JP2009178818A - Tool position measuring method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tool position measuring method and a device, having high repetition accuracy of a position of a minute tool such as a micro end mill in a non-contact state, hardly receiving a measurement error due to difference of a shape of a tool blade point, and directly measuring positions of the tool blade point and a material to be ground. <P>SOLUTION: The device includes: an incoherent light source illuminating a space between a tool 12 for grinding having a blade point such as a micro end mill, and a workpiece 22; and a camera 32 for photographing the tool 12 illuminated by the light source, the workpiece 22, and the gap between them. The device also includes an arithmetic operation means for measuring a position of the tool 12 by detecting light intensity in a region of the gap between the tool 12 and the workpiece 22, where the light intensity is changed depending on a distance from the tool 12 to the workpiece 22. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a tool position measuring method and apparatus for detecting the position of a micro tool such as a so-called micro end mill in a non-contact manner.

  Conventionally, a micro tool such as a micro end mill having a diameter φ of about 0.01 mm to 0.2 mm is often used for a mold of an optical component such as a micro lens array or a cutting process of a micro fluid machine. When such a tool is used, the distance between the tool and the work material must be accurately measured in order to perform highly accurate machining.

  There are various methods for detecting the tool position. Generally, as disclosed in Patent Document 1, a sliding body that contacts the tool is provided, and contact with the tool is electrically detected to detect the tool position. The position is detected. In addition, as disclosed in Patent Document 2, there is also a device that measures a tool using a transmission laser measurement device, an electric micrometer, a microscope, and the like. In addition, as disclosed in Patent Document 3, there is also a method of aligning the tool by imaging the tip of the tool with a CCD camera.

  In addition, as disclosed in Non-Patent Document 1, a method for measuring a micro tool using diffraction of laser light has been proposed.

JP 2006-75908 A JP-A-6-109440 JP 2006-1442412 A Panat Kachoeng Lung Luang Prototype of micro tool on-machine measurement unit using laser diffraction, Proc. Of the 2007 JSPE Spring Conference, (2007) 305

  In the contact-type tool position measuring device disclosed in Patent Document 1, in reality, a measuring force of about 0.3 N is applied to the work material, and in the case of a very small diameter tool, the cutting edge is damaged. There are often. In addition, in the case of the laser beam transmission method of the non-contact type tool position measuring device as disclosed in Patent Document 2, there is a problem that there is a measurement error due to a difference in the tool edge shape. Further, in the CCD camera system, the distance between the tool blade edge and the bed surface cannot be directly measured, and it is necessary to use a touch sensor, so that an error factor resulting therefrom increases.

  In the laser beam diffraction method disclosed in Non-Patent Document 1, the measurement object is a tool and a knife edge, not a tool and a work material. Furthermore, since the clearances are on the order of several tens of μm, the position of the tool cannot be detected with less accuracy, and the position of a micro tool such as a micro end mill cannot be accurately detected. .

  The present invention has been made in view of the above-mentioned background art. The position of a micro tool such as a micro end mill is non-contact, has high repeatability, is less susceptible to measurement errors due to the difference in the shape of the tool edge, and the tool edge and the object to be covered. An object of the present invention is to provide a tool position measuring method and apparatus capable of directly measuring the position of a work material.

  In the method of the present invention, the approach of the tool edge and the work material can be observed directly from the side surface, and the light intensity passing through the tool edge can be detected with high repetition accuracy by utilizing the fact that the light intensity passing therethrough is proportional to the square of the gap. It is characterized by.

  The present invention relates to a tool position measuring method for measuring the distance between a cutting tool having a cutting edge, such as a micro end mill, and a work material in a non-contact manner, wherein the gap between the tool and the work material is incoherent. Illuminate with light, take an image of the tool and the work material and the gap between them, measure the light intensity of the gap between the tool and the work material, and as the tool approaches the work material, the light In the tool position measuring method, the position of the tool with respect to the work material is measured based on the measurement value of the light intensity in the region of the gap between the tool and the work material where the strength decreases.

  Further, the present invention provides an incoherent light source capable of illuminating a gap between the tool and the work material in a tool position measuring device that measures the distance between the cutting tool having a cutting edge and the work material in a non-contact manner. An imaging device that images the tool illuminated by the light source, the work material, and a gap between the tool, and a gap between the tool and the work material such that the light intensity varies depending on the distance between the tool and the work material. In this region, the tool position measuring device includes a calculation means for measuring the position of the tool relative to the work material based on the measured value of the light intensity.

