Overview Of Printer Mechanism Operation; Printhead Mechanism - Epson LG1-1070 Service Manual

2.1 OVERVIEW OF PRINTER MECHANISM OPERATION

This section describes the PRINTER MECHANISM of the Model-5E 10\5E60 printer unit and explains
how the printer works. The Model-5E 10/5E60 has a PRINTER MECHANISM that features a 24-pin impact
dot printhead for serial printing. There are four main parts to the printer mechanism: 1) the printhead
mechanism, 2) the carriage movement mechanism, 3) the paper advance mechanism, and 4) the ribbon
advance mechanism. Each of these is described below.

2.1.1 Printhead Mechanism

The printhead mechanism consists of the printhead itself, the ink ribbon, and the PLATEN. The printhead
contains 24 wires in a zigzag arrangement in two rows of 12. A drive coil is provided for each of these
wires to make the wires move in and out of the printhead and print dots independently of each other.
The basic way that the wires are driven is described in the four steps below.
The control circuit outputs the drive signal to the printhead drive circuit. This changes the printhead
drive voltage, and current flows through the corresponding printhead coil. The coil acts as a solenoid
and generates a magnetic force.
2. This induced force causes the plate to approach the coil rod and the associated dot wire is rapidly
ejected to impact on the platen.
3. The dot wire presses the ink ribbon up against the paper as it hits the platen, and in this way prints
a dot on the paper.
4. As soon as the current througk the coil is switched off, the force induced in the coil rod stops. The
plate then returns to its original position (its position before the coil was energized) through the action
of the plate spring. After the dot wire hits the platen, the rebounding force of hitting the platen works
together with the wire return spring to pull the wire back to its original position in relation to the
plate.
Wire Resetting Spring
Stopper
\
Actuating
Actuating plate Sprin9
Figure 2-1 shows the action of the PRINTER MECHANISM when a single dot is printed. The printhead
tends to heat up after a period of continuous printing. To minimize the possibility of the dot wire drive
coils overheating within the printhead and any loss of performance, the head is equipped with a
thermistor that detects the head temperature. When this thermistor detects changes in the printhead
temperature, the voltage signal changes. This signal change is read by the control circuit for feedback
control.
Wire
Dot
\
Figure 2-1. How the Printhead Works
RIBBON
/
Paper
2-1
PLATEN
MASK
REV.-B
I