WO2015107751A1 - Surface shape measuring device and machine tool provided with same, and surface shape measuring method - Google Patents

Abstract

Provided is a surface shape measuring device (140) wherein a displacement meter (100) comprises: a light emitting unit (110) that projects a light beam (116) toward a measurement subject (130); an optical system (118) that focuses the scattered light of the light beam from the measurement subject (130); and a light receiving unit (120) that detects the focus position of the optical system (118). A movement mechanism (146) scans the light beam (116) by causing the displacement meter (100) and the measurement subject (130) to move relatively. A measurement control unit (156) is configured as follows: in order that the light receiving unit (120) is positioned, with respect to the light emitting unit (110), ahead of or following the scanning direction of the light beam (116), the light beam (116) is scanned by the movement mechanism (146), and during scanning of the light beam (116), the surface displacement of the measurement subject (130) is continuously measured, as surface shape data, by the displacement meter (100).

Description

Surface shape measuring device, machine tool provided with the same, and surface shape measuring method

The present invention relates to a surface shape measuring device that measures a surface shape by a noncontact displacement sensor using a light beam, a machine tool equipped with the surface shape measuring device, and a surface shape measuring method.

The demand for on-machine measurement technology in machine tools is increasing more and more. Traditionally, on-machine measurement applications have been limited to the positioning of workpieces (also referred to as "workpieces"), dimensional measurement of geometry, and the like. In recent years, on-machine measurement is being used also for correction for improving finishing accuracy by comparing on-machine measurement results with CAD data. In addition, researches such as automatically performing space error correction of the machine tool itself using the on-machine measurement results are also advanced.

Generally, a touch probe is used for on-machine measurement. The touch probe can be attached to the machine tool main body using ATC (Automatic Tool Changer). Furthermore, the touch probe can also transfer data by wireless communication with a computer for data processing, and is becoming more fulfilling as a measurement tool.

However, there are structural limitations to touch probes. That is, since it is a contact type, the possibility of damaging the finished workpiece can not be excluded. Furthermore, since the relief stroke at the time of contact is also small, the shape to be measured must be known in advance. In the case of workpiece position detection before machining, it is necessary that the workpiece be positioned in advance with an accuracy within a small relief stroke range.

On the other hand, in the non-contact measurement, the distance between the displacement sensor and the workpiece can be relatively large, such as several tens mm, without damaging the workpiece. For this reason, it is suitable for applications such as measurement for obtaining a processing offset before processing a casting, a forged product or the like, and further, high-speed scanning of the shape of a workpiece after finish processing.

As a typical method of non-contact measurement, there is a laser triangulation method (see, for example, Japanese Patent Application Laid-Open No. 10-332335 (Patent Document 1)). Heretofore, in the measurement of the surface shape of a metal material, it has been difficult to make a measurement using a laser displacement meter due to the lack of the amount of diffuse reflection light on the metallic glossy surface. Therefore, the need for pretreatment such as applying a powder to the surface has arisen, and there has been a situation where the practical use of a laser displacement meter in on-machine measurement has not progressed. In recent years, it has become possible to measure a metallic glossy surface by improving the sensitivity of an image sensor as a light receiving element and developing a semiconductor laser element. This makes it possible to use diffuse reflection triangulation laser displacement gauges on board the aircraft.

Japanese Patent Application Laid-Open No. 10-332335

The accuracy of triangulation-type laser displacement gauges is usually displayed with repetitive accuracy, and submicron accuracy is usually guaranteed. However, due to the use of laser light and the fact that the spot has a size rather than an ideal point shape, a unique measurement error is observed. This measurement error is characterized in that it contains spike noise that is much larger than the actual surface roughness and can not be removed by the time averaging process. Further, the measurement error described above is observed not only in the coherent laser beam but also in a triangulation displacement gauge using a noncoherent light beam.

The present invention has been made in consideration of the above problems, and its main object is to reduce an error observed when measuring a surface shape by triangulation using a light beam. It is providing a surface shape measuring device.

One aspect of the present invention is a surface shape measuring apparatus, which includes a displacement gauge, a moving mechanism, and a measurement control unit. The displacement meter includes a light emitting unit that emits a light beam toward a measurement target, an optical system that collects scattered light of the light beam from the measurement target, and a light receiving unit that detects a collection position by the optical system. The displacement gauge measures the displacement of the surface of the measurement object based on the light collecting position at the light receiving unit. The moving mechanism scans the light beam by relatively moving the displacement meter and the measurement object. The measurement control unit controls the moving mechanism and the displacement gauge. The measurement control unit causes the moving mechanism to scan the light beam so that the light receiving unit is positioned forward or backward with respect to the light beam scanning direction with respect to the light emitting unit, and the measurement object is measured by the displacement meter during the light beam scanning It is configured to continuously measure changes in surface displacement of the surface as surface shape data.

According to the configuration of the measurement control unit described above, it is possible to extract the above-mentioned spike-like error as an error pattern of a characteristic shape. Therefore, by removing the extracted error pattern, it is possible to efficiently reduce the noise included in the surface shape data.

Preferably, the surface shape measurement apparatus further includes a feature section extraction unit that extracts a feature section from a measurement range of surface shape data. The feature section is a section having a size equal to or less than the spot size of the light beam, and the surface shape data shows a change that is maximal in the first half or the second half of the feature section, and indicates a change that is minimal in the other half of the feature section .

Preferably, the feature section is a section having a size equal to or less than the spot size of the light beam, and satisfies a predetermined condition. In this case, the predetermined condition is that the surface shape data changes in one direction beyond the predetermined range with respect to the average value of the surface shape data in a part of the first half of the feature section, and the first half of a part of the second half of the feature section And the condition that the surface shape data changes beyond the predetermined range with respect to the average value in the opposite direction.

Alternatively, the feature section is a section having a size equal to the spot size of the light beam and satisfies a predetermined condition. In this case, the predetermined condition is obtained by rotating the waveform of the surface shape data in the first half of the feature section and the waveform of the surface shape data in the second half of the feature section by 180 degrees around the data point at the center of the feature section. It includes the condition that the correlation coefficient with the waveform exceeds a predetermined reference value.

The characteristic section extraction unit having any of the above-described configurations can extract an error of the characteristic pattern shape included in the measurement data of the laser displacement gauge. Therefore, by removing the extracted error pattern, it is possible to efficiently reduce the noise included in the surface shape data.

In a preferred embodiment, the surface shape measuring apparatus corrects the surface shape data so that the amount of change in the surface shape data relative to the average value of the surface shape data becomes small in each of the extracted one or more feature sections. It further comprises a data correction unit.

Preferably, the data correction unit averages the measurement values at any first measurement point of each feature section with the measurement values at second measurement points located at symmetrical positions across the middle point of the section. The surface shape data is corrected by replacing each measurement value at the first and second measurement points with an average value.

Alternatively, the data correction unit preferably corrects the surface shape data by replacing data in each feature section with the average value of the surface shape data.

The above-described characteristic error pattern can be removed by the data correction unit having any of the above-described configurations.

More preferably, in the above-described embodiment, the surface shape measuring apparatus performs low-pass filter processing on the surface shape data corrected by the data correction unit, leaving only fluctuations of a period longer than the spot size of the light beam. It further comprises a filter processing unit. This can further reduce the noise included in the surface shape data.

