US 2920221 A
Description (OCR text may contain errors)
Jan. 5, 1960 M. scHwAB SEWING MACHINE DRIVE SYSTEM 2 Sheets-Sheet 1l Filed Oct. l, 1954 IN V EN TOR. /Wax Sen/@ BY TTRNE Y M. SCHWAB SEWING MACHINE DRIVE SYSTEM Jan. 5, 1960 2 Sheets-Sheet 2 Filed OC'C. l, 1954 INVENTOR. //dx cwa BY ATTORNEY United States Patent() SEWING MACHINE DRIVE SYSTEM Max Schwab, Schwetzingen, Germany; Olga Brunhilde Schwab, sole heir of said Max Schwab, deceased Application October 1, 1954, Serial No.` 459,817
` 7 Claims. (Cl. S10-96) The present invention relates to an electric drive system for sewing machines, designed to enable the operator to stop the sewing machine with the needle bar in a' machine at will with the needle bar in a pre-elected position, for example in the highest dead point position. Various constructions have been suggested for this purpose. Some of them include rather complicated, purely mechanical speed reducing means. Others comprise a slow auxiliary drive of contsant speed, such as an aux-Y iliary motor or a subsidiary drive branched off from the main drive and including a magnetic clutch which, after cut-'olf of the main drive, continues torrotate the sewing machine at slowspeed until an interrupter, rotated by the sewing machine, stops the latter in the desired dead position. Y Since the driving coupling member in such devices y isa'ctuated by the auxiliary drive, the speed reduction results from the drag exerted by the sewing machine and from the slow rotation of the auxiliary drive. Obviously, when using either an auxiliary motor or a subsidiary drive taken off the main drive, new gears or other driving elements must be brought from a standstill to full rotational speed, only to have their momentum destroyed immediately thereafter, in order to bring the sewing machine to the required stop.
It is an object of the present invention to provide a solution of the problem .of stopping a sewing machine with the needle bar in a pre-elected dead position by less complicated means of faster response, and to eliminate the necessity of an vauxiliary motor or subsidiary drive branched off from the main drive.
It is another object of the invention to provide an electric drive for the described purpose which is characterized vby far less inertia` and greater simplicity than hitherto known constructions.
It is a still `further object not only to simplify the entire driving mechanism by eliminating any auxiliary motor or other complicated means for transmitting mechanical power, but to provide a'device that is dependable-in operation, more compact and lower in cost.
The novel features which I consider characteristic of my invention are set forth with particularity in the appended claims. T he invention itself, however, and any additional objects and advantages thereof will best be understood from the following description of several preferred embodiments of the device when read in conjunction with the accompanying drawings, in which:
Figure 1 is a sectional view of a clutch according to the present invention;
Fig. 2 is a circuit diagram;
p 2,920,221 Patented J an. 5, 1960 ICC cluding an electronic tube for regulating the current in-i tensity passing through the iield winding of an electromagnetic clutch.
The object of this inventionv is attained by transmitting power from a driving clutch member to a driven clutch member and, therefrom, to the sewing'machine, by electro-magnetic rather than by mechanical means. However, it is also possible, according to this invention, to transmit the torque momentum for the regular operation of the sewing machine by mechanical means and to transmit electro-magnetically only the torque required for running the sewing machine at reduced speed until the sewing needle reaches a pre-determined dead position.
The herein claimed device, comprising a magnetic brake and an electro-magnetic clutch, is designed to initiate, upon passing an excitation current through a socalled primary winding of the electro-magnetic clutch, a slipping movement of the, driven clutch member and, because of the ensuing eddy currents, an appreciably increased slipping tendency von the part of the driven clutch member while, at the same time, the previously 'active brake is disengaged. However, immediately upon the sewing machine reaching a predetermined angular,
As a result of this arrangement, the speed of the driven clutch member is reduced to the required low terminal speed without the insertion of speedreducing .gears or auxiliary drives. If, thereafter, the driven clutch member has atttained a certain rotary position at which the needle of the sewing machine is at the, say, highest point, the voltage supply to the electro-magnetic clutch is interrupted while the afore-mentioned braking action is instantaneously brought to pass. This is accomplished by means of a circuit including a timing device, such as a relay of the delayed closing type that, in order to assure an instantaneous braking action, produces a momentary release when the circuit isr opened by contact means rotating in synchronism with the sewing machine. According to the invention, the desired action is possible because, at full speed of the sewing machine, the insulatinginsert of the contact device merely exerts a chopping effect upon the control current which does not cause any response on the part of the relay. The purpose of the delayed closing of the relay is, therefore, to prevent rotation of the driven clutch member by the power source during a trst braking action while, upon reaching the desired dead position ,of the needle, the circuit including the magnetic clutch is instantaneously opened in order not to counteract the ensuing action of the brake.
