JP7766457B2 - Method and device for determining shape distortion of grinding wheel - Google Patents

Description

The present invention relates to a method and device for determining shape distortion of a grinding wheel, which has a flat grinding surface at its end face that slides against the workpiece during surface grinding.

In surface grinding, problems such as scratches, reduced flatness and flatness, extreme uneven wear, and insufficient machining allowance can occur due to deformation of the grinding wheel. Deformation of the grinding wheel can be measured by measuring the radial cross-sectional shape of the grinding wheel after grinding using a stylus displacement meter or laser displacement meter, but it is difficult to detect deformation during grinding and determine when dressing should begin. Therefore, dressing intervals are often set with sufficient margin, which shortens the life of the grinding wheel.

In response to this, as described in Patent Document 1, an increase in the grinding resistance of a grinding wheel is detected based on the power consumption of the motor that rotates the grinding wheel or the amount of axial deflection of the grinding wheel. This makes it possible to determine whether or not the grinding wheel needs to be dressed based on the increase in grinding resistance of the grinding wheel reaching a predetermined level, without having to stop the grinding process using the grinding machine.

Japanese Patent Application Laid-Open No. 2019-053699

However, because the conventional shape deformation detection device described above detects shape deformation across the entire grinding surface of a grinding wheel based on an increase in the grinding load across the entire grinding surface of the rotating grinding wheel, it was unable to detect local shape deformation at a specific location within the grinding surface of the grinding wheel. As a result, it was not possible to determine the appropriate timing to start dressing (truing), which corrects local shape deformation within the grinding surface, in grinding processes in which multiple workpieces are surface ground using the end face of a grinding wheel as the grinding surface, such as grinding processes using a double-disc surface grinder.

The present invention was made against the background of the above circumstances, and its purpose is to provide a grinding wheel shape deformation detection device that can determine an increase in localized shape deformation at a specific location on the grinding surface of the grinding wheel.

The inventors conducted extensive research in light of the above circumstances. They found that in a grinding process in which multiple workpieces are sequentially surface-ground using the flat end face of a grinding wheel as the grinding surface, the amplitude of the integrated intensity value waveform of the AE signal (high-frequency vibration or ultrasonic vibration) generated by contact with the workpiece during the grinding process increases over time. They discovered that when an evaluation value indicating the increase in amplitude of the integrated intensity value waveform of the AE signal exceeds a predetermined judgment threshold within the grinding surface, it is possible to determine shape deformation at a specific location within the grinding surface, and based on this judgment, it is possible to determine when to start dressing the grinding wheel at an appropriate time. The present invention was made based on this finding.

That is, the gist of the first invention is (a) a method for determining shape distortion of a grinding wheel in a grinding process in which an end face of a grinding wheel is brought into sliding contact with a plurality of workpieces as a grinding surface in succession to form flat grinding surfaces on the plurality of workpieces, the method determining local shape distortion within the grinding surface based on an AE signal generated due to contact between the grinding wheel and the workpieces, (b) periodically calculating an integral value of a signal component in a predetermined wavelength band of a power spectrum obtained by frequency analysis of the AE signal generated during the grinding process, and (c) an evaluation value calculation process for repeatedly calculating an evaluation value representing the average value of the difference or ratio between the maximum value and the minimum value of the waveform, or the moving standard deviation of the waveform, based on a waveform showing the AE signal intensity values periodically calculated by the integrated intensity value calculation process on a time axis ; and (d) a shape deformation determination process for determining whether shape deformation has occurred on the end face of the grinding wheel based on the evaluation value repeatedly calculated by the evaluation value calculation process exceeding a predetermined determination threshold.

The gist of the second invention is (a) a grinding wheel shape deformation determination device for determining local shape deformation within a grinding surface based on an AE signal generated due to contact between the grinding wheel and a plurality of workpieces in a grinding process in which an end face of a grinding wheel is brought into sliding contact with the plurality of workpieces as a grinding surface to continuously form flat grinding surfaces on the plurality of workpieces, (b) periodically calculating an integral value of a signal component in a predetermined wavelength band of a power spectrum obtained by frequency analysis of the AE signal generated during the grinding process, and (c) an evaluation value calculation unit that repeatedly calculates, based on a waveform showing the AE signal intensity values periodically calculated by the integrated intensity value calculation unit on a time axis , an average value of the difference or ratio between the maximum value and the minimum value of the waveform, or an evaluation value that represents the moving standard deviation of the waveform; and (d) a shape deformation determination unit that determines the occurrence of shape deformation on the end face of the grinding wheel based on the evaluation value repeatedly calculated by the evaluation value calculation unit exceeding a predetermined determination threshold.

The gist of the third invention is that in the second invention , the grinding wheel is fixed to a flange that rotates together with the rotating spindle, and the flange is equipped with a pair of outer AE sensors and inner AE sensors that are fixed at different radial positions on the flange and output the AE signals, an A/D converter that performs A/D conversion of the AE signals, and a transmitting module that wirelessly transmits the A/D converted AE signals, and includes a receiving circuit that receives the AE signals transmitted from the transmitting module, and an electronic control device that has the integrated intensity value calculation unit, the evaluation value calculation unit, and the shape deformation determination unit and processes the AE signals output from the receiving circuit.

