JP2000081329A - Shape measurement method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an error peculiar to a device and an error with time for improving measurement accuracy by achieving a shape being approximated to an object to be measured, obtaining the amount of error of the device caused by the shape- measuring device according to the measurement value of a primary standard where designing shape data is clear and the shape data, and correcting the measurement value of the object to be measured. SOLUTION: A guide 5 of a shape-measuring device is provided with a stage 11 for mounting an object to be measured, and the stage 11 travels in an X direction along the guide 5. A probe 15 that is mounted to a stage 13 can travel in a Z direction. The stages 11 and 13 are provided with a position detection means for detecting the amount of travel. Then, the probe 15 is brought into contact with an object 9 to be measured, the object 9 to be measured is S canned with a beam, and the coordinates information on the surface of the object 9 to be measured that is a contacting point between the probe 15 and the object 9 to be measured is obtained according to the position information of the stages 11 and 13. The amount of device error of the shape-measuring device being obtained from the measurement value of a primary standard being approximated to the shape of the object to be measured and shape data is corrected for the obtained measurement value, thus obtaining an accurate surface shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape measuring method for scanning a surface of an object to be measured, taking in positional information on the surface of the object as two-dimensional or three-dimensional coordinate values, and measuring the shape of the object to be measured. And a shape measuring device.

[0002]

2. Description of the Related Art In general, a measurement result obtained by a shape measuring device which scans a surface of an object to be measured two-dimensionally or three-dimensionally includes information on the shape of the object to be measured and a measurement which the shape measuring device itself has. The error (bias) is included as a whole.

In the prior art, in order to separate the measurement error from the measurement result and obtain the true shape of the measured object,
The errors of the shape measuring device are decomposed into error factors such as straightness errors on the reference plane, squareness errors on the reference plane, errors dependent on the probe, etc., and each is evaluated individually to obtain a correction value for each error factor. I was As a method of performing the evaluation for each error factor, a method of directly measuring each, for example, a method of evaluating the straightness of the reference surface with a straightness measuring device, a method of measuring the probe sphericity error with a roundness measuring device. There are a method of evaluation, a method of measuring using various prototypes on a shape measuring device, and separating and evaluating a specific error factor.

Next, a corrected measurement value can be obtained by subtracting each error individually evaluated for each error factor from the measurement value of the shape measuring device.

[0005]

The above-mentioned prior art has the following problems.

First, when each error is evaluated by a straightness measuring device or a roundness measuring device, the error of the measuring device which has performed the error evaluation is necessarily included in the evaluation result. It is extremely difficult to perform an evaluation with high accuracy. Secondly, since errors of the shape measuring apparatus are caused by various error factors intricately affecting each other, errors for each of these factors are completely separated and corrected from the measurement results using a prototype or the like. It is extremely difficult.

Third, in the prior art, when an error caused by each error factor changes with time, it may be difficult to correctly evaluate the change with time, and there is a possibility that erroneous error correction may be performed. Therefore, it is extremely difficult to obtain the high measurement accuracy required in the measurement of the aspherical optical element and the like in the conventional technology.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is based on a measurement value of a surface of an object to be measured obtained by a shape measuring device to determine an error inherent to the shape measuring device and an influence of a change with time of the error. It is an object of the present invention to provide a shape measuring method and a shape measuring device which can be reliably removed and obtain high measurement accuracy.

[0009]

According to a first aspect of the present invention, there is provided a shape measuring method comprising: scanning a surface of an object to be measured; acquiring position information of the surface of the object as two-dimensional or three-dimensional coordinate values; In a shape measuring method using a shape measuring device for measuring a shape of an object surface, a first measurement value is obtained by measuring a shape of a prototype having a shape approximate to an object to be measured and having apparent shape data in design. A second step of obtaining a device error caused by the shape measuring device from the first measured value and the shape data of the prototype, and a second step of measuring the shape of the object to be measured. A third step for determining a measurement of
A fourth step of correcting the second error amount using the device error amount and obtaining a measured value of the device under test.

