Method for automatic process monitoring in a continuous gear grinding process

Abstract

A method for automatic process monitoring during continuous gear grinding of a workpiece (23) with a preset tooth structure is proposed, the method enabling early detection of grinding wheel chipping. A plurality of workpieces are machined by a gear grinding machine (1). To this end, the workpieces are tensioned on at least one workpiece spindle (21) and successively engage in rolling engagement with a grinding wheel (16). At least one measured variable is monitored during machining. A warning indication (W) indicating grinding wheel chipping (19) is determined from the measured variable. If the warning indication indicates the presence of grinding wheel chipping, the grinding wheel is automatically checked. To this end, a dressing tool (33) is passed through the head region of the grinding wheel and a contact signal is determined during the passage through the head region. A chipping indication (A) is determined by analyzing the contact signal, wherein the chipping indication indicates whether a grinding wheel chipping exists. If this is the case, the grinding wheel is dressed at a required frequency in order to eliminate the grinding wheel chipping. Alternatively, the grinding wheel is directly checked during the first dressing stroke.

Description

Technical Field

[0001] The invention relates to a method for automatic process monitoring in a continuous gear grinding process using a gear grinding machine, a gear grinding machine configured to carry out such a method, and a computer program for carrying out such a method. Background Art

[0002] In continuous gear grinding, the gear blank is machined in rolling engagement with a worm-shaped grinding wheel (grinding worm). Gear grinding is a very demanding generative machining method that is based on a large number of synchronized, precise individual movements and is subject to many boundary conditions. Information on the basic principles of continuous gear grinding can be found, for example, in the book “Continuous Generating Gear Grinding” by H. Schriefer et al., published by Reishauer AG, Wallisellen 2010, ISBN 978-3-033-02535-6, Chapter 2.3 (“Basic Methods of Generating Grinding”), pages 121 to 129.

[0003] In theory, the tooth surface shape in the continuous gear grinding process is determined only by the trimmed contour shape of the worm and the setting data of the machine. However, in practice, deviations from the ideal state occur in automated production, which have a decisive influence on the grinding result. In the above-mentioned work by Schriefer et al., this is discussed in Chapter 6.9 ("Practical Know-How for Statistical Individual Deviation Analysis") on pages 531 to 541 and Chapter 6.10 ("Analysing and Eliminating Gear Tooth Deviations") on pages 542 to 551.

[0004] Traditionally, the quality of a tooth produced by the gear grinding method has only been assessed after the machining process has been completed by measuring the tooth outside the machining machine (“offline”) on the basis of a large number of measured variables. There are various standards that specify how the tooth is measured and how the measurement results are checked to see whether they are within or outside the tolerances. These standards also specify what relationship exists between the measurement results and the performance characteristics of the tooth. For example, a summary of such tooth measurements can be found in the aforementioned book by Schriefer et al., Chapter 3 (“Quality Assurance in Continuous Generating Gear Grinding”), pages 155 to 200.

[0005] In the case of manual operation, the operator recognizes deviations from the specified deviation during the machining process based on his experience or recognizes such deviations during a subsequent tooth inspection. The operator then guides the machining process into the stable range by means of changed setpoints. However, in order to automate the machining, it is desirable that the process monitoring intervenes automatically and stably.

[0006] Up to now, strategies suitable for process monitoring in continuous gear grinding processes have only been known in a preliminary manner from the prior art.

[0007] Thus, the company report “NORDMANN Tool Monitoring”, version of October 5, 2017, accessed on February 25, 2019 from https: / / www.nordmann.eu / pdf / praesentation / Nordmann_presentation_ENG.pdf, describes different measures for tool monitoring at universal cutting machines (page 3). Tool monitoring can be carried out during the cutting process by measuring the effective power, cutting forces or structure-borne noise (page 7). In particular, the tool monitoring can be used to detect tool breakage and tool wear (pages 9 to 14). A large number of sensors are provided for different measurement tasks in the scope of tool monitoring (pages 31 to 37). The effective power can be determined via current measurement (page 28). For this purpose, corresponding current sensors are known (page 37), or current monitoring can be carried out sensorlessly based on data from a CNC control (page 40). The report shows application examples for various cutting methods, which also include brief examples of a few methods relevant for gear machining, in particular hobbing (pages 41 and 42), hard skiving (page 59) and honing (page 60). Dressing methods are also used (page 92). However, the continuous gear grinding process is only briefly mentioned (e.g. pages 3 and 61).

[0008] Information on (circular) grinding and dressing can also be found in Klaus Nordmann, "Procedures in Schleifen und Abrichten", Schleifen+Polieren 05 / 2004, specialist publisher Velbert (Germany), pages 52-56. However, continuous gear grinding is not discussed in detail here either.

[0009] Usually, a vitrified, dressable grinding wheel is used in the gear grinding process. A serious problem in such grinding worms is local chipping in one or more worm threads of the grinding wheel. Chipping of the grinding wheel has the effect that the tooth flank of the tooth to be machined is not completely machined over its entire length when it engages with the grinding wheel in the area of ​​the chipping. In most cases, not all workpieces of a batch are affected to the same extent by chipping of the grinding wheel, because during the production of a batch, the grinding wheel is usually moved along its longitudinal axis in order to constantly bring unused areas of the grinding wheel into engagement with the workpiece (so-called shifting). Workpieces that are machined only by intact areas of the grinding wheel usually do not show any defects.

[0010] This makes it difficult to identify machining errors caused by grinding wheel chipping. Since only sample checks are usually performed during gear inspections, machining errors caused by grinding wheel chipping are usually not identified during the gear inspection process or are only identified afterwards. Such errors usually only appear during end-of-line testing (EOL testing) after the workpiece has been installed in the transmission. This requires an expensive disassembly process. In addition, the same machining error may have occurred on a large number of other workpieces in the middle of the time. This may result in a significant part of a production batch having to be discarded as NIO parts (NIO = "not normal"). Therefore, a single unidentified grinding wheel chipping may already cause very high subsequent costs. It is therefore desirable to reliably identify or even prevent grinding wheel chipping within the scope of automatic process monitoring.

[0011] In addition to chipping of the grinding wheel, other phenomena can also have a negative impact on the quality of the teeth produced in a production batch. It is therefore known that the blank is usually not pre-treated immediately, or that hardness differences and / or hardening deformations occur at the tooth surface of the blank. Small differences in the composition of the grinding worm can also lead to different grinding or dressing performance. Insufficient quality during dressing is also usually the cause of reduced quality in the produced teeth. In addition, due to the process, the radius of the worm is reduced by the corresponding dressing amount during dressing. Therefore, the engagement during the grinding process can change drastically during the processing of a production batch and often deteriorate. The setting values ​​selected at the beginning of the processing must then be changed. In other words, despite all precautions to ensure constant processing quality, individual differences are still inevitably produced in each workpiece during processing.

[0012] This means that in the automated grinding of a production batch, the setpoints, tools, clamping devices, and measuring and automation technology are determined before the machining process. At the start of the machining process, the operator then monitors the process and, after achieving scrap-free production, the production batch is then further processed quasi-automatically. The process can become unstable or be disrupted by two main influencing factors:

[0013] First: through the tool, i.e. through chipping or worse joint conditions after trimming; and

[0014] Second: through the workpiece, which may have machining errors in pre-machining.

[0015] Process monitoring should detect these effects and initiate automatic corrective measures. Summary of the invention

[0016] It is therefore the object of the present invention to specify a method for process monitoring in a continuous gear grinding process, by means of which process deviations can be detected and / or prevented at an early stage.

[0017] This object is achieved by the method according to claim 1. Further embodiments are given in the dependent claims.

[0018] That is, a method for process control during continuous gear grinding of a workpiece with a predetermined toothing by means of a gear grinding machine is proposed. The gear grinding machine has a tool spindle and at least one workpiece spindle. A worm-shaped profiled grinding wheel with one or more worm threads is tensioned on the tool spindle and can rotate about the tool axis. The workpiece can be tensioned on at least one workpiece spindle. The method comprises:

[0019] machining a workpiece by means of a gear grinding machine, wherein the workpiece is tensioned on at least one workpiece spindle for machining and successively engages in rolling engagement with a grinding wheel;

[0020] monitoring at least one measured variable during machining of the workpiece; and

[0021] A warning indicator indicative of a process deviation is determined from at least one monitored measured variable.

