US2376150A - Magnetic device - Google Patents

Description

y s. KARASICK 2,376,150

MAGNETIC DEVICE Filed Sept. ,6, 1940 3 Sheets-Sheet 1 FIG. 3

-/NVENTOR sA/gga KARASi/CK AT mvsv May 15, 1945. s. KARASICK MAGNETIC DEV CE Filed Sept. 6, 1940 3 Sheets-Sheet 2 lA/l ENTOR SAMUEL KARAS/CK BY ,0 v ATTORNEY s. KARASICK 2,376,150

MAGNETIC DEVICE Fild Sept. 6, 1940 s Sheets-Sheet 3 INVENTOR SAMUEL KARAS/CK Ill 17! IV/m ' [III-[Ill t at - May 15, 1945 A T TORNE Y Patented May 15, 1945 UNITED STATES PATENT OFFICE MAGNETIC DEVICE Samuel Karasick, Mount Vernon, N. Y. Application September 6, 1940, Serial No. 355,663

18 Claims.

This invention relates to magnetic devices and more particularly to magnetic devices employing permanent magnets to produce a magnetic field which can be controlled as to sign and magnitude. Such devices can be utilized for a variety of purposes, such as magnetic chucks or magnetic coupling units.

.In magnetic work holding devices of the type heretofore known, the magnetic holding circuit through the work-holding surface has "been rendered ineffective by diverting or shunting the flux therefrom, without any alteration of the reluctance ofthis circuit. This method of operatlon has the disadvantage that a powerful magnetic attraction must be overcome when the flux short-circuiting members are shifted so as to open the shunt circuit. This method also has the major disadvantage of leaving an appreciable flux through the work-holding surface, if the work is of high remanence. It is true that when a magnetic holding device of this sort is fully covered by a work-piece or pieces of high permeability, the reluctance of the holding circuit established through the work, is not very much greater than that through the shunt path. Thus the force required to overcome the mentioned attraction is reduced, as the change in total flux across the surfaces of the flux-producing poles is small. However, if flux is to be diverted from the work,

there must be a reluctance change, and therefore a mechanical force of considerable-magnitude is required to effect this change.

In the present invention, on the contrary, there is no short-circuiting or shunting of the flux since the magnetic circuit is effectively opened by increasing its reluctance so that no flux-diverting means are needed to bridge the adjacent poles of the magnets. This arrangement results in no appreciable increase in the total average amount of force required to shift the flux-carrying members, as compared to a lightly loaded device of the type already known. This follows because in the flux diverting chuck unless com pletely filled with work, asubstantialicrce is required to open the shunt or diversion paths in going from the off to the on position, which is as great as the force to be overcome in the chuck which is the subject of this invention, in opening the flux paths broken in passing from "On to off. However, to enable the principles of this invention to be applied to work holding devices, or magnetic coupling units of sub stantial size, I have provided power-operated means for effecting this shiftingof the flux-carrying or generatl'ngmembersf These power-operated means have specific features adapting them for use in connection with flux reversing devices, in which means for flux reversal and notmerely for flux diversion, are provided, as for example, in the magnetic chuck of the U. S. Patent #1187240 granted to Samuel Karasick.

In addition, the novel construction of the present invention greatly reduces the residual flux through'the work-holding surface particularly in the case of work material having high remanence and this residual magnetism may be annulled by a reverse flux.

The various features and advantages of the invention will appear more fully from the detailed description and claims when taken with the drawings in which:

Figs. 1 to 4 are diagrammatic showings useful in explaining the principle of the present-invention; wherein Fig. l is a diagrammatic showing of a fragment of a magnetic chuck illustrating a simple magnetic circuit therein; while Fig. 2 is a diagrammatic showing of an analogous electrical circuit corresponding thereto, and wherein Fig. 3 is a diagrammatic showing of a magnetic chuck provided with an auxiliary flux diverting path corresponding to prior magnetic chucks of the permanent magnet type, while Fig. 4.- is'a diagrammatic showing of an analogous electrical circuit corresponding to the magnetic circuit of the device of Fig. 3;

Fig. 5 is a diagrammatic showing of a fragment of a permanent magnetic chuck in accordance with the present invention, the chuck being illustrated in its flux-interrupted condition; while Fig. 6 is a diagrammatic showing of an electrical circuit analogous to the magnetic circuit-of the device illustrated in Fig. 5;

