US 3389358 A
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June 18, 1968 G. TUBBS 3,389,358
FLUX TRANSFER LIFTING MAGNET Filed July 19, 1966 WITNESSES INVENTOQR M fez WM yam-w ATTORNEY.
United States Patent 3,389,358 FLUX TRANSFER LIFTING MAGNET Lester G. Tubbs, Pittsburgh, Pa., assiguor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed July 19, 1966, Ser. No. 566,351 4 Claims. (Cl. 335-290) ABSTRACT OF THE DISCLOSURE An improved permanent magnet type lifting device is provided having an integral and rugged structure. Flux leakage is substantially reduced thereby permitting greater efficiencies with smaller permanent magnets. A protective skirt surrounding the keeper plate about its movement path excludes contaminating particles and takes the place of the traditional housing.
The persent invention relates to lifting apparatus, and more particularly to lifting apparatus including a permanent magnet.
Previously, the lifting and hoisting of magnetic loads has commonly been accomplished with electromagnetic devices. Inherent in such equipment are three operational limitations: (1) large amounts of electrical energy must be applied to the magnet to generate sufiicient lifting capabilities, (2) the size of the required electrical energy supply would make more difficult load movement over substantial distances, and (3) a power failure or an inadvertent switchinng of the operating signal when a load is engaged will cause the load to fall.
A permanent magnet lifting device in accordance with the present invention has none of these limitations, since (1) only a small amount of outside electrical energy is necessary, (2) portable movement of the load over substantial distances is feasible since the electrical energy requirements are such that portable batteries are adequate, and (3) a fail safe device is provided since a permanent magnet will not lose its lifting capability upon a power interruption of the provided independent switching circuit. Some of these features have been generally described in copending application Ser. No. 443,331, filed Mar. 29, 1965, entitled, Fail Safe Lifting Apparatus, by Raymond J. Radus and Lawrence R. Scott now Patent No. 3,316,514 and assigned to the same assignee as the present application.
In known permanent-magnet load-lifting devices the attractive magnetic force of a permanent magnet is bistably switched between different magnetic circuits of the device. These circuits are typically a circuit path' operating at the load end anda similar path at the opposite or keeper end. A lift mode exists when a majority of fiux is transferred to the load end by decreasing its reluctance and correspondingly. increasing the reluctance at the keeper end. In a converse manner a release mode exists when a majority of the flux is transferred to the keeper end with consequent reluctance changes in the respective circuits. Switching the permanent magnet flux between the magnetic circuit including the keeper end plate and the magnetic circuit including the load is accomplished by application of a low energy control signal to an electromagnetic coil integrated with one or more of the magnetic circuits. When load lifting is desired, the control winding is energized to transfer a majority of the flux to the load end by decreasing its reluctance. As the load is lifted with .the device in the lift mode, the keeper end plate is raised to create an air gap to further increase the reluctance of the keeper end circuit and drive even more of the flux through the load. Inadvertent switching to the release mode when the device is operating in the lift mode and Patented June 18, 1958 ice the keeper plate is in a position of maximum air gap is of no avail since the energized control winding is not of sufficient energy level to decrease the reluctance in the keeper circuit such that the majority of the flux can be transferred to the keeper plate. Only when the device carrying the load is lowered such that the keeper plate abuts the pole pieces and the control winding is appropriately energized does the reluctance at the keeper end become sufiiciently small to allow a transfer of a majority of the magnetic flux through the keeper plate.
It is an object of the present invention to provide an improved load-lifting apparatus utilizing at least one permanent magnet device.
It is a further object of the present invention to provide a new and improved load-lifting apparatus utilizing a permanent magnet and having pole pieces constructed to achieve more constant operational characteristics and requiring a minimum of maintenance.
It is still a further object of this invention to provide a new and improved load lifting apparatus utilizing a permanent magnet such that the device is a more integral and rugged unit thereby eliminating down-time from inadvertent dropping or the rough handling typically encountered with this type of apparatus.
A still further object of this invention is to provide new and improved lifting apparatus such that flux leakage is better kept to a minimum, thus effecting greater efficiencies with a smaller device.
In accordance with the present invention, a load lifting device utilizing the lifting force of a permanent magnet is arranged inan integral and rugged structure including an inner pole member substantially surrounded by a flux-providing permanent magnet and having an outer pole member substantially surrounding the permanent magnet. At the load end of the structure the fiux emitting end of the inner pole piece is made substantially equal in area to the fiux emitting end area of the outer pole piece. This structure provides a marked advantage in relation to the optimum utilization of the flux lines of the permanent magnet in terms of lifting a load positioned at the load end of the structure. Additionally, an improved keeper plate operation is provided by a surrounding non-magnetic skirt attached to the keeper plate which operates in conjunction with a sealer band fastened to the inner pole member. This assembly is more readily adapted for effectively sealing the keeper plate from dust and magnetic particles that would otherwise impede its movement and operation. Since the characteristics of a particular permanent magnet remain substantially constant over a considerable period of time, it greatly improves the operation of this device to have all interactions of the permanent magnet with its counterparts likewise remaining substantially constant.
