Device and method for detecting contact between tool and workpiece

Abstract

To provide a device and a method for detecting contact between a tool 4 and a workpiece 6 in a machine tool.SOLUTION: A device comprises: one measuring instrument 60 having a measuring scale 61 disposed in a shaft 2 so as not to rotate; at least one position sensor 64 fixed to the shaft 2; and one data processor 40, The tool 4 and the workpiece 6 are movable relative to each other. The tool 4 or the workpiece 6 is coupled to the shaft 2 so as not to rotate. The at least one position sensor 64 is configured to scan the measuring scale 61 and generate a position value P1 indicating the position of the shaft 2 through the scanning. The position value P1 is supplied to the data processor 40. The data processor 40 has means for analyzing the shift of the position value P1 to detect contact between the tool 4 and the workpiece 6 and transmitting the analysis result in accordance with the status of a displacement signal VS.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a device for detecting the contact between a tool and a workpiece in a machine tool according to claim 1, and to a corresponding method according to claim 7. The present invention can preferably be used in numerically controlled machine tools for forming workpieces by machining, in particular by milling, turning and grinding.

Background Art

[0002] The most widespread manufacturing method for workpieces manufactured by machines is based on machining, i.e., cutting. In this case, the material is appropriately cut from a so-called blank using a tool. As a result, a product having the desired shape and function is finally manufactured. In order to cut the material, the workpiece comes into contact with the tool. The tool has a structurally special cutting edge or a typical cutting edge. Examples of tools having a structurally special cutting edge are milling tools, drill tools or cutting tools, and an example of a tool having a typical cutting edge is a grinding machine. Regarding the cutting process, before one of the plurality of objects - the tool or the workpiece - is brought into contact with the other object, the one object is often rotated.

[0003] In order to move at least one of the plurality of objects, the machining is controlled by a computer that controls an electric drive device under the execution of a manufacturing program. In order to detect the actual position of the moved object, a position measuring device - a rotary encoder or a length measuring device - is provided. A plurality of measured values of the position measuring device are continuously supplied to the computer. The computer is called a CNC control device, and the machine tool for performing the machining is called a CNC machine.

[0004] A so-called spindle is provided to rotate the object in question. In this case, an electric motor drives the shaft—directly or indirectly—while the object is fixed to the shaft. A rotary encoder is provided to measure the rotation angle and / or rotational speed of the spindle. Furthermore, measuring devices capable of measuring the displacement of the shaft from its ideal position are known. European Patent Application Publication No. 3591344 describes such a measuring device.

[0005] A clamping device is provided to secure the workpiece for the purpose of machining. Since the new workpiece (blank) is clamped with a large tolerance and there may be variations in the dimensions of the blank, the precise position and dimensions of the newly clamped blank must be measured before the start of the machining process. For this purpose, a so-called switch is used. The switch is moved from the tool position toward the workpiece, and when the switch makes contact with the workpiece, it outputs a switch signal. The CNC control unit analyzes the switch signal and detects the position and dimensions of the workpiece by making contact at multiple locations on the blank (sampling). Only then can the actual machining process begin.

[0006] The drawback of this method is the time and effort involved. This is because, first, the tool must be replaced with a switch, and then returned to the original tool after the measurement process. Another drawback is particularly when cast parts are used as blanks. Often, slag remains on the surface of the cast part. The slag and the actual (metallic) surface cannot be distinguished by the switch, resulting in measurement errors. As a result, for example, less material than desired is removed during the first machining step. On the other hand, the total machining time is increased (the possible machining depth is limited only by the metal, not by the slag). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] European Patent Application Publication No. 3591344 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a device that allows for easy identification of the position of a workpiece in a machine tool. [Means for solving the problem]

[0009] This problem is solved by the apparatus described in claim 1.

[0010] In this case, a device is proposed for detecting contact between a tool and a workpiece in a machine tool. This device comprises a measuring instrument having a measuring scale positioned so as not to rotate on the axis, at least one position sensor fixedly positioned relative to the axis, and a data processor, wherein the tool and the workpiece are relatively movable relative to each other, and the tool or workpiece is coupled to the axis so as not to rotate. The at least one position sensor is configured to scan the measurement scale and generate a position value indicating the position of the axis from the scan. The position value is supplied to the data processor, which has means for detecting contact between the tool and the workpiece by analyzing the changes in the position value and transmitting the results of the analysis by the status of the displacement signal.

[0011] Furthermore, an object of the present invention is to provide a method for easily determining the position of a workpiece in a machine tool.

[0012] This problem is solved by the method described in claim 7.

[0013] In this case, a method is proposed for detecting contact between a tool and a workpiece in a machine tool using a device. In this method, the device comprises a measuring instrument having a measuring scale positioned so as not to rotate on the axis, at least one position sensor fixedly positioned on the axis, and one data processor, wherein the tool and the workpiece are movable relative to each other, and the tool or the workpiece is coupled to the axis so as not to rotate. The measurement scale is scanned by the at least one position sensor, and a position value indicating the position of the axis is generated from the scan. The position value is supplied to the data processor, which has means to analyze the change in the position value, thereby detecting contact between the tool and the workpiece, and transmits the result of the analysis as a displacement signal status.

[0014] Preferably, the measuring scale has one scale track, and a plurality of code elements on this scale track are arranged circumferentially around the axis, and a position sensor can measure a position value indicating the angular position of the axis by scanning these code elements. In a preferred configuration, three position sensors are provided to scan the scale track, arranged at appropriate intervals circumferentially around the axis, for example, at angular intervals of 120° each. In this case, the runout of the axis affects the angular position, which occurs as a change in the angular difference determined by the arrangement of these position sensors, measured by these position sensors according to the direction of the runout. The value and direction of the runout of the axis can then be calculated from the measured angular position.

