JP7742016B2 - Shape measuring instrument and its calibration method - Google Patents

Description

The present invention relates to a shape measuring machine and a calibration method thereof, and in particular to a shape measuring machine and a calibration method thereof used to calibrate a shape measuring machine for measuring the shape of a workpiece.

Conventionally, shape measuring machines have been known that measure the shape (roundness, etc.) of a workpiece by rotating a probe and the workpiece relatively around a rotation axis. For example, Patent Document 1 discloses a technology for non-contact measurement of the shape of the inner and side surfaces of the center hole of a cylindrical workpiece placed on a rotary table.

JP 2010-014656 A

With shape measuring instruments like those described above, a probe equipped with a non-contact optical sensor is used to measure the shape of the calibration standard, and a process called magnification calibration is required to correlate the probe's output signal with the actual calibrated displacement (see, for example, Japanese Industrial Standards JIS B7451:1997, Annex 2).

When calibrating magnification, the relative position of the calibration standard and the probe is adjusted while visually checking the position of the probe tip and its vicinity using a microscope or other device. During this process, there is a risk that the probe may come into contact (crash) with the calibration standard due to an operator error, resulting in damage to the probe.

Furthermore, because visual confirmation of the position is required, it is difficult to automate the calibration process, and the accuracy of the calibration process depends on the skill of the operator.

The present invention was made in light of these circumstances, and aims to provide a shape measuring machine and a calibration method therefor that can prevent the probe from coming into contact with a calibration standard during calibration (magnification calibration) of the shape measuring machine, thereby enabling the automation of the calibration process.

To solve the above problem, a shape measuring instrument according to a first aspect of the present invention comprises a stage holding a calibration standard having or capable of being set to a first measurement surface and a second measurement surface; a stage rotation mechanism that rotates the stage around a rotation axis; a probe capable of detecting displacement along a first direction; a stage imaging camera capable of capturing images of the surface of the stage; a first linear motion mechanism that moves the probe in the first direction; a second linear motion mechanism to which the probe and stage imaging camera are attached that moves the probe and stage imaging camera along a second direction perpendicular to the first direction; and a control unit that moves the stage imaging camera to at least two points along the second direction, detects the first measurement surface of the calibration standard at the at least two points, and controls the stage rotation mechanism based on the detection results of the first measurement surface to make the first measurement surface parallel to the second direction.

A shape measuring instrument according to a second aspect of the present invention is the first aspect, wherein the control unit moves the stage to align the first measurement surface with the rotation axis.

A shape measuring instrument according to a third aspect of the present invention is the same as that of the first or second aspect, but includes a rotating camera that is rotatable together with the stage, and the control unit detects the central axis of the probe based on an image of the probe captured by the rotating camera and aligns the central axis of the probe with the rotation axis of the stage.

A fourth aspect of the present invention relates to a shape measuring instrument according to any one of the first to third aspects, in which the control unit aligns the central axis of the probe with the rotation axis of the stage, then moves the probe away from the calibration standard along the first direction by a distance equal to or greater than the sum of the probe radius and the minimum working distance, and then lowers the probe to a position where it faces the first measurement surface.

A method for calibrating a shape measuring machine according to a fifth aspect of the present invention comprises the steps of: holding a calibration standard having or capable of being set to a first measurement surface and a second measurement surface on a stage; moving a stage imaging camera capable of capturing images of the surface of the stage to at least two points along a second direction perpendicular to the first direction in which the probe can detect displacement, and detecting the first measurement surface of the calibration standard at the at least two points; and controlling the stage rotation mechanism based on the detection results of the first measurement surface to make the first measurement surface parallel to the second direction.

This invention makes it possible to prevent probes from coming into contact with calibration standards and automate calibration procedures.

FIG. 1 is a front view showing a shape measuring instrument according to a first embodiment of the present invention. FIG. 2 is a block diagram showing a control system of the shape measuring machine according to the first embodiment of the present invention. FIG. 3 is a plan view (top view) for explaining the calibration method for a shape measuring machine according to the first embodiment of the present invention. FIG. 4 is a flowchart showing a method for calibrating a shape measuring machine according to the first embodiment of the present invention. FIG. 5 is a flow chart showing the calibration standard positioning process. FIG. 6 is a plan view for explaining the procedure for calculating the inclination θ of the reference surface of the calibration standard. FIG. 7 is a plan view for explaining the procedure for calculating the inclination θ of the reference surface of the calibration standard. FIG. 8 is a plan view for explaining the position adjustment of the calibration standard. FIG. 9 is a diagram showing an example of the position at which the first camera captures an image of the probe. FIG. 10 is an explanatory diagram showing an example of an image captured by a camera at each of the image capturing positions. FIG. 11 is a diagram showing a composite image of the first captured image and the third captured image. FIG. 12 is a diagram showing a composite image of the second captured image and the fourth captured image. FIG. 13 is a diagram for explaining the relative positioning process between the calibration standard and the probe. FIG. 14 is a diagram for explaining the magnification calibration process (block gauge). FIG. 15 is a diagram for explaining the magnification calibration process (screw-type magnification calibrator). FIG. 16 is a diagram for explaining the magnification calibration error. FIG. 17 is a diagram for explaining the positioning step of the calibration standard according to the second embodiment of the present invention. FIG. 18 is a diagram for explaining the positioning step of the calibration standard according to the second embodiment of the present invention. FIG. 19 is a flowchart showing the calibration standard positioning process according to the second embodiment of the present invention. FIG. 20 is a flowchart showing the calibration standard positioning process according to the third embodiment of the present invention. FIG. 21 is a diagram for explaining the Y vector registration process.

The following describes an embodiment of a shape measuring instrument and its calibration method according to the present invention, with reference to the accompanying drawings.

