US3389357A - Permanent magnet work holddown device - Google Patents

Description

June 18, 1968 w. SCHNEIDER 7 3,389,357

PERMANENT MAGNET WORK HOLDDOWN DEVICE Filed July 5, 1967 2 Sheets-Sheet 1 r f e0 .50

65 54 5 I INVENTOR.

57 mm chwsmsa 2 Sheets-Sheet 2 W. SCHNEIDER.

PERMANENT MAGNET WORK HOLDDOWN DEVICE June 18, 1968 Filed July 5, 1967 M INVENTOR.

14/. mm cwvz. 10.5.2.

BY J

Jn's a 7- rowan/5.x-

United States Patent 01 lice 3,389,357 Patented June 18, 168

3,389,357 PERMANENT MAGNET WORK HOLDDOWN DEVICE William Schneider, Pittsburgh, Pa., assignor to American Chain & Cable Company, Inc., New York, N. a corporation of New York Continuation-impart of application Ser. No. 481,670, Aug. 23, 1965. This application July 5, 1967, Ser. No. 651,289

10 Claims. (Cl. 335289) ABSTRACT OF THE DISCLOSURE A permanent magnet work holddown device that has a base plate fixedly secured to a work surface. A rectangular enclosure of nonmagnetic material is positioned on the base plate and houses a series of magnetic modules that include permanent magnets, end poles, a center pole and a control coil. A keeper plate is positioned between the lower portion of the modules and the base plate. Spring means urge the keeper plate away from the bottom surface of the modules. The control coils through a source .of DC current induce a magnetic field around the center pole either aiding or opposing the magnetic flux field.

Cross-reference to related application This application is a continuation-in-part of application Background of the invention (1) Field of the inventin.This invention relates to a permanent magnet work holddown device or chuck and more particularly to a permanent magnet chuck having an improved arrangement for magnetically holding and releasing a metallic work piece.

(2) Description of the prior art.Conventional electromagnetic chucks or work holddown devices require a source of continuous current to energize the electromagnet while the chuck is holdinga work piece in position. The electromagnetic chucks are not readily portable and are limited in application because a current source preferably direct current and associated equipment must be provided at the location where the electromagnetic chuck is used. This limits the use of the electromagnetic chucks to a specific location where the source of current is available. Another problem encountered with electromagnetic chucks is the continued replacement of the coils after relatively short periods of use. Where thechucks are used for extended periods the heat generated within the coil substantially reduces coil life. There have been instances where the operator inadvertently left the coil energized overnight and because of the heat generated therein the coil shortened and had to be replaced. The hereinafter described permanent magnet work holddown device does not require a continued source of current to maintain the Work piece in position thereon and is relatively portable for use on various metal working machines within a given installation.

Summary of the invention The permanent magnet chuck according to the herein described invention comprises a base plate that is fixedly secured to the machine work surface. A rectangular enclosure below the modules and is movable vertically relative thereto. Spring means urge the keeper plate away from the modules. The control coils are connected through a circuit including a switching means to a source of DC current contained in a power package secured to an external surface of the rectangular enclosure. The control coils extend around the center poles of the magnet within the modules and are arranged to induce a magnetic field either aiding or opposing the magnetic flux field.

When the control coils are energized by the switching device to oppose the flux field in the permanent magnet the metallic workpiece can be positioned on the upper face or surface of the chuck without the magnetism of the'permanent magnets intefering with the positioning of the work piece. To magnetically secure the work piece to the chuck the switching device reverses the direction of the current flow from the power source to complete a magnetic flux path through a work piece and thereby magnetically secure the work piece to the chuck. The bias keeper plate positioned beneath the control coils and poles of the magnet moves downwardly under the force of the spring means away from the magnet and against the upper surface of the base plate when the control coils are energized to complete a magnetic flux circuit through the work piece. The air gap between the bias keeper plate and the poles .of the magnet increase the magnetic flux path through the work piece to more firmly secure the work piece to the chuck. When it is desired to remove the work piece from the chuck the control coil is again energized in an opposite direction to first lift the bias keeper plate into engagement with the pole pieces of magnet and to create a major flux path through the pole pieces of the magnet and the bias keeper plate. The work piece can then be either removed or adjusted on the chuck.

