JP4517677B2 - Grinding equipment - Google Patents

Description

  The present invention relates to a grinding apparatus that can accurately determine the roundness of a workpiece on a machine.

  In general, in grinding a cylindrical workpiece, the roundness is obtained from the dimensions of the grinding part machined during or at the end of machining, and defective products are judged and grinding conditions are determined based on the roundness result. Changes, correction of the cutting amount of the grinding wheel, etc. are performed.

  At that time, in the past, the work piece was once removed from the machine, and the operator carried it to the roundness measuring device outside the machine to measure the roundness, and based on the obtained roundness result, Judgment of good products and creation of correction data were performed.

  However, the method of measuring outside the machine as described above has a problem that the productivity of the machine is lowered because a long time is required for the work.

  Therefore, recently, the sizing device installed on the machine measures the dimensions of the workpiece during or after machining on the machine, and based on the measurement results, calculates roundness and determines defective products. Judgment, creation of correction data, etc. are now performed. As a result, the labor of removing the workpiece from the machine and saving it can be saved, so that it is possible to immediately determine the roundness failure, and the correction data is immediately corrected based on the obtained roundness. The machine productivity is improved.

  However, when measuring the dimensions of a workpiece that has been or has been processed by a sizing device installed on the machine, coolant and fine chips adhering to the workpiece, and disturbances such as vibration and noise due to machine operation Therefore, measurement may not be performed with high accuracy. As a result, the roundness cannot be accurately determined, and there is a possibility that a workpiece which is not defective in roundness is erroneously determined to be defective in roundness, or erroneous correction data is created.

  The object of the present invention is to solve the above-described problems, and to provide a grinding apparatus that can accurately determine the roundness of a workpiece on the machine.

The invention according to claim 1 of the present invention includes a grinding wheel base that supports and rotates the grinding wheel, a main shaft that supports and rotates the workpiece, a feed device that moves the grinding wheel base back and forth, and a grinding wheel Or a sizing device that continuously measures the outer diameter of the workpiece after grinding, while rotating the workpiece, and relatively moving the grinding wheel in a direction approaching and separating from the workpiece. In the grinding apparatus for grinding the workpiece, measurement data storage means for storing measurement data for a plurality of rotations of the workpiece measured by the sizing device, and the stored measurement data for each rotation of the workpiece perform Fourier transform, and the coherence calculation means for calculating a coherence for each order for each one rotation conversion data converted by the Fourier transform was computed by the previous SL coherence calculation means And serial order for each of the coherence of the one rotation and preset the predetermined value compared respectively, the coherence removes converted data of the order of less than a predetermined value, converts the data of the coherence is equal to or larger than a predetermined value order Conversion data averaging means for averaging the plurality of rotations for each order , and normal data calculation for calculating the normal data of the measurement data by performing Fourier inverse transform on the conversion data averaged by the conversion data averaging means means, is characterized in that and a roundness calculating means for calculating a roundness than the normal data created by the normal data producing means.

According to claim 1 of the present invention, the measurement data for a plurality of rotations of the workpiece measured by the sizing device is Fourier-transformed for each rotation, and the coherence is calculated for each order for each rotation data converted. Te, the coherence removes converted data of the order of less than a predetermined value, the coherence is averaged every order for a given value or more of the following number of the plurality rotations conversion data, inverse Fourier the transform data averaged Since the conversion is performed and the regular data of the measurement data is calculated , the reliability of the measurement value is improved, and the roundness of the workpiece can be accurately obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, a work table 12 that is guided and supported so as to be movable in the left-right direction (Z direction) is installed on a bed 11 of a grinding apparatus 10.

  The workpiece table 12 is controlled and driven by a servo motor 50 with an encoder 51 provided on the bed 11, and moves in the Z direction via a Z-axis feed screw device 48. The servo motor 50 is controlled by a drive circuit 39 connected to the numerical control device 30 via the interface 34. The encoder 51 detects the movement position of the workpiece table 12 through the rotation angle of the servo motor 50, and this detected value is input to the numerical controller 30.

  On the workpiece table 12, a headstock 14 and a tailstock 16 that support the spindle 15 are provided coaxially facing each other in the left-right direction, and a workpiece W is provided on the spindle 15 and the tailstock 16. Both ends are supported by the centers 15a and 16a.

  The spindle 15 is rotationally driven by a servo motor 52 with an encoder 53 incorporated in the spindle stock 14, and the workpiece W is rotated together with the spindle 15. The servo motor 52 is controlled by a drive circuit 38 connected to the numerical controller 30 via the interface 34. The encoder 53 detects the rotation angle of the servo motor 52, and this detected value is input to the numerical controller 30.

