URScript gripper control

Exercise 46 (Integrating gripper control)

1. Run the following gripper code on the physical robots.

2. Analyze rg_grip. What does it do?

3. Modify it so that you can pick a place from the board and place it somewhere else.

4. Optional: Integrate the code to your existing project.

def gripper_example():
  CONTROL_BOX_IP = "localhost"
  # Change this on robots which use a separate control box.
  # For example, a robot with address 172.20.0.202 may have a
  # control box at address 172.20.0.102.

  global RPC = rpc_factory("xmlrpc", "http://" + CONTROL_BOX_IP_IP + ":41414")
  # Remote procedure call object for the OnRobot gripper.
  # Using RPC, we can call functions inside the gripper's control system.

  global TOOL_INDEX = 0
  # One robot can have many grippers. We have only 1.
  # This constant needed by OnRobot RPC functions.

  def rg_is_busy():
    return RPC.rg_get_busy(TOOL_INDEX)
  end

  # width: [0, 110]
  # force: [0, 40]
  # If force is too low, the gripper may not move.
  def rg_grip(width, force = 20):
    RPC.rg_grip(TOOL_INDEX, width + .0, force + .0)
    # `+ .0` required, because rg_grip expects float

    sleep(0.01) # Wait for the gripper to start moving before checking rg_is_busy()
    while (rg_is_busy()):
    end
  end

  rg_grip(0)
  rg_grip(50)
  rg_grip(0)
end

Warning

The code above does not work in the robot simulator, because it uses remote functions for the gripper which are not available in the simulator.

Troubleshooting

Symptom:

• Gripper does not move, even the status LED beside the gripper is green 🟢.

Explanation:

• The gripper’s IP address in URScript may be wrong.

Solution:

• Check its RPC address. On some robots, the gripper is connected to a separate control box, which address will be different than localhost.

Symptom:

• Gripper does not move and the status LED beside the gripper is blinking 🔴.

Explanation:

• Probably gripper’s safety function was triggered, because an usual force was applied on the gripper.

Solution:

• Reset the gripper’s safety trigger using the pendant. Create a new robot program on the pendant and add a gripper block. In the gripper block you will see a setting that can reset the security trigger. Then the gripper LED should turn green again.