[First embodiment]
(shape measuring machine)
First, the schematic configuration of a shape measuring machine will be described with reference to Figures 1 and 2. Figure 1 is a front view showing a shape measuring machine according to a first embodiment of the present invention.

The shape measuring machine 10 shown in Figure 1 is a device capable of measuring the outer shape of a workpiece W and the inner shape (roundness, etc.) of a small hole formed in a cylindrical workpiece. The small hole formed in the workpiece is, for example, a through hole formed along the central axis of the workpiece, and the inner diameter of the small hole is extremely small (for example, an inner diameter of 500 μm or less). In Figure 1, the X, Y, and Z directions are mutually perpendicular, with the X direction being the horizontal direction, the Y direction being the horizontal direction perpendicular to the X direction, and the Z direction being the vertical direction.

As shown in FIG. 1, the shape measuring instrument 10 includes a main body base 12, a stage rotation mechanism 14, a stage 18, a column 20, a carriage 22, a first arm 24X, a second arm 24Y, a displacement detector 26, a detector drive mechanism 28, and a control device 50.

The stage rotation mechanism (high-precision rotation mechanism) 14 is a rotation mechanism for rotating the workpiece W around the rotation axis C, and rotates the stage 18 (described later) with high precision around the rotation axis C parallel to the Z direction. The stage rotation mechanism 14 includes a rotor 16 rotatably mounted on the main body base 12, with the stage 18 supported on the upper surface of the rotor 16. The stage rotation mechanism 14 includes a motor (not shown) that rotates the rotor 16 with high precision around the rotation axis C, and an encoder (not shown) that detects the rotation angle of the rotor 16.

The stage 18 is used to place the workpiece W. The stage 18 may directly support and fix the workpiece W, or it may support and fix the workpiece W via a workpiece installation jig (not shown).

The stage 18 is supported on the support surface (top surface) of the rotating body 16 and is configured to be rotatable integrally with the rotating body 16 around the rotation axis C. As a result, the workpiece W supported and fixed on the stage 18 can be rotated integrally with the stage 18 around the rotation axis C. The rotating body 16 is an example of a "stage rotation mechanism."

The stage 18 is equipped with a linear motion mechanism and a tilting mechanism (neither shown). The linear motion mechanism moves the stage 18 in the X and Y directions by driving a motor (not shown), adjusting the position of the stage 18 in the XY plane (horizontal plane) perpendicular to the rotation axis C. The tilting mechanism rotates the stage 18 in the X and Y directions by driving a motor (not shown), adjusting the tilt of the stage 18 relative to the XY plane.

A column (support) 20 extending parallel to the Z direction is erected on the main body base 12. The lower end of the column 20 is fixed to the upper surface of the main body base 12.

The carriage 22 is supported by the column 20 so that it can move in the Z direction. The carriage 22 is configured to be movable in the Z direction by driving a motor (not shown).

The first arm 24X is supported by the carriage 22 so as to be movable in the X direction. The second arm 24Y is supported by the first arm 24X so as to be movable in the Y direction. The first arm 24X and the second arm 24Y are configured to be movable in the horizontal direction (X and Y directions) by a first linear motion mechanism 70X and a second linear motion mechanism 70Y (see Figure 2), respectively. The first linear motion mechanism 70X and the second linear motion mechanism 70Y are equipped with drive sources (motors, etc.) for moving the first arm 24X and the second arm 24Y in the horizontal direction, respectively.

Scales are provided on the sides of the first arm 24X and the column 20 along the X and Z directions, respectively. The control device 50 (an example of a control unit) can detect the position of the probe 30 in the ZX directions by reading the graduations on these scales using a sensor (not shown).

The displacement detector 26 is supported by the second arm 24Y via the detector drive mechanism 28. The displacement detector 26 has a probe 30. The probe 30 detects the shape of the workpiece surface (the outer surface or the inner surface of a hole formed in the workpiece). The probe 30 in this embodiment is a non-contact probe that can detect the surface shape of the workpiece without coming into contact with the workpiece surface.

The type of non-contact probe 30 is not particularly limited as long as it can detect the surface shape of the workpiece without contacting the surface. Non-contact probes that can be used include probes that use various techniques, such as a laser interferometer, a white light interferometer, SD-OCT (Spectral Domain-Optical Coherence Tomography), or SS-OCT (Swept Source-Optical Coherence Tomography).

Note that, although the following description will discuss an example of a non-contact probe, the type of probe 30 is not limited to non-contact. Probe 30 may also be a contact probe that can detect the surface shape of a workpiece by contacting its tip with the surface of the workpiece. A contact probe has a contactor that can come into contact with the surface of the workpiece, and detects the internal shape by detecting the displacement of the contactor when it is brought into contact with the surface of the workpiece. Examples of contact probes that can be used include probes that use various methods such as an LVDT (Linear Variable Differential Transformer), an interferometer, optical triangulation, and thin film distortion measurement. Furthermore, a method can be used for a contact probe in which the contactor of a contact probe is vibrated at a resonant frequency, and the resonance point changes upon contact.

The detector drive mechanism 28 is interposed between the second arm 24Y and the displacement detector 26. The detector drive mechanism 28 includes a linear motion mechanism and a tilt mechanism (neither of which are shown). The linear motion mechanism moves the displacement detector 26 in the X and Y directions by driving a motor (not shown), thereby adjusting the position of the probe 30 in the XY plane (horizontal plane) perpendicular to the rotation axis C. The tilt mechanism rotates the displacement detector 26 around the X and Y directions by driving a motor (not shown), thereby adjusting the tilt of the probe 30 relative to the XY plane. Therefore, by adjusting the position and tilt of the probe 30 in the horizontal direction (X and Y directions) using the detector drive mechanism 28 (linear motion mechanism and tilt mechanism), it is possible to perform relative alignment (probe alignment) between the probe 30 and the rotation axis C.

