Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
4 ~1 3
FIEL~ OF Tll]~ INV~NTl:ON
This invention relates to closure apparatus for
screwing a plastics screw closure on to a container provided
with a screwthread. The apparatus can be driven b~ a drive
means and is provided with a screw-on head for screwing on
the screw closure, and with a torque-dependent clutch
arranged between the screw on head and the drive means which
interrupts the screwing-on process when a predeterminable
desired torque is reached.
BACKGROUND OF THE INVENTION
_ _ _
Various forms of closure apparatus for screwing on
screw closures are known and are conventional. In order to
ensure that the screw closure is not screwed on too tightly,
which could possibly result in damage, such closure apparatuses
are provided with a torque-dependent clutch to linlit the
maximum torque which can be transmitted.
In practice, virtually only slipping clu-tches are used
for this purpose. Slipping clutches of this kind are known
for example, from published German Patent Application
No. 24 36 993. Mechanical tor~ue-limiting assemblies have
also already been proposed, for example, U.S. Patent
Specification No. 3 405 499.
Difficulties are caused in the known closure apparatuses
in particular due to the function of the clutches which
are susceptible to wear and which suffer from a wide range
of varlation in regard to the maximum torque values,
particularly under the fluctuating environmental conditions
to which bottle filling plant is exposed. In addition, the
clutch arrangements are expensive to construct, require
frequent adjustment and set~ing and are susceptible to trouble.
138
Sl~ RY OF Tl-IE INVE:NTION
An o~ject o~ the invention i5 to avoid the disadvantages
of the known constructions, and in particular to provide a
closure apparatus of the above-indicated kind, which transmits
a constant torque irrespective of environmental influences,
which is of simple construction, and which does not require
adjustment.
According to the invention, this is primarily achieved
by usiny a magnetic clutch as the torque-dependent clutch.
Although the problems associated with screwing on closure
apparatushave existed and been recognised for more than
20 years, the use of magnetic clutches in this field of
application has hitherto not been proposed. The probable
reason for this is primarily that the rising and falling
torque characteristic of magnetic clutches during full
rotation thereof, and the torque tolerances when there are
changes in the magnet spacing, indicated that magnetic
clutches of this kind would apparently not be suitable. The
present inventor however has found that magnetic
clutches are excellently well suited for use as clutches
with a torque limiting action in closure apparatus.
In a particularly advantageous form of a closure
apparatus according to the invention, the clutch has a clutch
plate at the drive side, and a clutch plate at the driven
side, spaced from the drive-side clutch plate and connected
to the screw-on head, the drive-side clutch plate and the
driven-side clutch plate having on the facing surfaces of
the plates permanent magnets of which the poles are so
arranged that the two clutch plates attract each other at
least in one relative position thereof. Such an arrangemcnt
7138
makes it possible to reduce the moments of rotary inertia
of the driven-side'clutch plate. In addition, the magnets,
which are disposed on both clutch plates, provide that there
is
a lower drop in torque from pole to pole when the driven-s-de
clutch plate is turned through a complete revolution For
this purpose, the arrangement has a magnet pole ring with
the poles having alternate polarities. A sufficiently
uniform torque performance which eliminates any 'chattering'
of the driven-side clutch plate when the clutch is rotating
is advantageously achieved by the clutch plate having at
least eight and preferably at least twelve magnets.
Making the magnets of an approximately cylindrical
configuration provides a particularly compact and simple
arrangement in respect of the magnets.
A particularly stable and wear-resistant arrangement
is produced if the clutch plate has a concentrically
extending shoulder against which the magnets lie laterally
and are supported thereby.
Embedding the magnets in a bed of curable plastics material
provides stable mounting on the clutch plate and a further
improvement in operating reliability. This arrangement
reliably eliminates in particular the danger of magnetic
shunts or leaks due to contamination by iron turnings or
filings and the like. In addition, this causes the mounting
of the magnets to be insensitive to shock and, in the event
of damage, a magnet arrangement which has been cast in place
in this way can be simply replaced.
A particularly compact and stable arrangement is
provided if the plastics bed is of an approximately annular
~4'7~
configuration and extends Erom the concentrically extendlng
shoulder of the clutch plate to an outer edge outside the
magnets and enclosiny the magnets.
- A further improvement in stability and damage in
assembly is achieved i~ the magnets of at least one clutch
plate are provided on that surface which faces towards the
other clutch plate, with a non-magnetic cover means. In
practice, brass has been found to be particularl~ suitable
for this purpose. Particularly when using oxide magnets,
a cover means of this type prevents damage to the magnets
by shock, or for example, prevents the magnets from coming
loose from the plastics bed. An arrangement of this kind
may be emboaied in a particularly advantageous manner if
the cover means has a ring which extends on its outside and
which surrounds the magnets embedded in the plastics bed
and also protects the magnets at the periphery t~ereof.
