US3824938A

US3824938A - Sewing machine construction

Info

Publication number: US3824938A
Application number: US00380837A
Authority: US
Inventors: G Tolle
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-01-16
Filing date: 1973-07-19
Publication date: 1974-07-23
Anticipated expiration: 1991-07-23
Also published as: DE2301936A1

Abstract

A sewing machine comprises a fixed base containing a main drive shaft connected to a needle bar to reciprocate the needle bar substantially vertically in the base. A looper mounting arm is pivoted at one end of the base and includes an opposite end with a revolving looper thereon which overlies a clamping assembly for engaging the material between the looper and the needle bar. The clamping assembly includes a lower part which is pivoted at its inner end adjacent the pivotal end of the looper arm to the base of the machine and rests at its opposite end on an upwardly extending support pin which is biased upwardly by a supporting spring. The clamp includes a top arm portion which is pivoted about a substantially horizontal pivot at its inner end on a bracket carried on the lower part of the clamping mechanism and its outer end extends below the looper arm adjacent the looper. The looper is revolved by a connection extending through the looper arm and through belting to the main drive shaft of the base. The looper arm is pivoted by an electromagnetic mechanism between a raised position in which it may be at rest and a lowered position in which it bears downwardly against the upper arm of the clamping part to urge a clamping frame thereon into engagement with the material which rests on a cover plate of the lower clamping part. In the sewing position, a roller of the looper arm engages against the pressure rail of the upper clamping part to urge the clamping frame over the material. The roller is carried on a bar which is biased downwardly in a direction toward engagement with the pressure rail and it may be compressed when the looper arm moves downwardly to engage the top clamping arm part. A pin on the rod member is confined in a slot to limit the amount of relative movement between the looper arm and the upper part of the clamp. The lower clamping part also includes a mechanism for controlling a sewing material support plate relative to a base plate and an intermediate plate for the purpose of shifting the material to be sewn during special sewing operations.

Description

[111 3,824,938 July 23, 1974 United States Patent 7 1 Tiille SEWING MACHINE CONSTRUCTION which is pivoted at its inner end adjacent the pivotal end of the looper arm to the base of the machine and rests at its opposite end on an upwardly extending support pin which is biased upwardly by a supporting spring. The clamp includes a top arm portion which is Giinter Tiille, Wendelinusstr. '15, Bruchsal, Germany July 19, 1973 [76] Inventor:

[22] Filed:

[21] Appl. No.: 380,837

pivoted about a substantially horizontal pivot at its inner end on a bracket carried on the lower part of the clamping mechanism and its outer end extends below Foreign Application Priority Data,

Jan. 16 1973 the looper arm adjacent the looper. The looper is re- Germany.., 230193 volved by a connection extending through the looper arm and through belting to the main drive shaft of the [52] U.S. Cl. base. The looper arm is pivoted by an electromagnetic mechanism between a raised position in which it may be at rest and a lowered position in which it bears downwardly against the upper arm of the clamping [51] Int.

[58] Field of Search............. 112/70, 73, 71, 65, 72,

part to urge a clamping frame thereon into engage- [56] References Cited ment with the material which rests on a cover plate of UNITED STATES PATENTS the lower clamping part. In the sewing position, a rollet of the looper arm engages against the Pressure rail 112/70 1 12/70 x of the upper clamping part to urge the clamping frame 112/70 X over the material. The roller is carried on a bar which 8 3 267 999 II //l 2 6 I 00500 353 69 964 6 9 7 23 is biased downwardly in a direction toward engagep Examiner H Hampton Hunter ment with the pressure rail and it may be compressed Attorney Agent, and Tuttle when the looper arm moves downwardly to engage the top clamping arm part. A pin on the rod member is [57] ABSTRACT confined in a slot to limit the amount of relative move- A sewing machine comprises a fixed base containing a T g loops; and i f Pa of main drive shaft connected to a needle bar to reciprot e E 3 f e ampmg P a so .I u es 8 cate the needle bar substantially vertically in the base. 1 f or 008m) P a 37 supliort A looper mounting arm is pivoted at one end of the p ate re atwe to a ate an merme late p ate base and includes an opposite end with a revolving f the P Shlftmg. the mammal to be sewn looper thereon which overlies a clamping assembly for mg Speclal Sewmg operatlons' engaging the material between the looper and the needle bar The clamping assembly includes a lower part 11 Claims, 8 Drawing Figures PATENTED M12319" 3 82 SHEEI 1 BF 3 1 SEWING MACHINE CONSTRUCTION BACKGROUND OF THE INVENTION l.'Field of the Invention I This invention relates in general to the construction of sewing machines and, in particular, to a new and use ful sewing machine which includes a base part mounting a needle for vertical reciprocation below a clamp ing assembly adjustably mounted on the base below an overhead pivotal arm supporting a revolving looper, and wherein the looper support arm is movable between a raised rest position and a lowered position for sewing in which it bears against the upper portion of the clamping mechanism.

