US3742880A - Double chain stitch sewing machine having compound feeding means - Google Patents

Abstract

Double chain stitch sewing machine in which the needle and the hook always assume in their loop pickup position the same position relative to one another for all adjustable stitch lengths which is achieved in that the adjusting element of the setting device for the stitch length is in driving connection with the feed eccentric so that in the position of the components of the machine which corresponds to the loop pickup position of the hook and the needle no rotation of the rocking shafts takes place as the adjusting element is moved along its setting position.

Description

United States Patent 1 Franz [451 July 3,1973

[ DOUBLE CHAIN STITCH SEWING MACHINE HAVING COMPOUND FEEDING MEANS [75] Inventor: Ludwig Franz, Kaiserslautern,

Germany [73] Assignee: Pfaff Industriemaschinen GmbH, Kaiserslautern/Pfalz, Germany [22] Filed: Feb. 17, 1972 [21] Appl. No.: 227,137

[30] Foreign Application Priority Data Feb. 22, 1971 Germany P 2i 08 309.0

[52] US. Cl. 112/199 [51] Int. Cl D05b l/l0 [58] Field of Search ll2/l99, 197, 198, ll2/200 [56] References Cited I UNITED STATES PATENTS l/l967 Lanzendorfer l 12/ l 99 3,285,210 ll/l966 Tretow et al. ll2/l99 Primary Examiner-H. Hampton Hunter Attorney-Robert H. Jacob [57] ABSTRACT Double chain stitch sewing machine in which the needle and the hook always assume in their loop pickup position the same position relative to one another for all adjustable stitch lengths which is achieved in that the adjusting element of the setting device for the stitch length is in driving connection with the feed eccentric so that in the position of the components of the machine which corresponds to the loop pickup position of the hook and the needle no rotation of the rocking shafts takes place as the adjusting element is moved along its setting position.

4 Claims, 7 Drawing Figures L l r l 43 62) l w" DOUBLE CHAIN STITCH SEWING MACHINE HAVING COMPOUND FEEDING MEANS BACKGROUND OF THE INVENTION The invention relates to a sewing machine having a double chain stitch hook controlled by an eccentric and a compound feeding means. The latter comprises a lower feed dog and a feeding means for the needle, where the swinging shaft for the rocking frame of the needle bar is connected with the rocking shaft that guides the support for the feed dog. The swinging movements of the swing shaft are derived from a feed eccentric and are adjustable in magnitude by means of a setting device for the stitch length.

It is an object of the invention to increase in such sewing machines the reliability of the stitch formation.

The forming of flawless chain stitches depends essentially in that during the loop pickup the loop of the needle thread which forms during the upward movement of the needle from its lowest position is large enough to insure that the point of the hook can correctly enter. In this connection, however, the loop may not yet have attained such a magnitude at which so called falling over of the loop takes place, i.e. a turning about its vertical axis. Furthermore, the formation of the so called thread triangle must make possible a reliable en tering of the needle.

A satisfactory forming of the thread triangle has been obtained by introducing a loop spreader which seizes and expands the hook thread above the edge of the hook in order to form the thread triangle in the presence of the loop of the needle thread that lies around the blade of the hook for the entrance of the needle. The problem of loop formation and loop positioning for insuring the reception of the loop by the hook has thus far not been satisfactorily solved in connection with all stitch lengths the machine can be set for.

Double chain stitch sewing machines having a compound feed means are known having a chain stitch hook that is movable parallel to the direction of feed and effects a rocking movement of equal shape or unequal shape which cooperates with a loop spreader for setting up the thread triangle necessary for the entrance of the needle.

With machines of this type the loop of the needle thread that is formed at the needle which develops when the needle moves upwardly from its lowest position is seized by the point of the hook and picked up by the hook, in connection with each stitch length setting every time at a different vertical spacing from the eye of the needle. Thus, the magnitude of the loop raising or lifting differs for each stitch length.

This is due to the fact that during its evenly shaped upward and downward movement the needle passes through stretches of different magnitude directed parallel to the direction of feed during the same period of time and thus since the center of the adjustable feed stretches (stitch lengths) always coincides in the known chain stitch sewing machines with the theoretical center of the needle, the point of the chain stitch hook that effects a rocking movement which remains the same, reaches the center of theneedle during a stitch forming cycle sooner or later depending on the adjusted stitch length. Accordingly, the needle and the hook also assume different positions with different stitch lengths relative to one another (loop pickup positions) in relation to the vertical distance of the point of the hook from the eye of the needle.

