JPH11257945A - Probe type shape measuring apparatus and shape measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate the shape of a surface to be measured from measured data precisely, by the use of a probe type shape measuring apparatus which measures the contour shape of a free curved surface. and a shape measuring method using the apparatus. SOLUTION: As sequence-of-points data to be obtained by representing by a rectangular coordinate system the operation locus of a probe 2 as against an arbitrary surface 1a to be measured, first sequence-of-points data, and second sequence-of-points data at positions shifted by a minute amount in the perpendicular direction to that of scanning of the first sequence-of-points data are found, by the scanning of the probe 2 by the user setting. For each point of the first sequence-of-points data, a group of several points in the vicinity of each point of the first sequence-of-points data from the first and second sequence-of-points data is selected, and the group of points is approximated by a plane, and the normal vector of the approximate plane is found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe-type shape measuring apparatus and a shape measuring method for the apparatus, and more particularly, to a probe-type shape measuring apparatus for measuring a contour shape of a free-form surface using a measuring probe and an apparatus therefor. And a shape measuring method.

[0002]

2. Description of the Related Art As a means for evaluating the shape of a lens surface having a high degree of design freedom such as an aspherical lens, a shape of a specific cross section is measured using a probe-type shape measuring device, and a paraxial radius of curvature R or the like is determined based on measurement data. There is a method for evaluating a shape error and the like. A conventional shape measuring device will be described with reference to the drawings. FIG. 1 is a schematic diagram of a probe-type shape measuring apparatus. Measurement probe 2
Is mounted on a stage 3 operable with at least two degrees of freedom, and continuously scans the surface 1a of the DUT 1. The trajectory of the probe at this time is measured as a point sequence of at least two-dimensional coordinates by a length measuring device (not shown). As a measurement probe, it is common to use a stylus with a spherical tip of several μm or a contact probe with a small-diameter ruby ball attached to the tip, but a non-contact probe such as an optical stylus is also used. . For measuring the shape of an object to be measured, such as a resin injection-molded product, whose surface is easily damaged, a method using a spherical surface having a radius of curvature R of about 1 mm or an optical stylus type is used.

Here, a case where the shape is measured with a contact probe using a spherical surface at the tip will be described as an example. Since the point of contact between the probe and the surface to be measured changes every time depending on the inclination (angle, inclination direction) of the surface to be measured, the coordinates measured by the length measuring device are regarded as the movement of the center position of the sphere at the tip of the probe, Of the object to be measured by estimating the position from the center to the contact point. As a shape evaluation method when the object to be measured is a rotationally symmetric body such as a paraboloid, it is general to evaluate a contour shape on a plane including a rotation axis. In this case, among the inclinations of the surface to be measured, the inclination component in the direction orthogonal to the scanning direction can be regarded as substantially zero, so that the motion trajectory and its normal vector are on the same plane. Therefore, it can be relatively easily solved as a contact problem between a curve and a circle in a two-dimensional plane.

[0004]

However, as anamorphic optical parts are widely used for scanning lenses and the like,
There has been a demand for measuring the cross-sectional shape of a portion where the tilt component in the direction orthogonal to the scanning direction is not zero, or for measuring the entire effective area. In this case, estimation of the contact position between the probe and the surface to be measured is a problem of contact between the unknown free-form surface and the spherical surface, and it is very difficult to estimate this from only the measurement data. In addition, even when the probe is an optical stylus type probe, the reflected light is inclined depending on the inclination of the surface to be measured, and the origin position of the output data of the probe changes in the order of several μm. It is very difficult to accurately estimate the shape. Therefore, it is necessary to obtain a normal vector in each measurement data and correct the fluctuation of the origin position. Therefore, an object of the present invention is to employ a method of obtaining a normal vector by approximating a plane from each measurement data and accurately estimating the shape of the measured surface with respect to an arbitrary measured surface, and relying on a probe. An object of the present invention is to provide a probe-type shape measuring apparatus that corrects an error and a shape measuring method in the apparatus.

