US2918610A

US2918610A - Magnetic chuck

Info

Publication number: US2918610A
Application number: US559307A
Authority: US
Inventors: Charles D Briggs
Original assignee: WALKER O S CO Inc
Current assignee: O S WALKER COMPANY Inc; WALKER O S CO Inc
Priority date: 1956-01-16
Filing date: 1956-01-16
Publication date: 1959-12-22
Anticipated expiration: 1976-12-22

Description

C. D- BRIGGS MAGNETIC CHUCK 3 Sheets-Sheet 1 Filed Jan. 16, 1956 IN V EN TOR.

CHARLES D. BRIGGS ATTORNEYS C. D. BRIGGS MAGNETIC CHUCK Filed Jan. 16, 1956:

3 Sheets-Sheet 2 Fig 4 IIIIIIIIIIII 52- Z l l N S N 4 S N 1 1 L 24 24 24' 4 OQQOOQQQ v 00000000 T I-IIIIIIIIIII I I I I N S N f S N s 1 L 24' 24' INVENTOR. CHARLES D. BRIGGS ATTORNEYS Dec. 22, 1959 c. D. BRlGGs 2,918,610

MAGNETIC CHUCK Filed Jan. 16, 1956 3 Sheets-Sheet 3 I Ill es a l I, 66 was f ee I, O Q

s2 Flg. 7

INVENTOR. CHARLES D BRIGGS ATTORNEYS United States Patent MAGNETIC CHUCK Application January 16, 1956, Serial No. 559,307 Claims. (Cl. 317-159) The present invention relates to chucks.

In a common type of permanent magnetchuck the magnets are usually alternated with bars of soft iron or other magnetic conducting material. The purpose of this construction is to permit magnetization of the chuck in a single operation with all of the magnets of the same polarity. Thisrequires that the magnetic circuit be completed through inactive bars. An object of the present invention is to provide a permanent magnet chuck in which magnets of opposite polarity are used whereby the magnetic circuit may be completed through magnets in series.

Another object of the present invention is to provide apermanent magnet chuck of the bar pole type in whichthe top surface of the chuck is divided relatively finelyby the use of narrow strips or bars of magnetic material. Although" so'callcd bar pole arrangements are permanent magnet common in electro-magnetic chucks, such fine divisions have not usually been possible in permanent magnet chucks without the loss of holding force. Since the available magnetic energy in a permanent magnet chuck is necessarilysmaller than in an electro-magnetic chuck of the samesize,'it is important that the flux be directed into useful passage through the work without excessive diversion through the leakage paths that are frequently associated with finely divided constructions. I

With theabove objects in view, the present invention comprises the permanent magnet chuck hereinafter described and particularly defined in the claims.

In the accompanyingdrawings Fig. 1 is a plan view, with the top plate partly cut away, of my preferred chuck,

' Figs; 2 and 3 'are sectional tively; and

Figs'.-4 and 5' are diagrams illustrating themethod of magnetizing'the magnets of the chuck.

elevations illustrating the parts in work-holding and work-release position, respec- I the pole pieces.

2,918,610 Patented Dec. 22

2 conductors, in order that magnetization of the chuck after assembly may be effected. As will be explained later, the present chuck construction lends itself to satis' factory magnetization with magnets of alternating polari ties. For the same volume of space taken by the mag netic material, therefore, the present invention has twice the magnetic energy of the conventional chuck.

The magnets 24 are spaced by spacers '26 of nonmagnetic material, and the entire assembly of magnetsam and spacers 26 is mounted on the base plate 1'4."Q'As shown in Fig. l the magnet assembly is of somewhat re duced width-at one end in order to accommodate the actuating devices to be described later.

Mounted on top of the magnet assembly is a 'sliding' plate which maybe termed a neutralizing plate, in'di-= cated generally at 30. The neutralizing platecomp'rises" a plurality of pole pieces, one for each magnet. The' pole pieces are'shown at 32; they are of machine steelsoft iron or other magnetic-conducting material.

