4.7 Servo Control
C141-E218 4-19
4.7.5 Spindle motor control Hall-less three-phase twelve-pole motor is used for the spindle motor, and the 3-
phase full/half-wave analog current control circuit is used as the spindle motor
driver (called SVC hereafter). The firmware operates on the MPU manufactured
by Fujitsu. The spindle motor is controlled by sending several signals from the
MPU to the SVC. There are three modes for the spindle control; start mode,
acceleration mode, and stable rotation mode.
(1) Start mode
When power is supplied, the spindle motor is started in the following sequence:
a) After the power is turned on, the MPU sends a signal to the SVC to charge
the charge pump capacitor of the SVC. The charged amount defines the
current that flows in the spindle motor.
b) When the charge pump capacitor is charged enough, the MPU sets the SVC
to the motor start mode. Then, a current (approx. 0.3 A) flows into the
spindle motor.
c) A phase switching signal is generated and the phase of the current flowed in
the motor is changed in the order of (V-phase to U-phase), (W-phase to U-
phase), (W-phase to V-phase), (U-phase to V-phase), (U-phase to W-phase),
and (V-phase to W-phase) (after that, repeating this order).
d) During phase switching, the spindle motor starts rotating in low speed, and
generates a counter electromotive force. The SVC detects this counter
electromotive force and reports to the MPU using a PHASE signal for speed
detection.
e) The MPU is waiting for a PHASE signal. When no phase signal is sent for a
specific period, the MPU resets the SVC and starts from the beginning.
When a PHASE signal is sent, the SVC enters the acceleration mode.
(2) Acceleration mode
In this mode, the MPU stops to send the phase switching signal to the SVC. The
SVC starts a phase switching by itself based on the counter electromotive force.
Then, rotation of the spindle motor accelerates. The MPU calculates a rotational
speed of the spindle motor based on the PHASE signal from the SVC, and waits
till the rotational speed reaches 4,200 rpm. When the rotational speed reaches
4,200 rpm, the SVC enters the stable rotation mode.
(3) Stable rotation mode
The SVC builds the FLL/PLL circuit into, and to become the rotational speed of
the target, controls a stable rotation with hardware.
The firmware calculates time of one rotation from PHASE signal. PHASE signal
is outputted from the SVC. And the firmware observes an abnormal rotation.