US3039026A

US3039026A - Magnetic chuck

Info

Publication number: US3039026A
Application number: US820792A
Authority: US
Inventors: George N Levesque
Original assignee: Brown and Sharpe Manufacturing Co
Current assignee: Brown and Sharpe Manufacturing Co
Priority date: 1959-06-16
Filing date: 1959-06-16
Publication date: 1962-06-12
Anticipated expiration: 1979-06-12

Description

June 12, 1962 G. N. LEVESQUE MAGNETIC CHUCK Filed June 16, 1959 1722@ #haar HMI United States Patent O 3,039,026 MAGNETIC CHUCK George N. Levesque, Warwick, RJ., assignor to Brown & Sharpe Mfg. Co., Providence, RJ., a corporation of Rhode Island Filed June 16, 1959, Ser. No. 820,792 4 Claims. (Cl. 317-159) The present invention relates to magnetic chucks and more particularly to a magnetic chuck having a finely divided work holding surface `adapted for the holding of thin stock.

It is a principal object of the invention to provide an improved magnetic chuck in which the magnets and pole pieces together with the magnetic inserts and spacing elements of the chuck work holding plate assembly are so constructed and arranged las to provide a holding surface adapted for holding very thin stock which may be of as little as .001" to .001 in thickness with a greater degree of firmness and tenacity than heretofore considered possible.

It is another object of the invention to provide an irnproved magnetic chuck of this general type having a finely divided magnetic surface in which the holding power provided by the magnetic flux acting upon thin stock is of a uniformly high strength over the entire work surface of the chuck.

With these and other objects in view, a feature of the invention consists in the improved construction and arrangement of the magnets, pole pieces, magnetic inserts, and spacer elements of a magnetic chuck `to provide for a very fine division of the magnetic areas and intervening nonconducting spaces together with an even distribution and maximum flow ofthe magnetic ux over the entire surface.

More specifically, a feature of the invention consists in the provision of a chuck having at least -two magnetic poles of opposite polarity, with work holding pole pieces sharply tapered from a root area of massive cross section at the underside of the work holding plate assembly to a small apex at the work face of the chuck, in combination with a series of downwardly tapered magnetic inserts together with their intervening spacers, said magnetic inserts and the apex portions of said pole pieces being so constructed and shaped as to provide a series of substantially equal work holding magnetic areas over the entire work holding surface of the chuck including specifically those adjacent to and overlying said pole pieces.

With the above and other objects in view as may hereinafter appear the several features of the invention will be readily understood by one skilled in the -art from the following description taken in connection with the accompanying drawings in which:

FIG. l is a plan View of a magnetic chuck embodying in a preferred form the several features of the invention;

FlG. 2 is a sectional View in side elevation taken on a line 2 2 of FIG. l;

FIG. 3 is a somewhat fragmentary sectional view similar to FIG. 2 but on an enlarged scale illustrating my improved construction of the magnetic work holding surface of the chuck; and

FIG. 4 is a diagrammatic view on an enlarged scale of a pole piece together with adjacent magnetic inserts and spacers to illustrate particularly the distribution of the flux from the pole piece into the adjacent magnetic spacers and into a workpiece mounted on the work holding surface of the chuck.

The invention is herein disclosed as embodied in a permanent magnet chuck of the general type having a roughly rectangular work surface comprised of a series of pole pieces spaced across the work holding surface,

ice

and a series of magnetic inserts and nonmagnetic spacers interposed between adjacent pole pieces to provide a holding surface having finely divided magnetic holding areas adapted for holding thin stock. Adjacent pole pieces are oppositely polarized by means of magnets which cause a flux to flow between the pole pieces ythrough the interposed magnetic inserts land across the many air gaps provided between the finely divided adjacent magnetic surface holding areas of the chuck.

Referring particularly to the drawings, the illustrated chuck comprises a circular casing 10 which may be of aluminum formed with a square cutout 12 to receive a rectangularly shaped chuck body, and a base plate 14 fastened to the casing 10 lby means of machine screws 16. The chuck ybody comprises an inner casing of nonmagnetic material generally designated at 18 within which are mounted four rectangularly shaped

pole pieces

20, 22, 24 and 26 which are separated -by three

magnets

28, 30 and 32 which are cross magnetized and are so arranged as to cause the

pole pieces

20 and 22 to have a north polarization and the

pole pieces

22 and 26 to have a south polarization. In the preferred embodiment of the invention shown, magnets of grain oriented barium ferrite are employed. It will be understood that the invention is not limited to the particular kind or shape of magnets employed and further that electromagnets may be substituted within the spirit and scope of the invention ifso desired.

