JP2015165210A - Surface shape measuring device and machine tool provided with the same - Google Patents

Abstract

An object of the present invention is to measure the surface shape of an object to be measured in a short time by minimizing the influence of a peculiar error that occurs during measurement using a non-contact displacement meter using a light beam. In a surface shape measuring apparatus, a displacement meter emits a light beam toward a measurement object, and based on scattered light of the light beam from the measurement object, the measurement of the measurement object. Measure the displacement of the surface. The measurement control unit 156 measures the displacement of the surface of the measurement object 130 with the displacement meter 100 at a plurality of measurement points while scanning the light beam 116 with the moving mechanism 146. The error range setting unit 160 sets an error range for the measurement value of the displacement meter 100 at each measurement point. The surface shape output unit 162 outputs a straight line or curve passing through each error range as a measurement result of the surface shape along the scanning direction of the light beam. Here, the shape of the curve is set so that the number of points having extreme values and the number of inflection points are as small as possible. [Selection] Figure 4

Description

  The present invention relates to a surface shape measuring device that measures a surface shape by a non-contact type displacement sensor using a light beam, and a machine tool including the surface shape measuring device.

  Conventionally, when machining with a machine tool, it is common to measure the shape of the workpiece with a non-contact sensor. Usually, as the non-contact type sensor, a triangulation type displacement meter using a light beam such as a laser displacement meter is used. The measured surface shape data is used, for example, for correcting machining defects by comparing with design data.

  Japanese Patent Application Laid-Open No. 2002-122423 (Patent Document 1) discloses an example of a method for specifying a correction portion by processing in a measured object such as a spherical lens having an uneven surface. Specifically, first, X, Y, and Z coordinate values of an arbitrary region on the surface of the object to be measured are measured, and the center coordinates of the spherical surface are approximated from the measured X, Y, and Z coordinate values. Next, the center of the spherical surface based on the design value is moved from the center coordinates obtained by the approximation calculation so that the spherical surface based on the design value is superimposed on the spherical surface that is the measured value of the object to be measured. Next, a correction part is specified by calculating the difference between the spherical surface based on the design value superimposed by the movement and the measured value of the object to be measured, and displaying the calculation result.

JP 2002-122423 A

  It is known that there is a unique measurement error in the triangulation displacement measurement using a light beam. This measurement error is characterized in that it includes spike noise that is much larger than the actual surface roughness and cannot be removed by the time averaging process. Even if the measurement data is subjected to a spatial averaging process such as moving average, it is not easy to completely remove the influence of spike-like noise. As a result, it becomes difficult to grasp the shape of the workpiece after machining, or it becomes difficult to extract machining defects or material defects by comparing measured data and design data. The above Japanese Patent Laid-Open No. 2002-122423 (Patent Document 1) does not take into consideration the presence of the above measurement noise.

  The present invention has been made in consideration of the above-mentioned problems, and its purpose is to minimize the influence of a specific error that occurs during measurement using a non-contact displacement meter with a light beam, The object is to provide a surface shape measuring apparatus capable of measuring the surface shape of a measurement object in a short time.

  In one aspect, the present invention is a surface shape measuring apparatus, and includes a displacement meter, a moving mechanism, a measurement control unit, an error range setting unit, and a surface shape output unit. The displacement meter emits a light beam toward the measurement object, collects the scattered light of the light beam from the measurement object, and calculates the displacement of the surface of the measurement object based on the change in the position where the scattered light is collected. taking measurement. The moving mechanism scans the light beam by relatively moving the displacement meter and the measurement object. The measurement control unit measures the displacement of the surface of the measurement object with a displacement meter at a plurality of measurement points while scanning the light beam with the moving mechanism. The error range setting unit sets an error range for the measurement value of the displacement meter at each measurement point. The surface shape output unit outputs a straight line or a curve passing through each error range as a measurement result of the surface shape along the scanning direction of the light beam. Here, the shape of the curve is set so that the number of points having extreme values and the number of inflection points are as small as possible.

  According to the above configuration, the error range can be set according to the magnitude of the measurement noise unique to the displacement meter using a light beam, so that a measurement result of the surface shape that is not affected by the measurement noise is obtained. be able to.

  Preferably, the error range is set according to the spot size of the light beam on the surface of the measurement object. In the case where the spot size of the light beam changes according to the distance from the displacement meter, the error range is preferably changed according to the measured value of the displacement meter.

  According to the study of the inventors of the present application, the magnitude of measurement noise unique to a laser displacement meter or the like changes according to the spot size of the light beam. Therefore, by setting the error range according to the spot size, the size of the error range can be made appropriate.

  In a preferred embodiment, the surface shape output unit applies a straight line or a curve to the measurement value at each measurement point, and when the fitted straight line or curve passes through each set error range, A curve is output as a measurement result of the surface shape. Further, when the applied straight line or curve does not pass through a part of the error range, the surface shape output unit reapplies the straight line or curve with the changed function shape to the measurement value at each measurement point. According to the above-described embodiment, the schematic shape of the measurement object can be grasped by a short-time measurement.