[0015] In addition to this scale track, the measuring scale may have a second scale track. Multiple code elements of this second scale track are arranged in a ring around the circumference of the axis. To scan these code elements, three position sensors may be provided at appropriate intervals around the circumference of the axis, similarly at 120° intervals in the illustrated example. From scanning the second measuring scale, the runout of the axis can be measured in the axial direction of the axis. Thus, the axial rotation of the axis, i.e., the tilt position of the axis relative to the unloaded position of the axis, can be measured. This tilt position is generated by the inclination of the multiple code elements in the ring relative to these position sensors.

[0016] The position values ​​of these position sensors, caused by the force acting on the axis, are supplied to a displacement calculation unit in the data processor, which continuously generates at least one displacement value that serves as an indicator of the axis's runout. Appropriate means are provided within the data processor to analyze the changes in the displacement value. A particularly preferred embodiment can be obtained by the following means.

[0017] In a preferred first embodiment, the means includes a threshold determination unit configured to determine a threshold value for the input displacement value during no-load operation and without contact between the tool 4 and the workpiece, and a comparison unit for comparing the threshold value with the actual input displacement value. In this case, the threshold determination unit is configured to generate one threshold value at the start of the method or to generate a series of new threshold values. As a result, the effect of displacement value drift is reduced. In the simplest configuration, the threshold determination unit generates only pre-determined and stored threshold values.

[0018] In a preferred second embodiment, the means includes a differentiation unit configured to generate a differential quotient from a series of input displacement values ​​and the time interval between inputs of the input displacement values, and a comparison unit for comparing the differential quotient with a pre-stored threshold.

[0019] In another preferred embodiment, it has a frequency analysis unit that analyzes the transition of the displacement value in the frequency domain. By appropriately analyzing the power spectral density of each frequency band measured by the rotational speed of the axis and the number of cutting edges of the tool, the contact between the tool and the workpiece can be estimated.

[0020] In a variation of this embodiment, the position value of at least one position sensor may be directly supplied to the frequency analysis unit. As a result, the displacement calculation unit can be omitted.

[0021] In another preferred embodiment, the means has a KI module that analyzes the transition of the displacement value by an artificial intelligence means, particularly by pattern recognition. This embodiment is particularly beneficial when the displacement value has statistically large fluctuations.

[0022] This embodiment can also be modified such that the position value of at least one position sensor is directly supplied to the KI module. As a result, the displacement calculation unit becomes unnecessary.

[0023] To enable cooperation between the data processor and another component, for example, the control device of a machine tool, it is beneficial for the data processor to include a command channel. Commands and optionally parameters can be supplied to the data processor via the command channel. The command can be, for example, a start command to initiate the method of the present invention. The parameters can be data that define boundary conditions for analyzing the position value within the data processor, such as the rotational speed of the axis, information about the tool (type of cutting edge, diameter, number...), etc.

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

[0025] Even more preferred embodiments of the device or method of the present invention can be read from the respective dependent claims and the embodiments described below.

Brief Description of the Drawings

[0026] [Figure 1] The apparatus of the present invention connected to a component of a machine tool is shown. [Figure 2] An embodiment of the measuring instrument of the present invention is shown. [Figure 3] A scale suitable for the measuring instrument of FIG. 2 is shown. [Figure 4] A first embodiment of the data processor of the apparatus of the present invention is shown. [Figure 5] A first embodiment for using the apparatus of the present invention connected to a machine tool is shown. [Figure 6] Another embodiment of the data processor of the apparatus of the present invention is shown. [Figure 7] Another embodiment for using the apparatus of the present invention connected to a machine tool is shown. [Figure 8] Another embodiment of the data processor of the apparatus of the present invention is shown. [Figure 9] Another embodiment for using the apparatus of the present invention connected to a machine tool is shown. [Figure 10] Another embodiment of the data processor of the apparatus of the present invention is shown. [Figure 11] Another embodiment of the data processor of the apparatus of the present invention is shown. [Figure 12] Another embodiment of the measuring instrument of the present invention is shown. [Figure 13] A scale suitable for the measuring instrument according to FIG. 12 is shown. [Figure 14] Another embodiment of the data processor of the apparatus of the present invention is shown.

Embodiments for Carrying Out the Invention

[0027] In the following description of the preferred embodiments of the present invention, the reference numerals of the components and functional groups shown in the drawings are also applied in the description of the following drawings.

[0028] Figure 1 shows the apparatus of the present invention connected to the components of a machine tool (in this case, a 5-axis machining center). The apparatus has one spindle motor 10 and one drive unit and one encoder for each moving axis. A control device 100 is provided to control the moving process, in particular for machining the workpiece 6.

[0029] The central component of the spindle motor 10 is the spindle motor 10 having a shaft 2. A tool 4 (e.g., a cutting tool) is coupled to the shaft 2 at its end so as not to rotate. As a result, the tool 4 rotates together with the shaft 2. A tool housing (e.g., a hollow shank taper) (not shown) is provided to fix the tool 4 to the shaft 2. Similarly, an angle measuring device 5 is mechanically coupled to the shaft 2. This coupling is performed by a mechanical coupling (not shown) that connects the rotatable shaft of the angle measuring device 5 to the shaft 2. Thus, the rotational position and / or number of rotations of the repeated rotations of the shaft 2 can be measured by the angle measuring device 5. The shaft 2 is supported within the housing of the spindle motor 1 by, for example, roller bearings.

[0030] To machine the workpiece 6, the shaft 2 of the spindle motor 1 is rotated at a rotational speed N. The angular position measured by the angle measuring instrument 5 is used to control the rotational speed. The tool 4 contacts the workpiece 6 through the relative movement of the spindle motor 10 relative to the workpiece 6. Thus, for example during milling, the desired contour is cut from the workpiece 6. This relative movement can be performed along linear drive axes X, Y, Z. In addition, so-called rotational axes A and B may also be provided. As a result, in the illustrated example, movement in the directions of five movement axes X, Y, Z, A, and B is possible. The movement of each of these axes is controlled by drive units 30X, 30Y, 30Z, 30A, and 30B (shown only schematically), which similarly drive the corresponding machine components (not shown). To detect the positions of each of the respective movement axes X, Y, Z, A, and B, separate encoders 20X, 20Y, 20Z, 20A, and 20B are provided on the machine tool.