According to a second aspect of the present invention, the shape measuring apparatus scans the surface of the object to be measured, takes in positional information of the surface of the object as two-dimensional or three-dimensional coordinate values, and measures the shape of the object. In a shape measuring device, a first prototype is obtained by measuring a prototype having a shape similar to the object to be measured, and the shape data in design is clear, and the shape data of the prototype is obtained from the first measured value. Measurement error detecting means for subtracting and obtaining an apparatus error amount caused by the shape measuring apparatus; and measuring a device under test to obtain a second measurement value, and further calculating a second measurement value using the apparatus error amount. And a shape measuring means for correcting the measured value of the object to be measured.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing an example of a three-dimensional (X, Y, Z space) shape measuring apparatus to which the present invention is applied.

In FIG. 2, an X-axis guide 5 and a pair of frames 3 are provided on a base 1, and Y-axis and Z-axis guides 7 are provided between the frames 3. Guide 5
Has a stage 11 for a measurement object on which the object 9 is mounted, and the stage 11 is configured to be movable in the X direction along the guide 5. The guide 7 includes a probe stage 13 on which a probe 15 is mounted, and the stage 13 is configured to be movable in the Y and Z directions along the guide 7.

Each of the stages 11 and 13 is provided with position detecting means (not shown) for detecting the amount of movement. FIG. 3 shows an example of a two-dimensional (X, Z space) shape measuring apparatus to which the present invention is applied. The shape measuring device shown in FIG. 3 has a guide 5 and a frame 3 provided on a base 1. The guide 5 includes a stage 11 for an object on which the object 9 is mounted, and the stage 11 is configured to be movable in the X direction along the guide 5.

A probe stage 13 on which the probe 15 is mounted is connected to a Z-axis slide 17. The Z-axis slide 17 is configured to be movable in the Z direction along the Z-axis guide 7. Therefore, the probe 15
Is movable in the Z direction. Each of the stages 11 and 13 (or the Z-axis slide 17) is provided with a position detecting means (not shown) for detecting a moving amount.

The shape measuring device shown in FIG. 3 is used to correct the straightness error of the running of each of the stages 11 and 13.
Reference surfaces 19 and 23 are provided in parallel with the guides 5 and 7. The straightness error of the running of the stages 11 and 13 is detected by the displacement sensors 21 and 25 with reference to the reference surfaces 19 and 23. Therefore, the shape measuring apparatus shown in FIG. 3 outputs a measured value from which the straightness error between the stage 11 and the stage 13 has been removed.

In the shape measuring apparatus shown in FIG. 2 or 3, the probe 15 is brought into contact with the object 9 to be measured, and
Are relatively scanned to acquire the position information of the stages 11 and 13 at a plurality of predetermined positions. Thereby, the contact point between the probe 15 and the object 9, that is, the coordinate information of the surface of the object 9 can be obtained as a measured value.

Hereinafter, an aspheric lens will be taken as an example of the object 9 to be measured, and for simplicity, a description will be given using a two-dimensional shape measuring apparatus shown in FIG. FIG. 4 is a diagram illustrating an example of a measurement value S1 obtained by two-dimensionally measuring the aspheric lens as the object 9 using the shape measuring apparatus illustrated in FIG. The measured value S1 shown in FIG. 4 is the true coordinate information S of the aspherical lens surface.
2 and the measurement error S3 of the shape measuring device are added. In FIG. 4, a solid line S1 indicates a measured value, a broken line S2 indicates coordinate information of a true shape of the aspherical lens, and a dashed line S3 indicates a measurement error of the shape measuring device.

In general, the measurement error of the shape measuring apparatus is dominated by the error of the probe 15 depending on the straightness and the squareness of the running of each of the stages 11 and 13 and the contact position on the probe 15. In other words, this means that the measurement error of the shape measuring device is substantially determined by the position and the posture of the object 9 to be measured in the shape measuring device.

