Method for automatic process monitoring during continuous generating grinding

Abstract

A method for automatic process monitoring during continuous generating grinding of pre-toothed workpieces is proposed, enabling early detection of wheel breakout. A generating grinding machine is used to machine multiple workpieces. For this purpose, the workpieces are clamped on at least one workpiece spindle and subsequently transferred into generating engagement with the grinding wheel. At least one measurement variable is monitored during machining. A warning indicator for wheel breakout is determined from the measurement variable. If the warning indicator indicates wheel breakout, the wheel is automatically inspected. For this purpose, a dressing tool is moved over the tip region of the wheel, and a contact signal is determined during its movement over the tip region. A breakout indicator is determined by analyzing the contact signal, and the breakout indicator indicates whether wheel breakout is present. If present, the wheel is dressed as necessary to remove the wheel breakout. Alternatively, wheel inspection is performed directly on the first dressing stroke.

Description

[Technical field]

[0001] The present invention relates to a method for automatic process monitoring during continuous generating grinding with a generating grinding machine. The present invention also relates to a generating grinding machine configured to carry out such a method, and to a computer program for carrying out such a method. [Background technology]

[0002] In continuous generating grinding, the gear blank is machined by rotating engagement with a grinding wheel (grinding worm) having a worm-type geometry. Generating grinding is a highly demanding generating machining method based on a variety of synchronized precise individual movements and subject to numerous boundary conditions. Information on the fundamentals of continuous generating grinding can be found, for example, in "Continuous Generating Grinding: A Practical Guide to Gear Mills," by John Wiley & Sons, Inc., 1999.

[0003] The tooth flank shape during continuous generating grinding is theoretically determined only by the dressed profile shape of the grinding worm and the machine setting data. In practice, however, deviations from the ideal conditions that decisively affect the grinding result frequently occur in automated production. The above details are described in Non-Patent Document 2 and Non-Patent Document 3.

[0004] The quality of gears produced using generating grinding methods is not traditionally assessed until after the end of machining by gear measurements outside the grinding machine (off-line) based on various measurement variables. In this situation, various standards exist on how to measure gears and how to check whether the measurement results are within or outside the tolerance standards. The standards also give an indication on the relationship between the measurement results and the service properties of the gears. An overview of such gear measurements can be found for example in non-patent document 4.

[0005] During manual operation, an operator finds deviations from the norm in the machining process based on his experience, or deviations are detected during a subsequent gear inspection. The operator then adjusts the machining process again with changed settings to be within the stable range. However, in order to automate machining, it is desirable for the process monitoring to be involved in an automatic stabilization mode.

[0006] So far, the prior art has disclosed only rudimentary details about suitable strategies for process monitoring for continuous generating grinding.

[0007] For example, Non-Patent Document 5 describes various means for tool monitoring on a typical metal cutting machine tool (page 3). Tool monitoring can be performed in process during the metal cutting operation by measuring the active power, the cutting force or the acoustic emission (page 7). This serves in particular to detect tool breakage and tool wear (pages 9-14). There are a variety of sensors available for different measurement tasks for the purpose of tool monitoring (pages 31-37). Active power can be determined by measuring the current (page 28). Corresponding current sensors for this are known (page 37) or the monitoring of the current can be performed without a sensor, based on data from the CNC controller (page 40). The presentation characterizes application examples in various metal cutting machining methods, including also a number of simple method examples, which are relevant when machining gears, in particular when gear hobbing (pages 41 and 42), hard skiving (page 59) and honing (page 60). Dressing methods are also covered (page 92). In contrast, continuous generating grinding is only briefly mentioned (eg, pages 3 and 61).

[0008] Information on (cylindrical) grinding and dressing can also be found in Non-Patent Document 6. However, continuous generating grinding is not covered in detail there either.

[0009] Dressable vitrified bonded grinding wheels are frequently used for generating grinding. With such grinding worms, local breakouts in one or more worm threads of the wheel are a very destructive problem. Wheel breakouts cause the tooth flanks of the gear to be machined not to be completely machined over their entire length when engaged with the wheel that is in the area of ​​the breakout. Since the wheel is shifted along its longitudinal axis during the production of a batch (so-called shifting) in order to continue to engage the still unused areas of the wheel with the workpieces, not all workpieces of one batch are usually affected to the same extent by a wheel breakout. Workpieces machined only by intact areas of the wheel usually do not show defects.

[0010] This makes it more difficult to detect machining defects due to wheel breakouts. Usually, in the inspection of gears, a mere sample control is performed, so that machining defects due to wheel breakouts often go undetected or are detected only very late during the inspection of the gears. Such defects often only become apparent at the end of line inspection after the installation of the workpiece in the transmission, which inevitably involves a costly dismantling process. In addition, the same machining defects may have already occurred on a number of further workpieces in the meantime. This may lead under certain circumstances to a situation where a significant part of a production batch has to be discarded as NOK part (NOK = "not OK"). Thus, even one undetected wheel breakout may result in very high subsequent costs. It is therefore desirable to reliably detect or even prevent wheel breakouts within the scope of automatic process monitoring.

[0011] In addition to wheel breakouts, other phenomena can also negatively affect the quality of gears produced over one production batch. For example, it is known that often not all blanks can be pre-machined in the same way, or that differences in hardness and / or hardening distortions occur on the tooth surfaces of blanks. Small differences in the composition of the grinding worm can also lead to different grinding or dressing behavior. Inappropriate quality in the dressing is another common cause of poor quality of the finished gears. In addition, during dressing, the radius of the grinding worm is always reduced by the respective dressing amount. Thus, during the machining of a production batch, the engagement conditions during generating grinding can change significantly and often even worsen. The settings selected at the beginning of machining have to be changed afterwards. Despite all precautions to ensure a constant machining quality, it is inevitable that individual differences will occur on each workpiece during machining.

[0012] Therefore, in the case of automatic generating grinding of one production batch, the settings, tools, clamping means as well as the measurement and automation techniques must be defined prior to machining. At the start of machining, an operator monitors the process and, after a defect-free production has been achieved, the production batch is further machined semi-automatically. This process can be destabilized or hindered by two important influences: Firstly, by the tool, especially by breakout or by worse engagement after dressing. Secondly, by a workpiece that may have machining defects from a previous machining It is.

[0013] Process monitoring shall then capture these effects and initiate measures for automated finishing. [Prior art documents] [Non-patent literature]

[0014] [Non-Patent Document 1] H. Schriefer et al., “Continuous Generating Gear Grinding”, Reishauer AG, Wallisellen 2010, ISBN978-3-033-02535-6, Chapter 2.3 (“Basic Methods of Generating Grinding”), pp. 121-129 [Non-Patent Document 2] H. Schriefer et al., “Continuous Generating Gear Grinding”, Reishauer AG, Wallisellen 2010, ISBN978-3-033-02535-6, Chapter 6.9 “Practical Know-How for Statistical Individual Deviation Analysis”, pp. 531-541 [Non-Patent Document 3] H. Schriefer et al., “Continuous Generating Gear Grinding”, Reishauer AG, Wallisellen 2010, ISBN978-3-033-02535-6, Chapter 6.10 “Analysing and Eliminating Gear Tooth Deviations”, pp. 542-551 [Non-Patent Document 4] H. Schriefer et al., “Continuous Generating Gear Grinding”, Reishauer AG, Wallisellen 2010, ISBN978-3-033-02535-6, Chapter 3 “Quality Assurance in Continuous Generating Gear Grinding”, pp. 155-200 [Non-Patent Document 5] Company presentation "NORDMANN Tool Monitoring" version of October 5, 2017 retrieved February 25, 2019 from https: / / www.nordmann.eu / pdf / praesentation / Nordmann_presentation_ENG.pdf [Non-Patent Document 6] Klaus Nordmann, "Prozessueberwachung beim Schleifen und Abrichten [Process monitoring during grinding and dressing]", Schleifen+Polieren May 2004, Fachverlag Moeller, Velbert (Germany), pp. 52-56. Summary of the Invention

[0015] It is therefore an object of the present invention to specify a method for process monitoring during continuous generating grinding, by means of which it is possible to detect and / or prevent process deviations at an early stage.

