Device and method for detecting approach of tool to workpiece

Abstract

To provide a device and a method for determining an approach of a tool to a workpiece that are a superior device and a superior method that can determine a position of a workpiece in a machine tool.SOLUTION: The device comprises: a measurement structure (60) including a measuring graduation arranged in a rotationally fixed manner on a shaft (2); at least one position acquirer arranged in a fixed manner relative to the shaft (2); and a computer (40). The at least one position acquirer is adapted to scan the measuring graduation and generate, from the scanned measuring graduation, a position value (P1) indicating a position of the shaft (2); and includes means for signaling, by an approach signal (AS) without touching the workpiece when a tool (4) is close to a workpiece (6) and the tool (4) reaches an approach position relative to the workpiece (6).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an apparatus for specifying the approach of a tool to a workpiece within a machine tool according to claim 1 and a method according to claim 8. The present invention can be advantageously used in numerically controlled machine tools for shaping a workpiece by machining operations involving cutting, particularly milling, turning and grinding.

Background Art

[0002] The most common manufacturing method for machine workpieces is based on machining by cutting, i.e. removing material. In this case, material is accurately removed from a so-called blank using a tool, and finally a product with the desired shape and function is completed. To remove the material, the workpiece is brought into contact with the tool. The tool has a blade with a defined geometry or an undefined blade. Examples of tools with a blade of defined geometry are a milling cutter, a drill or a turning tool, and a tool with an undefined blade is a grinding wheel. In the cutting process, it is often the case that one of the objects (tool or workpiece) is rotated before being brought into contact with the other object.

[0003] This machining is controlled by a computer which controls an electric drive while executing a manufacturing program to move at least one of the objects. To determine the actual position of the object being moved, a position measuring device (rotary encoder or length measuring device) is provided and the measured values are further supplied to the computer. This computer is called a CNC controller and the machine tool performing the machining is called a CNC machine tool.

[0004] A so-called spindle is provided to cause rotation in an object. This is an electric motor that drives a shaft directly or indirectly, to which the object is also attached. In this case, a rotary encoder is provided to measure the rotation angle and / or rotational speed of the spindle. Furthermore, measuring devices capable of measuring the deviation of the shaft from a target position are also known. Patent Document 1 describes such a measuring device.

[0005] A clamping mechanism is provided to secure the workpiece for machining purposes. Since clamping a new workpiece (blank) involves large tolerances and the blank's dimensions can vary, it is necessary to determine the precise position and dimensions of the newly clamped blank before starting machining. For this purpose, a probe is used instead of a tool. This probe is moved towards the workpiece and outputs a switch signal when it makes contact. The CNC controller analyzes the switch signal and identifies the workpiece's position and dimensions by approaching (touching) multiple locations on the blank. Only then can the actual machining process begin.

[0006] The drawback of this method is that it requires time associated with the process of first replacing the tool with a probe and then replacing it again after the measurement process. [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 an improved device that can determine the position of a workpiece within a machine tool. [Means for solving the problem]

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

[0010] A device is proposed for identifying the approach of a tool to a workpiece within a machine tool, wherein the tool and the workpiece are movable relative to each other, and the tool or workpiece is connected to a shaft so as not to rotate, and the tool is equipped with a coolant passage, through which a coolant can be supplied to the machining area where the tool is machining the workpiece. The device comprises a measuring structure (measuring setup) equipped with a measuring scale positioned on the shaft so as not to rotate, at least one position acquiring device positioned so as not to move in contrast to the shaft, and a computer. - At least one position acquisition device is configured to scan a measuring scale and generate position values ​​from which the position of the shaft is indicated. - Position values ​​are supplied to a computer, which has multiple means, and these means analyze the changes in position values ​​as the tool approaches the workpiece to identify when the tool is positioned relative to the workpiece in an approach region where shaft displacement occurs due to stagnant pressure in the coolant flow acting on the workpiece. Furthermore, when the tool reaches the approach position where it is positioned close to the workpiece, it notifies the workpiece with an approach signal without making contact with the workpiece.

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

[0012] This problem is solved by the method described in claim 8.

[0013] Therefore, a method is proposed for determining the approach of a tool to a workpiece within a machine tool, wherein the tool and the workpiece are movable relative to each other, and the tool or workpiece is connected to the shaft so as not to rotate, and the tool is equipped with a coolant passage, and a coolant can be supplied through the coolant passage to the machining area where the tool is machining the workpiece. This machine tool has a measuring structure (measuring setup) equipped with a measuring scale that is positioned so as not to rotate on the shaft, at least one position acquiring device positioned so as not to move in contrast to the shaft, and a computer, and according to this method, - At least one position acquisition device scans the measurement scale, from which a position value indicating the position of the shaft is generated. - Position values ​​are supplied to a computer, which has multiple means, and these means are used to analyze the changes in position values ​​as the tool approaches the workpiece, thereby identifying when the tool is positioned relative to the workpiece in an approach region where shaft displacement occurs due to stagnant pressure in the coolant flow acting on the workpiece. Furthermore, when the tool reaches the approach position where it is in close proximity to the workpiece, it notifies the workpiece with an approach signal without making contact with the workpiece.

[0014] Advantageously, the measuring scale has a scale track with code elements arranged circumferentially around the shaft, and by scanning these code elements with a position acquirer, a position value indicating the angular position of the shaft can be measured. In one advantageous embodiment, three position acquirers are provided for scanning the scale track, and these position acquirers are arranged at equal intervals circumferentially around the shaft. When the shaft deflects (bounces), the angular position measured by the position acquirers is affected according to the direction of the deflection, and this appears as a change in angular difference specified by the arrangement of the position acquirers. From this, the magnitude and direction of the shaft deflection can be determined again.