In another preferable embodiment, the surface shape measuring apparatus further includes a moving average processing unit which performs moving average on surface shape data in a variable moving average section. Here, the size of the moving average section is larger than the spot size of the light beam. The size of the moving average section when performing the moving average including the feature section is larger than the size of the moving average section when performing the moving average without including the feature section.

In still another preferred embodiment, the surface shape measuring apparatus further includes a moving average processing unit that performs weighted moving average on the surface shape data. Here, the size of the moving average section of the weighted moving average is larger than the spot size of the light beam. The weight for measurement points in the feature section is smaller than the weight for measurement points outside the feature section.

Even with the moving average processing unit having any of the above-described configurations, it is possible to suppress an error of the characteristic pattern shape included in the measurement data of the laser displacement gauge.

According to another aspect of the present invention, there is provided a machine tool provided with the surface shape measuring apparatus described above.
The present invention, in still another aspect, is a surface profile measurement method using a noncontact displacement meter. The above-described displacement meter includes a light emitting unit that emits a light beam toward an object to be measured, an optical system that condenses scattered light of the light beam from the object to be measured, and a light receiving unit that detects a condensing position by the optical system Including. In the surface shape measuring method, an object to be measured is measured along the scanning direction while maintaining the positional relationship between the light receiving unit and the light emitting unit so that the light receiving unit is positioned forward or backward in the scanning direction with respect to the light emitting unit. And moving the surface of the object to be measured based on a change in the measurement value of the displacement meter in accordance with the relative movement of the displacement meter.

Preferably, the step of determining the surface shape includes the step of extracting a feature section from the measurement range of the surface shape of the measurement object. The feature section is a section having a size equal to or less than the spot size of the light beam, and the measurement data of the surface shape of the measurement object shows a change which becomes maximum in the first half or the second half of the feature section. Show the change.

Preferably, in the step of determining the surface shape, in each of the one or more extracted feature sections, the measurement data is reduced so that the deviation of each measurement value from the average value of the measurement data of the surface shape of the measurement object is reduced. The method further includes the step of correcting.

Therefore, according to the present invention, it is possible to reduce an error observed when measuring the surface shape by triangulation using a light beam.

It is a figure which shows the structure of a laser displacement meter typically. It is a perspective view which shows typically the structure of the linear image sensor of FIG. It is a figure which shows an example of the data detected by the linear image sensor of FIG. FIG. 1 is a block diagram schematically showing a configuration example of a surface shape measuring apparatus according to a first embodiment. It is a figure which shows an example of the measurement result of the metal surface by a laser displacement meter. It is a figure for demonstrating the change of the imaging spot on a linear image sensor in, when the reflectance of a measurement object is non-uniform | heterogenous. It is a top view which shows typically the surface of the measurement object of FIG. FIG. 7 is a view showing an example of a luminance distribution detected by a linear image sensor in the cases of FIG. 6 and FIG. 7; It is a figure for demonstrating the magnitude | size of the measurement error resulting from the nonuniformity of the reflectance of a measurement object. It is a figure which shows the result of having repeatedly measured the displacement of the height direction in the micro area on a gauge block using a laser displacement meter. It is a figure which shows the result of having measured the displacement of the height direction in the range of 0.4 mm on a gauge block using a laser displacement meter. It is a figure which shows the maximum value of the light reception amount of an image sensor in each measurement point of FIG. FIG. 13 is a diagram showing the relationship between displacement in the height direction and the maximum light receiving amount in a region RC of FIG. 11 and FIG. 12. It is a figure which shows the result of having measured the surface shape of the square-like area | region of 0.5 mm one side by the laser beam of 50 micrometers in diameter diameter of a spot. It is a figure which shows the result of having changed the laser spot size into 400 micrometers in diameter, and having measured the surface shape of the same area | region as FIG. It is a flowchart which shows the processing procedure of measurement of surface shape, and the measured data. It is a figure for demonstrating the method to extract a characteristic area in FIG.16 S105. It is a figure for demonstrating the other method of extracting a characteristic area in FIG.16 S105. It is a figure for demonstrating the method to correct | amend surface shape data in FIG.16 S110. It is a figure which shows the result of having performed data correction shown to FIG.16 S110 with respect to the measurement data of FIG. FIG. 21 is a diagram showing the result of low-pass filter processing shown in step S115 of FIG. 16 on the data of FIG. 20; FIG. 18 is a diagram showing the result of low-pass filter processing shown in step S115 without performing data correction shown in step S110 of FIG. 16 on the measurement data of FIG. FIG. 6 is a block diagram schematically showing a configuration of a surface shape measuring apparatus according to a second embodiment. 10 is a flowchart showing an example of measurement of the surface shape and a processing procedure of the measured data in the surface shape measurement apparatus according to the second embodiment. FIG. 16 is a flowchart showing another example of the process of measuring the surface shape and processing the measured data in the surface shape measuring apparatus according to the second embodiment. FIG. 16 is a perspective view schematically showing a configuration of a machine tool according to a third embodiment. FIG. 27 is a block diagram showing a functional configuration of a portion related to the surface shape measuring device in the machine tool of FIG. 26.

Hereinafter, each embodiment will be described in detail with reference to the drawings. In each of the following embodiments, a surface shape measurement apparatus using a laser displacement meter will be described as an example, but a noncontact displacement meter using a noncoherent light beam instead of a laser beam is also described. The present invention can be applied. In the following description, the same or corresponding parts may be denoted by the same reference numerals, and the description thereof may not be repeated.

Embodiment 1
[Overview of Laser Displacement Gauge]
FIG. 1 is a view schematically showing the configuration of a laser displacement meter. Referring to FIG. 1, a laser displacement meter 100 includes a light emitting unit 110, a condensing lens 118 as an optical system, and a linear image sensor 120 as a light receiving unit. The light emitting unit 110 includes a laser diode 112 and a lens 114.

The laser beam 116 emitted from the laser diode 112 is shaped into substantially parallel light by the lens 114 and irradiated to the measurement object 130. The spot size w (also referred to as spot diameter) of the laser beam 116 on the measurement object is, for example, 50 μm in diameter. The light diffusely reflected on the measurement object 130 is condensed by the condenser lens 118 on the linear image sensor 120 disposed in the angular direction of the laser beam 116 and γ.

In FIG. 1, the direction of the laser beam 116 is taken as the Z-axis direction. A surface including the central axis of the laser beam 116 and the optical axis of the condenser lens 118 is referred to as an optical path. A direction parallel to the light road surface and perpendicular to the Z-axis direction is taken as an X-axis direction. The direction perpendicular to both the X-axis direction and the Z-axis direction is taken as the Y-axis direction. In the case of FIG. 1, the Y-axis direction is a direction perpendicular to the paper surface, and the XZ plane is parallel to the paper surface (optical road surface).

Here, the beam size of the laser beam (spot size on the measurement object) will be described. There are various definitions of the beam size of laser light. For example, in the case of a laser beam having a symmetrical beam profile such as the TEM00 mode, in a plane orthogonal to the optical axis, one square of e to the peak value (where e is the base of the natural logarithm) ( The beam size is defined by the width of the intensity distribution (13.5%). When the beam profile is broken, for example, a circle containing 86.5% of the total power of the beam with respect to the peak power is calculated, and the diameter of the circle is defined as the beam size. In this specification, in order to include various definitions, the beam size (the object size to be measured) is substantially in the range not less than the diameter of the circle containing 50% of the total power and not more than the diameter of the circle containing 95% of the total power. It is assumed that it is equal to the spot size above).

