Measurement system and measurement method

Abstract

The present invention accurately estimates a measurement error caused by measuring a measurement target in a state where a probe is eccentrically positioned relative to the measurement target. In the present invention: a side surface in a cavity provided in a part of a measurement target is irradiated with a laser while the laser is being rotated; reflected light resulting from the laser being reflected by the side surface in the cavity is detected; the distance from the irradiation position of the laser to the side surface in the cavity is measured from the reflected light; the amount of eccentricity, if the irradiation position of the laser is eccentric from the position of the center of the cavity, and the diameter of the cavity are calculated from the distance measurement result; and also, a distance measurement error due to the eccentricity of the irradiation position of the laser is estimated from the amount of eccentricity, the diameter of the cavity, and the scattered light characteristics of the measurement target.

Description

Measurement system and measurement method

[0001] The present invention relates to a measurement system and a measurement method for measuring the inner surface shape of a measurement object in a non-contact manner using a laser.

[0002] As a technology for measuring the shape of an object by irradiating light, for example, Patent Document 1 discloses a distance measuring device that includes a light emitting unit that outputs measurement light, a first polarization state control unit that controls the polarization state of the measurement light output from the light emitting unit, a second polarization state control unit that controls the polarization state of the measurement light whose polarization state has been controlled by the first polarization state control unit, and a light path switching element that selects the emission direction of the measurement light whose polarization state has been controlled by the second polarization state control unit, and when the object is, for example, cylindrical, measures the depth to the bottom of the cylindrical shape by using the measurement light emitted in a first direction, and measures, for example, the shape of the side surface of the cylindrical shape by using the measurement light emitted in a second direction.

[0003] Japanese Patent Application Laid-Open No. 2020-008496

[0004] When the probe is positioned eccentrically from the center of a cylindrical object and a laser is irradiated from the probe to measure the inner surface of the object, measurement errors occur depending on the diameter of the object, the amount of eccentricity of the probe, and the surface roughness of the object.

[0005] The present invention has been made in consideration of these problems, and aims to estimate measurement errors caused by eccentricity of the probe position relative to the measurement object from the diameter of the measurement object, the amount of eccentricity of the probe, and the scattered light characteristics of the measurement object.

[0006] The present application includes multiple means for solving at least part of the above-described problems, and an example thereof is as follows: That is, a measurement system for measuring the shape of a measurement object, the system comprising: a measurement unit including a laser irradiation unit and a rotation unit that rotatably supports the laser irradiation unit; and a measurement control unit connected to the measurement unit, wherein the measurement object has a cavity in a portion thereof, the laser irradiation unit is inserted into the cavity and irradiates a laser beam onto a side surface of the cavity while being rotated by the rotation unit, the measurement unit detects light of the laser reflected by the side surface of the cavity via the laser irradiation unit and sends the reflected light to the measurement control unit, the measurement control unit receives the reflected light and measures the distance from the reflected light between the irradiation unit and the side surface of the cavity, calculates the amount of eccentricity and the diameter of the cavity when the insertion position of the laser irradiation unit is eccentric from the center position of the cavity from the distance measurement results, and further estimates a measurement error of the distance caused by the eccentricity of the laser irradiation unit from the amount of eccentricity, the diameter of the cavity, and scattered light characteristics of the measurement object.

[0007] According to the present invention, it is possible to accurately estimate the measurement error (eccentricity-induced error) that occurs when measuring a measurement object with a probe that is eccentric with respect to the measurement object. Furthermore, by correcting the estimated measurement error, it is possible to reduce the actual measurement error and improve measurement accuracy.

[0008] Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiments of the invention.

[0009] 1 is a diagram showing an example of the configuration of an inner surface shape measuring device according to the first embodiment; FIG. 1 is a diagram showing an example of a probe being eccentric in the X-axis direction relative to a measurement object according to the first embodiment; FIG. 2 is a diagram showing an example of a calculation result when calculating a diameter inside a cylinder from a measurement distance according to the first embodiment; FIG. 3 is a diagram showing a state in which a distance measurement laser is irradiated from the probe to a measurement object according to the first embodiment; FIG. 4 is a diagram showing a distance measured during one rotation of the probe according to the first embodiment; FIG. 5 is a diagram showing a measured distance after circle fitting according to the first embodiment; FIG. 6 is a diagram showing the amount of detected light when measuring the distance of a measurement object according to the first embodiment; FIG. 7 is a diagram showing an example of a measurement object having a small diameter according to the first embodiment; FIG. 8 is a diagram showing the amount of detected light when measuring the distance of a measurement object having a small diameter according to the first embodiment; FIG. 9 is a diagram showing an example of a measurement object having a large diameter according to the first embodiment; FIG. 10 is a diagram showing the amount of detected light when measuring the distance of a measurement object having a large diameter according to the first embodiment; FIG. 11 is a diagram showing an example of scattered light characteristics of a measurement object having a small surface roughness according to the first embodiment; FIG. 12 is a diagram showing the amount of detected light when measuring the distance of a measurement object having a small surface roughness according to the first embodiment; FIG. 1 is a diagram showing a measurement diameter calculated from the measurement distance of a measurement object having a small surface roughness in the first embodiment. FIG. 2 is a diagram showing an example of scattered light characteristics of a measurement object having a large surface roughness in the first embodiment. FIG. 3 is a diagram showing the detected light amount when measuring the distance of a measurement object having a large surface roughness in the first embodiment. FIG. 4 is a diagram showing the measurement distance of a measurement object having a large surface roughness in the first embodiment. FIG. 5 is a diagram showing a measurement diameter calculated from the measurement distance of a measurement object having a large surface roughness in the first embodiment. FIG. 6 is a diagram showing an example of a method for estimating scattered light characteristics of a measurement object from the detected light amount obtained when measuring a measurement object in the first embodiment, and correcting measurement errors. FIG. 7 is a diagram showing an example of an irradiation angle of a distance measurement laser irradiated from a probe that is eccentric in the Y-axis direction with respect to the measurement object in the first embodiment. FIG. 8 is a diagram showing the detected intensity of reflected light when measuring the distance of a measurement object in the first embodiment. FIG. 9 is a diagram showing the irradiation angle of a distance measurement laser when measuring the distance of a measurement object in the first embodiment. FIG. 10 is a diagram showing scattered light characteristics of a measurement object estimated from the values ​​of the detected intensity and irradiation angle in the first embodiment.FIG. 1 is a diagram showing an example of a method for estimating a measurement error of a distance to a measurement object in the first embodiment. FIG. 2 is a diagram showing an example of a processing flow for estimating and correcting an error caused by eccentricity in the inner surface shape measurement device in the first embodiment. FIG. 3 is a diagram showing an example of a device GUI screen in the first embodiment. FIG. 4 is a diagram showing an example of the configuration of a measurement head in the second embodiment. FIG. 5 is a diagram showing the principle of switching a laser irradiation direction using polarized light at the probe tip in the second embodiment. FIG. 6 is a diagram showing an example of a state in which a probe is tilted with respect to a measurement object in the third embodiment. FIG. 7 is a diagram showing the detected light amount when measuring the distance to a measurement object in the third embodiment. FIG. 8 is a diagram showing the measured distance of a measurement object in the third embodiment. FIG. 9 is a diagram showing an example of a method for calculating the tilt of a probe with respect to a measurement object in the third embodiment. FIG. 10 is a diagram showing another example of a method for calculating the tilt of a probe with respect to a measurement object in the third embodiment. FIG. 11 is a diagram showing an example of a measurement processing flow by the inner surface shape measurement device when measuring a measurement object with the probe tilted with respect to the measurement object in the third embodiment.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiment is an example for explaining the present invention, and for clarity of explanation, appropriate omissions and simplifications have been made. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0011] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0012] When there are multiple components with the same or similar functions, they may be described using the same reference numeral with different subscripts. When there is no need to distinguish between these multiple components, the subscripts may be omitted.

