GB2026110A

GB2026110A - Electromagnetically releasable spring-actuated brake

Info

Publication number: GB2026110A
Application number: GB7910308A
Authority: GB
Original assignee: Binder Magnete GmbH
Current assignee: Binder Magnete GmbH
Priority date: 1978-07-25
Filing date: 1979-03-23
Publication date: 1980-01-30
Also published as: FR2432117B1; IT7948601A0; FR2432117A1; IT1162448B; DE2832523A1; GB2026110B; DE2832523C2

Abstract

An electromagnetically releasable spring-actuated brake has an associated mounting surface (3), a friction disc (6) which is rotatably driven, an electromagnetic release device (8) non- rotatably secured to the mounting surface (3) by means of bolts (1) and an armature (5, 14) mounted non-rotatably and for axial displacement between the friction disc (6) and the release device (8), and biased by springs (11) against the friction disc - a ring (2) surrounds the armature (5, 14) and has projections (16), which enter axial recesses (15) for axially guiding and tangentially supporting said armature and the ring (2) is seated practically without play on the bolts (1), and is of a suitable elastic and shock-absorbing design, and distributes the braking couple uniformly over all the bolts (1). Ring (2) may be of glass fibre reinforced polyamide - and may be made up of individual segments. A manual release yoke 21 may be provided. <IMAGE>

Description

SPECIFICATION Electromagnetically releasable spring-actuated brake The invention relates to an electromagnetically releasable spring actuated brake with a mounting surface, a friction disc driven in rotation, a release device non-rotatably secured to the mounting surface by means of free-standing bolts, and an armature mounted non-rotatably and so as to be capable of axial displacement between the friction disc and the release device, and biased by springs against the friction disc.

Electromagnetically releasable spring-actuated brakes are used as safety brakes in numerous applications. In the machine manufacturing industry, these spring brakes are generally designed as independent units. In many applications, the spring brake is also linked up with a unit via an electric motor.

The electromagnetic release system of the spring brake can be driven by d.c., a.c. or three-phase current. Under closed circuit conditions, the armature is raised by the release system from the friction disc, which is driven by the shaft to be braked. In non-energized condition, the armature is pressed against the friction disc by compression springs.

Spring brakes are known in which the release system is secured to the mounting surface by means of free-standing bolts. The bolts, which pass through the release system, permit adjustment for wear. In particular, however, the bolts are used for nonrotating axial guidance of the armature, through which the bolts pass to permit axial displacement.

The bolts thereby take up the braking couple.

The mechanical stresses applied to the bolts take the form of bending stress and shearing stress at the points at which the bolts are fixed to the mounting surface. One particular disadvantage thereof is that, owing to the unavoidable tolerances in the circular distribution of said bolts, the armature is always tangentially supported by only a small number of bolts. Even if the number of bolts is increased, the mechanical stresses of the braking moment are applied only to these few bolts. The high instantaneous loads placed on these bolts consequently lead to premature rupture.

This drawback could, of course, be remedied by increasing the cross-section of the bolts. This would, however, result in increasing the structural volume or, if the structural volume remained constant, in a reduction of the effective braking surface.

Afurther drawback of these known spring brakes resides in the hard metallic impact of the armature against the bolt shanks at the commencement of the braking operation.

In other known spring brakes, the bolts are braced by metal rings or sleeves. However, in this case, simple adjustment for wear is not possible. In order to adjust for wear, the entire spring brake has to be stripped down and the corresponding parts reconditioned.

An object of the invention is to provide an electromagnetically releasable spring-actuated brake having a long service life and high operational security without prejudice to the external dimensions, simplicity of adjustment for wear and economical manufacture.

According to the invention there is provided an electromagnetically releasable spring-actuated brake having a mounting surface, a friction disc driven in rotation, a release device non-rotatably secured to the mounting surface by means of free-standing bolts, and an armature mounted nonrotatably and so as to be capable of axial displaced ment between the friction disc and the release device, and biased by springs against the friction disc, wherein the armature is surrounded by a ring having inwardly facing projections which penetrate into axial recesses for axially guiding and tangentially supporting said armature, and the bolts pass through the ring without play.