Accordingly, the principal object .of this invention is to provide a permanent magnet work holding device that does not require a continuing source of current while the work piece is magnetically held on the work holding device.

Another object of this invention is to provide a permanent magnet work holding device that has a movable bias keeper plate that is disengaged from the pole pieces while the work piece is magnetically secured thereto and is engaged to the magnetic pole pieces while the work piece is positioned on the work holding device.

Another object of this invention is to provide a permanent magnet work holding device that includes a means to automatically increase the magnetic force holding the work piece thereon. I

These and other objectsand advantages of this invention will be more completely disclosed and described in the following specification, the accompanying drawings and the appended claims.

Brief description of the drawings In the drawings:

FIGURE 1 is a perspective view of the improved permanent magnet work holding device positioned on a work table with a work piece indicated in phantom lines.

FIGURE 2 is a fragmentary perspective view in transverse section taken along the line 2-2 of FIGURE 1 illustrating the center pole piece, the control coil and the bias keeper plate.

FIGURE 3 is a fragmentary perspective view in longitudinal section taken along the line 3-3 of FIGURE 1 illustrating the arrangement of the pole pieces and control coils.

FIGURES 4 and 5 are views in transverse section illustrating the bias keeper plate in both spaced relation to the pole pieces and in abutting relation with the pole pieces.

FIGURE 6 is a perspective view of the keeper plate illustrating the plurality of pin apertures for the guide pins and the plurality of recessed portions with the resilient springs positioned therein.

Description of the preferred embodiment Referring to the drawings and particularly FIGURES 2 and 3, my improved magnetic chuck or work holding device generally designated by the numeral 10 includes a plurality of modules containing pole pieces and a coil wound center pole. For convenience, however, the chuck 10 will be described as a unitary structure. It should be understood that the number of magnetic modules within the chuck may be increased or decreased depending upon the magnetic forces required to magnetically hold the work piece thereon.

The chuck 10 has a pair of side rails 12 and 14 fabricated from a nonmagnetic material. The side rails 12 and 14 are secured-to a base plate or mounting plate 16 by means of screws 18 extending through suitable apertures in both the base plate 16 and side rails 12 and 14. The side rails 12 and 14 each have a longitudinal groove or recess 20 in which the pole pieces are positioned. Secured to the ends of the spaced side rails 12 and 14 are end members 22 and 24. The end members 22 and 24 are secured to the base plate 16 in the same manner as the side rails 12 and 14 (not shown) and are secured to the ends of the side rails 12 and '14 by means of screws 26 (FIGURE 1). With this arrangement there is provided a rectangular enclosure for the permanent magnet modules.

The base plate 16 has a plurality of recessed portions in which pin members 30 are positioned and extend upwardly therefrom. A movable bias keeper plate 32 has longitudinal and lateral dimensions slightly smaller than the rectangular enclosure formed by the side walls 12 and 14 and end walls 22 and 24 So that the keeper plate 32 is movable vertically within the enclosure so formed. The bias keeper plate 32 has a plurality of vertical apertures 33 therein (FIGURE 6) in which a cylindrical bushing of non-magnetic material 36 is positioned in abutting relation with the cylindrical wall 34 of the vertical apertures 33. The keeper plate 32 has a plurality of cylindrical recessed portions 35 in which coil springs 37 are positioned and in an expanded position extend beyond the upper surface of the keeper plate 32 as illustrated in FIGURES 4, and 6.

The movable bias keeper plate 32 is positioned within the rectangular enclosure with the guide pins 30 extending upwardly through the vertical apertures 33 therein. With this arrangement the movable bias keeper plate 32 is free to move in a vertical direction relative to the base plate 16 and the springs 37 urge the keeper plate 32 toward the base plate 16.