FIG. 2 is a perspective view schematically showing the configuration of the linear image sensor of FIG. Referring to FIG. 2, linear image sensor 120 includes 1024 pixels (pixels) 122 linearly arranged. Each pixel 122 outputs a signal of a luminance level from 0 to a maximum of 255 according to the light reception amount.

FIG. 3 is a diagram showing an example of data detected by the linear image sensor of FIG. The horizontal axis in FIG. 3 indicates the pixel position, and the vertical axis indicates the brightness level. Referring to FIGS. 2 and 3, the light diffusely reflected on the measurement object 130 is condensed by the condensing lens 118 to a spot 124 on the linear image sensor 120, thereby generating a Gaussian as shown in FIG. 3. Distribution data are obtained. The distance to the object is calculated by triangulation from the barycentric position of the data in FIG.

Referring back to FIG. 1, the linear image sensor 120 is disposed at an angle based on the Scheimpflug Condition. That is, the detection surface of the linear image sensor 120 and the main surface of the condenser lens 118 intersect in one straight line, and the angle between these surfaces is β. The plane including the laser beam 116 is the object plane. In this case, the moving magnification M of the imaging spot 124 on the linear image sensor 120 with respect to the change in the distance between the measurement object 130 and the laser displacement meter 100 is given by the following equation (1). However, the focal length of the condenser lens 118 is f _0, and the distance from the irradiation position (laser spot 132) of the laser beam 116 on the measurement object 130 to the condenser lens 118 is l.

M = (f ₀ · sin γ) / (l · cos β) (1)
In the case of the present embodiment, since f ₀ = 55 mm, l = 80 mm, γ = π / 6, and β = 5π / 18 in the above equation (1), the moving magnification M is calculated as follows: Ru.

M = {55 × sin (π / 6)} / {80 × cos (5π / 18)} = 0.53 (1A)
[Configuration of surface shape measuring apparatus]
FIG. 4 is a block diagram schematically showing a configuration example of the surface shape measuring apparatus according to the first embodiment. Referring to FIG. 4, the surface shape measuring apparatus 140 includes a table 144 on which the measurement object 130 is placed, a saddle 142, a laser displacement meter 100, an X-axis drive mechanism 146X, and a Y-axis drive mechanism 146Y. , Z-axis drive mechanism 146Z, and a computer 150.

The table 144 is disposed on the saddle 142 and is movable in the X-axis direction. The saddle 142 is movable in the Y-axis direction. The X-axis drive mechanism 146X moves the table 144 in the X-axis direction. The Y-axis drive mechanism 146Y moves the saddle 142 in the Y-axis direction. The Z-axis drive mechanism 146Z moves the laser displacement meter 100 in the Z-axis direction. The X-axis drive mechanism 146X, the Y-axis drive mechanism 146Y, and the Z-axis drive mechanism 146Z function as a moving mechanism 146 for relatively moving the laser displacement meter 100 and the measurement object 130. Thus, the moving mechanism 146 causes the laser beam 116 to scan over the surface of the measurement object 130.

The configuration of the moving mechanism 146 is not limited to the example shown in FIG. For example, the measurement object 130 may be fixed, and the laser displacement meter 100 may be movable in three directions of X, Y, and Z.

The computer 150 includes a processor 152, a memory 154, and display devices and input / output devices (not shown). The processor 152 functions as a measurement control unit 156 and a data processing unit 158 by executing a program stored in the memory 154.

The measurement control unit 156 scans the laser beam 116 by controlling the laser displacement meter 100 and the moving mechanism 146. During the scanning of the laser beam 116, the measurement control unit 156 continuously measures the surface shape data 166 of the measurement object 130 using the laser displacement meter 100. The measured surface shape data 166 is stored in the memory 154. The surface shape data 166 is a data series in which the scanning position (the position where the laser beam is irradiated) on the measurement object 130 and the displacement of the surface of the measurement object 130 at the scanning position in the Z direction are associated. .

The data processing unit 158 performs data processing of measurement data in order to remove characteristic noise included in the measurement data (surface shape data 166) of the laser displacement meter 100. Details of the data processing content will be described later with reference to FIGS. 16 to 22.

The surface shape measuring apparatus 140 according to the present embodiment is characterized in the relationship between the scanning direction of the laser beam 116 and the direction of the laser displacement meter 100. Specifically, as shown in FIG. 1, the light receiving unit (linear image sensor 120) is forward or backward of the light emitting unit 110 in the scanning direction (in the case of FIG. 1, + X direction or −X direction) of the laser beam 116. The laser beam 116 is scanned to be located at In other words, the scanning direction of the laser beam 116 is aligned with the light path (parallel to the XZ plane in the case of FIG. 1) including the central axis of the laser beam 116 and the optical axis of the condenser lens 118.

By matching the scanning direction of the laser beam 116 with the direction of the laser displacement meter 100 as described above, characteristic error patterns as shown in the areas RA, RB, and RC of FIG. 11 appear in the measurement data. become. Therefore, if this characteristic error pattern is extracted and removed from the surface shape data 166, it is possible to efficiently reduce relatively large noise included in the surface shape data 166.

The laser beam 116 may be scanned so that the laser spot follows a curved trajectory on the surface of the measurement object 130. In this case, one of the measurement object 130 or the laser displacement meter 100 is rotated about the Z axis (C-axis direction) in order to position the light-receiving unit forward or backward in the scanning direction with respect to the light-emitting unit 110 A drive mechanism is required.

[About the cause of measurement error of laser displacement meter]
FIG. 5 is a view showing an example of the measurement result of the metal surface by the laser displacement meter. Specifically, FIG. 5 shows the result of measuring the displacement of the surface of the metal gauge block having a smooth surface using the laser displacement meter 100 at intervals of 0.1 mm. The scanning direction of the laser beam is parallel to the surface of the gauge block. As shown in FIG. 5, while the surface roughness of the gauge block is about 0.06 μm, noise as large as 36 μm was observed in the measurement data at 3σ (σ represents a standard deviation). As described in detail later, this noise is characterized in that it can not be removed by time averaging processing (processing of performing the same measurement repeatedly and averaging).

As a cause of error of the laser displacement meter, electrical noise, influence by temperature change, movement error of moving mechanism 146 (X-axis drive mechanism 146X, Y-axis drive mechanism 146Y, and Z-axis drive mechanism 146Z), measurement object 130 Inconsistencies in the reflectance of the surface of the surface of the substrate, laser speckle, etc. are considered.

Electrical noise can be improved by time averaging of the measurements. The repeatability of commercially available laser displacement gauges is often expressed in numbers after time averaging, and is submicron accuracy. Therefore, it is not the cause of the relatively large noise shown in FIG.

Although the error due to temperature change exists due to the outside air temperature, the electric circuit inside the laser displacement meter is the heat source, and the error caused by the thermal displacement of the measurement optical system is mainly. In the laser displacement meter used this time, a shift of measured value of 10 μm is observed after the power is turned on. However, the shift of the measured value due to the temperature change usually stabilizes in about 30 to 60 minutes after the power is turned on, so it can not cause the noise shown in FIG.

