Method for grinding a toothing or a profile of a workpiece
Patent Information
- Application Number
- EP2023789259
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-10-22
- Filing Date
- 2023-10-06
- Publication Date
- 2025-08-27
AI Technical Summary
Current grinding processes lack comprehensive monitoring capabilities, making it difficult to detect process deviations and potential operational disruptions in real-time, which can lead to suboptimal machining results and tool errors.
Implementing a rotational acceleration sensor connected to a data processing system to perform frequency analysis of spindle acceleration signals, allowing for the detection of amplitude limits and enabling continuous monitoring of the grinding process, including during tool dressing and run-up phases, with data evaluation using methods like FFT for improved process control.
Enhances the monitoring of the grinding process, allowing for timely identification of faulty components and process anomalies, improving the quality of the grinding operation by providing actionable warnings and adaptive process optimization.
Smart Images
Figure 1.1
Abstract
Description
[0001] Method for grinding a gear or profile of a workpiece
[0002] The invention relates to a method for grinding a gear or a profile of a workpiece by means of a grinding tool in a grinding machine, wherein the grinding tool is mounted on a tool spindle and the tool spindle is rotated by means of a first drive motor, so that a tool drive train is present, and wherein the workpiece is mounted on a workpiece spindle and the workpiece spindle is rotated by means of a second drive motor, so that a workpiece drive train is present, wherein at least one rotational acceleration sensor is arranged in the region of the tool drive train and / or in the region of the workpiece drive train, wherein the values recorded by the rotational acceleration sensor for the rotational acceleration of the tool spindle and / or the workpiece spindle are transmitted to a data processing system, in particular to a machine control system, and are evaluated by this.
[0003] A method of the generic type is disclosed in WO 2015 / 036519 A1. The document mentions that a rotational acceleration sensor can be arranged in a machine tool, wherein signal transmission occurs via a first and a second antenna coil to enable wireless signal transmission between the antenna coils.
[0004] Another method is known from WO 2022 / 100972 A2. Here, during the machining of gear teeth using a grinding worm, several machine parameters are monitored. These parameters can include the power or current consumption of the motors or structure-borne noise signals. These are evaluated by the machine control system to determine whether they are within permissible limits. If this is not the case, a corresponding warning is issued, indicating that the grinding process cannot be carried out properly.
[0005] WO 2022 / 207371 A1 discloses that signals are recorded during the hard fine machining of a workpiece, and if the measured signals lie outside a predetermined tolerance, the workpiece is measured in a measuring device after machining.
[0006] It has been found that it is desirable to achieve even greater significance when monitoring previously known variables.
[0007] The invention is therefore based on the object of developing a method of the type mentioned at the outset and of providing a grinding machine with corresponding equipment so that improved monitoring of the grinding process is possible.
[0008] The solution to this problem is characterized in that the measured signal of the rotational acceleration is subjected to a frequency analysis, wherein the individual frequency components are determined with regard to their amplitude, wherein respective limit values are predetermined for the amplitudes of the frequency components, wherein a signal is output by the data processing system if at least one of the limit values is exceeded, and wherein the frequency components are monitored only with regard to their amplitude.
[0009] The data processing system can also be an industrial PC connected to the machine.
[0010] The rotational acceleration sensor is preferably arranged between the first drive motor and the tool and / or between the second drive motor and the workpiece. However, the sensor can also be located beyond the respective specified areas; it simply needs to be capable of detecting the respective rotational acceleration of the spindle. For this purpose, the acceleration sensor can also be placed, for example, in the area of a spindle counterbearing.
[0011] The acquisition and evaluation of measurement data from the rotational acceleration sensor preferably takes place while the tool is engaging the gear teeth or the profile of the workpiece. The acquisition and evaluation of measurement data from the rotational acceleration sensor preferably takes place (only) while the tool is engaging the gear teeth or the profile of the workpiece.
[0012] Alternatively, it is also possible for the measurement data from the rotational acceleration sensor to be recorded and evaluated while the first and / or second drive motor is running, without the tool engaging the gear teeth or the profile of the workpiece. The signals from the rotational acceleration sensor are then evaluated virtually in "idle mode," which makes it possible to draw conclusions about the condition of machine components or the causes of impending malfunctions. These conclusions can be drawn particularly easily if the signals from the rotational acceleration sensor are evaluated periodically. The first evaluation can, for example, be carried out after the machine has been put into operation, followed by further evaluations at regular intervals; changes in the signals then allow conclusions to be drawn about changes in the machine.