[0022] That is, according to the invention, process monitoring is used to obtain indications of impermissible deviations of the machining process from its normal course in the gear grinding machine at an early stage and to derive warning indications therefrom. In the simplest case, the warning indication can be, for example, a binary Boolean variable which indicates in a binary manner whether there is a suspicion of a process deviation. However, the warning indication can also be, for example, a numerical value which is greater the greater the calculated probability of the process deviation, or a vector value which additionally indicates from which measurements the suspicion of a process deviation arises or what type of possible process deviation is identified. Many other executions of the warning indication are likewise conceivable.

[0023] In particular, the process deviation to be identified can be a grinding wheel chipping. Accordingly, the warning indication is a warning indication indicating a possible grinding wheel chipping. As explained in the introduction, an unidentified grinding wheel chipping can lead to a large part of the parts of a production batch having to be discarded as NIO parts, so it is particularly advantageous if the process control is set up to issue a warning indication indicating a possible grinding wheel chipping.

[0024] Different actions can be triggered automatically based on the warning indication. Thus, based on the warning indication, a decision can be automatically made whether the last machined workpiece is to be classified as an NIO part or to be sent to a special rechecking device. Based on the warning indication, a visual or acoustic warning signal can also be triggered in order to prompt the operator of the gear grinding machine to carry out a visual inspection of the grinding wheel.

[0025] Advantageously, if the warning indicates the presence of a grinding wheel chipping, an automatic inspection of the grinding wheel for grinding wheel chipping is triggered by the alarm indication.

[0026] This automatic check can be carried out in different ways. Thus, for example, it is conceivable to use an optical sensor or a digital camera for the check and to automatically determine whether there is a chipping of the grinding wheel, for example by means of digital image processing methods. It is also conceivable to check the acoustic emissions of the grinding wheel for this purpose, which are generated when the coolant jet hits the grinding wheel and are transmitted to the acoustic sensor via the coolant jet. However, it is advantageous to use a dressing device with a dressing tool for the automatic check, such as the dressing devices usually present on the gear grinding machine anyway. In this case, in order to check the grinding wheel, it is possible to specifically pass through only one head area of ​​the worm thread, or it is possible to carry out a complete dressing stroke, such as the dressing stroke carried out in the normal dressing of the grinding wheel.

[0027] If only the head area is passed, once the warning indication indicates that there is a grinding wheel chipping, the following steps can be performed specifically:

[0028] Pass the dressing tool over the head area of ​​the grinding wheel;

[0029] determining a contact signal during the passage through the head region, wherein the contact signal indicates contact of the dressing tool with the head region of the grinding wheel; and

[0030] The chipping indication is determined by analyzing the contact signal, wherein the chipping indication indicates whether there is chipping of the grinding wheel.

[0031] If there is no contact in a specific area of ​​the grinding worm thread, this is a strong indication that there has in fact been chipping of the grinding wheel. This is indicated by a chipping indication.

[0032] Regardless of the value of the warning indicator, passing the dressing tool over the head region can also be performed regularly, for example after machining a preset number of workpieces, in order to be able to detect grinding wheel chips that have not been detected during the machining process when monitoring the measured variables.

[0033] In the simplest case, the chipping indication can again be a binary Boolean variable which indicates in binary form whether a chipping exists. However, more complex implementations of the chipping indication are also conceivable. In particular, the chipping indication preferably also indicates the position of the grinding wheel chipping along at least one of the worm threads on the grinding wheel.

[0034] The contact of the dressing tool with the head region of the grinding wheel can be detected in different ways. The gear grinding machine can therefore have an acoustic sensor in order to acoustically detect the engagement of the dressing tool with the grinding wheel based on the structure-borne sound generated during the engagement. A contact signal is then derived from the acoustic signal determined by means of the acoustic sensor. If the dressing tool is tensioned on a dressing spindle driven to rotate by a motor, the contact signal can be derived alternatively or additionally from a power signal which represents the power consumption of the dressing spindle during the passage over the head region.

[0035] If the chipping indication indicates the presence of grinding wheel chipping, the method can provide for completely dressing the grinding wheel in order to further characterize and / or eliminate the grinding wheel chipping.

[0036] Yet, as explained, also can consider, directly carry out complete dressing process to check whether grinding wheel is broken.In this case, check whether grinding wheel is broken and characterize breaking according to the monitoring of this dressing process.

[0037] In order to monitor the dressing process and characterize the chipping of the grinding wheel in detail, a dressing power signal can be determined during dressing, which represents the power consumption of the dressing spindle and / or the tool spindle during dressing, and the chipping size can be determined by analyzing the variation curve of the dressing power signal during the dressing process. The chipping size reflects at least one feature of the chipping of the grinding wheel, such as where the chipping of the grinding wheel is located and / or how severely the associated worm thread is damaged in the radial direction.

[0038] The chipping size can then be used to automatically determine whether the chipping of the grinding wheel can be eliminated meaningfully by one or more dressings. If this is not the case, a signal can be sent to the user that the grinding wheel must be replaced, or further processing can be controlled so that other workpieces are only processed by the undamaged area of ​​the grinding worm.

[0039] Analyzing the variation curve of the dressing power signal to determine the chipping size can include the following steps: determining a fluctuation magnitude, wherein the fluctuation magnitude indicates a local variation in the magnitude of the dressing power signal along at least one of the worm threads. For example, the fluctuation magnitude can directly draw conclusions about the radial depth of the chipping of the grinding wheel.

[0040] As already explained, in the context of the process control proposed here, warning indicators representing process deviations, in particular grinding wheel chipping, are determined in order to indicate possible process deviations at an early stage. In order to determine the warning indicators, different measured variables can be monitored.

[0041] In particular, the monitored measured variables can include a deviation indicator, which indicates a deviation in the tooth thickness of the workpiece before machining. If the deviation indicator indicates that the tooth thickness deviation exceeds a permissible value or that other pre-machining errors are present, a warning indicator is set accordingly to interrupt machining so that damage to the grinding wheel can be avoided. Optionally, the grinding wheel can then be checked for possible chipping due to insufficient previous pre-treatment of the workpiece.

[0042] The deviation indication is advantageously determined here with the aid of a centering probe which is already present in the machine tool anyway and is known per se, and which is designed for contactless measurement of the tooth gap of a workpiece tensioned on a workpiece spindle. The tooth thickness measurement can be calibrated by means of a calibration workpiece, and limit values ​​can be defined which the signal of the centering probe must comply with, whereby tooth thickness deviations are considered permissible. For example, an inductive or capacitive sensor which operates contactlessly can be used as a centering probe. That is, in this case, the centering probe fulfills a dual function: on the one hand, it is used for centering before the start of machining, and on the other hand, it is used to determine tooth thickness deviations. However, instead of a centering probe, a separate sensor can also be used to determine the tooth thickness, for example a separate optical sensor, which may be preferred at high rotational speeds.

[0043] Early indication of the danger of chipping of the grinding wheel can also be obtained in the following way: the monitored measured variable includes the speed deviation between the rotational speed of the workpiece spindle and the generated rotational speed of the workpiece. If such a deviation exists, this indicates that the workpiece is not correctly tensioned on the workpiece spindle and is not correctly driven by the workpiece spindle (slipping). This can lead to the workpiece not being in the correct angular position when engaging with the worm, so that the worm thread cannot correctly enter the tooth gap of the workpiece. In this situation, the workpiece cannot be processed correctly and high processing forces may occur, causing serious damage to the worm. By monitoring the rotational speed of the workpiece spindle and the workpiece, this situation can be recognized in an ideal case and the processing process can be stopped before the workpiece comes into contact with the worm. It may also be possible to avoid chipping of the grinding wheel. If a speed deviation is determined, a warning indication is set accordingly. Optionally, the grinding wheel is checked for damage based on the warning indication.