These and other objects and advantagesof the present invention will become more apparent when considered in view of the following specifications and drawings, in which:
FIGURE 1 is a bottom view of the present load lifting apparatus illustrating construction details requisite to a desired operation of the lifting apparatus; and
FIGS. 2 and 3 are cross-sectional views of the present magnetic load lifting device along lines 11-11 and III- III of FIG. 1 respectively. These figures are necessary for the explanation of the construction and operation of the apparatus.
FIG. 1 is a bottom view of the apparatus showing the advantageous integral structure created by the inner pole piece 12, permanent magnet 10- and outer pole piece 14. The resin filler is not shown for purposes of simplifying the illustration. Spacer plates 52 and 54 extend the entire height of the apparatus. These plates are welded to inner pole member 12 at 29 and 35 and outer pole member 14 at 33 and 37. Chamfer 56 on inner pole piece 12 and chamfer 58 on outer pole piece 14 are provided for the purpose of concentrating the flux through the pole mem bers and the abutting load in accordance with predetermined flux density requirements. To achieve maximum efficiency as determined by the known specifications of permanent magnet 10, the end areas 60 and 62 of pole pieces 12 and 14 are predetermined and must be substantially equal. This equality of end area is achieved by boring out a portion 50 of inner pole member 12. With the end areas equivalent in this manner, the magnetic circuit is substantially uniform with flux equally distributed throughout the load end 18 and its attached load.
Referring to FIG. 2 a partial section of a lifting apparatus is shown including a magnetic memory device. This memory device is comprised of a permanent magnet substantially surrounding an inner pole piece 12, both of which are substantially surrounded by an outer pole piece 14. A control winding 16 is disposed about a portion of the inner pole piece 12. An increase or decrease in the number of turns of this control winding can easily be elfected depending upon both the specification of the permanent magnet and the particular construction specifications of the apparatus itself. The permanent magnet 10, for example, may be of the well known ceramic type. The pole pieces 12 and 14 may comprise a soft magnetic material.
Due to the substantially closed structural configuration of the outer pole piece 14 and the permanent magnet 10, flux leakage operating solely within the device itself is substantially limited. Consequently, a substantially greater flux strength is developed for any given permanent magnet and its associated magnet circuits. The magnetic memory device shown in FIGS. 2 and 3 has two ends at which magnetically attracted forces will develop. These ends will be termed a load end 18 and a keeper end 20. Filler material 13, typically of resin, is supplied below the permanent magnet 10 and above and around the control winding 16 to give physical protection to the critical portions of the magnetic memory device.
A keeper plate 22, composed of a soft magnetic material similar to the pole pieces, is secured to the keeper end 20 in a fashion to allow desired vertical movement of the keeper plate 22 for effecting transfer of the majority flux between the keeper end and the load end of the illustrated structure. As shown in FIG. 2 this movement is achieved when a bolt 26 is inserted through a bore 23 and counterbore 24 and secured to a pole piece end. A similar assembly can be provided as desired at other strategically located positions on the keeper plate. This assembly will permit keeper plate 22 to move a vertical distance D Surrounding the keeper plate 22, and attached in any convenient fashion to its sides, is a protective skirt 30, composed of a non-magnetic material. Operative by the relative motion of the keeper plate 22, the protective skirt 30 moves against a sealer band 31 which inhibits any dirt or magnetic particle passage through joint 34 which would otherwise adversely accumulate in air gap 36. This sealer band may be composed of felt or any similar dust resisting material; it completely surrounds and is permanently attached to outer pole piece 14. It should be observed that this dust seal eliminates entirely any particle collection by gravity since protective skirt 30 is permanently attached to the keeper plate sides. Anti-gravity particles are likewise blocked by the wiping action of sealer band 31 against the moving inner surface of protective skirt 30. A lifting hook 38 is attached to keeper plate 22 and may be utilized in conjunction with an external hoist to move and position the lifting apapratus and any attached load.
When the apparatus is lifted vertically, the keeper plate 22 will move a distance D away from the keeper end 20 and will then be stopped by the respective flange portions of the provide plurality of bolts 26. By an appropriate control signal supplied to the control winding 16, the
majority of the magnetic flux can be transferred to the load end causing a strong attractive force through inner pole piece 12, permanent magnet 10, outer pole piece 14 and load forming a flux path 40. Similarly, when the control Winding 16 is energized in a reverse direction and the keep plate is positioned to abut keeper end 20, as shown in FIG. 3, a majority of the flux can then be transferred to inner pole piece 12, permanent magnet 10, outer pole piece 14 and keeper plate 22 forming a flux path 44. With the inner pole piece being entirely continuous in relation to the passage of magnetic flux, and the permanent magnet and outer pole piece being substantially continuous, highly efiicient flux paths will be provided since they will form a substantially continuous ring of flux paths throughout the end areas of pole pieces 12 and 14.