A still better arrangement includes a timing relay device comprising two oppositely wound coils and a condenser inserted into the circuit of one of the coils. The storing of electric energy by the condenser prevents the flux of current to theV one coil for a period equal to the pick-up delay so that the action of the other coil, the pick-up coil of the relay, is not impeded.
Moreover, according to the present invention it is not only possible to transmit by electro-magnetic means the power for the terminal rotational movement of the 3 sewing machine, but' also the regular operating power, i.e.V the torque of the electric motor; in such a manner that the speed of the rotation can be controlled or regulated by an adjustable resistor. The terminal rotational motion canbe also regulated by inserting, say, a potentiometer into the circuit ahead of the field winding of the electro-magnetic clutch. Thus, the magnitude of the torque to be transmitted cannot only be adjusted atrwill, but the length of the angular path required for stopping thesewingr'nachjiue inY a preaelected position Vcan be also le'glllated.` W *I In orderto be effective,V the Yclutching device must i be'hbui 'n theprincipleof an induction motor. p The tgg momentum, resulting from an overload must cause ai automatic disengagement of the clutch.k VFor this purpose, the secondary clutchmember can beV a Vmetal disk or, preferably, bebuilt on the principle of afshortcircuited armature; As a result of movements of the two'clutch members 4,relative to, each other, induction currents are'producedwhich,together withl the rotating,
eld ofA the salient pole armature, develop torques that -actjuponfthe'primaryand secondary member, i.e. on the two'clltchmembers, so Vthat the'faster rotating driving cliut'clrmember carries the driven'clutch'member along.
spee'dof the sewingmachine can be kept constant "indeV i pendently of the-torque by inserting anelectronic tube into ther-control circuit. In this Vcase, a small tachometercompletely depressing the lever L. Under the described Y theopencontac'ts k-l and m-n. If now the operatingv l4 slide ring 25 that is mounted, say, on the front cover of the motor housing 2, with an insulating ring .Z6 therebetween.
Fig. 2 illustrates the yarrangement of an operating circuit for the embodiment shown in Fig. 1.V The field winding 23 of the driving clutch member 4 shown 1'n Fig. 1, `as well as the control coil 11 of the magnetic brake are schematically represented. Z7 is alcontrol which may be adapted as a foot or manual controlto start thesewingmachine and to regulatethe operatlng speed by appropriate movements of the lever L. Depression of the lever L opens the contacts a-b and closes t the contacts c-d which causes `a current lowfrom the negative terminal of a D.C. voltage source, through conductor e, slide f and one ofthe contact points of resistor 28, conductor g, field winding 23, conductor h, contacts c-d Aand conductor i to the positive terminal ofthe D C. source. The excitation'voltagedepends upon the.position of the lever L. 'Since-the field windingA 25 Yrotates with the continuouslyturning input shaft 1 (Fig. 1,), voltages are induced in the c onductorbars and current flows through theshort-circuiting rings-18, with `the resultrthat a given amount ,of` slip occurs in the rotation-of the driven clutch member 10, depending upon thedegree-ofA eXcitation.-. Thus, the speedfof the driven clutchmember1t)v can either be gradually increased, orrt'herhighest speed can be immediately attained by conditions-,Y the excitation coil 11 of the 'magnetic brake is .without current, because the circuit is interrupted at drive is disengaged by releasing or returning the lever L intothe Yillustrated or otiginalposition, the branch circuit,
' including the resistor 28 and the contactsjcV-d, is opened,
dynamo; coupled to` the driven'shaft, produces-a voltage which,` depending upon the speed of rotation, is opposed to 'theiiring'voltage applied to the electronic tube.V The rel-ativelytslow rotational speed attained by theY slipping clut'ch member can be adjustedV byfmeansofL a potentiorneten inserted ahead of the` grid of, thejelectronic tube. 'i
.,-Havin-g reference now'to the drawings, Fig. l illustrates a continuouslyL rotating input shaft 1 vof an electric motor Z-asrthe'p'ower source. The shaft is held by bearings-3 and=has theA driving clutch'member 4 mounted at the free end thereof, a clutch housing 5, fastened to the I frontV of the motor housing, concentrically withthe motorfshaft- 1, encloses the bearings 6 and 7 as well as theJtake-oif or.'V drivenv shaft 8, held' by said` bearings.V A Vsheave9 for driving-'the sewingl machine ismounted at--the free end ofthe driven shaft 8, outside the housing 5. Also keyed to the" driven shaft l8', at the other 'extremity thereof, is the driven clutch member 10; Mounted atj tlievinside ofy the'front-wallfof'the clutch housing 5 is the control-'coil 1'1- as stationary part of Va magnetic brak' .i
