JP5177388B2 - Prism angle measurement method using optical surface approximation method and the same method - Google Patents

Description

  The present invention relates to an optical surface approximation method for approximating a shape of an optical surface for manipulating light such as a prism to a straight line, and a prism angle measurement method for measuring an angle formed by a plurality of prism surfaces using the same method.

  In recent years, due to the development of optical recording and optical communication technologies, optical heads for optical disk devices, optical switches for optical communication, etc., have advantages such as transparency, mass productivity, and moderate polishing properties for processing optical signals. Various types of prisms having the following are used. In order to accurately exhibit the function of manipulating the optical signal, the prism angle, which is the angle formed by the prism surfaces, needs to be accurately formed. For this purpose, it is required to measure the prism angle with high accuracy.

Conventionally, the prism angle is measured by using an autocollimator that applies a parallel light beam emitted from a collimator to a prism surface, and then reflects the reflected light again into the collimator to detect an image shift near the focal point (Patent Document). 1).
JP-A-8-166225

  However, when the conventional autocollimator has waviness on the prism surface, even if the waviness is within the allowable range, the reflection direction of the reflected light varies depending on the position where the collimated light is applied, and the prism angle can be accurately determined. There was a difficulty that could not be measured.

  Furthermore, when measuring the angle of a minute prism whose side is 1 mm or less, there is a problem that the amount of reflected light from the prism surface is insufficient and the prism angle cannot be measured with high accuracy.

  The present invention has been made in view of the above-mentioned difficulties in the prism angle measurement method using a conventional autocollimator. Even if the prism surface has waviness, the area of the prism surface is further reduced. Provided are a prism surface approximation method capable of approximating the shape of each prism surface of a prism with high accuracy even if it is small, and a prism angle measurement method capable of measuring the angle between prism surfaces with high accuracy without variation. This is a technical issue.

The present invention is an optical surface approximation method for approximating the shape of an optical surface in one direction to a straight line,
Measure the position of a plurality of measurement points arranged on the optical surface at a predetermined interval in the one direction with a shape measuring instrument,
A first imaginary straight line passing through one measurement point and one measurement point adjacent to each other with an interval P between measurement points of 1 μm or more and 40 μm or less from the entire measurement range of the optical surface; On the other hand, a range in which only measurement points where the intersection angle β formed by the second virtual straight line passing through the adjacent measurement points satisfies Expression (1): P × β ≦ 10 (unit: μm · °) is arranged is extracted as a calculation range. And
An approximate straight line representing the optical surface is obtained based on position data of measurement points in the calculation range.

  Further, the present invention extracts, from the calculation range, a central range excluding a predetermined width range near both ends of the calculation range as a central range, and the optical surface based on position data of measurement points in the central range It is characterized in that an approximate straight line representative of is obtained.

  Further, the present invention is characterized in that a range close to both ends of the calculation range is excluded with a width of 10% to 20% with respect to the entire width of the calculation range.

  In the present invention, it is preferable that the shape measuring instrument irradiates a laser beam. In the present invention, if the shape measuring device can accurately measure a plurality of measurement points arranged on the optical surface, ultrasonic waves, LED light, X-rays, etc. can be used, but with sufficient resolution. It is preferable to irradiate with a laser beam because it has high measurement accuracy and does not require special environmental maintenance such as a measurement medium or shielding equipment, and can be measured at high speed.

Further, the present invention is a prism angle measuring method for measuring an angle α formed by one prism surface of the prism and another prism surface,
A prism holding step for holding the prism so that the one prism surface faces the shape measuring instrument and is rotatable about a rotation axis parallel to the prism ridgeline;
5. The shape measuring device measures the positions of a plurality of measurement points arranged on the prism surface at a predetermined interval in a direction perpendicular to the prism ridgeline of the prism by the optical surface approximation method according to any one of claims 1 to 4. A first approximate calculation step for obtaining a first approximate straight line representing the one prism surface;
A first intersection angle calculating step for obtaining an intersection angle θ1 concentric with the angle α between the reference line and the first approximate line, with one rotation direction as a positive direction with respect to a reference line perpendicular to the prism ridge line;
A rotation step of moving the prism to a position rotated by a rotation angle κ with a rotation axis parallel to the prism ridge line and directing the other prism surface to the shape measuring instrument;
A second approximation calculation step for obtaining a second approximation line representing the other prism surface by the optical surface approximation method according to any one of claims 1 to 4,
A second intersection angle calculating step for obtaining an intersection angle θ2 of the positive direction between the second approximate straight line measured in the same direction as the rotation angle κ and the reference line;
The one prism surface is expressed by an equation (2): α = | θ2-κ−θ1 | expressed by an absolute value of a value θ2-κ−θ1 composed of the intersection angle θ1, the intersection angle θ2, and the rotation angle κ. And a prism angle calculating step for obtaining an angle α formed by the other prism surface.