  A grinding wheel base 13 is guided and supported on the bed 11 so as to be movable in a horizontal X direction perpendicular to the Z direction. A grinding wheel 17 such as a CBN grinding wheel is parallel to the main shaft 15 on the grinding wheel base 13. And is rotationally driven by a motor 18 built in the grinding wheel base 13.

  The grinding wheel base 13 is controlled and driven by a servo motor 54 with an encoder 55 provided on the bed 11 and moves in the X direction via an X-axis feed screw device 49. The servo motor 54 is controlled by a drive circuit 37 connected to the numerical control device 30 via the interface 34. The encoder 55 detects the moving position of the grindstone table 13 through the rotation angle of the servo motor 54, and this detected value is input to the numerical controller 30.

  A sizing device 20 is installed on the workpiece table 12. The sizing device 20 includes a measuring unit 22 having a pair of upper and lower measuring elements 21 for engaging with the outer periphery of the workpiece W. The measurement unit 22 includes a differential transformer (not shown) in its main body, generates a measurement signal (analog signal), and outputs it to the numerical control device 30. The dimension of the workpiece W can be continuously measured by the sizing device 20 having the above configuration. Note that the measuring unit 22 is configured to be movable between a “standby position” and a “measurement position” by a cylinder 23. The “measurement position” is a position at which the outer diameter dimension of the workpiece W is measured, and the “standby position” is the distance from the workpiece W in the X-axis direction by separating the measuring element 21 from the outer periphery of the workpiece W. The position moved in the direction.

  The numerical controller 30 includes a central processing unit (CPU) 31, a memory 32, interfaces 33 and 34, and an AD converter 35. The measurement signal (analog signal) output by the sizing device 20 is converted into a digital signal by the A-D converter 35. Then, based on the measurement data converted into the digital signal, the CPU 31 performs frequency analysis (Fourier transform / Fourier inverse transform) on the workpiece W, which will be described later, coherence, roundness calculation, and the like. The interface 33 is connected to an input device 40 such as a keyboard for inputting control data and the like. The memory 32 stores a machining program for machining the workpiece W, measurement data measured by the sizing device 20, other data, and the like.

  A method for calculating the roundness of the workpiece W in the grinding apparatus 10 having the above configuration will be described with reference to the flowchart of FIG. In the following description, a case where a workpiece after grinding is measured will be described as an example.

  First, when grinding of the workpiece W is completed (step 100), the grindstone table 13 is moved backward, and the sizing device 20 is advanced in the X-axis direction so that the measuring element 21 of the sizing device 20 is the outer periphery of the workpiece W. Contact the surface (step 110). When the tracing stylus 21 of the sizing device 20 is brought into contact, the workpiece W is rotated at a predetermined rotational speed by the spindle 15, sampling measurement data corresponding to the rotational phase of the workpiece W is performed, and the numerical controller 30 It is converted into a digital signal by the A-D converter 35 and stored in the memory 32 (step 120). In the present embodiment, as an example, it is assumed that measurement data for three rotations of the workpiece W is sampled and measurement results as shown in FIGS. 4A, 4B, and 4C are obtained.

4A, 4B, and 4C show measurement data measured at the first rotation of the workpiece (FIG. 4A) and data measured at the second rotation of the workpiece (FIG. 4B). The measurement data (FIG. 4C) measured at the third rotation of the workpiece is shown in polar coordinates. In the following explanation, the measurement data measured at the first rotation of the workpiece is p ₁ (t), the data measured at the second rotation of the workpiece is p ₂ (t), and the measurement data measured at the third rotation of the workpiece. Is p ₃ (t).

  Subsequently, with respect to the measurement data for a plurality of rotations of the workpiece W stored in the memory 32, the measurement data for each rotation number of the workpiece is extracted and subjected to frequency analysis (Fourier transform) (step 130).

That is, in the present embodiment, measurement data p ₁ (t) measured for the first rotation of the workpiece, measurement data p ₁ (t) measured for the first rotation of the workpiece, and data p measured for the second rotation of the workpiece. ₂ (t), extracted for each measurement data p ₃ (t) measured at the third rotation of the workpiece, and Fourier transform is performed on the measurement data for each rotation of the workpiece W.

