101.59+295.58
i
−101.59−295.58
i
],
λ_{y}
= [−11.37 −101.59+295.58
i
−101.59−295.58
i
],
λ_{θ}
= [−9990 −5.0+8.7
i
−5.0−8.7
i
]. The parameters of planar motor and proposed controller gains were listed in
Table 1
. Sine wave profile was shown in
Fig. 2
. Sine wave profile was used to evaluate position tracking and yaw regulation of circular motion. Since the load force and torque are unknown disturbance, step function was represented for analysis. The position tracking error and yaw regulation with and without load were shown in
Fig. 4
. Desired and real position of planar motor was shown in
Fig. 5
. Error position of x, y and
θ
was used to identify the effect of load force and torque shown in
Fig. 6
. The position tracking error of x and y was the peak and valley. We propose arbitrary load torque and force in order to identify unknown constant effect. Since the load force of x and y were added at 1.0 sec. and 3.0 sec. as step function, there were the peaks of the position tracking error of x and y respectively. However, the position tracking error of x and y also asymptotically converged to zero. When the load torque of yaw were added from 2.0 [sec] to 4.0 [sec], the yaw regulation was the valley and peak respectively at each time. However, the yaw well regulated.
Planar motor Parameters and Control gains
Reference profiles
Load force and load torque
Position tracking error and yaw regulation performance at load and no load
Desired and real positions of x and y
Error position of x, y and θ
서 형 덕(HyungDuk Seo)
1986년 2월 22일생. 2013년 한양대학교 전기공학부 졸업. 2015년 동 대학원 전기공학부 석사, 현 현대오트론
관심분야 : 비선형 제어 및 모터 제어
Tel : 02-2220-4307
E-mail : gudejrwkd@gmail.com
신 동 훈(Donghoon Shin)
1981년 8월 26일생. 2009년 한양대학교 전기공학부 졸업. 현재 동 대학원 전기공학과 석 박통합과정.
관심분야: 비선형 제어 및 모터 제어
Tel : 02-2220-4307
E-mail : shin211@hanyang.ac.kr
이 영 우(李 榮 雨)
1984년 6월 21일생. 2010년 충북대학교 전기전자컴퓨터공학부 졸업. 현재 한양대학교 대학원 전기공학과 석 박통합과정.
관심분야: 비선형 제어 및 모터 제어
Tel : 02-2220-4307
E-mail : stork@hanyang.ac.kr
정 정 주(Chung Choo Chung)
1958년 9월 5일생. 1981년 서울대학교 전기공학과 졸업. 1983년 동 대학원 석사. 1993년 USC 공학 박사. 1993년~1994년 미국 콜로 라도 주립대 Research Associate. 1994년~1997년 삼성종합기술원 수석 연구원 (팀장). 1997년~현재 한양대학교 전기제어생체공학부 교수. 2000년~2002년 Asian Journal of Control, Associate Editor. 2003년~2005년 IJCAS, Editor. 2003년 IEEE CDC, Associate Editor. 2008년 IFAC World Congress Associate Editor 및 Co-Chair of Publicity. 2009년 ICASE-SICE Program Co-Chair. 2000년~ 2010년 ICROS 제어이론 연구회 회장. 2011년 ICCAS Organization Chair, 2011년 ISPS Program Committee. 2011년 IEEE Transactions on Control Systems Technology (TCST) Guest Editor. 현재 IEEE TCST Associate Editor and 및 IEEE Intelligent Vehicles Symposium Program Co-Chair.
관심분야: 비선형 제어 및 디지털 제어이론, 로봇시스템, 자동차, 평판디스 플레이 공정장비, 전력계통, 정보저장시스템 등에 제어이론 적용이다
Tel : 02-2220-1724
Fax : 02-2220-5307
E-mail : cchung@hanyang.ac.kr

Singular perturbation theory
;
planar motors
;
Position feedback
;
Nonlinear control
;
Yaw regulation

1. 서 론

Planar motors have been used for manufacturing at especially semiconductor industry. Planar motor is composed of puck and platen. The platen consists of teeth whose intervals are uniform. The puck contains four forcers which are symmetrically placed on each side. The puck is levitated on the platen by air bearings as shown in
Fig. 1
. X and Y axis motion are composed of resultant forces at each axis. Yaw mothion is generated by interaction of the different forcers.
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2. Modeling and Controller Design

In this section, we represent planar motor dynamics and tracking error dynamics. we prove the singular perturbation theory in order to make reduced order model. The auxiliary control input is used to couple the reduced order model. The dynamics of planar motor can be represented in the state space form as follows
[8]
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3. Simulation Results

To evaluate the position tracking and yaw regulation performances of the proposed method, simulations were performed using MATLAB/Simulink. The control frequency is 5 kHz. The eigenvalues of closed loop are
Planar motor Parameters and Control gains

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3. Conclusion

In this paper, we propose the position and yaw control method for the planar motor. The proposed controller was designed with the nonlinear control in order to improve position tracking error and yaw regulation. The proposed singular perturbation theory was used to make the reduced order model. Since the electrical dynamics was neglected using singular perturbation theory, this model was not required both a nonlinear observer and a current feedback. The simulation results showed that the position tracking and yaw regulation performance were improved by the proposed method. We observed that the position x, y and yaw were decoupled.
Acknowledgements

이 논문은 2013년도 정부(교육부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임(No.2013007682)

BIO

Krishnamurthy P.
,
Khorrami F.

Melkot H.
,
Khorrami F.
,
Ish-Shalom J.

Krishnamurthy P.
,
Khorrami F.
,
Ng T. L.
,
Cherepinsky I.

Krishnamurthy P.
,
Khorrami F.
,
Ng T. L.
,
Cherepinsky I.

Kim W.
,
Shin D.
,
Lee Y.
,
Chung C. C.

Shin S.
,
Shin D.
,
Lee Y.

Pelta E.

Khorrami F.
,
Krishnamurthy P.
,
Melkote H.

Khalil H.

Citing 'Simplified Nonlinear Control for Planar Motor based on Singular Perturbation Theory
'

@article{ DHJGII_2015_v64n2_289}
,title={Simplified Nonlinear Control for Planar Motor based on Singular Perturbation Theory}
,volume={2}
, url={http://dx.doi.org/10.5370/KIEE.2015.64.2.289}, DOI={10.5370/KIEE.2015.64.2.289}
, number= {2}
, journal={The Transactions of The Korean Institute of Electrical Engineers}
, publisher={The Korean Institute of Electrical Engineers}
, author={서, 형 덕
and
신, 동 훈
and
이, 영 우
and
정, 정 주}
, year={2015}
, month={Feb}