[Breaking Down Samsung's Printer] 'Oh, I found a Slug!' [Part 5]

Nov 26, 2007
Nikkei Electronics Breakdown Team
"Slug-shaped" aspherical lens in LSU
"Slug-shaped" aspherical lens in LSU
[Click to enlarge image]

We immediately started to tear apart the upper part of the multifunction printer. First of all, we began tackling the laser scanning unit (LSU) of the printer, which was in the upper part of the chassis. We took out the LSU and opened it.

"Looks like a slug," one of the engineers murmured.

The "slug" is an aspherical lens lying impressively in the unit. The lens irradiates the laser beam on a photoconductor drum at regular intervals. In a general laser printer, the light is reflected on a rotating polygon mirror and scanned on the photoconductor drum. An fθ lens, which converts a constant angular velocity motion to a constant velocity motion, irradiates the laser beam on the drum at intervals as equally as possible.

The fθ lens "has a two-element lens design in most cases, including the products from my company," the engineer said. Samsung, however, only used one "slug-shaped" lens to cover this function.

Cost reduction seems to be the main reason for Samsung's decision to use only one lens. Compared with the case using two lenses, this design not only cuts the component cost, but also reduces the production steps such as the optical axis alignment, hence further reducing the total cost. But the design tends to cause a problem of lower printing precision resulting from, for example, magnification error.

"Samsung probably didn't see any problems in the precision because it is an A4-compatible printer," one engineer speculated.

The polygon mirror used is a regular tetragon with four faces. This shape is easier to work on compared with mirrors with six or eight faces. This seems to be another cost-cutting measure.

A contact image sensor (CIS) is used for the reader of the scanner. SCX-4501K is capable of scanning at a resolution of 600 x 600dpi in the Photo Mode.

Inside LSU: The polygon mirror is beneath the circular object on the substrate in the upper part of the photo. A laser device is located in the upper right of the photo.
Inside LSU: The polygon mirror is beneath the circular object on the substrate in the upper part of the photo. A laser device is located in the upper right of the photo.
[Click to enlarge image]
A substrate on which the four-sided polygon mirror, etc are mounted: A motor driver IC (Sanyo Semiconductor Co Ltd's LB11870) for rotating the polygon mirror is mounted in the center.
A substrate on which the four-sided polygon mirror, etc are mounted: A motor driver IC (Sanyo Semiconductor Co Ltd's LB11870) for rotating the polygon mirror is mounted in the center.
[Click to enlarge image]
The CIS employed in SCX-4501K
The CIS employed in SCX-4501K
[Click to enlarge image]