JP7296334B2 - Straightness measurement system, displacement sensor calibration method, and straightness measurement method - Google Patents

Description

The present invention relates to a straightness measurement system, a displacement sensor calibration method, and a straightness measurement method.

As a method for measuring the straightness of the upper surface of an object to be ground, an on-machine measurement method is known, in which a displacement sensor is attached to the grindstone head to scan the surface to be processed, using the work feed function of the grinder. The on-machine measurement method generally uses a three-point method using a sensing unit including three displacement sensors (eg, Patent Document 1).

In order to accurately measure the straightness of the surface of the object to be measured, it is necessary to calibrate the zero points of the three displacement sensors so that the zero points of the three displacement sensors are positioned on a geometrically correct plane. A calibration reference device having a highly straight calibration reference surface is used to perform zero point calibration of the displacement sensor. Three displacement sensors measure the amount of displacement in the height direction of the calibration reference plane, and perform zero point calibration so that the zero points of the three displacement sensors are positioned on the same plane (for example, Patent Document 2).

JP 2015-169451 A JP 2016-166873 A

The accuracy required for zero point calibration depends on the pitch between sensors and the straightness to be evaluated. For example, when detecting a bend of 1 μm with a length of 1 m at a pitch between sensors of 100 mm, the amount of displacement in the height direction with respect to the absolute plane is about 40 nm. In order to measure such a displacement amount, the zero point calibration requires an accuracy of 10 nm level.

As a result of various experiments conducted by the inventors of the present application, it was found that even if the conventional method performs zero point calibration with sufficiently high accuracy, it may not be possible to measure straightness with the expected accuracy. . An object of the present invention is to provide a straightness measurement system, a displacement sensor calibration method, and a straightness measurement method that are capable of suppressing deterioration in straightness measurement accuracy.

According to one aspect of the invention,
a sensing unit including three displacement sensors;
a calibration reference device having a calibration reference surface;
When the calibration reference plane is opposed to the three displacement sensors, points to be measured of the three displacement sensors are arranged side by side in the first direction on the surface of the calibration reference plane, and the three displacement sensors the sensor measures displacement in the height direction of the calibration reference plane;
moreover,
a tilting mechanism that tilts one of the calibration reference plane and the sensing unit in the first direction with respect to the other when the calibration reference plane is opposed to the three displacement sensors;
Measured values of the three displacement sensors are acquired in a plurality of states in which the calibration reference plane has different tilt angles with respect to the sensing unit, and the tilt angles and the measured values of the three displacement sensors for each of the tilt angles are obtained. and a processing device for measuring the relative positional relationship of the points to be measured of the three displacement sensors in the first direction and the amount of deviation from the prescribed relative positional relationship. .

According to another aspect of the invention,
A sensing unit including three displacement sensors for measuring displacement in the height direction of points to be measured arranged side by side in a first direction on the surface of the calibration reference plane, wherein the amount of displacement in the height direction of the calibration reference plane is changed for each tilt angle of the calibration reference plane with respect to the first direction with respect to the sensing unit, and
Based on the tilt angles and the measured values of the three displacement sensors for each of the tilt angles, a relative positional relationship of the points to be measured of the three displacement sensors with respect to the first direction and a specified relative positional relationship. Displacement sensor calibration method is provided for determining the amount of deviation of .

According to yet another aspect of the invention,
A sensing unit including three displacement sensors for measuring displacement in the height direction of points to be measured arranged side by side in a first direction on the surface of the calibration reference plane, wherein the amount of displacement in the height direction of the calibration reference plane is changed for each tilt angle of the calibration reference plane with respect to the first direction with respect to the sensing unit, and
Based on the tilt angles and the measured values of the three displacement sensors for each of the tilt angles, a relative positional relationship of the points to be measured of the three displacement sensors with respect to the first direction and a specified relative positional relationship. Find the amount of deviation of
A straightness measurement method is provided in which, when measuring the straightness of the surface of an object by the three-point method using the sensing unit, the curvature is calculated taking into account the amount of deviation.

By measuring the amount of deviation in the relative positional relationship of the points to be measured of the three displacement sensors in the first direction, it is possible to reflect this amount of deviation in the straightness measurement. As a result, it is possible to suppress a decrease in straightness measurement accuracy.

