Casio MD-910 User manual

DOT PRINTER
JAN. 1997
MD-910
(without price)
TECHNICAL MANUAL

Features
The MD-910 series is a dot matrix compact printer that uses two serial print heads.
This printer has been developed as an output terminal for various applications such as POS terminals,
measuring/analyzing equipment, medical equipment and communication data equipment, and has
been designed to be as compact as possible.
• Compact and lightweight
• High-speed printing of up to 2.5 lines/sec. (for MD-910) or 1.8 lines/sec. (for MD-911)
• Clear printout with high resolution of 8 dots/mm
• Paper width of print head
• Longer life of print head
• Simple mechanism for high-reliability

Contents
1 Printer usage and Care..................................................................................................................... 1
2 Specifications/Operating principles ................................................................................................... 2
2-1 Specifications............................................................................................................................ 2
2-2 Outline of mechanism ............................................................................................................... 3
2-3 Mechanism and operation principles ........................................................................................ 3
2-3-1 Power transmission mechanism ................................................................................... 3
2-3-2 Sensor mechanisms ..................................................................................................... 4
2-3-3 Print head mechanism.................................................................................................. 5
2-3-4 Paper feed mechanism................................................................................................. 8
2-3-5 Ribbon cartridge drive mechanism ............................................................................. 11
2-4 External connection terminals................................................................................................. 11
2-4-1 Terminal arrangement ................................................................................................ 11
2-4-2 Terminal mechanism .................................................................................................. 12
2-4-3 Terminal circuit diagram ............................................................................................. 12
3 Disassembly/Reassembly............................................................................................................... 13
3-1 Tools .................................................................................................................................... 13
3-2 Disassembly procedure .......................................................................................................... 13
3-3 Assembly procedure ............................................................................................................... 14
3-3-1 Setting paper feed solenoid assembly........................................................................ 14
3-3-2 Setting the head assembly ......................................................................................... 15
3-3-3 Setting the paper feed assembly ................................................................................ 16
3-3-4 Setting the main body assembly................................................................................. 18
4 Parts list .................................................................................................................................... 26
5 Exploded view................................................................................................................................. 28

— 1 —
1 Printer usage and Care
(1) Use recommended register paper. Otherwise, printing quality and the life of the print head will not be
guaranteed. The width of paper must meet the specifications.
(2) Never allow a mechanical impact (including the entry of foreign matter) to the print head surface.
(3) Any dust on the print head surface must be wiped off by an applicator soaked in ethanol or the
equivalent.
(4) The dedicated ribbon cartridge should be taken off when the printer is carried or not used for a long
period.
(5) Do not feed current to the print head if it is wet or moist. If current is fed, the print head may be
damaged. If the print head is wet or moist, dry it fully and then start printing.
(6) Inserting register paper
• Cut the top end of the register paper
straight (it should never be fluffed or bent)
and insert it.
• When the top end of the register paper
comes out of the print head, check that it
is set straight and then pull it.
(7) Removing register paper
• Beforeremovingtheregister paper,be sure
to stop feeding current to the print head.
• Pull out paper straight in the direction of
paper exit.

— 2 —
Item Specifications
Printing method Dot matrix system
Printing direction Unidirectional printing
Printing speed 2.5 lines/sec. ±20 %; DC 5.0 V, 25 °C in
continuous printing
Printing format Number of dots 144 dots/line
Character configuration (5 + 1) ×8
Number of columns 24
Paper feeding Paper feeding pitch 3.52 mm (10 dots/line)
Rapid feed rate 5 lines/sec. ±20 %; DC 5.0 V, 25 °C in
continuous printing
Inking Dedicated cartridge (black or purple)
Detection Dot pulse Photointerrupter
Reset pulse Leaf switch detector
Paper feeding solenoid Drive voltage DC 5.0 V
Resistance 7 h±3 (temperature: 25 °C)
Printing solenoid Drive voltage DC 5.0 V
Resistance 1.7 h±0.3 (temperature: 25 °C)
Motor Type DC brush motor
Drive voltage DC 5.0 V
Max. current Approx. 1 A
Average current 0.3 A or less; DC 5.0 V, 25 °C in continuous
printing
Paper Type Plane or recommended paper
Paper width 57.5 mm
Cut sheet 45 to 55 kg
(thickness: 0.06 to 0.085 mm)
Copies Original paper (34 kg) + single copy (34 kg)
(Total thickness: 0.13 mm or less) Non-carbon
paper
Life of print head 1,500,000 lines
Exterior dimensions 90 (w)×45.5 (d) ×15.8 (h) ±0.5 mm
(excluding paper feeding nob and feet)
Weight 105 g ±10 %
2 Specifications/Operating principles
2-1 Specifications

