Method and device for determining shape distortion of grinding wheel

Abstract

To provide a device for determining shape-collapse of a grinding stone, which can make an increase of local grinding resistance in a specific portion in a grinding surface of the grinding stone, or an increase of local shape-collapse.SOLUTION: An evaluation value calculating part 72 calculates, as an evaluation value, an average value Rav of differences showing amplitude of waveforms, on the basis of waveforms indicating integrated strength values Xi of an AE signal calculated by an integrated strength value calculating part 70, and a shape-collapse determining part 76 determines occurrence of local shape-collapse in an end face 12a of a flat grinding stone 12, on the basis of the fact that the average value Rav of differences R calculated by the evaluation value calculating part 70 exceeds a shape-collapse determination threshold SPt for differences. This can determine local shape-collapse in the end face 12a of the flat grinding stone 12, which enables starting of dressing of the flat grinding stone 12 to be determined at an appropriate timing, without requiring skill.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and device for determining shape distortion of a grinding wheel, which determines shape distortion of a grinding wheel having a flat grinding surface at its end face that is brought into sliding contact with a workpiece during surface grinding. [Background technology]

[0002] 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. While 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, it is difficult to detect deformation during grinding and determine when dressing should begin. Therefore, dressing intervals are often set with sufficient margin, which reduces the lifespan of the grinding wheel.

[0003] 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 value 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 dressing of the grinding wheel is necessary based on the increase in the grinding resistance of the grinding wheel reaching a predetermined level, without having to stop the grinding process using the grinding machine. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-053699 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the conventional shape deformation determination device detects the shape deformation of the entire grinding surface of the grinding wheel based on the increase in grinding load on the entire grinding surface of the rotating grinding wheel, it was not possible to detect local shape deformation at a specific location on the grinding surface of the grinding wheel.As a result, it was not possible to determine the appropriate timing to start dressing (truing) to correct the local shape deformation on the grinding surface in a grinding process in which multiple workpieces are surface ground using the end face of the grinding wheel as the grinding surface, for example, in a grinding process using a double-disc surface grinder.

[0006] The present invention has been 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 local shape deformation at a specific location on the grinding surface of the grinding wheel. [Means for solving the problem]

[0007] The inventors of the present invention have conducted extensive research in light of the above circumstances. As a result, they have noticed that in a grinding process in which a flat end face of a grinding wheel is used as the grinding surface to sequentially surface-grind multiple workpieces, the amplitude of the integrated intensity value waveform of an AE signal (high-frequency vibration or ultrasonic vibration) generated by contact with the workpiece during the grinding process increases over time, and have found that it is possible to determine shape deformation at a specific location on the grinding surface based on an evaluation value indicating an increase in the amplitude of the integrated intensity value waveform of the AE signal exceeding a predetermined judgment threshold value on the grinding surface, and that it is possible to determine, based on this judgment, the start of dressing of the grinding wheel at an appropriate timing. The present invention was made based on this finding.

[0008] That is, the gist of the first invention is (a) a method for determining shape deformation 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 deformation within the grinding surface based on an AE signal generated due to contact between the grinding wheel and the workpieces, and (b) an AE signal generated during the grinding process. The integrated value of the signal component in a predetermined wavelength band of the power spectrum obtained by frequency analysis is periodically calculated, and the AE signal intensity value is calculated.(c) calculating an integrated intensity value by the integrated intensity value calculation step; Periodically The calculated AE signal strong name Degree value On the time axis Show did Based on the waveform, The average value of the difference or ratio between the maximum and minimum values, or the moving standard deviation of the waveform The evaluation value that represents repetition (d) calculating an evaluation value by the evaluation value calculation step; repetition The calculated evaluation The value is and a shape deformation determination step of determining whether a shape deformation has occurred on the end face of the grinding wheel based on whether a preset determination threshold value has been exceeded.

[0009] The gist of the second invention is (a) a grinding wheel shape deformation determination device that determines 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 successively form flat grinding surfaces on the plurality of workpieces, and (b) an AE signal generated during the grinding process. The integrated value of the signal component in a specified wavelength band of the power spectrum obtained by frequency analysis is periodically calculated and output as the AE signal intensity value. (c) an integrated intensity value calculation unit for calculating an integrated intensity value by the integrated intensity value calculation unit; Periodically The calculated AE signal strong name Degree value On the time axis Show did Based on the waveform, The average value of the difference or ratio between the maximum and minimum values, or the moving standard deviation of the waveform The evaluation value that represents repetition (d) an evaluation value calculation unit that calculates an evaluation value by the evaluation value calculation unit; repetition The calculated evaluation The value is and a shape deformation determining unit that determines whether a shape deformation has occurred on the end face of the grinding wheel based on whether a preset determination threshold value has been exceeded.

