End effector constraint in path planning

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End effector constraint in path planning

Post by Choisy » 03 Jun 2019, 09:15


Thank you for supplying useful robot simulation program.

I try to make press line in factory. (2 press & 1 manipulator between press)
Manipulator grabs the object in press and transfers to other press.

I code this simulation of which manipulator moves between target 1 and target 2 by path planning & other move by IKpath.

Question //
I want to make the end effector constraint during path planning and moving.
It means that end effector always looks -Z axis(absolute coordinate reference) during path moving.

How can i implement this?

Thank you in advance.

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Re: End effector constraint in path planning

Post by coppelia » 05 Jun 2019, 09:39


there are probably several ways to achieve this. Two come to my mind. The first is:
  • Instead of planning in the robot's joint space, do the planning in the Cartesian space (e.g. x/y/z, and optionally one rotation around z).
  • Use a state validation callback. In there, try to move the robot to the selected position/orientation , using IK. The difficulty lies in selecting the initial robot configuration to move to that position/orientation. Maybe using a cartesian space metric that allows selecting a previously found collision free configuration where the end-effector is closest to the one selected in the callback
The second idea is:
  • do path planning in the robot's joint space.
  • Here too, use a state validation callback. In there, use IK to try to correctly orient the end-effector, so that it is aligned with the z-axis. If the end-effector can be aligned and the robot is otherwise not colliding, the node is valid. Otherwise it is not valid
The second solution is probably faster than the first.


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