Control system for a drilling & coring device in lunar exploration

Abstract

China is endeavoring to implement the lunar exploration mission, namely Chang'e. In Phase III of the project, the aim is focusing on acquiring lunar soil sample and bringing them back to the earth. Due to the high efficiency of drilling in granular substance, a drilling and coring device is selected as the sampling tool to acquire the soil sample along the vertical direction. A novel flexible-tube coring method is adopted in the design of drilling and coring device. A flexible tube is mounted inside the hollow auger to wrap the central soil into closed space. Two steps are included in the whole sample-acquiring process: drilling and coring. In order to verify the proposed sampling method, we have developed a drilling and coring prototype to realize all the necessary operations. Herein, by use of the architecture of xPC Target, a control system based on 1553B communication is presented for the process control. Both the hardware design and software interface are discussed in this paper. Finally, experiments are conducted to verify the effectiveness of the control system.

Full text

Control System for a Drilling & Coring Device in Lunar Exploration
Qiquan Quan, Junyue Tang, Shengyuan Jiang, He Li, Shengcheng Li, Zongquan Deng, Shen Yin
Abstract— China is endeavoring to implement the lunar
exploration mission, namely Chang’e. In Phase III of the
project, the aim is focusing on acquiring lunar soil sample and
bringing them back to the earth. Due to the high efficiency of
drilling in granular substance, a drilling and coring device is
selected as the sampling tool to acquire the soil sample along
the vertical direction. A novel flexible-tube coring method is
adopted in the design of drilling and coring device. A flexible
tube is mounted inside the hollow auger to wrap the central soil
into closed space. Two steps are included in the whole sample-
acquiring process: drilling and coring. In order to verify the
proposed sampling method, we have developed a drilling and
coring prototype to realize all the necessary operations. Herein,
by use of the architecture of xPC Target, a control system
based on 1553B communication is presented for the process
control. Both the hardware design and software interface are
discussed in this paper. Finally, experiments are conducted to
verify the effectiveness of the control system.
Index Terms— Lunar soil sampling; drilling and coring;
flexible tube; high-ratio sampling; xPC Target
I. INTRODUCTION
The upsurge of human planets exploration appeared in
the middle and late 20th century. Especially, during the
period of 1950s to 1980s, the Soviet Union and the United
States had sent 83 probes to the moon, and the success ratio
has reached 55.5 percent of all the exploring missions [1].
Astronauts had been sent to the moon, acquiring lunar soil
of approximately 381 kg totally through drilling, scooping,
and digging methods. For the deep-layer soil sampling,
astronaut utilized the Apollo Lunar Surface Drill (ALSD)
to dig samples on the moon [2][3]. Due to the limited
delivering capability of rockets at that time, the Soviet
Union lunar exploration missions (LUNA) had to implement
automated lunar soil sampling and returning task. As the
first lunar sample return mission by the Soviet Union, Luna
16 was the first robotic probe to land on the Moon and return
a sample of lunar soil to Earth, acquiring lunar regolith of
101 grams. The mission of Luna 24 probe is to sample the
lunar regolith beneath moon surface, keeping the original
layer information of the soil. A slide-rail is mounted on
the side of the probe. The drilling head is pushed into the
moon along the slide for more than two meters. Finally, the
continuous sample is sent to returning capsule and brought
back to the earth.
At present, in order to explore the deep space and
discover the unknown world, China is launching the lunar
Corresponding author: Shengyuan Jiang, Email:jiangshy@hit.edu.cn.
The authors are with School of Mechatronics Engineering, Harbin
Institute of Technology. Shen Yin is with Beijing Spacecrafts, yin-
shen529@163.com. Email address: quanqiquan@hit.edu.cn(Q. Quan);
tangjunyue hit@163.com(J. Tang)
exploration mission, namely Chang’e project. There are
three phases in this project: circling, landing and returning.
