Gear Retaining Compression Ring

Conventional means of retaining plastic gears onto a shaft do not perform in extremely high precision drive trains— Even knurls on a shaft affect the output velocity by distorting the pitch circle of the gear. Additionally, using a keying feature also distorts the gear due to the asymmetrical mold flow from the necessary pocket on the plastic gear. Finally, Press fitting onto a smooth shaft reveals the plastic quickly experiencing creep and it free spinning under thermal cycles trying to transmit the required torque…

The solution that was patented utilizes a metal ring that itself is press fit onto the hub of the gear on a smooth shaft. This ring maintains substantial hoop stress and compression on the gear hub despite creep and thermal cycles. The ring is widely adaptable, cheap, and easy to assemble. Furthermore it can be extended to mount items such as the encoder disc. Since it’s introduction it is widely being adopted as it is even cheaper and more controllable than knurling.

Design Requirements:

• 10yr product lifetime in very hot, very cold climates or frequently transitioning

• Torque transfer to Plastic Gear/Pulley

• Very High tolerance. Cannot use knurls (as it distorts the shaft, no longer precision), Cannot use keying feature (as it distorts gear mold flow)

To really sympathize with issues of precision at this scale, you have to understand that 2D printers are basically an error amplification machine. An enormous amount of mechanical complexity is combined in teetering tolerance stackups and the output is ultra fine text or images. The human eye is impressively adapted to detect misplaced erroneous features and patterns. Furthermore, the design expectation is be able to print continuously for 5yrs or more, in severe environments (and occasionally abusive users! Don’t worry it’s usually the digital UX that’s the provocateur rather than the mechanical design ;p .).