[0016] This object is achieved by means of a method as defined in claim 1. Further embodiments are defined in the dependent claims.

[0017] Thus, a method is identified for process monitoring during continuous generating grinding of a pre-toothed workpiece with a generating grinder. The generating grinder comprises a tool spindle and at least one workpiece spindle. A grinding wheel having a worm-type shape and one or more worm threads is clamped on the tool spindle and rotatable about a tool axis. A workpiece may be clamped on the at least one workpiece spindle. The method includes: Machining a workpiece using a generating grinding machine, where for machining the workpiece is clamped on at least one workpiece spindle and subsequently transferred into generating engagement with a grinding wheel; monitoring at least one measurement variable during machining of the workpiece; determining a warning indicator for a process deviation from at least one monitored measurement variable; Includes.

[0018] According to the invention, process monitoring is used to obtain information about unacceptable deviations of the machining process on the generating grinding machine from its normal operation at an early stage and to derive a warning indicator from said information. In the simplest case, the warning indicator can be, for example, a two-valued Boolean variable specifying in a binary manner whether a suspected process deviation exists or not. The warning indicator can also be, for example, a numerical value that increases the greater the calculated probability of a process deviation, or additionally a vector variable indicating a measure based on the existence of a suspected process deviation or on the type of possible process deviation detected. Many other implementations of the warning indicator are also conceivable.

[0019] In particular, the process deviation to be detected may be a wheel breakout. Accordingly, the warning indicator is a warning indicator indicative of a possible wheel breakout. As already mentioned in the introduction, an undetected wheel breakout may lead to a situation where a large part of a production batch has to be rejected as a NOK part, and therefore it is particularly advantageous if the process monitoring is configured to output a warning indicator indicative of a possible wheel breakout.

[0020] Based on the warning indicator, different actions can be automatically triggered. Thus, based on the warning indicator, it can be automatically decided that the last machined workpiece is rejected as a NOK part or sent for special post-inspection. Based on the warning indicator, it is also possible to generate a light or sound warning signal to prompt the operator of the generating grinding machine to carry out a visual inspection of the grinding wheel.

[0021] Advantageously, if the warning indicator indicates a wheel breakout, the warning indicator triggers an automatic inspection of the wheel for wheel breakouts.

[0022] The automatic inspection can be carried out in various ways. For example, it is conceivable to use an optical sensor or a digital camera for the inspection and to automatically detect whether a wheel breakout is present, for example using digital image processing methods. For this purpose, it is also conceivable to inspect the acoustic emission of the wheel, which occurs when a coolant jet impinges on the wheel, and for the acoustic emission to be transmitted to an acoustic sensor via the coolant jet. A dressing device with a dressing tool, as is often present in generating grinding machines in both cases, is advantageously used for the automatic inspection. In this situation, it is possible either to move in a targeted manner over only the tip area of ​​the grinding worm thread to inspect the wheel, or to carry out a complete dressing stroke, as is also carried out in the case of normal dressing of the wheel.

[0023] When moving over the tip area only, specifically the following steps can be taken as soon as the warning indicator indicates a wheel breakout. moving a dressing tool over the tip area of ​​the grinding wheel; determining a contact signal while moving over the tip region, the contact signal being indicative of contact between the dressing tool and the tip region of the grinding wheel; and Determining a breakout indicator by analyzing the contact signal, the breakout indicator indicating whether a wheel breakout is present.

[0024] If contact does not occur within a particular area of ​​the grinding worm thread, this is a strong indicator that a wheel breakout does indeed exist. This is indicated by the breakout indicator.

[0025] In order to also be able to detect grinding wheel breakouts that remain undetected during monitoring of the measured variables during the machining process, the movement over the tip area with the dressing tool can also be carried out at regular intervals, independent of the value of the warning indicator, for example after machining a certain number of workpieces.

[0026] The breakout indicator, in the simplest case, can again be a binary Boolean variable indicating in a binary fashion whether a breakout is present or not, however, even more complex implementations of the breakout indicator are also contemplated, in particular the breakout indicator preferably also indicating the location of the wheel breakout along at least one worm thread on the wheel.

[0027] The contact of the dressing tool with the tip region of the grinding wheel can be detected in various ways. For example, the generating grinding machine can be equipped with an acoustic sensor to acoustically detect the engagement of the grinding wheel with the dressing tool based on structure-borne acoustic emissions generated during engagement. A contact signal is then derived from the acoustic signal measured using the acoustic sensor. If the dressing tool is clamped on a dressing spindle rotatably driven by a motor, the contact signal can alternatively or additionally be derived from a power signal representative of the power consumption of the dressing spindle during its movement over the tip region.

[0028] If the breakout indicator indicates the presence of a wheel breakout, the method may include the wheel being fully dressed to further characterize and / or remove the wheel breakout.

[0029] It is also conceivable to carry out a full dressing operation directly to check the wheel for breakouts, as already mentioned, whereby the checking of the wheel for breakouts and the characterization of the breakouts are carried out based on monitoring this dressing operation.

[0030] To monitor the dressing operation and to characterize the wheel breakout in more detail, a dressing power signal representative of the power consumption of the dressing spindle and / or the tool spindle during dressing can be measured during dressing, and by analyzing the change over time of the dressing power signal during dressing, a breakout measure can be determined. The breakout measure reflects at least one characteristic of the wheel breakout, for example where the wheel breakout is located and / or how deeply radially the affected grinding worm thread is damaged.

[0031] The breakout measure can then be used to automatically determine whether the wheel breakout can be adequately removed by one or more dressing operations, and if not, a signal can be output to a user that the wheel should be replaced, or further machining can be controlled such that further workpieces are machined using only undamaged areas of the grinding worm.

[0032] The analysis of the time-dependent changes in the dressing power signal to determine the breakout measure may include determining a variation variable, which is indicative of a local change in the magnitude of the dressing power signal along at least one worm thread, for example, which allows direct results to be derived regarding the radial depth of the wheel breakout.

[0033] As already mentioned, in the process monitoring proposed here, warning indicators for process deviations, in particular for wheel breakouts, are determined in order to obtain an early indication of possible process deviations. To determine this warning indicator, various measurement variables can be monitored.

[0034] In particular, the monitored measurement variables may include deviation indicators relating to the tooth thickness error of the workpiece before machining. If the deviation indicators indicate that the tooth thickness error exceeds an acceptable value or that other pre-machining defects exist, a warning indicator is set accordingly in order to interrupt the machining so as to avoid damage to the grinding wheel. If appropriate, the grinding wheel can then be inspected for possible breakouts due to improper pre-machining of the preceding workpiece.

[0035] Advantageously, in the present specification, the deviation indicator is determined using a toothing probe, which may already be present in the machine tool, is known per se and is designed to measure the tooth space of a workpiece clamped on a workpiece spindle without contact. The tooth thickness measurement can then be calibrated using a calibration workpiece and limit values ​​can be defined that the signal of the toothing probe must meet for the tooth thickness error to be considered acceptable. For example, an inductive or capacitive sensor operating without contact can be used as the toothing probe. In this case, the toothing probe thus performs a double function: on the one hand it is used for the toothing at the start of the machining and on the other hand it serves to determine the tooth thickness error. It is also possible to use another sensor to determine the tooth thickness instead of the toothing probe, for example another optical sensor, which may be preferable in the case of high rotational speeds.