Regarding phase III of Chang’e mission, the goal is to
sample lunar soil and return it back to the earth. According
to the history of lunar exploration of human beings, drilling
is considered to be an efficient way to obtain soil sample
with a certain depth [4] [5] [6]. Therefore, drilling and cor-
ing is the main process among the whole sample-acquiring
mission. The sampling goal is to acquire the soil sample
in two-meter deep and keep the stratification of original
geological layers. To fulfill this sampling objective, we have
proposed a novel sampling methods, namely flexible-tube
coring. The original bedding information of lunar soil is
expected to be obtained via this method.
Due to the harsh environments of lunar surface and outer
space, such as high-low temperature, vacuum, and low grav-
ity [7], it is a great challenge to develop a kind of sampling
device to work under the circumstances. Before launching of
the mission, experimental verification must be implemented
to confirm all the functions and performance. Thus, we have
developed a drilling and coring prototype to realize all the
necessary operations. Apart from the mechanical system of
a sampling prototype, a control system is also needed to
complete the sampling process in experiments.
This paper is organized as follows. A scheme of drilling
& coring device for lunar exploration is given in Section
II. Section III introduces the implementation of a control
system for the sampling device. Experiments are conducted
to verify the effective of the control system in Section IV.
Finally, Section V concludes this paper.
II. A DRILLING & CORING DEVICE FOR LUNAR
EXPLORATION
A. Basic Architecture of Lunar Probe
To realize the target of lunar soil sampling, a possible
lunar probe is proposed as shown in Fig. 1. There are
three main components in the lunar probe: lander, ascent
stage, and sampling device. Lander is employed to safely
bring the whole system onto the lunar surface. Sampling
device is arranged on the side of the probe to acquire lunar
soil core through drilling and wrap the flexible-tube filled
with soil onto a helical cylinder and consequently send the
wrapped soil core into a container which is located on top
of ascent stage. The ascent stage will be launched and the
soil container will be carried back to earth.
The sampling device consists of support rails, penetrating
drive unit, rotary-percussive driving mechanism, dodging
mechanism, and winding & transfer unit. The action pro-
cess of the sampling device can be described as follows.
978-1-4977-1334-3/13/$31.00 ©2013 IEEE
Proceeding of the IEEE
International Conference on Information and Automation
Yinchuan, China, August 2013
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Lander
Ascent
Stage
Penetrating
Drive Unit
Rotary-percussive
Driving Mechanism
Dodging Mechanism
Winding &
Transferring Unit
Support Rails
Sealing Container
Fig. 1. A possible scheme of lunar probe for soil sampling
When the probe is landing on the moon surface safely
and smoothly, it goes into the self-check stage of lunar
surface sampling to make sure that the related states of
actuators and sensors are normal. In the lunar sampling
stage, rotary-percussive driving mechanism (RPDM) drives
the auger to rotate. RPDM can move longitudinally along
the support rails via the passive wheels. The penetrating
drive unit provides continuous pressure on the auger to
improve cutting capability of drill bit.
The drill tool is driven by rotary-percussive driving
mechanism and penetrating drive unit to drill into the lunar
surface. The flexible tube inside the auger is employed
to acquire the central soil core gradually. Winding and
transfer unit upon the ascent stage pulls the flexible tube
out of the auger and wrap it into the winding drum and
consequently deliver it to a capsule container. Until now,
the drilling core of soil has been successfully acquired and
v2
v3
v1
v1
1 2
3
4
Fig. 2. Working procedures of lunar probe on the moon
sent to the designated container. The upward part of the
whole sampling device, namely dodging mechanism, begins
rotating to depart from ascent stage and thus leave enough
space for the ascending of ascent stage. Finally, the ascent
stage carries the sample of lunar soil back to the earth.
B. Lunar Regolith Sampling
Inside the auger, there is a specifically-designed flexible-
tube coring mechanism. The proposed flexible-tube sam-
pling method can keep the stratification of lunar soil layers
during the drilling process. The sampling process by using
the flexible-tube coring is illustrated as shown in Fig. 3.