  In another preferred embodiment, the measurement target is a workpiece machined based on design data. In this case, the surface shape output unit applies a straight line or a curve indicating the surface shape based on the design data to the measurement value at each measurement point, and when the fitted straight line or curve passes through each set error range, The fitted straight line or curve is output as the measurement result of the surface shape. Furthermore, the surface shape output unit determines that there is a processing defect or material defect near the measurement point where a part of the error range is set when the fitted straight line or curve does not pass through part of the error range. To do.

  According to the other embodiment described above, it is possible to grasp the outline shape of the workpiece and the presence or absence of processing defects or material defects by measuring in a short time.

  This invention is a machine tool provided with said surface shape measuring apparatus in another situation.

  Therefore, according to the present invention, it is possible to measure the surface shape of an object to be measured in a short time by minimizing the influence of a specific error that occurs during measurement using a non-contact displacement meter using a light beam. it can.

It is a figure which shows typically the structure of a laser displacement meter. 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. 1 is a block diagram schematically showing a configuration example of a surface shape measuring apparatus according to Embodiment 1. FIG. It is a figure which shows an example of the measurement result of the gauge block surface by a laser displacement meter. It is a figure which shows the more detailed measurement result of the gauge block surface by a laser displacement meter. It is a figure for demonstrating the measurement error resulting from the nonuniformity of the reflectance of a measurement object. It is a figure which shows an example of the luminance distribution detected by a linear image sensor. It is a figure for demonstrating the outline | summary of a data processing procedure. It is a flowchart which shows an example of the measurement procedure of a surface shape, and the procedure of data processing. It is a flowchart which shows the example of a change of a data processing procedure. It is a figure for demonstrating the specific example of the procedure shown in FIG. It is a flowchart which shows the data processing procedure in case design data is given. It is a figure for demonstrating the specific example of the data processing procedure of FIG. It is a figure which shows an example of the change of the beam diameter of the laser beam emitted from a laser diode. It is a figure for demonstrating the example of a change of step S105 of FIG. FIG. 10 is a perspective view schematically showing a configuration of a machine tool according to a third embodiment. It is a block diagram which shows the functional structure of the part regarding the surface shape measuring apparatus among the machine tools of FIG.

  Hereinafter, each embodiment will be described in detail with reference to the drawings. In the following embodiments, a surface shape measuring device using a laser displacement meter will be described as an example. However, in the case of a non-contact displacement meter using a non-coherent light beam instead of a laser beam, The present invention can be applied. In the following description, the same or corresponding parts are denoted by the same reference symbols, and the description thereof may not be repeated.

<Embodiment 1>
[Outline of laser displacement meter]
FIG. 1 is a diagram schematically showing a configuration of a laser displacement meter. Referring to FIG. 1, 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 is irradiated onto 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 collected by the condenser lens 118 on the linear image sensor 120 arranged in the angle direction of the laser beam 116 and γ. In FIG. 1, 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 surface of the measurement object 130 to the condenser lens 118 is l.

  The linear image sensor 120 is disposed at an angle based on a Scheimpflug Condition. That is, the detection surface of the linear image sensor 120 and the main surface of the condenser lens 118 intersect with each other in a straight line, and the angle formed by these surfaces is β. A surface including the laser beam 116 is a subject surface. With this arrangement, even if the distance between the measurement object 130 and the laser displacement meter 100 changes, the laser spot 132 is imaged on the linear image sensor 120 without being blurred.

  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 surface. A direction parallel to the optical path surface and perpendicular to the Z-axis direction is taken as an X-axis direction. A direction perpendicular to both the X-axis direction and the Z-axis direction is taken as a 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 path surface).

  Here, the beam size of laser light (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 symmetric beam profile as in the TEM00 mode, in a plane orthogonal to the optical axis, 1 / e 2 of the peak value (where e is the base of 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 including 86.5% of the total beam power is included on the basis of the peak power, and the diameter of this circle is defined as the beam size. In this specification, in order to include various definitions, the range of the beam size (measurement object) from the diameter of the circle including 50% of the total power to the diameter of the circle including 95% of the total power is substantially exceeded. 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, the linear image sensor 120 includes 1024 pixels 122 arranged in a straight line. Each pixel 122 outputs a signal with a luminance level from 0 to a maximum of 255 according to the amount of received light.

  FIG. 3 is a diagram illustrating 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 luminance level. Referring to FIGS. 2 and 3, the light diffusely reflected on the measurement object 130 is condensed by the condenser lens 118 onto the spot 124 on the linear image sensor 120, whereby a Gaussian as shown in FIG. Distributed data is obtained. The distance from the barycentric position 182 of the data in FIG. 3 to the object is calculated by triangulation. In the case of FIG. 3, the center line 180 of the luminance distribution and the gravity center position 182 coincide with each other.

[Configuration of surface shape measuring device]
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, surface shape measurement apparatus 140 includes table 144 on which measurement object 130 is placed, saddle 142, laser displacement meter 100, X-axis drive mechanism 146 </ b> X, and Y-axis drive mechanism 146 </ b> Y. , A 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. Therefore, the laser beam 116 scans the surface of the measurement object 130 by the moving mechanism 146.

