Brother MFC4820C Service Manual page 51

Controlling the paper stop position
To make the paper feed motor (DC motor) stop paper with precision during printing, the controller
controls the motor using PID control (Proportional, Integral and Differential control) using the PF
encoder. The controller sets parameters suitable for the paper feed amount, enabling the motor to
stop in position with high precision in a short space of time.
If the paper stop position is out of position, the controller compensates the error in the next paper
feeding operation by adjusting the encoder count so that errors will not accumulate. For example,
if the paper stop position is shorter than the specified stop position by a single encoder slit, then
the controller feeds the next sheet of paper by the specified encoder count plus 1.
Feeding paper at a constant speed
The controller controls the paper feed roller to rotate it at a constant speed even if the load to the
drive mechanism fluctuates. This control is mostly applied when paper is fed into and ejected from
the printer unit after printing; that is, when a highly precise stop position is not required.
Control according to property data
The outside diameters of individual paper feed and ejection rollers and the nozzle length of
individual print head units (for black ink) are measured beforehand. When these parts are installed
in the machine, their property data are stored in the EEPROM of the driver PCB. The controller
adjusts the paper feed amount according to the algorithm based on the information
Property data is managed using a two-dimensional code and printed on a property label attached to
the lower cover of the machine.
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