[0036] Due to the fact that the monitored measurement variables include the rotational speed difference between the rotational speed of the workpiece spindle and the resulting rotational speed of the workpiece, an early indication of the risk of wheel breakout can already be obtained. If such a difference exists, this indicates that the workpiece is not correctly clamped on the workpiece spindle and therefore not correctly turned by said spindle (slippage). This can lead to a situation where the workpiece is not in the correct angular position when moving into engagement with the grinding worm and the grinding worm thread cannot be correctly immersed in the tooth space of the workpiece. In such a situation, the workpiece is not machined correctly and high machining forces can occur, which can be so great that the grinding worm is seriously damaged. By monitoring the rotational speed of the workpiece spindle and the workpiece, it is possible to detect such a situation and ideally stop the machining process before the workpiece enters engagement with the grinding worm. Wheel breakouts can also be avoided in some cases. If a rotational speed deviation is detected, a warning indicator is set accordingly. If appropriate, the wheel is inspected for damage based on the warning indicator.

[0037] Further relevant measurement variables are the rotational angular positions of the workpiece spindle and of the workpiece clamped thereon before and after machining and / or the changes in these rotational angular positions during machining. In particular, the monitored measurement variables can include an angular deviation, which is determined by comparison of the angular positions of the workpiece spindle after machining of the workpiece with the corresponding angular positions of the workpiece itself and the angular positions of the workpiece spindle before machining of the workpiece with the corresponding angular positions of the workpiece itself. If this angular deviation indicates that the angular differences between the angular positions of the workpiece spindle and the workpiece itself after machining and before machining differ from each other, this indicates that the workpiece is not turned correctly by the workpiece spindle. This is then a reason to set a warning indicator accordingly and, if appropriate, to inspect the grinding wheel for damage for safety.

[0038] Here, the rotational speed and / or the angular position of the workpiece are advantageously also determined by means of the already mentioned toothing probe, which again performs a double function: on the one hand it is used for toothing before the start of machining, and on the other hand it serves to monitor the actual machining process. Instead of the toothing probe, it is also possible to use another sensor for determining the rotational speed and / or the angular position of the workpiece, for example another optical sensor, which may be preferable at high rotational speeds.

[0039] The engagement probe can advantageously be arranged on the opposite side of the workpiece from the grinding wheel, so that no collisions occur between the grinding wheel and the engagement probe and sufficient space remains for the gripping jaws arranged laterally in parallel to handle the workpiece.

[0040] The monitored measurement variables may also include a cutting power signal, indicative of the instantaneous metal cutting power during each machining process of an individual workpiece. In this case, the warning indicator may depend on the change in the cutting power signal over time throughout the machining of the workpiece. In particular, the occurrence of a pulse-like increase in the cutting power signal during machining may be indicative of a collision between the workpiece and the grinding worm thread, which may cause a wheel breakout, and a corresponding warning indicator may indicate this. The cutting power signal may in particular be determined by current measurements on the tool spindle, and in this respect may be a measure of the instantaneous power consumption of the tool spindle during the machining of the workpiece.

[0041] A further possible way of determining the warning indicator arises from the consideration that during machining of a workpiece with a damaged wheel, the amount of material removed in the area of ​​the wheel breakout is smaller than in the intact area of ​​the wheel. In the course of a shift movement, the workpiece moves progressively into the area of ​​the wheel breakout and / or out of this area. Correspondingly, the amount of material removed per workpiece will initially decrease accordingly and then rise again. This is directly reflected in the applied metal cutting energy per workpiece, i.e. in the integral value of the metal cutting power over time.

[0042] In this regard, the method may include performing continuous or non-continuous shifting movements between the wheel and the workpiece along the tool axis. The monitored measurement variables may then include a cutting energy index for each workpiece, the cutting energy index representing a measure for the integrated metal cutting power of the wheel while the respective workpiece is machined with the generating grinder. The warning indicator may then depend on how the cutting energy index changes over the production of multiple workpieces in a production batch, i.e., from workpiece to workpiece.

[0043] The cutting energy index may in particular be an integral value of the power consumption of the tool spindle during machining of an individual workpiece, or alternatively it may be another characteristic value derived from the power consumption of the tool spindle over the machining of an individual workpiece, for example a suitably determined maximum value of the power consumption.

[0044] In order to be able to carry out further analyses retrospectively, it is advantageous if the monitored measurement variables and / or variables derived therefrom, in particular the warning indicators, are stored together with the unique identifier of the respective workpiece in a database, these data being able to be read out again at any time thereafter, for example within the scope of subsequent machining of workpieces of the same type.

[0045] The invention also relates to a generating grinding machine designed to carry out the method described above. For this purpose, the generating grinding machine comprises: a tool spindle capable of clamping a grinding wheel having a worm-type geometry with one or more worm threads and drivable to rotate about a tool axis; at least one workpiece spindle for driving one pre-toothed workpiece at a time for rotation about a workpiece axis; A machine controller designed to carry out a method of the type described above; Equipped with.

[0046] The generating grinder may include additional components as described above in connection with the various methods.

[0047] In particular, the generating grinding machine can be equipped with a deviation determining device for determining an upward deviation of the tooth thickness of the workpiece to be processed. As already mentioned, the dimension determining device can in particular receive and evaluate signals from the toothing probe.

[0048] The generating grinding machine may also comprise 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 mentioned, the toothing probe may act as the second rotation angle sensor. A corresponding rotation angle can be determined by a rotation angle determining device from a signal of the rotation angle sensor, and a corresponding rotation speed can be derived therefrom by a rotation speed determining device.

[0049] The machine controller of the generating grinding machine can additionally comprise a cutting power determination device for determining the cutting power signal described above and an analysis device designed to analyze how the cutting power signal changes over time during machining of the workpiece. The machine controller can also comprise a cutting energy determination device for calculating a cutting energy index for each workpiece and a further analysis device designed to analyze how the cutting energy index changes between workpieces of a production batch. These devices can be implemented using software, for example by a machine controller comprising a microprocessor programmed to perform the aforementioned tasks. The cutting power determination device can be designed, for example, to read out power signals from an axis module for operating the tool spindle, and the cutting energy determination device can be designed to integrate these signals over the machining of the workpiece.

[0050] The machine controller may also comprise the above mentioned database in which the measured variables and, if appropriate, variables derived therefrom may be stored together with a unique identifier of each workpiece and, if appropriate, further process parameters. The database may also be implemented in a separate server connected to the machine controller via a network.

[0051] The machine controller may additionally have an interface for issuing the warning signal in digital form to a downstream connected device, a display for displaying the warning signal, an output device for outputting the warning signal, such as an audio output device, for example.

[0052] The generating grinding machine may advantageously also comprise a dressing device as described above, and the machine controller may comprise a dressing control device for controlling the dressing spindle and the dressing monitoring device for determining said contact signal and / or the dressing power signal and for determining said breakout indicator or measure from the change in the signal over time. These devices may be implemented using software. In addition, the machine controller may comprise an output device for outputting the breakout indicator or measure.

[0053] To detect the contact between the dressing tool and the grinding wheel, the generating grinding machine can be equipped with the acoustic sensor already mentioned. The generating grinding machine can also be equipped with a power measuring device for measuring the power consumption of the dressing spindle and / or a corresponding power measuring device for measuring the power consumption of the tool spindle. For this purpose, the corresponding power measuring device can be designed, for example, to read out a current signal from an axis module for operating the dressing spindle and / or the tool spindle.

[0054] To carry out the process monitoring, the generating grinding machine can be equipped with correspondingly configured control devices, which in particular can comprise the already mentioned dimension determining device, rotation angle determining device, rotation speed determining device, cutting power determining device, cutting energy determining device, analysis device, dressing monitoring device, power measuring device and output device.