  Here, the intersecting angle θ1 is concentric with the angle α means that the intersecting angle θ1 is translated to a position concentric with the portion of the angle α formed by one prism surface and the other prism surface. It means that they are continuously connected or overlap the angle α. If the intersection angle θ1 is an intersection angle other than the angle α and the concentric direction, Expression (2) is not established.

  According to the optical surface approximation method of the present invention, an optical surface is measured using a shape measuring instrument, a virtual straight line passing through one measurement point of interest and another measurement point is obtained, and a virtual straight line at each measurement point is obtained. As the optical surface having the deformed portion, for example, the waviness of the prism surface and the roundness of the prism corner can be reliably determined, and the shape of each prism surface can be accurately determined. Can be approximated.

  Further, according to the prism angle measuring method according to the present invention, the position of a plurality of measurement points on the prism surface is measured using a shape measuring instrument, and the prism surface is represented based on the position data of the plurality of measurement points. Since the approximate straight line is calculated and the prism angle is obtained from the relative position with respect to the reference line between the approximate straight lines, the prism angle can be measured with higher accuracy even if the prism surface is wavy.

  In addition, since a plurality of prism surfaces are measured using a shape measuring instrument, and the prism angle is obtained based on the position data of the measurement points, the prism surface has undulations, and a micro prism having a side of 1 mm or less. Thus, even if the area of the prism surface is small, the prism angle can be measured with high accuracy.

  According to the optical surface approximation method and the prism angle measurement method using the method according to the present invention, the object to be measured is scanned with a laser beam having sufficient resolution for high-accuracy measurement, and the reflected light from the object to be measured is reflected. The prism surface is measured using a laser shape measuring instrument that measures the shape of the object to be measured by measuring the distance to the object to be measured at each scanning position while detecting.

  As shown in FIG. 1, the laser shape measuring instrument 2 used in the prism angle measuring method of this embodiment irradiates laser light vertically downward (Z-axis direction) from the laser irradiation unit 21, and horizontally (X-axis direction and The shape of the prism surface of the prism 1 held via the rotation holding means 3 on the moving table 22 movable in the Y-axis direction) is measured. That is, the laser light is scanned along the prism surface by moving the prism 1 together with the table 22 in the X-axis direction (direction perpendicular to the paper surface of FIG. 1) with respect to the laser light emitted from the laser irradiation unit 21. It is configured as follows. The rotation holding means 3 is configured so that the prism 1 can be accurately rotated by a predetermined angle by a rotation shaft 32 parallel to the Y axis while the prism 1 is securely held by the chuck mechanism 31. .

  Next, the optical surface approximation method according to the present invention will be described with reference to FIGS.

  Here, as shown in FIG. 2, an example of an embodiment suitable for measuring the angle of the prism 1 having an allowable range of undulations on the prism surfaces 11 and 12 will be described. This prism 1 is a prism obtained by molding heat-softened glass. The prism surfaces 11 and 12 have an allowable range of swells (bulges), and the prism corners are rounded. . Such waviness of the prism surface can also occur when the prism surface is fire polished.

  FIG. 3 shows an arrangement of a plurality of measurement points M, M,... Obtained by measuring one prism surface 11 of the prism 1 with the laser shape measuring instrument 2. In FIG. 3, the value of the height position (or the distance from the laser irradiation unit) on the vertical axis (Z axis) is the scanning position (the value of the interval between measurement points) on the horizontal axis (X axis). It is exaggerated. As shown in FIG. 3, at a plurality of measurement points M, M,... On one prism surface 11, the central portion of the measurement range H is gently curved upward and both ends thereof are drooped by heating. It is an array. Even if linear approximation by the least square method or the like is performed on all of the measurement points M, M,. The obtained approximate straight line varies greatly depending on the degree of inclination of 11, and the prism angle cannot be measured with the required accuracy.