  The computing means is a computer that stores the correspondence between the light intensity and the distance in a region where the light intensity varies depending on the distance between the tool and the work material, and outputs the distance based on the light intensity.

  According to the tool position measuring method and apparatus of the present invention, it is possible to measure the position of a micro tool such as a micro end mill in a non-contact and highly accurate manner, and is less susceptible to measurement errors due to differences in the tool edge shape. Yes, the position of the tool edge and the work material can be directly detected with high accuracy. In addition, when coherent laser light diffraction is used, speckle noise is generated due to high coherence, but in this invention, an image of the gap between the tool and the work material is used by using incoherent light diffraction. Therefore, there is no problem of speckle noise. Further, as the light source, an inexpensive LED or other general light source can be used as compared with the laser light source, and the entire apparatus is also inexpensive.

  Hereinafter, an embodiment of a tool defect inspection apparatus according to the present invention will be described with reference to FIGS. As shown in FIG. 1, the tool position measuring apparatus 10 of this embodiment includes a tool 12 that is a micro end mill and a chuck portion 14 thereof, and the chuck portion 14 is connected to a spindle of a processing machine (not shown). However, in this embodiment, it is fixed to the mount 16 for experiment. The mounting base 16 is fixed to an XY stage 18 for positioning, and the XY stage 18 is provided with a piezo actuator 20 capable of aligning the XY stage 18 in the horizontal XY axis direction.

  On the tip side of the tool 12, a work material 22 to be machined is positioned so as to face. A side of the tool 12 is provided with an optical fiber 24 connected to a light source of incoherent light such as a halogen lamp (not shown), and a band through which light of a predetermined wavelength passes at an emission end of the light from the optical fiber 24. A condenser lens 28 for condensing light is provided on the side of the pass filter 26 and the tool 12. The band pass filter 26 allows light having a wavelength of, for example, 450 nm to pass therethrough.

  An objective lens 30 and an imaging lens 31 are provided on the opposite side of the tool 12. In addition, an objective lens 30 that captures an enlarged image of the tip of the tool 12 and a camera 32 that incorporates an image sensor such as a CCD that captures an image of the tool 12 are provided. It is output to the storage device.

  In the tool defect inspection apparatus 10 of this embodiment, the incoherent light guided from the light source by the optical fiber 24 passes through the bandpass filter 26 and is condensed by the condenser lens 28, and the work material 22 and the cutting edge of the tool 12 are collected. Pass through the gap. The light that has passed through the gap between the work material 22 and the cutting edge of the tool 12 is imaged on the image sensor of the camera 32 via the objective lens 30 and the imaging lens 31. Image information obtained from the image sensor is taken into a computer via an image input board, and light intensity is measured.

  In this embodiment, the detector 16 of the electric micrometer 34 for measuring the position of the tool 12 in the axial direction is in contact with the mounting base 16. Thereby, when the tool 12 advances and retreats with respect to the work material 22 by the piezo actuator 18 attached to the XY stage 18, the displacement amount is measured by the electric micrometer 34.

  Next, a method for measuring the distance between the tool 12 and the work material 22 in the present invention will be described. Here, the gap between the cutting edge of the tool 12 and the work material 22 is regarded as a slit, and when the incoherent light source / lens / imaging surface is located as shown in FIG. 2, the cutting edge of the tool 12 and the work material The relationship between the distance w to 22 and the light intensity by Franhofer diffraction at the center of the image plane is obtained.

Here, it is assumed that the coordinate system on the object plane is ξ, and the coordinate system on the image plane is x. Further, if the distance from the object plane to the imaging plane is L, the complex amplitude of light on the object plane is u ₀ , the complex amplitude of light on the imaging plane is u ₁ , and the wave number of the light source is k, the imaging plane The light intensity distribution I ₁ (x) at
The complex amplitude of light at the slit is
Further, when X≡kx / (2L), the equation (1) is
It becomes.

Further, the light intensity at the center of the image plane (x = 0) is sinc (wX) = 1,
Thus, the light intensity I ₁ (0) by Franhofer diffraction at the center of the image plane is the product of the square of the complex amplitude of light at the slit and the square of the distance w between the cutting edge of the tool 12 and the work 22. It is represented by By making the square of the complex amplitude of light at the slit part, that is, the light intensity at the slit part always constant, the light intensity at the center of the image plane is the distance w between the cutting edge of the tool 12 and the work material 22. It is proportional to the square.