[0044] Other relevant measured variables are the rotational angular position of the workpiece spindle and the workpiece tensioned thereon before and after machining or the change in said angular position during machining. In particular, the monitored measured variables can include an angular deviation, which has been determined by comparing the angular position of the workpiece spindle after machining the workpiece, the associated angular position of the workpiece itself, the angular position of the workpiece spindle before machining the workpiece and the associated angular position of the workpiece itself. If this angular deviation indicates that the angular position after machining is different from the angular position on the workpiece spindle and on the workpiece itself before machining, this in turn indicates that the workpiece is not correctly driven by the workpiece spindle. This in turn forms a motivation for setting a warning indication accordingly and optionally checking whether the grinding wheel is damaged for safety reasons.

[0045] The rotational speed or angular position of the workpiece is advantageously determined here also by means of the already mentioned centering probe. Here again, the centering probe can fulfill a dual function: on the one hand, it is used for centering before the start of machining and on the other hand, it is used to monitor the actual machining process. However, instead of the centering probe, a separate sensor can also be used to determine the rotational speed and / or angular position of the workpiece, for example a separate optical sensor, which is particularly preferred at high rotational speeds.

[0046] The centering probe can advantageously be arranged on the side of the workpiece facing away from the grinding wheel. In this way, no collision occurs between the grinding wheel and the centering probe, and for the processing of the workpiece, there is enough space for the clamping jaws that are arranged parallel and laterally.

[0047] The monitored measured variables can also include a cutting power signal, which indicates the current cutting power during the machining of each individual workpiece. The warning indication is then related to the temporal profile of the cutting power signal during the machining of the workpiece. In particular, a pulse-like increase in the cutting power signal during machining can be a sign of a collision between the workpiece and the grinding worm thread, which can lead to chipping of the grinding wheel, and the warning indication can indicate this accordingly. In particular, the cutting power signal can be determined by current measurement on the tool spindle and can in this respect be a measure that represents the current current consumption of the tool spindle during the machining of the workpiece.

[0048] Another possibility for determining a warning indication is the following consideration: When machining a workpiece with a damaged grinding wheel, the amount of material stripped in the region of the grinding wheel chipping is less than the amount of material stripped in the intact region of the grinding wheel. In the variation curve of the displacement movement, the workpieces increasingly enter the region of the grinding wheel chipping and / or leave this region. Accordingly, the amount of material stripped per workpiece first decreases and then increases again. This is directly reflected in the machining energy used per workpiece, i.e. in the integral of the machining power over time.

[0049] In this regard, the method can include performing a continuous or discontinuous displacement movement between the grinding wheel and the workpiece along the tool axis. The monitored measured variables can then include a cutting energy indication for each workpiece, wherein the cutting energy indication is a measure of the integrated cutting power of the grinding wheel during machining of the respective workpiece with the gear grinding machine. The warning indication can then be related to how the cutting energy indication varies during the production of a plurality of workpieces of a production batch, i.e. between the workpieces.

[0050] The cutting energy indicator can in particular be the integral of the current consumption of the tool spindle during the machining of a single workpiece. However, as an alternative thereto, the cutting energy indicator can also be another characteristic value which is derived from the current consumption of the tool spindle during the machining of a single workpiece, for example a suitably determined maximum value of the current consumption.

[0051] In order to be able to carry out subsequent analysis, it is advantageous if the monitored measured variables and / or variables derived therefrom, in particular warning indicators, are stored in a database together with a clear identification of the corresponding workpiece. These data can then be read again at any time, for example during subsequent processing of workpieces of the same type.

[0052] The invention also relates to a gear grinding machine which is designed to carry out the method described above. To this end, the gear grinding machine has:

[0053] a tool spindle, on which a helically profiled grinding wheel having one or more worm threads can be tensioned and driven for rotation about a tool axis;

[0054] at least one workpiece spindle for driving the workpiece provided with the toothing to rotate about a workpiece axis; and

[0055] A machine control system is provided which is designed for a method of the type explained above.

[0056] For this purpose, the gear grinding machine can have further components, as mentioned in the context of the various methods.

[0057] In particular, the gear grinding machine can include a deviation determination device in order to determine the deviation of the tooth thickness of the workpiece to be machined. As already explained, the deviation determination device can in particular receive and evaluate the signal of the centering probe.

[0058] The gear grinding machine can also have a first rotation angle sensor for determining the rotation angle of the workpiece spindle and a second rotation angle sensor for determining the rotation angle of the workpiece about the workpiece axis. As already explained, the centering probe can again be used as the second rotation angle sensor. From the signals of the rotation angle sensor, the corresponding rotation angle can be derived in the rotation angle determination device, and the corresponding rotation speed can be derived in the rotation angle determination device.

[0059] The machine control of the gear grinding machine can also include: a cutting power determination unit in order to determine the cutting power signal explained above; and an analysis device, which is designed to analyze how the cutting power signal changes over time during the machining of the workpiece. The machine control can also include: a cutting energy determination device in order to calculate a cutting energy indication for each workpiece; and a further analysis device, which is designed to analyze how the cutting energy indication changes between the workpieces of a production batch. These devices can be implemented in software, for example in the following way: the machine control includes a microprocessor, which is programmed to perform the mentioned tasks. The cutting power determination device can be designed, for example, to read current signals from the axis module to control the tool spindle, and the cutting energy determination device can be designed to integrate these signals during the machining of the workpiece.

[0060] The machine control device can also include the database explained above, in which the measured variables and the variables optionally derived therefrom can be stored together with the clear identification of the corresponding workpiece and optionally other process parameters. However, the database can also be implemented in a separate server, which is connected to the machine control device via a network.

[0061] The machine control device can also have an output device for outputting the warning signal, for example an interface for outputting the warning signal in digital form to downstream devices, a display for displaying the warning signal, an acoustic output device or the like.

[0062] The gear grinding machine can also advantageously have the aforementioned dressing device, and the machine control can include a dressing control device and a dressing monitoring device for controlling the dressing spindle, in order to determine the aforementioned contact signal and / or dressing power signal and to determine the aforementioned chipping indication or chipping size from the variation curve of these signals. These units can again be implemented in software. In addition, the machine control can have an output device in order to output a chipping indication or chipping size.

[0063] In order to detect the contact between the dressing tool and the grinding wheel, the gear grinding machine can have the acoustic sensor mentioned above. The gear grinding machine can also have a power measuring device for determining the power consumption of the dressing spindle and / or a corresponding power measuring device for determining the power consumption of the tool spindle. For this purpose, the corresponding power measuring device can be designed for reading the current signal from the spindle module, for example, to control the dressing spindle or the tool spindle.

[0064] For process control, the gear grinding machine can include a correspondingly configured control device, which can include in particular the above-mentioned deviation determination device, rotation angle determination device, rotation speed determination device, cutting power determination device, cutting energy determination device, analysis device, dressing monitoring device, power measurement device and output device.

[0065] The present invention also provides a computer program. The computer program includes instructions, which cause a machine control device in the above-mentioned type of gear grinding machine, especially one or more processors of the machine control device, to execute the method described above. The computer program can be stored in a suitable storage device, such as a separate control device with a server. In particular, a computer-readable medium is also proposed, on which the computer program is stored. The medium can be a non-volatile medium, such as a flash memory, a CD, a hard disk, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The preferred embodiments of the present invention are described below based on the accompanying drawings, which are only used for illustration and should not be understood as limiting. In the accompanying drawings:

[0067] Figure 1 A schematic diagram of a gear grinding machine is shown;

[0068] Figure 2 In region II, Figure 1 The enlarged part of

[0069] Figure 3 In region III, Figure 1 The enlarged part of

[0070] Figure 4 Four photographs showing a grinding wheel having chipping in one or more of the worm threads;

[0071] Figure 5 Photographs showing damaged gear;

[0072] Figure 6 The following diagram is shown, which shows exemplary characteristic signals of a centering probe in good and poor pre-machining (fluctuations in tooth thickness deviation) of two workpieces;

[0073] Figure 7The following diagram is shown, which shows in part (a) the time curve of the rotational speed of the workpiece spindle when the workpiece spindle is accelerated to the operating speed and in part (b) the generated signal of the centering probe when the workpiece is not completely driven;

[0074] Figure 8 shows a diagram showing the time curve of the current consumption of the tool spindle during workpiece machining when the grinding wheel is in contact with the workpiece which is not in the correct angular position;

[0075] Fig. 9 The following diagram is shown, which shows the curve of the current consumption of the tool spindle over time when machining a workpiece without grinding wheel chipping and with a grinding wheel having large chipping;