[0013] A special analysis in the so-called "idle" mode is designed so that data acquisition occurs during motor start-up (especially at constant rotational acceleration), and the system's dynamic behavior is recorded via the rotational acceleration sensor. This can also be used to draw conclusions about the machine status. In particular, it can be specified that the data acquisition of the rotational acceleration values from the rotational acceleration sensor occurs during the start-up from standstill to a specified final spindle speed.
[0014] Another alternative provides for the acquisition and evaluation of measurement data from the rotational acceleration sensor, which in this case is arranged in the area of the tool drive train, during the dressing of the tool using a dressing tool. This allows conclusions to be drawn about the dressing system. In this regard, a special embodiment of the invention provides for a rotational acceleration sensor to be arranged in the area of the drive train for driving the dressing tool, and for the data acquired by it to be evaluated. This can be very helpful for analyzing the dressing process, especially when the data analysis described below is performed.
[0015] The data processing system can output a signal if the measured rotational acceleration is above a specified tolerance.
[0016] The evaluation of the measured values for the rotational acceleration can be carried out - not according to the invention - in the time domain.
[0017] According to a preferred procedure, the said frequency analysis is carried out by means of a fast Fourier transformation (FFT).
[0018] However, alternative and well-known methods can also be used for this purpose, in particular a discrete Fourier transform (DFT), a root-mean-square analysis (determination of the RMS spectrum), a determination of the amplitude spectrum, a cepstrum analysis, a compensating sine function, or a determination of the auto-power spectrum (PSD analysis). These signal analysis methods are well-known per se and therefore need not be discussed in detail here.
[0019] The values of the rotational acceleration sensor are preferably recorded during a predetermined time interval while the workpiece is being ground with the grinding tool. It can also be provided that the values of the rotational acceleration sensor are recorded between two defined positions, in particular over a predetermined feed path while the workpiece is being ground with the grinding tool. The rotational acceleration can therefore be recorded both in a temporally defined manner and in a spatially defined manner (i.e., for example, over the course of the grinding stroke between predetermined positions, but also, for example, over a range of a feed or shift movement of a spindle). This makes it possible to observe particularly relevant sections of the grinding process and to make comparisons with previously stored data.
[0020] The grinding is preferably a generating grinding of a gear with a grinding worm.
[0021] A grinding machine for grinding a gear or a profile of a workpiece by means of a grinding tool, with a tool spindle for receiving the grinding tool and a first drive motor for driving the tool spindle, so that a tool drive train is present, and a workpiece spindle for receiving the workpiece and a second drive motor for driving the workpiece spindle, so that a workpiece drive train is present, can be designed such that a rotational acceleration sensor is arranged in the region of the tool drive train and / or in the region of the workpiece drive train, which is connected to a data processing system, in particular to a machine control system.
[0022] The proposed concept therefore envisages monitoring and evaluation of the grinding process, particularly the generating grinding process, by evaluating the rotational acceleration, which is recorded during the grinding process at the workpiece spindle and, if necessary, also or alternatively, at the tool spindle using a rotational acceleration sensor. It has been found that the rotational acceleration, particularly after the signal analysis described above (i.e., after a frequency analysis), provides very useful information about how the grinding process is progressing and whether it is proceeding properly.
[0023] This allows the grinding process to be effectively monitored and any defective or abnormal components to be identified in a timely manner. This particularly detects defects in the workpiece blank, waviness on the flanks of the ground gear, and even tool defects.
[0024] The assessment is preferably carried out by accessing data stored (in the machine control system) and thus learned insights from previous grinding processes. This allows process deviations (anomalies) to be detected more effectively, allowing the machine operator to be warned or the grinding process to be aborted.
[0025] In addition to the described detection of the rotational acceleration, further control-internal signals (i.e. those present in the machine control system) and also control-external signals (e.g. detected by sensors that record structure-borne noise, which originates, for example, from the machine bed or the hall floor) can be recorded and taken into account.
[0026] In addition, machine-internal data (such as set corrections, the diameter of the grinding worm, generated paths along which the workpiece and the tool are guided relative to each other) can be used to evaluate the process, for which purpose they can be adaptively filtered and sorted if necessary (for example, by dividing the entire grinding process into different strokes, dividing it into infeed, outfeed and full engagement of workpiece and tool).
[0027] Depending on the influencing factors on the process, especially with regard to the generated path (influenced by screw diameter and corrections), characteristic values can be calculated and output.
[0028] Using algorithms from statistics, and especially from the field of machine learning, these data are preferably evaluated, thereby determining the quality of the processing. The well-known algorithms from the field of machine learning include both supervised and unsupervised learning, "deep learning," and "reinforcement learning."
