Abstract
The Mine Detection Robot supports the mine removal work in countries where mines are buried, such as Afghanistan. The development started from September, 2003. Considering running on rough terrains, the robot has four crawlers, and hydraulic motors in front and rear were serially connected by piping so that they could rotate synchronously. Two work arms were mounted on the robot, one was a horizontal multi-joint SCARA type with motorized 2-link arm, while the other was a vertical multi-joint manipulator with 6 degrees of freedom. Also, domestic evaluation tests were carried out from February to March, 2005, followed by overseas validation tests in Croatia from February to March, 2006. These tests were conducted with a mine detecting senor mounted on the Robot, and the detection performance was evaluated by its mine detection rate.
Introduction
Currently, there reportedly are 50 ˜ 100 million landmines buried all over the world. The detection and removal of these landmines have still been in progress by a manual method proposed several decades ago and practiced since then. Relying on only such manual work, however, it would require hundreds of years to dispose all these mines completely. Under such circumstances, the development of landmine detection and removal system in a short period has become an urgent and much called-for business.
With a view to support removal work of landmines in mine-plagued countries such as Afghanistan, the project of “Research and Development for Supporting Humanitarian Demining of Anti-personnel Mines” funded by Japan Science and Technology Agency (JST) started.
This research and development program aims to develop a mine-detecting robot as part of the landmine detection and removal systems in the JST project (Ishikawa, J., Kiyota, M., and Furuta, K., 2005).
To be more specific, a ground penetrating radar and a metal detector for detection, a manipulator fitted with tools such as air hummer and hand for mine confirmation and an unmanned robot with these devices mounted which is capable to run on rough terrains.
The areas where landmines are buried used to be in the war zones where infrastructure such as roads and bridges has been destroyed, thus making it difficult to transport large mine-handling vehicles built on the basis of construction machine to such zones. Therefore, in this research, we developed a landmine detection robot with the following basic concepts; 1. It has a capacity of running on rough terrains. 2. Mine detector and confirmation device can be mounted on a single robot. 3. The robot is mountable on a two-ton vehicle and the vehicle body can be disassembled into modules for transportation by airplane or for maintenance service. 4. It is weather resistant for assured operation under such adverse climatic conditions as those in Afghanistan, and is capable of climbing slopes in mountainous terrains. 5. The vehicle body is structured resistant to explosion of an antipersonnel mine in a possible mishap to allow its operators safe return from a minefield.
The domestic evaluation tests were conducted from February to March, 2005, followed by the overseas evaluation tests in Croatia through February to March, 2006. These tests were undertaken by mounting a mine detector sensor on the robot for detection and evaluated by its detection rate.
This paper describes the mine detection robot, the sensor arm, the manipulator and the support vehicle which we developed, and the domestic evaluation tests and overseas validation tests in Croatia.
Overview
Appearance
Two work arms were mounted on the robot, one was a horizontal multi-joint SCARA type with motorized 2-link arm, while the other was a vertical multi-joint manipulator with 6 degrees of freedom. At the end of the arm of the former was mounted a sensor for mine detection and at the end of the arm of the latter was mounted tools which function to confirm the existence at a location where any slightest sign of a landmine has been detected by the armed sensor. All the work was manipulated by remote control.
Table 1 shows the specification of the robot, and Fig. 1 shows a picture of the robot mounted with the mine detection sensor and the manipulator.
Specification
Specification
Appearance of the robot
The system has two arms controlled by a robot controller.
Horizontal multi-joint SCARA type sensor arm Vertical multi-joint manipulator
Two units of PCs were used for the robot control and mine sensing. Two joysticks and one I/O box were connected to the PC for sending operational instruction to the robot. Fig. 2 shows the system schematic.
System configuration
Vehicle body
As shown in Fig. 3, the body had a simple ladder structure consisting of two square pipes as its main frame, and square pipes and channel material as cross members, which requires least number of reinforcements. Axles were penetrated through the main frame, and four independent crawlers were mounted, one for each axle on both sides of front and rear. A hydraulic motor was fitted to each axle via coupling. The weight and size of the robot were limited to within the load capacity and the cargo bed with 3800mm in length and 1900mm in width of a two-ton truck.
