Method and device for detecting upper slippage of grinding wheel

Abstract

To provide a grinding stone upper slip detection method and device which can correctly detect the occurrence of upper slip of a grinding stone by using an AE signal being the vibration generated due to crushing of abrasive grains and a vitrified bond in grinding processing.SOLUTION: A grinding stone upper slip detection device comprises: a frequency analysis unit 50 which frequency-analyzes an AE signal SAE generated in the time of grinding to a grinding object material 12 from a grinding wheel 20; and an upper slip detection unit 56 which detects upper slip of the grinding wheel 20 on the basis of the magnitude of a periodical change amount synchronized with rotation of the grinding object material 12 of the signal intensity of a prescribed frequency band of the signal intensities of the frequency spectra that are frequency-analyzed by the frequency analysis unit 50. With this, the device can correctly detect the occurrence of upper slip of the grinding wheel 20 on the basis of the magnitude of the periodical change amount synchronized with rotation of the grinding object material 12 of the signal intensity SP of the prescribed frequency band obtained by frequency-analyzing the AE signal SAE.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and device for detecting upward slip of a grinding wheel, which detects upward slip of a grinding wheel from an AE signal obtained during grinding of the outer peripheral surface of a workpiece. [Background technology]

[0002] For example, in the process of grinding the outer peripheral surface of a cylindrical workpiece with a grinding wheel, the abrasive grains of the grinding wheel may slide upward on the surface of the workpiece without cutting it. For example, when grinding a hard-to-cut material that tends to retain heat, such as a titanium alloy, this phenomenon of upward sliding of the grinding wheel is likely to occur when a high-hardness grinding wheel is used to grind with a small amount of cutting depth and low polishing efficiency. When upward sliding occurs, a pattern indicating a change in the metal structure of the surface of the workpiece is observed at the location of the upward sliding on the ground surface.

[0003] To detect such top slippage, for example, estimation is performed using changes in the power consumption of the electric motor that rotates the grinding wheel or changes in the grinding resistance measured by a dynamometer. However, there is a problem in that it is not possible to accurately determine the timing and magnitude of top slippage.

[0004] In response to this, Patent Document 1 proposes a carrying amount measuring device that includes a cutting table movement amount detection means for determining the amount of movement of the cutting table during grinding, an in-process gauge change amount detection means for determining the amount of change in an in-process gauge that detects the remaining amount of grinding on the workpiece, and a carrying amount calculation means for determining the carrying amount based on the obtained cutting table movement amount and in-process gauge change amount, and that resets the cutting table movement amount and in-process gauge change amount to zero when the amount of variation associated with one rotation of the workpiece detected by the in-process gauge becomes smaller than a predetermined value compared to the value at the initial stage of processing, and determines the carrying amount (= cutting table movement amount - in-process gauge change amount). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-119803 Summary of the Invention [Problem to be solved by the invention]

[0006] However, there was a problem in that the change in the grinding remaining amount determined by the carry-over amount measuring device described in Patent Document 1 could not be distinguished from the influence of the tool sharpness, and the upward slippage of the grinding wheel could not be accurately detected.

[0007] The present invention has been made in light of the above circumstances, and its purpose is to provide a method and device for detecting upward slippage of a grinding wheel that can accurately detect the occurrence of upward slippage of a grinding wheel by using an AE signal, which is a vibration generated due to the fracture of abrasive grains and vitrified bonds during grinding. [Means for solving the problem]

[0008] Based on the above circumstances, the inventors conducted further studies by frequency analyzing AE signals obtained during the grinding process of a workpiece using cylindrical plunge grinding. They found that when the AE signals were digitized using an A / D converter that performs A / D conversion at a sampling period significantly shorter than the rotational period of the workpiece, the frequency spectrum obtained by the frequency analysis showed a first peak in signal intensity, which was presumed to be due to the occurrence of fracture, followed by a second peak in signal intensity in a predetermined frequency band, for example, 45 to 75 kHz. They also found that when the time variation of the integrated value of the signal intensity constituting the second peak in signal intensity was represented as a waveform, it contained multiple periodic valleys with locally low values, and that these valleys corresponded to the rotational period of the workpiece. They also found that no such valleys were present in the time waveform showing the power consumption of the electric motor that rotates the grinding wheel. They also found that the depth of the valleys decreased when the rotational speed of the grinding wheel was reduced. After examining these three facts, we came to the conclusion that the magnitude of the trough waveform indicates the degree of the upward sliding phenomenon of the grinding wheel. The present invention was made based on this finding.

[0009] That is, the gist of the first invention is (a) a method for detecting upward slippage of a grinding wheel that grinds the outer peripheral surface of a workpiece, comprising: (b) a frequency analysis step of frequency-analyzing an AE signal generated from the grinding wheel when grinding the workpiece; and (c) an upward slip detection step of detecting upward slippage of the grinding wheel based on the magnitude of the amount of periodic change, synchronized with the rotation of the workpiece, in the integrated value of the signal intensity of a predetermined frequency band among the signal intensities of the frequency spectrum frequency-analyzed by the frequency analysis step.

[0010] The gist of the second invention is that in the first invention, the upper slip detection process represents the magnitude of the periodic change in the signal intensity integral value synchronized with the rotation of the workpiece by a moving standard deviation value of a plurality of the signal intensity integral values ​​obtained within a moving section that exceeds one rotation period of the workpiece.

