Fine-feed adjusting device of a sewing machine
BACKGROUND OF THE INVENTION 
     The present invention relates to a fine-feed adjusting device for a sewing machine, and more particularly to a device for fine adjustments of feed pitches of left-hand and right-hand stitchings, used especially in a buttonhole stitching. 
     In conventional pattern stitchings formed by the sewing machines, discrepancies have occurred in feed pitches between a forward feed and a backward feed due to types of fabrics, threads, pressing pressure and other factors, and the patterns have often appeared to be awkward. Especially in the buttonhole stitchings, if the left-hand stitching is on the forward feed and the right-hand side stitching is on the backward feed, and if the feed pitches of each feed do not coincide with each other, the stitchings become non-satisfactory. Therefore, a fine adjustment of the feed pitch has been necessary. There have been many proposals where machine operators handle appropriate adjusting members during the running of the sewing machine in order to finely adjust the feed pitches. However, the sewing machine, in which a pulse motor is a power source which actuates a feed adjusting device, is complicated in structure and expensive, and is also not durable. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a fine-adjusting device, in which, defects of the conventional devices would be eliminated. 
     This and other objects of the invention are attained by a fine-feed adjusting device for a sewing machine provided with a feed adjustment device actuated by means of a drive pulse motor having an output shaft and mounted to an attaching member secured to a machine frame of the sewing machine, comprising a feed adjusting member mounted on said attaching member, and pivotable relative to said output shaft such that it is turned about an axis of said output shaft; a drive gear mounted on said output shaft; a follower gear meshed with said drive gear and pivotally supported at an end of said feed adjusting member; means for operating the feed adjustment device including a feed rotation shaft rotatably pivoted to the machine frame, and a feed adjusting arm secured on the feed rotation shaft; a connecting rod pivotable between said feed adjusting arm and said follower gear; and a fine-feed adjusting member rotatably supported in said attaching member and having an eccentric portion inserted in a groove formed in said feed adjusting member, said fine-feed adjusting member being rotated by an external force so as to turn said feed adjusting member to make a fine adjustment to a feed pitch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a section of a fine-feed adjusting device; 
     FIG. 2 is an exploded perspective view of the fine-feed adjusting device; and 
     FIGS. 3 to 5 show various operation steps of the fine-feed adjusting device, wherein 
     FIG. 3 is a side view of the device in the position in which a feed pitch is zero, 
     FIG. 4 is a side view of the device with a slightly available feed pitch at a forward feed, as compared to the stage shown in FIG. 3, and 
     FIG. 5 is a side view of the device with a slightly available feed pitch at a backward feed, as compared to the stage shown in FIG. 3, and 
     FIG. 6 is a side view on an enlarged scale of a section of the feed adjusting member with the fine-feeding adjusting member. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A fine feed-adjusting device 1 according to the invention comprises a pulse motor 2, a feed adjusting member 3, a drive gear 4, a follower gear 5, a feed adjusting arm 6, a connecting rod 8 and fine feed-adjusting control member 9. 
     The pulse motor 2 is fixed with an attaching plate 11, from which an output shaft 12 extends. The output shaft 12 is provided thereon with a bush 13 which is restrained in an axial direction. The pulse motor 2 is connected to an attaching member 18 which is secured to a machine frame 15 with screws 16, by inserting the bush 13 into a hole 18a defined in attaching member 18 and securing to the member 18 with stepped screws 20. 
     The feed adjusting member 3 has a central hole 3a for the bush 13 and, at both ends thereof, arc-shaped oblong holes 3b moving around an axis of the output shaft 12. The stepped screws 20 are mounted into the oblong holes 3b with the stepped portions 20a thereof. Accordingly, the feed adjusting member 3 may turn around the axis of the output shaft 12 due to a space between the oblong holes 3b and the stepped portions 20a. 
     The drive gear 4 is fixed via a screw 21 on the output shaft 12 extending from the feed adjusting member 3. 
     The follower gear 5 is shaped as a segment and is in mesh with the drive gear 4. Gear 5 is formed with a hole 5a at a rotating center thereof for mounting on a pivot 22 implanted at one end of the feed adjusting member 3, and further is restrained against the movement in the axial direction by means of a collar 24 secured via a screw 23 to the pivot 22 and against rotation by means of a pair of stopper pins 25. 
     The feed adjusting arm 6 is fixed, with a screw 27, on one end of a feed rotation shaft 26 pivoted on the machine frame 15. The feed rotation shaft 26 is secured, at its other end, with a feed adjuster 29 which is one member of the feed adjusting device 28. Accordingly, when the feed rotation shaft 26 is rotated, the feed adjusting device 28 is actuated via the feed adjuster 29. 
     The connecting rod 8 is formed at its both ends with holes 8a, into which fixing pins 30 and 31 are inserted and secured with stopper rings 32, so that the connecting rod 8 is restrained against the axial movement. The fixing pin 30 is implanted in the follower gear 5 and the fixing pin 31 is implanted in the feed adjusting arm 6. 
