Is there a way to quickly query the gripper state using xarm_api?

[IrvingF7]

I am using the humble branch.

Basically, when using fake hardware or using xarm_moveit_servo, there is a remapping of the joint name when launching joint_state_publisher. This publishes a /joint_states topic that not only includes the robot's joints, but also the gripper's status because of the remapping. This is a different topic from /xarm/joint_states because the /xarm/joint_states one doesn't include the gripper info.

I am wondering if using anything from xarm_api can achieve something similar? I want to be able to see the gripper's status at the same frequency as my joint states (e.g. 100Hz).

Right now, I can keep the moveit_servo running alongside xarm_api without using it so that I have the joint_states topic. But there are two problems:

1. It seems like the drive_joint value is not really updated, even if I close/open the gripper. In my moveit code, I have architected it in a way that a move_group is running alongside the moveit_servo, so it seems like the drive_joint is correctly updated when I collect my data. (following the advice here: How can we teleop the Gripper from xarm_moveit_servo? #104)
2. I think it's not really recommended to keep the api running along with Moveit, right? So I would really like to see some alternative

I thought about just writing a custom publisher that constantly sends requests to the get_gripper_position service and publishes the result at 100hz, but I don't know if it's a good idea, and I want to hear from the official team.

Thank you in advance

Or, even better, the Xarm team can implement some kind of topic that is published by the xarm_api that works similarly to /xarm/joint_states

[penglongxiang]

Hi @IrvingF7, the real gripper is considered as an external hardware to the arm and does not have active reporting mechanism with xArm, so for now there is no synchronized auto-update of the gripper position for real hardware application.

We have noticed this demand for data collection in policy training, and recently added the active query mechanism inside controller firmware, and it will take some time to test and integrate into ROS support. For now, if you have a temporary solution you can stick to it and we will notify you as soon as the auto-report mechanism is available in ROS2. Sorry for the inconvenience.

[IrvingF7]

Hi @IrvingF7, the real gripper is considered as an external hardware to the arm and does not have active reporting mechanism with xArm, so for now there is no synchronized auto-update of the gripper position for real hardware application.

We have noticed this demand for data collection in policy training, and recently added the active query mechanism inside controller firmware, and it will take some time to test and integrate into ROS support. For now, if you have a temporary solution you can stick to it and we will notify you as soon as the auto-report mechanism is available in ROS2. Sorry for the inconvenience.

Got it! Thank you for getting back to me. In the future, when that feature is integrated into the ROS2 package, please pin me in this issue if you can still remember it. Really appreciate it!

[MinnaZhong]

Hi @IrvingF7,

We added this feature to the ROS2 package. Please update the firmware to V2.7.101 beta version and pull the latest code.

1. Update the firmware to V2.7.101.
   Download the offline package, enter 'Settings-My Device-Check Update-Install'.

2. Enable the gripper state report through ros service set_external_device_monitor_params.

ros2 service call /xarm/set_external_device_monitor_params xarm_msgs/srv/SetInt16List "{datas: [1, 100]}"

datas: [ param1, param2]

• param 1: Gripper Type. 1- Gripper; 2- Gripper G2; 3- BIO Gripper G2
• param 2: Frequency(HZ).

Note: If there is an error, you need to enable this report function again to get the gripper state.