2. Description of the Prior Art For the production of buttonholes, it is known to use sewing machines where the looper is arranged above the work support and the needle pierces the sewing material from the bottom to the top. Since, in machines of this type the arm receiving thelooper requires substantially more space in the range of the stitch forming point than an arm receiving the needle in a conventional manner, the arm must be arranged directly above the top side of the sewing material to ensure satisfactory stitches during the stitch forming process, it is customaryto bring the arm from its rest position remote of the stitch forming point into a lowered so-called sewingposition and to lock it in this position by suitable means. This ensures that the looper always has the same position relative to the needle and its path of motion when it is in the position cooperating with the nedle. A sewing material clamp is provided in these machines for receiving the sewing material, and the needle is arranged above and the looper below the sewing material. Such a clamp is formed substantially of a lower part and of an upper part and the lower part of the clamp is arranged stationary with regard to the needle movement, while the upper part bears resiliently on the lower clamp part, both parts being moved in a horizontal plane to. achieve the feed of the sewing material.

tance between the topside of the sewing material and the looper varies with a variation of the thickness of the sewing material. Since the needle and looper maintain their relative positions and the needle stroke is likewise invariable, the length of the needle thread loop, formed between the needle eye and the top side of the sewing material and to be engaged by the looper, varies with the thickness of the sewing material. This leads to an uncertainty of operation which is no longer acceptable in high speed industrial sewing machines.

For the elimination of this disadvantage, the individual clamp parts are interchanged with regard to this position so that the upper clamp part is rigid and the lower clamp part is movable, so that the lower clamp part can be moved down for the insertion of the sewing material. Such a solution, which meets the technical sewing requirements, has however, the disadvantage that the insertion of the sewing material would have to be effected on a work support moving away from the stitch forming point and assuming in addition an inclined position. In addition to these operational shortcomings, this solution also requires that the needle stroke be extended so far down thatthe needle would not be hindered in its lowest position by the movement of the work support and also some correlation ov lower clamp part and needle permitting the threading of the needle would have to be found.

SUMMARY OF THE INVENTION The invention provides a sewing machine with an arrangement which ensures a constant length of the needle thread loop formed between the top side of the sewing material and the needle eye despite different thicknesses of the sewing material, while permitting a simple insertion of the sewing material into a material clamp and an easy threading of the needle. The inventive sewing machine includes an upper clamp part and lower clamp part arranged vertically adjustable on the base part and the lower clamp part bears frictionally in the sewing position of the arm on the underside of the upper clamp part which bears on an abutment carried by the arm.

This invention makes it possible to bring the lower clamp part in its relief position into a substantially horizontal position and to move the upper clamp part together with the arm into its rest position for opening the clamp. When the clamp is closed, the upper clamp part together with the arm moves toward the lower clamp part until it bears on the latter and on the sewing material respectively above it. In the course of the lowering movement of the arm, a spring effecting the frictional connection between the lower clamp part and the upper clamp part urges the upper clamp part upward until the latter bears on the stop provided on the arm,

and necessary clamping pressure necessary for the sewing material between the two clamp parts is achieved during the further descending movement of the arm. In this way a position of the top side of the sewing material relative to the stopper and to the needle eye is achieved which is completely independent of the thickness of the sewing material, and a sufficient sewing certainty is ensured due to the constant length of the needle thread loop formed between the needle eye and the top side of the sewing material.

