A yarn sensor for textile spinning and bobbin-winding machines for optically scanning a longitudinally traveling yarn ( 3 ) within a measurement gap ( 19 ), particularly for detecting extraneous fibers, includes a light source ( 20 ), a first receiver ( 23 ) for directly transmitted light, two further receivers ( 21, 22 ) for light reflected from the yarn ( 3 ), and light transmitting elements ( 24, 25, 26, 27 ) between the light source ( 20 ), measurement gap ( 19 ) and receivers ( 21, 22, 23 ). In the absence of the yarn ( 3 ), the receivers ( 21, 22 ) detect projected images of the opposite wall ( 62 ) of the measurement gap ( 19 ), located essentially outside both sides of the area of the wall ( 62 ) of the measurement gap ( 19 ) illuminated by the direct radiation of the light-emitting diode ( 20 ). As a result, parasitic signals are suppressed, improving the detection of extraneous fibers.
1. A yarn sensor for optically scanning a yarn traveling in its lengthwise direction through a measurement gap, comprising:
a light source for projecting a beam of light across the measurement gap,
a first receiver for directly transmitted light,
a second receiver for light reflected from the yarn,
a third receiver for light reflected from the yarn, and
elements for transmitting the light between the light source, measurement gap and receivers,
the light transmitting elements comprising:
a first light-transmitting element disposed between the light source and the measurement gap and including a diaphragm and a lens, downstream of the light source in the direction of light projection, and arranged such that the diaphragm is projected at least approximately into infinity, and
second and third light-transmitting elements respectively disposed between the measurement gap and the second and third reflected light receivers,
each of the second and third light-transmitting elements comprising a lens disposed upstream in the projected direction of the light reflected from the yarn such that, in the absence of the yarn, projected images on an opposing surface of the measurement gap are detectable by the second and third receivers essentially outside both opposite sides of a projected image of the light source across the measurement gap.
2. The yarn sensor of claim 1 , wherein the light source is a light-emitting diode having an emission characteristic of a Lambert emitter.
3. The yarn sensor of claim 2 , characterized in that the light-emitting diode is a white light LED.
4. The yarn sensor of claim 1 , wherein a diffusor is disposed between the light source and the diaphragm upstream of the diaphragm.
5. The yarn sensor of claim 4 , characterized in that the diffusor is a film for generating divergent beams of light from beam of light of the light source.
6. The yarn sensor of claim 1 , wherein the lens of the first light transmitting element comprises a light entrance side arranged to homogeneously distribute the luminous intensity the light beam from the light source in the direction of the optical axis of the lens and comprises an exit side arranged to project the light beam arriving from the entrance side essentially parallel to the optical axis of the lens.
7. The yarn sensor of claim 1 , wherein the light transmitting elements are separated from the measurement gap by windows.
8. The yarn sensor of claim 1 , wherein a second diaphragm with a rectangular aperture is disposed between the lens of the first light transmitting element and the yarn.
9. The yarn sensor of claim 1 , wherein each of the second and third light transmitting elements comprises a diaphragm disposed between the yarn and the lens in path of the light reflected by the yarn.
10. The yarn sensor of claim 9 , wherein the diaphragm of each of the second and third light transmitting elements is embodied by a glass plate.
11. The yarn sensor of claim 1 , wherein a signal processing device is arranged to detect and evaluate signal interferences.
12. A yarn sensor for optically scanning a yarn traveling in its lengthwise direction through a measurement gap, comprising:
a light source for projecting a beam of light across the measurement gap, wherein the light source is a light-emitting diode having an emission characteristic of a Lambert emitter,
a first receiver for directly transmitted light,
a second receiver for light reflected from the yarn,
a third receiver for light reflected from the yarn, and
elements for transmitting the light between the light source, measurement gap and receivers,
the light transmitting elements comprising:
a first light-transmitting element disposed between the light source and the measurement gap and including a diaphragm and a lens, downstream of the light source in the direction of light projection, and arranged such that the diaphragm is projected at least approximately into infinity, and
second and third light-transmitting elements respectively disposed between the measurement gap and the second and third reflected light receivers,
each of the second and third light-transmitting elements comprising a lens disposed upstream in the projected direction of the light reflected from the yarn such that, in the absence of the yarn, projected images on an opposing surface of the measurement gap are detectable by the second and third receivers essentially outside both opposite sides of a projected image of the light source across the measurement gap.
13. The yarn sensor of claim 12 , characterized in that the light-emitting diode is a white light LED.