US3358629A - Apparatus for stopping a sewing machine with its needle in pre-determined position - Google Patents

Description

Dec. 19, 1967 L. BONO 3,358,629

- APPARATUS FOR STOPPING A SEWING MACHINE WITH ITS NEEDLE IN FIRE-DETERMINED POSITION Filed Oct. 18, 1965 2 Sheets-Sheet 1 Dec. 19, 1967 BONO 3, 9

APPARATUS FOR STOPPING A SEWING MACHINE WITH ITS NEEDLE IN PRE-DETERMINED POSITION Filed Oct. 18, 1965 2 Sheets-Sheet 2 United States Patent 3,358,629 APPARATUS FOR STOPPING A SEWING MACI IINE WITH ITS NEEDLE IN PRE-DETERMHJED POSI- TION Luigi Bono, Pavia, Italy, assignor to Necchi Societa per Azioni, Pavia, Italy Filed Oct. 18, 1965, Ser. No. 497,378 Claims priority, application Italy, Mar. 5, 1965, 748,086 9 Claims. (Cl. 112--219) ABSTRACT OF THE DISCLOSURE A sewing machine control system for effecting the stopping of the machine in correspondence to the sewing needle being at either of predetermined positions along the axis of reciprocation thereof, said system including a Zener diode and a tacho-generator for controlling the speed of the needle drive shaft and a pair of rotary contacts, one of which restricts the activation of a brake for said shaft in correspondence to said shaft rotating at a particular speed and the other of which restricts the actuation of said brake in correspondence to the needle being at particular positions along said axis thereof.

The present invention relates to a device for rapidly stopping a sewing machine in correspondence to its needle being in a pro-determined axial position.

The main purpose of this invention is that of reducing the dead working periods, in other words, to eliminate those preparatory operations which the operator must necessarily perform before he can commence a new sewing cycle.

The problem which must be resolved consists of bringing the machine in the shortest possible time from its full operating velocity to a stop position with the needle either in the fabric at the lower axial position or out of the fabric at the upper axial position of its reciprocating stroke. The device which is the object of the present invention is applied to sewing machines which can operate at different pre-established velocities, and it comprises a 3-phase constant speed electric motor which rotates continuously, an electromagnetic clutch to connect a driven shaft of the machine to the motor shaft, said driven shaft being operatively associated with the needle to reciprocate it between upper and lower axial positions, an electromagnetic brake adapted to exert upon said driven shaft a braking action, a tacho-generator keyed on said driven shaft and adapted to act upon both circuits of control: that of the brake and that of the clutch, a known mechanism which follows the angular rotation of said driven shaft and is pro-disposed to cooperate with means to stop the machine with the needle in a pre-determined position when the machine has slowed down to a pre-established reduced velocity, said device being characterized by the fact that it effects a reduction from said full operating velocity to said reduced velocity through the use of a Zener diode disposed in the excitation control circuit for the brake and the clutch, which diode is subjected to the voltage output of said generator.

The object device is characterized furthermore by the fact that during the time employed for the machine to slow down from full running velocity to said reduced velocity, the Zener diode is subjected to reverse voltages higher than the diode break-down voltage and that the generator output voltage which occurs during the preestablished reduced velocity of the machine corresponds to the break-down voltage of the Zener diode.

The objects of the present invention will become evident from a reading of the followed detailed description which is referred to the accompanying drawing, in which:

FIGURE 1 represents a schematic electrical layout of the velocity control device and the stopping control device of the machine while FIGURE 2 represents the characteristic voltage curve of a Zener diode.

FIGURE 3 is a vertical view of a sewing machine with portions thereof in cross section to show the machine operating parts.

Referring to FIGURE 3, sewing needle 1 is connected to a needle bar 2 which is driven by main shaft 3, said shaft having mounted thereon the tachometric dynamo 37 (schematically represented in FIGURE 3) as well as a needle position reading device in the form of a rotary switch comprised of rings 21, 22, and 23. Shaft 3 is driven by motor 11 via a belt 4. The motor 11 includes a motor shaft 5 which is coupled to a driven shaft 6 by means of a magnetic power coupling 51. A magnetic power brake 33 is keyed onto shaft 6. A more detailed description of the motor and of the coupling and brake appears in British Patent No. 927,630.