It has been found that the magnetic clutch transmits a
uniform torque in a particularly constant manner which is
independent of wear, when the spacing between the magnets
of the two clutch plates is at least 4 mm. In this case, any
fluctuation in spacing, for example, due to play in the
axial bearing, between the two clutch plates only slightly
influences the torque produced by the magnets. The invention
may be embodied in a particularly advantayeous manner if
~5 the spacing is at least six times the axial bearing play
~etween the drive side and the driven side. It is known
that, when th2 spacing between the magnets decreases or
increases, the forces between the magnets increase and decrease
respectively e~onentially at least as the square with respect
to the distance. Therefore, the greater the ratio between
- 5 -
38
bearing play and air gap, the lower is the influ~nce of
tolerances and fluctuations ln spacing between the two clutch
plates.
It will be seen that the technical advance and the
inventive content of the subject of this application are
ensured both by the individual features used and also in
particular by combination and sub-combination of the
features employed.
.BRIEF DESCRIPTION OF DRAWINGS
. . _ . _ . . . _ _ _
In the accompanying drawings:
Figure 1 is a cross-sectional view of one form of
closure apparatus according to the invention;
Figure 2 is a plan view of the driven-side clutch plate
of E'igure 1;
Figure 3 is a sectional view of the clutch plate of
Figure 2;
Figure 4 is a diagrammatic representation o axial
play and tolerances in the clutch; and
Figure 5 is a diagrammatic representation of the
inEluence of play and tolerances on torque.
Referring to Figure 1, the closure apparatus illustrated
has an outer clutch member 1 which is screwed on to a cylindri-
cal central member 2. The central member 2 is axially
displaceably fixed to a drive-side connecting member 3 which
can be flange-connected in known manner to a drive means
tnot shown). Provided on the central member 2 are pins 4
which are displaceable in longitudinal slots 5 in the
connecting member 3~ Also provided on the connecting member
3 is a peripheral shoulder 6 which supports a spring 7
of which the other end bears against the central member 2.
- 6 -
7~
It will be seen that, by virtue of this arrangement, the
central member 2 can be telescopically displaced in the
connecting member 3 in the longitudinal direction, against
the force of the spring 7; the pins 4 which slide in the
longitudinal slots 5 both limit the longitudinal stroke
movement and also provide for transmitting torque from the
connecting member 3 to the central member 2.
The spring 7 and the longitudinal mobility of the out~r
clutch member 1 relative to the connecting member 3 is
provided in known manner in order to adapt the clutch to
tolerances in the height of the bottles when applying the
apparatus to a bottle to be closed, and in particular also
to accommodate the travel movement of the screw closure when
it is being screwed on to the bottle. I-t will be
appreciated that, instead of the spring 7, it is also posslble
to use a different compensating device, for example, an
hydraulic device. The form of compensating device used does
not have any limiting effect on the present invention.
Disposed in the central member 2 is a roller bearing
8 which carries an inner clu-tch member 9. The inner clutch
member 9 is provided with a tapered screw-on head lO which
i~ arranged in known manner to accommodate a screw closure
16 and to grip it in a form-locking and/or ~orce-locking
manner during the screwing~on process. The screw-on head
lO, which is mounted rotatably in the roller bearing 8 is
connected to a driven-side clutch plate 11 which carries a
plurality of permanent magnets 12. The outer clutch member 1
is provided with a drive-side clutch plate 13 on which a
plurality o~ permanent magnets 14 is arranged. ~n air gap
15 is provided between the two clutch plates 11 and 13.
~47~38
As ean be seen from Figures 2 and 3, the magne~s 12
are disc-shaped oxide magnets which are arranged ~n a
concentric circle on the clutch plate 11. The polarities
of the magnets 12 alternate so in such a way that ~ North
Pole and a South Pole ~ollow each other alternately. The
spaces 12a between the magnets are completely filled with a
curable plastlcs material (for example, Araldite~. The
elutch plate 1i is closed by a cover means 18 of brass, which
also forms a ring 18a surrounding the clutch plate 11 and
the magnets 12 at the periphery thereof. The magnets are thus
protected from shock or impact and are also held mechanically
fast between the shoulder 11c o~ the clutch plate 11 and the
ring 18a of the eover means 18.
The driven~side clutch plate 13, which is not shown
in views corresponding to those of Figures 2 and 3, is oE
a configuration identieal with the clutch plate 11. Accordingly,
the driven-side clutch plate 13 which is secured to the inner
elutch member 9 and whieh is freely rotatably mounted therewith
in the rolling bearing 8 will in the rest condition be set
in a position in whieh respective northjsouth magnets of the
two eluteh plates 11 and 13 are disposed opposite each othPr.
