GB2121238A

GB2121238A - Switchable permanent magnetic holding device

Info

Publication number: GB2121238A
Application number: GB08315396A
Authority: GB
Inventors: Horst Baermann
Original assignee: Baermann Max GmbH; Max Baermann GmbH
Current assignee: Baermann Max GmbH; Max Baermann GmbH
Priority date: 1982-06-03
Filing date: 1983-06-03
Publication date: 1983-12-14
Also published as: JPH0259601B2; JPS58216405A; GB2121238B; FR2528223A1; FR2528223B1; GB8315396D0; DE3220801A1

Abstract

A permanent magnet energized holding device for holding of, or onto, ferromagnetic objects 13 and readily switchable between "on" and "off" positions, has outer and inner cup- shaped pole shoe members (1, 2) of good magnetically conductive material concentrically nested in spaced apart relation one inside the other with their rim edges or pole faces (11, 12) lying in a common plane. A ring-shaped stationary permanent magnet (7) is fixed in the space between the peripheral side walls (5, 6) of the cup members, and the cup members and stationary magnet are correspondingly divided magnetically into two portions at the same points therearound by non- magnetic mediums. A rotatable permanent magnet (10) sandwiched between the base walls (8, 9) of the cup members is rotatable therebetween by an operating shaft or other actuating means to switch the holding device between its "on" and "off" positions. In one rotative position of the rotatable magnet 10 the magnetic polarity thereof coincides with that of the stationary magnet 7 and reinforces the magnetic force thereof so as to increase the magnetic flux in the respective pole shoe members, while in another rotative position its magnetic polarity is in opposition to the magnetic polarity of the stationary magnet and reduces the magnetic flux in the pole shoe members of the device. <IMAGE>

Description

SPECIFICATION Switchable permanent magnetic holding device This invention relates to a switchable permanent magnetic holding device for holding of or onto ferromagnetic objects.

A permanent magnetic holding device for holding ferro-magnetic objects such as intended workpieces is described in US Patent No.

4055824 and comprises at least two pairs of plate-shaped pole shoes of material with high magnetic permeability, each pole shoe pair being divided by a non-magnetic medium such as brass.

Between each pair of plate-shaped pole shoes is one or more plate-shaped rigid permanent magnet having a circular recess in which a disc-shaped permanent magnet is turnably positioned. The rigid and the turnable magnets have at least two pole pairs with polarity alternating in the axial direction.

With the permanent magnets in the switched on position of the turnable magnet in the holding device, similar pole regions of the fixed and turnable permanent magnets, i.e. regions of the same magnetic polarity, lie adjacent to and magnetize the two magnetically divided pole shoes of each pole plate to provide a magnetic holding force thereat, while in the switched off position of the turnable magnet dissimilar pole regions of the fixed and turnable magnet, having opposite magnetic polarity, lie adjacent to the pole shoes of each pole plate and thus leave them unmagnetized and devoid of any magnetic holding force.

With permanent magnetic holding devices as described above, at least two of the holding surfaces thereof, i.e. one pair of pole shoes, ordinarily remain unused as, for instance, because of the presence outwardly adjacent the faces of such pole shoe pair of an actuating or control knob for rotating the turnable permanent magnet.

Furthermore, the holding surfaces of the rigid magnet are located diametrically outward relative to the rotatable permanent magnets with this type of holding device, resulting in an unavoidably large structure height or dimension.

The object of the invention is to provide an improved compact magnetic holding device.

According to the invention there is provided a switchable permanent magnetic holding device for releasable holding of or onto ferromagnetic articles comprising first and second pole shoes in the form of outer and inner body members of magnetically conductive material, each body member having a side wall and a base wall and the body members being in spaced relation to each other, one within the other with edges of the side walls arranged as pole faces in a common article-holding plane, each of said body members being separated at corresponding regions thereof by respective non-magnetic mediums into at least two separated pole parts, respective fixed permanent magnets disposed between and magnetizing the side walls of the body members and magnetically separated by non-magnetic mediums at regions corresponding to the regions of separation of the body members, and a rotatable permanent magnet disposed between and magnetizing the said base walls of the body members, the rotatable magnet being magnetized across the thickness thereof between the base walls with at least two pole pairs of alternating magnetic polarity to cause the poles of the rotatable magnet, in one relative rotary position thereof, to reinforce and increase the magnetic flux in the body members from the fixed magnets and, in a second relative rotary position, to oppose and reduce the magnetic flux in the body members from the fixed magnets.

Preferably the regions of separation extend diametrically of the body members and the nonmagnetic medium therein is brass or air.

