A New Approach for Terrain Description in Mobile Robots for Humanitarian Demining Missions

1. IARP/EURON Workshop on Robotics for Risky Interventions and Environmental Surveillance RISE 2008 A New Approach for Terrain Description in Mobile Robots for Humanitarian Demining Missions C. Salinas, M. A. Armada*, P. Gonzalez de Santos Automatic Control Department Instituto de Automatica Industrial – CSIC Arganda del Rey, Madrid, Spain * IARP Spain Representative Benicasim, Spain 7-9 January 2008

2. Summary of presentation Humanitarian demining missions requires the use of robust systems such as efficient mobile robots and improved sensors. This application domain involves performing tasks in non structured scenarios and dynamically changing environments. This paper is focused on a new approach based on omni-directional vision systems for terrain description. Computer vision systems are widely used in similar applications. However, conventional video cameras have limited fields of view which make them restricted for several applications in robotics.

3. Summary of presentation For example, mobile robots often require a full 360º view of their environment, in order to perform navigational tasks such localizing within the environment, identifying landmarks and determining free paths in which to move. The omnidirectional sensors allows the capture of much wider field of view; they can provide panoramic images of 360º around the robot. Certain techniques have been developed for acquiring panoramic images. This work outlines the fundamental principles of three of these techniques, and shows a direct application of a low-cost catadioptric omnidirectional vision sensor on-board a six-legged robot intended for antipersonnel landmine localization.

4. Introduction AroundNNN millionlandmines have been deployed over the last two decades, many other UXO are still in place, and, at the present stage, demining will take several more decades, even if no more mines were deployed in the future. Full clearance of antipersonnel-landmine infested fields is at present a serious political, economic, environmental and humanitarian problem. Rouhi A.M., (1997), Land Mines: Horrors begging for solutions, Chemical & Engineering News, Vol. 75, No. 10, pp. 14-22. Politicians have shown a real interest in solving this problem, and solutions are being studied in different engineering fields.

5. Robotics for HUDEM This is a very relevant socio-economic problem, that leads to consider: The role of ROBOTICS in Humanitarian Demining A high mine-clearance rate can only be accomplished by using new technologies such as improved sensors, efficient manipulators and mobile robots.

6. Robotics for HUDEM The best solution, albeit perhaps not the quickest, would be to apply a fully automatic system to solve this problem. However, any such solution still appears to remain a long way from succeeding. First of all, efficient sensors, detectors and positioning systems would be needed to detect, locate and, if possible, identify different mines. Then, adequate vehicles would have to be provided to carry the sensors over the infested fields. This paper presents some basic ideas on the configuration, sensing and controller of a mobile system for detecting and locating antipersonnel landmines in an efficient and effective way. The whole system has been configuredto work in a semi-autonomous mode with a view also to robot mobility and energy efficiency.

7. Robotics for HUDEM • There are many potential vehicles that can carry sensors • over infested fields; wheeled, tracked and even legged • vehicles can accomplish demining tasks effectively. • Wheeled robots are the simplest and cheapest, and • tracked robots are very good for moving over almost all • kinds of terrain, but legged robots also exhibit interesting • potential advantages in demining [*]. • [*] Gonzalez de Santos, P., Garcia, E., Cobano, J.A. and Guardabrazo, T., “Using Walking Robots for Humanitarian De-mining Tasks”, Proceedings of the 35th International Symposium on Robotics, Paris, France, March 23-26, 2004. • [*] Gonzalez de Santos, P., Garcia, E., Estremera. J. and Armada, M.A., • (2005) "DYLEMA: Using Walking Robots for Landmine Detection • and Location", International Journal of Systems Science, Vol. 36, No. • 9, pp. 545-558.

8. Robotics for HUDEM The idea of using legged mechanisms for humanitarian demining has been under development for at least the last seven years, and some prototypes have been already tested. TITAN VIII, a four-legged robot developed for general purposes at the Tokyo Institute of Technology, Japan [*], was one of the first walking robots adapted for demining tasks. [*] Hirose, S. and Kato, K., “Quadruped walking robot to perform mine detection and removal task”, Proceedings of the 1st International Conference on Climbing and Walking Robots, pp. 261-266, Brussels, Belgium, 1998.