[0015] In addition to this scale track, the measuring scale may also have a second scale track, the code elements of which are arranged in a ring around the shaft. For scanning, there may again be three positioning devices, these positioning devices also arranged at equal intervals around the shaft. From scanning the second measuring scale, the runout of the shaft in the axial direction can be measured. In particular, the rotation of the axis in the axial direction, i.e., the tilted position of the axis relative to the unloaded position of the shaft (which affects the tilt of the ring code elements relative to the positioning devices), can be measured.

[0016] The position values ​​from the position acquisition device are supplied to a displacement computer within the computer, which continuously generates at least one displacement value, which is a measure of the shaft's deflection caused by the forces acting on the shaft. Suitable means are provided within the computer to analyze the changes in the displacement value. Particularly advantageous embodiments are obtained from the following means:

[0017] In a first advantageous embodiment, the means includes a comparator, which can be used to determine when the approach position has been reached by comparing the incoming displacement value in real time with a threshold value.

[0018] In a second advantageous embodiment, the means includes a differentiator configured to form a difference quotient from sequentially incoming displacement values ​​and the time intervals in which they are received, and a comparator used to determine when an approach position has been reached by comparing the difference quotient with a pre-stored threshold.

[0019] In yet another advantageous embodiment, the means includes a frequency analyzer (spectrum analyzer) that analyzes the change in displacement values ​​in the frequency domain. By accurately monitoring the spectral output density in the frequency band determined by the number of coolant openings in the tool and the rotational speed of the shaft, it is possible to estimate that the approach position has been reached.

[0020] In a modification of this embodiment, since the position value of at least one position acquirer can be directly supplied to this frequency analyzer, the displacement calculator can be omitted.

[0021] In still another advantageous embodiment, the above means has an AI module that analyzes the transition of displacement values using artificial intelligence techniques, particularly by pattern recognition. This is particularly advantageous when the displacement values show large statistical fluctuations.

[0022] This embodiment can also be modified so that the position value of at least one position acquirer is directly supplied to the AI module, and thus the displacement calculator is not required.

[0023] It has been found advantageous for the computer to have a command channel in order to enable the computer to cooperate with other components, for example, the control unit of a machine tool. Through this channel, commands such as a start command to start the method according to the present invention and data if necessary can be supplied to the computer.

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

[0025] To determine a threshold value, preferably a threshold value determiner is provided. When the tool approaches the workpiece, this threshold value determiner recognizes that it has moved from the approach region to the processing region where the cutting of the workpiece will be performed, and determines the threshold value based thereon. The determination of the threshold value is preferably performed in a test run using a test workpiece. This test run can be started by the control device by sending a test start command to the computer.

[0026] The threshold value can preferably be stored in the computer, for example, in a comparator, in a frequency analyzer or in an AI module.

[0027] Further advantageous embodiments of the apparatus or method according to the present invention can be understood from the dependent claims and the embodiments described below, respectively. [Brief explanation of the drawing]

[0028] [Figure 1] This figure shows the apparatus of the present invention related to the components of a machine tool. [Figure 2] This figure shows an example of a measurement setup according to the present invention. [Figure 3] This figure shows the measurement scale suitable for the measurement setup shown in Figure 2. [Figure 4] This figure shows a first embodiment of the computer of the device according to the present invention. [Figure 5] This is a signal diagram showing the change in displacement value VL in relation to the threshold value S shown in Figure 4. [Figure 6] This figure shows yet another embodiment of the computer of the apparatus according to the present invention. [Figure 7] This is a signal diagram showing the change in displacement value VL in relation to the threshold value S shown in Figure 6. [Figure 8] This figure shows yet another embodiment of the computer of the apparatus according to the present invention. [Figure 9] This figure shows yet another embodiment of the computer of the apparatus according to the present invention. [Modes for carrying out the invention]

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

[0030] Figure 1 shows an apparatus according to the present invention relating to the components of a machine tool, in this case a 5-axis milling machine. This machine is equipped with a motor spindle 10 and further includes one drive unit and one position measuring device for each axis of motion. A control device 100 is provided to control the movement sequence, in particular for machining the workpiece 6.

[0031] The central component of the motor spindle 10 is a spindle motor 1 with a shaft 2. A tool 4 (e.g., a milling tool) is connected to the end of the shaft 2 in a way that prevents it from rotating (its rotation is constrained), allowing the tool to rotate with the shaft. A tool holder (not shown), such as a hollow tapered shank, is provided to mount the tool 4 to the shaft 2. An angle measuring device 5 (rotary encoder) is also mechanically connected to the shaft 2. This connection is made via a mechanical coupling (not shown) that connects the rotatable shaft of the angle measuring device 5 to the shaft 2. In this way, the angular position and / or cumulative rotations of the shaft 2 can be measured by the angle measuring device 5. The shaft 2 is supported within the casing of the spindle motor 1, for example, by roller bearings.

[0032] 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 for rotational speed control. The tool 4 is brought into contact with the workpiece 6 by the relative motion of the motor spindle 10 with respect to the workpiece 6. In this way, for example, during milling, the desired contour is cut out from the workpiece 6 by the milling cutter. The relative motion can be performed along linear drive axes X, Y, Z, and also includes so-called pivot axes A, B, so that in the illustrated example, movement along five motion axes X, Y, Z, A, B is possible. The movement along each axis is again controlled by drive units 30X, 30Y, 30Z, 30A, 30B (shown symbolically only) that drive the corresponding mechanical components (not shown). To determine the positions of each motion axis X, Y, Z, A, and B, the machine tool is further equipped with position measuring devices 20X, 20Y, 20Z, 20A, and 20B.

[0033] Here, I would like to point out that the movement of the axis is relative motion, and therefore, whether the drive unit moves the motor spindle 10 and consequently moves the tool 4, or moves the workpiece 6, is considered to be of equal importance.