Arfrictionlayer 12' is'fastened, preferablyl adjustable, to the.v frame of the control coil 11 s'o that the magnet disk 13r representing the movable part, of the brake Vbeing keyedto the take-off` shaft', enters into contact with the friction layer 12 upon excitation of the coil 11. A
membrane' 14 connects the magnetic disk'13; to the driven clutch member 10. The driven clutch ymember 10 represents, in eifect, a short-circuited armature ring", which clutch member 10 comprises a short circuit ring" 18 connected by the active conductor bars to the support disc of the driven clutch member 10 to form a squirrel cage winding therewith. The bars are cast or could be replacedy by rivets in the pierced openings' in the laminations-15; The driving clutch member 4 has a' Corresponding number of poles 19, 20, 21, 22; The number of.. poles can however be larger or smaller. Each of thepoles is equipped with one or several excitation coils of whiler .the branchrcircuit, including contacts adb, k-l andvmf-.n is closed.. Consequently, current flows from the negative terminal I(--) through the last named branch circuit to M1,..through control jcoil 1,1 of the magnetic bija'ke, conductornb 'to contact p kofav relay R-A and from there to-.contactfq'and through conductor 'r to'thepositive'v terminal f(+)" of thelv D'.VC. source. Passing current through control `coil. ll1factivates the magnetic brakeV which, through its action; destroys the kinetic energy ofthe vrotating-parts of thesewing machine and the driven clutchmer'nber10.Y 'At the same time, current liows fromV the' negative terminal (f) V'through the circuit branch including contacts q-b, conductor .sj -mass,pM2 and needle bari controlA shaftfCS. of the sewing machine,y
through contact rdisk CD, brush B conductor t and pointu. However, the current flow is interrupted when, as: a result of -the rotary motion ofthe needle bar control shaft, theinsulating insert Iof the contact disk `CD passes underneath the brush B.- u The angularposition of the insulating insert with respect to the brush corresponds witli the momentary reciprocating positionof the needle banofathe sewing machine. v Y
Fror'n point u, yone part of the current flows through relaycoilfWhpoints v, w and'vx to condenser YC and from the lield winding 23; Current to the `field Winding 23 which continuously rotates --wi'th the driven clutch m'e'mf be14 .is suppliedby means of 'a'brusli 24; contacting a there through conductonr to `the positiveV terminal k(--l'), while another part ofthe current Vflows through point y, relaycoilQW2,.point zjand conductor Z1 to the positive terminal' Thecoils W1 andv WZ arewired in oppostte `se se, vsot'hat their effect is cancelled out until the" condenser C isfully charged and then `blocks the ilow of current through coil W1'. During ythis interval, the pick-upcoil W2 prevails and actuates the relay; with the result that the brake circuit is interrupted at point rp,
while the branch circuit of the field winding 23 of 'they driving clutch member 4. is closed at point p1. Thus,-
relayR Iand condenser C together constitute a timingv device. Current, Hows from the negative terminal through contacts a--b,.m-n, field winding 23, conduc-4 tors h,' h1, a' slide-wire rheostat PR,-p'oints p1, q and conductor r to the positive terminal. 6+) The degree of excitation of the field winding 23 depends upon the vwith the driving clutch member 33.
resistance of rheostat PR so that, under the influence of the field winding 23, the driven clutch member is rotated, but with a `high slip momentum and, consequently, -at reduced lrotational speed, until the needle of the sewing` machine assumes the desired stopping point upon the insulating insert I of the contact disk CD reaching the position illustrated in Fig. 2, at which the circuit is interrupted by the instantaneous action of relay R, causing at point p1 a break in the current flow through field winding 23 and, at point p, a closing of the branch circuit of the magnetic brake, resulting in an instantaneous excitation of control coil 11 and a dead stop of the driven clutch member 10 and of the sewing machine connected therewith.
By providing a push-button switch P1, inserted into theV circuit, as illustrated,` the herein disclosed arrangement permits a sewing operation at greatly reduced speed upon depressing the switch.v
Figs. 3 to 5 illustrate an embodiment wherein the clutch is engaged and disengaged by means of a lever Z9. Upon operating this lever, the friction layer 30 of the driven clutch member 31, mounted on the take-off shaft 32, shown only in part, is placed into engagement with the driving clutch member 33.
