US3896748A

US3896748A - Low friction means for sewing machine work clamp

Info

Publication number: US3896748A
Application number: US512795A
Authority: US
Inventors: Stanley Kostenowczyk
Original assignee: Singer Co
Current assignee: Retail Holding NV
Priority date: 1974-10-04
Filing date: 1974-10-04
Publication date: 1975-07-29
Anticipated expiration: 1992-07-29
Also published as: ES439097A1; FR2286904B1; JPS5857197B2; DE2518912A1; JPS5147855A; GB1502911A; FR2286904A1; IT1038298B

Abstract

A mechanism for minimizing frictional resistance to movement of sewing machine work clamps which permits a substantial increase in machine speed. Plastic lined sockets carrying steel ball bearings are elevated through the throat plate in timed relationship with the sewing needle rise and prior to feeding work clamp movement. The balls impinge on the bottom work clamp raising the bottom work clamp and upper work clamp out of engagement with the throat plate thereby also increasing clamping pressure on the work material between the clamps. An arched clamp frame which supports the work clamps absorbs the reaction force through similar balls in plastic lined sockets impinging on a hardened steel plate on the underside of the bracket arm. Motion of the entire clamp assembly takes place on ball bearings which are retracted during needle penetration to obviate flagging of the work material.

Description

United States Patent Kostenowczyk LOW FRICTION MEANS FOR SEWING MACHINE WORK CLAMP [75] Inventor: Stanley Kostenowczyk, Cranford,

[73] Assignee: The Singer Company, New York,

[22] Filed: Oct. 4, 1974 [21] Appl. No.: 512,795

[52] US. Cl. 112/70 [51] Int. Cl. D05b 3/04 [58] Field of Search 112/70, 76, 77, 65, 73, 112/74, 75, 218

[56] References Cited UNITED STATES PATENTS 2,822,771 2/1958 Hale et a1. ll2/65 3,824,938 7/l974 Tolle ll2/7O Primary Examiner-H. Hampton Hunter Attorney, Agent, or Firm-Marshall .l. Breen; Edward L. Bell; Robert E. Smith [57] ABSTRACT A mechanism for minimizing frictional resistance to movement of sewing machine work clamps which permits a substantial increase in machine speed. Plastic lined sockets carrying steel ball bearings are elevated through the throat plate in timed relationship with the sewing needle rise and prior to feeding work clamp movement, The balls impinge on the bottom work clamp raising the bottom work clamp and upper work clamp out of engagement with the throat plate thereby also increasing clamping pressure on the work material between the clamps. An arched clamp frame which supports the work clamps absorbs the reaction force through similar balls in plastic lined sockets impinging on a hardened steel plate on the underside of the bracket arm. Motion of the entire clamp assembly takes place on ball bearings which are retracted during needle penetration to obviate flagging of the work material.

5 Claims, 4 Drawing Figures -YIIIIIIIIIIIIIIIIIIIIIIL Q l- LOW FRICTION MEANS FOR SEWING MACHINE WORK CLAMP BACKGROUND OF THE INVENTION Work clamps are customarily used on industrial sewing machines, such as bar tackers and the like which are cyclic in nature; i.e. start, automatically perform a complete operation, and stop. Thus cyclic sewing machines are designed to repetitively perform a specific function such as attachment of a belt loop, button sewing, buttonholing or pocket setting, for example. Generally work clamps are used to insure the most accurate stitching with the least operator attention thereby substantially decreasing possibility for error.

Work clamps function to hold work material between a lower work clamp immediately adjacent the sewing machine throat plate, and an upper, spring loaded, work clamp. Both clamps are supported by an arched clamp frame which is urged by a cam to pass through the cyclic motion required.

Present cyclic sewing machines are limited in speed of operation due in one respect to the friction between the lower work clamp and the throat plate. As the speed is increased the tacks produced by the machine become non-uniform and non-repetitive due to friction and frictional changes. The friction also generates forces severely stressing some of the parts further contributing to the non-uniformity. Thus bar tackers have required limitation in top speed to about 2,000 stitches per minute in order to insure uniformity of product.

