Mill Table Power Drive Motor Controller
The controller for the mill table power drive is different from the other
controllers because it controls a 24 Volt motor rather than one that operates at
line voltage.
This controller starts with a switch mode power supply that converts line
voltage to a regulated 25 Volts DC. This voltage powers
the green "On" lamp and is delivered to the motor direction switch which can
reverse the direction of the motor. The power is returned to a mosfet
switch and then to the SMPS negative after going through a sense resistor.
The mosfet switch is turned off and on by pulses coming from a variable pulse
width generator. The width of the on pulse is set by the "Speed Set"
potentiometer.
The fault sense circuit compares the current going through the mosfet switch to
a fixed value and, if this value is exceeded, shuts down the pulse width
generator, turns off the mosfet, and turns on the yellow fault lamp.
This comparison value is adjusted by the "Torque Adjust" trim pot which is on
the PC board.
This controller is final tested by checking control range, set point regulation
and fault circuit performance.
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