Development of a SMA-Fishing-Line-McKibben bending actuator

High power-to-weight ratio soft artificial muscles are of overarching importance to enable inherently safer solutions to human-robot interaction. Traditional air driven soft McKibben artificial muscles are linear actuators and it is impossible for them to realize bending motions through use of a single muscle. More than two McKibben muscles are normally used to achieve bending or rotational motions, leading to heavier and larger systems. In addition, air driven McKibben muscles are highly nonlinear in nature, making them difficult to be controlled precisely. A SMA(shape memory alloy)–fishing–line–McKibben (SFLM) bending actuator has been developed. This novel artificial actuator, made of a SMA-fishing-line muscle and a McKibben muscle, was able to produce the maximum output force of 3.0 N and the maximum bending angle (the rotation of the end face) of 61°. This may promote the application of individual McKibben muscles or SMA-fishing-line muscles alone. An output force control method for the SFLM is proposed, and based on MATLAB/Simulink software an experiment platform is set up and the effectiveness of control system is verified through output force experiments. A three-fingered SFLM gripper driven by three SFLMs has been designed for a case study and for which the maximum carrying capacity is 650.4 ± 0.2 g.