METHOD FOR MEASURING TOOLS

Description

AREA OF TECHNOLOGY

[0001] The invention relates to a method for measuring tools according to an optical principle as defined in claim 1.

[0002] In machining centers or machine tools, workpieces are frequently machined using cutting tools. To account for the influence of wear-related deformation of the tool on precise machining, the tools are typically measured with high accuracy at predetermined time intervals. This is often done in a measuring machine or in inspection devices outside the machine tool. STATE OF THE ART

[0003] From DE 10 2018 006 652 A1, a method for checking a tool is known in which a measuring beam of a laser is shadowed by the tool. A laser beam receiver outputs a signal that is representative of the degree of shadowing.

[0004] In DE 10 2016 224 000 A1 a method is described by which a tool breakage is detected using dark field illumination.

[0005] A method for determining the spatial orientation of a drilling tool is known from US patent 6,191,856 B1. In this method, the drilling tool is illuminated by several light sources from different directions, and the reflected light is captured by cameras. SUMMARY OF THE INVENTION

[0006] The invention is based on the objective of creating a method by which at least one dimension of a tool with cutting edges can be determined with high accuracy, wherein the associated device can be operated in a machining area of ​​a machine tool.

[0007] This problem is solved according to the invention by the features of claim 1.

[0008] A device suitable for carrying out the method serves to determine a dimension, for example, the relevant diameter or length, of a cutting tool. The device comprises a first light source such that light can be emitted from the first light source parallel to a first axis. Furthermore, the device comprises an image sensor to which a second axis (optical axis) can be assigned, which runs orthogonally to the image sensor. Finally, the device comprises an evaluation unit, i.e., an electronic circuit for evaluating the signals supplied by the image sensor. The first axis and the second axis are arranged at an angle to each other, i.e., they are not aligned parallel to each other.Furthermore, the device is configured such that light emitted by the first light source can be reflected by the cutting edge of the tool in such a way that the reflected light creates a series of light points (or a reflective band) on the image sensor. The evaluation unit can determine the positions of the light points, and the dimensions of the tool can be determined based on the positions of the light points on the image sensor.

[0009] The determination of the tool's dimensions is therefore not carried out using a transmitted light method, in which a light source emits light parallel to the optical axis of the image sensor. Instead, the device is designed to allow the use of a dark-field method. This enables the device, with the features of claim 1, to be designed in a comparatively compact manner while still operating with high accuracy.

[0010] The first light source can be configured to emit parallel light beams. Preferably, a laser light source that inherently emits parallel light beams or has collimator optics can be used in this configuration. Alternatively, the first light source can also emit beams that are focused or converge. In this context, LEDs, especially those with focusing optics, can be advantageously used. The first axis then preferably passes through the focal point of the first light source.

[0011] Advantageously, the device is designed such that at least one reference coordinate can be stored in the evaluation unit, whereby the tool dimension can be determined by combining the position of at least one of the light points with the reference coordinate. The evaluation unit, or the relevant electronic circuit, is preferably located within the device. However, it can also be located outside the device; for example, the evaluation unit can be part of the machine tool's control system or it can be arranged in a separate device.

[0012] In a further embodiment of the invention, the evaluation unit is set up in such a way that the dimensions of the tool can be determined by means of a compensation calculation based on the positions of several light points.

[0013] According to a further development of the invention, the device is configured such that the first axis and the second axis intersect. The angle of intersection between the first axis and the second axis is greater than 75°. The two axes thus intersect in space such that two pairs of congruent vertical angles are formed in the plane they span. According to generally accepted definitions, the smaller of these two vertical angles is the angle of intersection. The angle of intersection of the axes in question in space can therefore be at most 90°. Advantageously, the device is designed such that the angle of intersection between the first axis and the second axis is 90°.

[0014] Preferably, the device is designed to be mounted on a surface of a machine table that extends in a first plane. This first plane is oriented parallel to the second axis, with the first light source positioned such that the first axis runs obliquely to the first plane. Accordingly, the first axis penetrates the first plane at an angle that deviates from 90°.

[0015] In a further embodiment of the invention, the first axis and the second axis run in a second plane, wherein the second plane is inclined relative to the first plane by an angle greater than 20°, advantageously greater than 30° or greater than 40°.