[0034] Furthermore, it should be noted that the present invention can also be used in machine tools where the workpiece, rather than the tool, is connected to the shaft in a way that prevents it from rotating, and where it rotates together with the shaft. Typical examples include lathes and grinding machines.

[0035] The motor spindle 10 is equipped with an internal cooling supply unit (IKZ). In this regard, the machine tool is equipped with a coolant pump 12 that supplies coolant 14 to the motor spindle 10 via a coolant pipe 13. A coolant coupler 15 is provided on the shaft 2 to introduce the coolant 14 into the coolant passage 16. The coolant passage passes through the shaft 2 and guides the coolant to the machining area via the tool holder and the tool 4. The machining area is the area of ​​the machine tool where the workpiece 6 is machined (by cutting). The coolant 14 is supplied at high pressure here and is used to cool the machining area, especially the cutting edge of the tool 4. The cutting edge is either a fixed-shape blade (e.g., milling) or an irregular-shape blade (e.g., grinding), depending on the machining process.

[0036] When the coolant 14 strikes the workpiece 6, dynamic pressure (stagnation point pressure) is formed, which further acts on the tool 4 and, consequently, generates a force F acting on the shaft 2 of the motor spindle 10. This force F increases as the tool 4 approaches the workpiece 6. Its direction depends on the angle at which the coolant 14 strikes the workpiece 6, the geometric shape of the workpiece, the rotational speed N of the shaft 2, the geometric shape of the tool 4, and so on. Therefore, the force F may have both a component acting in the axial direction of the shaft 2 and a component of force perpendicular to it.

[0037] In the illustrated example, tool 4 is a substantially cylindrical grinding tool on which machining is performed on the front surface of tool 4. Correspondingly, the coolant 14 also emerges toward the workpiece 6 on the front side in the direction of movement Z. However, the present invention is not limited to a specific type or shape of tool. For example, tools equipped with an internal cooling supply are known, in which machining is performed by cutting edges arranged on the outer surface of the tool, such as a milling cutter. In this example, the coolant 14 emerges through appropriate openings (nozzles) on the outer surface of the tool, as shown in Figure 1. In this case, in order to achieve a constant supply of coolant, multiple coolant openings are provided distributed around the periphery, and advantageously, one opening is provided for each cutting edge of the milling cutter.

[0038] The control of the machine tool configured in this way is performed by a control device 100 under program control. This control device has a computer equipped with an appropriate operating system, on which the appropriate program is executed. This computer is equipped with normal peripheral devices such as a monitor, input devices, and memory. The control device 100 may also be a so-called numerical control.

[0039] The measurements from the position measuring devices 20X, 20Y, 20Z, 20A, and 20B, and the measurements from the angle measuring instrument 5, are supplied to the control device 100 via a suitable signal transmission channel. Similarly, a suitable signal transmission channel is provided for the control device 100 to control the drive units 30X, 30Y, 30Z, 30A, and 30B, and the spindle motor 1. These signal transmission channels can be designed to transmit analog or digital signals as per the specifications. In particular, the signal transmission channels may include a digital data interface, and preferably a serial data interface.

[0040] Similarly, the coolant pump 12 is controlled by the control device 100.

[0041] Thus, the machine tool is equipped with the apparatus according to the present invention, which has a computer 40 and a measurement setup (measurement structure) 60.

[0042] The measurement setup 60 is appropriately configured to identify the displacement (runout) of the shaft 2. Displacement occurs whenever a force acts on the shaft 2, directly or indirectly, for example, while the tool 4 is machining the workpiece 6, or as described above, when the tool 4 through which the coolant is flowing approaches the workpiece 6.

[0043] The measurement setup 60 is mounted on the shaft 2. The displacement (runout) of the shaft 2 can be determined by generating a position value indicating the position of the shaft 2 by scanning at least one measuring scale, which is mounted around the shaft 2 and rotates with the shaft, with at least one position acquisition device, which is mounted in opposition to the shaft 2 and does not move. Since the displacement of the shaft 2 causes a change in the position value, the displacement of the shaft 2 can be estimated by analyzing the generated position value.

[0044] Since the runout of shaft 2 affects the position value depending on the direction of the force acting on the shaft, the measurement setup 60 is particularly advantageous when there are multiple positioning devices arranged at different positions around the circumferential direction of shaft 2, especially when there are two or three positioning devices. When there are two positioning devices, it is particularly advantageous when they are arranged at an angle of 180° apart, and when there are three positioning devices, it is particularly advantageous when they are uniformly distributed around the shaft 2, i.e., when each positioning device is spaced at an angle of 120° apart.

[0045] A suitable embodiment of the measurement setup is described below with reference to Figures 2 and 3.

[0046] The measurement setup 60 can be a measurement setup known from Patent Document 1, which is explicitly referenced herein.

[0047] This example assumes a measurement setup 60 equipped with six position acquisition devices that generate position values ​​P1, P2, P3, P4, P5, and P6.

[0048] The position values ​​P1, P2, P3, P4, P5, P6 of the measurement setup 60 are supplied to the computer 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 shaft 2. Therefore, the position values ​​can be analog or digital signals. In either case, the processing of the position values ​​in the computer 40 is performed digitally. Where the digitization or conversion to digital data words takes place (whether already in the position acquisition device or in the computer) is irrelevant. Therefore, the transmission of position values ​​P1, P2, P3, P4, P5, P6 to the computer can be analog or digital. Particularly advantageous is the case where the position acquisition device already generates digital position values ​​P1, P2, P3, P4, P5, P6, and the transmission of these digital data words is performed via a digital interface, especially a serial interface.