The movement error of the moving mechanism 146 includes an error due to thermal displacement and a mechanical error. The error due to the thermal displacement is observed as a temporally slow fluctuation, similar to the influence of the temperature inside the laser displacement gauge described above. The mechanical error is caused by an error in the positional accuracy of the moving mechanism 146 when the laser beam is scanned to measure the surface shape. However, mechanical errors appear as large undulations as compared to the spiked noise, and thus are not considered as the cause of the noise shown in FIG.

In addition to the motion error of the moving mechanism 146, an error due to the vibration of the servo shaft is also considered. However, the noise due to the vibration of the servo axis can be removed by time averaging as well as the electrical noise, so it is not the cause of the noise shown in FIG.

From the above consideration, it is considered that one of the causes of the noise shown in FIG. 5 is the nonuniform microscopic reflectance of the surface of the measurement object 130. Non-uniformity in reflectance is caused by non-uniformity in material, scratches on metal surfaces, and irregularities. Since the laser beam for measurement has a spot size, unevenness in microscopic reflectivity within the laser spot size causes uneven brightness, which may cause measurement error.

FIG. 6 is a diagram for describing a change in an imaging spot on the linear image sensor when the reflectance of the measurement object is nonuniform. FIG. 7 is a plan view schematically showing the surface of the measurement object of FIG. FIG. 8 is a diagram showing an example of the luminance distribution detected by the linear image sensor in the cases of FIG. 6 and FIG.

6 to 8, in order to accurately determine the displacement in the height direction by the triangulation method, the luminance distribution in the imaging spot 124 on the linear image sensor 120 exhibits a Gaussian distribution, It is important that the center of the spot 124 be detectable. If the microscopic reflectance of the surface of the measurement object 130 is not uniform and uneven brightness occurs, a measurement error may occur because the brightness distribution deviates from the Gaussian distribution due to the uneven brightness.

As shown in FIGS. 6 and 7, it is assumed that there is a region on the surface 130A of the measurement object 130 that is smaller than the spot size of the laser spot 132 and higher in reflectivity than the surroundings. The relative position of the high reflectance area to the laser beam 116 is determined as the laser beam 116 is scanned in the + X direction (scanning direction) (ie, as the object to be measured moves in the −X direction), P1, P2,. It changes in order of P3.

When the high reflectance area is positioned at P1 with respect to the laser beam 116, as shown in FIG. 8A, the center of gravity 136 of the data deviates with respect to the center 134 of the imaging spot of the image sensor 120. For this reason, the measurement object 130 is measured to be located at a position (lower position) farther from the light emitting unit 110 than it actually is.

When the high reflectance area is positioned at P2 with respect to the laser beam 116, as shown in FIG. 8B, the center 134 of the imaging spot of the image sensor 120 and the barycenter 136 of the data coincide. For this reason, the measurement object 130 is measured to be at the same position as it is.

When the high reflectance area is positioned at P3 with respect to the laser beam 116, as shown in FIG. 8C, the center of gravity 136 of the data is at the center 134 of the imaging spot of the image sensor 120 (FIG. It shifts in the opposite direction to the case of A). For this reason, the measurement object 130 is measured so as to be closer (higher) to the light emitting portion 110 than it actually is.

FIG. 9 is a diagram for explaining the magnitude of the measurement error caused by the nonuniformity of the reflectance of the measurement object. In FIGS. 9A and 9B, the size of the laser spot 132 is largely described to facilitate the illustration. In FIG. 9A, as in the case of FIG. 8A, the case where the surface of the object to be measured is measured so as to be located by ε− more than the actual distance is shown. In FIG. 9B, as in the case of FIG. 8C, the case where the surface of the measurement object is measured so as to be positioned closer by ε + than in reality is shown.

The magnitude of the measurement error caused by the nonuniformity of the reflectance is determined by the spot size w of the laser spot 132 and the light receiving angle γ. Specifically, the maximum value of the measurement error (error when misrecognized around the periphery of the laser spot 132) ε _max is given by the following equation (2).

ε _max = w / (2 · tan (γ)) (2)
In the laser displacement meter used for the measurement of FIG. 5, the spot size w = 50 μm and the light receiving angle γ = π / 6. In this case, the maximum value ε _max of the measurement error is given by the following equation (2A), and becomes the same value as the measurement error in FIG.

ε _max = 25 / tan (π / 6) = 43 [μm] ... (2A)
When a laser diode is used as a triangulation-type light source, speckle caused by interference of reflected light is considered to be the cause of noise shown in FIG.

Since speckle is an interference phenomenon of laser light, measurement noise caused by speckle is closely related to surface roughness. Specifically, when the optical path length deviates by λ / 2 with the wavelength of the laser light being λ, the light becomes dark on the image sensor 120 due to interference, and the light on the image sensor 120 becomes bright due to the deviation of λ. When converted in terms of the unevenness of the surface of the object to be measured, fluctuation of luminance occurs on the image sensor 120 at an integral multiple of λ / 4.

In the gauge block to be measured in the case of FIG. 5, the surface asperities are several tens of nm or less, which is about one tenth of the wavelength λ of the laser light. In that case, speckle does not become a clear light and dark state and unevenness of low contrast occurs.

There have been various studies on laser speckle. The average speckle diameter on the image plane is known to be given by the following equation (3) (for example, Yasuhiko Arai and 3 others, "Optics", vol. 41, No. 2, p96-104, February 2012 ( See Non-Patent Document 1)).

σ = 1.22 × (1 + M) · λ · f / d (3)
In the above equation (3), σ is the average speckle diameter on the imaging plane, M is the magnification of the imaging optical system, λ is the wavelength of the laser light, f is the focal length of the lens, and d is the aperture diameter of the lens. In the laser displacement meter used in the measurement of FIG. 5, since M = 0.53, λ = 655 nm, d = 10 mm, and f = 33 mm, σ = 4.0 μm.

Since the width of each pixel of the linear image sensor 120 is 12 μm, it is considered that the influence of the average size speckle calculated above is averaged at each pixel of the linear image sensor 120. However, speckles with a diameter larger than the average value that appears due to non-uniformity in a specific location are not averaged in each pixel of the linear image sensor 120. Therefore, speckle noise can be a cause of the noise shown in FIG. 5 by the same mechanism as in the case of the non-uniform reflectance described with reference to FIGS. Speckle noise is usually treated as a statistic because it is unpredictable. However, in the microscopic range, speckle noise appears reproducibly and deterministically, and can not be removed by averaging with a time filter.

[About spike noise]
Hereinafter, the result of observing the spike noise shown in FIG. 5 in more detail will be described.

FIG. 10 is a diagram showing the result of repeatedly measuring the displacement in the height direction in a minute section on the gauge block using a laser displacement meter. In FIG. 10, measurement data at each measurement point (range of average value and ± 3σ, where σ is the same) when the measurement range of 0.1 mm is measured 20 times at a sampling interval of 1 μm for the same gauge block as FIG. 5 Standard deviation) is shown. Since the spot size of the laser beam is 50 μm, the measurement interval (1 μm) is sufficiently smaller than the spot size.