By the different magnitude of the loop rise of the needle thatresults in this manner with different stitch lengths and the different formation of the loop of the needle thread connected therewith, reliability of the seizing of the loop and its pickup by the point of the hook is not insured in connection with all adjustable stitch lengths. Since for reasons of suitability the mutual adjustment of looper and needle is related to a medium stitch length that is frequently needed, defective stitching can result in connection with all stitch lengths that differ therefrom.

In order to obtain for all adjustable stitch lengths an equal or at least nearly equal lifting of the loop it has already been proposed with a double chain stitch sewing machine having a compound feed means and a chain stitch hook that effects an elliptical movement derived, however, from two eccentrics, to adapt the hook movement to the magnitude of feed (stitch length) which has been set up in a particular case. With this manner of driving the hook the angular position of the eccentric that guides the longitudinal movements of the hook is changed for this purpose on the hook driving shaft by means of a setting device that is manually operable in relation to the adjustable magnitudes of feed (stitch lengths). Adjusting, however, is only possible during the time the machine stands still. For the sewing industry the possibility of locking a seam at its beginning and at its end that is more and more in demand, for example, by shortening the stitches, can therefore only be realized with considerable loss of time.

With a further known embodiment the adaptation of the hook movement takes place automatically in relation to the stitch length by a rocking frame having gears working in the manner of a planet gear, connected by means of a link with the rocking shaft of the feed dog and by a parallel crank drive having a sleeve supporting the eccentric for the longitudinal movement of the hook. By means of this rocking frame the angular position of the eccentric that controls the longitudinal movements of the hook is continuously changed in accordance with the rhythm of the movement of the feed dog shaft.

The two known adjusting means for adapting the looper movement to the said stitch length, are suitable only for such chain stitch hooks which are moved about the needle along a path having the form of an ellipse. In realizing these known measures for adapting the hook movement to the different stitch lengths, it is moreover not possible to avoid additional technical expenses.

SUMMARY OF THE INVENTION It is intended in accordance with the invention to so construct in a double chain stitch sewing machine the setting means for the stitch length while avoiding any additional structural expenses that with all adjustable stitch lengths the needle and the hook always assume the same relative position for pickup of the loop (equal loop lift of the needle, equal vertical spacing of the point of the hook from the eye of the needle).

in accordance with the invention this problem is solved in a double chain stitch sewing machine of the type referred to above, in that the setting member of the adjusting device for the stitch length which is in driven connection with the feed eccentric is so arranged that in the position of the machine parts which corresponds to the loop pickup position of hook and needle no turning of the rocking shaft takes place during adjusting of the setting member along its adjusting stretch.

The setting member is that member of the adjusting means for the stitch length by means of whose change of position the movement of constant magnitude derived from the feed eccentric is converted for transmission to the feed means into a movement which has a changed magnitude that corresponds to the desired stitch length.

In accordance with the proposal to utilize the loop pickup position of looper and needle as the reference position for the layout of the setting means for the stitch length of the composite feed means, it is accomplished that once during each individual stitch forming cycle needle and hook are located in the same mutual position, independently of the magnitude of feed or stitch length, and thus in accordance with the proposal of the invention in a position where the needle has moved by the same stretch upwardly out of its lowermost position upwardly to the moment of the entrance of the point of the hook into the needle thread loop independently of the stitch length, thus entering the thread loop at the same vertical distance above the eye of the needle. Uncertainties in the stitch formation that are caused by change of the stitch length are thereby avoided.

In order to realize the invention with a setting means for the stitch length where a pivotally supported arcuate slot member as a guiding slide that receives a slide block and is driven by the feed eccentric and the slide block is connected by way of a push bar with a crank secured to the feed dog rocking shaft it is recommended in accordance with the invention, to place the center of arcuation of the slide guide in the position of the machine components corresponding to the loop pickup position of needle and hook onto the circular are which the point of linkage of the push bar describes at the crank.

