A Performance and Schedulability Analysis of an Autonomous Mobile Robot Jiangyang Huang & Shane Farritor Mechanical Engineering University of Nebraska–Lincoln Ala’ Qadi & Steve Goddard Computer Science & Engineering University of Nebraska–Lincoln

Highway Robotic Safety Marker System RSM system is a mobile, autonomous, robotic, real-time system that automates the placement of highway safety markers in hazardous areas. The RSMs operate in mobile groups that consist of a single lead robot (the foreman) and worker robots (RSMs). prototype foreman. A prototype RSM

Tasks Performed by the Foreman Plan its own path and motion. Locate RSMs, plan their path, communicate destinations points, and monitor performance.

Foreman Design Power Unit Batteries, DC to DC converters, etc. Sonar Unit 24-sonar ring circuit board Communication Unit 9XStream OEM RF Module Motor Unit PIC16F84 MicroController Motor Circuit Board Driving Motor Steering Motor DM5406 Main Unit PC/104-Plus (Windows CE OS) Parallel Port RS232 RS485 TCP/IP Sensor Unit Rabbit 3000 Microprocessor, encoders, gyro Localization Unit Sick Laser LMS200

Foreman Path Planning Plan its own path and motion.  Sonar sensors are used to detect obstacles in the foreman’s path.  The sonar unit consists of a ring of 24 active sonar sensors, with 15  separation, that provides 360  coverage around the foreman. Sonar Sensor Distribution

Foreman Path Planning Sonar Send Task: Sends a command to its corresponding sonar sensor to transmit its signal. Sonar Receive Task: Reads the corresponding sonar sensor after the signal is echoed back to the sensor. Motor-Control Task: Computes the path of the foreman and controls its speed based on the data collected from the sonar signals.

Foreman Path Planning Task Set Foreman Motion Control Task Set TaskePd  max J Sonar-Send i e send =.085mspsps e send  sendi 0 Sonar-Receive i e recv =.03mspsps e send + e recv + max  t  recvi max  t Path-Plan- Speed-Control e plan =1.32mspsps e plan  plan 0

Case 1: Ideal Environment (No Obstacles) Foreman Path Planning

Case 1: Ideal Environment (No Obstacles)

Foreman Path Planning Maximum Safe Distance Depends on the obstacles. Speed might need to be adjusted at scan points due to obstacles. This means that the maximum speed for the zone after the obstacle is also dependent on the speed before reaching the obstacle. Case 2: Obstacles Exist

Example Scenario 1 D=D max, No period adjustments

Example Scenario 2 Period adjustments and Sonar Range Adjustments

Locate RSMs, plan their path, communicate destinations points, and monitor performance. A laser scanner is used to determine the location of the RSMs. RSM Motion Planning and Tracking

Taskepd  max J Scanning12msplpl plpl 00 Detecting.0172n n+12.69plpl plpl 00 Predicting3.8nplpl plpl 00 Planning16ms1500ms 00 Way Point8.33ms1500ms 00 Window Resizing 2msplpl plpl 00 RSM Motion Planning and Tracking Task Set

Relation Between RSM Location Estimation Error and the Laser Scan Period Average Error Maximum Error

Characteristics of the Task Set Some tasks have variable periods that depend on the system performance parameters. The accuracy of RSM position prediction is dependant in p l. (Higher accuracy with smaller period.) The foreman’s maximum traveling speed is dependant on p s. (Higher speed means smaller periods.)

Combine both task sets into one task set with fixed priority. Analyze the task set and devise the minimum number of online scheduling tests with minimum overhead. Combined Task Set Task Index TaskpPriority 1Sonar Send i psps 1 2Plan Speedpsps 2 3Sonar Receive i psps 3 4Scanningplpl 4 5Detectingplpl 5 6Predictingplpl 6 7Window Resizing plpl 6 8Planning Way Point i Proposed Solution

Offline Tests Theorem 4.1: All Sonar Send tasks (Task 1) will always their deadlines if Task Set Analysis

Offline Tests Theorem 4.1: All Sonar Send tasks (Task 1) will always their deadlines if Task Set Analysis Theorem 4.2: The Path-Plan/Speed-Control task (Task 2) will always meet their deadlines if

Offline Tests Theorem 4.1: All Sonar Send tasks (Task 1) will always their deadlines if Task Set Analysis Theorem 4.2: The Path-Plan/Speed-Control task (Task 2) will always meet their deadlines if Theorem 4.3: All Sonar Receive tasks (Task 3) will always their deadlines if

Online Tests Theorem 4.4: All tasks will meet their deadlines if Equations (9) and (10) hold. (9) (10) Task Set Analysis

Period Adjustments Task periods p l and/or p s may need to be adjusted to achieve the desired performance metrics in the following cases:  Adjusting the speed of the foreman—either because we want to move faster from one position to the other or because there is an obstacle in the path.  Increasing the accuracy of RSM path prediction.  Increasing the number of RSMs being controlled.

On Going And Future Work Developing an application-level control algorithm that can make dynamic performance/schedulability tradeoffs. Generalizing the modeling and schedulability analysis presented here so that it can be applied more easily to tasks of other real time mobile autonomous systems.

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