[0013] In the embodiments, processing performed by executing a program may be described. Here, a computer executes the program using a processor (e.g., a CPU or a GPU) and performs processing defined by the program using storage resources (e.g., a memory) and interface devices (e.g., a communication port). Therefore, the entity performing the processing by executing the program may be the processor. Similarly, the entity performing the processing by executing the program may be a controller, device, system, computer, or node having a processor. The entity performing the processing by executing the program may be any computing unit, and may include a dedicated circuit that performs specific processing. Here, the dedicated circuit may be, for example, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), a CPLD (Complex Programmable Logic Device), or the like.

[0014] The program may be installed on a computer from a program source. The program source may be, for example, a program distribution server or a computer-readable storage medium. When the program source is a program distribution server, the program distribution server may include a processor and a storage resource for storing the program to be distributed, and the processor of the program distribution server may distribute the program to be distributed to other computers. In addition, in the embodiments, two or more programs may be realized as one program, or one program may be realized as two or more programs. <First Embodiment> FIG. 1 is a diagram showing an example of the configuration of an inner surface shape measurement device. The inner surface shape measuring device is composed of a measurement head 100, a Z-axis stage 106 on which the measurement head is mounted so that it can be moved in the Z-axis direction (up and down in the drawing), a Y-axis stage 108 on which a measurement object is mounted and which allows the measurement object to be moved in the Y-axis direction (depth direction in the drawing), an X-axis stage 107 on which the Y-axis stage 108 is mounted and which allows the Y-axis stage and the object on the Y-axis stage to be moved in the X-axis direction (left and right direction in the drawing), a frame 109 that supports each stage, a distance measurement control unit 111 connected to the measurement head 100 via optical fiber 110, a stage controller 113 connected to the frame 109 via a cable 112 and which controls the movement of each stage, a processing device (PC) 114 connected to the distance measurement control unit 111 and the stage controller 113 via cables, an device display 115 connected to the PC 114 and which displays a device GUI screen described below, and an input unit 116 connected to the PC 114 and which allows a user of the inner surface shape measuring device to input data, etc., to the PC 114.

[0015] The measurement head 100 is composed of a fiber focuser 101 connected to an optical fiber 110, a probe 103 that irradiates a distance measurement laser onto the measurement object, a rotary motor 102 that rotatably supports the probe 103, and a reflecting mirror 104 attached to the tip of the probe 103.

[0016] A distance measurement laser emitted from a distance measurement control unit 111 is guided to the measurement head 100 via an optical fiber 110. The distance measurement laser guided to the measurement head 100 is irradiated into space by a fiber focuser 101, passes through a hollow rotary motor 102 and a hollow probe 103, and is reflected by a reflecting mirror 104 attached to the tip of the probe 103 in a direction approximately perpendicular to the probe 103. A cylindrical measurement target 105 is mounted on an X-axis stage 107 and a Y-axis stage 108, and the position of the measurement target 105 is adjusted to match the probe position. The measurement head 100 is mounted on a Z-axis stage 106, and by operating the Z-axis stage 106, the probe 103 is inserted into the cavity (cylinder) in the center of the measurement target 105. Rotating the rotary motor 102 rotates the probe 103, which in turn rotates the reflecting mirror 104 attached to the tip of the probe. The distance measurement laser reflected by the reflecting mirror 104 in a direction substantially perpendicular to the probe 103 is irradiated onto the inner cylindrical surface of the measurement object 105 while rotating in accordance with the rotation of the reflecting mirror 104. The irradiated distance measurement laser is reflected by the inner surface of the cylinder, and the reflected light is received by the fiber focuser 101 via the probe 103. The received reflected light is sent to the distance measurement control unit 111 via the optical fiber 110. The distance measurement control unit 111 calculates the distance from the probe 103 to the inner surface of the cylinder from the reflected light that has been sent.

[0017] This measures the distance to the inner surface of the cylinder at one cross section of the object 105. The inner surface shape measuring device performs measurements while moving the Z-axis stage, enabling it to measure the three-dimensional shape of the interior of the cylinder of the object 105. The distance measurement results (measured distances) to the inner surface of the cylinder of the object 105 are sent to a PC 114. In addition, position information (stage coordinates) of each stage is sent to a stage controller 113 via a cable 112 and then sent to the PC 114. The PC 114 combines the measured distance values ​​and stage coordinates to generate three-dimensional position information, and the measurement results are displayed on the device display 115. In the configuration example of FIG. 1 , the object 105 and the measuring head 100 are operated using each stage, but the measuring head 100 and the object 105 may also be operated using a robot. The measuring head 100 may also be attached to the spindle of a processing machine and operated.

