Method and device for detecting tool breakage

Abstract

Method for detecting a breakage of a tool (1) in the form of a die used in cold joining technology, comprising the following steps: a. Division of the visible side of the tool (1) into at least one tool segment to be examined (S1,..., Sn), which represents an area around at least one tool edge (2); b. Illuminating the visible side of the tool (1) with an illumination beam; c. Detecting a light-dark contrast pattern for the at least one tool segment (S1, ..., Sn) and determining an evaluation data set (HDmess) corresponding to the light-dark contrast pattern from it; d. Determining a match or deviation from the comparison of the evaluation data set (HDmess) of the light-dark contrast pattern detected for the at least one tool segment (S1, ..., Sn) with a reference data set (HD) of a corresponding break-free tool segment (S1, ..., Sn), wherein the illumination is done as darkfield illumination and The light-dark contrast pattern is detected by capturing radiation scattered by the tool within a predefined wavelength range.

Description

[0001] The invention relates to a method and a device for detecting a break in a tool. The invention particularly relates to a method and a device for detecting a break in a tool used in cold joining technology, in particular a die break and / or punch break of, for example, tools for semi-hollow punch riveting, solid punch riveting, clinching, and the like.

[0002] In machine tools, a tool occasionally breaks while a workpiece is being machined. If undetected, such a tool breakage would lead to defective parts, which must be avoided. Therefore, tools must be inspected at appropriate intervals to detect any breakage. If a breakage is detected in a tool, the tool must be replaced with an undamaged or unbroken one.

[0003] For punching and clinching machine tools, for example, it is common practice to replace the punch and die after a specified service life has been reached, regardless of whether a tool has actually broken. The specified service life is often an empirical value, so tool breakages repeatedly occur before the service life is reached.

[0004] Furthermore, a method is known from DE 10 2015 201 210 A1 in which the visible side of the tool is illuminated with incident light to detect a tool break. The light is reflected off the tool surface and creates a light-dark contrast pattern. The tool surface appears as a bright area, while the tool edges are displayed in dark.

[0005] The contrast pattern is captured segment by segment using imaging technology. By evaluating the light-dark contrast pattern, either an edge length or a ratio of light to dark areas is determined for each tool segment. By comparing it with corresponding reference values ​​from an intact tool, it is evaluated whether a break has occurred in the tool.

[0006] It has been shown that the accuracy of this method in a manufacturing environment is strongly influenced by extraneous light, such as that caused by the hall lighting or by process light from neighboring manufacturing processes, so that additional measures are required to reliably detect breakage points in the tool using this method.

[0007] Furthermore, DE 10 2010 043 632 A1 discloses a method for functionally monitoring an inspection device used to inspect container streams. The inspection device is used to image the mouth area of ​​a bottle-shaped container and operates according to the dark field principle. Damage and contamination in the mouth area cause a light-dark contrast in the inspection image, which is identified due to its asymmetry compared to the evenly illuminated mouth area.

[0008] The invention is therefore based on the object of overcoming the aforementioned disadvantages and of providing a possibility for the reliable and rapid recognition and detection of fractures in tools, in particular in tools for cold forming technology.

[0009] The object is achieved by a method according to patent claim 1 and a device according to patent claim 13. Further advantageous embodiments emerge from the subclaims and the following description.

[0010] A method is provided for detecting a fracture of a tool in the form of a die used in cold joining technology, comprising the following steps: a. Division of the visible side of the tool into at least one tool segment to be examined, which represents an area around at least one tool edge; b. Illuminating the visible side of the tool with an illuminating radiation; c. Detecting a light-dark contrast pattern for the at least one tool segment and determining therefrom an evaluation data set corresponding to the light-dark contrast pattern and d. Determining a match or deviation from the comparison of the evaluation data set of the light-dark contrast pattern detected for the at least one tool segment with a reference data set of a corresponding break-free tool segment.

[0011] According to the invention, the tool is illuminated as dark field illumination and the light-dark contrast pattern is detected by detecting radiation of a predetermined wavelength range scattered on the visible side of the tool.

