JPH07146125A - Straightness measuring apparatus - Google Patents

Abstract

PURPOSE:To provide a straightness measuring apparatus which eliminates the influence of the physical-property values of an object surface and which can perform a strict measurement. CONSTITUTION:Three optical sensors 4' which measure a distance up to a measuring face are arranged at equal intervals and in the same height position on a moving body 5' which can be moved freely in the horizontal direction, a horizontal groove 6 is formed in the moving body 5' so as to change the distance between the three sensors 4' and the measuring face, and piezoelectric elements 7 are arranged and installed. An arithmetic unit is installed in such a way that, in an initial state, the piezoelectric elements 7 are driven, that distance detection signals from the three sensors 4' are input, that the distance detection signals are input after that whenever the moving body 5' is moved by the interval of the sensors, that the distance between the measuring face and a reference horizontal face for the moving body is operated by a sequential multipoint method at every interval, that an operated distance is stored and that the straightness value is measured and evaluated. As a result, the straightness value can be measured and evaluated in such a way that the optical sensors 4' are not affected by the reflectance of an object face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a straightness measuring device used for straightness evaluation of a straight guide surface and straightness of a linear motion mechanism in a machine tool or a shape measuring machine.

[0002]

2. Description of the Related Art An example of a conventional straightness measuring device is shown in FIG. As shown in the drawing, a pair of left and right first guide bodies 1, a second guide body 2 guided by these both guide bodies 1, and a direction orthogonal to the first guide body 1 guided by the second guide bodies 2. A movable body 5 having a displacement sensor 4 that is movable in the (X direction) and that measures the distance (gap) to the measurement target surface L of the measured object 3 placed between the first guide bodies 1; , A moving device 5 is moved, a distance measurement signal of the displacement sensor 4 is input and sequentially stored, and an arithmetic unit (not shown) for evaluating straightness is configured. As the required measurement accuracy, the error of the scanning mechanism of the moving body 5 of the displacement sensor 4 is often in the same order as the shape accuracy (straightness) of the measurement target surface L of the DUT 3, In such a case, as shown in the drawing, two displacement sensors 4 are arranged side by side at the same height position in the traveling direction X of the moving body 5, and the sequential two-point method is applied to the arithmetic device as an algorithm.

This sequential two-point method will be described with reference to FIG. This method measures the distance between the reference horizontal plane of the moving body 5 and the target surface L (measures the target surface L by measuring the distance from the target surface L of the object to be measured 3 at intervals of two displacement sensors 4). The shape, that is, the straightness) and the deviation (scanning error of the displacement sensor 4) when the moving body 5 moves in the vertical direction are obtained each time.

Now, the progress of time is represented by i, the array of space is represented by j, the distance from the reference horizontal plane to the target surface L is X _j , and the displacement of the fixed reference plane of the displacement sensor 4 from the reference horizontal plane (of the displacement sensor 4). (Scanning error) Y _i , each displacement sensor 4 at each time
Letting the signals from S _a ^{(i )} and S _b ⁽ⁱ⁾ be respectively, there is a relationship of S _a ⁽ⁱ⁾ = X _j + Y _i S _b ⁽ⁱ⁾ = X _{j + 1} + Y _i . In the initial state, that is, S _a ⁽⁰⁾ = X ₀ + Y ₀ S _b ⁽⁰⁾ = X ₁ + Y ₀ , it is necessary to know only the amount of change after that, with Y ₀ as the base point. Therefore, if Y ₀ = 0, X ₀ and X ₁ are immediately obtained. Therefore, the next step, advancing the moving body 5 at time i = 1 in the X direction △ X ^{_{only, S a (1) = X}} 1 + Y 1 S b (1) = X 2 + Y 1 of the signal is obtained. In this _{case, X 2 = X 1 + (} S b (1) -S a (1)) Y 1 = S a (1) -X 1 = Y 0 + (S a (1) -S b (0)) Is obtained. In _{general, X j + 1 = X j} + (S b (i) -S a (i)) Y i = Y i-1 + (S a (i) -S b (i-1)) according to X _j , Y _i are sequentially obtained, X _j is sequentially stored and X _j is plotted for each ΔX to obtain the concavo-convex shape of the measurement target surface L, and the straightness is evaluated.

