The COMRADE System for Multi-Robot Autonomous Landmine Detection in Post-Conflict Regions Prithviraj Dasgupta1,Jose Baca Garcia1, K. R. Guruprasad2, Angelica Munoz-Melendez3, Janyl Jumadinova4 1Computer Science Department, University of Nebraska, Omaha, USA 2Mechanical Engineering Department, NIT, Karnataka, India 3Computer Science Department, INAOE, Mexico 4Computer Science Department, Allegheny College, PA, USA Abstract 1 Introduction We consider the problem of autonomous landmine Humanitarian demining is a crucial effort for the detection using a team of mobile robots. Previous safety and sustenance of human lives in post-conflict research on robotic landmine detection mostly regions. Unfortunately, recent surveys on landmine employs a single robot equipped with a landmine monitoring report that humanitarian demining ef- detection sensor to detect landmines. We envisage forts are considerably lagging behind anti-personnel that the quality of landmine detection can be signif- landmine planting activities due to several techno- icantly improved if multiple robots are coordinated logical and economic reasons [27]. This results in to detect landmines in a cooperative manner by enormous loss to human lives; e.g., in 2010 alone, incrementally fusing the landmine-related sensor explosions of landmines and similar devices resulted information they collect and to then use that in- in 4, 191 casualties, with civilians accounting for 70% formation to visit locations of potential landmines. of the casualties. One the major technological chal- Towards this objective, we describe a multi-robot lenges in humanitarian demining is to detect land- system called COMRADES to address different mines rapidly and with reasonable accuracy, while aspects of the autonomous landmine detection prob- reducing the number of false positives. We envis- lem including distributed area coverage to detect age that automating landmine detection operations and locate landmines, information aggregation to using multiple, off-the-shelf autonomous robots will fuse the sensor information obtained by different provide a reasonably accurate yet economical solu- robots, and, multi-robot task allocation (MRTA) tion to the problem of detecting landmines. Towards to enable different robots determine a suitable this objective, we describe a multi-robot system sequence to visit locations of potential landmines called COMRADE (COoperative Multi-Robot Au- while reducing the time required and battery tomated DEtection) System for humanitarian dem- expended. We have used commercially available ining. The central objective of COMRADES is to all-terrain robots called Coroware Explorer that are develop novel coordination techniques between mul- customized with a metal detector to detect metallic tiple low-cost, mobile robots, which enable them to objects including landmines, as well as indoor autonomously and collaboratively detect landmines Corobot robots, both in simulation and in physical with high accuracy in post-conflict regions. COM- experiments, to test the different techniques in RADES includes techniques that allows each robot COMRADES. to explore an initially unknown region while search- ing for landmines, recognize landmine-like objects on its sensors, share and fuse the landmine-related sen- Keywords: robotic landmine detection: coverage sor information with other robots and coordinate its and exploration; sensor information fusion; multi- actions with other robots, so that multiple robots robot task allocation can converge on the object to analyze and confirm it as a landmine. In this paper, we present the that our proposed techniques offer suitable means description and experimental results from different to rapidly perform autonomous landmine detection techniques for coverage, task allocation, and, multi- with inexpensive robots. sensor information aggregation and sensor schedul- The rest of our paper is structured as follows: In ing using multiple robots, that we have developed as the next section we provide an overview of existing part of COMRADES. Specifically, we describe the research on robotic landmine detection. In Section following aspects of multi-robot autonomous land- 3, we describe the main features of our proposed mine detection in COMRADES: system, the robots and the landmine detector used, and the user interface. The specific algorithms, tech- • A distributed area coverage technique that al- niques and results related to the three main techni- low a set of robots to dynamically partition an cal aspects of COMRADES - distributed area cover- initially unknown environment into a set of non- age, distributed task allocation and information fu- overlapping regions and search for landmines sion are addressed in Section 4 and finally we discuss within each region. The techniques are robust future directions of our work and conclude. to individual robot failures and are able to scale with the number of robots and size of the envi- ronment. 2 Related Work • A distributed information fusion technique to Autonomous landmine detection using robotic sys- aggregate landmine-related sensor information tems has been an active research topic over the past from different robots using a prediction market decade. Excellent reviews of the state-of-the-art based technique and a decision making tech- techniques in robotic landmine detection are avail- nique that uses the fused information to allo- able in [4, 24]. The research in this topic can be di- cate additional robots (sensors) to rapidly clas- vided into three major directions - designing robots sify the object. attached with suitable sensor devices to detect and • A multi-robot task allocation (MRTA) tech- possibly extract landmines, developing data and in- nique using a spatial queueing model that en- formation fusion techniques to improve the accuracy ables a set of robots to determine a suitable or- of detecting landmines, and, computational tech- der or performing a set of landmine detection niques to coordinate multiple robots and present the related tasks while reducing the time and en- information collected by the robots in a structured ergy spent in performing the tasks. and visualizable format to a human supervisor. Much of the recent research on autonomous land- To realize the above techniques, we have cus- mine detection has been concentrated on develop- tomized commercially available all-terrain robots ing robotic systems for detecting landmines; most called Coroware Explorer with a metal detector to of these systems consist of a single robot attached enable them to detect metallic objects including with appropriate sensors for landmine detection. For landmines. We have also developed a user inter- example, some of these robots include a mecha- face that allows shared autonomy between robots nism mounted on small robot platforms to flail the and humans. Humans can visualize information ground and detonate landmines along with vegeta- about the health and status of the robots and their tion clearing tools [26]. Many deployed robotic sys- progress in the landmine detection operation on a tems for landmine detection rely on tele-operation control station, as well as selectively supersede their rather than autonomy. Examples of such systems autonomous operations by remotely controlling the include a remote operated vehicle called MR-2, the movement and some operations of the robots. We enhanced tele-operated ordnance disposal system have verified the operation of the robots in differ- (ETODS), TEMPEST robot, etc. These robots ben- ent types of outdoor terrain and different operational efit from the improved precision in detecting and conditions. We have also used indoor robots called neutralizing landmines due to a human’s presence in Coroware Corobots, which have very similar features the loop, but they require humans to be in the vicin- to the outdoor Explorer robots, both in simulation ity of landmines to tele-operate the vehicle. Later and within an indoor arena to test the different improvements to some of these systems such as the techniques used in COMRADES. Our results show MR-2 have added partial autonomy in navigation 2 and increased the tele-operation range to 5 km us- sisting of metal detector, an infra-red sensor and a ing feedback sensors. In contrast to these larger chemical sensor is described in [47]. In [48], the robots, researchers have also investigated smaller authors report that Bayesian inference techniques robots that are highly agile, have a small footprint for fusing data using multiple sensors - metal de- and low weight, to reduce the risk of accidental ex- tector, GPR, infra-red camera and magnetometer, plosion of a landmine. Examples of such robots can significantly improve the detection rate of land- are the Ares, Shrimps, Pemexs, Dervishs and Tri- mines. The Advanced Landmine Imaging System dem robots and legged robots such as the AMRU, (ALIS) uses signatures from metal detectors and Shadow Deminer and COMET [24]. Despite their GPR to more accurately locate deep mines, although agility, smaller robots are limited in the weight of the sensors are operated manually and their signa- sensors that they can carry on-board and are not tures are inspected manually as well. This idea has suited for heavier, more robust sensors like ground been extended to robotic landmine detection by col- penetrating radar (GPR) or large-coil metal detec- lecting data from a metal detector array and GPR tors. To accommodate such sensors, robots such as mounted on a single robot and using a combination the Titan [13],