Volume measurement method and volume measurement apparatus

Abstract

To provide a volume measurement method and a volume measurement device capable of accurately measuring the volume of a workpiece. [Solution] The volume measuring device 1 measures the volume of the workpiece by emitting a measuring light 51 from a laser interferometer 30 in a first direction along the surface of the workpiece 10, scanning the line, and then moving the scanning position in a second direction perpendicular to the first direction. By changing the angle of the workpiece 10 and measuring the volume, a correlation curve showing the correlation between the volume and the rotation angle is obtained, the rotation angle corresponding to the inflection point in the correlation curve is detected as the appropriate rotation angle, and the angle of the workpiece 10 with respect to the measuring light 51 is set to the appropriate rotation angle to measure the volume of the workpiece 10.

Description

[Technical Field]

[0001] The present invention relates to a volume measurement method and a volume measurement device for measuring the volume of an object. [Background technology]

[0002] Conventionally, when measuring the volume of a workpiece with a non-linear shape, such as an engine cylinder head, a measuring device such as an optical interferometer is used to perform a line scan and measure each measurement point on the bottom surface of the workpiece cross-sectioned at a predetermined cross-section. In addition, a virtual surface corresponding to the lid of the workpiece is set, and the cross-sectional area at the cross-section is calculated by accumulating the distances from each measurement point to the virtual surface. The measurement position of the optical interferometer is moved in a direction perpendicular to the scanning direction of the line scan, and the cross-sectional area at each position is calculated, and the volume of the workpiece is measured by accumulating these cross-sectional areas (see, for example, Patent Document 1). As described above, when measuring the volume of a workpiece non-contact, a laser rangefinder using an optical frequency comb generator is used as an optical interferometer, and the light emitted from the laser rangefinder is irradiated onto the object via a telecentric lens (for example, Patent Document 2). This makes it possible to measure the position of each measurement point on the workpiece with greater accuracy. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-241737 [Patent Document 2] Japanese Patent Publication No. 2019-39714 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In Patent Document 2, the measuring light emitted from the laser rangefinder is irradiated onto the workpiece via a telecentric lens. However, even with a telecentric lens, the measuring light is not always incident on the workpiece at a constant angle. If the workpiece is tilted relative to the measuring light, errors may be introduced into the measurement accuracy of the measurement point, potentially resulting in errors in the measured cross-sectional area and the measured volume of the workpiece.

[0005] The present invention aims to provide a volume measurement method and a volume measurement device capable of accurately measuring the volume of a workpiece. [Means for solving the problem]

[0006] A volume measurement method according to a first aspect of this disclosure involves line scanning by emitting measurement light from a laser interferometer in a first direction along the surface of the workpiece, and then moving the scanning position in a second direction perpendicular to the first direction to measure the volume of the workpiece. By performing this volume measurement while changing the angle of the workpiece, a correlation curve showing the correlation between volume and rotation angle is obtained. Then, an inflection point in the correlation curve is identified, and the rotation angle corresponding to that inflection point is detected. After this, the angle of the workpiece is set to the detected rotation angle, and the volume of the workpiece is measured in that orientation.

[0007] This minimizes fluctuations in the workpiece volume due to errors, even if there is a deviation in the angle of incidence of the measurement light on the workpiece surface, allowing for accurate measurement of the workpiece volume. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram showing the schematic configuration of the volume measuring device of this embodiment. [Figure 2] A schematic cross-sectional view showing an example of a workpiece according to this embodiment. [Figure 3] A schematic diagram showing the general configuration near the workpiece support section of the volume measuring device of this embodiment. [Figure 4] A diagram showing an example of a laser interferometer. [Figure 5]This figure shows an example of a correlation curve obtained in this embodiment. [Figure 6] A flowchart showing the workpiece angle determination step of the volume measurement method of this embodiment. [Figure 7] A diagram showing an example of an angle at which the incidence of measurement light onto the measurement surface is obstructed. [Figure 8] A flowchart illustrating the main measurement step of the volume measurement method according to this embodiment. [Modes for carrying out the invention]

[0009] An embodiment relating to this disclosure will be described below. Figure 1 shows a schematic configuration of the volume measuring device according to this embodiment. As shown in Figure 1, the volume measuring device 1 of this embodiment comprises a workpiece support unit 20 that holds the workpiece 10 (object to be measured), a laser interferometer 30 positioned opposite it, and a control device 40 that controls the entire volume measuring device 1.

