Control grippers from Python using MODBUS RTU

bcastets

I share with you a python program I did to control Robotiq grippers from a PC using Python and MODBUS RTU protocol.

The code is hosted on github:
https://github.com/castetsb/pyRobotiqGripper

I did this program after receiving several questions about how to connect our gripper on different robots, PC,... If you want to make such prooject, I recommend that you check the user manual (https://robotiq.com/support/2f-85-2f-140/downloads-instruction-manual-cb-series?document=). Everything is explain in details with examples.
Robotiq grippers are using MODBUS RTU protocol and can be control just by writing command in their registers. I used  minimalMobus library to write in gripper register and request actions.

I hope this will help to understand how its working.

Guillaume_Charron

Another related post: https://dof.robotiq.com/discussion/92/controlling-the-robotiq-2-finger-gripper-with-modbus-commands-in-python?_ga=2.17431289.1133307955.1542044765-1547192274.1535646624

nicolasmarcstephan

Thank you for referring me here @bcastets !

You were right, this was exactly what I was looking for.

But unfortunately also this code doesn't work for me. MinimalModbus is installed and I checked the Robotiq User Interface where it shows me that the port is COM6 and the slave number is 9. The gripper is sitting on a Robotiq wrist camera. Could this be the problem?

This is the error message:

MinimalModbus debug mode. Will write to instrument (expecting 17 bytes back): '\t\x03\x07Ð\x00\x06Ä\r' (09 03 07 D0 00 06 C4 0D)
MinimalModbus debug mode. Clearing serial buffers for port COM6
MinimalModbus debug mode. No sleep required before write. Time since previous read: 7298031.00 ms, minimum silent period: 2.01 ms.
Traceback (most recent call last):
  File "...\pyRobotiqGripper-master\robotiqGripper.py", line 554, in <module>
    grip = RobotiqGripper("COM6")  # /dev/ttyUSB1
  File "...\pyRobotiqGripper-master\robotiqGripper.py", line 76, in __init__
    self.readAll()
  File "...\pyRobotiqGripper-master\robotiqGripper.py", line 235, in readAll
    registers = self.read_registers(2000, 6)
  File "...\pyRobotiqGripper-master\venv\lib\site-packages\minimalmodbus.py", line 844, in read_registers
    return self._generic_command(
  File "...\pyRobotiqGripper-master\venv\lib\site-packages\minimalmodbus.py", line 1170, in _generic_command
    payload_from_slave = self._perform_command(functioncode, payload_to_slave)
  File "...\pyRobotiqGripper-master\venv\lib\site-packages\minimalmodbus.py", line 1240, in _perform_command
    response = self._communicate(request, number_of_bytes_to_read)
  File "...\pyRobotiqGripper-master\venv\lib\site-packages\minimalmodbus.py", line 1406, in _communicate
    raise NoResponseError("No communication with the instrument (no answer)")
minimalmodbus.NoResponseError: No communication with the instrument (no answer)

MinimalModbus debug mode. Response from instrument: '' () (0 bytes), roundtrip time: 47.0 ms. Timeout for reading: 50.0 ms.

Process finished with exit code 1

Thank you so much for your help!

bcastets

@nicolasmarcstephan
It is a bit complex to control the gripper through the wrist camera. I would recommend to separate the connection.

You can mount a gripper coupling on top of the camera to separate communication.

nicolasmarcstephan

@bcastets

Thank you for your answer.

Is there an API for the wrist camera?

Otherwise I will just use the gripper coupling.

bcastets

@nicolasmarcstephan
Unfortunately we don't have API our documentation to make advance control of the camera and connected components.
The camera is made to be use in combinaison of UR robot and controlled via its URCAP on polyscope.