[0012] No. 3 The gist of the invention is the second ClearlyIn the grinding wheel, 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 signal, an A / D converter that performs A / D conversion of the AE signal, and a transmission module that wirelessly transmits the A / D converted AE signal, and the grinding wheel is fixed to a flange that rotates together with the rotating spindle, and the grinding wheel is fixed to a flange that rotates together with the rotating spindle, and the flange is equipped with a receiving circuit that receives the AE signal 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 signal output from the receiving circuit.

[0013] No. 4 The gist of the invention is 3 In the invention, the flange has an electronic component accommodating chamber that opens on the surface opposite to the surface to 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 performs A / D conversion of the AE signal, and a transmitting module that wirelessly transmits the A / D converted AE signal, and a cover plate that closes the opening of the electronic component accommodating chamber is fastened to the flange, and a screw hole is formed in 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.

[0014] No. 5 The gist of the invention is 4 In the present invention, the cover plate is formed with a window through which radio waves transmitted from the transmission module pass. [Effects of the Invention]

[0015] According to the method for determining shape deformation of a grinding wheel of the first invention, in the evaluation value calculation step, Periodically The calculated AE signal strong name Degree value On the time axis Show did Based on the waveform, The average value of the difference or ratio between the maximum and minimum values, or the moving standard deviation of the waveform The evaluation value represents repetition In the shape collapse determination step, the evaluation value is calculated. repetitionThe calculated evaluation The value is The occurrence of localized deformation on the end face of the grinding wheel is determined based on whether a preset threshold value has been exceeded. This makes it possible to determine 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.

[0016] According to the grinding wheel shape deformation determination device of the second invention, the evaluation value calculation unit calculates the integrated strength value by Periodically The calculated AE signal strong name Based on the waveform indicating the degree value, The average value of the difference or ratio between the maximum and minimum values, or the moving standard deviation of the waveform The evaluation value represents repetition The shape deformation determination unit calculates the evaluation value. repetition The calculated evaluation The value is The occurrence of localized deformation on the end face of the grinding wheel is determined based on whether a preset threshold value has been exceeded. This makes it possible to determine 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.

[0019] No. 3According to the grinding wheel shape deformation detection device of the present invention, the grinding wheel is fixed to a flange that rotates together with a rotating spindle, and the flange is equipped with a pair of outer AE sensors and inner AE sensors fixed at different radial positions on the flange and outputting 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 detect shape deformation at a specific location on the grinding surface, and based on this detection, it is possible to determine when to start dressing the grinding wheel at an appropriate time without requiring skill.

[0020] No. 4 According to the grinding wheel shape deformation detection device 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, a cover plate that closes the opening of the electronic component housing chamber is fastened to the flange, a surface of the cover plate opposite to the flange side is provided with threaded holes, and balancing weights for adjusting 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.