[0010] [Explanation of Work 10] The workpiece 10 of this embodiment has a shape with a recess, and when cut in a plane (cutting plane) that includes the incident direction of the laser light (measurement light 51), the cross-sectional surface shape of the recess is asymmetric with respect to the center line. Figure 2 is a schematic cross-sectional view showing an example of the workpiece 10 in this embodiment. For example, in this embodiment, a cylinder head used in the cylinder of an internal combustion engine is measured as the workpiece 10. The surface within the recess of the workpiece 10 becomes the measuring surface 11 for performing volume measurement in this embodiment. The surface shape of the cylinder head is generally different on the intake side (the +X side in Figure 2) where the intake valve is located and on the exhaust side (the -X side in Figure 2) where the exhaust valve is located. In other words, the area and angle of the inclined surfaces inside the cylinder head are different on the intake side and the exhaust side, resulting in an asymmetrical shape with respect to the center line Lc. In addition, since the volume in the combustion chamber of the cylinder head is an important parameter for the performance of the internal combustion engine of the vehicle, high-precision volume measurement that suppresses variations among the workpieces 10 is required. Usually, when measuring the volume of the cylinder head, intake valve seats 12A and exhaust valve seats 12B are arranged in the valve holes (omitted in FIG. 2), and the valve holes are closed for volume measurement. Since the combustion chamber of the cylinder head is asymmetric between the intake side and the exhaust side, the angles and diameter dimensions of the intake valve seats 12A and the exhaust valve seats 12B are also asymmetric. In addition, in the present embodiment, although a cylinder head in which the shape of the measurement surface 11 is clearly asymmetric between the intake side and the exhaust side is exemplified as the workpiece 10, it is not limited thereto. When a workpiece 10 is a product in which the shape of the measurement surface 11 is targeted between the +X side and the -X side in terms of design, usually, tolerances are included during manufacturing. Since it is difficult to prepare a workpiece 10 that appears to be a symmetric shape but is completely symmetric, in the present embodiment, any product in which a container shape is formed by the measurement surface 11 can be used as the workpiece 10.

[0011] [Description of the workpiece support portion 20] FIG. 3 is a diagram showing a schematic configuration near the workpiece support portion of the volume measuring device. The workpiece support portion 20 supports the workpiece 10 so that the posture of the workpiece 10 can be changed. As a configuration for supporting the workpiece 10 so that the posture of the workpiece 10 can be changed, in the present embodiment, as shown in FIGS. 1 and 3, a configuration is exemplified in which the workpiece support portion 20 includes a mounting table 21 on which the workpiece 10 is placed and a posture changing portion 22 that changes the angle of the mounting table 21. A rotation shaft 211 is provided on the mounting table 21, and the mounting table 21 is provided so as to be rotatable about the rotation shaft 211. Further, the mounting table 21 is provided so as to be movable in a direction along the rotation shaft 211. The workpiece 10 is placed on the mounting table 21 such that the X direction and the Z direction shown in FIG. 3 are perpendicular to the rotation shaft 211. That is, in the present embodiment, the rotation shaft 211 is a shaft parallel to the Y direction perpendicular to the X direction and the Z direction.

[0012] The posture changing unit 22 includes a rotation mechanism 221 that rotates the mounting table 21 around a pivot axis 211 using a power source such as a drive motor. The posture changing unit 22 controls the rotation mechanism 221 based on a control command value input from the control device 40, and rotates the mounting table 21 by a rotation angle corresponding to the control command value. As a result, the workpiece 10 placed on the mounting table 21 is also maintained at a predetermined rotation angle. Furthermore, the posture changing unit 22 includes, for example, a reciprocating mechanism 222 that moves the mounting table 21 along the pivot axis 211 (Y direction). The posture changing unit 22 controls the reciprocating mechanism 222 based on a control command value input from the control device 40, and moves the mounting table 21 forward or backward in a direction parallel to the pivot axis 211 by a reciprocating distance angle corresponding to the control command value. This makes it possible to shift the measurement position (irradiation position of the measurement light 51) of the measurement surface 11 of the workpiece 10 in the Y direction.