The detector drive mechanism 28 also includes a drive source (e.g., a motor) for rotating the detector around the rotation axis (probe rotation axis) AX. The detector drive mechanism 28 is an example of a "probe rotation mechanism."

As shown in FIG. 1, a camera support 18A is fixed to the surface of the stage 18, and a first camera CAM1 is attached to the camera support 18A. The first camera CAM1 is rotatable in conjunction with the rotation of the stage 18, and is capable of capturing images of a workpiece or the like placed on the surface of the stage 18. Note that while the first camera CAM1 is shown mounted on the stage 18 in FIG. 1, the present invention is not limited to this. For example, the first camera CAM1 may be mounted away from the stage 18 as long as it is rotatable around the rotation axis C.

In addition, a second camera CAM2 is fixed to the second arm 24Y, and the second camera CAM2 is capable of linear movement in the Y direction together with the second arm 24Y, allowing images of a workpiece or the like placed on the surface of the stage 18 to be taken from above.

The first camera CAM1 and the second camera CAM2 are examples of a rotating camera and a stage camera, respectively. For example, a CCD (Charge Coupled Device) camera can be used as the first camera CAM1 and the second camera CAM2.

When calibrating the shape measuring machine 10, as shown in FIG. 1, a holder 18B (including, for example, a clamping mechanism or gripping mechanism) is fixed to the surface of the stage 18, and a calibration standard (a magnification calibrator, such as a block gauge, hereinafter referred to as master M1) is held on this holder 18B. The first camera CAM1 and second camera CAM2 then photograph the master M1 held on the stage 18, adjust the posture of the master M1, and then measure the master M1. The calibration method according to this embodiment will be described later.

(Control system of shape measuring machine)
FIG. 2 is a block diagram showing a control system of the shape measuring machine according to the first embodiment of the present invention.

The control device 50 controls the operation of each part of the profile measuring machine 10 (including the operation of measuring the surface profile of the workpiece and the probe alignment operation described below). The control device 50 is realized by a general-purpose computer such as a personal computer or microcomputer. The control device 50 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), a storage device (e.g., an HDD (Hard Disk Drive) or SSD (Solid State Drive)), and an input/output interface. In the control device 50, various programs such as control programs stored in the storage device are loaded into the RAM, and the programs loaded into the RAM are executed by the CPU, thereby realizing the functions of each part within the profile measuring machine 10 and executing various arithmetic and control processes via the input/output interface.

The control device 50 is provided with an operation unit 52 (e.g., a keyboard and mouse) that accepts operation input from the user, and a display unit 54 that displays an operation UI (User Interface) and detection results.

As shown in Figure 2, the control device 50 includes a displacement calculation unit 56 and a drive control unit 58.

The displacement calculation unit 56 calculates the displacement of the workpiece based on the detection results of the displacement of the workpiece surface detected by the displacement detector 26, and measures the shape of the workpiece surface (e.g., the outer shape of the workpiece or the roundness of a hole, etc.).

The drive control unit 58 controls the first linear motion mechanism 70X, the second linear motion mechanism 70Y, the detector drive mechanism 28, and the stage rotation mechanism 14 to adjust the relative positions of the workpiece and the probe 30.

(Magnification calibration method)
Next, an outline of a method for calibrating the magnification of the shape measuring machine 10 will be described.

As shown in Figure 3, the master M1 is a block gauge made of a durable material, has a rectangular cross section, and has two parallel measuring surfaces (first measuring surface R1 and second measuring surface R2) (see, for example, International Organization for Standardization ISO 3650:1998 and JIS B7506:2004). The step difference G1 between the first measuring surface R1 and the second measuring surface R2 of the master M1 is a calibrated, known value. Hereinafter, the first measuring surface R1 and the second measuring surface R2 may be referred to as the reference surface R1 and the measurement surface R2, respectively. Note that the following description will be given assuming that the first measuring surface R1 is the reference surface, but the present invention is not limited to this, and the second measuring surface R2 may also be the reference surface.

In this embodiment, an example is described in which a master M1 having two measurement surfaces (first measurement surface R1 and second measurement surface R2) is used, but the present invention is not limited to this. For example, a gauge block having three or more measurement surfaces may be used, or a calibration standard (such as a screw-type magnification calibrator; see, for example, JIS B7451:1997) in which the measurement surface can be slid relative to a reference surface may be used. In other words, the calibration standard according to this embodiment may have at least two measurement surfaces or be capable of being set.

When calibrating the magnification of the shape measuring machine 10, first, the master M1 is held by the holding portion 18B of the stage 18. Then, the stage rotation mechanism 14 and other mechanisms are controlled to adjust the posture of the master M1 so that the reference surface R1 of the master M1 is parallel to the Y direction.

Next, the second linear motion mechanism 70Y is controlled to adjust the Y-direction position of the probe 30, while the probe 30 emits measurement light B1 to each of the two measurement surfaces R1 and R2 of the master M1, and the reflected light from the master M1 is detected to measure the shape of the master M1. Magnification calibration is then performed using the detection results of the reflected light from the master M1 and the known step amount d of the master M1.

Next, the magnification calibration method according to this embodiment will be described in detail with reference to Figure 4 onwards. Figure 4 is a flowchart showing the calibration method for the profile measuring machine 10.

First, master M1 is held by holder 18B of stage 18. Then, using images of the surface of stage 18 and master M1 captured by second camera CAM2 attached to second arm 24Y, the installation position and installation angle of master M1 are determined (step S10).

Next, using an image of the probe 30 captured by the first camera CAM1 mounted on the stage 18, the probe 30 is positioned so that its position and angle coincide with the rotation axis of the stage rotation mechanism 14 (step S12).