[0076] Fig.10 The following diagram is shown, which shows the curve of the average power consumption of the tool spindle when machining workpieces of a production batch by means of a grinding wheel with a large chipping;

[0077] Fig.11 The following graph is shown, which exemplarily shows the change curve of the acoustic signal over time when the head of a grinding wheel with chipping is dressed;

[0078] Fig.12 The following diagram is shown, which shows the time curve of the current consumption of the dressing spindle for a grinding wheel without chipping (part (a)) and for a grinding wheel with chipping (part (b));

[0079] Fig.13 Two diagrams are shown which show the time course of the current consumption of a dressing spindle (part (a)) or a tool spindle (part (b)) when dressing a grinding wheel with chipping;

[0080] Fig.14 A flow chart showing a method of process monitoring for early identification of grinding wheel chipping; and

[0081] Fig.15 The flow chart shows the further process after the detection of a grinding wheel chip. DETAILED DESCRIPTION

[0082] Exemplary Configuration of a Gear Grinding Machine

[0083] exist Figure 1, a gear grinding machine 1 is shown by way of example. The machine has a machine bed 11 on which a tool carrier 12 is guided movably in a feed direction X. The tool carrier 12 carries an axial slide 13, which is guided movably relative to the tool carrier 12 in an axial direction Z. A grinding head 14 is mounted on the axial slide 13 and can be pivoted about a pivot axis (the so-called A-axis) extending parallel to the X-axis in order to adapt the inclination angle of the tooth to be machined. The grinding head 14 in turn carries a movable slide on which a tool spindle 15 is movable relative to the grinding head 14 along a movable axis Y. A worm-shaped grinding wheel 16 is tensioned on the tool spindle 15. The grinding wheel 16 is driven by the tool spindle 15 to rotate about the tool axis B.

[0084] The machine tool 11 also carries a pivotable workpiece carrier 20 in the form of a rotating tower, which can be pivoted about the axis C3 between at least three positions. On the workpiece carrier 20, two identical workpiece spindles are mounted diagonally opposite each other, wherein Figure 1 Only one workpiece spindle 21 with an associated tailstock 22 can be seen. Figure 1 The workpiece spindle visible in FIG. 1 is in a machining position in which a workpiece 23 clamped on the workpiece spindle can be machined with a grinding wheel 16. Another workpiece spindle arranged at 180° and Figure 1 The workpiece spindle, which is not visible in the drawing, is in a workpiece change position, in which a finished workpiece can be removed from the spindle and a new blank can be loaded. The dressing device 30 is mounted offset by 90° to the workpiece spindle.

[0085] All driven axes of the gear grinding machine 1 are digitally controlled by a machine control device 40. The machine control device 40 receives sensor signals from a large number of sensors in the gear grinding machine 1 and outputs control signals to the actuators of the gear grinding machine 1 based on these sensor signals. The machine control device 40 includes in particular a plurality of axis modules 41, which provide control signals at their outputs for each machine axis (i.e., for at least one actuator, such as a servo motor, which is used to drive the relevant machine axis). The machine control device also includes an operating panel and a control device 42 with a control computer, which cooperates with the operating panel 43 and the axis modules 41. The control device 42 receives operating instructions and sensor signals from the operating panel 43 and calculates control instructions for the axis modules based on them. In addition, the control device outputs operating parameters to the operating panel for display based on the sensor signals.

[0086] The server 44 is connected to the control device 42. The control device 42 transmits a clear identification and selected operating parameters (especially measured variables and variables derived therefrom) to the server 44 for each workpiece. The server 44 stores these data in a database so that the associated operating parameters can be called up later for each workpiece. The server 44 can be arranged inside the machine, or the server can be arranged away from the machine. In the latter case, the server 44 can be connected to the control device 42 via a network, especially via an internal LAN, via a WAN or via the Internet. The server 44 is configured to preferably receive and manage data of a single gear grinding machine. When using multiple gear grinding machines, a second server is usually used because the stored data can be accessed centrally and large amounts of data can be better processed. In addition, these data are better protected on the second server.

[0087] exist Figure 2 In the figure, the enlarged Figure 1 Part II in FIG. The tool spindle 15 with the grinding wheel 16 tensioned thereon can be seen. The detector 17 is pivotally mounted on the fixed part of the tool spindle 15. The detector 17 can optionally be Figure 2 The detector 17 is pivoted between a measuring position and a parking position. In the measuring position, the detector 17 can be used to measure the toothing of the workpiece 23 on the workpiece spindle 21 in contact. This occurs "online", that is, while the workpiece 23 is still on the workpiece spindle 21. This allows early identification of machining errors. In the parking position, the detector 17 is located in the following area, in which the detector is protected from collisions with other components on the workpiece spindle 21, the tailstock 22, the workpiece 23 and the workpiece carrier 20. During workpiece machining, the detector 17 is in this parking position.

[0088] The centering probe 24 is arranged on the side of the workpiece 23 away from the grinding wheel 16. In this example, the centering probe 24 is designed and arranged according to the document WO2017 / 194251 A1. Regarding the functionality and arrangement of the centering probe, explicit reference is made to the mentioned document. In particular, the centering probe 24 can include an inductive or capacitive proximity sensor, as known from the prior art. However, it is also conceivable that the centering operation is performed using an optically working sensor, which, for example, directs a light beam to the tooth to be measured and detects the light reflected by the tooth, or the optically working sensor detects the interruption of the light beam caused by the tooth during the rotation of the tooth to be measured around the workpiece axis C1. In addition, it is conceivable that one or more additional sensors are arranged on the centering probe 24, which can detect process data directly on the workpiece, as proposed in US 6,577,917 B1. Such additional sensors can, for example, include a second centering sensor for a second tooth, a temperature sensor, another structure-borne sound sensor, a pneumatic sensor, etc.

[0089] In addition, the acoustic sensor 18 is Figure 2 The acoustic sensor 18 is used to record the structure-borne sound of the tool spindle 15 during the grinding of the workpiece and the dressing of the grinding wheel. In practice, the acoustic sensor is usually not used (e.g. Figure 2 15) on a housing part, but for example directly on the stator of a drive motor of the tool spindle 15 in order to ensure effective sound transmission. Acoustic sensors or structure-borne sound sensors of the type mentioned are known per se and are conventionally used in gear grinding machines.

[0090] The coolant nozzle 19 directs the coolant jet into the machining area. In order to record the noise transmitted via the coolant jet, a further acoustic sensor (not shown) can be provided.

[0091] exist Figure 3 The enlarged Figure 1 Part III in FIG. Here the dressing device 30 can be seen particularly clearly. A dressing spindle 32 is arranged on a pivot drive 31 that can be pivoted about an axis C4, on which a disc-shaped dressing tool 33 is tensioned. Alternatively or in addition, a fixed dressing tool can also be provided, in particular a so-called head dresser, which is provided to engage only with the head region of the worm thread of the grinding wheel in order to dress these head regions.

[0092] Batch processing of workpieces

[0093] In order to machine a workpiece (blank) that has not yet been machined, the workpiece is tensioned on the workpiece spindle located in the workpiece change position by means of an automatic workpiece changer. The workpiece change takes place simultaneously with the machining of another workpiece on another workpiece spindle located in the machining position. When the new workpiece to be machined is tensioned and the machining of the other workpiece is completed, the workpiece carrier 20 is pivoted 180° about the C3 axis so that the spindle with the new workpiece to be machined enters the machining position. Before and / or during the pivoting process, a centering operation is performed with the aid of an associated centering probe. For this purpose, the workpiece spindle 21 is set into rotation and the position of the tooth gap of the workpiece 23 is measured with the aid of a centering probe 24. The bite angle is determined on this basis. In addition, with the aid of the centering probe, indications of excessive changes in tooth thickness deviations and other pre-machining errors can be derived before machining begins. This will be described below in conjunction with the centering probe. Figure 6 Elaborate in detail.

[0094] When the workpiece spindle carrying the workpiece 23 to be machined has reached the machining position, the workpiece 23 is brought into collision-free engagement with the grinding wheel 16 by moving the tool carrier 12 along the X axis. The workpiece 23 is now machined by the grinding wheel 16 in rolling engagement. At the same time, the tool spindle 15 is slowly and continuously moved along the movement axis Y in order to allow the use of areas of the grinding wheel 16 that have not been used during the ongoing machining process (so-called displacement movement). Once the machining of the workpiece 23 is completed, the workpiece is optionally measured online with the aid of a probe 17.

