US3534697A - Sewing machine having means for stopping same with needle in pre-determined position - Google Patents

Description

United States Patent Inventors Pietro Sillano;

Nereo Bianchi, Pavia, Italy Filed July 18, 1968 Patented Oct. 20, 1970 Assignee Necchi Societa Per Azioni Via Rismondo Pavia, Italy Priority Nov. 29, 1967 Italy No. 32405/A/67 SEWING MACHINE HAVING MEANS FOR STOPPING SAME WITH NEEDLE IN PRE- DETERMINED POSITION 3 Claims, 2 Drawing Figs.

[1.8. CI 112/219, 1 12/252 Int. Cl D05b 69/00, D05b 65/00 [50] Field ofSearch ,.112/219(A), 219, 220, 252; 192/18,142

[56] References Cited UNITED STATES PATENTS 2,914,010 11/1959 Cohen ,.112/219(A)UX 3,174,450 3/1965 Becker et a1... ..112/2l9(A)UX 3,386,402 6/1968 Ross 112/252 3,404,767 10/1968 Farnum ..112/219(A)UX Primary Examiner-H. Hampton Hunter Attorney-Stevens, Davis, Miller and Mosher ABSTRACT: A sewing machine having a motor drive means and related circuitry adapted to stop the needle in particular positions whereby the needle does not interfere with the operation of thread cutting devices.

Patented Oct. 20, 1970 Sheet SEWING MACHINE HAVING MEANS FOR STOPPING SAME WITH NEEDLE IN PIKE-DETERMINED POSITION sewing threads can be cut without interference occurring betweenthe needle and the thread cutting means.

Thread trimming means in sewing machines are adapted to simultaneously cut the needle and hook threads at a point beneath the throat plate, that is: between the work feeding means and the hook, and the trimming means is actuated to perform its cutting function just before the machine is stopped and while the hook is performing its last revolution. It is necessary, therefore, to precisely correlate the trimming means with the other working parts of the machine in order to assure that no interference occurs between said trimming means and the needle.

Further, it is important that, at the end of a sewing cycle, the needle come to an at-rest position with its point slightly above the work fabric (so as to permit changing thereof) and with the needle slightly past its top dead-center position (so as to prevent unthreading of the trimmed end out of the needle eye since when sewing is resumed the thread take-up moves downward in correspondence to the needle direction). In known machines, therefore, it is necessary to very carefully adjust the working parts so as to assure the proper positioning of the needle at the end of the sewing cycle.

To this end, some known sewing machines have been provided with means which preclude actuation of the thread trimming knife while the machine is operating at high speed and with means for precisely determining the position to which the needle comes to rest at the end of the sewing cycle. The aforementioned known means, however, are complex and correspondingly expensive since they entail the assembly of relatively complicated components on the machine, such as: centrifugal regulators which regulate the actuation of the thread trimmer, or, feed back type electronic regulators to stabilize the machine running at a reduced speed, such stabilization being necessary in order to achieve a proper positioning of the needle.

The problem to resolve in this regard revolves about the provision of a simple device within the electrical control circuit of the machine, which device would effectively coordinate the actuation of the trimming knife and the stopping of the machine relative to the running speed of the machine being cut down to a predetermined reduced value.

It is an object of this invention, therefore, to provide an improved means for actuating the thread trimming knife and for accurately determining the position to which the needle comes to rest when the sewing machine stops.

It is a further object of this invention to provide such an im proved means which is very simple and correspondingly inexpensive to produce.

It is a specific object of this invention to provide a sewing machine having an improved means for effecting actuation of the thread cutting devices in correlation to the needle speed having been reduced to a predetermined low value and also having an improved means whereby actuation of the machine braking means is correlated to occur at a predetermined interval after actuation of the cutting means and in correspondence to the point of the needle being located above the work piece.

Other objects are those which are inherent in the present disclosure.