Therefore, in the example of this embodiment, a step of extracting, as a calculation range, a range in which only measurement points satisfying the following expression (1) are arranged from a measurement range H in which all measurement points M, M... On one prism surface 11 are arranged. And the measurement points at the hanging portions on both ends of the measurement range H are removed.
Formula (1): P × β ≦ 10 (unit: μm · °)
(In the formula, P represents an interval between measurement points and is in the range of 1 μm ≦ P ≦ 40 μm, and β passes through one measurement point of interest and another measurement point adjacent to the measurement point of interest. (It represents the angle of intersection formed by the first virtual straight line and the second virtual straight line passing through the target measurement point and another measurement point adjacent to the target measurement point on the other side.)

  Specifically, as shown in FIG. 4, attention is paid to one measurement point Mb selected from a plurality of measurement points M · M... And the first measurement point Ma passing through this measurement point Mb and the measurement point Ma on the left side thereof. A first virtual straight line Rab is obtained, and a second virtual straight line Rbc passing through the measurement point Mb and the measurement point Mc adjacent to the right is obtained. Then, an intersection angle βb formed by the first virtual straight line Rab and the second virtual straight line Rbc is calculated, and it is determined whether or not the intersection angle βb satisfies P × βb ≦ 10. For example, when the interval P between measurement points is 10 μm, if the intersection angle βb is 1 degree or less, the measurement point Mb is included in the calculation range, and if the intersection angle βb exceeds 1 degree, the measurement point Mb is approximated. It is excluded from.

  Next, paying attention to another measurement point Mc, a first virtual straight line Rbc passing through this measurement point Mc and the measurement point Mb adjacent to the left is obtained, and the measurement point Mc and the measurement point Md adjacent to the right are obtained. A second virtual straight line Rcd that passes through is obtained. Then, an intersection angle βc formed by the first virtual straight line Rbc and the second virtual straight line Rcd is calculated, and it is determined whether or not the intersection angle βc satisfies P × βc ≦ 10.

  In this way, it is determined whether or not the equation (1) is satisfied for all the measurement points, and the range where only the measurement points satisfying the equation (1) are arranged is extracted as the calculation range I from the measurement range H as shown in FIG. Then, the measurement points at the hanging portions on both ends of the measurement range H are excluded.

  In addition, since the measurement error of the intersection angle β increases as the distance P between the measurement points decreases, it becomes difficult to distinguish the hanging portions on both ends of the measurement range H. On the other hand, the measurement increases as the distance P between the measurement points increases. Since there are fewer points, more accurate approximation becomes difficult. Therefore, the distance P is preferably in the range of 1 μm to 40 μm, and more preferably in the range of 2 μm to 20 μm.

  Next, a step of extracting a range closer to the center from the calculation range I as a center range J is performed, and measurement points in a range having a predetermined width near both ends of the calculation range I are further excluded. Specifically, as shown in FIG. 5, by removing the range near the both ends of the calculation range I with a width of 10% with respect to the entire width of the calculation range I, the 80% range near the center of the calculation range I is centered. Extracted as range J. This avoids a decrease in measurement accuracy due to variations in the inclination of one prism surface 11 with respect to the X axis of the laser shape measuring instrument 2.

  Then, as shown in FIG. 6, a step of obtaining an approximate straight line L1 representing one prism surface 11 based on the extracted measurement points of the central range J is performed. Here, the approximate straight line L1 is obtained by performing linear approximation by the least square method on the measurement points in the central range J. Instead of performing linear approximation by the least square method, for example, a straight line passing through measurement points at both ends of the central range J may be used as an approximate straight line L1 representing one prism surface 11.

  Note that the smaller the range near the both ends excluding the calculation range I, the more easily affected by the prism corners, while the closer the range, the smaller the number of measurement points to be approximated. Approximation becomes difficult. Therefore, the width of the range near both ends excluding the calculation range I is preferably in the range of 10% to 20% with respect to the entire width of the calculation range I.

