Technology of using remotely controlled mobile complexes.

Technology of using remotely controlled mobile complexes..

TECHNOLOGY OF USING REMOTELY CONTROLLED MOBILE COMPLEXES

…When studying sciences, examples are no less instructive than rules
Isaac Newton

Recently, there has been much talk about the creation of low-manned and unmanned technologies for carrying out emergency rescue and special high-risk operations, primarily implying the equipping of rescue units with mobile robots and remotely controlled vehicles. Meanwhile, the successful elimination of the consequences of accidents largely depends not only on the technical capabilities of robots, but also on the organization, methods and techniques of conducting emergency rescue operations, including:

— analysis of the operational situation, i.e. the totality of factors and conditions in which preparation and conduct of work are carried out;
— assessment of the situation and making rational decisions on the implementation of actions of the emergency rescue unit;
— careful planning of actions;
— competent use of robots and remotely controlled vehicles, taking into account their technical capabilities, design features and limitations on use;
— preliminary training of operators to carry out important technological operations;
— ensuring emergency rescue operations.

Let us consider the technology of using remotely controlled mobile complexes using the example of eliminating the consequences of a radiation accident in the city of Sarov.

Operational situation

On June 17, 1997, at 10:50 a.m., in the Laboratory of the All-Russian Research Institute of Experimental Physics (VNIIEF), during the installation of a critical assembly on a critical stand1, conditions for a spontaneous chain reaction were created due to a violation of work regulations. A nuclear flash occurred with a sharp increase in the assembly temperature and the simultaneous formation of powerful neutron radiation. A powerful neutron flux initiated the occurrence of induced hard gamma radiation. As a result of the reaction, the assembly began to work as a constant source of heat and neutrons. An employee of the nuclear center conducting the experiment received a lethal dose of radiation.

1. The critical stand is a complex that includes a nuclear critical assembly and equipment necessary for conducting experiments, controlling the critical assembly and radiation safety, and allows for a controlled nuclear fission reaction to be carried out under specified conditions.

The critical stand (Fig. 1) was located in a special building in the center of an isolated room — a rectangular (in plan) box.

The floor of the box is concrete, covered with a special plastic. The power and remote control cables for the equipment, as well as telemetry, were located in rectangular channels covered with steel sheets.

The two entrances to the box, located opposite each other, were closed by special doors — dampers and «plugs», rather complex and heavy structures, driven by electric drives. The dampers moved along the walls inside the box, and the «plugs» were pushed into the doorways from the outside.

The box was equipped with an electric crane with a service area corresponding to the room, with the exception of a strip about 2 m wide along the walls.

The critical stand and crane were controlled remotely from the central control panel located in the adjacent room — the control room. The operations were monitored using a periscope.

 
Photo 1. General view of the critical stand.

The peculiarity of the situation was that there were containers with radioactive materials in the box. An increase in the temperature of the critical assembly could lead to a thermal explosion and ignition of radioactive materials with the formation of an aerosol, which, if released from the laboratory premises, would cause severe radioactive contamination of the air and the area.

Removing the containers from the box and transferring the assembly to a subcritical state manually” was impossible, since the powerful neutron flux posed a mortal danger to people. Therefore, the main means of eliminating the consequences of the accident should have been remotely controlled mobile complexes (robots).

Mobile robots

All robotic means available at that time and suitable for indoor operations were involved in the work:

• MRK-25, developed by the Special Robotics Design Bureau of the Bauman Moscow State Technical University;
• mobile robots “HOBO” and “RASCAL” from the mobile forensic explosive laboratory of the FSB of Russia;
• MRK MV-4, belonging to the emergency technical center of VNIIEF.

Mobile robot MV-4 (Photo 2) manufactured by Telerob (Germany) is designed primarily for work with hazardous objects at nuclear power and chemical industry enterprises. It is also used as part of the TEL600 complex when working with unexploded ordnance and explosive objects.

 
Photo 2. Mobile robot MV-4
(TV camera and control compartment are protected from neutron radiation).

The robot has a box-type body, a two-track chassis with spring-mounted support rollers, a manipulator, and front and rear view cameras.

The robot manipulator has 6 degrees of freedom with the ability to rotate in the horizontal plane by 360°. The gripper is equipped with a force sensor that allows the operator to control the compression force of the gripper. The manipulator can move in the vertical plane up by 100° and down by 80° relative to the body. The robot is controlled by cable or radio from the central control panel.

