Introduction to Scanners

Flatbed scanners
Sheetfed scanners
Handheld scanners

2.Introduction to Scanners

Scanner is a device that scans images, printed text, and handwriting etc and converts it to digital form or image. It is so named because the data is converted one line at a time or scanned down the page as the scanning head moves down the page.

Components inside a scanner are the following

Glass Plate and Cover
Scanning head
Stepper motor

2.1 Overview of components

i. Glass Plate and Cover

The glass plate is the transparent plate wherein the original is placed so that the scanner can scan it and the cover keeps out stray light that can affect the accuracy of the scan

ii. Scanning head

Scanning head is the most important component because it is the one which does actual scanning. It contains components like

1. Light source and mirror : It is the bright white light that is used to illuminate the original as it is being scanned and which bounces off the original and reflected off several mirrors

2. Stabilizer bar: It is a long stainless steel rod that is securely fastened to the case of the scanner and it provides a smooth ride as the scanner scans down the page

3. CCD (Charge Coupled Device) or CIS (Contact Image Sensor) : A CCD array is a device that converts photons into electricity. Any scanner that uses CCD use lens to focus the light coming from the mirrors within the scanning head.

Another technology used in some cheaper scanners is CIS wherein the light source is a set of LEDs that runs the length of the glass plate.

iii. Stepper Motor

The stepper motor in a scanner moves the scan head down the page during scan cycle and this is often located either on the scan head itself or attached to a belt to drive the scanner head.

2.2 Types of Scanners

1. Flatbed Scanners

The most commonly used scanner is a flatbed scanner also known as desktop scanner. It has a glass plate on which the picture or the document is placed. The scanner head placed beneath the glass plate moves across the picture and the result is a good quality scanned image. For scanning large maps or toposheets wide format flatbed scanners can be used.

2. Sheetfed Scanners

Sheet fed scanners work on a principle similar to that of a fax machine. In this, the document to be scanned is moved past the scanning head and the digital form of the image is obtained. The disadvantage of this type of scanner is that it can only scan loose sheets and the scanned image can easily become distorted if the document is not handled properly while scanning.

3. Handheld Scanners

Hand-held scanners although portable, can only scan images up to about four inches wide. They require a very steady hand for moving the scan head over the document. They are useful for scanning small logos or signatures and are virtually of no use for scanning maps and photographs.