[0011] The gist of the third invention is that in the second invention, the method further includes an upward slip determination step of determining upward slip of the grinding wheel based on whether the moving standard deviation value exceeds a predetermined determination threshold value.

[0012] The gist of the fourth invention is that in the third invention, the method further includes a rotational speed reduction control step of reducing the rotational speed of the grinding wheel by a predetermined value when the upward slippage of the grinding wheel is determined by the upward slippage determination step.

[0013] The gist of the fifth invention is (a) an upper slip detection device for a grinding wheel that detects upper slip of a grinding wheel that grinds the outer peripheral surface of a workpiece, including (b) a frequency analysis unit that performs frequency analysis of an AE signal generated from the grinding wheel when grinding the workpiece, and (c) an upper slip detection unit that detects upper slip of the grinding wheel based on the magnitude of the amount of periodic change, synchronized with the rotation of the workpiece, in the integrated value of the signal intensity of a predetermined frequency band among the signal intensities of the frequency spectrum frequency-analyzed by the frequency analysis unit.

[0014] The gist of the sixth invention is that in the fifth invention, the upper slip detection unit represents the magnitude of the periodic change in the signal intensity integral value synchronized with the rotation of the workpiece by a moving standard deviation value of a plurality of the signal intensity integral values ​​obtained within a moving section that exceeds one rotation period of the workpiece.

[0015] The gist of the seventh invention is that in the sixth invention, it further includes an upward slip determination unit that determines upward slip of the grinding wheel based on the moving standard deviation value exceeding a predetermined determination threshold value.

[0016] The paper of the eighth invention is the paper of the seventh invention, which further includes a rotational speed reduction control unit that reduces the rotational speed of the grinding wheel by a predetermined value when the upward slippage determination unit determines that the grinding wheel is slipping upward. [Effects of the Invention]

[0017] The grinding wheel slippage detection method of the first invention includes a frequency analysis step of frequency-analyzing an AE signal generated by the grinding wheel when grinding the workpiece, and an upper slippage detection step of detecting upper slippage of the grinding wheel based on the magnitude of the periodic change in signal intensity of a predetermined frequency band among the signal intensities of the frequency spectrum frequency-analyzed in the frequency analysis step, which is synchronized with the rotation of the workpiece. This makes it possible to accurately detect the occurrence of upper slippage of the grinding wheel based on the magnitude of the periodic change in signal intensity of the predetermined frequency band obtained by frequency analysis of the AE signal, which is synchronized with the rotation of the workpiece.

[0018] According to the grinding wheel top slip detection method of the second invention, the top slip detection step represents the magnitude of the periodic change in signal intensity that is synchronized with the rotation of the workpiece by the moving standard deviation value of multiple signal intensity values ​​obtained within a movement section that exceeds one rotation period of the workpiece, so that the occurrence of top slip of the grinding wheel can be accurately and quantitatively detected based on the magnitude of the moving standard deviation value.

[0019] According to the grinding wheel upward slip detection method of the third invention, an upward slip determination step is further included in which upward slip of the grinding wheel is determined based on whether the moving standard deviation value exceeds a predetermined determination threshold value, and therefore the occurrence of upward slip of the grinding wheel can be accurately determined by the upward slip determination step.

[0020] According to the grinding wheel slippage detection method of the fourth invention, a rotational speed reduction control step is further included in which, if the slippage of the grinding wheel is determined to be occurring in the slippage determination step, the rotational speed of the grinding wheel is reduced by a predetermined value. Therefore, if the grinding wheel is determined to be falling into a slippage state, the rotational speed of the grinding wheel is reduced and the slippage is automatically eliminated.

[0021] The grinding wheel slippage detection device of the fifth invention includes a frequency analysis unit that performs frequency analysis on the AE signal generated by the grinding wheel when grinding the workpiece, and an upper slippage detection unit that detects upper slippage of the grinding wheel based on the magnitude of the periodic change in signal strength of a predetermined frequency band among the signal strengths of the frequency spectrum frequency-analyzed in the frequency analysis step, which is synchronized with the rotation of the workpiece. This makes it possible to accurately detect the occurrence of upper slippage of the grinding wheel based on the magnitude of the periodic change in signal strength of the predetermined frequency band obtained by frequency analysis of the AE signal, which is synchronized with the rotation of the workpiece.

[0022] According to the grinding wheel top slip detection device of the sixth aspect of the invention, the top slip detection unit represents the magnitude of the periodic change in signal strength that is synchronized with the rotation of the workpiece by the moving standard deviation of multiple signal strength values ​​obtained within a movement section that exceeds one rotation period of the workpiece, so that the occurrence of top slip of the grinding wheel can be accurately and quantitatively detected based on the magnitude of the moving standard deviation.

[0023] The grinding wheel upward slip detection device of the seventh aspect of the invention further includes an upward slip determination unit that determines upward slip of the grinding wheel based on whether the moving standard deviation value exceeds a predetermined determination threshold value, so that the occurrence of upward slip of the grinding wheel can be accurately determined by the upward slip determination unit.

