Stepping motor

Details Stepping motor Stepping motor

1999-12-01

2001-03-27

Nguyen, Tran (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S06700R, C310S090000

Reexamination Certificate

active

06208046

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to stepping motors for optical pick-up devices and, more particularly, to a structural improvement in such stepping motors to simplify the support structure for a motor's rotating shaft engaging with a pick-up unit at a lead screw and feeding the pick-up unit by the screw in an axial direction, the structural improvement thus reducing the number of required elements, simplifying the assembling process and improving the operational reliability and productivity of stepping motors.
2. Description of the Prior Art
As well known to those skilled in the art, a stepping motor, also known as a step-servo motor, is provided within an optical pick-up device for feeding a pick-up unit. In such a stepping motor, a rotating shaft has a lead screw and engages with the pick-up unit at the lead screw, thus allowing the pick-up unit to reciprocate in an axial direction along the lead screw in accordance with a rotating action of the rotating shaft.
An example of conventional stepping motors for optical pick-up devices may be referred to Japanese Patent Laid-open Publication No. Heisei. 9-154,217. The above Japanese stepping motor is described hereinbelow with reference to
FIGS. 1 and 2
.
As shown in
FIG. 1
, the conventional stepping motor comprises a stator
100
and a rotating shaft
200
. The stator
100
consists of a casing
110
, two doughnut coils
120
and a yoke
130
.
In the stator
100
, the casing
110
has a hollow cylindrical shape, with the top and bottom walls radially and inwardly extending from the top and bottom circular ends of the casing's outer wall so as to form an annular shape. The top and bottom walls of the casing
100
also respectively extend from their inside ends toward each other in a vertical direction. That is, the top wall extends downwardly from its inside end to form an upper inner wall, while the bottom wall extends upwardly from its inside end to form a lower inner wall, with a gap being left between the ends of the two inner walls.
The yoke
130
, providing a passage for magnetic flux within the stator
100
, is horizontally positioned within the gap between the ends of the two inner walls of the casing
110
and is integrated with the interior surface of the outer wall of the casing
110
. The yoke
130
thus forms two annular chambers within the casing
110
, with the two doughnut coils
120
being respectively received within the two chambers.
The above stator
100
is fixedly supported on a first support plate
600
of an optical pick-up device at its bottom wall.
A rotating shaft
200
passes through the center of the first support plate
600
upwardly prior to being partially inserted into the center of the stator
100
in a direction from the bottom of the casing
110
. The above shaft
200
is externally threaded at a portion exposed to the outside of the support plate
600
, thus forming a lead screw
210
which movably engages with a pick-up unit.
A cylindrical magnet
220
is fixedly fitted over the top end portion of the rotating shaft
200
within the casing
110
of the stator
100
, and so the magnet
220
and the doughnut coils
120
are concentrically positioned within the casing
110
. When the coils
120
are turned on, an electromagnetic force is formed between the magnet
220
and the coils
120
within the casing
110
.
Both ends of the shaft
200
are each provided with a V-shaped groove
230
, with a steel ball
240
being rotatably seated on each groove
230
.
A guide plate
300
is positioned on the top wall of the stator
100
. Vertically formed at the central portion of the above plate
300
is a guide hole having a predetermined diameter.
A first holder
410
, or a movable holder having a depressed ball seat on its lower surface, is received within the guide hole of the guide plate
300
in a way such that the holder
410
is vertical movable within the guide hole of the plate
300
with the depressed seat being directed downwardly. A first steel ball
240
is rotatably seated between the depressed ball seat of the first holder
410
and the top groove
230
of the rotating shaft
200
.
The above guide plate
300
, positioned on the top wall of the stator
100
, is covered with a cap
500
that is fitted over the top end portion of the stator
100
. The top wall of the cap
500
is partially cut along a U-shaped cut line at one or more angularly spaced positions as shown in
FIG. 2
, thus forming one or more cut pieces. The cut pieces of the cap
500
are, thereafter, bent downwardly at an angle of inclination, thus forming one or more plate springs
510
.
When the cap
500
is fitted over the top end portion of the stator
100
, each plate spring
510
is brought into contact with the top surface of the first holder
410
at its free end, thus normally biasing the first holder
410
downwardly.
The skirt of the cap
500
comes into elastic engagement with the external surface of the casing
110
at its lower edge, and so the cap
500
is easily removable from the stator
100
when necessary.
A second steel ball
240
, rotatably seated on the bottom groove
230
of the rotating shaft
200
, is also rotatably seated in the depressed ball seat of a second holder
420
. That is, the second steel ball
240
is rotatably seated between the bottom groove
230
of the shaft
200
and the ball seat of the second holder
420
. The above second holder
420
is fixedly mounted to a second support plate
700
, thus being so-called “a fixed holder”.
It is thus noted that the rotating shaft
200
is elastically supported by the first holder
410
rather than the second holder
420
.
When the coils
120
of the stator
100
are activated by electric power from an external power source, an electromagnetic force is formed between the magnet
220
and the coils
120
, thus rotating the shaft
200
. When the rotating shaft
200
is rotated as described above, the pick-up unit, engaging with the lead screw
210
of the shaft
200
, axially moves along the lead screw
210
.
In the above-mentioned stepping motor, the rotating shaft
200
is designed to be rotated in opposite directions so as to allow the pick-up unit to axially reciprocate along the lead screw
210
as desired. The shaft
200
thus may undesirably move in the axial direction due to an inertia force, that is generated from the pick-up unit at a time the moving direction of the pick-up unit is changed. If such an undesirable axial movement of the rotating shaft
200
is not effectively absorbed by a shock absorption means, the shaft
200
may be impacted, damaged and deformed.
In an effort to absorb impact caused by such an undesirable axial movement of the rotating shaft
200
due to the inertia force, the conventional stepping motor is provided with the guide plate
300
, the first holder
410
and the plate springs
510
.
In a detailed description, the second steel ball
240
is rotatably seated between the bottom groove
230
of the rotating shaft
200
and the ball seat of the fixed second holder
420
, thus only rotatably supporting the bottom end of the shaft
200
. Meanwhile, the first steel ball
240
is rotatably seated between the top groove
230
of the rotating shaft
200
and the depressed ball seat of the first holder
410
which is normally biased downwardly by the plate springs
510
of the cap
500
, thus absorbing the impact caused by the undesirable axial movement of the shaft
200
.
Since the undesirable axial movement of the rotating shaft
200
, caused by the inertia force generated from the pick-up unit at a time the moving direction of the pick-up unit is changed, is absorbed by the plate springs
510
of the cap
500
elastically biasing the first holder
410
downwardly, the rotating shaft
200
is somewhat stably operated even when the axial moving direction of the pick-up unit is changed.
However, the above-mentioned stepping motor is problematic in that it has a complex construction.
That is, a V-shaped groove
230
is necessarily formed on each

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