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Differential Pitch Helix Coil for Copier Lamp

IP.com Disclosure Number: IPCOM000037522D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Grant, DE: AUTHOR

Abstract

In conventional copier lamps, when the lamp filament is coiled, and then formed into a vertical helix, the spacing of the coils is made uniform, as shown in Fig. 1. The lamp designer makes an attempt to keep the coils close together to form the compact light source needed for copier footprint uniformity. As the lamp operates, the tungsten creeps because of the high temperature that is needed for high light output, as shown in Fig. 2.

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Differential Pitch Helix Coil for Copier Lamp

In conventional copier lamps, when the lamp filament is coiled, and then formed into a vertical helix, the spacing of the coils is made uniform, as shown in Fig. 1. The lamp designer makes an attempt to keep the coils close together to form the compact light source needed for copier footprint uniformity. As the lamp operates, the tungsten creeps because of the high temperature that is needed for high light output, as shown in Fig. 2.

Creep is a normal behavior pattern for hot tungsten wire even though it has been crystallized in a vacuum furnace for an hour at 2600oC. When coils collapse onto each other, arcing occurs in the lamp and the shorted coil melts, destroying the lamp. Fig. 2 shows a conventional lamp near end-of-life due to creep or sag of the coils in the helix.

A new lamp with differential coil pitch in the helix is shown in Fig. 3. The coils at the top (burning orientation) are closer together. With lamp aging, the coils approach a uniform spacing, and then continue to sag toward the bottom of the helix. Eventually, they will become unequally spaced, as shown in Fig. 2 but, by the time this occurs, the lamp will be reaching a normal end-of-life due to tungsten evaporation.

Disclosed anonymously.

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