JPH0666527A - Three-dimensional measurement method - Google Patents

Abstract

PURPOSE:To make a method for measurement highly precise and to make a range of measurement wide by a method wherein a slippage of a period of a result of measurement by a measuring means of which the period of a lattice pattern is small is corrected by a result of measurement by a measuring means of which the period is large. CONSTITUTION:A combination of an open pattern 7 with a close pattern 8 of a liquid crystal shutter is made to be of 2 open patterns and two close patterns, for instance. An offset is given to the focus of projection of a measurement reference surface 1 by moving an axial stage 4, patterns of which the distribution of lightness is sinusoidal are projected 3, and the height of an object surface is measured 6 with these measures set as a condition A. Next, the combination of the liquid crystal shutter is made to be of 8 open patterns with 8 close patterns, the lattice patterns of which the period is large are projected 3 by moving the stage 4, and the height of the object surface is measured 3 with these measures set as a condition B. Although the precision of this measurement is lower than that under the condition A, the period of the lattice patterns is four times as large as that under the condition A, the allowance of displacement of the height of the object is four times as wide as the latter and thus accurate correction of the period can be executed. Although the result of measurement under the condition A is highly precise, a measuring point at which the correction of the period fails exists, and therefore the correction is executed by using the result of measurement under the condition B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional measuring method, and more particularly to a grid pattern projection method using a stripe operation.

[0002]

2. Description of the Related Art As one of the methods for measuring the height displacement of an object and a three-dimensional shape in a non-contact manner, a grid pattern projection method using a stripe operation has been conventionally considered.

In this method, a grid pattern (hereinafter referred to as a grid pattern) whose illuminance distribution is a sine wave is projected on an object, and this is measured at a height measurement point when a four-step stripe operation is performed for each ¼ cycle. The brightness value is measured from an angle different from the projection method, and the phase value of the projected grid pattern is calculated from each brightness value.
Since the phase of the grating pattern is modulated according to the height and displacement of the measurement point, the modulation amount of this phase is calculated and substituted into the geometrical relational expression of the optical device to measure the height displacement amount of the object. This is a method for obtaining a three-dimensional shape.

Here, since the phase value takes a value from 1π to 10π, when the phase modulation amount of the grating pattern due to the height displacement of the object exceeds π, a period shift occurs and the phase modulation amount is accurate. Therefore, when the absolute value of the phase difference between the adjacent measurement points changes by 80% or more of 2π, the method of performing the correction by determining that the modulation amount of the grating pattern has a period shift is performed. There is.

An example of a method of measuring the height displacement amount of an object at an arbitrary measurement point x in the geometrical relationship diagram of FIG. 3 will be described below.

In the grid pattern projection method using the stripe operation,
The phase φ of the projected grating pattern can be calculated by φ = arc tan ((I3-I1) / (I0-I2)) (Equation 1). At this time, I0, I1, I2, and I3 respectively have the phases of the projection grating pattern of 0, π / 2, π, and 3π / 2.
It is the brightness value of the image when it is shifted by only.

To shift the grid pattern, a plurality of liquid crystal shutters as shown in FIG. 4 are combined to generate an open / closed pattern, and the combination is moved to perform the shift. Further, the period of the lattice pattern can be changed by changing the number of combinations of liquid crystal shutters. The period of the grid pattern at the time of projection by the combination at this time is T.

First, the phase amount Φb of the projected grid pattern on the calculation reference plane is obtained in advance using Equation 1 for all measurement points on the X coordinate.

The phase modulation amount of the grating pattern at the measuring point x by the measuring object can be calculated by calculating the phase value Φx of the grating pattern at the measuring point x by the equation 1, ΔΦx = Фx−Фbx. Equation 2) and the amount of deformation of the lattice pattern due to this is Δx = (T / 2π) × ΔФx (Equation 3), and the height displacement at the point x of the object is Z = Δx × tan α・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (Equation 4) can be used to obtain the value.

As described above, the height of the object at any measurement point can be measured.

[0011]

According to the conventional method, it is assumed that the difference Δφxx ′ in the amount of phase modulation between adjacent measurement points x and x ′ in FIG. 5 changes by 41% of π in the + direction, for example. At this time, the phase value Δφx at x is 60, which is 10π.
%, The phase value Δφx ′ at x ′ exceeds + π, resulting in a negative phase value. At this time, the difference Δφx in the modulation amount of the phase measured at the adjacent measurement points x and x ′
x'is 79% of 2π in one direction, and in the conventional technology,
Since it is less than 80% of 2π, no period correction is performed, and although the height displacement direction of the object is the positive direction, the measured value is measured as the negative height displacement. Therefore, when the absolute value of the phase difference between adjacent measurement points changes by 80% or more of 2π in the conventional method, it is determined that the period exceeds one period of the lattice pattern and the correction is performed. When the absolute value of exceeds 20% of 2π, there is a problem that the measurement is not performed correctly. Also, the value of 80% can theoretically change to 50%, but even in this case, the absolute value of the phase difference between the adjacent measurement points can be corrected only up to 50% of 2π, and therefore the measurable step difference of the object can be obtained. There was a problem that was narrow.

Further, in order to widen the measurable step, there is a problem that the period of the lattice pattern cannot be changed because the measurement accuracy is lowered if the period of the lattice pattern is increased.