Fig. 7 is a diagrammatic showing of an electrical circuit analogous to the magnetic circuit of the device illustrated in Fig. 3 :but including a fac-.

tor corresponding to remanence;

Fig. 8 is a diagrammtaic showing of an electrical circuit analogous to the magnetic circuit of the device of Fig. 5 but likewise including the factor of remanence;

Figs. 9 and 10 respecitvely are a plan view and a side elevation ofone form of the chuck of the present invention, certain parts thereof bein broken away for clearness in illustration;

Fig. 11 is a vertical section thru this chuck taken substantially on the line H--ll of Fig, 10;

Fig. 12 is a fragmentary side elevation similar to 'Fig. 10 except that the pclesof the chuck are 55 illustrated in a neutralizing position;

Fig. 13 is a fragmentary side elevation similar to Figs. 10 and 12 except that the poles of the chuck are illustrated in a flux reversing position.

Referring especially to the diagrammatic showing of a portion of the chuck in Fig. 1, the character I designates a bottom plate of ferromagnetic material on which plate there is movably supported in spaced relation, an upwardly projecting permanent magnet 2, and a return yoke 2a. The upper or free ends of this permanent magnet and of this yoke are in close engagement with a work table T including pole pieces 3, 3, separated by an insulating spacer 4 of a width corresponding to the space between the magnet 2 and the yoke 2a. A work-piece 5 is shown bridging the two pole pieces 3, 3. The flux from the free end of the permanent magnet 2 will pass thru the work support by various paths 6, 1 and 8 of which path I, passing thru the work piece, represents useful flux.

Since the flux: distribution thru a magnetic device is frequently more easily understood if translated into an analogous electrical network, the magnetic circuit of Fig.1 has therefore been diagrammatically represented in Fig. 2, as a corresponding electrical network. Although it is true that magnetic and electrical circuits dilfer in several fundamental respects, yet it is well known that the laws of magnetic flux distribution and the laws of electric current flow, are mathematically alike so long as there are no magnetic saturation effects. Furthermore, the electrical analogy is rigorously accurate, if the networks are properly chosen.

In the electrical network of Fig. 2, the battery 9 corresponds to the magnetomotive force of the permanent magnet 2. The internal resistance of the battery 9 is represented by the resistor I and the parallel resistances H, [2 and I3 are the electrical analogue of the reluctance of the bottom plate I, the magnet 2 and the return yoke 2a. In this diagram, the resistor H is the electrical analogue of the flux leakage path 6 while the resistor I2 is the electrical analogue of the path 1 thru the work piece and the resistor I3 is the electrical analogue of the leakage path 8 in Fig. 1. The distribution of flux in the circuit of Figure 1 can bereadily seen from the analogous electrical circuit of Figure 2, in which the current corresponds to the flux of Figure l, and which can be determined by the well-known methods of circuit analysis, such as the application of Kirchoffs laws.

I the diagram of Fig. 3 the bottom plate I, the permanent magnet 2 and the return yoke 2a have been shifted with respect to the top plate T so that the return yoke 2a bridges two adjacent pole pieces 3, 3. With the several parts of the chuck in this flux-diverting position, there will be a flux path l traceable from the bottom plate I, magnet 2, lefthand pole piece 3 and the return yoke 2a. A branch 14 of this flux path extends from the free end of the permanent magnet 2, left hand pole piece 3, workpiece 5, righthand pole piece 3 and thence thru the return yoke 2a. Similarly, there will be leakage flux in a branch path represented by the dotted line ll. There is also a flux path due to remanence represented by the line l8, which path extends from the yoke 2a, righthand pole piece 3, the work 5, lefthand pole piece 3 and thence to the yoke 2a.

In Fig. 4 wherein tit electrical analogue of this-magnetic circuit is represented, the resistor 20 corresponds to the flux path 14, the resistor 2| corresponds to the reluctance of the path l5 and the resistor 22 corresponds to the reluctance of the flux path l1. From the consideration of these two diagrams, it will be seen that there will not be zero flux in path M which corresponds to resistor 20. However, this diversion of the flux by the path I5 may be likened to an electrical attenuator producing loss by a low impedance shunt member such as 2!, which effects a short-circuit or diversion of the current. Thus in the arrangement of Fig. 3, the flux path I5 is of low reluctance and the resistor 2! of Fig. 4 must be considered of a low .value which substantially shunts or short-circuits the resistor according to the flux path 15 of Fig. 3 as well as the resistor 22 corresponding to the flux leakage path ll.

