US3425375A

US3425375A - Thread control

Info

Publication number: US3425375A
Application number: US585120A
Authority: US
Inventors: Herbert V Jacobs; Michael L Wajda
Original assignee: Jacobs Machine Corp
Current assignee: Jacobs Machine Corp
Priority date: 1966-10-07
Filing date: 1966-10-07
Publication date: 1969-02-04
Anticipated expiration: 1986-02-04

Description

Feb; 4, 1969 H. v. JACOBS ET AL THREAD CONTROL Sheet Filed Oct. 7. 1966 INVENTORS. H ERBERT V. JACOBS BY M I C HAEL L. WAJ DA mmwuw ATTORNEYS.

Feb. 4, 1969 v, JACOBS ETAL 3,425,375

THREAD CONTROL Filed Oct. 7. 1966 t 1 107 "i Q @5. j'jg f 108 ct LOAD 76 3 70 INVENTORS.

V HERBERT V. JACOBS MICHAEL L. WAJDA Cauwu W,@W/ & Gem

ATTORNEYS.

United States Patent 3,425,375 THREAD CONTROL Herbert V. Jacobs, Merion Station, and Michael L. Wajda,

Philadelphia, Pa., said Wajda assignor to Jacobs Machine Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Oct. 7, 1966, Ser. No. 585,120 US. Cl. 112Z18 Int. Cl. Dc 11/00; G08b 21/00,- D03d 51/34 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to sewing machines and more particularly to a thread control for a sewing machine to determine breakage of the thread therein.

In industrial processes utilizing sewing machines, it is extremely advantageous to know when the thread in the machine has been broken. If the thread in the machine is broken without detection, the sewing process continues without any thread being used to fasten the product of the machine together. The end product is therefore useless unless the article may be run through the sewing machine again. In sewing machines of the type wherein a lock stitch is produced for fastening, the thread is constantly being drawn into tension as the thread is pulled to the needle by the take-up. However, when not being taken up, the thread is slack. Therefore, the thread in the machine is alternately not in tension and in tension even when not broken. When the sewing machine is in operation, the thread is primarily slack and, therefore, sensing the tension on the thread does not aid in determining whether or not the thread is broken.

It is, therefore, an object of the invention to overcome the aforementioned problems.

It is another object of the invention to provide a thread control which is adapted to determine the continuity of the thread in a sewing machine.

Another object of the invention is to provide a new and improved thread control which is adapted to determine whether the thread in a lock stitch type sewing machine is broken.

Another object of the invention is to provide a new and improved thread control having a novel sensing circuit for enabling determination of whether the thread is broken.

Another object of the invention is to provide a new and improved sensing circuit which is adapted to provide a control signal if a condition is not satisfied within a predetermined period of time.

These and other objects of the present invention are achieved by providing a thread control for a sewing machine comprising means responsive to the tension on said thread for providing a first signal when said thread is in tension and for providing a second signal when said thread is not in tension, means responsive to said first and second signals for determining that said thread is broken if said first signal is not received within a predetermined period after said second signal is received.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 1

FIG. 1 is a fragmentary side elevational view of the head of a sewing machine embodying the invention;

FIG. 2 is an enlarged fragmentary side elevational view showing the co-action between the take-up and the thread tension;

FIG. 3 is an enlarged fragmentary side elevational view similar to FIG. 2 with the take-up in an intermediate position of the take-up cycle;

FIG. 4 is a sectional view taken along the line 4-4 in FIG. 2;

FIG. 5 is an enlarged sectional view taken along the line 5-5 in FIG. 2;

FIG. 6 is an enlarged sectional view taken along the line 66 in FIG. 5;

FIG. 7 is an enlarged sectional view taken along the line 7-7 in FIG. 2; and

FIG. 8 is a schematic diagram of the sensing circuit embodying the invention.

Referring now in greater detail to the various figures of the drawings wherein similar reference characters refer to similar parts, a sewing machine embodying the invention is generally shown at 20 in FIG. 1. The sewing machine 20 is basically a conventional sewing machine and except as otherwise stated hereinbelow may be of the type shown in Gray Patent No. 1,020,089, patented Mar. 12, 1912.

The sewing machine 20 includes a take-up 22 which is pivotably mounted and is adapted to be drawn up and down within a vertical slot 24. The machine 20 further includes a thread tension 26 which is mounted below and adjacent the slot 24. Adjacent the thread tension 26 is a guide 28 which is secured to the side of the head of the sewing machine 20 as best seen in FIG. 7.