By contrast with known spring brakes, the armature is axially guided in a brake according to the invention, not by the bolts but by the ring surrounding the armature. This ring also takes up the tangential load of the braking couple. As the ring is not displaced axially on the bolts, it can be mounted on the bolts without any play, insofar as this is possible during manufacture and fitting. The braking couple is transmitted by the armature to the ring which, as it is seated without play, transmits that couple equally to all the bolts. The mechanical stress set up by the braking couple is thus uniformly distributed to all the bolts, with the result that the likelihood of premature rupture of individual bolts is excluded.

As the bolts are gripped by the ring without play over the entire axial extent of said ring, they are subjected to stress only at their points of attachment to the mounting surface. Bending stress such as occurs in known spring brakes is also precluded.

This means that the service life wiil be further prolonged.

Preferably the ring is designed for resilience and damping effect. The hard impacts of the armature when braking commences act against the ring and are resiliently taken up by the ring and damped, with the result that this impact stress does not act on the bolts.

The resilient, and particularly the damping, properties can be provided by means of corresponding ring pads or inserts. It is preferred to form the ring from an elastic, shock-absorbing material, glass fibre reinforced polyamide being preferably suitable for this purpose.

In order to keep the radial dimensions of the brake small, the bolts pass through the ring preferably in the region of the projections penetrating the recesses in the armature as the material thickness of the ring is in any case greater in said zones.

The axial bores of the ring that house the bolts can be suitably arranged in such a way that they join the inner circumference of the ring and are open along the axially extending line of junction. In this way, the radial material thickness of the ring can be reduced in order to make the radial dimensions of the brake smaller or to enlarge the diameter of the friction disc.

Also, the elasticity of the ring is increased in respect of the bolts by said open bores.

The ring can be manufactured in a single piece, preferably as a die casting, from a suitable material.

If convenient, for manufacturing or other reasons, the ring can also be made up of individual segments.

An improvement is obtained in relation to known spring brakes if each one of the individual segments only accommodates two bolts.

Adjustments for wear can be made in the same way as in known spring brakes. For this purpose, the release system is seated for axial displacement on the bolts and can be adjusted on said bolts by means of their threads. The end of the bolt projecting above the release device can, for example, have a thread on which a nut is placed, against which the release device is supported, or the bolts can have screwheads at their ends that project beyond the release device and be screwed to varying depths into the mounting surface by means of a thread.

The release device can be reliably placed against said nuts or screw-heads of the bolts and thereby be given a precisely adjusted axial position preferably by placing said axially bracing compression springs between the ring and the release device.

If necessary, a manual release yoke can be pivotally mounted on the ring engaging the armature to enable the brake to be released manually.

According to the invention, peak impact stress on the bolts are reduced in amplitude owing to the elastic, shock-absorbing properties of the ring, indexing errors and misalignment in the arrangement of the bolts can be eliminated within certain tolerances and the cross-section and/or the number of bolts can be reduced, with the resulting improvement in operational security and reduction of radial dimensions.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial cross-sectional view of a spring brake according to the invention; and Figure 2 is a view of the brake along line l-l of Figure 1 with additional manual release.

The spring brake is represented in Figure 1 as installed. Fixing bolts 1 are screwed into a mounting surface 3. The mounting surface 3 can be a part of a machine on which the brake is used, or a separate component of said brake.

A ring 2 is pressed along the shank 18 of the bolt 1 as far as the mounting surface 3. The ring 2 is of glass fibre-reinforced polyamide and includes axially extending inward facing projections 16. The shanks 18 of the bolts 1 are housed with practically no play in bores 17 which run axially in the projections 16 of the ring 2. The bores 17 join up with the inner circumferential surface of the projections 16, with the result that they are open along the axially extending line of junction.

