DEVICE AND METHOD FOR DETERMINING THE APPROACH OF A TOOL TO A WORKPIECE

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to a device for detecting the approach of a tool to a workpiece in a machine tool according to claim 1, as well as a corresponding method according to claim 8. It can be advantageously used in numerically controlled machine tools which form workpieces by machining, in particular by milling, turning and grinding. STATE OF THE ART

[0002] The most common manufacturing methods for mechanical workpieces are based on machining, i.e., the removal of material. This involves removing material from a so-called blank using tools, ultimately creating a product with the desired shape and function. To remove material, the workpiece is brought into contact with a tool. The tools have geometrically defined or undefined cutting edges.

[0003] Examples of tools with geometrically defined cutting edges are milling cutters, drills, or turning tools; a tool with indeterminate cutting edges is a grinding wheel. For the cutting process, one of the objects—the tool or the workpiece—is often set in rotation before it comes into contact with the other object.

[0004] The machining process is controlled by a computer, which, while executing a production program, activates electric drives to move at least one of the objects. Position measuring devices—rotary encoders or linear encoders—are used to determine the actual position of the moving object, and their measured values ​​are then fed to the computer. The computer is called a CNC controller, and the machine tool used to perform the machining is called a CNC machine.

[0005] A so-called spindle is provided to generate the object's rotation. This is an electric motor that directly or indirectly drives a shaft to which the object is attached. A rotary encoder is provided to measure the angle of rotation and / or speed of the spindle. Furthermore, measuring devices are known that can measure displacements of the shaft from an ideal position. EP 3 591 344 A1 describes such a measuring device.

[0006] Clamping devices are provided to secure the workpiece for machining. Since clamping a new workpiece (blank) is subject to large tolerances and the dimensions of the blanks can also vary, the exact position of the newly clamped blank and its dimensions must be determined before machining begins. For this purpose, so-called probes are used. These, instead of a tool, are moved towards the workpiece and emit a switching signal when they come into contact with the workpiece. The CNC control evaluates the switching signal and determines the position and dimensions of the workpiece by moving to several positions on the blank (probing). Only then can the actual machining begin.

[0007] A disadvantage of this procedure is the time it takes, as the tool must first be exchanged for the probe and then exchanged back again after the measuring process.

[0008] DE 101 27 972 C1 describes a device and a method for detecting the approach of a tool to a workpiece, which are based on the measurement of a dynamic pressure of a compressed air supply. SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide an improved device with which the position of a workpiece in a machine tool can be determined.

[0010] This object is achieved by a device according to claim 1.

[0011] A device for detecting the approach of a tool to a workpiece in a machine tool, in which the tool and the workpiece are movable relative to each other and the tool or the workpiece is connected to a shaft in a rotationally fixed manner, is proposed, wherein the tool has a coolant channel through which a coolant can be supplied to a machining area in which the machining of the workpiece by the tool takes place. The device comprises a measuring arrangement with a measuring graduation arranged in a rotationally fixed manner on the shaft and at least one position sensor which is arranged fixedly with respect to the shaft, and a computer, wherein the at least one position sensor is designed to scan the measuring graduation and to generate position values ​​therefrom which indicate a position of the shaft, and the position values ​​are fed to the computer, which comprises means which, by evaluating a course of the position values ​​when the tool approaches the workpiece, determine that the tool is located in an approach zone with respect to the workpiece in which a displacement of the shaft occurs which results from the back pressure of the coolant flow impinging on the workpiece, and signal by means of an approach signal when the tool reaches an approach position with respect to the workpiece at which the tool is close to the workpiece without touching it.

[0012] Furthermore, it is an object of the present invention to provide an improved method with which the position of a workpiece in a machine tool can be determined.

[0013] This object is achieved by a method according to claim 8.

[0014] A method is now proposed for detecting the approach of a tool to a workpiece in a machine tool, in which the tool and the workpiece are movable relative to each other and the tool or the workpiece is connected to a shaft in a rotationally fixed manner, wherein the tool has a coolant channel through which a coolant can be supplied to a machining area in which the machining of the workpiece by the tool takes place. The machine tool comprises a measuring arrangement with a measuring graduation arranged in a rotationally fixed manner on the shaft and at least one position sensor which is arranged fixedly with respect to the shaft, and a computer, wherein according to the method the measuring graduation is scanned by the at least one position sensor and from this position values ​​are generated which indicate a position of the shaft and the position values ​​are fed to the computer, which comprises means with which it is determined by evaluating a curve of the position values ​​when the tool approaches the workpiece that the tool is located in an approach zone with respect to the workpiece in which a displacement of the shaft occurs which results from the dynamic pressure of the coolant flow impinging on the workpiece and the means signal by means of an approach signal when the tool reaches an approach position with respect to the workpiece at which the tool is close to the workpiece without touching it.

[0015] The measuring graduation advantageously has a graduation track whose code elements are arranged in the circumferential direction of the shaft and whose scanning by the position sensors allows position values ​​to be measured that indicate the angular position of the shaft. In an advantageous embodiment, three position sensors are provided for scanning the graduation track, which are arranged at equal intervals in the circumferential direction of the shaft. Depending on the direction of the deflection, a deflection of the shaft influences the angular positions measured by the position sensors, which results in a change in the angular difference determined by the arrangement of the position sensors. From this, the magnitude and direction of the shaft deflection can be determined.

[0016] In addition to this graduation track, the measuring graduation can have a second graduation track, whose code elements are arranged in a ring around the circumference of the shaft. Three position sensors can be provided for scanning this second graduation track, which are also arranged at equal intervals in the circumferential direction of the shaft. From the scanning of the second measuring graduation, deflections of the shaft in its axial direction can be measured. In particular, a rotation of the axis in the axial direction—i.e., a misalignment of the axis relative to a rest position of the shaft—can be measured, which results in a tilting of the ring-shaped code elements relative to the position sensors.