  The configuration of the moving mechanism 146 is not limited to the example of 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, a display device and an input / output device (not shown), and the like. 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 measures the surface shape data 166 of the measurement object 130 at a plurality of measurement points using the laser displacement meter 100. The measured surface shape data 166 is stored in the memory 154. The surface shape data 166 includes a plurality of measurement points (also referred to as laser beam irradiation positions, that is, scanning positions) on the measurement object 130, and displacement in the Z-axis direction of the surface of the measurement object 130 at each measurement point. Is a data series associated with.

  The data processing unit 158 performs data processing on the data (surface shape data 166) measured by the laser displacement meter 100. By this data processing, characteristic noise included in the measurement data of the laser displacement meter is removed. Specific contents of the data processing will be described later with reference to FIGS. In the following, first, the cause of the characteristic noise will be described.

[Characteristic noise contained in laser displacement meter measurement data]
FIG. 5 is a diagram illustrating an example of a measurement result of the gauge block surface by a laser displacement meter. Specifically, FIG. 5 shows the result of measuring the displacement of the surface of the metal gauge block at a sampling interval of 0.1 mm using the laser displacement meter 100. The sampling interval is longer than the spot size (50 μm) of the laser beam used for measurement. As shown in FIG. 5, the surface roughness of the gauge block is about 0.06 μm, whereas the measurement data has a 3σ value (σ represents a standard deviation) and a noise as large as 36 μm (spike-like noise) ) Was observed.

  FIG. 6 is a diagram showing a more detailed measurement result of the gauge block surface by the laser displacement meter. In the case of FIG. 6, measurement data (surface shape data) is shown for the same gauge block as in FIG. 5 when a measurement range of 0.4 mm is measured at a sampling interval of 1 μm.

  This detailed measurement is characterized in that the sampling interval is considerably shorter than the spot size (50 μm) of the laser beam. Further, the light receiving unit (linear image sensor 120) is arranged in front of the light emitting unit 110 in FIG. 1 in the scanning direction. That is, the scanning direction of the laser beam is aligned with the optical path plane (XZ plane in FIG. 1) including the center axis of the laser beam and the optical axis of the condenser lens 118.

  With reference to FIG. 6, in a more detailed measurement, a relatively large error (spike-like noise) as observed in the regions RA, RB, and RC was observed together with fine noise. The errors seen in these areas RA, RB, RC have a characteristic shape. Specifically, as the measurement point (scanning position of the laser beam) moves from left to right, the height displacement measured by the laser displacement meter is initially lower than the average level of the data, and then It shows a change that becomes higher than the average level and finally returns to the original average level.

  Furthermore, the reproducibility of the measurement results shown in FIG. 6 was very good, and it was observed as if minute irregularities existed on the surface. Specifically, the data variation when the same measurement point was measured 20 times was 2.3 μm as a 3σ value. Therefore, this noise cannot be removed by the time averaging process (a process in which the same measurement is repeated and averaged).

  It is clear that the cause of the noise is not electrical noise, servo motor vibration, or the like. This is because the noise caused by these causes can be canceled by the time averaging process. Furthermore, the cause of the noise is not an influence of temperature change or a mechanical motion error of the moving mechanism 146. This is because the influence of the temperature change is stabilized 30 to 60 minutes after the power is turned on, and the mechanical motion error appears as a large swell compared to the spike-like noise.

  From the above, it is considered that the cause of the noise is non-uniformity in the microscopic reflectance of the surface of the measurement object 130. When the surface of the measurement object 130 has a non-uniform reflectance (brightness unevenness) smaller than the laser spot size, noise having a characteristic shape as seen in the regions RA, RB, and RC in FIG. 6 is generated. It is because it can explain what to do.

  Note that the non-uniformity of reflectance is caused by non-uniform materials, scratches on the metal surface, irregularities, and the like. Further, in the case of a laser displacement meter, the reflectance may be non-uniform due to speckle. Normally, the size of the average speckle diameter is smaller than the width of each pixel of the linear image sensor 120, but a speckle having a diameter larger than the average value that appears due to non-uniformity in a specific place is not included in each pixel. Since it is not averaged, it can cause noise seen in FIGS.

  FIG. 7 is a diagram for explaining a measurement error due to the non-uniformity of the reflectance of the measurement object. FIG. 8 is a diagram illustrating an example of a luminance distribution detected by the linear image sensor.

  In FIGS. 7A and 7B, the size of the laser spot 132 is shown large for easy illustration. It is assumed that the scanning direction of the laser beam is the + X direction, and the linear image sensor 120 as the light receiving unit is positioned forward of the scanning direction with respect to the central axis 116C of the laser beam.

  As shown in FIGS. 7A and 7B, it is assumed that there are regions (P1, P2) that are smaller than the spot size of the laser spot 132 and have a higher reflectance than the surroundings on the surface of the measurement object. The position of the high reflectance region changes in the order of P1 and P2 as the laser beam is scanned in the + X direction (scanning direction) (that is, as the measurement object moves in the −X direction).