Next, the relative positions of the master M1 and the probe 30 are adjusted so that the distance between the probe 30 and the master M1 is within the working distance range of the probe 30 (step S14). Here, the working distance of the probe 30 is the range of distances that can be measured by the probe 30. For example, in the case of a non-contact probe (e.g., a ToF (Time-of-Flight) type), the working distance depends on the reach of the measurement light, the detection accuracy of the reflected light, the influence of ambient light, etc. On the other hand, in the case of a contact-type probe, the working distance depends on the movable range of the tip of the probe.

Next, the second linear motion mechanism 70Y is controlled to adjust the Y-direction position of the probe 30 relative to the master M1, while the probe 30 emits measurement light B1 to each of the two measurement surfaces R1 and R2 of the master M1, and the reflected light from the master M1 is detected to measure the shape of the master M1. Then, magnification calibration is performed using the detection results of the reflected light from the master M1 and the known step amount d of the master M1 (step S16).

The following describes each step in the flowchart shown in Figure 4 in detail.

(Positioning of calibration standards)
Next, the process of positioning the master M1 (step S10) will be described with reference to a flowchart shown in FIG.

In the example shown in Figure 5, first the angle of the master M1 is adjusted (steps S100 to S108), and then the position of the master M1 is adjusted (step S110). Specifically, each step is performed as follows:

First, the second camera CAM2 is used to capture an image PI1 of the reference surface R1 of the master M1 held by the holder 18B of the stage 18 (step S100). Next, the second camera CAM2 is moved in the Y direction by the second linear motion mechanism 70Y (step S102), and the second camera CAM2 is used to capture an image PI2 of the reference surface R1 of the master M1 after the movement (step S104).

Next, the tilt θ of the reference surface R1 relative to the Y direction is calculated from the images PI1 and PI2 and the amount of movement in the Y direction (step S106), and the stage 18 is rotated by an angle θ using the stage rotation mechanism 14 to make the reference surface R1 of the master M1 parallel to the Y direction (step S108).

Figures 6 and 7 are plan views illustrating the procedure for calculating the inclination θ of the reference plane R1 relative to the Y direction.

In Figures 6 and 7, the trajectory of the Y-direction movement in step S102 is indicated by vector Y. The positions of the reference surface R1 of master M1 before and after the Y-direction movement are R1(Y1) and R2(Y2), respectively.

As shown in Figure 7, if the AB coordinate system is set as a two-dimensional Cartesian coordinate system tilted relative to the XY coordinate system, the straight lines along the reference planes R1 (Y1) and R2 (Y2) before and after movement in the Y direction can be expressed by the following equations (1) and (2), respectively.

R1 (Y1): A=a×B+b ₂ …(1)
R1(Y2): A=a×B+b ₁ ...(2)
As shown in Figure 7, if the length of vector Y (the amount of movement in the Y direction) is Y, the inclination of reference plane R1 relative to the B direction _{is θ1} , and the inclination of the Y direction relative to the B direction is _θ2 , the following equations (3) to (7) can be obtained from the geometric relationship.

θ=θ ₁ +θ ₂ …(3)
a = tan θ ₁ ... (4)
_L1 = _Ysinθ2 ...(5)
_L2 = _Ycosθ2 ×a...(6)
L ₁ +L ₂ =(b ₂ -b ₁ )...(7)
From the above relational expression, the inclination θ of the reference surface R1 with respect to the Y direction can be calculated using the known variables a, b ₁ , b ₂ and Y.

For simplicity, using the small angle approximation, the following equation (8) can be obtained from equations (5) to (7).

Yθ ₂ +Y×(1−(1/2)θ ₂ ² )×a=(b ₂ −b ₁ )…(8)
By modifying equation (8), the following equation (9) is obtained.

(a/2) θ ₂ ² - _{θ 2} + (b ₂ - _{b 1} )/Y-a=0...(9)
By solving the above quadratic equation (9) and substituting it into equation (1) together with equation (4), the inclination θ of the reference surface R1 with respect to the Y direction can be calculated.

By rotating the master M1 by the angle θ determined as described above, the reference surface R1 of the master M1 can be made parallel to the Y direction (step S108).

Next, the position of the master M1 is adjusted using the linear motion mechanism of the stage 18 to align the rotation axis C (center of rotation) of the stage 18 with the reference plane R1 (step S110).

In step S110, the position of the rotation axis C of the stage 18 is determined in advance. Next, the focal position of the second camera CAM2 is aligned with the reference surface R1 of the master M1. Then, as shown in Figures 8(a) and 8(b), the linear motion mechanism of the stage 18 is used to adjust the position of the master M1 so that the reference surface R1 of the master M1 coincides with the previously determined rotation axis C (position R1(2)).

In step S110, the upper and lower ends of the reference surface R1 of the master M1 may be detected by the second camera CAM2, and the master M1 may be tilted by the tilting mechanism of the stage 18.

The master M1 positioning process according to this embodiment allows the master M1 to be installed so that the reference surface R1 used for magnification calibration is parallel to the movement axis (Y direction) of the second linear motion mechanism 70Y, and so that the reference surface R1 coincides with the rotation axis C of the stage 18.

(Probe positioning)
Next, a description will be given of the positioning step (step S12) of the probe 30. In the positioning step of the probe 30, the probe rotation axis AX of the probe 30 is aligned with the rotation axis C of the stage 18 using the first camera CAM1 installed on the stage 18.

Figure 9 is a diagram showing an example of the positions at which the first camera CAM1 captures images of the probe 30. In the example shown in Figure 9, the first camera CAM1 captures images of the probe 30 at four capture positions P1 to P4, which are offset by 90 degrees from each other on the rotational orbit K of the first camera CAM1 centered on the rotational axis C.

In this embodiment, the direction in which the first camera CAM1 captures images of the probe 30 from the four imaging positions P1 to P4 is the X or Y direction, which is the same as the control direction (movement axis direction) in which the detector drive mechanism 28 linearly or tilts the probe 30. In other words, the first imaging position P1 and the third imaging position P3 are opposite each other in the first direction (Y direction). Furthermore, the second imaging position P2 and the fourth imaging position P4 are opposite each other in the second direction (X direction).

