Motor Controller Board; Power - Hologic QDR 4500 Technical Manual

MOTOR CONTROLLER BOARD

The Motor Controller board is a microprocessor controlled power driver circuit for use with a
two coil bipolar stepper motor. It receives high level commands through the Distribution Board
from the host computer, and applies 28 volt pulses to the stepper motor windings. The QDR 4500
uses four identical Motor Controller boards to control and drive the Table X (Table In/Out),
Table Y (Table Left/Right), C-Arm Rotate, and C-Arm Y (C-Arm Left/Right) stepper motors.
The motor windings are driven by two integrated H-bridges. These integrated circuits provide
internal level conversion and power limiting. Their logic level control inputs are driven from a
stepper motor control microcircuit that receives commands from the microprocessor. The control
circuit senses the current in the motor windings and adjusts the duty cycle of the applied voltage
in such a way as to limit the maximum motor current. The maximum value is determined by an
8-bit control word at a Digital to Analog Converter.
Each Motor Controller board monitors the position of its respective mechanism using a signal
received from an associated Position Encoder connected to the mechanism. The Position Encoder
is a precision potentiometer that divides a +/-3V reference source into a sense amplifier in
proportion to the position of the mechanism driven by the motor. The sense amplifier output is
converted to digital code that provides position feedback to the microprocessor.
The Motor Controller boards receive movement commands from the QDR 4500 computer via the
communications bus. Each Motor Controller board contains an ID switch and four status
indicators (LEDs). The ID switch is a 16-position rotary encoded switch (SW1) that is read
during system initialization to determine the Motor Controller board's address for communicating
with the QDR 4500 computer. ID switch settings for the four Motor Controller boards are as
follows:
Table X drive
Table Y drive
C-Arm Rotate drive 6
C-Arm Y drive
The four red status LEDs provide visual indications of motor drive power on, Stepper CPU
active, motor drive direction, and motor step pulses.
The Motor Controller board also has provision (JP2) for connecting limit switches to inhibit
motor operation when the mechanism goes beyond established mechanical limits. This feature is
not used in the QDR 4500 and therefore no cable is connected to JP2.

Power

Power input to the Motor Controller board is +28VDC. This voltage provides the motor drive
power and is converted down to +5VDC for use by logic circuits on the board. The +5VDC is
also converted to -5VDC. Two green LEDs provide visual indication of the power present on the
Motor Controller board.
Section 2 - Functional Description
4
5
7
2-5