Then, the second guide body 2 is replaced with the first guide body 1.
And moves in the direction Y to evaluate the straightness of the next measurement target surface L.

[0006]

However, in the above straightness measuring device, when the object 3 to be measured is likely to suffer surface damage such as liquid crystal glass or a silicon wafer, the displacement sensor 4 is required. As such, a non-contact optical (light reflection type) sensor is often used.

As described above, the displacement sensor 4 is provided with an optical sensor.
If it is used, the obtained signal is the surface inverse of the target surface L.
Emissivity α_iIt can be rewritten as follows including the distribution of. S_a ⁽ⁱ⁾= Α_j(X_j+ Y_i) S_b ⁽ⁱ⁾= Α_{j + 1}(X_{j + 1}+ Y_i) Thus, the surface reflectance α is included in the distance signal from the target surface L.
_iIs multiplied as a constant of proportionality.
Surface reflectance α_iCannot be separated, so the distance X _jOnly
There was a problem that information could not be obtained.

The present invention solves the above problems,
It is an object of the present invention to provide a straightness measuring device capable of performing strict measurement by eliminating the influence of the physical property value of the target surface which is proportionally received, such as the reflectance of the measuring surface with respect to the optical sensor.

[0009]

In order to solve the above-mentioned problems, the straightness measuring device of the present invention is provided with a movable body which is movable in the horizontal direction so as to face the measurement surface of the object to be measured, and this movable body is provided. , Three non-contact type sensors for measuring the distance to the measurement surface are arranged at equal intervals in the horizontal direction,
Variation means for varying the distance between the three sensors of the moving body and the measurement surface is provided, and in the initial state, the variation means is driven to input the distance detection signals of the three sensors,
Thereafter, the distance detection signals of the three sensors are input every time the mobile unit moves between the sensors, and the distance between the measurement surface and the reference horizontal plane of the mobile unit is calculated and stored by the multipoint method at each interval. A calculation device for evaluating the straightness based on the change in the distance is provided.

[0010]

According to the above structure, the distance between the measurement surface and the reference horizontal plane of the moving body and the moving body are not affected by the physical property value of the target surface by the sequential multipoint method using the distance detection signals of the three sensors. The error (linearity) of the scanning mechanism is sequentially calculated, the uneven shape of the measurement surface is obtained, and the straightness is evaluated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the same components as those of the conventional example shown in FIG.

FIG. 1 is a perspective view of an essential part of a straightness measuring device according to an embodiment of the present invention. A horizontal groove 6 is provided in the X direction at the tip of the moving body 5 ', a piezo element 7 is fitted in the horizontal groove 6, and the lower portion of the tip of the moving body 5'is equally spaced in the X direction at the same height position. Three optical sensors 4'for measuring the distance to the target surface L are provided. By applying an alternating voltage to the piezo element 7, the initial state (i = 0) described later
A reference displacement ΔY at is generated.

In the present invention, the surface reflectance can be measured separately by using the following algorithm of the sequential multi-point system in the arithmetic unit for inputting the distance detection signals of the three optical sensors 4 '. . This will be described with reference to FIG.

