Small-Beads Transmission and Its Application to Robot Joints

Small-beads are everywhere in our daily life. A collection of small-beads can behave macroscopically like liquid and flow. This paper presents a power transmission method referred to as “small-beads transmission” that can transmit power in all directions and convert linear motion into rotational motion and vice versa. The force transmission ratio is dependent on the resistance coefficient that is proposed to reflect the friction of small-beads and the dynamic responses of the internal particle force chains to external forces. Experiments on the resistance coefficient in pipes are conducted. The experimental results show that the proposed transmission method has great capability to provide isolation from external vibration and shock. Based on the experimental results, a small-beads transmission joint is designed and applied to robot legs to achieve human gait-like movement. This concept is also applicable to designing robotic joints and limbs, or orthoses and exoskeleton devices. The configuration of small-beads transmission is similar to that of the conventional hydraulic or pneumatic transmission in cylinder–piston system. However, the proposed method does not necessitate the use of tight sealing as that needed by hydraulic and pneumatic transmission, it is much easier to fabricate and also fit for hazardous environments.