JP7745394B2 - Dressing completion determination method and dressing completion determination device - Google Patents

Description

The present invention relates to a method and device for determining the completion of dressing, which can determine the completion of dressing, in which a grinding wheel is dressed or its shape is corrected by a dresser. In particular, the present invention relates to technology that eliminates the need for preliminary testing when the type of dresser or grinding wheel or the dressing conditions are changed, and that prevents erroneous determinations of the completion of dressing.

As a device for automatically determining the completion of dressing (sharpening, shape correction) for a grinding wheel, a device has been proposed that detects an AE signal (acoustic emission signal: a vibration wave in the ultrasonic range with a frequency of, for example, 100 kHz or higher) and determines the completion of dressing based on whether the difference between the AE signal and a previously calculated and stored master waveform is within a preset threshold. For example, Patent Document 1 discloses a grinding wheel forming state determination device and grinding wheel forming state determination method.

The grinding wheel forming state determination device and grinding wheel forming state determination method described in Patent Document 1 above are said to be able to easily determine the shape correction state of the grinding wheel even when the AE signal changes depending on the cross-sectional diameter of the grinding wheel, and to simultaneously determine the completion of dressing and detect wear on the dresser.

Patent No. 5219600

However, with the conventional dressing completion determination device described above, it was necessary to repeatedly perform preliminary tests to determine the master waveform and threshold value each time the type of dresser or grinding wheel was changed, making the preparation work cumbersome. Furthermore, when calculating the difference between the AE signal and the master waveform, highly accurate overlapping of the AE signal waveform and the master waveform on the time axis was required, which created the problem of being prone to erroneous determinations.

The present invention was made against the background of the above circumstances, and its purpose is to provide a method and device for determining the completion of dressing of a grinding wheel that can determine the completion of dressing with high accuracy without requiring complicated preparation work.

The inventors of the present invention have conducted extensive research in light of the above circumstances. As a result, they have discovered that when a dresser is moved across the dressing surface of a grinding wheel in a dressing process, repeatedly performing a scan each time a fixed depth of cut is applied, and focusing on the integrated intensity value of the AE signal generated during the dressing scan in which the dresser is scanned, the integrated intensity value of the AE signal increases with each dressing stroke, and that when dressing of the dressing surface is complete, the increase in the integrated intensity value of the AE signal during the dressing scan saturates. The present invention was made based on this finding.

That is, the gist of the first invention is a dressing completion determination method for a dressing completion determination device that automatically determines the completion of dressing of the dressing surface based on an AE signal generated by the fracture of abrasive grains of the grinding wheel due to contact between the grinding wheel and the dresser, by (a) repeatedly performing a dressing scan in which the dresser is brought into sliding contact with the dressing surface of the grinding wheel and the dresser is moved at a constant feed rate so as to traverse the dressing surface in the width direction every time a constant cutting amount is applied, and (b) (c) a dressing completion determination step of determining that an increase in the integrated intensity value of the AE signal intensity integrated for each dressing scan has saturated based on the integrated intensity value of the AE signal intensity calculated for each dressing scan by the integrated intensity value calculation step becoming equal to or less than the maximum value of the integrated intensity of the AE signal intensity obtained by the dressing scans repeated up to that point, and determining the completion of the dressing process based on this determination .

The gist of the second invention is (a) a dressing completion determination device that includes an AE sensor that detects an AE signal generated by the fracture of abrasive grains of a grinding wheel due to contact between the grinding wheel and a dresser, and that performs a dressing scan by causing the dresser to slide against a dressing surface of the grinding wheel and scan the dresser at a constant feed rate across the dressing surface in a width direction, and that automatically determines the completion of a dressing process of the dressing surface based on the AE signal, every time a constant cutting depth is provided, and (b) (c) a dressing completion determination unit that determines that an increase in the integrated intensity value of the AE signal intensity integrated for each dressing scan has saturated based on the integrated intensity value of the AE signal intensity integrated for each dressing scan by the integrated intensity value calculation unit becoming equal to or less than the maximum value of the integrated intensity of the AE signal intensity obtained by the dressing scans repeated up to that point, and determines the completion of the dressing process based on that determination .

The gist of a third invention is that, in the second invention, the device further includes: (d) an AE signal judgment threshold determination unit that determines an AE signal judgment threshold based on an AE signal intensity obtained from the AE sensor in a non-dressing state in which the dresser is separated from the dressing surface of the grinding wheel, and calculates a spark time that is a time during which the dresser is in contact with the dressing surface of the grinding wheel, from a time when the AE signal intensity obtained from the AE sensor exceeds the AE signal judgment threshold to a time when the AE signal intensity falls below the AE signal judgment threshold; and (e) a spark time calculation unit that calculates a spark time that is a time during which the dresser is in contact with the dressing surface of the grinding wheel based on a feed speed of the dresser by the dresser feed mechanism and a width dimension of the dressing surface of the grinding wheel. and (f) a shape modification pass/fail determination unit that determines completion of the shape modification based on the fact that the spark time calculated for each dressing scan by the spark time calculation unit exceeds the spark time determination threshold, and (g) the dressing completion determination unit determines completion of the dressing process based on the fact that an increase in the integrated intensity value of the AE signal intensity calculated for each dressing scan by the integrated intensity value calculation unit has saturated and the shape modification pass/fail determination unit has determined completion of the shape modification.

The gist of the fourth invention is that, in the second or third invention , (i) an AE signal judgment threshold determination unit is included that determines an AE signal judgment threshold based on the AE signal intensity obtained from the AE sensor in a non-dressing state in which the dresser is separated from the dressing surface of the grinding wheel, and (j) a signal that exceeds the AE signal judgment threshold among the signals output from the AE sensor during the dressing scan is used as the AE signal intensity used to determine the completion of the dressing process.

The gist of the fifth invention is that, in the fourth invention, (l) the AE signal judgment threshold value determiner determines the AE signal judgment threshold value based on an average value or a maximum value of an AE signal intensity obtained from the AE sensor when the dresser is scanned by a dresser feed mechanism in a state where the dresser is separated from the dressing surface of the grinding wheel, in a section in which a coefficient of variation is equal to or less than a predetermined value.

