Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
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Development of Explosion-proof Autonomous Plant
Operation Robot for Petrochemical Plants

KOJI SHUKUTANI*1

KEN ONISHI*2NORIKO ONISHI*1

HIROYOSHI OKAZAKI*3

HIROYOSHI KOJIMA*3SYUHEI KOBORI*3

For increasing the patrol frequency of petrochemical plants to ensure reliability whileconserving manpower, the robotization of plant patrol checks is being demanded by domestic andforeign petroleum gas operators. However, due to the problems of making a robot explosion-proof,
almost no robots satisfy these needs. Mitsubishi Heavy Industries, Ltd. (MHI) has alreadydeveloped a land-mobile, explosion-proof robot that can be controlled wirelessly within flammablegas atmospheres. Currently, by utilizing this explosion-proof mobility establishment technology, weare promoting the development of an explosion-proof robot for autonomous plant operation tosatisfy the above needs earlier than other countries. The robot under development moves
autonomously with map information and sensor information, and can automatically acquire plant
information such as images of instruments, thermal images, gas concentrations, etc., using theon-board cameras, gas detectors, etc.

|1. Introduction
Petrochemical plants under operation require periodical patrols by checkers to detect
abnormalities before a disaster occurs. However, there is always a danger of fire and explosion in
the plant. In addition, the patrol areas include many high or narrow places, and may be in severe
environments such as storms, extreme cold, etc., in some cases. Therefore, ensuring the safety ofworkers is an important issue for petroleum gas operators. Furthermore, there is the challenge ofensuring plant reliability by increasing the patrol frequency and that of improving the operational
efficiency through labor saving and automation to secure earnings regardless of changing crude oilprices.
MHI has completed the development of a remote-control type land-mobile, explosion-proof
robot that was started in fiscal 2014 assuming situation checks in a flammable gas atmospheres
where people cannot easily approach, such as in the case of a disaster in tunnels, plants, etc. This
robot acquired a type examination certificate based on the "Explosion protection guidelines
consistent with international standards (Ex2015)"(1) for the first time in Japan as a mobile robot
equipped with a large capacity battery.(2)(3)(4) This report describes, as an application example of theestablishment technology of explosion-proof mobility that can be controlled wirelessly withinflammable gas atmospheres, the development status of an autonomous mobile explosion-proof
robot (hereinafter referred to as "explosion-proof autonomous plant operation robot") that carries
out patrol checks of a petrochemical plant based on the development of a remote control typemobile explosion-proof robot.

|2. Outline of explosion-proof autonomous plant operation robot(first-generation machine)
Currently, in cooperation with domestic and overseas petrochemical plant operators, we aredeveloping a first-generation explosion-proof autonomous plant operation robot that autonomously
patrols inside a plant and gathers information. This robot is planned to be deployed to an actual*1

Engineering Manager, Nuclear Plant Component Designing Department, Nuclear Energy Systems Division, Power Systems*2

Chief Manager, Nuclear Plant Component Designing Department, Nuclear Energy Systems Division, Power Systems*3

Nuclear Plant Component Designing Department, Nuclear Energy Systems Division, Power Systems

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)2

plant as early as fiscal 2019, after trial operation and improvement in a simulation plant. Figure 1
presents an overview of the system and the specifications of the robot under development.
The explosion-proof autonomous plant operation robot (first-generation machine) canautonomously move around a certain floor of a plant according to previously acquired map
information and sensor information, and is designed to acquire plant information such as images ofinstruments, temperatures, gas concentrations, etc., using the on-board visible light camera, thermalcamera, gas detectors, etc., while moving according to the preset schedule and patrol route. Figure
2 shows the appearance and equipment configuration of the prototype explosion-proof autonomous
plant operation robot.

