JP2002156217A - Noncontact-type shape measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noncontact-type shape measuring method in which not only a plane but also a curved surface can be measured. SOLUTION: In the noncontact-type shape measuring method, light emitted from a light source for measurement is shone at a measuring-object face as spherical waves, the light from the light source is shone at a reference face, the phase distribution of reflected light is found on the basis of interference fringes formed by beams of reflected light on the respective faces, the face shape of an interference-fringes formation region on the measuring-object face is calculated on the basis of the phase distribution, the irradiation position of the spherical waves with reference to the measuring-object face is changed slightly by a known amount, the face shape of the interference-fringes formation region on the measuring-object face is calculated on the basis of the interference fringes in this case in the same manner, the continuous state of the face shape which is found in advance to the face shape which is found later is calculated on the basis of the known amount, the movement of the known amount, the face shape of the interference-fringes formation region and the continuous state are calculated repeatedly, and the shape of the measuring object is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a shape of a surface by a non-contact method using light.

[0002]

2. Description of the Related Art As methods for accurately measuring the shape of an object, there are a contact method using a stylus and a non-contact method using light. In the former, for example, a method of reducing the measuring force as much as possible by using the principle of an atomic force microscope or the like is used, but the disadvantage of scratching when measuring a soft metal surface has been completely solved. Absent. In the latter, a method of measuring the surface shape by light wave interferometry is generally used,
This includes a method of measuring a large area at a time using irradiation light as a plane, and a method of scanning a target area with point irradiation light. In the case of planar irradiation, it is necessary to make the incident wavefront almost the same shape as the measured shape by using a computer hologram or the like in order to generate a light wave almost perpendicular to the entire surface of the object.
However, it is necessary to create a hologram according to the target surface,
It is difficult to make accurate ones and lacks flexibility. In the case of point-like irradiation, since light emitted from the sensor to the scanning area needs to return to the sensor again, generally, a flat surface or a curved surface having a small curvature close thereto is measured. In the point irradiation method, if the light is always irradiated from the normal direction of the target surface, a curved surface having a large curvature can be measured.However, since the sensor unit needs to be moved so as to be tilted according to the target curved surface, The device becomes complicated.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-contact type shape measuring method which can measure not only a flat surface but also a curved surface.

[0004]

In order to achieve the above object, the present invention irradiates light emitted from a light source for measurement as a spherical wave to a surface to be measured, and applies light from the light source to a reference surface. Irradiate, determine the phase distribution of the reflected light from the interference fringes formed by the reflected light on each surface, calculate the surface shape of the interference fringe formation region on the measurement target surface based on the phase distribution, The irradiation position of the spherical wave is slightly changed by a known amount, the surface shape of the interference fringe formation area on the measurement target surface is similarly calculated from the interference fringe in that case, and the surface shape previously obtained based on the known amount is further calculated. And calculating the continuous state of the surface shape determined later and repeating the calculation of the surface shape and the continuous state of the interference fringe forming region by moving the known amount and determining the shape of the measurement target surface. Contact form measurement method It is intended to provide.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically shows a measuring device for carrying out the present invention. This apparatus comprises an XYZ stage 1 having a table movable along three orthogonal horizontal and vertical axes, and an XYZ stage 1
A laser light source 2 that emits parallel light toward the light source, and a portion arranged as described below in relation to the laser light source 2. XY
Condensing lenses L1 and L2, a filter P, a beam splitter B, and a condensing lens 13 are arranged along the optical axis of the laser light source 2 between the Z stage 1 and the laser light source 2 in the direction from the light source to the stage. Have been. A condensing lens L4 is provided on one side of the beam splitter B so as to receive the light split by the beam splitter B perpendicular to the optical axis.
And a CCD camera 3, and a reference mirror M and a support device 4 for the mirror on the other side. The CCD camera 3 is connected to a monitor 5 for displaying images. Also, XY
The Z stage 1, the CCD camera 3, and the support device 4 are connected to a computer 6 for each control.