As additional equipment, the MV-4 can be equipped with variable focal length television cameras, a rangefinder, a microphone for transmitting voice commands, and other special devices.

The mobile robotic complex MRK-252 (photo 3) was developed at the Bauman Moscow State Technical University (Russia) and is intended for carrying out explosives operations as part of the relevant units of the FSB and the Ministry of Emergency Situations of Russia.

2. In 1997, the MRK-25 was an experimental complex and did not undergo full-scale testing.

 
Photo 3. Mobile robotic complex MP-25
with installed protection from neutron radiation.

Structurally, the MRK-25 is a tracked vehicle with a variable configuration drive, in the box-shaped body of which the control system units, the on-board part of the communication channel and the battery are located, a manipulator or other technological equipment is mounted on the body of the robot.

The robot is equipped with a television system, a lighting system, an acoustic feedback unit, and a siren. All actuators are electromechanical with DC motors. The robot is controlled from a remote control station consisting of a control panel, two monitors, a communication channel control unit, and a battery, all mounted on a wheeled stand, which ensures high mobility when deploying the complex. Control can be carried out either by cable or by radio. The choice of the communication channel option is made depending on the operational situation and is carried out by connecting (disconnecting) the cable connector and switching the toggle switch on board the robot. To ensure hand control, the control panel is removable.

Multifunctional mobile robot HOBO(photo 4) by Kentree (Ireland) is intended primarily for use in law enforcement units during explosive works and anti-terrorist operations. The robot can be used for firefighting, as well as at nuclear power and chemical industry enterprises for work with radioactive and toxic substances and industrial waste.

Photo 4. Multifunctional mobile robot NOVO

The machine is built on a modular principle, which facilitates its maintenance and reconfiguration. The HOBO transport module has 6 wheels. To improve the machine's adaptation to a complex profile surface, its body is made in the form of sections connected by special hinges that provide the ability to rotate the outer axes relative to the longitudinal axis of the machine body. In this case, all wheels are driving. Power supply from batteries (continuous operation time of at least 2 hours); operation from an AC network of 110 or 220 V is possible. Unlike MV-4 and MRK-25, the HOBO manipulator module has a hydraulic drive, which provides a maximum lifting capacity of up to 75 kg.

Small-sized mobile robot RASCAL(Photo 5) from the same company is used together with heavier machines in explosive engineering units. The robot's low weight (only 33 kg) and small dimensions make it possible to carry it by one person.

 
Photo 5. Small-sized mobile robot RASCAL.
The RASCAL robot's camera was used to transmit information
about the progress of work to the command post monitor.

The robot is controlled by radio at a distance of up to 250 m, however, if it is necessary to operate in radio silence mode, it can be controlled by cable. The MRK RASCAL control panel can be used to control other KENTREE robots, which is very convenient when it is necessary to use robots of different sizes and purposes to perform work.

Technical characteristics of the robots under consideration are given in Table 1

Table 1

Technical characteristics of mobile robots

Organization and planning of work

General management of the operation to eliminate the consequences of the accident was carried out by the commission of the Ministry of Atomic Energy of Russia.

All liquidation work was carried out by a joint task force consisting of specialists from the VNIIEF center, the Ministry of Emergency Situations (MES) of Russia, Bauman Moscow State Technical University and the Federal Security Service (FSB) of Russia.

The VNIIEF plant, which worked around the clock, provided urgent production of devices, tools and attachments for mobile robots.

Before performing work with the help of robots, the following was carried out:

1. Study of the work site using diagrams, photographs, video footage3 and with the help of a periscope installed in the control room;
2. Installation of additional television cameras to facilitate operator observation of the operations being performed;
3. Preparation of a room similar in the arrangement of equipment to a box with a critical stand (analog room) for preliminary training of operators and practicing individual operations;
4. Protection of mobile robots from neutron radiation;
5. Practice of robot movement tactics.

After the accident, a video was filmed through the doorway by an American-made color television camera on a CCD matrix. The television camera worked for only 15 minutes and failed due to neutron radiation.

Calculations performed by VNIIEF specialists showed that in the box with the emergency critical assembly, the television camera and robot control system units would “last” no more than 4 minutes. This time was clearly not enough to carry out all the necessary work.