Figure 10 shows an example of images captured by the first camera CAM1 at each of the image capturing positions P1 to P4. Note that in Figure 10, the first image 100A to the fourth image 100D are images captured at the first image capturing position P1 to the fourth image capturing position P4, respectively.

When there is a relative misalignment between the probe 30 and the rotation axis C, for example, as shown in FIG. 10, in the captured images 100A to 100D captured by the first camera CAM1 at each of the capture positions P1 to P4, the attitude (position and tilt) of the probe 30 will differ depending on the capture position (i.e., the capture direction of the probe 30 by the first camera CAM1).

For example, of two imaging positions (first imaging position P1 and third imaging position P3) that face each other in the first direction (Y direction), in the first imaging image 100A taken from one imaging position (first imaging position P1), the probe 30A is tilted to one side in the second direction (X direction), whereas in the third imaging image 100C taken from the other imaging position (third imaging position P3), the probe 30C is tilted to the other side in the second direction (X direction). Furthermore, the positions in the second direction (X direction) are also shifted toward opposite sides.

The same is true for the second captured image 100B and the fourth captured image 100D at two opposing capturing positions (second capturing position P2 and fourth capturing position P4) in the second direction (X direction), with the positions and inclinations of the probes 30B and 30D shifted in opposite directions.

Figure 11 shows a first composite image 102A obtained by combining a first captured image 100A and a third captured image 100C captured from two opposing capture positions (first capture position P1 and third capture position P3) in the first direction (Y direction).

As shown in FIG. 11 , in the first composite image 102A obtained by combining the first captured image 100A and the third captured image 100C, the first midline ML1 between the central axis (first probe central axis) L1 of the probe 30A in the first captured image 100A and the central axis (third probe central axis) L3 of the probe 30C in the third captured image 100C indicates the position of the rotation axis C in the XZ plane (i.e., the position of the rotation axis C when the probe 30 is viewed from the first direction (Y direction)). The first midline ML1 refers to a line that passes through the center of the first probe central axis L1 and the third probe central axis L3 in the horizontal direction (X direction) in the first composite image 102A in the vertical direction (Z direction). In other words, the line that bisects the space between the first probe central axis L1 and the third probe central axis L3 in the left and right (X direction) in the first composite image 102A is called the first midline ML1.

The first midline ML1 in the first composite image 102A indicates the position of the rotation axis C. In other words, the first midline ML1 indicates the line along which the probe 30 moves in the first composite image 102A (in the XZ plane), and by adjusting the attitude of the probe 30 (position Dx and tilt α) so that the probe 30 coincides with the first midline ML1, it is possible to eliminate the relative misalignment between the rotation axis C and the probe 30 in the XZ plane.

Figure 12 shows a composite image 102B obtained by combining a second captured image 100B and a fourth captured image 100D captured from two opposing capture positions (second capture position P2 and fourth capture position P4) in the second direction (X direction).

As shown in FIG. 12 , in the second composite image 102B obtained by combining the second captured image 100B and the fourth captured image 100D, the second midline ML2 between the central axis (second probe central axis) L2 of the probe 30B in the second captured image 100B and the central axis (fourth probe central axis) L4 of the probe 30D in the fourth captured image 100D indicates the position of the rotation axis C in the YZ plane (i.e., the position of the rotation axis C when the probe 30 is viewed from the second direction (X direction)). The second midline ML2 refers to a line that passes through the center of the second probe central axis L2 and the fourth probe central axis L4 in the horizontal direction (X direction) in the second composite image 102B in the vertical direction (Z direction). In other words, the line that bisects the space between the second probe central axis L2 and the fourth probe central axis L4 in the left and right (X direction) in the second composite image 102B is called the second midline ML2.

The second midline ML2 in the second composite image 102B indicates the position of the rotation axis C. In other words, the second midline ML2 indicates the line along which the probe 30 moves in the second composite image 102B (in the YZ plane), and by adjusting the attitude of the probe 30 (position Dy and tilt β) so that the probe 30 coincides with the second midline ML2, it is possible to eliminate the relative misalignment between the rotation axis C and the probe 30 in the YZ plane.

Therefore, by calculating the two midlines ML1 and ML2 described above based on images captured by the first camera CAM1 at four imaging positions P1 to P4, which are offset by 90 degrees from each other on the rotational orbit K of the first camera CAM1 centered on the rotational axis C, it is possible to detect the rotational axis C (center of rotation), which is the movement target of the probe 30, and to adjust the relative deviation between the rotational axis C and the probe 30 in each direction (X direction and Y direction) independently.

When positioning the probe 30 in this embodiment, the control device 50, assuming that one of the two probes 30 in the first composite image 102A shown in FIG. 11 is the reference probe (probe 30A in the first captured image 100A in this example), detects the tilt angle (rotation angle around the Y direction) for aligning the probe center axis of the reference probe with the first midline ML1 as the tilt movement amount α. Furthermore, when the probe center axis of the reference probe is tilted by the tilt movement amount α to be parallel to the first midline ML1, the control device 50 detects the movement distance in the X direction required to align the probe center axis of the reference probe with the first midline ML1 as the linear movement amount Dx. The linear movement amount Dx corresponds to the distance along the X-direction movement axis of the detector drive mechanism 28 (see FIG. 11).

