Development of a uniaxial scissor unit into a tri-axis motion system via double universal joints

The scissor mechanism provides a high motion multiplication capacity, as a small displacement at the link level can generate a large displacement at the mechanism level, making it an ideal choice for lifting applications, such as hydraulics lifts, scissor jacks, and industrial machinery. Although the mechanism can provide a uniform extension, it is limited to a single axis, giving a single degree of freedom (DoF). This study presents a novel scissor kinematics-based parallel tri-axial motion system capable of 3 DoF, with one translation, 1 T (Z), and two rotations, 2R (A & B). The enhanced range of motion is achieved by integrating a double universal joint with the standard scissor mechanism. The addition of the universal joints allows the end effector (EE) rotation in two directions. While linear travel is determined by the scissor link lengths (which can be increased by incorporating multiple scissor rings), the rotational tilt is determined by the dimensions of the universal joint. The forward kinematics (FK) is also presented to determine the pose of the EE (Z, A, B) for a given set of scissor lengths (z₁, z₂, z₃). A proof-of-concept (PoC) is fabricated using custom-made 3D-printed parts using an FDM machine. Fundamental motion range analysis in a computational simulation environment showed that the system could have a vertical translation beyond 100 mm and a tile beyond 60° in either direction, making it eligible for multi-axis platforms for space posture adjustment and processes like Additive Manufacturing (AM).