Document Scanner

Overview

A document scanner converts paper into digital images by drawing each sheet past an imaging sensor under controlled illumination. This is a sheet-fed automatic-document-feeder (ADF) design built for batch capture: a stack of pages is loaded once and the machine separates, feeds, images, and stacks them without intervention. A single-pass duplex layout puts a sensor on each side of the paper path so both faces are captured in one transit, roughly doubling throughput over a flip-and-rescan design.

The unit is organised around a short, straight paper path. The Housing & Trays provides the hinged top cover, base chassis, and the input and output trays. The Paper Feed & Transport holds the pickup and separation rollers, transport rollers, drive motor, and the sensors that time each sheet. The Imaging Module module carries the two CIS bars, their LED illumination, and the glass windows the paper slides across. Everything is coordinated by the Main Board, which runs the scanner SoC and the USB and LAN interfaces, with the operator working through the Control Panel.

How it works

When a batch is loaded into the ADF tray, the Paper Feed & Transport pickup roller drives the top sheet forward while a retard roller holds the rest back, separating one page at a time. An ultrasonic sensor listens for the change in sound through two overlapped sheets to flag double feeds before they jam.

As each sheet crosses the Imaging Module glass, the two contact image sensors illuminate it line by line with red, green, and blue LEDs. The CIS rod-lens array focuses each scan line one-to-one onto a row of photodiodes, building the image one row at a time as the paper moves at constant speed. The Main Board digitises both sensor streams, corrects for illumination and skew, deskews and crops the page, and streams compressed images out over USB or Ethernet. The Power Supply subsystem supplies the motor and electronics, and the Control Panel selects scan jobs and reports feed status.