Sealing Tip
Flexible Tube
Flexible Tube
Interface
Dragging Wire
Rigid Tube
Auger
Drill Bit
v2
v1
Fig. 3. Scenes of coring process with flexible-tube method
1) Drilling and Coring: There is a set of coring tubes
inside the rotating auger, including rigid tube and flexible
tube. The flexible tube is arranged between auger and rigid
tube. Once drill bit contacts the lunar surface, one tip of
dragging wire is directly fixed at a point on the probe,
another tip is connected to the starting point of flexible
tube and keeps a tense state. Rigid tube moves downwards
with the auger synchronously, however, it does not rotate.
When the mechanism drills into the soil, the flexible tube is
utilized to wrap the central cut soil core. Since there is no
relative motion between the flexible tube and the cut soil
core, this coring method can keep the original stratification
of lunar soil. When the desired drilling depth is reached,
sealing tip at the end of flexible tube will be activated to
collect the soil sample into the closed space inside flexible
tube. The flexible tube filled with soil core is pulled out
from the hollow auger by the winding and transferring unit.
2) Winding and Transferring: As shown in Fig. 4, the
winding and transfer unit has different roles in the process
of drilling & sampling. Before the drilling bit gets to the
lunar surface, the winding and transferring unit coordinates
with penetrating drive unit drive the RPDM to penetrate in
clockwise. Once the drilling bit reaches to the surface, the
winding motor stops and keeps the dragging wire still.
After the whole drilling and coring process, the winding
motor drives the wire to be overlapped on the winding drum
and wind the flexible tube spiralling in counterclockwise.
Subsequently, the compressed spring in the ejection mech-
anism works to push the drum to move downwards rapidly.
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1 2 3 4
v2
v1
v3
v4
Fig. 4. Process of winding and transferring
As a result, the soil core together with winding drum are
transferred to a sealing container.
III. DEVELOPMENT OF A CONTROL SYSTEM
FOR SAMPLING DEVICE
The mechanical system of sampling device has been
completed based on the concept proposed in section II. Once
the mechanical system has been finished, the performance
of the sampling device depends on the control issues to a
certain degree. In order to realize the process control of the
sampling device, a control system should be developed to
control the corresponding motions.
Since the control system is used for experimental ver-
ification on the earth, as a convenient tool for rapid
control prototyping in real-time testing application, xPC
Target is adopted as the fundamental architecture to develop
the control system. The whole process consists of rotary,
percussive, penetrating, winding motions. It is expected
to realize velocity-mode control for each motion. In the
whole sampling process, the operator should also monitor
the penetrating pressure, the rotary motor’s speed and the
drilling bit’s temperature to judge if auger meets the stiff
stones or not. The control unit should collect the signals
from two load cells, one photoelectric encoder and one
temperature sensor.
A. Overall Layout of Control System
The composition of drilling & sampling device’s control
system is shown in Fig. 5.
Integrated
Controller
Drilling
& Sampling
Controller
1553B
Communi cation
Drilling &
Sampling
Device
Control System Mechanical System
Fig. 5. Composition of drilling & sampling control system
Among these, Integrated controller based on xPC-Target
is employed to simulate the central control unit distributed
on the probe as a control center, which sends command
signals to each payload and receives the corresponding
state data from sensors. Drilling & sampling controller is
deployed to realize the process control of the sampling
device, including motors control, signal acquisition, and
working state monitoring.
The Integrated controller is communicated with drilling &
sampling controller. Due to the harsh working environments
in space, communication between controller of sampling
device and earth terminal must be extremely reliable. There-
fore, MIL-STD-1553B communication is adopted to realize
the command transmitting and receiving. Fig. 6 shows the
control system’s overall layout of the sampling subsystems.
In 1553B communication, there are two channels: channel
A and channel B. Only one channel is inevitable while
another one is redundant to improve the reliability of
communication. On each channel, a coupling transformer
is used to extend the signal transmitting distance to 20 ft(6
m).