FIG. 1 is a schematic diagram showing a sensing unit having three displacement sensors and a surface to be measured. FIG. 2 is a diagram showing the relative positional relationship between the surface to be measured and the sensing unit for explaining the three-point method. FIG. 3A is a diagram showing the positional relationship between the three displacement sensors and the calibration standard when performing zero point calibration of the sensing unit, and FIG. 1 is a diagram showing the positional relationship between displacement sensors and a calibration standard; FIG. FIG. 4A is a diagram showing the positional relationship between the three displacement sensors and the calibration standard when the zero point calibration of the sensing unit is completed, and FIG. FIG. 4 is a diagram showing the positional relationship between three displacement sensors and a calibration standard in a state of being tilted about an axis; FIG. 5 is a scatter diagram showing an example of the relationship between the tilt angle Δθ and the zero point deviation Δh. FIG. 6A is a perspective view of a grinding apparatus equipped with a straightness measurement system according to an embodiment, and FIG. 6B is a side view of the sensing unit attached to the grindstone head. FIG. 7 is a schematic diagram of the sensing unit, the calibration standard, and the tilting mechanism, with the calibration standard facing the sensing unit. FIG. 8 is a flow chart showing the procedure of a displacement sensor calibration method for calibrating the displacement sensor of the straightness measurement system according to the embodiment. FIG. 9 is a diagram showing the positional relationship between the three displacement sensors and the calibration standard after the zero point calibration of the sensing unit has been completed in the modified example of the embodiment. FIG. 10 is a flow chart showing the procedure of the straightness measuring method according to this embodiment. FIG. 11 is a schematic diagram showing a sensing unit provided with three displacement sensors used in the example (FIG. 10) and a surface to be measured.

A straightness measuring system and a displacement sensor calibrating method according to an embodiment will be described with reference to FIGS. 1 to 8. FIG. A straightness measurement system according to an embodiment measures the straightness of the surface of an object to be measured using the three-point method.

In the three-point method, the positions in the height direction of three points located on a straight line on the surface of the object to be measured are measured simultaneously, and the degree of local curvature (curvature) of the plane is obtained from the measurement results. The curvature is integrated twice to obtain the straightness of the upper surface of the object to be measured. Straightness refers to the extent to which a shape of interest deviates from a geometrically correct straight line. Measuring the straightness of the upper surface of the object to be measured is equivalent to measuring the shape of unevenness in the height direction of the upper surface of the object to be measured.

First, a method of obtaining the local curvature of the surface of the object to be measured will be described with reference to FIG.
FIG. 1 is a schematic diagram showing a sensing unit 20 having three displacement sensors 21A, 21B, and 21C and a surface 50 to be measured. An xyz orthogonal coordinate system is defined in which the x-axis direction corresponds to the direction in which the curvature should be measured, and the y-axis direction corresponds to the height direction of the surface of the object to be measured. The displacement sensors 21A, 21B, and 21C measure the amount of displacement of the object in the y-axis direction. Non-contact displacement sensors such as laser displacement sensors can be used as the displacement sensors 21A, 21B, and 21C.

Three displacement sensors 21A, 21B, and 21C are arranged at a pitch p in the x-axis direction. Displacement sensor 21B is positioned centrally between the other two displacement sensors 21A and 21C. The zero point calibration of the three displacement sensors 21A, 21B, and 21C has been completed, and the zero points A ₀ , B 0 , and C ₀ of the three displacement sensors 21A, 21B, and _21C are aligned on a single straight line at pitch p lined up with In FIG. 1, the zero points A ₀ , B ₀ , and C ₀ are set at the lower ends of the displacement sensors 21A, 21B, and 21C, respectively, but the zero points A ₀ , B ₀ , and C ₀ are set at other positions. may For example, the zero point may be set at the position of the calibration reference plane during zero point calibration.

Displacement sensors 21A, 21B, and 21C measure the distances (displacements) from zero points A ₀ , B ₀ , and C ₀ to measurement points A, B, and C on the surface 50 to be measured, respectively. A line segment connecting the zero point _A0 and the measured point A is parallel to the y-axis. Similarly, the line segment connecting the zero point _B0 and the measured point B and the line segment connecting the zero point _C0 and the measured point C are also parallel to the y-axis.