In order to provide for a uniformly fine division of the work holding surface and at the same time to insure an even flow of the magnetic flux from one to another of the finely divided magnetic areas including particularly those disposed directly over the individual pole pieces, the

individual pole pieces

20, 22, 24, 26 are each formed with a large root area which comprises the full cross-sectional area of the individual pole piece. As shown in the drawings, the sides of each pole piece, as for example, the pole piece 22 is formed at its upper end with sloping

sides

36, 38 which form a taper starting at the underside of the work holding plate assembly and terminating in an apex 40 of small area at the work holding face of the chuck. The pole piece 24 is similarly provided with a tapered top portion comprising sloping sides 42, 44 which terminate in an apex 46 of small area at the top face of the work holding surface.

The

end pole pieces

20 and 26 of the magnet assembly are formed at their upper ends with outwardly sloping inner faces 50, 52 respectively which extend from the underside of the work holding plate assembly to an apex 5'4, 56 providing a small surface area at the work holding face of the chuck.

The portion of the work holding plate assembly between the two pole pieces 22, 24 is formed of a series of downwardly tapered magnetic inserts 58 which are separated from one another and from the tapered faces 38 and 42 of the pole pieces 22, 24 by means of thin nonmagnetic spacers 60 which are of uniform thickness and which provide suitable air gaps between the magnetic areas provided by the tip portions of the pole pieces 22, 24 and the magnetic inserts 58.

The portions of the work holding plate assembly extending between the

poles

22 and 20 and between the poles 24 and 26 are identical in construction with that portion of the work holding :surface above described and one another by identical amounts by means of said spacers 60.

The approximate dimensions of the illustrated chuck are given as follows: The three rectangular cross-magv netized grain oriented

barium ferrite magnets

28, 30 and 32 are preferably about .5 thick, the two so-ft steel pole pieces 22, 24 are approximately .3 thick, and the two side pole pieces 20, 24 will be approximately .2 thick. The magnetic inserts may, for example, have a thickness at the upper or butt end of .019" and a thickness at the bottom tip of the tapered portion thereof of .009. The length of each of the air gaps provided by the nonmagnetic spacing members are each ten thcusandths of an inch in thickness. The total air gap between adjacent polarized pole pieces is approximately .21. The dimensions above given while suitable for use in the small tine mesh chuck illustrated utilizing grain oriented barium ferrite magnets, may be varied over wide limits in accordance with the work requirements, and will depend also on the magnetic source employed. It will be understood that the invention is not limited to the construction shown and that substantial variations may be employed both in the'pattern and size of the magnets, and in the number and width of the magnetic inserts and spacers employed depending upon the use to which the chuck is to be put. In general, the beneiits of my invention will be realized most fully when at least iive or more such magnetic inserts are employed between adjacent magnet poles. In a magnetic chuck particularly adapted for the holding of very tine work pieces which may be in the order of .001 to .002 or more in thickness, a very tine division of the chuck work holding surface is to be desired.

My improved chuck work holding plate assembly hav- 'ing as component parts thereof the tapered pole pieces and correspondingly tapered magnetic inserts above described provides for a substantial increase in volume and for a more eflicient distribution of the flux channeled through the magnetic work holding surface and through the work pieces to be held thereby, particularly thin stock. It will be understood that for the holding of thin stock such as indicated at 64 in FIG. 4 a substantially uniform distribution of flux over the nely divided magnetic work holding surface is essential since a massive concentration of ilux at any particular point on the work holding surface, will result merely in the passage of the flux through the thin work without any substantial holding effect. In particular, my tapered pole piece construction provides a massive root area through which the entire amount of the flux generated by the magnetic source is readily channeled (see FIG. 4) across the magnetic inserts and intervening nonmagnetic spacers to another tapered pole piece which is similarly formed with a massive root area of suicient extent to channel the entire amount of the flux generated back to the magnetic source. With this arrangement a maximum amount of flux will be channeled through the upper or apex portion of the tapered pole piece 40 and through the intervening magnetic inserts and nonmagnetic spacers to the -apex portion 46 of the next adjacent pole piece of opposite polarity, so that each of the magnetic areas including Iboth the magnetic inserts and the apex portions of the individual pole pieces will receive substantially the same volume of magnetic flux and thus will form a very large number of magnetic holding circuits from one magnetic area to another across the intervening nonmagnetic spacers.