The gist of the fourth invention is that, in the third invention, the flange has an electronic component accommodating chamber that opens on a surface opposite to a surface on which the grinding wheel is fixed and accommodates the outer periphery side AE sensor and the inner periphery side AE sensor, an A/D converter that A/D converts the AE signal, and a transmitting module that wirelessly transmits the A/D converted AE signal, a cover plate that closes the opening of the electronic component accommodating chamber is fastened to the flange, a screw hole is provided on the surface of the cover plate opposite to the flange side, and a balancing weight for adjusting the rotational balance of the flange is fastened to the screw hole.

The gist of a fifth aspect of the present invention is that in the fourth aspect of the present invention, the cover plate is formed with a window through which radio waves transmitted from the transmission module pass.

According to the method for determining shape deformation of a grinding wheel of the first invention, in the evaluation value calculation step, an evaluation value representing the average value of the differences or ratios between the maximum and minimum values of the waveform, or the moving standard deviation of the waveform, is repeatedly calculated based on the waveform in which the AE signal intensity values periodically calculated in the integrated intensity value calculation step are plotted on a time axis, and in the shape deformation determination step, the occurrence of local shape deformation on the end face of the grinding wheel is determined based on whether the evaluation value repeatedly calculated in the evaluation value calculation step exceeds a predetermined determination threshold. This makes it possible to determine shape deformation at a specific location on the grinding surface, and based on that determination, it is possible to determine when to start dressing the grinding wheel at an appropriate time without requiring skill.

According to the grinding wheel shape deformation determination device of the second invention, the evaluation value calculation unit repeatedly calculates an evaluation value representing the average value of the difference or ratio between the maximum and minimum values of the waveform, or the moving standard deviation of the waveform, based on the waveform indicating the AE signal intensity value periodically calculated by the integrated intensity value calculation unit, and the shape deformation determination unit determines the occurrence of local shape deformation on the end face of the grinding wheel based on the evaluation value repeatedly calculated by the evaluation value calculation unit exceeding a predetermined determination threshold. This makes it possible to determine shape deformation at a specific location on the grinding surface, and based on that determination, it is possible to determine when to start dressing the grinding wheel at an appropriate time without requiring skill.

According to a third aspect of the present invention, the grinding wheel shape deformation detection device includes a grinding wheel fixed to a flange that rotates together with a rotating spindle, a pair of outer and inner AE sensors fixed to the flange at different radial positions and that output the AE signals, an A/D converter that performs A/D conversion of the AE signals, and a transmitter module that wirelessly transmits the A/D converted AE signals, a receiver circuit that receives the AE signals transmitted from the transmitter module, and an electronic control device that has the integrated intensity value calculation unit, the evaluation value calculation unit, and the shape deformation detection unit and processes the AE signals output from the receiver circuit. Thus, the AE signals generated by the rotating grinding wheel are received by the fixed receiver circuit, and the electronic control device processes the AE signals received by the receiver circuit to determine shape deformation at a specific location on the grinding surface, and based on this determination, it is possible to determine when to start dressing the grinding wheel at an appropriate time without requiring skill.

According to the fourth aspect of the present invention, the flange includes an electronic component housing chamber that opens on a surface opposite to the surface to which the grinding wheel is fixed and houses the outer AE sensor and the inner AE sensor, an A/D converter that A/D converts the AE signals, and a transmission module that wirelessly transmits the A/D converted AE signals, and a cover plate that closes the opening of the electronic component housing chamber is fastened to the flange, and a surface of the cover plate opposite to the flange side is provided with threaded holes, and balancing weights that adjust the rotational balance of the flange are fastened to the threaded holes. Thus, even if the center of gravity of the flange is offset from the center of rotation by mounting the outer AE sensor and the inner AE sensor, the A/D converter that A/D converts the AE signals, and the transmission module that wirelessly transmits the A/D converted AE signals, the balancing weights bring the center of gravity of the flange closer to the center of rotation, thereby effectively suppressing rotational vibrations caused by the offset center of gravity.

According to the grinding wheel shape deformation detection device of the fifth aspect of the present invention, the cover plate has a window that allows the radio waves transmitted from the transmitter module to pass through, so that even if the cover plate is made of a highly rigid metal, the radio waves transmitted from the transmitter module are transmitted through the cover plate.