In order to be able to move the lower clamp part easily away for threading the needle for replacing the latter, and to facilitate the insertion of the sewing material and its alignment with the lower clamp part, the lower clamp part is pivotally mounted onthe base part of the machine, and a driving motion delay connection is provided between the arm and the upper clamp part carried by the lower clamp part and pivoted on a substantially horizontal axle. The driving motion delay connection between the clamp and the arm insures that, de-

spite a common drive for arm and upper clamp part, the upper clamp part is lifted only by a certain amount from the lower clamp part, and the alignment of the sewing material is thus substantially facilitated.

In order to achieve the delayed movement between arm and upper clamp part, it is of advantage to provide between the arm and the upper clamp part a driver received by the arm and extending under the upper clamp part, which can be moved to a limited extent relative to the arm against the action of a spring.

In order to maintain the clamping pressure for the sewing material between the upper and lower clamp part along the entire stitch forming path, the driver is carried by a guide bar which has a pressure roller cooperating with a pressure bar secured on the upper clamp 3 part and extending parallel to the device for the sewing material.

In stitch group sewing machines, particularly buttonhole sewing machines, it is customary, in order to obtain a satisfactory stitch pattern, to move the clamp by means of a stepping mechanism. Since both the lower and the upper clamp part are pivotally mounted on the base part receiving the stepping mechanism and can thus be moved relative to the latter, it is necessary to arrange between the stepping mechanism and the clamp a driving connection permitting this pivotal movement but working free from play.

This is achieved accordingto another feature of the invention by arranging a coupling between the stepping mechanism and the lower clamp part which comprises a molded piece pivotally, mounted on the lower clamp part and a counterpiece embracing the molded piece which is frictionally connected with the spindle drive of the stepping mechanism.

A constructionally advantageous and also spacesaving arrangement for obtaining the frictional connection between spindle drive and stepping mechanism is achieved by arranging a bar inside a threaded spindle of the stepping mechanism designed as a tubular shaft, which bar is connected with the counterpiece of the coupling, and carries an abutment for a spring which is arranged between the abutments and the threaded spindle. For the adjustmentof the clamping force of this spring it is necessary to secure the abutment adjustably on the bar.

In stitch group sewing machines whose feed movement takes place in an oblique angle to the main shaft of the machine, it is necessary to deflect the movement,

which is derived from the stepping mechanism and generally directed parallel to the main shaft of the machine into the corresponding feeding direction. This is particularly difficult when the clamp or its lower part is pivotally mounted on the base part of the machine. According to another feature of the invention, this difficulty is eliminated by making the lower clamp with a base plate provided with guides extending parallel to the spindle axis, and with an intermediate plate connected with the molded piece of the 'coupling and moving along these guides, and a supporting plate for the sewing material, and with a journal displaceably mounted inside an oblique guideway which protrudes through an inclined guide of the intermediate'plate and extends in an angle to the inclined guide of the base plate and which is rigidly connected with the supporting plate.

A reliable guidance of the supporting plate for the v sewing material is achieved in that a guide slot extending parallel to the inclined guide of the base plate has a guide roller carried by the base plate.

In order to prevent tipping of unilaterial loading of the supporting plate, a supporting roller for the supporting plate received by the base plate is arranged on either side of the guide rollers carried by the base plate. The axis of this supporting roller extends in a plane perpendicular to the axis of the guide roller.

Accordingly, it is an object of the invention to provide a sewing machine which includes a base portion containing a drive shaft for reciprocating a needle in a vertical plane below a looper which is driven from the drive shaft and which is contained, on a pivotal looper arm which may be moved from a raised rest position to a lowered operating position overlying a clamp for the workpiece and wherein the clamp comprises a lower part which is movable on the base and which rests against a resilient element of the base and an upper part having a pressure bar which is engaged by the looper arm when it is in an operating position to press the upper part against the workpiece.

