Modbus Emergency Stop and Reset

BBlumhofer commented 1 year ago

Description

I am forced to use the Modbus TCP connection to the robot as it will be later controlled by a PLC. I built up a testing setup using pymodbus on a laptop. The example script works well for me but I can not activate reliable the emergency stop and can not reset the robot at all. I tried different methods to send the message. I attached a small code snippet with both commands. Can you explain me where my coding fault is or if it is a bug on the robot

Version

Robot: Gen3 Ultra Lightweight Robot 6DOF Firmware: 2.4.0-3

Steps to reproduce

run the code in python

Code example

#! /usr/bin/env python3

import time
from pymodbus.client.sync import ModbusTcpClient

# Default modbus port.
PORT = 502

# IP address of the robot that holds the modbus slave.
IP_ADDRESS = '192.168.1.10'

def reset():
    # instantiate modbus client connection
    client = ModbusTcpClient(IP_ADDRESS, PORT)
    assert client.connect(), "Unable to connect to the slave"

    client.write_coil(0, True)
    time.sleep(2)

    client.write_coil(2, False)

    client.close()

if __name__ == "__main__":
    reset()

Expected behavior

Activate emergency stop
wait 2s
reset robot to be able to start moving again

Any other information

felixmaisonneuve commented 1 year ago

Hi @BBlumhofer,

I am not sure what you mean when you say you cannot set the emergency stop in a reliable way. Is it because it won't work sometimes or is it because you cannot remove the error afterwards?

I am not a Modbus expert, but I think you need to set back the "Quick stop" to False (client.write_coil(0, False)) before clearing errors with client.write_coil(2, False). Otherwise I think the flag will stay active and the error will simply be triggered again.

If you are moving the arm with Actions, you think you could also write 2 in the Holding Registers 200. It will send an Action Stop that will abort your current action without causing an error

Best, Felix

BBlumhofer commented 1 year ago

Hi Felix,

There are two issues. At first, the E-Stop using Modbus does not work every time. This was fixed by using client.write_coil(0, False) before triggering it again. But resetting the robot does not work even with the solution you proposed. I don't move the arm using actions. I want to use ROS to do that. Below you can see the structure I planned to use.

graph TD

    A[Robot] -->|ROS Interface| C(Industrial PC)
    C--> F(Task and Path Planning)
    A-->| Modbus TCP|B(Safety PLC)
    B--> D(E-Stop)
    B--> E(Teach-Panel)

felixmaisonneuve commented 1 year ago

If by "resetting the robot" you mean clearing faults (to clear the emergency stop fault) so you can use the arm again, you can use the base's clear_faults service. We have an example of that here : https://github.com/Kinovarobotics/ros_kortex/blob/noetic-devel/kortex_examples/src/full_arm/example_cartesian_poses_with_notifications.py#L81-L90

It uses the service defined above : https://github.com/Kinovarobotics/ros_kortex/blob/noetic-devel/kortex_examples/src/full_arm/example_cartesian_poses_with_notifications.py#L41-L44

You can find something equivalent in C++ as well : https://github.com/Kinovarobotics/ros_kortex/blob/noetic-devel/kortex_examples/src/full_arm/example_full_arm_movement.cpp#L81-L97

If this is not what you meant, can you elaborate on what you need and what you want to do?

Best, Felix

BBlumhofer commented 1 year ago

Hi Felix, Yes, I meant clearing faults. Sorry for being to not precise on that.

To make it more clear what I am planning to do:

I have two parallel users: User 1 a Linux PC with ROS ( no issue there) User 2: A PLC to activate the E-Stop, apparent faults and manually move the robot
My PLC only supports Modbus (no cpp/python or ROS)
I need to activate the e-stop and clear the faults over Modbus while ROS controls the movement of the robot (Move it)
In addition: If the ROS PC is unavailable, I need to move the Robot via an HMI connected to the PLC.
To control the robot and the safety functions only via ROS is not an option because of safety regulations

I hope this helps you to understand what the issue is.

Best, Benjamin

felixmaisonneuve commented 1 year ago

Ok, I understand.

It should work the same way it does to set the emergency stop.

You ave to set client.write_coil(2, True) (that will clear faults), then set it back to client.write_coil(2, False) so you can re-enable it later.

I don't know why I didn't spot it earlier (I even copied it in my first response), but I think it will probably fix your issue

Best, Felix

BBlumhofer commented 1 year ago

Hi Felix,

Ah okay, thank you this worked for me! Thanks for your help.

Best, Benjamin

Kinovarobotics / kortex