[0055] The invention can also make use of a computer program. The computer program comprises instructions that cause a machine controller in a generating grinding machine of the type described above, in particular one or more processors of the machine controller, to carry out the method described above. The computer program can be stored in a suitable memory device, for example another control device comprising a server. In particular, a computer-readable medium on which the computer program is stored is also proposed. The medium can be a non-volatile medium, for example a flash memory, a CD, a hard disk, etc. [Brief description of the drawings]

[0056] [Figure 1] FIG. 1 is a schematic diagram showing a generating grinding machine. [Diagram 2] FIG. 2 shows an enlarged detail from FIG. 1 in region II. [Diagram 3] FIG. 3 shows an enlarged detail from FIG. 1 in area III. [Figure 4] FIG. 4 shows four photographs of a wheel with a breakout in one or more worm threads. [Diagram 5] FIG. 5 is a photograph of the damaged gear. [Figure 6] FIG. 6 shows, by way of example, the characteristic signals of the toothing probe in the case of good and bad pre-machining (variation of upper tooth thickness error) of two workpieces. [Figure 7] FIG. 7 shows (a) the change in rotational speed of the workpiece spindle over time during the ramp up to the working rotational speed and (b) the resulting meshing probe signal when the workpiece is turned incompletely. [Figure 8] FIG. 8 shows the power consumption of a tool spindle over time during machining of a workpiece when the grinding wheel is moved into contact with the workpiece in an incorrect angular position. [Figure 9]FIG. 9 shows the power consumption over time of the tool spindle while machining a workpiece with no breakout and with a large breakout on the grinding wheel. [Figure 10] FIG. 10 shows the average power consumption over time of a tool spindle during machining of workpieces across a production batch using a wheel with a large breakout. [Figure 11] FIG. 11 shows, by way of example, the evolution of the acoustic signal over time during tip dressing of a grinding wheel with a breakout. [Figure 12] FIG. 12 shows two plots of power consumption of the dressing spindle over time for (a) a wheel without a breakout and (b) a wheel with a breakout. [Figure 13] FIG. 13 shows two diagrams showing the change in power consumption over time of the dressing spindle (part (a)) and of the tool spindle (part (b)) during dressing of a grinding wheel with breakout. [Figure 14] FIG. 14 is a flow chart illustrating a method for process monitoring for early detection of wheel breakout. [Figure 15] FIG. 15 is a flow chart showing further processes after detection of a wheel breakout. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Preferred embodiments of the invention are described below with reference to the drawings, which serve only as illustration and are not to be construed as limiting.

[0058] Example designs of generating grinding machines

[0059] FIG. 1 shows, by way of example, a generating grinding machine 1. The grinding machine has a machine bed 11, in which a tool carrier 12 is guided so as to be movable along an infeed direction X. The tool carrier 12 carries an axis carriage 13, which is guided so as to be movable along an axial direction Z relative to the tool carrier 12. A grinding head 14 is mounted on the axis carriage 13, which can be swiveled about a pivot axis (the so-called A-axis) running parallel to the X-axis in order to adapt to the helix angle of the gear wheel to be processed. The grinding head 14 carries a shift carriage, on which a tool spindle 15 is movable along a shift axis Y relative to the grinding head 14. A grinding wheel 16 having a worm shape is clamped on the tool spindle 15. The grinding wheel 16 is driven by the tool spindle 15 to rotate about the tool axis B.

[0060] The machine bed 11 also carries a swivellable workpiece carrier 20 in the form of a rotating tower, which is swivellable about an axis C3 between at least three positions. Two identical workpiece spindles, opposite each other, are mounted on the workpiece carrier 20, of which only one workpiece spindle 21 is visible in FIG. 1 with its associated tailstock 22. The workpiece spindle visible in FIG. 1 is in a machining position, in which a clamped workpiece 23 can be machined with a grinding wheel 16. The other workpiece spindle (not visible in FIG. 1), arranged with an offset of 180°, is in a workpiece change position, in which a completely machined workpiece can be removed from this spindle and a new blank can be clamped. A dressing (truing) device 30 is mounted with an offset of 90° with respect to the workpiece spindle.

[0061] All drive axes of the generating grinder 1 are digitally controlled by a machine controller 40. The machine controller 40 receives sensor signals from various sensors in the generating grinder 1 and issues control signals to the actuators of the generating grinder 1 according to these sensor signals. The machine controller 40 comprises, inter alia, a number of axis modules 41, each of which has available at its output a control signal for one machine axis (i.e. for at least one actuator, such as for example a servo motor, serving to drive the respective machine axis). The machine controller 40 further comprises an operator control panel 43 and a control device 42, which comprises a control computer. The control device 42 communicates with the operator control panel 43 and with the axis modules 41. The control device 42 receives operating commands from the operator control panel 43 and the sensor signals and calculates therefrom control commands for the axis modules. It also outputs operating parameters for display to the operator control panel 43 based on the sensor signals.

[0062] A server 44 is connected to the control device 42. The control device 42 transfers a unique identifier for each workpiece and selected operating parameters (in particular the measured variables and variables derived therefrom) to the server 44. The server 44 then records this data in a database so that the relevant operating parameters can be retrieved for each workpiece. The server 44 may be located inside the machine or remote from the machine. In the latter case, the server 44 may be connected to the control device 42 via a network, in particular via a company LAN, via a WAN or via the Internet. The server 44 is preferably designed to receive and manage data from a single generating grinding machine. When several generating grinding machines are used, a second server is generally used. In this way, a central access to the stored data and a better handling of large amounts of data can be implemented. Furthermore, this data can be better protected on the second server.

[0063] FIG. 2 shows an enlarged view of detail II of FIG. 1. The tool spindle 15 with the grinding wheel 16 clamped thereon can be seen. A measuring probe 17 is pivotally mounted on the fixed part of the tool spindle 15. This measuring probe 17 is optionally pivotable between the measuring position of FIG. 2 and a waiting position. In the measuring position, the measuring probe 17 can be used to measure the engagement of the workpiece 23 on the workpiece spindle 21 in a contact manner. This is done "in-line", i.e. while the workpiece 23 is still located on the workpiece spindle 21. As a result, machining defects can be detected early. In the waiting position, the measuring probe 17 is in a range protected from collisions with the workpiece spindle 21, the tailstock 22, the workpiece 23 and further components on the workpiece carrier 20. During machining of the workpiece, the measuring probe 17 is in the waiting position.

[0064] A toothing probe 24 is arranged on the workpiece 23 on the side opposite the grinding wheel 16. In this example, the toothing probe 24 is constructed and arranged according to the description in WO2017 / 194251A1. Explicit reference is made to the specified document with regard to the function and arrangement of the toothing probe. In particular, the toothing probe 24 can be equipped with an inductively or capacitively operated proximity sensor, as known from the prior art. It is also conceivable to use optically operated sensors for the toothing operation, for example by directing a light beam on the gear to be measured and detecting the light reflected therefrom or by detecting the interruption of the light beam by the gear to be measured when said gear is rotating about the workpiece axis C1. Furthermore, it is also conceivable to arrange one or more further sensors on the toothing probe 24, which can directly acquire process data on the workpiece, as proposed for example in US Pat. No. 6,577,917 (B1). Such further sensors may include, for example, a second mesh sensor for the second gear wheel, a temperature sensor, a further acoustic emission sensor, an air pressure sensor, etc.

[0065] Furthermore, in Fig. 2, an acoustic sensor 18 is shown in a purely symbolic manner. The acoustic sensor 18 serves to pick up structure-borne sound of the tool spindle 15, which occurs during the grinding process of the workpiece and during dressing of the grinding wheel. In practice, the acoustic sensor is usually not arranged on the housing part (as shown in Fig. 2), but rather directly on the stator of the drive motor of the tool spindle 15, for example to ensure efficient conduction of sound. Acoustic or structure-borne sound sensors of the specified type are known per se and are routinely used in generating grinding machines.

[0066] A coolant nozzle 19 directs a coolant jet into the machining zone and a further acoustic sensor (not shown) may be provided to record noise transmitted through this coolant jet.

[0067] Figure 3 shows an enlarged view of detail III of figure 1. Here the dressing device 30 can be particularly well seen. A dressing spindle 32, to which a disk-shaped dressing tool 33 is clamped, is arranged on the swivel drive 31 so that it can swivel about the axis C4. Alternatively or additionally, in particular fixed dressing tools, known in the art as tip dressing devices, can be provided. These can be arranged to engage only with the tip regions of the worm threads of the grinding wheels in order to dress these.

