This paper presents a new type of constant-velocity transmission devices based on parallel mechanisms with properties of equal-diameter spherical pure rolling. The method we used is essentially an extension of the planar ellipse gear to the spherical one. Both the fixed and moving axodes of a specified parallel mechanism are obtained, as traced by the spatial instant screw axis (ISA) with respect to the fixed and moving coordinate systems. Based on Poinsot’s theorem and achievements, a series of these parallel mechanisms which satisfy constant-velocity condition have been disclosed correspondingly. Their motion range and transmission performances are also explored by taking the 3-4R mechanism as an instance. As the main part of this paper, two important applications for this type of constant-velocity transmission devices are also explored. One is used as a gearless spherical gear, and the other is used as a constant-velocity universal joint (CVJ). Simulations were fulfilled on ADAMS to verify the transmission performance in terms of different applications.

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