[0017] The position values ​​of the position sensors are fed into a displacement calculator in the computer, which continuously generates at least one displacement value, which is a measure of the shaft deflection caused by a force acting on the shaft. Suitable means are provided in the computer for evaluating the progression of the displacement values. Particularly advantageous embodiments result from the following means: In a first advantageous embodiment, the means comprise a comparator, with which the reaching of the approach position can be determined by comparing currently incoming displacement values ​​with a threshold value.

[0018] In a second advantageous embodiment, the means comprise a differentiator designed to form the difference quotient from successively arriving displacement values ​​and the time interval of their arrival, as well as a comparator with which the reaching of the approach position can be determined by comparing the difference quotients with previously stored threshold values.

[0019] In a further advantageous embodiment, the means comprise a frequency analyzer that evaluates the progression of the displacement values ​​in the frequency domain. By specifically monitoring the spectral power density of frequency bands determined by the shaft speed and the number of coolant openings in the tool, it is possible to determine whether the approach position has been reached.

[0020] In a variant of this embodiment, the position values ​​of at least one position sensor can also be fed directly to the frequency analyzer, so that the displacement calculator can be dispensed with.

[0021] In a further advantageous embodiment, the means comprise an AI module that evaluates the progression of the displacement values ​​using artificial intelligence methods, in particular pattern recognition. This is particularly advantageous when the displacement values ​​exhibit large statistical fluctuations.

[0022] This embodiment can also be varied in such a way that the position values ​​of at least one position sensor are fed directly to the AI ​​module, so that no displacement computer is required.

[0023] In order to enable the interaction of the computer with other components, for example a control unit of the machine tool, it has proven advantageous to equip the computer with a command channel via which commands and, if necessary, data can be supplied to the computer, for example a start command that starts the method according to the invention.

[0024] The command channel can be implemented together with the response data channel as a digital, preferably serial, interface.

[0025] To determine threshold values, a threshold value determiner is advantageously provided. This detects a transition from the approach zone to a machining zone where machining of the workpiece occurs when the tool approaches the workpiece, and then determines a threshold value based on this. Threshold values ​​are advantageously determined during a test run with a test workpiece. The test run can be initiated by the control unit by transmitting a test start command to the computer.

[0026] The threshold values ​​are preferably stored in the computer, for example in the comparator, the frequency analyzer or the AI ​​module.

[0027] Further advantageous embodiments of the device according to the invention or of the method according to the invention can be found in the respective dependent claims and in the exemplary embodiments described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] It shows Figure 1 shows a device according to the invention in connection with components of a machine tool, Figure 2 shows an embodiment of a measuring arrangement according to the invention, Figure 3 shows a measuring arrangement according to Figure 2 suitable measuring graduation, Figure 4 shows a first embodiment of a computer of a device according to the invention, Figure 5 shows a signal diagram with the course of the displacement values ​​VL in connection with the threshold value S according to Figure 4 , Figure 6 shows a further embodiment of a computer of a device according to the invention, Figure 7 shows a signal diagram with the course of the displacement values ​​VL in connection with the threshold value S according to Figure 6 , Figure 8 shows a further embodiment of a computer of a device according to the invention and Figure 9 shows a further embodiment of a computer of a device according to the invention. DESCRIPTION OF THE EMBODIMENTS

[0029] In the following description of advantageous embodiments of the present invention, reference numerals of components and functional groups described in one figure are retained in the subsequent figures.

[0030] Figure 1 shows a device according to the invention in conjunction with components of a machine tool, in this case a 5-axis milling machine. It has a motor spindle 10, as well as a drive and a position measuring device for each movement axis. A control unit 100 is provided for controlling movement sequences, in particular for machining a workpiece 6.

[0031] The central component of the motor spindle 10 is a spindle motor 1 with a shaft 2. At one end of the shaft 2, a tool 4 (for example a milling tool) is connected to the shaft 2 in a rotationally fixed manner, so that it rotates with it. A tool holder (not shown), for example a hollow shank taper, is provided for attaching the tool 4 to the shaft 2. An angle measuring device 5 (rotary encoder) is also mechanically coupled to the shaft 2. The coupling is achieved via a mechanical coupling (not shown) that connects a rotatable shaft of the angle measuring device 5 to the shaft 2. In this way, the angular position and / or the number of revolutions completed by the shaft 2 can be measured with the angle measuring device 5. The shaft 2 is mounted in the housing of the spindle motor 1, for example, via rolling bearings.

[0032] To machine the workpiece 6, the shaft 2 of the spindle motor 1 is set in rotation and rotates at a speed N. The angular position measured by the angle measuring device 5 is used to control the speed. The tool 4 is brought into contact with the workpiece 6 by a relative movement of the motor spindle 10 in relation to the workpiece. For example, in a milling operation, the desired contour is milled from the workpiece 6. The relative movement can occur along linear drive axes X, Y, Z; additionally, so-called swivel axes A, B can also be provided, so that in the example shown, movement in five axes X, Y, Z, A, B is possible. The movement of the individual axes is controlled via drives 30X, 30Y, 30Z, 30A, 30B (only indicated), which in turn drive corresponding mechanical components (not shown).To determine the position of the respective movement axes X, Y, Z, A, B, additional position measuring devices 20X, 20Y, 20Z, 20A, 20B are provided in the machine tool.

[0033] It should be explicitly pointed out at this point that the movement of the axes is a relative movement, so it is to be considered equivalent whether a drive moves the motor spindle 10 and thus the tool 4, or the workpiece 6.

[0034] It should also be noted that the present invention is also applicable to machine tools in which the workpiece, rather than the tool, is non-rotatably connected to the shaft and rotates with it. Typical examples of this are lathes and grinding machines.