  When the high reflectance region is located at P1 with respect to the center axis 116C of the laser beam, as shown in FIG. 8A, the data gravity center position 182 with respect to the center position 180 of the imaging spot of the image sensor 120. Shifts. For this reason, the measurement object 130 is measured so as to be located at a position (lower position) away from the light emitting unit 110 by ε− than the actual measurement. On the other hand, when the high reflectivity region is positioned at P2 with respect to the laser beam 116, the data center of gravity 182 is illustrated with respect to the center 180 of the imaging spot of the image sensor 120, as shown in FIG. 8 (A) shifts in the opposite direction. For this reason, the measurement object 130 is measured so as to be at a position (high position) closer to the light emitting unit 110 by ε + than actual.

  Therefore, as the relative position of the minute high reflectance region moves, the displacement in the height direction measured by the laser displacement meter is initially lower than the average level of the data and then higher than the average level. Finally, it shows a change that returns to the original average level. It should be noted that the direction of the error change described above is a case where the light receiving unit (linear image sensor 120) is located in front of the scanning direction with respect to the light emitting unit 110 in FIGS. 7A and 7B. There is. When the light receiving unit (linear image sensor 120) is located behind the light emitting unit 110 in the scanning direction, the direction of error change is reversed.

The magnitude of the measurement error due to the non-uniformity 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 measurement error (error when erroneously recognizing around the periphery of the laser spot 132) ε _max is given by the following equation (1).

ε _max = w / (2 · tan (γ)) (1)
In the laser displacement meter used in the measurement of FIGS. 5 and 6, 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 (1A), which is a value comparable to the measurement error of FIGS.

ε _max = 25 / tan (π / 6) = 43 [μm] (1A)
From the above equation (1), it can be seen that the maximum value of the measurement error increases as the laser spot size w increases. Specifically, when the surface shape of a square region having a side of 0.5 mm is measured with a laser beam having a spot size of 50 μm in diameter, the surface shape of the same region is changed by changing the laser spot size to 400 μm in diameter. When compared with the case of measurement, the maximum value of the surface irregularities measured by the laser displacement meter increased from 67 μm to 80 μm.

[Data processing procedure]
(1. Overview)
As described above, characteristic noises as shown in FIGS. 5 and 6 are generated in the measurement of the surface shape using the triangulation laser displacement meter. This characteristic noise cannot be removed by the time averaging process because of its reproducibility. Furthermore, since it contains a large spike-like noise (about 100 times the actual unevenness of the surface of the measurement object), the measurement noise cannot be completely removed even if the moving average process is performed. If the moving average section is too wide in order to suppress the influence of noise, it is impossible to detect the actually present unevenness level that can be detected.

  If attention is paid to the characteristic noise shape seen in the regions RA, RB, and RC in FIG. 6, it is possible to extract the noise from the data and cancel it. However, since this characteristic noise shape can be seen in a range below the spot size, the sampling interval must be about 1/10 to 1/20 of the spot size in order to accurately capture the shape. For this reason, there exists a demerit that measurement takes time.

  The following data processing procedure can be suitably used when the sampling interval is larger than ½ of the spot size, that is, when measuring the surface shape in a short time. In this case, the measurement noise is treated as random noise as seen in FIG. The data processing procedure will be described below.

  FIG. 9 is a diagram for explaining an outline of a data processing procedure. FIG. 9 shows the relationship between the measurement point MP (that is, the scanning position of the laser beam) on the measurement object and the measurement value MV (that is, the displacement in the height direction).

  Referring to FIGS. 4 and 9, data processing unit 158 that performs data processing of surface shape data 166 includes error range setting unit 160 and surface shape output unit 162.

  The error range setting unit 160 sets an error range ER for the measurement value MV of the laser displacement meter 100 at each measurement point MP. Specifically, as shown in FIG. 9, the error range ER is set in a range from MV−Δ to MV + Δ for each measurement value MV. The width Δ of the error range corresponds to the maximum value of the characteristic noise described with reference to FIGS. 5 and 6, and is determined according to the spot size of the laser beam. That is, as the spot size of the laser beam increases, the error range width Δ is set larger. Note that the characteristic noise level is reduced when the spot size of the laser beam is made as small as possible, so that more accurate measurement is possible.

  The surface shape output unit 162 outputs a straight line or a curve passing through each error range ER as a measurement result of the surface shape of the measurement object along the scanning direction of the laser beam. In the case of a curve, it is desirable to have a smooth shape with as little as possible unevenness. That is, the shape of the curve is determined so that the number of points having extreme values (maximum points, minimum points) and the number of inflection points are minimized. The case where there is no inflection point (when the number of inflection points is 0) is most desirable. In this case, the curve is convex upward or convex downward. In a curve having an inflection point, a connection point between an upward convex portion and a downward convex portion corresponds to the inflection point. In this specification, a case where a part includes a straight line portion (that is, a case where the straight line portion and the curved portion are connected) is also included in the curve.

(2. Explanation of data processing procedure)
The details of the data processing procedure will be described below while summarizing the above description.

  FIG. 10 is a flowchart illustrating an example of a surface shape measurement procedure and a data processing procedure. With reference to FIGS. 4 and 10, first, the measurement control unit 156 drives the moving mechanism 146 to scan the measurement target 130 with the laser beam 116, thereby causing the measurement target unit 130 to move on the surface of the measurement target 130. The displacement in the height direction (that is, the surface shape) is measured using the laser displacement meter 100 at a plurality of measurement points (step S100). The measurement data is stored in the memory 154 as the surface shape data 166.

