Platen Gap Adjustment Mechanism

The printer mechanism has an automatic platen gap adjustment function that ensures an optimum gap (between the platen and printhead) by measuring the thickness of the paper. Figure 2-4 shows the platen gap adjustment mechanism.

The carriage guide shaft supporting the front of the carriage has an elliptical section. The rotation of the platen gap motor is transmitted to the carriage guide shaft through the gears. Counterclockwise (CCW) rotation of the motor expands the platen gap and clockwise (CW) rotation reduces it (as viewed from the left side).

An encoder plate with equally-pitched slits is mounted coaxially with the rotor of the platen gap motor. When the motor rotates, the platen gap sensor (photo coupler) detects it and outputs pulses. Each pulse corresponds to 0.015 mm (horizontal distance), and the detection range is O to 0.7 mm.

Epson Sensor Measurement

Figure 2-4. Platen Gap Adjustment Mechanism

Table 2-4. Platen Gap Motor/Sensor Specifications

Motor Specifications

Sensor Specifications


4-phase 48-pole PM-type stepping motor


Photo interrupter

Supply voltage

36.5 ± 1 VDC


2-channel rectangular pulse (TTL level)

Winding resistance

250 ± 18 ohms/phase (at 25°C)

Supply voltage

5 VDC ±5%

Drive frequency

285 pps

Phase difference

Approx. 45°

Excitation system

2-2 phase excitation

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  • holly
    What is platan gap sensor?
    3 years ago

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