Figure 1

Outline of system and specifications of explosion-proof autonomous robot

Figure 2Appearance and equipment configuration of robot

The initial remote-control type robot adopted a pressurized explosion protection structure,
which is more complicated but can be lighter than a flameproof explosion protection structure, torealize the development concept of being light enough to be handled manually without requiringlifting equipment for its installation and maintenance. The explosion-proof autonomous plant
operation robot maintains this explosion protection performance, which corresponds to Zone 1 (forMitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
3example, an area where there is a possibility of frequently generating an explosive atmosphere,
such as in the vicinity of an opening which discharges flammable gas in the opening and closing ofa lid during normal operation and control). With regard to the traveling performance, while keeping
the light weight concept of the initial remote-control type robot due to the crawler drive system andpressurized explosion protection structure (total mass 60 kg), the following additions andimprovements in the specifications were made to facilitate autonomous patrol and information
gathering so that the robot can handle multi-floor operation including stair climbing simply by
updating the robot software.
(1) Adoption of filled type pressurized explosion protection structure
The remote-control type land-mobile, explosion-proof robot, which was the base of thisdevelopment, adopted a sealed type pressurized explosion protection structure with an air tightenclosure, among pressurized explosion protection structures that prevent inflammable gas
from entering the enclosure by pressurizing and sealing a protective gas in the enclosure to
make the internal pressure higher than the external pressure. However, to maintain theexplosion protection function, inert gas (N2) had to be sealed as the protective gas, which
required large pieces of equipment and resulted in complicated operation. For this reason, bymodifying the robot so that it has a structure with a pressure accumulation tank to maintain therobot internal pressure and replenish leaked protective gas, a filled type pressurized explosion
protection structure was adopted. As a result, air can be used for the protective gas according to
the explosion protection regulations and the operation is simplified. Figure 3 depicts anoverview of the explosion protection structure.
The explosion protection regulations stipulate that in the case of a pressurized explosion
protection structure, it is necessary to constantly monitor the internal pressure and to provide aprotection circuit that shuts off the power supply when the boundary is damaged. If a battery is
installed inside the robot in cases where only a pressurized explosion protection structure isused, damage to the robot body forming the boundary may cause the energized battery tocontact the flammable gas to initiate firing even when the power supply is shut off by theprotection circuit. Therefore, a nesting structure where a battery with a flameproof explosion
protection structure is incorporated in the robot body with a pressurized explosion protection
structure is adopted.

Figure 3(2)Explosion protection structure of robot

Power supply system for automatically charging internal battery
A non-contact power supply is adopted assuming charging in an outdoor adverse
environment (rain, dust, etc.). Glass is the only material that satisfies the antistatic property
requirement for explosion protection and has an electromagnetic wave heat generation
prevention property during non-contact power supply at the same time. Tempered glass with aMitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
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thickness of 6 to 10 mm is necessary to satisfy the strength for the explosion protection
structure. For this reason, the distance between the power supply side and the power receivingside is inevitably larger than the usual non-contact power supply device. Therefore, to realize
adequate power supply (where one hour of robot operation can be made by two hours ofcharging) even under this condition, a magnetic resonance method is adopted. Figure 4
provides an overview of the power supply system during trial verification. For theexplosion-proof autonomous plant operation robot (first-generation machine), power supply iscarried out in a non-hazardous area, but for the second-generation machine, power supply isplanned to be carried out in a dangerous area. The explosion protection regulations regulate theradiation of electromagnetic waves in flammable gas atmospheres in a conservative manner.
However, we have started consultation with the explosion protection certification agency basedon actual electromagnetic field intensity data.

Figure 4 Outline of power supply system(3)

Establishment of charging and filling stations for long-term operation
For the long-term operation of the robot, we established a station where power supply tothe battery mounted on the robot is carried out together with air filling to the accumulator tankfor maintaining the robot internal pressure, realizing simultaneous charging and filling when therobot returns to the station. The station employs a roller-based guiding mechanism so that therobot can be accurately positioned in the charging system and the filling system with as few
sensors as possible. By arranging the rollers of the station diagonally with respect to the robot
moving direction, the robot is guided to a position in contact with the innermost wall and one
side wall simply by advancing straight ahead. Figure 5 illustrates the prototype station.
The station was reduced in size to 1 m × 1 m assuming installation in a narrow offshore
plant, and as with the robot, its weight was reduced to 60 kg in mass so that it can be handledmanually without requiring lifting equipment.
(4) Equipped with autonomous moving system for autonomous plant patrol
The installed robot hardware includes a new explosion-proof 3D laser range finder(LiDAR). This hardware adopts an independent flameproof explosion protection structure,enabling flexible installation and relocation at any position of the robot with a pressurized
explosion protection structure. In addition, a self-position estimation and environmental map
generation software package called SLAM (Simultaneous Localization And Mapping) is
employed and a high-spec computer that can handle advanced software processing is installed.
Figure 6 presents the situation where the robot estimates its own position by comparing
information on the environmental map with information acquired by the LiDAR.
(5) Equipped with sensors for collection of plant information
A small camera with a pressurized explosion protection structure is installed on a pole
provided at the robot upper body to secure a field of vision similar to that of a patrol checker. ItMitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)5