The body members may be cup-, ring-, or railshaped with a U-shaped cross-section or square, and are preferably concentrically arranged.

In a surprising manner, the magnetic holding device of the invention fully utilizes the maximum inserted volume of permanent magnetic material without leakage, taking into account the flat design thereof, in that all lines of magnetic force emerging from the pole faces, onto the ferromagnetic surface onto which the holding device is placed for holding, are fully effective. This results in unusually high holding strength for the simple design of holding device.

Furthermore, relatively inexpensive permanent magnetic materials such as plastic-bonded injection-moulded and/or flexible permanent magnets on a barium-, strontium- or lead-ferrite basis, can be employed therein. If magnetically higher grade permanent magnet materials are used such as rare-earth cobalt magnets, then only a relatively small volume of permanent magnet material is required.

The holding device may be used universally for holding onto ferromagnetic bases. For example, the holding device may be used for supporting an antenna or lamp holder on vehicles whereby switching on of the device after placement on the vehicle body avoids scratching or marring of the paint surface. Of course, there are other possibilities for use of the holding device, such as a clamping element for machining of workpieces, for holding measuring instruments, or for other purposes.

In an advantageous embodiment of the invention, particularly in the case of a holding device in rail- or ring-shaped form, several turnable permanent magnets can be positioned between the outer and the inner hollow bodies, which together are inversely adjustable from the "on" to the "off" position by means of a rack or toothed ring.

The rotatable permanent magnets may be discshaped, square or rectangular and they can be made of either sintered or injection-moulded, plastic-bonded permanent magnet material. The stationary magnets may comprise a strip of flexible permanent magnetic material made, for example, of barium-, strontium- and/or lead-ferrite powder particles embedded in an elastomeric flexible binder. These magnets also may be made of rare-earth cobalt magnet material.

In order to avoid scratching or marring of the holding surface of the ferromagnetic base when the holding device is placed thereon, the interior space of the hollow inner body member of the device may be filled with an elastomeric material which projects slightly above or beyond the holding level of the device and is compressed when the device is magnetically attracted to and held against the holding surface of the ferromagnetic base.

To help understanding of the invention, a specific embodiment thereof will now be described with reference to the accompanying drawing, in which: Figure 1 is a vertical cross-section through a permanent magnetic holding device according to the invention and Figure 2 is a view from below of the holding device of Figure 1.

The permanent magnetic holding device of Figure 1 has an outer cup-shaped hollow body member 1 and an inner cup-shaped hollow body member 2, both of magnetically good conductive material such as soft iron, which are concentrically positioned or nested in spaced relation one inside the other about a common central axis, with their open sides facing outwardly in the same direction.

The cup-shaped hollow body members 1 and 2 are each magnetically divided at the same points therearound, i.e., at corresponding diametrical regions, into a least two magnetically separated pole parts or shoes by respective non-magnetic mediums 3, 4 such as air gaps or brass divider strips fitted between the pole parts of the respective body members 1, 2. A stationary permanent magnet 7 of strip-like form is fixedly positioned in the annular space between the concentrically disposed annular side walls 5 and 6 of the inner and outer hollow body members 2, 1 and is likewise magnetically divided, at the same diametrical points or regions as the two hollow body members 1, 2, by non-magnetic mediums such as by air gaps or brass spacer plugs.The permanent magnetic strip 7 may comprise, for example, a flexible permanent magnetic material such as barium-, strontium-, and/or lead-ferrite powder particles embedded in an elastomeric flexible binder. The magnet 7 is magnetized in the direction of its smallest thickness, i.e. its thickness between the annular side walls 5, 6 of the hollow body members 1, 2. The poles of the magnet 7 and the body members 1, 2 are indicated in the drawing by the letters N and S.

As shown, the permanent magnet strip 7 is so magnetized that, in the right-hand half of the nested cup-shaped body members 1 and 2, a south pole S of the permanent magnetic strip 7 lies against the inner circumferential surface of, and thus magnetizes with a corresponding south pole S, the annular side wall 6 of the outer cupshaped body member 1, while a north pole N of the permanent magnetic strip 7 lies against the outer circumferential surface of, and thus magnetizes with a corresponding north pole N, the annular side wall 5 of the inner cup-shaped body member 2.The permanent magnet strip 7 likewise magnetizes the left hand half of the nested body members in a similar but reversed polarity manner, a north pole N of the permanent magnetic strip 7 lying against the inner circumferential surface of, and thus magnetizing with a corresponding north pole N, the annular side wall 6 of the outer body member 1, while a south pole S of the permanent magnetic strip 7 lies against the outer circumferential surface of, and thus magnetizes with a corresponding south pole S, the annular side wall 5 of the inner body member 2.