     The fine feed-adjusting member 9 comprises a shaft part 9a and an eccentric part 9b, and is provided with a flange part 9c at one end of the shaft part 9a. The shaft part 9a is mounted and restrained against the axial movement in a pair of holes 18c formed in bent portions 18b of the attaching member 18. The eccentric part 9b is cylindrical as well as the shaft part 9a, and the eccentricity thereof is determined at such a position by an eccentric amount e with respect to the eccentricity of the shaft part 9a. 
     The eccentric part 9b is adapted to fit into a groove 3c formed as an extension from a hole 3d at one end of the feed adjusting member 3. If the fine feed-adjusting member 9 is rotated via a groove 9d, the feed adjusting member 3 is rotated about the axis of the output shaft 12, to rotate the feed adjusting member 6 via the connecting rod 8 and provide fine adjustment of the feed pitch. 
     The hole 3d formed in continuity of the groove 3c is an idle hole for holding the shaft part 9a of the member 9. 
     The device of the present invention is actuated as follows. If the pulse motor 2 rotates, the follower gear 5 rotates about a pivot 22 via the drive gear 4. Then, the feed adjusting member 6 rotates about the feed rotation shaft 26 via the connecting rod 8, and the feed adjusting device 28 is actuated by the feed adjusting device 29, whereby the feed pitch may be adjusted. 
     FIG. 3 shows the fine condition of the feed-adjusting device 1 when the feed pitch is zero. A line 0-A between the axis of the output shaft 12 and the axis of the pivot 22, is tilted by an angle α 1  toward the right with respect to a vertical line 0-B running through the axis of the output shaft 12. A line 0-C between the axis of the output shaft 12 and the axis of the eccentric part 9b of the fine feed-adjusting member 9, is tilted by an angle α 2  downward with respect to a horizontal line 0-D running through the axis of the output shaft 12. A line 0 1  -E between the axis of the feed rotation shaft 26 and the axis of the fixing pin 31, is tilted by angle α 3  toward the left with respect to a vertical line 0 1  -F running through the axis of the feed rotation shaft 26. The groove 9d of the feed fine-adjusting member 9 is positioned on a horizontal line 0 2  -G running through the shaft part 9a. 
     From the above described state, a slight pitch is made to the forward feed by rotating the fine feed-adjusting member 9 to the clockwise direction such that, for example, the groove 9d  is tilted upward with respect to the horizontal line 0 2  -G. Then, the line 0-C 1  between the axis of the output 12 and the axis of the eccentric part 9b of the fine feed-adjusting member 9, is tilted by Δα 2  upward. At the same time, the line 0-A 1  between the axis of the output shaft 12 and the axis of the pivot 22, is tilted by angle Δα 1  toward the right with respect to the line 0-A. Thereby, the line 0 1  -E 1  between the axis of the feed rotation shaft 26 and the axis of the fixing pin 31, is tilted by angle Δα 3  via the connecting rod 8 toward the right with respect to the line 0 1  -E 1 , whereby the feed adjusting device 28 is actuated via the feed adjuster 29, and a slight pitch is made to the forward feeding side. 
     From the state shown in FIG. 3, a slight pitch is made to the backward feed by rotating the fine feed-adjusting member 9 in the counterclockwise direction such that, for example, the groove 9d is tilted by an angle β 2  toward the horizontal line 0 2  -G. Then, the line 0-C 2  between the axis of the output shaft 12 and the axis of the eccentric part 9b of the fine feed-adjusting member 9, is tilted by angle Δα&#39; 2  downward with respect to the line 0-C. At the same time, the line 0-A 2  between the axis of the output shaft 12 and the axis of the pivot 22, is tilted by angle Δα&#39; 1  to the left. Thereby, the line 0 1  -E 2  between the axis of the feed rotation shaft 26 and the axis of the fixing pin 31, is tilted by angle Δα&#39; 3  via the connecting rod 8 to the left with respect to the line 0 1  -E 1  so that the feed adjusting device 28 is actuated via the feed adjuster 29, and the feed pitch is made to the backward feed. 
     As mentioned above, according to the invention, if the fine feed-adjusting member 9 is rotated by turning such as a screw drive inserted in the groove 9d, the fine adjustment may be made for the pitch of the forward or backward feed. For example in the buttonhole stitching, if the forward feed stitching at the left is slightly smaller than the backward feed stitching at the right, and then the feed-adjusting member 9 is rotated in the clockwise direction, the forward feed pitch is made larger, whereby the stitchings of the forward feed and the backward feed may be made equal. 
     The device of the present invention is formed and actuated as described above, wherein the feed adjusting device is operated by means of the pulse motor as the power source which is attached to the attaching member fixed to the machine frame of the sewing machine, and the feed adjusting member is pivoted relative to the attaching member such that it is turned about the axis of the output shaft of the pulse motor by rotating the fine feed-adjusting member the eccentric part of which is mounted in the groove defined in the feed adjusting member, and therefore, with respect to the feed pitch, the fine adjustment may be easily made by means of the simple and durable structure. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of sewing machines differing from the types described above. 
     While the invention has been illustrated and described as embodied in a sewing machine, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.