[0049] The computer 40 has means for determining the displacement of the shaft 2 by analyzing the transitions of position values ​​P1, P2, P3, P4, P5, and P6 coming from the measurement setup 60, and for evaluating the approach of the tool 4 to the workpiece 6. The evaluation result is notified by an approach signal AS, which is output to the control device 100, for example, via an output data channel 51.

[0050] Advantageously, the functions of the computer 40 can be controlled by commands coming in from an external unit via the command channel 52, in this case from the control device 100. In this example, the functions of the computer 40 can be started by the start command START. Furthermore, parameters PAR necessary for the computer to analyze position values ​​P1, P2, P3, P4, P5, P6, such as the rotational speed of the 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.) may be supplied to the computer 40 via the command channel 52.

[0051] As illustrated, the computer 40 can be a standalone device, but it can also be configured as a module (shown by a dashed line) located within the control unit 100. The functional module that performs the functions of the computer 40 may be partially or entirely implemented by a computer program that can be run on, for example, a computer (PC) included in the control unit 100 or the computer 40 itself. This is true for all embodiments of the computer described herein.

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

[0053] Figure 2 shows one embodiment of the measurement setup 60. This measurement setup includes a measurement scale 61 with two scale tracks and a total of six position acquisition devices 64, 65, 66, 67, 68, 69.

[0054] The measuring scale 61 is positioned on the shaft 2 so as not to rotate, and rotates together with the shaft. In this case, the code elements that make up the measuring scale 61 can be directly mounted on the shaft 2, for example, by magnetization if a magnetic scanning principle is used, or by forming reflective and non-reflective regions if an optical scanning principle is used. Alternatively, the measuring scale 61 can also be mounted on a scale carrier that is also connected to the shaft 2 in a non-rotating manner.

[0055] Figure 3 shows a suitable measuring scale 61 with scale tracks 62 and 63. Here, the first scale track 62 is used, on the one hand, to measure the angle of the shaft 2, i.e., to determine the angle of rotation, and on the other hand, to determine the displacement of the shaft 2 perpendicular to the axial direction. This displacement corresponds to the displacement of the measuring scale 61 in the plane of paper shown in Figure 2. In contrast, the second scale track 62 is used to determine the displacement of the shaft 2 in the axial direction.

[0056] The code elements of the first scale track 62 are arranged sequentially along the circumferential direction U of the shaft 2. In the illustrated example, the first scale track 62 is implemented as an incremental scale track and is equipped with a magnetic scanning principle, that is, the scale track consists of a regular arrangement of magnetic positive and negative poles arranged along the circumferential direction U of the shaft 2. The measuring scale 61 further includes a reference track 162, which, by using the reference track, sets a reference position for angle measurement of the incremental scale track, which is relative due to the constraints of the principle, at a predetermined angular position by a short arrangement of magnetic positive and negative poles (reference marks). In this way, absolute angle measurement becomes possible. Instead of the reference track 162, reference marks may be incorporated into the scale track 62.

[0057] Alternatively, the first scale track 62 may be digitally encoded so that absolute angle measurement is possible at any time, even without the reference track 162. Particularly advantageous is when the code elements of the first scale track 62 are arranged in the form of a sequential pseudo-random sequence (pseudo-random code, PRC).

[0058] The code elements of the second scale track 63 are arranged in a ring around the shaft 2. By measuring the position or change in the position of these code elements, it is possible to estimate the displacement of the shaft 2 in the axial direction WZ and the rotation of the shaft 2 in a direction intersecting the axial direction (a tilt that appears to jump out of the plane of the paper as shown in Figure 2).

[0059] In the embodiment shown in Figure 2, there is a first group of position acquirers 64, 65, 66 for scanning the scale track 62 and, if necessary, the reference track 162, and a second group of position acquirers 67, 68, 69 for scanning the second scale track 63. The two groups of position acquirers are each arranged at a constant angular interval, i.e., 120°, in the circumferential direction of the shaft 2.

[0060] The angular position of shaft 2 can be measured by scanning the scale track 62 using position acquisition devices 64, 65, and 66. When a force F acts on shaft 2, the shaft deviates (bends), meaning the rotation center M shifts (in Figure 2, the shifted rotation center is labeled M'). As shown by the dashed circle, the measurement scale 61 also shifts along with shaft 2. This affects the angular measurement of the first group of position acquisition devices 64, 65, and 66. Therefore, the magnitude and, in some cases, the direction of the force F acting on shaft 2 can be estimated by either analyzing the changes in the position values ​​P1, P2, and P3 of the individual position acquisition devices 64, 65, and 66, or by analyzing the changes in the angular difference between the position values ​​P1, P2, and P3 of the position acquisition devices 64, 65, and 66.

[0061] If the force F exerts an effect that shifts the position of the shaft 2 (and the corresponding scale track 62) perpendicular to the axial direction (which can be measured by scanning the scale track 62 with the first group of position acquirers 64, 65, 66), and also exerts an effect that tilts the shaft 2, that is, rotates it in a direction intersecting the axial direction, then this force can be measured by scanning the second scale track 63 with the second group of position acquirers 67, 68, 69.

[0062] The illustrated arrangement of the second group of position acquirers 67, 68, and 69 for scanning the second scale track 162 is considered particularly advantageous because, by analyzing the three position values ​​P4, P5, and P6, the pure motion of the shaft 2 in the axial direction WZ and the inclination of the shaft 2 can be uniquely distinguished and evaluated separately. For example, if it is necessary to capture only the motion (displacement) of the shaft 2 in the axial direction WZ, it is sufficient to place one of the position acquirers 67, 68, or 69 at any position on the circumference.