In a further setting device for the stitch length where a rocking lever pivotally arranged and connected with the rocking shaft for the feed dog on a displaceable journal pin for the change of the stitch length upon an arcuate path by means of a setting shaft for the stitch length is driven by the feed eccentric by means of an eccentric bar engaging a journal axis of the rocking lever, the invention can be realized in that in a position of the machine components corresponding to the loop pickup position of needle and hook, the center point of the path of the journal pin coincides with the axis of linkage of the eccentric bar on the rocking lever and the axis of rotation of the shaft for setting the stitch lengths.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in detail hereinafter with reference to the double chain stitch sewing machine having a compound feeding device and two embodiments of the setting device for the stitch length illustrated in the accompanying drawings in which FIG. 1 is an overall view ofa double chain stitch sewing machine having a compound feed means,

FIG. 2 is a perspective illustration of the hook drive and of the compound feeding device of the machine with a first embodiment of the adjusting means for the stitch length,

FIG. 3 is a perspective illustration of a second embodiment of a setting device for the stitch length with a compound feeding device illustrated in FIGS. 1 and FIG. 4 is a schematic illustration of the arrangement in accordance with FIG. 2,

FIG. 5 is a schematic illustration of the setting device for the stitch length in accordance with FIG. 3,

FIG. 6 is a graphic illustration of the constant path of movement of the hook, as well as the path of movement of the needle in connection with the smallest and the largest adjustable stitch length, and

FIG. 7 is a perspective illustration drawn to an enlarged scale for explaining the formation of a double chain stitch.

DESCRIPTION OF THE INVENTION The material support or work plate 30 of the machine carries the housing 31 which merges into the head 32. In the housing 31 the arm shaft 33 is rotatably journalled which at one end carries the balance wheel 34 which is in the form of a belt pulley. The arm shaft 33 is driven by way of the balance wheel 34 with a motor (not shown) in a conventional manner, for example, by means of a belt.

At the end of the arm shaft 33 which extends into the head 32, the arm shaft crank 35 is mounted which drives the needle bar 39 that is reciprocably movable by way of link 36 and needle bar driver 37 in the rocking frame 38.

The needle bar 39 supports the needle 40 at its lower end. The rocking frame 38 for the needle bar 39 is secured by means of screw 42 on the end of the rocking shaft 41 that extends in the housing 31 into the head 32 below the arm shaft 33 and parallel thereto. At the other end of the rocking shaft 41 a crank 43 is secured which is connected by a drawbar 44 with the crank 46 secured to the swinging shaft for the feed dog journalled on the work plate 30.

One end of a thrust rod 48 is linked by means of a stud 49 to a further crank 47 for the feed dog on the swinging shaft 45. At the other end of the thrust rod 48 a sliding block 50 is pivotally mounted which in its turn is slidably guided in the arcuate guiding slot 51 of an arcuated slot arm 53 that is pivotable about the stationary pin 52.

For displacing the sliding block 50 in the guiding slot 51 in order to change the stitch length an adjusting lever 54 is provided which is connected by a connecting bar 55 with the thrust rod 48. At the free end of the arcuated slot bar 53 one end of an eccentric link 56 is joined whose other end encompasses an eccentric 57.

This eccentric 57 is secured on a shaft 59 rotatably mounted in the work plate 30 which is driven from the arm shaft 33 by means of a cord chain 62 that extends around chain pulleys and 61. This first embodiment of an adjusting device for the stitch length which comprises the components 47-57 is identified as 58 in FIGS. 2 and 4. This form of construction is known as slide and slot stitch regulator.

The carrier 63 for the feed dog which for simplification is itself provided with the feed dog teeth has its pushing movements imparted to it by a crank 64 secured to swinging shaft 45, which crank is pivotally connected by means ofstud 65 with the carrier 63 for the feed dog. The lifting movements are imparted to the carrier 63 for the feed dog by an eccentric secured to the shaft 59 by way of an eccentric bar 67, a crank 69 secured on an intermediate shaft 68 journalled below the work plate 30, a further crank 70 and a link 71 which connects said crank 70 with one arm of the carrier 63 for the feed dog.

The drive of the double chain stitch book 72 which is secured on a hook support 73 and whose point is oriented in the direction opposite to the direction of the forward feed (arrow V) is derived from an eccentric 74 secured to the rocking shaft 59 and transmitted by an eccentric bar 75 to the hook carrier 73 which is pivotable about pin 76. A loop spreader 77 cooperates with the hook 72 and is secured to a slide bar 78 movably guided in the work plate 30. The slide bar 78 has imparted to it feed movements in a direction vertically to the direction of feed (arrow V) by an eccentric 79 se cured on the shaft 59 by way of an eccentric bar 80, a bell crank lever 82 pivotable about a stationary pin 81 and a link 83.