A further object of the invention is to provide a sewing machine which is simple in design, rugged in construction andeconomical to manufacture.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a front elevational view of a sewing machine constructed in accordance with the invention;

FIG. 2 is an enlarged partial elevational view showing the position of the parts in an intermediate position;

FIG. 3 is a view similar to FIG. 2 showing the parts in an operating or sewing position; FIG. 4 is a section taken along the line IV-IV of FIG. 1;

FIG. 5 is a section taken along the line VV of FIG. 1;

FIG. 6 is a section taken FIG. 5;

FIG. 7 is an exploded top perspective view of the lower part of the clamping assembly; and

FIG. 8 is an exploded perspective view of the coupling arranged'between the stepping mechanism and the lower part of the clamp.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings in particular, the invention embodied therein comprises a stitch group sewing machine designed as a buttonhole sewing machine which includes a stationary base part I and a looper arm 2 which is pivoted on a journal 3 to the stationary base part. The arm 2may be moved from a sewing position in which it bears downwardly on a clamping assembly generally designated 21 overlying the material to be stitched into a rest position which is remote from the stitchforming point and which the arm is tilted upwardly at its outer end. For this purpose, the arm 2 is connected to an actuator in the form of an electromagalong the line VI-VI of .netic 4 having an armature 4a which is engaged in an eyelet 2a which is spaced from the center of the pivot 3 of the looper arm 2. The actuator 4 includes means for locking the arm in the respective positions corresponding to the rest position indicated in FIG. 1 of the drawings and the sewing position indicated in FIG. 3.

-. The crank 7 is connected through a guide member 8 to the needle bar holder 11. The drive shaft 5 drives the needle to reciprocate it in timed relationship to a looper 12 which is mounted at the free end of the arm 2 for revolving movement. For this purpose, the main shaft 5 carries a belt pulley 13 which drives the looper shaft 16 through a belt 14 and a pulley 15. The shaft 16 mobility of the bolt 44.

has an outerend with a bevel gear 17 driving a bevel gear 17' affixed to a vertical shaft 18. Bevel gears 19, 19 transmit the rotary motion of the vertical shaft 18 into rotation of the shaft 20 which is horizontally disposed in the arm 2 and which drives the looper 12. The transmission between the shaft 5 and the needle 10 and the looper 12 is such that the looper speed in respect to the needle speed is 2:1.

In accordance with the invention, the clamping assembly 21 comprises an upper clamping part 22 and a lower clamping part 23 both of which are mounted on the base 1 for movement in respect-thereto. The upper clamping'part 22 is mounted on a horizontal axle for pivotal movement and this axle is carried on a support or bracket 24 affixed to the lower clamping part 23. The axis of the shaft 25 extends obliquely to the main shaft 5 of the machine. The front end of the upper clamp part 22 carries a clamping frame 26 which presses the sewing material against the lower clamp part and has a recess 27 for the passage of the needle 10 and of a buttonhole blade (not shown). The front end of the upper clamp part 22 is also provided with a pressure rail 28 extending parallel to the feeding direction of the sewing material. The rail 28 is engaged by a pressure roller 29 which is rotatably mounted at the lower end of a forked guide bar 30, which is displaceably received inside a 31 of the arm 2. The lower end of the guide bar (see FIG. 4) is equipped with a driver 32 which extends outwardly from under the pressure rail 28 and I carries a stop 33 which bears on the underside 34 of the arm 2. As can be seen particularly from FIGS. 1 to 3, the guide bar 30 carries a pin 35 extending perpendicularly to its longitudinal axis, which slides inside an oblong slot 36 of the housing 31 extending parallel to its longitudinal axis and which limits the longitudinal mobility of the guide bar 30. A spring 37 arranged between the lug 31 and the lower end of the guide bar 30 always keeps the upper clamping part 22 in its bottom position.

