Magnetic closure device

The present magnetic closure device has one or more holding members and one or more closure members, each with a surface configuration providing an increased frictional force, when two matching surface configurations cooperate. One member of a pair forming a closure device is a permanent magnet of so-called hard magnetic material, while the other member of a pair is a magnetic armature made of ferromagnetically soft, magnetizable material. The increased frictional force and the magnetic force combine to provide an effective closure device for articles of non-magnetic material, such as leather goods, textiles, and synthetic materials. The two members have a square or rectangular configuration and are corrugated whereby both members have the same configuration and the permanent magnet has poles of one polarity extending along the entire length of a ridge in the corrugation, and poles of the opposite polarity extending along the entire length of the valleys adjacent to a ridge. This type of closure device has greatly improved holding characteristics.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic closure device, especially for 
articles of non-magnetic materials, such as leather goods, textiles, 
synthetic materials, and so forth. 
Closure devices of various kinds and useful for non-magnetic articles are 
known in large numbers. The so-called slide closure devices including 
various kinds of zippers are to be mentioned in this respect. Further, 
so-called rotary closure devices are also well known, whereby the latter 
are mainly used in connection with briefcases and the like. 
Tension and pressure responsive closure means capable of taking up larger 
forces are also well known. Strapping closure devices belong in this group 
and are preferably used in connection with ski boots. In addition, there 
are buckle closure devices for belts and shoes. Especially the latter are 
well known in numerous embodiments. 
Most of the known closure devices, especially the zipper type of closures 
require numerous individual parts which can be closed or opened only by 
applying more or less force resulting in a respective wear and tear. 
Another disadvantage of known closure devices is seen in their relatively 
limited adjustability. Thus, especially briefcase closure devices normally 
have only one closing position. Another disadvantage of prior art devices 
is seen in the substantial costs for the manufacturing of a large number 
of individual parts and assemblying such parts, whereby the production of 
the individual parts also requires a substantial capital investment for 
machinery and tools. A further drawback of prior art devices is seen in 
the fact that they are prone to failure, since it is unavoidable that 
individual parts may break easily, because due to weight considerations 
such parts are of a rather light construction. Furthermore, especially 
those embodiments of the prior art which require a substantial number of 
links and levers and so forth are also prone to failure, because these 
links and levers may easily be damaged or bent or even broken. 
German patent publication No. 1,760,095 discloses a shoe closure device 
especially for ski boots, which is provided with a magnetic safety catch. 
Such a safety catch comprises two interlocking closure members provided 
with permanent magnets having plane surfaces contacting each other. The 
pulling or tension forces tending to separate the closure members are 
taken up solely in a mechanical manner by the steep serrated flanks of the 
closure members. Practical experience has shown that this type of closure 
device results in an increased pressure, especially along the edges of the 
closure device and such pressure is transmitted to the foot or the ankle 
of the person wearing such boots. Another drawback is seen in that for 
closing the two closure members a substantial stretching of the boot 
uppers is necessary to a position extending even beyond the closure 
position, because the serrated flanks must be relatively large for this 
purpose. This stretching is especially required where the ski probe or 
rather its tip is used for the closing. Thus, the shoe uppers may easily 
be damaged by the ski pole tip and the serrated flanks of the closure 
members are subject to rapid wear. 
U.S. Pat. No. 2,389,298 (Ellis) discloses a magnetic closure device wherein 
two serrated, permanent magnets are corrugated. Since the magnetic poles 
are located at the ends of the serrations there is room for improvement, 
especially since in Ellis the two permanent magnets begin to push away 
from one another when magnetic poles of equal polarity come to face each 
other. 
