Model-Based Performance Analysis of Twisted String Actuators With Comparison to Spooled Motor Tendon-Driven Actuators

Twisted string actuators (TSA) exhibit desirable traits for robotic applications like enabling high-force actuation. It is important to understand TSAs' key performance metrics to allow for ubiquitous usage. However, performance analysis of TSAs is challenging due to the strong coupling between the TSA model parameters. Comparing TSA's performance to motor-based actuators is essential in understanding the trade-offs of TSAs compared to motor-based tendon-driven actuators. This letter presented a model-based performance analysis of TSAs with a focus on four metrics: contraction range, linear velocity, effective torque input, and force output. Furthermore, the performance of TSAs was compared to another motor-based actuation technology namely spooled motor-tendon actuator (SMTA). A comparison framework was proposed by synthesizing models of TSAs and SMTAs. Simulation studies were conducted using the same type of motors to construct TSAs and SMTAs. The results showed that TSAs performed better in force outputs and effective torque inputs, whereas the SMTAs outperformed TSAs in terms of linear velocity and contraction range. In addition, a robotic assistive glove leveraging the advantageous performance of TSAs was realized, demonstrating the importance of the results. The findings suggest that TSAs are more suited for compact, high-force applications while SMTAs are more appropriate for high-speed robotic applications.