  Thus, in the example of this embodiment, since a virtual straight line passing through one measurement point of interest and another measurement point is obtained and the change in the inclination of the virtual straight line at each measurement point is determined, FIG. As shown in the prism 1 shown, the undulation of the prism surface and the roundness of the prism corner can be reliably discriminated, and the adverse effect due to the measurement point of the prism corner can be eliminated when obtaining the approximate straight line of the prism surface. Can do. Therefore, according to the example of the embodiment, the prism angle can be measured with high accuracy even if there is an allowable range of undulation on the prism surface.

  Hereinafter, a prism angle measurement method in the triangular prism of this embodiment will be described in order along the operation steps ST1 to ST9 shown in FIG.

ST1; "Prism holding step"
First, a prism holding step for setting the prism 1 having a prism shape to be measured to the rotation holding means 3 is performed. As shown in FIG. 8, the prism 1 is set with the prism ridge line 13 of the prism 1 parallel to the rotation axis 32 of the rotation holding means 3 and with one prism surface 11 of the prism 1 facing the laser irradiation unit 21. Here, an example in which an angle α formed by one prism surface 11 of the prism 1 and another prism surface 12 adjacent via the prism ridge line 13 is measured will be described.

ST2: “First measurement step”
Next, a first measurement step of measuring one prism surface 11 of the prism 1 with the laser shape measuring instrument 2 is performed. That is, as shown in FIG. 8, by moving the rotation holding means 3 in the X-axis direction while irradiating one prism surface 11 with laser light, a predetermined direction in the direction perpendicular to the prism ridge line 13 on one prism surface 11 is obtained. The relative position in the X-axis direction and the height position in the Z-axis direction (or the distance from the laser irradiation unit) are measured for each of a plurality of measurement points M, M,. As a result, position data of each measurement point M is obtained in which the data of the scanning position in the X-axis direction and the data of the height position in the Z-axis direction are combined in the scanning plane of the laser light. Thus, the position of each measurement point M is measured by the laser shape measuring instrument 2.

ST3: “First approximation calculation step”
Next, as shown in FIG. 9A, a first approximate straight line L1 representing one prism surface 11 is obtained based on the position data of each measurement point M obtained in the first measurement step ST2. One approximate calculation step is performed. As shown in FIG. 9A, a first approximate line is obtained from a plurality of measurement points M, M... On one prism surface 11 by the above-described prism surface approximation method.

ST4: “First intersection angle calculation step”
Next, as shown in FIG. 9A, the angle θ1 concentric with the angle α between the first approximate straight line L1 obtained in the first approximate calculation step ST3 and the reference line B perpendicular to the prism ridge line 13 is obtained. A first intersection angle calculating step is performed. Here, the acute angle measured from the reference line B to the first approximate straight line L1 with the clockwise direction as the positive direction is the intersection angle θ1. The reference line B is preferably parallel to the X axis of the laser shape measuring instrument 2 that is the scanning direction of the laser beam in order to simplify the processing of the measurement data, but is constant with respect to the scanning direction of the laser beam. It is not always necessary that the angle is parallel.

ST5: “Rotation step”
Next, the prism 1 is rotated by the rotation shaft 32 parallel to the prism ridge line 13, and the rotation step for directing the other prism surface 12 toward the laser irradiation unit 21 of the laser shape measuring instrument 2 is performed. That is, as shown in FIGS. 9B and 9C, by rotating the rotation holding means 3, the prism 1 is substantially complementary to the angle α measured around the rotation axis 32 of the rotation holding means 3. Is rotated clockwise by a rotation angle κ corresponding to. When it is difficult to rotate the prism 1 in the clockwise direction due to circumstances such as the shape of the measuring instrument or the object to be measured, the other prisms of the prism 1 can be rotated even if the prism 1 is rotated counterclockwise by 360 ° −κ. The surface 12 may be in the same position as when rotated clockwise by the rotation angle κ.

ST6; "Second measurement step"
Next, a second measurement step of measuring the other prism surface 12 of the prism 1 by the laser shape measuring instrument 2 is performed. As in the first measurement step ST2, the rotation holding means 3 is moved in the X-axis direction while irradiating the other prism surface 12 with laser light, so that the other prism surface 12 has a predetermined direction in the direction perpendicular to the prism ridge 13. The relative position in the X-axis direction and the height position in the Z-axis direction are measured for each of a plurality of measurement points N, N,. As a result, as shown in FIG. 9C, the scanning position data in the X-axis direction and the height position data in the Z-axis direction form a set within the scanning plane of the laser light. Position data is obtained. Thus, the position of each measurement point N is measured by the laser shape measuring instrument 2.