[0018] 2 shows an example of a measurement error (a measurement error caused by probe eccentricity, also called an eccentricity-induced error) that occurs when the probe 103 is eccentric. First, FIG. 2A shows the positional relationship between the measurement object 105 and the probe 103. When the probe 103 is positioned at the center of the cylinder of the measurement object 105 (object center), the amount of eccentricity is set to 0, and as shown in FIG. 2A, the amount of movement (eccentricity) of the probe position in, for example, the X-axis direction is set to the amount of eccentricity. While FIG. 2A illustrates probe eccentricity in the X-axis direction, naturally, the probe 103 may also be eccentric in the Y-axis direction.

[0019] FIG. 2B shows an example of a calculation result when the inner surface shape measurement device measures the distance to the cylindrical inner surface of the measurement target 105 when the probe 103 is eccentric with respect to the measurement target 105, and calculates the diameter inside the cylinder from the measured distance. If the diameter (measured diameter) calculated from the measurement distance when the probe 103 is at the center of the target is used as a reference, the measured diameter value increases as the eccentricity of the probe 103 from the center of the target increases, and may attenuate once the eccentricity exceeds a certain amount. The mechanism by which this measurement error occurs will be described later, but it is known to be caused by the size and surface roughness of the measurement target. Since measurement errors occur when the probe 103 is eccentric with respect to the measurement target 105, in order to accurately measure the measurement target 105, the inner surface shape measurement device must estimate the measurement error that occurs when the probe is eccentric, and if the error amount is large, either remeasure or correct the error to reduce it.

[0020] FIG. 3 is a diagram showing the mechanism by which measurement errors occur when the probe is decentered. The error generation mechanism will be explained using FIG. 3. FIG. 3A is a diagram showing the measurement target 105 as viewed from above. In FIG. 3A, the cylindrical inner diameter of the measurement target 105 is assumed to be 6 mm, for example. Furthermore, as an example, the probe 103 is decentered by 0.2 mm in the Y-axis direction with respect to the center of the target (the amount of eccentricity of the probe 103 is 0.2 mm). FIG. 3A shows an example in which a distance measurement laser is irradiated in the X-axis direction by a fiber focuser 101 and a reflecting mirror 104 mounted on the measurement head 100, and the distance to the cylindrical inner surface of the measurement target 105 is measured.

[0021] In this example, the beam diameter of the distance measurement laser to be emitted is, for example, 0.3 mm. In this case, the distance measurement laser emitted from the center of fiber focuser 101 and reflected by reflecting mirror 104 irradiates point a on measurement target 105 over a distance of 2.9933 mm. Meanwhile, the distance measurement laser emitted from the end of the lens in fiber focuser 101 and reflected by reflecting mirror 104 irradiates point b on measurement target 105 over a distance of 2.9996 mm. Because the irradiation angle at point a is larger than the irradiation angle at point b (the inclination of the surface onto which the laser is irradiated), depending on the scattered light characteristics of measurement target 105, the light reflected from point a may not return to fiber focuser 101, as indicated by the dotted arrow pointing from point a to fiber focuser 101 in FIG. 3A . Meanwhile, the light reflected from point b may return to fiber focuser 101, as indicated by the solid arrow pointing from point b to fiber focuser 101 in FIG. 3A . In such a case, the distance of 2.9933 mm when measured without error is measured as 2.9996 mm, resulting in a measurement error of 0.0063 mm.

[0022] 3B shows the distance (measured distance) to the inner surface of the cylinder of the measurement target 105 measured during one rotation of the probe 103. When the distance to the inner surface of the cylinder of the measurement target 105 is measured while the probe 103 is eccentric with respect to the measurement target 105, the measured distance has a sinusoidal waveform with one period, as shown in FIG. 3B. By performing circle fitting on the obtained sinusoidal waveform, it is possible to remove the fluctuation in distance due to eccentricity. In this embodiment, circle fitting refers to finding a circle (approximation circle) that best fits a set (point cloud) of position coordinates of each point (measurement point) where the distance is measured, and approximating each measured distance by the distance to each point on the circumference of the approximation circle. In circle fitting, for example, the center coordinates of the approximate circle to be determined are (a, b), the radius is r, and the coordinates of an arbitrary point on the circumference of the approximate circle are (x, y), and using the equation for a circle shown below in (Equation 1), a, b, and r are found so that the sum of squares of the distance from the center coordinates (a, b) to the coordinates of the measurement point (xi, yi) is minimized, as shown in (Equation 2). This allows the approximate circle to be determined.

[0023]

[0024] Figure 3C shows a graph (waveform) of the measured distance after circle fitting. In the direction perpendicular to the eccentricity direction (in this example, the 0° and 180° directions in Figure 3A), the irradiation angle of the measurement target changes within the beam diameter of the distance measurement laser described above, resulting in measurement errors. On the other hand, in the direction parallel to the eccentricity direction (in this example, the 90° and 270° directions in Figure 3A), the irradiation angle of the measurement target is less likely to differ within the beam diameter, resulting in almost no measurement errors. Therefore, as shown in Figure 3C, measurement errors occur in the 0° and 180° directions, but almost no distance errors occur in the 90° and 270° directions, resulting in two periods of distance fluctuation.

[0025] 3D shows the amount of light reflected from the inner surface of the cylinder (detected amount of light) detected when measuring the distance to the inner surface of the cylinder of the measurement target 105. As shown in Fig. 3D, the amount of light detected when measuring the distance is small (weak) in the direction perpendicular to the eccentricity direction, in this example, the 0° and 180° directions, because reflected light from the center of the laser is difficult to detect, and large (strong) in the direction parallel to the eccentricity direction, in this example, the 90° and 270° directions, because reflected light can be detected over the entire laser beam diameter.