Attempts to circumvent the problem by adding a teflon coating to certain critical parts, or by giving these parts a highly polished finish have not been sufficient to increase machine speed to enable greater production. Also lubrication of the critical parts is not desirable in as much as the proximity of the work material to these parts gives rise to soiling of the work material by the lubricant.

In the prior art, attempts to improve friction by the use of bearings which are permanently effective have given rise to increased flagging of the work beneath the sewing needle as well as greater soiling of material adjacent lubricated parts.

What is required is some means of reducing the friction on the work clamp sufficiently to allow a substantial increase in speed without sacrificing clamp mobility or creating a problem of soiling of the work material.

SUMMARY OF THE INVENTION The desired ends are obtained by this invention in which plastic lined sockets carrying ball bearings are elevated through the throat plate beneath the work clamps as the sewing needle is elevated. The work clamps are supported in the sewing machine by an arched clamp frame which transports the work clamp as directed by a cam in the sub-bed of the sewing machine. The arched clamp frame supports a leaf spring used to press the upper work clamp against the lower work clamp to trap fabric therebetween; and thereby also presses the lower work clamp against the sewing machine throat plate. Reaction to the pressure of the work clamp against the throat plate, or against the ball bearings carried in the plastic lined sockets elevated through the throat plate, is accommodated by similar ball bearings carried in plastic lined sockets supported on top of the arched clamp frame. The upper ball bearings impinge on a hardened steel plate carried on the underside of the sewing machine bracket arm.

The invention comprises the devices, combinations and arrangement of parts hereinafter described and illustrated in the accompanying drawings of a preferred embodiment in which:

FIG. 1 is a front side elevational view, partly in cross section, ofa sewing machine embodying the present invention;

FIG. 2 is a cross sectional view taken substantially along the line 22 in FIG. 1;

FIG. 3 is sectional view of the ball bearing and plastic socket to show details of construction; and

FIG. 4 is a cross sectional view taken substantially along the line 44 in FIG. 2.

In FIG. 1 is shown a sewing machine having a bracket arm 11, terminating in a head 12, projecting from an arm standard 13.

The arm standard 13 depends from a sub-base 15, as

I does a work supporting bed 16, having a work supporting throat plate 17.

Extending through the bracket arm 11 is a main shaft to which is affixed a drive pulley 21. Not shown is the conventional mechanism used to drive a needle bar 23 and a sewing needle 24 affixed to the end thereof. A belt 25 connects the drive pulley 21 to a hook shaft drive pulley 26 affixed to a hook drive shaft 27 located in the bed 16 of the sewing machine. A hook 28 located on the end of the hook drive shaft 27 opposite the hook drive shaft pulley 26 cooperates with the needle 24 in the formation of lock stitches. To achieve this end the drive pulley 21 and the hook drive shaft pulley 26 are in the ratio of 2 to 1 that the hook drive shaft 27 and the hook 28 affixed thereto rotate at twice the speed of the main shaft 20 and needle 24 operatively connected thereto.

Beneath the bracket arm 11 may be noted a work clamp mechanism the details of which are set out in great particularity in the U.S. Pat. No. 2,822,771, issued on Feb. 11, 1958 to A. N. Hale et al. which patent is hereby incorporated by reference and made a part of this application. The work clamps will be described only insofar as is pertinent and required to the disclosure of the instant invention.

Referring to FIG. 1, the work clamp assembly includes an arched clamp frame 30 attached by screws 31 to a base portion 32 supported on the bed 16. The base portion 32 and arched clamp frame 30 are urged to motion, in synchronism with sewing needle 24 retraction from the work fabric, by

cam followers

35, 36 impelled by

cam tracks

37, 38 in the cam 40 located in the subbase 15 of the sewing machine 10. The cam 40 is carried by gear 41 which is driven by drive gear 42 operatively connected to the sewing machine main shaft 20.