[0031] In this case, the movement of these axes is relative, and therefore, it should be noted that in any case, the drive device moves the spindle motor 10, i.e., the tool 4 or the workpiece 6.

[0032] Furthermore, the present invention can be used not only with tools, but also with machine tools in which the workpiece 6 is coupled to the shaft so as not to rotate, and which rotate together with the shaft. Typical examples of such machine tools are lathes and grinding machines.

[0033] The machine tool configured in this way is programmed and controlled by a control device 100. This control device 100 is configured as a computer having a drive system on which the corresponding program is executed. This computer has general peripheral devices such as a monitor, input devices, and memory devices. The control device 100 may also be a so-called numerical control device.

[0034] The measured values ​​from encoders 20X, 20Y, 20Z, 20A, and 20B, and the measured values ​​from the angle measuring instrument 5 are transmitted via an appropriate signal transmission channel. To control the drive units 30X, 30Y, 30Z, 30A, and 30B and the spindle motor 1 by the control device 100, the signal transmission channel may be configured to transmit analog or digital signals as needed. In particular, the signal transmission channel may be a digital data interface, preferably a serial data interface.

[0035] In this case, the apparatus of the present invention, which has a data processor 40 and a measuring instrument 60, is installed in the machine tool.

[0036] The measuring instrument 60 is appropriately configured to detect the displacement (runout) of the axis 2. Using the measuring instrument 60, a position value indicating the position of the axis 2 can be generated by scanning at least one measuring scale that is mounted around the axis 2 and rotates with the axis 2, using at least one position sensor that is fixedly positioned relative to the axis 2. When the axis 2 is displaced, the position value changes. As a result, the displacement of the axis 2 can be calculated by analyzing the generated position value.

[0037] Since the effect of the runout of axis 2 on the position value depends on the direction in which the force acts on the axis, a particularly preferred embodiment of the measuring instrument 60 is obtained when there are multiple position sensors, especially two or three, that are offset in the circumferential direction of axis 2. When there are two position sensors, these position sensors are preferably spaced at an angle of 180°. In the case of three position sensors, an even distribution across the circumference of axis 2, i.e., an angle of 120° between each of these position sensors, is very beneficial.

[0038] The measuring instrument 60 may be any measuring instrument known from European Patent Application Publication No. 3591344, which clearly describes the measuring instrument.

[0039] In this example, three position sensors are provided. A suitable measuring instrument 60 will be described in detail below in relation to Figures 2 and 3.

[0040] The position values ​​P1, P2, and P3 generated by the three position sensors of the measuring instrument 60 are transferred to the data processor 40 via the signal transmission channel 50 for analysis. It should be noted that, within the scope of this specification, the term "position value" means any kind of signal representing the position of axis 2. Therefore, the position value may be an analog signal or a digital signal. In all circumstances, the position value is processed digitally within the data processor 40. In this case, it is not important where the digitization or conversion to digital data words is performed (whether it is already performed within the position sensor or performed for the first time within the data processor). Therefore, the position values ​​P1, P2, and P3 can be transmitted to the data processor in analog or digital form. It is particularly preferable that the position sensor already generates the position values ​​P1, P2, and P3 and transmits the digital data words via a digital interface, especially a serial interface.

[0041] The data processor 40 has means for detecting contact between the tool 4 and the workpiece 6 by analyzing the transitions of position values ​​P1, P2, and P3 generated from the measuring instrument 60. The result of this analysis is signaled by the state of a displacement signal VS. This displacement signal VS is output to the control device 100 in this example via an output data channel 51. The output data channel 51 may be a simple signal cable to which the state of the displacement signal VS is output as a voltage level. However, the output data channel 51 may be configured as a digital data interface. The state of the displacement signal VS is output via the digital data interface as a data word or as part of a data word.

[0042] Preferably, the functions of the data processor 40 can be controlled by instructions generated from an external device, for example, via the instruction channel 52, in this case from the control device 100. In this example, the functions of the data processor 40 can be started by the start instruction START. Furthermore, it may be proposed that information (parameters PAR) is transferred to the data processor 40 via the instruction channel 52. The data processor 40 requires this information (parameters PAR), such as the rotational speed of the shaft 2, the feed rate of the spindle motor 10, or information about the tool 2 (type, diameter, number of cutting teeth, etc.), in order to analyze the position values ​​P1, P2, P3.

[0043] The data processor 40 may be a standalone device as shown in the figure. The data processor 40 may also be configured as a module located within the control unit 100 (indicated by dashed lines). Some or all of the functional modules that perform the functions of the data processor 40 can be implemented by a computer program, for example, on a computer (PC) included in the control unit 100 or the data processor 40. This data processor configuration is valid for all data processor configuration examples described herein.

[0044] The output data channel 51 and the instruction channel 52 may be configured as a bidirectional interface, preferably as a serial interface.

[0045] Figure 2 shows an embodiment of the measuring instrument 60. The measuring instrument 60 comprises one measuring scale 61 having at least one scale track and three position sensors 64, 65, and 66.

[0046] The measuring scale 61 is positioned so as not to rotate on the axis 2. As a result, the measuring scale 61 rotates together with the axis 2. In this case, for example, if a magnetic scanning principle is used, the multiple code elements constituting the measuring scale 61 may be positioned directly on the axis 2 by forming an excitation region, or in the case of an optical scanning principle, by forming a reflective region and a non-reflective region. Alternatively, the measuring scale 61 may be positioned on a scale carrier that is similarly coupled so as not to rotate on the axis 2.

[0047] Figure 3 shows a measuring scale 61 with a scale track 62 suitable for the measuring instrument of Figure 2. Multiple code elements of the scale track 62 are arranged front to back in the circumferential direction U of the axis 2. In the example shown in the figure, the scale track 62 is configured as an incremental scale track and employs a magnetic scanning principle. That is, the scale track is arranged in the circumferential direction U of the axis 2 and consists of multiple regularly consecutive positive magnetic poles and multiple negative magnetic poles. The measuring scale 61 further has a reference track 63. By employing the reference track 63, a reference position for relative angle measurement, which depends on the principle of the incremental scale track, is defined at a predetermined angular position by multiple short, consecutive positive magnetic poles and multiple negative magnetic poles (reference marks). Thus, absolute angle measurement becomes possible. Alternatively, the reference marks may be incorporated into the scale track 62.