In the embodiment of the present invention, coordinate information S2 indicating the shape of a true aspheric lens is obtained by the following method. First, another prototype spherical lens (best-fit spherical surface) approximating the aspheric lens which is the object 9 is prepared.
As described later, accurate shape data is obtained in advance for this prototype spherical lens by calculation. Then, the original spherical lens is measured at the same position and the same posture as when measuring the aspherical lens, and an actual measurement value of the original spherical lens is obtained. By this operation, the measured value of the prototype spherical lens is determined from the nature of the measurement error of the shape measuring device described above.
The same measurement error as in the measurement of the aspherical lens is included.

Here, a prototype spherical lens approximating an aspherical lens means a spherical lens (a lens having a best-fit spherical surface) whose radius of curvature is adjusted so as to best fit the shape of the aspherical surface. is there. FIG. 5 is a diagram showing the relationship between the actual measurement value S4 of the prototype spherical lens, the shape data S5 calculated by the prototype spherical lens (best-fit spherical surface), and the measurement error S6.
In the figure, a solid line S4 indicates an actual measurement value of the best-fit spherical surface, a broken line S5 indicates shape data of the best-fit spherical surface, and a dashed-dotted line S6 indicates a measurement error (hereinafter, referred to as a fitting residue).

Here, the measured value S4 of the prototype spherical lens
Is subtracted from the shape data S5 of the prototype spherical lens, which is known in advance, to obtain a fitting residue S6 at the measurement position of the shape measurement device. The fitting residue S6 includes a manufacturing error (deviation from the ideal spherical surface) of the prototype spherical lens and a measurement error of the shape measuring device.

However, the spherical lens has extremely high accuracy (1n
(m rms or less), the manufacturing error can be ignored if such a spherical lens is used as a prototype, and the fitting residue S6 represents a measurement error of the shape measuring device. Become. By the above method, a predetermined position ((X, Z) coordinates) of the shape measuring device
Measurement error S3 = fitting residue S6 can be obtained.

As described above, FIG. 4 is a diagram showing the relationship between the measured value S1 of the aspherical lens and the measurement error S3. As shown in FIG. 5, fitting residue S of the prototype spherical lens
6 is stored as data, and since the measurement errors S3 and S6 are the same value, subtraction correction is performed from the measurement value S1 of the aspherical lens in FIG. This makes it possible to obtain the true coordinate information S2 of the aspherical lens.

In the above-described embodiment, the DUT 9 and the approximate spherical surface are illustrated as convex surfaces, but the present invention is not limited to this, and may have any other shape, for example, a concave surface. In addition, instead of using a spherical surface manufactured with extremely high precision, the manufacturing error of the spherical lens is measured by another measuring device, for example, a Fizeau-type interferometer, and the result is previously subtracted from the spherical lens measurement result. The same effect can be obtained by placing the same.

FIG. 1 is a flowchart showing a procedure for obtaining the true shape of the measured object based on the above embodiment. First, in step S101, a prototype having a best-fit shape close to the shape of the measured object is measured using a shape measuring device. Next, in step S102, for the prototype having the best-fit shape, the shape data previously calculated is subtracted from the measured values obtained in step S101 to obtain a fitting residue.

Next, in step S103, the shape of the object to be measured is measured using a shape measuring device. Finally, in step S104, the fitting residue is subtracted and corrected from the measured value of the DUT obtained in step S103 to obtain true coordinate information of the DUT. In the above-described embodiment, the process of calculating the fitting residue and correcting the fitting error from the measurement result of the device under test includes:
It can be performed automatically by a computer connected to the shape measuring device. Therefore, the operator need only measure the object to be measured and a prototype having an approximate shape thereof.

In the case of continuously measuring an object having a relatively close shape, almost the same measurement error occurs in the measurement result due to the nature of the measurement error of the shape measuring apparatus described above. Therefore, when measuring an object having a relatively similar shape continuously, it is not necessary to measure a prototype having an approximate shape for each measurement of the object to be measured. May be performed only once.

Further, in the above-described embodiment, two-dimensional measurement has been described, but it is needless to say that the present invention can be applied to three-dimensional measurement. Further, according to the present invention, correct correction can be performed even when the measurement error of the measuring instrument changes with time. As is clear from the above description, according to the embodiment, the measurement error unique to the shape measuring device is removed from the coordinate value of the surface of the measured object obtained by the shape measuring device, and the high-precision measured value is obtained. It is possible to obtain.