Running system
As shown in Fig. 3, the drive system was of hydrostatic transmission (HST) type comprising a diesel engine and hydraulic devices. The engine was made appropriate for use at places in high altitudes of 2000m in Afghanistan with extra power for spin turns.
The hydraulic circuit system had two independent circuits, each with a hydraulic pump for the crawlers, one pump for the front and rear crawlers on the left side and the other for those on the right. A proportional magnetic valve was installed to control the swash plate for flow regulation in the hydraulics pump, which in turn controls the rotation speeds of the crawlers for steering of the vehicle.
An oilless bush which is robust to impact was fitted in the rotating portion of the axle with oil seals fitted on both sides to keep off miniscule dust.
The crawlers were made changeable to tires on the wheels by means of bolts for removal and installation in the same way as changing normal tires to studded ones on a car. This arrangement was devised since tires give higher mobility on relatively flat rough terrains.
Dust prevention and cooling system
The entire vehicle body including the under floor was tightly sealed by a body cover and the doors when the robot was not in operation. While the robot was in operation, the doors were opened for radiator cooling, ventilation and exhaust ventilation.
Taking outdoor temperatures (− 20 °C to 50 °C) in Afghanistan into consideration, a large-size cooling device was equipped for cooling the equipment including the control system. In order to secure its cooling capability, a thermal insulation bulkhead was provided around the engine to shut off the engine's radiation heat.
Control system
The control system consisted of a controller for oil hydraulics, a proportional solenoid valve driver, a remote control device, an image transmission device, a manipulator control device and a controller device of the mine sensor.
Running on rough terrain
Considering running on rough terrains, as shown in Fig. 3, the hydraulic motors in front and rear were serially connected by piping so that they could rotate synchronously. Pressure in the hydraulic pump was distributed to the serially connected hydraulic motors according to each crawler's load. The drive method normally used has one motor with a chain and a sprocket to synchronize two crawlers. However, in order to prevent sand dust from jamming onto the chain, the hydraulic motors were serially connected. In addition, as shown in Fig. 4, the crawlers were designed to swing up to ±25 degrees around their axle, which produced less slip of the crawlers on roads, making it easy to run on rough terrains and climb slopes. The crawlers were selected by weight of the vehicle and power of traction.
Crawler and ground
Sensor arm
The multi-joint SCARA type arm was adopted in order to secure a wide movement range and accurate positioning in horizontal direction. As for speed reduction, a planocentric type was adopted, but not harmonic drive type, considering the required resistance to vibration. Since the extent of waterproofness of the sensor arm body itself was limited to IP30, a jacket was provided to cover the entire arm for water- and dust tightness. In order to maintain a constant orientation of the mine sensor, a timing belt was used so that the joint portion of the sensor arm could rotate in a direction counter to the rotating direction of the arm. The purpose of using the timing belt was to reduce the weight of the arm's end, although a servo motor is generally used for such reverse rotation.
Specification of horizontal multi-joint SCARA type sensor arm
Specification of horizontal multi-joint SCARA type sensor arm
Specification of vertical multi-joint manipulator
For support demining work, it is necessary for manipulator to allow flexible movements and hegh accuracy. So we select the vertical multi-joint manipulator with 6 degrees of freedom. A soil fracturing breaker, a compressed air nozzle, a soil fracturing air hummer and a hand were mounted on one end of the manipulator. Necessary tools were designed to be taken out by rolling the hand by remote control to carry out intended work. And the hand is rolled by remote controll.
Gap control
Fig. 5 shows the schematic for gap control, while Fig. 6 shows the hardware configuration. The height from the ground to the distance sensor is measured by laser sensing. The measured data is used to make the ground penetrating radar or mine detection sensor and the metal detector follow with bumps and pockets on the ground for acquisition of effective mine detection data. When a step or level difference is too much to handle such step at a preset speed, the speed is reduced to give extra time for the arm to travel in latitudinal direction. Moreover, when the sensor cannot negotiate the step within the stroke range in height direction and became deactivated, a recovery or reset button can reactivate to continue the detection. As shown in Fig. 6, a whisker limit switch was fitted on the underside of the mine sensor to prevent the mine sensor from contacting obstacles. If the limit switch touches any obstacle such as ground, the sensor stops functioning temporarily. Signal from the limit switch was input to the PC to judge the existence of an obstacle. In this time, the control don't intend for grass and snow.
