User's Manual

4.7 Servo Control
4.7.5 Spindle motor control
Hall-less three-phase twelve-pole motor is used for the spindle motor, and the
PWM type 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 including the serial data
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 the serial data to the SVC to
charge the charge pump capacitor of the SVC.
b) When the charge pump capacitor is charged enough, the MPU sets the SVC to
the motor start mode.
It moves to 3) or 5) step depending on the condition of spindle motor. It is
treaded as the stop condition, it moves to the step 3). Whereas, it is treated as
the free-wheeling condition, it moves to the step 5).
c) 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).
The above operations mean the generation of rotational magnetic field.
d) During phase switching, the spindle motor starts rotating in low speed, and
generates a back electromotive force. The SVC detects this back
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 the phase switching to the SVC. The SVC starts a
phase switching by itself based on the back 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 7,200 rpm. When the rotational speed reaches 7,200 rpm,
the SVC enters the stable rotation mode.
(3) Stable rotation mode
The SVC builds the 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.
C141-E259 4-19