Torque limiter and reel mount

Details Torque limiter and reel mount Torque limiter and reel mount

2002-05-21

2004-11-16

Bagnell, David (Department: 3672)

Rotary shafts, gudgeons, housings, and flexible couplings for ro

Electrical or magnetic coupling

C242S356500, C360S096300

Reexamination Certificate

active

06817949

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a torque limiter which is used as, for example, a reel mount used for a magnetic recording/reproducing apparatus, such as a videotape or audiotape recorder.
2. Description of the Related Art
Referring to
FIGS. 5 and 6
, a structure of a conventional torque limiter will be described below.
FIG. 5
is a top view of a conventional torque limiter
500
.
FIG. 6
is a cross-sectional view of the conventional torque limiter
500
taken along line B—B shown in FIG.
5
.
In
FIG. 6
, reference numeral
1
a
denotes a reel in a cassette. A (magnetic) tape (not shown) is wound around the reel
1
a
. Reference numeral
1
b
denotes a body of the cassette, reference numeral
2
denotes a chassis of a conventional magnetic recording/reproducing apparatus, such as a videotape or audiotape recorder, used for recording/reproducing information to/from the magnetic tape of the cassette, and reference numeral
3
denotes a rotation shaft provided in the chassis
2
. The conventional reel mount is placed on the rotation shaft
3
so as to be rotatable with respect to an axis of the rotation shaft
3
(shown as a broken line in FIG.
6
). Reference numeral
303
denotes an upper reel mount member on which the reel
1
a
is mounted. Reference numeral
305
denotes a rotation engagement member which is movable up and down (i.e., in a direction parallel to the axis of the rotation shaft
3
) and is engaged with the upper reel mount member
303
and the reel
1
a
along a rotation direction of the conventional reel mount, reference numeral
304
denotes a spring which applies upward force to the rotation engagement member
305
with respect to the movement thereof such that the rotation engagement member
305
is engaged with a protruded portion of the upper reel mount member
303
and is supported by the upper reel mount member
303
and the spring
304
, and reference numeral
307
denotes a yoke board provided in the form of a disk and made of a ferromagnet, such as a rolled steel board.
The yoke board
307
is integrally formed with the upper reel mount member
303
. It is common practice in the field of magnetic recording/reproducing apparatuses to integrally form a yoke board member, such as the yoke board
307
, with an upper reel mount member, such as the upper reel mount member
303
, by outsert molding. The upper reel mount member
303
integrally formed with the yoke
307
is rotatable with respect to the axis of the rotation shaft
3
. The integral upper reel mount member
303
and yoke board
307
together form a first rotor of the conventional reel mount. Reference numeral
308
denotes a magnet which applies magnetic force so that the magnet
308
is attached to and rotated with the yoke board
307
due to rotation of the upper reel mount member
303
. Lines of magnetic force (not shown) generated by the magnet
308
form a magnetic loop passing through the yoke board
307
.
Reference numeral
310
denotes a lower reel mount member (a second rotor) integrally formed with a hysteresis board
311
having a disk-like shape. The hysteresis board
311
is made of a material having large magnetic hysteresis loss. It is common practice in the field of magnetic recording/reproducing apparatuses to integrally form a hysteresis board member, such as the hysteresis board
311
, with a lower reel mount member, such as the lower reel mount member
310
, by outsert molding. Similar to the upper reel mount member
303
, the lower reel mount member
310
integrally formed with the hysteresis board
311
is placed on the rotation shaft
3
so as to be rotatable with respect to the axis of the rotation shaft
3
. The lower reel mount member
310
is attracted by the magnetic force generated by the magnet
308
so as to be in contact with the upper reel mount member
303
.
Reference numeral
309
denotes a washer sandwiched between the lower reel mount member
310
integrally formed with the hysteresis board
311
and the upper reel mount member
303
. The washer
309
is engaged with the lower reel mount member
310
so as to be rotated therewith. Usually, grease (not shown) is applied to the washer
309
. Reference numeral
302
denotes a gear member provided to the outer circumference of the lower reel mount member
310
, which is engaged with an external gear (not shown). Reference numeral
306
denotes a reel bearing member provided on the upper reel mount member
303
and integrally formed with the yoke board
307
so as to come into contact with the reel
1
a
when the reel
1
a
is mounted on the conventional reel mount. Similar to the other reel mount members, it is common practice in the field of magnetic recording/reproducing apparatuses to integrally form a reel bearing member, such as the reel bearing member
306
, with a yoke board member, such as the yoke board
307
, by outsert molding.
When the reel
1
a
is mounted on the conventional reel mount, a position in a vertical direction of the reel
1
a
with respect to the chassis
2
is defined by the reel bearing member
306
. Reference numeral
4
denotes a chassis washer placed between the reel mount and the base of the rotation shaft
3
so as to define a space between the chassis
2
and the lower reel mount member
310
. Reference numeral
5
denotes a shaft washer placed on the rotation shaft
3
so as to define movement of the reel mount along a thrust (vertical) direction of the reel mount and to provide a space between the rotation shaft
3
and the upper reel mount member
303
.
Operation of the conventional reel mount is described below.
When the lower reel mount member
310
is rotated by the external gear through engagement with the gear member
302
, friction torque is generated between the upper and lower reel mount members
303
and
310
via the washer
309
due to the magnetic attraction generated by the magnet
308
on the lower and upper parts of the reel mount. Simultaneously, the hysteresis board
311
is rotated through the magnetic loop generated by the magnet
308
, so that magnetic hysteresis torque is generated. The friction torque and magnetic hysteresis torque result in clutch torque between the upper reel mount member
303
and the lower reel mount member
310
so that the reel
1
a
mounted on the upper reel mount member
303
is rotated by the rotation engagement member
305
while sufficient tension is applied to the magnetic tape wound around the reel
1
a.
However, in the conventional reel mount, it is difficult to generate stable clutch torque. Clutch torque generated by a reel mount is always required to be stable without being affected by various disturbances in order to provide reliable and stable operation of the torque limiter. Specifically, the clutch torque must be stable even if there are variations in the rotating speed of the reel mount, the environmental temperature or humidity, the operating time of the reel mount, etc. Friction torque, which contributes to the clutch torque generated by the conventional reel mount, is affected by the stability of a coefficient of friction between the washer
309
and the upper reel mount member
303
. The coefficient of friction refers to a value of a physical property of the materials used for the washer
309
and the upper reel mount member
303
. In consideration of the strength and the compatibility with a material of the reel in the cassette, i.e., to enable easy mounting of the reel on the upper reel mount member
303
, selection of the material for the upper reel mount member
303
is limited. Thus, it is very difficult to select a material for the upper reel mount member
303
which provides a stable coefficient of friction between the upper reel mount member
303
and the washer
309
in the conventional reel mount. Therefore, the torque limiting stability of the conventional torque limiter is unreliable and unstable.
The present invention provides solutions to the above-described problems of the conventional torque limiter as described below.
SUMMARY OF THE INV

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