[0005]

According to a first aspect of the present invention, there is provided a shape measuring means which scans a surface to be measured with a measuring probe, and obtains a motion trajectory of the probe as point sequence data in a rectangular coordinate system;
In a shape measuring apparatus provided with calculating means for calculating a contour shape of an object to be measured from measured point sequence data, the shape measuring unit scans a first point sequence data and a second point sequence data by scanning a probe according to a user setting. A second point sequence data at a position deviated by a small amount in a direction perpendicular to the scanning direction of the first point sequence data, wherein the calculating means calculates, for each point of the first point sequence data, Means for selecting a point group of several points near each point of the first point sequence data from the first and second point sequence data, approximating the point group to a plane, and obtaining a normal vector of the approximate plane; There is provided a shape measuring device.

According to a second aspect of the present invention, in the shape measuring apparatus according to the first aspect, the measuring probe is a contact-type probe having a spherical tip at the tip thereof, and the arithmetic means includes the normal vector and the contact-type probe. A shape measuring apparatus characterized in that it is means for obtaining a position of a contact point between the contact type probe and the object to be measured based on a radius of curvature of a tip of the probe.

According to a third aspect of the present invention, in the shape measuring apparatus according to the second aspect, the calculating means includes, in addition to the normal vector and the radius of curvature of the tip of the contact probe, a true sphere of the contact probe. A shape measuring apparatus characterized in that it is means for obtaining a position of a contact point between the contact probe and the object to be measured using a degree error model.

According to a fourth aspect of the present invention, in the shape measuring apparatus according to the first aspect, the measuring probe emits a convergent light beam to the surface to be measured and forms an image of reflected light from the surface to be measured. An optical stylus probe for measuring the distance to the surface to be measured from a change in a focal position, wherein the calculating means calculates the optical stylus based on the normal vector and the origin error characteristic model of the optical stylus probe; A shape measuring apparatus characterized in that it is means for correcting the origin error of the needle type probe.

According to a fifth aspect of the present invention, in the shape measuring apparatus according to the fourth aspect, the calculation means calculates the normal vector and the origin error characteristic model of the optical stylus type probe.
The origin error of the optical stylus probe is corrected, and in addition, the sensitivity of the optical stylus probe is determined by the normal vector and the sensitivity characteristic model of the optical stylus probe. A shape error measuring device for correcting a focus error error caused by the sensitivity of the optical probe and the sensor output value of the optical stylus probe.

According to a sixth aspect of the present invention, in the shape measuring apparatus according to any one of the first to fifth aspects, when an approximation error is larger than a predetermined value at the time of approximation to the plane, the measurement point is set to invalid data. The shape measurement device is characterized in that the shape measurement device is deleted from the point sequence.

According to a seventh aspect of the present invention, there is provided a shape measuring means which scans a surface to be measured with a measuring probe and obtains a motion trajectory of the probe as point sequence data in a rectangular coordinate system, and an object to be measured based on the measured point sequence data. A shape measuring method in a shape measuring device provided with a calculating means for calculating a contour shape of the first point sequence data, the first point sequence data and a scanning direction of the first point sequence data being orthogonal to a scanning direction of a probe set by a user. The second point sequence data at a position shifted by a small amount in the direction is obtained, and for each point of the first point sequence data, the first point sequence data of the first point sequence data is calculated from the first and second point sequence data. A shape measuring method characterized by selecting a point group of several points in the vicinity of each point, approximating the point group to a plane, and obtaining a normal vector of the approximate plane.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a probe-type shape measuring apparatus to which the present invention is applied, in which a probe 2 is mounted on a stage 3 operable with at least two degrees of freedom.
The surface 1a of the DUT 1 is continuously scanned. The trajectory of the probe at this time is measured as a point sequence of at least two-dimensional coordinates by a length measuring device (not shown). FIGS. 2 and 3 show a measuring method using the probe-type shape measuring apparatus shown in FIG.
This will be described with reference to FIG. FIG. 2 shows a state in which the apparatus shown in FIG. 1 is viewed from above, and broken lines 11 and 12 show measurement loci. In the case of measuring a two-dimensional contour shape, the probe is scanned along a locus (in this case, a straight line) specified by the user to measure the shape, and this is set as first point sequence data 11. Then, after a slight amount (about 0.01 mm) shift in the direction perpendicular to the scanning direction, the measurement returns to the same direction as the first measurement (in this case, a parallel straight line) and measures up to the vicinity of the measurement start point.
This is referred to as second point sequence data 12. At this time, the sampling pitch per scan and the shift amount between each scan are as follows.
Considering the partial curvature of the surface to be measured, it is set to be sufficiently small. In this example, the second point sequence data 12 is performed by one scan, but this may be measurement data by a plurality of scans sandwiching the first point sequence data 11.
The three-dimensional shape measurement is achieved by performing the above-described series of operations a plurality of times while shifting the position.