OBJECTS OF THE INVENTION 
In view of the above it is the aim of the present invention to achieve the 
following objects singly or in combination: 
to provide an improved magnetic closure device as compared to the prior art 
described above and which may be manufactured at low costs and relatively 
little capital investment; 
to provide a magnetic closure device of relatively low weight, wherein a 
permanent magnet and a magnetizable armature having the same configuration 
as the permanent magnet cooperate to achieve optimal closure forces; 
to combine in a magnetic closure device the magnetic and mechanical 
features in such a manner that an extensive stretching during the closing 
itself is substantially reduced or altogether avoided; 
to provide a magnetic closure device which is versatile and useful in many 
different applications to operate in the form of a zipper and even in the 
form of a button and/or snap button; and 
to provide a closure device which may be used for shoes, bags, belts, 
clothing, as well as for watch bands, safety belts, shoe and boot buckles 
including mountaineer boots and ski boots and many other applications, for 
example, briefcases and suitcases. 
SUMMARY OF THE INVENTION 
The above objects have been achieved according to the invention by a 
magnetic closure device comprising permanent magnet means and magnetizable 
armature means of ferromagnetically soft material. Both means are provided 
with profiled cooperating surfaces of such a shape that a quasi-magnetic 
translation is accomplished. Due to the combination of the magnetic 
holding force with the frictional forces, which are increased by the 
magnetic holding force and the magnetic instability force, a substantial 
closure force is accomplished which opposes any pulling or tension force 
tending to separate the two means. The surface area of one of the means 
may be relatively small as compared to the given surface area of the other 
means. The configurations of the surface areas have preferably contrary, 
but matching shapes such as corrugations whereby the ridges and valleys of 
the permanent magnet means have opposite magnetic polarities extending 
along the entire length of the respective ridge or valley. 
It is a particular advantage of the closure device according to the 
invention that it obviates all, or substantially all mechanical elements 
which heretofore have been necessary to provide a straping or clamping 
action. Further, within the practical considerations, there are no limits 
in selecting the proper size of the present closure device for any 
particular requirements. The present closure device is rather variable in 
its adjustability and any number of adjustable steps may be provided for a 
substantially continuous adjustability. The permanent holding magnet is 
employed with an optimal efficiency and is not used as a safety latch 
against undesired opening, rather it forms part of the closure itself. 
It is an essential further feature of the invention that due to the 
particular shape of the cooperating surface configurations, the pulling or 
tension force tending to separate the two surfaces extends perpendicularly 
to the resulting surface normal, whereby the optimal closure safety is 
assured. By using a corrugated armature and a corrugated permanent magnet 
with opposite magnetic polarities along the entire length of the ridges 
and valleys of the corrugations the magnetic closing forces are still 
substantially effective even if ridges of the permanent magnet face ridges 
of the soft magnetic material armature.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS 
FIG. 1a illustrates a permanent magnet member or means 10 according to the 
invention, comprising a contact surface 10a having a wavy or corrugated 
surface configuration 12a. For example, the ridges of the corrugations 
have a north magnetic pole N extending along the entire length of each 
ridge and the valleys have a south magnetic pole S extending along the 
entire length of each valley. FIG. 1b illustrates an armature member or 
means 11 having a contact surface 11a with a surface configuration 12b 
shaped for hugging cooperation with the surface configuration 12a of the 
permanent magnet member 10. Preferably, the permanent magnet member 10 is 
made of a permanent magnetic material alloy comprising a rare earth metal, 
for example, samarium is suitable for the present purposes. Such permanent 
magnetic material alloys are well known in the art. The armature member 11 
is made of a ferromagnetically soft and flexible material such as spring 
steel to form a strap as shown in FIG. 1b. 
Preferably the permanent magnet member 10 and if desired also the armature 
member 11, are coated either entirely or partially with a coat 16 of a 
synthetic material, for example, of the polyvinylchloride type. Further, 
the member 10 or its coating 16 may be provided with locating studs or 
lugs 17 which assure, even if the member 10 is produced by mass production 
means, that the member 10 will always be properly located in the same 
position as determined by the locating studs 17. Thus, the member 10 will 
always be located at the same position, for example, on a shoe upper. The 
surface area of the member 10 may be only a fraction of the surface area 
of the flexible spring type armature member 11, since the latter is 
substantially longer than the permanent magnet member 10. This feature not 
only utilizes the permanent magnets most efficiently, it also assures a 
rather large adjustability range of the closure device. Another advantage 
of constructing the armature member 11 as a flexible spring is seen in 
that the tearing open moment at the member 10 as a result of a force 
applied perpendicularly thereto, is substantially eliminated, so that the 
magnetic closure device will tend to remain closed. Another advantage of 
the surface configuration shown in FIGS. 1a and 1b is seen in that the 
armature member 11 will automatically tend to match itself against the 
shape of the item to be closed, so that, for example, in connection with 
shoes no pressure or substantially no pressure will be applied to the feet 
of the wearer. This feature is due to the ridges N and valleys S of 
opposite magnetic polarity whereby the armature will be effective in any 
position relative to the permanent magnet. 