As shown in FIG. 10, what appeared to be spike-like random noise in FIG. 5 has very good measurement reproducibility, and measurement results as if minute irregularities were present on the surface were obtained. The surface roughness of the gauge block is several tens of nm, and asperities close to 100 times the actual roughness are detected. The data variation at each measurement point is 2.3 μm at 3σ value. The error at each measurement point is noise caused by electrical noise, air fluctuation, servomotor vibration, etc., and can be canceled by time averaging processing.

FIG. 11 is a diagram showing the result of measuring the displacement in the height direction on the gauge block in the range of 0.4 mm using a laser displacement meter. In the case of FIG. 11, measurement data (surface shape data) when the measurement range of 0.4 mm is measured only once at a sampling interval of 1 μm are shown for the same gauge block as that of FIG.

Here, the measurement in FIG. 11 is characterized in that the laser beam 116 is scanned such that the light receiving unit (linear image sensor 120) is located forward in the scanning direction with respect to the light emitting unit 110 in FIG. . That is, the scanning direction of the laser beam is aligned with the light path (XZ plane in FIG. 1) including the central axis of the laser beam and the optical axis of the condenser lens 118.

As shown in FIG. 11, relatively large errors as seen in the regions RA, RB, and RC occur together with the fine reproducible noise. The errors found in these areas RA, RB, RC have characteristic shapes. Specifically, as the measurement point (laser beam scanning position) moves from left to right, the displacement in the height direction measured by the laser displacement gauge becomes lower than the average level of the data at first and then It shows a change that is higher than the average level and finally returns to the original average level.

The state of the change of the measurement data seen in the regions RA, RB, and RC in FIG. 11 is the same as that described in FIGS. That is, as the area of high reflectance moves from right to left in the laser spot (note that it is in the opposite direction to the scanning direction of the laser beam), the displacement in the height direction measured by the laser displacement gauge is In the first half it is lower than the actual and in the second half it is higher than the actual.

It should be noted that the direction of the above error change is that the light receiving unit (linear image sensor 120) is located forward in the scanning direction with respect to the light emitting unit 110 in FIG. When the light receiving unit (linear image sensor 120) is positioned behind the light emitting unit 110 in the scanning direction, the direction of the error change is reversed.

FIG. 12 is a diagram showing the maximum value of the light reception amount of the image sensor at each measurement point in FIG. The vertical axis in FIG. 12 indicates the luminance level at the pixel at which the amount of received light is largest. It can be read that in the regions RA, RB, and RC where relatively large measurement errors of the characteristic shape are observed in FIG.

FIG. 13 is a diagram showing the relationship between the displacement in the height direction and the maximum light reception amount in the region RC of FIG. 11 and FIG.

Referring to FIG. 13, as the measurement point (laser beam scanning position) moves, the maximum light receiving amount detected by image sensor 120 gradually increases, and the barycentric position of the luminance distribution on image sensor 120 It slips. As a result, the detected value (displacement in the height direction) of the laser displacement gauge largely fluctuates to the negative side (section of arrow A1).

When the light reception amount of the image sensor 120 reaches the maximum level, the position of the center of gravity of the luminance distribution on the image sensor 120 moves with the movement of the measurement point (the scanning position of the laser beam). As a result, the detection value (displacement in the height direction) of the laser displacement gauge changes from minus to plus (section of arrow A2).

Finally, the light reception amount of the image sensor 120 decreases, and the detected value (displacement in the height direction) of the laser displacement gauge returns to the correct value (average value) (section of arrow A3).

The above-mentioned characteristic phenomenon can be explained by uneven reflection on a minute area (area smaller than the laser spot size) of the surface of the measurement object, as already described. Alternatively, this characteristic phenomenon can be described as the case where the speckle diameter can not be ignored with respect to the spot size of the laser beam.

The average speckle diameter is calculated to be 4.0 μm as described using equation (3), smaller than 12 μm which is the pixel width of the linear image sensor 120, and approximately 1/12 of 50 μm of the spot size. It is a size. Therefore, since the averaging is performed in the pixel, the variation of the measurement value due to the influence of the average speckle diameter is small and can be removed by the averaging process by the spatial filter.

However, the errors caused by locally appearing large diameter speckles are very large and can not be easily removed by the averaging process of narrow areas, and as a result, they greatly affect the measurement values of the laser displacement gauge. However, the range in which such large-diameter speckles affect the measurement data is limited within the range of the laser spot size, as can be seen from FIG.

FIG. 14 is a view showing the measurement results of the surface shape of a square area of 0.5 mm on a side with a laser beam of spot size of 50 μm in diameter. FIG. 15 is a view showing the result of measuring the surface shape of the same area as FIG. 14 while changing the laser spot size to 400 μm in diameter. In FIGS. 14 and 15, Φ represents a diameter.

As shown in FIGS. 14 and 15, when the spot size of the laser beam was changed from 50 μm in diameter to 400 μm in diameter, the maximum value of the surface asperities measured by the laser displacement meter increased from 67 μm to 80 μm.

As the laser spot size increases, the effect is reduced because the errors due to average size speckle are averaged out. However, the range affected by large speckles that appear locally increases as the laser spot size increases, as shown by equation (2) above. Therefore, it is considered that the measurement error of the laser displacement meter increases as the spot size increases.

[About noise removal method]
As described above, the measurement error of the laser displacement meter is considered to be due to the influence of the local reflectance nonuniformity of the measurement object and the occasionally appearing large diameter speckle. The errors due to these factors have the following characteristics.

(A) Depending on the size of the laser spot size, the range affected by uneven reflectance and large diameter speckles is determined.

(B) As shown in the areas RA, RB, and RC of FIG. 11, by orienting the laser displacement meter such that the light receiving unit (image sensor) is positioned forward or backward in the scanning direction with respect to the laser beam. Characteristic error patterns appear. Specifically, the error changes to either plus or minus in the first half of the section (referred to as a characteristic section) in which the characteristic error pattern appears, and the error in the second half changes in the opposite direction to the first half. Furthermore, at points equidistant from the median of the feature interval, the absolute values of the errors are approximately equal (ie, the error pattern is approximately point symmetric with respect to the median).

The section (characteristic section) in which such a characteristic error pattern can be seen is equal to or less than the laser spot size. Therefore, according to the sampling theorem, it is necessary to set the sampling interval of the laser displacement gauge to 1/2 or less of the laser spot size in order to capture this error pattern (vertical movement of the measurement value). In order to accurately capture the shape of the vertical movement of the measurement value, the sampling interval of the laser displacement gauge is desirably 1/10 or less of the spot size. More preferably, the sampling interval of the laser displacement meter is set to 1/20 or less of the spot size.

Since the above characteristic error pattern dominates the measurement error of the laser displacement meter, if this error pattern can be extracted and removed by software processing, the measurement error of the laser displacement meter is efficiently reduced. can do. Hereinafter, the procedure of the noise removal will be described more specifically.

FIG. 16 is a flowchart showing the measurement of the surface shape and the processing procedure of the measured data. Hereinafter, operations of the measurement control unit 156 and the data processing unit 158 of FIG. 4 will be described mainly with reference to FIGS. 4 and 16.