Next, data processing will be described with reference to FIG. Consider an arbitrary point P1 _i (solid black point) 21 in the first point sequence data 11 obtained in the first measurement. FIG. 3 shows P1 _i 21 and measurement points in the vicinity thereof. The point P of the second point sequence data 12 is located near P1 _i 21.
There is 2 _i . Here, the second point sequence data 12 is obtained by one scan, but the same applies to point sequence data by two or more scans sandwiching the first scan. Here, point groups 22 and 2 near P1 _i 21 indicated by thick circles
3, 31, 32, and 33 are extracted. In the present embodiment, one point 22, 23 before and after the first point sequence data 11 and three neighboring points 31, 32, 33 from the second point sequence data 12 are selected. The point group to be extracted may be at least one point each of the first and second point sequence data. The coordinate data of these six points is copied and subjected to translational coordinate conversion such that P1 _i 21 is the coordinate origin. Here, these six points 21, 22, 23, 31, 3
P1 _i (origin) 21 by least square method for 2, 33
Are estimated on the plane z = ax + by passing through. Thereby, the partial differential in each axis direction can be easily obtained. ∂z / ∂x = a ∂z / ∂y = b At this time, the unit normal vector is

[0014]

(Equation 1)

## EQU1 ## The shape of the measured object is estimated using the normal vector.

A second embodiment of the present invention will be described. When the measurement probe is a contact probe, the unit normal vector obtained in the first embodiment and the radius of curvature R of the tip of the probe are used.
Therefore, the position P _{i of the} contact point is

[0017]

(Equation 2)

In particular, when the probe has a spherical surface, the contact point between the probe and the surface to be measured can be obtained with high accuracy.

Next, a third embodiment of the present invention will be described. In the second embodiment, the probe is calibrated before the measurement of the device under test. The sphericity error of the probe is obtained by the calibration work. For calibration, a calibration sphere with traceability is prepared, and the entire surface is scanned within the maximum allowable tilt angle to measure the shape. This measurement result is approximated to a spherical surface to obtain an approximate radius of curvature R _meas and shape error data. here,
Since the exact radius of curvature R _{ref of the} calibration sphere is known, the radius of curvature R _probe of the _probe is determined by R _probe = R _meas -R _ref . The sphericity error of the probe is shape error data obtained by separating a spherical component from measurement data. Since this is point sequence data of coordinates (x, y, z),
Convert to an error relationship. That is, since the partial differential in each axis direction is analytically obtained from the equation of the spherical surface, by converting (x, y, z) to (∂z / ∂x, ∂z / ｚy, z), To a suitable model f (∂z / ∂x, ∂z / ∂y)
And save the parameters. Next, a correction process for measuring the shape of an arbitrary sample will be described. As in the first embodiment, several points in the vicinity are approximated to a plane, and partial derivatives in each axis direction are obtained. / ∂y) to determine the sphericity error. By subtracting this as the z-coordinate error, the sphericity error of the probe can be corrected. A measurement can be made.