Generally, the objects of this invention are realized through a machine which comprises a needle position synchronizing unit comprising rotary contact rings, a motor shaft which drives the machine main shaft alternatively through a first and a second drive means, the first being directly connectable with said motor shaft to run at high speed and the second being connectable to said shaft through a speed reducer to run at a lower speed, the synchronizing unit comprising a first contact ring wired in series with a first relay and a microswitch, the conducting sector of said ring being correlated with the time factor of said relay whereby said relay is excited through said ring only when the latter rotates at said lower spced, said relay in turn actuating the control contact of a second relay which itself actuates a braking means, the synchronizing unit comprising another contact ring in series with said second relay, this second relay contact ring being correlated relativewith the first contact ring whereby the second relay is made to actuate said braking means at a predetermined interval after the first relay has been actuated to activate a thread cutting I'IICLIIIS.

Other characteristics and advantages of the invention will be described referring to the drawings herewith attached, giving by way of illustration an embodiment of the invention, in which:

FIG. I shows the invention and the sewing machine on which it is applied; and

FIG. 2 shows the schematic electrical layout for driving and controlling the device ofFIG. I.

In FIG. I the motor 10 is drivingly connected to a sewing machine II by a belt 22. The sewing machine is supported on a table 13 and usually comprises a base 14. a standard IS, an overhanging arm 16, and a head 17 in which there is reciprocably mounted a needle bar 18 carrying a needle I9. Mounted on the sewing machine main shaft 20, there are a balance or fly wheel 21, a pulley 22 on which the belt I2 is wound, and a synchronizing unit 23 composed of four contact or switch rings 24, 25, 26, and 27 on the outer surface of everyone of which a conductor sector and an insulator sector are provided and are respectively represented in white and black in the FIGS.

On the head I7 there is the upper thread tension device 28 connected with an electromagnet 29 which has the function, when sewing threads are trimmed, of releasing the upper thread tension. In the base 14 of the sewing machine, there is the hook 30 and, schematically represented, the trimming thread device 31 composed of a knife (not shown), an electromagnet 32, a cam follower 33 actuable upon excitation of said electromagnet 32 to coact with a cam 34 and thereby to actuate the not shown knife, and returnable to its rest position by a spring 35 upon de-excitation of the electromagnet 32. Under the table 13 of the sewing machine, a microswitch 36 is positioned and is actuated by one end of a lever 37 fulcrumed on a support 38 fixed under the table 13 and carrying at the other end a knee pad 39.

When the operator pushes the knee pad 39, the lever 37 is rotated counterclockwise about its fulcrum and thereby performs two distinct functions: it causes the lifting of the presser bar (not shown) and actuates the microswitch 36. Means connected with the lever 37 to accomplish the first function have not been shown and described because they do not form part of the invention. The effect of actuation of the microswitch 36 will be explained hereinafter.

The motor 10 is a usual three-phase induction motor whose shaft 45 is conneetable with the machine drive shaft 55 through either one of two coupling means. The first of said coupling means provides a direct coupling of shaft 45 to shaft 55 through face-to-face frictional engagement of friction disc 40 with clutch disc 54 whose facing surfaces are composed of a material having a high coefficient of friction, said discs 40 and 54 being respectively mounted on shafts and 55 and being integrally rotatable with the respective shafts. The second coupling means provides a speed reduction from shaft 45 to shaft 55 through a driving train extending from pulley 44 which is rigid with shaft 45, through belt means 46 around idler pulley 47 and to pulley 48 which is rigid with shaft 49, upon which is mounted worm 50 which in turn engages with worm wheel 51 which is rotatively rigid with disc 41. Wheel 51 and disc 41 are freely rotatable on shaft and disc 41 is frictionally engageable with disc 54 through means of respective facing surfaces on each disc 54 and 41, which surfaces are composed of a material having a high coefficient of friction. The driving ratio of worm set 50, 51 is such as to effect a speed reduction between shaft 45 and shaft 55. Pulley 56 is rigid with shaft 55 and through belt 12 drives the machine main shaft 20.

Clutch disc 54 is positioned axially between discs 40 and 41 and is axially slidable so as to engage either of said discs 40 and 41 at any one time. A spring means normally urges disc 54 into engagement with low speed disc 41 but said disc 54 can be slid against the urging of said spring means to engage high speed disc 40, such axial displacement of said disc 54 being realized through a pivoting of L-shaped lever 57 about pivot means 58 of bracket 59 which is rigid with the motor casing. A foot actuated pedal 60 is pivotable intermediate its ends about fixed pivot means and is connected to lever 57 through rigid link 61 so as to pivot lever 57 in either direction.

