Knitting machine with monitoring device and method for monitoring needles during operation of knitting machine

Abstract

In order to monitor a needle (3) during operation of the knitting machine, a knitting machine is provided with a monitoring device having a camera (4), a light source (5) and a control unit (11) with a camera control. The light source (5) and the camera (4) are arranged relative to each other such that a light beam (6) is emitted by the light source (5) that impinges on the at least one needle (3) and a light beam (7) reflected by the needle (3) is captured by the camera (4). The camera (4) has an area scanning camera element. An image of an image region (9) corresponding to at least one needle (3) or at least a part of the needle (3) is captured, wherein the image data is a measured brightness value of the reflected light beam (7). A frame rate fK, which is the number of images per unit time, and the intensity of the reflected light beam (7) of the light source (5) are selected to be sufficiently high such that, in at least two consecutive images, all needles (3) of an image region (9) comprising at least five needles (3) are imaged at a minimum distance from the image data. The position of each needle (3) on the image is identified from the image data, and a defective needle (3) is identified from the positions of the needles (3).

Description

Technical Field

[0001] The invention relates to a knitting machine with a monitoring device and a method for monitoring needles during operation of the knitting machine according to the generic terms of the independent claims. Background Art

[0002] A method for optical quality control of needles on automatic knitting machines is known from DE 40 14 661 A1. To detect gross defects, an image of the needle area to be monitored is displayed synchronously with the needle frequency on a semiconductor matrix server. The analog brightness signals of the discrete pixels are digitized and compared with reference data.

[0003] In the method for checking a needle with an optical scanning system described in DE 199 24 924 A1, light reflected by the needle from a first optical waveguide reaches a second optical waveguide. An intact, correctly arranged needle generates a basic signal sequence on a receiver. During operation, the signal sequence is recorded and compared with the basic signal sequence.

[0004] US 2022 / 0349097 A1 discloses the use of a camera module to monitor a knitting machine based on the surface of a knitted fabric, wherein the camera module compares images of the same vertical line.

[0005] DE 102 23 754 A1 describes the detection of defects in knitted fabrics by comparing information from an illuminated fabric web, recorded for example by a camera, with stored information.

[0006] A camera having an area scanning camera element for monitoring a moving network is known from DE 10 2015 119 444 B4.

[0007] In many methods for monitoring the needles of knitting machines, reference data are recorded in advance and used to detect defects during operation. Summary of the invention

[0008] The object of the present invention is to develop a knitting machine with a monitoring device and a method for monitoring needles during operation of the knitting machine, wherein direct monitoring of the needles without comparison with reference information is possible.

[0009] This object is solved by the independent claims.

[0010] A knitting machine according to the invention comprises a monitoring device for monitoring needles during operation of the knitting machine. The monitoring device is provided with a camera, a light source and a control unit with camera controls. The light source and the camera are arranged relative to each other such that a light beam impinging on at least one needle is emitted by the light source and a light beam reflected by the needle is captured by the camera.

[0011] The camera has an area scan camera element. The camera controls are implemented to capture an image corresponding to an image area of ​​at least one needle or at least a portion of the needle. The image data is a measured brightness value of the reflected light beam.

[0012] The camera has such a high frame rate and the reflected light beam of the light source has such a high intensity that in at least two consecutive images all needles in the image area from the image data are imaged at a minimum distance.

[0013] The image area includes at least five needles. The control unit is implemented to identify the position of each needle on the image from the image data and to identify defective needles from the positions of the needles.

[0014] The monitoring device enables the generation of at least two consecutive images in which all needles in the image area from the image data are distinguishably imaged. The generation of such images enables the identification and checking of the positions and therefore the distances between all visible needles. No reference information is required for this.

[0015] In one embodiment, the camera is implemented to operate at a speed greater than the maximum possible needle velocity f N (i.e., the number of needles passing the camera per unit time) frame rate f K operate.

[0016] By adapting the frame rate of the camera to the highest possible needle rate of the knitting machine, the monitoring device can be used independently of the operating mode of the knitting machine.

[0017] In one embodiment, the camera controls are implemented to combine pixels of an area scan camera element for reading out image data of an image area.

[0018] This increases the readout speed.

[0019] In one embodiment, the camera controls are implemented as a selection field for selecting selected pixels of an image area for readout of image data.

[0020] This also increases the readout speed.

[0021] In one embodiment, camera controls are implemented to move the selection field to make fine adjustments to the image area.