[0021] No. 5According to the grinding wheel shape deformation detection device 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 can be transmitted through the cover plate. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating the configuration of a double-disc surface grinding machine according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view briefly explaining the main parts of the double-disc surface grinding machine of FIG. 1. [Figure 3] FIG. 2 is a diagram showing an electronic component accommodating chamber formed on one side of the flange to which the surface grinding wheel in FIG. 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 accommodating chamber. [Figure 4] FIG. 4 is a cross-sectional view illustrating in detail a flange to which the surface grinding wheel of FIG. 3 is attached. [Figure 5] 4 is a view showing a cover plate that closes an opening of an electronic component housing chamber formed on one surface of the flange of FIG. 3. FIG. [Figure 6] 6 is a diagram illustrating a fixing device that detachably fixes the balancing weight W to the cover plate of FIG. 5. FIG. [Figure 7] 2A and 2B are diagrams illustrating the configuration of an electronic circuit board mounted on a flange 26. FIG. [Figure 8] 2 is a flowchart illustrating a main part of the control operation of the electronic control device of FIG. 1. [Figure 9] 10 is a flowchart illustrating a main part of another control operation of the electronic control device of FIG. [Figure 10] 3 is a schematic plan view illustrating an overlapping structure between an upper surface grinding wheel and 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. [Figure 11] 3 is a diagram showing the surface shapes along the movement trajectories 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. [Figure 12] 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 with a grinding volume of 200 cm3 using the double-disc surface grinding machines of FIGS. 1 and 2. [Figure 13] 3 is a schematic diagram illustrating the interval between a pair of surface grinding wheels along the movement trajectory of the workpiece on the double-disc surface grinding machine of FIG. 2 at the beginning of grinding. FIG. [Figure 14] 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. [Figure 15] FIG. 10 is a diagram showing the time-axis waveform of the AE signal intensity obtained from the outer periphery side AE ​​sensor. [Figure 16] 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. FIG. [Figure 17] FIG. 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 intensity obtained from the inner circumference side AE ​​sensor. [Figure 18] 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 in FIG. 16, together with the cumulative correction amount of the gap between a pair of surface grinding wheels. [Figure 19] 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 in FIG. 17, together with the cumulative correction amount of the gap between a pair of surface grinding wheels. [Figure 20] 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. [Figure 21] 10 is a diagram showing the time change of the moving standard deviation (evaluation value) of the time-axis waveform of the AE signal intensity 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. [Figure 22] 10A and 10B are diagrams showing the time change of the moving standard deviation Rm during grinding obtained for waveforms showing AE signal intensity values ​​in four integral frequency ranges from the AE signal obtained from the outer periphery side AE ​​sensor. DETAILED DESCRIPTION OF THE INVENTION

[0023] An embodiment of the present invention will be described in detail below with reference to the drawings. Note that the drawings in the following embodiment are for explaining the essential parts related to the invention, and the dimensions and shapes are not necessarily drawn accurately. [Example]

[0024] 1, a double-disc surface grinding machine 10 is equipped with a pair of opposing surface grinding wheels 12 and 14 that are rotatable relative to one another, and grinds both sides of a circular workpiece 16, made of, for example, hardened steel, into a flat surface while the workpiece is clamped and pressed between flat end faces 12a and 14a of the surface grinding wheels 12 and 14. The end faces 12a and 14a function as 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.

[0025] 2 is a perspective view showing the surface grinding wheels 12 and 14 and a carrier 18 that transports a circular workpiece 16 between the flat end faces of the surface grinding wheels 12 and 14. The carrier 18 is a disk with circular transport holes 20 that are equally spaced around the periphery and into which the circular workpiece 16 is fitted, and is driven to rotate by a work feed motor 54 (described later) about a second rotation center line CL2 that is parallel to a first rotation center line CL1 that is perpendicular to the surface grinding wheels 12 and 14.

[0026] The back surfaces of the surface grinding wheels 12 and 14 are brought into close contact with thick, circular flanges 26 and 28 shown in FIG. 3, which rotate integrally with a pair of main shafts 22 and 24 that are provided concentrically but independently on the double-head surface grinding machine 10. As shown in FIG. 4, the surface grinding wheels 12 and 14 are fixed to the flanges 26 and 28 using fastening bolts (not shown) that are threaded through through holes 27 (see FIG. 3) into nuts (not shown) embedded in the surface grinding wheels 12 and 14.

[0027] 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 pressed against 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 position of an electronic circuit board 44 including a transmitting module 52, allowing radio waves to be transmitted from the transmitting module 52 to the outside. Additionally, a plurality of screw holes 38 are formed at regular intervals around the periphery of the cover plate 32 on the side opposite the surface grinding wheel 12. A fixing bolt 39 for fixing a balancing weight W for adjusting the rotational balance of the flange 26 shown in FIG. 6 is fastened to the screw hole 38.

[0028] 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 disposed within the electronic component housing chamber 30 formed in the flange 26. As shown in Fig. 7, the electronic circuit board 44 is equipped with 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.

[0029] The outer periphery-side AE ​​sensor 40 and the inner periphery-side AE ​​sensor 42 are disposed at different radial positions along one radial direction of the flange 26. The outer periphery-side AE ​​sensor 40 is disposed at a position that is 80% or more, preferably 90%, of the radius of the flange 26 from the rotation axis CL of the flange 26 toward the outer periphery, while the inner periphery-side AE ​​sensor 42 is disposed at a position that is 35% or more and 50% or less, preferably about 40%, of the radius of the flange 26 from the rotation axis CL of the flange 26 toward the outer periphery.