The gist of the sixth invention is that, in any one of the second to fifth inventions, the AE sensors are a pair of AE sensors each provided at a different radial position within a range corresponding to the dressing surface of the grinding wheel on the flange to which the grinding wheel is fixed, and the dressing completion determination unit determines the completion of the dressing process based on the saturation of the increase in the integrated intensity value of the AE signal intensity obtained from each of the pair of AE sensors, which is accumulated for each dressing scan.

According to the dressing completion determination method of the first invention, a dressing scan is performed repeatedly each time a constant depth of cut is applied, in which the dresser is brought into sliding contact with the dressing surface of a grinding wheel and moved at a constant feed rate across the dressing surface in the width direction. The dressing completion determination device automatically determines the completion of the dressing process of the dressing surface based on AE signals generated by fracture of abrasive grains of the grinding wheel due to contact between the grinding wheel and the dresser. In this case, an integrated intensity value calculation step calculates an integrated intensity value of AE signal intensity generated during the dresser scan for each dressing scan, and in the dressing completion determination step, it is determined that the increase in the integrated intensity value of AE signal intensity integrated for each dressing scan has saturated based on the integrated intensity value of AE signal intensity calculated for each dressing scan becoming equal to or less than the maximum value of the integrated intensity of AE signal intensity obtained by the dressing scans repeated up to that point. Based on this determination , the completion of the dressing process is determined. This makes it possible to determine with high accuracy whether or not the dressing of the grinding wheel has been completed, without requiring any complicated preparation work.

According to the second aspect of the present invention, there is provided a dressing completion determination device which includes an AE sensor for detecting an AE signal generated by the fracture of abrasive grains of the grinding wheel due to contact between the grinding wheel and a dresser, and which performs a dressing scan by causing the dresser to slide against the dressing surface of the grinding wheel and scan the dresser at a constant feed rate across the dressing surface in the width direction, and which repeats this dressing scan every time a constant cutting depth is provided, and which automatically determines the completion of the dressing process of the dressing surface based on the AE signal. An integrated intensity value calculation unit calculates an integrated intensity value of the AE signal intensity generated during the dresser scan for each dressing scan, and a dressing completion determination unit determines that the increase in the integrated intensity value of the AE signal intensity integrated for each dressing scan has saturated based on the fact that the integrated intensity value of the AE signal intensity calculated for each dressing scan has become equal to or less than the maximum value of the integrated intensity of the AE signal intensity obtained by the dressing scans repeated up to that point, and determines the completion of the dressing process based on this determination . This makes it possible to determine the completion of dressing of the grinding wheel with high accuracy without requiring complicated preparation work.

According to the dressing completion determination device of the third invention, when the completion of shape modification is determined based on the fact that the spark time calculated by the spark time calculation unit, which is the time from when the AE signal intensity exceeds the AE signal determination threshold to when it falls below the AE signal determination threshold, exceeds the spark time determination threshold set by the spark time determination threshold setting unit, the completion of the dressing process is determined by the dressing completion determination unit based on the fact that the increase in the integrated intensity value of the AE signal intensity calculated for each dressing scan by the integrated intensity value calculation unit has saturated and the fact that the shape modification pass/fail determination unit has determined that the shape modification is complete, thereby further improving the accuracy of the determination of the completion of the dressing process.

According to the dressing completion determination device of the fourth invention, a signal exceeding an AE signal determination threshold determined based on a signal output from an AE sensor in a non-dressing state where the grinding wheel and the dresser are not in contact with each other is used by an AE signal supply unit as the AE signal intensity used for determining the completion of the dressing process, thereby further improving the accuracy of determining the completion of the dressing process.

According to the dressing completion determination device of the fifth invention, the AE signal determination threshold determiner determines the AE signal determination threshold based on the average or maximum value of the signal output from the AE sensor when the dresser feed mechanism scans the dresser while the dresser is separated from the dressing surface of the grinding wheel, in a section where the coefficient of variation is equal to or less than a predetermined value. This further improves the accuracy of determining the completion of the dressing process. Furthermore, the AE signal determination threshold need only be slightly larger than the average or maximum value of the signal and does not need to be determined based on strict experimental values, so it can be easily set, for example, to 1.1 times the average or maximum value.

According to the dressing completion determination device of the sixth aspect of the invention, the AE sensors are a pair of AE sensors respectively provided at different radial positions within a range of the flange to which the grinding wheel is fixed, corresponding to the dressing surface of the grinding wheel, and the dressing completion determination unit determines the completion of the dressing process based on the saturation of the increase in the integrated intensity value of the AE signal intensity obtained by integrating the AE signal intensity obtained from the pair of AE sensors for each dressing scan. This further improves the accuracy of the determination of the completion of the dressing process.