[0024] According to the grinding wheel top slip detection device of the eighth invention, a rotational speed reduction control unit is further included which reduces the rotational speed of the grinding wheel by a predetermined value when the top slip determination unit determines that the grinding wheel is top slipping. Therefore, when top slipping of the grinding wheel is determined, the rotational speed of the grinding wheel is reduced and the top slipping is automatically eliminated. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a diagram illustrating the configuration of a grinding apparatus according to an embodiment of the present invention, which is equipped with a grinding wheel slippage detection device that detects upward slippage of a grinding wheel during grinding. [Figure 2]2 is a diagram illustrating the mechanism by which an AE signal is generated from the grinding point of a grinding wheel during grinding by the grinding device of FIG. 1. FIG. [Figure 3] 2 is a diagram showing an example of a frequency spectrum obtained by performing frequency analysis on an AE signal SAE detected by the AE sensor of FIG. 1 using a frequency analysis unit. FIG. [Figure 4] 2 is a diagram showing an example of a change over time in the power consumption value of the electric motor that rotates the grinding wheel in the grinding device of FIG. 1. FIG. [Figure 5] 4 is a diagram showing an example of a waveform showing a signal strength (integral) value SPI within a predetermined frequency band B2 in the frequency spectrum of FIG. 3. FIG. [Figure 6] 6 is a diagram showing, with the time axis enlarged, a plurality of consecutive peak waveforms and valley waveforms included in a waveform showing a time change in the signal strength (integral) value SPI within the predetermined frequency band B2 in FIG. 5. FIG. [Figure 7] 7 is a diagram illustrating the period between the mountain-shaped waveforms included in the waveform of FIG. 6. FIG. [Figure 8] FIG. 6 corresponds to FIG. 6 and shows the waveform of the signal intensity (integral) value SPI obtained when the rotation speed of the grinding wheel in the grinding device of FIG. 1 is reduced compared to that in FIG. 6, with the time axis enlarged more than in FIG. 6. [Figure 9] This figure corresponds to Figure 6 and shows the waveform of the signal intensity (integral) value SPI obtained when the rotation speed of the grinding wheel in the grinding device of Figure 1 is further reduced compared to Figure 8, on the same time axis as Figure 8. [Figure 10] 7 is a diagram showing a waveform illustrating a change over time in the moving standard deviation value MSD of the signal strength (integral) value SPI within the predetermined frequency band B2 shown in FIG. 6. FIG. [Figure 11] 9 is a diagram showing a waveform illustrating a change over time in the moving standard deviation value MSD of the signal intensity (integral) value SPI shown in FIG. 8. FIG. [Figure 12] 10 is a diagram showing a waveform illustrating a change over time in the moving standard deviation value MSD of the signal intensity (integral) value SPI shown in FIG. [Figure 13]FIG. 11 shows abnormality level 1 and abnormality level 2 used as upper slip determination thresholds superimposed on the waveform showing the temporal change in the moving standard deviation value MSD in FIG. 10, and also shows a waveform showing the subsequent temporal change in the moving standard deviation value MSD when the rotation speed of the grinding wheel is reduced when abnormality level 2 is detected. [Figure 14] 2 is a flowchart illustrating a main part of the control operation of the electronic control device of FIG. 1. [Figure 15] 15 is a diagram illustrating a main part of a flowchart illustrating the control operation of the electronic control device of the other example of FIG. 14. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] An embodiment of the present invention will be described in detail below with reference to the drawings. Note that in the following embodiment, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of the various parts are not necessarily drawn accurately. [Example]

[0027] FIG. 1 is a diagram illustrating the configuration of a grinding apparatus 14 equipped with a top slip detection device 10 for a workpiece 12 according to one embodiment of the present invention. The grinding apparatus 14 uses a grinding wheel 20 to grind the workpiece 12, which is made of a difficult-to-cut material such as a titanium alloy. The workpiece 12 is a cylindrical or shaft-shaped metal part made of a difficult-to-cut material such as a titanium alloy (Ti-6Al-4V). The grinding wheel 20 is a grinding wheel configured by attaching a plurality of segmented grinding wheel pieces 20b, such as a vitrified grinding wheel, to the outer surface of a main body (metal base) 20a. The grinding wheel 20 is made of general abrasive grains such as fused alumina-based abrasive grains, silicon carbide-based abrasive grains, or ceramic abrasive grains, or superabrasive grains such as CBN abrasive grains or diamond abrasive grains, bonded together by an inorganic, organic, or metallic binder.

[0028] In FIG. 1, the grinding device 14 includes a grinding wheel 20, a spindle drive motor 62 that rotates and drives a rotating spindle that supports the grinding wheel 20 so that the grinding wheel 20 can rotate around the rotation center line C1 of the grinding wheel 20, a workpiece moving motor 66 that moves the workpiece 12 radially to press the grinding wheel 20 against the outer peripheral surface of the cylindrical workpiece 12, thereby changing the machining allowance, a workpiece rotation drive motor 68 that rotates and drives the workpiece 12 around a rotation center axis C2 that is parallel to the rotation center line C1 of the grinding wheel 20, and a grinding control device 72 that controls the spindle drive motor 62, workpiece moving motor 66, workpiece rotation drive motor 68, etc.

[0029] The grinding wheel 20 has a cylindrical or drum-shaped metal core (base metal), i.e., main body 20a, and a plurality of segment-shaped grinding stone portions 20b fixed to the outer surface of the main body 20a by adhesive or the like, and is attached to the end of a rotating spindle (not shown) that is rotated around the rotation center line C1 of the grinding wheel 20 by a spindle drive motor 62.

