Method and arrangement for optical control of the needles of knitting machines

Arrangement for optical quality control of needles of a knitting machine which in the operation of the knitting machine are successively and individually moved from a rest position to a stitch forming position, each needle having at least one critical portion in which faults may occur, said arrangement comprising an image sensor camera having an optical system and at least one image sensor, said image sensor camera being arranged on said knitting machine in such a manner that said optical system images the particular needles moving into the stitch forming position onto each image sensor, said arrangement further comprising a trigger device which triggers the acquisition of a test image of said particular needle when said needle reaches a predetermined position identified for all needles to be monitored, an analog to digital converter connected to the output of each image sensor for converting the analog image signals delivered by each image sensor to digital pixel signals, selecting means connected to the output of said analog to digital converter and triggered by said trigger device to select from said digital pixel signals those belong to predetermined test image zones which contain the images of said critical needle portions, and a signal processing circuit connected to the output of said selecting means to process the selected digital pixel signals to obtain information on the state of quality of said particular needle;

• wherein the image sensor camera includes a beam divider which is arranged in the beam path of the optical system and which on the one hand for continuous detection of major faults such as breakages, cracks and bends of the needles images the image of the needle portion to be monitored acquired by the optical system on a coarsely resolving image sensor with high image readout frequency and on the other hand directs said image to an exit at which a highly resolving image sensor for occasional determination of the wear data and gradually developing minor faults, such as fine cracks, may be disposed.

Arrangement for optical quality control of needles of a knitting machine which in the operation of the knitting mache are successively and individually moved from a rest position to a stitch forming position, each needle having at least one critical portion in which faults may occur, said arrangement comprising an image sensor camera having an optical system and at least one image sensor, and a coarsely resolving image sensor with high image readout frequency, said image sensor camera being arranged on said knitting machine in such a manner that said optical system images the particular needles moving into the stitch forming position onto each image sensor, said arrangement further comprising a trigger device which triggers the acquisition of a test image of said particular needle when said needle reaches a predetermined position identical for all needles to be monitored, an analog to digital converter connected to the output of each image sensor for converting the analog image signals delivered by each image sensor to digital pixel signals, selecting means connected to the output of said analog to digital converter and triggered by said trigger device to select from said digital pixel signals those belonging to predetermined test image zones which contain the images of said critical needle portions, and a signal processing circuit connected to the output of said selecting means to process the selected digital pixel signals to obtain information on the state of quality of said particular needle, said signal processing circuit comprising a plurality of reference memories in which at least one of reference images of the needle portion to be monitored, reference images of the test zones for different oscillation states and deflections of the needles are stored, and a processing unit which receives the digital pixel signals of the test image coming from the coarsely resolving image sensor and the digital pixel signals of the reference images read synchronously therewith from at least one of the reference memories and by comparison of the digital pixel signals calculates a similarity degree from at least one of the test image and for each test zone, and the processing unit is followed by a threshold comparison circuit which compares the similarity degrees with predetermined tolerance thresholds and for each similarity degree which does not reach the associated tolerance threshold furnishes an alarm signal;

• wherein reference memories are read out simultaneously with the digital pixel signals furnished by the analog to digital converter, the processing unit compares the digital pixel signals furnished by the reference memories in parallel with the digital pixel signals furnished by the analog to digital converter and on the basis of each comparison computes the similarity degree, and the processing unit is further followed by a maximum detector which o the simultaneously computed similarity degrees transfers to the threshold comparison circuit only the similarity degree exhibiting the greatest similarity.

A method for optical quality control of needles of a knitting machine which in the operation of the knitting machine are successively and individually moved from a rest position to a stitch forming position, each needle having at least one critical portion in which faults may occur, said method comprising the steps of acquiring a test image of each needle by means of an image sensor camera when said particular needle is moved away from its rest position, converting the analog image signals furnished by said image sensor camera to digital pixel signals, defining within the test image represented by said digital pixel signals test image zones which contain the images of said critical needle portions, processing the digital pixel signals belonging to said test image zones for recovering information on the state of quality of said particular needle, continuously detecting for major faults, such as breakages, coarse cracks and bends of the needle;

• wherein the test images of the needles are acquired during the normal operation of the knitting machine with a coarse image resolution at an image repetition frequency equal to at least one of the number of needles moved away from their test position per unit of time and an integer divisor of said number, the digital pixel signals of said test image zones are compared at the rhythm at which they are supplied by conversion of the analog image signals with corresponding digital pixel signals of at least one stored reference image the digital pixel signals of said test image zones are compared simultaneously with the pixel signals of a plurality of stored reference images which correspond to at least one of different oscillation and deflection states of the needles, a quantitative similarity degree is formed on the basis of said comparison, and an alarm signal is generated when said similarity degree does not reach a predetermined tolerance threshold;
• and wherein only the similarity degree indicating the greatest similarity is subjected to the comparison with the predetermined tolerance threshold.