[0012] With dark field illumination, the illuminating radiation is directed at a shallow angle onto the visible side of the tool. According to the law of reflection, the illuminating radiation is reflected at an equally shallow angle by flat or smooth surfaces on the visible side, so that the majority of the illuminating radiation is reflected away from the detection device, the detection area of ​​which is essentially directed directly onto the visible side of the tool. Only scattered radiation is reflected back towards the detection device by surface defects, such as cracks or surface roughness, or by edges. Consequently, when using dark field illumination, the surface defects and edges to be examined are displayed as bright areas, while the intact areas appear as dark areas. The contrast ratio is improved compared to bright field illumination, and the influence of extraneous light is reduced.

[0013] To reduce the influence of ambient light on the measurement results, only radiation within a specified wavelength range is detected to determine the light-dark contrast pattern. For example, only a red light component can be detected, for example, in a wavelength range from 600 nm to 780 nm, or a red light component including infrared radiation in a wavelength range from 600 nm to 1 mm. Alternatively, other wavelength ranges can also be detected.

[0014] Electromagnetic radiation is used as illumination radiation, preferably illumination radiation in a wavelength range of 10 -8 m to 10 -3 m is used.

[0015] In one embodiment, uniform illumination of the visible side of the tool and a particularly high contrast are achieved by implementing the dark field illumination by means of a ring-shaped illumination device.

[0016] For the detection of tool breakage, it has proven advantageous to direct the illumination beam onto the visible side of the tool at an angle ranging from 5 to 15 degrees. The illumination angle is the angle between the incident illumination beam and a plane formed by the surface of the tool.

[0017] Detection in step c) is performed by means of a detection device suitable for detecting electromagnetic radiation in the wavelength range used for the illumination radiation. In a preferred embodiment, the light-dark contrast pattern is detected in the form of an image from a camera for light-dark contrast detection. Alternatively, other suitable devices for detecting a light-dark contrast image can be used, which provide the determined data to a data processing system, which can process the results and display them on a user interface. The reference data required for each tool segment to be monitored can be stored in a data memory of the data processing system.

[0018] To reduce the influence of extraneous light, the camera preferably includes a bandpass filter, which can be placed in front of the camera lens, for example, and which only allows radiation in the wavelength range to be detected to pass through.

[0019] A tool segment is a predetermined area of ​​the visible side of the tool for which breakage detection is to be carried out. In one embodiment, the light-dark contrast pattern is detected for a single tool segment. Due to the technical effects of the method described above, it is advantageously possible to reliably detect a tool breakage even if the tool segments under consideration are selected to be relatively large, e.g., they comprise a size of at least a quarter or at least half of the visible side of the tool, or if the tool segment comprises the entire visible side. In particular, when detecting breakage in dies, fast yet reliable breakage detection is possible if, in one embodiment of the invention, the complete ring geometry of a die is recorded as a single tool segment. However, the tool segments can also be selected to be smaller.

[0020] If the visible side is divided into two or more tool segments, steps c) and d) are performed for each tool segment. More specifically, in one embodiment, in step c), a light-dark contrast pattern is detected for each of the tool segments, and an evaluation data set associated with the respective tool segment is created from this. In this embodiment, in step d), a match or deviation is determined for each of the tool segments by comparing the evaluation data set of the light-dark contrast pattern detected for the respective tool segment with a reference data set of a corresponding fracture-free tool segment.

[0021] The data set can be either a single location-related value of the tool, such as the length of an edge in a specific selection area that is assigned to a tool segment, or a set of further associated data that is required for the evaluation.

[0022] A first preferred embodiment of the invention is designed such that in the aforementioned steps c) and d) the ratio of light to dark area of ​​the light-dark contrast pattern is determined as the evaluation data set. The reference data set is defined as the ratio that would have to be present in the tool segment to be examined if the tool were intact. By simply comparing the evaluation data set with the reference data set, it is possible to determine the presence or absence of a tool break. If the ratio is higher than necessary according to the reference value, for example because too high a surface area of ​​the light component is detected in the selection window, this means that a tool element has broken away and the light component has therefore increased. It is therefore possible to detect in a simple and efficient manner whether the tool is broken.