— 3 —
2-2 Outline of mechanism
This printer mechanism is divided roughly into the following seven blocks:
• Power transmission
• Sensor
• Print head
• Paper feed
• Ribbon cartridge drive
• Frame
• Motor
For example external control circuits attached to this printer, please see the appropriate operating
manuals.
2-3 Mechanism and operation principles
The mechanism and operating principles are described for five blocks out of seven (i.e., excluding
the frame and motor).
2-3-1 Power transmission mechanism
This mechanism transmits a motor driving force to the head assembly, paper feed roller and ribbon
cartridge.
The head assembly is driven by the cylinder cam assembly connected to the gear box assembly
which encloses the motor.
The driving force transmitted to the cylin-
der cam assembly is sent to the PF cam
gear and PF6D cam through the paper
feed gear. Either the driving force trans-
mitted to the PF cam gear or the driving
force transmitted the PF6D cam can be
selected, depending on the operation sta-
tus, and is sent to the clutch gear through
the sector gear assembly.
The driving force of the clutch gear is
transmitted to the clutch wheel connected
to the paper feed roller, driving the paper
feed roller.
The driving force of the PF cam gear is
transmitted to the worm, worm gear and
ribbon drive pin respectively, so that the
ribbon cartridge is driven by the ribbon
drive pin.

— 4 —
2-3-2 Sensor mechanisms
This mechanism has two sensors for de-
tection, a dot pulse sensor and a reset
pulse sensor.
(1) Dot pulse sensor
The dot pulse sensor consists of an
encoder (slit disk) directly connected
to the motor and a photointerrupter
reading the rotation. The rotation read
(number of slits counted) is treated as
the DP signal that is the core of the
printing control.
(2) Reset pulse sensor
The reset pulse sensor uses a leaf switch which turns ON/OFF according to the head assem-
bly position.
This sensor detection signal represents the RP signal that specifies the print head home posi-
tion and printing start base position.

— 5 —
2-3-3 Print head mechanism
This printer has two print heads arranged at intervals on the left and right, so that the left half and
the right half of the register paper can be printed simultaneously as it is moved from left to right.
One movement causes the upper part of one line to be printed and the next movement causes the
lower part of the line to be printed. Therefore, two print head movements complete printing of one
line. The print heads, however, print the register paper only when they move from left to right.
(1) Printing control
Each print head has four printing so-
lenoids and each solenoid is turned
ON/OFF according to the printing data
and the corresponding printing pins
are activated to form character dots.
This printer, however, does not have
a serial/parallel conversion circuit.
Therefore, ON (L level)/OFF (H level)
signals are directly provided to the
eight data lines for each printing sole-
noid.
Printing timing is controlled by the DP
signal which is detected by the dot
pulse sensor and is treated as a clock
pulse and the RP signal which is de-
tected by the reset pulse sensor and
is treated as a starting point.

— 6 —
(2) Printing data and printing position
The number of printing columns and
one character dot matrix vary, depend-
ing on whether the printer is the MD-
910 or MD-911.
For the MD-910, the number of print-
ing columns is 24, and each 12 col-
umns of printing on the left and right is
performed by each print head. 4 dots/
line is produced by one print head
movement.
6 (5 + 1) horizontal dots make up one
character and the total number of hori-
zontal dots in the printable area is 144
(12 columns ×2 ×6 dots).
For the MD-911, the number of print-
ing columns is 40, and each 20 col-
umns of printing on the left and right is
performed by each print head. 4 dots/
line is produced by one print head
movement. 4.5 (4 + 0.5) horizontal dots
make up one character and the total
number of horizontal dots in the print-
able area is 180 (20 columns ×2 ×4.5
dots).
Printable Area
Home Position
5 mm 47.5 mm 5 mm
Direction of
Paper Feed
Printing Solenoid A
Printing Solenoid B
Printing Solenoid C
Printing Solenoid D
Printing Solenoid A
Printing Solenoid B
Printing Solenoid C
Printing Solenoid D
Printing Solenoid E
Printing Solenoid F
Printing Solenoid G
Printing Solenoid H
Printing Solenoid E
Printing Solenoid F
Printing Solenoid G
Printing Solenoid H
12 (20) Columns
72 (90) Dots
12 (20) Columns
72 (90) Dots
One Line
4 Dots/Line 4 Dots/Line
2/2 Line 1/2 Line
1st Print Head 2nd Print Head
144 (180) Dots
Printable Area
Printing Position
2 Dots/Line: LFHome Position
Printable Area in Detail
(Values parenthesized are for MD-911)