The permanent magnet portion of the chuck includes pair of end plates or poles 38 and 40 extending transverse of the enclosure and having tongue portions 42 extending from both ends thereof. An elongated center pole 44 is positioned between the end poles 38 and 40 and also has tongue portions 46 extending from the ends thereof. The tongue portions 42 and 46 extend into the longitudinal slots of side rails 12 and 14 to properly position the various pole pieces therein. The end plates or poles 38 and 40 and center pole 44 are supported by the side rails 12 and 14 so that there is a space between the lower surfaces of the poles and the upper surface of the base plate 16 slightly larger than the thickness of the bias keeper plate 32. This dimensional relationship provides an air gap between the bias keeper plate 32 and the lower surfaces of the pole pieces as will be later explained. The pole pieces 38, 40 and 44 are formed of a magnetically soft material that carries a magnetic flux but does not retain the same. The center pole 44 has recessed portions 48 below the tongue portions 46.

A coil 50 is wound about the lower portion of the center pole pieces 44 and is arranged to induce magnetic flux therein. The coil 50 is illustrated in section in FIG- URES 2, 4 and 5. The coil 50 has leads 52 and 54 that are suitably connected in a circuit that includes a switching device and a source of DC current such as a conventional 24 volt storage battery. The rectangular enclosure 55 illustrated in FIGURE 1 contains the switching device and the source of DC current and will hereinafter be referred to as a power pack 55. Positioned between the end pole 38 and the center pole 44 is an elongated permanent magnet 56. A similar permanent magnet 58 is positioned between the end pole 40 and the center pole 44. The permanent magnet may be made of any suitable material that retains a permanent source of flux in a constant direction even when the flux is opposed by a flux of a density less than the flux density used to originally magnetize the material. The modules comprising the end poles 38 and 40, the center pole 44 and the permanent magnets 56 and 58 are so arranged that the faces of the respective elements are in abutting relation to create the hereinafter described magnetic paths.

The chuck 10 including the power pack 55 is a unitary self-contained portable structure that may be easily transported from one machine to another. FIGURE 1 illustrates the manner in which the chuck 10 is secured to a work surface 60 by means of conventional clips 62 holding the base plate 16 in a fixed position. The work piece 64 illustrated in phantom in FIGURE 1 is positioned on the upper surface of the chuck 10. It should be noted that the end pole pieces 38 and 40 have upper planar surfaces 66 and 68 that are in the same plane as the upper surface 70 of center pole piece 44. Thus the upper surface of the chuck 10 is substantially planar and is in abutting relation with the planar undersurface of the work piece 64. With this planar arrangement little if any air gap will be present between the surfaces of the pole pieces 38, 40 and 44 and the undersurface of the work pieces 64 and will provide for maximum conductivity therebetween.

The magnetic chuck 10 functions in the following manner to magnetically secure a work piece thereto. The switching means within the power pack 55 is actuated to energize the control coils and create a flux path from the permanent magnet 56 through the center pole 44, the bias keeper plate 32 and the end pole 38. A similar flux path is created from permanent magnet 58 through center pole piece 44, bias keeper plate 32 and end pole piece 40. The metallic work piece 64 may then be positioned on the upper surface of the magnetic chuck 10 with the undersurface of the work element 64 abutting the upper surfaces 66, 68 and 70 of respective pole pieces 38, 40 and 44. Because the maximum flux path is through the bias keeper plate 32, little if any magnetic forces are exerted on the work piece 64. With this arrangement the work piece 64 may be adjusted and easily positioned on the upper surface of the chuck 10. When the work piece 64 is properly positioned and it is desired to magnetically secure the work piece 64 to the chuck 10, the switching means within the power pack 55 is actuated to energize the coil 50 with current flowing in a direction opposite to that previously described. The pulse of current flowing through the coil 50 creates a maximum flux path through the respective pole pieces and the work piece 64. For example, the circuit of maximum flux flows from permanent magnet 56 through end pole 38, work piece 64 and center pole 44. Similarly, the maximum flux path of permanent magnet 58 flows through pole piece 40, work piece 64 and center pole 44. The shifting of the maximum flux path through the work piece from the bias keeper plate 32 reduces the magnetic flux path through the bias keeper plate 32 and the resilient springs 37 and the weight of the bias keeper plate 32 overcomes the relatively minor magnetic flux flowing therethrough and the bias keeper plate is urged downwardly by the springs 37 as is illustrated in FIGURE 4 to provide an air gap between the undersurfaces of the pole pieces 38, 40 and 44. This air gap between the pole pieces and the bias keeper plate 32 increases the magnetic flux field through the work piece 64 to more securely hold the work piece 64 on the magnetic chuck 10.