[0029] This makes it possible to improve monitoring quality and thus stabilize the grinding process. It is easier to detect whether a process is faulty, and the type of error can also be identified more accurately. The prerequisite for this is that such an error or a similar error has been recorded in the data stored (in the machine control system).
[0030] In addition to detecting the error, this also enables faster troubleshooting. Based on this knowledge, the machine is able to intervene adaptively in the process and optimize it.
[0031] As mentioned, based on insights into the grinding process, the measurement signals in the process can be divided into areas that are meaningful for evaluating the process. Thus, not the entire machining process is necessarily assessed, but only relevant areas.
[0032] The drawing shows an embodiment of the invention.
[0033] Fig. 1 shows a workpiece spindle of a grinding machine with a workpiece to be ground,
[0034] Fig. 2a shows schematically the recording of the rotational acceleration of the workpiece spindle over time and
[0035] Fig. 2b shows schematically the amplitudes of the frequency components obtained from a Fast Fourier Transformation (FFT) of the signal according to Figure 2a.
[0036] Figure 1 shows a workpiece spindle 2, on which a 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 creates a workpiece drive train. It is essential that an angular acceleration sensor 4 is integrated into the area of the drive train, in the exemplary embodiment between the drive motor 3 and the workpiece 1. This sensor is capable of detecting the angular acceleration of the workpiece spindle 2 about its longitudinal axis. The values obtained are transmitted to a data processing system 5, which can be, for example, the machine control system. Alternatively, an industrial PC can also be used as the data processing system.
[0037] Also shown is a tailstock 6, which supports the workpiece 1. Alternatively to the illustrated solution, it would also be conceivable for the rotational acceleration sensor 4 to be arranged in the area of the tailstock 6. The only important thing in this respect is that the rotational acceleration of the workpiece spindle 2 can be recorded.
[0038] The measured values recorded by the rotational acceleration sensor 4 are schematically sketched in Figure 2a over time, ie the second derivatives of the angle of rotation ([).
[0039] The signal thus recorded is subjected to a Fast Fourier Transformation (FFT) to determine the individual frequency components and, in particular, their amplitude A. This is outlined in Figure 2b.
[0040] The recorded curve in Figure 2b has been subjected to a Fast Fourier Transformation (FFT) in order to decompose the periodic signal according to Figure 2a into its components (the "harmonics"). Fig. 2b shows the amplitude A of the individual frequency components of the recorded periodic signal over the order Or.
[0041] For the individual amplitudes A, a limit value Gr is specified which must not be exceeded in order to justify the assumption that the grinding process was carried out correctly. As can be seen from Figure 2b, this is not the case for the 7th order of the analyzed curve according to Figure 2a, since the limit value Gr was exceeded here. It can therefore be seen in Fig. 2b that a frequency component lies above the limit value Gr, so that it can be concluded that a proper grinding process did not take place. For the individual orders Or, different values for the permissible amplitude A can of course also be specified (in contrast to the representation in Figure 2b).
[0042] The grinding process is the final shaping process in gear manufacturing. Rotational errors in the workpiece and tool axes, especially during generating grinding, have a particularly detrimental effect on the noise behavior of the gear teeth in the transmission. These errors can be effectively measured using the rotational acceleration devices proposed by the invention and evaluated using order analysis. By establishing limits, improperly machined workpieces can be identified and sorted out during the grinding process.
[0043] Especially with higher-frequency signals (over 150 Hz), measuring the angle (using an angle measuring system) can be disadvantageous, whereas measuring the acceleration offers potential. The amplitude of the displacement of a torsional vibration decreases inversely with frequency with increasing frequency at a constant vibration velocity. The velocity amplitude increases linearly with frequency, while the acceleration increases quadratically with frequency.
[0044] The components of the rotary acceleration device to be integrated into the (workpiece) spindle essentially include the (rotating) acceleration sensor and a signal transmission unit. The two components can be installed together or separately.
[0045] Preferably, the rotational acceleration sensor is integrated into the workpiece spindle. The drive train consists, for example, of a rotary union, a workpiece spindle shaft, an intermediate flange, the clamping device, the workpiece, the tailstock center, and the tailstock spindle.
[0046] Preferably, the rotational acceleration sensor and the signal transmission unit are arranged in or near the workpiece spindle shaft, the intermediate flange, the clamping device or the tailstock spindle.
