Epson Stylus PHOTO 890 Service Manual page 53

EPSON Stylus Photo 890/1280/1290
Figure 2-20. CR Motor Driver Circuit Block Diagram (C393MAIN-C)
NOTE: When C393MAIN-C is installed, ASIC sends signals of IC9 and IC1 through IC8
and determines current of the CR motor.
ASIC (IC19) controls the CR position by referring to the pulses sent from the linear
encoder. Based on the data sent from ASIC, the CPU sets an appropriate drive current
value used to determine the CR position and the direction in which the CR moves.
ASIC outputs specified control signals to the motor driver. The motor driver IC9 then
outputs CR motor drive current to the CR motor.
Unlike stepping motors, the DC motor that drives the carriage can not detect the current
carriage position by referring to the pulses given. For this reason, a linear scale is
attached along the carriage operation range to detect the carriage position. The linear
encoder sensor outputs two kinds of TTL level pulses: Phase A and Phase B.
OPERATING PRINCIPLES
Direction for the CR's current movement is detected based on the pulse waveforms of
the shifted Phases A and B. Carriage position is, on the other hand, controlled based on
a cycle of Phase A output waveform (1 cycle=1/180 inches). Also, all rising and falling
edges of the waveforms in the both phases (1 cycle=720) are used to control the
position of the CR that is in its home position for ink system.
o
Home position detection
Home position is detected based on the pulses output from the linear scale sensor
and DC motor control current value. The basic home position detection sequence
is as described below:
1) The linear encoder pulse counter in the ASIC (IC19) is reset by an
initialization sequence at power-on.
2) The CR motor turns forward (clockwise) to move the carriage to the right.
ASIC(IC19)assumes that the CR is in contact with the right frame when the
following conditions are satisfied:
Electrical Circuit Operating Principles
1/180"
1/720"
Phase A
1/360"
Phase B
Phase A
Phase B
Lens
Photo
Photo
Comparators Comparators
Diodes Diodes
A
+
LED
A
B
+
B
-
Figure 2-21. CR Linear Scale Encoder Pulse
Revision C
Backward Rotation
(Counterclockwise)
Forward Rotation
(Clockwise)
Phase A
-
Phase B
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