Method for grinding teeth or contours of workpieces

Abstract

The invention relates to a method for grinding a toothing of a workpiece (1) by means of a grinding tool, the grinding tool being mounted on a tool spindle and the tool spindle being rotated by means of a first drive motor, and the workpiece (1) being mounted on a workpiece spindle (2) and the workpiece spindle (2) being rotated by means of a second drive motor (3), at least one rotational acceleration sensor (4) is arranged in the region of the tool drive train and / or in the region of the workpiece drive train, and wherein rotational acceleration values of the tool spindle and / or the workpiece spindle (2) recorded by the rotational acceleration sensor (4) are transmitted to a data processing system (5) and evaluated by the data processing system. In order to be able to improve the monitoring of the grinding process, the measured rotational acceleration signal is subjected to a frequency analysis, in which the amplitude of each frequency component is determined, the amplitude of the frequency component is assigned a respective limit value, the data processing system (5) outputs a signal if at least one limit value is exceeded, and only the amplitude of the frequency component is monitored.

Description

Technical Field

[0001] The invention relates to a method for grinding a toothed portion or a contour of a workpiece by means of a grinding tool in a grinding machine, wherein the grinding tool is received on a tool spindle and the tool spindle is rotated by means of a first drive motor, thereby forming a tool drive train, and wherein the workpiece is received on a workpiece spindle and the workpiece spindle is rotated by means of a second drive motor, thereby forming a workpiece drive train, wherein at least one angular acceleration sensor is arranged in the area of ​​the tool drive train and / or in the area of ​​the workpiece drive train, wherein angular acceleration values ​​of the tool spindle and / or the workpiece spindle recorded by the angular acceleration sensor are transmitted to a data processing system, in particular to a machine controller, and are evaluated by the machine controller. Background Art

[0002] A general method is disclosed in WO 2015 / 036519 A1, which states that an angular acceleration sensor can be arranged in a machine tool, wherein signal transmission is performed by means of a first antenna coil and a second antenna coil, so as to achieve wireless signal transmission between the antenna coils.

[0003] Another method is known from WO 2022 / 100972 A2. In this document, during the machining of the toothing, a grinding worm is used to monitor several machine parameters, which can be the power or current consumption of the motor or structure-borne sound signals. These parameters are then evaluated in the machine control system to determine whether they are within the permitted range. If they are not within the permitted range, a corresponding warning is issued, indicating that the grinding process cannot be carried out correctly.

[0004] WO 2022 / 207371 A1 discloses recording a signal during hard finishing machining of a workpiece, wherein the workpiece is measured with a measuring device after machining if the measured signal exceeds a predetermined tolerance.

[0005] It has been found that when monitoring known variables, a higher degree of accuracy is desirable. Summary of the invention

[0006] It is therefore the object of the present invention to further develop a method of the type mentioned at the outset and to provide a grinding machine with a suitable equipment, so that the monitoring of the grinding process can be improved.

[0007] According to the method, the solution to the object is characterized in that a frequency analysis is performed on the measured angular acceleration signal, wherein the amplitudes of the individual frequency components are determined, wherein corresponding limit values ​​are predetermined for the amplitudes of the frequency components, wherein when at least one limit value is exceeded, the data processing system outputs a signal and only the amplitudes of the frequency components are monitored.

[0008] The data processing system can also be an industrial PC connected to the machine.

[0009] The preferred location of the angular acceleration sensor is between the first drive motor and the tool and / or between the second drive motor and the workpiece. However, the sensor can also be arranged outside the area mentioned in each case; it must only be able to detect the corresponding rotational acceleration of the spindle. For this purpose, for example, the acceleration sensor can also be placed in the area of ​​the spindle counter bearing.

[0010] Preferably, measurement data from the angular acceleration sensor are recorded and evaluated when the tool comes into contact with the toothing or the contour of the workpiece.

[0011] Preferably, the measurement data from the angular acceleration sensor are (only) recorded and evaluated when the tool comes into contact with the toothing or the contour of the workpiece.

[0012] Alternatively, the measurement data from the acceleration sensor can also be recorded and evaluated during operation of the first drive motor and / or the second drive motor, without the tool engaging with the toothing or contour of the workpiece. Thus, the evaluation of the signals from the angular acceleration sensor is performed, so to speak, in an "idle" state, which allows conclusions to be drawn about the condition of machine components and the cause of an impending fault.

[0013] These conclusions can be drawn particularly easily if the evaluation of the signal from the angular acceleration sensor is repeated regularly. For example, a first evaluation can be carried out after the machine has been started, and further evaluations can be carried out regularly; changes in the signal then allow conclusions to be drawn about changes in the machine.

