Dynamic information storage or retrieval – Dynamic mechanism subsystem – Specific detail of storage medium support or motion production
Reexamination Certificate
1997-03-13
2002-10-22
Burgess, Glenton B. (Department: 2153)
Dynamic information storage or retrieval
Dynamic mechanism subsystem
Specific detail of storage medium support or motion production
Reexamination Certificate
active
06469975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for controlling the speed of a sled motor of an optical disk drive. More particularly, the present invention relates to a method for controlling the speed of a sled motor of an optical disk drive which uses a velocity profile to control the speed of the sled motor. The present disclosure is based upon Korean Application No. 96-6647, which is incorporated herein by reference.
2. Description of the Related Art
A compact disk (CD) player and a digital video disk (DVD) player are devices for reproducing audio data stored on an optical disk. On the other hand, a CD-ROM drive and a DVD-ROM drive are computer peripheral devices for reproducing digital data stored on an optical disk. The CD-ROM drive and DVD-ROM drive are random access devices, unlike the CD player and the DVD player, and thus make frequent movements to read the data on the disk.
In such an optical disk system in which a rotating speed and a pick-up position need to be accurately controlled while simultaneously maintaining a high speed operation, such as in the CD-ROM drive, system performance is maximized when the sled and spindle servos of the device are accurately controlled and are in appropriate harmony with one another.
FIGS. 1 and 2
show the sled driving shaft
14
and its peripheral devices in the CD-ROM drive. More specifically,
FIG. 1
shows the structure of a typical transferring mechanism of a pickup device in a CD-ROM drive, and
FIG. 2
shows the relative position of a sled motor and Hall-effect sensor in the CD-ROM drive of FIG.
1
.
A first gear
31
is installed at one end of the shaft of a sled motor
41
. The first gear
31
, a second gear
32
, a third gear
33
, a fourth gear
34
, and a rack-shaped fifth gear
35
are sequentially engaged. Thus, the driving force from the sled motor
41
is sequentially transferred through the first gear
31
, second gear
32
, third gear
33
, fourth gear
34
, and fifth gear
35
to the pickup device
13
, so that the pick up device
13
moves along the sled driving shaft
14
.
A magnetic plate
42
, on which a plurality of alternating north and south magnetic poles are formed as illustrated in
FIG. 3
, is installed on the shaft of the sled motor
41
between the first gear
31
and the sled motor
41
. Also, a Hall-effect sensor
44
is installed at a predetermined position on a printed circuit board
43
, separated by a predetermined distance from and opposed to the magnetic plate
42
. Here, the combination of the magnetic disk
42
and the Hall-effect sensor
44
generates a signal whose frequency is proportional to the rotational speed of the sled motor
41
.
FIG. 4
is a block diagram of a circuit for controlling the speed of a sled motor in a typical CD-ROM drive which uses a velocity profile to control the speed of the sled motor. The signal generated by the Hall-effect sensor
51
is amplified by an amplifier
52
. A frequency-to-voltage converter
53
receives the amplified signal and converts the frequency of the amplified signal into a voltage to generate a converted voltage signal whose instantaneous value is proportional to the frequency of the received amplified signal. A microcomputer
55
generates a target velocity profile and outputs a target voltage, which represents a target speed, to be lowpass filtered in a lowpass filter (LPF)
56
. Then, the converted voltage signal from the frequency-to-voltage converter
53
and the lowpass filtered signal are differentially amplified by being subtracted by a subtractor
57
and amplified by an amplifier and driver
58
. Afterwards, the amplified signal drives a sled motor
59
, so that the pick-up device moves in a desired manner.
When the CD-ROM drive is in an on-track state rather than a servo-control state, the converted voltage signal from the frequency-to-voltage converter
53
is differentially amplified with the lowpass filtered signal and a tracking error signal, which is output by a tracking error calculator
60
via a lowpass filter (LPF)
61
, to drive the sled motor
59
.
Thus, in the CD-ROM drive, the signal pulse generated by the Hall-effect sensor is converted into a voltage signal proportional to the frequency of the signal pulse and differentially amplified with a target speed voltage, so that the speed of the sled motor
41
is controlled to be close to the target speed.
Gains of the Hall-effect sensor
44
differ in each CD-ROM apparatus. Generally, the Hall gain depends on the magnetic field intensity of the magnetic plate
42
, the sensitivity of the Hall-effect sensor
44
, and. the distance between the magnetic plate
42
and the Hall-effect sensor
44
, the most critical factor being the distance between the magnetic plate
42
and the Hall-effect sensor
44
. If the distance is not adjusted precisely, which is very difficult, the output signal of the Hall effect sensor
44
which should reflect the actual rotating speed of the sled motor may not be accurate. Also, the inaccurate Hall gain due to the imprecise distance between the magnetic plate
43
and the Hall-effect sensor
44
results in an improper control of the sled servo.
If the Hall gain has an accurate or nominal value, the target velocity profile and the actual velocity profile have almost the same magnitude as shown in FIG.
5
. However, if the Hall gain is inaccurate, the target velocity profile and the actual velocity profile have different magnitudes at each instant, as shown in
FIGS. 6 and 7
.
Specifically, if the Hall gain is greater than the nominal value, the output signal of the Hall effect sensor which is controlled to be the same as the target speed is greater than the actual speed, as shown in FIG.
6
. Therefore, the actual rotating speed of the sled motor is smaller than the target speed. Contrarily, if the Hall gain is smaller than the nominal value, the output signal of the Hall effect sensor is smaller than the actual speed, as shown in FIG.
7
. In such a case, the actual rotating speed of the sled motor is larger than the target speed.
Conventionally, to reduce the effect of the variation of the gain and regulate the output signal of the Hall-effect sensor
44
, a variable resistor
54
is provided, as shown in
FIG. 4
, for adjusting the gain of the amplifier
52
. However, the adjustment using the variable resistor
54
is not very accurate, and therefore a significant error remains.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a method for controlling the speed of a sled motor of an optical disk drive which can minimize the variation of the actual speed of the sled motor by detecting the actual speed thereof, and adaptively adjust the target speed according to the detected actual speed using a microcomputer.
To accomplish the above object, there is provided a method of controlling the speed of a sled motor for an optical disk wherein the sled motor is first driven according to a predetermined target velocity profile stored in a microcomputer. Then, a frequency of a sinusoidal wave output by a Hall-effect sensor is detected, and it is determined whether the frequency of the sinusoidal wave is higher than a predetermined value. If the frequency of the sinusoidal wave is greater than the predetermined value, the target speed is incremented by a predetermined amount. On the other hand, if the frequency of the sinusoidal wave is smaller than the predetermined value, the target speed is decremented by the predetermined amount.
In the sled motor speed controlling method according to the present invention, the variation of the gain of the Hall-effect sensor can be compensated during the operation of the optical disk drive. As a result, a faster access time can be obtained since the actual rotating speed of the sled motor is detected by the microcomputer and the target speed is adaptively adjusted in accordance with the actual detected speed.
REFERENCES:
patent: 4672595 (1987-06-01), Senso
patent: 4680515 (1987-07-01), Crook
patent: 4745563
Burgess Glenton B.
Kupstas Tod
Samsung Electronics Co,. Ltd.
Sughrue & Mion, PLLC
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