[0035] The motor spindle 10 is equipped with an internal cooling supply (IKZ). For this purpose, a coolant pump 12 is provided in the machine tool, which supplies a coolant 14 to the motor spindle 10 via a coolant line 13. A coolant injector 15 is arranged on the shaft 2 and introduces the coolant 14 into a coolant channel 16, which guides it through the shaft 2 via the tool holder and the tool 4 to the machining area. The machining area is the area of ​​the machine tool in which the (machining) machining of the workpiece 6 takes place. The coolant 14 is supplied at high pressure and serves to cool the machining area, in particular the cutting edges of the tool 4. Depending on the machining operation, the cutting edges are specific (e.g. milling) or indefinite (e.g. grinding) cutting edges.

[0036] When the coolant 14 impacts the workpiece 6, a dynamic pressure is created, which in turn generates a force F that acts on the tool 4 and thus on the shaft 2 of the motor spindle 10. This force F is greater the closer the tool 4 is to the workpiece 6. Its direction depends on the angle at which the coolant 14 impacts the workpiece 6, its geometry, the speed N of the shaft 2, the geometry of the tool 4, etc. Thus, the force F can include components that act in the axial direction of the shaft 2 as well as components that act perpendicular to it.

[0037] In the example shown, the tool 4 is a substantially cylindrically shaped grinding tool, in which machining is carried out through the front side of the tool 4. Accordingly, the coolant 14 also exits from the front side in the direction of movement Z towards the workpiece 6. However, the present invention is not limited to a specific tool type or geometry. Tools with internal cooling are also known, in which machining is carried out by cutting edges arranged on the outer surface, for example milling tools. Here, the coolant 14 exits via corresponding openings (nozzles) in the outer surface of the tool, as in Figure 1 indicated by dashed lines. To achieve a constant coolant supply in this case, several coolant openings are arranged around the circumference, preferably one opening for each cutting edge of the milling cutter.

[0038] A machine tool configured in this way is controlled programmatically by a control unit 100. This comprises a computer with a suitable operating system on which corresponding programs run. The computer has standard peripheral devices such as a monitor, input devices, memory, etc. The control unit 100 can be a so-called numerical control.

[0039] Measured values ​​from the position measuring devices 20X, 20Y, 20Z, 20A, 20B and the angle measuring device 5 are fed to the control unit 100 via suitable signal transmission channels. Suitable signal transmission channels are also provided for controlling the drives 30X, 30Y, 30Z, 30A, 30B and the spindle motor 1 by the control unit 100. The signal transmission channels can be designed to transmit analog or digital signals, depending on requirements. In particular, the signal transmission channels can include digital data interfaces, advantageously serial data interfaces.

[0040] The coolant pump 12 is also controlled via the control unit 100.

[0041] The machine tool is now equipped with a device according to the invention, which comprises a computer 40 and a measuring arrangement 60.

[0042] The measuring arrangement 60 is suitably designed to detect displacements (deflections) of the shaft 2. Displacements always occur when a force acts directly or indirectly on the shaft 2, for example, during the machining of the workpiece 6 by the tool 4, or, as described above, when the tool 4, through which coolant flows, approaches the workpiece 6.

[0043] The measuring arrangement 60 is arranged on the shaft 2. Displacements (deflections) of the shaft 2 can be detected by scanning at least one measuring graduation arranged around the circumference of the shaft 2 and rotating therewith with at least one position sensor that is fixed relative to the shaft 2. Position values ​​are generated that indicate a position of the shaft 2. Since displacements of the shaft 2 cause changes in the position values, conclusions about the displacement of the shaft 2 can be drawn by evaluating the generated position values.

[0044] Since the effect of a deflection of the shaft 2 on the position values ​​depends on the direction from which a force acts on the shaft, particularly advantageous embodiments of the measuring arrangement 60 result when several position sensors are present, in particular two or three position sensors that are arranged offset in the circumferential direction of the shaft 2. If two position sensors are present, they are advantageously arranged at an angular distance of 180°; with three position sensors, a uniform distribution over the circumference of the shaft 2, i.e. an angular distance of 120° between each position sensor, is particularly advantageous.

[0045] A suitable design of a measuring arrangement will be described below based on the Figures 2 and 3 described.

[0046] The measuring arrangement 60 may be a measuring arrangement known from EP 3 591 344 A1, to which explicit reference is made here.

[0047] In the present example, a measuring arrangement 60 is assumed which has six position sensors which generate position values ​​P1, P2, P3, P4, P5, P6.

[0048] The position values ​​P1, P2, P3, P4, P5, P6 of the measuring arrangement 60 are fed to the computer 40 for evaluation via a signal transmission channel 50. It should be noted that, in this document, the term "position value" refers to any type of signal that represents a position of shaft 2. Position values ​​can therefore be analog or digital signals. The processing of the position values ​​in the computer 40 is always digital. Where the digitization, or conversion into digital data words, occurs (already in the position sensors or only in the computer) is irrelevant. Thus, the transmission of the position values ​​P1, P2, P3, P4, P5, P6 to the computer can be analog or digital.It is particularly advantageous if the position sensors already generate digital position values ​​P1, P2, P3, P4 P5, P6 and the transmission of these digital data words takes place via digital interfaces, in particular serial interfaces.

[0049] The computer 40 comprises means that, by evaluating the course of the position values ​​P1, P2, P3, P4, P5, P6 received from the measuring arrangement 60, detect displacements of the shaft 2 and evaluate them with respect to an approach of the tool 4 to the workpiece 6. The result of the evaluation is signaled by an approach signal AS, which is output, for example, to the control unit 100 via an output data channel 51.

