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(11) | EP 1 302 766 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A unit for detecting a marking on a fabric |
| (57) A unit (1) for detecting a marking (M) made on a fabric (T), the unit being set along
a path (P) for feeding of the fabric (T), and having a linear CMOS viewing sensor
(6) for detection of the marking (M), and a lighting device (7) provided with two
LED illuminators, which are set on opposite sides of the feed path (P) and are designed
for illuminating the marking (M) to transmit to the sensor (6) respective light signals
passing through the fabric (T) and reflected by the fabric (T) itself. |
[0002] In the textile industry, knitted fabric is normally produced in the form of a tube and is subsequently fed along a feed path to a cutting station for being opened along a marking directrix, which is usually defined as the so-called "needle waste" and must be detected uniquely by a detecting unit set in the cutting station itself.
[0003] Detecting units of a known type are designed to cooperate with a device for moving the fabric, which displaces the fabric in a direction transverse to the feed path so as to cause the needle waste to collimate continuously with a blade which performs cutting of the fabric itself, and are provided with a linear sensor defined by an array of photodiodes oriented in the direction of the fabric, and with an illuminator of a through type set on the opposite side of the feed path of the fabric with respect to the photodiodes.
[0004] In addition, known detecting units are also provided with an analogue multiplexer for converting the signals from the photodiodes by means of just one 8-bit A-D converter and have a scanning frequency of approximately 11 kHz for a total of one hundred scans of the entire array per second.
[0005] The detecting units of the type described above present a number of drawbacks due, among other things, also to the low number of sensors and to the simplicity of the detection algorithm, which limit the possibility of their use and their detecting capacity. For example, the low number of sensors, from which there derives a very limited resolution, prevents detection of particularly small needle waste or needle waste involving little contrast, and, in addition, in order to obtain a proper contrast it is frequently necessary to stretch the fabric to a greater extent than would be convenient for preventing a degradation of the quality of the fabric itself.
[0006] The positioning of the sensor and of the illuminator on opposite sides with respect to the feed path causes some types of fabric, which are particularly thick or anyway not permeable to light, not to be detected, since the light information is insufficient for it to reach the sensor.
[0007] Finally, in the case where the marking directrix is not indicated by differences of density of the threads in the fabric, but in other ways, such as by folds or lines traced with indelible felt pens or lines of different colour, the difficulty of detection very frequently renders any processing that is not very closely assisted by the operator other than advantageous, so that totally manual processing carried out by the operator is to be preferred.
[0008] The purpose of the present invention is to provide a unit for detecting a marking on a fabric which will be free from the drawbacks described above.
[0009] According to the present invention, a unit is provided for detecting a marking on a fabric, the said unit being set along a feed path of the fabric and comprising a sensor for the detection of said marking and a lighting device, which in turn comprises a first illuminator, set on the opposite side of the feed path with respect to the sensor and designed for illuminating said marking to transmit to the sensor a light signal that passes through the fabric, the unit being characterized in that said sensor is a linear CMOS viewing sensor having a viewing resolution on the fabric of at least 68 µm.
[0010] The invention will now be described with reference to the annexed drawings, which illustrate a non-limiting example of embodiment and in which:
- Figure 1 is a front elevation, with parts removed for clarity of exposition, of a preferred embodiment of the unit of the present invention; and
- Figure 2 illustrates a cross section according to the line Il-II of Figure 1.
[0011] With reference to Figures 1 and 2, number 1 designates as a whole a unit for detecting a marking M made on a knitted fabric T fed, in a substantially continuous way, along a vertical feed path P.
[0012] The unit 1 is set along the path P, and comprises a box-type body 2 having a front wall 3, which is designed to come into substantial contact with the fabric T and is provided with a window 4 enclosed by a glass 5.
[0013] The unit further comprises a sensor 6 for detection of the marking M, the said sensor being supported inside the body 2, and a lighting device 7 designed for illuminating the fabric T to send a light signal S to the sensor 6.
[0014] The sensor 6 is a linear CMOS viewing sensor having a viewing resolution on the fabric T of at least 68 µm, and a viewing area on the fabric T defined by a height, measured parallel to a direction D of feed of the fabric T itself, of 3 mm, and by a width, measured transverse to the direction D of feed, of 70 mm.
[0015] The ratio between the height and width of the sensor 6 and the ratio between the height and width of the viewing area are different from one another, in so far as the sensor 6 has a height of 125 µm and a width of 7.988 mm, whilst the height of the viewing area is 3 mm and the width of the viewing area is 70 mm, and in order not to lose sensitivity and/or resolution in reading, the unit 1 is further equipped with an anamorphic focusing device 8, which is designed to receive the light signal S and comprises two prisms 9 and 10 and a mirror 11, designed to develop a focal length of 25.5 cm in a direction orthogonal to a direction of passage of the light signal S with respect to the fabric T.
