A Performance and Schedulability Analysis of an Autonomous

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

Highway Robotic Safety Marker System n n RSM system is a mobile, autonomous, robotic, realtime 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 n Plan its own path and motion. n Locate RSMs, plan their path, communicate destinations points, and monitor performance.

Foreman Design Sonar Unit 24 -sonar ring circuit board Communication Unit Main Unit Motor Unit Parallel Port PIC 16 F 84 Micro. Controller 9 XStream OEM RF Module PC/104 -Plus (Windows CE OS) RS 232 DM 5406 Motor Circuit Board TCP/IP RS 485 Driving Motor Power Unit Batteries, DC to DC converters, etc. Localization Unit Sick Laser LMS 200 Sensor Unit Rabbit 3000 Microprocessor, encoders, gyro Steering Motor

Foreman Path Planning n Plan its own path and motion. q q 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 n Sonar Send Task: Sends a command to its corresponding sonar sensor to transmit its signal. n Sonar Receive Task: Reads the corresponding sonar sensor after the signal is echoed back to the sensor. n 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 Task e P d f max J Sonar-Sendi esend=. 085 ms ps esend fsendi 0 Sonar-Receivei erecv=. 03 ms ps esend+ erecv+ max Dt frecvi Path-Plan. Speed-Control eplan=1. 32 ms ps eplan fplan Foreman Motion Control Task Set max Dt 0

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

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

Foreman Path Planning Case 2: Obstacles Exist n n n 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.

Example Scenario 1 D=Dmax , No period adjustments

Example Scenario 2 Period adjustments and Sonar Range Adjustments

RSM Motion Planning and Tracking n 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 Task Set Task e p d f max J Scanning 12 ms pl pl 0 0 Detecting . 0172 n 2+. 1695 n+12. 69 pl pl 0 0 Predicting 3. 8 n pl pl 0 0 Planning 16 ms 1500 ms 0 0 Way Point 8. 33 ms 1500 ms 0 0 Window Resizing 2 ms 0 0 pl pl

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

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

Proposed Solution n n 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. Task Index Task p Priority 1 Sonar Sendi ps 1 2 Plan Speed ps 2 3 Sonar Receivei ps 3 4 Scanning pl 4 5 Detecting pl 5 6 Predicting pl 6 7 Window Resizing pl 6 8 Planning 1500 7 9 Way Pointi 1500 8 Combined Task Set

Task Set Analysis Offline Tests n Theorem 4. 1: All Sonar Send tasks (Task 1) will always their deadlines if

Task Set Analysis Offline Tests n Theorem 4. 1: All Sonar Send tasks (Task 1) will always their deadlines if n Theorem 4. 2: The Path-Plan/Speed-Control task (Task 2) will always meet their deadlines if

Task Set Analysis Offline Tests n Theorem 4. 1: All Sonar Send tasks (Task 1) will always their deadlines if n Theorem 4. 2: The Path-Plan/Speed-Control task (Task 2) will always meet their deadlines if n Theorem 4. 3: All Sonar Receive tasks (Task 3) will always their deadlines if

Task Set Analysis Online Tests n Theorem 4. 4: All tasks will meet their deadlines if Equations (9) and (10) hold. (9) (10 )

Period Adjustments n Task periods pl and/or ps may need to be adjusted to achieve the desired performance metrics in the following cases: q q q 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 n Developing an application-level control algorithm that can make dynamic performance/schedulability tradeoffs. n 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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