Development of a knee joint assist suit with a velocity-based mechanical safety device (Transient response analysis of the safety device and experiments)

Abstract

Safety is one of the most important issues in rehabilitation assist suits. We have proposed and developed a rehabilitation assist suit equipped with a velocity-based mechanical safety device (VBMSD) to address this issue. The assist suit aids flection and extension of a patient’s knee joint. The VBMSD switches off the motor of the assist suit when the angular velocity of the patient’s knee joint exceeds a preset threshold level. The VBMSD works even under failure of the assist suit’s computer, because it consists of only passive mechanical components without controllers, actuators, and batteries. In this VBMSD, the time delay between the instance of the velocity exceeding the threshold and the instance of the motor switched off is an important parameter. If the time delay is excessive, the motor may move a patient’s leg at unexpected high velocities. Therefore, it is necessary to analyze the length of time delay and to experimentally validate the analysis. The analysis will also be useful for the design of future VBMSDs. In this paper, we theoretically derive the time delay using the transient response analysis of the VBMSD. Furthermore, we simulate how quickly the VBMSD responds to a rapidly increasing velocity by using the derived time delay. Finally, we present experimental results to verify the analysis and simulation.

Keywords

• robot
• design
• mechanism
• rehabilitation assist suit
• mechanical safety device
• transient response analysis
• time delay