— 7 —
(3) Head drive mechanism
The head assembly is connected to the cylinder cam assembly via a shaft pin. The shaft pin is
inserted in a scribed groove on the outside of the cylinder cam assembly and moves along the
groove when the cylinder cam assembly is turned to drive the head assembly.
When the head assembly travels be-
yond the home position, the shaft pin
goes through a sharp curve in the
scribed groove, so it moves slowly.
At this time, printing is performed.
When the head assembly travels be-
yond the printable area, the direction
of movement is changed to the home
position because the direction of
groove is reversed and the head re-
turn spring tension is activated.
At this time, the head assembly trav-
els at high-speed because the groove
is turned to the slow curve.
Register paper feeding is performed
when the head assembly returns.
When the head assembly travels to
the home position, it returns to the
original groove position, and the op-
eration is repeated.

— 8 —
2-3-4 Paper feed mechanism
Since this printer completes one line of printing by dividing it into upper and lower halves, two types
of paper feeding are provided; one is paper feeding without LF (line feed) because the lower half is
printed after the upper half.
The other is paper feeding with LF because upper half of the next line is printed after completing
one line.
(1) Paper path
The register paper is loaded from the
back of the printer and moved to the
paper feed roller and the pressure
roller along the paper pressure guide.
The register paper moved is pressed
against the paper feed roller by the
pressure roller and fed upward when
the paper feed roller turns.
The register paper then passes
through the platen and the print head
and comes out to the back again.
When the register paper passes
through the platen and the print head,
it is printed by the ink ribbon of the
ribbon cartridge on the print head.

— 9 —
(2) Paper feeding without LF (line feed) mechanism
The PF cam gear that drives paper feeding turns one time per head assembly shuttle.
The cam inside the PF cam gear presses down the protrusion (part A) of the sector gear
assembly when the head assembly returns. The sector gear assembly has teeth on the oppo-
site side of the protrusion which engage with the clutch gear that is concentric to the paper feed
roller.
The paper feed roller has a clutch
wheel next to the clutch gear to trans-
mit the driving force.
Normallythisclutchwheelisnotincon-
tact.
The sector gear assembly has a ful-
crum at the middle, so if the protrusion
is pressed down, the teeth are raised
to turn the clutch gear. The clutch gear
then is pushed out by the PF clutch
spring and engages with the clutch
wheel to rotate the paper feed roller.
This rotation, i.e., the paper feeding,
depends on the amount of ascent of
the teeth of the sector gear assembly.
4 dots/line is ensured without LF.
When the cam inside the PF cam gear
goes past due to rotation, the protru-
sion of the sector gear assembly is
raised again by the sector gear spring
so that the clutch gear separates from
the clutch wheel and stops the paper
feed roller.

— 10 —
(3) Paper feeding with LF (line feed) mechanism
In paper feeding with LF mechanism, only the protrusion pressing down mechanism is different
from that of paper feeding without LF mechanism.
Two cotter pins are set on the outside of the PF cam gear and turn together with the PF cam
gear. The cotter pins are always exerting a force to uncoil but are restrained by the return ring.
One part of the return ring is thin, so that when the cotter pin passes through this thin part while
rotating, it springs out of the return ring.
When performing paper feeding without LF, no cotter pin spring is required, so the armature
assembly is inserted in the thin part of the return ring instead. The armature assembly is linked
with the paper feed solenoid.
When performing paper feeding with
LF, the paper feed solenoid turns ON
and the armature assembly is de-
tached from the return ring.
The PF6D cam is set on the outside
of the return ring and the driving force
of the PF cam gear is transmitted by
the cotter pin spring.
As the PF6D cam turns, the outer pro-
trusion (part B) of the sector gear as-
sembly is lowered and the paper feed
roller rotates in the same manner as
during paper feeding without LF
mechanism. At this time, the PF6D
cam is larger than the cam inside the
PF cam gear, so the rotation of the
paper feed roller is 6 dots/line, i.e., 2
more dots per line than with paper
feeding without the LF.

— 11 —
2-3-5 Ribbon cartridge drive mechanism
The PF cam gear that drives paper feed-
ing is also used to turn the ribbon cartridge.
The driving force of the PF cam gear is
transmitted to the worm where the direc-
tion of operation is changed 90 °.
The driving force converted is transmitted
from the worm to the worm gear and the
ribbon cartridge is turned by the ribbon
drive pin. Therefore, the ribbon cartridge
is always moving while printing is being
performed.
2-4 External connection terminals
External connection terminals are located within the PCB terminal assembly and their connections
are implemented by directly soldering the print pattern surface.
2-4-1 Terminal arrangement