Concentrically positioned flatwise between the flat base end walls 8, 9 of the body members 1, 2 and mounted for rotation about the central axis of the device, is a turnable disc-shaped permanent magnet 10 the flat opposite side surfaces of which are in flatwise magnetizing engagement with the opposing flat surfaces of the base end walls 8, 9.

The disc-shaped magnet 10 is diametrically divided by a neutral zone into two half sections one of which is magnetized through the smallest thickness of the magnet, i.e. axially thereof, in opposite direction to the other half section. The poles of the magnet 10 are again indicated in the drawing by the letters N and S.

The turnable, disc-shaped magnet 10 is provided with a centrally located square-shaped recess into which a banded sleeve 16 suitably of brass or other non-magnetic material and of like exterior shape engages and mates to rotatively interlock the sleeve 16 and magnet 10. The sleeve 16 is rotatably mounted in the base end walls 8, 9 of the body members 1, 2 for axial rotation about the central axis of the device. For the purpose of rotating the magnet 10 to switch the holding device on and off, the sleeve 16 is provided with a manual operating part such as a knurled control knob 14 suitably fastened thereon. A rod 19, e.g.

an antenna rod, may be engaged in the sleeve 16.

In Figure 1, the holding device is shown as being switched on. In the right hand half of the holding device in Figure 1, a south pole S of the turnable magnet 10 lies against the inner surface of the right hand half of the base end wall 8 of the outer body member 1 which is magnetized with a south pole S by the stationary magnet 7, while a north pole N of the turnable magnet 10 lies against the outer surface of the right hand half of the base end wall 9 of the inner body member 2 which is magnetized with a north pole N by the stationary magnet 7. In the left hand half of the switched-on device as shown in Figure 1, these magnetic pole conditions are completely reversed.

In this switched-on condition of the holding device, therefore, the magnetic flux induced in the body members 1 , 2 by the turnable magnet 10 complements, and thus increases, the magnetic flux induced therein by the stationary magnet 7, and a very high magnetic holding strength then results.

As can be seen in Figures 1 and 2, poles of alternating polarity are located on the respective opposite half-ring-shaped pole or holding surfaces 1 1, 12 of the body members 1,2 so that a ferromagnetic part or object 13 is attracted and held thereonto since the magnetic lines of force emitted by these pole surfaces 1 1, 12 then short circuit through the object 13.

If the turnable manget 10 is rotated by 1 800 from its Figure 1 position by turning the operating knob 14, the holding device then is placed in its switched-off condition because the poles and the magnetic flux of the magnets 7, 10 then short circuit through the halves of the outer and inner body members 1, 2 so that the magnetic flux is, in other words, balanced, i.e. the magnetic flux of the turnable magnet 10 opposes and neutralizes the magnetic flux induced in the body members 1, 2 by the stationary magnet 7. In this case, then, no lines of magnetic force emerge from, and thus no magnetic holding force is present at the pole or holding surfaces 1 1, 12, so that the holding device and the ferro-magnetic object 13 previously held thereto then can be readily separated from each other.

The inner space 1 5 of the cup-shaped inner body member 2 of the holding device may be filled with an elastomeric compressible material 18 in such a manner as to project slightly beyond the holding level or plane 1 7 of the device so that when the device is placed on a ferromagnetic holding object 13, e.g. on a vehicle body, the pole surfaces 11, 12 do not immediately come into contact with the object. When the holding device is switched on, the high magnetic holding strength thereof overcomes the slight cushioning effect of and compresses the elastomeric material 1 8 and is then fully effective to attract the pole surfaces 11, 12 onto the holding object 13 and hold the device in place thereon. In this manner, scratching or marring of the surface of the ferromagnetic part or object 13, when the holding device is placed thereon is avoided.

It will be appreciated that the holding device is not limited to the particular embodiment illustrated in the drawing and described hereinabove.The cup-shaped hollow body members 1, 2 could, for example, be magnetically divided or separated crosswise into four segmentshaped sections. In this case, the turnable magnet 10 would be magnetized in the direction of its smallest thickness, i.e. in its axial thickness direction, to form four segment-shaped pole regions. The permanent magnetic strip 7 fixed between the annular side walls 5, 6 of the body members 1, 2 also would be magnetically divided in such case into four segment-shaped sections magnetized in the direction of their smallest thickness, i.e. their thickness between the side walls 5, 6 of the body members 1, 2, with alternating poles.In this case, a turning angle of only 900 for the turnable magnet 10 would be required to switch the holding device from on to off position.