[0014] A specific analysis is designed to be performed during the above-mentioned "idle" operation in order to collect data during the motor startup (specifically at constant rotational acceleration) and record the dynamic system behavior via the angular acceleration sensor. Conclusions about the machine condition can also be drawn from this. Specifically, it can be specified that the data of the angular acceleration values ​​of the angular acceleration sensor should be collected during the startup of the spindle from a standstill to a specified final rotational speed.

[0015] Another alternative involves measuring and evaluating the data from an angular acceleration sensor during the use of the dressing tool, which in this case is located in the region of the tool drive train. This allows conclusions to be drawn about the dressing system. In this regard, a specific embodiment of the invention provides that the angular acceleration sensor is also arranged in the region of the drive train for driving the dressing tool and the data detected by the sensor are evaluated. This can be very helpful in analyzing the dressing process, in particular if the data analysis described below is performed.

[0016] If the measured acceleration exceeds a specified tolerance, the data processing system may output a signal.

[0017] The measured acceleration values ​​can be evaluated in the time domain - not according to the invention.

[0018] According to a preferred method, the above frequency analysis will be performed using Fast Fourier Transform (FFT).

[0019] However, alternative well-known methods can also be used for this purpose, in particular discrete Fourier transformation (DFT), root mean square analysis (determination of the RMS spectrum), determination of the amplitude spectrum, cepstrum analysis, equalized sinusoidal functions or determination of the autopower spectrum (PSD analysis). The mentioned signal analysis methods are well known and therefore do not need to be discussed in detail here.

[0020] Preferably, the values ​​of the angular acceleration sensor are acquired during predetermined time intervals while the workpiece is being ground with the grinding tool. It can also be provided that the values ​​of the angular acceleration sensor are acquired between two defined positions, in particular over a predetermined feed distance, while the workpiece is being ground with the grinding tool. Thus, angular accelerations defined both in time and in space can be recorded (i.e., for example over the course of the grinding stroke between the predefined positions, but also over the area of ​​the feed movement or displacement movement of the spindle). This makes it possible to observe particularly relevant sections of the grinding process and to compare them with previously stored data.

[0021] Preferably, the grinding is generating grinding of the gear using a grinding worm.

[0022] A grinding machine for grinding a tooth portion or a contour of a workpiece by means of a grinding tool comprises a tool spindle, a first drive motor, a workpiece spindle, and a second drive motor, wherein the tool spindle is used to receive a grinding tool, the first drive motor is used to drive the tool spindle, thereby forming a tool transmission system, the workpiece spindle is used to receive a workpiece, and the second drive motor is used to drive the workpiece spindle, thereby forming a workpiece transmission system. This grinding machine can be designed to arrange an angular acceleration sensor in the area of ​​the tool transmission system and / or in the area of ​​the workpiece transmission system, and the sensor is connected to a data processing system, specifically to a machine controller.

[0023] Therefore, the proposed concept for monitoring and evaluating a grinding process, in particular a generated gear grinding process, is implemented by evaluating the angular acceleration measured at the workpiece spindle during the grinding process and, if necessary, also or alternatively, evaluating the angular acceleration measured at the tool spindle by means of an angular acceleration sensor.

[0024] It has been found that, in particular after the above-described technical evaluation of the signal (ie after a frequency analysis), the angular acceleration provides very useful information about how the grinding process is shaping up and whether it is running properly.

[0025] This means that the grinding process can be effectively monitored and defective or protruding parts can be detected in time. Specifically, defects in the original part of the workpiece, ripples on the side of the ground gear, and tool defects can be detected.

[0026] Preferably, the evaluation is performed by reference to stored (in the machine controller) data and thus to knowledge gained from previous grinding processes.Process deviations (anomalies) can be detected more effectively so that the machine operator can be warned or the grinding process can be aborted.

[0027] In addition to the described angular acceleration measurements, further control-internal signals (ie signals present in the machine controller) and control-external signals (measured, for example, via sensors picking up structure-borne sounds which may originate from the machine tool or the hall floor) may also be recorded and taken into account.

[0028] In addition, machine-internal data (such as setting corrections, the diameter of the grinding worm, the generated path for guiding workpiece and tool relative to each other) can be used to evaluate the process, for which they can be adaptively filtered and sorted (for example, by dividing the entire grinding process into different strokes, subdivided into entry, exit and full engagement of workpiece and tool).

[0029] Depending on the factors influencing the process, in particular for the generated path (influenced by the diameter and the correction of the screw), characteristic values ​​can be calculated and output.

[0030] These data are preferably evaluated with the aid of statistical algorithms, in particular algorithms from the field of machine learning, and the quality of the machining process is determined.