In the electrical layout of FIGURE 1, there is indicated by numeral 10 the main switch of the electrical threephase line which supplies the motor 11, and by 12 the fuses for protecting said line against overload. From two wires of said line there is derived the electrical supply for the primary of the transformer 13. From the secondary of said transformer lead two electrical feed wires for the bridge rectifier 14 which is provided to furnish direct current to the electrical control devices of the machine. Between wires 15 and 16 connected respectively to the positive pole and to the negative pole of the rectifier 14 are connected the different electrical components which comprise the electrical layout, represented in the drawing according to usual schematic symbols.

On the first vertical line nearest the rectifier, there are placed in series the stator coil 17 of a tachometric dynamo (generator) and the variable resistance 18 adapted to vary the current intensity for exciting the said stator coil.

In the next vertical line, a servo-relay 19 is tied-in in series with a rotary switch constituted by three rings 21, 22, and 23 the first of which comprises a conducting sector 24 and includes two brushes 25 and 26 which slide upon its surface.

The ring 22 is conductive over its entire circumferential extent which is in sliding contact with sliding brush 27.

Ring 23 comprises a conducting sector 28 and its circumferential extent is contacted by sliding brushes 29 and 30. On the same vertical line, there are connected in series the micro-switches 31 and 20, the first of which determines, as will later on be described, the positioning of the needle either in its upper or lower dead axial position when the machine is stopped, while the second provides for bringing about the stopping of the machine.

Between the brushes 2.7 and 30 there is provided a contact 19' which is controlled by the relay 19.

On the next vertical line there is connected the excitation circuit of the brake 33, in the collector circuit of the transistor 34.

On this last mentioned line, there is also the push type self-returning switch having two contacts 35 and 35" whose function will be explained later. The base of the transistor 34 is connected through polarizing resistor 36 to the next vertical line which includes the tachometric dynamo (generator) 37.

On this generator line there is also provided a double contact push type self-returning switch 38 for providing full running velocity, the contact 35" of the switch 35, a diode 40, a Zener diode 41, and finally the contact 19" of the servo-relay 19.

Bridging the contact 35" are two conductors 43 and 44 which through the respective resistances 45 and 46 furnish the-control signal to the base of the transistor 47 which regulates a further power transistor 48-whose base is polarized by means of a potential divider consisting of the resistances 49 and 50 and upon whose collector circuit is placed the winding of'the clutch 51. A contact 38 forming part of the switch 38 serves to excite directly the winding of. the clutch. The diodes 53 and 54.

ner. Uponthe closing. of the main switch 10, the motor.

starts to turnwithout load since the clutch is not excited but the. brake is excited, whereby the machine. driven shaft remains stationary.

For controlling the machine, there is provided a pedal not illustrated, in the figure, which may assume three different positions corresponding to each of which the machine is actuated to run at a pre-established velocity. Pressing the pedal so as to reach. the first of said positions, there is obtained the opening of the micro-switch Z and the consequent.derexcit-ation of the servo-relay 19 whose contacts dispose themselves in the following: manner: 19' opens and interrupts the connection between the brushes 27 and 30; 19 opens de-ex-citing the brake 33; 19 closes to supply the clutch 51.

The machine driven shaft is now placed in motion and: its speed is controlled by the generator 37' which, by means of the transistors 47 and 48, maintains the velocity at a constant 150 revolutions per minute, this velocity being calibrated by means of the resistance 46.

Pressing further'the pedal so as to cause it to reach the second position, there is operated the switch 35, through which there is obtained the opening of the contacts 35' and 35" of which the first interrupts the emission circuit of the transistor 34, thereby precluding that the brake becomes excitedby the generator 37 when the driven shaft rotates at higher than the 150 rpm. which is the speed in eifect while the pedal is in the first position, and the opening of the second contact 35 results in the speed of. the driven shaft rising from said 150 rpm. to a higher median speed which is calibratable by means of the resistance 45. By pushing the pedal up to its third and last position, there occurs the switching of the contacts 38' and 38 of the switch 38 of which the first contact by opening, and since it is in series with the generator 37, eliminates the automatic velocity control and the second contact 38", by closing, short circuits the transistor 48 and thereby directly supplies the clutch circuit bringing the machine driven shaft to its full velocity.

When it is desired to bring about the rapid stopping of the machine and the positioning of the needle, the pedal is released and thereby the switches 35 and 38 automatically return to rest position, which corresponds to their positions as indicated in the figure. The closing of contacts 35" and 38 reestablishes velocity control which by means of a diode 4%), the Zener diode 41 and the transistor 34 reactivates the braking action by means of the output voltage supplied from the generator up until the machine is slowed down to the reduced velocity of 150 revolutions per minute, as more fully explained below.

