Epson LQ-300 - Impact Printer, Service Manual

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Operating Principles Service Manual
2.1.5 Ribbon Shift Mechanism
This printer can be equipped a color upgrade kit to print in color. The printer performs color
printing unidirectionally. option is composed of the color ribbon shift mechanism. The color
ribbon feed mechanism is shared in common with black ribbon feed mechanism, and the shift
mechanism shifts the ribbon cartridge up and down.
Table 2-2 shows the motor specifications. The motor control system is open-loop, so that when
the color is being changed, the positioning is controlled by stepping pulse.
Table 2-4. CS Motor Specifications
Category Requirement
Type 4-phase, 48-pole, PM-type stepping motor
Drive Voltage
35 VDC 10%
I
Coil Resistance
150 5% (per phase, at 25° C or 77°
Drive Pulse Color shift 500
DDS
Excitation Method Constant-voltage 2-2 phase excitation
1
The ribbon shift mechanism consists of the color ribbon and color upgrade kit. The color upgrade
kit is composed of the
motor, ribbon
shift
gear/cam, motor driver and color ribbon sensor.
The 1-inch-wide color ribbon is separated into four equal-width bands of different colors. The
ribbon shift mechanism shifts the ribbon cartridge up and down.
When the color ribbon cartridge loaded, it is possible to print in up to seven colors. One of the
four colors on the ribbon is selected by the color ribbon
motion, which inserts
a
portion of
the plastic posts into the slots in the printer mechanism as a fulcrum. Figure 2-9 illustrates the color
shift mechanism. The mechanism
the
ribbon cartridge by converting the gear rotation to
liner motion (up and down) of the color ribbon cartridge, using color shift cam gear.
Any color band can be selected by rotation of the CS motor, using the color home position (the
position of the black color band) as a starting point and reference position. Home position is
recognized by the
motor stepping pulse. When printer is powered on, the motor is first
at any phase position. Next, the CS motor is turned 235 steps ( black yellow). Then, the
motor returns one step black), and the motor is stopped. Finally, the motor returns 223
steps black) and stops. This position is home position.
Table 2-5 gives coloring sequences. For halftones, as shown in the table, a color is created by
printing one color on top of another.
Table 2-5. Coloring Sequences
Print Ribbon
Print Color
First Printing Second Printing
Black Black
—
Magenta
Magenta
—
Cyan Cyan
—
I Yellow
Yellow
l – l
Green Yellow Cyan
Orange
Yellow Magenta
I
Violet
I
Cvan
I
Note:
The printer prints the brighter first to prevent the ribbon from being stained,
. . . .
2-8