As a result, each measurement data is converted from data in the time domain to data in the frequency domain, and is represented by a value composed of a real part and an imaginary part with respect to the spatial frequency. Here, a value subjected to Fourier transform at the spatial frequency ω is defined as P (ω), and a value at the spatial frequency ω among values obtained by performing Fourier transform on the data p ₁ (t) measured at the first rotation of the workpiece is defined as P ₁ (ω ), P ₁ (ω) is P ₁ (ω) = a ₁ (ω) + b ₁ (ω) i (Equation 1)
It becomes. Here, a ₁ (ω) represents the real part of P ₁ (ω), and b ₁ (ω) represents the imaginary part of P ₁ (ω). Similarly, when the value in the spatial frequency omega of the workpiece two data measured in th rotation was Fourier transform values and _{P 2 (ω), P 2} (ω) is _{P 2 (ω) = a 2} (ω) + B ₂ (ω) i (Formula 2)
It becomes. Further, if the value measured at the spatial frequency ω among the values obtained by Fourier transform of the data measured at the third rotation of the workpiece is P ₃ (ω), P ₃ (ω) is P ₃ (ω) = a ₃ (ω) + b ₃ (ω) i (Formula 3)
It becomes.

In the following description, the above P ₁ (ω), P ₂ (ω), and P ₃ (ω) will be referred to as conversion data. The spatial frequency ω may be expressed by terms such as the number of peaks or the order, and will be expressed as the order (mount number) ω in the future description.

Subsequently, coherence is obtained for the transformed data obtained by Fourier transform for each rotation of the workpiece W obtained in step 130. (Step 140)
Now, the coherence will be described before proceeding to a specific description of step 140. Coherence is a value representing the degree of correlation between two signals and takes a value between 0 and 1. Now, assuming that the coherence of the output signal y with respect to a certain input signal x is γ, the coherence γ can be expressed by the following (formula 4).

Here, | <S _xy (ω)> _M | represents the M times average cross power spectrum of the input signal x and the output signal y, and <S _xx (ω)> _M is the M times average power of the input signal x. <S _yy (ω)> _M represents a power spectrum of M times average of the output signal y.

For example, when the coherence of an input signal and an output signal is obtained and the coherence becomes 1 at the spatial frequency ω ₁ , this means that the input signal and the output signal are coincident at the spatial frequency ω ₁ . The two signals are correlated in spatial frequency. Further, when the coherence becomes 0 at the spatial frequency ω ₂ , it indicates that the input signal and the output signal do not coincide at all at the spatial frequency ω ₂ , indicating that there is no correlation.

  Therefore, by determining the coherence, it is checked whether or not there is an irrelevant signal (for example, noise generated inside the system, system nonlinearity or system time delay) in the spatial frequency. be able to.

Now, returning to the description of the present embodiment, the calculation of the coherence in step 140 of FIG. 3 will be described in detail with reference to the flowchart of FIG. First, in the present embodiment, for the transformed data P ₁ (ω), P ₂ (ω), and P ₃ (ω) obtained by Fourier transform of the measurement data for the three rotations of the workpiece W obtained in step 130, the work is performed. Coherence γ ₁ (ω) is obtained when P ₂ (ω) and P ₃ (ω) are output with the transformation data P ₁ (ω) obtained by Fourier transform of the measurement data of the first rotation of the object (step 142). . Next, the coherence γ ₂ (ω) is obtained when P ₁ (ω) and P ₃ (ω) are output using the transformation data P ₂ (ω) obtained by Fourier transform of the measurement data of the second rotation of the workpiece. (Step 142). Finally, the coherence γ ₃ (ω) when P ₁ (ω) and P ₂ (ω) are output using the transformation data P ₃ (ω) obtained by Fourier transform of the measurement data of the third rotation of the workpiece as input. Is obtained (step 143). Then, Step 141 to Step 143 are performed for all orders.

FIG. 6 shows the results of coherences γ ₁ (ω), γ ₂ (ω), and γ ₃ (ω) calculated in step 140. FIG. 6 shows the results of obtaining coherence up to the twentieth order with the coherence on the vertical axis and the order (the number of peaks) on the horizontal axis. As shown in FIG. 6, it can be seen that the coherences γ ₁ (ω), γ ₂ (ω), and γ ₃ (ω) are rapidly decreased after the third order.

In the next step, a predetermined value is provided for the coherences γ ₁ (ω), γ ₂ (ω), and γ ₃ (ω) obtained in step 140, and the input side of the coherence having a coherence value equal to or larger than the predetermined value is set. A process of averaging the converted data is performed (step 150).

The details of step 150 in FIG. 3 will be described in detail with reference to the flowchart in FIG. First, for the order ω, it is determined whether or not the coherences γ ₁ (ω), γ ₂ (ω), and γ ₃ (ω) are each equal to or greater than a predetermined value (steps 152 to 154). Here, the predetermined value is set to 0.95, but this value can be set arbitrarily. Then, the conversion data on the input side is averaged for those having a coherence value of 0.95 or more.