Furthermore, release of the pedal causes switch 20 to assume the closed position as shown in the figure. Although switch 20 may be closed, relay 19 remains deexcited because the circumferential extent of sectors 24 and 28 is so limited that at above 150 rpm. the excitation impulses to relay 19 last for a shorter period of time than the time constant of said relay. Furthermore, contact 19 remains open until the machine has slowed down to the preestablished reduced Velocity of 150 revolutions per minute.

Having reached said reduced velocity, the generator which is coupled to the motor, does not any longer furnish a sufiicient output voltage to overcome the breakdown voltage of the Zener diode 41 so that, as soon as revolutions per minute has been reached, there ceases automatically the braking action, The Zener diodes present the characteristic that the breakdown voltageZ (see FIGURE 2), has a definite value within a very restricted interval so that through the use of said diodes it is possible to obtain in rapid fashion a change in velocity of the machine from the running velocity to a closely defined reduced velocity.

In fact, with reference to FIGURE 1, by varying the resistance 18 there is elfected an equalization of the voltage furnished by the generator relative to the breakdown voltage of the Zener diode, in correspondence to a velocity of the dynamoshaftequalito. 150 turns per minute.

- In correspondence. to said reduced velocity, the Zener diode assumes an internal resistance which is practically infinite, the brake thereby is deactivated and the machine finds itself, regulated to turn at said reduced value of velocity by means of the regulating circuit comprising the generator 37, the resistance 46 and the two transistors 47 and 48. Specifically when themachine reaches the reduced value of 150 r.p.m. the Zener diode opens the brake excitation circuit, and with the de-excitation of relay 19 and the. consequent closing of contact 19" the clutch 51 is tied into the speed regulatingcircuit of generator 37, said contact 19 remaining closed while the reduced speed of 15.0.r.-p.m. is ineifect so long as sectors 24 and 28 are not in contact with their corresponding brushes. The speed regulating circuit of the machine would not become activated only in the event that the reduced speed of 150 r.p.m. were to occur at the same time that the sectors 24 and 28' were in contact with their corresponding brushes.

The circumferential extent of conductive sector 28 is smaller than that of sector 24-and it is-calculated so as to provide, during said velocity of 150 revolutions per minute, a time period of current how to relay 19 which is longer than the time constant of the relay induction windingyso that the sector 28 causes relay 19-to become excited only when the velocity has slowed down to 150 r.p.m., since at greater velocity the current flow to the relay does not last long enough to overcome the time constant of the induction winding.

Upon relay 19 becoming excited, contact 19' closes thereby by-passing or short-circuiting sector 28, so that current continues to flow to relay 19-f0r as long as brush 25 is in contact with sector 24, it being kept in mind that sector 24 is wider than sector 28. The circumferential extent or width of sector 24 is calculated to provide a particular maximum distance from extreme upper or lower axial positions at which the needle may be stopped.

If the machines rotating parts have such a kinetic energy, or momentum, that sector 24 slides past and loses contact with brush 25 while relay 19 is excited, the effect. simply is that as sector 24 loses contact with brush 25, the relay 19 again becomes de-excited thereby returning contacts 19', 19", and 19 to their positions as shown in FIGURE 1. This interrupts the braking action and re-excites the clutch so that the machine driven shaft performs another revolution and the heretofore described braking operations are repeated so that the ma chine driven shaft is stopped the next time sector 24 con tacts brush 25.

In summary:

Sector 24 is correlated or phased relative to the needle so that it functions to stop the machine in correspondence to said needle being at either of particular axial positions.

The circumferential extent of sector 28 is such that relay 19 is excited only upon the driven shaft rotating at a certain velocity, and contact 19' serves to maintain the circuit continuity even after sector 28 has lost contact with brush 29 but while sector 24 is still in contact with brush 25.

The two sectors 24 and 28 perform respectively distinct functions so that it would not be possible to eliminate either without also sacrificing its particular function. For'example, the circumferential extent of sector 28 is not large enough to maintain a strong braking action for a long enough time period to effectively stop the machine driven shaft. If sector 28 were enlarged, the braking action would begin at a higher speed than 150 rpm. Stated otherwise, the circumferential extent of sector 28 provides for a braking action at a particular, closely determined speed of the driven shaft and said circumferential extent is governed by said speed.

