Epson Stylus Photo 870 Service Manual page 23

EPSON Stylus Photo 870/1270
2.4.2.3 Carriage Motor Driver Circuit
The EPSON Stylus Photo 870/1270 are equipped with a DC carriage
motor. A slave CPU is mounted on the C304MAIN board to control the
printer's DC motors. This relieves the CPU and ASIC of this duty, and
speeds up processing.
Unlike a stepper motor, the drive pulses that control the DC motor
cannot control the motor's movement precisely. Therefore, the printer
uses an encoder strip to mechanically detect the carriage position. The
encoder strip outputs two kinds of pulses, Phase A and Phase B, to
the IC8 ASIC, as shown in Figure 2-18. Because the pulses are out of
phase, the ASIC can use them to determine not only how far the
carriage travels, but also its direction of motion.
1/180 inch
P h a s e A
P h a s e B
P h a s e A
P h a s e B
L E N S
L E D
Encoder strip
Figure 2-18. Carriage Encoder Sensor Output Signal
Carriage motor
clockwise rotation
Carriage motor
counter-clockwise
rotation
P h o t o
C o m p a r a t o r s
D i o d e s
A
+
P h a s e A
A
-
B
+
P h a s e B
B
-
2.4.2.3.1 Home Position Detection (Capping Position Detection)
The printer does not use a home position sensor to detect the carriage
position. Instead, it performs the following sequence:
1. The linear encoder pulse counter in the Slave CPU (C90A26CA) is
reset during a power-on sequence.
2. The carriage is moved from left to right. The Slave CPU
(C90A26CA) assumes that the carriage comes in contact with the
right frame when the following conditions are satisfied:
" The slave CPU detects that the motor current rises to 720mA.
" The number of pulses output for the carriage movement above
is 30 or less. Let P1 equal this value.
3. The carriage is moved from right to left. The Slave CPU
(C90A26CA) assumes that it detects the carriage lock lever
position when the following conditions are satisfied:
" The Slave CPU (C90A26CA) detects that the motor current
rises to 500 mA.
" The difference between P1 and P2 (number of pulses output
while the carriage moves from the right frame) is 30 or less.
4. The carriage is moved from left to right again. If the Slave CPU
(C90A26CA) detects a motor current value greater than 720 mA, it
assumes that the carriage has come in contact with the right
frame again.
5. The difference between P1 and P3 (number of pulses output for
the carriage movement from the carriage lock lever to the right
frame) is 4 or less.
When all conditions are satisfied, the printer determines that the
carriage is in home position.
NOTE: If the drive voltage for the carriage motor reaches 800
mA during printing, the printer assumes that the
carriage is stuck and a fatal error occurs.
Chapter 2 Technical Overview
18