[0013] In this embodiment, the laser interferometer 30 has a galvanometer mirror 31 that reflects the measurement light 51 irradiated onto the workpiece 10, as shown in Figure 3. The galvanometer mirror 31 is rotatably mounted around a mirror pivot axis 311 and is rotated around the mirror pivot axis 311 by a mirror drive motor 312 (see Figure 1). As a result, the measurement light 51 emitted from the laser interferometer 30 is swung within a plane (cutting plane) perpendicular to the mirror pivot axis 311. In other words, the measurement light 51 is irradiated in a line along the line of intersection with the cutting plane on the measurement surface 11 of the workpiece 10. The direction along the line of intersection between the measurement surface 11 of the workpiece 10 and the cutting plane corresponds to the first direction of this disclosure. In this embodiment, the pivot axis 211 that rotatably supports the mounting base 21 described above is parallel to the mirror pivot axis 311. By driving the mirror drive motor 312, the measurement light 51 is swung within a cutting plane parallel to the XZ plane and irradiated onto the workpiece 10 via the telecentric lens 313. This allows the laser interferometer 30 to detect each measurement point on the measurement surface 11 of the workpiece 10 within the cutting plane. Furthermore, by moving the mounting table 21 in the Y direction using the actuator, the position of the cutting plane onto which the measurement light 51 of the workpiece 10 is irradiated can be moved in the Y direction, thereby enabling the detection of all measurement points on the measurement surface 11 of the workpiece 10.

[0014] [Description of Laser Interferometer 30] The laser interferometer 30 irradiates the workpiece 10 with measurement light 51, generates interference light between the reflected light 51R (which is the measurement light 51 reflected from the workpiece 10) and a predetermined reference light 52, and measures the distance from the laser interferometer 30 to the reflection point (measurement point) on the surface of the workpiece 10 by detecting the generated interference light. Figure 4 shows an example of a laser interferometer 30. The laser interferometer 30 comprises a first light source 32, a second light source 33, a light guide optical system 34, a first light detection unit 35, a second light detection unit 36, and a reference plane 37. The first light source 32 emits laser light which becomes the measurement light 51. The second light source 33 emits laser light that becomes the reference light 52. The measurement light 51 emitted from the first light source 32 and the reference light 52 emitted from the second light source 33 have orthogonal polarization planes; for example, the measurement light 51 is P-polarized and the reference light 52 is S-polarized. Furthermore, the first light source 32 and the second light source 33 are light sources that periodically modulate the intensity or phase of the emitted laser light, and each has a different modulation period.

[0015] The light guide optical system 34 comprises a first photosynthesis element 341, a first light separation element 342, a second light separation element 343, a first polarizer 344, and a second polarizer 345. The first photosynthesis element 341 is a polarizing beam splitter that transmits the measurement light 51 from the first light source 32 and reflects the reference light 52 from the second light source 33, thereby causing the mixed light, which is a mixture of the measurement light 51 and the reference light 52, to be emitted toward the first light separation element 342. The first light separation element 342 is a semi-transparent mirror that transmits a portion of the mixed light incident from the first light separation element 342 and reflects the remainder toward the first light detection unit 35. A first polarizer 344 is positioned between the first light separation element 342 and the first light detection unit 35. A portion of the mixed light, which is a mixture of the measurement light 51 and the reference light 52 reflected by the first light separation element 342, is received by the first light detection unit 35 as reference interference light 53 via the first polarizer 344.

[0016] The second light separation element 343 is a polarizing beam splitter. Mixed light transmitted through the first light separation element 342 is incident on it, transmitting P-polarized measurement light 51 toward the workpiece 10 and reflecting S-polarized reference light 52 toward the reference surface 37. The second light separation element 343 also mixes the measurement light 51 (reflected light 51R) reflected from the workpiece 10 and the reference light 52 (reflected reference light 52R) reflected from the reference surface 37, and emits the mixed light toward the first light separation element 342. The first light separation element 342 reflects the mixed light of the reflected light 51R and the reflected reference light 52R toward the second light detection unit 36. A second polarizer 345 is positioned between the first light separation element 342 and the second light detection unit 36. The mixed light, which is a mixture of the reflected light 51R and the reflected reference light 52R reflected by the first light separation element 342, is received by the second light detection unit 36 ​​as interference light 54 via the second polarizer 345.

[0017] In the laser interferometer 30 shown in Figure 4, periodic feature points corresponding to the modulation period between the measurement light 51 and the reference light 52 are obtained from the reference interference light 53 received by the first photodetector 35, and periodic feature points corresponding to the modulation period between the reflected light 51R and the reflected reference light 52R are obtained from the interference light 54 received by the second photodetector 36. The time difference in which these feature points are obtained corresponds to the difference |L2-L1|, which is the absolute value of the difference between the distance L1 from the second optical separation element 343 to the reference surface 37 and the distance L2 from the second optical separation element 343 to the workpiece 10. This allows for the accurate calculation of the distance from the laser interferometer 30 to the measurement point (reflection point) of the workpiece 10.

