in figure 1 A schematic diagram of the principle of a yarn sensor for monitoring the yarn movement in a knitting machine is shown in FIG. 2. It depicts a cross-sectional view perpendicular to the yarn extension line passing through the device. It is assumed that the yarn 1 is moved through a yarn transport direction, which is oriented perpendicular to the drawing plane. This U-shaped structure shown around the yarn 1 position very schematically describes the optical sensor unit, which is constructed in the form of a fork-shaped optoelectronic device pair. The fork-shaped optoelectronic device pair 2 has a light source 3 along one of its U-legs, which is constructed in the form of a single-LED, a photodiode row or a linear radiating other light source and on the other hand along it The other U-leg is provided with a photodetector device 4, which in the illustrated embodiment is composed of a combination of a plurality of single optical receiving diodes arranged along a preferred direction. The optical imaging elements 5, 6 are used for an optimal illumination of the intermediate space enclosed in a U-shape by the fork-shaped optoelectronic device pair 2 and an illumination of the individual receiving diode 41 as optimal as possible.
 The fork-shaped photoelectric device pair 2 made of a mechanically stable frame material such as plastic or metal is arranged relative to the yarn conveying section, that is, relative to the yarn 1 in such a way that the yarn 1 is ideal for yarn feeding and yarn feeding. Under tension, an upper yarn position 1'in the fork-shaped photodetector 2 is occupied. In this position 1'the yarn is detected by the uppermost receiving diode 41, which sends out a corresponding diode signal, which is amplified in an amplifier 7 and sent to a logic unit L, which provides a 100% The yarn tension is used as the measured value FSB.
 If, on the contrary, the yarn tension decreases, the yarn position decreases vertically downward, for example, figure 1 The intermediate position described in is correspondingly detected by an appropriately positioned receiving diode. In order to ensure that a reliable detection can be achieved with the aid of a fork-shaped photoelectric device under the falling yarn tension, for example, a spring bending member 8 that applies a spring force, which acts on the yarn 1 vertically from above, is , The yarn 1 maintains a stable yarn movement inside the fork-shaped photoelectric device pair 2 and therefore occupies a determined vertical position inside the fork-shaped photoelectric device pair 2, which can be reliably detected by means of a correspondingly arranged receiving diode .
 If the yarn tension drops further, so that the yarn 1 occupies a yarn position in the lower boundary region 9, it is suitable to take corresponding measures to stabilize the yarn tension accordingly.
 In the case of a yarn break, all the receiving diodes 41 receive a uniform and uniform light flow from the light source 3, so all the receiving diodes 41 send the same diode signal to the logic unit L, which generates another Display a binary logic signal FB of yarn broken. In this case, the knitting machine should stop as quickly as possible.
 In order to improve the light detection of the light emitted by the light source through the light detector device, the ambient light will also be incident on the light detector device, so the light source is operated in a beat or pulse mode. The tempo of the light source is controlled by the logic unit L in such a way that the light detector device can generate a single relationship between the received light and the light emitted by the at least one light source. In this way, the influence of external light can be eliminated as much as possible.
 in figure 2 A schematic side view of the photodetector device is described in, the photodetector device is in the form of a plurality of receiving diodes arranged in a preferred direction, and these receiving diodes are arranged inside the pair of fork-shaped optoelectronic devices 2. in figure 2 It is assumed that the yarn 1 is guided from left to right along a free yarn transport section 10 which is stabilized by the yarn running loop 11. In order to ensure that a yarn runs as stable as possible even in the case of a decreasing yarn tension, a bending member 13 to which a spring force 12 is applied is provided with sliding elements 14, wherein the sliding elements 14 slide on the yarn 1 Apply a guiding force F directed vertically downwards. Under a normal yarn tension, the yarn position is occupied figure 2 The horizontally extending yarn running position described in the upper part. Under the reduced yarn tension, the yarn in the range of the fork-shaped photoelectric device pair 2-due to the action of the spring force F-is deflected downward in such a way that the yarn runs as straight as possible and There is no substantial oscillation. This type of yarn guide can ensure that the position of the yarn moving downward can be accurately detected by the corresponding receiving diode 41.
