Sewing – Elements – Thread sensing
Patent
1989-11-01
1991-07-02
Nerbun, Peter
Sewing
Elements
Thread sensing
242 37R, D05B 6936
Patent
active
050277308
DESCRIPTION:
BRIEF SUMMARY
The invention relates, in general, to sewing devices and in particular to a new and useful sewing machine having a device associated with the machine shuttle which indicates the presence of the sewing thread.
A thread monitor for the opto-electronic monitoring of the thread of the bobbin is known from the U.S. Pat. No. 4,163,158. The thread monitor has a light source and a light detector, which are disposed radially to the shuttle axis. The light rays pass through an opening into the interior of the shuttle. If the bobbin is filled below a certain level, the light rays are reflected at reflection surfaces at the bobbin hub, then exit from the shuttle and reach the light detector. As soon as the light detector receives these light rays, a warning signal is emitted to announce the end of the thread.
With such thread monitors, the danger exists that light rays are reflected either from thread windings or from at least partially exposed reflection surfaces of the bobbin hub. The light rays reflected at the thread windings act like a false signal at the light detector and distort the signal formed from the reflected light rays.
Another opto-electronic thread monitor is known from the German Offenlegungsschrift 2,451,533. This monitor is used to monitor a single thread, which runs horizontally or vertically. A portion of the light rays incident on the thread is reflected in the direction of the light detector. As soon as a thread no longer contacts the monitoring point, for example, because of a thread breakage, light rays no longer reach the light detector. Thereupon a control circuit associated with the light detector emits a warning signal.
With threads that are not centered at the monitoring point, sagging due to gravity cannot be excluded in case of horizontal guidance, and unintended lateral deflection due to vibrations cannot be excluded in case of vertical guidance. Thus, the light rays coming from the light source can miss the thread, so that no reflected light rays reach the light detector. As a consequence, a warning signal is emitted even though there is no malfunction with respect to the thread. The known thread monitor thus operates relatively unreliably and is therefore unsuitable for indicating the end of the thread or a breakage of the thread in shuttles.
A thread monitor for the electro-mechanical monitoring of a single winding of the thread on the bobbin is known from the German Patent 1,203,584. The thread is conducted in a groove on the outside of the bobbin case along its periphery. It is sensed by a spring-loaded contact flap that is electrically connected to a bobbin case support. When the end of the thread has passed the contact flap, the flap touches the bobbin case, thus establishing the electrical connection between the contact flap and the bobbin case. As soon as a bobbin case-opening lever, which operates in pulse-like fashion and is connected to an electrical power source, strikes against a contact protrusion of the bobbin case, the circuit is closed and the sewing machine is stopped. With a thread monitor of this design, the thread is sensed through the action of frictional forces, so that wear of the thread and of parts of the shuttle, and of the thread monitor, cannot be excluded.
SUMMARY OF THE INVENTION
The invention provides a shuttle for a sewing machine with a thread monitor, which is non-contacting but at the very least wear-free, in such a fashion that the monitor responds only when a malfunction, such as the end of thread or a thread breakage, actually occurs at the thread.
With this arrangement, it is possible to perceive the scattered light rays that have been reflected by a single thread winding. For example, as long as the thread winding covers the support surface, the light detector receives the small portion of the scattered light rays that has been reflected in its direction. These scattered light rays form a relatively weak signal in the light detector. This weak signal can then be amplified in the control circuit to such an extent that it can be used as proof
REFERENCES:
patent: 4558654 (1985-12-01), Schilling
patent: 4569298 (1986-02-01), Lindh et al.
patent: 4805544 (1989-02-01), Dobner et al.
Dobner Reinhold
Mertel Bernhard
Willenbacher Erich
Nerbun Peter
Pfaff Industriemaschinen GmbH
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