1 is a diagram illustrating the configuration of a dressing apparatus equipped with a dressing completion determination device according to an embodiment of the present invention. 2 is a perspective view briefly explaining the main parts of a double-disc surface grinding machine using a surface grinding wheel that is dressed by the dressing device of FIG. 1. [0023]FIG. FIG. 2 is a cross-sectional view illustrating the mounting structure of the surface grinding wheel of FIG. 1. 4 is a diagram illustrating in detail a flange to which the surface grinding wheel of FIG. 3 is attached. FIG. The graph shows the AE signal intensities obtained from the outer AE sensor and the inner AE sensor during repeated dressing scans. 6 is a diagram illustrating calculation of spark time STs from the AE signal waveform of FIG. 5 and an integration interval of signal intensity. FIG. 10 is a diagram schematically showing integrated intensity values Xs and spark times STs of AE signals obtained for each dressing scan in a dressing process. FIG. FIG. 2 is a diagram showing the first half of a flowchart illustrating the control operation of the electronic control device of FIG. 1 . FIG. 2 is a diagram showing the second half of a flowchart illustrating the control operation of the electronic control device of FIG. 1 . 10 is a chart showing, in time series, the ratio (%) of actual spark time STs, which is the ST evaluation value obtained for each peak waveform, to the theoretical spark time ST (=Wd/Vd), the pass/fail judgment of the shape modification indicating whether the ratio of the actual spark time STs to the theoretical spark time ST exceeds 95%, the integrated intensity value Xs, which is the strength evaluation value obtained for each peak waveform, and the pass/fail judgment of the dressing indicating whether the integrated intensity value Xs is saturated, when using the AE signal intensity Xi based on the signal from the outer periphery side AE sensor 16 a and when using the AE signal intensity Xi based on the signal from the inner periphery side AE sensor 16 b. This is a line graph showing the ST evaluation value (actual spark time STs) and the integrated intensity value Xs, which is the intensity evaluation value, in time series when the AE signal intensity Xi based on the signal from the outer periphery AE sensor 16a is used. FIG. 1 is a diagram showing an example of the surface shape of a grinding wheel measured by a stylus-type shape measuring instrument, together with the difference ΔTH (mm) between the contact start height and the truing completion height. This figure shows the dressing depth CD until dressing completion is determined for five grinding wheels A to E, when dressing is performed using the same experimental conditions as experimental condition 1, and the truing amount ΔTH predicted from the surface shape of the grinding wheels measured in advance using a stylus-type shape measuring device.

The following describes in detail one embodiment of the present invention with reference to the accompanying drawings. Please note that the drawings in the following embodiment are for illustrative purposes only and are not necessarily drawn to scale or shape accurately.

In Figure 1, the dressing device 10 performs a dressing process by sliding a dresser 12 against the surface of the surface grinding wheel 14 to sharpen and modify the shape of the dressing surface 15. The dressing surface 15 is the portion of the grinding surface of the surface grinding wheel 14 that is the target of dressing (shape modification and sharpening) by the dresser 12, including the portion that contributes to grinding. The dressing device 10 includes AE sensors 16a, 16b that detect elastic waves generated when the grinding wheel 14 and the dresser 12 come into contact with each other during the dressing process and output an AE signal, a dresser scanning motor 18 that causes the dresser 12 to reciprocate and scan at a constant feed rate across the dressing surface 15 in the width direction while bringing the dresser 12 into sliding contact with the dressing surface 15 of the surface grinding wheel 14, and a dresser feed motor 20 that causes the dresser 12 to cut into the dressing surface 15 by a constant cutting amount for each scan. The dresser feed mechanism 22 repeatedly performs dressing scans by moving the dresser 12 back and forth at a constant feed speed across the width of the dressing surface 15 while sliding the dresser 12 against the dresser feed mechanism 5, each time a constant cutting depth is applied; a dressing drive control device 26 that controls the drive of the dresser scan motor 18 and dresser feed motor 20 of the dresser feed mechanism 22 and the grinding wheel rotation drive motor 24 that rotates the surface grinding wheel 14 according to commands; and an electronic control device 28 that outputs control commands to the dressing drive control device 26.

In this embodiment, the dresser 12 is a longitudinal single-stone dresser embedded with one end face of a single columnar diamond exposed. The dresser feed mechanism 22 includes a cutting mechanism (not shown) that feeds the dresser 12 longitudinally toward the surface grinding wheel 14, and a scanning mechanism (not shown) that moves the dresser 12 back and forth along the dressing surface 15 of the surface grinding wheel 14.

Figure 2 is a perspective view showing the main parts of a vertical double-disk surface grinding machine 32 to which the surface grinding wheel 14 and a similar surface grinding wheel 30 are applied. The double-disk surface grinding machine 32 is equipped with a pair of opposing surface grinding wheels 14 and 30 that are rotated relative to each other about a vertical rotation axis CL, and a carrier plate 36 that transports a circular workpiece 34, such as the inner or outer ring of a bearing, between the pair of surface grinding wheels 14 and 30, and performs surface grinding on both end surfaces of the workpiece 34.

The pair of surface grinding wheels 14 and 30 are similarly configured, so the following description will focus on the surface grinding wheel 14. As shown in FIG. 3, the back surface of the surface grinding wheel 14 is in intimate contact with a thick, disk-shaped flange 40 that rotates integrally with the spindle 38 of the double-head surface grinding machine 32. The back surface of the surface grinding wheel 14 is secured to the flange 40 using a fastening bolt (not shown) that threads into a nut (not shown) embedded in the surface grinding wheel 14. A flat, annular dressing surface 15 is formed on the end surface of the pair of end faces of the surface grinding wheel 14 that is not in intimate contact with the flange 40. In this embodiment, the width direction of the dressing surface 15 refers to the radial direction passing through the center line CL of rotation of the surface grinding wheel 14.

The flange 40 has an electronic component storage chamber 42 that opens onto the side opposite the surface grinding wheel 14. The opening of the electronic component storage chamber 42 is closed by a circular cover plate 44 made of a material that allows radio waves to pass through, such as plastic or ceramic, via a sealing rubber plate 46. The cover plate 44 and sealing rubber plate 46 are secured by fastening bolts 48 that pass through them and screw into the flange 40.

As shown in FIG. 4, an electronic component chamber 42 formed in the flange 40 contains an electronic circuit board 50 equipped with a pair of outer AE sensors 16a and inner AE sensors 16b, a preamplifier for amplifying the output signals of the outer AE sensors 16a and inner AE sensors 16b, an A/D converter for converting the output signals of the preamplifiers into digital signals, a transmitter module for transmitting the output signals of the outer AE sensors 16a and inner AE sensors 16b converted into digital signals by the A/D converter, and a pair of power supply batteries 52. The A/D converter has high resolution and converts the AE signal SAE into a digital signal at a sampling period of 10 μsec (microseconds) or less, preferably 5 μsec or less, and more preferably 1 μsec or less.