[0050] Advantageously, functions of the computer 40 are controllable, for example, by commands received via a command channel 52 from an external unit, in this case, the control unit 100. In the present example, the function of the computer 40 can be started by a START command. Furthermore, it can be provided to supply the computer 40 with parameters PAR via the command channel 52, which it requires to evaluate the position values ​​P1, P2, P3, P4, P5, P6, for example, the rotational speed of shaft 2, parameters of the internal cooling supply, the feed rate of the motor spindle 10, or information about the tool 4 (type, diameter, number of cutting edges, etc.).

[0051] The computer 40 can, as shown, be a standalone device, but it can also be implemented as a module arranged within the control unit 100 (shown in dashed lines). Function modules that execute the functions of the computer 40 can be implemented, partially or completely, by a computer program, for example, executable on a computer (PC) that is included in the control unit 100 or in the computer 40 itself. This applies to all embodiments of computers described in this document.

[0052] The output data channel 51 and the command channel 52 can be designed together as a bidirectional interface, advantageously as a serial interface.

[0053] Figure 2 shows an embodiment of a measuring arrangement 60. It comprises a measuring graduation 61 with two graduation tracks, as well as a total of six position sensors 64, 65, 66, 67, 68, 69.

[0054] The measuring graduation 61 is mounted on the shaft 2 in a rotationally fixed manner, so that it rotates with it. Code elements forming the measuring graduation 61 can be arranged directly on the shaft 2, for example, by magnetization if a magnetic scanning principle is used, or by forming reflective and non-reflective areas with an optical scanning principle. Alternatively, the measuring graduation 61 can be arranged on a graduation carrier, which in turn is connected to the shaft 2 in a rotationally fixed manner.

[0055] Figure 3 shows a suitable measuring graduation 61 with two graduation tracks 62, 63. The first graduation track 62 serves, on the one hand, for angle measurement, i.e., for determining the angle of rotation of shaft 2, and, on the other hand, for determining a displacement of shaft 2 perpendicular to the axial direction. This corresponds to a displacement of the measuring graduation 61 in the Figure 2shown in the drawing plane. The second graduation track 62, on the other hand, serves to detect displacements of shaft 2 in the axial direction.

[0056] The code elements of the first graduation track 62 are arranged one behind the other in the circumferential direction U of the shaft 2. In the example shown, the first graduation track 62 is designed as an incremental graduation track and, in particular, has a magnetic scanning principle, i.e. the graduation track consists of a regular sequence of magnetic positive and negative poles arranged in the circumferential direction U of the shaft 2. The measuring graduation 61 can additionally have a reference track 162, with which a reference position for the inherently relative angle measurement of the incremental graduation track is determined at a defined angular position by a short sequence of magnetic positive and negative poles (reference mark). In this way, an absolute angle measurement is enabled. Instead of the reference track 162, the reference mark can be integrated into the graduation track 62.

[0057] Alternatively, the first graduation track 62 can also be digitally coded, so that an absolute angle measurement is possible at any time, even without a reference track 162. It is particularly advantageous if the code elements of the first graduation track 62 are arranged in the form of a sequential pseudorandom code (PRC).

[0058] The code elements of the second graduation track 63 are arranged in a ring around the circumference of the shaft 2. The measurement of the position or position changes of these code elements allows conclusions to be drawn about displacements of the shaft 2 in its axial direction WZ, as well as about rotations of the shaft 2 transverse to the axial direction (tilting from the Figure 2 shown drawing plane).

[0059] In the example in Figure 2A first group of position sensors 64, 65, 66 is provided for scanning the graduation track 62 and, if applicable, the reference track 162, and a second group of position sensors 67, 68, 69 is provided for scanning the second graduation track 63. The position sensors of the two groups are each arranged at regular angular intervals in the circumferential direction of the shaft 2, i.e., at an angular interval of 120°.

[0060] By scanning the graduation track 62 with the position sensors 64, 65, 66, the angular position of the shaft 2 can be measured. If a force F acts on the shaft 2, it is deflected, ie the center of rotation M shifts (in Figure 2the shifted center of rotation is designated M'). As indicated by the dashed circle, the measuring graduation 61 shifts along with the shaft 2. This affects the angle measurement of the first group of position sensors 64, 65, 66, so that by evaluating the course of the position values ​​P1, P2, P3 of individual position sensors 64, 65, 66 and / or changing the angular difference between the position values ​​P1, P2, P3 of the position sensors 64, 65, 66, conclusions can be drawn about the amount and, if applicable, the direction of the force F acting on the shaft 2.

[0061] If the force F causes not only the displacement of the shaft 2 (and thus the graduation track 62) perpendicular to the axial direction (measurable with the first group of position sensors 64, 65, 66 by scanning the graduation track 62) but also a tilting of the shaft 2, i.e. a rotation transverse to the axial direction, this can be measured with the second group of position sensors 67, 68, 69 by scanning the second graduation track 63.

[0062] The illustrated arrangement of the second group of position sensors 67, 68, 69 for scanning the second graduation track 162 is considered particularly advantageous because, by evaluating the three position values ​​P4, P5, P6, pure movements of the shaft 2 in the WZ axial direction and tilting of the shaft 2 can be clearly distinguished and thus evaluated separately. For example, if only movements (displacements) of the shaft 2 in the WZ axial direction are to be recorded, one of the position sensors 67, 68, 69, arranged at any point on the circumference, is sufficient.

[0063] Frequently, forces F acting on shaft 2 cause both displacements perpendicular to the axial direction, which can be detected with the first group of position sensors 64, 65, 66, and tilting (rotations of the shaft 2) Figure 2shown circle from the drawing plane), detectable with the second group of position sensors 67, 68, 69. The processing of the position values ​​P1, P2, P3, P4, P5, P6 measured by the six position sensors 64, 65, 66, 67, 68, 69 thus allows a comprehensive determination of complex displacements of the shaft 2 which are caused by the action of a force F on the shaft 2.

