A robotic orthosis with a cable-differential mechanism

Robotic orthoses have potential to assist people having difficulty in walking due to their neurological disorders. However, it is important to design lighter orthoses since additional weight and inertia from the device cause discomfort to the wearer and even instability during walking in some extreme cases. To address this problem, a robotic orthosis with a cable differential mechanism is proposed in this paper. It is designed to assist stroke patients with hemiplegia. It has 2 active degrees of freedom at the hip and knee joints and one passive degree of freedom at the ankle. A cable differential mechanism is used to transmit the torques generated by the actuators, which are located near the pelvis of the wearer to reduce the inertial effect. The cable differential mechanism allows for the actuators to share the load with each other, which results in decrease of the maximum required torques by the actuators. Therefore, smaller actuators are possible to be used for further reduction of the weight. The proposed robotic orthosis with a cable differential mechanism, which is called “COWALK-Mobile 2,” is implemented and evaluated.