As shown in Fig. 1 each pole piece 32 extends across the chuck and overlies its corresponding magnet. Each pole piece has a bottom portion considerably wider than the magnet on which it is mounted, so that adjacent bottom portions 34 approach proximity to one another. They are separated by suitable nonmagnetic spacersfifi also extending substantially across the chuck. Above *the" base 34 each pole piece is formed with a boss 38 adapted to register substantially exactly with the underside; of one ofthe stripslS of the top plate. As shown in Fig.2 thebosss 38 engage the under side of every second strip 18,'and intermediate strips 18 are notengaged-"by There are thus twice as many bars l8- in the top plate as there are magnets 24 or pole piecesSZL Forpurposes of definition, each bar 18 "that overlie'sga; magnet will be termed an active bar, and the bars alternating therewith will be termed -intern1ediate bars;

As shownin Fig. 1 the neutralizer plate 30 is'rei;l11 e d in size atflone end in a manner similar to the magnet pack, in order to accommodate the actuatingmechanisin to be presently described; I 1

' Theplate 30 is adapted to be'moved into neutralizing position shown inFig. 3 wherein thebottom part of Fig; 6is a sectional elevation illustrating a chuck simi lar to that in Figs. 1, 2 and 3 but with a neutralizing plate of different construction,

Fig. '7 is a-top plan view'of a rotary chuck embodying the featuresof the present invention.

The chuck shown'in Figs; 1, 2 and 3 comprises side walls 10, end walls 12, a base 14 and a top plate-16. The side-and end walls are of any suitable material,,andthe baseis of materialof high magnetic conductivity. The top plate comprises a series of strips or bars 18" of magnetic conducting material, such as machine steel or soft iron, separated by brass or equivalent spacers 20. As shown in -Fig. 1 the strips l8 'alnd'20 extendcompletely across the chuck; The top plate is provided with steel end pieces 22 suitably secured to the end. walls 12.

Mounted on the base 14 is a plurality of permanent magnets 24. As shownin Fi-gs.. 2 ar d 3 the magnets are of alternating or *oppddre polarities. The provision of magnets with opposite polaritiesisbelieved to be new. as a practical matter, .since. it has been'icustomary to utilize magnets of the same polarity alternated with magnetic eachpole piece 32 spans two magnets. For this Settiri gthe magnet flux does not enter the top plate-and the workisr'eleased. 77

In order to actuate the 7 plate 30 so that it may be moved between its Fig. 2 and Fig. 3 positions, it-is pi"o-" vided at its end with depending yokes orfrarnes 40 oiie" at each side of the plate and accommodated'in the space afforded by the reduced end portion shown in Figfl. Received 'in the jawof each yoke is an eccentric 42. A shaft 44 extends across the chuck and has the two eccentrics mounted thereon. Theshaft is accomrnodated by a spacer 26 of less height than the spacers 2 6betweer1'tlie other magnets. The shaftextends throughonecf-th' side walls and a handle 46 is securedf-thereto. Rotation of the'handle by about 180 changesthe plate 30'from 1 magnet through the pole piece 32' work-holding to work-release position.

When the handle is in work holding position andno work is on the. chuck, the flux path is generally as indi-] cated by the dash line A in Fig. 2 namely, from a above it, thence into thev active strip 18 immediately above the magnet, through the intermediate bar or strip 18; then into the next active strip 18 and downthrough the pole piece and the .magnet immediately thereunder, and into the basejto complete the circuit. (Some leakage also occurs through the spacers 36 of the plate 30.) When a piece of work 50 is placed on the chuck, thefflux paths are as shownf diagrammatically at B and C. The path B; shows that? some of 'thefiux passes through thework at-two spate-a points and also passes through an intermediate bar 18 of the top plate; thus the stitching effect familiar in electromagnetic chucks is obtained. This efiect has been found advantageous, particularly in holding thin or irregular work pieces; for example, iwth a thin work piece, such as. a piece of sheet metal, little or none of the flux would follow a path like that shown at C, and fine division of the top plate results in holding the work fiat against the chuck. (In order to avoid confusion in the drawing, the return paths through the magnets are not shown for B and C.)

To release the Work, the neutralizing plate is simply moved into its position wherein each pole piece 32 spans two magnets, as shown in Fig. 3.

. Magnetization of .the magnets is preferably carried by the process described in conjunction with Figs. 4 and 5. Although permanent magnet chucks with magnets of alternating polarities have been suggested, the magnetization has presented some difficulty. Previously magnetized magnets cannot be used because they will have been stabilized against air gaps longer than those to which they will be subjected in service. Therefore it has been customary to use magnets alternating with magnet conductors, and the entire chuck has been magnetized at once, with all magnets of the same polarities, thereby reducing by half the volume of magnet material that might be accommodated in the available space.