To protect the electronic units and television cameras, appropriate materials were selected: paraffin, polyethylene, polypropylene (cadmium-plated and borated).

The control system units located in the housing were filled with polyethylene and polypropylene granules. Additionally, plates made of the same materials were attached to the housing.

The TV cameras were filled with molten paraffin with polyethylene cadmium crumbs. After the paraffin hardened, the TV cameras were in a cocoon with a large visor over the lens (photo 6). The experience of using protection was successful: the control system worked without failures, and although a small number of small white dots appeared on the monitor screen 8 minutes after the start of operation of the MRK-25 TV cameras in the assembly room, their number and brightness did not increase throughout the execution of all operations.

 
Photo 6. Protection of the MRK-25 TV camera

The technology for installing protective materials on a mobile robot was tested on the MRK-25, and then, using the mastered technique, protective materials were secured on the MV-4 and HOBO.

The Chernobyl experience showed that reliable control of a mobile robot requires continuous visual information about the work area from several angles. For continuous monitoring of the location of a moving robot in the room and the convenience of the operator, only television cameras installed on the robot itself are not enough. Therefore, a system for placing additional remote television cameras was thought out and implemented. Unfortunately, there were no radiation-resistant television cameras that could be installed in the box, and the regular television camera that filmed the room through the doorway failed. Additional television cameras included in the HOBO, RASCAL and MV-4 systems were used. One of the television cameras was attached to a periscope, through which everything that was happening in the box could be observed from the control room, where the operator's post was located. The second, installed on a rotating device at the entrance to the box in such a way that it could not be directly exposed to neutron radiation, was located in the room next to the laboratory. It allowed one to see through the doorway the part of the room where the containers with radioactive materials were located. Specially assigned employees controlled the rotating television camera and periscope at the command of the operator of the working robot or the work supervisor. The camera of the RASCAL robot, placed behind the operator of the working robot and aimed at its monitors, transmitted information about the progress of the work from the control room to the monitor installed in the minibus of the mobile explosive laboratory, in which the operation managers and employees not directly involved in the work were located.

The robot's movement tactics in the box were determined, firstly, by the need to reduce the time the machine spent in the neutron flux zone and, secondly, by the requirement not to expose the neutron flux to weakly protected sides and camera lenses.

To meet the first condition:

— the manipulator was turned to the working position in the biological protection zone;
— the cameras were immediately installed in the position necessary for the operation: on the gripper and the support-slewing device — in the direction of movement, the overview camera — back, which saved time on aiming the cameras, only a small turn was required;
— all robot movements were performed at the maximum possible speed.

To meet the second condition, the robot body was installed with its nose towards the radiation source, and the TV cameras were not turned at angles at which the radiation would directly affect the lens. The movement was carried out mainly forward and backward, without turns of 1800 and 3600, the installation locations of containers and other devices were determined in advance, and the robot's movement was practiced until it became automatic, while cables and hoses were laid according to a predetermined pattern.

After assessing the situation, a plan for eliminating the consequences of the accident was adopted, which included three stages:

• evacuation of containers with radioactive materials;
• hanging a vacuum gripper on the hook of a remotely controlled electric crane;
• removing the upper part of the critical assembly using a vacuum gripper and stopping the spontaneous chain reaction.

For each stage of the work, the following were defined: a working robot (performing the main operations), a backup robot (ensuring the evacuation of the working robot in the event of its failure due to radiation and continuing to perform unfinished work) and a backup robot. The purpose of the robots was determined taking into account their technical capabilities and the results of preliminary testing of operations in an analogous room.

At the first stage, the evacuation of five containers from the box was to be carried out by MRK-25. MV-4 backed up MRK-25, and HOBO was in reserve.

At the second stage, the vacuum gripper unit with a hose was hung on the hook of the electric crane using the MV-4. The MRK-25 insured the MV-4. The HOBO was in reserve.

Evacuation of containers using the MRK-25

There were five containers with radioactive materials in the box, each weighing about 40 kg.

The containers were installed at the left wall from the entrance to the box, at a distance of about 6 meters from the entrance. Only the lids of two containers were visible through the periscope due to the limited angle of view. This somewhat complicated the development of the route of movement, since the exact location of the containers was unknown.