  Next, the error range setting unit 160 sets an error range ER corresponding to the laser spot size for the measurement value MV of the laser displacement meter 100 at each measurement point MP (step S105).

  Next, the surface shape output unit 162 applies (fits) a straight line or a curve to the measurement value MV (also referred to as measurement data) at each measurement point using the least square method or the maximum likelihood method (step S110). ). Subsequently, the surface shape output unit 162 determines whether or not the fitted straight line or curve (hereinafter also referred to as an approximate straight line or approximate curve) passes through all the error ranges ER at each measurement point MP set in step S105. Determination is made (step S115).

  If the approximate line or approximate curve passes through each error range ER (YES in step S115), the surface shape output unit 162 outputs the approximate line or approximate curve as the measurement result of the surface shape of the measurement object. Output (step S120), the process is terminated.

  On the other hand, when the approximate straight line or approximate curve does not pass through each error range ER (NO in step S115), the surface shape output unit 162 has a function form of a straight line or curve to be applied to the measured value MV at each measurement point MP. To change. Then, the surface shape output unit 162 applies the straight line or the curve whose function shape is changed again to the measurement value MV at each measurement point MP (step S125). After that, the surface shape output unit 162 returns the process to step S115, and re-determines whether or not the new functional line or curve applied to the measurement data passes through the error range ER at each measurement point MP. To do.

  In the above-described steps S110 and S125 for applying a straight line or a curve, it is desirable to first apply a straight line or a functional curve having as few local maximum points, local minimum points, and inflection points as possible. As a result, when the approximate straight line or the approximate curve does not pass through a part of the error range ER (NO in step S115), a function curve having a large number of maximum points, minimum points, and inflection points is gradually measured. Try to fit the data. For example, when an n-order function (n ≧ 0) is applied to measurement data, a zero-order function (constant function) is first applied to measurement data, then a linear function is applied to measurement data, and then a quadratic function. It is desirable to gradually increase the order n, such as fitting a function.

(3. When dividing the measurement range into multiple sections)
FIG. 11 is a flowchart illustrating a modification example of the data processing procedure. The steps in FIG. 11 are replaced with steps S110 to S125 in FIG. Since steps S100 and S105 in FIG. 10 are common, they are not shown in FIG. As already described, in step S105, an error range ER corresponding to the laser spot size is set for the measurement value MV at each measurement point MP.

FIG. 12 is a diagram for explaining a specific example of the procedure shown in FIG.
In the examples of FIGS. 11 and 12, an example in which an n-order function (n ≧ 0) is applied to the measurement value MV at each measurement point MP is shown. In this case, it is desirable that the order of the n-order function is as small as possible. However, since it is difficult to approximate the measurement data of the entire measurement range so as to pass through all the set error ranges ER using an n-order function of one order, first, a first approximation that can be linearly approximated. The entire measurement range is divided into a seed section and a second kind section that is difficult to perform linear approximation (step S200). For example, in the example of FIG. 12, the measurement range is divided into three first type sections (section I, section III, section V) and two second type sections (section II, section IV).

  Next, the surface shape output unit 162 applies a zero-order function or a linear function to the measurement value MV of each measurement point MP in each first type section using the least square method or the maximum likelihood method (step S205). ). In the example of FIG. 12, zero-order functions 212 and 216 are applied to the measured values MV in the sections I and V, respectively, and a linear function 214 is applied to the measured values MV in the section III.

  Next, the surface shape output unit 162 determines whether or not the fitted zeroth-order or first-order function passes through each set error range ER in each first type section (step S210). As a result, when the approximate straight line does not pass through a part of the error range ER (NO in step S210), the surface shape output unit 162 changes the classification of the first type and second type sections (step S215). Specifically, for example, the range of the second type section is expanded and the range of the first type section is narrowed. Thereafter, the surface shape output unit 162 executes the above fitting (step S205) and determination (step S210) again.

  On the other hand, when the approximate straight line passes through each error range ER in each first type section (YES in step S210), the surface shape output unit 162 outputs the 0th order or the first order of the adjacent first type section. Under the constraint that the approximate function is smoothly continuous (smoothly continuous means that the derivative is also continuous), the n-th order function (n ≧ 2) for the measurement data in each second type interval Is applied (step S220). Since the order of the n-order function is preferably as small as possible, a quadratic function (initial value: n = 2) is applied first. By introducing a Lagrange multiplier, a constraint condition can be added to the least square method and the maximum likelihood method.

  In the example of FIG. 12, the quadratic function 220 is applied to the measurement data in the section II so as to smoothly follow the zero-order function 212 in the section I and the primary function 214 in the section III. A quadratic function 222 is applied to the measurement data in the section IV so as to smoothly follow the linear function 214 in the section II and the zero-order function in the section V.

  Next, the surface shape output unit 162 determines whether or not the n-order function applied by the above method passes through each set error range ER in each second type section (step S225). As a result, when the surface shape output unit 162 passes through each error range ER in which the n-order function applied to the measurement data passes through each second type section (YES in step S225), each first type The zero-order or linear function fitted in the section and the n-order function (n ≧ 2) fitted in each second type section are output as the surface shape measurement results (step S230).