[0048] The scale track 62 may be digitally coded so that absolute angle measurement is always possible without the reference track 63. It is particularly beneficial if the multiple code elements of the scale track 62 are arranged as consecutive pseudo-random codes (PRCs).

[0049] In the embodiment shown in Figure 2, position sensors 64, 65, and 66 are arranged circumferentially around the axis 2 at regular angular intervals, i.e., 120° intervals. The position sensors 64, 65, and 66 are fixed relative to the axis 2 such that when the axis 2 rotates, the measuring scale 61 passes right next to the position sensors 64, 65, and 66. Therefore, the angular position of the axis 2 can be measured by scanning the measuring scale 61 with the position sensors 64, 65, and 66. When a force F acts on the axis 2, the axis 2 oscillates, i.e., the center of rotation M moves (in Figure 2, this moved center of rotation is indicated by M'). As can be seen from the dashed circle, the measuring scale 61 also moves with the axis 2 relative to the position sensors 64, 65, and 66. This movement affects the angular measurement of the position sensors 64, 65, and 66. As a result, by analyzing the changes in the position values ​​P1, P2, and P3 of the individual position sensors 64, 65, and 66, and / or the changes in the angular difference between the position values ​​P1, P2, and P3 of the position sensors 64, 65, and 66, the value of the force F acting on axis 2, and possibly its direction, can be calculated.

[0050] The position values ​​P1, P2, and P3 generated by position sensors 64, 65, and 66 can be transferred to the data processor 40 via the signal transmission channel 50 for analysis, along with the measured angular position.

[0051] Figure 4 shows an embodiment of the data processor 40. The data processor 40 includes a displacement calculation unit 41, a threshold determination unit 42, a comparison unit 43, and a sequence control unit 44.

[0052] The displacement calculation unit 41 is appropriately configured to calculate a displacement value VL, which represents the amount of swing of shaft 2 from a stationary position, from position values ​​P1, P2, and P3 that are input continuously at regular time intervals during ongoing operation, and to output the displacement value VL to the threshold determination unit 42 and the comparison unit 43. The time interval is selected so that at least one displacement value VL is generated for each rotation of shaft 2.

[0053] The displacement value VL can be generated, as described above, based on the analysis of the transitions of individual position values ​​P1, P2, P3 and / or the analysis of the differences between the position values ​​P1, P2, P3 of multiple position sensors 64, 65, 66.

[0054] Optionally, the displacement calculator 41 may further calculate the angular position POS from the position values ​​P1, P2, and P3 and output it to the threshold determination unit 42 and / or comparison unit 43. As a result, in addition to this value, the direction of the swing of axis 2 can also be evaluated. Furthermore, it may be proposed to output the angular position POS to the control device 100 via the output data channel 51. As a result, for example, the angle measuring instrument 5 may be omitted.

[0055] The threshold determination unit 42 determines a threshold S, which is transmitted to the comparison unit 43, from the displacement value VL captured during at least one complete rotation of the shaft 2 while the shaft 2 is rotating and there is no contact between the tool 4 and the workpiece 6 during no-load operation. The threshold S is determined so that it is possible to detect whether the spindle motor 10 is continuously operating without load (whether there is contact between the tool 4 and the workpiece 6) by comparing it with the actual displacement value VL input into the comparison unit 43.

[0056] The threshold S can be calculated by determining a single average value from multiple displacement values ​​VL captured during at least one, preferably multiple, full rotations, and then multiplying it by a reliability coefficient or adding a constant. Alternatively, a single maximum value calculated from multiple displacement values ​​VL may be used as the threshold S. This maximum value is then similarly multiplied by a reliability coefficient or a constant is added to this maximum value. The reliability coefficient or constant is selected on a case-by-case basis so that even if the displacement values ​​VL vary statistically, the calculated threshold S does not exceed it during the no-load operation.

[0057] Finally, the comparison unit 43 generates a displacement signal VS by comparing the displacement value VL input from the displacement calculation unit 41 with a threshold S. The status of this displacement signal VS indicates whether or not the threshold S has been exceeded, and the displacement signal VS is output to the control device 100 via the output data channel 51. This comparison can be performed directly between the threshold S and the individually input displacement values ​​VL. As a result, the status of the displacement signal VS changes each time one displacement value VL exceeds the threshold S. Alternatively, the threshold S may be compared with one average value of multiple displacement values ​​VL, and in particular, the threshold S may be compared with at least all displacement values ​​VL calculated during one rotation of the axis 2.

[0058] The sequence in the data processor 40 is controlled by the sequence control unit 44. A start signal START and, optionally, a parameter PAR are transmitted to the sequence control unit 44. This control is performed by a control signal STRG output to a functional module (displacement calculation unit 41, threshold determination unit 42, comparison unit 43). The control signal STRG may include a check-back signal from the functional module to be transmitted to the sequence control unit 44. When the start signal START is received, the sequence control unit 44 initiates the following method steps: The displacement calculation unit 41 calculates multiple displacement values ​​VL sequentially from position values ​​P1, P2, and P3 at regular time intervals, and outputs these displacement values ​​VL to the threshold determination unit 42 and the comparison unit 43. The threshold determination unit 42 generates a threshold S for the displacement of axis 2 from a series of displacement values ​​VL, and then increases this threshold S by multiplying it by a reliability coefficient or by adding it to a constant. This threshold S is output to the comparison unit 43. The displacement value VL input from the displacement calculation unit 41 is compared with this threshold S in the comparison unit 43, and the comparison result is transmitted by the status of the displacement signal VS.