Schematic diagram
Hardware configration
The support vehicle was developed for the detection work by the mine detection robot. Fig. 7 shows its appearance. A generator, a control device, and a 20m cable reel were mounted on the support vehicle. The cable connects the equipment in the support vehicle and the mine detection robot to supply electric power and control signal. The cargo room was converted into an operation room with the cable duct, shelf, and air conditioning unit equipped, which allowed operations under temperatures of −20 °C to 50 °C. Moreover, the work stand inside could be used as an operation table in emergency. With all of these, operators could conduct the mine detection and analysis work under comfortable environment staying away from a minefield.
Support vehicle
Test site
The domestic evaluation test was conducted at a vacant lot where the Seto Bridge Exposition was held in Ban-nosu, Sakaide city in Kagawa prefecture. The evaluation test site had nine lanes (from 1st to 9th lane), each consisting of different surfaces, including flat, bumpy, water bearing and sloping ones. Each lane was 1m in width and 15m in length (with some exceptions). Fig. 8 shows the layout of the test site.
Test field layout
The detection test was conducted without being notified in advance where dummy mines were buried. Using the mine detection robot and the mine detection sensor, the detecting work was conducted in a demarcated minefield to identify the locations of buried mines to evaluate the detection performance. Fig. 9 shows the detecting work by an array radar in progress (Arai, I., Tomizawa, Y., and Goto, S., 2006). In the domestic evaluation tests, the frontal detection method was used.
Detectin using array radar(University of Electro-communications, TAU GIKEN)
In the domestic evaluation tests, the mine detection sensor was mounted on the mine detection robot to conduct the evaluation test. Since the mine detection sensor was moved by the sensor arm, the traveling accuracy of the sensor arm significantly influences the detection result. The sensor arm of the robot operable with an accuracy of ±3 mm could position the mine detection sensor correctly, which resulted in obtaining favorable detection results. Furthermore, overseas validation tests were scheduled in Croatia in response to a request from the Croatian government based on the results of the domestic evaluation tests. The items in the following section were listed for improvement prior to the overseas validation test.
Change of detecting area from frontal to lateral method
The sensor arm was fitted with 90 degrees rotated sideway for lateral detection, which keeps the robot from advancing into a minefield.
Extend sensor arm
The length of the sensor arm was extended to cover an area of 1000 mm×1000 mm from 800 mm×800 mm so that the detection zone of 1 m × 1 m could be secured even when the lateral detection was performed.
Support vehicle development
The support vehicle mentioned in Section 7 was developed in order to improve the efficiency of mine detecting work and analysis of the mine sensor data.
Inclination control
The arm was designed to move horizontally by detecting the inclination of the vehicle body to make the arm move in parallel to the ground even when the body was not positioned flat (as in a case of the body tilted when landed on a rock). In addition, ON/OFF of the tilt control was selected by a switch on the control box of the sensor arm and the manipulator. Two tilt sensors are mounted in the vehicle body for measure two axis angle.
Regarding feeding the information from the tilt sensor, the tilt right before the arm became activated was measured by pressing the sensing start button, and then the arm was controlled to become parallel to the ground according to the measured tilt of the body.
The arm was controlled in longitudinal and lateral directions separately as shown in Fig. 10 and Fig. 11.
Front view
Side view
Assuming L for travel distance (mm) and 6 for body inclination (°) with + denoting clockwise direction, when the arm moves L (mm) sideway, the sensor position becomes elevated by H (mm) with respect to the level plane because of the body inclination. The sensor is lowered by H′ (mm) when the arm travels L (mm) for horizontal movement of the sensor. In this way, the sensor position can be kept constant with respect to the ground even when the body becomes inclined.
The mine detection sensor was operated with a preset height value. It was also operated with height data set by manipulating the arm with a joystick on the sensor arm/manipulator operation box. Moreover, it was operated with a height data input from the keyboard of the detection display PC.
Marking of mine position
After detecting a mine, in order to mark its position, functions to guide the arm to the position of which coordinate (x, y) was input by the keyboard of the detection display PC and to turn on and off an solenoid valve at the position. Switching to activate these functions was also made possible by a switch on the sensor arm/manipulator control box.