ST7: “Second approximation calculation step”
Next, as shown in FIG. 9C, a second approximate straight line L2 representing the other prism surface 12 is obtained based on the position data of the measurement point N obtained in the second measurement step ST6. Perform approximate calculation steps. As shown in FIG. 9C, a second approximate line is obtained from the plurality of measurement points N · N... On the other prism surface 12 by the above-described prism surface approximation method.

ST8: “Second intersection angle calculation step”
Next, as shown in FIG. 9 (c), a second intersection angle calculation step for obtaining an intersection angle θ2 between the second approximate straight line L2 obtained in the second approximation calculation step ST7 and the reference line B is performed. Here, the angle measured from the reference line B to the second approximate straight line L2 with the clockwise direction as the positive direction is the intersection angle θ2 (that is, θ2 = θ1 + α + κ, see FIG. 10A). Actually, if the intersection angle θ3, which is an acute angle between the auxiliary line B ′ parallel to the reference line B and the second approximate straight line L2, is used, θ2 can be replaced with 180 ° + θ3, so the acute angle θ3 is measured. This makes it possible to easily measure θ2. As shown in FIG. 10B, when the angle measured from the reference line B to the second approximate straight line L2 with the counterclockwise direction being positive is defined as the intersection angle θ2, θ2 = − (− θ1) −α + κ = Θ1−α + κ.

ST9: “Prism angle calculation step”
Then, as shown in FIG. 10A, based on the intersection angle θ1, the rotation angle κ, the intersection angle θ2 (that is, 180 ° + θ3) and the reference line B obtained in each step, the equation (2) α = θ2− A prism angle calculation step of calculating the angle α from κ−θ1, that is, α = 180 ° + θ3−κ−θ1 is performed. Thus, the angle α formed by one prism surface 11 of the prism 1 and the other prism surface 12 can be obtained from the intersection angle θ1, the rotation angle κ, and the intersection angle θ2. With respect to other prism angles other than the prism angle α, the measurement is sequentially performed by the same operation.

  As described above, according to the prism angle measurement method of the present embodiment, the position of a plurality of measurement points on the prism surface is measured using a laser shape measuring instrument, and an approximation representing the prism surface based on the plurality of measurement points. Since the straight line is calculated and the prism angle is obtained from this approximate straight line, the prism angle can be measured with higher accuracy even if the prism surface has waviness.

  In addition, the prism surface is measured using a laser shape measuring instrument capable of narrowing the beam diameter to the micron order, and the prism angle is obtained based on the position data of the measurement point. Furthermore, even if the area of the prism surface is small, such as a micro prism with one side of 1 mm or less, the prism angle can be measured with high accuracy with little variation.

  Although the prism angle measuring method of this embodiment has been described above, the present invention can be implemented in other forms. For example, in the above-described embodiment, the example of measuring the prism angle of the prism 1 having the triangular prism shape has been described. However, the present invention is not limited to this, and a cross-sectional shape such as the prism 5 illustrated in FIG. Has a trapezoidal shape, and even when one prism surface 51 and another prism surface 52 are adjacent at an obtuse angle, each prism surface can be approximated with high accuracy, and the prism angle can be set with high accuracy. Can be measured. Further, the angle between the prism surfaces that are not adjacent to each other such as the prism surface 52 and the prism surface 53 of the prism 5 can be measured with high accuracy. Further, the waviness of the prism surface is not limited to the shape in which the central portion bulges in a convex shape like the prism 1 shown in FIG. 2, and for example, the shape in which the central portion is recessed in a concave shape, There may be multiple irregularities. Even with such undulations, the prism angle can be measured with high accuracy.

  The present invention can be carried out in other modes without various modifications, modifications, and variations based on the knowledge of those skilled in the art without departing from the spirit of the present invention. In addition, any invention-specific matters may be replaced with other technologies within a range where the same action or effect occurs, and the integrally-configured invention-specific matters are constituted by a plurality of members. Alternatively, the invention specific items configured by a plurality of members may be implemented in an integrated configuration.

