Safety brakes which release upon the application of an electric current
and which operate by means of spring pressure when the current is removed, are in
general known. They are usually mounted on the rear side of the motor, generally
an electric motor, on the so-called B-bearing side.
In countless technical installations for example lifts, it is required
by the regulations to include a safety brake which in the event of a fault for example,
a power cut, immediately brings the system to a standstill, and holds it in this
condition until the fault has been repaired. The inclusion of such brakes means
additional installation work, and requires more space.
Flexible bellow couplings that are stiff in the rotational direction,
are known for connecting two shafts. They are mainly installed between an electric
motor and a drive coupling, working machine, spindle or the like.
EP-A-0 786 852 shows an electric drive unit comprised of a regular
electric motor in combination with an electromagnetically releasable spring pressure
brake coupled to the motor's shaft end and attached to the front end of the motor.
The spring pressure brake presses an axially displaceable armature plate by spring
force against a brake disk and a brake surface, wherein the brake disk is coupled
to a sleeve element attached to the motor shaft in order to rotate with it. The
sleeve element is connected to a pulley or similar output element provided on the
sleeve element. The latter does not connect the motor shaft with a second shaft
nor is it able to compensate for a high degree of misalignment between drive and
In a similar manner, US Patent 3,338,349 also shows an electric drive
unit comprised of a regular electric motor in combination with an electromagnetically
releasable spring pressure brake coupled to the motor's shaft end and attached to
the front end of the motor. The spring pressure brake presses an axially displaceable
armature ring (which serves as a brake disk) against a brake surface, wherein the
brake disk is coupled to a sleeve element attached to the motor shaft to rotate
with it. The sleeve element extends into a separate output shaft. While the sleeve
element connects the motor shaft with said second shaft it is unable to compensate
for any degree of misalignment between the drive shaft and driven shaft.
The object of the present invention is to unite a coupling and a brake
into a unit, a so-called brake coupling combination in such a way that this unit
can be mounted in a simple manner on the drive side of an electric motor (A-bearing
side). The aim is in particular, to reduce the work and space requirement. Additionally,
costs need to be saved, reliability increased, ease of servicing improved. Preferably
the arrangement should be able to compensate for a high degree of misalignment between
drive and driven shafts.
This task is solved by the combination of features described in claim
1. The second side of the coupling transfers the angular momentum to the second
shaft. With this arrangement space is saved in the axial direction. The stiffness
to rotation of a bellows coupling can absorb at the same time axial, radial and
angular misalignment. Further, the housing of the safety brake may be constructed
in a generally rectangular shape, so that the usual shape of electric servomotors
is preserved. By mounting the brake on the drive motor shaft rather that on the
rear end of the motor an improvement in safety is achieved. For example if the brake
hub becomes disconnected from the motor shaft due to a mechanical failure, in the
arrangement of the invention, the drive becomes disconnected too. This is a "fail-safe"
situation, and is due to the fact that the drive passes from the motor shaft to
the drive external equipment via the brake hub.
An exemplary embodiment of a brake coupling combination, in accordance
with the invention will now be described with reference to the drawings in which:
- Figure 1 shows a simplified elevation of the coupling-brake combination;
- Figure 2 shows a cross-section on the line A-A in Figure 1 and shows more detail;
- Figure 3 shows an exploded partly cross sectional view showing coupling of the
coupling brake combination to the motor shaft; and
- Figure 4 shows a spring clip for use in the arrangement of Figures 1-3.
Referring to Figure 2, a brake-coupling combination is intended to
be flanged or screwed on to an electric motor 16 at the A bearing side i.e. the
end from which the drive shaft emerges. In Figure 2 the motor shaft is shown, with
the reference numeral 9. The brake coupling combination essentially consists of
a brake assembly 18 and a coupling assembly 19. The brake possesses a square flange
1, with which it is screwed to a correspondingly shaped part,
for example to the A-bearing case of a servomotor, or the motor housing. The flange
1 serves at the same time as a housing for the brake, and accommodates the many
individual parts thereof. Typically the brake coupling assembly is bolted onto the
motor 16 by four bolts, one of which passes through bore 17. The bolts are not shown
in Figure 2.
The brake assembly 18 itself consists of an electromagnet coil 2;
an armature plate 3; a hub 4 with a partially axially slit tube-like extension 20,
the hub 4 is connected to the motor shaft 9 such that relative rotation is not possible.
This may be achieved for example by use of a key in a keyway, or other conventional
means such as a taper or cross pin.
The brake also includes at least one brake disk 5 which is longitudinally
displaceable with respect to the hub 4 but which is connected to it such as to turn
with it. The brake disk 5 is sandwiched between the armature plate 3 and a flange
plate 13 which is longitudinally fixed with respect to the housing of the brake.
Brake pads 6 are mounted on either the brake disk itself or on the surfaces of the
armature and flange plate facing it to increase friction between these components.
Typically the hub 4 carries on its outer circumference, splines which engage inwardly
facing teeth on a boss in the centre of the brake disk 5. The brake assembly 18
also has at least two brake pads 6, disposed on the two sides of the brake disk
5. The brake also includes a plurality of guide pins 7 disposed and equally distributed
around the circumference to ensure good alignment of the moving parts in operation.