Depending from the arched clamp frame 30 by a shank portion 45 is an upper work clamp 46. A leaf spring 48 impinges on the extension of the shank portion 45 through the arched clamp frame 30 in a fashion to urge the upper work clamp 46 towards the bed 16. An adjusting screw 49 bears on the leaf spring 48 to increase or decrease the force exerted on the shank portion 45 of the upper work clamp 46. A projecting stud 50 is interengaged with the shank portion 45 to elevate the shank portion 45 and the upper work clamp 46 against the urgings of the leaf spring 48, whenever an angle bracket 51, affixed to a presser lifter mechanism,

is elevated by the presser lifter mechanism to a position where it will strike and lift the projecting stud.

Attached to the free extremity of the base portion 32 by screws is a lower work clamp 56. In its needle penetration position the lower work clamp 56 is supported by the throat plate 17. Work material is clasped between the upper work clamp 46 and the lower work clamp 56 and, under the urging of the leaf spring 48, both clamps and work material are pressed against the throat plate 17, a position designed to avert flagging of the work material.

Located in the work supporting bed 16 and supported on bearings therein is a lift shaft 60. A drive gear 61 affixed to the hook drive shaft 27 meshes with a lift shaft gear 63 attached to an extremity of the lift shaft 60. The gears are in a ratio of l to 2 so that, in view of the 2 to 1 ratio of the drive pulley 21 to the hook shaft pulley 26, the lift shaft is running at the same speed as the main shaft 20.

On the extremity of the lift shaft 60 opposite the lift shaft gear 63 is a hole, eccentric to the shaft center line, into which is inserted and held by set screw 64 a headed pivot pin 65, thereby forming a crank. Rotatably supported on the pivot pin 65 is a lift shaft connecting link 66 (see also FIG. 2). The lift shaft connecting link 66 is formed on the end opposite that accommodating the pivot pin 65 with a pair of slots 68 receiving levers 70 for oscillation about a pin 71 fast to the shaft link. The levers 70 are centrally pivoted on adjustment pins 74 held by set screws 75 to an adjusted position in the bed 16. The adjustment pins 74 are used for adjustment purposes as will be explained below and are formed with an eccentric shaft extension portion held fast by the set screws 75 to the bed 16. Thus as the pins 74 are revolved in the bed 16 by means of screw driver slots 76, the inclination of the levers 70 about the pin 71 varies. When the adjusted position is reached the set screw 75 may be seated against the adjustment pin to maintain that specific setting.

To the ends of the levers 70 opposite that oscillatable about pin 71, the levers are pivotably attached to push rods 83 which extend upwardly on either side of the rotating hook shaft (see FIG. 2). Pivotably supported on the ends of the push rods 83 are bearing means 85 (see FIG. 4) having a cup shaped end 86 receiving a molded or fabricated low friction synthetic resin polymer 87 fashioned with a socket 88 to receive a ball 90. Most ideally the synthetic resin polymer used would be poly tetra fluoro ethylene or a substantial equivalent thereof. The ball utilized must be of a sufficient diameter to preclude formation of a depression in the Synthetic resin polymer used, for the load supported.

As can be noted in FIG. 2 the balls 90 protrude through the throat plate 17 an amount adjustable by manipulation of the adjustment pins 74. Referring to FIG. 1 the balls protrude through the throat plate 17 beneath the lower work clamp 56, lifting it and the upper work clamp 46 against theurgings of the leaf spring 48.

Attached to the underside of the bracket arm 11 above the arched clamp frame 30 is a race plate of hardened steel material. Supported by the arched clamp frame 30 are second bearing means 97 receiving molded or fabricated inserts 98 of synthetic resin polymer, preferably poly tetra fluoro ethylene. The inserts are formed with sockets 99 for receiving balls 100. By means of an adjusting screw 101 clearance between the balls 100 and the race plate 95 may be taken up. and the position thus achieved locked by nut 102.

Thus for the sliding friction heretofor encountered on those members subject to clamping pressure is substituted rolling friction. A synthetic resin polymer is used which has very low friction properties and whose static coefficient of friction is the same as its dynamic coefficient of friction. These changes have enabled the top speed of the sewing machine to increase from a maximum 2,000 s.p.m. to 4,000 s.p.m. Although only two balls have been shown elevating the lower work.

clamp 56 it is obvious that this principle is expandable to encompass additional balls, or may even be utilized to elevate an entire work supporting surface for low friction transport.

