The twisted cord that stored the power for casting objects with the ballista was also used over the centuries to apply high forces, e.g. in boat construction, and is known as a Spanish windlass. Now, researchers within the DEXMART project have come up with the drive to mobilise robotic fingers, drawing upon the extremely powerful pull that a string can exert against a load when given a soft twist. The result: a powerful linear actuator for pulling the tendons of a robotic hand making use of extremely compact, low-torque motors; a 12 mm DC motor with a driving torque on the order of 5 mNm is capable of quickly lifting a 5 kg load over 3 cm (see video linked below).

This new twist to things, for which a patent is pending, is at the focus of continued actuator research and development within the DEXMART project. A scientific paper describing and modelling the concept as well as demonstrating the controlled actuator behaviour by means of simulation and experiments has been submitted for publication and presentation under the title “The Twisted String Actuation System: Modelling and Control” at the 2010 IEEE International Conference on Robotics and Automation. A second publication entitled “Twisted-String Gear for Linear Actuation” is in preparation for presentation at the VDI 2010 International Conference on Gears.

For more information about actuator research within DEXMART please contact Mr. Chris May.

>> Download video: Robotic finger does the twist (5.4 MB)