  On the other hand, when each n-th order function applied to the measurement data does not pass through each set error range ER in each second type section, the surface shape output unit 162 sets the order of the n-th order function to be approximated to 1 (Step S235), and then the fitting (S220) and determination (step S225) steps are re-executed.

(4. When design data is given)
When the measurement object is a workpiece machined based on the design data, an approximate straight line or an approximate curve indicating the surface shape along the scanning direction of the laser beam can be obtained by using the design data. Hereinafter, a specific description will be given with reference to FIGS. 4, 13, and 14.

  FIG. 13 is a flowchart showing a data processing procedure when design data is given. The steps in FIG. 13 are replaced with steps S110 to S125 in FIG. Since steps S100 and S105 in FIG. 10 are common, they are not shown in FIG. As already described, in step S105, the error range ER corresponding to the spot size of the laser beam is set for the measurement value MV at each measurement point MP.

  FIG. 14 is a diagram for explaining a specific example of the data processing procedure of FIG. In the example of FIG. 14, the surface shape based on the design data is expressed by a zero-order function (constant function).

  First, the surface shape output unit 162 uses a least-squares method for a straight line or a curve indicating the surface shape in the scanning direction of the laser beam based on the design data with respect to the measurement value MV (measurement data) at each measurement point MP. Or it applies by the maximum likelihood method (step S300). In this case, the offset value (shift amount) in the height direction or both in the height direction and the horizontal direction is a parameter, and these parameters are optimized by the least square method or the maximum likelihood method.

  As a result, when the obtained approximate line or curve passes through all the error ranges ER set for each measurement point MP (YES in step S305), the surface shape output unit 162 displays the approximate line or curve as The measurement result of the surface shape of the measurement object along the scanning direction of the laser beam is output (step S340), and the process ends.

  On the other hand, when an approximate line or curve indicating a surface shape based on the design data does not pass through a part of the error range ER among the error ranges ER set for each measurement point MP (NO in step S305), The surface shape output unit 162 determines that there is a processing defect or a material defect in the vicinity of the measurement point MP where the partial error range ER is set. In this case, the surface shape output unit 162 sets the vicinity of the measurement point determined to have the processing defect or the material defect as an inappropriate section, and sets the other sections as appropriate sections (step S310). In the example of FIG. 14, the sections I and III are set as appropriate sections, and the section II is set as an inappropriate section.

  Next, the surface shape output unit 162 is a straight line indicating the surface shape based on the design data with respect to the measurement value MV at each measurement point MP in the appropriate section (all appropriate sections when there are a plurality of proper sections). Alternatively, the curve is fitted by the least square method or the maximum likelihood method (step S315). As a result, when the fitted straight line or curve does not pass through a part of the error range ER set in the appropriate section (NO in step S320), the surface shape output unit 162 classifies the appropriate and improper sections. Is changed (step S325). Specifically, for example, the range of the inappropriate section is expanded and the range of the appropriate section is narrowed. Thereafter, the surface shape output unit 162 executes the steps of fitting (S315) and determination (S320) in the appropriate section again.

  On the other hand, when the fitted straight line or curve passes through each error range ER in the appropriate section (YES in step S320), the surface shape output unit 162 continues to the approximate straight line or curve in the adjacent proper section. A curve is applied to the measurement data in the improper section under the constraint condition (or smoothly continuous) (step S330).

  In the example of FIG. 14, zero-order functions 240 and 242 indicating the surface shape in the scanning direction of the laser beam based on the design data are applied to the measured values MV in the sections I and III. A quartic function 244 is applied to each measured value MV in the section II so as to be smoothly continuous with the zero-order functions 240 and 242 of the sections I and III.

  Next, the surface shape output unit 162 determines whether or not the curve applied to each measurement data passes through each set error range ER in each improper section (step S335). As a result, the surface shape output unit 162, in each improper section, when all the fitted curves pass through the set error ranges ER (YES in step S335), the surface shape output unit 162 uses the design data fitted in the appropriate section. A straight line or a curve indicating the surface shape based on the curve and a curve fitted in the inappropriate section are output as a measurement result of the surface shape.

  On the other hand, when the approximate line or curve does not pass through a part of the error range ER (NO in step S335), the surface shape output unit 162 changes the function form of the curve to be applied to the measurement data in each inappropriate area. . For example, when applying an n-order function, the order n is increased. And the surface shape output part 162 applies again the curve which changed the function form to the measurement data of an improper area (step S345). After that, the surface shape output unit 162 returns the process to step S335, and again determines whether or not the curve fitted to each measurement data passes through each set error range ER in each improper section (step). S335).

[Summary and effect]
To summarize the above, when measuring the surface shape of an object to be measured using a laser displacement meter (more generally, a triangulation displacement meter using a light beam), a spike-like shape that cannot be removed by time averaging processing is used. Large noise appears. The cause of this noise is considered to be due to the microscopic (smaller than the laser spot size) reflectance nonuniformity of the surface of the measurement object. Therefore, the magnitude of noise is determined according to the laser spot size, and the maximum value of the noise magnitude increases as the laser spot size increases.