The displacement values measured by the displacement sensors 21A, 21B, and 21C are denoted by a, b, and c, respectively. The distance from line segment AC to measured point B (hereinafter referred to as curvature gap) is denoted by g. A gap origin O is defined as the intersection of the line segment AC and the line segment B ₀ B. FIG. The curvature gap g is equal to the length of line segment OB and is expressed by the following equation.

式（２）を変形する際に、式（１）を利用している。 The second-order differential of the shape of the surface 50 to be measured at the point B to be measured is represented by the following equation.

Equation (1) is used when transforming Equation (2).

Next, the three-point method will be described with reference to FIG.
FIG. 2 is a diagram showing the relative positional relationship between the measurement target surface 50 and the sensing unit 20 for explaining the three-point method. While the sensing unit 20 is opposed to the surface 50 to be measured and is moved by an interval (hereinafter referred to as integration pitch) in the x-axis direction, displacements in the y-axis direction of the points A, B, and C to be measured are measured. From the measured values obtained at each position, the curvature gap g is determined using equation (1). When the curvature gap g is determined, the second derivative (curvature) of the surface 50 to be measured at the point B to be measured is determined using Equation (2). By performing second-order integration of the second-order differential value for each measured point B at the integration pitch, the displacement of the measured point B in the y-axis direction, that is, the shape of the measurement target surface 50 is obtained.

Next, a method for zero point calibration of the sensing unit 20 will be described with reference to FIGS. 3A and 3B.

FIG. 3A is a diagram showing the positional relationship between the three displacement sensors 21A, 21B, 21C and the calibration standard 60 when zero point calibration of the sensing unit 20 is performed. The three displacement sensors 21A, 21B, 21B face the calibration reference plane 61 of the calibration reference device 60. As shown in FIG. A calibration reference plane 61 is arranged perpendicular to the y-axis. Before zero point calibration, the zero points A ₀ , B ₀ , and C ₀ of the displacement sensors 21A, 21B, and 21C are not arranged on one straight line. For example, the zero point B ₀ is shifted from the line segment A ₀ C ₀ by g ₀ in the y-axis direction.

In this state, the displacement amounts a, b, and c from the zero points A ₀ , B ₀ , and C ₀ to the measurement points A, B, and C on the calibration reference plane 61 are measured. The shift amount _g0 of the zero point _B0 can be obtained by the following formula.

When performing zero point calibration, the calibration reference plane 61 may be tilted from a vertical posture with respect to the y-axis due to various factors.

FIG. 3B is a diagram showing the positional relationship between the three displacement sensors 21A, 21B, and 21C and the calibration reference device 60 when the calibration reference plane 61 is tilted about the z-axis. Using the displacement amounts a, b, and c measured when the calibration reference plane 61 is tilted, the deviation amount _g0 calculated by Equation (3) is the deviation calculated when the calibration reference plane 61 is not tilted. Identical to the quantity _g0 . Therefore, even when the calibration reference plane 61 is tilted, accurate zero point calibration can be performed.

However, it was found that when the three displacement sensors 21A, 21B, and 21C are deviated from the equal pitch state, the accuracy of the straightness measurement result is lowered even if the zero point calibration is performed accurately. Next, straightness measurement when the three displacement sensors 21A, 21B, and 21C are deviated from the equal pitch state will be described with reference to FIGS. 4A and 4B.

FIG. 4A is a diagram showing the positional relationship between the three displacement sensors 21A, 21B, and 21C and the calibration standard 60 after the zero point calibration of the sensing unit 20 is completed. The central displacement sensor 21B is shifted toward the one displacement sensor 21A. This deviation amount is expressed as Δx. Since _the zero point calibration is completed, the zero point _B0 is located on the line segment _A0C0 . At this time, the zero point _B0 of the central displacement sensor 21B also deviates from the midpoint of the line segment _A0C0 by Δx toward the zero _{point A0} , and the measured point B is also the midpoint of the line segment AC. It deviates from a given gap origin O by Δx in the x-axis direction toward the point A to be measured.

FIG. 4B is a diagram showing the positional relationship between the three displacement sensors 21A, 21B, and 21C and the calibration standard 60 when the calibration reference plane 61 is tilted about the z-axis from the state shown in FIG. 4A. The inclination angle of the calibration reference plane 61 with respect to the plane perpendicular to the y-axis is expressed as Δθ.