Experience has shown that lowering of the work clamp during work penetration by the needle is re quired to prevent flagging of the work. Flagging is caused by passage of the sewing needle through poorly supported fabric causing the work material to deflect. If the balls 90 of this invention were to remain elevated continuously, flagging might result with subsequent deleterious effect on loop formation resulting in a skipped stitch. For this reason the mechanism of this invention is required.

Having thus set forth the nature of the invention, what I claim is:

1. In a sewing machine having a frame, a sewing needle, means for reciprocating said sewing needle upwardly out of work material and downwardly through work material, said frame including a bed with an aperture for accommodating said reciprocation of said sewing needle, work clamp means for supporting and transporting work material on said bed, said work clamp means including an upper clamp member and a lower clamp member, and means for supporting and transporting said work clamp means when said sewing needle is out of work material, the improvement comprising: at least one ball and bearing means effective between said bed and said work clamp means, said bearing means including a socket for receiving said ball;

means for shifting said bearing means to position said ball in a space between said bed and said work clamp means lower clamp member in synchronism with said upward needle reciprocation to elevate said work clamp means by said ball impinging on said lower clamp member prior to transport of said work clamp means.

2. In a sewing machine as claimed in claim 1 wherein said socket of said bearing means is formed of a low friction synthetic plastic resin.

3. In a sewing machine as claimed in claim 2 wherein said means for supporting and transporting said work clamp means includes an arched clamp frame, resilient means supported on said arched clamp frame and in operative connection with said upper clamp member of said work clamp means urging said work clamp means into contact with said sewing machine bed, and at least one ball and bearing means between said arched clamp I frame and said sewing machine frame whereby reaction force of said resilient means is transferred to said sewing machine frame through said lost mentioned at least one ball and bearing means.

4. In a sewing machine as claimed in claim 3 wherein said means for elevating said ball and bearing means includes a crank revolving in synchronism with said needle reciprocations, a connecting link having one end pivotably connected to said crank, a lever pivotably connected to the other end of said connecting link, said lever itself pivotably connected to said frame, a push rod having one end pivotably connected to said lever, said push rod having its other end pivotably connected to said bearing means whereby said bearing means is elevated through said bed in synchronism with said upward needle reciprocation.

5. In a sewing machine having a frame including a work supporting bed, work clamp means including an upper clamp member and a lower clamp member, intermittently operative means for transporting said work ing transport of said work clamp means.

Claims

1. In a sewing machine having a frame, a sewing needle, means for reciprocating said sewing needle upwardly out of work material and downwardly through work material, said frame including a bed with an aperture for accommodating said reciprocation of said sewing needle, work clamp means for supporting and transporting work material on said bed, said work clamp means including an upper clamp member and a lower clamp member, and means for supporting and transporting said work clamp means when said sewing needle is out of work material, the improvement comprising: at least one ball and bearing means effective between said bed and said work clamp means, said bearing means including a socket for receiving said ball; means for shifting said bearing means to position said ball in a space between said bed and said work clamp means lower clamp member in synchronism with said upward needle reciprocation to elevate said work clamp means by said ball impinging on said lower clamp member prior to transport of said work clamp means.

3. In a sewing machine as claimed in claim 2 wherein said means for supporting and transporting said work clamp means includes an arched clamp frame, resilient means supported on said arched clamp frame and in operative connection with said upper clamp member of said work clamp means urging said work clamp means into contact with said sewing machine bed, and at least one ball and bearing means between said arched clamp frame and said sewing machine frame whereby reaction force of said resilient means is transferred to said sewing machine frame through said lost mentioned at least one ball and bearing means.

5. In a sewing machine having a frame including a work supporting bed, work clamp means including an upper clamp member and a lower clamp member, intermittently operative means for transporting said work clamp means, resilient means for urging said work clamp means against said bed and against work material interposed between said upper and said lower clamp members, wherein the improvement comprises; a. a ball and socket bearing means b. means shiftably supporting said ball and socket bearing means in said work supporting bed for movement intermittently against said lower clamp member into opposition to said resilient means during transport of said work clamp means.