The developed force sensory system (FSS) is based on strain gauge-sensing and targeted for the fabric gripper that is presented in:

• PN Koustoumpardis, S Smyrnis, NA Aspragathos, A 3-Finger Robotic Gripper for Grasping Fabrics Based on Cams-Followers Mechanism, International Conference on Robotics in Alpe-Adria Danube Region, 2017

The measurement chain of the FSS consists of:

• 4 strain gauges 350 Ohm Tokyo Instruments FLAB-3-350-11-1LJB-F
• 2 custom half Wheatstone bridges (custom made with 350 Ohm resistors)
• A Load Cell/Wheatstone Shield Amplifier bought by Robotshop.com. The shield is equipped with an AD8426 amplifier from Analog Devices that achieves gain up to 1000.
• A Nucleo F334R8 microcontroller.

The sensing principle of the FSS is shown below:

All components are installed onboard a small mobile robot which is equipped with a esp8266 Wi-Fi module for wireless communication with a laptop.

The FSS presente above was used for cooperative fabric transportation by two wheeled mobile robot in a leader-follower formation. Only the follower is equipped with the FSS and used the provided fabric force feedback to follow the leader.

The force control system of the follower is comprised of two parallel PID controllers.

• The onboard Nucleo MCU accepts code in C++ and can be programmed through the mbed online compiler while in cabled connection with the laptop. The MCU keeps the code that was last passed and runs it every time you switch it on or press the reset button.
• The Wifi communication between laptop and robot as well as the force control scheme is implemented in Python.
• To read the data from the FSS with the robot not moving and connected through usb cable with the laptop, you have to pass the code of src/mbed/Static_experiments_Nucleo.txt to the MCU throught the online compiler.
• For the wireless force control experiments (connection through Wi-Fi) the procedure is:
  • Pass the code at src/mbed/Control experiments_Nucleo_follower.txt and src/mbed/Control experiments_Nucleo_leader.txt to the follower and leader robots, respectively. Remember the follower is equipped with the FSS.
  • Run the code src/wifi_communication/server.py on the laptop
  • Switch-on or reset the robots.
  • To succesfully connect the robots with the laptop their IPs should be properly configured in the above files.

This work is related with the above publications:

• ID Dadiotis, JS Sakellariou, PN Koustoumpardis, Development of a low-cost force sensory system for force control via small grippers of cooperative mobile robots used for fabric manipulation. Adv. Mechanisms and Machine Science 2021, 102, 47–58.
• I. Dadiotis Development of a force sensory system for the control and coordination of mobile robots handling fabrics, Nemertes: Institutional Repository of University of Patras, Patras, Greece, 2020 (in Greek) http://hdl.handle.net/10889/13747

This thesis project was conducted at the Robotics Group, Department of Mechanical Engineering and Aeronautics at the University of Patras, Greece during 2019-2020 by Ioannis Dadiotis and supervised by Dr. J. Sakellariou and Dr. P. Koustoumpardis. Christos Chrysikos and Charalampos Rodopoulos contributed to the implementation of the WiFi communication and force control.