The outer AE sensor 16a and inner AE sensor 16b are arranged along one radial direction of the flange 40. The outer AE sensor 16a is located at a position 80% or more, preferably 90%, of the radius of the flange 40 from the rotation axis CL of the flange 40 toward the outer circumference, while the inner AE sensor 16b is located at a position 35% or more and 50% or less, preferably approximately 40%, of the radius of the flange 40 from the rotation axis CL of the flange 40 toward the outer circumference.

Returning to FIG. 1, the dressing device 10 is equipped with a receiving circuit 56 having an antenna 54 for receiving the AE signal SAE transmitted from the transmitting module in the electronic circuit board 50. The electronic control device 28 is a so-called microcomputer including a CPU, ROM, RAM, interface, etc., and the CPU utilizes the temporary storage function of the RAM and operates the dressing drive control device 26 in accordance with a program pre-stored in the ROM to repeatedly perform a dressing scan in which the dresser 12 is brought into sliding contact with the dressing surface 15 of the surface grinding wheel 14 and moved at a constant feed rate across the dressing surface 15 in the width direction, every time a constant cutting depth is provided. The electronic control device 28 also processes the AE signal SAE received by the receiving circuit 56 during dressing, determines when the dressing process for sharpening and shape correction of the dressing surface 15 is complete, outputs a dressing completion command signal to the dressing drive control device 26, and calculates numerical values, graphs, or figures that represent the state of the dressing surface, which are then displayed on the surface state display device 58.

The electronic control device 28 also functions as a dressing completion determination device, and functionally comprises a frequency analysis unit 60, an AE signal determination threshold setting unit 62, a spark time determination threshold setting unit 64, a spark time calculation unit 66, a shape modification pass/fail determination unit 68, an integrated intensity value calculation unit 70, a dressing pass/fail determination unit 72, and a dressing completion determination unit 74.

The frequency analysis unit 60, which corresponds to the frequency analysis process, performs frequency analysis (FFT) of the A/D converted AE signal SAE during dressing of the grinding wheel 14. This generates a power spectrum, which shows the magnitude of various signal powers for each frequency on the frequency axis (horizontal axis) in a two-dimensional coordinate system with the vertical axis representing signal power and the horizontal axis representing frequency. The frequency analysis unit 60 then discriminates signal components in a frequency band, e.g., a wavelength band of 45 to 75 kHz, that are sensitive to the fracture of abrasive grains in the surface grinding wheel 14 during the dressing process, and outputs the integrated value of these signal components as the AE signal intensity Xi. For example, Figure 5 shows the actual peak waveforms of the AE signal intensity Xi sequentially output from the frequency analysis unit 60 based on the AE signals SAE obtained from the outer AE sensor 16a and the inner AE sensor 16b during repeated dressing scans. The non-dressing section R1 in Figure 5 shows the no-load AE signal intensity XiN when the dresser 12 is not in contact with the dressing surface 15 of the grinding wheel 14, while the dressing section R2 shows the peak waveform of the AE signal intensity Xi that is repeatedly generated with each dressing scan as the dresser 12 comes into contact with the dressing surface 15 of the grinding wheel 14.

The AE signal judgment threshold setting unit 62 corresponds to the AE signal judgment threshold setting process. During the non-dressing section R1, in which the dresser 12 is scanned for dressing by the dresser feed mechanism 22 without contacting the dresser 12 with the dressing surface 15 of the grinding wheel 14, the AE signal intensity XiN at no load obtained from the outer AE sensor 16a and the inner AE sensor 16b is calculated, and an AE signal judgment threshold P is set based on the AE signal intensity XiN at no load to remove noise generated at no load in a subsequent process. The amount by which the AE signal magnitude (AE signal intensity) Xi exceeds the AE signal judgment threshold P is a signal component resulting from contact between the grinding wheel 14 and the dresser 12 during the dressing process, and is subject to the dressing completion evaluation described below. For example, the AE signal judgment threshold setting unit 62 determines the coefficient of variation CV of the no-load AE signal strength XiN from at least 100 pieces of data for the no-load AE signal strength XiN during no-load dressing, calculates the average value Xav or maximum value Xmax of the data in a section where the coefficient of variation CV is stable, for example, 0.1 or less, and sets the average value Xav x 1.1 or maximum value Xmax as the AE signal judgment threshold P.

The coefficient of variation CV of the no-load AE signal strength XiN is the standard deviation σ of each data point of the no-load AE signal strength XiN divided by the average value Xav of the no-load AE signal strength XiN.

The spark time determination threshold setting unit 64 corresponds to the spark time determination threshold setting process, and calculates the theoretical spark time ST (= Wd/Vd) from the constant scanning speed Vd of the dresser 12 set by the dressing drive control device 26 and the width dimension Wd of the dressing surface 15 of the grinding wheel 14. It then multiplies the theoretical spark time ST by a predetermined ratio (coefficient), such as 0.95, that determines whether shape modification is complete, to set the spark time determination threshold STt (sec).

The spark time calculation unit 66 corresponds to the spark time calculation process, and during the dressing scan in which the dresser 12 is repeatedly brought into contact with the dressing surface 15 of the grinding wheel 14 during the dressing process in the dressing section R2 of Figure 5, as shown in Figure 6, the actual spark time STs is calculated by counting (timing) the accumulated time from when the AE signal intensity Xi obtained from the outer periphery AE sensor 16a and the inner periphery AE sensor 16b exceeds the AE signal judgment threshold P to when it falls below it for each scan of the dresser 12. In Figure 6, the peak waveform of the AE signal intensity Xi is modeled as a trapezoid to easily explain the meaning of the spark time STs.

The shape modification pass/fail determination unit 68 corresponds to the shape modification pass/fail determination process, and for each scan of the dresser 12, determines whether the actual spark time STs calculated by the spark time calculation unit 66 is equal to or greater than the spark time determination threshold STt set by the spark time determination threshold setting unit 64, and if it is greater, determines that the shape modification has passed (completed).