[0059] This method is suitable for detecting the initial contact between a tool 4, such as a milling tool or grinding machine, and the workpiece 6 to be machined, depending on the type of machining, and for determining the start of the machining based on this detection. For this reason, the threshold S is determined to be a position where there is definitely no contact between the tool 4 and the workpiece 6. Subsequently, the tool 4 and the workpiece 6 are brought closer to each other by at least one drive device until mechanical contact occurs. Preferably, this method is performed on a rotating shaft 2, because at this time it is possible to detect the cutting edge of the tool 4 entering the workpiece 6.

[0060] In a simple embodiment, the threshold S is a constant value stored in the threshold determination unit 42. In this case, the step of generating and outputting the threshold S is omitted by transmitting the stored threshold S after the input of the start command START.

[0061] Instead of the start instruction START, for example, the application of the supply voltage of the data processor 40 may be considered a start instruction.

[0062] Figure 5 shows an embodiment for using the apparatus of the present invention connected to a machine tool. In this example, the machine tool has a minimum number of components required to function in accordance with the present invention, and includes a spindle motor 10, a drive unit 20X with an encoder 30X for measuring the position in the direction of movement X of the drive unit 20X, and a control unit 100.

[0063] Furthermore, the machine tool includes a measuring instrument 60 and a data processor 40.

[0064] The drive unit 20X is appropriately configured to move the spindle motor 10 in the direction of movement X. In the illustrated example, the drive unit 20X moves the spindle motor 10 toward the workpiece 6 until the tool 4 makes contact with the workpiece 6. Since the structure of the machine tool is known, the position of the tool 4 is also determined by the position of the drive unit 20X, which is measured by the encoder 30X.

[0065] The movement of the drive unit 20X, the rotation of axis 2, and the interaction with the data processor 40 can be controlled by a computer program that can be executed on the control device 100.

[0066] As explained at the beginning, the precise position of the workpiece 6 to be machined, which will be clamped by the clamping device within the operating range of the spindle motor 10, is not yet known. Only the rough position and rough direction, which are pre-set by the clamping device, are known. Similarly, the dimensions of the workpiece 6 (the product being machined) are also known. Before machining the contour of the workpiece, it is necessary to calculate the precise position of the workpiece 6. A preferred method is described below based on the signal transition graph shown in Figure 5: The spindle motor 10 is at position Q1 at the starting position. The control device 100 controls the spindle motor 10 at time t1. As a result, the spindle motor 10 rotates at rotational speed N. This rotational speed control is performed by the angle measuring device 5, which measures the angular position of the axis 2. Furthermore, the control device 100 sends a signal to the drive device 20X to move the spindle motor 10 toward the workpiece 6 in the direction of movement X, and sends a start command START to the data processor 40.

[0067] Next, the data processor 40 performs the method shown in Figure 4. That is, the displacement calculation unit 41 successively calculates a number of displacement values ​​VL, and the threshold determination unit 42 calculates a threshold S from these displacement values ​​VL. The threshold S is provided at position Q2 at time t2, and the threshold S and these input displacement values ​​VL are compared in the comparison unit 43. Finally, the tool 4 and the workpiece 6 come into contact near position Q3. In other words, the cutting edge of the tool penetrates the material of the workpiece 6. The force F generated at this time causes a rapid increase in the transition of these displacement values ​​VL. This increase exceeds the threshold S at position Q3 at time t3. Similarly, this is transmitted by a change in the station of the displacement signal VS.

[0068] When the status of the displacement signal VS indicates contact between the tool 4 and the workpiece 6, the control device 100 stores the actual position of the encoder 30X as the position of the workpiece 6 in the direction of movement X, and either stops the drive unit 20X or reverses the direction of movement so that the tool 4 and the workpiece 6 move further away from each other. Alternatively, the control device 100 may proceed directly to machining the workpiece 6, and may, in some cases, appropriately adjust the feed rate of the drive unit 20X or the rotational speed of the axis 2.

[0069] Although the above method was explained based on only one direction of movement in this example, in practice, the above method is repeated in multiple directions of movement (for example, five directions of movement as shown in Figure 1) until a sufficient number of contact points (coordinates of the workpiece) become available in order to recognize the precise position of the workpiece 6 or the product being machined and to begin actual machining.

[0070] Since the above method is a machining process, it is beneficial to select these contact points such that multiple contact points between the tool 4 and the workpiece 6 exist within an area that is guaranteed to be removed by the machining of the workpiece 6 (in Figure 5, the final contour of the completely machined workpiece 6 is shown by a dashed line), or such that the final contour of the workpiece 6 is not adversely affected by the method of the present invention, as ensured by a predetermined preliminary dimension (Uebermass) of the workpiece 6. For example, even if foreign matter adheres to the surface of the product being machined, such as leaving behind chips, contact between the tool 4 and the actual surface of the workpiece 6 can be recognized by the method described, because the tool cuts the foreign matter without significant runout of the axis 2.

[0071] Figure 6 shows another embodiment of the data processor 140. Unlike the data processor 40, the threshold determination unit 142 is configured to continuously calculate a threshold S at time intervals Δt during ongoing operation until contact between the tool 4 and the workpiece 6 is detected, and to transfer it to the comparison unit 43. This configuration is particularly useful when the position values ​​P1, P2, P3 or the displacement value VL generated from these position values ​​drift, that is, when the displacement value VL changes even without contact between the tool 4 and the workpiece 6 during rotation of the shaft 2 under no load. The cause of the drift may be, for example, localized and asymmetrical heating of the measuring instrument 60. As a result, the positions of the position sensors 64, 65, and 66 change relative to each other due to the effect of thermal expansion. Consequently, the position values ​​P1, P2, and P3 also change. The effect of thermal expansion can adversely affect the support of the shaft 2, causing the shaft 2 to displace even without the action of an external force. While the consequences of such effects may be negligible in many applications, considering these consequences significantly improves the sensitivity and accuracy of the apparatus of the present invention.

[0072] Figure 7 shows an embodiment for using the apparatus of the present invention, which is connected to a machine tool and a data processor 140.

[0073] In this embodiment, the displacement value VL drifts. That is, the change in the displacement value VL indicates that even during no-load operation, it is in a continuous upward process as the tool spindle 10 or tool 4 approaches the workpiece 6.