[0030] 1, the double-disc surface grinding machine 10 is equipped with a motor drive control device 60 that drives a workpiece feed motor 54, a grinding wheel rotation drive motor 56 that rotates the upper surface grinding wheel 12, and a grinding wheel rotation drive motor 58 that rotates the lower surface grinding wheel 14, and 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 that determines deformation of the end face (grinding surface) 12a of the surface grinding wheel 12 based on AE signals from the outer periphery side AE ​​sensor 40 and the inner periphery side 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 has 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.

[0031] The electronic control device 62 is a so-called microcomputer including a CPU, ROM, RAM, an interface, etc., and the CPU, utilizing the temporary storage function of the RAM, rotates the surface grinding wheels 12 and 14 in accordance with a program previously stored in the ROM, and also 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 so as 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, determining whether there is any local shape deformation, mainly 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.

[0032] 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 deformation determination threshold setting unit 74, and a shape deformation determination unit 76.

[0033] The frequency analysis unit 68 corresponds to the frequency analysis step, and performs frequency analysis (FFT) of the A / D converted AE signal SAE during grinding of the grinding wheels 12, 14, to generate 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 corresponds to the integrated intensity value calculation step, and discriminates signal components of the AE signal SAE in a frequency band that sensitively reflects contact vibration between the surface grinding wheel 12 and the workpiece 16 during grinding, for example, a wavelength band of 25 kHz to 200 kHz, preferably a wavelength band of 45 to 75 kHz, and outputs the integral value (area value) of the signal components as the AE signal intensity value Xi. The frequency analysis period and the integrated intensity value calculation period (period) are set to a time that is equal to or less than half the passage time Δt of the workpiece 16 along the arc-shaped movement locus TR in Fig. 10 between the upper surface grinding wheel 12 and the lower surface grinding wheel 14. 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.

[0034] The evaluation value calculation unit 72 corresponds to the evaluation value calculation step, and sequentially obtains, from the time waveform of the AE signal intensity value Xi, the intra-subsection difference R (=SPmax-SPmin) between the maximum value SPmax and the minimum value SPmin within a subsection set in advance of about several ms to tens of ms, and repeatedly calculates, for each evaluation value calculation section set in advance of, for example, about 20 s (seconds), the average value Rav (R1+R2+··+Rn / n) of the differences R1 to Rn for each subsection as an evaluation value for evaluating shape deformation, where n represents the number of subsections.

[0035] Furthermore, for each moving evaluation value calculation section set in advance to, for example, several seconds to several tens of seconds in the time waveform of the AE signal intensity Xi, the evaluation value calculation unit 72 calculates the moving standard deviation σm [=√(1 / n)Σ(SP1-SPav) 2 ] (where SPav is the interval average, and SP1 is the standard deviation) is repeatedly calculated as an evaluation value for evaluating shape deformation.

[0036] The shape deformation judgment threshold setting unit 74 corresponds to the shape deformation judgment threshold setting process, and automatically or by manual input sets a difference shape deformation judgment threshold SPt and a standard deviation shape deformation judgment threshold σt for judging shape deformation based on the evaluation values ​​(average difference Rav and moving standard deviation σm) when the local shape deformation of 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 from a surface grinding test previously performed using the double-head surface grinding machine 10.

[0037] The shape-deformation determination unit 76 corresponds to the shape-deformation determination step, and determines local shape deformation of the end face (grinding surface) 12a of the surface grinding wheel 12 based on the fact that the average value ΔRav of the small-area differences ΔR calculated by the evaluation value calculation unit 72 exceeds a difference-use shape-deformation determination threshold SPt, for example, shown in Figure 18 or 19, and that the end face (grinding surface) 12a has reached a predetermined size that requires dressing for shape correction. The shape-deformation determination unit 76 determines local shape deformation of the end face (grinding surface) 12a of the surface grinding wheel 12 based on the fact that the moving standard deviation σm for each evaluation value calculation section calculated by the evaluation value calculation unit 72 exceeds a standard deviation-use shape-deformation determination threshold σt, for example, shown in Figure 20 or 21. Alternatively, the shape deformation determination unit 76 determines that local shape deformation of the end face (grinding surface) 12a of the surface grinding wheel 12 has reached a predetermined size that requires dressing for correcting 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 has exceeded the difference shape deformation determination threshold SPt and the moving standard deviation σm for each section calculated by the evaluation value calculation unit 72 has exceeded the standard deviation shape deformation determination threshold σt. When the shape deformation determination unit 76 determines that the shape deformation 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.