  Hereinafter, specific examples of the prism angle measurement method of the present invention will be described. As a measurement sample, glass is heated and softened and formed into a right triangular prism and then cut into a length of 40 mm in the longitudinal direction, and the molding surface is unpolished and the length of two sides sandwiching the right angle Used was a prism having a cross section of a right isosceles triangle of approximately 0.7 mm. Here, the angle formed by the surface formed by the long side of the right-angled isosceles triangle and the surface formed by the other short side was determined. The cutting length of the measurement sample is not particularly limited as long as it can be fixed to the rotation holding means.

  In the laser shape measuring instrument, the optical path direction of laser light is defined as a vertical axis, that is, the Z axis, and horizontal axes orthogonal to the Z axis are defined as an X axis and a Y axis. Note that the X axis and the Y axis are orthogonal to each other. The right triangular prism is arranged so that one ridge line of the right triangular prism is parallel to the Y axis and the surface constituted by the long side is the first measured surface, and the first measured surface is irradiated with laser light. The prism was fixed by a rotation holding means. The rotation holding means includes a rotation stage, an XY stage, and a gonio stage.

  The right triangular prism is moved at intervals of 5 μm in the X-axis direction by the rotation holding means so that the laser beam scans from one ridge line of the first measured surface of the right triangular prism to the other ridge line, Data obtained by measuring the height of the first surface to be measured with a laser shape measuring instrument at intervals of 5 μm was obtained.

  Of the data of the measurement points on the first surface to be measured, extract the data of the measurement points where the slope of the straight line connecting the two measurement points adjacent to each other is 2 degrees or less, and among the extracted data Using the data of the measurement points excluding the 20% on both sides near the ridgeline, an approximate straight line on the XZ plane of the surface to be measured is calculated by the least square method, and the approximate straight line and the XY plane are further calculated. Was obtained (θ1 = −0.0822 °). The angle value was positive in the clockwise direction with reference to the X axis.

  Next, the surface constituted by the short sides is set as the second measured surface, and the right triangular prism is parallel to one ridge line of the right triangular prism so that the second measured surface is irradiated with laser light. After rotating around the axis (κ = 135.0127 °), the same as the first measured surface, the height of the second measured surface was measured at 5 μm intervals, and two adjacent points were measured. Extract the data of the measurement points where the slope of the straight line connecting the measurement points is 2 degrees or less, and use the data of the measurement points excluding the 20% on both sides near the ridge line of the extracted data. An approximate straight line on the XZ plane of the surface to be measured was obtained by calculation by the square method, and an intersection angle (θ2 = 179.9302 °) between this approximate straight line and the XY plane was obtained by calculation.

  The angle (α) between the first measured surface and the second measured surface, α = | θ2-κ−θ1 | = | −0.0822-135, based on the intersection angle θ1, the intersection angle θ2, and the rotation angle κ. Of 0127-179.9302 | = 44.99997 °.

  The present invention can also be applied to an object to be measured having a similar prismatic shape other than a prism.

It is a schematic side view which shows the laser shape measuring device used for the prism angle measuring method of this embodiment. It is a perspective view which shows the prism of the measuring object of the example of embodiment of the prism angle measuring method which concerns on this invention. It is an array figure of the measurement point explaining the 1st approximation operation step of the example of this embodiment. FIG. 4 is an array diagram of measurement points that represents an enlarged range S in FIG. 3. It is an array figure of the measurement point explaining the 1st approximation operation step of the example of this embodiment. It is an array figure of the measurement point explaining the 1st approximation operation step of the example of this embodiment. It is a flowchart which shows the operation | work step of the prism angle measuring method of this embodiment. It is a schematic perspective view explaining the prism holding step and the first measurement step in the prism angle measurement method of the present embodiment. It is a schematic side surface explaining the work step of the prism angle measuring method of this embodiment, the figure (a) shows the 1st approximation calculation step and the 1st crossing angle calculation step, and the figure (b) shows the rotation step. FIG. 4C shows a second measurement step, a second approximation calculation step, and a second intersection angle calculation step. It is a conceptual diagram explaining the prism angle calculation step in the prism angle measuring method of this embodiment by superimposing the reference line and the apex angle, (a) is an explanatory view when the clockwise direction is the positive direction, (b) Is an explanatory view when the counterclockwise direction is a positive direction. It is a perspective view which shows the prism of the other measuring object of the prism angle measuring method which concerns on this invention.