Transformer
PC1 PC2
Ethern et
Con troller
1553B Bus
A Cha nnel
1553B Bus
B C hannel
Integr ated Contr oller
Ch1
Ch2
Transformer
Fig. 6. Overall Layout of drilling & sampling control system
B. Hardware Architecture
As shown in Fig. 7, the control system for drilling and
sampling subsystem of probe consists of integrated con-
troller and drilling and sampling controller. The hardware
components of the control system will be presented in detail.
1) Drilling & sampling controller: Drilling & sampling
controller is based on Micro-controller unit (MCU) pro-
duced by Microchip. The related peripheral components
including D/A converter and A/D converter are connected
with MCU through SPI bus. Analog signals are transmitted
to the rotary driver, percussive driver, penetrating driver,
and winding driver to realize the motion control. Pene-
trating forces and temperatures of each driving motor can
be acquired through the A/D converter. Additionally, the
integrated I/Os of MCU send the digital control signal to the
Initiating Explosive Device (IED) to release the simulated
locking mechanism which fastens the active mechanism to
static structures. Concurrently, the integrated I/Os monitor
the states of limit switches which provide warning signals
telling the controller that the mechanism activates the prox-
imity sensor.
A communication chip produced by DDC Corporation
that supports the 1553B protocol is adopted to conduct the
communication between integrated controller and drilling &
sampling controller.
The printed circuit board (PCB) of drilling & sampling
controller and the control box are illustrated in Fig. 8. Motor
drivers for rotation, percussion, penetrating and winding,
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PCI-155 3B
Percussive
Motor
Rotar y
Motor
Penetrating
Motor
Wind ing
Motor
Motor
Driver
Motor
Driver
Motor
Driver
Motor
Driver
D
/
A1553B
Interface
protoco l chip
BU-6 1580
(16M clo ck )
Transfo rmers
70~85¡
A
B
A
A
B
B
70~85¡
70~8 5¡
70~85¡
A
B
A
A
B
B
Integrate d
Controller
A
/
D
I / O
48V 48Vė2 4/5V
Drilling &
Sampling
Controller
dsPIC33FJ
256
MC71 0A
(8M clock )
Load Cell 1
Load Cell 2
Limit Switch1
Unlock-1 Un lock-2
Unlock-3
IDE-1
Photoco uplin g
Unlock-4 Lim it Switch2
Limit Switch5
Limit Switch3
Limit Switch4
IDE-2
IDE-3 IDE-4
Transfo rmers
Transfo rmers
Transfo rmers
Temper ature
Sensor
Encod er
Fig. 7. Hardware of Drilling & Sampling Controller
transducers for load cells, DC powers are placed in the
control box compactly.
Fig. 8. Main PCB of drilling & sampling controller and control box
2) Integrated Controller: The workstation is composed
of two computers (master computer and slave computer),
which are connected through cross Ethernet line. Two indus-
trial computers are constituted via xPC Target architecture,
one computer namely Master computer, another one namely
Slave computer. The software MATLAB is installed on the
master computer while a core program produced by master
computer is used to boot the slave computer [8].
In the environment of MATLAB on master computer,
the control program has be written through the tool of
simulink. On the program panel, it is convenient to link
master computer and slave computer, download executing
program to slave computer, and start the execution. Herein,
graphical user interface (GUI) is employed to make an
interface for control and data acquisition.
Master
Computer
Slave
Computer QPCI-1553B
Program Development Real-time Controller
Program Download Control
Signal
1553B Bus
Real-time Control
Fig. 9. Architecture of xPC-Target
Slave computer executes the program downloaded from
master computer as a real-time unit. QPCI-1553B board is
installed on slave computer through the PCI slot for com-
munication. The communication board is a bridge between
drilling & sampling controller and integrated controller,
which sends and receives commands and data under 1553B
communication protocol.
3) 1553B Bus for Communication: 1553B is an abbrevi-
ation of MIL-STD-1553B bus, which uses dual redundant
transmission channels and can confirm good fault tolerance
and fault isolation [9]. The bus has three types of remote
terminals: bus controller (BC), remote terminal (RT) and
bus monitor (BM), including five working modes: BC to
RT, RT to BC, RT to RT, broadcasting and system control
[10].