The condenser lenses L1 and L2 are provided so as to appropriately adjust the diameter of the parallel light from the laser light source 2. The light having passed through the lens L2 passes through the filter P to have an appropriate light amount, and reaches the beam splitter B. The beam splitter B includes a half mirror inclined at 45 degrees with respect to the optical axis. The beam splitter B receives the light and transmits the light along the optical axis to the XYZ stage 1 side, and the reflected light perpendicular to the optical axis. Branch to The light transmitted through the beam splitter B is collected at the focal point by the condenser lens L3, and then spreads conically to reach the XYZ stage 1. The light reflected by the beam splitter B travels toward the reference mirror M, is reflected by the mirror, reaches the beam splitter B again, and the light transmitted through the beam splitter B passes through the condenser lens L4 and passes through the condenser camera L4.
Reach The support device 4 includes a piezoelectric actuator so as to move the supported mirror M back and forth accurately by a necessary distance in the direction of light coming from the beam splitter B.

Next, an embodiment of the method of the present invention using this apparatus will be described. First, the measurement target S is set in the XY direction so that the surface to be measured faces the optical axis extending from the laser light source 2.
It is fixed on the Z stage 1. When light is emitted from the laser light source 2, the light is condensed by the condenser lenses L1, L2,
The light passes through the filter P, the beam splitter B, and the condenser lens L3 to reach the measurement target S. The light that has passed through the condenser lens L3 is focused on the focal point of the condenser lens L3, and then reaches the measurement target S while expanding in a conical shape. Therefore, the light reaches the measurement target S as a spherical wave.

What is important here is that when the divergence angle of the spherical wave is sufficiently large with respect to the curvature of the irradiation surface, a point (a minute surface) perpendicular to the traveling direction of light exists. As described above, since there is a point perpendicular to the traveling direction of the light, the light reflected at that point travels along the same path, passes through the condenser lens L3, is partially reflected by the beam splitter B, and is partially reflected by the condenser lens L4. And reaches the CCD camera 3.

On the other hand, the laser beam from the laser light source 2 reaches the beam splitter B, and the light reflected here reaches the reference mirror M, where it is reflected and travels to the beam splitter B again. Then, the light transmitted through the beam splitter B reaches the CCD camera 3 via the condenser lens L4.

Accordingly, the light reflected by the beam splitter B and the light reflected by the reference mirror M reach the CCD camera 3 along the same path as the incident light reflected by the measurement target S. Since a phase difference occurs between the two lights according to the shape of the reflection surface of the measurement target S, interference fringes are formed. The phase distribution of the reflected light is obtained from the interference fringes. Then, the surface shape of the interference fringe formation region on the measurement target surface is calculated from the phase distribution. Various known methods such as a phase shift method can be applied as a method of calculating the phase distribution from the interference fringes and calculating the surface shape.

Next, the XYZ stage 1 is operated to change the position of the object to be measured by a known amount. Then, in this case, the surface shape of the interference fringe formation region on the measurement target surface is calculated from the interference fringes generated on the CCD camera 3 in the same manner. Further, the continuous state is calculated so that the previously obtained surface shape and the subsequently obtained surface shape are connected based on the known amount. Since the maximum value of the detectable phase difference is limited to an amount corresponding to one wavelength of the irradiation light, it is desirable to move the XYZ stage 1 by a distance such that the ranges where the interference fringes are generated overlap. However, if it is certain that the change in the surface shape remains within a half wavelength of the irradiation light, a discrete measurement may be performed in which the change is performed over a distance beyond the half wavelength. The positional relationship between adjacent measurement points can be obtained based on the distance between the centers of the interference fringes. The distance between the centers of the interference fringes can be obtained from the number of pixels between images on the monitor by preparing the following in advance. That is, a scale having a length scale is previously placed at the same position as the surface to be measured on the XYZ stage 1, an image is formed on the monitor 5 by the above-described device, and the relationship between the distance on the scale and the number of pixels is obtained. Keep it. In a normal measurement, a moving distance to an adjacent measurement point by the XYZ stage 1 is about several tens of microns to several hundreds of microns.

In this way, the three-dimensional shape of the surface to be measured is determined by repeating the movement of the known amount, the calculation of the surface shape of the interference fringe formation region, and the calculation of the continuous state of the interference fringe formation region before and after the movement. be able to. It should be noted that the device used in the present invention is not limited to the above-described device, and each component in the device can be replaced with a device having another similar function.