The end 62 of lever 57 is connected by member 63 in a known manner to the shaft 55 and pivotal movement of said lever 57 about pivot means 58 produces axial displacement of said shaft 55 and of disc 54. In the position shown in FIG. 1, L- shaped lever 57 is in an at-rest position in which clutch disc 54 is held in contact with the low speed disc 41 by a spring which is housed within member 63.

1f pedal 60 were now to be pivoted counterclockwise (by the operator's heel) to the position denoted 4, rigid link 61 would urge lever 57 to pivot clockwise which motion, however, would be impeded by the fact that clutch disc 54 is already contacting low speed disc 41. Lever 57 could not, therefore, pivot clockwise but said lever is sufficiently elastically deformable whereby, under the urging oflink 61, the horizontal leg of lever 57 would flex sufficiently for it to press against and actuate the microswitch 64 which is fastened to the underside of the motor casing. Furthermore, such clockwise urging of lever 57 by link 61 increases the force urging clutch disc 54 against low speed disc 41 thereby increasing the frictional adherence of the two discs to each other and thus enhancing the braking effect of low speed disc 41 upon shaft 55.

Finally, with reference to FIG. 1, microswitch 65, which is fastened to an end wall of the motor casing, is pressed against and actuated by the vertical leg of lever 57 pursuant to counterclockwise rotation of said lever. Further, 52 denotes an electromagnetic clutch and 53 denotes an electrically actuable brake, both these components being mounted on shaft 49.

The operation of the aforementioned components will now be described with reference to the electrical circuit which is schematically represented in FIG. 2 in which are also included the step-down converter 66, the bridge rectifier 67, the two relays 68, 69 and their respective contacts 71, 77, 74; and 70, 76,78.

Primarily, it should be noted that shaft 45 of motor 10 rotates continuously during normal operation of the machine whether or not stitching is being performed.

When pedal 60 is in rest position (FIG. 1), shaft 45 is rotating and clutch disc 54 is in contact with low speed disc 41; however, shaft 55 is held stationary by brake 53 whose winding is excited by virtue of its contacts being in the position which is shown in FIG. 2. Also, with the switch or contact rings 24, 25, 26, and 27 in their positions as shown in H6. 2, the needle 19 is at its lower dead-center position.

When pedal 60 is moved from position 0 to position 1, shaft 55 starts rotating at a low speed, this occurring by virtue of lever 57 actuating microswitch 65 to a closed position thereby bringing about excitation of relay 68 and a switching over of its contact 74 from right to left in FIG. 2 to close the circuit of clutch 52 and open that of brake 53. It is clear, therefore, that shaft 49 is now driven by pulley 48 via clutch 52. L-shaped lever 57 is connected with shaft 55 in a manner such that with pedal 60 in position 1, clutch disc 54 remains in contact with low speed disc 41.

When pedal 60 is then pressed further to position 2, lever 57 will pivot counterclockwise to an extent such that it displaces clutch disc 54 to a position away from low speed disc 41 and intermediate of the two discs 40 and 41 whereby neither one of these discs is in contact with clutch disc 54. The machine 11 is now totally independent of motor and the operator may now manually turn the fly wheel 21 to move the needle 19 to any desired position.

When pedal 60 is moved to position 3, lever 57 pivots further counterclockwise and axially displaces clutch disc 54 ,into contact with high speed disc 40 whereby shaft 55 is correspondingly turned at high speed. In fact, variations in the magnitude of this high speed can be obtained simply by the operator varying the foot pressure which is applied to pedal 60, the degree of said foot pressure determining the contact pressure between the respective discs 40 and 54 and, therefore, determining the efficiency of speed transmission therebetween.

