Two-dimensional Laser Scanner with Low Mechanical Cross

Coupling based on Piezoelectric Actuators

Chen Wei

, Luo Dong

, Liang Yuanbo

, Liu Peng

, Chen Liangpei

and Zhang Yizhou

Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, 1068 Xueyuan Avenue, Shenzhen, China

Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China

School of Microelectronics, Xidian University, Xi’an, China

Keywords: Laser Scanner, Piezoelectric Actuators, Mechanical Cross Coupling, Hysteresis Compensation.

Abstract: Traditional two-dimensional laser scanners usually employ two-degree-of-freedom flexible hinges.

However, these flexible hinges suffer from mechanical cross coupling between axes, which will reduce the

scanning accuracy and stability. To overcome the above disadvantages, a compact novel laser scanner based

on piezoelectric actuators is presented. The scanner uses only three one-dimensional flexible hinges to

achieve two-axis feature. The mechanical structure and principle are detailed. Then the capabilities of the

scanner are tested by a performance test system. The test results show that the scanner has a tilt angle of

43.19 mrad for X-axis with resonance frequency at 149.21 Hz and 2.41 mrad for Y-axis with resonance

frequency at 232.59 Hz. Its scanning nonlinearity is reduced from 3% to 0.5% for X-axis and from 6% to

1% after compensation. The test results and the actual scanning images prove the low mechanical cross

coupling.

1 INTRODUCTION

Due to high precision, fast response, large force

output and low power-consumption, amplified

piezoelectric actuators (APAs) are widely applied in

biological engineering, nanofabrication, and robotics

and so on (Bouchilloux et al., 2004, Domke et al.,

2011, Park et al., 2012, Yang et al., 2010).

Especially for laser scanners which can precisely

control the directions of laser beams, APAs are one

of the main driving methods (Sweeney et al., 2002).

In addition to APAs, flexible hinges are also the key

structure for laser scanner. They can withstands

stress and offers deformation when the scanner

works.

Generally, to achieve two-dimensional (2-D)

adjustments of laser beams, two-degree-of-freedom

(2-DoF) flexible hinges have to be used.

Unfortunately, almost all 2-DoF flexible hinges

suffer from mechanical cross coupling between axes.

In other words, motion of one axis can be affected

by the other one, which will significantly reduce the

accuracy and stability of laser scanner (Chen et al.,

2015b, Jing et al., 2015, Shao et al., 2018). Some

scanners employ two 1-D laser scanners to obtain

2-D features (Chen et al., 2015a). However, these

designs increase system complexity and volume.

There are two methods to deal with cross coupling

effect. One is to use decoupling control algorithm,

which is generally difficult to design and implement.

The other one is to reduce the mechanical coupling

ratio. Therefore, a novel structure with small or even

zero interference between axes is strongly demanded.

In this paper, a new two-dimensional laser

scanner based on three APAs is proposed. Through

special mechanical design, the scanner employs only

three 1-DoF flexible hinges to achieve two-

dimensional laser deflection, which can effectively

reduce the cross coupling. The structure and

principle of the scanner are detailed. To investigate

its performance, a test system is built up based on

position sensitive detector (PSD). The test results

show that the scanner has different resonant

frequency in the two axes. The scanning images also

prove the low mechanical cross coupling.

2 STRUCTURE AND PRINCIPLE

Flexible hinges are widely used in precision

positioning. Various geometries of flexible hinges

have been reported and studied (Wu et al., 2018).

Wei, C., Dong, L., Yuanbo, L., Peng, L., Liangpei, C. and Yizhou, Z.

Two-dimensional Laser Scanner with Low Mechanical Cross Coupling based on Piezoelectric Actuators.

DOI: 10.5220/0007360301290133

In Proceedings of the 7th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2019), pages 129-133

ISBN: 978-989-758-364-3

129

Figure 1: Structure of the scanner, (a) isometric view and

(b) exploded view.

However, mechanical cross coupling of multi-axis

flexible hinges is inevitable. Therefore, 2-D laser

scanner employs flexible hinges suffers from inter-

axis interference.

To overcome the above disadvantages, a novel

structure of laser scanner based on APAs is

introduced, as shown in Fig. 1. Figure 1(a) is the

isometric view of the scanner and Fig. 1(b) shows the

exploded view. The scanner consists of base, three

supports, three APAs and mirror.

Brackets 1 and 2 have same L-shaped features. Their

bottoms are fixed on the base. Two APAs

(P06.X100A, Harbin Core Tomorrow, China) are

fixed with the top edges of the two brackets, of

which their bottoms are connected to brackets 3.

Bracket 3 has a complex heterosexual structure, as

shown in Fig 2(c). APA 3 and mirror are fixed with

it.

Figure 2: Principle of the X-axis deflection (a) and Y-axis

deflection (b) and the structure of bracket 3 (c).

Figure 2 shows the working principle of the

proposed scanner. As shown in Fig 2(a), when

different voltages are applied to APAs 1 and 2, they

will have different displacement in the Z-direction.