The lower clamping part 23 is formed, as it can be seen best from FIG. 7, by a cover plate 38, a supporting plate 39 for the sewing material, an intermediate plate 40, and a base plate 41. The base plate 41 is pivotally mounted by means of a journal 42 on a bracket of the base andit bears, in the range of the stitch-forming point, on support means or a stiffening piece 43 displaceably mounted in the base part 41 (FIGS. 1 and 6). A bolt 44 forming a part of the stiffening piece 43 is surrounded bya spring 45 which is displaceable within a pot-shaped recess 46 of the base part 1. A nut provided at the bottom end of the bolt 44 limits the upward The base plate 41 of the lower clamp part 23 is provided with two

guides

47, 48 extending parallel to the main shaft 5, in which a roller 49 and a sliding block 50 are displaceably mounted. Both the sliding block 50 and the roller 49, which rotates about a vertical journal 51, are rigidly connected with the intermediate plate 40 of the lower clamp part 23, which is thus guided in the base plate 41. The intermediate plate 40 has an inclined guide 52 extending in an oblique angle to the

guides

47, 48, through which passes a journal 53 whose bottom end protrudes into an oblique guideway 52 of the base plate extending likewise in an oblique angle to the inclined guideway 52 of the intermediate plate 40. Due to this arrangement of the two

inclined guideways

52 and 54 in the intermediate plate 40 and in the base plate 41, respectively, the journal 53 is displaced inside the inclined guide 54 of the base plate 41. During a displacement along the

guides

47 and 48, the supporting plate 39 secured at the upper end of the journal 53 is moved parallel to the inclined guide 54 of the base plate 41. 'In order to prevent lifting of the supporting plate 39 and of the journal 53 the plate 41 is provided at its bottom end with a lateral flange which slides inside a cut 55 of the inclined guide 54 of the base plate 41. For the exact parallel guidance of the supporting plate 39, a guide roller 56 is arranged in the range of the front end of the base plate 41 on a journal 57 secured on the base plate 41, and it protrudes into a guide slot 58 of the supporting plate 39 extending parallel to the inclined guide 54 of the base plate 41.

The supporting plate 39 is rigidly connected with the cover plate 38 to receive the sewing material. For its support are provided in the range of the front two supporting rollers 60, rotating each about a horizontal axle 59, a supporting plate 39 and the supporting plate bears directly on one supporting roller 60 and extends over the cover plate 38 overlying the other supporting roller 60. The base plate 41 protrudes into a recess 64 for the cover plate 38 covering the supporting plate 39 and it is provided with an insert which can be considered a stitch plate 61 (FIG. 7) and which has an oblong slot 62 for a buttonhole blade (not shown) and a stitch hole 63 for the passage of the needle 10.

A sliding block 50 secured on the intermediate plate 40 has a substantially U-shaped cross section whose outwardly bent sides extend under the base plate 41 and serve to receive a molded piece 65 which forms a part of a coupling 67 arranged between a stepping mechanism 66 (FIG. 1) and the clamp 21. The molded piece 65 pivotally mounted on a journal 68 received by the sliding block 50 is embraced by a counter-piece 70 of the coupling 67 having a corresponding recess 69. The counter-piece 70 is rigidly connected with a bar 71. The bar 71 arranged substantially parallel to the main shaft 5 and it is received in the interior of a threaded spindle 72 and is provided at its free end with an adjustable abutment 73 for a spring 74 arranged between the abutment 73 and the end of the threaded spindle 72, which keeps the molded piece 65 in frictional connection with the counter-piece 70. The sliding block 50 thus bears on an angle-shaped carrier 75 which is connected with the threaded spindle 72. The spindle 72 is surrounded by a threaded nut 76 which is mounted for rotation and is axially locked in the base part 1 so that the spindle 72 is moved back and forth corresponding to the rotation of the threaded nut 76. On the threaded nut 76 is secured a belt pulley 77 which cooperates with the stepping mechanism 66 through a toothed belt 79 conducted over a guide pulley 78. The stepping mechanism 66 comprises two

eccentrics

80, 81 arranged on the lower main shaft 5, which impart to a pair of belt pliers 82 both a feeding movement and a spreading and clamping movement, so that the movement derived from the feed eccentric is transmitted over the toothed belt 79 as an intermittent rotary movement to the threaded nut 76.