[0074] At the starting position, the spindle motor 10 is also at position Q1. The control device 100 controls the spindle motor 10 at time t1. As a result, the spindle motor 10 rotates. The rotational speed is controlled by the angle measuring device 5, which measures the rotational position of the axis 2. Furthermore, the control device 100 sends a signal to the drive device 20X to move the spindle motor 10 toward the workpiece 6 in the direction of movement X, and sends a start command START to the data processor 140.

[0075] Next, the data processor 140 performs the method described above in relation to Figure 4. That is, the displacement calculation unit 41 continuously calculates the displacement value VL, and the threshold determination unit 142 calculates the first threshold S from the displacement value VL. This threshold S is provided at position Q2 at time t2, and this threshold S and the input displacement value VL are compared in the comparison unit 43.

[0076] Unlike the embodiment described based on Figure 5, the threshold determination unit 142 continuously calculates a new threshold S at each time interval Δt and outputs the updated threshold S to the comparison unit 43. In this way, the comparison is always performed using a threshold S that takes into account the drift of the displacement value VL.

[0077] Ultimately, the tool 4 and the workpiece 6 come into contact near position Q3. Compared to the increase in the displacement value VL caused by drift, the force F generated in this case causes the change in the displacement value VL to increase more dramatically and rapidly. This change exceeds the threshold S used at time t3 at position Q3. As a result, the status of the displacement signal VS also changes.

[0078] Figure 8 shows another embodiment of the data processor 240. Similarly, the data processor 240 has a displacement calculation unit 41 and a sequence control unit 44. Unlike the above embodiment, the data processor 240 has a differential unit 246. This differential unit 246 calculates the differential quotient DQ between a plurality of continuously input displacement values ​​VL and the time interval between these displacement values ​​VL, and outputs it to the comparison unit 243.

[0079] Similarly, the comparison unit 243 compares the input differential quotients DQ with a suitable threshold S stored in a memory provided for such comparison within the comparison unit 243. If one differential quotient DQ exceeds this threshold S, the comparison unit 243 transmits this information by changing the status of the displacement signal VS.

[0080] Figure 9 shows an embodiment for using the apparatus of the present invention, which is connected to a machine tool and a data processor 240.

[0081] In this embodiment as well, the displacement value VL drifts, and the change in the displacement value VL indicates that even during no-load operation, it is in a continuous upward process as the tool spindle 10 or tool 4 approaches the workpiece 6.

[0082] The start command START is input to the data processor 240 at time t1 at position Q1, and the control device 100 controls the spindle motor 10. As a result, the spindle motor 10 rotates. Furthermore, the control device 100 sends a signal to the drive device 20X to move the spindle motor 10 toward the workpiece 6 in the direction of movement X. Subsequently, the displacement calculation unit 41 starts generating displacement values ​​VL at regular time intervals and transfers these displacement values ​​VL to the differentiation unit 246. The differentiation unit 246 generates the differential quotient DQ between the multiple displacement values ​​VL that are input consecutively and the time intervals in which these displacement values ​​VL are input.

[0083] During no-load operation, i.e., the differential quotient DQ calculated at position Q2 at time t2 while the tool 4 is approaching the workpiece 6, is approximately constant (at the illustrated position DQ1).

[0084] When the tool 4 comes into contact with the workpiece 6, the displacement value VL increases, and therefore the differential quotient DQ also increases. In the illustrated example, the differential quotient DQ2 is still below the threshold S just before position Q3, and at time t3, it exceeds this threshold S at position Q3, and the comparison unit 243 changes the status of the displacement signal VS accordingly.

[0085] Figure 10 shows another embodiment of the data processor 340. The data processor 340 has a frequency analysis unit 347 in addition to a displacement calculation unit 41 and a sequence control unit 44 (which are optional in this example).

[0086] The frequency analysis unit 347 is appropriately configured to analyze the changes in the displacement value VL input from the displacement calculation unit 41 in the frequency domain. Mathematical methods such as Fourier analysis (FFT, DFT, Gerzel algorithm, etc.), order ratio analysis, and adaptive filtering may be used here.

[0087] When a tool with a structurally special cutting edge, such as a milling tool, is used as tool 4, the analysis of the displacement value VL in the frequency domain is particularly useful. When the tool 4 and the workpiece 6 come into contact during the rotation of the shaft 2, the shaft 2 vibrates significantly as each cutting edge penetrates the workpiece 6. Therefore, contact between the tool 4 and the workpiece 6 can be detected by appropriately analyzing the power spectral density in the frequency band, which depends on the rotational speed of the shaft 2 and the number of cutting edges of the tool 4. Similarly, the results of this analysis can be output by the status of the displacement signal VS.

[0088] In this embodiment, the displacement calculation unit 41 may be omitted as an option. As a result, the position values ​​P1, P2, and P3 are directly supplied to the frequency analysis unit 347. This embodiment is based on the understanding that when the shaft 2 rotates, the runout of the shaft 2 affects the respective position values ​​P1, P2, and P3 measured at the same time intervals by the individual position sensors 64, 65, and 66, respectively, as a change in the position difference of the continuously measured position values. This change in position difference can similarly be detected by the frequency spectrum.

[0089] Figure 11 shows another embodiment of the data processor 440. This data processor 440 has a KI module 448 in addition to an (optional) displacement calculation unit 41 and a sequence control unit 44.

[0090] The KI module is configured to analyze the changes in the displacement value VL input from the displacement calculation unit 41 using artificial intelligence means, for example, by comparing it with a pre-calculated pattern ("machine learning"), and to detect contact between the tool 4 and the workpiece 6. Preferably, the KI module self-learns. As a result, the detection of the contact process is continuously improved.

[0091] In this variation of the embodiment, the displacement calculation unit 41 can be omitted. As a result, here as in the previous example, the position values ​​P1, P2, and P3 are directly supplied to the KI module 448, and the time progression of these position values ​​P1, P2, and P3 is analyzed.