[0018] Note that the laser interferometer 30 shown in Figure 4 is just one example and is not limited to it. For example, a Michelson interferometer, a heterodyne interferometer, a homodyne interferometer, etc., may be used as the laser interferometer 30.

[0019] Although not shown in Figure 4, as described above, a galvanometer mirror 31 and a telecentric lens 313 are positioned between the second optical separation element 343 and the workpiece 10 of the laser interferometer 30. By driving the mirror drive motor 312, the measurement light 51 emitted toward the workpiece 10 is swung along the X direction, and the measurement light 51 is irradiated onto the workpiece 10 via the telecentric lens 313. As a result, as shown in Figure 3, the measurement light 51 incident on the measurement surface 11 of the workpiece 10 is maintained to be approximately parallel regardless of the rotation angle of the galvanometer mirror 31. However, even with the use of the telecentric lens 313, it is difficult to completely eliminate optical distortion. In particular, when the angle of incidence of the measurement light 51 incident on an asymmetrical workpiece 10 varies, an error occurs in the position (distance) of the measurement point, and as a result, the error included in the volume measurement also increases. As will be described in detail later, in this embodiment, in order to address the above-mentioned problems, the orientation of the workpiece 10 is changed to an appropriate rotation angle in order to minimize the effect of errors, and then the volume of the workpiece 10 is measured.

[0020] [Description of control device 40] Returning to Figure 1, the control device 40 will be described. The control device 40 is composed of a general-purpose computer, such as a personal computer. The control device 40 includes a memory 41 for storing various programs and data, and a processor 42 that reads and executes the programs stored in the memory 41 to realize various functions. The processor 42 functions as a volume measurement unit 421, a workpiece angle setting unit 422, a correlation curve acquisition unit 423, and a rotation angle detection unit 424 by reading and executing a program stored in the memory 41.

[0021] The volume measurement unit 421 controls the laser interferometer 30 to irradiate the measurement surface 11 of the workpiece 10 with measurement light 51 along the cutting plane, and calculates the distance from the laser interferometer 30 to the measurement point on the measurement surface 11 based on the received light signals output from the first light detection unit 35 and the second light detection unit 36 ​​of the laser interferometer 30. In other words, the position of each measurement point on the measurement surface 11 of the workpiece 10 can be determined relative to the laser interferometer 30.

[0022] Furthermore, once the volume measurement unit 421 calculates the measurement points on the measurement surface 11 of the workpiece 10 in the cutting plane, it detects the edges 13 of the recesses on the ±X sides of the workpiece 10 and sets the line segment connecting the pair of edges 13 as the workpiece reference plane 14. The volume measurement unit 421 then measures the distance from each measurement point to the workpiece reference plane 14 and calculates the area (cutting area) of the region between the measurement surface 11 of the workpiece 10 and the workpiece reference plane 14 by summing these distances. Furthermore, the volume measurement unit 421 controls the posture change unit 22 to move the mounting table 21 in the Y direction, performs the above-described cutting area calculation process at each position in the Y direction, and calculates the volume of the workpiece 10 by accumulating these cutting areas. Alternatively, a single workpiece reference surface 14 may be generated from any three or more points on the workpiece surface.

[0023] The workpiece angle setting unit 422 controls the posture changing unit 22 to rotate the mounting table 21 on which the workpiece 10 is placed around the pivot axis 211, thereby changing the angle of incidence of the measuring light 51 onto the workpiece 10.

[0024] The correlation curve acquisition unit 423 calculates a correlation curve between each rotation angle when the mounting table 21 is rotated to change the rotation angle and the volume of the workpiece 10 calculated from the detection result of the measurement points of the laser interferometer 30 based on the rotation angle.

[0025] FIG. 5 is a diagram showing an example of the correlation curve obtained in the present embodiment. In the present embodiment, rotating the mounting table 21 to change the rotation angle means changing the posture of the workpiece 10 and means changing the incident angle of the measurement light 51 to the workpiece 10. That is, in the present embodiment, the workpiece angle setting unit 422 changes the posture of the workpiece 10, the volume measurement unit 421 detects the measurement points in each posture, and the volume measurement unit 421 measures the volume of the workpiece 10. Thereby, the correlation curve acquisition unit 423 calculates a correlation curve 60 showing the change in the volume of the workpiece 10 when the incident angle of the measurement light 51 to the workpiece 10 is changed as shown in FIG. 5.