In the diagram of Fig. 5 there is represented the flux-reversing arrangement of the present invention as distinguished from the flux-diverting arrangement illustrated in Figs. 1 and 3. In the arrangement of Fig. 5, two shiftable permanent magnets 2, 2 with a common interposed return yoke 2a are supported in spaced relation on the bottom plate 5. In this arrangement, the top plate T is illustrated as having four pole pieces 3, 3 of which the two end pole pieces are shown as partially broken away. As in the arrangement previously described, the pole pieces are separated by pieces of insulating material 4. It will be noted however, that the cross section of the pole pieces 3, 3 has been modified in that the upper surfaces of these pieces are much wider than the lower surfaces thereof. However, the width of these lower surfaces of the pole pieces 3, 3 are so related to the spaces between the magnets 2 and the return yoke 2a as well as the width of the upper end surface of these parts, that in the releasing position of this magnet as illustrated in Fig. 5, the magnets 2, 2 and the return yoke 2a engage only the insulating pieces 4 with substantial air gaps 24, 25, 26 and 2'! between the ends of these parts and lower ends of the pole pieces 3.

In the electrical analogue of this chuck illus* trated in Fig. 6, the magnetomotive forces of the magnets 2, 2 are represented by the batteries 9 and 9a, while the resistors 30 and 3! represent the internal reluctance of magnets 2, 2. The resistances in the network of Fig. 6 and the corresponding reluotances in the magnetic arrangement of Fig. 5 are shown in the following table:

Now if. 32 and 33 are equal, and 34 and 35 are equal in the network of Fig. 6, no current will flow in resistor 38. Consequently resistor 33 will be conjugate to batteries 9 and ta. However, if the flux in paths 48 thru the work piece 5 do not neutralize or if the current in resistor 33 is not zero, this condition can be secured by unbalancing the resistances previously assumed to be equal. Furthermore, current can be made to flow in either direction in resistor 38 by slightly unbalancing the network in either sense, corresponding to a small movement one way or the other from the exact centering in Fig. 5. It

count.

should be observed that in the arrangement of Fig. 5, fiuxis not diverted, but instead two equal and opposite fluxes in paths 48 balance each other thereby producing zero resultant flux.

However, the arrangements illustrated in Figs. 1 to 6 inclusive are not strictly complete since no proper recognition is given therein of some of the properties of actual ferromagnetic materials and particularly of that property known as retentivity, whereby any ferromagnetic material retains some degree of flux when once magnetized. This property does not lend itself well to representation in an electrical analogue, yet an approximation thereto may be represented by introducing sources of voltage into an electrical network corresponding to those ferromagnetic portions of the magnetic circuit having appreciable retentivity. To be strictly accurate, the pole pieces should be assumed to have some remanent flux, yet this has been ignored since it has been assumed that ,all of the remanent flux is concentrated in the work piece. This approximation. is justified in magnetic chuck applications since in these cases the work piece may have very high remanence, being of hardened steel or the like, while the pole pieces 3, 3 are of magnetically soft iron material, the remanence of which is negligible compared to the work piece.

Figure 7 shows the electrical analogue of the chuck of Fig. 3' when this factor of remanence is taken into account. And Figure 8 likewise shows the electrical analogue of the chuck of Fig. when this factor of remanence is taken into ac- An examination of Fig. '7, shows that this remanent flux, here represented by the current due to source of the electromoti've force 50, will produce a substantial flux represented by current 5i in the path through resistors 52 and 53 corresponding to flux in path It of Fig. 3.

Similarly in Fig. 8, a battery 54 corresponds to the remanent flux but the flux due thereto is greatly reduced by the presence in the circuit network of the resistors 34 and 35 corresponding to the high reluctance of the air gaps 26 and 21,

so that even without reversal the remanent flux to a shift with respect to the table T, of the movable parts of the chuck including the magnets 2, 2 and return yoke 20., past the neutral position in Fig. 5, which is the zero flux condition when path 38 and sources of current 9 and 9a. are conjugate. It is this residual flux which-I have overcome by reversing features shown in U. S. Patent #2,187,240 and which I overcome still more effectively by the means of the present invention.