[0026] FIG. 4 shows an example of measurement error due to probe eccentricity when measuring objects with different diameters. First, we will explain the case where the diameter of the object is small. FIG. 4A shows an example of an object 401 with a small diameter. FIG. 4B shows the detected light intensity when the probe 103 rotates once to measure the distance to the cylindrical inner surface of the object 401. FIG. 4C shows the measured distance obtained by this measurement. In FIG. 4A, the cylindrical inner diameter of the object 401 is, for example, φ6 mm. As described in the description of FIG. 3C, when the probe 103 is eccentric, the irradiation angle changes significantly depending on the rotation angle of the probe 103. Therefore, as shown in FIG. 4B, the detected light intensity also changes significantly depending on the rotation angle of the probe 103. Similarly, as shown in FIG. 4C, the measured distance also changes significantly depending on the rotation angle of the probe 103. Note that, like FIG. 3C, FIG. 4C shows the measured distance after circle fitting. Under the same conditions as the example shown in FIG. 3A, a measurement error of up to approximately 0.006 mm occurs.

[0027] Next, we will explain the case where the diameter of the measurement object is large. Figure 4D shows an example of a measurement object 402 with a large diameter. Figure 4E, similar to Figure 4B, shows the detected light intensity when the probe 103 rotates once to measure the distance to the cylindrical inner surface of the measurement object 402. Figure 4F shows the measured distance obtained by this measurement. In Figure 4D, the cylindrical inner diameter of the measurement object 402 is, for example, φ100 mm. In this example, even under the same conditions as the example shown in Figure 3A, i.e., the eccentricity of the probe 103 in the Y-axis direction is 0.2 mm and the beam diameter of the distance measurement laser is 0.3 mm, the difference in irradiation angle between the center and edge of the laser within the beam diameter is smaller than in the example shown in Figure 4A (where the cylindrical inner diameter of the measurement object 401 is φ6 mm). The difference in measured distance between the center and edge of the laser is also 0.0003 mm, smaller than 0.006 mm in the example shown in Figure 4A. Therefore, the detected light amount changes less as shown in FIG. 4E compared to FIG. 4B, and the measured distance also changes less as shown in FIG. 4F compared to FIG. 4C.

[0028] The measurement errors described above depend not only on the internal diameter of the cylinder to be measured, but also on the surface roughness of the cylinder's inner surface. Hereinafter, we will explain the measurement error that occurs when the probe is eccentric when the surface roughness of the measurement object varies. Figure 5 shows an example of the measurement error that occurs when the probe is eccentric when measuring an object with a small surface roughness. Figure 5A shows the scattered light characteristics of the measurement object, Figure 5B shows the amount of light detected when the probe rotates once and measures the distance to the cylinder's inner surface of the measurement object, Figure 5C shows the measured distance obtained by this measurement, and Figure 5D shows the measured diameter calculated from the measured distance.

[0029] As shown in Figure 5A, when the surface roughness of the measurement object is small, the reflected light from the measurement object can be detected over the entire laser beam diameter at a small irradiation angle, resulting in a strong detection intensity. However, as the irradiation angle increases, the reflected light becomes more difficult to detect, resulting in a rapid decrease in detection intensity. As described above, when the probe is eccentric, the irradiation angle changes significantly depending on the probe rotation angle. Therefore, when measuring a measurement object with small surface roughness and the scattered light characteristics shown in Figure 5A, the detected light intensity changes significantly depending on the probe rotation angle, as shown in Figure 5B. Similarly, as shown in Figure 5C, the measured distance also changes significantly due to the large change in irradiation angle depending on the probe rotation angle. Note that Figure 5C shows the measured distance after circle fitting. When the measured diameter is calculated from the measurement distance shown in Figure 5C, as shown in Figure 5D, the measured diameter value increases as the probe's eccentricity from the center of the measurement object increases, and attenuates once the eccentricity exceeds a certain value. Note that the detected light intensity and measurement distance vary depending on the scattered light characteristics of the measurement object as well as the focusing angle (lens diameter) of the fiber focuser.

[0030] FIG. 6 shows an example of measurement error due to probe eccentricity when measuring an object with high surface roughness. FIG. 6A shows the scattered light characteristics of the object, FIG. 6B shows the detected light intensity when the probe rotates once to measure the distance to the inner surface of the cylinder of the object, FIG. 6C shows the measured distance obtained by this measurement, and FIG. 6D shows the measured diameter calculated from the measured distance. As shown in FIG. 6A, when the object has high surface roughness, there is no sudden drop in detected intensity even when the irradiation angle is large, compared to FIG. 5A. When measuring an object with this scattered light characteristic, even if the irradiation angle changes significantly depending on the probe rotation angle due to probe eccentricity, the change in detected light intensity is small, as shown in FIG. 6B. Similarly, as shown in FIG. 6C, even if the irradiation angle changes significantly depending on the probe rotation angle, the change in measured distance is small. Note that FIG. 6C shows the measured distance after circle fitting. When the measured diameter is calculated from the measurement distance shown in Figure 6C, as shown in Figure 6D, the measured diameter increases as the eccentricity of the probe from the center of the object to be measured increases, and once the eccentricity exceeds a certain amount, the diameter value attenuates, but the change in the measured diameter is smaller than in Figure 5D.

[0031] FIG. 7 shows an example of a method for estimating the scattered light characteristics of a measurement object from the detected intensity obtained when measuring the measurement object and correcting measurement errors. If the surface roughness of the measurement object is unknown in advance, it may be possible to estimate the surface roughness of the measurement object from the detected intensity of reflected light from the cylindrical inner surface when the probe rotates once to measure the distance to the cylindrical inner surface of the measurement object. In FIG. 7 , in STEP 1, the detected intensity values ​​of reflected light for each rotation angle when the probe rotates once are obtained. From the obtained detected intensity values, the detected intensity distribution corresponding to the rotation angle, as shown in STEP 1, can be determined. As described in the explanations of FIGS. 4 , 5 , and 6 , the detected intensity distribution varies depending on the diameter and surface roughness of the measurement object. Therefore, as shown in STEP 2, the scattered light characteristics of the measurement object are estimated from the detected intensity distribution obtained in STEP 1. If the scattered light characteristics are known in advance, this STEP can be skipped.