[0031] Known algorithms in the field of machine learning include supervised learning and unsupervised learning, "deep learning" and "reinforcement learning".

[0032] This makes it possible to improve the monitoring quality and thus stabilize the grinding process. Whether a process fault exists can be identified more effectively and the type of fault can also be identified more accurately. The prerequisite is that the data stored (in the machine control system) includes information about this fault or similar faults.

[0033] In addition to identifying errors, this also enables faster fault diagnosis. Based on this understanding, the machine is able to intervene and optimize the process adaptively.

[0034] As mentioned, based on the knowledge of the grinding process, the in-process measurement signals can be subdivided into areas that are meaningful for process evaluation. Therefore, it is not necessary to evaluate the entire machining process, but only the relevant areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings show an embodiment of the invention.

[0036] Figure 1 shows a spindle of a grinding machine with a workpiece to be ground,

[0037] Figure 2a schematically shows the time course of the angular acceleration of the workpiece spindle, and

[0038] Figure 2b Schematically shows the Figure 2a The amplitude of the frequency component obtained by performing a fast Fourier transform (FFT) on the signal.

[0039] List of reference numerals:

[0040] 1 Workpiece (gear)

[0041] 2 workpiece spindles

[0042] 3. Drive motor

[0043] 4 Angular Accelerometers

[0044] 5Data processing system (machine controller)

[0045] 6 tailstock DETAILED DESCRIPTION

[0046] Figure 1 A workpiece spindle 2 is shown, on which the workpiece 1 to be ground is clamped in the form of a gear. The workpiece spindle 2 is driven by a drive motor 3. This constitutes a workpiece drive train. In the present embodiment, it is essential to integrate an angular acceleration sensor 4 in the drive train between the drive motor 3 and the workpiece 1, which is able to detect the angular acceleration of the workpiece spindle 2 about its longitudinal axis. The values ​​obtained in this way are transmitted to a data processing system 5, which can be, for example, a machine controller system. Alternatively, an industrial PC can also be used as a data processing system.

[0047] Also shown is a tailstock 6 which supports the workpiece 1. As an alternative to the solution shown, it is also conceivable to arrange the angular acceleration sensor 4 in the region of the tailstock 6. It is only important that the angular acceleration of the workpiece spindle 2 can be recorded.

[0048] Figure 2a The measurement result of the angular acceleration sensor 4 recorded over time, namely the second derivative of the rotation angle, is schematically shown.

[0049] The signal thus recorded is subjected to a fast Fourier transformation (FFT) in order to determine the individual frequency components and in particular their amplitudes A. Figure 2b shown.

[0050] Therefore, Figure 2b The recorded curve is subjected to FFT (Fast Fourier Transform) Figure 2a The periodic signal in is decomposed into its components ("harmonics"). Figure 2b The relationship between the amplitude A and the order Or of each frequency component of the recorded periodic signal is shown.

[0051] For each amplitude A, a limit value Gr is specified which must not be exceeded in order to justify the assumption that the grinding process is being performed correctly. Figure 2b It can be seen that according to Figure 2a This is not the case for the 7th order of the analyzed curve, since here the limit Gr is exceeded. Figure 2b It can be seen that the frequency components are above the limit Gr, so it can be concluded that the grinding process is not performed correctly.

[0052] Of course, different allowable amplitude A values ​​can also be specified for each order Or (with Figure 2b The opposite is true).

[0053] The grinding process is the last shaping process to produce a gear. Rotational errors of the workpiece and tool axis have a particularly negative influence on the noise behavior of the teeth in the gearbox, especially during generating grinding. These can be effectively measured with the angular acceleration device proposed by the invention and evaluated using order analysis. With limited teaching, workpieces that are not machined correctly can be detected and sorted out during the grinding process.

[0054] Specifically, for high-frequency signals (over 150 Hz), measuring angular displacement (using an angle measurement system) may be disadvantageous, whereas measuring acceleration has great potential here. The amplitude of the vibration displacement of torsional vibration decreases with increasing frequency at a constant vibration velocity. The velocity amplitude increases linearly with frequency, while the acceleration increases quadratically with frequency.

[0055] The components of the angular acceleration device to be integrated into the (workpiece) spindle essentially include a (rotational) acceleration sensor and a signal transmission unit. These two components can be constructed together or separately.

[0056] A preferred option is to integrate the angular acceleration sensor into the workpiece spindle.The drive train consists of, for example, a rotary feedthrough, a workpiece spindle, an intermediate flange, a clamping device, a workpiece, a tailstock center section and a tailstock sleeve.

[0057] Preferably, the angular acceleration sensor and the signal transmission unit are arranged in or near the workpiece spindle, the intermediate flange, the clamping device or the tailstock sleeve.