1 is a diagram illustrating the configuration of a double-disc surface grinding machine according to an embodiment of the present invention; FIG. 2 is a perspective view briefly explaining a main part of the double-disc surface grinding machine of FIG. 1 . This figure shows an electronic component storage chamber formed on one side of the flange to which the surface grinding wheel in Figure 1 is fixed, opposite the surface grinding wheel side, and a pair of outer and inner AE sensors, an electronic circuit board, and a pair of power supply batteries provided within the electronic component storage chamber. 4 is a cross-sectional view illustrating in detail a flange to which the surface grinding wheel of FIG. 3 is attached. FIG. 4 is a view showing a cover plate that closes an opening of an electronic component accommodating chamber formed on one surface of the flange of FIG. 3; FIG. 6 is a diagram illustrating a fixing device that detachably fixes the balancing weight W to the cover plate of FIG. 5. FIG. 10A and 10B are diagrams illustrating the configuration of an electronic circuit board mounted on a flange 26. FIG. 2 is a flowchart illustrating a main part of the control operation of the electronic control device of FIG. 1 . 10 is a flowchart illustrating another main control operation of the electronic control device of FIG. 1 . 3 is a schematic plan view illustrating an overlapping structure between an upper surface grinding wheel, a lower surface grinding wheel, and a carrier for feeding a workpiece in the double-disc surface grinding machine of FIG. 1 and FIG. 2. FIG. 3 is a diagram showing the surface shape along the movement trajectory of the workpiece of the upper surface grinding wheel and the lower surface grinding wheel on the grinding surface of the double-disc surface grinding machine of FIG. 1 and FIG. 2. FIG. 3 is a diagram showing the surface shape along the movement trajectory of the workpiece of the upper surface grinding wheel and the lower surface grinding wheel after grinding for ³ minutes with a grinding volume of 200 cm using the double-disc surface grinding machine of FIGS. 1 and 2 . 3 is a schematic diagram illustrating the distance between a pair of surface grinding wheels along the movement path of the workpiece on the double-disc surface grinding machine of FIG. 2 at the beginning of grinding. FIG. 3 is a schematic diagram illustrating the change in the distance between one surface grinding wheel and the other surface grinding wheel along the movement trajectory of the workpiece on the double-disc surface grinding machine of FIG. 2 in the later stage of grinding. FIG. FIG. 10 is a diagram showing the time-axis waveform of the AE signal intensity obtained from the outer peripheral AE sensor. 16 is a diagram showing the envelope of the maximum value and the envelope of the minimum value of the time-axis waveform of FIG. 15 . 10 is a diagram showing the envelope of the maximum value and the envelope of the minimum value of the time-axis waveform of the AE signal strength obtained from the inner periphery side AE sensor. FIG. 17 is a diagram showing the time change of the difference (evaluation value) between the envelope of the maximum value and the minimum value of the time-axis waveform of FIG. 16, together with the cumulative correction amount of the gap between a pair of surface grinding wheels. FIG. 18 is a diagram showing the time change of the difference (evaluation value) between the envelope of the maximum value and the minimum value of the time-axis waveform of FIG. 17, together with the cumulative correction amount of the gap between a pair of surface grinding wheels. FIG. 16 is a diagram showing the time change of the moving standard deviation (evaluation value) of the time-axis waveform of FIG. 15 together with the cumulative correction amount of the gap between a pair of surface grinding wheels. FIG. 10 is a diagram showing the time change of the moving standard deviation (evaluation value) of the time-axis waveform of the AE signal strength obtained from the inner circumference side AE sensor, together with the cumulative correction amount of the gap between a pair of surface grinding wheels. FIG. 10A and 10B are diagrams showing the time change of the moving standard deviation Rm during grinding obtained for waveforms showing AE signal strength values in four integral frequency ranges from the AE signal obtained from the outer periphery side AE sensor.

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 double-disc surface grinding machine 10 is equipped with a pair of opposing surface grinding wheels 12 and 14 that can rotate relative to one another. Both sides of a circular workpiece 16, made of, for example, hardened steel, are ground flat while the workpiece is clamped and pressed between the flat end faces 12a and 14a of the surface grinding wheels 12 and 14. The end faces 12a and 14a function as the annular grinding surfaces of the surface grinding wheels 12 and 14. The surface grinding wheels 12 and 14 are rotated in opposite directions by wheel rotation drive motors 56 and 58, which will be described later.

Figure 2 is a perspective view showing the surface grinding wheels 12 and 14 and the carrier 18 that transports the circular workpiece 16 between the flat end faces of the surface grinding wheels 12 and 14. The carrier 18 is a circular plate with circular transport holes 20 evenly spaced around its periphery, into which the circular workpiece 16 fits, and is driven to rotate by a work feed motor 54 (described below) about a second rotation center line CL2 that is parallel to the perpendicular first rotation center line CL1 of the surface grinding wheels 12 and 14.

The back surfaces of the surface grinding wheels 12 and 14 are in intimate contact with thick, circular flanges 26 and 28 (see Figure 3), which rotate integrally with a pair of concentric but independent main shafts 22 and 24 on the double-head surface grinding machine 10. As shown in Figure 4, the wheels are fixed to the flanges 26 and 28 using fastening bolts (not shown) that thread through holes 27 (see Figure 3) into nuts (not shown) embedded in the surface grinding wheels 12 and 14.

The flange 26, which secures the upper surface grinding wheel 12 of the surface grinding wheels 12 and 14, has an electronic component storage chamber 30 that opens on the side opposite the surface grinding wheel 12. The opening of the electronic component storage chamber 30 is closed by a sealing rubber plate 34 held down by a circular steel cover plate 32, as shown in FIG. 5. The cover plate 32 and the sealing rubber plate 34 are secured by fastening bolts 37 that pass through them and thread into threaded holes 35 in the flange 26. The cover plate 32 has one of several rectangular windows 33 formed in alignment with the electronic circuit board 44 containing the transmitter module 52, allowing radio waves to be transmitted from the transmitter module 52 to the outside. Additionally, the surface of the cover plate 32 opposite the surface grinding wheel 12 has several threaded holes 38 formed at regular intervals around the periphery of the cover plate 32. As shown in Figure 6, a fixing bolt 39 for fixing a balancing weight W that adjusts the rotational balance of the flange 26 is fastened to the threaded hole 38.

A pair of outer AE sensors 40 and inner AE sensors 42, an electronic circuit board 44, and a pair of power batteries 46 are arranged within the electronic component housing 30 formed in the flange 26. As shown in FIG. 7, the electronic circuit board 44 includes a preamplifier 48 that amplifies the output signals of the outer AE sensor 40 and inner AE sensor 42, an A/D converter 50 that converts the output signal of the preamplifier 48 into a digital signal, and a transmission module 52 that wirelessly transmits the output signals of the outer AE sensor 40 and inner AE sensor 42 that have been converted into digital signals by the A/D converter 50. The A/D converter 50 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 40 and inner AE sensor 42 are positioned at different radial positions along one radial direction of the flange 26. The outer AE sensor 40 is positioned at 80% or more, preferably 90%, of the radius of the flange 26 from the rotation axis CL of the flange 26 toward the outer circumference, while the inner AE sensor 42 is positioned at 35% or more and 50% or less, preferably 40%, of the radius of the flange 26 from the rotation axis CL of the flange 26 toward the outer circumference.

