PC Computer Hardware Output Devices
Page printer (Image printer) Print a complete page or photograph at a time. Impact printer are used electromechanical mechanism that causes hammers or pins to strike against a ribbon and paper to print the text. Non impact printers do not use electromechanical printing head to strike against ribbon and paper. They use thermal, chemical, electrostatic, laser beam or ink jet technology for printer the text. Usually, a non impact type printer is faster than an impact type printer. The disadvantage of non impact type printer is that they produce single copy of the text whereas impact printers can produce multiple copies of text.Printers
Printer is an out put device which provide a hard copy on piece of paper and may resemble like type writer. The printer of different types has different speeds and qualities of printing. Their basic classification is this is:
The printers have been classified above as to how they print. There are one more classification which depends on technology used in their manufacture. According to this consideration printer are classified into following two broad
Categories
Thermal printers use a thermal (heating) process. Heat applied by the head on to special paper of which surface turns into a different color, creating characters where the heat was applied. Others use an electrostatic process in which top layer of a special type of paper is actually burned away, allowing a darker second layer to show through . Both processes require special paper that generally costs more that standard typing paper.
The main type of printer that are used widely are summarized below:
- Impact Printer
- Non Impact Printer
- Serial Character Printer
- Line Printer
- Line Printer
- Page Printer
- Dot Matrix Printer
- Daisy wheel Printer
- Chain Printer
- Drum Printer
- Character Printer
- Laser Printer
- Ink jet Printer
- Thermal Printer
- Electrostatic Printer
If you want a printed copy of a very long program or a report that is fifteen or twenty pages long, the normal procedure is to tell the computer to list or print the material on printer. The computer then sends data to printer at a speed; the printer can handle usually 18 characters per second to 200 characters per second. At this speed, the computer will has to wait for a long time. This problem is solved by interfacing the device known as printer buffer which is sometimes called printer spooler. The buffer generally takes only a second or two to accept all the material to be printed out. It then frees thee computer for other work and sends the material in the buffer on to the printer at a speed the printer can handle. Dot matrix printer produces letters and shapes by pushing a matrix of tiny into a ribbon 
Serial Character Printers
These printers are of following four types
which strikes the paper. Thus each letter consists of a pattern of tiny ink dots on the paper. Some printers form number letters and graphics with the help of a 5x7 matrix formed by dots. The printer head has seven needles arranged in a vertical line and five rows horizontally. Electronic pulses instruct the print head to choose the correct pattern of dots which are fired on to a typewriter ribbon and then on to paper as the print head moves across.
The print out from 5x7 matrix printer is cruder than a print out from 9x9 matrix. A few of the dot matrix printer uses an overlapping dot pattern to create higher quality output which is almost similar to electronic type writer. In that case the printer is called letter quality printer.
To print on 5x7 matrix es there are 9pins contained in the print head. They are about one inch long and are driven by several hammers which force each pin into contact with the ink ribbon (and paper) at a certain time. The force on these hammers comes from the magnetic pull of small wire coils (solenoids) which are energized at a particular time, depending on the character to be printed. Timing of the signals sent to the solenoids is programmed into the printer for each character, and translate from information sent by the computer about which character to print.
Daisy wheel Printer 
carrying a character at its end touching the periphery. As the wheel spins a hammer punches them against the ribbon at right moment. This wheel can be easily changed with a similar wheel within a moment if you want different styles of letters or unusual symbols, you can change the daisy wheel. When the right letter hover over on the page, a hammer comes down and slums the letter against the ribbon on to the paper. Daisy printer makes sharper image on the page, but they cost more and print a slower s rate than dot matrix printers around 45 to 60 character per second. The output in the form bits, that computer produces, are turned into character of different type by the printer.
Thermal Printer 
A thermal printer uses a hot needles pressed against heat sensitive paper to form character. It is not possible to produce multiple copies simultaneously, like impact printers
The advantage of this type of printer over dot matrix type is that the thermal unit is much quieter. The disadvantages are that a special type of paper must be used and is not possible to produce multiple copies.
Line Printer
These are high speed printer which prints a complete line at time. The printing speed 
is at the rate of 20 line to 80 line per second . Typical bar printer can print about 150 lines per minute for numbers and 100 lines per minute for alphanumeric character . Line printers are normally designed for heavy printing application and can operate for few hours. The main disadvantage of using line printer is that hammer movement and movement of drum, chain or band must be synchronized very accurately, otherwise lines gets blurred.
Speed of such machine is limited by the speed of paper movement. A special type of paper is used which holds electro-static charge in the form of spot. The printing process involves placing of spot to form the character. The paper then passes through a powered ink bath whence powder ink sticks to position of spots. The ink is melted by high temperature so as to make a permanent record.
Line Printer are three types
Drum Printer
Chain Printers
Band printers
Drum Printers
A drum printer has a cylindrical drum having the various character embossed 
on its surface. Each character position along the text line contains a band of raised character set. There is a magnetic driven hammer in each character position of the line . The drum rotes rapidly and one revolution is required to print each line a fast acting hammer opposite each and strike the paper against proper character as it passes. Thus , in one rotation, hammers of several position may ‘fire” when A appears . At the end of the rotation the line has been printed.
Chain printer
A chain printer has a steel band on which the various characters are embossed. 
The chain moves at a high but constant speed past the printing position. Magnetically controlled hammers force the paper against the appropriate print head. Each chain may contain 4 set of different styles for each of 64 or 120 characters. For printing a line , all character s in the lines are sent from memory to the printer buffer register. As the band rotes , a hammer is activated when desired character as specified by buffer register comes in front of it . Speeds of 50 lines per second can be achieved. Using continuous stationary with inter leaved carbons seven copies may be obtained. The noise level of printer is high. Its speeds lines in the range of 400-2400 lines per minute.
Band Printer
The band printer works on the similar manner to the chain printer, 
but here are bands of steels are used instead of chain and can be easily replaced quite often. Thus different scripts may be used with the same printer
No comments:
Post a Comment