METHOD FOR GRINDING A TOOTHING OR A PROFILE OF A WORKPIECE

Abstract

A method for grinding a toothing of a workpiece with a grinding tool in a grinding machine, wherein during the engagement of the grinding tool in the toothing to be ground, a first and a second machine parameter are measured, and both machine parameters measured are compared with a predefined stored value, wherein a signal is output if at least one of the machine parameters exceeds or falls below the predefined stored value, taking account of a tolerance range. To enable a conclusion to be drawn about the course of the grinding process by monitoring relevant variables, at least one of the machine parameters contains periodic signal components, wherein the signal components are broken down by a frequency analysis into the individual frequency components and the frequency components are used, with regard to their frequency and/or amplitude, for comparison.

Claims

1-15. (canceled)

16. A method for grinding a toothing or a profile 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, wherein the workpiece is received on a workpiece spindle and the workpiece spindle is rotated by means of a second drive motor, wherein at least during the engagement of the grinding tool in the toothing to be ground or in the profile to be ground, a first and a second machine parameter are measured and both measured machine parameters or a variable derived from the machine parameter are compared with a predetermined stored value, wherein a signal is output if at least one of the machine parameters or the variable derived therefrom, taking into account a tolerance band, exceeds or falls below the predetermined stored value, wherein at least one of the machine parameters or the variable derived from this machine parameter contains periodic signal components, wherein these signal components are broken down into the individual frequency components by a frequency analysis and the frequency components being used for comparison with regard to their frequency and/or their amplitude.

17. The method according to claim 16, wherein both machine parameters or the variables derived from these machine parameters contain periodic signal components.

18. The method according to claim 16, wherein the frequency components are used for comparison only with regard to their amplitude.

19. The method according to claim 16, wherein the frequency analysis is performed by means of a Fast Fourier Transform.

20. The method according to claim 16, wherein the frequency analysis is performed by means of a Discrete Fourier Transform.

21. The method according to claim 16, wherein the frequency analysis is performed 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 sinus function or by a determination of the auto power spectrum (PSD analysis).

22. The method according to claim 16, wherein the measurement of the first and second machine parameters is performed during a predetermined time interval during grinding of the workpiece with the grinding tool.

23. The method according to claim 16, wherein the measurement of the first and second machine parameters is carried out over a predetermined feed path during grinding of the workpiece with the grinding tool.

24. The method according to claim 16, wherein the first machine parameter is the power or current consumption of the motor of the tool spindle.

25. The method according to claim 16, wherein the second machine parameter is the power or current consumption of the motor of the workpiece spindle.

26. The method according to claim 24, wherein from the course of the total power or current consumption of the motor the course of the power or current consumption is subtracted which results in a grinding stroke without cutting of material or only with low cutting in a finishing grinding stroke.

27. The method according to claim 16, wherein one of the machine parameters is the structure-borne sound of the grinding machine or a part thereof, which is detected via a structure-borne sound sensor.

28. The method according to claim 16, wherein the variable derived from the machine parameter is the cutting energy per volume required to machine a predetermined volume of the allowance to be removed on the toothing or on the profile.

29. The method according to claim 16, wherein a characteristic value which characterises the grinding process for the ground workpiece is determined and output from the measured machine parameters and/or from the variable derived from the machine parameter.

30. The method according to claim 16, wherein the grinding tool is a grinding worm and the workpiece is a gear wheel.

Description

[0036] The drawing shows examples of embodiments of the invention.

[0037] FIG. 1 first shows in a general manner for a first grinding process in the upper figure the course of the power consumption or current consumption of the motor that drives the grinding spindle, and in the lower figure the course of the power consumption or current consumption of the motor that drives the workpiece spindle, and

[0038] FIG. 2 shows, according to an embodiment of the method according to the invention for a second grinding process, in the left figure the course of the power consumption or the current consumption of the motor which drives the workpiece spindle, and in the right figure the amplitudes of the frequency components of a periodic course of the power or the current obtained from a Fast Fourier Transformation (FFT).

[0039] FIG. 1 shows the curve of the power P or current I over time t, which results for a motor for driving a grinding spindle (S) and for the motor for driving a workpiece spindle (W) in a gear grinding machine (shown for a roughing stroke in which the workpiece is ground to quality). At the top of FIG. 1, the curve of the power PS is plotted over time as it is absorbed by the motor of the grinding spindle; the same curve for the amperage IS of the motor is correspondingly obtained via the applied motor voltage. The same applies to the lower illustration in FIG. 1, where the same information is plotted for the motor for driving the workpiece spindle.