Where the permanent magnets encounter a large variation of load surface contact and air gaps between the magnetic pole pieces and the work piece fluctuations in load conditions are created. In order to compensate for these fluctuations in load conditions the control coil is designed to provide sufficient ampere turns for effective flux transfer from the movable keeper plate 32 to the work piece 64. If the air gap between the work piece 64 and the top surface of the magnet is of sufficient magnitude a portion of the magnetic lines of flux will return to the movable keeper plate 32, which is in close contact with the bottom pole faces, as soon as the control energy through the coil is cutoff.

Also because of the hysteresis characteristics of the magnetic circuit and the residual magnetic properties of the pole pieces, a time lag exists from the initial application of control energy until flux transfer is accomplished. This time element is a function of ampere-turns, magnet configuration, pole piece material, and air gaps at the magnet pole faces.

It is therefore desirable to separate the movable keeper plate 32 from the magnet pole faces at substantially the exact instant when the flux through the movable keeper plate passes through a minimum. This is accomplished by the application of an external force on the movable keeper plate in a direction which causes the keeper plate to move away from the pole faces. The spring members positioned between the keeper plate and the pole faces are normally in compression when the keeper plate is in contact with the pole faces. The springs exert a force of sufficient magnitude to overcome the small residual magnetic forces to cause the keeper plate to release from the pole faces at the exact instant of flux transfer and be held in a released air gap position after the control energy has been turned off.

It should be understood that other apparatus such as solenoids, leaf springs and other devices capable of producing a force and a movement can be used in lieu of the resilient springs between the keeper plate and the pole faces.

To release the work piece 64 from the magnetic chuck 10, the switch within the power package 55 is actuated to send a pulse of current through the coils 50 in a direction opposite to that previously described to create a maximum flux path through the pole pieces and the bias keeper plate. The magnetic flux created by the pulse of current is sufiicient to magnetically attract the bias keeper plate 32 against the bias of springs 37 so that it moves upwardly into abutting relation with the underside of the pole pieces as is illustrated in FIGURE 5. In this position the maximum flux path is from the permanent magnets through theend pole pieces, then through the bias keeper plate and the center pole piece. The shifting of the fiux path from the work piece 64 to the bias plate 32 releases the magnetic forces holding the work piece 64 on the upper surface of chuck and the work piece may be either repositioned thereon or removed therefrom.

Where it is desired for certain applications where greater magnetic forces are required to hold the work piece on the chuck, the switch means within the power package 55 may be retained in an on position to energize the coil 50 with current in the proper direction to increase the magnetic flux through the work piece to more securely hold the work piece on the upper surface of chuck 10. In a majority of the instances wherein the chuck 10 is utilized to secure a work piece 64 thereto all that is required is a momentary pulse of current through the control coils 50 to either engage or disengage the work piece 64 to the permanent magnet chuck 10.