[0063] The force F applied to shaft 2 often exerts both a displacement perpendicular to the axial direction (measurable by the first group of position acquirers 64, 65, 66) and a tilting effect (a rotation that causes the circle shown in Figure 2 to jump out of the plane of the paper) (measurable by the second group of position acquirers 67, 68, 69). By processing the position values ​​P1, P2, P3, P4, P5, P6 measured by the six position acquirers 64, 65, 66, 67, 68, 69, it becomes possible to comprehensively determine the complex displacement of shaft 2 caused by the force F applied to shaft 2.

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

[0065] Figure 4 shows one embodiment of the computer 40. The computer 40 includes a displacement computer 41, a comparator 43, and a sequential control unit 44.

[0066] The displacement calculator 41 is configured to continuously identify a displacement value VL representing the amount of swing of the shaft 2 from the unloaded position from the incoming position values ​​P1, P2, P3, P4, P5, P6 while the operation is in progress, and to output this displacement value to the comparator 43. Advantageously, the displacement value VL is formed at regular intervals. This interval is selected so that at least one displacement value VL is generated for each rotation of the shaft 2, for example, by forming the average value of the displacement of the shaft 2 during one rotation.

[0067] As already mentioned, the displacement value VL can be generated based on the analysis of the transitions of individual position values ​​P1, P2, P3, P4, P5, P6 and / or the analysis of the differences between the position values ​​P1, P2, P3, P4, P5, P6 of multiple position acquirers 64, 65, 66, 67, 68, 69.

[0068] One possible progression of the displacement value VL is shown in Figure 5. This is an idealized progression, and here, the rotational variation of the runout of shaft 2 is not taken into account. Such a progression appears, for example, when the motor spindle 10 equipped with tool 4, as shown in Figure 1, is actually being moved toward the workpiece 6 at a constant feed rate in the direction Z with coolant supplied. In this case, since a force F acts in the axial direction WZ, the displacement value VL is determined based on the position values ​​P4, P5, P6 measured by the second group of position acquisition devices 67, 68, 69.

[0069] In contrast, when approaching along the direction of movement X shown in Figure 1, the displacement value VL can be determined based on the analysis of position values ​​P1, P2, and P3 measured by the first group of position acquisition devices 64, 65, and 66. This is because the force generated by supplying the coolant mainly causes the displacement of shaft 2 perpendicular to the axial direction WZ.

[0070] Generally speaking, in order to determine the displacement value VL, a suitable combination of position values ​​P1, P2, P3, P4, P5, and P6 from position acquisition devices 64, 65, 66, 67, 68, and 69 can be selected according to the approach boundary conditions (direction of approach, geometric shape of the workpiece, configuration of the internal cooling supply unit, etc.).

[0071] As shown in Figure 5, the approach of the tool 4 to the workpiece 6 can be divided into three regions: idle region I, approach region II, and machining region III. This approach is performed while the internal cooling supply unit is running.

[0072] In the idle region I (up to position Z1 or time t1), the coolant supply has not yet had any effect, so there is no displacement of shaft 2, or only a negligibly small, almost constant displacement occurs.

[0073] In approach region II (between position Z1 and position Z2 or between time t1 and time t2), the displacement of shaft 2 increases. This is due to stagnation pressure generated when the coolant 14 bounces back or collides with the workpiece 6. The force F acting on tool 4 at this time increases as tool 4 approaches the workpiece 6.

[0074] In machining region III (from position Z2 onwards or from time t2 onwards), the tool 4 and the workpiece 6 eventually come into contact, and cutting is performed. At this time, the force F and the force generated during machining of the workpiece 6 overlap, so the change in the illustrated displacement value VL has a point where it changes abruptly at the transition between approach region II and machining region III. In other words, the collision of the tool 4 with the workpiece 6 causes a sharp increase in the change in the displacement value VL.

[0075] Selectively, the displacement calculator 41 can further calculate the angular position POS from the position values ​​P1, P2, and P3 and output it to the comparator 43, thereby determining the direction in addition to the amount of runout of the shaft 2. Furthermore, the angular position POS may be output to the control device 100 via the output data channel 51, so that the angle measuring instrument 5 may be omitted in some cases.

[0076] The displacement value VL is supplied to the comparator 43. This comparator compares the displacement value VL coming from the displacement computer 41 with a threshold S to form an approach signal AS indicating whether the threshold S has been reached or exceeded, and outputs this approach signal AS to the control device 100 via the output data channel 51.

[0077] Here, the threshold S is selected such that it is reached or exceeded in the approach region II, specifically at the approach position ZA where the tool 4 is fairly close to the workpiece 6 without touching the workpiece—that is, before reaching the machining region III. The threshold S may be stored in the comparator 43 or supplied to the computer 40 via the command channel 52.

[0078] The threshold S can be determined in a test run that passes through all three regions. Since cutting is performed at this time, a test workpiece is advantageously used as the workpiece 6.

[0079] In a preferred embodiment, the computer 40 has an additional threshold determination unit 42 for determining a threshold S. This threshold determination unit is supplied with a displacement value VL and, again, a test start command TEST, which is supplied to the computer from the control unit 100 via a command channel 52. Here, the threshold determination unit 42 is appropriately configured to recognize from the transition of the displacement value VL whether the tool 4 is in the idle region I, the approach region II, or the machining region III. In particular, the threshold determination unit 42 recognizes a transition (jump) from the approach region II to the machining region III and determines the approach position ZA and the displacement value VL as the corresponding threshold S from this transition. After the threshold S is determined, the threshold determination unit 42 outputs a test stop signal STP to the control unit 100 via an output data channel 51, which allows the control unit to immediately stop the movement of the tool 4 toward the workpiece 6 (along the direction of movement Z) and the associated cutting operation.