First, the measurement control unit 156 is a laser so that the light receiving unit (linear image sensor 120) is positioned forward or backward of the scanning direction (+ X direction or −X direction) of the laser beam 116 with respect to the light emitting unit 110 of FIG. With the displacement gauge 100 oriented, the laser beam 116 is scanned by the moving mechanism 146. Furthermore, the measurement control unit 156 continuously measures the displacement of the surface of the measurement object 130 by the laser displacement meter 100 during the scanning of the laser beam 116 (step S100). The measurement data is stored in the memory 154 as surface shape data 166. The sampling interval of the surface shape data 166 needs to be 1/2 or less of the spot size of the laser beam, desirably 1/10 or less of the spot size, and more desirably 1/20 or less.

The data processing unit 158 performs data processing on the surface shape data 166 after the measurement by the measurement control unit 156. As shown in FIG. 4, the data processing unit 158 includes a feature section extraction unit 160, a data correction unit 162, and a filter processing unit 164.

First, the feature section extraction unit 160 extracts a feature section in which the above-mentioned characteristic error pattern is observed from the measurement range of the surface shape data (step S105). As described above, the feature section is a section having a size equal to or smaller than the spot size of the light beam, and the surface shape data shows a change which becomes maximum in the first half or the second half of the feature section. Show the change. Hereinafter, with reference to FIGS. 17 and 18, a method of extracting a feature section will be described.

FIG. 17 is a diagram for explaining a method of extracting a feature section in step S105 of FIG. Referring to FIG. 17, the feature section extraction unit 160 in FIG. 4 sequentially cuts out measurement data MD of the section I1 equal to the spot size w of the laser beam from the measurement range of the surface shape data. Then, the feature section extraction unit 160 sets the waveform of the measurement data MD in the first half I2 of the cut out section I1 and the waveform of the measurement data MD in the second half I3 of the section I1 180 degrees around the data point MP at the center of the section I1. The correlation coefficient with the waveform obtained by rotating is determined. When the calculated correlation coefficient exceeds a predetermined reference value, the feature section extraction unit 160 specifies the cut out section I1 as a feature section.

FIG. 18 is a diagram for explaining another method of extracting a feature section in step S105 of FIG. Referring to FIG. 18, the feature section extraction unit 160 in FIG. 4 detects that the measurement data MD exceeds the predetermined value TH with respect to the average value AV in the section I4 smaller than the spot size w of the laser beam. Extract the part that is changing in both directions. Then, in a part of the first half I5 of the section I4, the characteristic section extraction unit 160 changes the measurement data MD in one direction (plus direction or minus direction) beyond the predetermined range TH with respect to the average value AV of the measurement data MD. If the measurement data MD changes in a direction opposite to the first half I5 in a part of the second half I6 of the section I4 beyond the predetermined range TH with respect to the average value AV, the section I4 is specified as the feature section .

Again, referring to FIGS. 4 and 16, data correction unit 162 changes the amount of change with respect to the average value of surface shape data 166 (that is, the average value of each measured value) in each of the extracted one or more feature sections. Surface shape data 166 is corrected so as to reduce the deviation from. For example, a method of correcting the surface shape data 166 using the symmetry of the error pattern in each feature section can be considered.

FIG. 19 is a diagram for explaining a method of correcting the surface shape data 166 in step S110 of FIG. Referring to FIG. 19, the solid line graph represents data MD (surface shape data 166) measured in the characteristic section I7. The graph in the alternate long and short dash line is folded data RD obtained by folding measurement data MD of the second half to the first half side and folding data MD of the first half to the second half side at the boundary line BR between the first half I8 and the second half I9 Represents Since the measurement data MD and the aliasing data RD are substantially symmetrical with respect to the boundary line BR, the characteristic data is removed by averaging the measurement data MD and the aliasing data RD for each measurement point. The dashed line in FIG. 19 can be obtained.

Specifically, the data correction unit 162 compares the measured values at any first measurement point in each feature section with the measured values at second measurement points located at symmetrical positions across the middle point of the section. Then, the surface shape data is corrected by replacing the measured values at the first and second measurement points with the determined average value.

As another method, the data correction unit 162 may correct the surface shape data 166 by replacing the data in each feature section with the average value of the surface shape data 166.

Again referring to FIGS. 4 and 16, filter processing unit 164 performs spatial low-pass filter processing on the surface shape data corrected by data correction unit 162 (step S115). In this case, since the range in which the characteristic error pattern appears is equal to or less than the laser spot size, the cut-off wavelength of the spatial low pass filter for noise removal may be adjusted to the laser spot size at the time of measurement. This leaves only periodic fluctuations longer than the spot size of the laser beam. As spatial low-pass filter processing, for example, moving average processing in which the size of the moving average section is set equal to the spot size can be used.

Hereinafter, the result of performing the data processing of steps S105, S110, and S115 of FIG. 16 on the measurement data of FIG. 11 will be described.

FIG. 20 is a diagram showing the result of performing data correction shown in step S110 of FIG. 16 on the measurement data of FIG. By performing the data correction shown in step S110, the fluctuation range (noise component) of the data is reduced from 3σ = 0.026 mm to 3σ = 0.012 mm.

FIG. 21 is a diagram showing the result of performing the low-pass filter process shown in step S115 of FIG. 16 on the data of FIG. Specifically, moving average processing is performed by setting the size of the moving average section to 50 μm, which is equal to the spot size. By performing the moving average process, the fluctuation range of the data was reduced from 3σ = 0.012 mm to 3σ = 0.004 mm.

FIG. 22 is a diagram showing the result of performing the low-pass filter process shown in step S115 without performing the data correction shown in step S110 of FIG. 16 on the measurement data of FIG. Specifically, moving average processing is performed by setting the size of the moving average section to 50 μm, which is equal to the spot size. In this case, the fluctuation range of the data is reduced only from 3σ = 0.026 mm to 3σ = 0.009 mm.

In the case of FIG. 22, if the size of the moving average section is made larger than the spot size of the laser beam, the measurement noise can be further reduced, but the noise due to the characteristic error pattern should be completely eliminated. I can not do it. Furthermore, if the size of the moving average section is increased too much, there is a disadvantage that the detection of unevenness which can be originally detected can not be detected.

[Summary of Embodiment 1]
As described above, when measuring the surface shape of the measurement object by the laser displacement meter while scanning the laser beam, a large spike-like error appears. The features of the error are as follows.

(A) The error of the laser displacement gauge has very good repeatability. Therefore, noise removal can not be performed by averaging a plurality of measurements (time averaging processing).

(B) A characteristic error pattern having a point-symmetrical shape appears by orienting the laser displacement gauge such that the light receiving unit (image sensor) is positioned forward or backward in the scanning direction with respect to the laser beam. .

(C) The range in which the above-mentioned characteristic error pattern appears depends on the laser spot size.

The above-mentioned errors can be explained by speckle noise having a diameter that can not be ignored with respect to the spot size of the laser light, or non-uniformity of the local reflectance of the surface of the measurement object. Then, the measurement error of the laser displacement gauge can be efficiently reduced by extracting and removing the characteristic error pattern of the above-mentioned error. Furthermore, since the amount of light reception of the image sensor changes sharply in the part where the error is increasing, the fluctuation rate of the amount of light reception of the image sensor can be used as an index of measurement reliability, and the characteristic error pattern and the object to be measured It can also be used to distinguish between the above-mentioned inherent unevenness.

