Passive Two-Way Ratchet Brake Applicable to the Roll Axis of Weight Assist Device

In industrial fields, when workers perform repetitive tasks holding heavy tools for prolonged periods of time, adopting a weight assist device (WAD) can relieve workers' muscle fatigue and increase their work efficiency and productivity. These WADs, with a multi-degree-of-freedom counterbalance mechanism, can maintain posture in the pitch axis; however, they face the limitation of not being able to maintain posture in the roll axis due to the absence of a rotation limiting device. Consequently, workers are easily exposed to dangerous situations, such as collisions and pinching. To overcome these drawbacks, this study proposes a passive brake using a ratchet structure capable of rotating in both directions, which can be applied to the roll axis of a WAD. The two-way ratchet joint brake is actuated by the contact of the ratchet ring and the stopper. Due to the normal force between the contacts, it does not rotate below a certain torque and rotates only when a certain torque is exceeded. In the free rotation state, the brake can help the device to quickly return to the stationary state. In the design stage, we set parameters, such as the contact angle, to design a brake with a reference torque to keep stationary below a certain torque. The performance of the brake was verified in terms of stationary state maintenance.