Implementation

Biomimetic Robotic Applications

TSAs are commonly found in biomimetic robotic applications such as robotic hands and exoskeletons. A five-fingered robotic hand with joints powered by TSAs was developed and had demonstrated several pinching and grasping abilities and similar degrees of freedom as a typical human hand. A multi-fingered robotic hand driven by TSA is shown in the figures below. Fig(a) shows several pinching and grasping tasks of the TSA whereas Fig (b) shows the anthropomorphic hand which uses active dual-mode twisted actuation to compromise the tradeoff between torque and speed of TSA. The flexibility feature of TSA is very useful for assistive and power augmentation devices. In addition to the robotic hand, a portable soft exosuit for upper extremity rehabilitation was also developed to provide shoulder and elbow assistance.

Tensegrity Robots

Tensegrity robots use an impedance controlled twisted string actuators as an alternative to traditional spooled cable actuation for reliable and robust environmental interactions. The traditional approach uses intermediate mechanisms such as gear boxes and spools which add weight and inefficiencies to the mechanism resulting in a common failure mode as the string goes back and falls off the spool, wrapping around the motor axis. As a solution to this problem, TSA was introduced and was actually used in the tensegrity robots as it provides a simple, compact, light-weight,inherently compliant mechanical approach to control the tension of the strings. Since the force distribution properties and controllable compliance are essential for tensegrity robots, TSAs are ideal actuators to control the strings and adjust the force and stiffness along the desired trajectory.

References:

1. I. W. Park and V. SunSpiral, “Impedance controlled twisted string actuators for tensegrity robots,” in Proc. Int. Conf. Control, Automation

and Systems, 2014, pp. 1331–1338.

2. Zhang, Jun., et al., “Robotic Artificial Muscles: Current Progress and Future Perspectives,” IEEE Transaction on Robotics, pp. 1-21, 2019.