JP5807437B2 - Chatter vibration detector - Google Patents

Description

  The present invention relates to a chatter vibration detection apparatus that detects chatter vibration generated when a workpiece is machined using a machine tool.

  As a chatter vibration detection device, chatter vibration in a predetermined frequency band occurs when the magnitude of vibration in a predetermined frequency band exceeds a reference value and the degree of change in vibration speed within a certain time exceeds the reference value. (For example, refer to Patent Document 1).

JP 2000-233368 A

In the conventional technology, since the determination condition is to compare the magnitude of vibration in a predetermined frequency band with a reference value, a predetermined frequency band in which chatter vibration may occur is set according to the combination of tools and workpieces. Furthermore, it is necessary to set an appropriate reference value for each frequency band. Even in the same tool, the vibration situation varies depending on the change in sharpness due to wear of the tool, so it is complicated and difficult to set an appropriate reference value in any state of all tools. For this reason, the occurrence of chatter vibration may not be detected when an appropriate reference value cannot be set.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a chatter vibration detection apparatus capable of reliably detecting simple chatter vibration.

A feature of the invention according to claim 1 for solving the above-described problem is a chatter vibration detection device that detects the occurrence of chatter vibration that occurs when a workpiece is machined using a tool,
Vibration measuring means for measuring the first vibration of the machine tool and the second vibration after a predetermined time from the measurement of the first vibration;
Power spectrum calculation means for performing a Fourier analysis of the time domain of the vibration and calculating a power spectrum that is a magnitude of vibration in a constant frequency band of a desired frequency domain;
Recording means for recording a first power spectrum that is a power spectrum of the first vibration and a second power spectrum that is a power spectrum of the second vibration;
An increase degree calculating means for calculating an increase degree of the magnitude of vibration in the predetermined frequency band of the second power spectrum with respect to the magnitude of vibration in the predetermined frequency band of the first power spectrum;
Chatter vibration determination means for determining that chatter vibration of the frequency of the increased frequency band has occurred when there is an increased frequency band that is the predetermined frequency band having the degree of increase equal to or greater than a first predetermined value;
When the chatter vibration determination means determines that chatter vibration has occurred, the chatter vibration determination means includes an output means for outputting chatter vibration and a frequency of chatter vibration.

  The feature of the invention according to claim 2 for solving the above-described problem is that the first predetermined value is larger by a second predetermined value than an average value of the degree of increase in all frequency bands of the frequency domain. It is a value.

The feature of the invention according to claim 3 for solving the above-described problem is that, when there are a plurality of the increased frequency bands, the chatter vibration determining means includes:
When there is a super increase frequency band that is the increase frequency band having the increase degree equal to or greater than a third predetermined value with respect to the average value of the increase degree of the increase frequency band, the super increase frequency band It is to determine that chatter vibration of frequency has occurred.

  A feature of the invention according to claim 4 for solving the above-described problem is that at least one of the degree of increase, the first predetermined value, the second predetermined value, and the third predetermined value is a magnification. It is.

According to the first aspect of the present invention, the presence or absence of chatter vibration can be detected by comparing the magnitudes of vibrations of the first power spectrum and the second power spectrum in all frequency bands in a desired frequency region. For this reason, it is possible to realize a chatter vibration detection apparatus that does not cause a detection failure of occurrence of chatter vibration in a desired frequency region.
When this chatter vibration detector is used in a machine tool, the presence of chatter vibration and the output of the chatter vibration frequency of this chatter vibration detector are used to prevent machining defects due to chatter vibration and to prevent chatter vibration. Processing conditions can be selected.

According to the second and third aspects of the invention, chatter vibration can be separated and detected even when the magnitude of vibration is increased due to causes other than chatter vibration. For this reason, it is possible to realize a chatter vibration detection apparatus that does not cause a detection error of occurrence of chatter vibration in a desired frequency region.
When this chatter vibration detection device is used in a machine tool, it is possible to provide a machine tool that can detect chatter vibration more accurately and can reduce unnecessary machining interruption due to a detection error.

According to the invention which concerns on Claim 4, since the said increase degree is determined by magnification, it can determine even if the magnitude | size of a vibration is small. For this reason, it is possible to realize a chatter vibration detection device that can detect the occurrence of chatter vibration even in the early stage of chatter vibration generation where the magnitude of vibration is small.
When this chatter vibration detection device is used in a machine tool, it is possible to provide a machine tool that can stop machining before a defective product is generated.

It is a general view which shows the machine tool and chatter detection means of this embodiment. It is a flowchart of chatter vibration detection of this embodiment. It is a figure which shows the 1st power spectrum of this embodiment. It is a figure which shows the 2nd power spectrum (when there exist multiple increase frequency bands) of this embodiment. It is a figure which shows the 2nd power spectrum (when one increase frequency band exists) of this embodiment.