With a 24 volt DC power supply it is possible to move a one inch plate a distance of about A; of an inch by energizing the control coil 50 in a direction to provide maximum magnetic flux through the spaced one inch plate. Thus it is preferred to dimension the elements of the chuck 10 so that the bias keeper plate 32 is spaced from the undersurfaccs of the pole pieces a distance of about /8 of an inch. In FIGURE 3 several of the control coils have been omitted and the magnetic poles of the pole pieces indicated thereon. For example, the center pole piece serves as a north pole for both permanent magnets 56 and 58.'The end pole 40 serves as a south pole for the permanent magnets 56 and 58 positioned on opposite sides thereof.

It is apparent with the above described permanent magnet lifting device that it is now possible to fabricate a relatively portable magnetic chuck or work holding device that quickly and efficiently engages and disengages the work piece therefrom. The spacing of the bias keeper plate 32 by the arrangement above described provides an apparatus wherein the work piece is secured to the magnetic chuck with a greater magnetic force by providing an open circuit i.e. the air gap between the bias keeper plate and the respective pole pieces.

A suitable permanent magnet for use in the above described work holddown device may be fabricated from a ceramic barium ferrite material having a coercive force of about 2200 oersteds and a residual induction of 4000 gausses. Suitable permanent magnets may be purchased from the Indiana General Corporation under the trade name of Indox #5, or from Westinghouse Electric Corporation under the trade name Wcstro Alpha. The keeper plate and pole pieces may be fabricated from a cold rolled steel designated CRS 1018 or CRS 1010. The nonmagnetic members may be fabricated from aluminum or nonmagnetic stainless steel. The bolts may be fabricated from brass or other material having the desired tensile strength and being nonmagnetic. A suitable coil for use in the work hold down device comprises turns of copper wire having 1.35 ohms per coil. To transfer the flux from the keeper plate to the load, current of l to 1.5

amps was found adequate.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a permanent magnet work holddown device the combination comprising,

a permanent magnet module including,

a center pole piece of magnetic material,

a pair of permanent magnets positioned on opposite sides of said center pole piece and having face portions abutting said center pole piece adjacent face portions,

a pair of end pole pieces of magnetic material positioned on opposite sides of said pair of permanent magnets and having face portions abutting said adjacent permanent magnet face portions,

said center pole piece and said pair of end pole pieces having bottom walls arranged in substantially the same plane,

said center pole piece and said pair of end pole pieces having top walls arranged in substantially the same plane,

a coil extending around said center pole piece adjacent said bottom wall, said coil connected to a source of direct current through a switch means operable to reverse the direction of flow of current through said coil,

a base member,

a pair of side members of nonmagnetic material secured to said base member in spaced relation to each other,

said module positioned between and secured to said side members so that the bottom Wall of said center pole piece and said end pole pieces are spaced a preselected distance from said base member,

a keeper plate of magnetizable material positioned between said base member and the bottom walls of said center pole piece and said end pole piece, said keeper plate so dimensioned to provide an air gap between the bottom walls of said pole pieces and said base plate,

said coil operable upon energization and flow of current therethrough in a first direction to transmit sufficient flux through said center pole piece to move said keeper plate into engagement with the bottom walls of said center and end pole pieces to provide a flux path therethrough for the permanent magnets, and

said keeper plate arranged to be disengaged from the bottom walls of said pole pieces and provide an air gap therebetween when the path of maximum flux from said permanent magnets extends through the pole pieces and a magnetic work piece positioned on the top walls of said center and end pole pieces.

2. In a permanent magnetic work holddown device as set forth in claim 1 which includes guide means associated with said keeper plate and said base plate,

said guide means operable to guide said keeper plate as it moves vertically relative to said base plate and maintains said keeper plate in a preselected trans verse position relative to said base plate.

3. In a permanent magnetic work holddown device as set forth in claim 1 which includes,

means positioned between said keeper plate and the bottom walls of said pole pieces, said means operable to urge said keeper plate away from the bottom walls of said pole pieces when said coil is de-energized.

4. In a permanent magnetic work holddown device as set forth in claim 1 which includes,

a plurality of recessed portions in the top wall of said keeper plate, coil springs positioned in said recessed portions and abutting the bottom wall of said pole pieces, said coil springs operable to move said keeper plate away from the bottom walls of said pole pieces when said coil is de-energized.