  Based on the principle described above, when the cutting edge of the tool 12 approaches the work material 22, by measuring the light intensity of the gap, the light intensity rapidly decreases with respect to the distance of the gap, Tool position measurement with high repeatability is possible.

  FIG. 3 shows an image in which the ball end mill with R = 0.05 mm is close to the work material 22 in the embodiment of the present invention. The light intensity at the center of the tool 12 at this time is shown in FIG. The maximum light intensity when the gap between the cutting edge of the tool 12 and the work material 22 is sufficiently open is set to 1, and the light intensity from the gap is normalized. Hereinafter, the normalized light intensity is simply referred to as light intensity, and the unit is expressed in a dimensionless manner. Each light intensity distribution indicated by broken lines 1 to 6 of the arrows schematically represents the light intensity distribution when the cutting edge of the tool 12 approaches the work material 22. Only the left side of the broken line in the light intensity distribution in FIG. 4 is moving indicates that only the cutting edge side of the tool 12 is moving. The light intensity distribution at the distance between the cutting edge of the tool 12 and the work material 22 in FIG. 3 corresponds to the solid line indicated by the arrow 4 in FIG.

  As described above, according to the tool position measuring method and apparatus of this embodiment, it is possible to detect a change from the position of arrow 4 to the positions of arrows 5 and 6 shown in FIG. Thus, the position of the blade edge of the tool 12 can be directly detected without optical contact.

  Next, the experimental result about the detection of the tool position by the tool position measuring method and apparatus of this invention is demonstrated. Here, two types of tools shown in Table 1 were used, and experiments were performed in three directions defined in FIG. An image of the observed tool edge is shown in FIG.

  Regarding the change in the light intensity in the theoretical slit shape described in the above embodiment, the change in the light intensity due to the difference in the slit shape between the knife edge and the tool blade edge in Table 1 and the work material was measured. First, the contact position between the tool edge and the work material is estimated by the method of the above-described embodiment, and the tool edge is gradually moved away from the work material from that position, and the light intensity at that time is measured. The obtained light intensity curves are shown in FIGS. The horizontal axis in the figure indicates the distance between the tool blade edge and the work material, and the vertical axis indicates the normalized light intensity. The obtained curves are defined by dividing them into A, B, and C regions as shown in FIGS.

In the case of the knife edge shown in FIG. 7, it agrees well with the theoretical curve of u _S ² = 0.26 μm ^{−2 in} the region A of FIG. 7, and in the case of an actual ball end mill and square end mill, the region A of FIGS. It is in good agreement with the theoretical curve of u _S ² = 0.6μm ^-2 . The reason for the difference in the curve between the knife edge and the measurement result in each direction of each end mill is considered to be due to the light diffraction factor.

That is, in the measurement of the end mill, the light intensity with respect to the slit width was measured with the three-dimensional shape of the tool edge and the work material as a slit, but actually, as shown in FIG. Even if the slit width approaches zero at the center of measurement, the slit width around the center is wide, and therefore, it is affected by light diffraction from the peripheral portion. For this reason, it is considered that the light intensity curve obtained by the end mill is pushed up due to the influence of light diffraction. Therefore, the knife edge u _S ² is smaller than the value that matches the experimentally obtained light intensity curve. This factor is considered to be due to the fact that the light intensity curve changes depending on the rotation direction because the shape around each slit changes depending on the rotation direction.

  Moreover, in each area | region, the change of the light intensity which is proportional to the square of the distance w of a tool and a workpiece has arisen in A area | region. On the other hand, the output signal is saturated in the C region because the light intensity incident on the CCD of the camera is large. In the B region, it does not coincide with the theoretical curve as in the A region, and the output signal is not saturated as in the C region.

  Therefore, the γ value of CCD, which is considered as this factor, was examined. The tool and the work material were removed from the measurement apparatus of the above embodiment, and the γ curve of the CCD used was obtained using a variable ND filter. The result is shown in FIG. The input light intensity is 0.8 or more, greatly deviating from the line of γ = 1.0, and the output is small with respect to the input. Therefore, the region B in FIG. 7 and the like approaches a curve obtained by theory when the entire region is corrected to γ = 1.0. However, when the measurement is performed using the A region having a sudden change, only the A region may be provided without any correction.