Then the bracket 3 will tilt with APA 3 and

mirror in the X-axis. If a voltage is applied to APA 3,

it will have a –z direction displacement and the

mirror will tilt in the Y-axis (Fig. 2(b)). If applying

three different voltages to the APAs, the mirror will

tilt in X-axis and Y- axis simultaneously. Note that

there are only three 1-d flexible hinges on the

bracket 3 and they are working in different

directions. These hinges have no mechanical cross

coupling, as same as the scanner.

After design, the scanner has been manufactured and

assembled.

3 PERFORMCE TEST

3.1 Performance Test System Design

To study the performance of the scanner, a test

system was built up, as shown in Fig. 3. It consists

of a He-Ne laser, a PSD (DRX-2DPSD-0A01-X,

Daruixin, China), a drive circuit and power supply, a

data acquisition card(USB 6361, National

Instrument (NI), USA), and a software system (in

PC).The software system was designed based on

NI’s LABVIEW software. Different control signals

were generated by the software, output by the data

PHOTOPTICS 2019 - 7th International Conference on Photonics, Optics and Laser Technology

130

Figure 3: Performance test sytem.

acquisition card and amplified by the drive circuit.

The circuit can provide maximum voltage of

150volts and power of 30 watts, which enough drive

the scanner to work. Then, the PSD can real-time

detect and output the position information of laser

spot reflected by the scanner, which is collected by

the same data acquisition card. At last, the software

can figure out the performance of scanner, such as

deflection angle, open-loop frequency response,

hysteresis effects and nonlinearity.

3.2 Performance Test

Voltages from 0 volt to 150 volts are applied to the

scanner and the relationship between the deflection

angle and drive voltage is shown in Fig. 4. The

maximum angle of the scanner is 43.19 mrad for X-

axis and 2.41 mrad for Y-axis. It is clear that the

Figure 4: Relationship between the deflection angle and

drive voltage.

scanning angles of both axes are linear to the drive

voltages. The great difference in angles of different

axes may be attributed to the different mechanical

structures. The tilt mechanism of Y-axis needs to be

optimized and improved.

Figure 5: Frequency response of the scanner.

Figure 6: Scanning waveforms of the scanner with a drive

voltage of a 5-Hz triangle wave for X-axis (a) and Y-axis

(b).

Sine waveforms of different frequencies are used

to the scanner to study the dynamic response of the

scanner, as shown in Fig. 5. The first resonant

frequency of X-axis is 149.21 Hz and 232.59 Hz for

Y-axis.

Triangle waves of different frequencies are

applied to the scanner to study its relative

performance, as shown in Fig. 6. It can be found that

the rising line and falling line of the waveform

deviate from standard triangle waveform, which is

caused by the hysteresis effect of the PZT stack in

the APA. The amplitude of the drive triangular

Two-dimensional Laser Scanner with Low Mechanical Cross Coupling based on Piezoelectric Actuators

131

Figure 7: Scanning hysteresis loops of the scanner before

and after compensation and the comparison of

nonlinearities for X-axis and Y-axis.

waveform for Y-axis is much bigger than X-axis.

Hence, the distortion in Fig. 6(b) is larger than Fig. 6

(a).

The hysteresis effect of the piezoelectric ceramic

is originated from its inherent characteristics. In our

previous work, a hysteresis compensation algorithm

is introduced to restrain the hysteresis and proves its

Effectiveness (Sweeney et al., R. 2002). Therefore,

the algorithm is also applied to the scanner in this

paper. As shown in Fig. 7, the nonlinearity

produced by the hysteresis effect is reduced from

3% to 0.5% for X-axis and from 6% to 1%.

Some scanning images (Fig. 8) show single-axis

scans and a 2D scan. The single-axis scans are very

straight thus demonstrating the high linearity and

low inter-axis interference of the scanner. The 2D

image, produced with the x-axis driven by a 30-Hz

sine waveform and the y-axis was driven by a 20-Hz

cosine wave, shows a Lissajous-Figure.

Figure 8: Scanning images of the scanner.

4 CONCLUSIONS

A compact new 2-D laser scanner based on

piezoelectric actuators is designed, prototyped, and

experimentally tested. The scanner proposed a novel

mechanical structure to reduce the mechanical cross

coupling ratio. Different from traditional 2-D laser

scanner, it uses only 1-D flexible hinges to achieve

2-D deflection. A performance test system was built

up to test the capabilities of the prototype scanner. In

addition, a hysteresis compensation algorithm is

applied to the scanner to improve the scanning

linearity. From the test results, the scanner has a tilt

angle of 43.19 mrad for X-axis with resonance

frequency at 149.21 Hz and 2.41 mrad for Y-axis

with resonance frequency at 232.59 Hz. Its scanning

nonlinearity is reduced from 3% to 0.5% for X-axis

and from 6% to 1%. Some actual scanning images

are presented as well.

Some improvement of the scanner, such as structural

optimization for the Y-axis and closed-loop control

technology is undertaking to achieve larger scanning

angle and higher accuracy.

ACKNOWLEDGEMENTS

This work was supported by National Natural

Science Foundation of China (Grant No. 61605234)

and Shenzhen Science and Technology

Development Foundation (Grant No.

JCYJ20160531174039457).

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