[0030] The main body 20a contains the AE sensor 22, the preamplifier 24, a transmitter circuit 26 that modulates the AE signal SAE amplified by the preamplifier 24 using a predetermined carrier wave and transmits the modulated signal, and a storage battery 44 that functions as a power source for these components. Also provided in a fixed position on the grinding machine 14 are a receiver circuit 30 having an antenna 28 for receiving the AE signal SAE transmitted from the transmitter circuit 26, a band-pass filter 32, a demodulator circuit 33, an A / D converter 34, and an electronic control device 36. The AE sensor 22, transmitter circuit 26, receiver circuit 30, band-pass filter 32, demodulator circuit 33, A / D converter 34, and part of the electronic control device 36 constitute the top slip detection device 10.

[0031] The AE sensor 22 detects, from the inner circumferential surface of the grinding wheel 20b, extremely high-frequency acoustic emissions, for example, in the ultrasonic range of 20 kHz or higher, that are generated when the abrasive grains contained in the grinding wheel 20b are crushed and propagate through the grinding wheel 20b, and outputs an AE signal SAE, which is an analog signal representing the crushing vibration. The preamplifier 24 amplifies the AE signal SAE output from the AE sensor 22. The bandpass filter 32 has a predetermined passband that exclusively passes the carrier wave received by the receiving circuit 30. The demodulation circuit 33 outputs the AE signal SAE demodulated from the carrier wave, and the A / D converter 34 converts the AE signal SAE into a digital signal.

[0032] The A / D converter 34 converts the AE signal SAE into a digital signal at a sampling period of, for example, 65 ms, which is 1 / 10 or less of the rotation period of the workpiece 12. The shorter (faster) the sampling period of the A / D converter 34 is relative to the rotation period of the workpiece 12, the clearer the waveform of the frequency spectrum obtained by frequency analysis of the AE signal SAE becomes, and the more accurate the detection of top slip of the grinding wheel 20 relative to the workpiece 12 can be.

[0033] 2, the grinding stone portion 20b of the grinding wheel 20 is composed of a well-known vitrified grinding stone structure consisting of abrasive grains 38, an inorganic binder (vitrified bond) 40 that binds the abrasive grains 38, and pores 42. The sliding contact between the grinding stone portion 20b of the grinding wheel 20 and the workpiece (work) 12 generates vibrations that are presumed to be caused by cracks Ca, i.e., the occurrence of fractures, in the abrasive grains 38 themselves, and vibrations that are presumed to be caused by frictional or elastic vibrations that are generated by contact, i.e., rubbing Cb, between the abrasive grains 38 and the workpiece 12, and grinding vibrations, i.e., AE waves, including these vibrations, are detected by the AE sensor 22.

[0034] As shown in FIG. 3 , the frequency spectrum obtained by frequency analysis of the AE signal SAE detected by the AE sensor 22 includes a first peak P1 between 25 and 40 kHz, which indicates a peak in signal intensity presumably due to cracks Ca, i.e., fractures, in the abrasive grains 38 themselves, and a second peak P2 within a frequency band B2 between 45 and 75 kHz, which includes signal intensities sensitive to upward slippage of the abrasive grains 38 relative to the workpiece 12. Since upward slippage can be detected using a portion of the signal intensity within the 45-75 kHz frequency band B2, the signal intensity does not necessarily have to be within the 45-75 kHz frequency band B2. For example, the center frequency band B1 between 55 and 60 kHz corresponds to the region where the signal intensity at the center of the second peak P2 within frequency band B2 is greatest. Therefore, signal intensities within a predetermined frequency range including at least a portion of the center frequency range B1 can be used to detect upward slippage.

[0035] The inventors conducted a test to confirm the relationship between the upward sliding of the grinding wheel 20 relative to the workpiece 12 and the signal intensity integral SPI within a predetermined frequency range in the frequency spectrum of the AE signal SAE. First, the inventors conducted a grinding test under the grinding test conditions shown below. They collected power consumption data from the spindle drive motor 62 that rotates the grinding wheel, and performed frequency analysis of the A / D converted AE signal SAE to calculate the signal intensity integral SPI within a predetermined frequency range (45 to 75 kHz). Figure 4 shows the change in power consumption data from the spindle drive motor 62 during grinding. Figure 5 shows the change in the signal intensity integral SPI. In this grinding test, the ratio of the peripheral speed of the grinding wheel to the peripheral speed of the workpiece was set constant (approximately 200:1).

[0036] (Grinding test conditions) FFT analysis data length: 65 ms Integral analysis pitch Δt: 65 ms Integration frequency range: 45-75kHz Processing machine: Cylindrical grinder Grinding wheel: GC 150 H 12 V99 Grinding wheel outer diameter: 405mmφ Grinding wheel peripheral speed: 42m / s, 37m / s, 33m / s Outer diameter of workpiece: 58mmφ Workpiece peripheral speed: 0.21 m / s, 0.18 m / s, 0.16 m / s Cutting speed: 0.13 mm / min Spark Out: 10rev. Grinding oil: SEC-1500P (dilution ratio 50 times) Work material: Titanium alloy (Ti-6Al-4V) Polishing efficiency Z': 0.2

[0037] The inventors of the present invention did not find any significant periodic pulsations in the power consumption values ​​at the beginning of grinding when the grinding wheel peripheral speed was 42 m / s and the workpiece peripheral speed was 0.21 m / s, as shown in FIG. 4. However, they did find a continuous pulsation waveform consisting of peaks and valleys in the signal intensity integral value SPI at the beginning of grinding, as shown in FIG. 5 (which uses the same time axis as FIG. 4) and FIG. 6 (which uses the same time axis as FIG. 4). This valley waveform then decreased to its initial value. When the pulsation waveforms shown in FIGS. 5 and 6 are enlarged, the pulsation period of the signal intensity integral value SPI is 0.88 seconds, which corresponds to the rotation period of the workpiece 12 of 0.86 seconds, as shown in FIG. 7.