In accordance with the invention, there is also provided with the sewing machine a copper bar 30 which is mechanically connected to but electrically isolated from the head of the machine. The copper bar 30 is fastened to the mounting block 32 which preferably comprises silicone or nylon by

fasteners

34 and 36.

As best seen in FIGS. 1, 4 and 5, the bar 30 is mounted above and adjacent the thread tension 26. The mounting block 32 depends from a mounting bracket 33 which is secured to the head of the sewing machine 20 by a fastener 35.

As best seen in FIG. 2, the

fasteners

34 and 36 act as terminals to which electrical leads 38 are attached. The bar 30 is basically L-shaped and the bottom leg 40 thereof, as best seen in FIG. 5, extends horizontally toward the body of sewing machine 20.

As best seen in FIGS. 2 and 3, the thread tension 26 includes a spring 42. Spring 42 is mounted about the thread tension 26 to a pivotably mounted disc 43. Disc 43 is conventionally mounted in the thread tension 26 so that it is adapted to be spring urged about the axis of the thread tension. The disc is normally urged in the direction of arrow 45, shown in FIGS. 2 and 3. Therefore, the tendency of spring 42 is to be urged against copper bar 30. Spring 42 is substantially U-shaped and, as best seen in FIGS. 2, 4 and 6, includes a pair of

legs

44 and 46 and a U-shaped web 48 which is inclined at an angle from

legs

44 and 46.

As best seen in FIGS. 1, 2 and 6, the thread 49 passes about thread tension 26 up through the U-shaped web 48 of spring 42, underneath guide 28, through the opening in take-up 22, and passed to the needle 53 via a guide 55. As best seen in FIG. 2, when the thread 49 is slack, the spring 42 is urged against copper bar 30, thus, providing a closed circuit in a sensing device as will hereinafter be seen. The thread is slack during most of the cycle of the sewing machine. That is, only when the take-up 22 is rising, as shown in FIG. 3, is the thread 49 brought into tension. When the take-up 22 does rise and the thread is drawn into tension, the thread between guide 28 and spring 42 draws the spring 42 towards guide 28 which causes the spring to pivot in the direction of arrow 51. This action opens the circuit between the spring 42 and bar 30. When take-up 22 reaches its uppermost position, as shown in FIG. 2, the thread 49 slackens again. The disc 43 is urged by the spring action of thread tension 26 in the direction of arrow 45. The spring 42 is, therefore, urged against bar 30 and thereby again closes the circuit therebetween. It can, therefore, be seen that the spring 42 is pivoted away from bar 30 each time the take-up 22 is moving in the direction of arrow 57. The circuit formed between spring 42 and bar 30 is thereby opened each time a stitch is formed by sewing machine 20.

The spring 42 because of its securement to the thread tension 26 is electrically grounded to the sewing machine 20. The copper bar 30 is mounted to the sewing machine by mounting block 32 which is comprised of an insulating material. The copper bar 30 is therefore isolated electrically from the spring 42 unless they are actually in contact. The spring 42 and copper bar 30 therefore act as an electrical switch to provide an indication of whether or not thread 49 is in tension. Whenever the thread 49 is slack, the switch is closed. Conversely, the switch is opened each time the thread 49 is drawn into tension.

The sensing circuit 50 for deter-mining whether the thread in the sewing machine is broken is shown schematically in FIG. 8. Circuit 50 basically comprises a uni-junction transistor 52, a relay 54, a first switch 56, a second switch 58 and a reset switch 60. The uni-junction transistor 52 includes an emitter 62, a first base 64 and a second base 66. The emitter of uni-junction transistor 52 is connected to a capacitor 68 which is in turn connected to the first terminal 70 of switch 58. The emitter is also connected via serially connected resistor 72 and variable resistor 74 to a second terminal 76 of switch 58 and to diode 78. Diode 78 is connected to a first terminal 80 of switch 56 and via a resistor 82 to a negative source of voltage (V).

'The first base 64 of uni-junction transistor 52 is connected via a reistor 84 to the first arm 85 of relay 54 and, to a first end of coil 86 of relay 54 and to diode 88. Diode 88 is connected across coil 86 which is connected at its other end to the negative source of voltage (V). A first contact 89 associated with arm 85 of relay 54 is connected to a first terminal 90 of reset switch 60. A second terminal 92 of reset switch 60 is connected to ground as are

terminals

69 and 70 of

switches

56 and 58, respe tively. Terminal 76 of switch 58 is connected to the negative potential via resistor 94.