Furthermore, when one of the two probes 30 in the second composite image 102B shown in FIG. 12 is designated as the reference probe (in this example, probe 30B in the second captured image 100B), the control device 50 detects, as the tilt movement amount β, the tilt angle (rotation angle around the X direction) for making the probe central axis of the reference probe parallel to the second midline ML2. Furthermore, when the probe central axis of the reference probe is tilted by the tilt movement amount β to make it parallel to the second midline ML2, the control device 50 detects, as the linear movement amount Dy, the movement distance in the Y direction required to align the probe central axis of the reference probe with the second midline ML2. The linear movement amount Dy corresponds to the distance along the Y-direction movement axis of the detector drive mechanism 28 (see FIG. 12).

The control device 50 can calculate the probe center axes C1-C4, midlines ML1 and ML2, linear movement amounts Dx and Dy, and tilt movement amounts α and β from each composite image 102A and 102B using known image processing such as edge extraction.

In this way, the control device 50 detects the relative deviation between the probe 30 and the rotation axis C in each direction independently based on the images captured by the first camera CAM1 at each imaging position. The drive control unit 58 then controls the detector driving mechanism 28 based on the results detected by the control device 50. Specifically, the drive control unit 58 controls the detector driving mechanism 28 to move the probe 30 by a linear movement amount Dx in the X direction and a linear movement amount Dy in the Y direction, and to tilt the probe 30 by a tilt movement amount β around the X direction and a tilt movement amount α around the Y direction. The direction (orientation) in which the detector driving mechanism 28 is moved or tilted is determined depending on which probe is used as the reference probe in the composite images 102A and 102B shown in Figures 11 and 12.

In this way, when the drive control unit 58 controls the detector drive mechanism 28 to change the attitude of the probe 30 based on the results detected by the control device 50, the relative misalignment between the probe 30 and the rotation axis C in three-dimensional space is eliminated. This completes the basic alignment of the probe 30.

The shooting position of first camera CAM1 is not necessarily limited to the above. For example, first camera CAM1 may capture images of probe 30 from at least three shooting positions on the rotational orbit K of first camera CAM1. Also, while the shooting direction of first camera CAM1 is shown to match the control direction (X direction and Y direction) of detector drive mechanism 28, this is not necessarily limited to this. For example, the shooting direction of first camera CAM1 may be a direction different from the control direction of detector drive mechanism 28.

The positioning process for the probe 30 according to this embodiment allows the probe 30 to be aligned so that its probe rotation axis AX coincides with the rotation axis C of the stage 18. Furthermore, in this embodiment, the alignment accuracy of the probe 30 does not depend on the installation accuracy of the first camera CAM1, enabling highly accurate probe alignment at low cost.

(Relative positioning of calibration standard and probe)
Next, a description will be given of the step (step S14) of relatively positioning the master M1 and the probe 30. FIG.

As shown in Figure 13(a), the master M1 positioning process (step S10) has aligned the reference surface R1 of the master M1 with the rotation axis C of the stage 18, and the probe 30 positioning process (step S12) has aligned the probe rotation axis AX of the probe 30 with the rotation axis C of the stage 18 (position 30a).

13B, in the relative positioning step of the master M1 and the probe 30 (step S14), first, the first linear motion mechanism 70X moves the probe 30 to the opposite side (-X side) of the master M1 with respect to the rotation axis C of the stage 18 (position 30b). Here, the amount of movement D _X of the probe 30 in the X direction satisfies D _X ≧ r + WD, where r is the radius of the probe 30 and WD is the minimum working distance of the probe 30.

Here, the minimum working distance of the probe 30 is the smallest value in the range of distances that can be measured by the probe 30. For example, in the case of a non-contact probe, the working distance is the shortest distance from the measurement light emission aperture to the master M1 surface that can be detected by the measurement light. On the other hand, in the case of a contact probe, it is the shortest distance from the position of the probe tip (probe) when it is in the center position (neutral position) of the detection stroke to the master M1 surface that can be detected by the probe.

Next, as shown in (c) of Figure 13, the probe 30 is lowered to a calibration measurement position 30c where the height of the emission aperture of the measurement light B1 of the probe 30 is lower than the upper ends of the reference surface R1 and measurement surface R2 of the master M1, but higher than the lower ends. In other words, by moving the probe 30 in the Y direction, the probe 30 is lowered so that the emission aperture of the measurement light B1 of the probe 30 is positioned so that it can face the reference surface R1 and measurement surface R2. This moves the probe 30 to a position where it can measure the reference surface R1 and measurement surface R2 of the master M1.

(Magnification calibration)
Next, the magnification calibration step (step S16) will be described. Figure 14 is a diagram (plan view and front view) for explaining the magnification calibration step.

As shown in Figure 14, in the magnification calibration process (step S16), the second linear motion mechanism 70Y is controlled to adjust the Y-direction position of the probe 30, and measurement light B1 is emitted to the reference surface R1 and measurement surface R2 of the master M1, respectively. The reflected light from the master M1 is detected to measure the shape of the master M1. Magnification calibration is then performed using the detection results of the reflected light from the master M1 and the known step amount d of the master M1.

Note that while Figure 14 illustrates an example in which a block gauge is used as the master M1, the present invention is not limited to this. For example, as shown in Figure 15, it is also possible to use a screw-type magnification calibrator M2 (hereinafter referred to as the master).

In the master M2 shown in Figure 15, the measurement surface can be moved using a screw (not shown), and the amount of movement G2 of the measurement surface due to the operation of the screw is calibrated. Note that Figure 15 only shows two reference surface positions (R21 and R22). Here, reference surface positions R21 and R22 are examples of the first and second measurement surfaces.

According to this embodiment, the amount of movement at each step when moving the probe 30 to the calibration measurement position 30c can be calculated, preventing the probe 30 from coming into contact with the master (M1, M2). Furthermore, the accuracy of the calibration work does not depend on the skill of the operator.

Furthermore, according to this embodiment, each process consists of image processing of images captured by the first camera CAM1 and the second camera CAM2, and the movement amount calculated by the device configuration or image processing of the shape measuring machine 10, eliminating the need for visual confirmation, etc., and enabling the automation of calibration work.