Returning to FIG. 1, the double-disc surface grinding machine 10 is equipped with a motor drive control device 60 that drives the workpiece feed motor 54, the grinding wheel rotation drive motor 56 that rotates the upper surface grinding wheel 12, and the grinding wheel rotation drive motor 58 that rotates the lower surface grinding wheel 14. It also includes an electronic control device 62 that outputs a drive command signal to the motor drive control device 60 in response to a grinding start operation and determines deformation of the end face (grinding surface) 12a of the surface grinding wheel 12 based on AE signals from the outer AE sensor 40 and inner AE sensor 42 resulting from contact (sliding contact) between the surface grinding wheel 12 and the workpiece 16 during grinding. The double-disc surface grinding machine 10 also includes a receiving circuit 66 with an antenna 64 for receiving the AE signal SAE transmitted from the transmitting module 52 on the electronic circuit board 44.

The electronic control device 62 is a so-called microcomputer including a CPU, ROM, RAM, and an interface. The CPU, utilizing the RAM's temporary storage function and according to a program pre-stored in the ROM, rotates the surface grinding wheels 12 and 14 and operates the motor drive control device 60 to rotate the carrier 18 so as to continuously feed the workpiece 16 between the end faces (grinding surfaces) 12a and 14a of the surface grinding wheels 12 and 14. During continuous grinding of the workpiece 16, the distance between the end faces (grinding surfaces) 12a and 14a of the surface grinding wheels 12 and 14 is automatically or manually adjusted over time by applying a cumulative (cut-in) correction amount AA to compensate for wear on the end faces (grinding surfaces) 12a and 14a, so that the thickness dimension of the workpiece 16 falls within a preset tolerance. The electronic control device 62 also functions as a shape deformation determination device, processing the AE signal SAE received by the receiving circuit 66 during grinding to determine whether there is any local shape deformation, primarily on the end face (grinding surface) 12a of the surface grinding wheel 12, and displaying the shape deformation and the need to start dressing on the surface condition display device 78.

The electronic control device 62 functionally comprises a frequency analysis unit 68, an integrated intensity value calculation unit 70, an evaluation value calculation unit 72, a shape collapse determination threshold setting unit 74, and a shape collapse determination unit 76.

The frequency analysis unit 68, which corresponds to the frequency analysis process, performs frequency analysis (FFT) of the A/D converted AE signal SAE during grinding of the grinding wheels 12, 14, generating a power spectrum showing various signal powers indicating the magnitude of frequency components on the frequency axis (horizontal axis) for each frequency in a two-dimensional coordinate system with the vertical axis indicating signal power and the horizontal axis indicating frequency. The integrated intensity value calculation unit 70, which corresponds to the integrated intensity value calculation process, discriminates signal components from the AE signal SAE in a frequency band that sensitively reflects contact vibrations between the surface grinding wheel 12 and the workpiece 16 during grinding, such as a wavelength band of 25 kHz to 200 kHz, preferably a wavelength band of 45 to 75 kHz, and outputs the integrated value (area value) of the signal components as the AE signal intensity value Xi. The frequency analysis period and integrated intensity value calculation period (period) are set to a time that is less than half the passage time Δt of the workpiece 16 between the upper surface grinding wheel 12 and the lower surface grinding wheel 14 along the arc-shaped movement trajectory TR in Figure 10. This is to enable highly sensitive detection of vibrations occurring when the workpiece 16 enters between the upper surface grinding wheel 12 and the lower surface grinding wheel 14.

The evaluation value calculation unit 72 corresponds to the evaluation value calculation process, and sequentially obtains the intra-subsection difference R (= SPmax - SPmin) between the maximum value SPmax and the minimum value SPmin within a subsection set in advance of approximately several ms to tens of ms from the time waveform of the AE signal intensity value Xi. It also repeatedly calculates the average value Rav (R1 + R2 +... + Rn/n) of the differences R1 to Rn for each subsection for each evaluation value calculation subsection set in advance of, for example, approximately 20 seconds, as an evaluation value for evaluating shape deformation. Here, n indicates the number of subsections.

In addition, the evaluation value calculation unit 72 repeatedly calculates, for each moving evaluation value calculation section of the time waveform of the AE signal strength Xi, which is preset to be, for example, several seconds to several tens of seconds, the moving standard deviation σm [=√(1/n)Σ(SP1-SPav) ² ] (where SPav is the section average and SP1 is the standard deviation) of the time waveform within the evaluation value calculation section as an evaluation value for evaluating shape deformation.

The shape distortion judgment threshold setting unit 74 corresponds to the shape distortion judgment threshold setting process, and automatically or manually sets, based on the evaluation values (average difference Rav and moving standard deviation σm) obtained from a surface grinding test previously performed using the double-disc surface grinding machine 10, when local shape distortion on the end face (grinding surface) 12a of the surface grinding wheel 12 reaches a predetermined size that requires dressing to correct the shape of the end face (grinding surface) 12a.