It is also possible to install in the machine instead of the adjusting device 58 for the stitch length a second embodiment 84 of an adjusting device illustrated perspectively in FIG. 3 and schematically in FIG. 5 for the combined feed means which generally is referred to as link stitch regulator.

The adjusting mechanism 84 for the stitch length (FIGS. 3 and 5) has a setting shaft 85 journalled in the housing 31 which is provided at the end extending through the housing 31 with a handle (not shown) and has rigidly connected thereto a U-shaped yoke 86. At the free ends of the legs 87 two crank arms 88 are mounted for pivotal movement about support studs 89 secured to the legs 87. The crank arms 88 are connected for mutual rotation by a cylindrical bolt 90 extending through bores in the crank arms 88 parallel to and at a distance from the support studs 89 on which bolt the crank arms 88 are secured. The crank arms 88 and the bolt 90 thus constitute a unitary structure referred to hereafter as rocking lever 91.

The rocking lever 91, which if designed accordingly, can also be constructed with a single crank arm 88, in order to achieve the purpose for which this device is intended, is driven by an eccentric 92 secured to arm shaft 33 by way of an eccentric bar 93 that is in engagement with bolt 90. The rocking lever 91 is connected by means of a link 94 with a crank 95 for the feed dog secured to the swinging shaft 45. The link 94 is rotatably disposed on bolt 90 and linked to the crank 95 by means of a pin 96.

.By means of this arrangement rocking movements are only imparted to the swinging shaft 45 for the feed dog, when the longitudinal axes of the support studs 89 are disposed outside a line of alignment extending through the longitudinal axis of the bearing pin 96. If, however, the supporting pins or studs 89 and 96 are in the same line of alignment, then the rocking lever 91 and link 94 effect pure rotational oscillations about the bearing studs 89 and 96 and accordingly no movement is imparted to the swinging shaft 45 for the feed dog.

The mechanism in accordance with the invention opcrates as follows:

As the arm shaft 33, which is driven by a motor not illustrated, is driven by a belt which is disposed about the balance wheel 34, the needle bar 39 supporting needle 40 has imparted thereto up and down movements by way of arm shaft crank 35 and the needle bar link 36 that engages the needle bar driver 37. Simultaneously feeding movements in the direction parallel to the direction of feed (arrow V) are imparted to needle bar 39 derived from the eccentric 57 on shaft 59 driven by way of the cord chain 62 by arm shaft 33. The constant rocking movements derived from eccentric 57 by way of eccentric bar 56 transmitted to the arcuated slot arm 53 of the adjusting mechanism 58 for the stitch length are in the arrangement in accordance with FIG. 2 picked up by sliding block 50 guided in the slide guide 51 at such a magnitude that depends on the distance of the sliding block 50 from the pin 52 of the arcuated slot bar 53, and are transmitted to the needle bar 39 supporting the needle by way of thrust rod 48, joint stud 49, the cranks 47 and 46 secured to the feed dog swinging shaft 45, the drawbar 44 and crank 43 onto the rocking shaft 41 and thereby onto the needle bar rocking frame 38 with the needle bar 39 supporting the needle 40 secured thereto. The position of the sliding block 50 in the guiding slide 51 and thereby the magnitude of the oscillating movements of the needle 40 can be set with the adjusting lever 54 for the stitch length. This lever is connected by way of bar 55 with the thrust bar 48 which carries the sliding block 50.

The feed dog support 63 imparted to it simultaneously with the rocking frame 38 feed movements of the same size as the needle 40 by way of crank 64 secured to swinging shaft 45 and the stud 65. The feed movements of the feed dog support 63 and of the needle 40 are changeable together by means of the adjusting mechanism 58 for stitch length by operating adjusting lever 54 for stitch length.

The customary lifting movements for the feed dog support 63 are derived from the eccentric 66 mounted on shaft 59, and are transmitted by the eccentric bar 67, crank 69,intermediate shaft 68, crank and link 71 to the feed dog support 63.

As a result of these driving connections the feed dog support 63 which for the sake of simplicity in the embodiment of FIG. 2 is itself provided with teeth that engage the work blank effects a movement referred to as rectangular. Besides its vertical reciprocating longitudinal movements the needle bar 39 also effects movements in the direction parallel to the direction of feed.