[0022] As an electronic adjustment, moving the selection field is a much simpler adjustment than a mechanical adjustment (eg by adjusting an adjustment screw). Using a control unit to move the selection field allows automatic adjustment.

[0023] In one embodiment, the camera and light source are arranged such that the image area captures at least five driven pins in the area of ​​the reversal point.

[0024] This allows a lower height of the image region and thus a faster readout and evaluation of the image data.

[0025] In one embodiment, the distance between the camera and the needle is 5 cm to 40 cm, and / or the distance between the light source and the needle is 5 cm to 40 cm.

[0026] Positioning the camera at least 5 cm or more away from the needle facilitates handling of the knitting cylinder and mounting of the camera.

[0027] In one embodiment, the light source is implemented to emit the light beam that impinges on the needle as a converging light beam bundle.

[0028] Due to the converging beam bundle, the intensity of the beam impinging on the area scanning element of the camera is greater for a good needle and lower for a damaged needle due to the rough damaged surface.

[0029] In one embodiment, the control unit is implemented to determine a median value of the distance between the imaged needles based on the image data of the plurality of images, and to determine a floating average value as a standard distance based on the median value of the images, and to compare each individual distance determined between two needles with the standard distance in order to detect defective or missing needles.

[0030] The formation of the median value and the updated standard distance enables fast and reliable detection of defective or missing needles.

[0031] The method according to the invention has corresponding features and advantages.

[0032] Further features and advantages are set out in the description which follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is further explained with reference to the examples schematically shown in the accompanying drawings. The drawings show:

[0034] Figure 1 is a schematic diagram of a circular knitting machine having a monitoring device;

[0035] Figure 2 is a simplified view of a row of needles with an image area marked;

[0036] Figure 3 is a block diagram of the monitoring device;

[0037] Figure 4a , Figure 4b , Figure 4c is a continuous image of image data having an image area of ​​five needles in a rising or falling area of ​​the needle;

[0038] Figure 5 is an image of an image area with seven needles in the area of ​​the reversal point. DETAILED DESCRIPTION

[0039] Figure 1 A circular knitting machine 1 is shown with a knitting cylinder 2 and a stitch forming needle 3. For the sake of clarity, Figure 1 The yarn feed is not shown.

[0040] The circular knitting machine 1 has a monitoring device equipped with a camera 4 and a light source 5. The light source 5 and the camera 4 are arranged together so that a light beam 6 impinging on the needle 3 is emitted from the light source 5 and a light beam 7 reflected by the needle 3 is captured by the camera 4. The angle between the incident light beam 6 and the reflected light beam 7 is about 60°. The camera 4 is located approximately at the height of the needle 3 and the light source 5 is above it. The camera 4 and the light source 5 are attached to a common holder 8 on the circular knitting machine 1.

[0041] The distance between the camera 4 and the needle 3 and / or the distance between the light source and the needle 3 is 5 cm to 40 cm.

[0042] Figure 2 A simplified row of needles 3 is shown, whereby an image region 9 is marked with five needles 3. Also marked is a region 10 below the needle heads 3a within the image region 9, which can be masked using, for example, a digital mask.

[0043] like Figure 3 As shown in the block diagram of , the monitoring device includes a control unit 11 having a camera control unit, and the control unit 11 is connected to the camera 4. The camera control unit is integrated into the control unit 11.

[0044] In an alternative, the camera control unit is arranged within the camera 4 .

[0045] The camera control unit comprises, for example, a frame grabber card. The control unit 11 is equipped with a microprocessor. The camera control unit is implemented to mask out any pixels that may be outside the path traversed by the needle head 3a by using a digital mask. In this example, the pixels in the area 10 are masked out.

[0046] In an alternative, the control unit 11 is implemented as a hardware unit with a camera control unit.

[0047] The power source 12 is connected to the control unit 11 and the light source 5 .

[0048] The control unit 11 comprises a switch 13 for generating a stop signal, which switch is connected to a machine control unit 14. When the switch 13 is switched by the control unit 11, a stop signal is sent to the machine control 14 and the circular knitting machine 1 stops.

[0049] In an alternative, the control unit 11 is connected to the machine control system via a bus system, for example a CAN bus or an Ethernet bus, via which the stop signal is sent.

