This paper proposes a new type of scanning laser range sensor for planetary exploration. The proposed sensor has advantages of small size, light weight, and low power consumption with the help of micro electrical mechanical systems technology. We are in the process of developing a miniature two dimensional optical sensor which is driven by a piezoelectric actuator. In this paper, we present the mechanisms and system concept of a micro scanning laser range sensor

Goto, Hiroshi

Kasamura, Kenji

Katoh, Hiroshi

Kubota, Takashi

Mizuno, Takahide

Nakamura, Satoru

Nakatani, Ichiro

Saito, Hirobumi

English

NASA Technical Reports Server

MICRO SCANNING LASER RANGE SENSOR
FOR PLANETARY EXPLORATION
*Ichiro Nakatani, *Hirobumi Saito, *Takashi Kubota,
*Takahide Mizuno, *Hiroshi Katoh, *Satoru Nakamura,
*Kenji Kasamura, **Hiroshi Goto
2 //Yz/
*The Institute of Space and Astronautical Science
3-1-1, Yoshinodai, Sagamihara-shi, Kanagawa-ken 229, JAPAN
**OMRON Corporation, Central R&D Laboratory
45, Wadai, Tsukuba-city, Ibaraki 300-42, JAPAN
Abstract
This paper proposes a new type of scanning laser range sensor for planetary exploration. The proposed
sensor has advantages of small size, light weight, and low power consumption with the help of micro
electrical mechanical system technology. We are in the process of developing a miniature two
dimensional optical sensor which is driven by a piezoelectric actuator. In this paper, we present the
mechanism and system concept of a micro scanning laser range sensor.
1. Introduction
As increasingly many missions are being proposed for the moon and planet explorations, autonomous
navigation technology for spacecraft in deep space is getting more important than ever. In recent years,
many researchers have been extensively studying and developing planetary landers or rovers for
unmanned surface exploration of planets[ 1][2] [3] [4] [5].
In a planetary exploration mission, it is important for a lander to land in a plain and safe place. A
planetary rover is also required to travel safely over a long distance in unknown terrain without
collision with big stones, rocks etc. Hence, it is necessary for a lander or a rover to recognize the
terrain on the planetary surface.
There have been developed various kinds of sensors for this purpose[6][7][8]. However conventional
sensors have many problems with weight, size, power consumption, reliability, etc. In this paper, we
propose a scanning laser range sensor using micro electrical mechanical system (MEMS) technology. A
two dimensional optical scanner is one of the most promising devices to recognize the three
dimensional terrain. So we are in the process of developing a miniature two dimensional optical sensor
which is driven by a piezoelectric actuator. The scanner system consists of two elements, a resonator
and a piezoelectric actuator. The resonator has two typical vibration modes, twisting and bending mode
of the torsional spring. Actuating the resonator with piezoelectric element at the resonance frequency
leads to the resonant rotating vibration of the resonator with large amplitude. When the piezoelectric
actuator is driven simultaneously with both the resonance frequencies, optical beam reflected on the
mirror of the vibrating resonator is scanned in two perpendicular directions. The proposed technology
will remarkably reduce the weight, size, and power consumption compared with the conventional
sensor.
This paper is structured as follows. In Section 2, the concept of recognition sensor is discussed. Then a
scanning mechanism is described in Section 3. In Section 4, a method to obtain range image by a
micro scanning laser range sensor is explained. Final Section is for discussion, conclusion, and future
work of the research.
https://ntrs.nasa.gov/search.jsp?R=19960054144 2020-06-16T03:42:39+00:00Z
2. Concept of Recognition Sensor
Several sensors and methods have been proposed to recognize the terrain on the planetary surface; for
example, a laser range finder, stereo vision etc. However, conventional laser range finders have
problems with weight, size, power consumption, reliability, etc. for the purpose of scanning the
terrain area. It is difficult and takes a long time to find correspondent points in stereo vision methods.
Hence, we have proposed a new type, of two dimensional optical scanner sensor.
