Investigation of Twisted String Actuation with a Programmable Mechanical Load Test Stand

Twisted string actuation has been proven to be an effective solution for generating linear motion with high tensile force from low-torque rotary motors. Its inherently slender form has predestined this little-known actuator type for driving the fingers in tendon-driven robotic hands. In the European project DEXMART, 24 electrical motors were compactly integrated into the robotic forearm, each capable of generating 80 N of tractive force from about 5 mNm of torque [1-3]. A number of forms of twisted string actuation have been proposed over the past few decades [4-10], and more and more research institutes and companies are exploring its advantageous properties and application potential. In support of the development of linear motion devices based on twisted string actuation, a test stand has been developed for investigating and characterising their performance. A linear electromagnetic motor serves as a programmable mechanical load in a microcontroller-based closed-loop controller. Thus, the twisted string actuator can operate according to a predefined load profile or drive a load with a programmable dynamic behaviour. The test stand set-up will be described and its operating performance demonstrated by means of various load cases.