5. In a permanent magnetic work holddown device as set forth in claim 1 in which said center pole piece and said end pole pieces each has vertical end walls abutting said side members,

said side members each having longitudinally extending recessed portions spaced above said base member,

said vertical end walls of said central pole piece and said end pole pieces having tongue portions extending laterally therefrom, said tongue portions positioned in said side member recessed portions thereby supporting said center pole piece and said end pole pieces in preselected spaced relation with said base member.

6. In a permanent magnetic work holddown device as set forth in claim 1 in which said side members each have vertical end walls,

end members of nonmagnetic materials spanning the distance between said spaced side members and abutting said end walls, and

means rigidly securing said end members to said base plate and said side members and thereby forming a rigid enclosure for said module.

7. In a permanent magnetic Work holddown device as set forth in claim 1 in which said base plate includes a plurality of vertical apertures therein,

said keeper plate having a plurality of vertical apertures axially aligned with said apertures in said base plate, and

pin members extending through said apertures in said base plate and said keeper plate and arranged to provide vertical guides for said keeper plate as said keeper plate moves toward and away from said center pole piece and said end pole piece bottom walls.

8. In a permanent magnetic work holddown device as set forth in claim 1 which includes guide means associated with said keeper plate and said base plate,

said center pole piece and said end pole pieces each having vertical end walls abutting said side members,

said side members each having longitudinally extending recessed portions spaced above said base member,

said vertical end walls of said central pole piece and said end pole pieces having tongue pieces extending laterally therefrom, said tongue portions positioned in said side member recessed portions thereby supporting said center pole piece and said end pole pieces in preselected spaced relation with said base member.

9. In a permanent magnetic work holddown device as set forth in claim 1 in which said center pole piece and said end pole pieces each has vertical end walls abutting said side members,

said side members each having longitudinally extending recessed portions spaced above said base memher,

said vertical end Walls of said central pole piece and said end pole pieces having tongue portions extending laterally therefrom, said tongue portions positioned in said side member recessed portions thereby supporting said center pole piece and said end pole pieces in preselected spaced relation with said base member,

said base plate having a plurality of vertical apertures therein,

said keeper plate having a plurality of vertical apertures axially aligned with said apertures in said base plate, and

pin members extending through said apertures in said base plate and said keeper plate and arranged to provide vertical guides for said keeper plate as said keeper plate moves toward and away from said center pole piece and said end pole piece bottom walls.

10. In a permanent magnetic work holddown device as set forth in claim 1 in which said center pole piece and said end pole pieces each has vertical end walls abutting said side members,

said side members each having longitudinally extending recessed portions spaced above said base member,

said vertical end walls of said central pole piece and said end pole pieces having tongue portions extending laterally therefrom, said tongue portions positioned in said side member recessed portions thereby supporting said center pole piece and said end pole pieces in preselected spaced relation with said base member,

said side members each having vertical end walls,

end members of monmagnetic materials spanning the distance between said spaced side members and abutting said end walls,

means rigidly securing said end members to said base plate and said side members and thereby forming a rigid enclosure for said module,

said base plate including a plurality of vertical apertures therein,

said keeper plate having a plurality of vertical apertures axially aligned with said apertures in said base plate, and

pin members extending through said apertures in said base plate and said keeper plate and arranged to provide vertical guides for said keeper plate as said keeper plate moves toward and away from said center pole piece and said end pole piece bottom walls.

References Cited UNITED STATES PATENTS OTHER REFERENCES Alpha-Lift, Great Lakes Supply Company, Cleveland,

Tr oy 335-229 XR Ohio, January 1965, 4 pp., copy in 335-290. Besuch et a1 335285 XR 5 De Bennetot. BERNARD A. GILHEANY, Primary Examiner.

1 335 291 HARRIS, Examiner.

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