When the displacement sensor 21B is not displaced, the displacement sensor 21B measures the amount of displacement in the height direction of the midpoint of the line segment AB (gap origin O). The amount of displacement in the height direction of the point to be measured B shifted by Δx in the x-axis direction is measured. The height difference of the point B to be measured with respect to the gap origin O is called zero point deviation Δh.

The zero point deviation Δh will be detected as the curvature gap g (FIG. 1). Therefore, when calculating the curvature using equation (2), the curvature is 2×Δh/p ² . Thus, although the calibration reference plane 61 with zero curvature is measured, the curvature becomes a finite value. This is because the three displacement sensors 21A, 21B, and 21C are not arranged at equal pitches.

ずれ量Δｘは、傾斜角Δθを横軸とし、ゼロ点偏差Δｈを縦軸としたグラフの傾きに相当することがわかる。ゼロ点偏差Δｈは、３個の変位センサ２１Ａ、２１Ｂ、２１Ｃの測定値から、以下の式で求めることができる。

すなわち、ゼロ点偏差Δｈは、両端の変位センサ２１Ａ、２１Ｃの測定値ａ、ｃの平均値と中央の変位センサ２１Ｂの測定値ｂとの差である。傾斜角Δθを変化させ、傾斜角Δθごとにゼロ点偏差Δｈを、式（５）を用いて計算する。計算によって得られた傾斜角Δθとゼロ点偏差Δｈと値に基づいて散布図を作成する。 Next, with reference to FIG. 5, a method for obtaining the amount of deviation Δx will be described.
When the tilt angle Δθ is sufficiently small, the displacement amount difference Δh is approximated by the following equation.

It can be seen that the deviation amount Δx corresponds to the inclination of the graph in which the horizontal axis is the inclination angle Δθ and the vertical axis is the zero point deviation Δh. The zero point deviation Δh can be obtained from the measured values of the three displacement sensors 21A, 21B, and 21C using the following formula.

That is, the zero point deviation Δh is the difference between the average value of the measured values a and c of the displacement sensors 21A and 21C at both ends and the measured value b of the central displacement sensor 21B. The tilt angle Δθ is changed, and the zero point deviation Δh is calculated for each tilt angle Δθ using equation (5). A scatter diagram is created based on the values of the tilt angle Δθ and the zero point deviation Δh obtained by the calculation.

FIG. 5 is a scatter diagram showing an example of the relationship between the tilt angle Δθ and the zero point deviation Δh. The horizontal axis represents the tilt angle Δθ in units of “mrad”, and the vertical axis represents the zero point deviation Δh in units of “nm”. The slope of the approximate straight line in this scatter diagram, that is, the ratio of the amount of change in the zero point deviation Δh to the amount of change in the inclination angle Δθ, corresponds to the amount of deviation Δx.

Next, a grinding apparatus equipped with a straightness measuring system according to an embodiment will be described with reference to FIGS. 6A to 7. FIG.

FIG. 6A is a perspective view of a grinding machine equipped with a straightness measurement system according to an embodiment. This grinding apparatus includes a movable table 40 , a table guide mechanism 41 , a grindstone head 45 , a grindstone 46 , a guide rail 48 , a processing device 30 , an input/output device 31 , a sensing unit 20 and a calibration standard 60 . The movable table 40 is reciprocated in one direction in the horizontal plane by a table guide mechanism 41 . A work to be ground is supported on the movable table 40 . This object to be ground corresponds to the measurement object whose straightness is measured by the straightness measurement system according to the embodiment.

A grindstone head 45 is supported above the movable table 40 by a guide rail 48 so as to be able to move up and down. The grindstone head 45 is movable in a horizontal plane in a direction perpendicular to the feed direction of the movable table 40 . An xyz orthogonal coordinate system is defined in which the feeding direction of the movable table 40 is the x-axis direction, the moving direction of the grindstone head 45 is the z-axis direction, and the vertically upward direction is the positive direction of the y-axis.