The integrated intensity value calculation unit 70 corresponds to the integrated intensity value calculation process, and calculates an integrated intensity value Xs for each dressing scan by integrating components of the AE signal intensity Xi obtained from the outer periphery AE sensor 16a and the inner periphery AE sensor 16b that exceed the AE signal judgment threshold P within the section STs during the dressing scan period in which the dresser 12 repeatedly contacts the dressing surface 15 of the grinding wheel 14 during the dressing process of the dressing section R2 in Figure 5. Figure 7 shows the peak waveforms of the AE signal intensity Xi obtained sequentially for each dressing scan, schematically represented as rectangular waveforms, and the integrated intensity values Xs correspond to the areas of the rectangular waveforms.

The dressing pass/fail determination unit 72, which corresponds to the dressing pass/fail determination process, determines whether the increase in the integrated intensity value Xs calculated for each dressing scan by the integrated intensity value calculation unit 70 from the start of the dressing process has saturated. If the integrated intensity values Xs of the AE signal intensities Xi obtained from the outer AE sensor 16a and the inner AE sensor 16b are both saturated, the dressing pass/fail determination unit 72 determines that the dressing has passed (sharpening passed). For example, if the integrated intensity value Xs becomes equal to or less than the maximum integrated intensity value Xsp up to that point (Xs≦Xsp), the dressing pass/fail determination unit 72 determines that the increase in the integrated intensity value Xs has saturated. This saturation of the increase in the integrated intensity value Xs indicates saturation of the dressing effect. If STs≧STt and Xs>Xsp, the integrated intensity value Xs for the current dressing scan is updated (set) as the maximum integrated intensity value Xsp. This prevents erroneous judgments when peak waveforms of the AE signal strength Xi occur intermittently when the grinding machine is used in a retrofit manner that is not linked to the NC.

The dressing completion determination unit 74 determines the completion of the dressing process based on the fact that the shape modification pass/fail determination unit 68 determines that the actual spark time STs exceeds the spark time determination threshold STt, and the fact that the increase in the integrated intensity value Xs of the AE signal intensity Xi integrated for each dressing scan by the integrated intensity value calculation unit 70 has saturated. That is, when the shape modification pass/fail determination unit 68 determines that the shape modification is successful and the dressing pass/fail determination unit 72 determines that the dressing related to the dressing is successful (sharpening passed), the dressing completion determination unit 74 determines that the dressing is completed, stops the dressing operation by the dressing drive control device 26, and displays a message indicating the completion of dressing on the surface condition display device 58.

Figures 8 and 9 are flowcharts explaining the main control operations of the electronic control device 28. In Figures 8 and 9, in step S1 (hereinafter, "step" will be omitted), a theoretical spark time ST (= Wd/Vd) is calculated from the constant scanning speed Vd of the dresser 12 by the dressing drive control device 26 and the width dimension Wd of the dressing surface 15 of the grinding wheel 14, both of which have been input in advance. In S2, the theoretical spark time ST is multiplied by a predetermined ratio (coefficient), such as "0.95," which determines whether shape modification is complete, to set a spark time determination threshold STt (sec). In this embodiment, S1 and S2 correspond to the spark time determination threshold setting unit 64.

In S3, the no-load AE signal intensity XiN obtained based on signals from the AE sensors 16a and 16b when the dresser 12 is not in contact with the dressing surface 15 of the grinding wheel 14 in the non-dressing section R1 is read. In S4, it is determined whether the number of data points for the no-load AE signal intensity XiN read in the non-dressing section R1 exceeds 100. If the determination in S4 is negative, S3 and subsequent steps are repeated; if the determination is positive, in S5, the coefficient of variation CV (= σ/Xav) of the no-load AE signal intensity XiN is calculated. Next, in S6, it is determined whether the coefficient of variation CV of the no-load AE signal intensity XiN is equal to or less than 0.1. If the determination in S6 is negative, S3 and subsequent steps are repeatedly executed. However, if the determination is positive, in S7, the average value Xav x 1.1 or maximum value Xmax of the data in the section where the coefficient of variation CV is stable, for example, below 0.1, is set as the AE signal determination threshold P. In this embodiment, S3 to S7 correspond to the AE signal determination threshold setting unit 62.

Next, in S8, the dressing process begins. With the dresser 12 in sliding contact with the dressing surface 15 of the surface grinding wheel 14, the dresser 12 is reciprocally scanned across the dressing surface 15 in the width direction at a constant feed rate, and the dresser 12 cuts into the dressing surface 15 by a constant amount with each scan. This causes the dressing surface 15, against which the dresser 12 is sliding, to be flattened and sharpened.

In S9, the AE signal intensity Xi during the dressing process is read. In S10, it is determined whether the magnitude of the AE signal intensity Xi is equal to or greater than the AE signal judgment threshold P. If the determination in S10 is positive, contact between the surface grinding wheel 14 and the dresser 12, i.e., the abrasive grains of the surface grinding wheel 14 have begun to break down, so in S11, the integrated intensity value Xs (= Xs + Xi) is calculated. In addition, in S12, the actual spark time STs (= STs + Δt), which is the accumulated time since contact between the surface grinding wheel 14 and the dresser 12, i.e., the abrasive grains of the surface grinding wheel 14 have begun to break down, is integrated by sequentially adding the integration period Δt.

If the magnitude of the AE signal intensity Xi falls below the AE signal determination threshold P and the determination in S10 is negative, then in S13 it is determined whether the previous AE signal intensity Xi _-1 was below the AE signal determination threshold P. If the determination in S13 is positive, S9 and subsequent steps are repeatedly executed, but if the determination is negative, then in S14 the spark time STs is determined and the integrated intensity value Xs of the AE signal intensity Xi is determined in S15. In this embodiment, S9, S10, S12, S13, and S14 correspond to the spark time calculation unit 66, and S9, S10, S11, S13, and S15 correspond to the integrated intensity value calculation unit 70.