The shape distortion determination unit 76 corresponds to the shape distortion determination process and determines whether local shape distortion of the end face (grinding surface) 12a of the surface grinding wheel 12 has occurred based on the fact that the average value ΔRav of the small-area differences ΔR calculated by the evaluation value calculation unit 72 exceeds the difference shape distortion determination threshold SPt, for example, as shown in Figure 18 or 19, and whether the end face (grinding surface) 12a has reached a predetermined size that requires dressing for shape correction.The shape distortion determination unit 76 determines whether local shape distortion of the end face (grinding surface) 12a of the surface grinding wheel 12 has reached a predetermined size that requires dressing for shape correction, based on the fact that the moving standard deviation σm for each evaluation value calculation interval calculated by the evaluation value calculation unit 72 exceeds the standard deviation shape distortion determination threshold σt, for example, as shown in Figure 20 or 21. Alternatively, the shape distortion determination unit 76 determines that local shape distortion of the end face (grinding surface) 12a of the surface grinding wheel 12 has reached a predetermined size that requires dressing to correct the shape of the end face (grinding surface) 12a, based on the fact that the average value Rav of the section differences R calculated by the evaluation value calculation unit 72 exceeds the difference shape distortion determination threshold SPt and the moving standard deviation σm for each section calculated by the evaluation value calculation unit 72 exceeds the standard deviation shape distortion determination threshold σt. When the shape distortion determination unit 76 determines that the shape distortion of the end face (grinding surface) 12a has reached a predetermined size that requires dressing for sharpening, a message to that effect is displayed on the surface condition display device 78.

Figure 8 is a flowchart explaining the main control operations of the electronic control unit 62. In Figure 8, in step S1 (hereinafter, "step" will be omitted), which corresponds to the shape deformation determination threshold setting process or shape deformation determination threshold setting unit 74, a pre-entered differential shape deformation determination threshold SPt is read. In the following step S2, the AE signal SAE during the grinding process is read. Next, in step S3, which corresponds to the frequency analysis process or frequency analysis unit 68, frequency analysis of the AE signal SAE is performed, and a power spectrum is generated, showing various signal powers indicating the magnitude of frequency components for each frequency on the frequency axis (horizontal axis) in two-dimensional coordinates with the vertical axis indicating signal power and the horizontal axis indicating frequency.

Next, in S4, which corresponds to the integrated intensity value calculation step or integrated intensity value calculation unit 70, frequency components in a predetermined frequency band in the power spectrum, for example, a frequency band of 2.5 kHz to 200 kHz, preferably a frequency band of 45 to 75 kHz, are discriminated, and the integral value (area value) of the discriminated signal components is calculated as the AE signal intensity value Xi.

Next, steps S6 and S7, which correspond to the evaluation value calculation step or evaluation value calculation unit 72, are executed. In S6, the difference ΔR (= SPmax - SPmin) within a small interval between the maximum value SPmax and the minimum value SPmin within a small interval set in advance of approximately several ms to tens of ms is sequentially calculated from the time waveform of the AE signal intensity value Xi. In S7, for each evaluation value calculation interval set in advance of approximately 20 seconds, for example, the average value ΔRav ((R1 + R2 +... + Rn)/n) of the differences R1 to Rn for each small interval is calculated as an evaluation value for evaluating shape deformation.

Then, steps S8 and S9, which correspond to the shape deformation determination process or shape deformation determination unit 76, are executed. In S8, it is determined whether the average value Rav of the small interval differences R exceeds the difference shape deformation determination threshold value SPt. If the determination in S8 is negative, steps S2 and onward are repeatedly executed. However, if the determination in S8 is positive, it is determined in S9 that a shape deformation of such magnitude that dressing to correct the shape of the end face (ground surface) 12a has occurred, and an alert indicating the occurrence of shape deformation is output on the surface condition display device 78. This alert indicates that dressing needs to be started.

Figure 9 is a flowchart explaining other key control operations of the electronic control unit 62. In Figure 9, steps S11 to S14 are similar to steps S1 to S4 in Figure 8, so their explanation will be omitted.

In S15, which corresponds to the evaluation value calculation process or evaluation value calculation unit 72, for each moving evaluation value calculation section of the time waveform of the AE signal intensity Xi, which is preset to, for example, several seconds to several tens of seconds, the moving standard deviation σm [=√(1/n)Σ(SP1-SPav) ² ] (where SPav is the section average) of the time waveform within the evaluation value calculation section is repeatedly calculated as an evaluation value for evaluating shape deformation.

In S16, which corresponds to the shape deformation determination process or shape deformation determination unit 76, it is determined whether the moving standard deviation σn for each evaluation value calculation section exceeds the standard deviation shape deformation determination threshold σt. If the determination in S16 is negative, S12 and subsequent steps are repeatedly executed. However, if the determination in S16 is positive, it is determined in S17 that a shape deformation of such magnitude that dressing to correct the shape of the end face (ground surface) 12a has occurred, and an alert indicating the occurrence of shape deformation is output on the surface condition display device 78. This alert indicates that dressing needs to be started.