The method of operation of the sewing machine is as follows:

With the arm 2 at its rest position remote of the stitch forming point, the sewing material is placed on the cover plate 38 of the lower clamp part 23. Since the frame 26 of the upper clamp part 22 is only lifted by a small amount from the lower clamp part 23, the insertion and particularly the alignment of the sewing material is relatively simple. The lower clamp part 23 assumes during the insertion substantially a horizontal position, the base plate 41 bearing on the stiffening piece 43 is formed by the bolt 44, and the spring 45 being-substantially relaxed. The driver 32 provided at i the bottom end of the guide bar 30 extends under the pressure rail 28, and the pin 35 bears on the bottom end of the oblong slot 36 with the spring'37 relaxed, so that the upper clamp part 22 is held in its raised position.

For moving the arm 2 from its rest position into the sewing position, the magnet 4 is excited so that the arm 2 performs a pivotal movement about the journal 3. The upper clamp part 22 moves in synchronism with the arm downwardly and turns about the axle 25. As soon'as the frame 26 bears on the sewing material, the arm 2 is displaced relative to the guide bar 30 because the spring 37 has a flatter characteristic than the spring 45 so that the pressure roller 29 bears on the pressure rail 28 and the spring 37 is compressed. The guide bar 30 moves upwardly in the lug 31 until the pin 35, securing it against rotation, has reached the upper range of the oblong slot 36. The stop 33 secured on the bottom end of the guide bar 30 (FIG. 4) bears then on the bottom 34 of the arm 2. Arm 2 and upper clamp part 22 now form, a rigid unit, so that the spring 45 is compressed during the further descending movement until the arm has reached the sewing position fixed by the end position of the magnet 4. During thepivotal movement of the arm, the lower clamp part 23 is turned by a corresponding angular. amount about the journal 42. Since the journal 42 is relatively far from the stitch forming point, the angular amount of the pivotal movement is relatively small, so that the lower clamping part 23 still assumesa substantially horizontal position after the pivotal movement. After the arm is locked in its sewing position, the correlation of needle 10 or needle stroke and looper 12 is secured. Since the lower clamp part 22 also carries the stitch plate 38 it is pressed down in dependance on the thickness of the sewing material. The variation of the thickness of the sewing material is thus compensated by the level of the stitch plate or of the lower clamp part 23 receiving it, so that the distance of the top side of the sewing material from the looper 12 and needle eye respectively remains constant, assuming a certain needle position. The length of the needle thread loop formed between needle eye and top side of the sewing material remains thus constant, independent of the thickness of thesewing material. The conditions for the stitch formation are thus always the same, regardless of the thickness of the sewing material, which ensures a good sewing certainty.

For the formation of the seam, for example, of a buttonhole, the needle penetrating the sewing material from the bottom to the top and the looper 12 are driven by the driving means from the shaft 5. The pressure roller 29 rolls off on the pressure rail 28 so that the clamping pressure expended by the compressed spring 45 prevails between the upper clamp part 22 and the lower clamp part 23. The two

eccentrics

80, 81 of the stepping mechanism transmit through belt pliers 82, and the toothed belt 78 an intermittent rotary movement on the belt pulley 77 rigidly connected with the threaded nut 76. The non-rotatable threaded spindle 77 is displaced in the direction corresponding to the rotation of the threadednut 76 and moves the carrier 75 con- 8 nected with it parallel to its axis. The carrier 75 bears on the end face of the sliding block 50 and imparts to the latter a longitudinal movement. The intermediate plate guided in the

guides

47, and 48 by means of the guide roller 49 and the slide block 50 respectivelyperforms a longitudinal movement and the journal 53 is displaced inside the inclined guide 52 of the intermediate plate 40 moving at the same time along the inclined guide 54 provided in the base plate 41. Since the supporting plate 38 for the sewing material is rigidly connected with the journal 53, it performs a pushing movement determinant by the position of this inclined guide 54 and is guided additionally by the guide roller 56 carried by the base plate 41 and protruding into its guide slot 58.

After the first buttonhole bight and the corresponding overstitches have been sewn, the movement transmitted by the belt pliers 82 to the toothed belt 79 is reversed by means (not shown), so that the threaded nut 76 is driven opposite to its original direction of rotation. Since the sliding block 50 bears frictionally onthe carrier 75 rigidly connected 'with it overthe pivotally mounted molded piece 65 and the spring-loaded counter-piece 70, the reversal of the direction of rotation of the clamp 21 is effected completely free from play.