is planned that a manipulator equipped with a thermal camera with a pressurized explosion
protection structure on its tip will be installed on the robot in the future to obtain a wide
observation field. In addition, a microphone with a pressurized explosion protection structure
for collecting sound information emitted from plant equipment has already been developed as asingle unit. Furthermore, it is planned that a function to present the heat and gas distribution in
the plant and its temporal change to the plant operator will be offered.
(6) Establishment of IoT platform
In addition to Wi-Fi, LTE is also constantly provided as a wireless communication
method to connect the robot and the plant operator. Furthermore, as a means to respond to thedisruption of communication infrastructure in the event of a disaster, an optical fiber reel for
wired communication can be retrofitted as optional equipment.
We are developing an image processing technology for detecting abnormalities
regardless of environmental conditions (weather, time, etc.) and a data storage and processing
system for presenting a comparison over time for each specified place to the plant operator for
detecting abnormalities of equipment based on transmitted plant information. This data can bemonitored even at remote locations via a secure cloud, and it is also possible to edit theautomatic operation schedule of the robot as necessary. In addition, it is planned to remotely
control the robot via the same platform for implementing work that is difficult to performautonomously, such as the reading of dirty instruments, manipulating switch boards (expected
as a function of the future second-generation machine), operating valves to collect samples,etc.).

Figure 5

Appearance of station

Figure 6

Self-position estimation|3. Future prospects
Most domestic petrochemical plants are onshore downstream facilities for refining
operations, and it is relatively easy for human workers to respond to various events in patrol checks
or in the case of an accident. Therefore, the requirements for the performance and thecost-effectiveness of a robot that replaces human workers are inevitably stringent. On the other
hand, in the case of upstream facilities for petroleum and gas mining mainly located overseas, andfor offshore facilities in particular, the work environment is severe even under normal operation,
manpower costs at the site are high, and human workers cannot approach at all in the event of an
accident, making the remedy and recovery of the situation difficult. Therefore, it is considered thatthe demand for manpower saving in the plant is extremely high. However, it is not easy to automate
all equipment in such environments where flammable gases are present. Therefore, it is thoughtthat there is great expectation for an explosion-proof autonomous plant operation robot that collects
information and implements various tasks such as valve operation and sample collection as one
device constituting an IoT platform for automation and manpower saving. Figure 7 is theconceptual model of the explosion-proof autonomous plant operation robot.
To expand the market for plant patrol check robots including overseas in the future, it isnecessary to advance development and verification in a step by step manner in cooperation withusers through pilot operation in an actual plant. These efforts include the reliability improvement ofautonomous operation, the analysis of collected plant information, and the implementation ofabnormality diagnosis technology in addition to certificate acquisition of overseas standards

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
6(overseas explosion protection standards such as IECEx and ATEX) and the development of themanipulator and autonomous mobile technology for climbing stairs between floors. Although there
are many challenges and difficulties that still have to be overcome, we would like to steadily
accelerate the commercialization of explosion-proof autonomous plant operation robots.

Figure 7

Autonomous plant operation robot|4. Conclusion
MHI is working on technological development for the establishment of explosion-proof
mobility that can be controlled wirelessly within flammable gas atmospheres. In this report, anexplosion-proof autonomous robot that performs autonomous patrol check of a petrochemical plant
was introduced as an application example of this technology. In the future, we will conduct
verification tests and evaluations at domestic and overseas plants, develop a small manipulator andan autonomous stair climbing function, and enable light-duty tasks such as valve operation andpatrols on multiple floors. By 2019, we will introduce a prototype autonomous patrol robot
equipped with a manipulator to an actual plant, and gradually expand the mobility, abnormality
detection functions, and information processing functions.
Technologies for wireless traveling over a long period of time in flammable gas atmospheres
can be applied not only to plant operation support, but also to plant inspection. Since announcing
the acquisition of a type examination certificate for our remote-controlled explosion-proof mobile
robot in 2016, we have received many inquiries about applicability to inspections of pipes andtanks during service or just after stopping service. For actual inspections, explosion protection not
only for mobility, but also for the inspection equipment itself (such as ultrasonic probe, lasersensor, etc.) is not easy. However, we will continue to cooperate with users to contribute to themaintenance of plant health and the extension of operating life.

References
(1)
(2)
(3)
(4)

Ex2015，Technology Institution of Industrial Safety，（2015）
Proceedings of the 34th Annual Conference of the RSJ，1Y3-03（2016）
Proceedings of the 35th Annual Conference of the RSJ，1E3-04（2017）
Proceedings of the 36th Annual Conference of the RSJ，3F3-03（2018）