[0026] The rotation angle detection unit 424 identifies the inflection point 61 of the calculated correlation curve 60 and detects the rotation angle corresponding to the inflection point 61 as the appropriate rotation angle θ that the mounting table 21 should be set in the measurement of the workpiece 10. A as. As described above, due to the optical distortion of the telecentric lens 313, the incident angle of the measurement light 51 incident on the workpiece 10 fluctuates, and the volume measurement result fluctuates. For example, in FIG. 5, when the rotation angle of the mounting table 21 is set to θ1, the volume of the workpiece 10 is V1. However, due to factors such as the optical distortion of the telecentric lens 313, when the incident angle of the measurement light 51 fluctuates within the range corresponding to θ1±Δφ in FIG. 5, the volume measurement value may change within the range ΔV1 from the volume V2 (<V1) corresponding to θ1+Δφ to V3 (>V1) corresponding to θ1-Δφ. That is, even when the incident angle of the measurement light 51 fluctuates slightly due to optical distortion or the like, the change in the volume measurement result becomes large. On the other hand, at the position of the appropriate rotation angle θ A even when the incident angle of the measurement light 51 fluctuates within the range of θ A ±Δφ, the change in the volume measurement value is ΔV A(<ΔV1) can be suppressed within the range. This means that even if the incident angle of the measurement light 51 with respect to the workpiece 10 fluctuates, the influence is small. Therefore, based on the correlation curve 60, the rotation angle detection unit 424 detects the rotation angle corresponding to the inflection point 61 as the appropriate rotation angle θ for the workpiece 10. A When there are multiple inflection points 61, the rotation angle corresponding to the inflection point 61 with a smaller volume fluctuation within a predetermined angle range (θ A ±Δφ) may be detected as the appropriate rotation angle θ. A

[0027] In addition, the rotation angle detection unit 424 acquires the type of the workpiece 10 and stores it in the memory 41 in association with the detected appropriate rotation angle θ for the workpiece 10. That is, in the volume measurement device 1 of the present embodiment, it is possible to measure the volumes of a plurality of types of workpieces 10 with different design data. When measuring the volume of a workpiece 10 with the same design data, the appropriate rotation angle θ corresponding to the type of the workpiece 10 is read from the memory 41 and set. For example, when the design data of the cylinder head of the first vehicle type is different from the design data of the cylinder head of the second vehicle type, the appropriate rotation angle θ corresponding to the volume measurement of the cylinder head of the first vehicle type, and the appropriate rotation angle θ corresponding to the volume measurement of the cylinder head of the second vehicle type are stored in the memory 41 respectively. A A A A The type of the workpiece 10 may be input to the control device 40 by manual input by an operator, for example. A code for specifying the type of the workpiece 10 may be given to a part of the workpiece 10, and the type of the workpiece may be specified by reading the code with a code sensor such as a camera.

[0028] [Explanation of the operation of the volume measurement device 1] Next, the operation of the volume measurement device 1 will be described. When the volume of the workpiece 10 is measured by the volume measurement device 1, a workpiece angle determination step for obtaining the appropriate angle of each workpiece 10 is performed in advance. Then, a main measurement step for measuring the volume of the workpiece 10 to be measured is performed. Figure 6 is a flowchart showing the workpiece angle determination step of the volume measurement method of this embodiment. First, let's explain the workpiece angle determination step. In the workpiece angle determination step, the workpiece 10 is placed on the mounting table 21 so that the surface to be measured for volume faces the laser interferometer 30. When the operator inputs that the workpiece angle determination step should be started, the control device 40 identifies the type of workpiece 10 (step S1). The type of workpiece 10 can be identified, for example, by the operator operating the input means to input the type of workpiece 10 or an ID that identifies that type, or by reading a code on the workpiece 10 using a code sensor (not shown) such as a camera provided in the volume measuring device 1.

[0029] Next, the workpiece angle setting unit 422 controls the posture changing unit 22 to set the rotation angle of the mounting table 21 to a predetermined initial value (step S2). In other words, it sets the incidence angle of the measuring light 51 onto the workpiece 10 to a predetermined initial value.