At the end of the sewing operation the sewing machine is stopped, with the needle in bottom position, and the arm 2 is moved into the rest position from the sewing position by the electromagnet 4 to be re-excited again. With the arm 2 moving upwardly the spring 45 expending the clamping pressure between the upper and lower clamp part relates so that the clamp 21 performs a pivotal movement about the journal 42 and the lower clamp part 23 is moved from its sewing position to the charging position slightly above the horizontal. After the spring 45 is relaxed, the spring 37 relaxes in the further course of the pivotal movement of the arm. This has the effect that the upper clamp part 22 remains on the sewing material during the further upward movement of the arm until the pin 35 of the guide bar 30 is in the range of the bottom end of the oblong slot 36 provided in the lug 31. Only at the end of this relative movement between arm 2 and upper clamp part 22 which is achieved by the lost motion stroke of the driving connection between arm and clamp 21 and the guide bar 30 is moved upwardly by the driver 32 extending under the pressure rail 28. The arm 2 continues its pivotal movement about the journal 3 until it reaches its rest position and the upper clamp part 22 performs a pivotal movement about the axle 23 and is held in the rest position of the arm by the driver 32 extending under the pressure rail 28.

By the lost motion stroke in the driving connection between arm 2 and the upper clamp 22, the upper clamp part is only lifted by a certain amount from the lower clamp part, even though it is carried along by the arm moving into its rest position. This amount is so selected that it does not prevent the insertion and removal of the sewing material, and on the other hand, permits the easy alignment of the sewing material by frame 26 directly above the lower clamp part 23 or its recess 27.

If the needle 10 is to be exposed for threading or replacement, with the arm 2 in rest position, the clamp 21 can be turned about the journal 42 independently of the arm 2. The sliding block 50 rigidly connected with the intermediate plate 40 participates in the pivotal movement, while the counter-piece 70 connected with the bar 71 maintains its position. During the relative movement between sliding block 50 and counter-piece 70, the molded piece 65 mounted on the journal 68 performs a pivotal movement about this journal and changes its relative position to the recess 69 of the counter-piece 70. But, since the counter-piece 70 is held by the spring 74 in frictional connection with the molded piece 65, the driving connection between the stepping mechanism 66 and the clamp 21 is restored unchanged and completely free from play after the latter has reached again its starting position.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

l. A sewing machine comprising a fixed base, an arm having one end pivoted to said fixed base and having an opposite end, a revolving looper on said arm adjacent said opposite end, a main drive including a rotatable drive shaft rotatably mounted in said base, a needle bar mounted for generally vertical reciprocation adjacent the opposite end of said arm in said base and connected to said drive shaft for reciprocation thereby, means connected between said drive shaft and said looper to revolve said looper upon rotation of said drive shaft, a clamp assembly for securing material located between said base and said arm, means mounting said clamp for movement relative to said base and said arm, said clamp having a top and a bottom relatively movable parts between which the material to be sewn is positioned, said arm being pivotal between a raised rest position and a lowered sewing position in which it bears against the top part of said clamp to urge it against the material to be sewn over the bottom part of said clamp, and means on said base bearing against the underside of said bottom part of said clamp.

2. A sewing machine, according to claim 1, including means pivotally mounting the lower portion of said clamp on said base part adjacent one end of said lower portion of said clamp, said means on said base bearing against the underside of said bottom comprising an upwardly extending pin member carried on said base and means biasing said pin member upwardly against said bottom part of said clamp.

3. A sewing machine, according to claim 2, including a lost motion connection between said clamp and said arm including a rod member movable against the upper portion of saidclamp to move it downwardly against the material positioned on the lower portion of said clamp, a spring biasing said rod member in a direction away from engagement with said upper portion of said clamp.

4. A sewing machine, according to claim 1, including first pivot means pivotally supporting the lower portion of said clamp on said base, second pivotal means carried on said lower portion of said clamp pivoting the upper portion of said clamp on said lower portion, said arm having a pin carried thereby adjacent said looper extending into engagement with said upper part of said clamp, means mounting said pin on said arm for displaceable movement, and a spring biasing said pin in a direction toward engagement with said clamp, said pin being engageable with said upper portion of said clamp when said arm is moved into an operating position and effecting downward movement of said clamp by the downward movement of said arm in accordance with the biasing force of said spring.