'According to the method shown in Figs. 4 and 5 hereof, the magnets are magnetized one pair at a time. The method is carried out with the base 14, the magnet pack and the plate 30 in position. The magnetizing apparatus comprises a head having a heavy core 46 energized by a winding 48. Shoes 50 of magnetic conducting material ,are, connected with pole pieces 52 which are adapted to engage accurately with two of the bosses 38 on the plate 30 above two adjacent magnets 24. The pole pieces 52 may be made changeable in order to accommodate chucks with top plate bars of different sizes and spacings. The coil is then energized, thereby energizing the magnetic material of the two magnets 24. The current is then turned off. 'In order to release the magnetizing head which is now magnetically held to the chuck by the magnets themselves, it is only necessary to slide the plate 30 to a position in which one of the pole pieces 32 spans the two magnets as shown in Fig. 5. The head may then be raised, as indicated in Fig. 5. The neutralizing plate 30 is moved back toits original position over the magnets,

and the chuck parts are slid to the left, to bring the next' two magnets 24' under the magnetizing head. By this method magnets are not at any time subjected to air gaps any longer than the leakage gaps represented by the spacers 36, which are substantially the same as the gaps to which they will be subjected in service.

After magnetization, the top plate 22 and the side and end walls, are fixed to the chuck, and it is then ready for service.

g In Fig. 6, I show a modified construction in which a neutralizing plate 30 is not provided with bosses but is of uniform height; that is, the pole pieces 32 engage the underside of the top plate and each spans the distance between the approximate centers of two adjacent inactive bars of the top plate, when the chuck is in holding position. Release of the work is effected by moving the top plate 30 so that the spaces between adjacent pole pieces 32' overlie the magnets, in the same manner as in Fig. 3. T heconstruction of Fig. 6 is simpler to manufacture than that of Fig. 2 and is especially suitable when the parts are of considerable size. On the other hand, when the conducting strips 18 are narrow .and .the magnets are correspondingly small, the boss construction of Fig. 2 is preferred because of the smaller amount of leakage flux.

The construction indicated in Fig. 6 is, in principle,

adaptable to a rotary chuck of the type shown in Fig. 7,v in which the top plate 54 is circular. The top plate isprovided with a number of inserts 56 of magnetic mate- 4 rial, separated from the top plateproper by non-magnetic spacers 58. As shown in Fig. 7 there are twelve inserts 56. The width of each insert 56 with its spacer 58 is approximately the same as the size of the sector of the top plate lying adjacent the spacer members.

Each insert 56 may be termedan active pole of the top plate corresponding to the active bars of Fig. 2, in that each pole piece 56 overlies a magnet 60.

A neutralizing plate 62 is interposed between the magnet 60 and the top plate. The neutralizing plate 62 comprises a rotary plate having sectors 64 each of the same angular width as one of the insert sectors of the top plate. The sectors of the rotary neutralizing plate are separated by non-magnetic spacers 66. In Fig. 7 the parts are shown in holding position. Angular motion of the neutralizing plate by about one-half the width of each magnet effects neutralization. The work is released by rotat ing the neutralizing plate 64 by a suitable cam means similar to that shown in Fig. 2 but not repeated in Fig. 7.

The chucks of Figs. 6 and 7 may be magnetized in identical fashion to those previously described by following the steps indicated in Figs. 4 and 5.

Having thus described the invention, I claim:

1. A permanent magnet work-holding device compris ing a top plate having a plurality of active pole pieces and spacers of non-magnetic material interposed between the pole pieces, a plurality of permanent magnets disposed below the top plate in spaced relation to each other and to the underside of the top plate with the axes of the magnets substantially perpendicula to the top plate and with the top ends of the magnets in alternately N and S relation, the direction in which the magnets are spaced corresponding to the direction in which the pole pieces of the top plate are spaced, the magnets having a centerto-center spacing corresponding substantially to the center-to-center spacing of every second pole piece of the top plate, and control means for said magnets intermediate the top ends of the magnets and the underside of the top plate, said means comprising an array of spaced magnetically-conductive elements, having a center-to-center spacing corresponding to the center-to-center spacingof the magnets, and means for effecting relative movement between the magnets and said array of conductive elements from a work-holding position in which each element of the array is in flux-conductive relation between a single magnet and a pole piece of the top plate to a release position in which each element of the array spans the unlike poles of two adjacent magnets.

2. Apparatus according to claim 1 wherein the magnetically-conductive elements of the array have magnetcontacting faces that are wider than the magnets.

3. Apparatus according to claim 1 wherein the magnetically-conductive elements of the array have magnet contacting faces that are wider than the magnets but have a width less than the center-tocenter spacing of adjacent magnets. v

4. Apparatus according to claim 1 wherein the top of each magnetically-conductive elements of the array has a surface contacting the underside of the top plate, said surfaces each having a width corresponding approximately to the width of a pole piece of the top plate.

5. Apparatus according to claim 1 wherein the magnets are fixed in position and the array of spaced magnetically-conductive elements is bodily movable relative to the magnets and to the top plate.

References Cited in the file of this patent UNITED STATES PATENTS Simmons May 18, 1943