[0016] Furthermore, the device can include a second image acquisition unit which has a second image sensor to which a third axis can be assigned, which runs orthogonally to the second image sensor and to the second axis.

[0017] The invention comprises a method for determining the dimensions of a cutting tool. In this method, the light emitted by the first light source is reflected by the cutting edge of the tool in such a way that the reflected light generates a series of light points on the image sensor. The evaluation unit determines the positions of the light points and, based on these positions, determines the dimensions of the tool.

[0018] Advantageously, the device is mounted in a machining area where a workpiece will later be machined using a tool. After mounting the device, position values ​​are determined that uniquely define its position within the machining area. A probing method can preferably be used to determine the required position values. Based on these position values, reference coordinates for the position of the image sensor and the orientation of the first axis within the machining area are determined. Therefore, after this step, the exact position and orientation of the image sensor within the coordinate system of the machining area are known.

[0019] Advantageously, before determining the tool's dimensions, a reference body is connected to a tool holder of the machine tool. This reference body is then positioned in front of the device and measured using the image sensor, i.e., its dimensions are determined, using the first light source. Preferably, the reference body also has cutting edges or cutting-like edges. During the subsequent determination of the tool's dimensions, the tool is also connected to the tool holder of the machine tool. Based on the results of the reference body measurement, a correction value is generated, which contains information about the exact position of the tool holder relative to the reference coordinates of the image sensor. The correction value is then stored, for example, in the evaluation unit or control system, or in another device.

[0020] Advantageously, the tool, and in particular one or more cutting edges, is qualitatively inspected before or after its dimensions have been determined. For this purpose, the device can, in particular, include a second image acquisition unit with a second image sensor. A third (optical) axis, perpendicular to both the second image sensor and the second axis, can be assigned to the second image sensor. This allows for an additional view of the tool.

[0021] According to a further aspect of the invention, the device also includes a control unit for processing control commands and converting them into movements of the tool holder along at least one axis. Furthermore, according to this additional aspect, the device includes at least one position measuring device for determining the actual position of the tool holder along the at least one axis. Corresponding actual position values ​​or position signals of the tool holder or the tool attached to it are supplied to the control unit for position control. The position measuring device serves to determine the tool's position when determining its dimensions, i.e., outside of a machining process.

[0022] Advantageous embodiments of the invention can be found in the dependent claims.

[0023] Further details and advantages of the method according to the invention will become apparent from the following description of an exemplary embodiment with reference to the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a perspective view of the device for determining a dimension of a tool, Figure 2 is a side view of the tool, Figure 3 is a schematic representation of a machine tool with control and the device for determining a dimension of the tool, Figure 4 is a flowchart for a method for determining a dimension of the tool, Figure 5 is a representation of received light points and an evaluation graphic. DESCRIPTION OF THE EXECUTION FORMS

[0025] The Figure 1Figure 1 shows an embodiment of the device V. The device V comprises a first light source 1, here a laser diode, with a collimator 1.1. In operation of the device, the first light source 1 emits light parallel to a first axis T.

[0026] Furthermore, the device V comprises an image sensor 2, for example a CMOS sensor or a CCD sensor. A lens is arranged in front of the image sensor 2, which is designed such that an entocentric image can be achieved on the image sensor 2. A second axis Y can be assigned to the image sensor 2, which is oriented orthogonally to the image sensor 2. Radially adjacent to the image sensor 2 is a second light source 3, which in the presented embodiment is designed as a ring light consisting of several LEDs arranged around the second axis Y.

[0027] The device V is designed to be mounted on a surface of a machine table that extends in a first plane xy. This first plane xy is oriented parallel to the second axis Y, with the first light source 1 arranged such that the first axis T runs obliquely to the first plane xy. The first axis T and the second axis Y run according to the Figure 1 in a second plane which is inclined relative to the first plane xy. In the presented embodiment, the angle between the first plane xy and the second plane is 45°.

[0028] Both the image sensor 2 with its lens and the second light source 3 are covered by a transparent disc, which in the presented embodiment is circular. The device V is intended to be installed in a machining area of ​​a machine tool or processing machine. Contamination of the device V by coolant, lubricant, and / or chips is generally to be expected there. Such contamination can be effectively removed from the transparent disc by means of compressed air flowing at high speed from nozzles of a first nozzle unit 5. The device V also has a third light source 4.