The invention having been described what is claimed is:

1. In a magnetic chuck having -a magnetic iiux generating means, the combination of a work holding assembly which comprises pole pieces of opposite polarity, cach of said pole pieces having a root area at the underside of said work holding plate assembly of substantial cross section sufficient for carrying a large proportion of the flux generated by said flux generating means and a tapered portion projecting `upwardly from said root portion through the work holding plate assembly terminating in a small apex `forming a portion of the work holding surface of said working holding plate assembly, and interposed between said pole pieces a series of downwardly tapered magnetic inserts providing a series of magnetic holding areas in the surface of said work holding plate assembly, and nonmagnetic spacers disposed between and separating each of said magnetic inserts and pole pieces from one another to provide magnetic flux circuits of substantially uniform maximum strength and tenacity between adjacent magnetic holding areas across the width of said Work holding assembly.

2. In a magnetic chuck the combination with a magnetic ux generating means of a work holding plate assembly comprising at least two magnetic pole pieces of opposite polarity connected with said flux generating means, each of said pole pieces having a root area at the underside of said work holding plate assembly of substantial cross section sufficient for carrying a large proportion of the flux generated by said flux generating means and a tapered portion projecting from said root portion upwardly through the work holding plate assembly and terminating in a small apex forming a portion of the work holding surface of said work holding plate assembly, and interposed between said pole pieces a series of downwardly tapered magnetic inserts, and nonmagynetic spacers disposed between and separating each of said magnetic inserts and pole pieces from one another, said magnetic inserts and the apex portions of said pole pieces being so constructed and arranged as to provide in said work holding surface a series of holding magnetic areas of substantially equal width whereby lines of flux of substantially equal density are directed from one to another of said magnetic areas comprised by said pole pieces and magnetic inserts.

3. In a magnetic chuck, the combination of work holding plate assembly comprising at least two polarized pole pieces of opposite polarity each having a iiux carrying root area at the underside of said work holding plate assembly of substantial cross section tapered upwardly to a small apex forming a surface magnetic holding area in said work holding plate assembly, and interposed between said polarized pole pieces, a series of at least `five downwardly tapered magnetic inserts providing intervening magnetic holding areas of said work holding plate assembly, and means providing nonmagnetic gaps of substantially yuniform thickness between each of said tapered magnetic inserts and said polarized tapered pole pieces, the surface magnetic holding areas of said polarized pole pieces and magnetic inserts being so constructed and arranged as to provide a series of holding surface magnetic areas of substantially uniform width to provide magnetic flux circuits of substantially uniform strength and tenacity between adjacent magnetized holding areas along lines projected from one to the other of and including the apexes of said polarized pole pieces.

4. In a magnetic chuck the combination wtih magnetic ilux generating means, of a work holding plate assembly comprising a plurality of pole pieces of alternating polarity connected with said magnetic ux generating means and spaced from one another across said work holding plate assembly, each of said pole pieces having a root area at the underside of said Work holding plate assembly of a substantial cross section suiiicient for carrying a maximum flux `generated by said magnetic flux generating means, and a tapered portion adjacent to said root area tapered upwardly to a small apex forming a portion of the surface area of said work holding plate assembly, and in each of the spaces provided between adjacent pole pieces a series of downwardly tapered magnetic inserts and nonmagnetic spacers separating each of said magnetic inserts and pole pieces from one another, the butt ends of said tapered magnetic inserts and the apexes of said polarized pole pieces appearing as magnetic holding areas in the surface of said work holding plate assembly in, L..

to provide substantially uniform magnetic flux circuits of maximum strength and tenacity between adjacent magnetized holding areas across the Width of said Work holding assembly.

References Cited in the tile of this patent UNITED STATES PATENTS 1,254,664 Downes et al Jan, 29, 1918 6 Hitchcock July 23, 1946 Simmons Jan. 25, 1955 Smit et al Jan. 13, 1959 Anderson et al Apr. 14, 1959 FOREIGN PATENTS Great Britain July 13, 1949 Belgium Sept. 27, 1954