The second base 66 of uni-junction transistor 52 is connected to ground via resistor 96 and to the emitter 62 of the uni-junction transistor via capacitor 68. Switch 56 further includes an arm 98 which is normally urged against terminal '69. The switch 56 is a schematic representation of the electrical switch formed by spring 42 and bar 30. That is, each time the spring 42 is drawn away from bar 30, the arm 98 would likewise be disengaged from terminal 69 thereby opening switch 56. Switch 56 is therefore normally closed.

Switch 58 includes an arm 100 which is normally urged away from terminal 70. The switch 58 is preferably associated with the treadle switch of sewing machine 20 which would urge arm 100 against terminal 70 to close switch 58 when the sewing cycle of the sewing machine 20 is initiated. The switch 58 is thus normally open and when the sewing machine is started, arm 100 is closed against terminal 70.

The reset switch 60 includes a spring urged arm 102 which is normally urged against

terminals

90 and 92 thus closing the switch. When the arm 102 is pressed, it is urged away from the terminals and 92 opening the switch and as will hereinafter be seen resetting the circuit.

Relay 54 also includes a second arm 104 and a terminal 106 associated therewith. Relay arm 104 is connected via a first line 107 to a load 108. Terminal 106 is connected via a second line 110 to a load 108. The arm 104 is normally urged away from terminal 106. When the relay coil 86 is energized, the arm 104 is drawn against terminal 106 which thereby closes the circuit to load 108 and initiates operation thereof.

In operation, the uni-junction transistor 52 forms a voltage divider between the negative source of voltage ('V) and ground when the arm 98 of switch 56 is closed and arm of switch 58 is open. The switch 56 is opened each time the sewing machine 20 makes a stitch. That is, each time the takeup is moved in the direction of arrow 51 as hereinbefore mentioned, the thread 49 is drawn into tension and switch 56 is thereby opened. If the thread should break, the spring 42 is not drawn away from bar 30 and thus switch 56 does not open.

Prior to starting the sewing machine 20, switch 58 is open which causes the capacitor 68 to be charged to the potential of V. The emitter 62 is therefore at a more negative potential than the base 64 of the uni-junction transistor. The uni-junction transistor 52 is thus cut-off and acts as a voltage divider.

Assuming that the sewing machine is started, switch 58 is closed thereby and that the thread in the sewing machine is continuous and operational, the closing of switch 58 by urging arm 100 against terminal 70 enables capacitor 68 to discharge through

resistors

72 and 74. The voltage at emitter 62 thereby starts to increase from V towards ground. Since the thread is in operative condition, the switch 56 is opened and thereby causes capacitor 68 to be charged through diode 78 and resistor 82 and the capacitor is thus charged again to V. The closing of arm 98 when the tension on the thread is released starts the discharge of capacitor 68 again. The voltage in emitter 62 therefore begins to rise. If the thread continues to remain operative, the switch 56 will again be opened prior to the voltage at emitter 62 increasing greatly enough to change the state of uni-junction transistor 52. The operating condition of circuit 50 remains in this condition unless the switch 56 fails to open which is indicative that the thread is broken.

Assuming that switch 58 is closed as operation of the sewing machine is initiated and the thread in the sewing machine 20 is broken: As switch 58 is closed, the capacitor 68 begins to discharge. The voltage therefore begins to rise at the emitter 62. The uni-junction transistor 52 is driven to saturation whenever the voltage at emitter 62 increases to a potential greater than the potential at base 64. This saturation potential is reached at emitter 62 in a fixed period of time based on the values of capacitor 68 and

resistors

72 and 74. This period, which is referred to as the time constant, can be varied by adjustment of resistor 74 and is preferably preset to be substantially as long as it takes the sewing machine to sew two stitches at its top speed. Therefore, if the arm 98 does not open from terminal 69 within the time that it takes for the sewing machine to make two stitches, the voltage at emitter 62 exceeds the potential of base 64.

When the emitter reaches the greater potential, the unijunction transistor 52 becomes conductive between the first base 64 and emitter 62. The capacitor 68 is then charged via emitter 62 and base 64 through relay coil 86. The surging current through relay coil 86 causes arm 85 to be magnetically drawn against the terminal 89. The closed circuit between arm 85 and terminal 88 completes a closed circuit from V to ground through relay coil 86 which thereby continues to cause the relay arm 85 to remain magnetically drawn against terminal 89. The second arm 104 of the relay 54 is also drawn towards coil 86 and contacts terminal 106 which thereby causes a complete circuit to load 108. The load 108 is preferably comprised of an indicating light or alarm signal which warns that the thread in the sewing machine is broken. The load also preferably includes a device for closing or shutting off the machine.

