X-bit labs

Flatbed Scanner Guide: Glance from Inside (page 8)

Category: Other

by Sergey Samarin

[ 01/11/2004 | 11:56 PM ]

Interface Controller

It is the interface controller that ensures communication between the scanner and the computer. As I have mentioned above, a scanner may come without a controller chip, if the controller is integrated into the scanner processor. Throughout their history, scanners used to connect to the computer across SCSI, IEEE1284 (parallel or printer port) or even RS-232 (serial interface). Currently available models of SOHO scanners use USB, FireWire or SCSI. Once, Bluetooth scanners were rumored to appear, but they never did. Of course, scanners with different interfaces use different, incompatible, controller chips.

In our case, we have SCSI and USB ports as well as
two connectors for attaching additional units

SCSI (Small Computer Systems Interface)

Scanners with the SCSI interface were very popular just a few years ago, but their time has come to an end. Newer high-speed interfaces (USB and FireWire) that don’t require additional adapters or delicate and careful connection have become the killers of SCSI in the world of SOHO scanners. The advantages of the SCSI interface include high bandwidth and the opportunity to connect up to seven various devices to one SCSI bus (i.e. to one SCSI host-adapter). Its disadvantages are high cost and the necessity to use an additional controller.

USB (Universal Serial Bus)

The USB interface is the most popular for scanners produced today as this interface is integrated into all modern mainboards as the main means to connect peripheral devices to the computer. CIS scanners are power-supplied through the USB port, which is a nice feature for portable computer owners. This energetic freedom couldn’t be obtained with SCSI.

FireWire (or IEEE1394)

This is my favorite. FireWire is a serial high-speed I/O interface differing from USB by the fact that it doesn’t require a controller for establishing communication. FireWire works according the peer-to-peer principle that is why FireWire is less hungry for processor resources than USB.

A new version of this interface (FireWire 800 or IEEE1394b) is going to be used in peripheral devices soon. It is going to be the fastest peripheral interface ever invented.

Belt Motor

There is one thing in a scanner that moves – the scan head. It includes an optical unit with a system of lenses and mirrors, a light-sensitive matrix, a cold-cathode lamp (if it is a CCD scanner) and an inverter board. The belt gear transfers the motion of the stepping motor to the scan head.

That’s where the belt is fastened to the scan head

Components of the belt mechanism

A special spring put onto the belt itself provides tight contact between the belt and the wheels. The carriage with the scan head moves along the guides that lead along the scanner case (see the picture).