A fourth embodiment of the present invention will be described. When the measuring probe is of the optical stylus type, there is a characteristic that the origin position of the sensor output shifts depending on the inclination of the surface to be measured.
Therefore, the origin error characteristic is modeled similarly to the calibration shown in the third embodiment. At the time of actual measurement, the origin error is obtained from the partial differential using the above-described origin error characteristic model and corrected, as in the third embodiment. As described above, by correcting the probe error, highly accurate shape measurement can be performed.

A fifth embodiment of the present invention will be described. The optical stylus type probe obtains a sensor output (focus error output) proportional to the distance to the surface to be measured, and the sensitivity of the sensor, which is a proportional coefficient at this time, depends on the inclination of the surface to be measured. Change. Therefore, the characteristic of the sensor sensitivity change depending on the inclination of the surface to be measured in the optical stylus probe is calibrated. As the calibration work, the calibration sphere of the third embodiment is used, and the sensor output is taken in while scanning in the measurement axis direction of the probe at a plurality of positions. By linearly approximating this, the coordinates of the sensor output origin position and the sensor sensitivity are obtained. The origin is approximated to a spherical surface using the coordinates of the origin.
Next, the axial partial derivatives of the above-described spherical equation are obtained from the x and y coordinates of each point, and the relationship between the partial derivatives and the sensor sensitivity is modeled and stored. When measuring the shape of the object to be measured, the sensitivity at each point measurement is obtained from each axial partial differential using the above-described sensitivity characteristic model, and the focus error error is obtained and corrected from this and the optical stylus sensor output. That is, the sensitivity at the time of each point measurement is obtained, and the distance between the measured surface and the origin of the probe is accurately obtained from the sensitivity and the sensor output. By correcting this, high-speed and high-accuracy shape measurement can be performed.

A sixth embodiment of the present invention will be described. In the first embodiment, when the approximation to the plane, when the square sum of errors is greater than the specific value, potential point P _i on the object to be measured is estimated is abnormal data dependent on scratches and dust Is very high, P _i is deleted from the point sequence data. By removing abnormal data due to scratches or dust in the measurement data, the shape can be more stably evaluated.

[0023]

According to the first and seventh aspects of the present invention, the normal vector of each point can be obtained more easily with respect to an arbitrary surface to be measured, and the error depending on the probe can be corrected. Shape measurement can be performed accurately. Optical components such as an aspherical lens and its mold are representative of the object to be measured which requires high accuracy. These DUTs have no edge or a portion where the inclination angle fluctuates rapidly within the effective range.
Alternatively, there is a common feature that the surface roughness is sufficiently small. Assuming that the surface to be measured is sufficiently smooth, it can be assumed that the point group obtained by extracting several points in the vicinity of each measurement point is almost on one plane, so that the accuracy of approximation to the plane is high and the normal vector The accuracy of the estimation is high. Therefore, high accuracy of the optical component can be guaranteed and stable measurement can be performed. As described above, when the roughness of the surface to be measured is at the mirror level and there are no edges or scratches, the correction can be performed most efficiently, and highly accurate measurement can be performed.

According to a second aspect of the present invention, in addition to the effect of the first aspect, when a contact-type spherical probe is used, the contact between the probe and the measured surface can be easily made on an arbitrary measured surface. By obtaining the points, the shape can be measured with high accuracy.

Effect corresponding to claim 3: In addition to the effect corresponding to claim 2, by correcting the sphericity error of the tip spherical surface, the shape can be measured with higher accuracy.

Advantageous Correspondence of Claim 4: In addition to the effect corresponding to claim 1, even if the measuring probe is of the optical stylus type, the shape can be measured accurately.

Effect corresponding to claim 5: In addition to the effect corresponding to claim 4, shape measurement can be performed with higher accuracy and even when the probe output does not sufficiently converge.

