Angle-adjustable tripod universal joint

An angle-adjustable tripod universal joint, comprising:

• a tripod;
• three rollers;
• and
• a universal joint outer part, wherein
• an inner wall of the universal joint outer part is provided with three roller tracks;
• wherein for each roller,
• the roller is disposed in a corresponding roller track and rolls along the corresponding roller track,
• a spherical shaft head on the tripod is rotatably disposed in an inner cavity of the roller,
• an inner wall of the roller track is provided with at least one guiding groove,
• the roller has a cylindrical peripheral shape,
• a bottom surface of the guiding groove is a plane surface,
• two side surfaces of the guiding groove are flat surfaces perpendicular to the plane surface, wherein two ends of the roller are in clearance fit with the two side surfaces of the guiding groove,
• the bottom surface of the guiding groove is provided with an elongated slot extending along the length direction of the guiding groove,
• a part of the peripheral surface of the roller is inserted in the guiding groove, and
• the peripheral surface of the roller is tangent to the plane surface so that the plane surface of the roller track and the roller are in linear contact and have a contact line consisting of two unconnected line segments separated by the elongated slot,
• wherein the roller track and the roller generate a frictional resistance torque by frictional forces on the two unconnected line segments, and the frictional resistance torque is configured to counteract a deflection torque generated by the spherical head shaft of the tripod acting on a surface of the inner cavity of the roller.