Fundamentals of Wave and Cycloid Gears for Robot and Servo Design

Many of today's precision applications require gears that dramatically reduce speed, power density, and transmission accuracy. Major choices in these designs include cycloid and cycloid gears and gear sets that rely on wave-inducing subcomponents with elliptical or Reuleaux or other polygonal shapes. Cycloids and cycloid gears include elements that rotate around other elements and trace curves. Cycloids delineated by points on the circumference of a rolling element include an epicycloid (the element rolls along the outside of the sun gear or other reference member) and a hypocycloid in which the element rolls within a ring or other reference member. In contrast, trochoids (and their subtypes) are not traced by a point on the circumference of the rolling element, but by some point inside or outside. A particularly common subtype of planetary gearing is the planetary gearing.

Consider a robotic joint that employs a motor (running at a few thousand rpm) with gearing that reduces the output speed by a factor of 100. The gearing in this design also helps boost acceleration torque for the highest power density—a priority design goal for SCARA and cobots, whose total assembly is essentially a cantilevered mass.