[0038] Next, the inventors observed the waveform change of the signal intensity integral value SPI at the initial stage of grinding by decreasing the peripheral speed of the grinding wheel from 42 m / s (workpiece peripheral speed: 0.21 m / s) to 37 m / s (workpiece peripheral speed: 0.18 m / s) and 33 m / s (workpiece peripheral speed: 0.16 m / s). As shown in Figures 8 and 9, the pulsation waveform was the same as that in Figure 6, but the trough waveform became smaller and the amplitude of the pulsation waveform decreased as the peripheral speed of the grinding wheel decreased. The reason why the amplitude of the pulsation waveform of the signal intensity integral value SPI decreased as the peripheral speed of the grinding wheel decreased is thought to be that as the peripheral speed of the grinding wheel decreased, the depth of cut of the abrasive grains increased, and the amount of cut per rotation of the grinding wheel increased, thereby reducing the upward sliding of the abrasive grains at the initial stage of grinding.

[0039] From these facts, it was estimated that in grinding of difficult-to-cut materials, which is less efficient than general grinding, with a cutting speed of 0.13 mm / min and a grinding efficiency Z' of 0.2, the valley waveform in the pulsating waveform of the signal intensity integral value SPI shown in Figure 6 indicates that the grinding wheel slipped upward in synchronization with the rotation of the workpiece.

[0040] 1, the electronic control device 36 is a so-called microcomputer including a CPU, ROM, RAM, an interface, etc. The CPU uses the temporary storage function of the RAM to process input signals according to a program previously stored in the ROM, thereby performing frequency analysis of the AE signal SAE to generate a frequency spectrum, calculates a signal intensity integral (accumulated value) SPI within a predetermined wavelength band including, for example, 55-60 kHz from the frequency spectrum, displays a moving standard deviation MSD of the signal intensity integral SPI on the display device 46, and determines whether the moving standard deviation MSD exceeds a predetermined upper slip determination threshold HS, and displays the determination result on the display device 46. If the signal intensity integral SPI exceeds the predetermined upper slip determination threshold HS, the determination result is sent to the grinding control device 72, and the rotational speed of the grinding wheel 20 is reduced by a predetermined value to suppress upper slip.

[0041] The signal intensity integral SPI is calculated at an integral analysis pitch Δt of 65 msec, which is 1 / 13.4 of the rotation period T (0.87 seconds = 58 × π / 210) of the workpiece 12, and this integral analysis pitch Δt is sufficiently smaller than the pulsation period 0.88 seconds of the signal intensity integral value SPI in Figure 6. The moving standard deviation value MSD is calculated using the following formula 1. In formula 1, n is the number of analysis data within the moving section (an integer), and x i is the i-th signal strength integral value SPI, x av is the average value of the signal intensity integral value SPI within the moving section, T is the workpiece rotation period (seconds), and Δt is the analysis data length (ms).

number

[0042] The moving section including n pieces of analysis data is equal to the rotation period T of the workpiece 12, so the moving standard deviation MSD increases as the amplitude of the pulsation waveform of the signal strength integrated value SPI increases. That is, the moving standard deviation MSD indicates a value corresponding to the magnitude of the periodic change (amplitude) of the pulsation waveform of the signal strength integrated value SPI. In this regard, the amplitude of the pulsation waveform of the signal strength integrated value SPI, the moving average value of the amplitude of the pulsation waveform, the depth or area of ​​the trough waveform, the moving average value of the depth or area of ​​the trough waveform, etc. may be used instead of the moving standard deviation MSD as an amplitude evaluation value indicating the amplitude of the pulsation waveform of the signal strength integrated value SPI, i.e., the magnitude of the periodic change.

[0043] The electronic control device 36 functionally comprises a frequency analysis unit 50 , a signal strength integral value calculation unit 52 , a moving standard deviation calculation unit 54 , and an upward slip detection unit 56 having an upward slip determination unit 58 .

[0044] During grinding of the workpiece 12 by the grinding wheel 20, the frequency analysis unit 50 repeatedly and continuously performs frequency analysis (FFT analysis) of the AE signal SAE output from the A / D converter 34 at predetermined analysis intervals, and generates a frequency spectrum indicating the magnitude of the frequency components of the AE signal SAE in a two-dimensional coordinate system with the vertical axis indicating the signal intensity integral value SPI (power) and the horizontal axis indicating the analysis frequency, as shown in Figure 3, for example.

[0045] The signal intensity integral calculation unit 52 performs an integration operation (summing up) on the signal intensity values ​​SP included in a specific frequency band B2, for example, 45 to 70 kHz, which is a small region of the frequency spectrum frequency-analyzed by the frequency analysis unit 50, whose intensity changes relatively sensitively to the upward sliding of the grinding wheel 20 relative to the workpiece 12, to sequentially calculate the signal intensity integral SPI at a period sufficiently shorter than the rotation period of the workpiece 12, for example, a period equal to or shorter than 1 / 10 of the rotation period, and preferably at the same period as the frequency analysis period by the frequency analysis unit 50. For example, Figures 6, 7, and 8 show the waveforms of the signal intensity integral SPI over time when the peripheral speed of the grinding wheel 20 is 42 m / s, 37 m / s, and 33 m / s.

