Development of an ankle joint assist suit with hardware-based safety devices (Design using quality function deployment)

When developing rehabilitation assist suits, safety consideration for patients is one of the most important issues. In this paper, we propose an ankle joint assist suit with a velocity-based safety device and a commercial torque limiter. The velocity-based safety device switches off the assist suit’s motor if it detects an unexpected high joint angular velocity. The torque limiter cuts off the torque transmission if it detects an unexpected high joint torque. These devices work even when the assist suit’s computer breaks down, because they consist of only passive mechanical components without actuators, controllers, or batteries. First, we describe the design requirements for this assist suit. Next, we clarify the relationship between the design requirements and the assist suit parts by using Kato’s multispace-quality function deployment (M-QFD). Finally, we present the assist suit design incorporating this relationship.