A description will be given based on an embodiment in which the chatter vibration detection device 8 of the present invention is connected to the machine tool 1.
As shown in FIG. 1, the machine tool 1 performs desired machining by relatively moving a spindle 3 and a workpiece 4 which are held movably by a bed 5 and which rotates and holds a tool 2. Motion control such as rotation of the spindle 3 and feed of the spindle 3 is controlled by the NC device 6. The chatter vibration detecting device 8 includes a vibration measuring means 80 provided with a vibration sensor 801 installed on the main shaft 3, a recording means 81 for recording data such as detection data and calculation results of the vibration measuring means 80, and a power spectrum by Fourier analysis. Power spectrum calculation means 82 for performing calculation, increase degree calculation means 83 for calculating the degree of increase in vibration magnitude, chatter vibration determination means 84 for determining whether or not chatter vibration has occurred, chatter vibration occurrence and chatter vibration frequency. Output means 85 for outputting is provided.

  Chatter vibration has a characteristic that the magnitude of the vibration suddenly increases with time at a specific frequency. The present invention makes use of this characteristic to measure a vibration by providing a predetermined time difference, which is a time until the magnitude of chatter vibration becomes detectable during machining of a workpiece, for each frequency band. Comparing the magnitude of vibration, if there is a frequency band where the magnitude of vibration increases as time passes, it is judged that chatter vibration has occurred with the frequency of that frequency band and detects chatter vibration It is.

  The power spectrum in FIGS. 3 to 5 shows the magnitude of vibration in the frequency band for each frequency band shown on the horizontal axis by Fourier analysis of the measured vibration. Any of vibration amplitude, vibration speed, vibration acceleration, and the like may be used as the magnitude of vibration.

Hereinafter, a process of detecting chatter vibration will be described with reference to the power spectrum of FIGS. 3 to 5 based on the flowchart of FIG. 2 in an example in which the frequency domain is 1 to n Hz and the frequency band is 1 Hz.
Immediately after the start machining tool contacts the workpiece at the beginning, by measuring the vibration of the spindle using a vibration sensor 801 that is connected to the vibration measuring means 80, for recording the vibration data W ₁ to the recording means 81 (S1). The vibration data _{W 1} and Fourier analysis, is recorded into the first recording unit 81 as a power spectrum representing the magnitude _V 11 _{~V 1n} of vibration of each frequency band up 1~nHz as shown in FIG. 3 (S2). Wait for a predetermined time t. The predetermined time t is preferably 0.1 second to 1 second (S3). Using vibration sensor 801 that is connected to the vibration measuring means 80 measures the vibration of the spindle, for recording vibration data W ₂ to the recording unit 81 (S4). Vibration data _{W 2} and Fourier analysis, is recorded to the second recording means 81 as a power spectrum representing the magnitude _V 21 _{~V 2n} of vibration of each frequency band up 1~nHz as shown in FIG. 4 (S5). The value of the counter _{C 1} to 0 (S6). 1 is added to the counter _{C 1} (S7). In the frequency band C _1, it calculates the size of the degree of increase of the vibration of the second power spectrum for the first power spectrum. Specifically, the magnification _{sV c1} increases using the formula _{sV c1 = V 2c1 / V 1c1} , calculated by increasing the degree calculation means 83, and records the recording unit 81 (S8). It is determined whether or not the magnification sV _c1 is equal to or greater than a predetermined value K ₁ (sV _C1 ≧ K ₁ ?). If sV _C1 ≧ K ₁ , the process moves to step S10, and if not, the process moves to step S11 (S9). Assuming that an increasing frequency of frequency C ₁ is generated, the frequency C ₁ and the magnification sV _C1 are recorded in the recording means 81 (S10). It is determined whether n frequencies have been determined. If C ₁ = n, the process moves to step S12, and if not, the process moves to step S7 (S11).
Here, assuming that the value of the predetermined value K ₁ is 1.3 and steps S8 to S11 are repeated, sV _a = V _2a / V _1a = 1.33 at the frequency aHz in FIG. 2 and FIG. aHz is an increased frequency. Similarly, sV _b = 1.35, sV _c = 1.32, sV _d = 2.17, and sV _e = 1.38, and five increasing frequencies from aHz to eHz are generated. To do.

It is determined whether the number N of increased frequencies is 2 or more. If N> 2, the process moves to step S15; otherwise, the process moves to step S13 (S12). It is determined whether or not the number N of increased frequencies is 1. If N = 1, the process moves to step S14, otherwise ends (S13). Outputs chatter vibration frequency _{C 1} ends (S14). An average value sVH of the increase magnifications of the N increase frequencies is calculated. Specifically, the increase degree calculation means 83 calculates using sVH = ΣsVc1 / N. In this example, when the average value sVH of the increasing magnifications of the five increasing frequencies is calculated, sVH = 1.51 is obtained (S15). The value of the counter _{C 2} to 0 (S16). 1 is added to the counter _{C 2} (S17). Ratio of increase in magnification _{sV c1} to the average value sVH the fold increase is determined whether a predetermined value _{K 2} or more. If sV _c1 / sVH ≧ K ₂ , the process moves to step S19, and if not, the process moves to step S20 (S18). Outputs chatter vibration frequency _{C 1} ends (S19). It is determined whether the determination of N frequencies has been completed. If C ₂ = N, the process ends. If not, the process proceeds to step S17 (S20).
As 1.2 the value of the predetermined value _{K 2} where, as a result of repeated from step S17 to step _S20, sV a /sVH=1.33/1.51=0.88<1.2 next, the same manner SV _b /sVH<1.2, sV _c /sVH<1.2, sV _d /sVH>1.2, and sV _e /sVH<1.2. Thus, it is output when chatter vibration of frequency dHz is generated.