Second Embodiment
FIG. 23 is a block diagram schematically showing the configuration of the surface shape measuring apparatus according to the second embodiment. Data processing unit 158A in FIG. 23 differs from data processing unit 158 in FIG. 4 in that data processing unit 158A in FIG. 23 includes moving average processing unit 163 instead of data correction unit 162 and filter processing unit 164. Since the surface shape measuring apparatus 140A of FIG. 23 is the same as the surface shape measuring apparatus 140 of FIG. 4 except for the data processing unit 158, the same or corresponding parts are denoted by the same reference numerals and the description is repeated. Absent.

FIG. 24 is a flowchart showing an example of measurement of surface shape and processing procedure of measurement data in the surface shape measurement apparatus according to the second embodiment. In the data processing procedure of FIG. 24, step S120 is executed instead of steps S110 and S115 of FIG. Steps S100 and S105 are the same as in the case of FIG.

In the example of FIG. 24, the moving average processing unit 163 of FIG. 23 performs moving average on the surface shape data 166 in a variable moving average section (step S120). The size of the moving average section is larger than the spot size of the light beam. When the moving average processing unit 163 performs moving average including a section (referred to as a feature section) in which a characteristic error pattern as seen in the regions RA, RB, and RC in FIG. The size of the moving average section is set larger than in the case of performing the moving average without including. For example, the size of the moving average section when performing the moving average including the feature section is set to 5 times or more of the spot size.

FIG. 25 is a flowchart showing another example of measurement of surface shape and processing procedure of measurement data in the surface shape measurement apparatus according to the second embodiment. In the data processing procedure of FIG. 24, step S125 is executed instead of steps S110 and S115 of FIG. Steps S100 and S105 are the same as in the case of FIG.

In the example of FIG. 25, the moving average processing unit 163 of FIG. 23 performs weighted moving average on the surface shape data 166 (step S125). The size of the moving average section of the weighted moving average is set to be larger than the spot size of the light beam, for example, five or more times the spot size. The moving average processing unit 163 sets weights for measurement points in the feature section where characteristic error patterns as seen in the regions RA, RB, and RC in FIG. 11 are observed more than weights for measurement points outside the feature section. Set small.

As described above, it is possible to efficiently remove the error included in the laser displacement gauge by suppressing the variation of the data in the feature section more than the variation of the data outside the feature section.

Embodiment 3
Embodiment 3 discloses a machine tool provided with the surface shape measuring apparatus of Embodiment 1 or 2. Although the case where the machine tool is a vertical machining center is described below, the machine tool may be another type such as a horizontal machining center or a lathe.

FIG. 26 is a perspective view schematically showing the configuration of the machine tool according to the third embodiment. Referring to FIG. 26, machine tool 200 includes a processing apparatus 10, an NC (Numeric Control) apparatus 24, an ATC (Automatic Tool Changer) 28, and a computer 150.

The processing apparatus 10 comprises a bed 12, a column 14 mounted on the bed 12, a spindle head 20 with a spindle 22 and a saddle 16 with a table 18.

The spindle head 20 is supported on the front surface of the column 14 and is movable in the vertical direction (Z-axis direction). A tool (not shown) or a measuring head 42 is removably attached to the tip of the spindle 22. The main spindle 22 is supported by the main spindle head 20 so that its central axis (CL in FIG. 2) is parallel to the Z axis and can be rotated about its central axis. The measurement head 42 incorporates the laser displacement meter 100 shown in FIGS. 4 and 23, a control circuit and a drive battery of the laser displacement meter, and a communication device for performing wireless communication.

The saddle 16 is disposed on the bed 12 and is movable in the back and forth horizontal direction (Y-axis direction). A table 18 is disposed on the saddle 16. The table 18 is movable in the left and right horizontal directions (X-axis direction). The workpiece 2 is placed on the table 18. The saddle 16 corresponds to the saddle 142 of FIGS. 4 and 23, and the table 18 corresponds to the table 144 of FIGS. The workpiece 2 corresponds to the measurement object 130 of FIGS. 4 and 23.

The processing apparatus 10 is a machining center that performs three-axis control that relatively moves the measurement head 42 and the workpiece 2 in the directions of three orthogonal axes relative to the X axis, the Y axis, and the Z axis. Unlike the configuration of FIG. 1, the processing apparatus 10 may be configured to move the spindle head 20 supporting the measurement head 42 in the X-axis and Y-axis directions with respect to the workpiece 2.

The NC device 24 controls the overall operation of the processing device 10 including the above-described three-axis control. ATC (Automatic Tool Changer) 28 automatically exchanges the tool and the measuring head 42 with respect to the spindle 22 respectively. The ATC 28 is controlled by an NC unit 24.

FIG. 27 is a block diagram showing a functional configuration of a portion related to the surface shape measuring device in the machine tool of FIG. 27, the Z-axis feed mechanism 34, the Y-axis feed mechanism 32, and the X-axis feed mechanism 30 provided in the processing apparatus 10 are shown.

Referring to FIGS. 26 and 27, Z-axis feed mechanism 34 drives spindle head 20 supported by column 14 to move it in the Z-axis direction. The Y-axis feed mechanism 32 drives the saddle 16 disposed on the bed 12 to move it in the Y-axis direction. The X-axis feed mechanism 30 drives the table 18 mounted on the saddle 16 and supporting the workpiece 2 to move it in the X-axis direction. The NC device 24 controls the Z-axis feed mechanism 34, the Y-axis feed mechanism 32 and the X-axis feed mechanism 30, respectively. The X-axis feed mechanism 30, the Y-axis feed mechanism 32, and the Z-axis feed mechanism 34 correspond to the X-axis drive mechanism 146X, the Y-axis drive mechanism 146Y, and the Z-axis drive mechanism 146Z in FIGS. 4 and 23, respectively.

The computer 150 includes a processor 152, a memory 154, and a communication device 168 that wirelessly communicates with the measurement head 42. The processor 152 functions as the measurement control unit 156 and the data processing units 158 and 158A described in FIGS. 4 and 23 by executing the program stored in the memory 154.

The measurement control unit 156 cooperates with the NC device 24 to continuously change the relative positional relationship between the measurement head 42 and the workpiece 2, whereby the laser beam 116 scans along the surface of the workpiece 2. Do. The measurement control unit 156 detects displacement data in the height direction (Z-axis direction) at a plurality of measurement points in the scanning direction of the laser beam 116 from the measuring head 42 as surface shape data of the workpiece 2 during scanning of the laser beam 116. get. The specific procedure is as follows.

First, based on the control from the measurement control unit 156, the NC device 24 is either one of the X-axis feed mechanism 30 and the Y-axis feed mechanism 32, or the X-axis feed mechanism 30, the Y-axis feed mechanism 32, and the Z axis. By driving at least two axes of the feed mechanism 34, the relative positional relationship between the measuring head 42 and the workpiece 2 is continuously changed. Here, the laser displacement gauge is oriented such that the light receiving unit of the laser displacement gauge is positioned forward or backward with respect to the light emitting unit of the laser displacement meter in the scanning direction of the laser beam 116.