[0080] The sequence within the computer 40 is controlled by a sequential control unit 44, which receives the start command START, the test start command TEST, and optionally the parameter PAR via the command channel 52. This control is performed by a control signal STRG output to the functional modules (displacement computer 41, threshold determination unit 42, comparator 43). The control signal STRG may include feedback from the functional modules to the sequential control unit 44.

[0081] After receiving the start command START, the sequential control unit 44 initiates the following method steps: - The displacement calculator 41 continuously calculates the displacement value VL from the position values ​​P1, P2, P3, P4, P5, and P6 at regular time intervals, and outputs the displacement value VL to the comparator 43. - The displacement value VL coming from the displacement calculator 41 is compared with a threshold value S in the comparator 43, and an approach signal AS is formed and output from there.

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

[0083] If the threshold S is not yet available, the following methods, initiated by the test start command TEST, can be performed beforehand to determine the threshold: - The displacement calculator 41 continuously calculates the displacement value VL from the position values ​​P1, P2, P3, P4, P5, and P6 at regular time intervals, and outputs the displacement value VL to the threshold determination unit 42. - The threshold determination unit 42 identifies the transition from the approach region II to the machining region III, and based on this transition, determines the approach position ZA and the corresponding displacement value VL as the threshold S, thereby forming the threshold S for the displacement of the shaft 2. This threshold S is output 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 drive unit, the rotation of the shaft 2, the activation of the internal cooling supply unit, and the interaction with the computer 40 necessary to carry out the above-described method can be controlled by a computer program that can be executed on the control device 100.

[0086] As explained at the beginning, the exact position of the workpiece 6 to be machined, which is clamped by the clamping means within the working area of ​​the motor spindle 10, is not yet known. All that is known is the approximate position and orientation of the workpiece, determined by the clamping means. The dimensions of the workpiece 6 (the blank workpiece) are also known. Before machining the contour of the workpiece, the exact position of the workpiece 6 needs to be determined. A preferred method is described below, based on the signal diagram shown in Figure 5, which relates to the computer 40 shown in Figure 4:

[0087] At the starting position, the motor spindle 10 is in a predetermined position within the idle region I. First, the control device 100 controls the spindle motor 1 so that the motor rotates and the internal cooling supply is activated. Next, the control device 100 sends signals to the drive units 20X, 20Y, 20Z, 20A, and 20B required for the desired direction of movement, causing the motor spindle 10 to move toward the workpiece 6, and then sends a start command START to the computer 40. This movement is performed at a constant feed rate.

[0088] Here, the computer 40 performs the method described in relation to Figure 4. That is, the displacement computer 41 continuously obtains the displacement value VL and the comparator 43 compares it with a threshold S. As the displacement value VL changes, if it reaches or exceeds the threshold S, an approach signal AS is sent to the control device 100.

[0089] When an approach signal AS is received, the control device 100 stores the actual position values ​​of at least the position measuring devices 30X, 30Y, 30Z, 30A, and 30B, which are affected by the movement of the motor spindle by the drive units 20X, 20Y, 20Z, 20A, and 20B, as the position of the workpiece 6 at the selected approach point, and stops the drive units or reverses their direction of movement so that the tool 4 and the workpiece 6 are separated from each other again until the motor spindle 10 or the tool 4 is back in the free-spinning region I.

[0090] This method is actually repeated at various positions on the workpiece 6 until enough close points (workpiece coordinates) are obtained to determine the precise location of the workpiece 6 or the blank of the workpiece and begin the actual machining process.

[0091] Alternatively, once the control device 100 reaches a certain point of approach, it may proceed directly to machining the workpiece 6. For this purpose, the feed rate is adjusted, and in particular reduced, as necessary.

[0092] For example, when the threshold S is not yet available, such as at the start of continuous production, the control device 100 can determine the threshold using the method described above for determining the threshold.

[0093] In this case as well, the motor spindle 10 is in a predetermined position within the idle region I at the start. The control device 100 controls the spindle motor 1 so that the motor rotates and the internal cooling supply is activated. Next, the control device 100 sends signals to the drive units 20X, 20Y, 20Z, 20A, and 20B required in the desired direction of movement to move the motor spindle 10 toward the workpiece 6, and sends a test start command TEST to the computer 40.

[0094] Here, the computer 40 performs the method for determining the threshold, as described in relation to Figure 4. That is, the displacement computer 41 continuously calculates the displacement value VL and supplies it to the threshold determination unit 42. The threshold determination unit determines the actual threshold S from the change in the displacement value VL and outputs it to the comparator 43. Finally, the threshold determination unit 42 sends a test stop command STP to the control device 100.

[0095] When a test stop command STP is received, the control device 100 stops the drive unit or reverses the direction of movement, and separates the tool 4 and the workpiece 6 from each other again until the motor spindle 10 or the tool 4 is back in the free-spinning region I.

[0096] This method is repeated at various positions on the workpiece 6 until a threshold S is obtained for a sufficient number of approach points (workpiece coordinates) to determine the precise position of the workpiece 6 or the blank of the workpiece.

[0097] Figure 6 shows yet another embodiment of the computer 240. This computer still has a displacement computer 41 and a sequential control unit 44. Unlike the embodiments described above, the computer 240 here includes a differentiator 246, which differentiates the transition of the displacement values ​​VL by, for example, calculating the difference quotient DQ from the sequentially incoming displacement values ​​VL and the time intervals between the inputs of those displacement values ​​to the differentiator 246, and outputs the result to the comparator 243.

[0098] The comparator 243 compares the incoming difference quotient DQ with an appropriate threshold S stored in a memory specifically provided for the comparator 243. If the difference quotient DQ exceeds the threshold S, the comparator 243 notifies this by outputting an approach signal AS.

[0099] Figure 7 shows the change in displacement value VL in relation to the threshold S, where the threshold, in this example, gives the slope (or difference quotient DQ) of the change in displacement value VL at approach position ZA.