[0068] Machining of a batch of workpieces

[0069] To machine a workpiece (blank) that has not yet been machined, the workpiece is clamped by an automatic workpiece changer to the workpiece spindle in the workpiece change position. The change of the workpiece is carried out simultaneously with the machining of another workpiece on the other workpiece spindle in the machining position. Once the workpiece to be newly machined is clamped and the machining of the other workpiece is finished, the workpiece carrier 20 is swiveled 180° about the C3 axis and the spindle with the workpiece to be newly machined is moved to the machining position. Before and / or during the swiveling process, a centering operation is carried out using a corresponding centering probe. To do this, the workpiece spindle 21 is rotated and the position of the tooth space of the workpiece 23 is measured using the centering probe 24. The rotation angle is determined on this basis. In addition, indications for excessive variations in the upper tooth thickness error and other pre-machining defects can be derived using the centering probe even before the start of machining. This is explained in more detail below with reference to FIG. 6.

[0070] When the workpiece spindle carrying the workpiece 23 to be machined has reached the machining position, the workpiece 23 is moved into engagement with the grinding wheel 16 without collision by moving the workpiece carrier 12 along the X-axis. The workpiece 23 is then machined in rotary engagement by the grinding wheel 16. During this time, the tool spindle 15 is continuously slowly shifted along the shifting axis Y (so-called shifting movement) in order to allow the not yet used areas of the grinding wheel 16 to be continuously used during machining. As soon as the machining of the workpiece 23 has been finished, the workpiece is optionally measured in-line using the measuring probe 17.

[0071] Simultaneously with machining, the completely machined workpiece is removed from the other workpiece spindle and a further blank is clamped on this spindle. Every time the workpiece carrier swivels about the C3 axis, either before or within the swivel period, i.e. time-neutral, selected components are monitored and the machining process is not restarted until all defined requirements are met.

[0072] If, after machining a certain number of workpieces, the use of the grinding wheel 16 has progressed to the point where the wheel becomes significantly dull and / or the tooth flank form is inaccurate, the wheel is dressed. For this purpose, the workpiece carrier 20 is swiveled ±90° and the dressing device 30 is moved into a position facing the grinding wheel 16. The grinding wheel 16 is then dressed using the dressing tool 33.

[0073] Grindstone breakout

[0074] Wheel breakouts can occur during machining. Figure 4 shows various forms of wheel breakouts 51 on a grinding worm. In part (a), a single worm thread is almost completely spalled over a certain angular range. In contrast, in part (b), multiple worm threads are locally damaged at many different points within the tip region. In part (c), multiple localized damage zones are also present, but these are deeper than in part (b). In part (d), the wheel is significantly damaged in two regions, and multiple adjacent worm threads have almost completely spalled within these regions. All cases of damage can occur in practice and have different effects during machining of a workpiece.

[0075] FIG. 5 shows an incorrectly machined gear. All teeth 52 are damaged in their tip regions because the gear is placed in engagement with the grinding wheel at an incorrect angular position, and the wheel threads cannot engage correctly in the tooth spaces of the gear. This situation can occur if the meshing operation is performed incorrectly or if the gear is not turned correctly while the workpiece spindle is rotated up to its operating rotational speed. This situation often leads not only to damage to the gear, but also to serious wheel breakouts of the grinding wheel. This situation must also be detected and prevented as early as possible.

[0076] Indication of possible wheel breakout via process monitoring

[0077] In order to prevent wheel breakouts as far as possible or to be able to detect them at an early stage once they have occurred, various operating parameters are continuously monitored during the machining of a production batch. In addition, the parameters or variables derived therefrom are recorded in a database to make it possible to carry out later analyses. In this context, the rotational speeds, angular positions and power consumption values ​​of the tool spindle, the workpiece spindle and the dressing spindle, the rotational speeds and angular positions of the workpiece itself, the signals of the toothing probe, the positions of the linear axes of the machine are of particular importance. In the exemplary embodiment of figures 1 to 3, a control device 42 serves for the monitoring. In particular, the operating parameters of the generating grinder discussed below are monitored.

[0078] (a) Determination of pre-machining defects using a toothing probe

[0079] Fig. 6 shows schematic signals as received from the registration probe 24. These are binary signals, exhibiting a logic value of 1 when the tooth tip area is located in front of the registration probe and a logic value of 0 when the tooth space is located in front of the registration probe. The pulse width Pb and / or the pulse duty ratio of the derived registration probe signal is a measure for the tooth thickness and thus for the deviation between the measured thickness and the required thickness ("deviation indicator"). In part (a) of Fig. 6, the pulse width Pb is small, indicating a small (possibly negative) deviation, whereas in part (b) the pulse width Pb is large, indicating a large (possibly excessively large) deviation. The variation of the pulse width Pb is shown here in a deliberately exaggerated manner for illustrative purposes.

[0080] Thus, direct conclusions can be drawn from the signal pattern of the tooth registration probe 24 regarding deviations of each tooth. From this, indications regarding pre-machining defects, such as excessively large or irregular deviations, can be derived.

[0081] The control device 42 receives the signal of the toothing probe and derives therefrom a warning indicator, indicating whether an indication for a previous machining fault is present. If an indication is present, the machining is stopped before contact occurs between the workpiece 23 and the grinding wheel 16, in order to prevent damage to the grinding wheel 16. In addition, the warning indicator can trigger an inspection of the grinding wheel for damage caused by a preceding workpiece.

[0082] (b) Monitoring the rotational speed of the workpiece spindle and the workpiece

[0083] FIG. 7 shows the rotation speed n of the workpiece spindle 21. w and the resulting rotational speed of the workpiece 23 clamped thereon, compare with one another. wcan be read out directly from the machine controller (part (a) of FIG. 7). In contrast, the rotational speed of the workpiece is determined using the meshing probe 24. In this respect, FIG. 7 shows in part (b) a schematic signal as received by the meshing probe 24. In this example, the signal has a continuously decreasing period length Pd, while the workpiece spindle 21 has already reached its desired rotational speed. The signal therefore indicates that the workpiece 23 is still accelerating, while the workpiece spindle 21 has already reached its desired rotational speed. Thus, in this example, the workpiece 23 is not turning correctly on the workpiece spindle 21.

[0084] Such cases may occur when the pre-machining of the workpiece clamping base, such as the bore faces and planes, is exceeded by the tolerances. The turning of the workpiece generally occurs in a defined frictional engagement: a frictional torque acts on the workpiece bore via the enlargement of the collet chuck, and a radial frictional force is generated on the two planes by the axial contact pressure. However, if the workpiece bore is too large and / or the planes are too inclined, this frictional engagement decreases and exceeds a critical value, resulting in slippage between the workpiece spindle and the workpiece.

[0085] If a deviation between the rotational speed of the workpiece and the rotational speed of the workpiece spindle is detected, it is appropriate to immediately stop further machining in order to prevent damage to the grinding wheel 16. Since it cannot be excluded that damage has already occurred to the grinding wheel 16, it is additionally appropriate to inspect the grinding wheel 16 for damage.

[0086] For this purpose, the control device 42 monitors the signal of the toothing probe 24 and the rotational speed signal of the workpiece spindle from the assigned axis module 41. In case of deviations, the control device 42 sets a warning indicator. On the basis of the warning indicator, machining is stopped before contact between the workpiece 23 and the grinding wheel 16 occurs. In addition, the warning indicator can trigger an inspection of the grinding wheel for damage caused by a preceding workpiece.

[0087] (c) Monitoring the workpiece spindle and workpiece rotation angle

[0088] As an alternative or in addition to the comparison of the rotational speeds, a comparison of the rotational angle of the workpiece spindle with the associated workpiece is also possible, to be carried out before and after machining. The presence of a deviation here also indicates that slippage is present, and it is appropriate to check the grinding wheel 16 for possible damage. Accordingly, the control device 42 sets a warning indicator in this case as well.

[0089] (d) Instantaneous metal cutting power monitoring

[0090] A further possible way of detecting a possible wheel breakout early is shown in FIG. 8. The figure shows the power consumption I of the tool spindle during the machining of an individual workpiece in a measurement curve 61. s as a function of time. The power consumption (current consumption) of the tool spindle I s is a direct measure of the instantaneous metal cutting power. In this respect, it can be considered an example of a cutting power signal.

