Let there be light- Big shades lift easily with low-friction gears

Large shades go up with half the effort, thanks to a new gearbox sporting low-friction gears made from Delrin acetal. The low-friction gearbox provides mechanical advantage so window shades smoothly rise with a lift weight up to 7 lb. Without the gearbox, similarly sized shades would take double the force.

The gearbox was designed by Performance Gear Systems Inc., Downers Grove, Ill. (www.performance-gear.com), using a parallel-axis configuration that operates in two directions. This is key to lifting and lowering the shade. A retractable pull-cord assembly activates the gears which link to a drive shaft located in the shade head rail. Two shaft-mounted pulleys produce up and down movement of the shade's lift cords. The gearbox safely retracts the cord to a preset length after the shade is adjusted, so the cord is out of reach of small children.

The gearbox contains three gears, an input gear, parallel-mounted cluster gear, and output gear. All three gears are molded by Performance Gear from a specially formulated ultralow-friction grade of Delrin acetal from DuPont Engineering Polymers, Wilmington, Del. (plastics.dupont.com). It contains 10% by weight DuPont Teflon PTFE fluoropolymer in micropowder form.

Other gearbox components include the housing, housing cap, and retainer. The retainer holds the gears in the housing and has a bearing shaft for input and output gears. Performance Gear molds these parts from DuPont Zytel 132F nylon resin, an unreinforced, fast-cycling PA66 grade.

Jean M. Hoffman
Machine Design, October 20, 2003