Lab 9: Robot Arm Path Planning

 

Lead TAs:

Challenge Statement:

Perform path planing for a 2 link RR robot arm.

Demo:

  1. Using the robotic arm from lab 8, perform the following while avoiding the obstacle shown in the map below. The end effector cannot leave the map.

    1. Move from the reference configuration to the start position (inputed by the user) and wait for user input.
    2. Move from the start position to an end position (inputed by the user) and wait for user input.
    3. Go back to the start position and stop there.
    4. If the robot ever touches the obstacle, no credit will be given for any more points the robot moves to in that run.
    5. Three tries will be given in order to improve your score if needed.All tries are independent of each other. Progressively easier positions can be requested, each for a 10 point penalty and only once per try. A request cannot be made on the first try.

Map:

map1
Map in cartesian space. Red indicates an obstacle. All numbers are in inches.

How to:

Note that the way point based planner is only suggested. Feel free to implement any other planner to solve this task.

  1. Add the planner from lab 5 to the previous lab's code.
  2. Pick waypoints in the map given below which is the C-Space version of the cartesian map given above. The obstacle can be approximated to be a prallelogram for easy collision detection.
  3. Use inverse kinematics from the previous lab to get good C-Space angles for the given start and end positions.
  4. Run the planner one these positions to reach the goal position.
  5. Make sure the planner is working on C-Space angles and not X-Y positions.

C-Space Map:

map2
A representation of the cartesian map with the obstacle in the robot's configuration space. Red : Obstacle, Blue : Approximation of the obstacle as a parallelogram, Black : Outside the map.

Other tips:

  1. Remember to check all configurations generated by inverse kinematics. It is not necessary that all configurations will be reachable under the constraints of the obstacle.
  2. As the trajectory taken by the robot is important and it is wrong to first move one joint and then the next, it may be necessary to write a basic trajectory planner or set relative speeds using motor teaming.

Evaluation:

  1. When moving to the start position from the reference configuration:
      i) End effector within a half inch radius of the start position - 10 points
      ii) End effector within a quarter inch radius of the start position - 20 points
  2. When moving to the end position from the start position :
      i) End effector within a half inch radius of the end position - 20 points
      ii) End effector within a quarter inch radius of the end position - 30 points
  3. When moving to the start position from the end position :
      i) End effector within a half inch radius of the start position - 30 points
      ii) End effector within a quarter inch radius of the start position - 50 points

Grading Sheet : Lab 9


Last Updated : 10/16/07 by Kaushik Viswanathan
(c) 1999-2007: Howie Choset, Carnegie Mellon