[0100] Computer 240 may have a threshold determination unit 242, similar to computer 40, to determine a threshold S in relation to control device 100. The threshold determination unit 242 is supplied with displacement values ​​VL and / or difference quotient DQ for this purpose. The graph formed by a series of displacement values ​​VL or difference quotient DQ all show a sharp increase recognized by the threshold determination unit 242 when transitioning from approach area II to machining area III. Based on this position, the slope of the transition of the displacement value VL at approach position ZA (difference quotient) is determined as the threshold S.

[0101] The control for determining the threshold S is also performed here by the test start command TEST and the test stop signal STP.

[0102] Therefore, computer 240 can be used as a substitute for computer 40.

[0103] Figure 8 shows yet another embodiment of the computer 340. This computer has a frequency analyzer 347 in addition to a displacement calculator 41 and a sequential control unit 44 (which are optional in this example).

[0104] The frequency analyzer 347 is appropriately configured to analyze the transition of the displacement value VL input from the displacement computer 41 in the frequency domain. Here, mathematical methods such as Fourier analysis (FFT, DFT, Goertzel analysis, etc.), order analysis, or adaptive filtering can be used.

[0105] Analysis of the displacement value VL in the frequency domain is particularly advantageous when a tool 4 is used, for example in a milling machine, where the coolant 14 is dispensed through corresponding openings (nozzles) on the outer surface of the tool 4. When the shaft 2 is rotating and the tool 4 approaches the workpiece 6, the coolant flow from each nozzle causes the shaft 2 to run out due to the rotation period. By monitoring the spectral power density in the frequency band, which depends on the rotation speed of the shaft 2 and the number of nozzles, the proximity between the tool 4 and the workpiece 6 can be detected. This monitoring can also be performed by comparing it with an appropriate threshold S. The results of the analysis can again be output as a proximity signal AS.

[0106] In this embodiment, it is advantageous that multiple displacement values ​​VL are generated each time the shaft 2 rotates in order to reliably capture the maximum value of the shaft 2's runout caused by each individual nozzle.

[0107] Selectively, in this embodiment, the displacement calculator 41 can be omitted, so the position values ​​P1, P2, P3 are supplied directly to the frequency analyzer 347. This is based on the finding that the runout of shaft 2 appears as a change in the position difference of sequentially measured position values, resulting from the position values ​​P1, P2, P3, P4, P5, P6 of position acquirers 64, 65, 66, 67, 68, 69 measured at the same time intervals while shaft 2 is rotating. This change in position value can again be detected in the frequency spectrum.

[0108] In any case, the frequency analyzer 347 can again be appropriately configured to determine a threshold S based on identifying the transition from the approach region II to the processing region III.

[0109] Therefore, computer 340 can also serve as a substitute for computer 40.

[0110] Figure 9 shows yet another embodiment of the computer 440. This computer has an AI module 448 in addition to an (optional) displacement computer 41 and sequential control unit 44.

[0111] The AI ​​module 448 is appropriately configured to recognize the approach of the tool 4 to the workpiece 6 by analyzing the changes in the displacement value VL input from the displacement computer 41 using artificial intelligence methods, for example, by comparing it with a pre-determined pattern ("machine teaching"). These patterns correspond to the threshold S in previous examples and can be determined in cooperation with the control device 100 during a test run. Advantageously, the AI ​​module is self-learning, and its recognition of the approach process is continuously improved.

[0112] In one modified example of this embodiment, the displacement computer 41 can be omitted. In this case as well, as in the previous examples, the position values ​​P1, P2, P3, P4, P5, and P6 are supplied directly to the AI ​​module 448, and their temporal changes are analyzed.

[0113] When it is recognized that the approach position ZA has been reached, this is again notified by the approach signal AS.

[0114] This computer 440 can also serve as a replacement for computer 40.

[0115] The present invention is not limited to the embodiments described, and can be implemented in alternative ways within the scope of the claims by those skilled in the art.

Claims

1. A device for determining the proximity of a tool (4) to a workpiece (6) in a machine tool, the tool (4) and the workpiece (6) being movable relative to each other, the tool (4) or the workpiece (6) being connected to a shaft (2) so as not to rotate, the tool (4) being provided with a coolant passage (16) through which a coolant (14) can be supplied to a machining area where machining of the workpiece (6) is performed by the tool (4), a measuring structure (60) having a measuring scale (61) arranged so as not to rotate on the shaft (2), at least one position acquirer (64, 65, 66, 67, 68, 69) arranged so as not to move in position relative to the shaft (2), and a calculator (40, 240, 340, 440); at least one said position acquirer (64, 65, 66, 67, 68, 69) is adapted to scan said measuring scale (61) and to generate therefrom position values ​​(P1, P2, P3, P4, P5, P6) indicative of the position of said shaft (2); The position values ​​(P1, P2, P3, P4, P5, P6) are supplied to the computer (40, 240, 340, 440), which has means for determining, by analyzing the progression of the position values ​​(P1, P2, P3, P4, P5, P6) when the tool (4) approaches the workpiece (6), that the tool (4) is located in an approach area (II) relative to the workpiece (6) where a displacement of the shaft (2) occurs due to a stagnation point pressure of the coolant flow impinging on the workpiece (6), and means for notifying by an approach signal (AS) when the tool (4) reaches an approach position (ZA) relative to the workpiece (6) where the tool (4) is located close to the workpiece (6) without contacting the workpiece (6). Device.

2. 2. The device according to claim 1, wherein the measuring scale (61) comprises a first graduation track (62) whose code elements are arranged circumferentially around the shaft (2).

3. 3. Device according to claim 2, characterized in that the measuring scale (61) comprises a second graduation track (62) whose coding elements are arranged annularly around the shaft (2).

