Speed differential planetary gear train

A speed differential planetary gear train comprising,

• a first rotatable shaft connected to an eccentric for rotation therewith, the eccentric rotating about the axis of the first shaft.
• a two gear cluster comprising a first external gear and a second external gear, said cluster being journaled on said eccentric for rotation about the axis of the eccentric,
• said first external gear meshing and rotating within a first internal gear disposed around it, thereby forming a first gear system,
• said second external gear meshing and rotating within a second internal gear disposed around it, thereby forming a second gear system,
• means preventing rotation of one of said internal gears,
• and means connecting the other of said internal gears to a second shaft for rotation therewith, said second shaft having an axis of rotation which is colinear with the axis of rotation of the first shaft,
• the two said systems both being standard involute systems with N = PD for each gear,
• said external gears having different numbers of teeth,
• the gears of the said train being further related substantially in accordance with the following equations:
• 1) E = (D.sub.int - D.sub.ext) /2
• 2) F.sub.F,A = E.sub.B,C
• 3) 0.84 d.sub.int .ltoreq. D.sub.ext ##EQU3## wherein N is an integer equal to the number of teeth on the respective gear;
• P is the diametral pitch of the respective gear;
• D is the gear diameter;
• E is the offset between the center of the eccentric and the axis about which the eccentric rotates;
• the non-rotating internal gear is designated as F;
• the external gear which meshes with the non-rotating internal gear is designated as A;
• the other external gear is designated as B;
• and the other internal gear is designated as C.