Furthermore, in this embodiment, during magnification calibration, the measurement surfaces (reference surface R1, measurement surfaces R2, R21, and R22) of the masters (M1, M2) are parallel to the Y direction (second direction). Furthermore, measurement light B1 from the probe 30 can be incident perpendicularly to the measurement surfaces (from the X direction, first direction), making it possible to perform magnification calibration with higher accuracy.

Here, the accuracy of magnification calibration will be explained using a block gauge as an example. As shown in Figure 16, when the reference surface R1 of the master M1 is tilted at an angle θ with respect to the Y direction during magnification calibration, if the amount of movement of the probe 30 in the Y direction is L, the step amount G1 (F) measured by the probe 30 is expressed by the following equation (10):

G1(F)=G1/cosθ+Lsinθ…(10)
In this case, the error in magnification calibration is expressed by the following equation (11).

G1/G1(F)=1/{1/cosθ+(L/G1)sinθ}…(11)
As shown in equation (11), if the reference surface R1 of the master M1 is tilted with respect to the Y direction, G1<G1(F), and the value after calibration will be smaller than the actual displacement amount. Also, as shown in equation (11), the Y-direction movement amount L, which varies depending on the measurement conditions, is included in the calibration error, and the error amount is not stable.

In contrast, in this embodiment, when calibrating the magnification, the reference surface R1 and measurement surface R2 of the master M1 are parallel to the Y direction, making it possible to perform magnification calibration with higher accuracy.

Second Embodiment
Next, a second embodiment of the present invention will be described. In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

In this embodiment, the angle and position of the master M1 can be adjusted simultaneously during the master M1 positioning process (step S10).

Figures 17 and 18 are diagrams for explaining the positioning process of master M1. In this embodiment, in the positioning process of master M1 (step S10), the position of the rotation axis C (center of rotation) of stage 18 (position C(Y1) before movement) is assumed to have been calculated in advance.

When the second camera CAM2 is moved in the Y direction while the master M1 is held on the stage 18, the movement direction within the field of view of the second camera CAM2 (the inclination _θ2 of the Y direction relative to the B direction in FIG. 7) can be determined. Since the Y direction movement amount Y is a specified movement amount, if it is known, the Y direction movement amount (vector Y) within the field of view of the second camera CAM2 can be calculated.

Therefore, as shown in Figure 17, the position R1 (Y2) of the reference surface R1 of master M1 within the field of view of second camera CAM2 after movement in the Y direction and the position C (Y2) of the rotation axis C of stage 18 can be calculated from the position R1 (Y1) of the reference surface R1 of master M1 before movement in the Y direction and the position C (Y1) of the rotation axis C of stage 18.

Next, as shown in FIG. 18, the amount of movement (N) of the position of master M1 is adjusted so that the reference surface R1 of master M1 coincides with the position C (Y2) of the rotation axis C of stage 18 after movement in the Y direction. That is, as shown in FIG. 18, the N vector is calculated, which is the perpendicular vector drawn from the position C (Y2) of the rotation axis C of stage 18 after movement in the Y direction to the position R1 (Y2) of the reference surface R1 of master M1. Then, by operating the linear motion mechanism of stage 18 to move master M1 according to the N vector, it is possible to align the reference surface R1 of master M1 with the position C (Y2) of the rotation axis C of stage 18.

Next, the stage rotation mechanism 14 rotates the master M1 by an angle θ, thereby making the reference surface R1 of the master M1 parallel to the Y direction.

Figure 19 is a flowchart showing the positioning process for the master M1 according to the second embodiment of the present invention.

First, the rotation axis C (center of rotation) of the stage 18 within the field of view of the second camera CAM2 is calculated in advance (step S130). In step S130, the rotation axis C of the stage 18 can be detected, for example, by placing a workpiece of a known shape (e.g., circular or rectangular) on the stage 18, rotating the stage 18, and processing the image captured by the second camera CAM2. Note that the method for calculating the rotation axis C is not limited to the above example.

Next, the second camera CAM2 is used to capture an image PI1 of the reference surface R1 of the master M1 held by the holder 18B of the stage 18 (step S132). The second camera CAM2 is then moved in the Y direction by the second linear motion mechanism 70Y (step S134), and the second camera CAM2 is used to capture an image PI2 of the reference surface R1 of the master M1 after the movement (step S136).

Next, the tilt θ of the reference plane R1 relative to the Y direction is calculated from the images PI1 and PI2 and the Y direction movement amount (step S138). Note that the procedure for calculating the tilt θ in step S138 is the same as in the first embodiment, so a description thereof will be omitted (see Figures 6 and 7). Then, the Y vector is calculated from the Y direction movement amount Y and angle θ in step S134 (step S140).

Next, the position C(Y2) of the rotation axis C after movement in the Y direction is calculated from the position C(Y1) of the rotation axis C before movement in the Y direction and the Y vector (step S142). Then, the N vector is calculated from the position C(Y2) of the rotation axis C after movement in the Y direction and image PI2 (step S144).

Next, the master M1 is moved along the N vector (step S146), and the master M1 is rotated by an angle θ to make the reference surface R1 of the master M1 parallel to the Y direction (step S148).

According to this embodiment, the angle and position of the master M1 can be adjusted simultaneously, reducing the amount of work required to position the reference surface R1 of the master M1.

[Third embodiment]
Next, a third embodiment of the present invention will be described. In the following description, the same components as those in the first or second embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

In this embodiment, before and after calculating the rotation axis C (center of rotation) of the stage 18 (step S130 in the second embodiment), movement in the Y direction is performed to calculate and register the Y vector.

Figure 20 is a flowchart showing the process for positioning the master M1 according to the third embodiment of the present invention.