  Next, it was confirmed that high repeat positioning accuracy was obtained immediately before the tool blade edge contacted the work material. With the apparatus of FIG. 1 of the above embodiment, each tool blade edge in Table 1 was moved to a position where the light intensity was 0.5, and the position was measured with an electric micrometer. This was repeated 20 times, and the difference between the minimum value was obtained from the standard deviation σ and the maximum value of all measured values.

The results are shown in Table 2, and the frequency distribution is shown in FIGS. The horizontal axis indicates the position where the light intensity 0.5 is detected, the plus side indicates that the workpiece is approached, and the minus side indicates that the workpiece is away from the workpiece.

The repeat positioning accuracy was highest in the direction 3 for each tool, followed by the direction 2 and the direction 1 in order. Considering the factors that cause differences in positioning accuracy depending on the measurement direction from the correlation with the light intensity curve, the measurement sensitivity increases as the measurement direction with a larger u _S ² that matches the light intensity curve increases. It is assumed that

Next, the repeat positioning accuracy obtained in the above experiment and the difference between the maximum value and the minimum value of all measured values were compared with a conventional contact-type blade edge position measuring device (catalog value 2σ = ± 1 μm). First, the measurement apparatus of FIG. 1 of the above-described embodiment was reconfigured as shown in FIG. The contact-type cutting edge position measuring device 40 and the cutting edge of the tool 12 are made to face each other, the tool 12 is gradually approached to the work material 22, and the position when the contact-type cutting edge position measuring device 40 outputs a detection signal is represented by an electric micro. Measurement was performed with a meter 34. This was repeated 20 times and the results are shown in Table 3.

  From Table 3, the repeatable positioning accuracy of the contact-type edge position measuring device 40 is σ = 0.100 μm, whereas the experimental result of this measuring device is σ ≦ 0.048 μm from Table 2, and the accuracy of this device is Was found to be about twice as good.

  From the above experimental results, the tool position measuring method and apparatus according to the present invention have sufficient repeated positioning accuracy as a position measuring apparatus that directly measures the distance between the tool blade edge and the work material without contact. Further, by directly observing the tool edge shape, it is free from errors due to the difference in the tool edge shape.

It is a whole lineblock diagram showing the tool position measuring device of one embodiment of this invention. It is a figure which shows the measurement principle of the tool position measuring apparatus of this embodiment. It is the image which image | photographed the state which the ball end mill and the work material adjoined. It is a graph which shows the change of the light intensity distribution by the light intensity in a tool center, and the approach of a tool to a work material. It is a front view of a tool blade edge. It is the image which image | photographed two types of tool blade edges from a different direction. It is a graph which shows the change of the clearance gap between a work material and a knife edge, and light intensity. It is a graph which shows the change of the clearance gap between a work material and a ball end mill, and light intensity. It is a graph which shows the change of the clearance gap between a work material and a square end mill, and light intensity. It is a graph which shows the measurement result of (gamma) value of CCD of an imaging device. It is a graph showing the frequency distribution which shows the repeat positioning accuracy in the light intensity 0.5 about a ball end mill. It is a graph showing the frequency distribution which shows the repeat positioning accuracy in the light intensity 0.5 about a square end mill. It is a perspective view which shows a contact-type tool position measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Tool position measuring device 12 Tool 22 Work material 24 Optical fiber 32 Camera

Claims (3)

  In a tool position measuring method for measuring the distance between a cutting tool having a cutting edge and a work material in a non-contact manner, a gap between the tool and the work material is illuminated with incoherent light, and the tool and the work material are illuminated. An image of the cutting material and the gap between the tool and the workpiece is measured by measuring the light intensity of the gap between the tool and the workpiece, and the light intensity decreases as the tool is brought closer to the workpiece. A tool position measuring method, comprising: measuring a position of the tool with respect to the work material based on a measured value of the light intensity in a region of a gap with the work material.   In a tool position measuring device that measures the distance between a cutting tool having a cutting edge and a work material in a non-contact manner, an incoherent light source capable of illuminating a gap between the tool and the work material, and illumination with the light source In the region of the gap between the tool and the work material such that the light intensity varies depending on the distance between the tool and the work material, A tool position measuring apparatus comprising a calculation means for measuring the position of the tool with respect to the work material based on a measured value of light intensity. The computer according to claim 2, wherein the calculation means is a computer that stores a correspondence between the light intensity and the distance in a region where the light intensity varies depending on a distance between the tool and the work material, and outputs the distance based on the light intensity. Tool position measuring device.