An object of the present invention is to solve the above problems and to improve the accuracy of the three-dimensional measuring method and widen the measuring range in the three-dimensional measuring method by the grid pattern projection method using the stripe operation.

[0014]

[Means for Solving the Problem] In an object height and three-dimensional measuring method by a grid pattern projection method using a stripe operation, two measuring means having different grid pattern periods are used.
It is characterized in that the period deviation of the result measured by the measuring unit having a small period is corrected by using the result measured by the measuring unit having a large period.

[0015]

By using two measuring means having different grating pattern periods, the phase modulation amount of the grating pattern can be accurately determined even when the height and displacement of the object to be measured are large. A wide range of possible and highly accurate three-dimensional shape and height can be measured.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a flow chart of a measuring method according to the present invention. FIG. 2 shows the configuration of a measuring device for carrying out the present invention. A method of correcting the period of the lattice pattern and measuring the height over a wide range, which is a feature of the present invention, will be described.

The combination of the liquid crystal shutters shown in FIG. 4 is, for example, two open / two closed to generate an open / close pattern. At this time, the stage 4 is moved and an offset is applied to the projection focus to project a sine wave pattern of lightness distribution.

With this projection condition as condition A, the height of the object plane is measured using the grid pattern projection method using stripe operation under this condition, and the measurement result is stored. Since the period of the grid pattern is small, this measurement result provides high measurement accuracy, but the period correction may fail if the height displacement of the object is large at the adjacent measurement points. At this time, the allowable amount of height displacement of the object at the adjacent measurement points is within a maximum of π in terms of the amount of phase modulation. Therefore, using Equations 3 and 4, the allowable height of the object is Zmax = (T / 2π) × π × tanα (Equation 5) Therefore, Zmax = T / 2 · tanα (Equation 6) Since the period of the lattice pattern is T, the height of the object and the allowable amount of displacement are small when T is small.

Next, a combination of liquid crystal shutters, for example, 8
Fully open / 8 closed, the stage 4 is moved to generate a sinusoidal pattern with a large brightness distribution.

With this projection condition as condition B, the height of the object plane is similarly measured. This measurement result shows that the measurement accuracy is condition A.
Although it is lower than the measurement result of, the period of the lattice pattern is wide, and T of Expression 6 is four times as large as that of the condition A.
The allowable amount of height displacement of the object is as wide as four times, and accurate period correction can be performed, so that accurate measurement can be performed within the range of measurement accuracy. The number of combinations at this time is 8 open / 8 closed in the example, but may be set according to the height displacement amount of the object.

Since the measurement result of the condition A includes measurement points at which the cycle correction has failed, the measurement result is corrected by the following method using the measurement result of the condition B measured next.

The height displacement of the object at the measurement point is extracted from the measurement result of condition B and compared with the result of measurement under condition A.
At this time, the difference between condition B and condition A is ΔZba, and ΔZb
If a is larger than Zmax under the condition A, the measurement result under the condition A has a cycle shift corresponding to the difference from the condition B, and therefore the frequency k which is erroneously determined is calculated by the formula 7.

K = ΔZba / (Zmax × 2) (Equation 7) At this time, since the frequency k is an integer value and the fraction is a measurement error, it is discarded. The measurement result za under the condition A is corrected by the equation 8 using k, and the final height Z of the object is obtained.

Z = za + k × Zmax (Equation 8) The height of the object and the three-dimensional shape can be accurately measured by the above method. In the example, the arrangement of the optical system is shown as a configuration in which it is projected obliquely to the measurement reference plane 1 and is imaged in the vertical direction, but the configuration is not limited to this example and another configuration may be used.

The projection focus position was moved by moving the position of the projection device to the means for generating a grid pattern having a sine-shaped lightness distribution, but the projection focus was changed by using an optical system such as a lens in the projection device. You may move.

The two types of projection means having different periods of the grid pattern are constructed by using the same projection device, but the projection means having the long cycle of the grid pattern is projected from a different angle from the projection means having the short cycle. It may be configured by one projection device. In addition, although an example of using a liquid crystal shutter as the actual lattice of the lattice pattern has been described, if an accurate lattice pattern can be generated and shifted, an interference fringe or a glass plate having a lattice-like pattern formed of a metal film or the like is used. Is also good.

[0027]

As described above, according to the present invention, in the grid pattern projection method using the stripe operation, it is possible to measure a three-dimensional shape with a wide measurement range and high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a measurement flowchart of the present invention.

FIG. 2 is a diagram showing a configuration of a measuring device according to an embodiment of the present invention.

FIG. 3 is a diagram showing a geometrical relationship of an optical system according to an example of the present invention.

FIG. 4 is a diagram showing an example of a liquid crystal shutter.

FIG. 5 is a diagram for explaining problems in the conventional art.

[Explanation of symbols]

 1 Measurement Reference Surface 2 Imaging Camera 3 Lattice Pattern Projector Using Liquid Crystal Shutter 4 Axis Stage 5 Image Memory 6 Measurement Control Device

Front page continuation (72) Inventor Kengo Nishigaki 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (1)

[Claims] 1. A height of an object and a three-dimensional measuring method by a grid pattern projection method using a stripe operation, wherein two measuring means having different grid pattern cycles are used and the cycle of the result measured by the measuring means having a small cycle. A three-dimensional measuring method with high accuracy and a wide measuring range, characterized in that the deviation is corrected by using a result measured by a measuring means having a large cycle.