Smiths Medical Medfusion 3000 Series, Technical & Service Manual

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Theory of Operation
44
40-5648-51B
Motor drive description
A two-phase bipolar stepper motor drives the syringe
plunger. The motor control interface drives the stepper
motor.
Coil “B”
Motor Current
Control
Coil “A”
Motor Current
Control
Motor
Motor
Current
Detector
Motor Current
Phase A/A*
Motor Current
Phase B/B*
ø
Direction
ø
Count Reference
ø
Enable*
ø
Current Reference
Motor Current Detect
ø
Direction
ø
Enable
Flowchart of Motor Drive Description
The main microprocessor controls which motor wind-
ing is active, designated as A or B, the direction of cur -
rent in each winding, and the magnitude of the current.
Coil A & B PWM current references
The pulse-width modulated signals from the main
microprocessor are low pass filtered to create an analog
voltages for control of motor current in each coil.
Motor current regulators, U26, U35
Two regulator ICS independently regulate the current
for windings A and B.
•
The watchdog_alarm signal activates the N-chan -
nel mosfet to disable the motor current in both
windings through the “BRAKE” pin of the regulator
IC.
Motor current detector, U40
The watchdog alarm function is tested at power-up by
verifying the mtr_current_detect* signal is at a logic
high when the watchdog alarm condition is active.
•
Similarly, the mtr_current_detect* signal should
be at a logic low when either motor winding has suf -
ficient current and the watchdog alarm condition is
not present.