If, in lieu of the' adjusting means 58 for the stitch length, the machine is provided with the adjusting mechanism 84 shown in FIGS. 3 and 5, then the feed movements for the needle 40 and the feed dog support 63 are derived from the feed eccentric 92 secured to the arm shaft 33 and transmitted by way of eccentric bar 93 to the rocking lever 91, which thereby effects a constant rocking movement about the bearing studs 89.

If the longitudinal axis of the bearing pin 96, is in alignment with the longitudinal axis of the studs 89, then the rocking lever 91 and link 94 effect pure rotary oscillations about the bearing studs 89 and 96 and accordingly no movement is imparted to crank 95 of the swinging shaft 45, so that the feed movement of needle and feed dog support is zero.

If the needle and the feed dog support are to be set to a desired length of feed (stitch length), then the U- shaped yoke 86 is manually turned by means of the setting shaft for stitch length. The support studs 89 that are provided on the legs 87 are thereby swung out of alignment with the support pin 96. Thus the pin 96 and the crank secured to the swinging shaft 45 have imparted thereto rocking movements whose magnitude depends on the distance of the bearing stud 89 from the stud 96. The rocking movement of swinging shaft 45 is transmitted, as described above to the feed means (needle and feed dog support).

The double chain stitch hook 72 which cooperates with the needle 40 (see FIG. 7) for forming the double chain stitches has imparted to it constant longitudinal loop catching and dropping movements from the eccentric 74 on the shaft 59 which drives the hook support 73 with the hook 72 by way of the eccentric bar 75.

For forming and keeping open what is referred to as the thread triangle for the entering stitch of the needle the loop spreader 77 which has the shape of a pin and is fastened to sliding bar 78 cooperates with the book 72. The sliding bar 78 with the loop spreader 77 has imparted to it longitudinal movements directed transversely of the direction of feed (arrow V) derived from the eccentric 79 on shaft 59 by way of eccentric bar 80, angular lever 82 and link 83, while the loop spreader 77 is moved forward to hook 72 and over the blade of the hook for seizing the hook thread 97, then seizes during its return movement that part of the hook thread 97 which extends from the eye of the hook to the penultimate stitch between the hook eye and the loop of the needle thread 98 disposed about the hook blade and spreads it for the entrance of the needle 40 and thereupon releases it again during the repeated forward movement. The forming of the chain stitch is generally known and only mentioned here for the sake of completeness.

While in the adjusting devices for the stitch length of double chain stitch sewing machines having a compound feeding means the lowermost position of the needle was the reference position for the construction and adjustment of the adjusting means of the stitch length, and accordingly the portions of the paths of the feed means for all adjustable stitch lengths were equally distributed on both sides of a vertical line through the needle in the lowermost position, whereby the hook was at an equal distance from the needle merely in the low position of the needle, in accordance with the invention the loop pickup position (SA) of needle and hook becomes the reference position for the construction and adjustment of stitch length and the drive for the hook.

For an explanation of the problems of sewing technique arising in this connection and the fixing of a new reference position evolving therefrom for the forming and adjusting of operational components essential for all adjustable stitch lengths in order to meet conditions for obtaining equal stitch forming requirements, particularly the loop thrust, the courses of movement for the needle and the hook as well as all principally kinematic relationships of the adjusting devices 58 and 84 for the stitch length and the combined feed means are illustrated graphically in FIGS. 4, and 6.

The courses of movements of the point of the needle for the greatest and smallest stitch length and the course of movement of the point of the hook are illustrated graphically to a greatly enlarged scale in FIG. 6.

As in FIGS. 2 and 7 the feed direction of the material is also indicated in FIG. 6 by an arrow V. The curve A in a solid line indicates the path of movement of the point of the needle for the largest stitch length, and the curve B in dot and dash lines indicates the course of movement for the smallest stitch length. The path of movement of the point of the hook is indicated by C.

The division of the courses of movement A and B of the point of the needle into 24 parts (designated 0 to 23) and of the point of the hook (0 to 23') results from the equal angular division of the arm shaft into 24 parts and the distribution over a complete rotation of the shaft, i.e. the points of intersection indicated in curves A and B by numbers 0-23 or in curve C by 0 to indicate those locations in each case, where during one rotation of the shaft the point of the needle, respectively the point of the hook is located for the largest and the smallest stitch length.