The driving clutch member is keyed to a continuously rotating motor shaft 34. A field winding 35, comprising a part of the driving clutch member, is applied with voltage by means of a brush 36 and a slide ring 37 mounted on the insulating plate 38. The field winding is held by a magnet pole 39, provided with cut-outs 40, 41, 42 and 43. Obviously, another number of poles will be equally appropriate. The pole plate is coaxially rotatable within the driven clutch member 31, preferably designed as a squirrel cage armature 44. Here too, larmature rods.45 are provided which are shortcircuited by means of the disk 31 and the short-circuit ring 46, respectively.
`In the absence of engaging pressure upon the clutch lever 2,9, the latter assumes the position illustrated in Fig. 5 and the friction layer 30 remains out of Contact Under these conditions, current flows from the negative terminal of a D.C. source through switch S, points a1, b1 and c1 to mass M1 and .control coil 11 of a brake magnet such as shown in Fig. 1, and from there through conducter d1 and points e1, f1 of an electro-magnetic relay R and, finally, through conductor g1 to the positive terminal (-1-). Consequently, the brake is actuated and the kinetic energy of the rotating clutch member that is not in engagement with the power source is destroyed. At the Same time, current flows from the negative terminal through switch S, point a1, conductor h2, mass M2 and needle bar control shaft CS of the sewing machine, contact disk CD, brush B, conductor i1 to point k1 of a relay R. Obviously, the current flow will be interrupted when, as a result of the rotary motion of the contact disk, the insulating insert of the contact disk passes into juxtaposition with-the brush B. From Ypoint k1, current flows through relay coil W1, points l1, m1 and n1 to condenser C and from there through conductor g1 to the positive terminal Simultaneously, current flows from point k1 through pointv c1 to relay coil W2, and from there through point p2 and conductor q1 to the positive terminal The relay coils W1 and W2 are wired in opposite sense so that their effect is cancelled out until the condenser C is fully charged and blocks the flow of current through coil W1, which permits coil W2 to trip the relay; with the result that the brake circuit is opened at point e1 and the field winding 35 of the driving clutch member is energized by current flowing from the negative terminal'(-) through switch S, points a1, b1, field winding 35, conductor s1, points t1, f1 and conductor g1 to the positive terminal (-1- The energized field winding 35 produces an induction current in armature rods y45 so that the driven clutch member 31 is rotated, but at reduced speed, depending upon-the degree of excitation of the field winding and the amount of slip resulting therefrom. The sewing machine is turned over in this manner until the brush B passes over the insulating insert I of the contact disk CD, at which time the electromagnetic relay R instantaneously opens the circuit at point t1 so that the field winding 35 is inactivated, while the circuit is closed at point e1 and the control coil 11 is re-energized which causes an immediate braking action resulting in a complete stop of the needle bar of the sewing machine in the desired dead position. By means of a switch S1, the contact disk CD may be eliminated to permit stitch-by-stitch sewing.
Fig. 6 illustrates an electronically controlled device. With the clutch disengaged, current flows from the negative terminal of a D.C. source through conductor t trol shaft CS of the sewing machine, contact disk CD,V
brush B, conductor g2 to point h3 of the relay R, provided, however, that the current flow is not interrupted by the insulating insert I of the contact disk. From' point h1,
current flows through point m2, relay coil W2, point n2, conductors o2, e2 to the positive terminal The relay coil W1 is wired oppositely to the relay coil W2, so .that the effect of the two coils is cancelled out until the condenser C is charged and pick-up coil W2 is able to actuate the relay into closing the circuit at point p3. Plate current flows from the line terminal A through the electronic tube 47, conductor q2, series resistor PR, field winding 23/35 (Fig. l or 3, respectively), conductor r2, points p3, s2 and conductor t2 to line terminal B. In `this manner, the voltage of excitation current flowing through field winding 23/35 of the driving clutch member can be adjusted by ignition voltage, applied between control grid G and cathode K of the electronic tube 47. The ignition voltage is obtained in the usual manner froma control amplifier 48. The input voltage of the control amplifier represents the difference between the voltages of a tachometer dynamo 49, actuated by the take-off shaft '8/32 (Fig. 1 or 3, respectively) and a potentiometer 50, fed by a storage battery 51. The arrangement provides, furthermore, an adjustment resistor PR1 between amplifier 48 and con# trol grid G.