[0050] The display device 15 is connected to the control unit 11, for example, for displaying the image selected by the control unit 11. Since the image is at the frame rate f of the camera 4 K The display device 15 is not perceptible, so only selected images are displayed, for example, selected images every 1 / 30 second. The display device 15 also displays the distance between the specific needle 3 and the specific position in the knitting cylinder 2 determined by the control unit 11 (for example, the number of needles 3). The specific needle 3 is, for example, the needle 3 determined to be defective or missing. The specific position is, for example, a repair position.

[0051] The camera 4 has an area scan camera element. The camera control unit is implemented to capture an image of the image area 9 with at least five drive-out pins.

[0052] In an alternative, the image region 9 comprises 3 to 20 needles.

[0053] The image data of the image are the brightness values ​​of the light beam 7 reflected at the needle 3, which are measured by each pixel of the area scan camera element.

[0054] Figure 4a , Figure 4b , Figure 4c Shows Figure 2 Three consecutive images of the image region 9 are schematically shown in FIG.

[0055] Camera 4 has a high frame rate f as follows K , and the reflected light beam 7 of the light source 5 has such a high intensity that Figure 4a , Figure 4b , Figure 4c In the three consecutive images of FIG. 1 , all needles 3 from the image region 9 of the image data are imaged at a minimum distance.

[0056] In this example, the camera control is implemented to capture an image of an image area in which there are at least five depictions of the needle heads 3a.

[0057] exist Figure 4a , Figure 4b , Figure 4c In the image of FIG. 1 , the five needles 3 can be identified as depictions of the needle heads 3 a, ie, as bright spots corresponding to the needle heads. The depiction of the needle heads 3 a is from the lower left to the upper right.

[0058] A minimum distance between traces, such as the right side of a bright spot and the right side of a subsequent bright spot, is given if the spacing between traces is at least three times the width of the trace. The minimum distance ensures sufficient distance between traces to enable identification of missing or damaged needles.

[0059] For example, the image area 9 comprises 256 pixels in a row and 200 pixels in a column. The spacing between the depictions is about 50 pixels. The extent of the depiction is about 10 pixels, and the distance between the edges of the depiction is about 40 pixels. The spacing between the depictions is about five times the width of the depiction. The distance between the depictions corresponds to the distance between the needles 3.

[0060] The minimum distance is 20 to 50 pixels, for example, where the width of the depiction is 5 to 15 pixels.

[0061] Different depictions of the needle heads 3a of five needles 3 are shown in three images ( Figure 4a , Figure 4b , Figure 4c ), the depiction moves to the lower left.

[0062] The light source 5 has an optical system, whereby a light spot is generated by the optical system, which substantially illuminates only the needle 3 of the image region 9. In this example, the light spot substantially illuminates the needle head 3a of the needle 3. The light spot is, for example, circular and has, for example, a diameter of 5 mm.

[0063] Alternatively, the light source 5 has an optical system that generates an elliptical or rectangular light spot.

[0064] The light source 5 is a spotlight, in particular a LED spotlight having an output of at least 3 Watts.

[0065] In an alternative, the light source 5 is provided as a LED spotlight having an output of 12 Watts.

[0066] In an alternative, the light source 5 is embodied as a stroboscopic light source.

[0067] The light source 5 is implemented by its optical device to emit a light beam 6, which hits the needle 3 as a converging light beam. The converging light beam that hits the needle 3 is reflected more strongly at the convex needle head 3a than the parallel light beam. In addition, the light beam 6 of the converging light beam is more strongly scattered at the rough broken surface of the damaged needle 3.

[0068] In an alternative, the camera 4 is equipped with a telecentric lens.

[0069] Frame rate K is the number of images captured by the camera 4 per unit time.

[0070] The camera control is implemented so that the needle speed f of the circular knitting machine 1 is greater than N(i.e., the number of needles 3 passing the camera 4 per unit time) K Operate the camera 4.

[0071] If the speed of the circular knitting machine 1 is 1000 stitches per second, that is, the needle rate f N If the frame rate is 1 kHz, a slightly higher frame rate f is used. K , for example 1.1 kHz, or for example 1.5 kHz, or for example 2 kHz.

[0072] The camera control is implemented to set the exposure time of the camera 4 (i.e. the time during which the area scanning element of the camera 4 measures the intensity of the incident light as a brightness value) to 2% to 15% of the frame interval. In this example, the exposure time is set to 3% to 5% of the frame interval. At a frame rate of 2 kHz, the frame interval has a value of 0.5 ms.

