Sewing – Elements – Driving mechanisms
Reexamination Certificate
2000-04-03
2001-02-06
Izaguirre, Ismael (Department: 3765)
Sewing
Elements
Driving mechanisms
C112S192000
Reexamination Certificate
active
06182589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates, generally, to a driving apparatus for an oscillating catcher of a sewing machine.
More particularly, the present invention relates to a driving apparatus for an oscillating catcher of a sewing machine, which is capable of providing greater stitching security and/or a greater stitching width during the sewing of a zig-zag stitching procedure than comparable devices currently known to the art.
2. Description of the Prior Art
Various designs for driving devices for oscillating catchers are known in the prior art. The function of such driving devices is to place the catcher of the sewing machine into an oscillating rotational motion for the purpose of seizing with the point of the catcher of the loop of the upper thread, as well as for guiding the catcher about the spool capsule. The catcher is driven, in most cases, with a crank, which is put into motion by a revolving, or oscillating driving element. In many cases, the crank is driven via a toothed rack, or a toothed gear, mounted on a driving shaft of the catcher.
In Switzerland Patent No. 241,880, the toothed rack is guided tangentially relative to the toothed gear in a longitudinal guide, and driven via a connecting rod secured on a crank.
In United Kingdom Patent Specification No. 1,035,881, the teeth of the toothed rack of the apparatus disclosed therein are directly formed on an extension of a connecting rod. The connecting rod is put into an oscillating motion via a swinging lever. The two driving devices taught in this prior art reference can be employed for both horizontally and vertically oscillating catchers.
The driving devices of the types specified in the foregoing prior art have the distinct drawback that an attainable rotational speed for the catcher is relatively low at the moment that the loop is picked up by the point of the catcher. However, the rotational speed of the catcher cannot be varied at will with conventional devices known to the prior art, because the driving movements of the needle bar and of the catcher of a double-stitch sewing machine have to be synchronized. As long as the needle moves in a central position, i.e., in the zero position, and is therefore not deflected sideways for zig-zag sewing, the movements of the catcher exactly match the position of the needle.
The loop of the upper thread can be securely seized and uniformly guided. When zig-zag seams are sewn, the phase position between the eye of the needle and the point of the catcher changes at the moment that the loop is taken over by the catcher, depending upon the contemporaneous lateral position of the needle, i.e., at the moment of its lateral deflection from the center position. This is because, while the point of the catcher is moving past the needle for seizing the loop of the upper thread offered by the needle, the needle is already moving upwards. This lateral displacement of the needle during zig-zag sewing necessarily changes the spacing between the eye of the needle and the point of the catcher. If this spacing is smaller or larger than the nominal (or rated) spacing, faulty stitches may occur, because the shape and size of the loop of the thread changes with the deflection, as well, and the point of the catcher will not pick up the loop in the most unfavorable case.
The maximally achievable zig-zag width, i.e., the deflection of the needle, is influenced by, and/or upwardly limited by, the deviation of the phase position between the eye of the needle and the point of the catcher. The effects of such phase displacement are described and illustrated in the handbook by Renters, entitled
Der Naehmaschinen
-
Fachmann
, which translates to
The Sewing Machine Expert
, in English. The relevant portions of this reference are found in Volume 3, published in 1957.
In summation, it becomes clear that a greater zig-zag width would be attainable if the deviations from the conditions present when a straight seam is sewn did not exist.
The foregoing discussion makes clear that the stitching security and the maximally achievable stitching width during zig-zag sewing are very strongly influenced by the speed of the relative movements between the needle and the catcher. Both the translatory movement of the needle bar and the needle, and the oscillating motion of the catcher take place in non-uniform ways, conditioned by the movement pattern (acceleration/deceleration) of their crank drives. In order to improve the motional conditions within the range in which the loop of the thread is picked up by the point of the catcher, or to reduce the phase shift between the eye of the needle and the point of the catcher in said range, it would be necessary to either retard the movement of the needle or to increase the speed at which the catcher is moving.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a driving apparatus for an oscillating catcher of a sewing machine having greater stitching security and/or a greater stitching width during a zig-zag sewing procedure.
The foregoing and related objects are achieved by the driving apparatus of the present invention for an oscillating catcher of a sewing machine, in which the driving apparatus includes a toothed pinion being eccentrically mounted on a driving shaft for the catcher for the sewing machine. Transmission means, having teeth, is guided in a back-and-forth movement by an oscillating crank drive, with the teeth of the transmission means engaging the tooth pinion on the driving shaft.
By arranging the toothed driving gear eccentrically on the driving shaft of the catcher, it is possible to substantially increase the speed of the point of the catcher when it seizes the loop of the upper thread offered by the needle. The angular position of the highest eccentricity of the toothed gear, with respect to the point of the catcher, is selected in this connection so that the point of the catcher is moving past the needle within a given range, or at the time when the loop is being picked up, at the highest possible speed. The pinion eccentrically mounted on the driving shaft of the catcher can be manufactured economically. For the purpose of guiding the toothed rack on the toothed gear, it is possible to make provision for a guiding disk arranged coaxially with the eccentrically-positioned tooth gear; the tooth gear preventing the toothed rack from lifting off the toothed gear with the aid of an abutting guide.
In an alternative embodiment of the present invention, the toothed rack, which is preferably formed on the end of a connecting rod, is kept engaged with the teeth of the toothed gear by a spring force.
In another advantageous embodiment of the present invention, the speed curve of the point of the catcher during pick-up of the loop of the thread can be further optimized if the teeth of the toothed rack are arranged along a curved line. The use of a toothed belt as a transmission means was found to be advantageous with respect to concern about the generation of noise.
Other objects and features of the present invention will become apparent when considered in combination with the accompanying drawing figures which illustrate certain preferred embodiments of the present invention. It should, however, be noted that the accompanying drawing figures are intended to illustrate only certain embodiments of the claimed invention and are not intended as a means for defining the limits and scope of the invention.
REFERENCES:
patent: 1613605 (1927-01-01), Corrall et al.
patent: 2325467 (1943-07-01), Beyer
patent: 3029762 (1962-04-01), Szuba et al.
patent: 5396853 (1995-03-01), Huang
patent: 6032597 (1927-01-01), Inagaki
Anderegg Christian
Stucki Andre
Fritz Gegauf AG Bernina-Nahmaschinefabrik
Izaguirre Ismael
Schindler Edwin D.
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