In S16, it is determined whether the confirmed spark time STs is equal to or greater than the spark time determination threshold STt set in S2. If the determination in S16 is negative, the spark time STs is initialized in S17, and S9 and subsequent steps are executed. However, if the determination in S16 is positive, a pass flag for the spark time STs is set in S18, and it is determined that the shape modification of the dressing surface 15 is complete. In this embodiment, S16 and S18 correspond to the shape modification pass/fail determination unit 68.

In S19, it is determined whether the integrated intensity value Xs of the confirmed AE signal intensity Xi has saturated, i.e., whether it is equal to or less than the maximum integrated intensity value Xsp up to that point (Xs≦Xsp). If the determination in S19 is negative, in S20 the maximum integrated intensity value Xsp is updated to the previous integrated intensity value Xs, and S9 and subsequent steps are executed. However, if the determination in S19 is positive, in S21 a dressing pass (sharpening pass) flag is set for the sharpening, and it is determined that dressing is complete. In this embodiment, S19 and S21 correspond to the dressing pass/fail determination unit 72.

Then, in S22, which corresponds to the dressing completion determination unit 74, the pass flag for the spark time STs is set, and a dressing completion determination is made based on the fact that the pass flag for the dressing regarding sharpening has been set.

The results of a dressing experiment conducted by the present inventors under the following experimental condition 1 will be described below with reference to FIGS. 5, 10 and 11. FIG.
(Experimental Condition 1)
Processing machine: Vertical axis double-head surface grinding machine Grinding wheel specifications: 83A 80 H 12
Type of grinding wheel: Surface grinding wheel with an outer diameter of 585 mmφ Grinding wheel shaft rotation speed: 900 rpm
Grinding oil: NK-81P (dilution ratio: 50)
Dresser: 1.0 mm diamond embedded LL needle dresser Dressing depth: 0.01 mm
(Signal processing conditions)
FFT analysis data length: 65 ms
Integral analysis pitch Δt: 65 ms
Integration frequency range: 45 to 75 kHz

Dressing was performed under the above dressing conditions, and the AE signals obtained from the outer AE sensor 16a and inner AE sensor 16b were frequency analyzed to integrate frequency components in the range of 45 to 75 kHz, thereby obtaining the AE signal intensity Xi for each frequency analysis period. In addition to the above integration, an average value or an effective value obtained through a bandpass filter may also be used. Figure 5 shows the AE signal intensity Xi obtained at this time on the time axis (horizontal axis). In Figure 5, the AE signal intensity Xi exhibits a mountain-shaped peak waveform in the section where the dresser is in contact with the surface grinding wheel during the dressing scan, and these are numbered from No. 1 to No. 20.

Figure 10 shows, in chronological order, the ratio (%) of actual spark time STs, which is the ST evaluation value obtained for each peak waveform, to the theoretical spark time ST (= Wd/Vd); the pass/fail judgment of shape correction, which indicates whether the ratio of actual spark time STs to theoretical spark time ST continuously exceeds 95%, i.e., whether it has saturated; the integrated intensity value Xs, which is the strength evaluation value obtained for each peak waveform; and the pass/fail judgment of dressing, which indicates whether the integrated intensity value Xs has saturated. According to this, when the AE signal intensity Xi based on the signal from the outer periphery AE sensor 16a was used, the pass/fail judgment of shape correction was made for peak waveform No. 8, and the pass/fail judgment of dressing for dressing was made for peak waveform No. 18. Furthermore, when the AE signal intensity Xi based on the signal from the inner periphery AE sensor 16b was used, the pass/fail judgment of shape correction was made for peak waveform No. 8, and the pass/fail judgment of dressing for dressing was made for peak waveform No. 18. In 17, the dressing (sharpening) was judged to be acceptable.

Figure 11 shows the ST evaluation value (actual spark time STs) and the integrated intensity value Xs, which is the intensity evaluation value, in time series when using the AE signal intensity Xi based on the signal from the outer periphery AE sensor 16a. Both the ST evaluation value and the intensity evaluation value increase with each dressing scan after dressing begins, but the ST evaluation value is judged to be pass (saturated) before the intensity evaluation value is judged to be pass (saturated).

Next, the inventors performed dressing using the same experimental conditions as Experimental Condition 1 on five grinding wheels, Wheel A to Wheel E, which differ in the degree of shape deformation, and compared the dressing depth CD until dressing completion was determined with the truing amount ΔTH predicted from the surface shape of the grinding wheels measured in advance using a stylus-type shape measuring device.

The dressing cut-in depth CD (= 0.01 x Nsw) until dressing completion is determined is calculated from the dressing cut-in depth of 0.01 mm during dressing and the number of scans Nsw of the dresser 12 until dressing completion using each of grinding wheels A to E is determined.

Figure 12 shows an example of the surface shape of a grinding wheel measured using a stylus-type shape measuring instrument. Note that this measurement data is of the shape of the upper surface grinding wheel 14, but for measurement purposes, it has been inverted upside down. The surface shape of the surface grinding wheel 14 shown in the example of Figure 12 is concave on the inner periphery compared to the outer periphery, and this must be flattened to complete truing. In this case, the amount of cut required to complete truing is the truing completion height, where the concave shape on the inner periphery is deepest, from the contact start height, where the dresser and the surface of the surface grinding wheel 14 first come into contact. Therefore, the difference ΔTH (mm) between the contact start height and the truing completion height is determined as the expected truing amount.

Figure 13 compares, for each of the grinding wheels A through E, the actual dressing cut-in depth CD until dressing completion is determined and the truing amount ΔTH predicted from the grinding wheel's surface shape measured in advance using a stylus-type shape measuring device. Figure 13 shows, for each of the grinding wheels A through E, that when the predicted truing amount ΔTH is large, the actual dressing cut-in depth CD is also large. This confirms that there is a correlation between the actual dressing cut-in depth CD until dressing completion is determined and the truing amount ΔTH predicted from the grinding wheel's surface shape measured in advance using a stylus-type shape measuring device. Because the predicted truing amount ΔTH is the value at the time shape correction is completed, the actual dressing cut-in depth CD is greater than the predicted truing amount ΔTH by the amount required to remove any remaining damage.