On the other hand, While sector 28 determines when the braking action is to commence, sector 24 determines how long it is to last. Specifically, sector 24 does not permit the braking action to continue if the needle is too far removed from one of its extreme axial positions. Sector 24 is larger than sector 28 to an extent so as to maintain relay 19 excited long enough to provide effective braking action; however, the maximum extent of sector 24 is determined by the maximum distance from the extreme axial positions at which it is permissible to stop the needle. In other words, if it is desired to stop the needle within a close distance from its extreme axial positions, sector 24 must be smaller than if it is permissible to stop said needle within a relatively larger distance from said extreme axial positions.

With the excitation of the servo-relay 19, there is also obtained the de-excitation of the clutch through the opening of the contact 19".

The velocity of the machine being of reduced value and the excitation of the brake circuit being considerable, the machine stops with the needle at its upper or lower axial dead point, depending upon the position of the switch 31.

, Switch 31 is actuated by hand to either the left or right hand position, as referred to FIGURE 1, before the machine is started. Each position, left and right, corresponds to the needle being either in upper or lower axial position, depending upon the phasing between the needle bar and ring 21 which is rigidly mounted on the driven shaft. Therefore, the positions which switch 31 is manually set determines the axial position of the needle with the driven shaft in stopped position.

There has not been illustrated the three positioned pedal since its function does not enter within the essence of the invention and since its operation and use is known in the art. It is noted that in going from its rest to its successive positions, the pedal successively actuates 20, 35, and 38 and these elements remain so actuated although the pedal moves to its next succeeding position. Elements 20,

.35, and 38 return to their rest position only upon the definite release of the pedal.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.

What is claimed is:

1. A sewing machine including a motor drive shaft, a driven shaft, and an electromagnetic clutch coupling the aforementioned shafts to each other, an axially reciprocable needle operatively associated with said driven shaft and reciprocatingly driven thereby between the top and bottom axial positions, an electromagnetic brake operable to exert a braking action upon said driven shaft, a generator drivingly connected to said driven shaft and providing a voltage output proportional to the speed of said driven shaft, a stopping means for stopping said driven shaft in correspondence to said needle being at one of various pre-established axial positions, said stopping means comprising respective energizing circuits for said brake and said clutch, said circuits including a Zener diode and the voltage output of said generator being impressable upon said brake circuit through said Zener diode, said generator providing a voltage output in opposition to the normal bias of said diode, and said generator output being impressable upon said clutch circuit with said Zener diode serving to limit the said voltage output to said clutch to a value no greater than the diode breakdown voltage, a follower means having respective positions corresponding to respective positions of said needle, and switch means operative to simultaneously excite and de-excite said brake and clutch, respectively, said switch means being operatively associated with said follower means, said follower means being correlated to actuate said switch means in correspondence to particular positions of said needle.

2. The sewing machine of claim 1, wherein said switch means includes a first switch for energizing said brake from a voltage source other than said generator output, and a second switch for simultaneousiy de-energizing said clutch relative to said generator output, said first and second switches alternately operating in reverse manner.

3. The sewing machine of claim 1, including a relay means to control said switch means, and further including mechanically operable contact means, a first of which is actuable to connect said clutch across a voltage source other than said generator output and to simultaneously interrupt the voltage output of said generator, a second of which is actuable to alternately excite and de-excite said brake by means of said other voltage source, and a third of which is actuable to alternately connect and disconnect said relay means across said other voltage source.

4. The sewing machine of claim 3, including an energizing circuit for said relay means and wherein said follower means comprises a rotary switch rotatively driven by said driven shaft and electrically connected in series with said third contact means in the energizing circuit of said relay means, said rotary switch alternately opening and closing the relay energizing circuit in correspondence to the rotation of said rotary switch, said relay circuit being closed by said rotary switch only in correspondence to particular rotary positions thereof.

5. The sewing machine of claim 3, wherein said driven shaft is operable at a maximum rotative speed which exceeds a certain minimum speed, with said switch means and contact means being positioned whereby said brake is de-excited, relative to all voltage sources and said clutch is excited directly from said other voltage source and deexcited relative to said generator output, the speed of said driven shaft being reduceable to said minimum speed through a switching action of said contact means whereby said generator is connected to provide an output reversely impressed across said Zener diode to said brake, said generator being calibrated to provide a voltage output exceeding the diode breakdown voltage in correspondence to said driven shaft rotating at above said minimum speed, said diode being operative to interrupt the excitation of said brake by means of said generator output in correspondence to said driven shaft assuming said minimum speed, said generator being calibrated to provide an output voltage equal to said breakdown voltage in correspondence to said shaft rotating at said minimum speed.

