Task Planning

1
Task Planning

• Three types of planning
• Gross Motion Planning concerns objects being
  moved from point A to point B without problems,
  i.e. movement of manipulator without collision
  with obstacles
• Grasping Planning concerns
• where to grasp the object so that no collision
  will occur
• the grasp configurations so that object will not
  fall off the gripper during transportation
• Fine Motion Planning concerns the motions of the
  robot when it is
• approaching a surface, i.e. guarded motion and
• in contact with a surface, i.e. compliant motion

2
Gross Motion Planning

• Concerns objects moving from Point A to Point B
  without collision gt obstacle avoidance problem
• Gross in the sense that there is no contact of
  the robot with any parts
• Objective is to plan a path to move a part from
  an initial position and orientation to a final
  position and orientationnin the presence of
  obstacle without colliding with the obstacls.
• The planned path should be optimal, e.g. the
  shortest one.
• In general, path planning is a search in the
  6-Dimension space (3 translational and 3
  rotational). However, the no. of degrees of
  freedom is usually less than 6. Why?
• Configuration space is needed before an optimal
  path can be defined.

3
Gross Motion Planning (contd)

• Configuration space defines the positions and
  orientations of the part (both initial and final)
  and the obstacles.
• Path Planning is to define the explicit free
  space in the configuration space for the object
  to move from the intitial location to the final
  location.
• One possible approach
• Shapes and sizes of part (to be moved) and
  obstacles (stationary) are known
• To define the configuration space, the moving
  part is shrinked to a reference point (e.g.
  centroid) while the obstacles are grown to
  compensate the lost.
• Once the configuration is defined, the optimal
  path can be found.
• Example (Given in class)

4
Grasping Planning

• Concerns
• where to grasp the object so that no collision
  will occur and
• the object will not fall off during
  transportation.
• Three main considerations
• Safety - collision free, contact free
• Reachability - able to reach initial
  configuration, with object in the gripper, move
  in a collision free path to the final
  destination and
• Stability - the grasp should be stable in the
  presence of forces exerted on the object while in
  motion.

5
Grasping Planning (contd)

• Three main goals
• must identify a single configuration, i.e.
  position and orientation of the gripper
• must consider the detailed interaction of the
  grippers shape, surfaces of contact and
• must deal with the interaction of the choice of
  grasp consideration and the constraints imposed
  by the sequence of operations
• Most approaches consist of three steps
• choose a set of potential grasp configurations
• Prune those that are not reachable by the robot
  or may lead to collision and
• choose the optimal from the remaining ones.

6
Grasping Planning (contd)

• Note
• These approaches assume the configurations of
  objects are known
• With the help of sensors, e.g. vision,
  configurations of objects can be computed
• Touch sensors are often used to achieve the
  actual grasping of the objects.

7
Fine Motion Planning

• Concerns the motions of the robot when it is
• approaching a surface gt guarded motion
• in contact with a surface gt compliant motion
• Force and tactile sensors are usually used
• Guarded Motion
• Movement along a specific direction until certain
  event occurrs
• Compliant Motion
• After contact, the type of motion must comply
  with the constraints imposed by the surface
• Motion is usually continuous and guided by
  contact with the surface
• Example (given in class)