As described above, according to the dressing completion determination method of the dressing completion determination device (electronic control device 28) of this embodiment, a dressing scan is performed in which the dresser 12 is brought into sliding contact with the dressing surface 15 of the surface grinding wheel 14 while moving the dresser 12 at a constant feed rate across the width of the dressing surface 15, and this is repeated each time a constant depth of cut is applied. When automatically determining the completion of the dressing process of the dressing surface 15 based on the AE signal SAE, in the integrated intensity value calculation process (integral intensity value calculation unit 70), the integrated intensity value Xs of the AE signal intensity Xi generated during the dresser scan is calculated for each dressing scan, and in the dressing completion determination process (dressing completion determination unit 74), the completion of the dressing process is determined based on saturation of the increase in the integrated intensity value Xs of the AE signal intensity Xi calculated for each dressing scan. This makes it possible to determine with high accuracy whether the grinding wheel has been dressed, without the need for complicated preparation work.

Furthermore, according to the dressing completion determination device (electronic control device 28) of this embodiment, the integrated intensity value calculation unit 70 calculates the integrated intensity value Xs of the AE signal intensity Xi generated during the dresser scan for each dressing scan, and the dressing completion determination unit 74 determines the completion of the dressing process based on the saturation of the increase in the integrated intensity value Xs of the AE signal intensity Xi calculated for each dressing scan. This makes it possible to determine the completion of dressing of the grinding wheel with high accuracy without requiring complicated preparation work.

Furthermore, according to the dressing completion determination device (electronic control device 28) of this embodiment, when the shape modification pass/fail determination unit 68 determines that the shape modification is complete based on the actual spark time STs calculated by the spark time calculation unit 66 exceeding the spark time determination threshold STt set by the spark time determination threshold setting unit 64, the dressing completion determination unit 74 determines that the dressing process is complete based on the saturation of the increase in the integrated intensity value Xs of the AE signal intensity Xi calculated for each dressing scan by the integrated intensity value calculation unit 70 and the determination by the shape modification pass/fail determination unit 68 that the shape modification is successful (completed). This further improves the accuracy of the determination of the completion of the dressing process.

Furthermore, according to the dressing completion determination device (electronic control device 28) of this embodiment, it is determined that the increase in the integrated intensity value Xs of the AE signal intensity Xi integrated for each dressing scan has saturated based on the integrated intensity value Xs of the AE signal intensity Xi integrated for each dressing scan becoming equal to or less than the maximum integrated intensity Xsp of the AE signal intensity obtained by the dressing scans repeated up to that point. This allows a clear determination of the completion of the dressing process.

Furthermore, according to the dressing completion determination device (electronic control device 28) of this embodiment, among the signals output from the AE sensors 16a, 16b during the dressing scan, signals that exceed the AE signal determination threshold P determined based on the signals output from the AE sensors 16a, 16b in the non-dressing section R1 are used as the AE signal intensity Xi used to determine the completion of the dressing process. This further improves the accuracy of determining the completion of the dressing process.

Furthermore, according to the dressing completion determination device (electronic control device 28) of this embodiment, the AE signal determination threshold determiner 62 determines the AE signal determination threshold P based on the average or maximum value of the AE signal intensity Xi output from the AE sensors 16a, 16b during unloaded scanning, in which the dresser feed mechanism is caused to scan the dresser 12 while the dresser 12 is separated from the dressing surface 15 of the surface grinding wheel 14. This further improves the accuracy of determining the completion of the dressing process. Furthermore, the AE signal determination threshold P need only be slightly larger than the average or maximum value of the AE signal intensity Xi, and does not need to be determined based on strict experimental values. Therefore, it can be easily set to, for example, approximately 1.1 times the average or maximum value of the AE signal intensity Xi.

Furthermore, according to the dressing completion determination device (electronic control device 28) of this embodiment, the spark time calculation unit 66 calculates the actual spark time STs, which is the time during which the dresser 12 is in contact with the dressing surface 15 of the surface grinding wheel 14, as the time from when the AE signal intensity value Xi exceeds the AE signal determination threshold P to when it falls below the AE signal determination threshold P. This allows the spark time STs to be calculated accurately, making it possible to determine with high precision whether a sufficient dressing width has been obtained, i.e., whether correction (truing) of the grinding wheel shape has been completed.

Furthermore, according to the dressing completion determination device (electronic control device 28) of this embodiment, the AE sensors 16a, 16b are a pair of AE sensors respectively provided at different radial positions within a range corresponding to the dressing surface 15 of the surface grinding wheel 14 on the flange 40 to which the surface grinding wheel 14 is fixed, and the dressing completion determination unit 74 determines the completion of the dressing process based on the saturation of the increase in the integrated intensity value Xs of the AE signal intensity Xi obtained from the pair of AE sensors 16a, 16b, which is obtained by integrating the AE signal intensity Xi for each dressing scan. This further improves the accuracy of determining the completion of the dressing process.

One embodiment of the present invention has been described above using the drawings, but the present invention can also be applied in other forms.

For example, the electronic control device 28 in the above-described embodiment was equipped with a spark time judgment threshold setting unit 64, a spark time calculation unit 66, and a shape correction pass/fail judgment unit 68. However, depending on the type of work, as shown in Figure 10, the shape correction pass/fail judgment is made before the dressing pass/fail judgment for sharpening. In such cases, these do not necessarily have to be provided. In this case, the dressing completion judgment unit 74 judges the completion of dressing based solely on the judgment result of the dressing pass/fail judgment unit 72.

In addition, in the above-described embodiment, the completion of dressing was evaluated based on whether the integrated intensity value Xs, which is the sum of the scan AE signal intensity Xi for each dressing scan that exceeds the AE signal judgment threshold P, has saturated. However, if the AE signal judgment threshold P is small enough that it does not significantly affect the accuracy of the dressing completion judgment, the completion of dressing may be evaluated based on whether the integrated intensity value Xs of the scan AE signal intensity Xi for each dressing scan has saturated, without using the AE signal judgment threshold P.

