Brother FAX 1840C, Service Manual

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3.2.2.4 Carriage drive mechanism
The head/carriage unit, which integrates the print head unit and carriage, is supported and guided by
the CR guide rail and CR support chassis. The CR timing belt (1/25.4 inch pitch) transmits the
carriage motor rotation to the carriage. Clockwise motor rotations move the carriage to the right;
counterclockwise ones to the left.
The CR encoder sensor on the back of the head/carriage unit scans the CR encoder strip under the
engine chassis to monitor the current head position relative to the home position. The controller uses
this signal for proportional, integration, differential (PID) control ensuring uniform speed. The strip's
1/150 dpi markings offer a choice of four speeds to match the print resolution: 40.0, 33.3, 32.0, and
20.0 ips.
CR encoder strip
Idle pulley
CR timing belt
Carriage motor
Carriage
motor pulley
(Paper feed roller)
Head/carriage unit
CR guide rail
CR support chassis
Aging
Maintenance mode function code 69 is for adjusting the initial PWM value. The firmware
automatically adjusts this CR drive parameter as the head/carriage unit works to minimize speed
deviations and to match the current mechanism. This aging sometimes resolves problems with ink
clogging uneven operation.
For further details on maintenance function code 69, see Chapter 8, Section 8.5.16 .