[0095] While a workpiece is being machined, the finished workpiece is removed from the other workpiece spindle and another blank is tensioned on the spindle. During each pivoting of the workpiece carrier about the C3 axis, the selected components are monitored before the pivoting or during the pivoting time, i.e. time-neutrally, and the machining process is continued only when all defined requirements are met.

[0096] If, after machining a certain number of workpieces, the use of the grinding wheel 16 has developed to the point where the grinding wheel is too blunt and / or the flank geometry is too inaccurate, the grinding wheel is dressed. To this end, the workpiece carrier 20 is pivoted by ±90° so that the dressing device 30 is brought into its position opposite the grinding wheel 16. The grinding wheel 16 is now dressed with the dressing tool 33.

[0097] Grinding wheel chipping

[0098] During processing, the grinding wheel may break. Figure 4Different forms of grinding wheel chipping 51 on a grinding wheel worm are described. In part (a), a single worm thread is almost completely broken within a certain angular range. In part (b), multiple worm threads are locally damaged at multiple different positions in the head area. In part (c), there are also multiple local damages, but deeper than in part (b). In part (d), the grinding wheel is equally severely damaged in two areas, where multiple adjacent worm threads are almost completely broken. All these damage situations can occur in practice and lead to different effects when machining workpieces.

[0099] Figure 5 Description of an incorrectly machined gear. Since the gear engages the grinding wheel in the wrong angular position, so that the grinding wheel thread does not properly enter the gear tooth gap, all teeth 52 are damaged in their head area. This situation can occur if the centering operation is carried out incorrectly or if the gear is not properly driven when the workpiece spindle is accelerated to its operating speed. This situation usually leads not only to gear damage, but also to severe chipping of the grinding wheel. This means that this situation should be detected and prevented as early as possible.

[0100] Indication of possible grinding wheel chipping through process monitoring

[0101] In order to prevent chipping of the grinding wheel as far as possible or to be able to detect chipping at an early stage if it occurs, various operating parameters are continuously monitored during the processing of a production batch. In addition, the parameters or the variables derived therefrom are also stored in a database in order to be able to perform subsequent analyses. Of particular importance in this regard are the speed, angular position and current consumption of the tool spindle, workpiece spindle and dressing spindle, the speed and angular position of the workpiece itself, the signals of the centering probe and the positions of the linear axes of the machine. Figures 1 to 3 In the embodiment of the present invention, the control device 42 is used for monitoring. In particular, the operating parameters of the gear grinding machine to be discussed below are monitored:

[0102] (a) Determine the pre-machining error with the aid of a centering probe

[0103] Figure 6 A typical signal is described, as received from the centering probe 24. It is a binary signal which indicates a logical 1 if there is a tooth head region in front of the centering probe and a logical 0 if there is a tooth gap in front of the centering probe. The pulse width Pb or the duty cycle derived from it of the signal of the centering probe is a measure of the tooth thickness and thus the deviation between the measured thickness and the expected thickness (“deviation indicator”). Figure 6 In part (a), the pulse width Pb is small, which indicates that the deviation is small (maybe even negative), while in part (b), the pulse width Pb is large, which indicates that the deviation is large (maybe too large). Figure 6The change in pulse width Pb is shown in an intentionally exaggerated manner.

[0104] In other words, conclusions about the deviation of each tooth can be drawn directly from the signal pattern of the centering probe 24. From this, it is possible to deduce an indication of a pre-processing error, such as an excessive deviation or an unevenness.

[0105] The control device 42 receives the signal of the centering probe and derives therefrom a warning indication, which indicates whether there is an indication of a pre-machining error. If this is the case, machining is stopped before contact between the workpiece 23 and the grinding wheel 16 is caused in order to prevent damage to the grinding wheel 16. In addition, the warning indication can trigger an inspection of the grinding wheel to determine whether there is damage caused by a previous workpiece.

[0106] (b) Monitor the speed of the workpiece spindle and workpiece

[0107] Figure 7 How to set the speed n of the workpiece spindle 21 w The speed n of the workpiece spindle 21 is compared with the speed of the workpiece 23 clamped thereon. w Ability to directly control the machine ( Figure 7 The rotational speed of the workpiece is determined again with the aid of the centering probe 24. For this purpose, Figure 7 In part (b) a typical signal is shown, as received from the centering probe 24. In this example, the signal has a period Pd of continuous decline during which the workpiece spindle has reached the desired rotational speed. The signal therefore indicates that the workpiece 23 is still accelerating, while the workpiece spindle 21 has reached its desired rotational speed. That is, in this example, the workpiece 23 is not properly driven on the workpiece spindle 21.

[0108] This can happen if tolerance values ​​are exceeded during pre-machining of the workpiece clamping base (e.g. borehole and flat sides). The workpiece is usually driven with a defined friction fit; that is, by the expansion of the clamping jaws, a friction torque acts on the workpiece borehole and radial friction forces are generated on the two flat sides by the axial pressing force. However, if the workpiece borehole is too large and / or the flat sides are too skewed, this friction fit is reduced and slippage occurs between the workpiece spindle and the workpiece above a critical value.

[0109] If a deviation is detected between the rotational speeds of the workpiece and the workpiece spindle, it is sensible to immediately stop further processing in order to prevent damage to the grinding wheel 16. Since it cannot be ruled out whether the grinding wheel 16 has already been damaged, it is also sensible to check whether the grinding wheel 16 is damaged.

[0110] For this purpose, the control device 42 monitors the signal of the centering probe 24 and the rotational speed signal of the workpiece spindle from the associated axis module 41. In the event of a deviation, the control device 42 sets a warning indication. Before contact between the workpiece 23 and the grinding wheel 16 is caused, the machining is stopped according to the warning indication. In addition, the warning indication can trigger an inspection of the grinding wheel to determine whether there is damage caused by the previous workpiece.

[0111] (c) Monitor the rotation angle of the workpiece spindle and workpiece

[0112] Instead of comparing the rotational speeds or in addition thereto, a comparison of the rotation angles of the workpiece spindle and the associated workpiece can also be performed before and after machining. If there are deviations here as well, this also indicates that slippage is present and it is sensible to check the grinding wheel 16 for possible damage. Accordingly, in this case, the control device 42 also sets a warning indication.

[0113] (d) Monitor the current cutting power

[0114] exist Figure 8 Another possibility for early detection of possible grinding wheel chipping is described in FIG. 61 . The current consumption I of the tool spindle as a function of time during the machining of a single workpiece is shown in the measurement curve 61 . s The current consumption of the tool spindle is I s is a direct indication of the current cutting power. In this respect, it can be understood as an example of a cutting power signal.

[0115] In the present example, curve 61 shows a sudden sharp rise and a subsequent sharp fall in the current consumption at the start of machining. This indicates that one of the teeth of the workpiece has collided with the worm thread of the grinding wheel 16. Even in this case, it is sensible to immediately stop further machining and check the grinding wheel 16 for possible damage. For this purpose, the control device 42 again sets a corresponding warning indicator.

[0116] (e) Monitoring cutting energy for each workpiece

[0117] Another (but relatively late) possibility for identifying possible grinding wheel chipping is based on monitoring the energy that has been applied to the cutting process for each workpiece ("cutting energy"). This is a measure of the amount of material that is cut during the machining of the relevant workpiece. When machining through a grinding worm area that is damaged by chipping, the amount of material that is cut is usually less than when machining through an undamaged worm grinding area. It is therefore possible to obtain an indication of possible grinding wheel chipping by monitoring the cutting energy for each workpiece.

[0118] This is Fig. 9 and 10 Detailed description in. Fig. 9The measurement curve 62 shows the current consumption I of the tool spindle as a function of time during machining of a single workpiece with an undamaged grinding worm. s . The measurement curve 63 describes the course of the current consumption when machining in the area of ​​a large chipping of the grinding worm. Due to the chipping, the cutting power and thus the current consumption of the tool spindle are greatly reduced. The integral of the current consumption during the duration required for machining a single workpiece (i.e. the area under the corresponding measurement curve) is a measure of the total cutting energy that has been used for the workpiece, i.e. a measure of the amount of material removed per workpiece. When machining in the area of ​​a chipping of the grinding wheel, this integral is smaller than when machining through an undamaged area of ​​the grinding wheel.