[0046] The moving standard deviation calculation unit 54 repeatedly calculates the moving standard deviation value MSD within a moving section including n pieces of analysis data of the signal intensity integral value SPI sequentially calculated by the signal intensity integral value calculation unit 52 for each calculation period of the signal intensity integral value SPI according to Equation 1. For example, Figures 10, 11, and 12 show the waveforms of the moving standard deviation value MSD over time when the peripheral speed of the grinding wheel 20 is 42 m / sec, 37 m / sec, and 33 m / sec.

[0047] The upper slip detection unit 56 detects upper slip of the grinding wheel 20 based on the magnitude of the periodic change in the signal intensity integral SPI in a predetermined frequency band, for example, 45 to 75 kHz, of the signal intensity of the frequency spectrum frequency-analyzed by the frequency analysis unit 50, which is synchronized with the rotation of the workpiece 12. Specifically, the upper slip detection unit 56 expresses the magnitude of the periodic change in the signal intensity integral SPI in synchronization with the rotation of the workpiece 12 using a moving standard deviation MSD of multiple n signal intensity integrals SPI obtained within a movement section including one rotation period of the workpiece 12. The upper slip detection unit 56 further includes an upper slip determination unit 58 that determines upper slip of the grinding wheel 20 based on whether the moving standard deviation MSD exceeds either a first upper slip determination threshold M1 or a second upper slip determination threshold M2, which are experimentally determined in advance.

[0048] The upward slip determination unit 58 displays the moving standard deviation value MSD and the fact that the moving standard deviation value MSD has exceeded either the first upward slip determination threshold M1 or the second upward slip determination threshold M2, which are experimentally determined in advance, on the display device 48. The occurrence of the upward slip phenomenon can be notified simply by displaying the numerical value of the moving standard deviation value MSD.

[0049] As shown in Fig. 13, the upper slip determination unit 58 sets a first upper slip determination threshold M1, which is a value for determining whether or not there is an upper slip abnormality, to, for example, "50." If the moving standard deviation value MSD is equal to or less than the first upper slip determination threshold M1, it is determined that there is no abnormality, but if the moving standard deviation value MSD exceeds the first upper slip determination threshold M1, it is determined that there is an abnormality level 1. The second upper slip determination threshold M2, which is a value for determining whether or not an upper slip abnormality has occurred, is set to, for example, "200." If the moving standard deviation value MSD is equal to or less than the second upper slip determination threshold M2, it is determined that there is an abnormality level 1, but if the moving standard deviation value MSD exceeds the second upper slip threshold M2, it is determined that there is an abnormality level 2, which requires correction of the upper slip abnormality.

[0050] When the upper slippage determination unit 58 determines that the upper slippage of the grinding wheel 20 is abnormal level 2, the upper slippage detection unit 56 outputs the determination result to the rotational speed reduction control unit 74 of the grinding control device 72, and causes the grinding control device 72 to reduce the rotational speed of the grinding wheel 20 by a predetermined value.

[0051] The grinding control device 72 is an electronic control device functionally equipped with a rotational speed reduction control section 74, and controls the spindle drive motor 62, workpiece moving motor 66, workpiece rotation drive motor 68, etc. Upon receiving a grinding start command signal, the grinding control device 72 performs cutting at a preset cutting speed while rotating the grinding wheel 20 and workpiece 12 in a preset operation, and when grinding of the workpiece 12 is completed, stops the rotation of the grinding wheel 20 and workpiece 12 and returns them to their original positions. When an abnormal level 2 of upper slippage of the grinding wheel 20 is transmitted from the upper slippage detection section 56 of the electronic control device 36, the grinding control device 72 reduces the rotational speed of the grinding wheel 20 so that the upper slippage decreases.

[0052] Fig. 14 is a flowchart illustrating the main control operations of the electronic control device 36. In step S1 of Fig. 14 (hereinafter, "step" will be omitted), prior to grinding, grinding conditions such as those shown in the grinding test conditions described above are input. Next, in S2, the first upper slip determination threshold M1 and the second upper slip determination threshold M2 are set, and then in S3, grinding of the workpiece 12 by the grinding device 14 is started, and the grinding wheel 20 is rotated at a peripheral speed of, for example, 42 m / sec.

[0053] In S4, the AE signal SAE output from the AE sensor 22 during the grinding process and A / D converted by the A / D converter 34 is sequentially read in. Next, in S5, which corresponds to the function of the frequency analysis unit 50 or the frequency analysis step, a frequency analysis (FFT) is performed for each data length of, for example, 65 ms, and a frequency spectrum, for example, as shown in Fig. 3, is generated.

[0054] Next, in S6, which corresponds to the function of the signal intensity integral value calculation unit 52 or the signal intensity integral value calculation process, the signal intensity values ​​SP included in a specific frequency band B2, for example, 45 to 70 kHz, in the frequency spectrum frequency-analyzed in S5 are integrated (accumulated) to sequentially calculate the signal intensity integral values ​​SPI at a period sufficiently shorter than the rotation period of the workpiece 12, for example, at a period equal to or shorter than 1 / 10 of the rotation period, for example, the same period as the frequency analysis period of S5.