9. Robotics for HUDEM AMRU-2, an electropneumatic hexapod developed by the Free University of Brussels and the Royal Military Academy, Belgium [*] is one relevant example of walking robots used as test-beds for humanitarian demining tasks. [*] Baudoin, Y. Acheroy, M., Piette, M., and Salmon, J.P., “Humanitarian demining and robotics”, Mine Action Information Center Journal. Vol. 3, No. 2, 1999. AMRU-1 Sliding Robot, equipped with a 3D scanner (RMA) AMRU-2: feasability-study on multilegged robots at RMA and ULB

10. Robotics for HUDEM COMET-1 was perhaps the first legged robot developed on purpose for demining tasks [*]. [*] Nonami, K., Huang, Q.J., Komizo, D., Shimoi, N. and Uchida, H., “Humanitarian mine detection six-legged walking robot”, Proceedings of the 3rd International Conference on Climbing and Walking Robots, pp. 861-868, Madrid, Spain, 2000.

11. Robotics for HUDEM These robots are based on insect configurations, but there are also different legged robot configurations, such as sliding- frame systems, being tested as humanitarian demining robots [*]. [*] Habumuremyi, J.C., “Rational designing of an electropneumatic robot for mine detection”, Proceedings of the 1st International Conference on Climbing and Walking Robots, pp. 267-273, Brussels, Belgium, 1998. To sum up, there is a great amount of activity in developing walking robots for this specific application Field.

12. Robotics for HUDEM The IAI-CSIC holds experience in the design, development and control of walking robots, gait generation, terrain adaptation, robot teleoperation, collaborative control and other fields. All these technologies are mature enough to be merged in order to produce efficient robotic systems. This paper, thus, presents the SILO6 walking robot’s ongoing results under development at IAI-CSIC, which has been configured on purpose for demining tasks. P. Gonzalez, M. Armada, J. Estremera, M.A. Jiménez: “Walking machines for humanitarian demining”, European Journal of Mechanical and Environmental Engineering, vol. 44, nº 2, 1999, pp. 91-95, Belgian Society of Mechanical and Environmental Engineering RIMHO II

13. Radio Ethernet aerial DGPS antenna Operator station Walking robot Scanner (manipulator) Sensor head Dylema Project • The DYLEMA (DYLEMA project funded by CICYT-Spain) whole system has been configured with the aim of putting together different subsystems. These subsystems are: • Sensor head. • Scanning manipulator. • Locator. • Mobile robot.

14. Attachment to robot’s body Joint3 Joints 4 and 5 Joint 2 Joint 1 Infra-red sensors Sensor head Dylema Project Sensor head. The sensor head is configured to detect potential alarms but also to allow the controller to maintain the sensor head at a given height over the ground using simple range sensors. It is based in a commercial metal detector. Scanning manipulator. The sensor head is basically a local sensor and so the system needs to use a manipulator to move the sensor head and to adapt it to terrain irregularities.

15. Dylema Project Locator. After detecting a suspect object, the system has to mark the object’s exact location in a database for subsequent analysis and deactivation. We considered that an accuracy of about 2 centimetres is adequate for locating landmines. Mobile robot. A mobile platform to carry the different subsystems across infected fields is of vital importance for thorough demining. In our case, the platform is based on a legged robot.

16. Magnetic compass Manipulator GPS antenna Sensor head Mobile platform Dylema Project DYLEMA implementation

17. Aerial Radio Ethernet Host Computer DGPS antenna RS232 Analogue to Digital Converter Communications Walking robot Parameters Trajectories Manipulator Parameters Trajectories PC bus Gait Generation and Stability Monitor DGPS Metal detector Inclinometers Driver 3-Axis Controller (Axes 1-3) D ... D 3-Axis Controller (Axes 21-23) D Motion Processes Terrain Adaptation Altitude Control Attitude Control D D DC Motor + Encoder Manipulator Kinematics Trajectory Generation (KIN library) Trajectory Control Robot Kinematics (WALK library) Axis Control (LINK library) Leg Kinematics (KIN library) Hardware Interface (ROB and LM libraries) Leg Control (LEG library) Axis Control (LINK library) Hardware Interface (ROB and LM libraries) Equipment and Sensor Data Acquisition Dylema Project

