Design of a New Compact Velocity-Based Mechanical Safety Device for a Knee Joint Assist Suit

Abstract

Safety is important in rehabilitation assist suits. To address this issue, we have developed a velocity-based mechanical safety device (VBMSD) for an assist suit to aid flexion and extension of a patient's knee joint. The VBMSD turns off the assist suit's motor when the knee joint angular velocity generated by the motor is equal to or higher than a preset threshold level. The name for this level is the “detection velocity level (DVL).” The DVL is adjustable according to the requirement of each patient's gait exercise. In addition, the VBMSD works even when the assist suit's computer has broken down, because it consists of only passive mechanical components such as springs. However, not only safety, but portability is also important in the assist suit because patients wear it. Therefore, the VBMSD attached to it is also required to be as small and light as possible. In this paper, we introduce a new compact velocity-based mechanical safety device (compact VBMSD) designed in this study. Comparing the previous VBMSD and the compact VBMSD, we describe how much smaller and lighter the compact VBMSD is. Furthermore, we check that the compact VBMSD does not theoretically resonate with a walking cycle (0-IHz) in their gait exercise. Finally, in order for many patients to use it, we confirm that the DVL in the compact VBMSD is adjustable up to the kneejoint angular velocity of 6 rad/s, which is the velocity level of healthy adults' walking.