US2920257A - Sewing machine motor control - Google Patents

Description

Jan. 5, 1960 MILES ETAL 2,920,257

' SEWING MACHINE MOTOR CONTROL Filed May 9, 1957 IN VEN TORI United States Patent SEWING MACHINE MOTOR CONTROL John H. Miles and Oliver B. Elliott, Atlanta, Ga. Application May 9, 1957, Serial No. 658,153 '2 Claims. (Cl. 318 -266) This invention relates to a sewing machine control, and more particularly to a braking device for automatically stopping the machine such that the needle comes to rest at a predetermined point in its travel.

In conventional motor-operated sewing machines it is usually necessary to manually turn the machine to withdraw -the needle from the cloth before the cloth can be removed from the machine. This is required because the cloth can be removed satisfactorily only when the needle is in its uppermost position. Such manual operation causes a loss of valuable operating time and often results in broken needles and tangled thread.

Accordingly, it is an object of this invention to provide a sewing machine which is not subject to the aforementioned difliculties.

Another object of the invention is to provide a control means for automatically stopping the needle in a predetermined position.

A further object of the invention is to provide a speedresponsive brake control means for a motor-operated sewing machine.

A still further object is to provide a positive-acting brake utilizing the combined actions of friction and magnetic torque to eflfect the desired braking.

In accordance with these objects, a preferred embodiment of the invention comprises a sewing machine having a flywheel which is provided with an insert of magnetically permeable material. Pivotally mounted adjacent the flywheel is an electromagneL'the yoke of which is adapted to frictionally engage the periphery of the flywheel to provide both frictional and magnetic torque braking action. The electromagnet is actuated by a speed-responsive control circuit which produces the desired braking to stop the machine completely and then de-activates the electromagnet so that the machine may be started again immediately.

This preferred embodiment of the invention is illustrated in the accompanying drawing in which the single figure is a perspective view of the novel brake structure as applied to a sewing machine together with a diagrammatic view of the electrical control system.

Referring now to the drawing, the device of this invention comprises a sewing machine flywheel or cylinder of non-magnetic material 1 with an iron insert 2 inlaid in flywheel 1 so that the ends of insert 2 are flush with and of the same curvature as the periphery of flywheel 1. Parts 1 and 2 are mounted on the main crankshaft of the sewing machine.

An electromagnet yoke 3 with coil 4 are arranged with the ends of yoke 3 curved to fit the periphery of flywheel 1. Yoke 3 has a leaf spring or floating mounting 5 such that when the magnet is energized it will be attracted into contact with iron insert 2 as the latter rotates past magnet 3. This will cause a braking force to be applied to the flywheel 1 at a definite previously chosen position of the flywheel in its rotation to stop the machine at this position. If the machine stops a few degrees either before or beyond the chosen position it will be satisfactory.

2 Magnet 3, 4 normally rests against stop 17. Arrow 18 shows the direction of rotation of the machine.

A speed sensitive device of centrifugal type is mounted on the-side of flywheel 1 or on the machine crankshaft. This speed sensitive device consists of weights 6 and 10, rocker arms 7 and 18 mounted on fulcrums 8 and 13, connecting link 11 tying arms 7 and 18 together by means of pivots 9 and 14, and spring 1 2 which oppose the centrifugal force of weights 6 and 10 by applying tension between fulcrum point 13 and pivot 9 of link 11. Pivot 9 is movable with respect to fulcrum 13.

When the machine. decelerates to a predetermined speed the weights 6 and 10 are drawn toward the center. of the flywheel by spring 12 overcoming decreasing centrifugal force. This rotates rocker arm 7 about fulcrum 8 so that the outer end of 7 moves outward from the center of the flywheel until the end of arm 7 strikes insulated strip =16 and deflects normally closed contact 15 to an open position. When contact 15 opens it sets in motion a sequence of operations to de-energize the sewing machine motor 19 and'to energize braking magnet 3, 4.

Device 22 is a lmulti contact instantaneous type relay or contactor well known in the art of electrical controls.

Device 28 is a relay or contactor well known in the art of electrical controls. It has a copper cylinder (or one turn conductor of low resistance) surrounding the magnetic circuit. The purpose of this copper cylinder (or Slug) is to cause a short time delay between the opening of the coil circuit 29 and the opening of the contact 31. This time delay may be approximately one to two seconds.

Device 36 is a bridge type full wave rectifier well known in the electrical control art.

Device 34 including contact 21 and resistor 20 is a simple rheostatic control well known .in the electrical control art and used in most electrically driven sewing machines.

When the-machine operator presseson knee control (or foot control) 34, contact 21-moves along resistor 20 allowing currentto'flow from bus 33 through resistor 20, to conductor 42, to motor 19, toibus 32 which is opposite in polarity to bus "33. This starts'themachineand keeps it under the speed control of the operator by means of the rheostat 20, 21.

