US2138864A - Electromagnetic device and circuits for operating the same - Google Patents

Description

s. "KARASICK 2,138,864

ELECTROMAGNETIC DEVICE AND CIRCUITS, FOR OPERATING THE SAME De'z. 6, 1938.

Filed Sept. 26, 1933 INVENTOR v SAMUEL R'nzznszcx I I. (I

ATTORNEY Patented Dec. 6, 1938 UNITED STATES PATENT OFFICE ELECTROMAGNETIC DEVICE AND CIRCUITS FOR OPERATING THE SAME 12 Claims.

This invention relates to combined electromagnetic holding devices and demagnetizers as well as to the circuits for operating the same. 1

In holding devices or chucks of this character.

5 it has been customary to provide for direct current operation, and to effect demagnetization of the work on the chuck by reversing the direction of flow of current through the chuck by the use of a reversing switch, but, even by the most care-- ful manipulation of the reversing switch only partial demagnetization of the work could be effected. Where an electromagnetic chuck was used to hold work including ferromagnetic pieces, the residual magnetism of the work caused it to adhere tightly to the chuck even through the chuck windings had been deenergized and as a result the work could be removed only with great difliculty unless the reversing switch was carefully manipulated to effect a partial demagnetization. This effect was especially troublesome if the work was of hardenecl steel.

Furthermore, it has never been practicable to secure any great degree of demagnetization by this method of manual operation of a reversing switch and where the work requires complete demagnetization, it has been necessary to provide a separate device known as a demagnetizer for this purpose.

The present invention has for its purpose the construction and arrangement of an electromagnetic chuck energized either by direct current or by alternating current whereby the work may be firmly held by direct current and be completely demagnetized by alternating current. This has not been commercially practical .with chucks of the type heretofore known owing to the presence of closed loops of conducting material surround-- ing each pole of the chuck. Such loops have acted as 'short-circuited transformer windings and have effectively prevented any substantial amount of alternating magnetic flux from issuing from the poles of the chuck and passing through the work. I

It is also a purpose of this invention to provide a magnetic device which is simple to assemble, inexpensive to manufacture and reliable in operation alternatively as a chuck and as demagnet izer. Other features of this invention will appear from the following description of a preferred form thereof, together with the appended claims.

In. the drawing, Fig. 1 represents a perspective view of apreferred form of the invention with a portion thereof broken away to show the internal arrangement of the several parts;' Fig. 2 is a.

transverse cross section of the cover plate shown in Fig. 1; Fig. 3 is a perspective view of a modifled form of cover plate and Fig. 4. is a circuit arrangement including switching means by which the device of Fig. 1 can be operated either as a holding device or as a demagnetizer.

Referring to Figure 1 of the drawing, the numeral I generally designates a core. This core is built up of a plurality of laminae each of which is a stamping from any suitable ferromagnetic material in sheet form, such as Norway iron, having a body portion 2 provided with a series of integral uprights or core elements 3 and extensions terminating in lugs 4. These laminae are first shellacked or enameled and then fastened together in any well-known manner, such as by rivets, to form an integral structure. The core I when thus assembled is placed in a suitable mold or support. and a base 5 of aluminum or other suitable material is molded about the core I with the lugs 4 of the core engaged by lugs 6 which are cast integral with the base. When the base and assembled core have thus been made, each of the uprights or core elements is provided with a spool I provided with a coil or helical winding of the type well-known in the art, adapted to produce a magnetic flux in the said core when elec-- tric current flows through the mentioned winding. A suitable circuit arrangement for'energizing these windings will be hereinafter referred to. The chuck in this form is provided with a face plate on whichthe work to be held rests and which prevents dust or moisture from entering the core or coils of the device. This face plate is made up of a frame 8 and a series of pole pieces 9-9, each polepiece being separated from the others and from the frame 8 as will be further described. These polepieces, like the core, are also constructed of shellacked or enameled laminae and are held together by rivets l0 while the lateral surface of the polepieces as well as the opposing inner surface of the frame, are provided with notches H which cooperate in the manner to be described.

In assembling the face plate the frame 8 is placed on a level surface and the pole pieces 9 are located and tightly held within the framell with a separation between adjacent polepieces and also between the polepieces and the frame as indicated in Fig. 1. when thus arranged, a suitable plastic non-conducting material I2 such as a synthetic resin or a phenol condensation material, is introduced under proper heat and pressure to completely fill all the spaces between the polepieces as well as between the polepieces and the frame. When this material has hardened, it

engages the notches ll of the frame and polepieces to constitute an integral face plate which can be screwed or otherwise fastened to the base 5. The use of the nonconducting material i2 eliminatesthe closed conducting loops about the pole-piece of the chuck so that the alternating flux can pass through the work and thereby demagnetiZe it thoroughly.

