ENCAD T-200 Service Manual download pdf (Page 32)

Theory of Operation 2-9

ENCAD T-200 and T-200+ Service Manual

Stepper Motor Controller

Figure 2-6. Stepper Motor Controller.

The media is driven by a Stepper Motor, which drives the media in a

direction perpendicular to the width of the printer. The media in the

printer can advance forward and backward, depending upon the

commands which the Stepper Motor receives from the microprocessor.

The Stepper Motor Controller contains two identical circuits, one for

each winding of the stepper motor. The circuit is a combination of two

simpler types of circuits and can be thought of as a variation of either

one.

A waveform generator receives digital data from the CPU and gener-

ates a sine wave output. This signal is fed into a comparator circuit

that is measuring the current through the winding of the stepper

motor. If the current is too low, a pulse of 24V is generated. When the

current goes above the output of the waveform generator, the pulse

turns off. Every time the output of the waveform generator is changed

by the microprocessor, the motor moves 1 “micro-step”.

Each circuit contains four main functions (see Figure 2-6):

1. Reference waveform generator

The microprocessor uses a D/A (digital to analog) converter to set

the desired level for the current in the stepper motor winding. The

output of the D/A converter varies in time to create a reference

waveform. This reference waveform is centered around 10V.

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ENCAD T-200 Service Manual Page 32