Ashitey Trebi-Ollennu

CAMPOUT: a control architecture for tightly coupled coordination of multirobot systems for planetary surface exploration

Exploration of high risk terrain areas such as cliff faces and site construction operations by autonomous robotic systems on Mars requires a control architecture that is able to autonomously adapt to uncertainties in knowledge of the environment. We report on the development of a software/hardware framework for cooperating multiple robots performing such tightly coordinated tasks. This work builds on our earlier research into autonomous planetary rovers and robot arms. Here, we seek to closely coordinate the mobility and manipulation of multiple robots to perform examples of a cliff traverse for science data acquisition, and site construction operations including grasping, hoisting, and transport of extended objects such as large array sensors over natural, unpredictable terrain. In support of this work we have developed an enabling distributed control architecture called control architecture for multirobot planetary outposts (CAMPOUT) wherein integrated multirobot mobility and control mechanisms are derived as group compositions and coordination of more basic behaviors under a task-level multiagent planner. CAMPOUT includes the necessary group behaviors and communication mechanisms for coordinated/cooperative control of heterogeneous robotic platforms. In this paper, we describe CAMPOUT, and its application to ongoing physical experiments with multirobot systems at the Jet Propulsion Laboratory in Pasadena, CA, for exploration of cliff faces and deployment of extended payloads.

Mars rover pair cooperatively transporting a long payload

The objective of the Robot Work Crew (RWC) project is to investigate key challenges in multi-robot coordination when performing tightly coupled coordination tasks such as transporting and handling of long objects on challenging planetary terrain. In this paper, we focus on tightly coupled coordination of two Mars rovers transporting a long payload. We have developed practical decentralized compliancy control and coordinated comply control algorithms that effectively address compliant control for compliantly coupled multiple mobile robots. Experiments at the Jet Propulsion Lab in Pasadena, CA of two Mars rovers carry an extended payload over uneven, natural terrain are used to validate and illustrate the approach.

Rover autonomy for long range navigation and science data acquisition on planetary surfaces

This paper describes recent work undertaken at the Jet Propulsion Laboratory in Pasadena, CA in the area of increased rover autonomy for planetary surface operations. The primary vehicle for this work is the Field Integrated, Design and Operations (FIDO) rover. The FIDO rover is an advanced technology prototype that is a terrestrial analog of the Mars Exploration Rovers (MER) being sent to Mars in 2003. We address the autonomy issue through improved integration of rover based sensing and higher level onboard planning capabilities. The sensors. include an inertial navigation unit (INU) with 3D gyros and accelerometers, a sun sensor, mast and body mounted imagery, and wheel encoders. Multisensor fusion using an Extended Kalman Filter (EKF) approach coupled with pattern recognition and tracking algorithms has enabled the autonomy that is necessary for maximizing science data return while minimizing the number of ground loop interactions. These algorithms are coupled with a long range navigation algorithm called ROAMAN (Road Map Navigation) for an integrated approach to rover autonomy. We also report the results of algorithm validation studies in remote field trials at Black Rock Summit in Central Nevada, Californias Mojave Desert, and the Arroyo Seco at JPL.

Design and analysis of a sun sensor for planetary rover absolute heading detection

The paper describes a new sun sensor for absolute heading detection developed for the Field Integrated, Design and Operations (FIDO) rover. The FIDO rover is an advanced technology rover that is a terrestrial prototype of the rovers NASA/Jet Propulsion Laboratory (JPL) plans to send to Mars in 2003. Our goal was to develop a sun sensor that fills the current cost/performance gap, uses the power of subpixel interpolation, makes use of current hardware on the rover, and demands very little computational overhead. The need for a sun sensor on planetary rovers lies in the fact that current means of estimating the heading of planetary rovers involves integration of noisy rotational-speed measurements. This noise causes error to accumulate and grow rapidly. Moreover, the heading error affects the estimate of the x and y position of the rover. More importantly, incremental odometry heading estimation is only reliable over relatively short distances. There is an urgent need to develop a new heading-detection sensor for long traverses [for example, 100 m per Sol (Martian Day)], as requested for future Mars mission. Results of a recent FIDO field trial at Black Rock Summit in Central Nevada and several operations readiness tests at the JPL MarsYard using the sun sensor have demonstrated threefold to fourfold improvement in the heading estimation of the rover compared to incremental odometry.

Mars Exploration Rover surface operations: driving spirit at Gusev Crater

Spirit is one of two rovers that landed on Mars in January 2004 as part of NASAs Mars Exploration Rover mission. As of July 2005, Spirit has traveled over 4.5 kilometers across the Martian surface while investigating rocks and soils, digging trenches to examine subsurface materials, and climbing hills to reach outcrops of bedrock. Originally designed to last 90 sols (Martian days), Spirit has survived over 500 sols of operation and continues to explore. During the mission, we achieved increases in efficiency, accuracy, and traverse capability through increasingly complex command sequences, growing experience, and updates to the on-board and ground-based software. Safe and precise mobility on slopes and in the presence of obstacles has been a primary factor in development of new software and techniques.