In FIG. 2 a particular condition of the apparatus is shown, namely, when the keeper plate is at a maximum distance away from the keeper end. It should be noted that even in its maximum lift position, the movable protective skirt 30 remains in contact with stationary sealer band 31 such that throughout the allowable operating range of keeper plate 22, the air gap 36 will always be sealed and no dirt or magnetic particles can accumulate in this region of the structure. The counterbore 24 is sealed by a cover plate 48 which may be of the knockout type. Removing this cover plate permits the depth to which bolt 26 can be set to be adjusted as needed. It becomes apparent that with air gap 36 entirely sealed off from any contamination, the magnetic flux circuit operative with the keeper plate 22 will remain substantially constant over the useful life of the apparatus.
Fail safe operation is provided as shown in FIG. 2 when a primary circuit exists at the load end through path 40 and the keeper plate 22 is in a position of maximum air gap 36. An accidental switching or energizing of the control winding to try to force the primary circuit through the flux path 44 as shown in FIG. 3 will not be effective since the additional reluctance developed by the air gap 36 as shown in FIG. 2 is too great to permit a transfer away of the strong attractive force at the load end.
Referring to FIG. 3, a partial section is shown illustrating the construction including spacer plate 52. The apparatus is positioned over a magnetic load 80 which is resting on a suitable support surface 81. The keeper plate 22 is initially held to the pole pieces 12 and 14 by a multitude of flux paths 44 providing a strong attractive force; under these conditions a majority of flux is in a primary circuit at the keeper end 20 in conjunction with the keeper plate 22. By the application of an appropriate control signal the control winding 16 is energized to trans fer a majority of the flux from the keeper end 20 to the load end 18. Now the primary circuit exists between the load end 18 and the load 80, with the keeper plate 22 now being free to move away from keeper end 20 when the entire device is hoisted. Upon lifting by an external hoist connected through lifting hook 38, the keeper plate moves a distance D Thus, with the keeper plate at its position of maximum air gap, as shown in FIG. 2, a strong attractive force is developed at the load end and the load will be picked up. It should be noted that the accidental application at this time of a control signal that would normally switch the majority of the flux to the keeper end will not be effective when the keeper plate is at a maximum distance from keeper end 20. Therefore, a lifted load cannot accidentally be dropped. It should also be observed that the control signal required to switch the majority of flux from one end to the other end of the device, need only be applied to the control winding only while the device is being separated from the load or the keeper plate is being lifted from the keeper end, and then may be disconnected.
Release of the load is achieved when the load has been set on a support surface and the keeper plate 22 moves from its maximum air gap condition as shown in FIG. 2 to a position abutting the keeper end 20 as shown in FIG. 3. Only now will an appropriate energization of the control winding in its release direction force the majority of the flux to transfer to the keeper end 20 with its abutting keeper plate 22. Upon lifting by an external hoist the apparatus will now be disengaged from the load and can be moved to any desired other position.
Although the present invention has been described with a certain degree of particularly, it should be understood that the present disclosure has been made only by way of example and that numerous changes in details of construction and combinaiton and arrangement of parts and elements may be resorted to without departing from the scope and spirit of the present invention.
I claim as my invention:
1. In a magnetic apparatus for lifting a load, the
combination of: Y
a magnetic memory device comprised of an inner pole piece, a permanent magnet substantially surrounding said inner pole piece, and an outer pole piece substantially surrounding said permanent magnet, said magnetic memory device having a first magnetic circuit at a keeper end of the device and a second magnetic circuit at the opposite and load end of said device, with the magnetic flux from the permanent magnet being divided between :said circuits according to their respective reluctances; said pole pieces at the load end having substantially equal end surface areas related to the strength of the permanent magnet to achieve a predetermined flux concentration per unit surface area in contact with said load;
a control winding disposed about at least one of said pole pieces to control the reluctances in said first and second magnetic circuits such that a transfer of a majority of the magnetic flux to a selected one of said magnetic circuits can thereby be accomplished; and,
a keeper plate, operative with said keeper end of the magnetic memory device and movable in position to permit the transfer of a majority of the magnetic flux to the keeper end only when the keeper plate is abutting said keeper end.
2. A magnetic apparatus for lifting a load as set forth in claim 1 wherein said apparatus will develop a strong attractive force for a magnetic load when a majority of the flux is operating at said second magnetic circuit through the load end; and wherein said apparatus will release a magnetic load when a majority of the magnetic flux is operating in said first magnetic circuit at the keeper end in conjunction with said keeper plate abutting said keeper end.
3. A magnetic apparatus for lifting a load as set forth in claim 1 such that when a majority of the magnetic flux is operating at the load end through a lifted magnetic load, an inadvertent energizing of the control winding to release said load will be of no avail when said keeper plate is not Iabutting said keeper end and the load will not be dropped.
4. "A magnetic device for lifting a load as set forth I in claim 1, wherein said keeper plate is surrounded throughout its movement path by both magnetic and nonmagnetic protective means to prevent contaminating particles from hindering the desired movement and operation of said keeper plate.
References Cited UNITED STATES PATENTS 3,316,514 4/1967 Radus eta'l 335-2 91 OTHER REFERENCES Alpha-Lift, Great Lakes Supply Company, Cleveland, Ohio, January 1965, 4 pages, copy in 335-290.
BERNARD A. GILHEANY, Primary Examiner.
GEORGE HARRIS, 111., Examiner.