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Design and analysis of a new gear-driven compliant torsional spring for upper-limb biomedical rehabilitation device

Wearable devices such as prosthetics, exoskeleton, robotic manipulator, orthosis are necessary for training rehabilitation process for disabled people. They require a compact size, a light weight and a safe interact between people and equipment. This paper proposes a design and analysis of a new gear-driven compliant torsional spring for rehabilitation device of an upper limb. The device consists of a DC motor, a gear trainer, a compliant torsion spring (CTS) fitted to the output shaft and fixed in cover to absorb vibrations and ensure safety. The CTS is the most important element to allow a light mass, a high flexibility and a great deformable ability. The dynamics of the device is determined by Lagrange method. The energy deformation, stress and strain of the CTS are analyzed by finite element method. The stiffness of the CTS is about 216∗104N/m, frequency of the CTS is approximately 1685 Hz. The results showed that the maximum deformation capacity is about 7.4919 mm. The relationship between the deformation and moment is linear. The largest strain energy is 0.65239 mJ. The relationship between the strain energy and moment is nonlinear. The maximum stress is 367.15 MPa, which is much less than the yield strength of AL7075 (503 MPa). The relationship between stress and moment is linear. The coefficient of safety of the structure is about 1.37. In the future, the device will be fabricated, the experiments are conducted to test the properties of the device. Finally, the proposed biomedical rehabilitation device is desired to be transferred to hospitals and centers of physiotherapy exercises.