[0073] The camera control is preferably implemented at a speed greater than the maximum possible needle speed f of the circular knitting machine. N The frame rate f K Operate the camera 4.

[0074] In an alternative, the speed of the circular knitting machine 1 is, for example, 6000 stitches per second, and the needle rate f N is 6 kHz. Use a frame rate of, for example, 7 kHz.

[0075] The area scan camera element of Camera 4 has approximately 2500 x 2000 pixels.

[0076] In order to read out the image data of the image area 9, i.e. the brightness values, the camera control unit is implemented to combine the pixels of the area scanning camera element. This process is called binning. 4 x 4 pixels are combined respectively, so that the pixels to be read out are reduced to 600 x 500.

[0077] The camera controls are implemented to select a selection field of selected pixels for the image area 9. The selection field is called the region of interest (ROI).

[0078] For example, the selection field has a size of 256 x 30 to 200 pixels. The camera control is implemented for moving the image area 9 for fine adjustment of the image area 9, i.e. for adjusting the image area 9 precisely to the needles 3. As a result, after the camera 4 and the light source 5 are installed, the image area 9 can be adjusted precisely to the five desired needles 3 of the knitting cylinder 2.

[0079] In an alternative, the area scan camera element of camera 4 is provided with 1300 x 1100 pixels, for example.

[0080] In another alternative, the area scan camera element has 256 x 200 pixels.

[0081] The control unit 11 is implemented to recognize the position of each needle 3 on the image from the image data (ie, the brightness value of the pixel), and recognize the defective needle 3 from the position of the needle 3 .

[0082] The control unit 11 is implemented to determine a median value of the distance between the imaged needles 3 based on the image data of multiple images, and determine a floating average value as a standard distance based on the median value of the images, and compare each individual distance determined between two needles 3 with the standard distance to detect defective or missing needles 3.

[0083] During operation of the circular knitting machine 1, the light source 5 and the camera 4 are arranged relative to each other for monitoring the needles 3 by the monitoring device, so that a light beam 6 is emitted by the light source 5, which hits at least five needles 3, and a light beam 7 reflected by the needles 3 is captured by the camera 4 using an area scanning element. An image of an image area 9 is captured by the camera control, whereby the image area 9 corresponds to at least five needles 3. The image data are measured brightness values ​​of the light beams 7 reflected by the five needles 3.

[0084] In this example, the image data are brightness values ​​of the light beams 7 reflected at the five needle heads 3 a.

[0085] The images are taken by the camera 4 at a high frame rate f K to be recorded, and with such high intensities of the light beam 6 emitted by the light source 5 and the light beam 7 reflected by the needle heads 3a of the needles 3 that in at least two consecutive images from the image data the needle heads 3a of all needles 3 depicting the image area 9 have a minimum distance.

[0086] The light beam 6 impinging on the needle 3 (particularly the needle head 3a) is emitted by the light source 5 as a convergent light beam bundle.

[0087] The camera control is set at a speed greater than the maximum possible needle speed f of the circular knitting machine 1. N (Pin 3 at this pin rate f N The frame rate f of camera 4) K Operate the camera 4. At the maximum needle rate f N When the frame rate is 1.5 kHz, the frame rate f K For example, 2 kHz; at the maximum needle rate f N When the frame rate is 6 kHz, the frame rate f K For example, 7 kHz.

[0088] The camera control combines pixels of the area scan camera element and / or selects a selected field of selected pixels of the image area 9 to read out the image data brightness of the image area 9. If necessary, the selected field is moved by the camera control to fine-tune the image area.

[0089] The control unit 11 recognizes the position of each needle 3 from the image data, and recognizes a defective needle 3 from the positions of the needles 3 .

[0090] The control unit 11 determines the median of the distance between the imaged needles 3 based on the image data of the plurality of images, determines a floating average as a standard distance based on the median of the images, and compares each individual distance determined between two needles 3 with the standard distance to detect defective or missing needles 3.

[0091] The position of the needle 3 in the image is determined by the control unit 11 in the following way: the analog brightness values ​​of the pixels are converted into values ​​from 0 to 255 by the camera 4, i.e. digitized. A minimum brightness value is determined, for example a value of 50, which indicates the needle 3 or the needle head 3a. For evaluation, the value 0 is determined column by column if the highest value measured in the column is below 50, or the value 1 is determined if the highest value measured in the column is between 50 and 255. The position of the first needle 3 in the image is determined by the first determined value 1, for example, moving from left to right in the image. For example, if the image extends over more than 10 pixels, the next 9 columns also have the value 1. Then, between the images, the value of the column is 0 until the next column with the value 1, at which the position of the second needle 3 is determined.