 In a particularly advantageous manner, the individual receiving diodes are arranged on top of each other (as shown) along their vertical preferred direction, in order to ensure that the spatially varying yarn extension can be at least one Detected by the receiving diode. Furthermore, instead of a plurality of individual receiving diodes, it is also possible to use a diode array, which can also achieve a much finer resolution of the detection of the yarn position even under reduced yarn tension.
 However, if the receiving diodes arranged side by side in the preferred direction are used, the change in yarn tension-caused by the detection of the yarn extension line by the discrete receiving diodes-is shown by a step-shaped change measurement signal. The measurement signal can be interpolated in the logic unit L and converted into a continuous signal if necessary. However, if there is yarn tension to be adjusted on the basis of the measured value FSB sent by the logic unit L, this stepped signal curve of the measured signal sent by each receiving diode is in principle no problem.
 As already described at the beginning, the presence of a dynamic signal component in the sensor signal of the optical sensor unit is used to prove a good yarn. The dynamic signal component usually originates from the surface roughness of the yarn or can also be caused by an artificially generated yarn oscillation in the case where a yarn with a smooth yarn surface is used. in figure 2 In this example, it is assumed that the yarn relates to a nylon-or Perlon yarn, which has an electrostatic charge, which has been absorbed only by the friction of the yarn on a device component that is not electrically grounded. produce. At least one electrode E is arranged in the area of the optical sensor unit 2, and an alternating electric potential is applied to it, thereby generating an alternating field whose spatially effective distance extends into the area of the free yarn transport section, thereby The yarn 1 acquires an oscillating offset force that is oriented laterally relative to the conveying section and is placed in oscillation, which results in a dynamic sensor signal share which is finally used as an undamaged yarn judgement standard. Electrode E should be regarded as representative of the electrode configuration for each alternative. The electrode configuration can capacitively generate an electric alternating field in the yarn area so that the yarn can be controlled relative to it. The conveying section is offset laterally.
 in image 3 A specific embodiment for adjusting yarn tension and monitoring the occurrence of yarn breakage is schematically described in. As already mentioned in the introduction, each individual yarn feeder of the knitting machine has a yarn storage 15 that determines or influences the yarn tension. It can be regarded as a drum rotating around an axis 16. A plurality of yarns with yarn 1 wound around the circumference. in image 3 The arrow shown along the yarn extension line 1 in the middle indicates the yarn conveying direction. In the conveying direction along the yarn conveying section before and after the yarn storage 15 according to figure 1 The embodiment shown in is provided with a yarn sensor FS1, FS2 respectively. Each individual yarn sensor FS1 and FS2 is as before figure 1 Described in is composed of a fork-shaped photoelectric device pair 2 and a logic unit L. The yarn sensor FS1 arranged in front of the yarn storage 15 in the yarn conveying direction can detect the occurrence of yarn breakage. The yarn sensor FS2 connected behind the yarn storage 15 can detect the yarn tension caused by the yarn storage 15 in addition to detecting yarn breakage. If, for example, a yarn break is detected by one of the two yarn sensors FS1 or FS2, the logic signals of the two yarn sensors reach a regulator 17, which stops the drive motor M of the yarn storage 15 . The drive motor M can be configured either as a motor or as an eddy current coupling K that can be controlled by a changing magnetic field, which can be connected to a toothed belt drive device S of the knitting machine and the cylinder of the yarn storage 15 in between. between.
 If the two yarn sensors FS1 and FS2 do not detect yarn breakage, the drive device M of the yarn storage 15 is adjusted according to the yarn sensor FS2 that detects the yarn tension, and the yarn sensor FS2 is in the yarn conveying direction. It is connected to the back of the yarn storage 15. With this configuration, the operational reliability of known knitting machines, in particular circular knitting machines, can be decisively improved and, in addition, the quality of knitted fabrics can ultimately be improved.
 Reference number table
 1---Yarn, 2-fork photoelectric device pair, 3-light source, 4-photodetector device, 41-receiving diode, 5,6-optical lens, 7-amplifier, 8-spring bending part, sliding Element, 9-Boundary value area, 10-Free yarn delivery section, 11-Yarn guide ring, 12-Spring, 13-Bend, 14-Sliding element, 15-Yarn storage, 16-Drive shaft, 17 -Regulator.