For example, when all values of coherences γ1 (ω), γ2 (ω), and γ3 (ω) are 0.95 or more at the order ω, conversion data P1 (ω), P2 (ω), P3 Average (ω). When the coherence γ1 (ω) is less than 0.95 and the coherence γ2 (ω) and γ3 (ω) are 0.95 or more, the conversion data P1 (ω) is removed and the conversion data P2 ( ω) and P3 (ω) are averaged.

In this embodiment, as shown in FIG. 6, coherences γ1 (ω), γ2 (ω), and γ3 (ω) are all 0.95 or more for the second and third orders, but 0 for the fourth and subsequent orders. Since it is less than .95, the Fourier transforms P1 (ω), P2 (ω), and P3 (ω) in the second and third orders are averaged, and the signals after the fourth order are not correlated. Remove. In the following description, the averaged conversion data is assumed to be Pt (ω).

Subsequently, the inverse Fourier transform is performed on the converted data Pt (ω) averaged in step 150 (step 160). As a result, a value converted from frequency domain to time domain data is obtained. Note that this inverse Fourier transformed value is referred to as p _a (t), and in the following description, _pa (t) will be referred to as normal data. Thereafter, normal data p _{a (t)} of calculate the roundness based on (step 170), the creation of the determination and correction data of defective products is performed.

  The results processed from step 100 to step 170 are shown in FIG. FIG. 8 shows a result (a) of measuring the workpiece of the present embodiment with a roundness measuring device outside the machine and all data p (t) of the workpiece W measured on the machine for each phase. The averaged result (b) and the result (c) obtained by performing the processing from step 130 to step 170 on all data p (t) measured on the machine are shown in polar coordinates.

First, as shown in FIG. 8 (b), before performing the processing from step 130 to step 170 of the present invention, such as coolant and vibration due to adhesion of coolant and fine chips, dust in the atmosphere and machine operation, noise, etc. It can be seen that due to the influence of the disturbance, the workpiece cannot be measured with high accuracy compared to FIG. 8A measured outside the machine.
However, as shown in FIG. 8 (c), it can be seen that by performing the processing according to the present invention, a result substantially the same as the result of FIG. 8 (a) measured by the roundness measuring device outside the machine is obtained.

  Based on the above results, even when measurement data contains data with low reliability, the coherence is obtained from the measurement data, and only data with higher reliability than the result of coherence is used, and data with low reliability is removed. By doing so, the reliability of measurement data becomes high and the roundness of the workpiece W can be calculated | required correctly.

  In this embodiment, the roundness of the workpiece after grinding is obtained. However, the present invention is not limited to this. For example, the roundness of the workpiece during grinding may be measured.

The figure which shows the top view of the grinding apparatus of this invention. The figure which shows the side view of the grinding apparatus of this invention. The figure which shows the flowchart of this invention. The figure which shows the measurement data measured at step 120 The figure which shows the detail of the flowchart of this invention. Diagram showing the calculation result of coherence The figure which shows the detail of the flowchart of this invention. The figure which shows the result of having measured the workpiece outside and on the machine.

Explanation of symbols

10: Grinding device 20: Sizing device 30: Numerical control device γ ₁ (ω), γ ₂ (ω), γ ₃ (ω): Coherence in order ω W: Workpiece

Claims (1)

A grinding wheel base that supports and rotates the grinding wheel, a spindle that rotates and supports the workpiece, a feed device that moves the grinding wheel table back and forth, and an outer diameter of the workpiece during or after grinding. A sizing device for continuously measuring the workpiece while rotating the workpiece, and grinding the workpiece by relatively moving the grinding wheel in a direction approaching and separating from the workpiece,
Measurement data storage means for storing measurement data for a plurality of rotations of the workpiece measured by the sizing device;
A coherence calculating means for performing a Fourier transform on the stored measurement data for each rotation of the workpiece, and calculating a coherence for each degree of the converted data for each rotation converted by the Fourier transform;
Compared before Symbol coherence of each order of each one rotation calculated by the coherence calculation means preset with a predetermined value, respectively, the coherence removes converted data of the order of less than a predetermined value, a predetermined coherence Conversion data averaging means for averaging the conversion data of the order equal to or greater than a value for each order for the plurality of rotations ;
Normal data calculating means for performing inverse Fourier transform on the converted data averaged by the converted data averaging means and calculating normal data of the measurement data;
Grinding apparatus being characterized in that and a roundness calculating means for calculating a roundness than the normal data created by the normal data producing means.

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