[0119] In addition to the integral of the current consumption, other variables can also be used as a measure of the total cutting energy, such as the average value, the maximum value (optionally after a smoothing operation in order to eliminate outliers) or the result of a fit to a preset shape of the current variation curve. In this regard, the measure of the total cutting energy is also referred to as a cutting energy indicator.

[0120] Fig.10 Indicates the average current consumption I of the tool spindle if the grinding wheel is damaged during machining from workpiece to workpiece N. av How it changes. Machining starts with a grinding wheel with a large central chip. At the beginning of the machining cycle, the workpiece is machined by the first, undamaged end of the grinding wheel. As machining proceeds, the grinding wheel is continuously moved so that more and more of the area with the chip is used for machining. Towards the end of the cycle, the opposite, likewise undamaged end of the grinding wheel engages the workpiece. Accordingly, the average current consumption I of the tool spindle is av Initially it decreases and then increases again towards the end of the cycle. This results in an average current consumption I from the first workpiece to the Nth workpiece. av characteristic change curve.

[0121] The cycle ends at point 65, the grinding wheel is dressed, and a new cycle begins. During the dressing, the damaged worm thread is gradually restored, so that the average current consumption I av The changes become smaller and smaller in subsequent cycles.

[0122] That is to say, if Fig.10 As shown in the example, the current variation curve 64 can be evaluated as an indication of a chipping of the grinding wheel. In order to check whether there is actually a chipping, it is also meaningful to stop processing and check whether the grinding wheel has possible damage. For this reason, in this case, the control device 42 also provides a corresponding warning indication.

[0123] Automatically check whether the grinding wheel has cracks

[0124] The grinding wheel can be automatically checked for possible damage by passing a dressing tool over the grinding wheel in the region of the head of its worm thread and detecting the contact between the grinding wheel and the dressing tool.

[0125] As in Fig.11 As described in , the contact can be detected acoustically. For example, the acoustic signal V during the trimming process is shown as an example a The time variation curve of Figure 2 As determined by the acoustic sensor 18 shown in FIG. 1 , during the dressing process, the dressing tool intentionally contacts only the head region of the worm thread. The signal indicates when the dresser engages and disengages the head region. If the grinding wheel is not damaged, a periodic signal can be expected. If the signal has gaps, such as Fig.11 If there is a gap 72 in the worm screw, then this indicates a break in the worm thread.

[0126] Alternatively, the dressing process can also be started directly and automatically, as described below, because even when dressing, it is possible to reliably detect whether the grinding wheel is chipped. However, disadvantageously, a significantly lower grinding wheel speed must be used when dressing, thereby slightly increasing the non-productive time of this control measure.

[0127] Other methods for automatically checking whether the grinding wheel is damaged are also conceivable. Thus, for example, it is possible to check whether the grinding wheel is damaged using an optical sensor or it is possible to check whether the grinding wheel is damaged using the noise caused by the coolant jet from the coolant nozzle 19 when it hits the grinding wheel. The measurement of structure-borne noise using a coolant jet is known per se (see, for example, Klaus Nordmann, "Prozessüberwachung beim Schleifen und Abrichten", Schleifen+Polieren 05 / 2004, Professional Publishers Velbert (Germany), pp. 52-56), however, it has not been used to identify grinding wheel chipping.

[0128] Other symptoms of grinding wheel chipping

[0129] If a chip is reliably confirmed in this way, it is sensible to completely dress the grinding worm and thereby determine further features of the chip and / or eliminate it. Fig.12 and 13 In the description.

[0130] Fig.12 Describes how grinding wheel chipping can be characterized in detail during dressing using current measurement. Fig.12In part (a) a measurement curve 81 is shown which describes the current consumption I of the dressing spindle as a function of time in the case of a dressed grinding wheel when the grinding wheel is evenly worn and has no chipping. d The measured curve 81 is always above the lower envelope 82. Part (b) shows the current consumption I for a grinding wheel with a single, deep chipping. d During the working period of the dressing tool in the chipping area of ​​the grinding wheel, the current consumption I d It shows strong fluctuations, especially strong declines.

[0131] In the simplest case, such fluctuations can be detected by monitoring whether the value of the current consumption drops below the lower envelope 82. In the area where this occurs, it can be inferred that there is a chipping of the grinding wheel. Of course, more sophisticated methods can also be used to identify fluctuations in the current consumption. For example, a mean value 83 of the current consumption can be formed, and the deviation from the mean value downward (here: minimum value 84) and / or upward (here: maximum value 85) can be monitored to see whether it is within a specific tolerance range. Regardless of how the fluctuations are identified in detail, the position of the chipping along the relevant worm thread can be inferred from the time point or rotation angle at which the fluctuation occurs. The degree of damage to the worm thread can be inferred from the size of the fluctuation.

[0132] Fig.13 It is shown that both the current consumption of the dressing spindle and the current consumption of the tool spindle can be used to characterize the chipping of the grinding wheel. d The time curve, in part (b), describes the current consumption I of the tool spindle during the dressing of a grinding wheel with chipping. s It can be seen that not only the current consumption of the dressing spindle shows fluctuations, but also the current consumption of the tool spindle during the time period of dressing in the area of ​​chipping. However, these fluctuations are more pronounced in the current consumption of the dressing spindle, so that the current consumption of the dressing spindle is usually preferred over the current consumption of the tool spindle as a measured variable for characterizing chipping of the grinding wheel.

[0133] By optionally multiple dressing, a grinding wheel chipping characterized in this way can be eliminated. If the chipping is very large and its elimination by dressing may take a long time, it can also be sensible to abandon the further dressing process and replace the damaged grinding wheel or use the grinding worm only in the undamaged area of ​​the grinding worm for further workpiece processing.

[0134] Example of a method for automated process control

[0135] Fig.14 and15 A possible method for automatic process control that implements the above considerations is described by way of example.

[0136] In the machining process 110, workpieces of a workpiece batch are machined one after the other by means of a gear grinding machine. Before and during the machining 111 of each workpiece, in particular the previously described measured variables are determined and monitored in a monitoring step 112. In particular, the pulse width Pb of the signal of the centering probe is monitored in order to determine whether a pre-machining error exists. In addition, the rotational speed n of the workpiece spindle is monitored. W The speed of the workpiece n A Is the difference between the two larger than a (selected small) threshold n? t In addition, the angular changes of the workpiece spindle during machining are monitored Angular change with the workpiece Is the difference between the two greater than a (also chosen small) threshold?

[0137] In addition, the current consumption of the tool spindle is monitored for each workpiece. s (t), and monitor the change of the average spindle current I from workpiece to workpiece N av (N) In step 113, a warning indication W is continuously determined based on the results of the monitoring.

[0138] Based on the warning indication, the following decision is automatically made in decision step 114:

[0139] 1. If the warning indication does not indicate any problem (e.g., as long as the warning indication is less than a threshold value W t ), then workpiece processing continues normally.

[0140] 2. If the warning indicates a possible problem, the processing of the workpiece is temporarily stopped. Based on the warning, a decision is made whether to sort the workpiece immediately (which makes sense, for example, if the warning indicates incorrect pre-processing or tensioning of the workpiece with slippage), or whether to wait for the grinding wheel to be checked first.

[0141] The grinding wheel is then checked for possible chipping in step 120. In the present example, for this purpose, a dressing tool is passed over the head region of the grinding worm thread in step 121. In step 122, it is determined by acoustic or current measurement whether there is contact between the dressing tool and the worm, and a contact signal is output accordingly. In step 123, a chipping indication A is determined from the time curve of the contact signal. In decision step 124, it is checked whether the chipping indication A exceeds a certain threshold value A. t .

[0142] If this is not the case, continue workpiece processing so. Here, optionally, reduce the stripping power, so as to reduce the probability that the warning indication shows a possible problem again in a subsequent workpiece.