[0016] In particular, the mirror 11 is set inside the body 2 in a position directly facing the glass 5 and has a reflecting surface 12 of its own inclined by an angle of 45° with respect to the glass 5. The two prisms 9 and 10 are supported inside the body 2 by a two-axes slide 13, which is designed to enable correct positioning of the prisms 9 and 10 themselves with respect to the sensor 6, which is fixed on a support that enables movements along four axes during assembly to obtain a proper collimation with the optical system.
[0017] The lighting device 7 comprises two illuminators 20 and 21, of which the illuminator 20 is set on the opposite side of the path P of feed with respect to the sensor 6 and is designed to illuminate the marking M so as to transmit to the sensor 6 a light signal S that passes through the fabric T, whilst the illuminator 21 is set on the same side as the sensor 6 with respect to the path P and is designed to illuminate the marking M so as to transmit to the sensor 6 a light signal S reflected by the fabric T. Consequently, the illuminator 20 is set outside the body 2 in a position facing the window 4, whilst the illuminator 21 is set inside the body 2, which is also set in a position facing the window 4.
[0018] Both of the illuminators 20 and 21 are built with solid-state monochromatic emitters, are activatable alternately with respect to one other, and each comprises two rows of LEDs 24 set on opposite sides of the viewing area. In particular, the LEDs 24 of each row define a given angle with respect to the path P so as to enhance the surface roughness of the fabric T.
[0019] The illuminators 20 and 21 are alternately lit up and turned off with respect to one another, and at each lighting-up there is acquired an image of the fabric T detected by the sensor 6. Operating in this manner, it is possible to acquire alternately images of different perspectives of the same portion of fabric T. In addition, the fact of keeping the illuminators 20 and 21 cyclically turned on and turned off enables optimal exploitation of the characteristics of the LEDs 24 in such a way as to double their lighting power.
[0020] Finally, as illustrated schematically in Figures 1 and 2, the unit 1 comprises a digital signal processor (DSP) and a microcontroller 25, which are set in a dedicated housing outside the body 2, and are connected to the sensor 6 by means of shielded and differential electrical lines for detecting the marking M. The microcontroller 25 is a microprocessor containing an on-board memory and peripheral equipment, and its use together with that of the DSP makes possible implementation of a very sophisticated mathematical algorithm to obtain, in this way, a proper detection of many of the types of markings M.
[0021] It is understood that the invention is not limited to the embodiment described and illustrated herein, which is thus to be considered purely as an example of embodiment of the unit for detecting a marking on a fabric, which hence may undergo further modifications as regards embodiments and arrangement of parts, as well as regards details of construction and assembly.
1. A unit (1) for detecting a marking (M) on a fabric (T), said unit being set along
a path (P) of feed of the fabric (T) and comprising a sensor (6) for the detection
of said marking (M) and a lighting device (7), which in turn comprises a first illuminator
(20), set on the opposite side of the feed path (P) with respect to the sensor (6)
and designed for illuminating said marking (M) so as to transmit to the sensor (6)
a light signal (S) that passes through the fabric (T), the unit (1) being characterized in that said sensor (6) is a linear CMOS viewing sensor (6) having a viewing resolution on
the fabric (T) of at least 68 µm.
2. The unit according to Claim 1, characterized in that the viewing sensor (6) has a viewing area on the fabric (T) defined by a height,
measured parallel to a direction of feed of the fabric (T) itself, equal to 3 mm,
and by a width, measured transverse to the direction of said feed, of 70 mm.
3. The unit according to Claim 2, characterized in that the ratio between the height and width of the viewing sensor (6) and the ratio between
the height and width of the viewing area are different from one another, the unit
comprising an anamorphic focusing device (8), which is designed to receive said light
signal (S) and comprises two prisms (9, 10) and a mirror (11) designed to develop
a given focal length in a direction orthogonal to the direction of passage of the
light signal (S) through the fabric (T) .
4. The unit according to Claim 3, characterized in that said focal distance is 25.5 cm.
5. The unit according to any one of the preceding claims, characterized in that the lighting device (7) comprises a second illuminator (21) set on the same side
of the sensor (6) with respect to the path (P) of feed of the fabric (T) and designed
for illuminating said marking (M) so as to transmit to the sensor (6) a light signal
(S) reflected by the fabric (T).
6. The unit according to Claim 5, characterized in that both of said illuminators (20, 21) are built using solid-state monochromatic emitters,
and are activatable alternately with respect to one another.
7. The unit according to Claim 6, characterized in that each illuminator (20, 21) comprises two rows of LEDs (24) set on opposite sides of
the viewing area, said LEDs defining a given angle with respect to the path (P) of
feed of the fabric (T) to enhance the surface roughness of the fabric (T) itself.
8. The unit according to Claim 5, characterized in that it comprises a digital signal processor (DSP), and a microcontroller (25) for detecting
said marking (M).
9. A unit for detecting a marking on a fabric, substantially as described with reference
to the annexed drawings.