The above described switchable, permanent magnetic holding device may be seen to comprise at least two pole shoes, each of which is separated into at least two portions by a nonmagnetic medium, and a rotatable and a fixed permanent magnet which are disposed between the pole shoe portions, wherein an outer hollow body which is open on one side and an inner hollow body of material which is a good magnetic conductor, for example soft iron, which are arranged concentrically within one another such that all the pole faces on which lines of force occur, lie in a holding plane, each hollow body being divided into at least two parts by at least one non-magnetic medium such as, for example, brass or air, and a fixed magnetically divided permanent magnet is provided between the hollow body walls of the inner and outer hollow bodies, a rotatable permanent magnet is disposed between the hollow body base of the outer hollow body and the hollow body base of the inner hollow body, the permanent magnets being magnetized in the direction of their least thickness such that the opposite, adjacent pole faces of each hollow body portion comprise poles of different polarity in the "on" position such that the poles of the rotatable magnet and the poles of the fixed magnet amplify the magnetic flux in the respective hollow body portions and balance the magnetic flux in the "off" position.

Claims

1. A switchable permanent magnetic holding device for releasable holding of or onto ferromagnetic articles comprising first and second pole shoes in the form of outer and inner body members of magnetically conductive material, each body member having a side wall and a base wall and the body members being in spaced relation to each other, one within the other with edges of the side walls arranged as pole faces in a common article-holding plane, each of said body members being separated at corresponding regions thereof by respective non-magnetic mediums into at least two separated pole parts, respective fixed permanent magnets disposed between and magnetizing the side walls of the body members and magnetically separated by non-magnetic mediums at regions corresponding to the regions of separation of the body members, and a rotatable permanent magnet disposed between and magnetizing the said base walls of the body members, the rotatable magnet being magnetized across the thickness thereof between the base walls with at least two pole pairs of alternating magnetic polarity to cause the poles of the rotatable magnet, in one relative rotary position thereof, to reinforce and increase the magnetic flux in the body members from the fixed magnets and, in a second relative rotary position, to oppose and reduce the magnetic flux in the body members from the fixed magnets.

2. A magnetic holding device as claimed in claim 1 wherein the fixed magnets are in strip form and are magnetized in a direction across their thickness with pole pairs of opposite magnetic polarity, their pole pairs being of reversed magnetic polarity on opposite sides of the regions of separation, and the rotatable magnet is magnetized in a direction across its thickness with pole pairs of opposite magnetic polarity and with its poles corresponding to the separated first magnets, being of reversed magnetic polarity.

3. A magnetic holding device as claimed in claim 1 or claim 2 wherein the body members are cup-shaped with a U-shaped cross-section.

4. A magnetic holding device as claimed in claim 1 or claim 2 wherein the body members are ring-shaped with a U-shaped cross-section.

5. A magnetic holding device as claimed in claim 1 or claim 2 wherein the body members are rail-shaped with a U-shaped cross-section.

6. A magnetic holding device as claimed in any preceding claim wherein the regions of separation extend diametrically of the body members.

7. A magnetic holding device as claimed in any preceding claim wherein the rotatable magnet is fixed on an operating sleeve rotatably mounted in the body members.

8. A magnetic holding device as claimed in any preceding claim wherein a plurality of rotatable permanent magnets are positioned between the base walls of the outer and inner body members which rotatable magnets together are inversely rotatably adjustable from their said pole shoe magnetic reinforcing "on" position to their pole shoe magnetic opposing "off" position.

9. A magnetic holding device as claimed in any preceding claim wherein the rotatable magnet or magnets are rotatable by means of a rack or toothed ring.

10. A magnetic holding device as claimed in any preceding claim wherein the rotatable magnet or magnets are disc-shaped.

11. A magnetic holding dev#ice as claimed in any preceding claim wherein the rotatable magnet or magnets are square or rectangular.

12. A magnetic holding device as claimed in any preceding claim wherein the rotatable magnet or magnets are of a sintered or injection-moulded plastic-bonded permanent magnetic material.

13. A magnetic holding device as claimed in any preceding claim wherein the rotatable and fixed permanent magnets are of barium ferrite, strontium ferrite, or lead ferrite, and/or rare-earth cobalt magnetic material.

14. A magnetic holding device as claimed in any preceding claim wherein the inner space of the inner body member is filled with an elastomeric material which projects slightly beyond the holding plane of the outer and inner body members.

15. A magnetic holding device as claimed in any preceding claim wherein the non-magnetic medium is the separation regions is brass or air.

16. A magnetic holding device substantially as hereinbefore described with reference to the accompanying drawing.