[0055] Next, in S7, which corresponds to the function of the moving standard deviation calculation unit 54 or the moving standard deviation calculation step, the moving standard deviation value MSD within a moving section including n pieces of analysis data of the signal strength integrated value SPI sequentially calculated in S6 is repeatedly calculated for each calculation period of the signal strength integrated value SPI according to Equation 1, for example, as shown in FIG. 10 .

[0056] Next, in S8, which corresponds to the function of the upward slip determination unit 58 or the upward slip determination step, a threshold determination is made based on whether the moving standard deviation value MSD calculated in S7 exceeds the first upward slip determination threshold M1 or the second upward slip determination threshold M2. Next, in S9, which corresponds to the function of the upward slip detection unit 56 or the upward slip detection step, the determination result of S8 is output to the display device 48. For example, if the moving standard deviation value MSD is equal to or less than the first upward slip determination threshold M1, a message indicating no abnormality is output, but if the moving standard deviation value MSD exceeds the first upward slip determination threshold M1, an abnormality level 1 is output, and if the moving standard deviation value MSD exceeds the second upward slip determination threshold M2, an abnormality level 2 is output, indicating that correction of the upward slip abnormality is required.

[0057] Then, in S10, it is determined whether or not grinding of the workpiece 12 has been completed. If the determination in S10 is negative, the threshold determination is updated in S11, and then S4 and subsequent steps are repeatedly executed, but if the determination in S10 is positive, this control routine is terminated.

[0058] As described above, the upper slip detection device 10 or upper slip detection method of this embodiment includes a frequency analysis unit 50 that performs frequency analysis on the AE signal SAE generated from the grinding wheel 20 when grinding the workpiece 12, and an upper slip detection unit 56 that detects upper slip of the grinding wheel 20 based on the magnitude of the periodic change in signal strength of a predetermined frequency band among the signal strengths of the frequency spectrum frequency-analyzed by the frequency analysis step 50, which changes synchronously with the rotation of the workpiece 12. This makes it possible to accurately detect the occurrence of upper slip of the grinding wheel 20 based on the magnitude of the periodic change in signal strength SP of the predetermined frequency band, which is obtained by frequency analysis of the AE signal SAE, which changes synchronously with the rotation of the workpiece 12.

[0059] According to the top slip detection device 10 or top slip detection method of this embodiment, the top slip detection unit 56 represents the magnitude of the periodic change in signal intensity SP that is synchronized with the rotation of the workpiece 12 by the moving standard deviation value MSD of multiple signal intensity integral values ​​SPI obtained within a movement section that exceeds one rotation period T of the workpiece 12. Therefore, the occurrence of top slip of the grinding wheel 20 can be accurately and quantitatively detected based on the magnitude of the moving standard deviation value MSD.

[0060] According to the upward slip detection device 10 or the upward slip detection method of this embodiment, an upward slip determination unit 58 is further included that determines upward slip of the grinding wheel 20 based on whether the moving standard deviation value MSD exceeds a preset upward slip determination threshold M (first upward slip determination threshold M1 and second upward slip determination threshold M2), so that the occurrence of upward slip of the grinding wheel can be accurately determined by the upward slip determination unit 58.

[0061] According to the top slip detection device 10 or top slip detection method of this embodiment, a rotational speed reduction control unit is further included which reduces the rotational speed of the grinding wheel by a predetermined value when the top slip determination unit determines that the grinding wheel is slipping topwise. Therefore, when top slip of the grinding wheel is determined, the rotational speed of the grinding wheel is reduced and the top slip is automatically eliminated. [Example]

[0062] Next, another embodiment of the present invention will be described. In the following description, parts common to the above embodiment will be designated by the same reference numerals and will not be described again.

[0063] FIG. 15 is a flowchart illustrating the main control operations of the electronic control unit 36, and mainly shows the differences from FIG.

[0064] 15 , in S8, threshold determination is performed based on whether the moving standard deviation value MSD exceeds the first upper slip determination threshold M1 or the second upper slip determination threshold M2. Then, in S91, S92, and S93 corresponding to the upper slip detection unit, if the moving standard deviation value MSD is equal to or less than the first upper slip determination threshold M1, a "no abnormality" is output. In S92, if the moving standard deviation value MSD exceeds the first upper slip determination threshold M1, an abnormality level 1 is output. In S93, if the moving standard deviation value MSD exceeds the second upper slip determination threshold M2, an abnormality level 2 is output, indicating that correction of the upper slip abnormality is required. Then, in S94 following S93, a signal to reduce the peripheral speed of the grinding wheel 20 to correct the upper slip abnormality is output to the rotational speed control unit 74, and the rotational speed control unit 74 reduces the peripheral speed of the grinding wheel 20 by, for example, 5 m / s. As a result, when the peripheral speed of the grinding wheel 20 is reduced, for example, from 42 m / sec to 37 m / sec, the moving standard deviation value MSD is reduced from "200" toward "0" as shown in FIG.

[0065] According to the upper slip detection device 10 or upper slip detection method of this embodiment, a rotation speed reduction control unit 74 is further included which reduces the rotation speed of the grinding wheel 20 by a predetermined value when the upper slip determination unit 58 determines that the grinding wheel 20 is slipping upward. Therefore, when upper slippage of the grinding wheel 20 is determined, the rotation speed of the grinding wheel 20 is reduced and the upper slippage is automatically eliminated.

