AttributeError when trying to connect to the gripper on ROS Noetic

[PatrickReitz]

Hi,

I am currently trying to connect the robotiq_2f_85 gripper to ROS Noetic on Ubuntu 20.04
The package built just fine, but now I am trying to run the commands from the original tutorial
When I try to connect to the gripper with the command

rosrun robotiq_2f_gripper_control Robotiq2FGripperRtuNode.py /dev/ttyUSB0

I get the following error:

File "/home/user/reitz/workspace/src/robotiq/robotiq_2f_gripper_control/nodes/Robotiq2FGripperRtuNode.py", line 86, in
mainLoop(sys.argv[1])

File "/home/user/reitz/workspace/src/robotiq/robotiq_2f_gripper_control/nodes/Robotiq2FGripperRtuNode.py", line 72, in mainLoop
status = gripper.getStatus()

File "/home/user/reitz/workspace/src/robotiq/robotiq_2f_gripper_control/src/robotiq_2f_gripper_control/baseRobotiq2FGripper.py", line 107, in getStatus
status = self.client.getStatus(6);

File "/home/user/reitz/workspace/src/robotiq/robotiq_modbus_rtu/src/robotiq_modbus_rtu/comModbusRtu.py", line 108, in getStatus
response = self.client.read_holding_registers(0x07D0, numRegs, unit=0x0009)

File "/usr/lib/python3/dist-packages/pymodbus/client/common.py", line 114, in read_holding_registers
return self.execute(request)

File "/home/user/reitz/workspace/src/robotiq/robotiq_modbus_rtu/src/robotiq_modbus_rtu/robotiqmodbus/client/sync.py", line 85, in execute
return self.transaction.execute(request)

File "/usr/lib/python3/dist-packages/pymodbus/transaction.py", line 116, in execute
_buffer = hexlify_packets(self.client.framer._buffer)

AttributeError: 'ModbusRtuFramer' object has no attribute '_buffer'

Any idea how to fix this?

[lianghongzhuo]

There is an incompatible version upgrade for pymodbus. We grab the v1.2 to our fork.
https://github.com/TAMS-Group/robotiq/blob/noetic-devel/robotiq_modbus_rtu/src/robotiq_modbus_rtu/robotiqmodbus/README.md
You can try our fork to see if the problem still exists.

[blueed9696]

How did you install v1.2 pymodbus?

[lianghongzhuo]

we do not need to install v1.2 pymodbus. We import this file https://github.com/TAMS-Group/robotiq/blob/noetic-devel/robotiq_modbus_rtu/src/robotiq_modbus_rtu/robotiqmodbus/client/robotiqrtuframer.py instead
Just install our fork https://github.com/TAMS-Group/robotiq and test your gripper.
Install the pymodbus from deb package.

[lianghongzhuo]

@Patrick-Re Hi, have you tried our fork of robotiq? Is it work on your 2finger gripper?
It would be great if you can let us know. As we only have a 3finger gripper for testing.

[blueed9696]

@lianghongzhuo I have tried it, but it does not work for 2 finger gripper. I have same issues with Patrick.

[lianghongzhuo]

https://github.com/TAMS-Group/robotiq/blob/noetic-devel/robotiq_2f_gripper_control/nodes/Robotiq2FGripperRtuNode.py#L54

Could you try change this line to :

gripper.client = robotiq_modbus_rtu.comModbusRtu.communication(retry=True)

If the above not work, you can also try uncomment: https://github.com/TAMS-Group/robotiq/blob/noetic-devel/robotiq_2f_gripper_control/nodes/Robotiq2FGripperRtuNode.py#L76
and
https://github.com/TAMS-Group/robotiq/blob/noetic-devel/robotiq_2f_gripper_control/nodes/Robotiq2FGripperRtuNode.py#L82

[lianghongzhuo]

reference: https://github.com/TAMS-Group/robotiq/blob/noetic-devel/robotiq_3f_gripper_control/nodes/Robotiq3FGripperRtuNode.py

[lianghongzhuo]

If the above modification works, feel free to make a pull request and I can update our code

[PatrickReitz]

Hi, sorry for the late update.
Thank you very much for your help, it is working now.
v1.2 of pymodbus did not work for us and we had issues elsewhere. But we installed v1.3.1 on our system instead and that fixed all issues.

pip uninstall pymodbus pip install pymodbus==1.3.1

was all it took

[lianghongzhuo]

Hi, sorry for the late update. Thank you very much for your help, it is working now. v1.2 of pymodbus did not work for us and we had issues elsewhere. But we installed v1.3.1 on our system instead and that fixed all issues.

pip uninstall pymodbus pip install pymodbus==1.3.1

was all it took

Yes, install v 1.3.1 works, or you could also try the new commit I just pushed.