[0091] In this example, curve 61 shows a sudden increase and a subsequent drop in this power consumption at the beginning of machining, indicating that a collision has occurred between one of the teeth of the workpiece and the worm thread of the grinding wheel 16. In this case, it is appropriate to immediately stop further machining and also to inspect the grinding wheel 16 for possible damage. The control device 42 also sets a corresponding warning indicator in this case.

[0092] (e) Monitoring of metal cutting energy per workpiece

[0093] A further possibility for the detection of a possible wheel breakout (albeit relatively slow) is to monitor the energy that has been used for metal cutting machining of each workpiece ("metal cutting energy"). This energy is a measure of the amount of material removed during machining of the respective workpiece. The amount of material removed during machining by a grinding worm area damaged by a breakout is generally less than the amount during machining by an undamaged grinding worm area. Thus, by monitoring the metal cutting energy per workpiece, it is possible to obtain an indication of a possible wheel breakout.

[0094] This is shown in more detail in Figures 9 and 10. Figure 9 shows, in a measurement curve 62, the power consumption I of the tool spindle during the machining of an individual workpiece by an undamaged grinding worm. s as a function of time. Measurement curve 63 on the other hand shows the change over time in the power consumption during machining with the grinding worm in a region with a large breakout. Due to the breakout, the metal cutting power and therefore the power consumption of the tool spindle are greatly reduced. The integral of the power consumption (i.e. the area under the respective measurement curve) during the time period required to machine an individual workpiece is a measure of the total metal cutting energy used on the workpiece, i.e. the amount of material removed per workpiece. During machining with an area of ​​wheel breakout, this integral is smaller than during machining with an undamaged region of the wheel.

[0095] Instead of the integral of the power consumption, other variables such as the average value, the maximum value (after smoothing, if appropriate, to remove spurious values), or the result of fitting the current variation over time to a predefined function can also be used as a measure of the total metal cutting energy, which in the present context is also called the cutting energy index.

[0096] Figure 10 shows the average power consumption of the tool spindle during machining when the grinding wheel is damaged, I av Fig. 1 shows how the average power dissipation I of the tool spindle varies across N workpieces. Suppose machining begins with a wheel with a large central breakout. At the beginning of the machining cycle, the workpiece is machined with the undamaged end of the first wheel. In the course of machining, the wheel is shifted continuously so that the area with the breakout is increasingly used for machining. Towards the end of the cycle, the opposite end of the wheel, which is also undamaged, comes into engagement with the workpiece. Correspondingly, the average power dissipation I of the tool spindle av decreases initially and then increases again towards the end of the cycle. As a result, from the first workpiece to the Nth workpiece, the average power dissipation I av A characteristic change occurs over time.

[0097] At point 65 the cycle ends, the wheel is dressed and a new cycle begins. During dressing the damaged worm threads are gradually restored, so that the average power consumption I av The change in becomes gradually smaller in later cycles.

[0098] The current variation over time 64, as shown by way of example in Fig. 10, can therefore be evaluated as an indication of a wheel breakout. It is appropriate here to stop the machining and also to inspect the wheel for possible damage, in order to check whether a breakout is indeed present. For this purpose, the control device 42 in this case also sets a corresponding warning indication.

[0099] Automatic checking of grinding wheels for breakouts

[0100] Inspection of the grinding wheel for possible damage can be carried out automatically due to the fact that the dressing tool moves over the grinding wheel in the tip area of ​​its worm thread and contact between the grinding wheel and the dressing tool is detected.

[0101] The detection of contact can be performed acoustically, as shown in Figure 11. For example, during a dressing process where the dressing tool is purposely brought into contact only with the tip region of the worm sled, an acoustic signal V, as can be determined, for example, by the acoustic sensor 18 shown in Figure 2, is generated. a The change in time of is illustrated as measurement curve 71. This signal indicates when the dressing device moves in and out of engagement with the tip region. If the wheel is not damaged, a periodic signal is expected. On the other hand, if the signal has gaps, such as gap 72 in FIG. 11, this indicates a breakout in the worm thread.

[0102] Alternatively, even in the case of dressing, in order to be able to detect reliably whether a wheel breakout is present, the dressing process can be started automatically directly, as explained below, but with the disadvantage that in the case of dressing a significantly lower wheel rotation speed must be used, which therefore leads to some longer non-productive times due to this control measure.

[0103] Other methods are also conceivable for automatically checking the grinding wheel for damage. For example, it is possible to inspect the wheel for damage using optical sensors. It is also possible to inspect the wheel for damage by utilizing the noise generated by the coolant jet from the coolant nozzle 19 as it impinges on the wheel. The measurement of structure-borne sound using a coolant jet is known per se (see, for example, Klaus Nordmann, "Prozessueberwachung beim Schleifen und Abrichten [Process monitoring when grinding and dressing]", Schleifen+Polieren, May 2004, Fachverlag Moeller, Velbert (Germany), pp. 52-56). However, it has not been used so far to detect wheel breakouts.

[0104] Further characterization of wheel breakouts

[0105] If a breakout is positively identified in this way, it is appropriate to fully dress the grinding worm and at the same time further characterize the breakout and / or remove it, as shown in Figures 12 and 13.

[0106] Figure 12 shows how wheel breakouts can be further characterized by measuring the current during dressing. In part (a), it shows the power consumption I of the dressing spindle when the wheel is uniformly worn and does not have any breakouts. d As a function of time during dressing of the wheel, the measurement curve 81 is always above the lower envelope curve 82. In part (b), the power consumption I d The time course of the power consumption I d indicates strong fluctuations, especially a strong decline.

[0107] In the simplest case, such a variation can be detected by monitoring whether the value of the power consumption falls below a lower envelope curve 82. In the region of such a case, it can be concluded that a wheel breakout is present. Of course, it is also possible to use more improved methods for detecting variations in the power consumption. For example, the average value 83 of the power consumption can be calculated and it can be monitored whether the deviation downwards (here for a minimum value 84) and / or upwards (here for a maximum value 85) from this value are within a certain tolerance range. In each case, regardless of how the detection of the variations is performed, the position of the breakout along the respective worm thread can be concluded based on the time or the rotation angle at which the variations occur. The degree of damage to the worm thread can be inferred from the magnitude of the variations.

[0108] Figure 13 shows that it is possible to characterize wheel breakout using not only the power consumption of the dressing spindle but also the power consumption of the tool spindle. In part (a), the power consumption of the dressing spindle I d Part (b) shows the power consumption of the tool spindle during dressing of the grinding wheel with breakout I s The time-dependent variation of the power consumption of the tool spindle as well as the power consumption of the dressing spindle is shown. It is clear that the power consumption of the tool spindle as well as the power consumption of the dressing spindle show variations during the time period during which dressing is performed in the area of ​​the breakout. However, these variations are more pronounced in the case of the power consumption of the dressing spindle and, in general, the power consumption of the dressing spindle is preferred over the power consumption of the tool spindle as a measurement variable for characterizing the wheel breakout.

[0109] Wheel breakouts characterized in this way can be removed possibly through repeated dressing. If the breakout is very large and requires a significant amount of time to remove it by dressing, it may be appropriate to dispense with further dressing processes and instead replace the damaged wheel or use the grinding worm only in its undamaged areas for further machining of the workpiece.

[0110] Example of a method for automatic process control

[0111] 14 and 15 show, by way of example, a possible method for automatic process control implementing the above concepts.

[0112] In the machining process 110, the workpieces of the workpiece batch are successively machined using a generating grinder. Before and during the machining 111 of each workpiece, inter alia, the measurement variables explained above are determined and monitored in a monitoring step 112. In particular, the pulse width Pb of the signal of the toothing probe is monitored in order to determine whether a pre-machining fault is present. In addition, the rotation speed n of the workpiece spindle is also monitored. W and the rotation speed of the workpiece n A The absolute value of the difference between t Furthermore, it is monitored whether the change in the angle of the workpiece spindle, Δφ, is greater than W and the change in angle of the workpiece, Δφ A The absolute value of the difference between t In addition, the power consumption of the tool spindle I s The time course of the spindle current I av Changes in (N) are monitored. From the results of these monitoring operations, a warning indicator W is continually determined in step 113.