The following describes the shape distortion that occurs during surface grinding on the double-disc surface grinding machine 10. Fig. 10 is a plan view showing the overlap of the carrier 18, the upper surface grinding wheel 12, and the lower surface grinding wheel 14. In Fig. 10, the workpiece 16 fitted into the transport hole 20 of the carrier 18 is ground as it is transported circumferentially between the upper surface grinding wheel 12 and the lower surface grinding wheel 14 in a sliding contact state. Figs. 11 and 12 show the surface shapes of the end face 12a of the upper surface grinding wheel 12 and the end face 14a of the lower surface grinding wheel 14 along the arc-shaped movement locus TR of the workpiece 16 before grinding and after grinding with a grinding volume of 200 ^cm3 , as waveforms measured with a stylus-type surface profile measuring device. 11 and 12, the horizontal axis represents the distance X (mm) of the movement locus TR of the workpiece 16, with 0 mm representing the innermost position of the workpiece 16, negative values representing the movement distance from the entrance to the innermost position, and positive values representing the movement distance from the innermost position to the exit. The vertical axis represents the vertical distance Z (mm) with the exit being 0 mm.

Figure 13 shows a schematic representation of the surface shapes of the end face 12a of the upper surface grinding wheel 12 and the end face 14a of the lower surface grinding wheel 14 along the movement trajectory of the workpiece 16. In the double-disc surface grinding machine 10, the surface shape of the end face 14a of the lower surface grinding wheel 14 is flat, but from the entrance of the end face 12a of the upper surface grinding wheel 12 to the center of the movement trajectory of the workpiece 16, it is flat. However, from the center of the movement trajectory of the workpiece 16 to the exit, it slopes linearly toward the point where the target thickness dimension Tm is formed between the end face 14a and the end face 14a, so that the target thickness dimension Tm of the workpiece 16 after grinding is obtained.

Similar to Figure 13, Figure 14 schematically illustrates the surface shapes of the end face 12a of the upper surface grinding wheel 12 and the end face 14a of the lower surface grinding wheel 14 along the movement trajectory of the workpiece 16. As the grinding process progresses, the shape of the end face 12a of the upper surface grinding wheel 12 changes as a result of the application of the cutting-in correction value Th to achieve the target thickness dimension Tm. In this state, the portions of the end face 12a of the upper surface grinding wheel 12 corresponding to the entrance and exit of the movement trajectory of the workpiece 16 wear, while the application of the cutting-in correction value Th reduces the entrance width of the movement trajectory of the workpiece 16 from Ti1 to Ti2. As this deformation of the end face 12a of the upper surface grinding wheel 12 progresses, the impact when the workpiece 16 enters the inlet increases, so dressing is performed to correct the shape and return it to the shape before grinding shown in Figures 11 and 13. The cumulative cutting-in correction amount AA in Figures 18 to 21, described below, is the cumulative value of the cutting-in correction value Th.

The inventors conducted a surface grinding test under the following experimental conditions, and the results obtained will now be described.
(Surface grinding test conditions)
Processing machine: Vertical axis double-head surface grinding machine, carrier-through type Surface grinding wheel: WA/HA 80 H 12
Grindstone outer diameter: 585mmφ
Grinding wheel spindle rotation speed: 900 rpm
Carrier rotation speed: 2 rpm
Removal allowance: 0.2 mm
Grinding wheel axis alignment: 0.16 mm
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
(Calculation conditions)
Data length of moving maximum and minimum values (same as data length of standard deviation): 2 seconds
Moving average data length: 20 seconds
Data pitch (small interval) of moving maximum/minimum values and moving average values: 65 ms

Figure 15 shows the continuous waveform of the AE signal integrated intensity Xi obtained from the outer AE sensor 40 during the surface grinding test. Figure 16 shows the envelope of the maximum and minimum values of Figure 15. Figure 17 shows the envelope of the maximum and minimum values of the continuous waveform of the AE signal integrated intensity Xi obtained from the inner AE sensor 42. Figure 18 shows the waveform showing the moving average ΔRav of the difference, which is an evaluation value calculated from the maximum and minimum values of the AE signal integrated intensity waveform obtained from the outer AE sensor 40 in Figure 16. Figure 19 shows the waveform showing the moving average ΔRav of the difference, which is an evaluation value calculated from the maximum and minimum values of the AE signal integrated intensity waveform obtained from the inner AE sensor 42 in Figure 17. As shown in Figures 18 and 19, the moving average ΔRav of the difference increases over time, reflecting the deformation of the end face 12a of the surface grinding wheel 12. Figures 18 and 19 show the cumulative cutting-in correction amount that is automatically or manually applied to bring the thickness of the workpiece within the tolerance after surface grinding.

Figure 20 shows the moving standard deviation σ calculated as an evaluation value from the continuous waveform of the AE signal integrated intensity Xi shown in Figure 15 obtained from the outer AE sensor 40 during surface grinding. Figure 21 shows the moving standard deviation σm calculated as an evaluation value from the continuous waveform of the AE signal integrated intensity Xi obtained from the inner AE sensor 42. These moving standard deviations σm increase over time, reflecting deformation of the end face 12a of the surface grinding wheel 12. Note that Figures 20 and 21 show the cumulative cutting-in correction amount that is applied automatically or manually to bring the thickness dimension of the workpiece within the tolerance after surface grinding.

In the above grinding test, 45 to 75 kHz was used as the integral frequency range when determining the AE signal intensity value Xi from the power spectrum obtained by frequency analysis of the AE signal. However, the inventors also determined the AE signal intensity value Xi for four other integral frequency ranges: 25 to 45 kHz, 80 to 100 kHz, and 100 to 200 kHz. They also calculated the moving average value ΔRav of the difference and the moving standard deviation Rm from the waveforms of these AE signal intensity values Xi. Figure 22 shows the change over time in the moving standard deviation Rm during grinding, determined for each of the waveforms showing the AE signal intensity values for the four integral frequency ranges.