A friction disc 6 is mounted by means of a many-sided drive means 4 on the shaft to be braked, not shown. The disc 6 is located inside the ring 2 adjacent to the mounting surface 3.

An armature, consisting of a core 5 and an aluminium housing 14 surrounding said core, is located inside the ring 2 and axially adjacent to the friction disc 6. The housing 14 has, in its outer perimeter, axially extending recesses 15 whose shape matches that of the projections 16 of the ring 2. By means of the recesses 15 and the projections 16 of the ring 2 which engage in the recesses, the armature is constrained so as to be non-rotary relative to the ring, but capable of axial displacement in the ring.

A release device 8 is fitted onto the shanks 18 of the bolts 1 projecting beyond the ring 2. This release device consists of a magnetic core 9, a magnetic coil 10 and an insulating housing 7 surrounding them.

The bolts 1 have threads at their free ends on which nuts 13 are screwed if required. Compression springs 12 are placed in the axial bores in the front face of ring 2 facing the release device, which springs rest against the front face of the insulating housing 7 and biasing the release device 8 against the nuts 13. The axial position of the release device can be adjusted in this way by means of the nuts 13.

Bores in which compression springs 11 are housed are provided in the armature and release device 8 respectively in the armature housing 14 and the insulating housing 7. The bores are located inwardly of the magnetic cores 5 and 9. The compression springs 11 are supported on the release device 8 and bias the armature housing 14 against the friction disc 6. When the release device 8 is actuated, the coil 10 is energized and the armature is raised from the friction disc 6 against the bias of the compression springs 11, so that the disc can rotate freely. If the current energizing the coil 10 is interrupted, the armature is pressed against the friction disc 6 by the compression springs 11 and the braking is operative.

Adjustments can be made for the wear of friction disc 6 by means of the nuts 13.

Figure 2 additionally represents a manual release system. This consists of a manual release yoke 21 which is pivotally mounted by means of bolts 20 on bearings 19 which are provided on the outer periphery of ring 2. At a certain distance from the pivot point determined by the bolts 20, the yoke 21 engages studs 22 which project radially from the armature housing 14. By pivoting the release yoke 21 by means of a knob, the armature can also be raised by hand from the friction disc 6 against the bias of compression springs 11.

Claims

1. An electromagnetically releasable springactuated brake having a mounting surface, a friction disc driven in rotation, a release device nonrotatably secured to the mounting surface by means of free-standing bolts, and an armature mounted non-rotatably and so as to be capable of axial displacement between the friction disc and the release device, and biased by springs against the friction disc, wherein the armature is surrounded by a ring having inwardly facing projections which penetrate into axial recesses for axially guiding and tangentially supporting said armature, and the bolts pass through the ring without play.

2. A brake according to Claim 1, wherein the ring is elastic and shock-absorbing.

3. A brake according to Claim 2, wherein the ring is made of an elastic and shock-absorbing material.

4. A brake according to Claim 3, wherein the ring is made of a glass fibre reinforced polyamide.

5. A brake according to any one of the preceding claims, wherein the bolts pass through the ring in the region of the projections.

6. A brake according to any one of the preceding claims, wherein the bolts pass through axial bores in the ring that join up with the inner circumference of the ring and are open along the axially extending line ofjunction.

7. A brake according to any one of the preceding claims, wherein the ring is made up of individual segments.

8. A brake according to any one of the preceding claims, wherein the release device is seated on the bolts in such a way as to be axially displaceable and is axially displaced by means of th reads on the bolts.

9. A brake according to any one of the preceding claims, wherein the springs are axially biasing compressions springs placed between the ring and the release device.

10. A brake according to any one of the preceding claims, wherein a manual air-release yoke is pivotally mounted on the ring and engages the armature.

11. Electromagnetically releasable springactuated brake constructed and arranged to operate substantially as herein described with reference to the accompanying drawings.