Khatib: Real-time Obstacle Avoidance for Manipulators and Mobile Robots

1. 5/17/2012 CS326A #6 1 Khatib: Real-time Obstacle Avoidance for Manipulators and Mobile Robots Jeffrey Yu Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training�. � Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion. � Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience.Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training�. � Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion. � Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience.

2. 5/17/2012 CS326A #6 2 Plan Review the motion problem Show how previous approaches are similar Show how the potential field approach is different Describe details of the potential field approach Summarize strengths and weaknesses

3. 5/17/2012 CS326A #6 3 Review: Motion Planning Problem Move a robot from a start position to an end position Avoid obstacles along the way Complete the task in a reasonable amount of time Previous approaches: roadmap, cell decomposition, probabilistic roadmap In your opening, establish the relevancy of the topic to the audience. Give a brief preview of the presentation and establish value for the listeners. Take into account your audience�s interest and expertise in the topic when choosing your vocabulary, examples, and illustrations. Focus on the importance of the topic to your audience, and you will have more attentive listeners.In your opening, establish the relevancy of the topic to the audience. Give a brief preview of the presentation and establish value for the listeners. Take into account your audience�s interest and expertise in the topic when choosing your vocabulary, examples, and illustrations. Focus on the importance of the topic to your audience, and you will have more attentive listeners.

4. 5/17/2012 CS326A #6 4 Previous Approaches: Common Characteristics Find a valid path to the goal Transform valid path into forces of motion Apply forces to the robot

5. 5/17/2012 CS326A #6 5 Potential Field Approach Design a force to guide the robot towards the goal Design forces to guide the robot away from obstacles Apply the total force to the robot

6. 5/17/2012 CS326A #6 6 Example Combination of forces move steer the robot around a corner

7. 5/17/2012 CS326A #6 7 Goal Force: Design Criteria Move the robot towards the goal state Bring the robot to rest at the goal state Stay within robot safety and operational limits

8. 5/17/2012 CS326A #6 8 Goal Force #1 Basic spring-like force Stable at the goal Weakness: cyclic motion away from the goal

9. 5/17/2012 CS326A #6 9 Goal Force #2 Drag term brings the robot to rest Weakness: long distances produce high acceleration and high-velocity motion

10. 5/17/2012 CS326A #6 10 Goal Force #3 (Final) Based on goal force #2 Produces straight-line, velocity-limited movement toward the goal Motion perturbed near obstacles

11. 5/17/2012 CS326A #6 11 Obstacle Force: Design Criteria Steer robots away from an obstacle�s surface Influence is negligible away from an obstacle�s surface Two methods: analytic obstacle equations and shortest distance to an obstacle

12. 5/17/2012 CS326A #6 12 Obstacle Forces: Analytic Equations Function f(x) = 0 describes obstacle surface Influence starts at f(x)=x0, approaches infinity at f(x)=0 No distance calculation needed

13. 5/17/2012 CS326A #6 13 Obstacle Forces: Shortest Distance Produces motion away from the closest point of danger Real-time sensing possible

14. 5/17/2012 CS326A #6 14 Strengths Calculations done in operational space: avoid translation to and from configuration space Calculations done in control domain: no conversion from intermediate path representation to command forces Less upfront effort expended planning a possibly obsolete path

15. 5/17/2012 CS326A #6 15 Weaknesses Failure due possible even if a valid path exists Workarounds: Random walks Roadmap connecting local minima Motion attempted even if no valid path exists Failure modes are observable to bystanders

16. 5/17/2012 CS326A #6 16 Other Topics Manipulator optimizations End-effector decoupling parameters can be computed at a lower rate than the end-effector force vector Applications Khatib et al 1984: PUMA 560 with machine intelligence Corp vision module Khatib, Burdick, and Armstrong 1985: real-time end-effector motion with active force control

17. 5/17/2012 CS326A #6 17 Summary: Potential Field Methods Artificial forces guide robot motion Sacrifices reliability for speed Determine the best close for your audience and your presentation. Close with a summary; offer options; recommend a strategy; suggest a plan; set a goal. Keep your focus throughout your presentation, and you will more likely achieve your purpose.Determine the best close for your audience and your presentation. Close with a summary; offer options; recommend a strategy; suggest a plan; set a goal. Keep your focus throughout your presentation, and you will more likely achieve your purpose.