The nominal lifting capacity of the MRK-25 manipulator was only 15 kg. Nevertheless, it was decided to use the MRK-25 for evacuating containers, since, firstly, the maximum (on a short arm) lifting capacity of the manipulator is almost three times higher, and secondly, the manipulator drives had a sufficient power reserve.

For ease of handling containers, the manipulator's gripping device was equipped with additional jaws with curved ends, overlapping each other like a beak. This design allowed, in the event of insufficient gripping force, and, as a result, the handle slipping out when lifting the container, to hang the latter on additional jaws like on hooks. If it was impossible to lift the container with the manipulator, additional jaws provided the ability to evacuate the container by dragging it behind the robot.

Additionally, a hook on a short leash was attached to the front eyebolts on the MRK-25 body. It was assumed that, if necessary, this hook could be hooked onto the container handle by the manipulator, and then the container could be pulled out by dragging it.

Before starting work, the analogous room was used to practice the MRK-25 movement options to the containers and their evacuation (see Table 2).

Table 2

Container evacuation options

Careful preparation for the operation yielded results: the evacuation of the containers was carried out using the first method in just 12 minutes. The total time of the work, taking into account the preparation of the robot for movement and opening (closing) the doors, was 23 minutes.

Hanging a vacuum gripper using MV-4

To transfer the critical assembly to a subcritical state, it was planned to remove the upper copper hemisphere of the assembly using a vacuum gripper.

Structurally, the vacuum gripper was an aluminum hemisphere with a fitting at the top, to which a hose was attached using a clamp. The other end of the hose, with a total length of about 35 meters, was connected to the compressor.

It was supposed to put the hemisphere of the vacuum gripper on the upper hemisphere of the critical assembly using a remotely controlled electric crane, fasten the hemispheres by creating a vacuum between them with a compressor, and then, by lifting the vacuum gripper with a crane, remove the copper hemisphere from the assembly and thus stop the spontaneous chain reaction.

The MV-4 was chosen to hang the vacuum gripper on the crane hook clamp.

The operation was practiced in a similar room. The first experience showed that everything is not as simple as it seems. The work was hindered by the slings hung on the crane, in addition, the crane hook rotated around its axis even with a slight touch of the loops of the gripping device. After 4 hours of training, the operation was performed in the following order:

— robot placement in the initial position and securing the vacuum gripper in the manipulator;
— opening the “plug” and the gate;
— robot approaching the hook of the electric crane;
— hooking the vacuum gripper onto the hook by the MV-4 manipulator;
— lifting the hook with the vacuum gripper;
— robot return to the initial position and closing the doors.

To test the operability of the vacuum gripper, a 50 kg hemisphere mock-up was used. Reliable grip of the hemisphere mock-up and confident performance of lifting, lowering and movement in the horizontal plane confirmed the operability of the structure.

During the operation, everything initially went according to plan — MV-4 safely entered the box and hung the vacuum gripper on the hook. Trouble began when, having completed its task, the robot moved in reverse towards the exit of the box. While moving, its own cable and hose of the vacuum gripper got under the track. The track rewound the cable and hose under itself and pulled them onto the body. The robot stopped and could not move further, there were 1.5 meters left to the entrance.

The work had to be continued, so they decided to leave MV-4 in the box. The gate and plug were closed, pressing down the MV-4 control cable.

The vacuum gripper was aimed at the assembly slowly, stopping first at 10 and then at 5 cm, measuring the change in neutron flux. After gripping the upper part of the assembly, the hose broke off during an attempt to lift it, leaving the hemisphere of the gripper on the assembly. There was a sharp increase in the neutron flux, which after some time stabilized at a slightly higher level.

When analyzing the situation, it was suggested (which was then experimentally confirmed) that under the influence of high temperature and neutron radiation, the rubber hose was deformed, lost its elasticity and flexibility — it became loose. When pulling the hook, the hose jumped out of the place of attachment to the vacuum gripper.

Change in the work plan

The failure of the MV-4 robot at the second stage and an unsuccessful attempt to remove the critical assembly hemisphere using a vacuum gripper led to a change in the original plan:

• First, in order to continue work on transferring the assembly to a subcritical state, it was necessary to remove the MV-4 mobile robot, which was stuck in front of the entrance to the room and interfering with the work.
• secondly, it was necessary to consider possible options for stopping the spontaneous assembly reaction, and practice their use using the remaining MRK-25 and NOVO robots on a mock-up of the critical stand in an analogous room.