[0064] The position values ​​P1, P2, P3, P4, P5, P6 generated by the position sensors 64, 65, 66, 67, 68, 69 can be fed to the computer 40 for evaluation via the signal transmission channel 50.

[0065] Figure 4 shows an embodiment of a computer 40. The computer 40 comprises a displacement computer 41, a comparator 43 and a sequence controller 44.

[0066] The displacement computer 41 is suitably designed to continuously determine displacement values ​​VL from the incoming position values ​​P1, P2, P3, P4, P5, P6 during operation. These displacement values ​​indicate the amount of deflection of the shaft 2 from a rest position, and to output them to the comparator 43. The displacement values ​​VL are advantageously generated at constant time intervals. These intervals are selected such that at least one displacement value VL is generated for each revolution of the shaft 2, for example, by calculating an average value of the displacement of the shaft 2 within one revolution.

[0067] As already mentioned above, the generation of the displacement values ​​VL can be based on the evaluation of the course of individual position values ​​P1, P2, P3, P4, P5, P6 and / or the evaluation of the difference between the position values ​​P1, P2, P3, P4, P5, P6 of several position sensors 64, 65, 66, 67, 68, 69.

[0068] A possible course of the displacement values ​​VL is shown in Figure 5 This is an idealized curve in which rotation-dependent fluctuations in the deflection of shaft 2 are not taken into account. Such a curve occurs, for example, if Figure 1 the motor spindle 10 with the tool 4 is moved in the direction of movement Z with active coolant supply at a constant feed rate towards the workpiece 6. In this case, the determination of the displacement values ​​VL is based on the position values ​​P4, P5, P6 measured by the second group of position sensors 67, 68, 69, since the force F acts in the axial direction WZ.

[0069] If the approach takes place in the Figure 1indicated direction of movement X, the determination of the displacement values ​​VL can, however, be based on the evaluation of the position values ​​P1, P2, P3 measured by the first group of position sensors 64, 65, 66, since the forces resulting from the coolant supply predominantly cause a displacement of the shaft 2 perpendicular to the axial direction WZ.

[0070] In general, to determine the displacement values ​​VL, depending on the boundary conditions of the approach (direction of approach, geometry of the workpiece, design of the internal cooling supply, ...), suitable combinations of position values ​​P1, P2, P3, P4, P5, P6 of the position sensors 64, 65, 66, 67, 68, 69 can be selected.

[0071] As in Figure 5As shown, the approach of the tool 4 to the workpiece 6 can be divided into three areas: an idle area I, an approach area II, and a machining area III. The approach takes place with the internal cooling supply activated.

[0072] In the idle range I (up to a position Z1 or a time t1) the coolant supply does not yet have an effect, therefore no or only a negligible, largely constant displacement of shaft 2 occurs.

[0073] In approach zone II (between position Z1 and position Z2, or time t1 and time t2), there is an increase in the displacement of shaft 2, the cause of which is due to a dynamic pressure that arises when coolant 14 strikes or reflects from workpiece 6. The force F acting on tool 4 increases the further the tool 4 approaches workpiece 6.

[0074] In machining area III (from position Z2, or time t2), contact finally occurs between tool 4 and workpiece 6, thus resulting in machining. Force F and the forces occurring during machining of workpiece 6 overlap, so that the illustrated curve of the displacement values ​​VL exhibits a jump in the transition between approach area II and machining area III. In other words, the impact of tool 4 on workpiece 6 causes a sudden increase in the curve of the displacement values ​​VL.

[0075] Optionally, the displacement calculator 41 can additionally calculate an angular position POS from the position values ​​P1, P2, P3 and output it to the comparator 43, so that in addition to the magnitude, the direction of the deflection of the shaft 2 can also be evaluated. Furthermore, it can be provided to output the angular position POS to the control unit 100 via the output data channel 51, so that the angle measuring device 5 can be dispensed with if necessary.

[0076] The displacement values ​​VL are fed to the comparator 43. By comparing the displacement values ​​VL received from the displacement computer 41 with a threshold value S, the comparator generates an approach signal AS that indicates whether the threshold value S has been reached or exceeded, and outputs the approach signal AS to the control unit 100 via the output data channel 51.

[0077] The threshold value S is now selected such that it is reached or exceeded in approach zone II, namely at an approach position ZA at which the tool 4 is already close to the workpiece 6 without touching it, i.e., before the machining zone III is reached. The threshold value S can be stored in the comparator 43 or supplied to the computer 40 via the command channel 52.

[0078] The threshold value S can be determined in a test run in which all three areas are traversed. Since this involves machining, it is advantageous to use a test workpiece as workpiece 6.

[0079] In a preferred embodiment, the computer 40 for determining the threshold value S further comprises a threshold value determiner 42. The displacement values ​​VL are supplied to this threshold value determiner, as well as a test start command TEST, which in turn is supplied to the computer from the control unit 100 via the command channel 52. The threshold value determiner 42 is now suitably designed to detect from the course of the displacement values ​​VL whether the tool 4 is in the idle range I, the approach range II, or the machining range III. In particular, the threshold value determiner 42 detects the transition (jump) from the approach range II to the machining range III and, based on this transition, determines the approach position ZA and the associated displacement value VL as the threshold value S.After the threshold value S has been determined, the threshold value determiner 42 outputs a test stop signal STP to the control unit 100 via the output data channel 51, which can then immediately stop the movement of the tool 4 in the direction of the workpiece 6 (in the direction of movement Z) and thus the machining.

[0080] The processes in computer 40 are controlled by the sequence controller 44, which receives the start command START, the test start command TEST, and, if applicable, the PAR parameter via command channel 52. Control is carried out via control signals STRG, which are output to the function modules (displacement computer 41, threshold value determiner 42, comparator 43). The control signals STRG can also include feedback from the function modules to the sequence controller 44.