Incidentally, all the magnet members will be designated by reference 
numeral 100, even if somewhat different surface configurations are 
illustrated. Similarly, all the armature members will be designated by the 
reference numeral 11, even if different surface configurations are 
involved. 
FIG. 2 illustrates another embodiment of a permanent magnet member 10 
having a tongue and groove surface configuration. The respective closure 
member, which is not shown, will have the same surface configuration and 
would normally be longer than the length of the permanent magnet member 10 
of FIG. 2. The ridges constitute north magnetic poles N and the valleys or 
groove bottoms constitute south magnetic poles S. However, the arrangement 
in this embodiment and any other embodiment could be vice versa with the 
south poles S along the ridges and the north poles N along the valleys. 
FIG. 3 illustrates a still further embodiment of a permanent magnetic 
member 10 having a serrated surface configuration 12a, whereby the 
corresponding armature member would have the same serrated surface 
configuration and could be longer than the given length of the magnetic 
member, if desired. The frictional forces which combine with the magnetic 
forces are especially larger in the embodiments of FIGS. 2 and 3. Thus, 
these embodiments would be suitable for such purposes as belts, seat 
belts, and the like. 
FIG. 4 illustrates in a somewhat schematic perspective view a closure 
device according to the invention in its closed condition, whereby the 
permanent magnet member 10 is pivoted by a pivot 25 to a substrate or 
strap 24. Similarly, the armature member 11 having a corrugated or wavy 
surface configuration is pivoted by means of a pivot 23 to a strap 22. The 
pivoting just described has the advantage that forces extending 
perpendicularly to the longitudinal extension of the closure device cannot 
be effective for creating moments tending to open the magnetic closure 
device. Another advantage of the pivoting is seen in the closure device is 
more easily adaptable to the contours of the article to be closed. FIG. 4 
also shows the direction of the pulling force Pz and the direction of the 
frictional force. Both forces extend perpendicularly to the normal N' to 
the surface of the armature member 11. 
FIGS. 5a and 5b are schematic illustrations of the embodiment of FIG. 4, 
whereby FIG. 5a shows the fully closed condition, whereas FIG. 5b 
illustrate a condition wherein the armature member 11 begins to open. In 
the normal, closed condition the magnetic force Pm substantially causes 
the friction force Pr due to the static friction coefficient .mu.0, 
whereby Pr corresponds to: Pr=Pm.multidot..mu.0. As the device begins to 
open, the static friction coefficient changes to a gliding friction 
coefficient .mu.1 and in addition the magnetic instability force Pim 
becomes effective due to the shifting of the two members 10 and 11 
relative to each other along inclined surfaces. Such magnetic instability 
force tends to restore the original closed condition and is effective in 
the direction of the inclined surfaces as shown in FIG. 5b. At this 
instance the frictional force Pr becomes: 
EQU Pr=Pm.multidot..mu.1+Pim [f(s)] 
As a result this effect or rather this magnetic instability force 
contributes to the increase of the forces effective to tend to keep the 
device in the closed condition, such increase of the forces occurring in 
response to an attempt to open the device. This feature of the invention 
has the advantage that it increases the closing safety so that the closure 
device will automatically close itself again, if the frictional force is 
only exceeded momentarily and the applied momentary pulling force will 
contribute to the automatic closing. 
In view of the foregoing disclosure, it will be appreciated that the 
present invention is suitable for closing many different items from 
garments, shoes and the like to briefcases, luggage and so forth. 
Although the invention has been described with reference to specific 
example embodiments, it is to be understood, that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.