[0029] Furthermore, the device V includes a second image acquisition unit 7 which is located in the Figure 1The image acquisition unit 7 has a second image sensor whose optical axis, hereinafter referred to as the third axis Z, is arranged perpendicular to the optical axis of the image sensor 2, or to the second axis Y. The second image acquisition unit 7 also includes a further, in particular ring-shaped, light source. A second nozzle unit 9, from which compressed air can flow, is attached in the area of ​​the second image acquisition unit 7 for the removal of contaminants. The device V also has a fourth light source 8 in the area of ​​the second image acquisition unit 7.

[0030] The components of the device 1 are surrounded by a housing 6, which protects against external influences and is hermetically sealed. In the presented embodiment, the housing 6 also contains a [missing information - likely a component or device]. Figure 1 Evaluation unit 10 not shown (see Figure 3 ).

[0031] In the Figure 2A tool W is shown, here a milling tool with helical cutting edges S, as well as an associated coordinate system with the direction axes x, y, z. The tool W rotates around a tool axis A during machining. For the precise machining of workpieces, it is necessary to determine dimensions D, H, here the diameter and length of the tool W at predetermined time intervals, as these change during operation due to wear.

[0032] The Figure 3Figure 1 schematically shows elements of the machine tool, in particular a machine tool, as well as the device V for determining the dimensions D, H of the tool W. Accordingly, the machine tool includes a control unit C. The control unit C serves, among other things, to process programmed control commands and translate them into motion sequences. For this purpose, control signals Sx, Sy, Sz are transmitted from the control unit C to drives Dx, Dy, Dz, which cause a tool holder, in particular with the tool W fixed to it, to move along the first directional axis x, a second directional axis y, and the third directional axis z. Figure 1The tool W is moved within the machining area. Its actual position is recorded by position measuring devices Jx, Jy, Jz for the respective directional axes x, y, z. The corresponding actual position values ​​of the tool W, or position signals Px, Py, Pz, are then fed to the control unit C for position control, as is standard practice in CNC machines. A corresponding machining center can also have more than the three axes of motion mentioned above. When calculating the control signals Sx, Sy, Sz, the dimensions D, H of the tool W must be taken into account to ensure that material removal occurs precisely at the desired location on the workpiece. Therefore, tools were typically measured outside the machining area before the start of the machining process, and the relevant dimensions were stored electronically in a table, preferably within the control unit C.

[0033] The invention enables a precise determination of the dimensions D and H of the tool W with the cutting edges S in the machining area. For this purpose, the following process steps are carried out in the presented embodiment according to the Figure 4 Procedure: In step S1, the device V is first brought into the machining area and positioned there in a desired position, e.g. on a machining table, in a comparatively rough manner.

[0034] In step S2, a probe is clamped into the tool holder of the machine tool, and several previously defined points on the housing 6 are probed to determine their position. This process step is executed using a cycle stored in the control unit C, which is essentially familiar from the standard measurement of a workpiece blank's position. The absolute positions of the probed points are determined using the position measuring devices Jx, Jy, Jz. The resulting position values ​​Vx, Vy, Vz of the device V are fed to the control unit C. Knowing the exact dimensions of the device V, the reference coordinates Vmx, Vmy, Vmz of the center of the image sensor 2 and the orientation TDC of the first axis T can now be determined in step S21 within the coordinate system of the machine tool.If the device V remains permanently in the machining area of ​​the machine tool, determining the position values ​​Vx, Vy, Vz, and thus step S21, is only necessary once after the device V is mounted in the machining area. Accordingly, under these conditions, step S3 can be initiated directly after step S2.