In Fig. 3 there is disclosed a slightly modified form of face plate for the chuck in which the adjacent polepieces 9a are in dove-tailed relation but the several pole-pieces 9a and the frame 8 are separated from one another by nonconducting material I2. Otherwise the construction of the face plate is the same as that disclosed in Figs. 1 and 2.

In Fig. 4 there is disclosed a circuit arrangement whereby the devices of Figs. 1, 2 and 3 can be utilizei either as a chuck or as a demagnetizer, in which arrangement reference character 2| represents a source of alternating current, such as the usual 115 or 230 volt alternating current power service supplied by a commercial power company. This source is connected over conductors 22 and 23 to terminals 24 and 25 of the primary winding 26 of a power transformer under the control of a manual switch 21. This transformer is provided with a secondary winding 28 having end terminals 29 and 30 as well as a center tap terminal 3| while the portion of the secondary winding between terminals 30 and 3i is further provided with a mid-tap terminal 32. In addition to the secondary winding, the transformer has a tertiary winding 33 with end terminals 34 and 35, and also with the center-tap terminal 36. This tertiary winding serves to energize the cathodes of the rectifier tubes 3! and 38 of the two-element gas-filled high-current type which operate in the manner to be described, as a full wave rectifier. A four-pole double-throw switch 39 is provided so that either the direct current output of the double-halfwave or full wave rectifier or else the alternating voltage across the entire secondary winding 28 of the transformer can be connected alternatively at will to the magnetic chuck C.

In describing the operation of the circuit network of Fig. 4, it will first be assumed that switch 39 is closed to its lefthand or "hold position. Let it be further assumed that at the given instant, terminal 3| of the secondary transformer winding 28 is positive with respect to terminal 32 thereof. Current will then flow from terminal 3| through conductor 40 to switch blade 42 of switch 39, contact 46 and thence to the anode 48 of rectifier tube 38. Since this anode is now positive, an arc will strike and current will flow through this are to the cathode 49 and over conductors 50 and 5| to the terminals 34 and 35 of the tertiary or filament winding of the transformer and thence from terminal 36 over conductor 52 to terminal 53 of the chuck, over conductor 54 through coils 55, 58, 50, 62 and 64 in parallel to conductor 65 and through coils 55, 51, 59, BI and 53 of the chuck C to conductor 66 and to terminal 51 of the chuck. From terminal 61 current will flow through conductor 58 and blade 44 of switch 39, contact 41 and over conductor 59 to terminal 32 of the transformer. However, on the next half cycle terminal 39 of transformer is positive with respect to terminal 32 so that current will flow from terminal 30 through conductor TI to blade 4| of switch 39, thence to contact and through conductor 19 to the anode H of tube 31. Since this anode is now positive,

current will flow across the arc which strikes to the cathode 12 of the tube and as before to conductors and 5!. The remainder of the circuit which includes the energizing coils and which terminates at the terminal 32 of the transformer is the same as that which has been previously disclosed. In this manner the chuck is energized by rectified alternating current, whereby a high intensity unidirectional flux is produced in the core extensions and a work piece thereon.

The term high intensity" as here used means flux densities of approximately the value required to reach or pass moderately beyond the knee of the saturation curve in the magnetic circuit of the chuck, and the work held thereon.

It has been found that the inductance of energizing coils of the chuck is suflicient to filter out ripples in the rectified current thus supplied, to such an extent that no filter condensers or additional filter reactors are needed.

It now it is desired to demagnetize the chuck or any work thereon, switch 39 is thrown to the right hand position. This opens the anode circuits of the rectifier tubes 31, 38 at the same time the load circuit through the chuck is opened, avoiding the danger of a tube fiashover, due to the high surge voltage developed when the chuck circuit is opened. Alternating current will now flow from terminal 29 of transformer over conductor 15 to switch blade 43, thence to contact 14 which is connected to terminal 53 of the chuck. From terminal 53 current will flow over conductor 54 through coils 55, 58, 60, 62 and 64 in parallel, to conductor 65 and to terminal 16 which is connected to contact '13 of switch 39. From contact 13 current flows to switch blade 4| through conductor 11 to terminal 30 of the transformer. It should be pointed out that the alternating current voltage applied to the chuck is at least four times the rectified direct or pulsating output voltage, neglecting the arc drop in tubes 31 and 38. Also only half the coils of the chuck C are in circuit, corresponding to the fact that the alternating current impedance of a winding of the chuck at 60 cycles is about four to five times its direct current resistance. It has been i'ound that to-secure efiicient demagnetizing action, the root mean square value of the alternating current in the chuck should be about equal to the direct current used in the same winding to hold the work.

While a particular embodiment of the invention has been described, it will be understood that my invention is capable of still further modification and that this application is intended to cover any variations, uses, or adaptations of my invention falling within the scope of the invention and the limits of the appended claims.