[0113] Based on the warning indicators, the following determinations are made automatically in decision step 114: 1. If the warning indicator does not indicate any problem (e.g., threshold W t As long as the applied current is lower than the reference current (as long as the applied current is lower than the reference current), machining of the workpiece continues normally. 2. If the warning indicator indicates a possible problem, machining of the workpiece is temporarily stopped. Based on the warning indicator, it is decided whether the workpiece is immediately removed (which is appropriate, for example, if the warning indicator indicates a pre-machining defect or a slippage of the clamping connection of the workpiece) or whether an inspection of the grinding wheel is first performed.

[0114] The grinding wheel is then checked for possible breakouts in step 120. For this purpose in this example, in step 121, a dressing tool is moved over the tip area of ​​the grinding worm thread. In step 122, it is determined by acoustic or power measurements whether there is contact between the dressing tool and the grinding worm and a contact signal is output accordingly. In step 123, a breakout indicator A is determined from the change in the contact signal over time. In decision step 124, whether the breakout indicator A is greater than a predefined threshold A is determined. t It is checked whether it has been exceeded.

[0115] Threshold A t If not, machining of the workpiece continues, in which case, if appropriate, the cutting power is reduced to reduce the probability that the warning indicator indicates a possible problem in the subsequent workpiece.

[0116] On the other hand, if the breakout indicator exceeds the threshold, in process 130 the wheel breakout is characterized in more detail and, if appropriate, removed. For this purpose, the wheel is generally dressed with multiple dressing strokes (step 131), during which the dressing power signal is determined for each dressing stroke (step 132). At each dressing stroke, a breakout measure M is determined from the dressing power signal (step 133). In decision step 134, it is checked whether the breakout measure M indicates that the breakout can be properly removed. If not, in decision step 136, it is checked whether the breakout is confined to a small enough area of ​​the wheel such that machining is nevertheless still feasible using undamaged areas of the wheel. If neither is possible, in step 137, the operator is instructed to replace the wheel. On the other hand, if the breakout measure M indicates that the breakout can be adequately removed by dressing, then in decision step 135 it is checked whether the last performed dressing process was already sufficient to remove the breakout. If so, machining continues (step 138). If not, the characterization and removal process 130 is repeated and machining continues again until the breakout measure M indicates that the breakout has been sufficiently removed.

[0117] Overall, it is therefore possible to determine automatically, instantly and reliably for each workpiece whether machining is possible or, in case of doubt, whether the machining that has been carried out should be checked separately.

[0118] Variations

[0119] Although the present invention has been described with reference to preferred exemplary embodiments, the present invention is by no means limited to these examples, and various modifications are possible without departing from the scope of the present invention. For example, the generating grinding machine can be constructed differently from the above-mentioned examples, as will be appreciated by those skilled in the art. The described method can, of course, include other means for monitoring and determining.

[0120] Further considerations

[0121] In summary, the present invention is based on the following considerations:

[0122] Despite the complexities during generating grinding, a robust process control that provides the required quality immediately and as uninterrupted as possible is the aim of automated production. In addition, it is appropriate to assign an annex to each gear regarding the machining and final quality of each gear produced in an automated manner. Online data should be available for a reliable traceability of all relevant production steps at the time of "pushing the button" and for generalized and / or efficient process optimization.

[0123] The invention therefore uses measures to ensure that indicators of process deviations, in particular breakouts of various magnitudes, are detectable and a warning signal is output, which can be determined in particular on the basis of a signal of a toothing probe or by measuring the current value of the tool spindle.

[0124] A warning signal allows the immediate halt of machining, the completely or partially machined workpiece is automatically removed as a NOK part using a handling device, if appropriate, and the control device determines and optionally stores the shift position (Y position) of the grinding worm in case of a defect. The grinding wheel is then checked for breakouts. For this, at the working rotational speed of the grinding spindle, the tip area of ​​the grinding worm with the smallest absolute value is dressed using a dressing device, and at the same time the current and / or the signal of the acoustic signal is sensed in order to reliably detect the breakout. Alternatively, the check for breakouts is carried out using another method, for example optically, acoustically by a coolant jet or by a complete dressing stroke. This process can also be carried out by a toothing probe at defined intervals and without a warning signal, since in this way it is possible to detect relatively small breakouts on the grinding worm that have not occurred as a result of an incorrectly machined workpiece. If this measurement detects a breakout, the control device determines: Further machining the production batch and blocking off the damaged area on the grinding worm to prevent further machining; dressing the grinding worm and then possibly carrying out further machining with reduced metal cutting values, or Replacing the grinding worm and completing the machining of the production batch with a new grinding worm.

[0125] It should be noted that during wheel dressing, the first dressing stroke is usually performed at the setting for the production batch. For large and very large breakouts, long dressing times may be required. In this situation, adaptive or self-learning dressing can provide significant time savings and can also avoid time-consuming grinding worm replacement.

[0126] Also, if a warning signal is determined, but this measurement does not detect a breakout on the grinding worm, the control device determines: Carrying out further machining of the production batch with reduced metal cutting values, or Stopping machining of a production batch and notifying the operator.

[0127] For this reason, automatic process monitoring of a production batch during grinding and dressing can be performed by a CNC generating grinding machine using peripheral automation technology for the transfer of workpieces, using a separate control device with a connected server. The control device is preferably configured in such a way that all sensor data, corresponding settings and machining values ​​of the generating grinding machine, preferably power values ​​at the tool spindle, workpiece spindle and dressing spindle, as well as signals of the toothing probe, are continuously sensed and stored in the server for each workpiece of the production batch. In this case, as an option, it is possible to perform a time-neutral component monitoring at each automatically performed workpiece change, which clears the machining in the absence of objections. Among other things, cutting power signals and cutting energy indicators are also determined, which signals and indicators are associated with other data in the control device and also with data stored in the server after machining of the first workpiece. An early warning indicator can then be output. [Explanation of symbols]

[0128] 1. Generating grinding machine 11 Mechanical Bed 12 Tool Carrier 13-axis carriage 14 Grinding head 15 Tool Spindle 16 Grindstone 17 Measuring probe 18 Acoustic Sensor 19 Coolant nozzle 20 Workpiece Carrier 21 Workpiece Spindle 22 Tailstock 23 Workpiece 24 Tooth alignment probe 31 Rotating Device 32 Dressing spindle 33 Dressing Tools 40 Machine Controller 41 Axis Module 42 Control Device 43 CNC Operator Control Panel 44 Server 51 Grindstone Breakout 52 teeth 61~63 Measurement curve 64 Current Changes with Time 65 Dressing hours 71 Measurement curve 72 Gap 81 Measurement curve 82 Envelope Curve 83 Average 84 Minimum 85 Maximum 110 Machining Process 111 Machining of workpieces 112 Surveillance Determination of 113 W 114 Judgment Step 120 Breakout Detection Process 121 Move 122 Determining the Contact Signal 123 A Decision 124 Judgment Step 130 Characterization / Removal 131 Dressing 132 Determination of Dressing Power 133 M Decision 134~136 Judgment step 137 Replacing the grindstone 138 Further Machining au arbitrary unit A Breakout Indicator A t Breakout indicator threshold B Tool axis C1 Workpiece axis C3 Pivot axis of the workpiece carrier C4 Pivot axis of dressing device I av Tool Spindle Average Power Consumption I d Power consumption of the dressing spindle I s Tool spindle power consumption M Breakout Measure n A Workpiece Rotation Speed n t Rotational speed difference threshold n W Workpiece spindle rotation speed N is the number of workpieces in the batch Pb Meshing signal / tooth pulse width Pd Mesh signal / tooth signal period duration t time V a Acoustic signal W warning indicator W t Warning indicator threshold X feed direction Y-shifting axis Z axis direction Δφ A Change in angle of the workpiece Δφ t Angle change difference threshold Δφ W Workpiece spindle angle change