[0030] Then, the volume measurement unit 421 performs a volume measurement process to measure the volume of the workpiece 10 (step S3). Specifically, the volume measurement unit 421 controls the laser interferometer 30 to irradiate the workpiece 10 with measurement light 51 along the cutting plane and detects multiple measurement points on the intersection line between the cutting plane and the measurement surface 11. Then, the volume measurement unit 421 detects the edge 13 of the measurement surface 11 from these measurement points and sets the workpiece reference surface 14. Note that, as described above, the workpiece reference surface 14 may be set by generating a single workpiece reference surface 14 from any three or more points on the upper surface of the workpiece. Furthermore, the volume measurement unit 421 calculates the cross-sectional area enclosed by the workpiece reference surface 14 and the measurement surface 11 by accumulating the distance from each measurement point to the workpiece reference surface 14. The volume measurement unit 421 controls the advance / return mechanism 222 of the posture change unit 22 to move the mounting table 21 in the Y direction, calculates the cross-sectional area for each position in the Y direction in the same manner as above, and accumulates these to calculate the volume of the workpiece 10. The volume measurement unit 421 stores the calculated volume in the memory 41 in association with the rotation angle of the mounting table 21.

[0031] Subsequently, the workpiece angle setting unit 422 determines whether or not the volume measurement process in step S3 has been performed for all rotation angles within a predetermined angle range (step S4). This "pre-set predetermined angular range" refers to the range of angles in which a part of the workpiece 10 does not obstruct the incidence of the measuring light 51 onto the measuring surface 11. Figure 7 shows an example of an angle in which the incidence of the measuring light 51 onto the measuring surface 11 is obstructed. For example, the example shown in Figure 7 is the posture of the workpiece 10 when the rotation angle is set beyond the predetermined angular range, and the incidence of the measuring light 51 onto a part of the workpiece 10 (the side corner portion 16 in Figure 7) is obstructed. In this case, since the measuring light 51 cannot be irradiated onto the side corner portion 16, the measurement point on the side corner portion 16 cannot be detected. The angle range of the rotation angle is preferably set for each type of workpiece 10. For example, table data containing pre-stored angle ranges for different types of workpieces is stored in memory 41, and the workpiece angle setting unit 422 reads the angle range corresponding to the workpiece type from the table data. Alternatively, in step S1, the operator may input the angle range when inputting the type of workpiece 10.

[0032] If NO is determined in step S4, the workpiece angle setting unit 422 controls the posture changing unit 22 to change the rotation angle of the mounting table 21 (workpiece 10) by a predetermined interval (step S5), and then returns to step S3. The angle by which the rotation angle is changed is not particularly limited, but it is preferable to use an interval of about 0.1°, for example. On the other hand, if the result in step S4 is determined to be YES, the correlation curve acquisition unit 423 calculates a correlation curve 60 as shown in Figure 5 based on the volume measurement results for each rotation angle stored in the memory 41 in step S3 (step S6). The rotation angle detection unit 424 then identifies an inflection point 61 from the obtained correlation curve 60 and determines the rotation angle corresponding to the identified inflection point 61 as the appropriate rotation angle θ. A The rotation angle detection unit 424 also detects the type of workpiece 10 and the appropriate rotation angle θ detected in step S7. AThe two are associated and stored in memory 41.

[0033] Figure 8 is a flowchart showing the main measurement step of the volume measurement method of this embodiment. In this embodiment, by performing the workpiece angle determination step described above in advance, the appropriate rotation angle θ for each workpiece 10 is determined. A The data is stored in memory 41 beforehand, and then the measurement step is performed. In this measurement step, the control device 40 first identifies the type of workpiece 10 to be measured (step S11). Similar to step S1, the type of workpiece 10 may be identified by an operator operating an input means or by entering an ID that identifies the type, or the code sensor provided in the volume measuring device 1 may be used to read a code on the workpiece 10 that identifies the type.

[0034] Next, the workpiece angle setting unit 422 reads the appropriate rotation angle corresponding to the type of workpiece 10 from the memory 41 (step S12), and controls the posture change unit 22 to set the rotation angle of the mounting table 21 on which the workpiece 10 is placed to the appropriate rotation angle (step S13). After the above, the volume measuring unit 421 measures the volume of the workpiece 10 in the same manner as in step S3 (step S14). As a result, even if there is a deviation in the incident angle of the measuring light 51 for an asymmetrical workpiece 10, the effect of this deviation on the measured volume can be minimized, making it possible to perform highly accurate volume measurement. Furthermore, by pre-storing appropriate rotation angles for multiple types of workpieces 10 in the memory 41, it becomes unnecessary to perform a workpiece angle determination step each time a workpiece 10 is measured. For the same type of workpiece 10, it is sufficient to read the appropriate rotation angle from the memory 41 and set the orientation of the workpiece 10.