Explanation of symbols

1, 5 Prism 11, 51 One prism surface 12, 52 Other prism surface 13 Prism ridgeline 2 Laser shape measuring device 21 Laser irradiation unit 3 Rotation holding means 32 Rotating axis B Reference line B 'Auxiliary line H Measurement range I Calculation range J Center range L1 First approximate straight line L2 Second approximate straight line M, Ma, Mb, Mc, Md Measurement point of one prism surface N Measurement point Rab of other prism surface First virtual straight line Rbc Second virtual straight line P Measurement point Interval ST1 Prism holding step ST2 First measurement step ST3 First approximation calculation step ST4 First intersection angle calculation step ST5 Rotation step ST6 Second measurement step ST7 Second approximation calculation step ST8 Second intersection angle calculation step ST9 Prism angle calculation step α Prism angle β, βb, βc Intersection angle formed by the first virtual line and the second virtual line κ rotation Degree θ1 intersection angle between the first approximate straight line and the crossing angle θ3 second approximate straight line and the reference line and parallel to the auxiliary line between the intersection angle θ2 second approximate straight line and the reference line and the reference line

Claims (5)

An optical surface approximation method for approximating a shape of one direction of an optical surface to a straight line,
Measure the position of a plurality of measurement points arranged on the optical surface at a predetermined interval in the one direction with a shape measuring instrument,
A first imaginary straight line passing through one measurement point and one measurement point adjacent to each other with an interval P between measurement points of 1 μm or more and 40 μm or less from the entire measurement range of the optical surface; On the other hand, a range in which only measurement points where the intersection angle β formed by the second virtual straight line passing through the adjacent measurement points satisfies Expression (1): P × β ≦ 10 (unit: μm · °) is arranged is extracted as a calculation range. And
An optical surface approximation method, wherein an approximate straight line representing the optical surface is obtained based on position data of measurement points in the calculation range.   From the calculation range, a central range excluding a range of a predetermined width near both ends of the calculation range is extracted as a central range, and an approximate straight line representing the optical surface is obtained based on position data of measurement points in the central range. The optical surface approximation method according to claim 1, wherein the optical surface approximation method is obtained.   3. The optical surface approximation method according to claim 2, wherein a range close to both ends of the calculation range is excluded with a width of 10% to 20% with respect to the entire width of the calculation range.   4. The optical surface approximating method according to claim 1, wherein the shape measuring instrument irradiates a laser beam. A prism angle measurement method for measuring an angle α formed by one prism surface of a prism and another prism surface,
A prism holding step for holding the prism so that the one prism surface faces the shape measuring instrument and is rotatable about a rotation axis parallel to the prism ridgeline;
5. The shape measuring device measures the positions of a plurality of measurement points arranged on the prism surface at a predetermined interval in a direction perpendicular to the prism ridgeline of the prism by the optical surface approximation method according to any one of claims 1 to 4. A first approximate calculation step for obtaining a first approximate straight line representing the one prism surface;
A first intersection angle calculating step for obtaining an intersection angle θ1 concentric with the angle α between the reference line and the first approximate line, with one rotation direction as a positive direction with respect to a reference line perpendicular to the prism ridge line;
A rotation step of moving the prism to a position rotated by a rotation angle κ with a rotation axis parallel to the prism ridge line and directing the other prism surface to the shape measuring instrument;
A second approximation calculation step for obtaining a second approximation line representing the other prism surface by the optical surface approximation method according to any one of claims 1 to 4,
A second intersection angle calculating step for obtaining an intersection angle θ2 of the positive direction between the second approximate straight line measured in the same direction as the rotation angle κ and the reference line;
The one prism surface is expressed by an equation (2): α = | θ2-κ−θ1 | expressed by an absolute value of a value θ2-κ−θ1 composed of the intersection angle θ1, the intersection angle θ2, and the rotation angle κ. And a prism angle calculation step for obtaining an angle α formed by the other prism surface;
The prism angle measuring method characterized by having.

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