[0058] However, the angular acceleration sensor can also be positioned in the drive train of the tool spindle. This consists, for example, of the tool spindle, the tool spindle and the counter-bearing shaft. In this case, the acceleration sensor and the signal transmission unit are preferably located in or near the tool spindle, the tool spindle or the counter-bearing shaft.

[0059] Angular acceleration sensors suitable for rotating systems according to the invention are manufactured and provided, for example, by Discom, Elektronische Systeme und Komponenten GmbH (Electronic Systems and Components GmbH). The angular acceleration sensors detect any deviation from uniform rotation.

[0060] The angular acceleration sensor preferably consists of a fixed stator and a rotor mounted on the rotating axis to be measured. The stator provides power to the rotor and receives data from the rotating part of the angular acceleration sensor (preferably from two acceleration sensors mounted at 180°). The signal transmission from the rotor to the stator can be done optically.

[0061] While the above references an angular acceleration sensor integrated into a workpiece or tool spindle, it will be appreciated that more than one such sensor may be provided.

[0062] This embodiment shows the use of FFT. Alternatively, any other known frequency analysis method can be used, in particular discrete Fourier transform (DFT), frequency analysis by means of root mean square analysis (determination of the RMS spectrum), by determining the amplitude spectrum, by cepstrum analysis (including variants such as power cepstrum), by equalizing sinusoidal functions or by determining the self-power spectrum (PSD analysis). The described methods are all known in the analysis of measurement data and therefore do not need to be discussed in detail here. It is only important that the individual frequency components of the measured periodic signal components are determined by frequency analysis and that the results obtained therefrom are used for comparison with the permitted limit values, in particular the maximum permitted values ​​of the individual amplitudes of the "harmonics".

[0063] In principle, the proposed method can be used for any grinding cycle, especially for variable speed grinding.

Claims

1. A method for grinding a tooth or a profile of a workpiece (1) by means of a grinding tool in a grinding machine, in particular for generating a gear with a grinding worm, in, The grinding tool is received on a tool spindle and the tool spindle is rotated by means of a first drive motor, thereby forming a tool drive train, and The workpiece (1) is received on a workpiece spindle (2) and the workpiece spindle (2) is rotated by means of a second drive motor (3), thereby forming a workpiece drive train. wherein at least one angular acceleration sensor (4) is arranged in the area of ​​the tool drive train and / or in the area of ​​the workpiece drive train, wherein the angular acceleration values ​​of the tool spindle and / or the workpiece spindle (2) recorded by the angular acceleration sensor (4) are transmitted to a data processing system (5) and evaluated by the data processing system, It is characterized in that a frequency analysis is performed on the measured angular acceleration signal, wherein the amplitude of each frequency component is determined, wherein corresponding limit values ​​are predetermined for the amplitude of the frequency components, and wherein when at least one of the limit values ​​is exceeded, the data processing system (5) outputs a signal and only monitors the amplitude of the frequency components.

2. The method according to claim 1, characterized in that The angular acceleration sensor (4) is arranged between the first drive motor and the tool and / or between the second drive motor (3) and the workpiece (1).

3. The method according to claim 1 or 2, characterized in that: The recording and evaluation of the measurement data from the angular acceleration sensor (4) is performed during the meshing of the tool with the toothing or the contour of the workpiece (1).

4. The method according to claim 1 or 2, characterized in that: The recording and evaluation of the measurement data from the angular acceleration sensor (4) is performed during operation of the first drive motor and / or the second drive motor without the tool meshing with the toothing or the contour of the workpiece (1).

5. The method according to claim 1 or 2, characterized in that: The recording and evaluation of the measurement data from the angular acceleration sensor (4) is carried out during the dressing of the tool by means of a dressing tool.

6. The method according to any one of claims 1 to 5, characterized in that The frequency analysis is performed with the aid of a Fast Fourier Transform (FFT).

7. The method according to any one of claims 1 to 5, characterized in that The frequency analysis is performed with the aid of a discrete Fourier transform (DFT).

8. The method according to any one of claims 1 to 5, characterized in that The frequency analysis is performed by means of a root mean square analysis (determination of the RMS spectrum) or by determination of the amplitude spectrum or by means of a cepstrum analysis or by means of an equalized sinusoidal function or by determination of the autopower spectrum (PSD analysis).

9. The method according to any one of claims 1 to 8, characterized in that While the workpiece is being ground with the grinding tool, the value of the angular acceleration sensor (4) is recorded during predetermined time intervals.

10. The method according to any one of claims 1 to 9, characterized in that The value of the angular acceleration sensor (4) is detected between two defined positions.

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