[0092] When contact between the tool 4 and the workpiece 6 is detected, this contact is newly transmitted by a displacement signal VS.

[0093] Figure 12 shows another embodiment of the measuring instrument 160. This measuring instrument 160 has one measuring scale 161 and six position sensors 64-69.

[0094] Similarly, the measuring scale 161 is positioned so as not to rotate on axis 2. As a result, this measuring scale 161 rotates together with axis 2.

[0095] Figure 13 shows a suitable measuring scale 161. This measuring scale 161 has one scale track 62 and optionally one reference track 63, similar to the measuring scale 61 shown in Figure 3. In this case, the measuring scale 161 further has one second scale track 162. Multiple code elements of this second scale track 162 are arranged around the axis 2. This arrangement allows for the measurement of the axial displacement WZ of the axis 2.

[0096] In the embodiment shown in Figure 12, in addition to the position sensors 64, 65, and 66 provided for scanning the scale track 62 and optionally the reference track 63, another set of position sensors 67, 68, and 69 are provided for scanning the second scale track 162. These position sensors are also arranged circumferentially around axis 2 at regular angular intervals, i.e., at 120° angular intervals.

[0097] When a force F displaces axis 2 (i.e., scale track 62) perpendicular to the axial direction (which can be measured by scanning the scale track 62 using position sensors 64, 65, and 66), and also tilts axis 2, i.e., rotates it perpendicular to the axial direction, this tilt, i.e., rotation, can be measured by scanning the second scale track 162 using position sensors 67, 68, and 69.

[0098] The arrangement of position sensors 67, 68, and 69 for scanning the illustrated second scale track 162 is considered particularly beneficial. This is because, by analyzing the three position values ​​P4, P5, and P6, the pure movement of axis 2 in the axial direction WZ and the tilt of axis 2 can be uniquely distinguished and therefore analyzed separately. For example, if only the movement (displacement) of axis 2 in the axial direction WZ needs to be determined, it is sufficient to place exactly one of the displacement sensors 67, 68, and 69 at any one position on the circumference for this purpose.

[0099] Instead of two separate scale tracks 62,162, only one scale track may be provided. Multiple code elements are configured so that both the angular position of axis 2 and the displacement of axis 2 in the axial direction WZ can be measured. This configuration is well realized when the multiple code elements of scale track 62 are arranged in a herringbone pattern. Even with such a scale track, complete understanding of all displacement directions can be achieved by six appropriately configured position sensors 64-69.

[0100] The position values ​​P1-P6 generated by the position sensors 64-69 can be supplied to the data processor 540 via the signal transmission channel 50.

[0101] Figure 14 shows another embodiment of the data processor 540. Similar to the data processor 40 described in Figure 4, the data processor 540 includes a displacement calculation unit 541, a threshold determination unit 542, a comparison unit 543, and a sequence control unit 544.

[0102] Furthermore, the displacement calculation unit 541 calculates a displacement value VL that indicates the deflection of axis 2 in a plane perpendicular to the axial direction at regular time intervals. In addition, the displacement calculation unit calculates a second displacement value VLZ that indicates the displacement of axis 2 in the axial direction WZ based on position values ​​P4, P5, and P6 generated from scanning of the second scale track 162 by position sensors 67, 68, and 69.

[0103] The threshold determination unit 542 determines a second threshold SZ based on the second displacement value VLZ in addition to the threshold S. Similarly, this second threshold SZ is determined so that the second displacement value actually input during no-load operation does not exceed the second threshold SZ.

[0104] The threshold S and the second threshold SZ are supplied to the comparison unit 543. This comparison unit 543 checks whether shaft 2 is operating under no load by comparing it with the actual input displacement value VL or second displacement value VLZ. The comparison unit 543 outputs the result of the comparison as a displacement signal VS and a second displacement signal VSZ.

[0105] Similarly, other embodiments of the data processors 140, 240, 340, and 440 can also be appropriately extended to analyze the position values ​​P1, P2, P3, P4, P5, and P6 of the measuring instrument 160.

[0106] The present invention is not limited to the embodiments described and can be alternatively implemented by those skilled in the art within the scope of the claims. [Explanation of Symbols]

[0107] 2 axes 4 Tools 5 Goniometer 6 Workpiece 10 Spindle motors, tool spindles 40,140,240,340,440,540 data processors 347 Frequency Analysis Unit 448 KI module 41,541 Displacement Calculation Unit 42,142,542 Threshold determination unit 43,243,543 Comparison section 246 Differential part 44,544 Sequence Control Unit 50 signal transmission channels 51 Output data channels 52 instruction channels 60,160 Measuring instruments 61,161 measurement divisions 162 Second scale track 62 scale tracks 63 Standard Tracks 64-69 Position Sensor 100 Control device X,Y,Z,A,B movement axis 30X, 30Y, 30Z, 30A, 30B Encoders 20X, 20Y, 20Z, 20A, 20B drive unit P1, P2, P3 position values VS displacement signal VSZ Second displacement signal VL displacement value VLZ 2nd displacement value STRG control signal S threshold SZ Second Threshold DQ,DQ1-DQ3 differential quotient POS angular position START start command PAR parameters P1-P6 Position Values PC Computer U Circumferential direction X direction of movement WZ Axial direction F force M,M′ rotation center point Q1,Q2,Q3 position Time points t1, t2, t3 Δt time interval

Claims

1. A device for detecting contact between a tool (4) and a workpiece (6) in a machine tool, said device comprising a measuring device (60, 160) having a measuring scale (61, 161) arranged non-rotatably on said axis (2), at least one position sensor (64, 65, 66, 67, 68, 69) arranged stationary with respect to said axis (2), and a data processor (40, 140, 240, 340, 440, 540), said tool (4) and said workpiece (6) being movable relative to each other, said tool (4) or said workpiece (6) being non-rotatably connected to said axis (2), said at least one position sensor (64, 65, 66, 67, 68, 69) is configured to scan said measuring graduation (61, 161) and generate from said scanning position values ​​(P1, P2, P3, P4, P5, P6) indicative of a position of said axis (2), The position values ​​(P1, P2, P3, P4, P5, P6) are supplied to the data processor (40, 140, 240, 340, 440, 540), and the data processor (40, 140, 240, 340, 440, 540) has a means for detecting contact between the tool (4) and the workpiece (6) by analyzing the progression of the position values ​​(P1, P2, P3, P4, P5, P6) and transmitting the result of the analysis by the status of a displacement signal (VS).