A PLC (Programmable Logic Controller) 26 incorporated in the NC device 24 outputs a trigger signal to the communication device 168 at a predetermined cycle in synchronization with the driving of the above-mentioned feed mechanism. When the communication device 168 receives the trigger signal, it sends a measurement command f to the measurement head 42, and the measurement head 42 follows the measurement command f to determine the distance D from the measurement head 42 to the workpiece 2 (that is, the displacement of the surface of the workpiece 2) Measure Data F of the measured distance D is transmitted from the measurement head 42 to the measurement control unit 156 via the communication device 168.

The PLC 26 further obtains positional information of the X-axis feed mechanism 30, the Y-axis feed mechanism 32, and the Z-axis feed mechanism 34 in synchronization with the timing of distance measurement by the measurement head 42 described above. Detect location data. The PLC 26 transmits data of the detected position of the measurement head 42 to the measurement control unit 156.

Based on the position data of the measurement head 42 acquired from the PLC 26 and the data F of the distance D acquired from the measurement head 42, the measurement control unit 156 measures the height direction at each measurement point along the scanning direction of the laser beam 116. The displacement data (in the Z-axis direction) is stored in the memory 154 as surface shape data 166.

The processor 152 further functions as data processing units 158 and 158A that perform data processing for removing noise included in the surface shape data 166 described above. The operations of the data processing units 158 and 158A are as described in the first and second embodiments. The errors contained in the surface shape data 166 can be efficiently reduced by the data processing units 158 and 158A.

It should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims.

Reference Signs List 2 workpiece, 10 processing device, 16, 142 saddle, 18, 144 table, 24 NC device, 30 X axis feed mechanism, 32 Y axis feed mechanism, 34 Z axis feed mechanism, 42 measuring head, 100 laser displacement gauge, 110 Light emitting unit, 112 laser diode, 114 lens, 116 laser beam, 118 condensing lens (optical system), 120 linear image sensor (light receiving unit), 130 object to be measured, 132 laser spot, 140, 140 A surface shape measuring apparatus, 146 Movement mechanism, 146X X axis drive mechanism, 146Y Y axis drive mechanism, 146Z Z axis drive mechanism, 150 computer, 152 processor, 154 memory, 156 measurement control unit, 158, 158A data processing unit, 160 feature section extraction unit, 162 data Correction unit 163 the moving average processing unit, 164 filter unit, 166 surface shape data, 168 communication device, 200 a machine tool.

Claims (14)

1. A light emitting unit that emits a light beam toward a measurement target, an optical system that collects scattered light of the light beam from the measurement target, and a light reception unit that detects a collection position by the optical system; A displacement gauge that measures the displacement of the surface of the measurement object based on the light collection position at the light receiving unit;
   A moving mechanism for scanning the light beam by relatively moving the displacement meter and the measurement object;
   And a measurement control unit that controls the movement mechanism and the displacement gauge.
   The measurement control unit
   Causing the moving mechanism to scan the light beam such that the light receiving unit is positioned forward or backward in the scanning direction of the light beam with respect to the light emitting unit;
   A surface shape measuring apparatus configured to continuously measure, as surface shape data, a change in displacement of the surface of the measurement object by the displacement gauge during scanning of the light beam.
2. It further comprises a feature section extraction unit that extracts a feature section from the measurement range of the surface shape data,
   The feature section is a section having a size equal to or less than the spot size of the light beam,
   The surface shape measurement apparatus according to claim 1, wherein the surface shape data indicates a change that is a maximum in the first half or the second half of the feature section, and indicates a change that is a minimum in the other half of the feature section.
3. The feature section is a section having a size equal to or smaller than the spot size of the light beam and satisfies a predetermined condition.
   The predetermined condition is that, in a part of the first half of the feature section, the surface shape data changes in one direction beyond a predetermined range with respect to the average value of the surface shape data, and a part of the second half of the feature section The surface shape measuring apparatus according to claim 2, comprising a condition that the surface shape data changes with respect to the average value beyond the predetermined range in a direction opposite to the first half.
4. The feature section is a section having a size equal to the spot size of the light beam and satisfies a predetermined condition.
   The predetermined conditions include rotating the waveform of the surface shape data in the first half of the feature section and the waveform of the surface shape data in the second half of the feature section by 180 degrees around a data point at the center of the feature section. The surface shape measuring apparatus according to claim 2, comprising the condition that the correlation coefficient with the waveform obtained by the value exceeds a predetermined reference value.
5. The image processing apparatus further comprises a data correction unit that corrects the surface shape data so that the amount of change in the surface shape data with respect to the average value of the surface shape data becomes small in each of the one or more extracted feature sections. The surface shape measuring device according to any one of 2 to 4.
6. The data correction unit averages a measurement value at an arbitrary first measurement point of each of the feature sections with a measurement value at a second measurement point located at a symmetrical position across the middle point of the section The surface shape measurement apparatus according to claim 5, wherein the surface shape data is corrected by replacing each measurement value at the first and second measurement points with a value.
7. The surface shape measuring apparatus according to claim 5, wherein the data correction unit corrects the surface shape data by replacing data in each of the feature sections with an average value of the surface shape data.
8. The filter processing unit according to any one of claims 5 to 7, further comprising: a low pass filter processing for leaving only fluctuations of a period longer than a spot size of the light beam on the surface shape data corrected by the data correction unit. The surface shape measuring device according to any one of the preceding claims.
9. The surface shape data further includes a moving average processing unit that performs moving average in a variable moving average section,
   The size of the moving average section is larger than the spot size of the light beam,
   5. The size of the moving average section when performing moving average including the feature section is larger than the size of the moving average section when performing moving average without including the feature section. The surface shape measuring device according to item 1.
10. It further comprises a moving average processing unit that performs weighted moving average on the surface shape data,
    The size of the moving average section of the weighted moving average is larger than the spot size of the light beam,
    The surface shape measuring apparatus according to any one of claims 2 to 4, wherein a weight for the measurement point in the feature section is smaller than a weight for the measurement point outside the feature section.
11. A machine tool comprising the surface shape measuring device according to any one of claims 1 to 10.
12. It is a surface shape measuring method using a noncontact displacement meter,
    The displacement meter includes a light emitting unit that emits a light beam toward a measurement target, an optical system that collects scattered light of the light beam from the measurement target, and light reception that detects a collection position by the optical system. Including
    The surface shape measuring method is
    The displacement meter may be the object to be measured along the scanning direction while maintaining the positional relationship between the light receiving unit and the light emitting unit such that the light receiving unit is positioned forward or backward in the scanning direction with respect to the light emitting unit. Moving relative to the object,
    Determining the surface shape of the measurement object based on the change in the measurement value of the displacement gauge in accordance with the relative movement of the displacement gauge.
13. The step of determining the surface shape includes the step of extracting a feature section from a measurement range of the surface shape of the measurement object,
    The feature section is a section having a size equal to or less than the spot size of the light beam,
    13. The surface shape measurement according to claim 12, wherein the measurement data of the surface shape of the measurement object indicates a change that is maximum in the first half or the second half of the feature section, and indicates a change that is minimum in the other half of the feature section. Method.
14. In the step of determining the surface shape, in each of the one or more extracted feature sections, the measurement data is reduced so that a deviation of each measurement value from an average value of measurement data of the surface shape of the measurement object is reduced. The surface shape measuring method according to claim 13, further comprising the step of correcting.

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