18. Dylema Project

19. (a) (b) (c) Omni-directional vision Systems There are several techniques to obtain omni-directional images, and according to the features required for mobile robot system, such us the case of Silo6 six-legged robot, a catadioptric hyperbolic vision system is adequate and will benefit the tasks performed by such mobile robot. Omni-directional vision sensors: (a) Dioptric, (b) Polidioptric and (c) Catadioptric

20. Image plane Image plane (a) (b) (c) Catadioptric omnidirectional vision systems Projection of (a) spherical, (b) hyperbolic and (c) parabolic mirror and their corresponding reflected rays. Hyperbolic projection

21. Catadioptric omnidirectional vision systems Several simulations where done; as a result a low-cost catadioptric system was developed (a) Representation of the catadioptric system and the 3 dimensional points attached in the world frame, (b) the top view of the system (c) the position of these points in a 2D acquired image.

22. Experimentation and results A standard camera mounted on a mobile robot and aligned with its forward direction of motion is sufficient for vehicles that can move in a constrained set of directions (e.g., a car), where the primary vision tasks typically consist of obstacle detection and avoidance. Nevertheless, a camera with a limited field of view is not ideally suited to robots with omni-directional motion capability, and intended for navigation in unstructured environments, and when other vision tasks must be performed such as building a local representation or localizing within its environment, detection or scanning rough terrains. For these tasks it would be much better to use a vision sensor that could provide panoramic images, i.e., 360◦ images around the robot: these are also referred to as omni-directional images.

23. Experimentation and results Omni-directional image acquired by our system and its corresponding panoramic image. It is easily to detect that both images are distorting from our point of view; however for omni-directional theory it is straightforward to calculate the deformation angle and to introduce it into the system. (a) Omni-directional and (b) panoramic images

24. Experimentation and results The prototype was tested on-board of six-legged robot Silo6, a sequence acquired by the system is presented in Figure 8, where corresponding entities do not vanish due to limited field of view (enclosed by green). The displacements of such entities considerably vary with different kind of motion. With this system it is possible to detect all objects around the robot only acquiring a single image per time. The terrain area around the robot can be easily separated form the peripheral area, such as trees, bushes stones, and moving objects

25. Experimentation and results -

26. Experimentation and results The system has the capability to detect several obstacles, stationary or moving objects. It is possible to apply image processing techniques as optical flow for segmenting these objects and avoiding them. Also it is able tracking the trajectory of the manipulator and using the vision to correct its movement, especially in situation where two objects are close and the distance between them is smaller than the sensor head diameter.

27. Experimentation and results Other important issue is the capability to observe with a single image the environment and the robot itself. The area covered by the image includes the space between the scanning system manipulator and the robot. This system also provides the feature to observe the 360 °view for teleoperated applications, saving the security of the operator and the robot itself.

28. Conclusions • The removal of antipersonnel landmine is a global issue. In this work we presented the possibility of designing a low-cost system based on omni-directional sensors, to improve the efficiency of humanitarian de-mining tasks. Because these tasks require devices that can automate the location of unexploded ordnance, it is proposed that they can be accomplished by using robotic systems capable of carrying scanning sensors over infested fields • The ongoing prototype has very useful features, because they can benefit several tasks involved in humanitarian demining missions. The robotic system can be able to respond in advance, i.e. obstacle situated in a distance larger than the manipulator range. The system will be capable to make online corrections of its trajectory. Other important point is the benefit of the efficiency of a complete coverage of a minefield wider area, since the system has a previous knowledge of the terrain and its obstacles. • The next step in this research will be the test of the catadioptric vision system in specific online tasks on hexapod mobile platform and to study particular image processing algorithms for panoramic images to terrain description (HUDEM 2008 CAIRO, EGYPT).

29. AcknowledgementsDYLEMA project is funded by the Spanish Ministry of Education and Science through grant DPI2004-05824This work has been supported in part by Consejería de Educación of Comunidad de Madrid under grant RoboCity2030 S-0505/DPI/0176.C. Salinas acknowledges the support received from Comunidad de Madrid Fellowship in Research Personnel Training (FPI)