Double Worm Gear Reduction

This is a unique gear reduction that transmits torque between two parallel shafts and features a novel interlocking feature between a helical-worm idler pair. Beyond the concept design, extensive depth was performed on optimizing tooth geometry for efficiency, tolerance stackup, and endurance testing.

Design Requirements:

• 1:100 reduction in an extremely small space (size of pinky tip ~20x30x45mm)

• Input and output shafts are parallel, orientation and position are locked

• Robust, endure 3.5M revolutions from input shaft and with part-part variations up to 4sigma

• Cheap and easy to assemble….duh!

While contracting at HP, I regularly designed mechanisms for drive transmission working inside the very tight constraints of printers.  One of the dozens of such puzzles I addressed was for a speed reduction drive. The predecessor drive utilized an electronically actuated clutch. It had an undesirable failure mode, noisy, complicated to assemble and required expensive proprietary parts.  I created an elegant solution using specialized worm gears and introduced a new molding strategy to make manufacturing feasible.  By conducting many in-depth analysis I made the gears more robust to molding and assembly variations.  The new design significantly reduced cost and prolonged the life of the motor and its success has inspired others to use it elsewhere for their systems within the printer.

A large challenge in the later phases was determining issues from part variations at the upper end of the tolerance band. I utilized a contact model simulation to develop a custom tooth geometry to tolerate large C-C variation whilst maintaining tooth strength.