Data processing: generic control systems or specific application – Generic control system – apparatus or process – Optimization or adaptive control
Reexamination Certificate
1999-12-09
2003-02-11
Black, Thomas (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Optimization or adaptive control
C700S073000, C700S074000, C708S300000, C708S320000
Reexamination Certificate
active
06519496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feedback controller for performing a feedback control through detecting a driving state of a driving unit, a digital filter device which is preferably applicable to the feedback controller, and a storage device having a head for at least reproducing information stored in an information storage medium.
2. Description of the Related Art
Hitherto, there is widely used in various fields a feedback controller in which a feedback signal is generated through detecting a driving state of a driving unit, an arithmetic processing such as a phase compensation for a stabilization of a control system is performed, and a driving control of the driving unit is performed in accordance with the feedback signal after the arithmetic processing.
According to the feedback controller as mentioned above, in order to enhance the tracking efficiency, there is adopted such a scheme that a phase-lag compensation is established, a feedback gain is increased to establish a high frequency band.
It is known that when it is intended to increase a gain to a high frequency by the phase-lag compensation, a phase cross frequency is increased, and then the gain margin and the phase margin are decreased, so that a stability of a control system is damaged.
Therefore, there is a need to establish a high frequency band through increasing a gain cross frequency to some extent. However, in the even that in order to increase the gain cross frequency, the feedback gain is increased, there is a need to establish a phase-lead compensation over a high frequency so that a control system is stabilized in the high frequency. In this case, there is a possibility that the stability of the control system is damaged by a high-order resonance of a movable mechanism unit.
In order to solve this problem, there is adopted a scheme that a notch filter or a low pass filter is applied to a high-order resonance frequency. However, in case of a digital filter used in a digital control using a microprocessor unit (MPU), such as a digital signal processor (DSP) and the like which are used for the purpose of establishing low cost and high-performance, the digital filter does not sufficiently operate at a frequency close to the Nyquist frequency which is ½ of the sampling frequency. Therefore, in the event that a high-order resonance frequency of the movable mechanism unit exists at a frequency band close to the Nyquist frequency, it is difficult to ensure a sufficient stability of the control system.
The above-mentioned problem will be described referring to by way of example a feedback controller adopted in an optical storage device for accessing an optical disk. As the optical disk, for example, a phase change optical disk and a magneto optical disk exist. Here, typically, an optical storage device for accessing the magneto optical disk will be considered.
Hereinafter, first, a guide line of the optical storage device will be described, and then problems of the feedback control system will be described.
FIG. 1
is a perspective view of an optical storage device.
A spindle motor
101
for driving an optical disk
200
is fixed on a drive base
100
, for example, made of an aluminum. Further, on the drive base
100
, there are provided a movable mechanism unit
110
having an objective lens
111
and a magnetic coil
112
, and a magnetic circuit
121
having a permanent magnet disposed in such a manner that the movable mechanism unit
110
is sandwiched by the permanent magnet. The magnetic circuit
121
having the permanent magnet and the magnetic coil
112
constitutes a voice coil motor (VCM). As a current is supplied to the magnetic coil
112
, the movable mechanism unit
110
moves in a direction of an arrow A-A′ by an interaction of the current flowing through the magnetic coil
112
and the magnetic circuit. A laser beam is applied from a fixed optical unit
130
to the objective lens
111
. The laser beam is emitted from the objective lens
111
so that an optical spot is projected onto an optical disk
200
and reflected therefrom. The reflected light is returned through the objective lens
111
to the fixed optical unit
130
, so that information stored in the optical disk
200
is picked up.
FIG. 2
is a schematic construction view of an optical system of an optical storage device.
A laser beam emitted from a semiconductor laser
131
passes through a collimator lens
132
and a polarization beam splitter
133
, and reflects-on a reflecting mirror
113
, and further passes through the objective lens
111
, and finally be condensed on the optical disk
200
.
Here, only the reflecting mirror
113
other than the objective lens
111
is mounted on the movable mechanism unit
110
, and other all optical elements constitute the fixed optical unit
130
.
A signal light reflected on the optical disk
200
, which carries information recorded on the optical disk
200
, passes through the objective lens
111
, reflects on the reflecting mirror
113
, enters the polarization beam splitter
133
, and goes to a beam splitter
134
side. An incident light to the beam splitter
134
is divided into two parts one of which enters Wollaston prism
135
whereby the light is separated in accordance with the polarization direction. And the light thus separated enters via a lens
136
a photo detector
137
for picking up information recorded on the optical disk
200
.
On the other hand, another of the two parts of light divided by the beam splitter
134
enters via a lens
138
a beam splitter
139
wherein the light is further divided into two parts one of which enters a photo detector
140
for a tracking error detection, and another enters a wedge prism
141
wherein a light beam is further divided into two parts and is projected onto a photo detector
142
for a focus error detection.
FIG. 3
is a block diagram of a feedback controller for driving the movable mechanism unit
110
of the optical storage device.
A position of the movable mechanism unit
110
is detected by a positional sensor
150
. The positional sensor
150
comprises the photo detector
140
for tracking an error detection, as shown in
FIG. 2
, and a signal processing circuit (not illustrated) for processing signals obtained by the photo detector
140
. A detection signal obtained by the positional sensor
150
is fed to a differential circuit
152
in which a difference between the detection signal and a target value signal representative of a position of the movable mechanism unit
110
, outputted from a target value generating circuit
151
, is calculated to generate an error signal. The error signal thus generated is attenuated in high frequency component by an anti-aliasing filter
153
for suppressing a frequency component exceeding Nyquist frequency which is the half of a sampling frequency of an A/D converter
154
. The A/D converter
154
converts the error signal thus obtained into a digital signal. A signal outputted from the A/D converter
154
is fed to a phase compensation filter
155
wherein the signal is subjected to a phase compensation processing so as to ensure a stability of a control system through a digital operation. A signal subjected to the phase compensation processing by the phase compensation filter
155
is fed to a driving circuit
156
in the form of a control signal to control the movable mechanism unit
110
to a target position. Incidentally, it is acceptable that the driving circuit
156
receives a digital control signal, or alternatively it is acceptable that the driving circuit
156
receives an analog control signal in such a manner that the output of the phase compensation filter
155
is converted into the analog control signal by a D/A conversion.
The driving circuit
156
supplies a driving signal (here a current signal) to an electromagnetic coil
112
(cf.
FIG. 1
) of the movable mechanism unit
110
in accordance with the entered control signal, and whereby the movable mechanism unit
110
is controlled to a target position.
FIGS.
Kawabe Takayuki
Watanabe Ichiro
Barnes Crystal J.
Black Thomas
Fujitsu Limited
LandOfFree
Feedback controller, digital filter device, and storage device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Feedback controller, digital filter device, and storage device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Feedback controller, digital filter device, and storage device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3129315