Springs 8 also disposed and equally distributed around the circumference urge the
armature plate towards the flange plate, and hence into the braking condition. The
brake pads 6 may be fixed to the brake disk, so as to engage the inwardly facing
surfaces of the armature plate 3, and a flange plate 13 on the other side of the
brake disk 5. Alternatively the brake pads can be on the mutually facing surfaces
of the armature plate 3 and the flange plate 13.
The shaft 9 of the motor 16 passes through the hub 4 including the
partially axially slit tube-like extension 20 and into the coupling unit 19 of the
coupling brake combination.
The coupling unit 19 couples the motor drive shaft 9 with a driven
shaft 12 connecting to other machines and consists of flexible bellows 11 (made
of metal), by a locking ring 10b locked onto the motor shaft 9 via the tube-shaped
axially slit extension 20 of the hub 4 at one end and on a correspondingly adapted
coupling hub 14 that is in turn locked onto a driven shaft 12, at the other end.
The flange plate 13 as well as holding the brake together, and providing
the reaction force, also offers the possible connection of drive transmission by
means of a centering adjustment 15.
In operation, when the electromagnet coil 2 is excited it attracts
the armature plate 3 thereby pulling the armature plate 3 away from the brake disk.
Once there is no longer any frictional contact between the armature plate 3, the
brake disk 5, the brake pads 6 and the flange plate 13 there is no braking effect.
If the electricity supply to the electromagnet coil 2 is interrupted, the armature
plate 3 is released, and is immediately moved in the direction of the brake disk
5 and flange plate 13, by the springs 8. As the brake disk 5 is free to move longitudially
on the splines on the hub 4, it moves in the direction of the flange plate 13, balancing
the braking effect on the two sides of the brake disk.
The flexible bellows 11 are movable in all directions and can compensate
for any kind of misalignment of the shafts, axial, radial and angular. By the attachment
by the locking rings 10 or 10' (radially slit and clamped by a screw not shown in
more detail), the flexible bellows 11 can be secured on the short end of the shaft
so that space can be saved. The locking rings 10, 10' in addition, achieve a locking
of the bellows and the locking between the hub 4 and the drive shaft 9 on the one
hand, and the coupling hub 14 and the drive shaft 12 on the other hand
Referring to figure 3, there is shown an exploded view of a portion
of the coupling and brake combination. The same or corresponding parts have been
given the same reference numerals as in Figures 1 and 2. Figure 3 shows a motor
shaft 9, and a hub 4 which supports a brake disk (not shown). The hub 4 is sized
to fit on the motor shaft 9 and has key-ways (not shown) to prevent mutual rotation
between the shaft 9 and the hub 4. The hub 4 has a longitudinally extending cylindrical
sleeve portion 20 which has one or more longitudinal slits 23. It also has an outwardly
facing annular groove 21 in its outer cylindrical surface. A metal bellows assembly
11 has a generally cylindrical right hand-end 26 sized to fit over the left-hand
end of the cylindrical sleeve forming the extension 20 of the hub 4. The metal bellows
assembly 11 is held in place on the extension 20 of the hub 4 by means of a locking
ring 10b sized to fit around the cylindrical end 26 of the metal bellows 11. The
locking ring 10b has an inwardly facing annular groove 22 in its inner surface,
to receive a spring clip 25. The spring clip 25 is shown in Figure 4. As it is located
in the annular groove 22, as the locking ring 10b is passed over the sleeve 20,
but before it is tightened down, the spring clip 25 comes to rest in the outwardly
facing annular groove 21. This serves to locate the locking ring 10b on the sleeve
The locking ring 10b has a radial split or slot with a tangential
bolt 24 passing across it. When the locking ring 10b is assembled and in place around
the cylindrical end 26 to the metal bellows assembly 11, which in turn is in place
on the cylindrical extension 20 of the hub 4, the bolt 24 can be tightened. This
urges the radial slot in the locking ring 10b closed, which causes the ring to grip
the cylindrical extension 26 of the metal bellows 11 against the outer surface of
the extension 20 of the hub 4. The tightening also tends to urge the slot 23 in
the cylindrical sleeve 20 of the hub 4 in a dosing direction, thereby causing the
hub 4 to grip tightly against the motor shaft 9. Accordingly, the locking ring 10b
serves a dual function of holding the metal bellows 11 to the brake hub 4 and also
holding the brake hub 4 to the motor shaft 9. This is particularly advantageous
because it dispenses with the need to provide a separate fixing means to prevent
longitudinal movement of the brake hub 4 with respect to the motor shaft 9. The
result is that the flexible coupling can be mounted closer to the motor. This is
particularly advantageous in situations where there is a limited amount of available
motor shaft, or a limited amount of space for the entire assembly. Such situations
are common when a brake is being retrofitted to an existing installation. The coupling
and brake combination in accordance with the present invention therefor saves a
considerable amount of space and allows braking assemblies to be retrofitted to
motors in spaces which were previously considered too small.