Evacuation of the MV-4 mobile robot using the MRK-25

The complexity of the problem was that the MV-4 could only be evacuated in such a way that the pulling force in the direction coincided with the longitudinal axis of its body and practically did not deviate from the axis of the doorway of the box. Otherwise, the mobile robot could turn around during evacuation and completely block the passage.

To ensure the necessary direction, the “plug” was pushed to its extreme position and a block was welded to its inner surface along the axis of the “plug”, through which a cable with a carabiner attached to the winch was thrown.

The plan was to open the damper, use the MRK-25 to insert the carabiner into the MV-4 evacuation ring, and, after returning the MRK-25 to its original position, use the winch to reel in the cable and pull the MV-4 out of the room along the path of the «plug». As soon as the damper closed, the rescuers were to manually pull the cable out of the block on the «plug», secure it to the winch and pull the MV-4 to the side, releasing the «plug» guides.

The first part of the operation was successful. The cable was passed between the MRK-25 tracks and laid on the floor in a long snake to the block on the plug, a carabiner was installed in the gripping device of the manipulator. When the damper was opened, the MRK-25 moved toward the MV-4, hooked the carabiner onto the evacuation ring and returned to its original position. At the command of the work manager, the winch was turned on and the MV-4 was carefully pulled out of the box.

The second part of the operation could not be carried out according to plan? The damper did not close due to a failure of the movement drive. Powerful neutron radiation through the open opening prevented rescuers from approaching the robot.

The MRK-25 came to the rescue again. The mobile robot hooked the carabiner in the designated place and the rescuers pulled out MV-4, after which the “plug was closed.”

In total, about 14 minutes were spent on this operation using the MRK-25.

Analysis of options for transferring the critical assembly to a subcritical state

The method for stopping the spontaneous chain reaction was selected from several options. The specialists considered:

— chemical dissolution of the copper shell;
— melting the assembly shell by slowly feeding an additional steel screen;
— shooting the assembly with special cartridges or a cumulative charge
— drilling the assembly shell with a drill clamped in the HOBO gripper;
— drilling the assembly shell with a drill clamped in the grip of the HOBO manipulator;
— destruction of the shell with a cumulative cord;
— removal of the upper part of the assembly with a modernized vacuum gripper and some others. For a number of options, special devices were made and methods for their use were worked out.

Method of melting the assembly shell was based on calculations of the mass and shape of an additional steel screen, with the help of which it would be possible to raise the temperature of the assembly and melt the copper shells. It was assumed that the chain reaction would stop when the molten copper drained and the volume of the metal decreased. The danger of using this method was that it was difficult to smoothly feed the screen with an electric crane. The temperature could rise above the calculated value and then the uranium would start to melt and its aerosols could appear. Nevertheless, it was believed that the reaction would be controllable. A screen was made, which could be hung on the hook of the crane using a robot.

Method of shooting the assemblyconsisted of tearing out metal from the upper and lower hemispheres with heavy bullets and thereby reducing the critical mass. For this purpose, it was proposed to use a HOBO adapted for firing from a gun.

Method of drilling assembly shellsprovided for a reduction in the mass of copper shells by drilling out the material. Two drilling options were considered: a drill in a chuck clamped by the HOBO manipulator grip and a drill clamped by the HOBO manipulator grip. Experiments on a mock-up assembly showed that the drilling method was inefficient, and that the addition of a significant mass to the drill could cause an unpredictable effect.

Method of shell destruction with a cumulative cordwas considered as one of the main ones due to its effectiveness — after the detonation of the cumulative cord embedded in heat-resistant material according to a certain pattern, the upper copper shell was divided into four segments and fell out of the assembly clip (photo. 7). Two options for installing the charge on the assembly were considered: the first — with the help of HOBO, the second — with the help of a crane, on the hook of which the explosive device was installed by a robot.

