Integrating Compliant Actuator and Torque Limiter Mechanism for Safe Home-Based Upper-Limb Rehabilitation Device Design

Stroke patients may prefer to rehabilitate at home, which limits their access to appropriate training devices and safety without supervised assistance by qualified personnel. However, most training devices are bulky and lack adequate safety for home-based training. To address this limitation, we have developed a device with a variable stiffness actuator (VSA) that was designed in the vsaUT-II and an effective torque limiter mechanism. First, compared with traditional actuators with very high mechanical impedance, actuators with adaptive compliance have many advantages for rehabilitation devices. For instance, compliant actuators can guarantee patient safety, especially, when a muscle spasm occurs. Moreover, stiffness can be adjusted to adapt to a specific level of patient impairment. Compliance in our device was realised using a VSA. Second, to avoid any danger in the absence of professionally supervised assistance, a novel torque limiter mechanism was designed. The mechanism can be released and effectively reduces the driving force whenever a spasm occurs. The experimental results prove that by adjusting the ratio between the internal springs and actuator output, the output stiffness is changed. The dynamic modeling of the device was also designed within a small deflection of the elastic elements. The torque limiter mechanism was evaluated with variable stiffness for ensuring safety in various conditions.