A grindstone 46 is attached to the lower end of the grindstone head 45 . The grindstone 46 has a columnar shape and its central axis is parallel to the z-axis direction. The grindstone head 45 is lowered to such an extent that the grindstone 46 contacts the object to be ground supported by the movable table 40, and the movable table 40 is fed in the x-axis direction while rotating the grindstone 46, thereby grinding the object to be ground. done. By moving the grindstone head 45 in the z-axis direction and repeating the same processing, the entire upper surface of the object to be ground can be ground.

The processing device 30 controls the feeding of the movable table 40 in the x-axis direction, the movement of the grinding wheel head 45 in the z-axis direction and the vertical movement in the y-axis direction, and the rotation of the grinding wheel 46 . Various commands are input from the input/output device 31 to the processing device 30 , and processing results and the like by the processing device 30 are output to the input/output device 31 . The input/output device 31 includes, for example, a display, pointing device, keyboard, and the like.

A sensing unit 20 is detachably attached to the side surface of the grindstone head 45 . During grinding, the sensing unit 20 is removed from the grindstone head 45 . The sensing unit 20 is attached to the grindstone head 45 when measuring the straightness of the upper surface of the object to be ground and when performing the zero point calibration of the sensing unit 20 . The sensing unit 20 is attached to the grindstone head 45 by, for example, the attractive force of a magnet, screwing, or the like. During zero point calibration of the sensing unit 20 , the calibration standard 60 is placed on the movable table 40 and moved to a position facing the sensing unit 20 .

6B is a side view of the sensing unit 20 with the sensing unit 20 attached to the grindstone head 45. FIG. The sensing unit 20 includes three displacement sensors 21A, 21B, 21C as described with reference to FIGS. 1-4B.

FIG. 7 is a schematic diagram of the sensing unit 20 , the calibration standard 60 , and the tilting mechanism 65 with the calibration standard 60 facing the sensing unit 20 . A tilting mechanism 65 is placed on the movable table 40, and the calibration standard 60 is held thereon. The upper surface of calibration standard 60 is used as calibration reference plane 61 . A goniometer stage, for example, is used as the tilt mechanism 65 . The tilt mechanism 65 can tilt the calibration standard 60 held thereon in the x-axis direction. The tilt angle measurements are input to the processor 30 . Measured values of the amount of displacement by the three displacement sensors 21A, 21B, and 21C are input to the processing device 30. FIG.

Next, a displacement sensor calibration method according to an embodiment will be described with reference to FIG.
FIG. 8 is a flow chart showing the procedure of the displacement sensor calibration method according to the embodiment. FIG. 7 will be referred to as necessary in the following description.

First, the tilting mechanism 65 is placed on the movable table 40, and the calibration standard 60 is held thereon. The sensing unit 20 is attached to the grindstone head 45 (FIG. 6A). With the calibration reference plane 61 facing the sensing unit 20, the processing device 30 (FIG. 7) reads the measured values of the displacement amounts from the three displacement sensors 21A, 21B, and 21C, and performs zero point calibration of the sensing unit 20. (step S1). Zero point calibration is performed using equation (3).

After performing the zero point calibration, the calibration reference plane 61 is tilted in the x-axis direction with respect to the sensing unit 20, and the processing device 30 detects displacement amounts from the three displacement sensors 21A, 21B, and 21C for each tilt angle Δθ. A measurement value is obtained (step S2).

The processing device 30 calculates the displacement amount Δx (FIGS. 4A and 4B) based on the relationship between the tilt angle Δθ and the measured value of the displacement amount. Specifically, the deviation amount Δx is calculated from the slope of the scatter diagram shown in FIG.

If the calculated deviation amount Δx is within the allowable range, calibration of the displacement sensor ends (step S4). When the calculated deviation amount Δx exceeds the allowable range, the position of the displacement sensor 21B is finely adjusted in the direction in which the calculated deviation amount becomes smaller (step S5). After that, the procedure from step S1 to step S3 is repeated.

Next, the excellent effects of the above embodiment will be described.
According to the above-described embodiment, the displacement amount Δx (FIGS. 4A and 4B) of the displacement sensor 21B in the x-axis direction can be reduced until it falls within the allowable range. As a result, it is possible to measure the straightness with high accuracy.

For example, when the deviation amount Δx is 20 μm and the tilt angle Δθ is 1 mrad, the zero point deviation Δh is 20 nm from the equation (4). This deviation is of a size that cannot be ignored in straightness measurement. By applying this embodiment, the deviation amount Δx can be kept within the allowable range, so that the zero point deviation Δh can be reduced to the allowable upper limit value or less.