[0035] [Effects of this embodiment] The volume measuring device 1 of this embodiment includes a laser interferometer 30, a workpiece support unit 20 that supports the workpiece 10, and a control device 40. The laser interferometer 30 emits a line-shaped measuring light 51 along the X direction to the surface (measuring surface 11) of the workpiece 10, and detects a measurement point on the line of intersection between the cutting plane and the measuring surface 11 of the workpiece 10 based on the interference light 54 of the reflected light 51R reflected from the measuring surface 11 of the workpiece 10 and the reflected reference light 52R. The workpiece support unit 20 has a mounting table 21 that can change the orientation of the workpiece 10 by rotating the workpiece 10 around a pivot axis 211. The control device 40 functions as a volume measuring unit 421, a workpiece angle setting unit 422, a correlation curve acquisition unit 423, and a rotation angle detection unit 424 when the processor 42 reads and executes a program stored in the memory 41. The volume measurement unit 421 scans the cutting plane of the laser interferometer 30 in the Y direction to acquire each measurement point on the measurement surface 11 of the workpiece 10, and measures the volume of the workpiece 10 based on these measurement points. The workpiece angle setting unit 422 rotates the workpiece 10 around a pivot axis 211 perpendicular to the cutting plane. The correlation curve acquisition unit 423 acquires a correlation curve showing the correlation between the rotation angle of the workpiece 10 and the volume of the workpiece 10. The rotation angle detection unit 424 detects the rotation angle corresponding to the inflection point in the correlation curve as the appropriate rotation angle.

[0036] As a result, when measuring the volume of the workpiece 10, even if the angle of incidence of the measurement light 51 onto the workpiece 10 is shifted due to optical distortion of the telecentric lens 313, the change in volume due to the shift in the angle of incidence can be minimized, and highly accurate volume measurement of the workpiece 10 can be performed.

[0037] In this embodiment, in step S4, the rotation angle of the mounting table 21 (workpiece 10) is changed within a predetermined angle range that has been set in advance. This prevents the inconvenience of the measurement light 51 not being incident on the measurement surface 11 due to a part of the workpiece 10, and allows for proper detection of the measurement point on the measurement surface 11.

[0038] In this embodiment, the cylinder head of an internal combustion engine is used as the workpiece 10, and its volume is measured. Such cylinder heads are typically formed with an asymmetrical shape on the exhaust and intake sides, and the measured volume is prone to fluctuations due to the shift in the incident angle of the measuring light 51 caused by optical distortion of the telecentric lens 313. The volume of the combustion chamber in the cylinder head is an important parameter related to the output and fuel efficiency of the vehicle's internal combustion engine, so highly accurate volume measurement is necessary. In this embodiment, such a cylinder head can be used as the workpiece 10, and the volume of its combustion chamber can be measured with high accuracy.

[0039] In this embodiment, in the workpiece angle determination step, a correlation curve is calculated for each of the multiple types of workpieces 10 formed based on multiple design data to detect the appropriate rotation angle, and the obtained appropriate rotation angle and the type of workpiece 10 are stored in the memory 41. Then, in the measurement step, the appropriate rotation angle corresponding to the type of workpiece 10 is read from the memory 41 to set the orientation of the workpiece 10. This eliminates the need to perform a workpiece angle determination step each time the volume of workpiece 10 is measured, thereby simplifying the volume measurement process.

[0040] [Differentiation] The present invention is not limited to the embodiments described above, but also includes the following modifications to the extent that the objectives of the present invention can be achieved.

[0041] In the above embodiment, the work support unit 20 includes a mounting table 21 on which the workpiece 10 is placed, and the angle of incidence of the measuring light 51 onto the workpiece 10 is changed by rotating the mounting table 21 around the pivot axis 211. Alternatively, the angle of incidence of the measurement light 51 onto the workpiece 10 may be changed by changing the orientation of the laser interferometer 30 relative to the mounting table 21.

[0042] Furthermore, in the above embodiment, an example was shown in which the cutting plane is scanned in the Y direction by moving the mounting table 21 in the Y direction, but the laser interferometer 30 may also be moved in the Y direction.

