Gear transmissions of various sizes are used in various fields of mechanical engineering, automotive, marine, and aerospace industries according to the needs. This paper presents the modeling and analysis of the modal and harmonic characteristics of a planetary gear transmission for an elbow orthosis. Orthoses are used during the rehabilitation of patients in the postoperative period or during the restoration of lost limb functions. When modeling the planetary gear, the connection elements are made of 45 steel and PLA polylactide. Using ANSYS Workbench, the planetary gear of the gearbox was analyzed for modal and harmonic characteristics at three different torque values: 1732 N-mm, 3464 N-mm, 5196 N-mm. The modal and harmonic analysis of the stress-strain state of the planetary gear is carried out, a comparative analysis is performed, and the vibration characteristics, including natural frequencies, mode shapes, and harmonic response, are discussed. Also, the stress-strain state of the sun-satellite contact problem made of steel 45 and PLA polylactide is calculated and the corresponding analytical calculation of equivalent contact stresses is performed according to Hertz's theory.
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