[0038] 8 is a flowchart illustrating the main control operations of the electronic control device 62. In FIG. 8, in step S1 (hereinafter, "step" will be omitted), which corresponds to the shape-deformation determination threshold setting step or shape-deformation determination threshold setting unit 74, a pre-entered difference shape-deformation determination threshold SPt is read. In the following step S2, the AE signal SAE during grinding is read. Next, in step S3, which corresponds to the frequency analysis step or frequency analysis unit 68, frequency analysis is performed on the AE signal SAE, and a power spectrum is generated in which various signal powers indicating the magnitude of frequency components are plotted 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.

[0039] Next, in S4 corresponding to the integrated intensity value calculation step or the 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.

[0040] Next, S6 and S7 corresponding to the evaluation value calculation step or the 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 about several ms to 10 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, for example, about 20 s (seconds), 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.

[0041] Then, S8 and S9 corresponding to the shape deformation determination step or the shape deformation determination unit 76 are executed. In S8, it is determined whether the average value Rav of the small section differences R exceeds the difference shape deformation determination threshold value SPt. If the determination in S8 is negative, S2 and the following steps are repeatedly executed. However, if the determination in S8 is positive, it is determined in S9 that shape deformation of such magnitude that dressing for correcting 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 suggests that dressing needs to be started.

[0042] Fig. 9 is a flowchart illustrating other essential control operations of the electronic control device 62. In Fig. 9, steps S11 to S14 are the same as steps S1 to S4 in Fig. 8, and therefore their explanation will be omitted.

[0043] In S15 corresponding to the evaluation value calculation step or the evaluation value calculation unit 72, for each moving evaluation value calculation section set in advance, for example, from several seconds to several tens of seconds, of the time waveform of the AE signal intensity Xi, the moving standard deviation σm [=√(1 / n)Σ(SP1-SPav) 2 ] (where SPav is the interval average) is repeatedly calculated as an evaluation value for evaluating shape deformation.

[0044] In S16, which corresponds to the shape deformation determination step or the shape deformation determination unit 76, it is determined whether the moving standard deviation σn for each evaluation value calculation section exceeds the shape deformation determination threshold value σt for standard deviation. 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 for correcting the shape of the end face (grinding surface) 12a has occurred, and an alert indicating the occurrence of shape deformation is output on the surface condition display device 78. This alert suggests that dressing needs to be started.

[0045] The following describes shape deformation 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 in the circumferential direction in a sliding contact state between the upper surface grinding wheel 12 and the lower surface grinding wheel 14. 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 before grinding, along the arc-shaped movement locus TR of the workpiece 16, and the grinding volume of 200 cm3. 3 The surface profile after grinding is shown as a waveform measured using a stylus-type surface profile measuring device. In Figures 11 and 12, the horizontal axis represents the distance X (mm) of the movement path 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) from the exit, with 0 mm representing the position.

[0046] 13 is a schematic diagram showing 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, but from the center to the exit of the movement trajectory of the workpiece 16, it is linearly inclined 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.

[0047] Similar to FIG. 13 , FIG. 14 shows the surface profiles 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 path of movement 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 depth-of-cut 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 path of movement of the workpiece 16 are worn, while the application of the depth-of-cut correction value Th causes the entrance width of the path of movement of the workpiece 16 to shrink 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 entrance becomes greater. Therefore, dressing is performed to restore the shape to the pre-grinding shape shown in FIGS. 11 and 13 . An accumulated cutting-in correction amount AA in FIGS. 18 to 21 described later is an accumulated value of the cutting-in correction value Th.