Next, a modification of the above embodiment will be described with reference to FIG.
FIG. 9 is a diagram showing the positional relationship between the three displacement sensors 21A, 21B, and 21C and the calibration standard 60 after the zero point calibration of the sensing unit 20 is completed. 4A and 4B show the case where the position of the displacement sensor 21B is shifted in the x-axis direction. The measurement point B may deviate from the gap origin O in some cases. Also in this case, the deviation .DELTA.x from the gap origin O to the point B to be measured can be obtained in the same manner as in the above embodiment.

In practice, it is difficult to determine whether the position of the displacement sensor 21B is displaced in the x-axis direction or whether the orientation of the displacement sensor 21B is displaced from the normal orientation. In either case, the displacement Δx of the point B to be measured from the gap origin O is obtained, and the position or orientation of the displacement sensor 21B is finely adjusted so that the displacement Δx falls within the allowable range.

Although the position and orientation of the central displacement sensor 21B are finely adjusted in the above-described embodiment and modification, the position or orientation of at least one of the displacement sensors 21A and 21C at both ends may be finely adjusted. That is, in FIGS. 4A and 4B, by moving one of the points A and C to be measured in the x-axis direction, fine adjustment may be made so that the point B to be measured is positioned at the midpoint of the line segment AC. . Thus, by finely adjusting the position or orientation of at least one of the three displacement sensors 21A, 21B, 21C, the relative positional relationship of the three displacement sensors 21A, 21B, 21C can be adjusted.

A prescribed relative positional relationship is defined as a state in which measured points A, B, and C of the three displacement sensors 21A, 21B, and 21C are arranged at a pitch p in the x-axis direction. At this time, the processing device 30 measures the amount of deviation between the relative positional relationship of the three displacement sensors 21A, 21B, and 21C at the points A, B, and C to be measured in the x-axis direction and the prescribed relative positional relationship. It can be said.

Next, a straightness measuring method according to another embodiment will be described with reference to FIGS. 10 and 11. FIG. Hereinafter, descriptions of configurations common to the embodiment and modifications shown in FIGS. 1 to 9 will be omitted.

FIG. 10 is a flow chart showing the procedure of the straightness measuring method according to this embodiment. The procedure from step S1 to step S3 is the same as the procedure from step S1 to step S3 shown in FIG. A shift amount Δx (FIGS. 4A and 4B) is obtained by the procedure from step S1 to step S3.

When the displacement amount Δx is obtained, the curvature is calculated by taking the displacement amount Δx into consideration when calculating the curvature by the three-point method (step S6). After that, the straightness is obtained based on the calculated curvature value (step S7).

Next, with reference to FIG. 11, a method of determining the curvature with the amount of deviation .DELTA.x taken into consideration will be described.
FIG. 11 is a schematic diagram showing a sensing unit 20 including three displacement sensors 21A, 21B, and 21C used in this embodiment, and a surface 50 to be measured. The central displacement sensor 21B is displaced by a displacement amount Δx in the x-axis direction. The intersection of the line segment AC and the line segment B ₀ B is the actual gap origin O'. The actual gap origin O' is shifted along the line segment AC from the original gap origin O located at the midpoint of the line segment AC. The actual gap origin O' coincides with the position of the measured point B on the calibration reference plane 61 shown in FIG. 4B.

The length b' of the line segment B ₀ O' is calculated by the following formula according to the formula of internal division points.

曲率ギャップｇは、以下の式で算出される。

本実施例では、式（１）に代えて式（８）を用いて曲率ギャップｇを計算する。この曲率ギャップｇに基づいて、式（２）を用いて曲率を計算することができる。式（８）では、式（１）に対して右辺の第３項が新たに追加されている。この右辺の第３項が、変位センサ２１Ｂのずれに起因する補正項に相当する。 By transforming equation (6), the following equation is obtained.

The curvature gap g is calculated by the following formula.

In this embodiment, the curvature gap g is calculated using equation (8) instead of equation (1). Based on this curvature gap g, the curvature can be calculated using equation (2). In Equation (8), the third term on the right side is newly added to Equation (1). The third term on the right side corresponds to the correction term due to the displacement of the displacement sensor 21B.

