Communication Systems for Multi Robot Systems

Copyright ® IF AC Bio-Robotics, Information Technology and Intelligent Control for Bio-Production Systems, Sakai, Osaka, Japan, 2000

COMMUNICATION SYSTEMS FOR MULTI ROBOT SYSTEMS

Michio Kise*, Noboru Noguchi**, Kazunobu Ishii***, Hideo Terao****

* Ph.D. candidate, Bio Production Engineering, Graduate School of Agriculture, Hokkaido University, KIta9, Nishi9, Kita-ku, Sapporo, Japan **Associate Professor, Graduate School of Agriculture, Hokkaido University ***Assistant Professor, Graduate School of Agriculture, Hokkaido University ****Professor, Graduate School of Agriculture, Hokkaido University

This paper dealt with a communication system between the field mobile robot and the control station. The control station had two functions; one was the function as a control system that could gather vehicle and travel status from a robot working at field, and send a control commands to the robots. another was the function as a decision support system that determined next task by collecting and analyzing the data of the field and crop status. In the research, both the data formats, from robot to control station, and control station to robot, were proposed. Communication test based on proposed data formats was carried out. The control station could monitor the updated status of the mobile robot. And the robot could change own behavior including an emergency stop by receiving the control command from the control station. Using this communication system, field maps including terrain and required engine power in rotary tillage were made by a GIS software. Copyright © 2000lFAC [Key words] Autonomous mobile robots, Control station, Control system, Decision support system, Navigation system

I.

was required to ensure safety for products. Matsuo et

INTRODUCTION

al. (1998) developed safety devices that can detect Almost researches relating agricultural autonomous

obstacles on a field using an ultrasonic sensor and a

guidance are half way through practicable use even

touch sensor, and stop an engine by a remote

though a lot of time was spent for them in the past.

controller. But, since the operator himself must solve

These researches were distinguished two types, one

the troubles when the safety device activated,

was the automatic system which aimed to automate a

someone has to sit at the field and watch the robot

part of the operation such as automatic guidance, and

operation. It seems a drawback for the productivity

the another was autonomous system which aimed to

and effectiveness of the robot.

treat all tasks in field operation. The major objective

The communication system between some field

of the former was to reduce fatigue of a farmer and

mobile robots and a control station that manages the

production costs by effective work. Dead reckoning

robots was able to contribute to solve such kind of

Direction Sensor (GDS) or

safety issues. There were three advantages if the

Gyroscope, vision-base guidance system, and GPS

communication system between robots and the

base guidance system were reported in the past

control station was constructed . First advantage was

with Geomagnetic

(Noguchi, et aI., 1998). On the other hand, the

the control station could send an emergency stop

autonomous vehicle aims to automate all tasks at a

command when a trouble occurred on robots by

field including turning functions. For examples, a

simultaneously monitoring all robots . Second was the

tilling robot with a total station and GDS and a robot

control station could manage multi-robots in respect

tractor using Kalman filter with DGPS and FOG have

of improvement of robot productivity. Finally, third

been developed in Japan (Yukumoto, et aI., 1997 ;

was the control station itself could monitor the field

Inoue, et aI., 1999). Both systems autonomously

conditions and adjust input resources to the fields by

performed a rotary tillage within Scm error. These

analyzing the soil and crop status in real time.

robots achieved the accuracy for practical use, but it

The goal of this study is to construct a total robot

79

system consists of some field mobile robots and a

control station. Commands system sent an emergency

a

stop command or the other commands to reflect on

communication system between the robots and the

decision of the control station. The tasks of the

control station.

control system was to detect unusual conditions of

control

station.

This

paper

dealt

with

the robots through the monitoring system, and to enhance the safety by sending the stop or restart commands by the commands system.

MULTI OBJECTIVE COMMUNICATION

2.

SYSTEM

2.3 Decision Support System The decision support system considered Map-base PF.

2.1 Functions of the Multi Objective Communication

Map-base PF creates an application map for next

System

events by analyzing crop growth, yield, and soil The total robots system, which was defined in thi s

nutrients. In this situation, the decision support

paper, was composed of the robots working at fields

system is essential to build an application map for the

and control station that managed the robots, as

input resources such as chemical and fertilizer. The

illustrated in Fig. I. The control station had two

idea on the research is to function the decision

functions. One was to monitor the robots working at

support system by integrating the information from

fields and send control commands to the robots

the robots. Because the control station communicated

occasionally. Another was a role of a decision

with the robots, the control station could adjust the

supports system that collected data including crop

application rate of input resources such as a fertilizer.

and tield information through the robots, and made a

2.4 Communication Protocol

schedule for next events. And also mobile robots have three key functions; autonomous guidance, communication with a control

The concept of the total robot system adopted a

station,

centralized

and

modification of own

behavior

by

acquiring commands from the control station.

managing

"top-down-system".

