Variable Stiffness Control and Rubbing

The variable stiffness module provides three services. The following is written for r1_gripper, and is similar for r2_gripper.

  • Calibration: Initially, the variable stiffness motors must be moved to the zero position. This is done by a call to the r1_gripper/CalibrateRubbing.
  • Setting the stiffness: The r1_gripper/SetRubbingStiffness service takes the stiffness parameter between 0 (minimum) and 15 (maximum) and instructs the variable stiffness motors to the correct position.
  • Rubbing motion: The variable stiffness motors can be used to create a rubbing motion by the gripper through a call to the r1_gripper/Rub service. This service takes the number of times the gripper should perform the rubbing as parameter.

Preparation

Arduino preparation (optional) in case of uploading Arduino code again. The installation of Arduino IDE for Ubuntu can be done following the instruction from http://blog.markloiseau.com/2012/05/install-arduino-ubuntu

Execution

Setting communication

Checking the USB port's number of the Variable Stiffness module of the Clopema gripper

$ dmesg

The USBport is shown as ttyUSB0 for ARDUINO NANO

...
[24412.986199] usb 7-1: Product: ARDUINO NANO
[24412.986203] usb 7-1: Manufacturer: Gravitech
[24412.986208] usb 7-1: SerialNumber: 13JP0077
[24412.992240] ftdi_sio 7-1:1.0: FTDI USB Serial Device converter detected
[24412.992302] usb 7-1: Detected FT232RL
[24412.992307] usb 7-1: Number of endpoints 2
[24412.992312] usb 7-1: Endpoint 1 MaxPacketSize 64
[24412.992317] usb 7-1: Endpoint 2 MaxPacketSize 64
[24412.992321] usb 7-1: Setting MaxPacketSize 64
[24412.994262] usb 7-1: FTDI USB Serial Device converter now attached to ttyUSB0

Execute the rubbing node

Run the rubbing node with the correct usb port

$ catkin_make    # if rubbing.cpp is modified
$ . devel/setup.bash    # source the setting file
$ rosrun rubbing rubbing_node /dev/<ttyUSBport>    # connect to USB port of the variable stiffness module

Call services of the rubbing node

Run different services of the node

  • Calibration service

This service sets the zero position of the variable stiffness module. The stiffness is set to zero (the most compliant stage of the gripper). This service has to be called before any other service.

$ rosservice call /r1_gripper/CalibrateRubbing    # call calibrate service

  • Stiffness control service

The stiff level of the gripper varies from 0 to 15. The higher level of stiffness the more stiff the gripper is.

$ rosservice call /r1_gripper/SetRubbingStiffness "stiffness: 10"    # set the stiffness level to 10

  • Rubbing movement control service

Before calling rubbing service, the stiffness should be set at 15. This service performs the rubbing motion between the two fingers. The required parameter is the number of rubbing movement.

$ rosservice call /r1_gripper/Rub "times: 3"    # rub the two fingers 3 times