Brakes – Operators – Spring
Reexamination Certificate
1999-12-29
2001-02-06
Schwartz, Chris (Department: 3613)
Brakes
Operators
Spring
C188S161000
Reexamination Certificate
active
06182803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spring-actuated electromagnetic brake having a noise suppressing device for suppressing a striking noise generated when an armature is attracted onto a field upon magnetization of the field to release the brake.
2. Description of the Related Art
Noise suppressing devices incorporated in conventional spring-actuated electromagnetic brakes so as to reduce a striking noise emitted when an armature is attracted onto a magnetized field to release the brake are generally classified into five groups as enumerated below.
(1) An O-ring fitted in an annular groove or recess formed in one of two opposed surfaces of the field and armature in such a manner that the O-ring partially projects from the annular recess when the brake is in the engaged state (Japanese Patent No. 2669944).
(2) A cushioning sheet member disposed between the field and the armature (Japanese Utility Model Laid-open Publication No. HEI 5-25994).
(3) A plurality of tubular noise-suppressing rubber blocks each received in one of plural recesses formed in an attracting surface of the field in such a manner that when the brake in the engaged state, the tubular noise-suppressing rubber block partially projects from the attracting surface (Japanese Utility Model Laid-open Publication No. HEI 7-16576).
(4) A plurality of tubular noise-suppressing rubber blocks each received in one of plural recesses formed in an attracting surface of the field in such a manner that the tubular noise-suppressing rubber block partially projects from the attracting surface when the brake is in the engaged state. In combination with the tubular noise-suppressing rubber blocks, an armature formed from a vibration-damping steel sheet is used (Japanese Utility Model Laid-open Publication No. HEI 8-7808).
(5) A plurality of solid cylindrical noise-suppressing rubber blocks each received in one of plural recesses formed in an attracting surface of the field in such a manner that the solid cylindrical noise-suppressing rubber block partially projects from the attracting surface when the brake is in the engaged state.
The conventional noise-suppressing devices enumerated above still each have a problem, as discussed below.
(1) The O-ring, if the diameter of its circular cross section is small, can achieve only a limited elastic deformation, failing to perform the desired noise suppressing function. By contrast, if the diameter of the circular cross section of the O-ring becomes large, a correspondingly large cross-sectional area is required for the annular recess, which will deteriorate attracting power of the field.
(2) The cushioning sheet member disposed between the field and the armature exerts direct influence on the attracting power of the field. Namely, the larger the thickness of the cushioning sheet member, the lesser the attracting power of the field. By contrast, as the thickness of the cushioning sheet becomes small, the durability of the cushioning sheet member decreases.
(3, 4 and 5) The hollow or solid cylindrical noise-suppressing rubber blocks incorporated in the spring-actuated electromagnetic brake are shown in
FIGS. 6A and 7A
. The brake shown in
FIG. 6A
is in its engaged position, while the grake shown in
FIG. 7A
is in its released position. When the brake shown in
FIG. 6A
is to be released, an electromagnetic coil
2
embedded in a field
1
is excited to magnetize the field. Upon magnetization of the field, an armature
3
is attracted onto the field
1
. As the armature
3
moves toward the field, the cylindrical noise suppressing blocks
11
′ (
FIG. 7B
) are axially compressed by the armature
3
. In this instance, due to the cylindrical shape of the rubber blocks
11
′, it is likely that the cylindrical rubber blocks undergo local elastic deformation concentrated on respective tip end portions, as best shown in FIG.
7
B. The locally concentrated elastic deformation will soon deteriorate the durability of the rubber blocks.
(4) The armature formed from a vibration-damping steel sheet required an increased number of parts used and hence is relatively expensive to manufacture. Additionally, in order to generate the necessary attraction, the armature has a relatively large thickness. This will add to the overall size of the brake.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a spring-actuated electromagnetic brake having a noise suppressing device which is free from local deformation when subjected to a compressive force, is highly durable, and is able to achieve a great suppression of striking noise when the brake is released.
To achieve the foregoing object, the present invention provides a spring-actuated electromagnetic brake which comprises: a stationary field having an electromagnetic coil embedded therein for magnetizing the field; a brake plate mounted on a rotating shaft for co-rotation with the rotating shaft; an armature disposed between the field and the brake plate and movable only in the axial direction of the rotating shaft; a brake spring urging the armature against the brake plate to normally hold the brake in the engaged state; and a noise-suppressing device for suppressing a striking noise emitted when the armature is attracted onto the field to release the brake when the electromagnetic coil is excited to magnetize the field. The the noise-suppressing device is a plurality of hemispherical elastic members disposed in a plurality of recesses formed in one of two opposed surfaces of the field and the armature. The hemispherical elastic members each have a hemispherical surface which, when the brake is in the engaged state, projects from a corresponding one of the recesses and is in contact with the other of the two opposed surfaces.
Preferably, the recesses are arranged concentrically with the axis of the rotating shaft and spaced in the circumferential direction at equal angular intervals.
With this arrangement, when the electromagnetic coil is excited to release the brake, the field is magnetized. Upon magnetization of the field, the armature is attracted onto the field. As the armature approaches the field, the hemispherical elastic members undergo elastic deformation to thereby suppress a striking noise generated when the armature strikes on the field. When compressed between the field and the armature, each hemispherical elastic member undergoes elastic deformation as a whole and does not produce any local deformation. Thus, the durability of the elastic body is extremely high.
When current to the electromagnetic coil is removed to engage the brake, the field is demagnetized and the armature is urged against the brake plate by the force of the brake spring. In this instance, since the hemispherical elastic members are allowed to spring back to its original shape, an elastic recovery force of the elastic members acts on the armature in the same direction as the biasing force of the brake spring. Thus a certain reduction in the braking time (response time) of the brake can be achieved.
The above and other objects, features and advantages of the present invention will become apparent to those versed in the art upon making reference to the following detailed description and the accompanying sheets of drawings in which a certain preferred embodiment incorporating the principle of the present invention is shown by way of illustrative example.
REFERENCES:
patent: 4684838 (1987-08-01), Casanova
patent: 4982825 (1991-01-01), Sekella
patent: 5067593 (1991-11-01), Tanaka et al.
patent: 5154261 (1992-10-01), Tanaka et al.
patent: 5186286 (1993-02-01), Lindberg
patent: 5433297 (1995-07-01), Kuivamaki
patent: 7-16576 (1995-03-01), None
Fujii Masayuki
Hirai Tatsuya
Dann Dorfman Herrell and Skillman, P.C.
Schwartz Chris
Skillman Henry H.
Tsubakimoto Chain Co.
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