At the same time the operator presses on foot control 34, a circuit is completed from bus 33 through contact 21 and conductor 23 through coil 24 of relay 22, through conductor 44 and then to bus 32. This operates the plunger of relay 22 to close contact 25. This completes a circuit from bus 33, through conductor 35, contacts 15, conductor 43, contacts 25, coil 24 on relay 22 to bus 32. This seals relay 22 in closed position through its contact 25. Also contact 26 on relay 22 closes completing the circuit from the positive side of rectifier 36, through contact 26, conductor 40, coil 29 of relay 28, to the negative side of rectifier 36. This energizes relay 28 to close contact 31. Contact 27 is open on relay 22.

Now with the machine running and the operator controlling its speed by means of exerting more or less pressure on control element 34, relay 22 and relay 28 will both be in the energized position with contacts 25, 26 and 31 closed and contact 27 open.

Assume now that the operator desires to stop the machine. The operator releases pressure on control rheostat 34 which opens contact 21 by means of the rheostat spring. This action sets in motion a sequence of operations to de-energize the sewing machine motor 19 and to energize the braking magnet. This sequence is described as follows:

At the time contact 21 opens, relay 22 remains energized through the following circuit: from bus 32, through Patented Jan. 5, 1960 i closed contact 15, conductor 35 to bus 33. tion keeps motor 19 energized temporarily through the following circuit. H v

. Starting at busf32,-th'rough motor 19, conductor ,42,

resistor 20, conductor 23, contact 25, conductor 43, nor-' mally 'closed contact 15, conductor 35 to bus 33. This circuit keeps motor 19 turning at reduced power input until the machine slows down in speed to a low value at which the speed sensitive centrifugal device operates under the influence of spring 12 overcoming the centrifugal force of weights 6 and 10. Operation of this device extends rocker arm 7 until it strikes insulating strip 16 as arm 7 passes. Striking of strip 16 by arm 7 opens contactlsw I This action sets up the following rapid sequence which takes place during the time insert 2 in flywheel 1 is rotating through a portion of one revolutionto a position for its ends to line up with pole pieces of yoke 3. This sequence-opens the following circuits: Beginning at bus 33, through conductor 35, opened contact 15, conductor 43, contact 25, conductor 23, resistor 20, conductor 42, motor 19, conductor 37 to bus 32; This de-energizes the motor 19. Also coil 24 of relay 22 is de-energized by the opening of contact 15. This action unseals relay '22 and it drops open instantaneously, opening contacts 25 and 26 and closing contact 27. Contact 2'7- completes the circuit from the positive side of the rectifier 36 through contact 27, conductor 41, contact 31, conductor 39, magnet coil 4, conductor 38 to negative side of rectifier 36. Due to the action of eddy currents in copper slug '30, contact 31 is held closed for a short time after coil 29 is de-energized by the opening of contact 26.

As flywheel 1 rotates iron insert 2' into proximity with energizedmagnet 3, 4 the latter is attracted to insert 2 and the magnet 3, 4 rotates very slightly about pivot until the curved faces of yoke 3 contact the circular ends of insert 2 thus applying considerable friction force to the flywheel 1 to stop the machine quickly with the insert 2 and yoke 3 still in contact. This is the desired stopping position.

In very short interval after the machine has stopped the influence of copper slug 30 has decreased to the point where relay 28 drops open to de-energize magnet coil 4 by opening of contact 31. This leaves the machine free to start or be rotated when desired.

A principle of our device is to co-ordinate the deceleraconductor 44, coil 24,contact -25, conductor 43, normally I This condition of the machine with the de-energizing of the motor and the application of the brake at a point and speed of rotation such that the energy-of rotation does not exceed the capacity of the brake and machine parts and the brake is applied only a certain portion of the rotation.

While we have shown and described our invention in considerable detail we do not desire it to be limited to the arrangement shown-but seek to cover in the following claims all variations or modifications which may appear to those skilled in the art or which fall within the true spirit and scope of our invention.

What we claim as new and desire to'secure by Letters Patent of the United States is:

1. In a sewing machine, a rotatable shaft, a flywheel mounted on said shaft, a' magnetically permeable insert in said flywheel, a substantially U-shaped yoke member.

of magnetically permeable material pivotally mounted adjacent said flywheel and adapted to have the ends there of move in and out of frictional engagement with said flywheel, a' coil wound on said yoke to form an electromagnet therewith, means responsive tothe speed of said rotatable shaft for energizing said coil, .and means for automatically de-energizing said coil after said rotatable shaft has been stopped.

2. A braking control system for sewing machines comprising a motor, a shaft driven by said motor, a circular flywheel mounted on said shaft, a magnetically permeable insert in said flywheel,an electromagnet pivotally mounted adjacent said flywheel, said electromagnet having a complementary arcuate portion adapted to frictionally engage the periphery of said circular flywheel, means responsive to the speed of said shaftfor automatically energizing said electromagnet and de-energizing said motor, and time-delay-means for automatically de-energizing said electromagnet after said rotatable shaft has been stopped.

References Cited inthe file of this patent UNITED STATES PATENTS 542,309 Potter Julyj9, 1895 1,849,847 Mittnacht Mar. 15, 1932 2,572,635 Lennox Oct. 23, 1951 2,604,864 Merchant July 29,- 1952 a FOREIGN PATENTS p 155,428 Australia Feb. 25, 1954

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