In this connection the low position of the needle is indicated at 0, the position of the hook point at 0' as seen in the rear reversing position of the point 72 in the direction of material feed. The width of rocking of the point 72 is indicated at D and E indicates the height of the loop thrust of the needle 40. The hook 72 and the needle or parts thereof are illustrated the position of loop reception, where the needle has moved upwardly from its lowest position at 0 by the distance E (loop lift) whereby, asis known the loop of the needle thread is formed into which the looper point must enter, and the looper point is centrally of the needle above the eye of the needle in the circle identified by SA.

FIGS. 4 and 5 show corresponding angular positions of the points of greatest eccentricity of the feed eccentrics 57 and 92 likewise identified by 0 and SA.

While with the double chain stitch sewing machines having a compound feed means known heretofore the path portions of the different feed stretches were disposed symmetrically with respect to a reference line passing centrally of the needle in low position, it can be seen from the courses of movement of the needle and the point of the hook illustrated in FIG. 6 that show the actual relationships merely to an enlarged scale, that the reliance in accordance with the invention on the basis for the construction and adjustment of the gear components of the machine the path portions of the different feed stretches are not symmetrical to a reference line extending centrally of the needle disposed in loop catching position, but that the larger-part at any time is displaced in a direction opposite to the direction of feed.

This distribution of the path portions of the feed stretches evolves best from the angular position of the feed eccentrics 57 and 92 on their shafts 59, respectively 33 schematically illustrated in FIGS. 4 and 5. The points of greatest eccentricity of the feed eccentrics 57 and 59 are located in the loop pickup position of the needle and the hook at the positions indicated at SA. Starting with this position one reversing point of the arcuate slot element 53 or of rocking lever 91 is reached after turning of the eccentrics 57 and 92 by about 45 in the direction of the arrows, which corresponds to the rear reversing point of the needle and the feed dog as seen in the direction of feed, arrow V. The thrust or lift which in this connection acts on the arcuate slide 53, respectively swinging lever 91 and thereby on the feed means amounts to only a fraction of the total thrust derived from eccentric 57 or 92, which explains the displacement of the larger part of the feed stretches from the reference line passing through the center of the needle in loop pickup position, opposite to the direction of feed, arrow V.

The loop pickup position of needle and hook described above is attained independently of stitch length once during each stitch forming cycle, i.e. during each rotation of the arm shaft, and this in that the slide guide 51 in which the sliding block is adjustably guided is so formed and so connected with the eccentric 57 that drives with a constant movement the arcuate slot guide 53, that for the position designated SA of the point of greatest eccentricity of the feeding eccentric 57 the center point of arcuation of the slide guide Slin the loop pickup position (circle SA, FIG. 6) of needle and hook is along the arc of the circle that the linkage position 49 of the push bar 48 describes on the crank 47 which is fastened to the feed dog swinging shaft 45.

lf the adjusting lever 54 is actuated in the loop pickup position in order to change the stitch length by changing the distance of the slide block 50 from the journal bolt 52 of the arcuate slot guide 53, then push bar 48 that carries the slide block 50 effects a true rotation about the stud 49. Accordingly no movement is trans mitted to the swinging shaft 45 of the feed dog as the slide block 50 moves along the setting stretch F (FIG. v

With the adjusting mechanism 84 for the stitch length setting up of the loop pickup position SA once per stitch forming cycle is attained by the needle and hook independently of the stitch length in that the feed eccentric 92 assumes such a position relative to the arm shaft 33, that in-the position indicated in solid lines in FIG. of the loop pickup setting SA of needle and hook that corresponds to the position of the remaining parts of the gear the center point of the arcuately shaped path G, which the joint pins 89 of the rocking lever 91 (FIG. 3) connected with the feed eccentric 92 describe as the joint pins 89 are displaced with respect to the joint stud 96 on the crank 95 by turning of the adusting shaft 85 for the stitch length fixed to the U- shaped yoke 86, coincides with the linking axis 90 on rocking lever 91 and with the axis of rotation of adjusting shaft 85 for the stitch length.

As the adjusting shaft 85 is rotated in this setting to change the stitch length, then with the conditions explained above, the distance between the swinging shaft 45 and the common axis of linkage (bolt 90) of the rocking lever 91 and the eccentric bar 93 is not changed so that no movement is imparted to the crank 95 secured to swinging shaft 45 and therefore not to the feed means.