When a chuck constructed according to the principles of this invention is tested, it is found that the resistance to the mentioned shifting of the said movable parts, is not materially different from that of a chuck of the conventional type, as represented in Figs. 1 and 3, except that as the position of Fig. 5 is approached, there is a sudden slight increase in the resistance to motion, so that ordinarily an operator will overthrow beyond the balanced or neutral position in shifting the magnets. 2 and yokes 2a with respect to the table T. Yet it is precisely at this point beyond the neutral position that a hardened steel workpiece releases. The flux reversal rather than annulment or neutralization is responsible for release of the work, may be shown by the adhesion of a soft iron test piece, if applied, to the table after the hard steel test piece has been removed.

The principle of the invention set forth above is adaptable to various applications, for example, the invention may be incorporated in a permanent magnet type of chuck as disclosed in Figs. 9 to 12 inclusive. This chuck is shown as incorporated in a surface grinding machine of the well-known type including a frame which carries a table 55 adapted to be reciprocated longitudinally thereon at right angles to the axis of a grinding wheel (not shown), by a motor 51 of any suitable type, such as a hydraulic motor operated by oil under pressure as more fully disclosed in U. S. Patent #2,161,2l6 issued to W. H. Wood. The magnetic assembly of this chuck is mounted for reciprocation, with the table, along the longitudinal axis of the chucks work support and the table as will be more fully set forth. The present chuck forms a part of the table of the grinder thereby obviating the need of clamping the chuck to thetable. It will be appreciated that. where the chuck is clamped to the table, strains are introduced into the work surface of the chuck so that it is necessary to grind it in order to have a true surface for supporting the work to be ground.

The chuck comprises a hollow, open-topped, rectangular casing 58 cast integral with the table 56 from suitable non-magnetic material such as aluminum or the like. This casing houses a movablemagnetic assembly of the chuck as well as a hydraulic motor for reciprocating the same. The grinder frame 55 is provided with spaced longitudinal guide ways 60 and BI (Fig. 11). These guide ways receive the spaced ways 63 and 64 integral with the table and extending parallel to the long sides of the casing along the lower corners thereof. A ferromagnetic bottom member 65 of approximately the width of the space within the casing and of a length approximately equal to the holding portion of the chuck, is fixed to the inner bottom surface of the left end portion of the casing as viewed in Figs. 9 and 10, being magnetically insulated therefrom by brass washers 65, if the casing is made of magnetic material. member 65 is accurately ground smooth for a purpose to be set forth. The bottom member slidably supports the magnetic assembly which includes upwardly extending permanent magnets 6! or other unidirectional flux producing members formed preferably of an alloy known as Alnico, and upwardly extending soft iron yokes. 68, one yoke being interposed between each pair of 'magnets. The yokes and magnets are separated by non-magnetic spacers 69 being clamped in this relation by the by the clamping bolts Ill, to complete the magnetic assembly, the lower surface of which is ground smooth to slide on the smooth upper surface of the bottom member with a negligible air gap therebetween. It will be understood that the magnets extend transversely of the casing and are approximately equal in length to the width of the space therein. The magnets 61 are so arranged that their upper ends constitute north poles while the upper ends of the yokes BB interposed therebetween constitute south poles. Thus the yokes and the bottom member constitute return flux paths for the lower ends or south poles of the Alnico magnets. The magnets are tapered at their upper ends and they are made relatively short due to the high reluctance of Alnico which necessitates that the magnets be about three times as large in The upper surface of the bottom cross section as the return yoke (Figs. 10 and 12). It is preferred to make the tapered upper ends of the magnets 61 of separate pieces of soft Norway iron brazed to the Alnico portions of the magnets proper. This construction is indicated in Figs. 10, 12 and 13 by the cross-hatching of the magnet. It will be understood that this use of soft iron results in increased holding power over the construction where the tapered portions of the magnets are also made of Alnico.

The top of the chuck portion of the casing is closed by a top plate or work table T, this table being adapted to be secured to the upwardly extending sides of the casing by suitable fastening screws 12. The table T as well as the pole pieces 13 mounted therein are made of ferromagnetic material, preferablylaminated, to constitute polepieces. These pole-pieces extend transversely of the top plate, being spaced from each other by suitable non-magnetic material cast therein. The space between the lower surfaces of the polepieces is equal to the space between the magnets 61 and the yokes 68. The pole pieces are of the cross section illustrated in Figs. 10 and 12, having relatively wide upper surfaces but relatively narrow lower surfaces substantially equal to the width of the upper surfaces of the yokes and the upper surfaces of the tapered magnets. lit will be understood that this cross-sectional shape of the pole-pieces 13 reduces flux leakage across the space between the pole-pieces and causes a greater part of the flux due to the permanent magnets to issue from the upper or work-holding surface of the top plate. The lower surfaces of the pole-pieces, as well as the upper surfaces of the magnets and yokes, are accurately ground so that there is a negligible air gap between these par s.

