Hologic DISCOVERY A, Technical Manual

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Discovery QDR Series Technical Manual
2-5
2.4 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 24-volt pulses to the stepper motor
windings. The Discovery uses four identical Motor Controller Boards to control and drive
the Table X (Table In/Out), Table Y (Table Left/Right), C-Arm Y (C-Arm Left/Right), C-
Arm R (Arm rotation, A/SL only) 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
voltage received from an associated Position Encoder connected to the mechanism. The
Position Encoder is a precision potentiometer that divides a +/-3V reference source. The
output voltage is fed to a sense amplifier in proportion to the position of the mechanism
driven by the motor. The sense amplifier output is converted to digital value that provides
position feedback to the microprocessor.
The Motor Controller Boards receive movement commands from the Discovery 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 address for
communicating with the Discovery computer. ID switch settings for the Motor Controller
Boards are as follows:
Table X drive 4
Table Y drive 5
C-Arm Rotation 6
C-Arm Y drive 7
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 Discovery and, therefore, no cable is connected to JP2.
2.4.1 Power
Power input to the Motor Controller Board is +24VDC. 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 a visual indication of the
power present on the Motor Controller Board.