[0035] After the probe has been removed from the tool holder of the machine tool, a reference body is clamped into the tool holder in the subsequent step S3. The exact dimensions Dr, Hr of this reference body, which, for example, has a substantially cylindrical shape and features cutting-edge-like edges parallel to its longitudinal axis and circumferentially, are known. The reference body is then moved into the intended measuring position, taking into account the determined reference coordinates Vmx, Vmy, Vmz of the center of the image sensor 2 and the orientation OT of the first axis T. During the reference measurement, the tool holder preferably rotates with the reference body. Knowing the reference coordinates Vmx, Vmy, Vmz of the center of the image sensor 2, the diameter Drm and the height Hrm of the reference body can be determined, analogous to the procedure explained below in connection with step S4.Based on the known dimensions Dr, Hr and the measured dimensions Drm, Hrm of the reference body, correction values ​​Qx, Qy, Qz can be determined and stored in step S31. These values ​​contain information about the exact position of the tool holder or the tool axis A relative to the center of the image sensor 2 with the reference coordinates Vmx, Vmy, Vmz. Because the described determination of the correction values ​​Qx, Qy, Qz is performed with the reference body or tool holder rotating, errors related to movement around the tool axis A are implicitly taken into account later.

[0036] Now the reference body can be placed in the magazine of the machining center and the tool W to be measured can be clamped into the tool holder.

[0037] In step S32, the operator of the machining center can select whether to perform a qualitative inspection of the tool W before actually determining its dimensions D and H, for example, to check for damage to the cutting edges S. If a qualitative inspection is selected, step S41 follows. In step S41, the tool W is first moved into the area of ​​the second image acquisition unit 7. For positioning, the nominal dimensions Dn and Hn of the tool W are retrieved from a table stored in the control unit C and read into the evaluation unit 10. At the desired position, an image of the tool W is then captured from below, parallel to the z-direction, and displayed on a screen. In step S42, the tool W is then positioned in front of the image sensor 2, and the third light source 4 and the first ring light 3 are switched on.Tool W is rotated and, if necessary, moved in the z-direction. The images generated by image sensor 2 can be viewed on the display, allowing a decision to be made as to whether tool W is still suitable for machining a workpiece. If not, the process can be stopped at this point and an alternative tool can be checked. If tool W is in proper working order, the actual determination of tool W's dimensions D and H can begin.

[0038] If a qualitative assessment of the tool W was not selected in step S32, the nominal dimensions Dn, Hn (in the case of a new tool W) or the dimensions of the tool W measured before the last machining operation are read from a table stored in the control unit C immediately after step S32. Subsequently, the tool W is positioned accordingly in front of the image sensor 2, and the first light source 1 is switched on. In the presented embodiment, the tool W rotates during the measurement in step S4. During operation of the device V, the first light source 1, here a laser light source, emits light parallel to the first axis T with the aid of the collimating optics 1.1. The second axis Y, which is orthogonal to the image sensor 2 and thus represents the optical axis with respect to the image sensor 2, is inclined relative to the first axis T. This creates dark-field illumination.The light emitted by the first light source 1 strikes the cutting edge S of the tool W. Light reflected from the cutting edge S is generated on the image sensor 2 according to the . Figure 5 A series of light points L or reflective bands. Figure 5 shows the light points L, which are caused by reflection at the lower left end (see the Figure 2 ) of the rotating tool W, are created. Since this is dark-field illumination, the actual image differs from the representation in the Figure 5 inverted, accordingly, in reality bright points of light L are present against a dark background.

[0039] The image is now scanned along the light points L with an increment or a raster of one pixel width. The respective distance between two adjacent dashed lines in the Figure 5This corresponds to a pixel width of 8 µm in the presented embodiment. Specifically, each of the light points L in the row extending essentially in the x-direction is assigned a z-position within the corresponding grid. The actual position of the tool W in the z-direction is measured by the position measuring device Jz of the machine tool, and the corresponding position signal Pz is generated. It is therefore possible to determine the location of the light points L relative to the coordinate system within the machining area of ​​the machine tool. In conjunction with the results of the previously performed reference measurements, particularly taking into account the correction value Qz, the absolute value of each z-position zL within the coordinate system of the machine tool can be determined with very high accuracy.

[0040] Using the respective z-positions zL as input values, a balancing calculation is performed in evaluation unit 10, from which a spline or a smoothed line gz is generated according to the Figure 5 The point Gz with position z0 on line gz, which has the smallest z-value (in the presented embodiment, the leftmost point of line gz), is decisive for determining the dimension H of the tool W's length. The tool W is clamped in a defined position in the tool holder with respect to the z-direction. Furthermore, the position Pz in the z-direction of the tool holder is known by the position measuring device Jz. Taking the correction value Qz into account, the relative position between the stored reference coordinate Vmz and the position z0 of point Gz on the image sensor 2 can thus be precisely determined.

