Variable Grounding Flexible Limb Tracking Center of Gravity for Sit-to-Stand Transfer Assistance

Wearable robotic limbs support sit-to-stand (STS) transfer with increased stability while maintaining a compact size, as well as providing body weight support. This paper proposes a new robotic limb, Variable Grounding Flexible Limb (VGFL). The VGFL achieved a novel strategy in which its grounding point tracks the forward shift of the wearer's center of gravity (CoG) during STS. Since the strategy keeps the distance between the grounding point and the CoG close, an upward force can efficiently work for the STS assistance. To implement the strategy, this paper utilized the High-Strength and Flexible Mechanism (HSFM). The HSFM can change its grounding point while being capable of lifting body weight with one motor. Owing to these unique characteristics, the VGFL can realize the strategy without multiple actuators and complex controllers. Furthermore, real-world experiments confirmed that the grounding point of the VGFL accurately tracked the forward shift of the CoG during the STS assistance. Moreover, experiments conducted with three healthy subjects showed that the VGFL reduced the surface myoelectricity of the lower limbs during STS transfer. The VGFL could demonstrate high support performance in STS with the CoG tracking strategy.