In recent years, a motor wherein current paths are electronically altered by plural transistors has been widely used as a drive motor in office automation equipment and audio-visual equipment. A disk drive apparatus, such as an optical disc drive apparatus (DVD, CD, and the like) and a magnetic disk drive apparatus (HDD, FDD, and the like), includes such a motor. As an example of such a conventional motor, a motor wherein current paths are altered by PNP-type and NPN-type bipolar power transistors is disclosed on lines 16 to 31 in the first column and FIG. 34 in the specification of the U.S. Pat. No. 5,982,118.
FIG. 35 shows a prior art motor, and the operation of the prior art motor is described below. A rotor 2011 has a field part formed by a permanent magnet. In a position detector 2041, three position sensors detect the magnetic field of the field part of the rotor 2011. In other words, the position detector 2041 produces two sets of three-phase voltage signals, that is, Kp1, Kp2 and Kp3, and Kp4, Kp5 and Kp6, in response to the three-phase output signals of the three position sensors in response to the rotation of the rotor 2011. A first distributor 2042 produces three-phase lower-side signals Mp1 Mp2 and Mp3 in response to the voltage signals Kp1, Kp2 and Kp3, thereby controlling the activation of lower-side NPN-type bipolar power transistors 2021, 2022 and 2023. A second distributor 2043 produces three-phase higher-side signals Mp4, Mp5 and Mp6 in response to the voltage signals Kp4, Kp5 and Kp6, thereby controlling the activation of the upper-side PNP-type bipolar power transistors 2025, 2026 and 2027. Accordingly, three-phase drive voltages are supplied to windings 2012, 2013 and 2014.
In the prior art configuration shown in FIG. 35, the position detector 2041 comprises three position sensors for detecting the rotational position of the rotor 2011. This has caused the necessity of a substantial space for installing these position sensors and the complexity of the wiring, resulting in an increase in cost. On the other hand, a motor with no position sensor is disclosed on line 54 of the second column to line 45 of the third column and FIG. 1 in the specification of the U.S. Pat. No. 5,473,232. In the motor, the back-electromotive forces of the windings are detected so as to obtain the rotational position of the rotor. In the motor with no position sensor, however, the rotational position cannot be detected correctly at a low rotational speed of the motor, since the magnitudes of the back-electromotive forces become too small to detect at a low rotational speed of the motor. So, it is difficult to drive and control the motor at a low speed. In particular, in the case when the rotational speed is controlled by using a pulse signal which responds with the detected back-electromotive forces, a large fluctuation occurs in the rotational speed of the motor at a low speed because of the inaccurate detection of the pulse signal.
A motor with a single position sensor is disclosed on line 30 of the fifth column to line 41 of the 12th column and FIG. 1 in the specification of the U.S. Pat. No. 5,729,102. In the motor, the rotational electrical angle is estimated from the output of the single position sensor, and sinusoidal currents are supplied to the windings in response to the estimated rotational electrical angle. However, in the case of the motor with the single position sensor, positional information in the stop state of the rotor is insufficient, thereby starting and acceleration of the motor with the single position sensor becomes unstable. Accordingly, the starting and acceleration of the rotor are not carried out smoothly, resulting in a starting failure. Furthermore, in the configuration of the motor according to the specification of the U.S. Pat. No. 5,729,102, it is difficult to estimate the rotational electrical angle with a fine step resolution. In particular, the error in the estimated electrical angle becomes larger at a higher rotational speed. Accordingly, precise rotation control of the motor has been difficult.
In an optical disc drive apparatus for reproducing signals from DVD-ROM, CD-ROM, and CD disks, stable operation is required over a wide range of rotational speed from 10,000 rpm for high-speed reproduction to 200 rpm for CD reproduction. In a rewritable disk drive apparatus for recording information on a high-density disk and/or reproducing information from a high-density disk such as DVD-RAM/RW and CD-R/RW, the disk is required to be rotated precisely. In these disc drive apparatuses, it is necessary to smoothly start and accelerate the disk and to carry out information reproduction in a short time. In addition to the optical disc drive apparatuses, magnetic disc drive apparatuses such as HDD and FDD are also required to be low cost and to carry out stable rotation of the disk during the whole operation which includes the operation of the starting and acceleration thereof.