[0023] Another preferred embodiment of the invention is designed such that in the aforementioned steps c) and d) the length of the boundary line along the light-dark contrast pattern is detected or determined as an evaluation data set.

[0024] It is further provided according to the invention that at least one value is stored as a reference data set for each tool segment, which value corresponds either to the edge length along the tool edge or to the percentage ratio of the light to the dark area portion of the light-dark contrast pattern in the said tool segment.

[0025] It is advantageous to determine the respective match or discrepancy by comparing the length of the boundary line to the respective edge length or by comparing the ratio of the light to the dark area in the relevant window of the tool segment. In the case of a match, there is no break, whereas in the case of a discrepancy, the break can be displayed accordingly in the selection window.

[0026] During the evaluation, an imaging method is preferably used by means of which the detected light-dark contrast pattern as well as one or more of the monitored tool segments are displayed on a user interface with a frame highlighting the relevant tool segment (also referred to as a selection area or selection window).

[0027] It is further advantageous if the reference data set is displayed as a graphic element or in another suitable manner in or next to the frame (selection area) on the user interface. For example, the color of the frame or the line shape of the frame can visually indicate the evaluation result of the agreement or deviation in step d) on the user interface, allowing a break in a tool in the corresponding tool segment to be immediately identified. For example, a green frame can indicate a break-free area, and a red frame can indicate an area where, for example, a die break or tool break was detected.

[0028] The method can preferably be used to detect a die break and / or a punch break in a machine tool, and in particular in a riveting tool. Accordingly, the tool is preferably a die or a punch.

[0029] Furthermore, a device is specified with an illumination device which is configured to illuminate the visible side of a tool in the form of a matrix as dark field illumination with illumination radiation, an image acquisition device which is configured to capture a light-dark contrast pattern of a predetermined wavelength range based on radiation scattered at the tool, and a data processing device which divides the visible side of the tool into at least one tool segment to be examined, wherein the tool segment represents an area around at least one tool edge,wherein the data processing device determines a corresponding evaluation data set from the light-dark contrast pattern for the at least one tool segment and determines a match or a deviation from the comparison of the evaluation data set of the light-dark contrast pattern detected for the at least one tool segment with a reference data set of a corresponding break-free tool segment.

[0030] The device can be used in particular to carry out the method described above and as such achieves the same technical effects and advantages described for the method.

[0031] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood from the drawings and in conjunction with the following description of the exemplary embodiments. Where the term "may" is used in this application, it refers to both the technical possibility and the actual technical implementation.

[0032] The following examples are explained using the attached drawings. They show: Fig. 1 a schematic illustration of a top view of a die with edge break shown on a user interface, and Fig. 2 a schematic representation of an apparatus for carrying out the method with a flow chart illustrating the steps of the method.

[0033] The invention will be described with reference to the following exemplary embodiment of a tool 1 assessed according to the present inventive method with reference to Fig. 1 and Fig. 2, wherein like reference numerals in the figures indicate like structural or functional features. The illustrated tool 1 represents a die for use in a riveting process. The die 1 consists of a central, substantially round die center 1a, which is surrounded by a ring element 1b. An annular gap 1c is provided between the die center 1a and the ring element 1b.

[0034] The image of the die 1 is displayed on a user interface 3 of a data processing device 4. The visible side of the die 1 is illuminated by an illumination device 5 in the form of a ring-shaped light source (see Fig. 2). The ring illumination 5 is designed as an LED (light-emitting diode) dark-field illumination. For this purpose, the ring illumination is arranged centrally above and at a short distance from the die 1. The illumination radiation falls at a shallow angle α onto the visible side of the die 1. Due to the shallow illumination angle α, the majority of the illumination radiation is reflected away from the camera 6. Only illumination radiation scattered at edges, curved and rough surfaces reaches the detection field of the camera 6. The camera 6 is designed for light-dark detection. In this way, the camera 6 detects a "light" area or line in the area of ​​the tool edges 2, whereas the die center 1a, the ring element 1b and the annular gap 1c are detected as dark areas. The tool edges 2 are therefore detected as light boundary lines or boundary areas between dark areas.