Figure ! shows the concept model of the proposed recognition sensor, which consists of an optical
scanner device, a micro lens, a laser diode, a photo detector, a piezoelectric micro actuator to drive the
scanner, driver circuits, and signal processing circuits. Target size, weight, and power consumption
are shown in Table l.
Optical Scanner Laser Beam
Actuator _"_ilrr°r /_¢ ctor
Driver
)0[mm]
__! _)i.! !_ _'_ Laser
Printed Circuit _ Lens
Figure 1. Concept of Recognition Sensor
Table 1. Specification of LRF
Laser Range Finder size
Conventional LRF 20[cm] (L)
201cml(W)
(Rotating Mirrors) 20[cml(H)
Advanced LRF 15[cm] (L)
15[cm](W)
(Polygon Mirrors) 15[cm](H)
Micro LRF
(Piezo-Mechanism)
target
3.0[cm] (L)
3.0[cm] (W)
2.0[cm] (H)
weight
15[kg]
3[kg]
target
0.5[kg]
power
x00[w]
60[w]
target
3[w]
3. Scanning Mechanism
3.1 Two Dimensional Optical Scanner
A miniature two dimensional optical scanner is shown in Figure 2. The developed optical scanner[9]
consists of two elements, a resonator and a piezoelectric actuator. Here the center of gravity is shifted
from each rotational axis P and Q. So the resonator has two typical vibration modes, twisting and
bending of the torsional spring as shown in Figure 3. Actuating the resonator with a piezoelectric
actuator at each resonance frequency leads to the resonant rotating vibration of the resonator with a
large amplitude. The resonance frequency f is described by the following equation.
where K and I_ denote stiffness of torsional spring and rotational inertia moment of resonator
respectively. As a result, optical beam reflected on the mirror of the vibrating resonator can be scanned
in the two directions of 0 T and 0 B .
8 T
Mirror _ "_"x, Inertia Generator
I "gFt__ ealTg _]
To " "__
_ Laser Beam
Piezoelectric Actuator
Figure 2. Structure of Scanner Sensor
8 R
Figure 3. Resonance Vibration Modes
3.2 Piezoelectric Micro Actuator
A multilayered piezoelectric actuator is often used because it is easy to realize miniaturization and high
speed response of the actuator. However the multilayered type requires high voltage over 100 volts to
obtain several microns amplitude of the resonator. It is needed to avoid generating heat at the miniature
devices. The new actuator[10], which is called moonie, is developed as shown in Figure 4. The
actuator consists of a multilayered piezoelectric actuator and metal plates fixed on the top of the
actuator. The plates has shallow cavity to transform and magnify the radial strain of the actuator into the
axial strain.
When the piezoelectric actuator generates the strain in X direction as the axial strain by supplying
electrical field, the contraction strain in Y direction is produced. The plate is deformed by the
contraction strain as shown in Figure 4(b). So a magnified strain in X direction can be obtained.
Applying the moonie actuator in the two dimensional optical scanner, low voltage driving, less than 10
volts can be realized. It can reduce generate heat at the actuator and driving circuits.
(a)
Piezoelectric Actuator
Plate _
Figure 4. Structure of Moonie Actuator
3.3 Scanning Angle Detection
It is necessary to detect the scanning beam angle for making three dimensional terrain map of planetary
surface. In the developed resonance type sensor[l 1], the phase difference between the scanning
orientation and driving voltage wave form is 90[deg] which is constant regardless of the oscillation
frequency and amplitude. So it is possible to detect the scanning angle by monitoring the driving
voltage to the actuator. The scanning angle is calculated by the following equations:
2VT(t) 1 ) (2),0 T (t) = 4- 0 0 1 - ( V0T
_// 2VB(t) 1 ) (3),0 B (t) = _+0 o 1 -- ( VOB
where V0 is maximum amplitude of the driving voltage wave form to the actuator and 00 is maximum
scanning angle of the scanner.
3.4 Performance of the scanner
The performance of the scanner angle is shown in Figure 5. The developed scanner can scan an optical
beam in two directions with approximately 40[deg] at 4[p.m] piezoelectric actuator amplitude. In this
case, the resonance frequency of the resonator is 121[Hz] for twisting mode and 288[Hz] for bending
mode. So the scanning speed of 242[scan/sec] and 576[scart/sec] is obtained if a to-and-fro scanning is
applied. The scanning speed is adjustable by changing the resonator shape. The maximum speed is
over 2000[line/s] by reducing air viscous resistance against the resonator. Two dimensional scanning