— 12 —
Terminal No. Terminal name Remarks
1 Motor (–) Motor is ON with GND
2 Phototransistor emitter Dot pulse sensor
3 Phototransistor collector
4 LED cathode
5 LED anode
6 Printing solenoid D (–) 1st print head
7 Printing solenoid B (–) Each solenoid is ON with GND
8 Printing solenoid A (–)
9 Printing solenoid C (–)
10 Common (+) Power side of print head, motor and paper
feeding solenoid
11 Printing solenoid H (–) 2nd print head
12 Printing solenoid F (–) Each solenoid is ON with GND
13 Printing solenoid E (–)
14 Printing solenoid G (–)
15 Paper feeding solenoid (–) Solenoid is ON with GND
16 Reset pulse sensor output Power side
17 Reset pulse sensor output GND side
2-4-2 Terminal mechanism
2-4-3 Terminal circuit diagram
2345 6789 1110 161512 13 14
Printing
Solenoid
D
Motor Dot Pulse Sensor 1st Printing Head 2nd Printing Head Reset Pulse Sensor
Paper Feeding Solenoid
Printing
Solenoid
A
Printing
Solenoid
B
Printing
Solenoid
C
Printing
Solenoid
H
Printing
Solenoid
E
Printing
Solenoid
F
Printing
Solenoid
G
1
M
Note: 1. For motor polarity, terminal No. 1 should be minus.
2. For reset pulse sensor, terminal No. 17 should be GND.
+
–
17

— 13 —
3 Disassembly/Reassembly
Prior to maintenance work, be sure to observe the following caution:
CAUTION
(1) When the printer is operating satisfactorily, do not unnecessarily disassemble, reas-
semble or adjust the printer. In particular, do not loosen any screws on the compo-
nents.
(2) Check that the printer is in good condition before turning on the power.
(3) Never try to print without register paper in the printer.
(4) Check that the register paper is set properly.
(5) In maintenance work, never leave any parts or screws in the printer.
(6) In disassembly and reassembly, check that any wires and cords are not damaged
and are laid out properly. Handle these wires and cords carefully.
3-1 Tools
The list of necessary tools is as follows:
1. Philips head screwdriver
2. Tweezers
3. Small radio pliers
4. Oil brush
5. Small pincers
3-2 Disassembly procedure
To perform disassembly, reverse the assembly procedure (item 3-3).
Disassemble each part gradually from the frame.

— 14 —
3-3 Assembly procedure
The assembly procedure is described by major assembly blocks.
Part names in text are the same as those in Parts List.
3-3-1 Setting paper feed solenoid assembly
(1) Place the core in core base as-
sembly.At this time, align the pro-
trusion of the core with the hole
of the core base assembly.
(2) Insert the bobbin assembly where
the core has already been fitted
in the core base assembly.At this
time, the lead wires face outside
and there should be no gap be-
tween the bobbin assembly and
the core base assembly.

— 15 —
(3) First apply Froil G-311S to the arma-
ture pivot of the bobbin assembly, then
install the armature spring and the ar-
mature assembly. At this time, check
the direction of armature spring.
(4) Secure the armature assembly with
the E-ring and attach the armature
spring to the hole of the armature as-
sembly.
Note:When installing the E-ring and
armature spring, use small radio
pliers or tweezers.
3-3-2 Setting the head assembly
(1) Two tips of FPC are extended from the
head assembly. Bend the two tips at
right angles from the notch line.

— 16 —
(2) Place the ribbon mask in the head as-
sembly.At this time, align the holes of
the ribbon mask with the protrusions
of the head assembly.
Note:The ribbon mask is very thin, so
take care not to bend it when in-
stalling it.
(3) Install the head return spring in the
head assembly.
3-3-3 Setting the paper feed assembly
(1) Apply Froil G-311S to the two parts of
the paper feed roller shaft where pa-
per feed bracket touches.
(2) Apply Epnoc grease AP to the brake
groove of the paper feed roller.
Note:The paper feed roller must be
free from sticky oil.
(3) Place the paper feed roller in the pa-
per feed bracket. At this time, the
longer shaft should be inserted first.

— 17 —
(4) Install the PF bracket bushing in the
bushing groove of the paper feed
bracket and secure the paper feed
roller.
(5) Install the brake spring in the brake
groove of the paper feed roller.
(6) Attach the platen to the paper feed
bracket with two platen spacers and
two screws (M2 ×2.5).
(7) Insert the clutch wheel in the paper
feed roller shaft coming out of the pa-
per feed bracket.
Note:When inserting, push the clutch
wheel until the claws of the
clutch wheel are engaged with
the shaft groove of the paper
feed roller.
(8) Insert the clutch gear in the paper feed
roller shaft.
(9) Apply Froil G-311S to the gear section
of the clutch gear.