[0035] Contrary to the actually recorded light-dark contrast pattern of the die, in which the tool edges are visible as bright lines and, for example, the annular gap 1c as a dark area, in Fig. 1 For reasons of clarity, an inverted representation is shown, ie areas that are “dark” or of low contrast in the dark field image are shown here as white areas.

[0036] The image data detected by the camera 6 are passed on to the data processing device 4 for further evaluation.

[0037] Fig. 2 shows a flowchart of the method for detecting a breakage of the die 1.

[0038] In step a), the visible side of the die 1 is divided into at least one tool segment or a number of tool segments S1,..., Sn to be examined, each tool segment comprising an area around the tool edges 2. By way of example, six selection windows around the tool segments S1,..., S6 are shown, with which the method is explained. In the same way, however, the method can also be carried out with only a single tool segment, which can, for example, be selected to be larger than the tool segments S1 to S6 and preferably comprises the entire die ring geometry, represented by the dashed selection window S7 in Fig. 1.

[0039] The matrix 1 is positioned centrally below the illumination device 5 and camera 6, and in step b), the visible side of the matrix 1 is irradiated with illumination radiation at an illumination angle α. The illumination is performed as dark-field illumination.

[0040] In step c), a light-dark contrast pattern is detected based on the illumination radiation scattered by the die 1, which corresponds to the visible side of the die 1. During detection, only radiation of a predetermined wavelength range is recorded in order to reduce the influence of external radiation on the evaluation. In the example shown, the camera 6 is equipped with a bandpass filter 7 for this purpose, so that only radiation in the red light range is detected. From the light-dark contrast pattern, a corresponding evaluation data set HDmess is determined for each of the tool segments S1, ..., S6. The evaluation data set can, for example, be an edge length, e.g. the length of a "light" area in a tool segment. For each tool segment, reference data sets HD are also available, which contain the reference values ​​for an intact die.

[0041] In step d), the evaluation data sets HDmess are compared with the reference data sets HD. For tool segments S1 to S3 and S6, a match is found between the data sets, i.e., an intact die is present in tool segments S1 to S3 and S6.

[0042] However, for tool segments S4 and S5, the detected edge length is shorter than in the reference data set. A deviation is detected, thus identifying damage to die 1 in these segments.

[0043] Instead of finding edges and determining the edge length as the HDmess evaluation data set, the ratio of the dark to the light area of ​​the light-dark contrast pattern can also be detected in this selection window. For a fracture-free tool, for example, a ratio according to the reference value should be present in the area of ​​tool segment S5. However, since only dark portions are detected and the light area portions are missing, a die fracture can be clearly detected in the area of ​​ring element 1b. The same applies to the area of ​​tool segment S4, where the "light" area portion is too small compared to the reference data set, from which it can be deduced that a fracture of ring element 1b has already occurred in this segment.

[0044] The reference data set HD is displayed on the user interface as a graphical element in the frame R of the selection window in the said tool segment as the length of a solid line representing the length of the expected tool edge in this area.

[0045] Furthermore, the evaluation result of the agreement or deviation in step d) is visually indicated by the line shape of the frame R. A solid line indicates a match between the evaluation data set HDmess and the reference value, while a deviation is represented as a dashed line. However, a color representation is preferred, e.g., as a green frame R or red frame R, depending on whether a break was detected in the area or not.

[0046] The invention is not limited in its implementation to the preferred embodiments specified above. Rather, a number of variants are conceivable, which utilize the presented solution even in fundamentally different embodiments. For example, the line representing the length of the tool edge 2 in the selection window can be displayed as colored lines, e.g., red or green, to indicate whether the detected edge length matches the expected edge length in this tool segment S1,..., S6. Furthermore, the die can also consist of several parts, and several segments of the multi-part die can be monitored.

[0047] The camera 6 and the illumination device 5 can be mounted stationary, e.g., on a frame, and the tools to be examined are brought into the camera's illumination or detection range. Alternatively, the camera and illumination device can also be mounted on a positioning device, such as a robot arm, and moved toward the tools to be examined.