[0092] The distance between the first determined values ​​1 of the column is evaluated by the control unit 11 as the distance between the pins 3. The control unit 11 determines a median value for the distances determined between the pins 3 shown in the images from the image data of the plurality of images, and determines a floating mean value as a standard distance from the median value of the images. For example, the last 50 images are considered. Alternatively, the last 20 to 100 images are considered.

[0093] In order to detect defective or missing needles 3 , the control unit 11 compares each individual distance determined between two needles 3 with a standard distance.

[0094] If the distance exceeds a threshold value, a defective or missing needle 3 is detected.

[0095] The defective needle 3 is, for example, a bent needle 3. The missing needle 3 is, for example, a needle 3 in which the needle head 3a is broken.

[0096] The first threshold value of the distance is 1.2 times the standard distance. If the first threshold value is exceeded, a defective needle 3 is detected.

[0097] The second threshold of the distance is 1.5 times the standard distance. If the second threshold is exceeded, the missing needle 3 is detected.

[0098] The position of the needles 3 relative to the knitting cylinder 2 is determined, for example, during installation by the control unit 11 relative to a specific position in the knitting cylinder 2 (for example, relative to a specific lock S of the knitting cylinder 2), or relative to a repair position as the number of needles 3. When the circular knitting machine 1 is operating, the needles 3 shown in the figure are counted down from the maximum number of needles 3 in the knitting cylinder 2 in each revolution. When a defective needle 3 is detected, the current distance to, for example, the repair point is also displayed on the display device 15.

[0099] In an alternative embodiment, the position of the needles 3 relative to the knitting cylinder 2 is determined by the control unit 11 by counting the needles 3 by means of a position encoder 16 relative to the knitting cylinder 2 .

[0100] Figure 5 An image of a second example is shown which corresponds to the first example except for the following features: The camera 4 and the light source 5 are arranged such that the image area 9 comprises seven drive-out pins 3 in the area of ​​the reversal points.

[0101] A damaged needle can be seen at the fifth position from the left.

[0102] In this example, for example, the minimum brightness value displayed by the needle 3 or needle head 3a is determined to be a value of 220. The brightest pixel of the damaged needle is below this minimum brightness value. The damaged needle is ignored when the control unit 11 determines the position and distance. The distance between adjacent needles 3 is 1.5 times the standard distance determined from the median value.

[0103] The control unit 11 detects a defective needle 3 and sends a stop signal to the machine control 14 via the switch 13 .

[0104] Reference Symbols List 1. Circular knitting machine 2. Knitting tube 3. Needle 3a. Needle head 4. Camera 5. Light source 6. Beam 7. Beam 8. Retainer 9. Image Area 10. Scope 11. Control unit 12. Power supply 13. Switch 14. Machine Controls 15. Display device 16. Position encoder S lock.

Claims

1. A knitting machine having a monitoring device for monitoring needles (3) during operation of the knitting machine, wherein: The monitoring device is provided with: a camera (4) having a light source (5) and a control unit (11) having camera controls, wherein the light source (5) and the camera (4) are arranged relative to each other such that a light beam (6) is emitted by the light source (5) and impinges on at least one needle (3), and a light beam (7) reflected by the needle (3) is captured by the camera (4), Wherein, the camera (4) comprises an area scan camera element, and wherein the camera control is implemented for capturing an image of an image area (9) corresponding to at least one needle (3) or to at least a portion of the needle (3), wherein the image data are measured brightness values ​​of the reflected light beam (7), Features: The camera (4) has a high frame rate f K , i.e. the number of images per unit time, and the reflected light beam (7) of the light source (5) has such a high intensity that in at least two consecutive images, all needles (3) from the image area (9) of the image data are imaged at a minimum distance, wherein the image area (9) includes at least five needles (3), and the control unit (11) is implemented to identify the position of each needle (3) on the image from the image data and to identify defective needles (3) from the positions of the needles (3).

2. The knitting machine with a monitoring device according to claim 1, characterized in that: The camera control is implemented to be greater than the maximum possible needle velocity f N The frame rate f K To operate the camera (4), the needle rate f N is the number of needles (3) passing the camera (4) per unit time.