The use of spherical waves for measurement enables so-called on-machine measurement in which the shape of a member is measured while the member is mounted on a processing machine after or during processing of the member by cutting or the like. FIG. 2 shows a state in which the workpiece W is machined using the rotating grindstone (or cutting tool) C as a tool. The tool is a spherical tool whose working surface is constituted by a part of a spherical surface. FIG. 2 shows a case where the processing surface of the work material is non-rotationally symmetric and aspheric. The work material shown in FIG. 2 has a shape used for a scanning system lens such as an f-θ lens of a laser beam printer, a micro lens array, a diffraction grating, a free screen mirror, and the like. Processing and measurement are performed, for example, as follows.

The distance between the focal position of the spherical wave forming condensing lens (objective lens) and the work surface when the work surface is irradiated with the spherical wave in the above-described measuring apparatus is determined from the center of the tool used for processing. Match the distance to the tool surface. After cutting by the tool, the measuring device is arranged so that the objective lens is at the above-mentioned distance with respect to the cut surface by moving the tool away from the workpiece. As described above, the laser (for example, the wavelength λ
Irradiation (= 632.8 nm He-Ne laser) produces interference fringes on the CCD camera. The reference mirror M is moved by λ / 4 in the irradiation optical axis direction, and a total of four fringe images are sampled. The center of the concentric stripes obtained at this time is a point on a plane perpendicular to the irradiation optical axis, and indicates a point where the tool has contacted during machining. From the four image data, the position and the phase distribution of the center O of the concentric stripes in the measured surface are obtained by the phase shift method. The phase φ is converted into the distance d from the following equation, and the relative height (position in the optical axis direction) at the center O is obtained. λ is the wavelength of the irradiation light.

D = λ · φ / (4π) The workpiece is moved by the sampling interval, and the three-dimensional relative position of the center of the concentric stripes is obtained in the same manner as described above. This procedure is repeated while scanning a required area on the work material. Thereby, the three-dimensional shape by cutting can be measured. In this way, if the work material is machined using a spherical tool and the shape is measured while irradiating the work surface with a spherical wave at the same irradiation distance as the diameter of the spherical tool, the same as during machining at the time of measurement The movement may be given to the work material or the measuring machine. Therefore, there is an advantage that the measurement is simplified, for example, the same NC program as in the machining can be used. It should be noted that even when machining with a tool other than a spherical tool, shape measurement based on irradiation of a spherical wave can be performed. In this case, although the measurement cannot be performed by the same movement as in the processing, the above-described advantage by using the spherical wave can be obtained.

[0016]

As described above, according to the present invention, it is possible to provide a non-contact type shape measuring method having the following effects. That is, an interference fringe is formed by irradiating light to a minute region of the measurement target surface, and scanning on the measurement target surface obtains a surface shape obtained from the interference fringe and a continuous state between the minute regions,
Based on this, the three-dimensional shape of the measurement target surface can be measured. Since a spherical wave is used as irradiation light on the surface to be measured, a point (a minute surface) perpendicular to the traveling direction of light exists in the irradiation surface. Therefore, by utilizing this, precise measurement can be performed by a device having a simple structure.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus used to carry out the method of the present invention.

FIG. 2 is a perspective view showing one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 XYZ stage 2 Laser light source 3 CCD camera 4 Support device B Beam splitter L1, L2, L3 Condensing lens M Reference mirror P Filter

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F064 AA09 BB01 BB03 FF01 GG12 GG22 GG41 HH03 HH08 JJ01 2F065 AA51 BB05 BB16 CC21 CC22 FF51 FF67 GG04 JJ03 JJ26 LL04 LL10 LL12 LL21 Q12 SS13

Claims (1)

[Claims] 1. A light emitted from a light source for measurement is radiated to a surface to be measured as a spherical wave, and a light from the light source is radiated to a reference surface, and interference formed by light reflected on each surface. Obtain the phase distribution of the reflected light from the fringes, calculate the surface shape of the interference fringe formation region on the measurement target surface based on the phase distribution, slightly change the irradiation position of the spherical wave on the measurement target surface by a known amount, Similarly, from the interference fringes in the case, calculate the surface shape of the interference fringe formation region on the measurement target surface,
Further, the continuous state of the previously obtained surface shape and the subsequently obtained surface shape is calculated based on the known amount, and the movement of the known amount and the calculation of the surface shape and the continuous state of the interference fringe formation region are repeatedly performed to measure the object. A non-contact shape measurement method, characterized by determining a shape of a surface.