Control of the Washer Module
DSX™ System Service Manual 12-13
Using YZ CLK the SHARED CLOCK can be switched from Y (Logic 0) to Z (Logic 1).
If TWO CLK is set to a logic 1 then both Y and Z motors are pulsed with the SHARED
CLOCK this condition over-rides the SHARED CLOCK.
MOTOR DRIVERS
The three motor drivers are identical, using the A2919, and are all set for 0.5 Amps peak
current. Using the above Bit pattern generator the motors are driven in quarter steps (1/4).
PUMP SELECTION, DRIVES AND CURRENT MONITORING
Pump speed is controlled by regulation of the mean dc current to the motor. That
regulation is via the PWM outputs of the H8 controller. The frequency of the PWM is set
and the on period of the cycle is adjusted to produce the duty cycle required for the pump
output necessary. This frequency is determined by test and is preset for each motor.
The PWM output for the dispense pumps is gated to one of four pumps, using DP1-DP4
to enable the required dispense pump. These signals also enable the required pinch valve.
All four dispense pump drives are identical. The current is switched via a FET employing
low side switching. The return current passes through a one-ohm resistor; the resulting
voltage drop is integrated, amplified and then passed to the analogue inputs of the H8
controller. The voltage read is proportional to the actual current drawn by the motor.
The actual current drawn is proportional to the PWM duty cycle, the frequency (fixed) and
the load on the motor. The current will increase if the motor is stalled and it will decrease
from the norm if the motor is running with a light load (i.e. not pumping fluid). The
controller, and corrective action taken can detect any large difference from the norm.
CAUTION: AT LOW NOMINAL CURRENTS (LOW PWM PERIOD)
THERE MAY BE NO (OR UNDETECTABLY LOW) DIFFERENCES
BETWEEN THE CURRENT LEVELS IN THE DIFFERENT STATES.
VOLTAGE GENERATION AND REGULATION
The Vcc is derived from +12 volts via a linear regulator LM7085CT fitted with a
17°C/Watt heatsink.
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