[0048] The inventors conducted a surface grinding test under the following experimental conditions, and the results obtained will now be described. (Surface grinding test conditions) Machine: Vertical axis double-head surface grinder, carrier-through type Surface grinding wheel: WA / HA 80 H 12 Grindstone outer diameter: 585mmφ Grinding wheel spindle 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 times) Dresser: 1.0mm LL needle dresser with embedded diamonds 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 standard deviation data length): 2 seconds Moving average data length: 20 seconds Data pitch (small interval) of moving maximum / minimum values ​​and moving average values: 65 ms

[0049] FIG. 15 shows the continuous waveform of the AE signal integrated intensity Xi obtained from the outer AE sensor 40 during the surface grinding test. FIG. 16 shows the envelopes of the maximum and minimum values ​​of FIG. 15. FIG. 17 shows the envelopes of the maximum and minimum values ​​of the continuous waveform of the AE signal integrated intensity Xi obtained from the inner AE sensor 42. FIG. 18 shows 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 FIG. 16. FIG. 19 shows 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 FIG. 17. As shown in FIGS. 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. 18 and 19 show the cumulative cutting-in correction amount that is automatically or manually applied to bring the thickness dimension of the workpiece after surface grinding into the tolerance range.

[0050] 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 the 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.

[0051] In the above grinding test, the integral frequency range used when determining the AE signal intensity value Xi from the power spectrum obtained by frequency analysis of the AE signal was 45 to 75 kHz, but 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, and calculated the moving average value ΔRav of the differences and the moving standard deviation Rm from the waveforms of the AE signal intensity values ​​Xi. Figure 22 shows the time change in the moving standard deviation Rm during grinding determined for the waveforms showing the AE signal intensity values ​​in the four integral frequency ranges.

[0052] In Figure 22, the moving standard deviation Rm increases as the 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 becomes larger in the integral frequency range of 80 to 100 kHz, the integral frequency range of 25 to 45 kHz, the integral frequency range of 100 to 200 kHz, and the integral frequency range of 45 to 75 kHz, in that order, clearly indicating shape deformation.

[0053] As described above, in the shape-deformation determination device (electronic control device 62) of this embodiment, the evaluation value calculation unit 72, which corresponds to the evaluation value calculation step, calculates the average difference Rav 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, which corresponds to the integrated intensity value calculation step. The shape-deformation determination unit 76, which corresponds to the shape-deformation determination step, determines the occurrence of local shape deformation on the end face (grinding surface) 12a of the surface grinding wheel 12 based on the average difference Rav calculated by the evaluation value calculation unit 72 exceeding the difference-use shape-deformation determination threshold SPt and / or the moving standard deviation σn exceeding the standard deviation-use shape-deformation determination threshold σt. This makes it possible to determine the local shape deformation on the end face (grinding surface) 12a of the surface grinding wheel 12, and based on this determination, it is possible to determine the start of dressing of the surface grinding wheel 12 at an appropriate time without requiring skill.

[0054] Furthermore, according to the shape deformation determination device (electronic control device 62) of this embodiment, the grinding wheel 12 is fixed to the flange 26 which rotates together with the rotating spindle 22, and the flange 26 is equipped with a pair of outer periphery AE sensors 40 and inner periphery AE sensors 42 which are fixed at different radial positions on the flange 26 and output AE signals, an A / D converter 50 which performs A / D conversion of the AE signals, and a transmitting module (transmitting module) 52 which transmits the A / D converted AE signals wirelessly, and includes a receiving circuit 66 which receives the AE signals transmitted from the transmitting module 52, an integrated intensity value calculation unit 70, an evaluation value calculation unit 72, a shape deformation determination unit 76, and an electronic control device 62 which 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 a fixed receiving circuit 66, and the electronic control device 62 processes the AE signal received by the receiving circuit 66, thereby making it possible to determine any deformation of the shape within the end face (grinding surface) 12a of the surface grinding wheel 12, and from that determination, it is possible to determine when to start dressing the surface grinding wheel 12 at an appropriate time without requiring any skill.

[0055] According to the shape deformation determination device (electronic control device 62) of this embodiment, the flange 26 has an opening on the surface opposite to the surface on which the surface grinding wheel 12 is fixed, and is equipped with an electronic component storage chamber 30 that houses an outer periphery side AE ​​sensor 40 and an inner periphery side AE ​​sensor 42, an A / D converter 50 that performs A / D conversion of the AE signal, and a transmission module 52 that wirelessly transmits the A / D converted AE signal, and 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 surface of the cover plate 32 opposite to 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 periphery side AE ​​sensor 40, the inner periphery side AE ​​sensor 42, the A / D converter 50 that performs A / D conversion of the AE signals, and the 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, and therefore rotational vibration due to the offset center of gravity is suitably suppressed.

