Sensors and Actuators A 125 (2006) 482–485

Design and mechanism analysis of a novel typecompact single mirror laser scanner

Nanying He∗, Weipu Jia, Mali Gong, Lei HuangCenter for Photonics and Electronics (9003-4401), Department of Precision Instrumentation, Tsinghua University,

Beijing 100084, PR China

Received 22 May 2004; received in revised form 25 July 2005; accepted 25 July 2005Available online 12 September 2005

Abstract

A novel type of laser scanner employing a permanent magnetic suspension and spherical hinges has been developed. It consists of a singlemirror based on linear electromagnetic actuators. This system has design features of playing the role of a two-dimensional tilt actuator bymeans of driving the electromagnetic actuators, and it provides good mechanical characteristics such as low distortion and damping, highoptical angular deflection, and high dynamical performance (more than 1 kHz). This paper describes the configuration of the device andp©

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resents experimental results to demonstrate its performance and effectiveness.2005 Elsevier B.V. All rights reserved.

eywords: Laser scanner; Tilt; Mechanism analysis; Actuator

. Introduction

Widely applied in many fields, laser beam scanners aresed to control the direction of laser beams for special pur-oses, including radar scanning, target acquisition, laser wire-

ess communication, etc.[1–3]. To achieve these purposes,e present in this paper a novel type laser beam scanner,hich adopts a magnetic suspension structure to reduce theechanical friction and abrasion. In this device, we proposenovel scanning method realized by a permanent magnetic

uspension structure. The performance of this device in termsf factors such as the scanning precision, stability, sensitivitynd efficiency can be improved essentially according to theagnetic suspension mechanism. The device with sphericalinges avoids a complex structure of movement mechanism

o be a compact structure.The device (seeFigs. 1 and 2) comprises a mirror and

hree bearing for orientating the mirror according to a

∗ Corresponding author. Tel.: +86 10 62792548; fax: +86 10 62781449.E-mail addresses: hny01@mails.tsinghua.edu.cn (N. He),

predetermined equation for the controlled deflection olaser beam. The mirror is supported to oscillate arounX-andY-direction and move alongZ-direction. The means foorientating the mirror comprise a plurality of electromagsupplied with currents, which are controlled and variabtime to exert magnetic forces on said mirror.

The control system is composed of the PSD procesunit and three PID controllers for the actuators. The cucontrol is used in order to improve the performance ofloop and to reduce the phase shift.

In this paper, the different design aspects and their deare presented, and the basic principle of the systeexplained in Section2. On the basis of the basic principexperiments are performed and results are presented intion 3. In the last section, conclusions are drawn.

2. System configuration

2.1. Bearing structure

iawp@ntl.pim.tsinghua.edu.cn (W. Jia), gongml@tsinghua.edu.cnM. Gong), hl@mail.tsinghua.edu.cn (L. Huang).

This system is suspended by three electro-magnetic actu-ators that are radially spaced by 120◦ along a circle. The

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N. He et al. / Sensors and Actuators A 125 (2006) 482–485 483

Fig. 1. Scanner.

electro-magnetic actuators are wound by coils to play therole of Z-direction positioning actuator. From the combina-tion of these actuators, the tilt motions can be obtained. Thecross-section of one bearing is shown inFig. 3. It includesfour main parts, actuator and three spherical hinges, and theseparts are bound with each other by sintering. Each actuatorconsists of four main parts: coil, magnet, yoke and axis. Threespherical hinges are supported by these actuators, and playthe role ofZ-direction motion with them. The mirror on thehinges is driven by the hinges to play the tilt motion and itsXY-direction shift is compensated by the deflection of thehinges. Each spherical hinge has two hinge points. One isuniversal and the other is unipolar, thus the hinges and themirror can compose a kinematic link system.

Fig. 3. Cross section of bearing.

2.2. Movement mechanism

The structure of the system is shown inFig. 4. Create acoordinate systemOXYZ at the prime center of the mirror.The plane of the mirror is defined byA′, B′ andC′, A′A′′,B′B′′ andC′C′′ are fixed with the mirror, so the offset angleof the mirror is same toA′′B′′C′′-plane.B′B′′ is the normaldirection ofA′B′C′-plane andA′′B′′C′′-plane, so

{A′′B′′•B′B′′ = 0

B′′C′′•B′B′′ = 0(1)

Fig. 2. Schema of scanner.

Fig. 4. Structure of scanner.

484 N. He et al. / Sensors and Actuators A 125 (2006) 482–485

The deflection angle of the mirror (θx andθy) is shown asFig. 4.

θx = tan−1�x

�z= tan−1XB′ − XB′′

ZB′ − ZB′′

θy = tan−1�y

�z= tan−1 YB′ − YB′′

ZB′ − ZB′′

(2)

Due to the characteristic of the hinge,AA′′ is in the planewhich is defined byAB and paralleled withZ-direction, soAA′′ is vertical to the plane’s normal directionNAB = (XC, YC,0)T, and the as that ofB′B′′ andC′C′′, NBC = (XA, YA, 0)T,NCA = (XB, YB, 0)T.