When pedal is released by the operators foot, said pedal is returned to thc rest position which is shown in FlG. 1, by means ofa not shown spring, and shaft 55 slows down to a low speed and subsequently stops with the needle positioned at its bottom dead-center position. Specifically, when pedal 60 is released and is returned to the FIG. 1 position. clutch disc 54 is displaced axially to the right into contact with low speed disc 41 by the spring mounted in member 63, this cutting down on the speed of shaft 55 while also causing lever 57 to pivot clockwise thereby releasing switch which, therefore, opens. Relay 68, however, remains temporarily excited through the circuit provided by contact 70, microswitch 36, contact 71 of relay 68, rings 24, 25, 26, and brush 72 up until the insulator sector of ring 24 comes into contact with brush 73, at which moment the circuit of relay 68 is interrupted so that contact 71 opens and contact 74 switches over from the circuit of clutch 52 to that of brake 53. Shaft 49, therefore, is no longer driven by pulley 48 but is, instead, braked by brake 53 and transmits such braking action to clutch disc 54 and thereby to shaft 55. The machine 11, therefore, stops with the ring 24 in the position shown in FIG. 2 and with the needle 19 in its lower dead-center position. In order for the operator to now move the needle to a position out of the work fabric, the operator must press against the knee pad 39 thereby bringing about the aforementioned raising of the not shown presser foot and the switching over of the microswitch 36 towards the right in H6. 2 whereby relay 68 becomes energized. Contact 74 thereby is switched over to the circuit of clutch 52 so that the shaft 55 is rotated at slow speed for about three-fourths of a revolution and stops when the insulator sector of ring 25 contacts brush 75 thereby opening the circuit of relay 68.

When it is desired to stop the machine with the needle out of the fabric and also to cut the sewing threads, the operator must release the pedal 60 with the front of his foot and press down on it with the heel of his foot so as to bring the pedal to the position 4. This operation effects a greater gripping action between discs 54 and 41 and, therefore, a greater slowing down action on shaft 55, and it also effects an elastic flexing of the horizontal arm of lever 57 whereby it closes switch 64 which is in the circuit of relay 69 together with switch ring 27. Closing of switch 64 will result in current pulses being sent to relay 69, the duration of each pulse being dependent upon the circumferential extent of the conductor sector of ring 27 and the rotational speed of said ring. In fact, said extent is calculated as a function of the relay time constant to be such that relay 69 will become excited only when the rotational speed of ring 27 is not above a certain maximum predetermined value.

When relay 69 is excited by virtue of shaft 20 having slowed down to a certain speed, contacts 70, 76, and 78 of relay 69 are all switched over with contact closing the circuit to relay 68 through ring 25; self-exciting contact 76 closing the circuit to relay 69 through closed contact 77 of relay 68 to thereby maintain a closed circuit to relay 69 even when brush 79 contacts the insulator portion of ring 27; and contact 78 closing to excite the electromagnets 32 and 29 which respectively control the thread cutting knife and the opening of the thread tensioning device. Relay 68 will remain excited through contact 70 and ring 25 for so long as brush is in contact with the conductor sector of said ring 25, this being for about three-quarters of a revolution considering that the synchronizing unit rings rotate clockwise in H6. 2.

The angular displacement between the conductor sector of ring 27 and the insulator sector of ring 25 defines a period, beginning with the excitation of relay 69, during which the rotational speed of shaft 20 may stabilize itself at a constant low speed value, this period lasting for about three-fourths of a revolution of shaft 20. At the end of this period, the insulator portion of ring 25 contacts brush 75 and relays 68 and 69 become de energized so that the related contacts switch over the respective positions shown in FIG. 2. The braking operation will now be repeated as previously set forth excepting that now the needle will be out of the work fabric.

it is emphasized that the ring 27 which controls the thread cutting knife also serves to prepare the machine for the braking operation which is itself controlled by ring 25.

Relative to known devices which are directed to achieving analogous functions, the present invention provides a prcparation time in anticipation of the braking action, said time being equal to the time required for the main shaft to rotate three-quarters of a revolution.

ln known devices, the braking action is controlled only by a ring such as ring pursuant to its insulator sector passing its brush at a reduced speed which, however, was not accurately stabilized at a predetermined value because the time interval from the instant that pedal 60 was shifted to position t up until the instant that the insulator sector of ring 25 passes under brush 75 would be different each time that pedal 60 was so shifted, the result being that the machine stopping would comrnence at a different value of reduced speed each time. The precision of the needle positioning upon the stopping of the machine, as is well known, is largely dependent upon the constancy of the reduced speed and, therefore, such precision is compromised in machines according to the prior art.

The herein given details of a preferred embodiment are not intended to limit the scope of the claims which are originally filed or as presented subsequently by way of amendment, the scope of said claims being intended to apply to all variations, modifications, substitutions, or equivalents which are obvious or well within the purview of one skilled in the art.