[0056] 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 the radio waves transmitted from the transmission module 52 to pass through. As a result, even if the cover plate 32 is made of a highly rigid metal, the radio waves transmitted from the transmission module 52 are transmitted through the cover plate 32.

[0057] Although one embodiment of the present invention has been described above with reference to the drawings, the present invention can also be applied to other embodiments.

[0058] For example, in the above-described embodiment, the double-head surface grinding machine 10 is a vertical type in which a pair of surface grinding wheels 12 and 14 are provided so as to be rotatable relative to each other around the vertical first rotation center line CL1. However, the double-head surface grinding machine 10 may also be a horizontal type in which a pair of surface grinding wheels 12 and 14 are provided so as to be rotatable relative to each other around the horizontal first rotation center line CL1.

[0059] Furthermore, 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, but it may also process the AE signal output from one of the pair of outer AE sensor 40 and inner AE sensor 42.

[0060] Furthermore, the electronic control device 62 in the above-described embodiment calculates, as evaluation values, the average value Rav of the difference representing the amplitude of the waveform and the moving standard deviation σm of the time waveform of the AE signal intensity Xi based on the waveform showing the integrated intensity value Xi of the AE signal. However, it may also be configured to calculate either the average value Rav of the difference or the moving standard deviation σm as an evaluation value, and determine the occurrence of local shape deformation on the end face (grinding surface) 12a of the surface grinding wheel 12 based on whether the evaluation value exceeds the shape deformation judgment threshold SPt or the shape deformation judgment threshold σt.

[0061] In the above-described embodiment, the integral frequency range used when determining the AE signal intensity value Xi from the power spectrum obtained by frequency analysis of the AE signal is 45 to 75 kHz, but four other integral frequency ranges, 25 to 45 kHz, 80 to 100 kHz, and 100 to 200 kHz, may also be used. In short, any integral frequency range within a specific frequency band within the range of 25 to 200 kHz may be used.

[0062] In the above-described embodiment, the AE signal intensity value Xi is obtained by integrating a predetermined frequency range in the power spectrum obtained by frequency analysis of the AE signal, but 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.

[0063] Furthermore, in the above-described embodiment, a disk-shaped carrier 18 is used to move the workpiece 16 along an arc-shaped movement locus 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, but a linear carrier may also be used to move the workpiece 16 along a linear movement locus between the end face 12a of the upper surface grinding wheel 12 and the end face 14a of the lower surface grinding wheel 14.

[0064] Furthermore, the surface grinding wheels 12, 144 of the above-described 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.

[0065] It should be noted that the above is merely one embodiment of the present invention, and various modifications can be made to the present invention without departing from the spirit of the present invention. [Explanation of symbols]

[0066] 10: Double-head surface grinder 12: Surface grinding wheel (upper) 12a: End face (ground surface) 16: Work material 26: Flange 30: Electronic parts storage room 40: Outer AE sensor 42: Inner circumference AE sensor 44: Electronic circuit board 46: Power battery 48: Preamplifier 50: A / D converter 52: Transmitting module 62: Electronic control device 68: Frequency analysis section 70: Integrated intensity value calculation unit 72: Evaluation value calculation unit 74: Threshold setting unit for determining shape distortion 76: Shape collapse judgment unit 78: Surface status display device

Claims

1. 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 step of determining whether or not the evaluation value repeatedly calculated in the evaluation value calculation step exceeds a predetermined determination threshold value. A method for determining shape deformation of a grinding wheel.

2. 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 the evaluation value repeatedly calculated by the evaluation value calculation unit exceeds a predetermined determination threshold value, and determines whether the end face of the grinding wheel has been deformed. A device for determining shape deformation of a grinding wheel.

3. 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, 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 for processing the AE signal output from the receiving circuit.

3. The device for determining shape deformation of a grinding wheel according to claim 2.

4. 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, Balancing weights for adjusting the rotational balance of the flange are fastened to the screw holes.

4. The device for determining deformation of a grinding wheel according to claim 3.

5. The cover plate has a window formed therein for passing radio waves transmitted from the transmission module.

5. The shape collapse determination device according to claim 4.

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