[0040] The power and current curve to be expected when manufacturing proper gears is shown with the respective dot and dash line. Dashed lines above and below the dot and dash line indicate the permissible tolerance band for the power or current curve. EL indicates the area where a grinding worm enters the gear to be ground, VS indicates the full cut where the actual grinding takes place, and AL indicates the exit of the tool from the workpiece.

[0041] The drawn line indicates the actual course of the power or current during the grinding of a specific workpiece.

[0042] It can be seen that the power or current consumption at the grinding spindle is normal, which would indicate proper grinding. In fact, however, this is not the case. Due to a flank shape error (namely due to an opposite flank line deviation between the right and the left tooth flank), the grinding spindle consumes the expected current, but not the workpiece spindle, whose power consumption is outside the expected range, as can be seen from the lower illustration in FIG. 1.

[0043] It should therefore be noted that, depending on the position or orientation of the flank form error, the power consumption or current consumption at the grinding spindle may well still lie within the permissible tolerance band, while only the simultaneous consideration of the power consumption or current consumption at the workpiece spindle reveals that there have been problems here with the pre-machining of the gear and that there is a corresponding flank form error.

[0044] In the present embodiment, it is thus generally provided that (at least) during the engagement of the grinding tool in the toothing to be ground, a first machine parameter in the form of the power or the amperage of the tool spindle and a second machine parameter in the form of the power or the amperage of the workpiece spindle are measured. The two measured machine parameters PS/IS, PW/IW are compared with a predefined stored value. As shown in FIG. 1, it is immediately apparent from the lower partial figure that the course of the power or the current intensity has left the permissible tolerance band, so that a warning signal is emitted. The machine control thus indicates a problem during grinding and that there is possibly no good part.

[0045] FIG. 2 shows a specific procedure according to the invention, according to which the said procedure has been specifically designed here to make improved problems visible during the grinding process and to be able to issue a corresponding warning message.

[0046] The left-hand illustration in FIG. 2 again shows the power or current consumption at the workpiece spindle (see the drawn-out line), which here lies within the permissible tolerance band. However, it can also be seen that the power or current consumption changes periodically, i.e. it shows the course of a superimposed oscillation.

[0047] This superimposed vibration can impose a detrimental fine ripple on the tooth flank, which can lead to noise when the gearing is in use; this is particularly disadvantageous in the field of electromobility.

[0048] According to a possible embodiment of the invention, it is therefore envisaged here that, in refinements of the above procedure, a variable derived from the machine parameter (here: from the power or current consumption of the workpiece spindle) is considered in order to assess or evaluate the grinding process.

[0049] The recorded waveform in the left partial image in FIG. 2 is subjected to a Fast Fourier Transformation (FFT) to decompose the periodic signal into its components (harmonics). This is shown in the right partial image in FIG. 2. Here, the amplitude A of the individual frequency components of the detected periodic signal is schematically plotted above the order Or. It can be seen that a frequency component is above a limit value Gr, so that it can be concluded that no proper grinding process has taken place.

[0050] It should be noted that the illustration in FIG. 2 is only very schematic and that, of course, individual limit values can be set for each individual frequency component resulting from the FFT. In particular, expert knowledge stored in the machine control system can be used here to cause it to issue a warning signal in a given case.

[0051] With the proposed procedure, it is possible in particular to be able to point out improper process conditions very quickly, before a complete batch of workpieces has possibly been produced incorrectly. This can save considerable costs.

[0052] Of course, other parameters can also be used for monitoring the process, with particular thought being given to recording the structure-borne sound of the machine or the hall floor, which equally allow statements to be made, particularly after an analysis of the recorded signals (for example by means of an FFT), about how the grinding process has proceeded and whether it is to be expected that a good part has been ground.

[0053] The embodiment shows the use of an FFT. Alternatively, any other known method for frequency analysis can be used, such as in particular the Discrete Fourier Transform (DFT), the frequency analysis by a root mean square analysis (determination of the RMS spectrum), by a determination of the amplitude spectrum, by a cepstrum analysis (including the variants, such as power cepstrum), by a compensation sinus function or by a determination of the auto power spectrum (PSD analysis). In measured value analysis, the described methods are all known as such, so that they do not need to be discussed in more detail here. It is only essential that the individual frequency components of the measured periodic signal components are determined by a frequency analysis and that the results obtained from this are used for the comparison with permissible limit values (in particular for the maximum permissible magnitudes of the individual amplitudes of the harmonics).