As shown in FIG. 5, in the second power spectrum, when only sV _d = V _2d / V _1d = 1.82 has an increased frequency, chatter vibration having a frequency of dHz is generated via steps S13 and S14. Is output.

As described above, according to the chatter vibration detection apparatus of the present invention, occurrence of chatter vibration can be detected at 1 Hz intervals for vibrations in all frequency bands in a desired frequency region. Since the degree of increase is determined by the increase magnification, chatter vibration can be accurately detected by comparing the ratio even when chatter vibration immediately after the occurrence of chatter vibration is small.
Furthermore, even when the magnitude of vibration at a plurality of frequencies increases due to an increase in machining efficiency, vibrations at a frequency having an increase magnification greater than a predetermined value than the average value of the increase magnifications at a plurality of frequencies. By detecting as chatter vibration, chatter vibration can be accurately detected.

In the above embodiment, the degree of increase is compared by the increase magnification of the vibration magnitude of the second power spectrum with respect to the first power spectrum, but the degree of increase is compared by the difference in the vibration magnitude of the second power spectrum with respect to the first power spectrum. May be.
In addition, an example in which the vibration measurement and power spectrum calculation immediately after the start of machining is compared with a single time interval with a predetermined time interval and the presence / absence of chatter vibration has been described has been described. The chatter vibration may be determined over a long period of time by repeating it continuously and repeatedly, and comparing the change in the magnitude of the vibration before and after that.
Although the vibration is measured by the vibration sensor 801 installed on the main shaft 3 for rotating the tool 2, the vibration sensor 801 may be installed on the workpiece side. In addition, a sound sensor such as a microphone may be used instead of the vibration sensor 801 to measure sound waves caused by vibration. In this case, restrictions on the measurement place are reduced, and chatter vibration can be easily measured.
The example in which the minimum value of the determination frequency is 1 Hz and the interval is 1 Hz has been described. However, the determination may be made with a desired frequency range and a desired interval, and it may be determined with an interval of about 5 Hz in a range of about 20 to 2000 Hz. Good.

1: Machine tool 2: Tool 3: Spindle 4: Work piece 5: Bed 6: NC device 8: Chatter vibration detection device 80: Vibration measurement means 81: Recording means 82: Power spectrum calculation means 83: Increase degree calculation means 84: Chatter vibration determination means 85: output means 801: vibration sensor

Claims (4)

A chatter vibration detector that detects the occurrence of chatter vibration that occurs when machining a workpiece using a tool,
Vibration measuring means for measuring the first vibration during machining of the machine tool and the second vibration after a predetermined time from the measurement of the first vibration;
Power spectrum calculation means for performing Fourier analysis of the first vibration and the second vibration and calculating a power spectrum that is a magnitude of vibration in a constant frequency band of a desired frequency region;
Recording means for recording a first power spectrum that is a power spectrum of the first vibration and a second power spectrum that is a power spectrum of the second vibration;
An increase degree calculating means for calculating an increase degree of the magnitude of vibration in the predetermined frequency band of the second power spectrum with respect to the magnitude of vibration in the predetermined frequency band of the first power spectrum;
Chatter vibration determination means for determining that chatter vibration of the frequency of the increased frequency band has occurred when there is an increased frequency band that is the predetermined frequency band having the degree of increase equal to or greater than a first predetermined value;
A chatter vibration detection device comprising output means for outputting chatter vibration and a frequency of chatter vibration when chatter vibration is determined to have occurred by the chatter vibration determination means.   2. The chatter vibration detecting apparatus according to claim 1, wherein the first predetermined value is a value larger by a second predetermined value than an average value of the degree of increase in all frequency bands in the frequency domain. When there are a plurality of the increased frequency bands, the chatter vibration determination means,
When there is a super increase frequency band that is the increase frequency band having the increase degree equal to or greater than a third predetermined value with respect to the average value of the increase degree of the increase frequency band, the super increase frequency band The chatter vibration detection apparatus according to claim 1, wherein the chatter vibration detection apparatus determines that chatter vibration at a frequency has occurred.   The chatter vibration detection according to any one of claims 1 to 3, wherein at least one of the degree of increase, the first predetermined value, the second predetermined value, and the third predetermined value is a magnification. apparatus.

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