First, the Y vector is registered (step S160). In step S160, as shown in FIG. 21, a known shape S1 is placed on the stage 18 so that it fits within the field of view of the second camera CAM2. Here, the known shape S1 is preferably a shape whose reference coordinates can be determined with high precision, such as a circular hole shape, a point, or a reticle.

Next, the second camera CAM2 acquires an image of the known shape S1, and calculates the coordinates of the reference position of the known shape S1 (reference coordinates C1 (Y1)). In Figure 21, a circular hole shape is used as an example of the known shape S1, and the position coordinates of the center of the circular hole are used as the reference coordinates.

Next, the second camera CAM2 is moved in the Y direction by a predetermined distance, an image of the known shape S1 is acquired by the second camera CAM2, and the coordinates of the reference position of the known shape S1 (reference coordinates C1 (Y2)) are calculated.

Next, the control device 50 calculates and registers (stores) the Y vector from the reference coordinates C1 (Y1) and C1 (Y2) before and after the Y-direction movement.

Next, the rotation axis C (center of rotation) of the stage 18 within the field of view of the second camera CAM2 is calculated in advance (step S162). Note that the procedure for calculating the rotation axis C (center of rotation) of the stage 18 is the same as in the second embodiment, so a description thereof will be omitted.

Next, the second camera CAM2 is used to capture an image PI1 of the reference surface R1 of the master M1 held by the holder 18B of the stage 18 (step S164). The second camera CAM2 is then moved in the Y direction by the second linear motion mechanism 70Y (step S166), and the second camera CAM2 is used to capture an image PI2 of the reference surface R1 of the master M1 after the movement (step S168). Here, the distance moved in the Y direction in step S168 is equal to the distance moved in the Y direction during pre-registration of the Y vector in step S160 (see Figure 21).

Next, the tilt θ of the reference plane R1 relative to the Y direction is calculated from images PI1 and PI2 and the amount of movement in the Y direction (step S170). Note that the procedure for calculating the tilt θ in step S138 is the same as in the first embodiment, so a description thereof will be omitted (see Figures 6 and 7).

Next, the angle and position of the master M1 are adjusted. Steps S172 to S178, described below, are the same as steps S172 to S178 in Figure 19, respectively.

Next, the position C(Y2) of the rotation axis C after movement in the Y direction is calculated from the position C(Y1) of the rotation axis C before movement in the Y direction and the Y vector (step S172). Then, the N vector is calculated from the position C(Y2) of the rotation axis C after movement in the Y direction and image PI2 (step S174).

Next, the master M1 is moved along the N vector (step S176), and the master M1 is rotated by an angle θ to make the reference surface R1 of the master M1 parallel to the Y direction (step S178).

According to this embodiment, as with the second embodiment, the angle and position of the master M1 can be adjusted at the same time, thereby reducing the amount of work required to position the reference surface R1 of the master M1.

Furthermore, in this embodiment, known shapes such as circles have shapes that allow reference coordinates to be calculated with high precision, and the distance actually moved in the Y direction within the field of view of the second camera CAM2 is determined, so the Y vector can be calculated with high precision.

10...Profile measuring instrument, 12...Main body base, 14...Stage rotation mechanism, 16...Rotating body, 18...Stage, 20...Column, 22...Carriage, 24X...First arm, 24Y...Second arm, 26...Displacement detector, 28...Detector drive mechanism, 30...Probe, 32...Camera, 34...Camera bracket, 50...Control device, 52...Operation unit, 54...Display unit, 56...Displacement calculation unit, 58...Drive control unit, 60...Photography control unit, 70X...First linear motion mechanism, 70Y...Second linear motion mechanism, CAM1...First camera, CAM2...Second camera, M1-M2...Calibration standards (masters)

Claims (2)

a stage on which a calibration standard having or capable of being set to a first measurement surface and a second measurement surface is held;
a stage rotation mechanism that rotates the stage around a rotation axis;
a probe capable of detecting a displacement along a first direction;
a stage photographing camera capable of photographing an image of the surface of the stage;
a first linear motion mechanism that moves the probe in the first direction;
a second linear motion mechanism to which the probe and the stage photographing camera are attached, the second linear motion mechanism moving the probe and the stage photographing camera along a second direction perpendicular to the first direction;
a control unit that moves the stage photographing camera to at least two points along the second direction, detects the first measurement surface of the calibration standard at the at least two points, and controls the stage rotation mechanism based on the detection results of the first measurement surface to make the first measurement surface parallel to the second direction;
a rotating camera that is rotatable together with the stage,
the control unit moves the stage to align the first measurement surface with the rotation axis, detects a central axis of the probe based on an image of the probe taken by the rotating camera, aligns the central axis of the probe with the rotation axis of the stage, and after aligning the central axis of the probe with the rotation axis of the stage, moves the probe away from the calibration standard along the first direction by a distance equal to or greater than the sum of a radius of the probe and a minimum working distance, and then lowers the probe to a position where the probe faces the first measurement surface . holding a calibration standard having or capable of being set to a first measurement surface and a second measurement surface on a stage;
moving a stage imaging camera capable of capturing images of the surface of the stage to at least two points along a second direction perpendicular to a first direction in which a probe can detect displacement, and detecting the first measurement surface of the calibration standard at the at least two points;
controlling a stage rotation mechanism based on a detection result of the first measurement surface to make the first measurement surface parallel to the second direction;
moving the stage so that the first measurement plane coincides with a rotation axis of the stage;
detecting a central axis of the probe based on an image of the probe captured by a rotating camera that is rotatable together with the stage, and aligning the central axis of the probe with a rotation axis of the stage;
a step of aligning a central axis of the probe with a rotation axis of the stage, separating the probe from the calibration standard along the first direction by a distance equal to or greater than the sum of the radius of the probe and a minimum working distance, and then lowering the probe to a position where the probe faces the first measurement surface;
A method for calibrating a shape measuring machine comprising: