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Textile Systems: Development of a Faulty Needle Sensor for Knitting Machines

Client

Universal Textile Machine Corporation, Lawrence, MA.

Problem

Knitting needles often break or develop erratic defects causing runs, holes, or total ruptures in the fabric. Since those are very fast machines, the losses can be considerable. Some machines have as many as 2,000 needles and run at over 30 RPM. The sensor must be able to check as many as four possible defects while the needles are passing by a full speed and vibrating about the X and Y axes at a wide range of frequencies. To be effective, the sensor must be able to work at less than 500 microseconds reliably.

Solution

The picture below shows the development sequence. The first working prototype was the one at the top left, and the final commercial unit is the one at the bottom right. All of them worked, but some were too delicate or not reliable. The last four at the bottom were optimizations. The principle of operation patented consisted on the finding that a single parameter can detect all possible defects, and that is the differential distance between the front of the hook and the front of the stem. Two sensor elements disposed to sense simultaneously each part of the needle respond to the differential measured and, if incorrect, send a signal to an electronic processor which stops the machine. Sensor force against the needles stabiliizes them against lateral vibration. Needle defects are shown in the picture. The top left needle is a good one. The bottom left has a jammed latch. The center one has a broken tang. The top right has a broken hook. The bottom one has a sticky latch causing the yarn to accumulate.

Picture of the Faulty Needle Sensor for Knitting Machines