[0081] After the start command START is received, the sequence control 44 initiates the following process steps: Continuous determination of displacement values ​​VL from position values ​​P1, P2, P3, P4, P5, P6 at constant time intervals in the displacement computer 41 and output of the displacement values ​​VL to the comparator 43. Comparison of displacement values ​​VL arriving from the displacement computer 41 with the threshold value S in the comparator 43 and formation and output of the approach signal AS therefrom.

[0082] Instead of the start command START, for example, switching on a supply voltage of the computer 40 can also be interpreted as a start command.

[0083] If no threshold value S is available, the following procedure for determining threshold values ​​can be carried out in advance, which is started with the test start command TEST: Continuous determination of displacement values ​​VL from position values ​​P1, P2, P3, P4, P5, P6 at constant time intervals in the displacement computer 41 and output of the displacement values ​​VL to the threshold value determiner 42. Formation of a threshold value S of the displacement of shaft 2 in the threshold value determiner 42 by determining the transition from approach area II to processing area III and, based on this transition, determining the approach position ZA and the associated displacement value VL as the threshold value S. Output of the threshold value S to the comparator 43.

[0084] In a simplified embodiment, the threshold value S is a constant value stored in the comparator 43.

[0085] The movement of the drives required to carry out the described methods, the rotation of the shaft 2, the activation of the internal cooling supply, as well as the interaction with the computer 40 can be controlled by a computer program executable on the control unit 100.

[0086] As already described in the introduction, the exact position of a newly machined workpiece 6, which is clamped in the working area of ​​the motor spindle 10 by means of clamping devices, is still unknown. Only the rough position and orientation of the workpiece, which are specified by the clamping devices, are known. The dimensions of the workpiece 6 (workpiece blank) are also known. Before machining the workpiece contour, it is necessary to determine the exact position of the workpiece 6. A preferred method is described below using the Figure 5 shown signal diagram in conjunction with the Figure 4The following is described by the computer 40 shown: In the starting position, the motor spindle 10 is located at a position in the idle range I. Initially, the control unit 100 controls the spindle motor 1 so that it rotates and activates the internal cooling supply. Subsequently, the control unit 100 signals the drives 20X, 20Y, 20Z, 20A, 20B required for the desired direction of movement to move the motor spindle 10 toward the workpiece 6 and sends the start command START to the computer 40. The movement occurs at a constant feed rate.

[0087] The computer 40 now carries out the Figure 4 described method, ie the displacement computer 41 continuously determines displacement values ​​VL and the comparator 43 compares these with the threshold value S. If the course of the displacement values ​​VL reaches or exceeds the threshold value S, the approach signal AS is transmitted to the control unit 100.

[0088] After the arrival of the approach signal AS, the control unit 100 stores the current position values ​​of at least the position measuring devices 30X, 30Y, 30Z, 30A, 30B, which are influenced by the movement of the motor spindle by the drives 20X, 20Y, 20Z, 20A, 20B, as the position of the workpiece 6 at the selected approach point and stops the drives or reverses the direction of movement so that the tool 4 and the workpiece 6 move away from each other again until the motor spindle 10 or the tool 4 is again in the idle range I.

[0089] In practice, this process is carried out repeatedly at different positions of the workpiece 6 until a sufficient number of approximation points (workpiece coordinates) are available to know the exact position of the workpiece 6, or the workpiece blank, and to be able to start the actual machining.

[0090] Alternatively, the control unit 100 can also proceed directly to machining the workpiece 6 after reaching an approach point. For this purpose, the feed rate is adjusted, in particular reduced, if necessary.

[0091] If no threshold values ​​S are yet available, for example at the start of series production, the control unit 100 can determine them using the method for determining threshold values.

[0092] In this case, too, the motor spindle 10 is initially located at a position in the idle range I. The control unit 100 controls the spindle motor 1 so that it rotates and activates the internal cooling supply. The control unit 100 then signals the drives 20X, 20Y, 20Z, 20A, and 20B required for the desired direction of movement to move the motor spindle 10 toward the workpiece 6 and sends the test start command TEST to the computer 40.

[0093] The computer 40 now carries out the Figure 4 The method described for determining threshold values ​​is carried out, i.e., the displacement computer 41 continuously determines displacement values ​​VL and feeds them to the threshold value determiner 42. This determines the current threshold value S from the course of the displacement values ​​VL and outputs it to the comparator 43. Subsequently, the threshold value determiner 42 transmits the test stop command STP to the control unit 100.

[0094] After the test stop command STP arrives, the control unit 100 stops the drives or reverses the direction of movement so that tool 4 and workpiece 6 move away from each other again until the motor spindle 10 or the tool 4 are again in the idle range I.

[0095] This process is also carried out repeatedly at different positions of the workpiece 6 until threshold values ​​S are available for a sufficient number of approach points (workpiece coordinates) in order to be able to determine the exact position of the workpiece 6 or the workpiece blank.

[0096] Figure 6 shows a further embodiment of a computer 240. It further comprises the displacement computer 41 and the sequence control 44. In contrast to the previous embodiments, the computer 240 now has a differentiator 246 which differentiates the course of the displacement values ​​VL, for example by calculating difference quotients DQ of successively arriving displacement values ​​VL and the time interval between their arrival at the differentiator 246 and outputting them to a comparator 243.

[0097] Comparator 243, in turn, compares incoming difference quotients DQ with a suitable threshold value S, which is stored in a memory provided for this purpose in comparator 243. If a difference quotient DQ exceeds the threshold value S, comparator 243 signals this by outputting the approach signal AS.

[0098] Figure 7 shows the course of the displacement values ​​VL in connection with the threshold value S, which in this example indicates a gradient of the course of the displacement values ​​VL (or a difference quotient DQ) at the approach position ZA.

