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Service Guide ML520/521
Chapter 2 Principles of Operation
Spacing Operation
The carriage frame, which contains the printhead and space motor, moves along the carriage shaft parallel to the platen. When the space motor rotates, the driving force is transmitted to the motor gear. As the motor gear rotates, the carriage moves along the platen. For every revolution of the DC servo motor, the carriage frame moves 0.8 inch (20.32 mm).
As the DC servo motor rotates, a slotted disk (called the encoder disk), rotates with the servo motor and passes through the photosensor. The position of the carriage frame can be determined by counting the pulses generated by the photosensors.
In the same way, the rotation of the space motor can be recognized and controlled by measuring the phase relationship and the pulsewidth of the signals generated by the photosensors.
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