[0048] The exemplary embodiments are not to scale and are not limiting. Modifications within the scope of expert practice are possible. List of reference symbols 1 tool 1a Matrix center 1b Ring element 1c Annular gap 2 tool edges 3 User interface 4 Data processing device 5 Lighting equipment 6 Camera 7 bandpass filters α Illumination angle a), b), c), d) Process steps S1, ... Sn tool segments HDmess evaluation data set HD reference dataset R frame

Claims

[1] Method for detecting a fracture of a tool (1) in the form of a die used in cold joining technology, comprising the following steps: a. dividing the visible side of the tool (1) into at least one tool segment (S1,..., Sn) to be examined, which represents an area around at least one tool edge (2); b. Illuminating the visible side of the tool (1) with an illuminating radiation; c. detecting a light-dark contrast pattern for the at least one tool segment (S1, ..., Sn) and determining therefrom an evaluation data set (HDmess) corresponding to the light-dark contrast pattern; d. Determining a match or deviation from the comparison of the evaluation data set (HDmess) of the light-dark contrast pattern detected for the at least one tool segment (S1, ..., Sn) with a reference data set (HD) of a corresponding break-free tool segment (S1, ..., Sn), wherein the illumination is done as dark field illumination and the light-dark contrast pattern is detected by detecting radiation of a given wavelength range scattered by the tool. [2] Method according to claim 1, characterized by that the dark field illumination is realized by an annular illumination device (5). [3] Method according to one of the preceding claims, characterized by that the illumination radiation strikes the surface of the tool (1) at an illumination angle (α) in a range of 5 to 15 degrees. [4] Method according to one of the preceding claims, characterized by that the detection in step c) is carried out by means of an image from a camera (6) for light-dark contrast detection. [5] Method according to claim 4, characterized by that the camera (6) contains a bandpass filter (7). [6] Method according to one of the preceding claims, characterized by that in step a) a single tool segment is selected which covers the entire visible side of the tool. [7] Method according to one of claims 1 to 5, characterized by that the visible side of the tool (1) is divided into a number of tool segments to be examined and steps c) and d) are carried out for each tool segment. [8] Method according to one of the preceding claims, characterized by that in steps c) and d) the ratio of the light to the dark area of the light-dark contrast pattern is detected as the evaluation data set (HDmess). [9] Method according to one of the preceding claims, characterized by that in steps c) and d) the length of the boundary line along the light-dark contrast pattern is detected as an evaluation data set (HDmess). [10] Method according to one of the preceding claims, characterized bythat at least one value is stored as a reference data set (HD) for each tool segment (S1, ..., Sn), which value corresponds either to the edge length along the tool edge (2) or to the percentage ratio of the light to the dark area portion of the light-dark contrast pattern in the said tool segment (S1, ..., Sn). [11] Method according to claim 8, characterized by that the determination of the respective agreement or deviation is carried out by comparing the length of the boundary line to the respective edge length or by comparing the ratio of the light to the dark area portion in the relevant tool segment (S1, ..., Sn). [12] Method according to one of the preceding claims, characterized by that the specified wavelength range is a range from 600 nm to 1 mm or a range from 600 nm to 780 nm. [13] Device for carrying out the method according to one of claims 1 to 12, comprising: a lighting device (5) which is designed to illuminate the visible side of a tool (1) in the form of a matrix as dark field lighting with illuminating radiation, an image capture device (6) configured to capture a light-dark contrast pattern of a predetermined wavelength range based on radiation scattered by the tool, a data processing device (4) which divides the visible side of the tool (1) into at least one tool segment (S1,..., Sn) to be examined, wherein the at least one tool segment represents an area around a tool edge (2), wherein the data processing device (4) determines a corresponding evaluation data set (HDmess) from the light-dark contrast pattern for the at least one tool segment (S1,..., Sn) and establishes a match or a deviation from the comparison of the evaluation data set (HDmess) of the light-dark contrast pattern detected for the at least one tool segment (S1,..., Sn) with a reference data set (HD) of a corresponding break-free tool segment (S1,..., Sn).

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