The circuit 50 remains in this warning state until the reset switch 60 is opened by pressing arm 102 away from

terminals

90 and 92. The opening of the switch opens the circuit including relay coil 86 to prevent further flow of current therethrough and thereby causing

arms

84 and 104 to be urged away from

terminals

89 and 106, respectively. The condition of the circuit is restored to its state prior to initiation of the operation of the sewing machine 20.

It can therefore be seen that this invention provides a new and improved circuit for detecting a broken thread in a lock stitch type sewing machine. The operation of the circuit 50 is such that if after a predetermined period of time the spring 42 is not urged away from the bar 30 by action of the take-up, it indicates that the thread is broken. The sensing device is clamped into a state of equilibrium to indicate that the thread is broken and cannot be turned oil? until the reset switch 60 is actuated. The operation of the sewing machine may be turned off by the device and thereby enable someone to rethread the sewing machine prior to reoperation thereof. The solid state circuitry utilized in the circuit enables great reliability and is also inexpensive to operate because current drain is minimal.

Although the time constant in the preferred embodiment is equal in time to the sewing time of two stitches by the sewing machine 20, by varying the resistance of resistor 74, the time constant may be increased or decreased.

Load 108 may take many forms. It may also include a buzzer or other form of alarm in addition to a warning lamp to notify an operator that the machine is temporarily put out of order because of a thread breaking. The switch 56 which is schematically illustrative of the spring 42 and copper bar 30 thus generates two conditions. The first condition when the switch is open is indicative of the thread being in tension. The second condition when the switch is closed is indicative that the thread is slack. Circuit 50 utilizes the two conditions of the switch to determine a breakage in the thread. That is, the circuit 50 is operative in a first state in which relay 54 is not energized unless the first condition of the switch 56 is not detected within a predetermined period after the second condition of the switch 56 is first detected or in that predetermined period after the operation of the circuit 50 is initiated by closing switch 58.

Without further elaboration the foregoing will so fully illustrate my invention, that others may, by applying current or future knowledge, readily adapt the same for use under various conditions of service.

What is claimed as the invention is:

1. A signalling device comprising a uni-junction transistor, a switch, delay means and an alarm, said transistor comprising an emitter electrode and two base electrodes,

said transistor normally being non-conductive, the emitter of said transistor being connected to said switch via said delay means, said switch providing a first voltage to said emitter when in a first position and a lower second voltage when in a second position, said uni-junction transistor being driven conductive when said emitter reaches a predetermined voltage intermediate said first and said second voltages, said delay means delaying the build-up of voltage at said emitter when said switch is in said first position and dropping said emitter voltage to said second voltage when said switch is in said second position, said transistor being adapted to initiate said alarm when driven conductive, said delay means being adapted to delay the build-up of voltage at said emitter for a predetermined period of time so that if said switch remains in said first position for said time said alarm is initiated.

2. The invention of claim 1 wherein said switch is pro-v vided on a sewing machine having a thread tension means including a pivotably mounted spring, and a take-up for alternately drawing the thread taut and enabling the thread to be slack, said switch comprising said spring of said thread tension means and a conductive member mounted adjacent thereto, said switch being in said first position when the thread of said sewing machine is slack and in said second position when said thread is taut.

3. The invention of claim 1 and further including a relay having a coil, a first base of said transistor being connected to said coil of said relay, said relay being adapted to initiate said alarm when said uni-junction transistor is driven conductive.

4. The invention of claim 3 wherein said relay includes a pair of switches which are closed by energization of said relay, a first one of said switches of said relay initiating an alarm and a second of said switches locking said signalling device in a state to continuously operate said alarm.

5. The invention of claim 4 and further including a reset switch, said second switch of said relay being associated with said reset switch, said reset switch being adapted to de-energize said relay to enable said signalling device to return to its initial state and terminate operation of said alarm.

References Cited UNITED STATES PATENTS 2,868,151 1/1959 Winz 112-219 2,940,407 6/1960 Mitchell 112-219 3,268,047 8/ 1966 Grygera et al.

FOREIGN PATENTS 229,683 10/ 1963 Austria. 984,079 2/ 1965 Great Britain.

H. HAMPTON HUNTER, Primary Examiner.

US. Cl. X.R. 139-370; 200--61.l8