The

"top-down-system"

were

simulating

2.2 Control System

robot

the

system

system,

advantages mainly and

so-called of

the

capability

of

comprehending

all

behaviors of the robots. Basically, because field works must be decided before the events occurred,

The monitoring system , which can overview the robots

status

and

the

commands

system

"top-down-system" was more suitable for such a kind

are

fundamental components of the control system.

of total robot system .

Monitoring system can obtain a position, an attitude,

The data format from the control station to the robots

and a view generally recognized by a driver at the

(commands data) was consisted of a header field and a commands field. A header tield included time stamp, field ID, and robot ID. A commands field included a

Conwnand.

Autonomous lIJidance

@< )))~

.z~

Sendin, d.ta to control sbtion Acquisition COmrntnds from control sution

III ~- . . "

~ Control station

Control system Desicion support system

.. . . .

shift number, an engine speed, a stop, and PF commands suitable for the kind of field operations. The data format from robots to the control station (robot data) was composed of a header field, a robot monitoring field, and PF data tield. The robot monitoring tield is used for monitoring system of the control system. The control station could understand the driving status of the engine by monitoring an

robot

engine speed, and predict rollover of the vehicle by monitoring a roll angle and a pitch angle. Fig. I . Total Robot System

80

Table 2 Communication data

3. EVALUATION OF DEVELOPED COMMUNICATION SYSTEM

Commands Data ContenlS Header time Field ID Robot ID Work ID Shift Engine Speed Stop Implement Position Depth of Tillage Seeding Weed Fertilizer Chemical Terminator

3.1 Experimental System Communication test based on the data formats proposed in section 2.4 was carried out. A control station and a robot were utilized as the tested system. The control station consisted of a PC and a SS wireless modem, and a robot tractor, an RTK-GPS, a FOG, a IMU, and an SS wireless modem were employed as the test equipment. The specifications of these instruments were shown in Table 1.

Examples OxOI .Ox02 172814 0 0 0 9 I 0 0 0 0 0 0 OxOd.OxOa

Comments

Bit 16 10 2 2 4 6

Universal time

Ito 16 I=Max O=Stop. I=Go O=Down . I=up

4 0 0 0 0 16

CR. LF

3.2 Communication Data Robot Data Contents Header time Field ID Robot ID Work ID

The communication data adopted in the test was constructed based on the formats defined in section 2.4, as shown In Table 2. All commands data excepting stop command and engine speed command, and PF commands were set zero as dummy, because the tested robot didn't have such functions. Each data

Examples OxOI .Ox02 172814

Longitude

9778

Shift Engine Speed Travel Speed Exhaust Temperature

3.3 Evaluation of Control System

Vehicle Direction Roll angle Pitch Angle PTO Speed Implement Position Engine Load Depth of Tillage Seeding Weed Fertilizer Chemical Yield Terminator

Rotary tillage with 130 m X 9 rows, 1.0 mls at the engine speed of 2800 rpm was carried out at the field for evaluating the developed system. The control station and the GPS base station were set in the building close to the field. The autonomous guidance system with steering controller applied PID controller adopted with offset sensed by the RTK-GPS and a

2 4

3369375000

Altitude

speed based on PTO test.