2. 2. The device according to claim 1, wherein the measuring graduation (61, 161) has a graduation track (62) with a number of code elements arranged in the circumferential direction of the shaft (2).

3. 3. The device according to claim 2, characterized in that the measuring graduation (161) further comprises a second graduation track (162), the code elements of which are arranged in a ring shape around the circumference of the shaft (2).

4. 3. An apparatus according to claim 1 or 2, wherein the means in the data processor (40, 140, 240, 340, 440, 540) comprises a displacement calculation unit (41) which calculates from the position values ​​(P1, P2, P3, P4, P5, P6) a displacement value (VL) indicative of a run-out of the shaft (2) from a no-load position.

5. said means in said data processor (40, 140, 240, 340, 440, 540) having a threshold value determining unit (42, 142) configured to determine a threshold value (S) of the input displacement value (VL) during no-load operation and without contact between the tool 4 and the workpiece (6) and a comparing unit (43) for comparing said threshold value (S) with the actual input displacement value (VL); and / or said means in said data processor (40, 140, 240, 340, 440, 540) comprising a differentiation unit (246) adapted to generate a differential quotient (DQ) of successively incoming displacement values ​​(VL) and a comparison unit (243) for comparing said differential quotient (DQ) with a pre-stored threshold value (S); and / or The means in the data processor (40, 140, 240, 340, 440, 540) has a frequency analysis unit (347) for analyzing the transition of the displacement value (VL) in the frequency domain, and / or 5. Apparatus according to claim 4, wherein said means in said data processor (40, 140, 240, 340, 440, 540) comprise a KI module (448) for analysing the course of said quantile values ​​(VL) by means of artificial intelligence means, in particular by pattern recognition.

6. The means in the data processor (340, 440) comprises a frequency analysis unit (347) for analyzing the transition of the position values ​​(P1, P2, P3, P4, P5, P6) in the frequency domain, and / or 3. Apparatus according to claim 1 or 2, characterized in that the means in the data processor (340, 440) comprise a KI module (448) for analysing the progression of the position values ​​(P1, P2, P3, P4, P5, P6) by means of artificial intelligence means, in particular by pattern recognition.

7. A method for detecting contact between a tool (4) and a workpiece (6) in a machine tool by means of an apparatus, the apparatus comprising a measuring device (60, 160) having a measuring scale (61, 161) arranged non-rotatably on the axis (2), at least one position sensor (64, 65, 66, 67, 68, 69) arranged stationary with respect to the axis (2), and a data processor (40, 140, 240, 340, 440, 540), the tool (4) and the workpiece (6) being movable relative to each other, the tool (4) or the workpiece (6) being non-rotatably connected to the axis (2), the measuring graduation (61, 161) is scanned by the at least one position sensor (64, 65, 66, 67, 68, 69) and position values ​​(P1, P2, P3, P4, P5, P6) indicative of the position of the axis (2) are generated from the scanning; The position values ​​(P1, P2, P3, P4, P5, P6) are supplied to the data processor (40, 140, 240, 340, 440, 540), and the data processor (40, 140, 240, 340, 440, 540) has a means for detecting contact between the tool (4) and the workpiece (6) by analyzing the progression of the position values ​​(P1, P2, P3, P4, P5, P6) using the means, and transmitting the result of the analysis by the status of a displacement signal (VS).

8. 8. The method according to claim 7, wherein the means in the data processor (40, 140, 240, 340, 440, 540) comprises a displacement calculation unit (41) and a displacement value (VL) indicative of a run-out of the shaft (2) from a no-load position is calculated by this displacement calculation unit (41) from the position values ​​(P1, P2, P3, P4, P5, P6).

9. The means in the data processor (40, 140, 240, 340, 440, 540) includes a threshold value determining unit (42, 142) for determining a threshold value (S) of the input displacement value (VL) by the threshold value determining unit (42, 142) during no-load operation without contact between the tool 4 and the workpiece (6), and a comparison unit (43) for comparing the threshold value (S) with the displacement value (VL) actually input by a comparison unit (43), and / or said means in said data processor (40, 140, 240, 340, 440, 540) comprising a differentiation unit (246) in which a differential quotient (DQ) of successively input displacement values ​​(VL) is generated by said differentiation unit (246) and a comparison unit (243) in which said differential quotient (DQ) is compared by a comparison unit (243) with a pre-stored threshold value (S); and / or The means in the data processor (40, 140, 240, 340, 440, 540) comprises a frequency analysis unit (347) in which the progression of the displacement value (VL) is analyzed in the frequency domain by a frequency analysis unit (347), and / or 9. The method according to claim 8, wherein the means in the data processor (40, 140, 240, 340, 440, 540) comprises a KI module (448) in which the progression of the quantile value (VL) is analysed by means of artificial intelligence means, in particular by pattern recognition, by means of the KI module (448).

10. The means in the data processor (340, 440) comprises a frequency analysis unit (347) in which the progression of the position values ​​(P1, P2, P3, P4, P5, P6) is analyzed in the frequency domain by a frequency analysis unit (347), and / or 8. The method according to claim 7, wherein the means in the data processor (340, 440) comprises a KI module (448) in which the progression of the position values ​​(P1, P2, P3, P4, P5, P6) is analysed by means of artificial intelligence means, in particular by pattern recognition, by means of the KI module (448).

11. A method according to any one of claims 7 to 10, initiated by a start command (START) supplied to said data processor (40, 140, 240, 340, 440, 540) via a command channel (52).

12. A method according to any one of claims 7 to 10, carried out during rotation of the shaft (2).

13. A machine tool comprising the device according to claim 1 or 2.

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