Printer Mechanism Operation

The printer mechanism is a 9-pin serial dot matrix impact mechanism. Figure 2-2 shows a drawing of the mechanism. The name in the rectangles indicate relationship between each mechanism and the control circuit on the PEGX board.

Epson Print Head Diagram
Figure 2-2. Printer Mechanism Block Diagram

The printer mechanism is composed of the following:

• Carriage Mechanism

• Home Position Sensor

• Ribbon Feed Mechanism

• Paper Feed Mechanism

2.2.1 Printhead

The printhead is an electromagnetic induction 9-pin serial dot head. Nine dot wires are driven individually to print a dot pattern on the paper, positioned between the platen and ribbon, by hitting the ink ribbon against the paper and the platen. Print data expanded on the PEGX board is converted into dot-image data for one vertical row, and output to the printhead by the printhead drive circuit. A character is printed by serially printing the dot patterns for each vertical row in the horizontal direction as the carriage moves. Figure 2-3 shows the printhead mechanism

Platen

Dot Wire

Ribbon Mask

Dot Wire

Dot Matrix Print Head Mechanism

Actuating Plate Spring

Figure 2-3. Printhead Mechanism

Platen

Ribbon Mask

Actuating Plate Spring

Figure 2-3. Printhead Mechanism

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2.2.2 Carriage Mechanism

The carriage is driven by the carriage motor via a timincjtoelcarriageaswB lteftsaa0p<^haratbagtt«ei plfelamy Since a stepPer motor is used for the carriage motor, position. The carriage motor is controlled by a very simple, open-loop system. Figure 2-4 shows the carriage mechanism.

Printer Stepper Motor Mechanism
Figure 2-4. Carriage Mechanism

2.2.3 Home Position Sensor

The home position sensor detects the home position of the carriage. A home-Positio'seek is performed when the printer is initialized. The control circuit stores the home position, which is referenced to control the carriage motor position.

Carriage movement is conveyed to the series of gears in the ribbon feed mechanism. The ribbon feed mechanism converts bidirectional horizontal carriage movement into single directional rotational movement so that the ribbon can be taken up during printing. Figure 2-5 shows the ribbon feed mechanism.

Ribbon Feed Motor

Ribbon Breaking Spring

Figure 2-5. Ribbon Feed Mechanism

Ribbon Breaking Spring r"

Figure 2-5. Ribbon Feed Mechanism

The paper feed mechanism is composed of the paper feed motor, platen, push tractor unit, paper tension unit, and release mechanism. Either the friction feed or tractor feed system can be selected depending on the paper used. (There are two paper entrances. One is for friction feed and the other is for tractor feed.) Rotational movement of the paper feed motor is conveyed to the platen in the case of friction feed, and to the push tractor unit (the platen also rotates) in the case of tractor feed. The conveyance mechanisms are switched using the release lever. The paper tension unit is mounted at the top of the platen, and is rotated by the paper feed motor. The paper ejection is assisted by friction between the platen and the paper tension unit.

2.2.5.1 Push Tractor Feeding Method (Figure 2-6)

Paper feeding is performed by driving the paper feed motor with the paper release lever set forward to load fan-fold paper into the tractor unit. A paper tension unit is installed at the exit of the case to prevent irregular paper feeding and slackening.

Paper Release Lever

Paper Tension Roller Gear

Paper Tension Roller Tf» ns m i'ss'F e'ff

Paper Release Lever

Paper Tension Roller Gear

Paper Tension Roller Tf» ns m i'ss'F e'ff

Paper Feed Motor Epson

Platen Gear

Paper Feed Motor Pinion Gear Paper Feed Transmission Gear (i) Side View

Platen Gear

Paper Feed Motor Pinion Gear Paper Feed Transmission Gear (i) Side View

(ii) Top View (a) Gear Arrangement

(ii) Top View (a) Gear Arrangement

Paper Tension Roller,

Paper Tension Roller,

Roller Gear Printer Mechanism

Paper Holding Roller

End Sensor

Paper Feed Roller (Release State)

Paper Holding Roller

End Sensor

Paper Feed Roller (Release State)

(b) Paper Path

Figure 2-6. Push Tractor Feeding Method

2.2.5.2. Friction Feeding Method (Figure 2-7)

The paper is loaded from the upper paper entrance with the paper release lever set backward. The paper is held against the platen by the paper feed roller and is fed due to friction with the platen and paper feed roller. As in the push tractor feed method, the paper tension unit is used to prevent paper feed problems.

Paper Tension Roller^Gear err

PaDer Tension Roller Transmission Gear

Paper Release Lever

Tractor Transmission Gear Tractor Gear

Paper Tension Roller^Gear

Paper Release Lever

Tractor Transmission Gear Tractor Gear

Pwatrftcftar

Epson 850 Printer

Feed Motor Pinion Gear

Paper Feed Transmission Gear (i) Side View

Pwatrftcftar

Feed Motor Pinion Gear

Paper Feed Transmission Gear (i) Side View

Friction/Tractor Sensor

(ii) Top View (a) Gear Arrangement

(ii) Top View (a) Gear Arrangement

Paper Tension Support Roller

Paper Holding Roller

Paper Holding Roller

Paper Feeder Sensor Epson Stylus 2200

Paper End Sensor

Platen

Paper Feed Roller (Friction State)

Platen

Paper End Sensor

Paper Feed Roller (Friction State)

(b) Platen Path

Figure 2-7. Friction Feeding Method

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