3. The knitting machine with a monitoring device according to claim 1 or 2, characterized in that: The camera control is implemented to combine pixels of the area scan camera element to read out image data of the image area (9).

4. The knitting machine according to any one of claims 1 to 3, characterized in that The camera control is implemented as a selection field for selecting selected pixels of the image area (9) for reading out the image data.

5. The knitting machine according to claim 4, characterized in that The camera control is implemented for shifting a selection field to fine-tune the image area (9).

6. The knitting machine with a monitoring device according to any one of claims 1 to 5, characterized in that: The camera (4) and the light source (5) are arranged such that the image area (9) captures at least five driven-out needles (3) in the region of the reversal point.

7. A knitting machine with a monitoring device according to any one of claims 1 to 6, characterized in that: The distance between the camera (4) and the needle (3) is 5 cm to 40 cm, and / or the distance between the light source (5) and the needle (3) is 5 cm to 40 cm.

8. The knitting machine with a monitoring device according to any one of claims 1 to 7, characterized in that: The light source (5) is embodied to emit a light beam (6) as a converging light beam bundle which impinges on the needle (3).

9. The knitting machine with a monitoring device according to any one of claims 1 to 8, characterized in that: The control unit (11) is implemented to determine a median value of the distance between the imaged needles (3) based on the image data of a plurality of images, and to determine a floating average value as a standard distance based on the median value of the images, and to compare each individual distance determined between two needles (3) with the standard distance in order to detect defective or missing needles (3).

10. A method for monitoring needles (3) during operation of a knitting machine having a monitoring device, wherein: The monitoring device is provided with: a camera (4) having a light source (5) and a control unit (11) having camera controls, wherein the light source (5) and the camera (4) are arranged relative to each other such that a light beam (6) is emitted by the light source (5) and impinges on at least one needle (3), and a light beam (7) reflected by the needle (3) is captured by the camera (4), wherein the camera (4) comprises an area scan camera element and wherein an image of an image area (9) is captured by the camera control, wherein the image area (9) corresponds to at least one needle (3) or to at least a portion of a needle (3), The image data is a measured brightness value of the light beam (7) reflected at the at least one needle (3), characterized in that: The image is captured by the camera (4) at a high frame rate f K The image is recorded with such high intensity of the light beam (6) emitted by the light source (5) and the light beam (7) reflected by the needle (3) that in at least two consecutive images all needles (3) from the image area (9) of the image data are imaged at a minimum distance, wherein the image area (9) includes at least five needles (3), and the control unit (11) identifies the position of each needle (3) from the image data and identifies defective needles (3) from the positions of the needles (3).

11. Method for monitoring needles (3) during operation of a knitting machine according to claim 10, characterized in that The camera (4) is controlled by the camera controller to generate a frame rate f K operation, where the frame rate f K is greater than the maximum possible speed f at which the needle (3) passes the camera (4) N .

12. Method for monitoring needles (3) during operation of a knitting machine according to claim 10 or 11, characterized in that The pixels of the area scan camera element are combined by the camera control to read out image data of the image area (9).

13. The method according to any one of claims 10 to 12, characterized in that: A selected field of selected pixels of the image area (9) is selected by the camera control for reading out the image data.

14. The method according to claim 13, characterized in that The selection field is shifted by the camera control to fine-tune the image area (9).

15. Method for monitoring needles (3) during operation of a knitting machine according to any one of claims 10 to 14, characterized in that The camera (4) and the light source (5) are arranged so that at least five driven needles (3) are captured in the image area (9) near the reversal point.

16. Method for monitoring needles (3) during operation of a knitting machine according to any one of claims 10 to 15, characterized in that The distance between the camera (4) and the needle segment is 5 cm to 40 cm, and / or the distance between the light source (5) and the needle segment is 5 cm to 40 cm.

17. Method for monitoring needles (3) during operation of a knitting machine according to any one of claims 10 to 16, characterized in that The light beam (6) impinging on the needle (3) is emitted by the light source (5) as a converging light beam bundle.

18. Method for monitoring needles (3) during operation of a knitting machine according to any one of claims 10 to 17, characterized in that The control unit (11) determines a median value of the distance between the imaged needles (3) from the image data of the plurality of images, determines a floating average value as a standard distance from the median value of the images, and compares each individual distance determined between two needles (3) with the standard distance to detect defective or missing needles (3).

Images