Clamping device with variable clamping force

Details Clamping device with variable clamping force Clamping device with variable clamping force

2001-06-13

2004-02-24

Cao, Allen (Department: 2652)

Dynamic information storage or retrieval

Dynamic mechanism subsystem

Specific detail of storage medium support or motion production

Reexamination Certificate

active

06697320

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a clamping device with variable clamping force, especially to a clamping device by employing force balance between restoring force of resilient body and centrifugal force of moving mass to provide variable clamping force at different rotational speed application of an optical disk drive.
BACKGROUND OF THE INVENTION
Optical disk drives with higher transfer rate and faster access capability become more and more popular as the information storage demand is drastically increased. Historically, the access speed is increased from 1× speed at early stage to 52× speed (max) nowadays. In other word, the rotational speed of spindle motor is also increased from 200~500 RPM to more than 10,000 RPM. A drive operating at high-speed access will induce more vibration and centrifugal force on disk; therefore, the clamping device should guarantee sufficient clamping force to prevent the disk flip-flop away from turntable.
However, cost of the optical disk drive increases as aimed at providing larger constant clamping force for a traditional clamping device. Moreover, the tray motor exhausts more power and larger current during the loading and unloading process. Meanwhile, unpleasant noise possibly occurs and the disk may be dropped out of the tray if a large jerk happened by overcoming the so-called larger de-clamping force.
As shown in
FIG. 1
, a prior art of clamping device is comprised of a spindle motor
1
a
to rotate an optical disk
3
a
. A turntable
2
a
is to support the optical disk
3
a
thereon, thus maintaining suitable run out for a pick-up head to stably access information from disk. A rubber pad
20
a
is attached on the turntable
2
a
to provide sufficient friction at full speed.
Moreover, a clamping device is put upon the optical disk
3
a
to prevent it from dropping out. A base
4
a
and an annulus magnet
40
a
are the main components of the clamping device. A metal cover
41
a
is then fixed atop the annulus magnet
40
a
. On the other hand, an annulus yoke
21
a
with low carbon-concentration is mounted on the turntable
2
a
; a place axially aligned with the annulus magnet
40
a
, thus forming a constant air gap of a magnetic close-loop to firmly clamp the disk
3
a
. Alternatively, same effect will be achieved by mounting the magnet atop the turntable
2
a
and the annulus yoke
21
a
of low carbon-concentration atop the base
4
a.
Functionally, when the optical disk
3
a
is put on the tray (not shown) of an optical disk drive, the spindle motor
1
a
will then be activated to start up. If the built-in servo system detects the existence of a disk on the tray, lens of the pick-up head will be on focus to the tracks of a disk. The spindle motor
1
a
is accelerated to full speed after servo on. For the unloading process, the spindle motor
1
a
will be braked right before de-clamping the optical disk
3
a
and the tray will be moved out slowly if the user likes to take back the disk
3
a
and trigger the eject button.
Based upon the theory of Rotor Dynamics, the centrifugal force of a rotary body is proportional to eccentric amount (imbalance) and square of rotational speed. Therefore, the clamping device should exert sufficient attraction force in normal direction and the rubber pad
20
a
should possess large static friction coefficient to provide secure clamping force.
However, there are some drawbacks of prior art with constant clamping force listed as following:
(1) Most of the disks are produced with thickness 1.2 mm on the market, while the allowable thickness of a standard optical disk defined by the Red Book is ranged from 1.1 mm to 1.5 mm. The thicker of the disk, the weaker of the clamping force.
(2) The optical disk drive should be able to read CDDA, VCD, and DATA disks. Functionally, DATA disk is operated at full speed while the rest at lower speed. It seems not suitable for a clamping device to provide constant clamping force no matter what the angular velocity of the disk is.
Although larger clamping force can be achieved either through increasing the magnetic energy of magnet or reducing the air gap of magnetic loop, however, cost is indeed increased for adopting high-end magnet and larger clamping force makes the disk de-clamping more difficult.
SUMMARY OF THE INVENTION
Goal of the present invention is aimed at proposing a clamping device with variable clamping force. A novel clamping device can provide variable clamping force for optical disk drives to operate at different rotational speed. Physically, people have an intuition to apply smaller clamping force at lower speed while larger one at higher speed, thus providing stable operation and cost reduction opportunity.
To achieve above object, the present invention comprises a base, a resilient body with restoring property, an annulus magnet (or an annulus yoke) which can exert attraction force to a turntable of the optical disk drive, and a linking member which can change height of the annulus magnet (or the annulus yoke) relative to base according to the centrifugal force caused by variation of rotational speed of the optical disk drive. The centrifugal force is proportional to square of rotational speed such that the gap between the annulus magnet and the annulus yoke is accordingly adjustable. Variable clamping force is thus generated by variation of the gap.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which:


REFERENCES:
patent: 4649532 (1987-03-01), Aldenhoven
patent: 5193084 (1993-03-01), Christiaens
patent: 5379287 (1995-01-01), Heinrich
patent: 5646934 (1997-07-01), Mizuno et al.
patent: 6532205 (2003-03-01), Sato et al.

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