In Figure 22, the moving standard deviation Rm increases as grinding time progresses in all integral frequency ranges of 25 to 45 kHz, 80 to 100 kHz, and 100 to 200 kHz, and can be used to determine shape deformation. However, the signal increases in the integral frequency range of 80 to 100 kHz, 25 to 45 kHz, 100 to 200 kHz, and 45 to 75 kHz, in that order, clearly indicating shape deformation.

As described above, in the shape deformation determination device (electronic control device 62) of this embodiment, the evaluation value calculation unit 72 corresponding to the evaluation value calculation process calculates, as an evaluation value, the average value Rav of the difference representing the amplitude of the waveform and/or the moving standard deviation σm of the time waveform of the AE signal intensity Xi based on the waveform indicating the integrated intensity value Xi of the AE signal calculated by the integrated intensity value calculation unit 70 corresponding to the integrated intensity value calculation process; and the shape deformation determination unit 76 corresponding to the shape deformation determination process determines the occurrence of local shape deformation on the end face (grinding surface) 12a of the surface grinding wheel 12 based on the average value Rav of the difference R calculated by the evaluation value calculation unit 72 exceeding the difference shape deformation determination threshold SPt and/or the moving standard deviation σn exceeding the standard deviation shape deformation determination threshold σt. This makes it possible to determine localized deformation within the end face (grinding surface) 12a of the surface grinding wheel 12, and based on this determination, it is possible to determine when to start dressing the surface grinding wheel 12 at the appropriate time, without requiring any skill.

In addition, according to the shape deformation determination device (electronic control device 62) of this embodiment, the grinding wheel 12 is fixed to a flange 26 that rotates together with the rotating main shaft 22, and the flange 26 is equipped with a pair of outer AE sensors 40 and inner AE sensors 42 that are fixed at different radial positions on the flange 26 and output AE signals, an A/D converter 50 that performs A/D conversion of the AE signals, and a transmitting module (transmitting module) 52 that wirelessly transmits the A/D converted AE signals, and includes a receiving circuit 66 that receives the AE signals transmitted from the transmitting module 52, an integrated intensity value calculation unit 70, an evaluation value calculation unit 72, and a shape deformation determination unit 76, and an electronic control device 62 that processes the AE signals output from the receiving circuit 66. As a result, the AE signal generated by the rotating surface grinding wheel 12 is received by the fixed receiving circuit 66, and the electronic control unit 62 processes the AE signal received by the receiving circuit 66, making it possible to determine if there is any deformation in the end face (grinding surface) 12a of the surface grinding wheel 12. Based on this determination, it is possible to determine when to start dressing the surface grinding wheel 12 at the appropriate time, without the need for skilled personnel.

According to the shape deformation determination device (electronic control device 62) of this embodiment, the flange 26 has an opening on the side opposite to the side on which the surface grinding wheel 12 is fixed, and is equipped with an electronic component storage chamber 30 that houses an outer AE sensor 40, an inner AE sensor 42, an A/D converter 50 that A/D converts the AE signal, and a transmission module 52 that wirelessly transmits the A/D converted AE signal. A cover plate 32 that closes the opening of the electronic component storage chamber 30 is fastened to the flange 26, and a screw hole 38 is provided on the side of the cover plate 32 opposite the flange 26 side, and a balancing weight W for adjusting the rotational balance of the flange 26 is fastened to the screw hole 38 with a fixing bolt 37. As a result, by installing the outer AE sensor 40, inner AE sensor 42, A/D converter 50 that A/D converts the AE signals, and transmission module 52 that wirelessly transmits the A/D converted AE signals, even if the center of gravity of the flange 26 is offset from the center of rotation, the balancing weight W brings the center of gravity of the flange 26 closer to the center of rotation, thereby effectively suppressing rotational vibrations caused by the offset center of gravity.

According to the shape collapse determination device (electronic control device 62) of this embodiment, the cover plate 32 is formed with a rectangular window 33 that allows radio waves transmitted from the transmission module 52 to pass through. This allows the radio waves transmitted from the transmission module 52 to be transmitted through the cover plate 32, even if the cover plate 32 is made of a highly rigid metal.

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, in the above-described embodiment, the double-disc surface grinding machine 10 was a vertical type in which a pair of surface grinding wheels 12 and 14 were provided so that they could rotate relative to each other around a vertical first rotation center line CL1. However, the double-disc surface grinding machine 10 may also be a horizontal type in which a pair of surface grinding wheels 12 and 14 are provided so that they can rotate relative to each other around a horizontal first rotation center line CL1.

Furthermore, while the electronic control device 62 in the above-described embodiment processes the AE signals output from the pair of outer AE sensor 40 and inner AE sensor 42, it may also process the AE signal output from one of the pair of outer AE sensor 40 and inner AE sensor 42.

In addition, the electronic control device 62 in the above-described embodiment calculates the average difference Rav, which represents the amplitude of the waveform, and the moving standard deviation σm of the time waveform of the AE signal intensity Xi as evaluation values based on the waveform indicating the integrated intensity value Xi of the AE signal. However, it may also be possible to calculate one of the average difference Rav or the moving standard deviation σm as an evaluation value, and determine the occurrence of localized shape deformation on the end face (grinding surface) 12a of the surface grinding wheel 12 based on whether that evaluation value exceeds the shape deformation determination threshold SPt or the shape deformation determination threshold σt.

