Robot Highway Safety Markers

algorithm focuses on the sporadic task model, which puts only a lower bound on the time separation interval between the release of jobs of the same task. This flexibility of the sporadic model makes it conducive to many applications. The proposed algorithm guarantees that each job meets its deadline while saving the maximum amount of energy.

Real-time Systems ResearchThe control operations of the barrel robot demand both logical and temporal correctness. Temporal correctness requires these operations to be computed and executed within allowable response times. Instead of a single control loop for these operations, real-time task sets are used. In real-time scheduling theory, a task is a schedulable unit of work that executes with a known pattern. The real-time task set provided by microC OS-II, a real-time operating system driving the barrel robot, is used to implement the local planning and control operations. The use of real-time task sets allows temporal correctness to be analyzed and guaranteed in advance. It provides maintainability and extensibility; if the processor is upgraded, only the tick-rate of the processor needs to be updated in the software. It reduces latency between the receipt of a waypoint from the lead robot and the time at which the barrel robot begins to move. As the robot is moving to a waypoint, a new waypoint is calculated. The robot highway safety marker serves as a suitable application to study research problems in real-time systems. For example, the limited power in the barrel robot requires the system to be aware of energy constraints. An interesting area of research is scheduling algorithms to maximize the battery life in such an embedded system. Dynamic voltage scaling (DVS) algorithms aim at reducing the energy consumption of the system by operating the CPU at a lower frequency and thus operating at a lower voltage. An ongoing research project is evaluating a proposed DVS algorithm that works in conjunction with the earliest-deadline-first (EDF), dynamic priority scheduling algorithm. The

By: Xiangrong Shen, Jason Dumpert, Chon-Ming Lee, Rohini Krishnapura, Ala Qadi

Field TestsThe RSM has been tested in field environments. The picture on the right shows all robots operating as a team to close the right lane of a two-lane road. The desired and actual paths taken in

Lines connecting symbols only approximate robot motion between points. The maximum deviation from the desired path was 23 cm and the maximum final error for all robots was 11 cm. This accuracy is well within the requirements for barrel placement and exceeds the accuracy of current human deployment.

the tests were plotted as shown in the figure below (lower right). The symbols on each actual path represent where individual robots reached a waypoint and their position was updated.

ObjectiveProper traffic control is critical in highway work zone safety. Traffic control devices such as signs, barricades, cones, and plastic safety barrels are often used. Accidents can occur because of improper work zone design, improper work zone housekeeping, and driver negligence. Automated safety devices could improve work zone design and housekeeping and therefore increase safety.

DescriptionSafety barrels guide traffic and serve as a visible barrier between traffic and work crews. These barrels consist of a brightly colored plastic drum (approximately 130cm high and 50cm in diameter) that is attached to a heavy base. Often, hundreds of barrels aremanually placed in a typical work zone. The Robotic Safety Marker (RSM) replaces the heavy base of a typical safety barrel with a mobile robot. The mobile robot can transport the safety barrel and robots can work in teams to provide traffic control. Shown above is the robot base next to a plastic safety barrel. The RSM can self-deploy and self-retrieve, removing workers from this dangerous task. The robots can move independently so they can be deployed in parallel and can quickly reconfigure as the work zone changes. The robot base has two electric motors. Each wheel is driven by its own motor. A castor supports the rear of the robot and the reversible, variable speed motors allow the robot to move in any direction as well as turn in place.

Planning and ControlAlthough, each robot moves individually, a single lead robot (general) provides global planning and control and issues commands to each barrel robot (troops). The lead robot plans the path, communicates waypoints, and monitors performance of each barrel robot. The graph below (left) shows the global plan for two robots to move from random locations on the roadside shoulder to positions in a taper, to close a lane. To obtain the desired robot path, a parabola is created between the initial position,and orientation, and the final position. Each barrel robot does not have

knowledge of other robots, and performs only local tasks. It receives a waypoint from the lead robot and createslocalized positions between the initial position and the desired waypoint.

University of Nebraska, LincolnSponsored by The National Academy of Sciences IDEA Program

and The National Science Foundation

Department of Mechanical EngineeringDr. Shane Farritor

Computer Science and Engineering Department

Dr. Steve Goddard