The right end of the magnetic assembly as illustrated in Figs. 10 and 12 has fastened thereto by the clamping bolts, a plate 15 to which there is secured the piston rod 16 carried by the piston ll of a hydraulic motor 79. This motor is housed in the right hand portion of the casing 58,

being covered by a top member 88, which with the table T completes the closure of the casing. The plate '15 also supports a valve actuating rod 8i which rod is provided with a lug 82 extending into a notch 83 in the valve stem 84 of a suitable slide valve mechanism SV. The slide 5 valve mechanism includes a hollow cylindrical member 85 within which the valve stem 84 reciprocates with a close fit. The cylidrical member has oil ports 8'1 thru which oil is supplied to the motor 'i' 9 under the control of the valve stem 84. I

The valve stem which is rotatable by the handle 88, is cut away to provide passages 39 partially encircling the stem but leaving parts 90 of its surface intact. The parts 91 close the oils ports 81 on the oil supply side when the handle 88 is rotated from the motor-operating position shown in Fig. 9 to the motor-stopping position. This hydraulic motor with its slide valve mechanism may be similar to that disclosed in the mentioned Patent #2161216.

In the operation of this motor, oil. under pressure is supplied thru the oil line 9! and passes thru either the branch pipe Qla or the branch pipe 9H), under the control of the slide valve mechanism SV, either to the right hand surface or to the left hand surface of the piston 11 depending on the position of the slide valve. The oil ahead of the piston flows away thru the exhaust pipe 92. Thus when the oil is supplied thru the branch Bid to the left hand face of the piston, it moves toward the right of Fig. 9 carrying with it the magnetic assembly of the chuck. When the piston reaches the right hand end of its stroke, the lug 82 on the actuating rod 81 moves the slide valve mechanism so that oil is now supplied through the branch pipe 91b to the right hand surface of the piston. The piston as well as the magnetic assembly are then moved toward the left until the lug 82 on the actuating rod 8!, shifts the slide valve so that oil is now introduced into the motor thru the branch pipe am. This reciprocation of the motor and the magnetic assembly is continued until the handle or throttle 88 is positioned to shut off the oil supply from both surfaces of the piston, thereby stopping its operation, It will be appreciated that the handle controls the slide valve to open or close the oil supply lines. This permits the stopping of the motor at any point in its travel. It will be understood that when the motor has shifted the magnetic assembly to the position illustrated in Fig. 9, the chuck is in a condition to retain work thereon. However, when the handle 88 is moved to a position so that the magnetic assembly is reciprocated by the hydraulic motor "l9 between the position shown in Fig. 9 and the position shown in Fig. 13, the flux through the work piece will be alternately reversed with an interval of complete neutralization between each reversal. This interval of complete neutralization occurs when the magnetic assembly is in substantially the position shown in Fig. 12. During this reversal of the flux thru the work piece, this piece is withdrawn from the table of the chuck along the top surface thereof.

What I claim is:

1. In a device of the class described, a unit having spaced pole pieces of ferromagnetic material supported thereby, a magnetic unit including a ferromagnetic piece and a series of spaced permanent magnets as well as spaced ferromagnetic yokes in alternate relation supported on said piece with the spacing between the magnets and the yokes being such that one of said units is positionable with respect to the other unit in each of three different positions, in the first p0- sition of which a magnet contacts each alternate pole piece and a yoke contacts each of the remaining alternate polepieces, in the second position of said last-mentioned unit each magnet and yoke is in operative relation to the next adjacent space between said polepieces with substantial air gaps between said polepieces and said magnets as well as said yokes, and in the third position of said last-mentioned unit each magnet and yoke is in contact with the next adjacent polepiece, and means for moving said last-mentioned unit thru said second position to each of said first and third positions alternately.