Under the influence ofjthe field winding 23/35, the driven clutch member 10/23 and the sewing machine are rotated at reduced speed until the needle -bar reaches the desired position, at which time the insulation insert I turns into contact with ybrush B. At this point, the relay R opens instantaneously the circuit including the field winding 23/35' at point p3 -and'closes, at point c2, again the clrcuit including the control coil of the brake magnet 11. The tachometer-dynamo 49 prevents too high a terminal speed, because of the increase in opposing voltage delivered upon an increase in the rate of rotation of the takeoff shaft 8/32.
While I have disclosed several embodiments of the present invention, it is to be understood that the embodiments are given by example only and not in a limiting sense, the scope of the present inventionbeing determined by the objects and the claims.
o 1. A system for driving a reciprocally acting device comprising a rotating control shaft and stopping said control shaft at a predetermined rotary position, said system comprising, a first electric contact device connected with said control shaft to be actuated in positional dependence upon said control shaft, a power input shaft continuously driven when the drive system is in operative condition,
, 7 1 a power take-off shaft and transmission means connecting vsaid take-off shaft with said control; shaft for driving said control shaft, a variable slip clutch having an electric connecting said currentv supply means with said clutch control winding and including a control'rheostat for varying the slip of said' clutch, said rheostat having a' control member `displacablel between device stopping. and full speed positions, Ya second electric contact memberconf nected with said rheostat controllmember'and being in activeconditionsonlyv when said control member is in said stopping position, a time relay delay device having delayed pickup and momentary drop-off characteristic, saidv relay device having relay control means connected to saidcurrent supply means through said two contact membersfs'oV as topick up with delay only when said rheostat control member, previously displaced, is returned to said stoppingppositionfand said control shaft is simultaneously ina given'position, abrake control circuit connecting said brake control coil with said current supply means through said second contact-memberand throughsaidfrelay device only when said relay device is in dropped-off conditionp said second control circuit including a current-limiting` resistor for causing said clutch to Vcontinue driving said takeloff shaft at Yreduced speed until said relay device drops off to actuate said brake.
3.V A drive system according to claim `2, said two clutch members having respective magnetizable bodies and forming togetherari induction motor system, said winding being disposed onf said driving member and said driven member forming `a short-circuitedrotor, whereby electric energy ion the takegoffv side of saidclutch is yconsumed by electro-dynamic brakingwithin said clutch during (said interval.
4. In a dir-.ive system according to' clairn l, said relayl device comprising an electro-magnetic relay and saidl relay controlnmeans comprising a pick-up coil said relay, andsaidfirst contact device formingan interrupter having a single break gap and being series-connected with said pick-up coil, whereby vthe'` current supplied Vto said' pick-up coil is chopped 1by* said rst contact device and thus remainsinsuilcient to operate `said 'relay as long as the speed of said control shaft is excessive.
,5. VIn a drive'system according to claim 4, Vsaidelectromagnetic relay having another coil opposingly related tosaid pick-up coil, a direct current circuit energized fromY said current supply means and including vvsaidA other coil, and a condenser in said direct current'circuit in serles with said other coil, whereby said pick-up coil becomes ef-V fective only after charging of said condenser.
6. A Vsystem for driving a reciprocally actingdevice comprising a rotating control shaft and stopping said control shaft at a predetermined rotary position, said system comprising a power input shaft'continuously driven when y the drive system is-in operative condition, a power take-off shaft drivingly connected with said control shaft, a con-v trollable slip clutch having a driving member,mountedV on said input `shaft and a driven member mounted on said ,take-off shaft, said driving clutch member and Vsaid driven clutchl member forming together a dynamofelectric V.sys-
tem and having a' ield winding disposed onsaid driving part being connected Withsaid driven clutch member for Vacting'on said driven clutch member when Ysaid brake is in operation, an electric control circuit connected with said eld winding and having adjustable current control means for supp-lying controllableex'citation to said eld winding to thereby vary the slip'ofk said clutch, said control nieans so as to Vstop said take-off shaft when saidV conmeans to operate said brake in dependence upon said control means so as to stop said take-,off shaft when said coni trol means is adjusted for maximum slip of said clutch,
a speed regulator of variable resistance connected'in saidl control circuit, and a speed responsive current source conf nected with said control shaft to provide a voltageV pro portional to the speed of the driven device, andmeans connecting said source with said regulator for controlling;
said resistance to maintain the speed of the driven device at a constant value in accordance with the adjustment of said current control means.'
7. In a drive'system according to claim '67, said regulator deviceY comprising an electronic tube havin-g a'plate circuitin series with said control circuit and having a grid circuit which forms part of said connecting means between said source and-said regulating device. Y
References Cited in the lile of this patent Y,
UNTTED STATES PATENTS Reece Feb. 15, 1,955
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