[0047] It is also possible to install the rotational acceleration sensor in the drive train of the tool spindle. This consists, for example, of the tool spindle shaft, the tool dome, and the counterbearing shaft. Preferably, the acceleration sensor and the signal transmission unit are located in or near the tool spindle shaft, the tool dome, or the counterbearing shaft.
[0048] A rotational acceleration sensor suitable for use in the rotating system according to the invention is manufactured and offered, for example, by Discom - Elektronische Systeme und Komponenten GmbH. The rotational acceleration sensor detects the deviation from uniform rotation.
[0049] The angular acceleration sensor preferably consists of a stationary stator and a rotor mounted on the rotating shaft to be measured. The stator provides the rotor's power supply and receives the data from the rotating part of the angular acceleration sensor (preferably from two acceleration sensors installed 180° apart). The signal can be transmitted from the rotor to the stator optically. When reference is made above to an angular acceleration sensor integrated into the workpiece or tool spindle, this naturally also means that more than one such sensor can be provided.
[0050] The example illustrates the use of an FFT. Alternatively, any other known frequency analysis method can be used, such as, in particular, the Discrete Fourier Transform (DFT), frequency analysis using root-mean-square analysis (determining the RMS spectrum), determining the amplitude spectrum, cepstrum analysis (including variants such as power cepstrum), a compensating sine function, or determining the auto-power spectrum (PSD analysis). All of the methods described are well-known in measured value analysis, so they need not be discussed in detail here.It is only essential that the individual frequency components of the measured periodic signal components are determined by means of a frequency analysis and that the results obtained from this are used for comparison with permissible limit values (in particular for the maximum permissible values of the individual amplitudes of the harmonics).
[0051] The proposed method can be used in principle for any grinding cycle, especially for grinding at variable speeds. Reference symbols; 1 Workpiece (gear)
[0052] 2 workpiece spindles
[0053] 3 Drive motor
[0054] 4 rotational acceleration sensor
[0055] 5 Data processing system (machine control) 6 Tailstock
Claims
Patent claims; Method for grinding a toothing or a profile of a workpiece (1) by means of a grinding tool in a grinding machine, in particular generating grinding of a gear with a grinding worm, wherein the grinding tool is mounted on a tool spindle and the tool spindle is rotated by means of a first drive motor, so that a tool drive train is present, and wherein the workpiece (1) is mounted on a workpiece spindle (2) and the workpiece spindle (2) is rotated by means of a second drive motor (3) is rotated so that a workpiece drive train is present, wherein in the area of the tool drive train and / or in the area of the workpiece drive train at least one rotational acceleration sensor (4), wherein the values recorded by the rotational acceleration sensor (4) for the rotational acceleration of the tool spindle and / or the workpiece spindle (2) are transmitted to a data processing system (5) and evaluated by the latter, characterized in that that the measured signal of the rotational acceleration is subjected to a frequency analysis, wherein the individual frequency components are determined with regard to their amplitude, wherein respective limit values are predetermined for the amplitudes of the frequency components, wherein a signal is output by the data processing system (5) if at least one of the limit values is exceeded, and wherein the frequency components are monitored only with regard to their amplitude.
2. Method according to claim 1, characterized in that the rotational 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. Method according to claim 1 or 2, characterized in that the acquisition and evaluation of measurement data from the rotational acceleration sensor (4) takes place during the engagement of the tool in the toothing or the profile of the workpiece (1).
4. Method according to claim 1 or 2, characterized in that the acquisition and evaluation of measurement data from the rotational acceleration sensor (4) takes place during the operation of the first and / or second drive motor, without any engagement of the tool in the toothing or the profile of the workpiece (1).
5. Method according to claim 1 or 2, characterized in that the acquisition and evaluation of measurement data from the rotational acceleration sensor (4) takes place during the dressing of the tool by means of a dressing tool.
6. Method according to one of claims 1 to 5, characterized in that the frequency analysis is carried out by means of a fast Fourier transformation (FFT).
7. Method according to one of claims 1 to 5, characterized in that the frequency analysis is carried out by means of a discrete Fourier transformation (DFT).
8. Method according to one of claims 1 to 5, characterized in that the frequency analysis is carried out by a root-mean-square analysis (determination of the RMS spectrum) or by a determination of the amplitude spectrum or by a cepstrum analysis or by a compensation sine function or by a determination of the auto power spectrum (PSD analysis).
9. Method according to one of claims 1 to 8, characterized in that the detection of the values of the rotational acceleration sensor (4) takes place during a predetermined time interval during the grinding of the workpiece with the grinding tool. Method according to one of claims 1 to 9, characterized in that the values of the rotational acceleration sensor (4) are detected between two defined positions.