Sewing – Elements – Starting or stopping
Reexamination Certificate
2002-08-12
2003-05-20
Nerbun, Peter (Department: 3765)
Sewing
Elements
Starting or stopping
Reexamination Certificate
active
06564733
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a means for monitoring the lower thread on double thread lockstitch sewing machines with a preferably rotating hook.
BACKGROUND OF THE INVENTION
A means for recognizing the approaching end of the lower thread of a sewing machine with a double thread lockstitch hook, which makes it possible to still have a defined residual thread length available after the recognition of the approaching thread end regardless of the particular thread strength being used, is shown in DE 40 31 058 C1.
A web, which is directed essentially in parallel to the flanges of the bobbin and whose lateral surfaces are reflective, is provided for this purpose on the hub of the bobbin. Openings are provided in the flanges of the bobbin, whose surfaces have a light-absorbing layer or have a dull finish, for the infrared rays emitted from a reflection head, which fall laterally on the thread roll, passing through the flange of the bobbin or through the openings in the flange when the bobbin is still filled sufficiently, and are absorbed. As long as the infrared rays are not reflected by the reflection head, no signal can be sent by the reflection head.
If the thread roll has been used up to the extent that the external diameter of the residual thread length is smaller than the external diameter of the web, the infrared rays passing through the openings in the flange fall on the lateral surface of the web and are sent back to the reflection head. A signal, which is used for the further control of the sewing machine and which can be used either to stop the machine immediately or to still form a defined number of residual stitches, is generated as a result.
Since it makes no difference for the absorption of the infrared ray whether it falls on the stationary surface of the flange of the bobbin or on the stationary thread roll or whether the latter are rotating, the approaching end of the bobbin thread can be recognized or displayed with this means in the case of a machine operating properly, but it is not possible to recognize a disturbance in sewing, e.g., a thread break, because if a break of the needle thread or of the lower thread occurs during sewing while the bobbin is still filled with a relatively large amount of thread, the infrared ray is not sent back by the flange of the bobbin or the thread roll to the reflection head, and no output signal is consequently generated.
An improvement of the above-described means, which pertains essentially to the increase in the reliability of operation of the said means, is shown in DE 41 15 520 A1, in which infrared rays emitted by a reflection head are likewise returned by a reflection surface arranged at the bottom of the hook body to the reflection head. Openings for the infrared ray are provided for this purpose both in the upper part of the bobbin housing, on the one hand, and in the two flanges of the bobbin, on the other hand. Moreover, the bobbin is equipped in an advantageous embodiment with two webs arranged at spaced locations from one another, in which openings, which are arranged on the same pitch circle as the openings in the flanges of the bobbin, are likewise provided for the infrared ray. The arrangement of all openings is selected now to be such that in the case of a bobbin having only a residual thread length, the infrared ray emitted by the reflection head reaches the reflection surface through the openings of the upper part of the bobbin housing, of the first bobbin flange, the two webs, the lower part of the bobbin housing as well as the hook body and is returned therefrom to the reflection head. The signal originating from this as a result can then be used either to stop the machine immediately or to still work off at least part of the residual thread length.
If the bobbin is still filled with thread to such an extent that the openings in the webs of the bobbin are covered by the residual thread roll, the infrared ray is absorbed. It makes absolutely no difference whether this happens with the bobbing rotating or stopped. If breaking of the needle thread or lower thread occurs during sewing with the bobbin still filled with a relatively large amount of thread, the infrared ray is not returned by the flange of the bobbin or the thread roll to the reflection head in this means, either, and no output signal is consequently generated, either.
Even though contamination of the reflection surface by settling dust generated during the sewing is counteracted in this means by the needle thread moving over the reflection surface during the stitch formation, this means is nevertheless relatively susceptible to fault because of the plurality of openings through which the infrared light ray passes and is correspondingly expensive to manufacture, especially because it additionally also requires an adapted bobbin housing lower part and a hook body provided with a reflection foil besides an adapted bobbin housing top part and a corresponding bobbin.
DE 34 47 138 A1 shows a means for double thread lockstitch sewing machines, which generates signal sequences that can be assigned to the particular instantaneous operating state depending on that operating state, wherein a signal sequence with a sequence changing in a pronounced sinus-like pattern is generated in the case of a sufficiently filled bobbin and trouble-free sewing operation, a signal sequence with intermittent residual ripples is generated in the case of a bobbin that is no longer filled sufficiently, and, finally, a signal sequence of a constant pattern is generated in the case of stoppage of the bobbin, which corresponds to a disturbance. When the bobbin is still filled sufficiently and rotating, the infrared light ray emitted by a reflection head is reflected alternatingly by the thread reserve covering the openings and by the reflecting surfaces of the particular bobbin flange, which surfaces are located between these openings, as a result of which the above-mentioned signal sequence changing in a pronounced sinus-like pattern is generated. By contrast, the openings are free in the case of a bobbin having only the residual thread length, and the signal sequence is formed alternatingly by the likewise reflecting inner side of a first bobbin flange and the reflecting outer side of the second bobbin flange. Even though this signal sequence is called a “a signal sequence with horizontal residual ripples” in A
1
, with respect to
FIG. 3
in that document, it can be assumed in light of the essentially equal degree of reflection of the inner and outer sides of the bobbin flanges that a signal sequence thus formed is basically a continuous signal. Since the infrared light ray reaches the inner side of a bobbin flange either through one of the openings and is reflected by same or falls on the area of the outer side of the bobbin flange located between the openings and is reflected by same during the stoppage of the bobbin, it is obvious that there can be no substantial difference between the signal sequence generated in the case of a bobbin that is filled only with a residual thread length and is rotating and the bobbin that is likewise filled only with a residual thread length but is stopped. It is therefore extremely difficult to distinguish a rotating bobbin from a stopped bobbin based on the signal sequences thus generated in the case of bobbins filled with a residual thread length only.
SUMMARY OF THE INVENTION
The basic object of the present invention is therefore to provide a means for monitoring the three possible operating states of a double thread lockstitch sewing machine, namely, when the degree of filling of the bobbin is still above a residual thread length, or the machine is processing thread of the residual thread length, or when there is a disturbance causing the stoppage of the bobbin, e.g., a thread break, which means can be manufactured at a low cost and is very extensively insensitive to contamination by dust generated during sewing.
According to the invention, a monitor is provided for a bobbin thread on double thread lockstitch s
Butzen Edgar
Manuel Karl
Neurohr Manfred
McGlew and Tuttle , P.C.
Nerbun Peter
Pfaff Industrie Maschinen AG
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