Figure 12-9.A typical print wire arrangement in a 24-pin
dot matrix print head.
column one as shown in figure 12-9. Near letter quality
can be printed with just one pass of the print head. The
print wires are smaller in diameter than the ones on a
nine-pin print head, resulting in even smoother
The dot matrix print head is mounted to a low
friction slide that is mounted to one or two carriage rails.
The carriage rails are usually finely polished steel to
further reduce friction. The print head is moved across
the length of the platen by a wire, belt, or chain that is
connected to the print head mount and to the carriage
motor. As the motor turns, it pulls the mount either right
or left. On the rails are right and left limit switches that
prevent the carriage motor from pulling the print head
too far in either direction. The limit switches maybe
mechanical switches or optical sensors. Figure 12-10
shows a basic carriage assembly.
Daisy Wheel Printers
The daisy wheel printer uses a single print hammer
and produces letter quality print. A daisy wheel is a
small plastic disk with a number of petal-like
projections. A character die is located on the end of
each projection as shown in figure 12-11.
The daisy wheel is rotated by the print head
mechanism until the desired character is in the proper
position to be struck by the print hammer. The hammer
drives the die into the inked ribbon, which prints the
character on the paper as shown in figure 12-12. The
print head is then moved one space, the wheel is rotated
to the next character to be printed and the hammer is
fired again. This process is repeated until the entire line
has been printed.
Many daisy wheel printers are
capable of bidirectional printing.
The daisy wheel print head is mounted to a carriage
assembly that is very similar to the assembly used with
dot matrix printers.
Daisy wheel printers are slow and limited in the
characters printed to those on the wheel. Despite these
limitations, they are still used for their ability to print
letter quality documents and make carbon copies.
TOPIC 4NONIMPACT PRINTERS
Nonimpact printers form characters using methods
other than striking an inked ribbon and the paper. Types
of nonimpact printers include the following:
Figure 12-10.A basic printer carriage.