2

0744310485

was compressed and distinguished by bit size. The of decimal points, therefore absolute position could be acquired by adding a fixed value. The engine load was estimated from exhaust temperature and engine

Universal time

o o o

Latitude

latitude and longitude in robot data represented a part

Bit 16 10

Comments

9 3210 7 450

Part of the decimal point of the latitude Part of the decimal point of the longitude Height of positionx 100[m] O=Manual position. I=Max [rpm] 10[oVs]

20 20 6 4

8

6

[~]

6

38

with respect to True north [0]

22

[0]

6 670

[0]

9 7 7 6 I 6

[rpm] O=Down. I=up [N*m]

o 85

o

4

o o o o

o o

o o

o

o

OxOd.OxOa

16

CR. LF

Table I Components of The Tested System

Components Robot RTK-GPS FOG IMU Wireless modem

Products Name & Manufacturers

~ I;: I

Features

- . 2.5

Control Contents; GL320 (KubOla Lld .) Steering. Hitch . FNR MS740 (Trimble Lld .) 2cm error. 20Hz JG-35FO (JAE Lld .) 0.5 deglh of bias JCS7401 A (JAE Lld.) 0.2 degrees error JX 1200A (Clarion Lld .) SS wireless

·2.5

L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ __ _

25

50

75

100

125

..rlm l

Fig. 2 Trajectory by vehicle guidance

81

~

150

~

E

"f"1".~

-,.~~~~",f:';"!:'f~,", d~ \..;

adding the information of other input resources.

7.5

-...

ferti li zers, chemicaL and yield.

~2.S

-::2.5

; : J<

•

~ 7S

so

:m

l~

:25

·"£5

x:~ht:m :

-0.:' .0.: 0.0 0. : 0.::

o. ~

4.

CO:\CU;SIO:\S

Fig. 3 Field topology map The communication system contributed on the multi robot farming and Precision Farming control station has been proposed. The communication system can remotely co. lect useful information regarding the robot status and field environment from the robots . d at r.deld. And. to ensure the safety of the actIvate

.t ;m;

is

:0

20

iio;W :

robot. the communication system commits to monitor

Fig. 4 Map of required engine power in rotary

the robot status and send the commands to the robot.

tillage

robo~

In the research. both the data formats from the

to the control station, and from the control station to the robot. were proposed. And prototype of the

heading error sensed by a FOG as control parameters

communication system was constructed. To confirm

traveled with 3cm error over rotary ti llage, as shown

~he

in Fig, 2. Fig.2 showed only recorded straight path

effectiveness and performance of the prototype

system, communication test was carried out. The

because turning was done by human driver.

control station could monitor the updated status of the

The control station could monitor the current robot

mobi le robot. And the robot could change own

position, travel speed. engine speed. and engine load.

bchavior including an emergency stop by receiving

The robot could stop by acquisitioning commands

the control command from the control station. Gsing

data from control station. Both results suggested that

this communication system, field maps including

validity of the data format as monitoring system and

terrain and required engine power in rotary ti llage

functions of the control system were proved.

could be made by a GIS software.

3.4 Evaluation of Decision Support System REFERE:\CES

Field maps, field topology and required engine power map in rotary tillage, were made by a GIS software with collected data at the base station.

!noue, K., Ootsuka, K.. Sugimoto, :'v1 .. Murakami, :\..

This shows

and Li. W. (1999). Sensor fusion Techniques for

validity of Decision support system. Field maps were

Automatic Guidance by the method of Kalman

helpful for understanding field status because of their visualization.

These

interpolated with

maps

filter using DGPS and Gyrocompass, Journal of

were illustrated and

the JSAM. VoI. 61(4). 103-113 Ylatsuo, Y., Yukumoto, 0., Kobayashi, T., noguchi. :\., Irie. Y.. Ichisugi, :\., and Suzuki, :'v1. (1 998).

Kriging method by the GIS

software (Transform; Fortner Ltd. ), and coordinate of the maps were same with Fig. 2. Field

topographical

maps

could

be

used

Development

for

Tilling

Robot

(Part

5),

Proceeding of the annual meeting of JSAM /998.

evaluation of field elevation and terrain, as shown in

417-4 18

Fig. 3. The color indicated field height. The map

~oguch i.

showed that the field had 83 cm of maximum

:\., Reid, J.• Wi il, J.. and Benson. E. (1 998).

Vehicle automation system based on multi-sensor

elevation and sloped down to north with 0.69 degrees over the field.

intgration.

1998

ASAE

Meeting.

Paper

::\0.983111

Tne GIS map of required engine power in rotary tillage calculated by engine load could

of

represe~t

Yukumoto. 0 .. and Ylatsuo, Y. (i 997), :\avigation technology for tilting robots. Proceeding of

fossil energy input, as shown in Fig. 5. It could assist

mobile Int. symposium on Bus-system LBS and PA, 59-94

to recognize entire energy-balance over the field by

82

agr;(ultural