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A7 COIL BD Operation
Illustration detail of COIL BD.
Achieving Smooth Velocity
To acheive smooth velocity in the MOTOR it is necesary to achieve smooth rotating torque. This is done by creating a magnetic field with the COILS that the MAGNET
will align itself with. When the MAGNET's poles are nearly in alignment with the magnetic field, the torque potential is the greatest. As the MAGNET rotates away from
perfect alignment, the COILS need more current to create the same amount of torque.
To create the smoothest torque, the A6 uses a sinusoidal current in the COILS. When the MAGNET's polarization is furthest out of alignment with the COIL's magnetic
field, the current sinusoid is at its peak. When the MAGNET and the field are nearly perfrectly aligned, the current drops to near zero. The COIL current then changes
polarity and becomes negative to repel the MAGNET pole and continue the smooth torque. As the next pole starts to approach, the current sinusoid turns around and
reaches its peak again.
The A6 monitors the signals from the ENCODER while the MOTOR is running. If the MOTOR is running too slowly, it increases the peak of the COIL current sinusoid
to create more torques to increase the speed. If the motor is going too fast, it reduces the current.
1234563 – 12/12/94
A7 COIL BD Components
The A7COIL BD is made up of:
• 6 triangular-shaped coils of wire, arranged around the central SHAFT of the
MOTOR.
• 3 HALL EFFECT SENSORS, which detect magnetic fields. They are used in
the MOTOR to determine the position of the MAGNET poles relative to the
coils.
• 3 THERMAL FUSES, which protect the components in the event of
overheated coil or other malfunction.
Operation
The work of the SLOW SCAN MOTOR gets done between the A7 COIL BD and
the MAGNET. The MAGNET is located directly over the A7 BD. Rotation of the
MOTOR is achieved as follows:
1. The HALL EFFECT SENSORS determine how the polalization of the
MAGNET is aligned with the COILS.
2. The A6 CONTROLLER BD changes the amount or direction of the current
flow in the in the COILS to create a magnetic field.
3. The MAGNET tries to align itself to the magnetic field.
4. Resulting in rotation of the MAGNET.
5. The process is repeated creating a smooth rotation of the MOTOR.
Scan/Erase Subsystem
8–37
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