[0041] Similarly, dimension D is determined, with the tool W rotating during the measurement. Because the actual position of the tool W is determined by the position measuring device Jx and a corresponding position signal Px is sent to the evaluation unit 10, the radius R, and thus the dimension D of the diameter of the tool W, can be determined immediately after the position x0 of point Gx on the image sensor 2 has been determined. To increase accuracy, the position of the tool axis A is corrected by the correction value Qx.

[0042] Here, too, in evaluation unit 10, a least-squares adjustment is performed, from which a smoothed line gx is generated using the respective x-positions xL as input values. The point Gx with the coordinate or position x0 on the line gx, which has the smallest x-value, is decisive for determining the dimension D of the diameter. In evaluation unit 10, the stored reference coordinate Vmx is combined with the position x0; in particular, a difference (Vmx-x0) is calculated, whereby the dimension D of the diameter of the tool W is determined by this combination.

[0043] The invention was described using a tool W in the form of an end mill. However, shell end mills can also be measured. Likewise, the invention can be applied to radius cutters, angle cutters, prism cutters, etc., whereby different reflective bands or rows of light points are produced depending on the design. Furthermore, the invention is also applicable to other tools with cutting edges, for example, drilling tools.

Claims

1. Method for determining a dimension (D, H) of a tool (W) with cutting edges (S) by means of a device (V) comprising a first light source (1), an image sensor (2) and an evaluation unit (10), wherein light is emitted parallel to a first axis (T) by the light source (1) and a second axis (Y) is assignable to the image sensor (2), which axis runs orthogonally to the image sensor (2), wherein the first axis (T) and the second axis (Y) are arranged inclined relative to each other, wherein further the light emitted by the first light source (1) is reflected by the cutting edge (S) of the tool (W) in such a way that the reflected light generates light points (L) arranged in a row on the image sensor (2), wherein positions (xL, zL) of the light points (L) are determined by the evaluation unit (10) and the dimension (D, H) of the tool (W) is determined based on the positions (xL, zL) of the light points (L), characterized in that - before determining the dimension (D, H) of the tool (W), a reference body is connected to a tool holder of the processing machine and measured using the image sensor (2), - during the subsequent determination of the dimension (D, H) of the tool (W), the tool (W) is connected to the tool holder of the processing machine and a correction value (Qx, Qy, Qz) is formed based on the results of the measurement of the reference body, with the correction value containing the information about the exact location of the tool holder relative to reference coordinates (Vmx, Vmy, Vmz) of the image sensor (2), - the dimension (D, H) of the tool (W) is determined based on the positions (xL, zL) of the light points (L), taking into account the correction value (Qx, Qy, Qz).

2. Method according to Claim 1, wherein the dimension (D, H) is determined based on the positions (xL, zL) of the light points (L) by means of a compensation calculation.

3. Method according to Claim 1 or 2, wherein the device (V) is mounted in a processing space and subsequently position values (Vx, Vy, Vz) by means of which the position of the device (V) in the processing space is uniquely determined are ascertained, wherein, based on the position values (Vx, Vy, Vz), reference coordinates (Vmx, Vmy, Vmz) for the position of the image sensor (2) and the orientation (OT) of the first axis (T) in the processing space are determined.

4. Method according to any one of the preceding claims, wherein the tool (W), in particular its cutting edge (S), is qualitatively assessed in addition to the determination of the dimensions (D, H).

5. Method according to any one of the preceding claims, wherein the device (V) comprises a second image acquisition unit (7), which has a second image sensor, to which a third axis (Z) is assignable, which third axis runs orthogonally to the second image sensor and to the second axis (Y), wherein the tool (W), in particular its cutting edge (S), is qualitatively assessed in addition to the determination of the dimensions (D, H).

6. Method according to any one of the preceding claims, wherein the reference body has cutting edges or cutting-edge-like edges.

7. Method according to Claim 6, wherein the reference body has a substantially cylindrical shape and has the cutting-edge-like edges parallel to its longitudinal axis and in the circumferential direction.