Next, the excellent effects of this embodiment will be described.
In this embodiment, the calculated value of the curvature gap g is corrected based on the displacement of the position or posture of the displacement sensor 21B. As a result, it is possible to suppress a decrease in the calculation accuracy of the curvature due to the displacement of the position or posture of the displacement sensor 21B. As a result, the straightness can be obtained with higher accuracy.

It goes without saying that each of the above-described embodiments is an example, and partial substitutions or combinations of configurations shown in different embodiments are possible. Similar actions and effects due to similar configurations of multiple embodiments will not be sequentially referred to for each embodiment. Furthermore, the invention is not limited to the embodiments described above. For example, it will be obvious to those skilled in the art that various changes, improvements, combinations, etc. are possible.

20 sensing units 21A, 21B, 21C displacement sensor 30 processing device 31 input/output device 40 movable table 41 table guide mechanism 45 grindstone head 46 grindstone 48 guide rail 50 surface to be measured 60 calibration standard 61 calibration reference surface 65 tilt mechanism A, B , C measured points A ₀ , B ₀ , C ₀ zero point g curvature gap O original gap origin O′ actual gap origin

Claims (7)

a sensing unit including three displacement sensors;
a calibration reference device having a calibration reference surface;
When the calibration reference plane is opposed to the three displacement sensors, points to be measured of the three displacement sensors are arranged side by side in the first direction on the surface of the calibration reference plane, and the three displacement sensors the sensor measures displacement in the height direction of the calibration reference plane;
moreover,
a tilting mechanism that tilts one of the calibration reference plane and the sensing unit in the first direction with respect to the other when the calibration reference plane is opposed to the three displacement sensors;
Measured values of the three displacement sensors are acquired in a plurality of states in which the calibration reference plane has different tilt angles with respect to the sensing unit, and the tilt angles and the measured values of the three displacement sensors for each of the tilt angles are obtained. and a processor for measuring the relative positional relationship of the points to be measured of the three displacement sensors with respect to the first direction and the amount of deviation from the specified relative positional relationship. 2. The straightness according to claim 1, wherein the specified relative positional relationship of the points to be measured of the three displacement sensors is a state in which the points to be measured of the three displacement sensors are arranged at equal pitches in the first direction. measurement system. The processing device is
For each tilt angle, the zero-point deviation, which is the difference between the average value of the measured values of the displacement sensors at both ends and the measured value of the central displacement sensor, is obtained, and the ratio of the change amount of the zero-point deviation to the change amount of the tilt angle is 3. The straightness measuring system according to claim 1 or 2, wherein the amount of deviation is determined based on. 4. The processing device according to any one of claims 1 to 3, wherein when the straightness of the surface of the object is measured by the three-point method using the sensing unit, the straightness is obtained by adding the amount of deviation. Straightness measurement system as described. A sensing unit including three displacement sensors for measuring displacement in the height direction of points to be measured arranged side by side in a first direction on the surface of the calibration reference plane, wherein the amount of displacement in the height direction of the calibration reference plane is changed for each tilt angle of the calibration reference plane with respect to the first direction with respect to the sensing unit, and
Based on the tilt angles and the measured values of the three displacement sensors for each of the tilt angles, a relative positional relationship of the points to be measured of the three displacement sensors with respect to the first direction and a specified relative positional relationship. Displacement sensor calibration method for determining the amount of deviation. Further, based on the amount of deviation, at least one position or posture of the three displacement sensors is corrected so that points to be measured of the three displacement sensors are arranged at equal pitches in the first direction. 5. The displacement sensor calibration method according to 5. A sensing unit including three displacement sensors for measuring displacement in the height direction of points to be measured arranged side by side in a first direction on the surface of the calibration reference plane, wherein the amount of displacement in the height direction of the calibration reference plane is changed for each tilt angle of the calibration reference plane with respect to the first direction with respect to the sensing unit, and
Based on the tilt angles and the measured values of the three displacement sensors for each of the tilt angles, a relative positional relationship of the points to be measured of the three displacement sensors with respect to the first direction and a specified relative positional relationship. Find the amount of deviation of
A straightness measuring method for calculating a curvature taking into account the amount of deviation when measuring straightness of a surface of an object by a three-point method using the sensing unit.

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