Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-07-08
2001-06-05
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559120, C250S221000
Reexamination Certificate
active
06242755
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and a device for contactless measuring of a strand-like textile material of indeterminate extended length, and more particularly to such a method and device basically operative by irradiating the textile material within a measuring range of at least one ray source, imaging the textile material on a sensor range of a receiving device comprising sensor cells, and converting the signals produced by the individual sensor cells into measured values for the dimensions of the textile material.
In the case of strand-like material such as, e.g., yarns, etc., properties must be continuously measured or monitored in a series of production or processing steps. In particular, properties such as the diameter of the particular material to be measured and its variations require measurements with a high degree of precision.
In order to determine the diameter, Swiss Patent CH 643,060 teaches illuminating a strand-like body by a light source and receiving the illumination state thereby produced by means of an image sensor wherein its photosensors are individually scanned and the local illumination state determined by each photosensor is examined to determine whether it reaches or exceeds a given threshold value. The signals of the photosensors must reach or exceed this threshold value if they are to be considered as a contribution to the total measured value and transformed in an evaluation device into measured values for the diameter of the body. If the signal of a photosensor reaches or exceeds the threshold value the photosensor is evaluated as illuminated. If the signal does not reach the threshold value the photosensor is evaluated as not illuminated. The reference contemplates possible use in yarn cleaners.
A yarn Nm 40 has a diameter of approximately 250 &mgr;m. Suitable and customary image sensors for determining the diameter of such a yarn have a resolution of 10 to 30 &mgr;m. The image resolver described in Swiss Patent CH 643,060 is, e.g., a CCD line sensor which contains 500 photoreceivers or sensor cells in a width of 7.5 mm and thus has a resolution of 15 &mgr;m resulting from the interval and the width of the photoreceiver. Thus, an error of ±6% can occur, conditioned by the method described in it, when determining the diameter, and in other image sensors cited above up to a range of ±10%. However, a measured value with an error of less than 1% is required for yarn cleaning.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a method by which the precision of determining the dimensions of the material to be measured is increased and deviations of the determined value from the actual value which occur in the above-described threshold-value method are reduced. It is a further object of the invention to provide a device for carrying out the method.
The invention solves this problem by providing a method and a device for contactless measuring of a strand-like textile material of indeterminate extended length, basically operative for irradiating the textile material within a measuring range of at least one ray source, imaging the textile material on a sensor range of a receiving device comprising sensor cells, and converting the signals produced by the individual sensor cells into measured values for the dimensions of the textile material. According to the present invention, the signals of the sensor cells covered only partially by the image of the textile material (referred to herein as edge pixels) are converted into measured values in a pro rata manner proportional to the amount of the partial covering to be taken into account in the overall measuring of the textile material.
The magnitude of the possible error and the deviation of the determined value of the textile material from its actual value is decisively reduced in a simple yet effective manner by the separate evaluation and proportional accounting for the signals of the edge pixels, i.e., the partially covered sensor cells. In particular, it is not necessary to create or even to develop special designs for sensors but rather the customary and thus economical series of known sensors can be used.
According to the principle of the invention, an absolute measurement of the yarn thickness is not performed or intended. Instead a calibration procedure is initially performed by means of establishing a standard gauge of measurement of the sensor signals against a known diameter. All further measurements of sensor signals thereafter during actual operation are made in relation to this standard gauge. Advantageously, therefore, even a blurry representation of the yarn edges does not lead to a distortion of the measured result because any such blurriness, i.e. the representation of a yarn edge as an area, even though narrow, will be present during calibration, if at all, e.g., because of the use of the optical devices, distance of the yarn from the CCD sensor, etc. It is also advantageous that, in the preferred embodiment the two opposite yarn edges result in partial coverage of only two corresponding edge pixels (i.e. sensor cells) which also contribute to the accuracy of the measurement performed under the present invention.
It is especially advantageous and simple to detect the radiation strength as a measure of the pro rata degree of coverage of the sensors. However, the measuring of the frequency of signals is also possible, for example.
It is preferable to use a light source as an economical radiation source. Further possibilities are constituted by an operation like a stroboscope or with infrared illumination with suitable sensors.
A parallel ray beam is preferably generated by the ray source since in this manner a substantially sharp delimitation is obtained between light and shadow which improves an image of the edge zones of the material to be measured. An even sharper formation of the contours is achieved with laser beams. In addition, laser beams offer advantages during optical scanning by virtue of their monochromatic light in contrast to the color mixture of a normal incandescent lamp.
In order to detect the dimensions of non-circular material to be measured an arrangement in which the material to be measured is irradiated and imaged from different directions is especially suitable.
The determination of a proportional component out of the signals of the edge pixels in combination with the high, reproducible measuring precision of line sensors such as is offered, e.g., by a CCD line sensor, is advantageous in the determination of dimensions.
It is also advantageous if an analog image of the material to be measured differing from the actual magnitude is projected onto the sensor range of the receiving device. An enlarged image covers a greater number of sensor cells or pixels and results in a higher resolution without altering the sensor cells of the receiving device. This significantly increases the measuring precision of the method without using, for example, an expensive line sensor whose sensor cells exhibit a correspondingly reduced width instead of using the economical series sensor cells. Textile material to be measured whose diameter or cross section is greater than the width of the sensor range of the line sensor used can also be detected with a reduced analog image of the material to be measured on the sensor range.
An improved proportionality factor for the measure of the covering of the edge pixels is created by the determination of differential values from the measured absolute values of the radiation strength received even taking into account disturbing influences such as stray or scattered light or foreign extraneous radiation.
The device for carrying out the method of the invention combines in an advantageous manner an electronic computational device which takes into account in the evaluation the extent of the covering of the edge pixels in a proportional manner with a device for the retransmission or further processing of the measured result and, in a further advantageous development, wi
Henze Herbert
Rienas Gerhard
Kennedy Covington Lodbell & Hickman, LLP
Le Que T.
W. Schlafhorst AG & Co.
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