[0032] A method for estimating the scattered light characteristics of a measurement object will be described with reference to FIG. 8 . FIG. 8 shows an example of a method for estimating the scattered light characteristics of a measurement object from a detected intensity distribution. The irradiation angle of the distance measurement laser emitted from the probe 103 on the inner cylindrical surface of the measurement object 105 varies depending on the rotation angle of the probe 103. For example, as shown in FIG. 8A , if the probe 103 is eccentric in the Y-axis direction with respect to the center of the measurement object 105, the irradiation angle becomes large when the rotation angle is 0 degrees, and as the rotation angle increases, the irradiation angle becomes smaller, and when the rotation angle is 90 degrees, the irradiation angle becomes 0 degrees. In other words, since the irradiation angle differs for each rotation angle of the probe 103, the scattered light characteristics of the measurement object can be estimated from the irradiation angle value for each rotation angle of the probe 103 and the detected intensity distribution determined in STEP 1.

[0033] More specifically, it is assumed that the detection intensity corresponding to the rotation angle of probe 103 has been obtained as shown in FIG. 8B . As shown in FIG. 8C , the irradiation angle of measurement target 105 corresponding to the rotation angle of probe 103 is geometrically determined from the eccentricity direction and amount of eccentricity of the probe. From the values ​​of the detection intensity and irradiation angle corresponding to the rotation angle shown in FIGS. 8B and 8C , it is possible to estimate the detection intensity relative to the irradiation angle of measurement target 105, i.e., the scattered light characteristics of measurement target 105, as shown in FIG. 8D . Once the scattered light characteristics of the measurement target are known, it is possible to estimate the measurement error when the probe measures the distance to the cylindrical inner surface of the measurement target after one rotation, as shown in STEP 3, from the diameter of the measurement target and the eccentricity of the probe.

[0034] 7 and 8, in order to estimate the scattered light characteristics of the measurement object, it is necessary to decenter the probe with respect to the measurement object and to provide an irradiation angle. Therefore, one method for estimating the scattered light characteristics of the measurement object is to intentionally decenter the probe from the center of the measurement object and perform measurement.

[0035] A method for estimating measurement errors will be described with reference to FIG. 9 . FIG. 9 shows an example of a method for estimating measurement errors. In the example shown in FIG. 3 , a measurement error was described that occurs due to the difference in distance to the measurement target between light irradiated from the center and light irradiated from the edge of the beam diameter of the fiber focuser 101. To improve the accuracy of estimating such measurement errors, in the example shown in FIG. 9 , a laser composed of multiple light beam elements is emitted from the fiber focuser 101, and the distance to the measurement target is measured using each light beam element. The intensity distribution of the multiple light beam elements irradiated from the fiber focuser 101 is set to a Gaussian distribution, and the intensity of the light beam elements decreases from the center to the edge of the fiber focuser 101. Therefore, the measured distance using each light beam element is weighted by the intensity of the light beam element.

[0036] In this way, the distance to the measurement target is measured using multiple light beam elements, and the sum of all measured distances is calculated. The calculated sum of measured distances is then divided by the number of light beam elements to calculate the average measured distance for the light beam elements emitted from the fiber focuser 101. The measurement error at each rotation angle can be accurately estimated from this average measured distance, the diameter of the measurement target (the radius value can be obtained from the diameter), the eccentricity of the probe 103, and the scattered light characteristics of the measurement target estimated in STEP 2. Once the measurement error can be estimated, the actual measurement value can be corrected for the estimated measurement error, as shown in STEP 4, thereby reducing the actual measurement error.

[0037] FIG. 10 shows an example of a process flow for estimating and correcting eccentricity-induced errors (measurement errors) in the inner surface shape measuring device shown in FIG. 1 . In process flow 1000, first, in S1001, the inner surface shape measuring device measures the measurement object using the measurement head 100 and distance measurement control unit 111. In S1002, the distance measurement control unit 111 calculates the diameter and eccentricity of the measurement object by performing circle fitting on the measured distance, as described in the description of FIG. 3B . In S1003, the user of the inner surface shape measuring device checks whether they have scattered light characteristic data for the measurement object. If they have scattered light characteristic data for the measurement object, in S1004, the user inputs the scattered light characteristic data for the measurement object into the PC 114 using the input unit 116 or a storage medium (not shown in FIG. 1 ). Alternatively, the user specifies a file of scattered light characteristic data pre-stored in the PC 114 via the input unit 116. The input or specified scattered light characteristic data is sent to the distance measurement control unit 111. If scattered light characteristic data for the measurement object is not available, in S1005 the distance measurement control unit 111 estimates the scattered light characteristics of the measurement object from the detection intensity distribution as described in the explanation of Fig. 8. Note that even if the measurement object itself does not have scattered light characteristic data when checking the scattered light characteristic data for the measurement object in S1003, if the measurement object is made of the same material and has the same cutting conditions as the measurement object, the scattered light characteristics of the measurement object and the other measurement object will be roughly similar, and therefore if scattered light characteristic data for such other measurement object is available and made of the same material and under the same cutting conditions, it may be input or specified in S1004 as the scattered light characteristic data for the measurement object.

[0038] In S1006, the distance measurement control unit 111 estimates the eccentricity-induced error from the diameter of the measurement target, the eccentricity of the probe 103, and the scattered light characteristics of the measurement target received in S1004 or estimated in S1005, as described in the description of FIG. 9 . The measured, calculated, or estimated values ​​are sent to the PC 114 and displayed on the device display 115. In S1007, the user determines whether to perform remeasurement based on the amount of error estimated by the distance measurement control unit 111 in S1006. If remeasurement is to be performed, the user operates each stage by issuing instructions to the stage controller 113 via the PC 114, and causes the inner surface shape measuring device to perform remeasurement with the eccentricity of the probe 103 reduced. If the user determines not to perform remeasurement, the process proceeds to the next step, where the user determines in S1008 whether to correct the eccentricity-induced error. If the user determines not to make correction, the distance measurement control unit 111 outputs raw data (actual measurement values) such as the measurement distance in S1009, and if the user determines to make correction, the distance measurement control unit 111 outputs data in which the actual measurement values ​​have been corrected for errors caused by eccentricity in S1010. Note that in the above explanation, the user operates (gives instructions for) the stage when re-measuring, but the PC 114 may also give instructions for adjusting the stage to the stage controller 113 based on the amount of eccentricity of the probe, etc.

