Question: what specs are necessary for real-time system to run EGM? about abb_libegm HOT 4 CLOSED

Hello @bhomberg,

For me it has worked fine with an ordinary laptop, running Ubuntu with ROS and controlling ABB robots via EGM. However, I haven’t really had any applications with hard real-time requirements.

Regarding the external axis, if you intend to control it via EGM, then you would need at least RobotWare 6.07.01. This is because partial support for external axis was added to EGM in that version, and it is partial support due to these limitations:

• It is only possible to control one mechanical unit in each RAPID task via EGM.
  RobotWare option Multitasking [623-1] is required to have more than one task.
• Coordinated movements via EGM is not supported.
  E.g. RobotWare option MultiMove Coordinated [604-1].

Note: There was a change in the EGM protocol between RobotWare 6.06 and 6.07, and abb_libegm has not been updated to handle those changes yet.

I hope this helps!

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Hi @jontje -- thanks for your answer, that's very helpful! I have a couple follow-up questions: how fast have you been updating the trajectories -- are you updating every 4ms (the max rate I saw listed in the ABB documentation) or less frequently? Do you send the full trajectory, just the next waypoint, or a few waypoints ahead?

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I have primarily used 4 ms rate, and I have implemented two main interfaces in abb_libegm. Both are based on an inner asynchronous UDP loop, which is executed when the robot controller requests new references (at the specified rate). The new references are always only for the next time instance.

Rough description of the two interfaces:

EGMControllerInterface:

1. Waits until the robot controller requests new references.
2. Notifies an external control loop (implemented by the user) that new references should be provided.
3. The external control loop calculates new references and provides them to the interface.
4. The interface sends the references to the robot controller.
5. Repeat from 1.

Note: If you want to optimize the control loop, then it might be better to implement your own version of a controller interface. For example, by integrating the external control loop directly into the asynchronous UDP loop.

EGMTrajectoryInterface:
Accepts trajectories (from a user), which are put in a queue.

1. When the robot controller requests new references, then the interface processes the trajectory at the head of the queue.
2. The interface interpolates between points in the active trajectory and calculates the new references, which are sent to the robot controller. This is repeated every time the robot controller requests new references, until all points in the trajectory has been processed.
3. Repeat from 1.

Examples:
I have used the interfaces for different things.

• EGMControllerInterface for velocity control.
• EGMTrajecotryInterface for executing joint trajectories from MoveIt.

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This is very helpful @jontje! Thanks for your answers.

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