In addition, in the above-described embodiment, the outer AE sensor 16a and the inner AE sensor 16b were used, but only one of the outer AE sensor 16a and the inner AE sensor 16b may be used. In this case, the dressing pass/fail determination unit 72 determines whether dressing is pass/fail based on only the signal detected from either the outer AE sensor 16a or the inner AE sensor 16b.

In the above-described embodiment, a surface grinding wheel 14 with a circularly flat dressing surface 15 was used for dressing, but a grinding wheel with a cylindrical grinding surface may also be used. In this case, the dresser 12 is scanned across the cylindrical grinding surface in a direction parallel to the centerline of rotation.

Furthermore, the surface grinding wheel 14 in the above-mentioned embodiment and the grinding wheel with a cylindrical grinding surface may be made of abrasive grains bonded with various bonds, such as resinoid grinding wheels and vitrified grinding wheels.

Furthermore, while the dresser 12 in the above-described embodiment was a single-stone dresser with one columnar diamond embedded in it, a rotary dresser with multiple diamonds embedded in its outer periphery or other dressing tools may also be used.

Please note that the above is merely one embodiment of the present invention, and various modifications can be made to the present invention without departing from its spirit.

10: Dressing device 12: Dresser 14: Surface grinding wheel 16a: Outer peripheral AE sensor 16b: Inner peripheral AE sensor 28: Electronic control device (dressing completion determination device)
62: AE signal determination threshold setting unit 64: Spark time determination threshold setting unit 66: Spark time calculation unit 68: Shape correction pass/fail determination unit 70: Integrated intensity value calculation unit (integrated intensity value calculation step)
72: Dressing pass/fail determination unit 74: Dressing completion determination unit (dressing completion determination step)
STs: actual spark time STt: spark time determination threshold Xs: integrated intensity value

Claims (6)

A dressing completion determination method for a dressing completion determination device, which automatically determines the completion of dressing of a dressing surface based on an AE signal generated by fracture of abrasive grains of the grinding wheel due to contact between the grinding wheel and the dresser, by repeatedly performing a dressing scan in which the dresser is moved at a constant feed rate across the dressing surface in a width direction while being brought into sliding contact with the dresser on the dressing surface, each time a constant depth of cut is provided, the method comprising:
an integrated intensity value calculation step of calculating an integrated intensity value of AE signal intensity generated during a dresser scan for each dressing scan;
a dressing completion determination step of determining that an increase in the integrated intensity value of the AE signal intensity calculated for each dressing scan in the integrated intensity value calculation step has saturated based on the integrated intensity value of the AE signal intensity calculated for each dressing scan becoming equal to or less than a maximum value of the integrated intensity of the AE signal intensity obtained by the dressing scans repeated up to that point, and determining completion of the dressing process based on this determination . a dressing completion determination device for automatically determining the completion of a dressing process of the dressing surface based on the AE signal, the dressing scan being performed by causing the dresser to slide against the dressing surface of the grinding wheel and scan the dresser at a constant feed rate across the dressing surface in a width direction, the dressing scan being performed repeatedly every time a constant depth of cut is applied, the dressing completion determination device comprising: an AE sensor for detecting an AE signal generated by fracture of abrasive grains of the grinding wheel due to contact between the grinding wheel and the dresser;
an integrated intensity value calculation unit that calculates an integrated intensity value obtained by integrating AE signal intensities generated during the dressing scan for each of the dressing scans;
a dressing completion determination unit that determines that an increase in the integrated intensity value of the AE signal intensity integrated for each dressing scan has saturated based on the integrated intensity value of the AE signal intensity integrated for each dressing scan by the integrated intensity value calculation unit becoming equal to or less than a maximum value of the integrated intensity of the AE signal intensity obtained by the dressing scans repeated up to that point, and determines completion of the dressing process based on that determination . a spark time calculation unit that calculates a spark time, which is a time period during which the dresser is in contact with the dressing surface of the grinding wheel, from a time point when the AE signal intensity obtained from the AE sensor exceeds the AE signal threshold value until a time point when the AE signal intensity obtained from the AE sensor falls below the AE signal threshold value; and
a spark time determination threshold setting unit that sets a spark time determination threshold that is shorter than a theoretical spark time calculated based on the feed speed of the dresser by the dresser feed mechanism and the width dimension of the dressing surface of the grinding wheel;
a shape modification pass/fail determination unit that determines completion of the shape modification based on whether the spark time calculated for each dressing scan by the spark time calculation unit exceeds the spark time determination threshold,
3. The dressing completion determination device according to claim 2, wherein the dressing completion determination unit determines the completion of the dressing process based on the saturation of an increase in the integrated intensity value of the AE signal intensity calculated for each dressing scan by the integrated intensity value calculation unit and the completion of the shape modification determined by the shape modification pass/fail determination unit. an AE signal judgment threshold determining unit that determines an AE signal judgment threshold based on an AE signal intensity obtained from the AE sensor in a non-dressing state in which the dresser is separated from the dressing surface of the grinding wheel;
4. The dressing completion determination device according to claim 2 , wherein a signal exceeding the AE signal determination threshold among signals output from the AE sensor during the dressing scan is used to determine completion of the dressing process. 5. The dressing completion determination device according to claim 4, wherein the AE signal determination threshold value determining unit determines the AE signal determination threshold value based on an average value or a maximum value of an AE signal intensity obtained from the AE sensor when the dresser is scanned by a dresser feed mechanism with the dresser separated from the dressing surface of the grinding wheel , in a section in which a coefficient of variation is equal to or less than a predetermined value. The dressing completion determination device of any one of claims 2 to 5, characterized in that the AE sensors are a pair of AE sensors each provided at a different radial position within a range corresponding to the dressing surface of the grinding wheel on the flange to which the grinding wheel is fixed, and the dressing completion determination unit determines the completion of the dressing process based on the saturation of the increase in the integrated intensity value of the AE signal intensity obtained from each of the pair of AE sensors, which is accumulated for each dressing scan.