In addition, in the above-described embodiment, 45 to 75 kHz was used as the integral frequency range when calculating the AE signal intensity value Xi from the power spectrum obtained by frequency analysis of the AE signal, but four other integral frequency ranges may also be used: 25 to 45 kHz, 80 to 100 kHz, and 100 to 200 kHz. In other words, any integral frequency range within a specific frequency band within the range of 25 to 200 kHz will suffice.

In addition, in the above-described embodiment, the AE signal intensity value Xi was used, which was obtained by integrating a predetermined frequency range in the power spectrum obtained by frequency analysis of the AE signal. However, the average value or effective value of a signal that has passed through a band-pass filter that passes frequency components in a specific frequency band of the AE signal may be used instead of the AE signal intensity value Xi. In this case, the band-pass filter corresponds to the integrated intensity value calculation unit 70.

In addition, in the above-described embodiment, a disk-shaped carrier 18 was used to move the workpiece 16 along an arc-shaped movement trajectory TR between the end face 12a of the upper surface grinding wheel 12 and the end face 14a of the lower surface grinding wheel 14. However, a linear carrier may also be used to move the workpiece 16 along a linear movement trajectory between the end face 12a of the upper surface grinding wheel 12 and the end face 14a of the lower surface grinding wheel 14.

Furthermore, the surface grinding wheels 12 and 144 in the above-mentioned embodiments may be made of superabrasive grains and general abrasive grains bonded together with various bonds, such as resinoid grinding wheels and vitrified grinding wheels.

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: Double-head surface grinding machine 12: Surface grinding wheel (upper side)
12a: End surface (ground surface)
16: Workpiece 26: Flange 30: Electronic component housing chamber 40: Outer circumference side AE sensor 42: Inner circumference side AE sensor 44: Electronic circuit board 46: Power supply battery 48: Preamplifier 50: A/D converter 52: Transmission module 62: Electronic control device 68: Frequency analysis unit 70: Integrated intensity value calculation unit 72: Evaluation value calculation unit 74: Shape collapse judgment threshold setting unit 76: Shape collapse judgment unit 78: Surface condition display device

Claims (5)

A method for determining shape distortion of a grinding wheel in a grinding process in which an end face of a grinding wheel is brought into sliding contact with a plurality of workpieces as a grinding surface, successively forming flat grinding surfaces on the plurality of workpieces, the method determining local shape distortion within the grinding surface based on an AE signal generated due to contact between the grinding wheel and the workpieces, comprising:
an integrated intensity value calculation step of periodically calculating an integrated value of signal components in a predetermined wavelength band of a power spectrum obtained by frequency analysis of the AE signal generated during the grinding process, and setting the integrated value as an AE signal intensity value ;
an evaluation value calculation step of repeatedly calculating an average value of differences or ratios between maximum and minimum values of the waveform, or an evaluation value representing a moving standard deviation of the waveform, based on a waveform that shows the AE signal intensity values periodically calculated in the integrated intensity value calculation step on a time axis;
and a shape deformation determination process for determining whether shape deformation has occurred on the end face of the grinding wheel based on whether the evaluation value repeatedly calculated by the evaluation value calculation process exceeds a predetermined determination threshold. In a grinding process in which an end face of a grinding wheel is brought into sliding contact as a grinding surface against a plurality of workpieces in succession to continuously form flat grinding surfaces on the plurality of workpieces, a grinding wheel shape deformation determination device is provided for determining local shape deformation within the grinding surface based on an AE signal generated due to contact between the grinding wheel and the workpieces,
an integrated intensity value calculation unit that periodically calculates an integrated value of a signal component in a predetermined wavelength band of a power spectrum obtained by frequency analysis of an AE signal generated during the grinding process, and outputs the calculated value as an AE signal intensity value ;
an evaluation value calculation unit that repeatedly calculates, based on a waveform that shows the AE signal intensity values periodically calculated by the integrated intensity value calculation unit on a time axis , an average value of differences or ratios between maximum values and minimum values of the waveform, or an evaluation value that represents a moving standard deviation of the waveform ;
and a shape deformation determination unit that determines whether shape deformation has occurred on the end face of the grinding wheel based on whether the evaluation value repeatedly calculated by the evaluation value calculation unit exceeds a predetermined determination threshold. The grinding wheel is fixed to a flange that rotates together with the rotating spindle,
The flange is fitted with a pair of outer periphery side AE sensors and an inner periphery side AE sensor which are fixed at different positions in a radial direction of the flange and which output the AE signal, an A/D converter which performs A/D conversion of the AE signal, and a transmission module which wirelessly transmits the A/D converted AE signal,
The grinding wheel shape deformation determination device according to claim 2, further comprising: a receiving circuit for receiving the AE signal transmitted from the transmitting module; and an electronic control device having the integrated intensity value calculation unit, the evaluation value calculation unit, and the shape deformation determination unit, and processing the AE signal output from the receiving circuit. the flange has an opening on a surface opposite to a surface on which the grinding wheel is fixed, and includes an electronic component accommodating chamber for accommodating the outer peripheral side AE sensor and the inner peripheral side AE sensor, an A/D converter for A/D converting the AE signal, and a transmitting module for wirelessly transmitting the A/D converted AE signal;
a cover plate for closing the opening of the electronic component accommodating chamber is fastened to the flange;
A screw hole is provided on the surface of the cover plate opposite to the flange side,
4. The grinding wheel shape deformation detection device according to claim 3 , wherein a balancing weight for adjusting the rotational balance of the flange is fastened to the screw hole. The shape deformation determination device according to claim 4 , wherein the cover plate has a window formed therein for passing radio waves transmitted from the transmitting module.