Impact printers have print heads that strike an inked ribbon, causing characters to be imprinted on the paper. Dot matrix and daisy wheel are examples of impact printers.
The following are some advantages of an impact printer:
- Uses less expensive ink than inkjet or laser printers
- Uses continuous feed paper
- Has carbon-copy printing ability
The following are some disadvantages of an impact printer:
- Low-resolution graphics
- Limited color capability
Types of Impact Printers
A daisy wheel printer uses a wheel that contains letters, numbers, and special characters. The wheel rotates until the required character is in place, and then an electromechanical hammer pushes the character into the ink ribbon. The character then strikes the paper, imprinting the character on the paper.
A dot matrix printer is similar to a daisy wheel printer, except that it has a print head containing pins that are surrounded by electromagnets instead of a wheel. When energized, the pins push forward onto the ink ribbon, creating a character on the paper. The number of pins on a print head, 9 or 24, indicates the quality of the print. The highest quality of print that is produced by the dot matrix printer is referred to as near letter quality (NLQ).
Most dot matrix printers use continuous-feed paper, also known as tractor feed. The paper has perforations between each sheet, and perforated strips on the side are used to feed the paper and to prevent skewing or shifting. Sheet feeders that print one page at a time are available for some higher quality printers. A large roller, called the platen, applies pressure to keep the paper from slipping. If a multiple-copy paper is used, you can adjust the platen gap to the thickness of the paper.