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Service Guide ML590/ML591
Chapter 2 Principles of Operation
2.2.02 Spacing Mechanism
The spacing mechanism consists of a carriage shaft (mounted parallel to the platen), and a
carriage frame which moves along the shaft. The carriage frame is driven by a DC servo motor
mounted on the carriage frame. Items included in the spacing mechanism are listed below.
Space Motor Assembly
DC Servo Motor
Motor gear
Sensor
Encoder Disk
Carriage Frame
Carriage Shaft
Space Rack
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), passes between a light
source and two photosensors. 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 pulse width of the signals generated by the photosensors.