  In consideration of the characteristics of the noise, in the surface shape measuring apparatus according to the first embodiment, an error range corresponding to the laser spot size is set for the measurement values at each measurement point. Then, a straight line or a curve passing through each set error range is output as a measurement result of the surface shape along the scanning direction of the laser beam. The shape of the curve in this case is set so that the number of points having extreme values and the number of inflection points are as small as possible (in the case of an n-order function, the one having the smallest order n is selected). . As a result, surface shape data that is not affected by the spike-like noise can be obtained in a short time. Therefore, for example, it can be suitably used when grasping the schematic shape of the measurement object. Note that the size of the noise becomes smaller when the spot size of the laser beam is made as small as possible, so that more accurate measurement is possible.

  Further, in the case where the measurement object is a workpiece machined based on the design data, a straight line or a curve indicating the surface shape based on the design data is applied to the measurement data so as to pass within the set error range. If there is a part (processing defect or material defect) that does not pass within the set error range, an approximate straight line or curve indicating the surface shape based on the design data, the design data and the measurement data in the vicinity of the part A different curve is fitted, and the fitted curve is output as a measurement result of the surface shape of the part. As a result, it is possible to grasp the general shape of the workpiece, as well as the presence or absence of processing defects or material defects, by measuring in a short time.

<Embodiment 2>
In FIG. 1, the laser beam 116 emitted from the laser diode 112 is shaped into a substantially parallel light by the lens 114, but in reality, the beam size of the laser beam 116 changes according to the distance from the laser diode 112. To do.

  FIG. 15 is a diagram illustrating an example of a change in the beam diameter of laser light emitted from a laser diode. Referring to FIG. 15, when the beam waist portion is a reference position, when the beam size at the reference position is 50 μm, the beam size is up to 460 μm at a position shifted in the height direction by ± 10 mm from the reference position. To increase.

  As described with reference to FIG. 7 and the like, the maximum value of the noise generated during measurement by the laser displacement meter changes according to the size of the beam size (ie, spot size) on the surface of the measurement object. To do. Therefore, desirably, the error range set in step S105 of FIG. 10 also needs to be changed according to the measured value of the laser displacement meter.

  FIG. 16 is a diagram for explaining a modified example of step S105 in FIG. FIG. 16 shows the relationship between the measurement points MP1 to MP5 (that is, the scanning position of the laser beam) on the surface of the measurement object and the measurement value (that is, the displacement in the height direction). It is assumed that the measurement value d1 at the measurement point MP3 is a reference position corresponding to the beam waist position in FIG.

  As shown in FIG. 16, the measurement value d2 at the measurement points MP2 and MP4 is lower than the reference position (d1), and the measurement value d3 at the measurement points MP1 and MP5 is lower than the measurement value d2 at the measurement points MP2 and MP4. Even lower. Therefore, when the width of the error range set for the measurement value d1 at the measurement point MP1 is Δ1, the width of the error range for the measurement value d2 at the measurement points MP2 and MP4 is set to Δ2 which is larger than Δ1. Further, the width of the error range with respect to the measurement value d3 at the measurement points MP1 and MP5 is set to Δ3 which is larger than Δ2. A curve passing through each error range set in this way is output as a measurement result of the surface shape.

  As described above, in the surface diameter measuring apparatus according to the second embodiment, the size of the error range set in step S105 of FIG. 10 is changed according to the measurement value of the laser displacement meter. The size of the error range to be set is determined in advance according to the size of noise observed through experiments.

<Embodiment 3>
The third embodiment discloses a machine tool provided with the surface shape measuring device of the first or second embodiment. Although the case where the machine tool is a vertical machining center is described below, the machine tool may be of other types such as a horizontal machining center or a lathe.

  FIG. 17 is a perspective view schematically showing the configuration of the machine tool according to the third embodiment. Referring to FIG. 17, machine tool 200 includes a machining device 10, an NC (Numerical Control) device 24, an ATC (Automatic Tool Changer) 28, and a computer 150.

  The processing apparatus 10 includes a bed 12, a column 14 installed on the bed 12, a spindle head 20 having a spindle 22, and a saddle 16 having 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 measurement head 42 is detachably attached to the tip of the main shaft 22. The main shaft 22 is supported by the main shaft head 20 so as to be rotatable about its central axis (CL in FIG. 18).

  The measurement head 42 incorporates the laser displacement meter 100 shown in FIG. 1, a control circuit for the laser displacement meter, a driving battery, and a communication device for performing wireless communication.

  The saddle 16 is disposed on the bed 12 and is movable in the front-rear 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 direction (X-axis direction). The workpiece 2 is placed on the table 18. The saddle 16 corresponds to the saddle 142 in FIG. 4, and the table 18 corresponds to the table 144 in FIG. The workpiece 2 corresponds to the measurement object 130 of FIG.

  The processing apparatus 10 is a machining center that linearly moves the measuring head 42 and the workpiece 2 relatively in directions of three axes orthogonal 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 that supports the measurement head 42 in the X-axis and Y-axis directions with respect to the workpiece 2.

