Brakes – Operators – Electric
Reexamination Certificate
1999-05-10
2001-11-27
Butler, Douglas C. (Department: 3613)
Brakes
Operators
Electric
C188S171000, C188S073370, C310S051000
Reexamination Certificate
active
06321883
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electromagnetically actuated brake, in particular for an electric motor. The invention further relates to the combination of an electric motor with such a brake, wherein a rotor of the brake is mounted in a rotationally stable manner on a drive shaft of the electric motor.
DESCRIPTION OF THE PRIOR ART
In a brake of the kind mentioned above, an armature plate is provided which can be moved axially in the long direction of the axis of rotation of the shaft, so that the armature plate is movable by a magnetic force produced by an electromagnet against the force of a spring loading. In the opposite direction the armature plate can be moved by the spring force. Thus by energizing or de-energizing the electromagnet the brake can be actuated in such a way that it is either applied or raised.
In particularly common use are brakes of this kind in which at least one compression spring is integrated into a magnetic body of the electromagnet, the force of which presses the armature plate against the brake rotor when the electromagnet is or becomes de-energized. While the electromagnet is energized, a magnetic force is generated that raises the armature disk away from the brake rotor against the spring loading so that the brake rotor and such rotatable parts as may be connected thereto can rotate about the axis of rotation.
In modern production lines drive mechanisms are often used that employ electric motors with such brakes. The processes of switching the brakes off and on, i.e. of energizing and de-energizing, and of maintaining an energized state contribute to sound generation just as does the operation of the electric motors. In particular with respect to regulations specifying certain upper limits for sound levels in the workplace, it is becoming increasingly important for brakes not to generate much noise during operation.
In the electromagnetically actuated brakes both direct-current and alternating-current electromagnets are known. To energize an electromagnet by direct current, the current is customarily produced by rectification of an alternating current. In the simplest case a diode is used for this purpose, so that a pulsating direct current is generated. This pulsating current can be smoothed with additional electronic circuitry. However, such circuits are usually expensive. When the magnet is kept energized for long periods, in particular when the brake is raised so that an armature plate is apposed to the magnetic body, the pulsating direct current can set the armature plate into vibration. As a result, resonant oscillations can be induced. The armature plate itself can be a component of the resonantly oscillating system.
Given that the nominal voltages of a.c. mains supplies vary throughout the world, designs are being sought by means of which one and the same electromagnet can generate a predetermined magnetic force, as independently as possible from the nominal voltage. Electronic circuits used for this purpose, by way of which the brake is connected to an a.c. mains supply, should be of the simplest possible construction. In particular, such circuits can employ an electronic switch in the form of a semiconductor switch. This switch in some circumstances turns the excitation current to the electromagnet on and off at a frequency higher than the mains frequency. The pulsating current thus generated can set the armature plate into vibration, in particular when it is raised and apposed to the magnetic body. Because the pulsating excitation current in general comprises a plurality of high frequencies, the initiation of undesired oscillations in the brake or its components results.
The stationary parts of the brake can with relatively little effort be so arranged that substantially no interfering oscillations are generated by a direct action on the stationary components.
Even an excitation current pulsating at high frequency can be smoothed by means of an electronic circuit. However, this electronic circuit necessarily occupies a relatively large volume, which is inconsistent with the desired miniaturization and compact construction of brakes of this generic kind.
Another approach to solving the problem is to reduce the pulsation of the current by employing a regulatory circuit. For example, such a circuit can operate according to the pulse-width modulation procedure. However, circuits of this kind are relatively elaborate and expensive; moreover, they can cause the electronic switch to turn on and off very often, which in turn generates high frequencies. Moreover, frequent switching increases the switching losses of the electronic switch, and therefore care must be taken to dissipate the heat adequately. Because of the high degree of integration of modern brakes of this generic kind, the solution of the heat-dissipation problem is made more difficult.
The axially movable armature plate plus the electromagnet and the spring element together constitute a system capable of oscillation, and the possibility that it will be set into undesired oscillation cannot be altogether excluded. In particular, it can be stimulated to oscillate by magnetostriction.
A means of noise attenuation when a brake of this generic kind is applied, i.e. when the armature plate strikes against the brake rotor, has been disclosed in the German patent DE 28 53 802 A1, namely to vulcanize a layer of rubber onto the brake rotor. When, the brake is being raised or is kept in the raised state, however, this measure has no attenuating effect.
As another means of noise attentuation, in this case during the process of raising the brake, from DE 41 26 672 C2 a damping disk is known, which is disposed between the armature plate and the magnetic body in order to lessen the sound produced when the moving armature plate makes contact. The damping disk is made of sheet metal and comprises a plurality of elevations that are elastically deformed when struck by the armature plate. However, when the brake is permanently in the raised state, the armature disk does not rest against the damping disk over its entire area, so that the system composed of armature plate and damping disk is additionally susceptible to being set into oscillation. These oscillations can in particular be transmitted to other components of the brake.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a brake of the kind cited above in which vibrations of the armature plate, initiated by various mechanisms, are damped. In a further development of the invention the induction of vibrations caused by impact of the armature disk against the magnetic body while the brake is being raised can be mitigated.
According to the present invention there is provided an electromagnetically actuated brake comprising a shaft rotatable about its long axis; a brake rotor mounted on the shaft in a rotationally stable manner and comprising a braking surface by means of which the shaft can be braked; a magnetic body which can energized electromagnetically to produce a magnetic force; a spring-loaded armature plate which is mounted on the shaft and is movable axially parallel to the long axis of the shaft by the magnetic force produced in the magnetic body against the force of its spring loading whereby in a braked state the armature plate is apposed to the braking surface of the brake rotor; a first damping means which is located between the armature plate and at least one of the magnetic body and the brake rotor to attenuate oscillations of the brake; and a second damping means which is located adjacent the first damping means in the axial direction of the shaft and which comprises a material different from that of the first damping means.
When the damping means are located between the armature plate and the magnetic body not only do they attenuate the transmission of oscillations and/or impacts from the armature plate to the magnetic body and conversely, but also attenuate an initiation of oscillations in the armature plate. In addition, as the damping means are made of different materia
Becker Gunter
Fischer Horst
Pfann Jochen
Butler Douglas C.
Sew-Eurodrive GmbH & Co.
Sy Mariano
Westman Champlin & Kelly P.A.
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