Servo Motor Controller - ENCAD NovaJet Pro 600e Service Manual

NovaJet PRO 600e Service Manual

Servo Motor Controller

The Carriage Assembly is driven by the Servo Motor. The speed of the
Carriage Assembly is controlled by varying the duty cycle of the signal
applied to the controller. The microprocessor checks the position of the
Carriage Assembly approximately 1,000 times per second (during the
servo interrupt). It then updates the PWM (pulse width modulator)
register in the gate array which sets the duty cycle to make adjust-
ments to the Carriage Assembly speed. A linear optical encoder is used
to monitor the Carriage Assembly position.
The optical encoder strip runs the length of the Stabilizer Bracket
and contains 150 lines and spaces per inch. Thus there are 300
edges per inch. The detector circuit actually consists of two optical
edge detectors. They are separated from each other by one half the
width of one of the optical lines on the encoder strip. This allows 4
evenly spaced pulses to be developed for each line on the encoder
strip. This is known as quadrature signals. It gives an effective
resolution of 600 lines per inch. See figure 2-9 for a graphical repre-
sentation of quadrature signals. For 300 dpi resolution, one of the
detectors is not used.
2-12 Theory of Operation
Figure 2-8. Servo Motor Controller.