We claim:

1. A sewing machine comprising a stopping device adapted to stop the machine main shaft with the sewing machine com ing to rest at a predetermined position relative to the work fabric, the machine comprising a thread cutting means, a main shaft drivingly connected with a sewing needle to reciprocate same axially, a motor for driving said main shaft, first and second drive coupling means between said motor and said main shaft respectively adapted to provide a high and low speed drive ratio from said motor to said main shaft, a braking means for stopping said main shaft, electrical circuitry for actuating said thread cutting means and said braking means, said circuitry comprising a first and a second electrical switch means drivingly connected with said main shaft, said first switch means controlling the actuation of said braking means and said second switch means controlling the actuation of said thread cutting means, said second switch means being adapted to actuate the said cutting means into an operative condition thereof in correspondence to said low speed drive ratio being in effect between the motor and said main shaft, said first switch means being correlated with said second switch means whereby said first switch means is adapted to actuate said braking means to a nonbraking position for a period of time commencing with the actuation into operative condition of said cutting means and terminating subsequently thereto whereupon said first switch means is adapted to actuate said braking means into a braking position at a moment when said main shaft is at a rotary position thereof corresponding to said needle being at a particular predetermined position along the axial stroke thereof, said first and second switch means being correlated with each other whereby upon actuation of said braking means by said first switch means, said second switch means actuates said cutting means to a nonoperative condition, said first switch means comprising a pair of rotary switches, a relay, contact means for connecting either of said rotary switches alternatively in series with said relay, said rotary switches each comprising a conductor sector and an insulator sector successively arranged along the circumferential extent of said rotary switches, said rotary switches being integrally rotatable with each other, respective brush means In contact with the surfaces of said rotary switches, said relay being arranged to actuate said braking means into an operative braking position in correspondence to the insulator sector on a one of said rotary switches contacting its related brush means and thereby deenergizing said relay, the insulator sector on a one of said rotary switches being correlated with said main shaft whereby it contacts its related brush means with the needle point positioned above the work fabric, and the insulator sector of the other rotary switch being correlated with said main shaft whereby it contacts its related brush means with the needle point positioned below the work fabric, said contact means comprising an operator-actuablc switch normally positioned so as to connect said relay with said other of said rotary switches and actuable by the machine operator so as to connect said relay with the said one of said rotary switches, including a second relay operatively associated with a contact which opens and closes the circuit to said thread cutting means, said second switch means being arranged to open or close the excitation circuit of said second relay, said second switch means comprising a rotary switch integrally rotatable with the rotary switches of said first switch means and also comprising a conductor sector and an insulator sector arranged successively along the circumferential extent of said rotary switch, a brush means contacting the surface of the second switch means rotary switch, said second relay having a time factor correlated with the circumferential extent of the conductor sector of said second switch means rotary switch whereby said second relay is energized by said second switch means only when said main shaft is driven at a speed in accordance with said low speed drive ratio, the conductor sector of said second switch means being arranged to contact its related brush at a time interval in advance of the time at which the insulator sector on said one rotary switch of said first switch means contacts its related brush.

2. The sewing machine of claim ll, said time interval being equal to substantially the time it takes for said main shaft to rotate threequarters of a revolution.

3. The sewing machine of claim ll, including an operator-actuable contact in series with said second relay and said second switch means, a circuit arm by-passing said second switch means and said operator-actuable contact and including a first contact actuated by the first mentioned relay and a second contact in series with the first contact and actuated by said second relay, another contact in series with the first mentioned relay and with said one rotary switch and actuable by said second relay, whereby upon actuation of said operatoractuable contact and upon said main shaft rotating at a speed according to said low speed drive ratio, said second relay becomes energized thereby actuating said cutting means to an operative position thereof and also thereby closing said second contact and said another contact, said first contact being thereby closed by virtue of the first mentioned relay being energized through a circuit including said another contact and said one rotary switch, the first mentioned relay becoming de-energized by virtue of the insulator sector of said one rotary switch contacting its related brush whereupon said braking means is actuated to a braking position and said first contact is simultaneously opened to de-energize said second relay which in turn functions to actuate said cutting means to an inoperative position thereof.

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