Claims

1. 1. A method for automatic process monitoring in continuous generating grinding of a pre-toothed workpiece (23) with a generating grinding machine (1), comprising: The generating grinding machine (1) comprises a tool spindle (15) and at least one workpiece spindle (21), a grinding wheel (16) having a worm-type shape with one or more worm threads is clamped on the tool spindle (15), the grinding wheel (16) is rotatable about a tool axis (B), and the workpiece (23) is configured to be clamped on the at least one workpiece spindle (21), The method comprises: machining the workpiece (23) using the generating grinding machine (1), for which the workpiece (23) is clamped on the at least one workpiece spindle (21) and subsequently transferred into generating engagement with the grinding wheel (16); monitoring at least one measurement variable during said machining of said workpiece (23); determining a warning indicator (W) for an unacceptable process deviation from the at least one monitored measurement variable; Including, said warning indicator (W) being a warning indicator for a possible wheel breakout (51) of said wheel (16); If the warning indicator (W) indicates a possible wheel breakout (51), the wheel (16) is automatically checked for wheel breakouts (51).

2. The generating grinding machine (1) comprises a dressing device (30) having a dressing tool (33), and the automatic checking of the grinding wheel (16) for wheel breakouts (51) comprises: moving the dressing tool (33) over a tip region of the grinding wheel (16); determining a contact signal indicative of contact between the dressing tool (33) and the tip region of the grinding wheel (16) during said movement over the tip region; determining a breakout indicator (A) indicative of whether a wheel breakout (51) is present by analyzing the contact signal; The method of claim 1 , comprising:

3. The generating grinding machine includes an acoustic sensor (18) for acoustically detecting the engagement of the dressing tool (33) with the grinding wheel (16), and the contact signal is determined by an acoustic signal (V ａ 3. The method of claim 2, comprising:

4. 4. The method according to claim 2 or 3, wherein the dressing device (30) comprises a dressing spindle (32) to which the dressing tool (33) is clamped, and the contact signal comprises a tip dressing power signal indicative of power consumption of the dressing spindle (32) during the movement over the tip area.

5. 5. The method of claim 2, wherein the breakout indicator (A) indicates a position of the wheel breakout (51) along at least one of the worm threads of the wheel (16).

6. The method comprises: dressing the grinding wheel (16) if the breakout indicator (A) indicates the presence of a wheel breakout (51); The method according to any one of claims 2 to 5, comprising:

7. 2. The method of claim 1, wherein the generating grinding machine (1) comprises a dressing device (30) having a dressing tool (33), and the automatic checking of the grinding wheel (16) for wheel breakouts (51) comprises dressing the grinding wheel (16) with at least one dressing stroke.

8. The method comprises: determining, during said dressing, a dressing power signal representative of the power consumption of the dressing spindle (32) or the tool spindle (15) during said dressing; determining a breakout measure (M) reflecting at least one characteristic of the wheel breakout by analyzing the time course of the dressing power signal during the dressing; repeating said dressing of said grinding wheel (16) depending on said breakout measure (M); The method of claim 6 or 7, comprising:

9. The analysis of the time course of the dressing power signal comprises: The method of claim 8 , comprising determining a variation variable, the variation variable indicative of a local change in magnitude of the dressing power signal along at least one of the worm sleds.

10. The at least one monitored measurement variable is A deviation index (Pb) for the upper tooth thickness error of the workpiece (23) before the machining of each workpiece, and / or The rotation speed (n Ａ ) and the resulting rotational speed (n Ｗ ) and / or 10. The method according to claim 1, further comprising at least one of the angular deviations being determined by comparison of an angular position of the workpiece spindle (21) after the machining of the workpiece (23) with a corresponding angular position of the workpiece (23) itself and an angular position of the workpiece spindle (21) before the machining of the workpiece with a corresponding angular position of the workpiece itself.

11. 11. The method according to claim 10, wherein the generating grinding machine comprises a toothing probe (24) for contactlessly determining the angular position of a workpiece (23) clamped on the at least one workpiece spindle (21), and the deviation index (Pb), the rotational speed and / or the respective angular position of the workpiece (23) are sensed by means of the toothing probe (24).

12. 1. A method for automatic process monitoring in continuous generating grinding of a pre-toothed workpiece (23) with a generating grinding machine (1), comprising: The generating grinding machine (1) comprises a tool spindle (15) and at least one workpiece spindle (21), a grinding wheel (16) having a worm-type shape with one or more worm threads is clamped on the tool spindle (15), the grinding wheel (16) is rotatable about a tool axis (B), and the workpiece (23) is configured to be clamped on the at least one workpiece spindle (21), The method comprises: machining the workpiece (23) using the generating grinding machine (1), for which the workpiece (23) is clamped on the at least one workpiece spindle (21) and subsequently transferred into generating engagement with the grinding wheel (16); monitoring at least one measurement variable during said machining of said workpiece (23); determining a warning indicator (W) for an unacceptable process deviation from the at least one monitored measurement variable; Including, said warning indicator (W) being a warning indicator for a possible wheel breakout (51) of said wheel (16); said at least one monitored measurement variable comprising a cutting power signal indicative of instantaneous metal cutting power during said machining of each individual workpiece (23); the warning indicator (W) being determined by the occurrence of a pulse-like increase in the cutting power signal during the machining process; method.

13. The cutting power signal represents the instantaneous power consumption (I ｓ 13. The method of claim 12, wherein the measurement is a measure of

14. 1. A method for automatic process monitoring in continuous generating grinding of a pre-toothed workpiece (23) with a generating grinding machine (1), comprising: The generating grinding machine (1) comprises a tool spindle (15) and at least one workpiece spindle (21), a grinding wheel (16) having a worm-type shape with one or more worm threads is clamped on the tool spindle (15), the grinding wheel (16) is rotatable about a tool axis (B), and the workpiece (23) is configured to be clamped on the at least one workpiece spindle (21), The method comprises: machining the workpiece (23) using the generating grinding machine (1), for which the workpiece (23) is clamped on the at least one workpiece spindle (21) and subsequently transferred into generating engagement with the grinding wheel (16); monitoring at least one measurement variable during said machining of said workpiece (23); determining a warning indicator (W) for an unacceptable process deviation from the at least one monitored measurement variable; Including, said warning indicator (W) being a warning indicator for a possible wheel breakout (51) of said wheel (16); The method includes performing a continuous or discontinuous shift movement between the grinding wheel (16) and the workpiece (23) along the tool axis (B), The at least one monitored measurement variable is a cutting energy index (I ａｖ ), The cutting energy index (I ａｖ ) represents a measure for the integral metal cutting power of the grinding wheel (16) while the respective workpiece (23) is machined with the generating grinding machine (1); The warning indicator (W) is adapted to monitor the cutting energy indicator (I) over the production of multiple workpieces (23) in a production batch. ａｖ ) changes, method.

15. The cutting energy index (I ａｖ 15. The method according to claim 14, wherein the integral of the power consumption of the tool spindle (15) during the machining of each workpiece (23) is a measure of the integral of the power consumption of the tool spindle (15) during the machining of each workpiece (23).

16. a tool spindle (15) capable of clamping a grinding wheel (16) having a worm-type shape with one or more worm threads and configured to be driven in rotation about a tool axis (B); At least one workpiece spindle (21) for driving a pre-toothed workpiece (23) in rotation about a workpiece axis (C1); A machine controller (40); Equipped with The machine controller (40) is configured to execute the method according to any one of claims 1 to 15. Generating grinding machine (1).

17. A computer program comprising instructions for causing a machine controller (40) of a generating grinding machine (1) according to claim 16 to carry out the method according to any one of claims 1 to 15.

18. 20. A computer readable medium having recorded thereon the computer program of claim 17.

Images