Photo 7. Destruction of the assembly shell with a cumulative cord

At the same time, the option of removing the upper part of the assembly with a modernized vacuum gripper was being worked out.Watching a video of the first attempt to remove the assembly with a vacuum gripper showed that the assembly had slightly turned and lifted above the bed. Therefore, it was decided to try to remove the assembly again using a vacuum gripper of a modified design — to avoid destruction of the rubber hose from thermal and neutron radiation, a meter-long duralumin tube was placed between the metal hemisphere of the gripper and the hose.

In addition to methods of influencing the assembly directly, options were developed for removing the steel diaphragm from the stand, which made it difficult to install a vacuum gripper on the assembly. It was supposed to remove the diaphragm with a powerful magnet (photo 8) using HOBO or with a crane, on the hook of which the magnet would be installed by a robot.

 
Photo 8. Magnetic device for removing the diaphragm

Removing the assembly using a modernized vacuum gripper

When practicing the operation of hanging the modernized vacuum gripper on the hook of an electric crane using the MRK-25, we encountered two problems:

• the slings and the suspension device of the first vacuum gripper with hoses hanging down on both sides remained on the hook;
• it was difficult to manipulate the new gripper (the total length of which was almost 1.5 meters), constantly clinging to all protruding parts of the robot — the stand of the overview TV camera, cables, tracks, and so on.

To solve these problems, firstly, a light long bed made of thin steel was installed on the MRK-25 body (photo 9), along which the grip tube slid like a guide when hung, and, secondly, a carabiner was attached to the modernized grip instead of a suspension device on a short cable, designed to hook onto slings hanging in the form of loops from the hook clamp of the crane.

 
Photo 9. Practicing the operation of hanging a modernized vacuum gripper on the hook of an electric crane using the MRK-25 (a light long tray made of thin steel is installed on the robot body)

In addition, the MRK-25 was equipped with a system for its evacuation in case of failure.

After preparation for the work, the MRK-25 with a carabiner in the manipulator grip, with a vacuum grip fixed to the cradle and a correctly laid hose, was brought to its original position near the entrance to the box. As soon as the «plug» was removed, the robot entered the room, headed for the hook clip, lowered in a given place to the required height, and hooked the carabiner to the loop of the sling. Then the crane lifted the vacuum grip and brought it to the crit stand.

Before the operation, a number of auxiliary works were performed: installation of a metal table near the stand using the MRK-25 to place the removed assembly hemisphere on it; delivery of a magnetic gripper to the stand by a robot to remove (if necessary) the diaphragm; equipping the MRK-25 with fire nozzles and fire hoses to extinguish a possible fire (photo 10).

 
Photo 10. Equipping the MRK-25 with fire nozzles to extinguish a possible fire

When everything was done, the stage of work of the crane with a vacuum gripper began. The vacuum gripper “stuck” to the upper part of the assembly, lifted it above the stand, moved it and placed it on the table. The assembly was transferred to a subcritical state.

The entire operation lasted 50 minutes.

At 1:15 am on June 24, 1997, the work to eliminate the consequences of the accident was completed.

The elimination of the radiation accident in a short time and without harm to the health of rescuers became possible thanks to the use of remotely controlled mobile complexes (robots).

The experience gained in using robots in the situation under consideration allowed us to define some basic principles of the technology of their use in eliminating local radiation accidents. In particular:

• the use of robots should be preceded by a thorough study of the accident site and approaches to it using all available sources and means of obtaining information;
• during the work it is necessary to conduct video recording, which will allow obtaining material for analysis and evaluation of the technological operations and work methods performed;
• when using robots, their additional adaptation to external conditions is a mandatory element of preparation;
• before carrying out work, measures must be taken to evacuate the robot in the event of its failure;
• robots must be provided with a certain level of autonomy. This is ensured by including in the robotic complex a vehicle for prompt delivery of the complex to the work site, a mobile power plant, communications equipment, a life support system for the crew, etc.

Since the use of robots is accompanied by a large volume of auxiliary work, it is necessary to have a special repair shop in the robotic complex.

The success of the operation depends not least on the skill and experience of the operators. Each operation performed by the robot must be practiced in conditions as close to real as possible. Operations requiring the interaction of several remotely controlled machines must be practiced especially carefully.

In addition, it should be noted that in the expeditions participating in the elimination of accidents with the help of robots, it is desirable to include designers-developers or test operators. This allows them, knowing the design features of robots, to more fully use the potential inherent in them to perform specific tasks and accumulate experience for further modernization or creation of new machines.