pattern is determined by the ration of the resonance frequencies. Figure 7 shows an example of the
scanning pattern.
5O
-_ 40
_ 3c
_- 20
o_ 10
| f _ J i
OB.j
/¢
• • i i i
I 2 3 4 5
PZT Displacement [laml
Figure 5. Scanning Angle Data
Micro Snanning LRF
Figure 6. Scanning Pattern
4. Range Image
Laser range sensors for planetary exploration require high accuracy and high frame rate performance.
This leads to using phase-comparison system by intensity modulated CW laser. The laser beams are
radiated to target objects reflected and returned to the sensor with some phase shift proportional to the
target distance. The intensity of the semiconductor laser is modulated at 10.7 [MHz]. The reflected
beam from the object is received by an APD photo detector. The signal received by the detector passes
into the detection circuit of the range and reflectance. The range is determined by the phase difference
of returned signal and the reference signal as shown in Figure 7. In order to obtain sufficient sensitivity
and accuracy, nearly 100 waves are integrated for each range data. The data of range and reflectance are
converted into digital data by an A/D converter. Optical scanning in two dimensional directions help to
obtain three dimensional terrain recognition.
_q RF _ Semiconductor
driver laser (LD)
[ I ,  o o e=ordetector _ (APD)
Intensity
modulated beam
Reflected beam
I _
Figure 7 Range Data Measurement
5. Conclusion
This paper presents a scanning laser range sensor for terrain recognition of planetary surface. The
concept of micro scanning laser range sensor is proposed with the help of micro electrical mechanical
system technology. The proposed micro sensor is expected to solve some problems with weight, size,
power consumption. Experimental study is under going. When the proposed sensor is used in space
environment, there are some items for further study as follows: range drift due to temperature change,
vibration and shock problerhs at launch. Those problems are under study.
Reference
[1] C.Champetier, J.Serrano, J.de Lafontaine, "Autonomous and Advanced GNC Techniques for the
Interplanetary Rosetta Mission," Proc. of 1st ESA Int. Conf. on Spacecraft Guidance, Navigation
and Control Systems, pp.559-570, 1991.
[2] J.de Lafontaine, "Autonomous Spacecraft Navigation and Control for Comet Landing," Journal of
Guidance, Control and Dynamics, Vol.15, No.3, pp.567-576, 1992.
[3] W.T.Fowler, E.Pinon III, et.al. "Mini spacecraft for a Multiple-Asteroid Rendezvous Mission,"
AIAA Aerospace Design Conf., AIAA 93-0998, 1993.
[4] J.Kawaguchi, Y.Morita, T.Hashimoto, T.Kubota, H.Yamakawa, and H.Saito, "Nereus Sample
Return Mission," Proc. of the 45th Congress of International Astronautical Federation, IAF-94-
Q.5.354, 1994.
[5] I.Nakatani, T.Kubota, T.Yoshimitsu, "Path Planning for Planetary Rover using Extended Elevation
Map," Proc. of Int. Symposium on Artificial Intelligence, Robotics and Automation in Space,
pp.87-90, 1994.
[6] .J.R.Kerr et al., "Real Time Imaging Range finder for Autonomous Land Vehicle," SPIE Vo. 1007
Mobile Robots III, pp.349-356, 1988.
[7] I.S.Kweon et al., "Experimental Characterization of tile Perception Laser Range finder," Technical
Report CMU-RI-TR-91-1, 1991.
[8] Y.Wakabayashi, M.Honda, T.Adachi, T.Iijima, "Small Image Laser Range Finder for Planetary
Rover," Proc. of Int. Symposium on Artificial Intelligence, Robotics and Automation in Space,
pp.201-204,1994.
[9] H.Goto, K.Imanaka, "Super Compact Dual Axis Optical Scanning Unit Applying a Torsional
Spring Resonator Driven by a Piezoelectric Actuator," Proc. of SPIE, Vo1.1544, pp.272-281,
1991.
[10] H.Goto, H.Kamoda, M.Yoneda, K.Imanaka, "Miniature 2-Dimensional Optical Scanner Utilizing
a multilayered Piezoelectric Actuator with New Displacement Expansion Mechanism," Proc. of
Actuator'92, pp.68-70, 1992.
[11] H.Kamoda, H.Goto, K.Imanaka, "Two Dimensional Optical Sensor Using a Dual Axis Miniature
Optical Scanner," Proc. of SPIE, Vol. 1751, pp.280-288, 1992.
[12] H.Goto, H.Ohta, K.Imanaka, T.Yada, "Scanning Optical Sensor for Micro Robot," Proc. of
IARP Workshop on Micro Machine Technology and Systems, pp. I-6, 1993.



Micro Scanning Laser Range Sensor for Planetary Exploration

Micro Scanning Laser Range Sensor for Planetary Exploration

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server