It is seen that by the construction and adjustment of the operational components that are already present and needed at any rate in a double chain stitch sewing machine with a compound feed device, equal stitch forming conditions can be obtained for all stitch lengths by using the loop pickup position of the needle and the hook as reference position.

The result achieved with the examples of a combined feed means with a so-called slide and block stitch regulator 58 and a link stitch regulator 84 can also be obtained with an eccentric stitch regulator, if care is taken that in the loop catching position of needle and hook no movement is imparted to the feed means as the stitch length adjusting member is operated. Eccentric stitch regulators which during sewing operations permit a change in stitch length are however not frequently used with sewing machines of this type.

Having now described my invention with reference to the embodiments illustrated in the drawings, what 1 desire to protect by letters patent is set forth in the appended claims.

I claim:

I. Sewing machine having a double chain stitch hook and a compound feeding means, comprising a feed dog and a needle bar supported in a rocking frame and connected to a feeding mechanism including a swinging shaft, a feed dog mounted on a feed dog support connected to a rocking shaft, said swinging shaft and said rocking shaft being connected to a feeding eccentric and being operatively linked to one another, an adjusting device having a setting member for the stitch length operatively connected to said eccentric, where for obtaining an identical loop rise of the needle with all adjustable stitch lengths said setting member is disposed in the position of the machine components corresponding to the loop pickup position (SA) of the needle and the hook, while said swinging and said rocking shaft do not rotate in response to displacement of the setting member along its path of adjustment.

2. Sewing machine in accordance with claim 1, where said adjusting device includes a pivotally journalled, arcuated slot member, a sliding block received in said slot member, a crank on said swinging shaft, a push bar connecting said sliding block with said crank, the center point of curvature of said slot member being located in that position of the component parts of the machine which corresponds to the loop pickup position of the needle and hook along the are described by the point of linkage of said push bar with said crank.

3. Sewing machine in accordance with claim 1, where said adjusting device for the stitch length includes a stitch length setting shaft, a rocking lever device connected with the rocking shaft for said feed dog and pivotally mounted on a bearing pin which is displaceable along an arcuate path, said rocking lever having a pivot axis in driving engagement with said feeding eccentric, the center point of the path of said bearing pin and the components of the machine in the position corresponding to the loop pickup position of the needle and the hook coinciding with the pivot axis of said feeding eccentric at said rocking lever and the axis of rotation of said setting shaft.

4. Sewing machine in accordance with claim 3, comprising a U-shaped yoke rigidly connected to said setting shaft and having legs, a crank secured to said rocking lever, and a link between said crank and said rocking lever, said rocking lever being journalled on said yoke.

Claims (4)

1. Sewing machine having a double chain stitch hook and a compound feeding means, comprising a feed dog and a needLe bar supported in a rocking frame and connected to a feeding mechanism including a swinging shaft, a feed dog mounted on a feed dog support connected to a rocking shaft, said swinging shaft and said rocking shaft being connected to a feeding eccentric and being operatively linked to one another, an adjusting device having a setting member for the stitch length operatively connected to said eccentric, where for obtaining an identical loop rise of the needle with all adjustable stitch lengths said setting member is disposed in the position of the machine components corresponding to the loop pickup position (SA) of the needle and the hook, while said swinging and said rocking shaft do not rotate in response to displacement of the setting member along its path of adjustment.

2. Sewing machine in accordance with claim 1, where said adjusting device includes a pivotally journalled, arcuated slot member, a sliding block received in said slot member, a crank on said swinging shaft, a push bar connecting said sliding block with said crank, the center point of curvature of said slot member being located in that position of the component parts of the machine which corresponds to the loop pickup position of the needle and hook along the arc described by the point of linkage of said push bar with said crank.

3. Sewing machine in accordance with claim 1, where said adjusting device for the stitch length includes a stitch length setting shaft, a rocking lever device connected with the rocking shaft for said feed dog and pivotally mounted on a bearing pin which is displaceable along an arcuate path, said rocking lever having a pivot axis in driving engagement with said feeding eccentric, the center point of the path of said bearing pin and the components of the machine in the position corresponding to the loop pickup position of the needle and the hook coinciding with the pivot axis of said feeding eccentric at said rocking lever and the axis of rotation of said setting shaft.

4. Sewing machine in accordance with claim 3, comprising a U-shaped yoke rigidly connected to said setting shaft and having legs, a crank secured to said rocking lever, and a link between said crank and said rocking lever, said rocking lever being journalled on said yoke.

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