Automatic lock
The arm was tightly locked by an air pressure actuator to minimize the effect of vibration on the arm and others when the mine detection robot not in action was moved place to place. This locking was made automatically operable by pressing a button.
Overseas validation test
Test site
The overseas validation tests were conducted at a test site designed for antipersonnel mine detector evaluation in Benkovac city, Croatia. At the test site, there were lanes with lm in width and 16m in length as shown in Fig. 12, similar to those used in the domestic evaluation tests. Among them, the 1st, 3rd and 7th lanes were used for the tests. The cables of Fig. 12 between MHV and support vehicle transmit power and signal for control arm and data of sensors. Fig. 13 shows the layout of the test site.
Cover shot of test field
Test field layout
The tests were conducted almost in the same way as the domestic ones, except for a restriction which mandated completion of the detection work for one lane by four o'clock in the afternoon. Because of this confinement, the operability of the whole system including the mine detection robot, the sensor arm and the support vehicle and the detection speed became important e etecting performance of the mine detection sensor.
Two kinds of mine detection sensor, array radar and SAR-GPR (Synthetic Aperture Radar – Ground Penetrating Radar), were also mounted on the robot in the overseas evaluation tests. Fig. 14 shows a detection test scene using the SAR-GPR. The sensor is a very adaptive system and can select operation frequency depending on the soil condition, and high clutter reduction can be achiebved using signal processing. (Sato, M., Xuan, F., Kobayashi, T., and Takahashi, K., 2006). The detection test proceeded as follows; dividing one lane into sixteen areas first, conducting the detection and then shifting the robot by 1m upon completion of the detection of one area before working on next area.
Detection using SAR-GPR (Synthetic Aperture Radar-Ground Penetrating Radar) (Tohoku university)
Fig. 15 shows a area for side detection. Time required to complete detection of one area was about five minutes with the array radar and about ten minutes with the SAR-GPR respectively.
Area of side detection
Some tests were conducted in a climatic condition of − 10°without any operational problem. The robot worked as expected also in rainy weather as shown in Fig. 16 and in snowstorms, which proved the high resistance to adverse climatic conditions and waterproofness of the system.
Detection work in rainy weather
Fig. 17 shows the team members of Clean Enterprise of Fuji Heavy Industries Ltd. who participated in the validation tests in Croatia with a minefield near the test site in the backdrop.
Test team and minefield
The mine sensor arm worked at a constant speed with a weight capacity of 35 kg without any problem despite its extension by 400 mm, meeting the specification required for the mine detection sensor. It contributed to the improvement of detection rate, while enhancing the operability as evidenced by completion of all the detection work as scheduled. The tests demonstrated that the robot would not pose any performance problem for installation of the mine detection sensor.
On the other hand, however, the tests also clearly indicated areas where improvement, modification, specification change and additional features to the robot are required to serve better for the intended purpose. Valuable data and hints were obtained in connection with such issues as control method with the mine detection robot tilted, merits and drawbacks of mounting both of the sensor arm and manipulator, cost, handling the cable between the robot and support vehicle, maintainability, serviceability and easiness of adjustments. These issues became identified as a result of our engineers conducting both the domestic tests and the overseas tests in Croatia by themselves, and in this respect the findings were all the more practical. The Clean Enterprise of Fuji Heavy Industries Ltd. calls such thing “shop floor technology” and places much importance in putting robots to practical use.
In addition, we came to hear and learn first hand from staff of the CROMAC CTDT (Croatia Mine Action Center - Center for Testing, Development and Training) and people there engaged in mine detection and disposal who provided us with information hard to obtain in Japan, their way of thinking and ideas. The number of inventions as of now totals 35 (solely by the Clean Enterprise of Fuji Heavy Industries Ltd.).
We would like to express our deepest gratitude to those people of the CROMAC-CTDT, especially Mr. Tomislav who managed and supervised the tests at the site, people of the JST (Japan Science and Technology Agency), Hisao Saito, manager of Nakajima Co., Ltd. who is a member of the overseas tests, Eihiko Suzuki, senior manager of Yamamoto Rikuso Co., Ltd. who was in charge of driving and operation of the support vehicle at the overseas tests, and all other people who were involved in this development program.