[0099] The computer 240, analogous to the computer 40, can include a threshold value determiner 242 to determine threshold values ​​S in conjunction with the control unit 100. For this purpose, the displacement values ​​VL and / or the difference quotients DQ are fed to the threshold value determiner 242. The graphs formed by the sequences of displacement values ​​VL or difference quotients DQ each exhibit a sudden increase at the transition from the approach area II to the processing area III, which is detected by the threshold value determiner 242. Starting from this position, the gradient of the displacement values ​​VL at the approach position ZA (the difference quotient) is determined as the threshold value S.

[0100] The determination of threshold values ​​S is controlled via the test start command TEST and the test stop signal STP.

[0101] Thus, computer 240 can replace computer 40.

[0102] Figure 8shows a further embodiment of a computer 340. In addition to the (optional in this example) displacement computer 41 and the sequence control 44, it includes a frequency analyzer 347.

[0103] The frequency analyzer 347 is designed to evaluate the course of displacement values ​​VL received from the displacement computer 41 in the frequency domain. Mathematical methods such as Fourier analysis (FFT, DFT, Goertzel algorithm, etc.), order analysis, or adaptive filtering can be used here.

[0104] An evaluation of the displacement values ​​VL in the frequency domain is particularly advantageous when a tool 4 is used in which the coolant 14 exits via corresponding openings (nozzles) in the outer surface of the tool 4, for example in a milling cutter. If the tool 4 approaches the workpiece 6 while the shaft 2 is rotating, the coolant flow from each nozzle causes a rotationally periodic deflection of the shaft 2. By specifically monitoring the spectral power density of frequency bands, which depends on the speed of the shaft 2 and the number of nozzles, the approach between the tool 4 and the workpiece 6 can be detected. The monitoring can in turn be carried out by comparison with suitable threshold values ​​S. The result of the evaluation can in turn be output as an approach signal AS.

[0105] For this embodiment, it is advantageous if a plurality of displacement values ​​VL are generated for each revolution of the shaft 2 in order to reliably detect the maxima of the deflection of the shaft 2 caused by the individual nozzles.

[0106] Optionally, the displacement calculator 41 can be omitted in this embodiment, so that the position values ​​P1, P2, P3 are fed directly to the frequency analyzer 347. This is based on the knowledge that, when the shaft 2 rotates, deflections of the shaft 2 result in a variation in the position difference between successively measured position values ​​in sequences of position values ​​P1, P2, P3, P4, P5, P6 from the position sensors 64, 65, 66, 67, 68, 69, which are measured at equal time intervals. This variation in the position difference is, in turn, detectable in the frequency spectrum.

[0107] In any case, the frequency analyzer 347 can also be suitably designed to determine threshold values ​​S, again based on the determination of the transition position from the approach area II to the processing area III.

[0108] The computer 340 can therefore also replace the computer 40.

[0109] Figure 9 shows a further embodiment of a computer 440. In addition to the (optional) relocation computer 41 and the sequence control 44, it includes an AI module 448.

[0110] The AI ​​module 448 is suitably designed to evaluate the progression of displacement values ​​VL received from the displacement computer 41 using artificial intelligence methods, for example, by comparing them with previously determined patterns ("machine teaching"), and thus detect the approach of the tool 4 to the workpiece 6. These patterns correspond to the threshold values ​​S of the previous examples and can be determined in test runs in conjunction with the control unit 100. The AI ​​module is advantageously self-learning, so that the detection of approach processes is continuously improved.

[0111] In a variant of this embodiment, the displacement computer 41 can be omitted, so that here too, as in the previous example, the position values ​​P1, P2, P3, P4, P5, P6 are fed directly to the AI ​​module 448 and their temporal progression is evaluated.

[0112] If the approach position ZA is detected, this is again signaled with the approach signal AS.

[0113] This computer 440 can also replace computer 40.

[0114] The present invention is not limited to the described embodiments, but can also be carried out alternatively by a person skilled in the art within the scope of the claims.

Claims

1. Device for detecting when a tool (4) approaches a workpiece (6) in a machine tool in which the tool (4) and the workpiece (6) are movable relative to one another and the tool (4) or the workpiece (6) is connected non-rotatably to a shaft (2), wherein the tool (4) comprises a coolant channel (16) through which a coolant (14) is suppliable to a machining area in which the machining of the workpiece (6) by the tool (4) takes place, encompassing a measuring arrangement (60), having a measuring scale (61) that is arranged non-rotatably on the shaft (2), and at least one position sensor (64, 65, 66, 67, 68, 69) that is arranged statically in relation to the shaft (2), and also a computer (40, 240, 340, 440), wherein • the at least one position sensor (64, 65, 66, 67, 68, 69) is suitably configured to scan the measuring scale (61) and to generate therefrom position values (P1, P2, P3, P4, P5, P6) that indicate a position of the shaft (2), and • the position values (P1, P2, P3, P4, P5, P6) can be supplied to the computer (40, 240, 340, 440), which comprises means that, as a result of evaluation of a trend in the position values (P1, P2, P3, P4, P5, P6) when the tool (4) is approaching the workpiece (6), are able to detect that the tool (4) is in an approach area (II), with reference to the workpiece (6), in which a displacement of the shaft (2) occurs that results from the backpressure of the coolant stream impinging on the workpiece (6), and are able to use an approach signal (AS) to signal when the tool (4) reaches an approach position (ZA), with reference to the workpiece (6), in which the tool (4) is close to the workpiece (6) without touching said workpiece.

2. Device according to Claim 1, wherein the measuring scale (61) comprises a first division track (62), the code elements of which are arranged in the circumferential direction of the shaft (2).

3. Device according to Claim 2, wherein the measuring scale (61) further comprises a second division track (62), the code elements of which are arranged in a ring around the circumference of the shaft (2).