A′A′′•NAB = 0

B′B′′•NBC = 0

C′C′′•NCA = 0

(3)

The length of the hinges is known as:

{|A′A′′| = |B′B′′| = |C′C′′| = H1

|AA′′| = |BB′′| = |CC′′| = H2(4)

The input of the system is theZ-position ofA, B andC(ZA, ZB, ZC), and theXY-position ofA, B andC is fixed:

f thel nate

systemO(0, 0, 0) should be in the mirror plane:

∣∣∣∣∣∣∣XA′ YA′ ZA′

XB′ YB′ ZB′

XC′ YC′ ZC′

∣∣∣∣∣∣∣ = 0 (6)

Due to Eqs.(1)–(6), the input of the system (ZA, ZB andZC) can be calculated by the target output (θx andθy), andthe work space of the system can be defined by the design ofthe three hinge (H1 andH2) and the range of the actuators’movement (ZA, ZB andZC).

3. Experimental results

The experiment is taken by the input of one actuator keep-ing the other two actuators at constant position. The staticand dynamical performance of the system is presented.

Fig. 5 shows the experimental results of open loopcontrol. As can be seen from the figure, the tilt angle (θx

and θy, show in abscissa) is linear to the input voltage(show in ordinates). The linearity is influenced by theelectromagnetic actuators and spherical hinges. The offsetof actuators and deformation of hinges is slight and shows al rityi ricalh

step-f andt witht

urveo n oft goodp hased

XA = −L

2, YA = −

√3

6L

XB = 0, YB =√

3

3L

XC = L

2, YC = −

√3

6L

(5)

To remain the reflection center (the entrance point oaser beam) on the mirror, the zero point of the coordi

Fig. 5. Experimental results with open-loop control.

inear characteristic with small range. The low non-lineas mainly due to the manufacturing accuracy of the spheinges.

Fig. 6shows the transient response of the scanner forunction signal, including overshoot, attenuation ratioransition time. The over shoot of the system decreaseshe raise of the input voltage.

Fig. 7 shows the closed-loop frequency response cf the scanner. The gain bandwidth and stability margi

he closed-loop control system is presented to show aerformance at the frequency more than 1 kHz and little peformation.

Fig. 6. Transient response of the system.

N. He et al. / Sensors and Actuators A 125 (2006) 482–485 485

Fig. 7. Frequency response of the system.

4. Conclusion

This paper has introduced a new compact laser scannerand the environment in which the scanner operates. A typeof linear electro-magnetic actuator composed of just magnetsand coils has been designed and optimized in this paper, andthe experimental results obtained appeared to show the gooddynamic behavior. The proposed model can be applied to anyother system, which requires a linear actuator.

References

[1] Lei Huang, Mali Gong, Weipu Jia, Ping Yan, Ruizhen Cui, HaitaoZhang, Stability analysis for a novel permanent magnetic suspensionlaser beam scanner, Jpn. J. Appl. Phys. 41 (2002) 1343–1346.

[2] L. Sung-Q, D.-G. Gweon, A new 3-DOF Z-tilts micropositioning sys-tem using electromagnetic actuators and air bearings, Precision Eng.24 (2000) 24–31.

[3] M. Hafez, T.C. Sidler, R.P. Salathe, G.L.M. Jansen, J.C. Compter,Design, simulations and experimental investigations of a compact sin-gle mirror tip/tilt laser scanner, Mechatronics 10 (2000) 741–760.

Biographies

Nanying He graduated from the Department of Precision Instrument atTsinghua University, Beijing, China. He received the BS and MS degreein mechanical Engineering from Tsinghua University. His research inter-ests are focused on the precise machines and instruments.

Weipu Jia is currently associate professor in the Department of Preci-sion Instrument at Tsinghua University. He is also the senior memberof Chinese Mechanical Academy and the member of Chinese OpticalAcademy. He graduated from Tsinghua University with BS degree. Hisresearch field is precise optical instruments-on which he has publishedover 30 papers and 20 patents.

Lei Huang received the BS degree in mechanics engineering, the MSand PhD degree in Optical Engineering degree from Tsinghua Univer-sity. Currently he is an assistant researcher in Tsinghua University. Hisr

M hongU MSd logyo Engi-n in ther y andP ghuaU e andf

esearch is focusing on Solid Laser and Optical Data Storage.

ali Gong received the BS degree in optical engineering from Huazniversity of Science and Technology, Wuhan, China in 1982, theegree in optics from University of Electronic Science and Technof China, Chengdu, China in 1984 and the PhD degree in Opticaleering from Tsinghua University, in 1989. Then he was engagedesearch of advanced solid laser in Southwest Institute of Technologhysics, Chengdu, China until 1998. Now, he is a professor of Tsinniversity and focuses on advanced solid laser, optical data storag

ree space optical communication (SPIE member).