2. In a device of the class described, a unit having spaced pole pieces of ferromagnetic material supported thereby, a magnetic unit including a ferromagnetic piece and a series of spaced permanent magnets as well as spaced ferromagnetic yokes in alternate relation supported on said piece, the cross-section of each magnet being at least twice as great as that of each yoke, the spacing between the magnets and the yokes being such that one of said units is positionable with respect to the other unit in each of three different positions, in the first position of which a magnet contacts each alternate pole piece and a yoke contacts each of the remaining alternate polepieces, in the second position of said last-mentioned unit each magnet and yoke is in operative-i relation Ito'the next: adjacent space between said polepieces .withlsubstantial air gaps between 'saidpolepiece's and said magnets as well as said I yokes, and in the third position of said last-mentioned unit each magnet and yoke is in contact with the next adjacent polepiece, and means for moving said last-mentioned unit thru said secend position to each of said'first and third positions alternately.

3. In a device of the class described, a unit having spaced pole pieces of ferromagnetic material supported therein with at least their inner surfaces exposed, said spaced polepieces being of equal widths, a magnetic unit including a ferromagnetic piece and a series of spaced permanent magnets of high coercive force alternating with a series of spaced ferromagnetic yokes, both of said seriesbeingmagnetically connected to said ferromagnetic piece and extending lengthwise in a direction whereby said yokes can contact the mentioned surfaces of certain of said pole pieces, said permanent magnets being shorter than said yokes' and of greater width than said pole pieces, and tapered soft iron pole pieces attached to said permanent magnets and being of a length to con tact'with the inner surfaces of the remainder of said first mentioned pole pieces, each of 'said soft iron @polepieces being wider at its surface or attac hme'nt to its magnet than at its surface of engagement with the inner surface of one of said first mentioned pole pieces.

4'. In a' device of the class decribed, a unit havingspaced pole pieces of ferromagnetic material supported therein with their inner and outer surfaees exposed, said spaced pole .pieces being of equal widths, a magnetic unit including a ferromagnetic piece and a series of spaced permanent magnets of high coercive force alternating with a series ofspaced ferromagnetic yokes, both of said series being magnetically connected to said fferromagneticpiece and extending lengthwise in a direction whereby said yokes can contact the inner surfaces of certain of said pole pieces; said permanent magnets being shorter than said yokes and of greater width than said pole pieces, and tapered soft iron pole pieces attached to said permanent magnets and being of a length to.

and of said yokes being less than the Width of the spaces between the inner surfaces of said first mentioned pole pieces.

5. In a magnetic device, a body containing spaced flux-carrying members of equal width, and a, movable unit provided with a plurality of flux-producing members comprising spaced permanent magnets alternating with spaced soft iron members, said unit being movable to bring said flux-producing members into contact with said flux-carrying members to develop a holding condition and being movable to a position out of contact therewith to introduce a high reluctance gap between said flux-producing members and said flux-carrying members.

6. In a magnetic device, a body containing equally spaced flux-carrying members of equal width, and a unit provided with a plurality of flux-producing members comprising spaced permanent magnets alternating with spaced soft iron members, each of said magnets terminating in a fuzz-concentrating piece of relatively low reluctance attached thereto, said pieces and said members being movable into contact with. said flux-carrying'members to develop a holding condition and being movable to a position out'of contact therewith to introduce a high reluctance gap between said flux-producing members and said flux-carrying members.

7.111 a magnetic device, a work-holding unit consisting of a series of equally spaced fluxcarrying members mounted in non-magnetic material and adapted to support a work piece across certain of said membersa series of flux-producing members comprising a plurality of permanent magnets and return yokes with a member of one series positionable in contact with a member of the other series in the work holding position, said magnets and return yokes being spaced whereby there exists therebetween a leakage path of invariable reluctance greater than that of the flux path through a work piece engaging said mem bers when the flux producing members are in the work holding position, and means for shifting said flux-producing members relative to said fluxcarrying members to effectively increase the reluctance of the flux path through said work piece and'through said flux-carrying members'to an amount greater than that of the invariable leakage pathaforesaid.

8. In a magnetic work-holding device, a workholding unit comprising equally Spaced fluncarrying members of high permeability, nonmagnetic material surrounding said members, fluxproducing members including a plurality of permanent magnets and cooperating parts spaced to provide at least one invariable flux path including non-magnetic material, and means adjustable at will to bring said flux-producing members into engagement with said flux-carrying members to provide a flux path of high density through said flux-carrying members as well as through work supported thereon and alternatively to reduce the flux in said lastmentioned path to a low value while simultaneously increasing the flux in said invariable path.

