Epson Stylus PHOTO 1270 Service Manual page 50

EPSON Stylus Photo 870/1270
determine the CR position and the direction in which the CR moves. The
slave CPU outputs specified control signals to the motor driver. The
motor driver IC18 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.
1/180"
1/720"
Phase A
Phase B
Phase A
Phase B
Lens
LED
Figure 2-16. CR Linear Scale Encoder Pulse
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.
OPERATING PRINCIPLES
1/360"
Backward Rotation
(Counterclockwise)
Forward Rotation
(Clockwise)
Photo Photo
Comparators Comparators
Diodes
Diodes
A
+
Phase A
A
-
B
+
B
Phase B
-
Electrical Circuit Operating Principles
"
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 IC15 Slave CPU
(C90A26CA) is reset by an initialization sequence at power-on.
2) The CR motor turns forward (clockwise) to move the carriage to
the right. Slave CPU (C90A26CA) assumes that the CR is in contact
with the right frame when the following conditions are satisfied:
!
The slave CPU detects the motor control current value is
720mA.
!
P1 (= number of pulses output during the above carriage
movement) is 30* or less.
* Specified value that indicates CR is in the home position. (All
edges in the waveform are used in this condition.)
3) The CR motor rotates backward (counterclockwise) to move the
carriage back to the left, and the Slave CPU (C90A26CA) assumes
that the carriage enters the CR lock lever position when the
following conditions are satisfied:
!
Slave CPU (C90A26CA) detects the motor control current
value is 500 mA.
!
Difference between P1 and P2 (= number of pulses output
while the CR moves from the right frame) is 30 or less.
4) The CR motor rotates backward to move the carriage to the right
again, and if Slave CPU (C90A26CA) detects the motor control
current value is 720 mA, it assumes that the CR comes in back in
contact with the right frame.
5) Difference between P1 and P3 (= number of pulses output for the
CR's movement from the CR lock lever position to the right frame)
is 4 or less.
When all the conditions in the sequence are satisfied, the printer detects
the CR is in the home position.
Revision B
50