What. I claim is:

1. An electromagnetic holding and demagnetizing device comprising a plurality of fiux producing units, a source of alternating current, a source of direct current. and means operated at will for connecting a plurality of units to said direct current source and for connecting alternatively a portion only of said last-mentioned units to said alternating current source.

2. An electromagnetic holding and demagnetizing device comprising a plurality of flux producing units, a source of alternating current, a rectifier connected to an alternating current source, and means operated at will for connecting a plurality of said units to the output of said rectifier or to connect a lesser number of said lastmentioned units to said alternating current source.

3. In a system of the class described, an electromagnetic chuck having a plurality of core extensions each provided with a coil, a pair of conductors connecting the coils on alternate extensions into one group, a pair of conductors connecting the remaining coils in a second group, a source of alternating current, a source of pulsating direct current, means for connecting said pairs of conductors and coils connected thereto to said direct current source and alternatively to connect one of said groups of coils to said source of alternating current, the alternating voltage applied to said last-mentioned group of coils being a multiple of the direct current voltage applied to both groups of coils.

4. In a system-of the class described, an electromagnetic chuck having a plurality of core extensions each provided with a coil, said coils being arranged into at least two groups with the coils of each group connected in multiple, a source of alternating current, a source of pulsating direct current, means for connecting said groups of coils in series to said direct current source and alternately to connect one of said groups of coils to said source of alternating current.

5. In a system of the class described, an electromagnetic chuck having a plurality of core extensions, means for producing a high intensity unidirectional flux in the said core extensions and in a work piece held thereby, and selectively operable means for producing at will in said core extensions and said piece, an alternating flux of V at least the same effective intensity as said unidirectional fiux and at frequencies in the commercial power range.

6. An electromagnetic chuck comprising magnetic circuit means for establishing a high intensity unidirectional magnetic field for holding magnetizable material, and selectively controlled means including at least a portion of said first means for establishing an alternating magnetic field of an intensity approximately equal to said unidirectional magnetic field to substantially demagnetize said material, said alternating field having a commercial power frequency.

'7. In a magnetic work holder, a support having a work holding surface, magnetic pole areas terminating in said surface, a source of unidirectional current, coils associated with'pole areas,'

' directional current source and for introducing alternating current from said alternating current source into certain of said coils arranged to afford an alternating current therein having an effective (root-mean-square) value approximately equal to the value of the direct current applied to said coils.

8. In combination, a combined magnetic holding and demagnetizing device, a commercial alternating current source for operating said device, said device comprising a core having core elements, at least a portion of said elements being each equipped with a coil, the impedance of. which at the frequency of said source being several times as great as the direct current resistance thereof, a first circuit including certain of said coils and connectible to said alternating current source, a second circuit connectible to said alternating current source and including rectifying means for supplying rectified current to certain of said coils, a transformer connected in one of said circuits, said transformer having. such a transformation ratio that the total electromotive force in one of said circuits is materially greater than that in the other circuit, and means effective at will for connecting either of said circuits to said alternating current source.

9. In combination, a combined magnetic holding and demagnetizing device, a commercial alternating current source for operating said device, said device comprising a core having core elements equipped with coils,.the impedance of which at the frequency of said source being sevthat in the other circuit, andmeans efiective' at will for connecting either of said circuits to said alternating current source.

10. In combination, a combined magnetic holding and demagnetizing device, a commercial alternating current source for operating said device, said device comprising a core having core elements equipped with coils, the impedance of which at the frequency of said source being several times as great as the direct current resistance thereof, a first circuit including certain of said coils and connectible to said alternating current source, a second circuit connectible to said alternating current source and including rectifying means for supplying rectified current to certain of said coils, the inductance of the coils in said first circuit being materially less than the inductance of the coils in said second circuit, a transformer connected in one of said circuits, said transformer having such a transformation ratio that the total electromotive force in one of said circuits is materially greater than that in the other circuit, and means effective at will for connecting either of said circuits to said alternating current source.

11. In combination, a combined magnetic holding and demagnetizing device, a commercial alternating current source for operating said device, said device comprising a core having core elements equipped with coils, a first circuit connectible to said alternating current source and including certain of said coils and rectifier means for supplying rectified alternating current thereto, the inductance of said circuit being sufllciently great to render rectified current substantially continuous, the inductive reactance of said circuit at the frequency of. said source being at leastfour times the direct current resistance thereof, a second circuit including at least certain of said coils and connectible to said alterhating current source, the inductive reactance of said second circuit being not more than onefourth of the inductive reactance of said first circuit, and means for connecting either of said circuits to said alternating current source.

.12. The method of holding a ferrous work piece on an electromagnetic chuck and subsequently destroying a remanent magnetism that has been induced in said work piece by being held on said electromagnetic chuck, which method comprises applying unidirectional current to said chuck to hold said work piece thereon, leaving the work piece on said chuck, disconnecting said unidirectional current, then applying to said chuck alternating current at frequencies of the

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