[0043] As an example of how the workpiece 10 is supported by the workpiece support unit 20, an example of placing the workpiece 10 on the mounting table 21 has been shown, but the workpiece 10 may also be gripped by an arm or the like. In this case, the angle of incidence of the measuring light 51 to the workpiece 10 may be changed by changing the posture of the arm that supports the workpiece 10.

[0044] In the above embodiment, an example was shown in which the mounting base 21 is rotated around the pivot axis 211. However, the configuration may also be such that the inclination angle of the pivot axis 211 can be changed.

[0045] In the above embodiment, a cylinder head is used as an example of the workpiece 10, and an example is shown in which the measurement light 51 from the laser interferometer 30 is irradiated onto a cutting plane that includes the direction from the exhaust side to the intake side (X direction) and the incident direction of the laser light (measurement light 51) (Z direction). However, for example, the cutting plane onto which the measurement light 51 is irradiated may be a plane that includes the Y direction and the Z direction. In this case, the cutting plane is scanned in the X direction, and the volume of the workpiece 10 is calculated by integrating the cutting area in each cutting plane. Furthermore, by providing a pivot axis 211 of the mounting table 21 along the X direction and rotating the mounting table 21 around the pivot axis 211, a correlation curve similar to that in the above embodiment can be obtained. [Explanation of Symbols]

[0046] 1...Volume measuring device, 10...Workpiece, 11...Measuring surface, 20...Workpiece support, 21...Mounting platform, 22...Position change unit, 30...Laser interferometer, 31...Galvanometer mirror, 40...Control device, 41...Memory, 42...Processor, 51...Measurement light, 60...Correlation curve, 61...Inflection point, 211...Rotation axis, 221...Rotation mechanism, 222...Advance / retraction mechanism, 311...Mirror rotation axis, 312...Mirror drive motor, 313...Telecentric lens, 421...Volume measuring unit, 422...Workpiece angle setting unit, 423...Correlation curve acquisition unit, 424...Rotation angle detection unit.

Claims

1. A volume measurement method that measures the surface shapes of multiple workpieces and measures the volume between the workpiece surface and a predetermined reference plane, using a laser interferometer that emits measurement light onto the surface of a workpiece and detects measurement points on the surface of the workpiece based on the interference light between the reflected light reflected from the surface of the workpiece and a predetermined reference light, A volume measurement process is performed to measure the volume of the workpiece based on the multiple measurement points obtained by scanning the measurement light along a second direction perpendicular to the first direction, using the plane containing the first direction and the direction of emission of the measurement light as the cutting plane, and performing the volume measurement process for each rotation angle when the workpiece is rotated around a rotation axis perpendicular to the cutting plane, thereby obtaining a correlation curve showing the relationship between the rotation angle and the volume of the workpiece. The rotation angle corresponding to the inflection point in the correlation curve is detected as the appropriate rotation angle. A volume measurement method comprising setting the angle at which the workpiece is supported to the appropriate rotation angle and measuring the volume of the workpiece.

2. When obtaining the correlation curve, the rotation angle is changed within a predetermined angle range. The volume measurement method according to claim 1.

3. The aforementioned workpiece is the cylinder head of an internal combustion engine. The volume measurement method according to claim 1.

4. For each of the multiple types of workpieces formed based on multiple design data, the correlation curve is calculated to detect the appropriate rotation angle, and the obtained appropriate rotation angle is stored in memory in association with the corresponding type of workpiece. The appropriate rotation angle corresponding to the type of workpiece to be measured is read from the memory and set as the rotation angle for supporting the workpiece. The volume measurement method according to claim 1.

5. A laser interferometer that emits measurement light onto the surface of a workpiece and detects a measurement point on the surface of the workpiece based on the interference light between the reflected light from the surface of the workpiece and a predetermined reference light, A volume measuring unit that emits the measurement light from the laser interferometer in a first direction along the surface of the workpiece to detect a plurality of measurement points along the first direction, and measures the volume of the workpiece based on the plurality of measurement points obtained by scanning the measurement light along a second direction perpendicular to the first direction, A workpiece angle setting unit rotates the workpiece around a pivot axis perpendicular to the cutting plane, with the plane including the first direction and the direction of emission of the measuring light being used as the cutting plane. A correlation curve acquisition unit acquires a correlation curve showing the relationship between the volume of the workpiece and the rotation angle when the workpiece is rotated around the pivot axis. A rotation angle detection unit that detects the rotation angle corresponding to the inflection point in the correlation curve, A volume measuring device equipped with the following features.

Images