AMT Datasouth XL 300 SERIES, Руководство по обслуживанию

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2.6: CARRIAGE DRIVE
Carriage motion is controlled by a stepper motor. The motor is a 1.5 degree two-phase
type. The carriage is driven by the motor through a capstan and set of wire cables. The
capstan is sized so that one step of the motor corresponds to 1/100 of an inch (the
separation of sub-columns at 10 characters per inch).
The motor is controlled by the microprocessor which provides step sequencing and timing
functions. The motor can be stepped in one phase-on or two-phase-on modes. This dual
capability means the motor can be half stepped. When motion begins, the step rate is
ramped up to the running rate, and correspondingly the step rate is ramped down to a stop
at the end of a motion. The motor is half-stepped whenever the step rate is less than the
motor's resonant frequency.
Power is delivered by a chopping current regulator operating off the +55V supply. Power
can be cut off from the motor by disabling the “system ready” (see section on system
clamp). When the printer is idle “system ready” is disabled by the processor and the motor
is not energized. When the carriage motor is idle and system ready is enabled, the amplifier
will maintain a holding current of 0.5 amps in each winding of the motor.
Any change in the inputs to the carriage amplifier (ie. a step command) is detected by the
amplifier which responds by increasing its current limit level. This is achieved by changing
the reference voltage on the comparator in the current limiting circuit.
Because the carriage motor runs open loop, the microprocessor must keep track of carriage
position by keeping track of steps it commands the motor to take. Upon initialization at
power on, the processor must locate the position of the carriage. This is accomplished by
moving the carriage to the left side of the mechanism until it interrupts the photo-
interrupter switch located on the left end plate.
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