  The NC device 24 controls the operation of the entire processing device 10 including the above-described orthogonal three-axis control. An ATC (automatic tool changer) 28 automatically changes the tool and the measuring head 42 with respect to the spindle 22. The ATC 28 is controlled by the NC device 24.

  FIG. 18 is a block diagram showing a functional configuration of a part related to the surface shape measuring device in the machine tool of FIG. FIG. 18 shows a Z-axis feed mechanism 34, a Y-axis feed mechanism 32, and an X-axis feed mechanism 30 provided in the machining apparatus 10.

  17 and 18, the Z-axis feed mechanism 34 drives the spindle head 20 supported by the column 14 to move in the Z-axis direction. The Y-axis feed mechanism 32 drives the saddle 16 disposed on the bed 12 to move in the Y-axis direction. The X-axis feed mechanism 30 drives the table 18 that is placed on the saddle 16 and supports the workpiece 2 to move 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 respectively correspond to the X-axis drive mechanism 146X, the Y-axis drive mechanism 146Y, and the Z-axis drive mechanism 146Z in FIG.

  The computer 150 includes a processor 152, a memory 154, a communication device 168 for performing wireless communication with the measurement head 42, and the like. The processor 152 functions as the measurement control unit 156 and the data processing unit 158 described with reference to FIG. 4 by executing the program stored in the memory 154.

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

  First, based on the control from the measurement control unit 156, the NC device 24 is configured so that 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 feed mechanism. 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.

  A PLC (Programmable Logic Controller) 26 built in the NC device 24 outputs a trigger signal to the communication device 168 in a predetermined cycle in synchronization with the driving of the feeding mechanism. When the communication device 168 receives the trigger signal, it transmits a measurement command f to the measurement head 42, and the measurement head 42 distances D from the measurement head 42 to the workpiece 2 according to the measurement command f (that is, 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 acquires positional information of the X-axis feed mechanism 30, the Y-axis feed mechanism 32, and the Z-axis feed mechanism 34 in accordance with the timing of distance measurement by the measurement head 42, so that the measurement head 42 Detect position data. The PLC 26 transmits the detected position data 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 is in 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 the surface shape data 166.

  The processor 152 further functions as a data processing unit 158 for performing data processing of the surface shape data 166 described above. The operation of the data processing unit 158 is as described in the first and second embodiments. As a result of data processing by the data processing unit 158, a measurement result of the surface shape from which noise is removed can be obtained in a short time.

  The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2 Workpiece, 10 Processing device, 16,142 Saddle, 18,144 Table, 20 Spindle head, 22 Spindle, 24 NC device, 30 X-axis feed mechanism, 32 Y-axis feed mechanism, 34 Z-axis feed mechanism, 42 Measuring head , 100 laser displacement meter, 110 light emitting unit, 112 laser diode, 114 lens, 116 laser beam, 118 condensing lens, 120 linear image sensor (light receiving unit), 130 measuring object, 132 laser spot, 140 surface shape measuring device, 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 data processing unit, 160 error range setting unit, 162 surface shape Output unit, 166 surface shape data, 00 machine tools.

Claims (6)

A light beam is emitted toward the measurement object, the scattered light of the light beam from the measurement object is collected, and the displacement of the surface of the measurement object is changed based on a change in the collection position of the scattered light. A displacement meter to be measured;
A moving mechanism for scanning the light beam by relatively moving the displacement meter and the measurement object;
A measurement control unit that measures the displacement of the surface of the measurement object at a plurality of measurement points by the displacement meter while scanning the light beam by the moving mechanism;
An error range setting unit for setting an error range for the measurement value of the displacement meter at each measurement point;
A surface shape output unit that outputs a straight line or a curve passing through each of the error ranges as a measurement result of the surface shape along the scanning direction of the light beam,
The shape of the curve is a surface shape measuring device set so that the number of points having extreme values and the number of inflection points are as small as possible.   The surface shape measuring apparatus according to claim 1, wherein the error range is set according to a spot size of the light beam on a surface of the measurement object. The spot size of the light beam changes according to the distance from the displacement meter,
The surface shape measurement apparatus according to claim 2, wherein the error range is changed according to a measurement value of the displacement meter. The surface shape output part is
Fit a straight line or a curve to the measured value at each said measuring point,
When the fitted straight line or curve passes through each of the set error ranges, the fitted straight line or curve is output as a surface shape measurement result;
If the fitted straight line or curve does not pass through some of the error ranges, the modified straight line or curve is re-applied to the measured value at each of the measurement points. 4. The surface shape measuring apparatus according to any one of 3 above. The measurement object is a workpiece machined based on design data,
The surface shape output part is
A straight line or a curve indicating the surface shape based on the design data is applied to the measurement value at each measurement point,
When the fitted straight line or curve passes through each of the set error ranges, the fitted straight line or curve is output as a surface shape measurement result;
When the fitted straight line or curve does not pass through a part of the error range, it is configured to determine that there is a processing defect or a material defect in the vicinity of the measurement point at which the part of the error range is set. The surface shape measuring device according to any one of claims 1 to 3.   A machine tool comprising the surface shape measuring device according to any one of claims 1 to 5.

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