Herein, integrated controller (Industrial computers) works
as BC (Bus controller) while drilling & sampling controller
takes a role as RT (Remote terminal). The network topology
of 1553B is shown in Fig. 10, in which the bus controller is
in charge of sending commands, taking part in transferring
message, receiving status of responding and monitoring the
whole system. And the remote terminals mainly work for
responding the effective commands from BC, returning the
status word and finishing the corresponding actions.
Bus Controller
(BC)
Remote Terminal
(RT)
Chan A
Chan B
Integrated Controller Drilling & sampling controller
1 1 0 1 0 1
Message
Fig. 10. The network topology diagram of 1553B bus
The transmission medium of 1553B is shielded twisted-
pair cable (STP), and the couplings have direct coupling and
transformer coupling two modes. We choose the transformer
coupling to transfer the message in order to avoid the signal
attenuation in long distance.
C. Software Interface
1) Software Design of Integrated Controller: The soft-
ware of master computer is mainly realized by joint-
programming of Simulink and GUI in MATLAB, and the
GUI is written by clicking the callback commands. Once
you click the control module and conduct the background
callback program, it will change the words in Simulink con-
currently. So commands will be sent to the slave computer
through 1553B communication.
The GUI of control system is shown in Fig. 11. On the
panel, it is easy for operators to enter different working
phase of drilling & coring and change the drilling parame-
ters. The values of sensors and the states of limit switches
are displayed online.
2) Software Design of Drilling & Sampling Controller:
The program diagram of drilling & sampling controller is
shown in Fig. 12. The controller is initialized and then
executes the main program in circles. In the main pro-
gram, the controller (MCU) receives totally 14 words from
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Fig. 11. A GUI for integrated controller
the integrated controller for one sending/receiving time.
The message including the following information: working
phase selection, motor control commands, data of sensors.
Depending on the value of working phase, the drilling and
sampling device will switch among different phases.
Master
PC
Receive 14th
Word
Slave
PC
Judge the
Work Time
Case 1:
System
Self-Check
Case 3:
Lunar
Surface
Drilling
Case 4:
Winding
&
Transferring
Case 6:
Enable
Close
Motor
and Relay
Enable
Read Mast er PC
1 to 13 Word s
Motors driv ing &
Singals co llecting
Send to Ma ster PC
1-14 Wo rds
Judge th e End
1553B
Communication
NO
YES
Motor and Relay Output
1553B
Communication
Between Master
and Slave PC
1553B
Communication
Case 2:
Idle
Drilling
Case 5:
Dodging
Unlock
Finish
Fig. 12. Software architecure of drilling & sampling controller
IV. EXPERIMENTAL VERIFICATION
In order to verify the proposed flexible-tube drilling and
coring concept, a drilling & coring device is developed for
experimental setup, including mechanical platform and the
control system. As shown in Fig. 13, a simulator for lunar
probe is built as the fundamental platform. The drilling
& coring prototype is mounted on the simulator of probe.
Monitoring cameras are employed to watch over sampling
process of drilling device in real time. A lunar soil container
is filled with simulant of lunar soil for drilling experiments.
Herein, the simulant of HIT-1 is selected as the object for
experimental test.
Drilling and coring
prototype Operation
platform
Integrated controller
Drilling & sampling
controller
Monitor
Lunar soil container
Monitoring camera
Fig. 13. A simulator for lunar probe to achieve sampling process
A. Realization of Drilling & Sampling Process
Since the drilling device works under the earth condition,
low-gravity compensation methods have been adopted to
reduce the effects of gravity through weight compensation.
Two compensation masses are mounted for the sliding
RPDM and dodging mechanism, respectively. In the whole
control process, the master computer sends and receives the
commands through the GUI interface, and operators can
watch the monitoring cameras to achieve the corresponding
sampling procedures. As shown in Fig. 14, the drilling &
sampling control system can complete the whole action
procedures and achieve the purpose of drilling & sampling.