[0066] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention can also be applied to other embodiments.

[0067] For example, in the above-described embodiment, the AE sensor 22 was provided inside the main body (metal base) 20a to which the grinding wheel portion 20b of the grinding wheel 20 was attached, but when a disk-shaped grinding wheel that does not use the main body (metal base) 20a is used, the AE sensor 22 may be provided on a flange that clamps the grinding wheel and fixes it to the rotating main shaft, or on a table to which the workpiece 12 is fixed.

[0068] Furthermore, in the above-described embodiment, the upward slip determination unit 58 determines whether the moving standard deviation value MSD has exceeded either the first upward slip determination threshold M1 or the second upward slip determination threshold M2, which are experimentally set in advance. However, the upward slip determination unit 58 may use a single upward slip determination threshold, for example, the second upward slip determination threshold M2.

[0069] Furthermore, although the upper slip detection unit 56 in the above-described embodiment includes the upper slip determination unit 58, it does not necessarily have to include the upper slip determination unit 58. The upper slip detection unit 56 may numerically display on the display device 48 the maximum value of the moving standard deviation value MSD, which represents the magnitude of the amount of periodic change in the signal intensity integral value SPI that is synchronized with the rotation of the workpiece 12, or may numerically display on the display device 48 the changing waveform of the moving standard deviation value MSD, as shown in Fig. 10 or 13, for example.

[0070] Furthermore, the upper slip detection unit 56 in the above-described embodiment determines upper slip of the grinding wheel 20 based on whether the moving standard deviation value MSD exceeds either the first upper slip determination threshold M1 or the second upper slip determination threshold M2, which are experimentally set in advance, but it may also use either the first upper slip determination threshold M1 or the second upper slip determination threshold M2.

[0071] It should be noted that the above is merely one embodiment, and the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0072] 10: Upper slip detection device 12: Work material 14: Grinding equipment 20: Grinding wheel (grinding stone) 22:AE sensor 34: A / D converter 50: Frequency analysis section 52: Signal intensity integral value calculation unit 54: Moving standard deviation calculation unit 56: Upper slip detection unit 58: Upward slip detection unit 74: Rotation speed reduction control section S5: Frequency analysis process S5: Frequency analysis process S6: Signal intensity integral value calculation step S7: Moving standard deviation calculation process S8: Upward slip determination process S9: Upper slip detection process SAE:AE signal B2: Specified frequency band (45 to 75 kHz frequency band) M1: First upper slip threshold M2: Second upper slip threshold SP: Signal strength value SPI: Signal strength integral value MSD: Moving standard deviation

Claims

1. A method for detecting upward slippage of a grinding wheel that grinds an outer peripheral surface of a workpiece, comprising: a frequency analysis step of frequency-analyzing an AE signal generated by the grinding wheel when grinding the workpiece; and an upward slip detection step of detecting upward slip of the grinding wheel based on the magnitude of a periodic change in the signal intensity integral value of a predetermined frequency band among the signal intensities of the frequency spectrum frequency-analyzed in the frequency analysis step, the change being synchronized with the rotation of the workpiece. A method for detecting upper slip of a grinding wheel.

2. The upper slip detection step represents the magnitude of the periodic change amount of the signal intensity integral value synchronized with the rotation of the workpiece by a moving standard deviation value of a plurality of the signal intensity integral values ​​obtained within a moving section exceeding one rotation period of the workpiece.

2. A method for detecting top slip of a grinding wheel according to claim 1.

3. and a step of determining whether the grinding wheel has slipped upward based on whether the moving standard deviation value has exceeded a predetermined threshold value.

3. The method for detecting top slip of a grinding wheel according to claim 2.

4. The method further includes a rotation speed reduction control step of reducing the rotation speed of the grinding wheel by a predetermined value when the upward slippage of the grinding wheel is determined in the upward slippage determination step.

4. The method for detecting slippage of a grinding wheel according to claim 3.

5. A grinding wheel slippage detection device that detects upward slippage of a grinding wheel that grinds the outer peripheral surface of a workpiece, a frequency analysis unit that performs frequency analysis on an AE signal generated by the grinding wheel when grinding the workpiece; and an upper slip detection unit that detects upper slip of the grinding wheel based on the magnitude of a periodic change in the signal intensity integral value of a predetermined frequency band among the signal intensities of the frequency spectrum frequency-analyzed by the frequency analysis unit, the change being synchronized with the rotation of the workpiece. A grinding wheel slippage detection device characterized by the above.

6. The upper slip detection unit represents the magnitude of the periodic change amount of the signal intensity integral value synchronized with the rotation of the workpiece by a moving standard deviation value of a plurality of the signal intensity integral values ​​obtained within a moving section exceeding one rotation period of the workpiece.

6. The device for detecting upper slippage of a grinding wheel according to claim 5.

7. and an upward slip determination unit that determines upward slip of the grinding wheel based on whether the moving standard deviation value exceeds a predetermined determination threshold value.

7. The device for detecting upper slippage of a grinding wheel according to claim 6.

8. The apparatus further includes a rotation speed reduction control unit that reduces the rotation speed of the grinding wheel by a predetermined value when the upward slip determination unit determines that the grinding wheel is slipping upward.

8. The device for detecting upper slippage of a grinding wheel according to claim 7.

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