Q. In a magnetic device, a body containing equally spaced flux-carrying members, a second body containing flux-producing members having unlike poles and spaced to afford invariable flux paths between unlike poles of said flux producing members, means for bringing the flux-producing members of the second body and the flux-carrying members of the first body into engagement, said flux-carrying members being adapted to engage a ferromagnetic work piece to produce a path of low magnetic reluctance through said work piece, and means for increasing the reluctance of said last mentioned path to a valuein excess of that in the invariable flux paths aforesaid.

10. In a magnetic device, a body containing equally spaced flux-carrying members of uniform width, a unit comprising flux-producing members including permanent magnets, each magnet having attached thereto a flux-concentrating part made of soft-iron, said parts being positionable into engagement with said fluxcarrying members respectively, and means for displacing said unit to introduce high reluctance gaps between saidfiuX-concentrating parts and said flux-carrying members.

11. In a magnetic work-holding device, equall spaced flux-carrying member of uniform width adapted to engage a ferromagnetic Work piece, flux-producing means including permanent magspaced flux-carrying members of uniform Width adapted to engage a ferromagnetic work piece, permanent magnets terminating in integral fluxconcentrating members adapted to engage said flux-carrying members, and means for disengaging said flux-concentrating members from said flux-carrying members, whereby the flux produced by the permanent magnets is caused to pass independently of said Work piece and of said flux-carrying members through a path of reluctance exceeding that of the path through the work piece when said flux-carrying and flux concentrating members are in engagement, but of less reluctance than the path through the work piece when the members aforesaid are disengaged.

13. In a magnetic work-holding device, equally spaced flux-carrying members of uniform width adapted to engage a ferromagnetic work piece,

permanent magnets respectively terminating in integral flux-concentrating members and adapted to engage said flux-carrying members, and means for disengaging said fluxconcentrating members from said flux-carrying members. whereby the flux path through the work is effectively interrupted. said flux returning through a leakage path independent of said flux carrying members and work piece.

14. In a device of the class described, equally spaced flux-carrying elements of uniform width arranged to support a ferromagnetic work piece, flux-producing members respectively engaging said elements to develop at least one flux path through said work piece, said members being arranged to have a leakage path between opposite poles thereof, and means operable at will in the flux path through said work piece to impede the passage of flux therethrough while the reluctance of said leakage path remains substantially constant.

15. In a device of the class described, a memher having equally spaced pole pieces of ferromagnetic material supported thereby, said pole pieces having substantially equal dimensions, a movable magnetic assembly including a ferro magnetic member and a series of spaced permanent magnets as well as spaced ferromagnetic yokes supported on said member in alternate relation for cooperation with said pole pieces, said permanent magnets being of a width, namely in the direction in which said assembly is movable, several times that of said ferromagnetic yokes, and tapered end parts of ferromagnetic material attached to said permanent magnet members and adapted to contact the lower surface of said pole pieces, the contacting ends of said parts being substantitally equal in width to that of said yokes, this width bein less than that of the spaces between the lower surfaces of said pole pieces.

16. In a device of the class described, a unit having a series of spaced ferromagnetic members non-magnetically mounted therein carrying flux from one surface of the body to the other, said members having substantially equal dimensions but being Wider at the top face of said unit than at the bottom surface thereof, the width or said members at said top face being greater than the spaces therebetween at said face while the width of said members at said bottom surface is substantially less than the spaces therebetween at said surface, and sources of magnetic flux assembled in a movable unit adapted to engage the bottom surface of said unit, the Width of each of said flux sources in the direction of motion being substantially equal to the width of the ferromagnetic members at the bottom surface of said uni 17. In a magnetic device, a body containing equally spaced flux-carrying members, a second body containing fiux-producing members having unlike poles and spaced to aiford invariable flux paths between unlike poles of said flux producing members, means for bringing the flux-producing members of the second body and the flux-carrying members of the first body into magnetic relation, said flux-carrying members being adapted to engage a ferromagnetic work piece to produce a path of low magnetic reluctance through said work piece, and means for increasing the reluctance of said last-mentioned path to a value in exccess of that in the invariable flux paths aforesa1 18. In a magnetic work-holding device, equally spaced flux-carrying members of uniform Width adapted to engage a ferromagnetic workpiece, permanent magnets respectively terminating in integral flux-concentrating members and adapted to be magnetically connected with said fiux-carrying members, and means for magnetically disconnecting said fiuX-concentrating members from said flux-carrying members, whereby the flux path through the work is effectively interrupted, said flux returning through a leakage path independent of said flux carrying members and work piece.

SAMUEL KARASICK.

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