Therefore, for example, it is possible to realize a high measurement accuracy required for measuring an aspherical optical element.

[0030]

According to the shape measuring method of the first aspect,
Since the apparatus error amount of the shape measuring apparatus can be accurately obtained in advance (second step), the shape of the object to be measured is subtracted by subtracting the apparatus error amount from the measured value of the object to be measured (fourth step). (Coordinate information) can be obtained with high accuracy.

Further, when a straightness measuring instrument or a roundness measuring instrument is used and errors of these measuring instruments are introduced, various error factors including the errors of the measuring instruments affect each other in a complicated manner. Since the measurement error can be removed, the shape (coordinate information) of the measured object can be obtained with high accuracy. Further, even when an error caused by each error factor changes with time, the shape (coordinate information) of the measured object can be obtained with high accuracy.

According to the second aspect of the present invention, the measuring error detecting means accurately obtains the device error amount of the shape measuring apparatus in advance, and the shape measuring means obtains the measuring error of the measured object by the measuring error detecting means. The shape (coordinate information) of the device under test can be obtained with high accuracy by performing correction using the obtained device error amount. In addition, when using a straightness measuring instrument or a roundness measuring instrument, and errors of these measuring instruments are included, various error factors including the errors of the measuring instruments described above are complicatedly affecting each other. Since the error can be removed, the shape (coordinate information) of the measured object can be obtained with high accuracy.

Further, even when the error caused by each error factor changes with time, the shape (coordinate information) of the measured object can be obtained with high accuracy.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a procedure for obtaining a true shape of an object to be measured.

FIG. 2 is a three-dimensional (X, Y, Z space) subject to the present invention.
FIG. 2 is a diagram showing an example of a shape measuring device.

FIG. 3 is a diagram showing an example of a two-dimensional (X, Z space) shape measuring apparatus to which the present invention is applied.

4 is a diagram showing an example of measured values obtained by two-dimensionally measuring an aspheric lens as an object to be measured using the shape measuring device shown in FIG.

FIG. 5 is a diagram showing a relationship between actual measured values of a prototype spherical lens, shape data of the prototype spherical lens (best-fit spherical surface), and fitting residues.

[Explanation of symbols]

 1 Base 3 Frame 5, 7 Guide 9 Object to be measured 11, 13 Stage 15 Probe 17 Z-axis slide 19, 23 Reference plane 21, 25 Displacement sensor S1, S4 Measured value S2 True coordinate information S3 Measurement error S5 Shape data S6 Measurement Error (fitting residue)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F062 AA04 AA51 CC20 DD23 DD33 EE04 EE62 FF04 FF13 HH01 HH13 2F069 AA04 AA66 DD19 EE20 FF07 GG01 GG11 GG62 GG71 HH01 JJ07 JJ13 LL02

Claims (2)

[Claims] 1. A shape measuring method using a shape measuring apparatus for measuring the shape of a surface of an object to be scanned by scanning the surface of the object to be measured. A first step of measuring a prototype that is known to obtain a first measurement value, and a second step of determining a device error amount caused by the shape measurement device from the first measurement value and the shape data of the prototype. Step 2, measuring the object to be measured, a third step of obtaining a second measured value, correcting the second measured value using the apparatus error amount, and measuring the measured value of the object to be measured. And a fourth step of obtaining the shape. 2. A shape measuring apparatus for measuring the shape of an object to be measured by scanning the surface of the object to be measured, wherein a prototype having a shape similar to the object to be measured and whose shape data in design is clear is measured. A first measurement value, and a measurement error detecting means for obtaining a device error amount caused by the shape measurement device from the first measurement value and the shape data of the prototype, and measuring the object to be measured. A shape measurement unit for obtaining a second measurement value by using the apparatus error amount, and further correcting the second measurement value using the device error amount to obtain a measurement value of the object to be measured.