5. A sewing machine, according to claim 4, wherein said pin carries a pressure roller at its lower end, said upper clamping arm having a material engaging frame at its outer end and having a pressure rail overlying said frame engaged by said pressure roller and which extends parallel to the material feed direction.

6. A sewing machine, according to claim 1, wherein said lower part of said clamp includes an upper plate part for supporting the material and an intermediate part supported on a clamp base part, a stepping mechanism connected to said shaft, a coupling connected between said intermediate part and said stepping mechanism including a molded piece and a counter-piece engaged by said molded piece, a threaded spindle, a nut rotatably mounted on said base but held against axial displacement and threadably engaged over said spindle, rotation of said nut shifting said spindle axially, said spindle being connected to said counter-piece and being engageable through said counter-piece with said molded piece to shift said intermediate plate with said upper plate relative to said base portion.

7. A sewing machine, according to claim 6, wherein said spindle is hollow, a bar engaged in the interior of said threaded spindle, said bar being connected to said counter-piece and having an abutment at its outer end, and spring means engaged between said spindle and said abutment urging saidbar with said counter-piece toward the opposite end of said spindle.

8. A sewing machine, according to claim 7, wherein said abutment is adjustably connected to said bar.

9. A sewing machine, according to claim 8, wherein said lower clamp part base plate is provided with guideways extending parallel to the axis of said spindle, said intermediate plate having a mold piece movable along said base plate connected with said coupling, said top plate comprising a supporting plate for the sewing material, a journal displaceably mounted inside an inclined guide of the base plate protruding through an inclined guide of said intermediate plate and extending at an angle to the inclined guide of said base plate and connected to said supporting plate for the sewing material.

10. A sewing machine, according to claim 8, wherein said supporting plate (39) has a guide slot (58) extending parallel to the inclined guide (54) of the base plate (41) and a guide roller (56) carried by the base plate (41).

11. A sewing machine, according to claim 9, wherein there are supporting rollers (60) for supporting plate (39) arranged at both sides of said guide roller of said base plate (41) and received by said base plate, the axle (59) of said supporting rollers (60) extending in a plane perpendicular to the axle of said guide roller

Claims

1. A sewing machine comprising a fixed base, an arm having one end pivoted to said fixed base and having an opposite end, a revolving looper on said arm adjacent said opposite end, a main drive including a rotatable drive shaft rotatably mounted in said base, a needle bar mounted for generally vertical reciprocation adjacent the opposite end of said arm in said base and connected to said drive shaft for reciprocation thereby, means connected between said drive shaft and said looper to revolve said looper upon rotation of said drive shaft, a clamp assembly for securing material located between said base and said arm, means mounting said clamp for movement relative to said base and said arm, said clamp having a top and a bottom relatively movable parts between which the material to be sewn is positioned, said arm being pivotal between a raised rest position and a lowered sewing position in which it bears against the top part of said clamp to urge it against the material to be sewn over the bottom part of said clamp, and means on said base bearing against the underside of said bottom part of said clamp.

3. A sewing machine, according to claim 2, including a lost motion connection between said clamp and said arm including a rod member movable against the upper portion of said clamp to move it downwardly against the material positioned on the lower portion of said clamp, a spring biasing said rod member in a direction away from engagement with said upper portion of said clamp.

7. A sewing machine, according to claim 6, wherein said spindle is hollow, a bar engaged in the interior of said threaded spindle, said bar being connected to said counter-piece and having an abutment at its outer end, and spring means engaged between said spindle and said abutment urging said bar with said counter-piece toward the opposite end of said spindle.

11. A sewing machine, according to claim 9, wherein there are supporting rollers (60) for supporting plate (39) arranged at both sides of said guide roller of said base plate (41) and received by said base plate, the axle (59) of said supporting rollers (60) extending in a plane perpendicular to the axle of said guide roller (56).