[0039] 11 shows an example of an apparatus GUI screen displayed on the apparatus display 115. In this example, the left side of the apparatus GUI screen displays, as an example, a detected intensity 1101 corresponding to the rotation angle of the probe 103 and a measured distance (shape profile) 1102 corresponding to the rotation angle of the probe 103. Also, the right side of the apparatus GUI screen displays, as an example, a data file input field 1103 relating to the scattered light characteristics of the object to be measured, a diameter display field 1104, an eccentricity amount display field 1105, an eccentricity-induced error estimated value display field 1106, a remeasurement input field 1107, an eccentricity-induced error correction input field 1108, and an error-corrected diameter display field 1109.

[0040] If scattered light characteristic data for the measurement target is available in advance, the user inputs the file name of the file in which the scattered light characteristic data is recorded in a data file input field 1103 relating to scattered light characteristics. The file in which the scattered light characteristic data is recorded is assumed to be stored in advance in PC 114 or in a separate storage medium connected to PC 114. If scattered light characteristic data for the measurement target is not available in advance, distance measurement control unit 111 estimates the scattered light characteristics from the detected intensity distribution as per S1005 in process flow 1000 shown in FIG.

[0041] A diameter display field 1104 displays the value of the measured diameter calculated by the distance measurement control unit 111 in S1002 of the process flow 1000 shown in Fig. 10. An eccentricity amount display field 1105 displays the amount of eccentricity calculated by the distance measurement control unit 111 in S1002 of the process flow 1000 also shown in Fig. 10. An eccentricity-induced error estimated value display field 1106 displays the estimated value of the eccentricity-induced error estimated by the distance measurement control unit 111 in S1006 of the process flow 1000 shown in Fig. 10.

[0042] As shown in S1007 of the process flow 1000 in Fig. 10 , the user determines whether or not to perform remeasurement based on the error estimate displayed in the eccentricity-induced error estimate display field 1106, and sets the necessity in the remeasurement input field 1107. A button labeled "Execute" or a check mark or the like is displayed in advance in the remeasurement input field 1107. When performing remeasurement, the user clicks the button or check mark or the like using the input unit 116 to cause the inner surface shape measuring device to perform remeasurement. Note that if the device display 115 is equipped with a touch panel or the like, the user may directly touch the button or check mark or the like with a finger, a touch pen, or the like.

[0043] Next, as shown in S1008 of the process flow 1000 in FIG. 10 , the user determines whether to correct the eccentricity-induced error and enters the necessary information in an eccentricity-induced error correction input field 1108. Similar to the remeasurement input field 1107, the eccentricity-induced error correction input field 1108 displays a button labeled "Execute" or a check mark. To correct the error, the user clicks the button or check mark using the input unit 116 to instruct the inner surface shape measuring device to correct the eccentricity-induced error. If the device display 115 is equipped with a touch panel or the like, the user may directly touch the button or check mark with a finger or a touch pen. When the distance measurement control unit 111 executes eccentricity-induced error correction as shown in S1010 of the process flow 1000 in FIG. 10 , the measured diameter calculated after the error correction is displayed in an error-corrected diameter display field 1109.

[0044] As described above, the first embodiment enables accurate estimation of measurement errors (eccentricity-induced errors) that occur when measuring an object with the probe eccentric relative to the object. Furthermore, correcting the estimated measurement errors reduces the actual measurement errors and improves measurement accuracy. Second Embodiment: In the inner surface shape measurement device of the first embodiment, the reflecting mirror 104 attached to the tip of the probe 103 reflects the distance measurement laser that passes through the probe 103 in a direction substantially perpendicular to the probe 103, and irradiates the side of the object 105 with the distance measurement laser to perform side measurement. On the other hand, by switching the irradiation direction of the distance measurement laser emitted from the probe 103 between a direction substantially perpendicular to the probe 103 and a direction substantially parallel to the probe 103, it is also possible to perform side and depth measurements of the object 105. An example of the configuration of such an inner surface shape measurement device will be described with reference to FIG. 12 . FIG. 12 shows another example of the configuration of a measurement head in the inner surface shape measurement device. Note that in FIG. 12 , the same components as those in the inner surface shape measurement device and measurement head 100 shown in FIG. 1 are designated by the same reference numerals.

[0045] In Figure 12, the measurement head 1200 is composed of a fiber focuser 101 connected to the optical fiber 110, a probe 103 that irradiates the measurement object with distance measurement laser light, a rotary motor 102 that rotatably supports the probe 103, λ / 4 plates 1201 and 1202 that are arranged on the optical path of the light emitted from the fiber focuser 101, and a polarizing beam splitter 1203 attached to the tip of the probe 103.

[0046] The distance measurement laser emitted from the distance measurement control unit 111 is guided to the measurement head 1200 via the optical fiber 110 and emitted into space from the fiber focuser 101. The linearly polarized light emitted from the fiber focuser 101 is converted into circularly polarized light by the λ / 4 plate 1201, and then becomes linearly polarized again by passing through the λ / 4 plate 1202 attached to the rotary motor 102. The distance measurement laser that passed through the λ / 4 plate 1202 is reflected or transmitted by the polarizing beam splitter 1203 attached to the tip of the probe 103 depending on the polarization direction, and is irradiated onto the measurement target 105 or the measurement target 1204. At this time, by switching the polarization using the polarization switcher 1301 (included in the fiber focuser 101 in FIG. 12 ) mounted on the measurement head 1200, it is possible to switch the direction between side measurement and depth measurement.