4. 2. The apparatus of claim 1, wherein the means in the calculator (40, 140, 240, 340, 440, 540) comprises a displacement calculator (41) for determining a displacement value (VL) indicative of a runout of the shaft (2) from the no-load position from the position values ​​(P1, P2, P3, P4, P5, P6).

5. 5. The apparatus of claim 4, wherein the means in the computer (40, 240, 340, 440) further comprises: It has a comparator (43) used to make it possible to identify when said approach position (ZA) has been reached by comparing the real-time incoming displacement value (VL) with a threshold value (S), or a differentiator (246) adapted to form a difference quotient (DQ) of the successively incoming displacement values ​​(VL), and a comparator (243) used to make it possible to identify when said approach position (ZA) has been reached by comparing said difference quotient (DQ) with a threshold value (S), or a frequency analyzer (347) used to analyze the course of said displacement value (VL) in the frequency domain, thereby making it possible to identify that said approach position (ZA) has been reached, or - it has an AI module (448) that uses artificial intelligence techniques, in particular pattern recognition, to make it possible to identify that said approach position (ZA) has been reached by analyzing the evolution of said displacement values ​​(VL), A device that is at least one of the above.

6. 2. The apparatus of claim 1, wherein the means in the computer (340, 440) comprises: a frequency analyzer (347) used to analyze the progression of said position values ​​(P1, P2, P3, P4, P5, P6) in the frequency domain, thereby making it possible to identify that said approach position (ZA) has been reached, or - it has an AI module (448) that uses artificial intelligence techniques, in particular pattern recognition, to make it possible to identify that the approach position (ZA) has been reached by analyzing the progression of the position values ​​(P1, P2, P3, P4, P5, P6), A device that is at least one of the above.

7. 2. The apparatus according to claim 1, wherein the means in the computer (40, 240) further comprises a threshold determiner (42, 242), which recognizes that when the tool (4) approaches the workpiece (6), it has transitioned from the approach region (II) to the machining region (III) where cutting of the workpiece (6) is performed, and determines a threshold value (S) based on this.

8. A method for determining the approach of a tool (4) to a workpiece (6) in a machine tool, 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 a shaft (2), the tool (4) being provided with a coolant passage (16) through which a coolant (14) can be supplied to a machining area where machining of the workpiece (6) is performed by the tool (4), the machine tool having a measuring structure (60) with a measuring scale (61) non-rotatably arranged on the shaft (2), at least one position acquirer (64, 65, 66, 67, 68, 69) arranged in a position that is fixed relative to the shaft (2), and a calculator (40, 240, 340, 440), - by at least one of said position acquirers (64, 65, 66, 67, 68, 69), said measuring scale (61) is scanned and position values ​​(P1, P2, P3, P4, P5, P6) indicative of the position of said shaft (2) are generated therefrom; The position values ​​(P1, P2, P3, P4, P5, P6) are supplied to the computer (40, 240, 340, 440), which has means used to determine, by analyzing the progression of the position values ​​(P1, P2, P3, P4, P5, P6) as the tool (4) approaches the workpiece (6), that the tool (4) is located in an approach area (II) in which a displacement of the shaft (2) occurs due to a stagnation pressure of the coolant flow impinging on the workpiece (6), and which notify by an approach signal (AS) when the tool (4) reaches an approach position (ZA) in which the tool (4) is located close to the workpiece (6) without contacting the workpiece (6). method.

9. 9. A method according to claim 8, wherein the means in the calculator (40, 140, 240, 340, 440, 540) comprises a displacement calculator (41) by means of which a displacement value (VL) indicative of a run-out of the shaft (2) from an unloaded position is determined from the position values ​​(P1, P2, P3, P4, P5, P6).

10. 10. The method of claim 9, wherein the means in the computer (40, 240, 340, 440) further comprises: a comparator (43) used to identify when said approach position (ZA) has been reached by comparing the incoming displacement value (VL) in real time with a threshold value (S), or a differentiator (246) used to form a difference quotient (DQ) of the successive incoming displacement values ​​(VL) and a comparator (243) used to identify when said approach position (ZA) has been reached by comparing said difference quotient (DQ) with a threshold value (S), or a frequency analyzer (347) used to determine when the approach position (ZA) has been reached by analyzing the course of the displacement value (VL) in the frequency domain, or - it has an AI module (448) that is used to identify the arrival of said approach position (ZA) by analyzing the evolution of said displacement values ​​(VL) using artificial intelligence techniques, in particular by pattern recognition, A method that is at least one of the above.

11. 9. The method of claim 8, wherein the means in the computer (340, 440) comprises: a frequency analyzer (347) used to determine when said approach position (ZA) has been reached by analyzing the progression of said position values ​​(P1, P2, P3, P4, P5, P6) in the frequency domain, or - it has an AI module (448) that uses artificial intelligence techniques, in particular pattern recognition, to identify when said approach position (ZA) has been reached by analyzing the evolution of said position values ​​(P1, P2, P3, P4, P5, P6), A method that is at least one of the above.

12. 9. The method of claim 8, wherein the method is initiated by a start command (START) supplied to the computer (40, 240) via a command channel (52).

13. 9. The method according to claim 8, wherein the means in the computer (40, 240) further comprises a threshold determiner (42, 242) used to recognize, when the tool (4) approaches the workpiece (6) in a test run, that the workpiece (6) has transitioned from the approach region (II) to the machining region (III) where cutting of the workpiece (6) is performed, and to determine a threshold value (S) based on the recognition.

14. 14. The method of claim 13, wherein the test run is initiated by a test start command (TEST) provided to the computer (40, 240) via the command channel (52).

15. A machine tool equipped with the device according to any one of claims 1 to 7.

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