[0143] On the other hand, if the chipping indication exceeds the threshold, then in process 130, the chipping of the grinding wheel is characterized in detail and optionally eliminated. For this reason, the grinding wheel is usually dressed with multiple dressing strokes (step 131), and a dressing power signal is determined for each dressing stroke during dressing (step 132). The chipping size M is determined in each dressing stroke according to the dressing power signal (step 133). In decision step 134, it is checked whether the chipping size M indicates that the chipping can be meaningfully eliminated. If this is not the case, then in decision step 136, it is further checked whether the chipping is limited to a sufficiently small area of ​​the grinding wheel so that it can still be processed by the undamaged area of ​​the grinding wheel. If this is also not feasible in a meaningful way, then in step 137, the operator is instructed to replace the grinding wheel. On the other hand, if the chipping size M indicates that it is feasible to eliminate the chipping by dressing, then in decision step 135, it is checked whether the last dressing process performed is sufficient to eliminate the chipping. If this is the case, continue processing (step 138). Otherwise, the characterization and elimination process 130 is repeated until the chip size M indicates that the chip has been sufficiently eliminated, and processing is resumed again.

[0144] Overall, a decision can thus be made automatically, quickly and reliably for each workpiece: whether machining is possible or not, or whether the machining already achieved should be checked individually in case of doubt.

[0145] Modification

[0146] Although the invention has been described above with reference to preferred embodiments, the invention is not in any way limited to these examples and a large number of modifications are possible without departing from the scope of the invention. Thus, as is known to a person skilled in the art, the gear grinding machine can also be designed differently from the examples described above. The method described can of course also include other measures for monitoring and decision making.

[0147] Other considerations

[0148] In summary, the invention is based on the following consideration: Despite the complexity of gear grinding, a robust process control is the goal of automated production, which provides the required quality as trouble-free and fast as possible. It is also meaningful to associate automatically created documentation about its processing and final quality with each gear. For reliable traceability of all relevant production steps with "clicks" and for general process optimization and / or efficiency improvement, online data should be available.

[0149] Therefore, the present invention uses the following measures: the indication of process deviations, especially chippings of different sizes, can be detected and a warning signal can be output. In particular, the warning signal can be determined based on the signal of the centering probe or by measuring the current value on the tool spindle.

[0150] The warning signal can immediately stop the processing, the fully or partially processed workpieces are optionally automatically sorted as NIO parts with the help of a processing instrument, and the control device determines and optionally stores the displacement position of the grinding wheel worm or the Y position in the case of defects. The grinding wheel is then checked for chipping. To this end, the minimum amount of the head area of ​​the grinding worm is dressed with a dresser at the operating speed of the grinding spindle, and the signals of the current and / or acoustic sensors are detected in this process in order to reliably identify chipping. Alternatively, the presence of chipping is checked by another method, for example optically, acoustically with the help of a coolant jet, or through a complete dressing stroke. This process can also be performed at fixed time intervals and without a warning signal from the centering probe, because smaller chipping on the grinding worm can be identified, which is not caused by an incorrectly processed workpiece. If the measurement determines that there is a chipping, the control device makes the following decision:

[0151] It is prohibited to continue processing the production batch and to use the damaged area on the grinding worm for further processing;

[0152] Dressing the grinding worm and possibly continuing machining thereafter with reduced stock removal values; or

[0153] The grinding worm is replaced and the production batch is completed with the new grinding worm.

[0154] When dressing a grinding wheel, it should be noted that the first dressing stroke is usually carried out with the set values ​​for the production batch. Therefore, in the case of large and very large chipping, long dressing times may be required. In this case, adaptive or self-learning dressing can save a lot of time and can save the equally time-consuming replacement of the grinding worm.

[0155] However, if the measurement does not determine the presence of chipping on the grinding worm, the control unit makes the following decisions despite the detection of the warning signal:

[0156] Continue processing the production batch with reduced cutting values;

[0157] Processing of the production batch is stopped and the operator is notified.

[0158] For this purpose, during grinding and dressing with the aid of a CNC gear grinding machine with peripheral automation technology for the transport of workpieces, the production batch can be automatically monitored in the process by means of a separate control device and a connected server. The control device is therefore set up so that, for each workpiece of a production batch, all sensor data of the gear grinding machine, the corresponding set values ​​and processing values, preferably the current values ​​at the tool spindle, the workpiece spindle and the dressing spindle, and the signals of the centering probe are preferably continuously detected and stored in the server. Optionally, at each automatically performed workpiece change, a time-neutral component monitoring can be carried out, which can allow processing if there are no objections. In particular, a cutting power signal and a cutting energy indication are also determined, which are linked to other data in the control device and, after the first workpiece is processed, are also linked to the data stored in the server. Warning indications can then be output at an early stage.

[0159] Reference numerals list

[0160] 1 Gear grinding machine

[0161] 11 Machine Tools

[0162] 12 Tool carrier

[0163] 13 Axial slide

[0164] 14 Grinding head

[0165] 15 Tool spindle

[0166] 16 Grinding wheel

[0167] 17 Detector

[0168] 18 Acoustic Sensor

[0169] 19 Coolant nozzle

[0170] 20 Workpiece carrier

[0171] 21 Workpiece spindle

[0172] 22 Tailstock

[0173] 23 Workpiece

[0174] 24 Centering probe

[0175] 31 Pivot device

[0176] 32 Dressing spindle

[0177] 33 Dressing tools

[0178] 40 Machine control device

[0179] 41 axis module

[0180] 42 Control Equipment

[0181] 43 CNC operation panel

[0182] 44 Server

[0183] 51 Grinding wheel crack

[0184] 52 teeth

[0185] 61-63 Measurement curve

[0186] 64 Current change curve

[0187] 65 Repair time

[0188] 71 Measurement curve

[0189] 72 Gap

[0190] 81 Measurement curve

[0191] 82 Envelope Curve

[0192] 83 Average

[0193] 84 Min.

[0194] 85 Max.

[0195] 110 Process

[0196] 111 Workpiece processing

[0197] 112 Monitoring

[0198] 113 Confirm W

[0199] 114 Decision-making Steps

[0200] 120 Crack Identification Process

[0201] 121 Pass

[0202] 122 Confirm contact signal

[0203] 123 Confirm A

[0204] 124 Decision-making Steps

[0205] 130 Characterization / Elimination

[0206] 131 Trim

[0207] 132 Determine trim power

[0208] 133 Confirm M

[0209] 134-136 Decision-making Steps

[0210] 137 Replace grinding wheel

[0211] 138 Continue processing

[0212] au arbitrary unit

[0213] A. Collapse Indicator

[0214] A t Threshold for crack indication

[0215] B Tool axis

[0216] C1 Workpiece axis

[0217] C3 Pivot axis of workpiece carrier

[0218] C4 Pivot axis for dressing equipment

[0219] I av Average current consumption of tool spindle

[0220] I d Current consumption of dressing spindle

[0221] I s Current consumption of tool spindle

[0222] M chip size

[0223] n A Workpiece speed

[0224] n t Speed ​​difference threshold

[0225] n W Workpiece spindle speed

[0226] N is the number of workpieces in a batch

[0227] Pb Pulse width of centering signal / tooth

[0228] Pd Duration of the signal period of the centering signal / tooth

[0229] t time

[0230] V a Sound signal

[0231] W Warning indicator

[0232] W t Thresholds for warning indications

[0233] X feed direction

[0234] Y Shift Axis

[0235] Z-axis direction

[0236] Angular variation of the workpiece

[0237] Threshold of angle change difference

[0238] Angular variation of the workpiece spindle

Claims

1. A method for automatic process monitoring during the continuous gear grinding of a workpiece (23) with a predetermined gearing by means of a gear grinding machine (1), in, The gear grinding machine (1) has a tool spindle (15) and at least one workpiece spindle (21), wherein a worm-shaped grinding wheel (16) is tensioned on the tool spindle (15), the grinding wheel having one or more worm threads, wherein the grinding wheel (16) is rotatable about a tool axis (B), and wherein the workpiece (23) can be tensioned on the at least one workpiece spindle (21), The method comprises: The workpiece (23) is machined by means of the gear grinding machine (1), wherein the workpiece (23) is tensioned on the at least one workpiece spindle (21) for machining and successively brought into rolling engagement with the grinding wheel (16); and monitoring at least one measured variable during machining of the workpiece (23), determining a warning indicator (W) for an impermissible process deviation from at least one monitored measured variable, The invention is characterized in that the warning indication (W) is a warning indication for possible grinding wheel chipping (19), and If the warning indication (W) indicates the presence of a grinding wheel chip (19), an automatic inspection of the grinding wheel (16) is performed to determine whether a grinding wheel chip (19) is present.