[0047] FIG. 13 illustrates the principle of switching the laser irradiation direction using polarization at the probe tip. The polarizing beam splitter 1203 at the tip of the probe 103 transmits light oscillating parallel to the plane of incidence (P-polarized light) and reflects light oscillating perpendicular to the plane of incidence (S-polarized light). Therefore, by electrically controlling the polarization of the distance measurement laser 1300 to P-polarized light or S-polarized light using the polarization switcher 1301 located in the fiber focuser 101 in the measurement head 1200, the irradiation direction of the distance measurement laser 1300 can be switched between a direction approximately perpendicular to the probe 103 and a direction approximately parallel to the probe 103. To rotate the distance measurement laser 1300 while irradiating it in a direction approximately perpendicular to the probe 103, the polarization direction of the incident light must be rotated in accordance with the rotation of the polarizing beam splitter 1203, thereby maintaining a constant polarization state relative to the polarizing beam splitter 1203. For this purpose, two λ / 4 plates 1201 and 1202 are used. By positioning the axis of the first λ / 4 plate 1201 at 45 degrees to the polarization direction of the incident light, linearly polarized light is converted into circularly polarized light. The second λ / 4 plate 1202 and polarizing beam splitter 1203 are attached to the rotary motor 102 (not shown in FIG. 11 ) and rotate together with the rotary motor 102. The circularly polarized light is converted back into linearly polarized light by passing through the second λ / 4 plate 1202, and the polarized light incident direction always remains constant with respect to the polarizing beam splitter 1203 as the rotary motor 102 rotates. This allows the distance measurement laser, which is pointed in a direction approximately perpendicular to the probe 103, to be rotated.

[0048] As described above, according to the second embodiment, the irradiation direction of the distance measurement laser emitted from the probe 103 can be switched between a direction approximately perpendicular to the probe 103 and a direction approximately parallel to the probe 103, enabling side and depth measurements of the object to be performed. <Third Embodiment> Figure 14 shows an example of the detected light intensity and measured distance obtained when measuring the object with the probe of the inner surface shape measurement device tilted relative to the object. As shown in Figure 14A, the measurement head of the inner surface shape measurement device is tilted relative to the object 1400, causing the probe 103 to be inserted into the cylindrical object 1400 in a tilted state. When measurement of the cylindrical object 1400 is performed in this state, the detected intensity of the reflected light from the inner surface of the cylindrical object 1400 fluctuates over two periods as shown in Figure 14B, and the measured distance has an elliptical shape error as shown in Figure 14C. In other words, because the probe 103 is tilted, the shape of a cross section of the object 1400 from which the distance within the cylinder is measured becomes elliptical rather than the essentially perfect circle it would be (if the probe 103 were not tilted). Because the distance of an ellipse is measured in this way, the measured distance includes an ellipse error, which is a measurement error in the major axis direction of the ellipse. In such cases, it is difficult to distinguish whether the measurement error included in the measured distance is an ellipse error or an error caused by eccentricity.

[0049] Therefore, the inclination of the probe 103 is calculated first, and then the measurement of the measurement object is performed. FIG. 15 shows an example of a method for calculating the inclination of the probe relative to the measurement object. As shown in FIG. 15A , the depth measurement described in the second embodiment is performed on the measurement object 1400, for example, to measure the distance to the top surface of the measurement object 1400. That is, the irradiation direction of the distance measurement laser emitted from the probe 103 is switched from a direction approximately perpendicular to the probe 103 (the irradiation direction when measuring the side surface inside the cylinder) to a direction approximately parallel to the probe 103 (the irradiation direction when measuring the depth inside the cylinder), and the distance to the top surface of the measurement object 1400 is measured. At this time, the position of the probe 103 is changed to measure the distance to at least three points on the top surface of the measurement object 1400. This makes it possible to calculate the relative inclination of the probe 103 with respect to the measurement object 1400.

[0050] 15B, a probe is inserted into the cylinder of the measurement object 1400 to measure the distance to the inner surface of the cylinder (inner diameter). At this time, the insertion position (insertion depth) of the probe is changed to measure the inner diameter at least at two locations (two cross sections) inside the cylinder. This makes it possible to calculate the relative inclination of the probe 103 with respect to the measurement object 1400 from the amount of deviation between the center coordinates of the inner diameter of at least two cross sections.

[0051] FIG. 16 shows an example of a measurement and processing flow by the inner surface shape measuring device when measuring an object with the probe tilted relative to the object. Note that in FIG. 16, the same processing steps as those in process flow 1000 shown in FIG. 10 are denoted by the same reference numerals. In process flow 1600, first, in S1601, the inner surface shape measuring device performs depth measurement using the measurement head 100 and distance measurement control unit 111 to measure the distance to the top surface of the object 1400. At this time, the distance is measured at least at three points on the top surface of the object 1400. In S1602, the distance measurement control unit 111 calculates the tilt of the measurement head 100 relative to the object 1400, i.e., the tilt of the probe 103. In S1603, the distance measurement control unit 111 determines whether the tilt of the measurement head 100 relative to the object 1400 is within the allowable tilt angle. This determination is made, for example, by determining whether the amount of elliptical shape error (elliptical amount) is within a predetermined measurement accuracy. If the tilt angle is not within the allowable range, the tilt of the measurement head 100 or the measurement object 1400 is adjusted in S1604 so that the posture of the measurement object 1400 or the probe 103 is within the allowable range. For tilt adjustment, for example, a tilt adjustment stage (such as a goniostage) is mounted between the Z-axis stage and the measurement head or on the Y-axis stage 108 in FIG. 1 , and the measurement head or the measurement object is mounted on that stage to adjust the tilt. If it is determined in S1603 that the tilt angle is within the allowable range or if the adjustment is completed in S1604, the probe 103 is inserted into the cylinder of the measurement object 1400 and measurement is performed (S1001). The processing of each step from S1001 onwards is exactly the same as the processing of each step from S1001 onwards in the processing flow shown in FIG. 10 .

[0052] As described above, according to the third embodiment, even if the measurement head 100 is tilted with respect to the measurement object 1400, the tilt can be calculated prior to measurement. This makes it possible to measure the measurement object 1400 by adjusting the tilt as appropriate, thereby improving measurement accuracy.

[0053] Although the above describes various embodiments and variations of the present invention, the present invention is not limited to the above-described exemplary embodiments and includes various variations. For example, the above-described exemplary embodiments have been described in detail to facilitate understanding of the present invention, and the present invention is not limited to those including all of the components described herein. Furthermore, it is possible to replace part of the components of one exemplary embodiment with the components of another exemplary embodiment. It is also possible to add the components of another exemplary embodiment to the components of one exemplary embodiment. Furthermore, it is also possible to add, delete, or replace part of the components of each exemplary embodiment with other components. Furthermore, some or all of the above-described components, functions, processing units, processing means, etc. may be implemented in hardware, for example, by designing them as integrated circuits. Furthermore, the control lines and information lines in the figures are those considered necessary for explanation, and are not necessarily all shown. It is also possible to consider that almost all components are interconnected.