Fig. 14. Verification experiments of drilling & sampling process
As shown in Fig. 15 (a), the flexible tube filled with
the sample is dragged from the inner space of the auger.
Subsequently, the flexible tube is wound onto a cylinder and
then transferred into a sealing container as shown in Fig. 15
(b) and (c). Consequently, the flexible tube with sample is
like that in Fig. 15 (d). The sampling ratio is approximately
80% for the granular soil.
B. Analysis of Drilling & Coring Test
From the experiments, we find that the drilling strategy
plays an important role in drilling and coring. If the drilling
parameters are well matched, this will lead to high sampling
ratio and low power consumption, and vice versa.
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(a) Dragging the flexible
tube from the auger
(b) Winding the flexible
tube
(c) Flexible tube on the
winding drum
(d) Flexible tube with
sample
Fig. 15. Experimental sampling scenes
In the whole working procedures, we adopt the velocity
control mode to drive the rotary motor, percussive motor,
penetrating motor and winding motor. The rotary speed is
150 rpm and penetrating velocity is 100 mm/min. Fig. 16
shows the corresponding results of the velocity of auger and
penetrating, the auger’s torque and the penetrating force in
the drilling and coring process. The driving torque of rotary
motor increases gradually when the drilling depth is deepen-
ing. The penetrating force provided by the penetrating unit
varies from 50 N to 100 N.
100 200 300 400 500 600 700
0
50
100
150
200
250
300
n(rpm)
Time t (s)
Velocity of auger
Filtered velocity of auger
0
20
40
60
80
100
120
100 200 300 400 500 600 700
Time t(s)
v /(mm/min)
Penetrating velocity
Filtered penetrating velocity
0 100 200 300 400 500 600 700
0.5
1.0
1.5
2.0
2.5
3.0 Torque of auger
Filtered torque of auger
T(Nm)
Time t (s)
0100 200 300 400 500 600 700
-50
0
50
100
150
F
p
(N)
Penetrating force
Filtered penetrating force
Time t (s)
200
(a) Rotary speed of auger (b) Penetrating velocity
(c) Rotary torque of auger (d) Penetrating force
Fig. 16. The sampling data during the drilling process
From numerous drilling experiments of granular sub-
stance, we have found that rotary speed and penetrating
velocity are in the range of 100 - 150 rpm and 100 - 200
mm/min, respectively. If the rotary speed is less than 50
rpm, rotary torque will increase sharply leading to drilling
error. If the hard layer is encountered, the percussive motion
will be activated to penetrate the substance. Overall, for the
granular substance, if a suitable match of drilling parameters
is selected, the proposed flexible tube sampling method can
acquire a high sampling ratio of lunar soil.
V. CONCLUSIONS
This paper presents a control system for drilling &
sampling device for lunar exploration. The whole control
system includes two aspects: integrated controller (upper-
level) and drilling & sampling controller (lower-level). By
use of a QPCI-1553B board, the integrated controller sends
control commands and receives state data via the 1553B
communication protocol. A friendly user interface has been
developed on integrated controller for system control and
state monitoring. The drilling & sampling controller works
in a loop, distinguishing the different working phases of
drilling & sampling and executing the corresponding com-
mands from upper-level controller and returning the working
states of sensors. The sampling process has been realized
in the controlling experiments and the data collected from
the experiments shows the control system can reflect the
states of sensors. The proposed flexible-tube coring method
performs a high sampling ratio of more than 80% in depth,
which has been verified in the numerous experiments.
ACKNOWLEDGEMENT
The project is supported by fundamental research funds
for the central universities(Grant No. HIT.KLOF.2010052,
No.HIT.NSRIF.2014051 and HIT.KLOF.2009064), Na-
tional Natural Science Foundation of China(51105092),
Heilongjiang Postdoctoral Grant(No.LBH-Z11168), China
Postdoctoral Science Foundation(No.2012M520722).
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