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Preplan motion

This page provides an overview of how to preplan motions through the preplan_motion skill.

Example​

Consider the following scenario. A process editor is working on an application that uses an on-arm camera to take multiple images of a static object. The following image shows the process.

process_no_preplan

The process starts with the robot arm moving to a predefined pose. Then the on-arm camera is used to perform a coarse pose estimation of the object. The pose is used to compute a set of three poses. The robot arm will move to each of the three poses. The on-arm camera is then used to take an image of the object from each pose. At each move_to_pose_X skill, the robot will first compute the trajectory to the pose before executing the motion. This results in some "waiting" time before the robot starts moving. To eliminate this "waiting" time, the user can preplan the motion using the preplan_motion skill by putting it in parallel with all the move_to_pose_X skills. The preplan_motion skill computes trajectories to each pose and stores them in the motion planner cache. The trajectory can then be quickly retrieved and executed by all move_to_pose_X skills. The new process looks like this:

process_with_preplan

How to preplan motions for a sequence of move_robot skills​

This section assumes the user has already configured a sequence of move_robot skills and they can be successfully executed. To preplan the motion for all move_robot skills:

  1. Put a preplan_motion skill in parallel with all move_robot skills.
  2. Configure the preplan_motion skill with three Skill calls of move_robot skills.
  3. Make sure the Skill calls are configured with the identical parameters as each corresponding move_robot skill.

preplan_motion_skill_call

note

In some more complex scenarios, there might be some other skills in between the move_robot skills that modify the world state. For example, in a pick and place process, there is a attach_object_to_robot skill between two move_robot skills that moves the robot arm to pick and place poses. To accurately preplan the motion for these move_robot skills, the user needs to make sure the attach_object_to_robot skill is also configured in the preplan_motion's Skill call parameter. This also applies to detach_object and any other skills that modify the world state.