6. The sewing machine of claim 1, including a speed regulating means, and wherein said generator output is connected to said clutch through said speed regulating means which permits various speeds of said driven shaft in correspondence to a constant voltage output from said generator.

7. Device for stopping a sewing machine with the needle in pre-determined position in which the machine may assume different pre-established velocities, comprising an electric motor for continuous rotation, a driven shaft and an electromagnetic clutch to couple said driven shaft ofthe machine to the shaft of said motor, an electromagnetic brake adapted to exercise a braking action on said driven shaft, a regulating circuit for said brake and clutch, a tachometric dynamo keyed on said driven shaft adapted to act upon both the regulating circuits of the. brake and of the clutch, a mechanism for sensing the angular position ofsaid driven shaft cooperating with said means for stopping the machine with the needle in predetermined position when the machine has arrived at a pre-established reduced velocity, a:Zener diode in the brake and clutch regulating circuits, said dynamo and diode being correlated with each other whereby the voltage output of said dynamo is imposed upon said diode to produce a. resultant voltage in the brake and clutch regulating circuits, said resultant voltage determining the speedof said' driven shaft.

8; Devicefor the stopping of a sewing machine with the needle in pre-determined position according toclaim 7, characterized by the fact that during the timerequired for the machine to pass from full running velocity to said reduced velocity, the Zener diode is subjected to reverse voltages higher than its breakdown voltage, said breakdown voltage corresponding to the voltage outputoffsaid dynamo at said reduced velocity of saiddriven shaft.

9. Device for stopping. a sewing machine with the:

needle in pre-determined position according to claim 7, characterized by the fact that said reduced velocity corresponds to a velocity at which there may be regulated the machine for sewing.

References Cited UNITED STATES PATENTS JORDAN FRANKLIN, Primary Examiner.

H. H. HUNTER, Examiner.

Claims (1)

1. A SEWING MACHINE INCLUDING A MOTOR DRIVE, SHAFT, A DRIVEN SHAFT, AND AN ELECTROMAGNETIC CLUTCH COUPLING THE AFOREMENTIONED SHAFTS TO EACH OTHER, AN AXIALLY RECIPROCABLE NEEDLE OPERATIVELY ASSOCIATED WITH SAID DRIVEN SHAFT AND RECIPROCATINGLY DRIVEN THEREBY BETWEEN THE TOP AND BOTTOM AXIAL POSITIONS, AN ELECTROMAGNETIC BRAKE OPERABLE TO EXERT A BRAKING ACTION UPON SAID DRIVEN SHAFT, A GENERATOR DRIVINGLY CONNECTED TO SAID DRIVEN SHAFT AND PROVIDING A VOLTAGE OUTPUT PROPORTIONAL TO THE SPEED OF SAID DRIVEN SHAFT, A STOPPING MEANS FOR STOPPING SAID DRIVEN SHAFT IN CORRESPONDENCE TO SAID NEEDLE BEING AT ONE OF VARIOUS PRE-ESTABLISHED AXIAL POSITIONS, SAID STOPPING MEANS COMPRISING RESPECTIVE ENERGIZING CIRCUITS FOR SAID BRAKE AND SAID CLUTCH, SAID CIRCUITS INCLUDING A ZENER DIODE AND THE VOLTAGE OUTPUT OF SAID GENERATOR BEING IMPRESSABLE UPON SAID BRAKE CIRCUIT THROUGH SAID ZENER DIODE, SAID GENERATOR PROVIDING A VOLTAGE OUTPUT IN OPPOSITION TO THE NORMAL BIAS OF SAID DIODE, AND SAID GENERATOR OUTPUT BEING IMPRESSABLE UPON SAID CLUTCH CIRCUIT WITH SAID ZENER DIODE SERVING TO LIMIT THE SAID VOLTAGE OUTPUT TO SAID CLUTCH TO A VALUE NO GREATER THAN THE DIODE BREAKDOWN VOLTAGE, A FOLLOWER MEANS HAVING RESPECTIVE POSITIONS CORRESPONDING TO RESPECTIVE POSITIONS OF SAID NEEDLE, AND SWITCH MEANS OPERATIVE TO SIMULTANEOUSLY EXCITE AND DE-EXCITE SAID BRAKE AND CLUTCH, RESPECTIVELY, SAID SWITCH MEANS BEING OPERATIVELY ASSOCIATED WITH SAID FOLLOWER MEANS, SAID FOLLOWER MEANS BEING CORRELATED TO ACTUATE SAID SWITCH MEANS IN CORRESPONDENCE TO PARTICULAR POSITIONS OF SAID NEEDLE.

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