Reconfigurable robots for all-terrain exploration

While significant recent progress has been made in development of mobile robots for planetary surface exploration, there remain major challenges. These include increased autonomy of operation, traverse of challenging terrain, and fault-tolerance under long, unattended periods of use. We have begun work which addresses some of these issues, with an initial focus on problems of high risk access, that is, autonomous roving over highly variable, rough terrain. This is a dual problem of sensing those conditions which require rover adaptation, and controlling the rover actions so as to implement this adaptation in a well understood way (relative to metrics of rover stability, traction, power utilization, etc.). Our work progresses along several related technical lines: 1) development a fused state estimator which robustly integrates internal rover state and externally sensed environmental information to provide accurate configuration information; 2) kinematic and dynamical stability analysis of such configurations so as to determine predicts for a needed change of control regime (e.g., traction control, active c.g. positioning, rover shoulder stance/pose); 3) definition and implementation of a behavior-based control architecture and action-selection strategy which autonomously sequences multi-level rover controls and reconfiguration. We report on these developments, both software simulations and hardware experimentation. Experiments include reconfigurable control of JPSs Sample Return Rover geometry and motion during its autonomous traverse over simulated Mars terrain.

Rover localization results for the FIDO rover

This paper describes the development of a two-tier state estimation approach for NASA/JPLs FIDO Rover that utilizes wheel odometry, inertial measurement sensors, and a sun sensor to generate accurate estimates of the rovers position and attitude throughout a rover traverse. The state estimation approach makes use of a linear Kalman filter to estimate the rate sensor bias terms associated with the inertial measurement sensors and then uses these estimated rate sensor bias terms to compute the attitude of the rover during a traverse. The estimated attitude terms are then combined with the wheel odometry to determine the rovers position and attitude through an extended Kalman filter approach. Finally, the absolute heading of the vehicle is determined via a sun sensor which is then utilized to initialize the rovers heading prior to the next planning cycle for the rovers operations. This paper describes the formulation, implementation, and results associated with the two-tier state estimation approach for the FIDO rover.

Distributed Control of Multi-Robot Systems Engaged in Tightly Coupled Tasks

NASA mission concepts for the upcoming decades of this century include exploration of sites such as steep cliff faces on Mars, as well as infrastructure deployment for a sustained robotic/manned presence on planetary and/or the lunar surface. Single robotic platforms, such as the Sojourner rover successfully flown in 1997 and the Mars Exploration Rovers (MER) which landed on Mars in January of 2004, have neither the autonomy, mobility, nor manipulation capabilities for such ambitious undertakings. One possible approach to these future missions is the fielding of cooperative multi-robot systems that have the required onboard control algorithms to more or less autonomously perform tightly coordinated tasks. These control algorithms must operate under the constrained mass, volume, processing, and communication conditions that are present on NASA planetary surface rover systems. In this paper, we describe the design and implementation of distributed control algorithms that build on our earlier development of an enabling architecture called CAMPOUT (Control Architecture for Multi-robot Planetary Outposts). We also report on some ongoing physical experiments in tightly coupled distributed control at the Jet Propulsion Lab in Pasadena, CA where in the first study two rovers acquire and carry an extended payload over uneven, natural terrain, and in the second three rovers form a team for cliff access.

Distributed surveillance and reconnaissance using multiple autonomous ATVs: CyberScout

The objective of the CyberScout project is to develop an autonomous surveillance and reconnaissance system using a network of all-terrain vehicles. We focus on two facets of this system: 1) vision for surveillance and 2) autonomous navigation and dynamic path planning. In the area of vision-based surveillance, we have developed robust, efficient algorithms to detect, classify, and track moving objects of interest (person, people, or vehicle) with a static camera. Adaptation through feedback from the classifier and tracker allow the detector to use grayscale imagery, but perform as well as prior color-based detectors. We have extended the detector using scene mosaicing to detect and index moving objects when the camera is panning or tilting. The classification algorithm performs well with coarse inputs, has unparalleled rejection capabilities, and can flag novel moving objects. The tracking algorithm achieves highly accurate (96%) frame-to-frame correspondence for multiple moving objects in cluttered scenes by determining the discriminant relevance of object features. We have also developed a novel mission coordination architecture, CPAD (Checkpoint/Priority/Action Database), which performs path planning via checkpoint and dynamic priority assignment, using statistical estimates of the environments motion structure. The motion structure is used to make both preplanning and reactive behaviors more efficient by applying global context. This approach is more computationally efficient than centralized approaches and exploits robot cooperation in dynamic environments better than decoupled approaches.

Robot work crews for planetary outposts: close cooperation and coordination of multiple mobile robots

We report on the development of cooperating multiple robots. This work builds form our earlier research on autonomous planetary rovers and robot arms. Here, we seek to closely coordinate the mobility and manipulation of multiple robots to perform site construction operations- as an example, the autonomous deployment of a planetary power station- a task viewed as essential to a sustained robotic presence and human habitation on Mars. There are numerous technical challenges; these include the mobile handling of extended objects, as well as cooperative transport/navigation of such objects over natural, unpredictable terrain. We describe an extensible system concept, related simulations, a hardware implementation, and preliminary experimental results. In support of this work we have developed an enabling hybrid control architecture wherein multi-robot mobility and sensor-based controls are derived as group compositions and coordination of more basic behaviors under a task-level multi-agent planner. We summarize this Control Architecture for Multi-robot Planetary Outposts (CAMPOUT), and its application to physical experiments where two rovers carry an extended payload over natural terrain.