4. Device according to one of the preceding claims, wherein the means in the computer (40, 140, 240, 340, 440, 540) encompass a displacement computer (41) that is able to use the position values (P1, P2, P3, P4, P5, P6) to determine displacement values (VL) that indicate a deflection of the shaft (2) from a resting position.

5. Device according to Claim 4, wherein the means in the computer (40, 240, 340, 440) further encompass: • a comparator (43) that, as a result of comparison of currently available displacement values (VL) with a threshold value (S), can be used to detect when the approach position (ZA) is reached, and / or • a differentiator (246), configured to calculate the difference quotient (DQ) of successively available displacement values (VL), and a comparator (243) that, as a result of comparison of the difference quotients (DQ) with a threshold value (S), can be used to detect when the approach position (ZA) is reached, and / or • a frequency analyser (347), which, as a result of evaluation of the trend in the displacement values (VL) in the frequency domain, can be used to detect when the approach position (ZA) is reached, and / or • an AI module (448), which, as a result of evaluation of the trend in the displacement values (VL) using artificial intelligence methods, in particular using pattern recognition, can be used to detect when the approach position (ZA) is reached.

6. Device according to one of Claims 1 to 4, wherein the means in the computer (340, 440) encompass • a frequency analyser (347), which, as a result of evaluation of the trend in the position values (P1, P2, P3, P4, P5, P6) in the frequency domain, can be used to detect when the approach position (ZA) is reached, and / or • an AI module (448) that, as a result of evaluation of the trend in the position values (P1, P2, P3, P4, P5, P6) using artificial intelligence methods, in particular using pattern recognition, can be used to detect when the approach position (ZA) is reached.

7. Device according to one of the preceding claims, wherein the means in the computer (40, 240) further encompass a threshold value determiner (42, 242) that, when the tool (4) is approaching the workpiece (6), can identify a transition from the approach area (II) to a machining area (III), in which the workpiece (6) undergoes machining, and can determine a threshold value (S) therefrom.

8. Method for detecting when a tool (4) approaches a workpiece (6) in a machine tool in which the tool (4) and the workpiece (6) are movable relative to one another and the tool (4) or the workpiece (6) is connected non-rotatably to a shaft (2), wherein the tool (4) comprises a coolant channel (16) through which a coolant (14) is suppliable to a machining area in which the machining of the workpiece (6) by the tool (4) takes place, and the machine tool encompasses a measuring arrangement (60), having a measuring scale (61) that is arranged non-rotatably on the shaft (2), and at least one position sensor (64, 65, 66, 67, 68, 69) that is arranged statically in relation to the shaft (2), and also a computer (40, 240, 340, 440), wherein • the measuring scale (61) is scanned by the at least one position sensor (64, 65, 66, 67, 68, 69) and position values (P1, P2, P3, P4, P5, P6) that indicate a position of the shaft (2) are generated therefrom, and • the position values (P1, P2, P3, P4, P5, P6) are supplied to the computer (40, 240, 340, 440), which comprises means that, as a result of evaluation of a trend in the position values (P1, P2, P3, P4, P5, P6) when the tool (4) is approaching the workpiece (6), are used to detect that the tool (4) is in an approach area (II), with reference to the workpiece (6), in which a displacement of the shaft (2) occurs that results from the backpressure of the coolant stream impinging on the workpiece (6), and the means use an approach signal (AS) to signal when the tool (4) reaches an approach position (ZA), with reference to the workpiece (6), in which the tool (4) is close to the workpiece (6) without touching said workpiece.

9. Method according to Claim 8, wherein the means in the computer (40, 140, 240, 340, 440, 540) encompass a displacement computer (41) that is used to use the position values (P1, P2, P3, P4, P5, P6) to determine displacement values (VL) that indicate a deflection of the shaft (2) from a resting position.

10. Method according to Claim 9, wherein the means in the computer (40, 240, 340, 440) further encompass: • a comparator (43) that, as a result of comparison of currently available displacement values (VL) with a threshold value (S), is used to detect when the approach position (ZA) is reached, and / or • a differentiator (246), which is used to calculate difference quotients (DQ) of successively available displacement values (VL), and a comparator (243) that, as a result of comparison of the difference quotients (DQ) with a threshold value (S), is used to detect when the approach position (ZA) is reached, and / or • a frequency analyser (347), which, as a result of evaluation of the trend in the displacement values (VL) in the frequency domain, is used to detect when the approach position (ZA) is reached, and / or • an AI module (448), which, as a result of evaluation of the trend in the displacement values (VL) using artificial intelligence methods, in particular using pattern recognition, is used to detect when the approach position (ZA) is reached.

11. Method according to either of Claims 8 to 9, wherein the means in the computer (340, 440) encompass • a frequency analyser (347), which, as a result of evaluation of the trend in the position values (P1, P2, P3, P4, P5, P6) in the frequency domain, are used to detect when the approach position (ZA) is reached, and / or • an AI module (448) that, as a result of evaluation of the trend in the position values (P1, P2, P3, P4, P5, P6) using artificial intelligence methods, in particular using pattern recognition, is used to detect when the approach position (ZA) is reached.

12. Method according to one of Claims 8 to 11, wherein the method is started by a start command (START) that is supplied to the computer (40, 240) via a command channel (52).

13. Method according to one of Claims 8 to 12, wherein the means in the computer (40, 240) further encompass a threshold value determiner (42, 242) that is used in a test run when the tool (4) is approaching the workpiece (6) to identify a transition from the approach area (II) to a machining area (III), in which the workpiece (6) undergoes machining, and to determine a threshold value (S) therefrom.

14. Method according to Claim 13, wherein the test run is started by a test start command (TEST) that is supplied to the computer (40, 240) via the command channel (52).

15. Machine tool, equipped with a device according to one of Claims 1 to 7.