2. The method according to claim 1, wherein: The gear grinding machine (1) has a dressing device (30) having a dressing tool (33), and wherein automatically checking whether the grinding wheel (16) has a grinding wheel chip (19) comprises the following steps: Passing the dressing tool (33) through the head region of the grinding wheel (16); determining a contact signal during passage through the head region, wherein the contact signal indicates contact of the dressing tool (33) with the head region of the grinding wheel (16), and A chipping indication (A) is determined by analyzing the contact signal, wherein the chipping indication (A) indicates whether a grinding wheel chipping (19) exists.

3. The method according to claim 2, wherein the gear grinding machine has an acoustic sensor (18) for acoustically detecting the engagement of the dressing tool (33) with the grinding wheel (16), and wherein the contact signal comprises an acoustic signal (V a ), the acoustic signal being determined by means of the acoustic sensor (18).

4. The method according to claim 2 or 3, wherein: The dressing device (30) has a dressing spindle (32) on which the dressing tool (33) is tensioned, and wherein the contact signal comprises a head dressing power signal, which represents the power consumption of the dressing spindle (32) during a passage through the head region.

5. The method according to claim 2 or 3, wherein: The chipping indication (A) indicates the location of the grinding wheel chipping (19) along at least one of the worm thread lines on the grinding wheel (16).

6. The method according to claim 2, wherein the method comprises: If the chipping indication (A) indicates the presence of grinding wheel chipping (19), the grinding wheel (16) is dressed.

7. The method according to claim 1, wherein: The gear grinding machine (1) has a dressing device (30) having a dressing tool (33), and wherein the automatic inspection of the grinding wheel (16) for the presence of grinding wheel chips (19) comprises dressing the grinding wheel (16) by means of at least one dressing stroke.

8. The method according to claim 6 or 7, wherein: The dressing device (30) has a dressing spindle (32) on which the dressing tool (33) is tensioned, wherein the method comprises: determining a dressing power signal during dressing, wherein the dressing power signal is indicative of power consumption of the dressing spindle (32) or tool spindle (15) during dressing; Determining a chipping size (M) by analyzing a variation curve of a dressing power signal during dressing, wherein the chipping size (M) reflects at least one characteristic of the chipping of the grinding wheel; and The dressing of the grinding wheel is repeated according to the chipping size (M).

9. The method according to claim 8, wherein the analysis of the variation curve of the trimmed power signal comprises: A fluctuation magnitude is determined, wherein the fluctuation magnitude indicates a local variation in magnitude of the dressing power signal along at least one of the worm threads.

10. The method according to claim 1, wherein at least one monitored measured variable and / or at least one variable derived therefrom is stored in a database together with an unambiguous identification of the corresponding workpiece (23).

11. A method for automatic process monitoring during the continuous gear grinding of a workpiece (23) with a predetermined gearing by means of a gear grinding machine (1), in, The gear grinding machine (1) has a tool spindle (15) and at least one workpiece spindle (21), wherein a worm-shaped grinding wheel (16) is tensioned on the tool spindle (15), the grinding wheel having one or more worm threads, wherein the grinding wheel (16) is rotatable about a tool axis (B), and wherein the workpiece (23) can be tensioned on the at least one workpiece spindle (21), The method comprises: The workpiece (23) is machined by means of the gear grinding machine (1), wherein the workpiece (23) is tensioned on the at least one workpiece spindle (21) for machining and successively brought into rolling engagement with the grinding wheel (16); and monitoring at least one measured variable during machining of the workpiece (23), determining a warning indicator (W) for an impermissible process deviation from at least one monitored measured variable, wherein at least one monitored measured variable comprises a deviation indication (Pb) for a tooth thickness deviation of the workpiece (23) prior to machining; and / or At least one of the monitored measured variables includes the rotational speed (n A ) and the resulting rotational speed (n w ), and / or At least one of the monitored measured variables comprises an angular deviation determined by comparing the angular position of the workpiece spindle (21) after machining the workpiece (23), the associated angular position of the workpiece (23) itself, the angular position of the workpiece spindle (21) before machining the workpiece, and the associated angular position of the workpiece itself.

12. A method according to claim 11, wherein the gear grinding machine has a centering probe (24) for contactlessly determining the angular position of a workpiece (23) tensioned on at least one workpiece spindle (21), and wherein the deviation indication (Pb), the rotational speed of the workpiece (23) or the corresponding angular position is detected by the centering probe (24).

13. A method for automatic process monitoring during the continuous gear grinding of a workpiece (23) with a predetermined gearing by means of a gear grinding machine (1), in, The gear grinding machine (1) has a tool spindle (15) and at least one workpiece spindle (21), wherein a worm-shaped grinding wheel (16) is tensioned on the tool spindle (15), the grinding wheel having one or more worm threads, wherein the grinding wheel (16) is rotatable about a tool axis (B), and wherein the workpiece (23) can be tensioned on the at least one workpiece spindle (21), The method comprises: The workpiece (23) is machined by means of the gear grinding machine (1), wherein the workpiece (23) is tensioned on the at least one workpiece spindle (21) for machining and successively brought into rolling engagement with the grinding wheel (16); and at least one measured variable is monitored during machining of the workpiece (23), and determining a warning indicator (W) for an impermissible process deviation from at least one monitored measured variable, The warning indication (W) is a warning indication for possible grinding wheel chipping (19), and In this case, at least one monitored measured variable comprises a cutting power signal which indicates the current cutting power during machining of each individual workpiece (23), and in which the warning indication (W) is associated with the occurrence of a pulsed increase in the cutting power signal during machining.

14. The method according to claim 13, wherein: The cutting power signal is the current current consumption (I S ) measurement.

15. A method for automatic process monitoring during the continuous gear grinding of a workpiece (23) with a predetermined gearing by means of a gear grinding machine (1), in, The gear grinding machine (1) has a tool spindle (15) and at least one workpiece spindle (21), wherein a worm-shaped grinding wheel (16) is tensioned on the tool spindle (15), the grinding wheel having one or more worm threads, wherein the grinding wheel (16) is rotatable about a tool axis (B), and wherein the workpiece (23) can be tensioned on the at least one workpiece spindle (21), The method comprises: The workpiece (23) is machined by means of the gear grinding machine (1), wherein the workpiece (23) is tensioned on the at least one workpiece spindle (21) for machining and successively brought into rolling engagement with the grinding wheel (16); and monitoring at least one measured variable during machining of the workpiece (23), determining a warning indicator (W) for an impermissible process deviation from at least one monitored measured variable, Wherein, the warning indication (W) is a warning indication for possible grinding wheel chipping (19), The method comprises performing a continuous or discontinuous displacement movement between the grinding wheel (16) and the workpiece (23) along a tool axis (B); At least one of the monitored measured variables comprises a cutting energy indicator (I av ), Wherein, the cutting energy indication (I av ) is a measure of the integrated cutting power of the grinding wheel (16) during the machining of a corresponding workpiece (23) by the gear grinding machine (1); and The warning indication (W) and the cutting energy indication (I av ) during the production of multiple workpieces (23) of a production batch.

16. The method according to claim 15, wherein: The cutting energy indication (I av ) is a measure of the integration of the current consumption of the tool spindle (15) during the machining of a single workpiece (23).

17. A gear grinding machine (1), comprising: a tool spindle (15) on which a worm-shaped profiled grinding wheel (16) having one or more worm threads can be tensioned and driven to rotate about a tool axis (B); At least one workpiece spindle (21) for driving a workpiece (23) with a preset tooth portion to rotate around a workpiece axis (C1); and Machine control device (40); It is characterized in that The machine control (40) is configured to carry out the method according to any of the preceding claims.

18. A computer-readable medium having a computer program stored thereon, the computer program comprising instructions for causing a machine control device (40) in a gear grinding machine (1) according to claim 17 to execute a method according to any one of claims 1 to 16.

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