Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1993-05-25
1994-12-06
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356429, G01V 904
Patent
active
053713745
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to an optical sensor for a thread storage and feed device, and more particularly, to an optical sensor having a shield element interposed between a receiver and surfaces or objects associated with the thread storage and feed device to prevent the surfaces or objects from reflecting undesirable light to the receiver.
BACKGROUND OF THE INVENTION
As soon as the thread enters the passage area transversely to its longitudinal direction, it will reflect part of the incident light in essentially undefined directions due to its three-dimensional shape and its irregular surface. Part of the light reflected will fall on the receiver, which will then produce a signal representative of the presence of the thread. On the other hand, the sensor can also be constructed such that the receiver will produce a signal representative of the absence of the thread, when no thread is present. Especially in a thread storage and feed device in which a thread supply consisting of non-separated thread windings is produced and advanced approximately transversely to the longitudinal direction of the thread, the sensor will, for example, scan the size of the thread supply so as to be able to control with the aid of the signals produced during such scanning either the supplementation of the thread supply or an interruption of the supplementation of the thread supply (maximum sensor). It is, however, just as well possible to detect by means of the sensor the moment at which the thread supply has reached a predetermined reference position on the storage surface and to derive a signal therefrom (reference sensor). The reliability of the sensor depends on the possibility of producing strong and unequivocal signals on the basis of the presence or absence of the thread, and, in this respect, the reliability has hitherto been impaired by interfering optical influences in or at the passage area. Such interfering influences may by lints, which can not practically be avoided when threads are being processed, or some type of surfaces or objects which, from the incident light reflect light which falls onto the receiver.
In the case of an optical sensor, which is provided in a thread storage and feed device and which is known from EP-A1-03 27 973, the element whose surface is in contact with the thread is a reflector consisting of a reflective strip embedded between light-transmitting glass layers. The reflector is positioned in an axially extending cavity of a finger of the finger or rod cage. The light source is combined with a receiver responding to that part of the light of the light source which is reflected by said reflector and using reflected light variations, which are caused by the thread passing through, for the purpose of signal generation. Scattered light reflected by the thread or by lints or by extraneous elements is, in comparison with the light reflected by the reflector, too weak for generating a signal. However, lints or other extraneous elements in the passage area may cause the same reflected light variation as the thread, and, consequently, they may result in an incorrect signal.
In the case of an opto-electronic sensor provided in a thread storage and feed device and known from WO90/06 504, a sharply defined image of the thread in the passage area is produced by means of depth of field limitation with the aid of an image-forming optics and is then used for signal generation, said forming of an image and said signal generation being carried out irrespectively of whether there is any surface on the passage area side facing away from the light source and, if this is the case, irrespectively of the kind of surface. On the contrary, the scattered light reflected by the thread from the light of the light source is used for producing the sharp image.
In the case of an opto-electronic sensor of a colour selector of a multicolour weaving machine (FR-A-24 47 416), the colour selector enveloping surface, which is arranged behind the thread, is black or provided with a black covering so that no reflected lig
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patent: 4313472 (1982-02-01), Weidmann
patent: 4643230 (1987-02-01), Aemmer et al.
patent: 4772800 (1988-09-01), Kanai et al.
patent: 4857749 (1989-08-01), McCarty
patent: 4990793 (1991-02-01), Bonigk et al.
Allen Stephone B.
Iro AB
Nelms David C.
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