The attraction foree between the two elutch plates is
determined by the dimensions of the ma~nets and the si~e
of the air gap 15. Dimensioning the magnet arrangement in
dependence Oll the desired torque is part of the known art
and is fully familiar to the man skilled in the art. The
large number of magnets on each clutch plate 11 and 13
advantageously ensures that, when the two clutch pla-tes
11 and 13 are rotated relative to each other, the distanee
between two successive poles is so slight that 'chattering'
~4'7~3~
o~ the clutch plate 13 or the screw~on head lO is avoided.
Sharpl~ rising or falling changes in the torque performance
when the clutch rotates is avoided thereby avoiding damage
to the screw closure 16. In this respect, clutch arrangements
with ten to fourteen magnets have been found particularly
suitable.
Locating the magnets 12 and 14 respectively in the annular
gap between the cover means 18 and the clutch plate 11 is
the simplest way of providing a clutch component wherein the
magnets are protected from mechanical loadings, for example,
due to shock or impact when the clutch is being assembled.
In addition, casting the magnets 12 and 14 in plastics
material ensures that contamination, for example, metal
turnings or filings and the like, cannot subsequently cause
a magnetic shunt between the magnets, which could detrimentally
affect the force acting in the air gap 15.
The air gap 15 between the magnets ~2 and 1~ is about
4 mm in the embodiment illustrated. However, the effective
distance between the magnets is about 6 mm as the brass
cover means 18 is also disposed in the space between the
magnets 12 and 14. The effective spacing between the
magnets is thus about 6 mm. This relatively wide spacing
advantageously ensures that bearing tolerances and play
in the general assembly have only an insignificant influence
on the torque to be transmitted.
Figure 4 shows how the tolerances of the drive side
(clutch plate 11, cover means 18), the driven side (clutch
plate 13, covcr means 18, spacer ring 17) and the tolerances
of the rolling bearing ~ and the play therein are added
together. It is preferable that, when determining the
~3~447~38
dimension~ of th~ clutch assembly, the spacing be~ween the
magnets 12 and 1~ is at least six times the value of the
tolerances T1 (drive side), T2 (driven side~, T3 (rol].ing
bearing) and the rolling bearing play S1 (Figure 4). This
ensures that the torque performance is advantageously
influenced only to a slight extent, by the component
tolerances. This makes it unnecessary to provide for
specific match~ng of the clutch and the clutch co~ponents
in the course of the manufacturing process, and permits
economical mass production of the closure apparatus. In
practice, it has also been found that this dimensioning first
pérmits practical use of the clutch. As, in closure
apparatuses for bottle closures, the vertical loading of
the screw-on head lO against the pressure of the spring 7
causes a heavy axial loading of all movable parts, including
those parts which influence the tolerances T1 to T3 and
the play S1, a change in the tolerances T1 to T3 and the
play S1 due to wear phenomena is to be observed, in contrast
to the conventional magnetic clutches which are more usually
~0 stationary. For this reason inter alia, the use of magnetic
clutches whose force transmission characteristic decisively
depends on the air gap or the working distance be-tween the
rows of magnets, was considered as impossible in closure
apparatuses.
Flgure 5 is a diagrammatic graph showing the nature
of the torque transmission characteristic of the clutch
arrangement in dependence on the tolerance range (including
additional tolerances due to wear phenomena)O It will ~e
seen from the graph that the torque pattern is scarcely
influenced b~ the use of the large air gap or the distance
- 10 -
.. , ~ . i.. ,.. ~. .... . . .
~L~4~7~8
between the rows of ma~nets. Accordingly, there is only
an extraordinarily sli~ht change ~ in ~orque, upon a
fluctuation T in the axial spacing. Dimensioning of this
kind is far from the thoughts of the man skilled in the
art, in itself, as the man skilled in the art will
normally seek to keep the air gap as small as possible in
order to produce the maximum possible forces or torque
transmission and to be able to make the magnets 12 and 14
of small dimensions. The invention deliberately moves away
from this principle and proposes an air gap, or spacing
between the rows of magnets, which is at least six times
greater than the maximum tolerances to be expected in the
axial direction.
The influence of fluctuations Tx in the axial spacing
on the torque ~ in a 'conventional' design of this kind
is also shown in Figure 5.
It will be seen therefore that the invention provides
a closure apparatus which is of a simple construction,
which can be economically manufactured in mass production,
and which is also wear-free and ensures a uniform torque
pattern.
.