[0054] 100: Measurement head, 101: Fiber focuser, 102: Rotation motor, 103: Probe, 104: Reflection mirror, 105: Measurement object, 106: Z-axis stage, 107: X-axis stage, 108: Y-axis stage, 109: Frame, 110: Optical fiber, 111: Distance measurement control unit, 112: Cable, 113: Stage controller, 114: PC, 115: Device display, 203: Measurement object (small diameter), 402: Measurement object (large diameter), 1200: Measurement head, 1201: λ / 4 plate, 1202: λ / 4 plate, 1203: Polarizing beam splitter, 1204: Measurement object, 1301: Polarization switcher, 1400: Measurement object

Claims

1. A measurement system for measuring the shape of a cavity provided in at least a part of an object to be measured, comprising: a measurement unit including a laser irradiation unit and a rotation unit that rotatably supports the laser irradiation unit; and a measurement control unit connected to the measurement unit, wherein the laser irradiation unit is inserted into the cavity and irradiates a laser onto a side surface of the cavity while being rotated by the rotation unit, the measurement unit detects light of the laser reflected by the side surface of the cavity via the laser irradiation unit and sends the reflected light to the measurement control unit, and the measurement control unit receives the reflected light and measures the distance from the reflected light from the laser irradiation unit and the side surface of the cavity, calculates the amount of eccentricity and the diameter of the cavity when the insertion position of the laser irradiation unit is eccentric from the center position of the cavity from the distance measurement results, and further estimates a measurement error of the distance caused by eccentricity of the laser irradiation unit from the amount of eccentricity, the diameter of the cavity, and the scattered light characteristics of the object to be measured.

2. A measurement system according to claim 1, wherein the measurement control unit corrects the estimated measurement error for the distance measurement result.

3. A measurement system according to claim 1, wherein the measurement control unit grasps the value of the detected intensity of the reflected light corresponding to each rotation angle of the laser irradiation unit, calculates the irradiation angle of the laser on the side surface of the cavity corresponding to each rotation angle of the laser irradiation unit, and estimates the scattered light characteristics of the measurement object from the detected intensity value and the irradiation angle.

4. A measurement system according to claim 1, wherein the laser irradiation unit irradiates a plurality of light beam elements constituting the laser onto the side surface of the cavity, and the measurement control unit receives a plurality of reflected light beams corresponding to each of the plurality of light beam elements from the measurement unit, measures the distance from each of the plurality of reflected light beams, calculates an average value of the distances measured from each of the plurality of reflected light beams, and further uses the average value to estimate the measurement error.

5. A measurement system as claimed in claim 1, wherein the laser irradiation unit switches the irradiation direction of the laser to a direction approximately perpendicular to the irradiation direction during measurement inside the cavity before being inserted into the cavity, and irradiates the laser at multiple points on the surface of the object to be measured that faces the laser irradiation unit, the measurement unit detects reflected light of the laser from the multiple points via the laser irradiation unit and sends the reflected light to the measurement control unit, and the measurement control unit receives the reflected light and measures the distance from the reflected light between the laser irradiation unit and the multiple points, and calculates the tilt angle of the measurement unit with respect to the object to be measured from the distance measurement result.

6. A measurement system as claimed in claim 1, wherein the laser irradiation unit irradiates a laser onto the side surfaces of a plurality of locations within the cavity that are inserted at different positions from one another; the measurement unit detects the reflected light of the laser reflected by the side surfaces of the plurality of locations within the cavity via the laser irradiation unit and sends the reflected light to the measurement control unit; and the measurement control unit receives the reflected light and measures the distance from the reflected light between the laser irradiation unit and the side surfaces of the plurality of locations within the cavity, and calculates the tilt angle of the measurement unit relative to the measurement object from the distance measurement result.

7. A measurement method for measuring the shape of an object, comprising: irradiating a rotating laser onto a side surface of a cavity provided in a part of the object; detecting light reflected from the laser by the side surface of the cavity; measuring the distance from the reflected light between the laser irradiation position and the side surface of the cavity; calculating the amount of eccentricity and the diameter of the cavity from the distance measurement results when the laser irradiation position is eccentric from the center position of the cavity; and estimating a measurement error of the distance caused by the eccentricity of the laser irradiation position from the amount of eccentricity, the diameter of the cavity, and the scattered light characteristics of the object.

8. A measurement method according to claim 7, wherein the estimated measurement error is corrected for the distance measurement result.

9. A measurement method according to claim 7, comprising: determining a value of the detected intensity of the reflected light corresponding to each rotation angle of the laser; calculating an irradiation angle of the laser on the side surface of the cavity corresponding to each rotation angle of the laser; and estimating the scattered light characteristics of the object to be measured from the value of the detected intensity and the irradiation angle.

10. A measurement method according to claim 7, comprising: irradiating a side surface of the cavity with a plurality of light beam elements constituting the laser; detecting a plurality of reflected light beams corresponding to each of the plurality of light beam elements; measuring the distance from each of the plurality of reflected light beams; calculating an average value of the distances measured from each of the plurality of reflected light beams; and further using the average value to estimate the measurement error.

11. A measurement method according to claim 7, wherein, before irradiating the side surface of the cavity with the laser, the direction of irradiation of the laser is switched to a direction approximately perpendicular to the direction of irradiation during measurement inside the cavity, the laser is irradiated at multiple locations on the top surface of the object to be measured, light reflected from the multiple locations is detected, the distance from the reflected light to the laser irradiation position and the multiple locations is measured, and the relative tilt angle of the object to be measured is calculated from the distance measurement result.

12. A measurement method according to claim 7, comprising irradiating a laser onto the side surfaces of a plurality of locations in the cavity that are inserted at different positions, detecting light reflected from the laser by the side surfaces of the plurality of locations in the cavity, measuring the distance from the reflected light between the laser irradiation position and the side surfaces of the plurality of locations in the cavity, and calculating the relative tilt angle of the object to be measured from the distance measurement results.

Images