Effect corresponding to the sixth aspect: In addition to the effect corresponding to the first aspect, by removing abnormal data due to scratches, dust, etc., more accurate shape measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a probe type shape measuring apparatus to which the present invention is applied.

FIG. 2 is a diagram showing an example of a measurement trajectory of the probe-type shape measuring device of the present invention.

FIG. 3 is a diagram showing an example of point sequence data obtained by a first shape measurement in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DUT, 1a ... Surface of a DUT, 2 ... Measuring probe, 3 ... Stage, 11 ... First point sequence data, 12 ... Second point sequence data, 21 ... First point sequence data , Arbitrary points in the first point sequence data, 22, 23... Points before and after an arbitrary point in the first point sequence data, 31, 32, 33. Point cloud near a point.

Claims (7)

[Claims] 1. A shape measuring means for scanning a surface to be measured with a measuring probe to obtain an operation trajectory of the probe as point sequence data in a rectangular coordinate system, and obtaining a contour shape of the object to be measured from the measured point sequence data. In a shape measuring apparatus provided with a calculating means, the shape measuring means is configured to scan the first point sequence data with a small amount in a direction orthogonal to the scanning direction of the first point sequence data by scanning a probe according to a user setting. 2nd position
Means for calculating point sequence data of the first point sequence data, wherein the calculating means calculates the first and second points for each point of the first point sequence data.
A point group of several points near each point of the first point sequence data is selected from the point sequence data, and the point group is approximated to a plane, and a normal vector of the approximate plane is obtained. Shape measuring device. 2. The shape measuring apparatus according to claim 1, wherein the measuring probe is a contact probe whose tip is a spherical surface, and wherein the calculating means calculates the normal vector and a curvature of the tip of the contact probe. A shape measuring device, which is means for determining a position of a contact point between the contact probe and the object to be measured, based on a radius. 3. The shape measuring apparatus according to claim 2, wherein the calculating means calculates a sphericity error model of the contact type probe in addition to the normal vector and a radius of curvature of a tip of the contact type probe. A shape measuring device, which is means for determining a position of a contact point between the contact probe and the object to be measured. 4. The shape measuring apparatus according to claim 1, wherein the measurement probe irradiates a convergent light beam on the surface to be measured and focuses the light reflected from the surface to be measured. An optical stylus probe for measuring a distance from the surface to be measured, wherein the calculating means calculates the origin of the optical stylus probe based on the normal vector and the origin error characteristic model of the optical stylus probe. A shape measuring device, which is a means for correcting an error. 5. The shape measuring apparatus according to claim 4, wherein the calculating means corrects an origin error of the optical stylus probe based on the normal vector and an origin error characteristic model of the optical stylus probe. In addition, the sensitivity of the optical stylus probe is determined by the normal vector and the sensitivity characteristic model of the optical stylus probe, and the sensitivity of the optical stylus probe and the sensor of the optical stylus probe are determined. A shape measuring device, which is means for correcting a focus error error due to an output value. 6. The shape measuring apparatus according to claim 1, wherein, when approximating the plane, if an approximation error is larger than a predetermined value, the measured point is deleted from the point sequence as invalid data. A shape measuring apparatus characterized in that: 7. A shape measuring means for scanning a surface to be measured with a measuring probe and obtaining a motion trajectory of the probe as point sequence data in a rectangular coordinate system, and obtaining a contour shape of the object to be measured from the measured point sequence data. What is claimed is: 1. A shape measuring method in a shape measuring device provided with an arithmetic unit, wherein a first point sequence data is shifted by a small amount in a direction orthogonal to a scanning direction of the first point sequence data by scanning of a probe by a user. 2nd position
And for each point of the first point sequence data, select a point group of several points near each point of the first point sequence data from the first and second point sequence data. A shape measurement method, wherein the point group is approximated to a plane, and a normal vector of the approximate plane is obtained.