When three optical sensors 4'are arranged in the traveling direction X, S _a ⁽ⁱ⁾ = α _j (X _j + Y _i ) S _b ⁽ⁱ⁾ = α _{j + 1} (X _{j + 1} + Y _i ) S _c ⁽ⁱ⁾ = α _{j + 2} (X _{j + 2} + Y _i ) ... (1) A signal is obtained. In the initial state, i 0, Y ₀ = 0
S _a ⁽⁰⁾ = α ₀ X ₀ S _b ⁽⁰⁾ = α ₁ X ₁ S _c ⁽⁰⁾ = α ₂ X ₂ (2) At this time, apply an alternating voltage to the piezo element 7. by moving the optical sensor 4 'upward △ Y only, the signals of the incremental △ S _a, is △ S _b and △ S _c was obtained.
At this time, S _a ⁽⁰⁾ + ΔS _a = α ₀ (X ₀ + ΔY) S _b ⁽⁰⁾ + ΔS _b = α ₁ (X ₁ + ΔY) S _c ⁽⁰⁾ + ΔS _c = Α ₂ (X ₂ + ΔY) (3) From this, immediately α ₀ = ΔS _a / ΔY α ₁ = ΔS _b / ΔY α ₂ = ΔS _c / ΔY (4) Substituting (4) into (2), X ₀ ,
X ₁ and X ₂ are obtained. That is, X ₀ = (S _a ⁽⁰⁾ / ΔS _a ) ΔY X ₁ = (S _b ⁽⁰⁾ / ΔS _b ) ΔY X ₂ = (S _c ⁽⁰⁾ / ΔS _c ) ΔY … (5) Next, when i is advanced by 1 step, S _a ⁽¹⁾ = α ₁ (X ₁ + Y ₁ ) S _b ⁽¹⁾ = α ₂ (X ₂ + Y ₁ ) S _c ⁽¹⁾ = α ₃ (X ₃ + Y ₁ ) (6) From this, Y ₁ = S _a ⁽¹⁾ / α ₁ -X ₁ or Y ₁ = S _b ⁽¹⁾ / α ₂ -X ₂ (7) ₁ is obtained. When i is further advanced by 1 step, S _a ⁽²⁾ = α ₂ (X ₂ + Y ₂ ) S _b ⁽²⁾ = α ₃ (X ₃ + Y ₂ ) S _c ⁽²⁾ = α ₄ ( X ₄ + Y ₂ ) (8) is obtained, and Y ₂ = S _a ⁽²⁾ / α ₂ -X ₂ (9) is obtained from the first expression of (8). Also, from the third equation of (6) and the second equation of (8), α ₃ = (S _b ⁽²⁾ −S _c ⁽¹⁾ ) / (Y ₂ −Y ₁ ) ... (10) X ₃ = S _b ⁽²⁾ / α ₃ -Y ₂ (11) is obtained. If this is generally written, S _a ⁽ⁱ⁾ = α _j (X _j + Y _i ) S _b ⁽ⁱ⁾ = α _{j + 1} (X _{j + 1} + Y _i ) S _c ^{(i) of (} ₁ ⁾ = In α _{j + 2} (X _{j + 2} + Y _i ) and i + 1, S _a ^{(i + 1)} = α _{j + 1} (X _{j + 1} + Y _{i + 1} ) S _b ^{(i + 1)} = α _{j + 2} ( X _{j + 2} + Y _{i + 1} ) S _c ^{(i + 1)} = α _{j + 3} (X _{j + 3} + Y _{i + 1} ) ... (12) Generally in (1), α _j , X _j , and α _{j + 1} , X _{j + 1} ,
Y _i is known, and from (12), Y _{i + 1} = S _a ^{(i + 1)} / α _{j + 1} −X _{j + 1} (13) The third equation of (1) and (12) From the second expression of α _{j + 2} = (S _b ^{(i + 1)} −S _c ⁽ⁱ⁾ ) / (Y _{i + 1} −Y _i ) ... (14) X _{j + 2} = S _b ^{(i + 1)} / α _{j + 2-} Y _{i + 1} (15) is obtained. From (13), (14), and (15), α _j ,
X _j and Y _i are successively obtained.

Therefore, according to this method, the distance X _j (j = 0 ... n + 1) from the reference horizontal plane to the target surface L, the reflectance distribution α _j (j = 0 ... n + 1) of the target surface L, and the sensor 4 '. The scanning locus Y _i (i = 0 ... N) of is obtained.

As described above, the distance X _j from the reference horizontal plane to the target surface L can be measured without being affected by the reflectance α _j of the target surface L which the optical sensor 4 ′ receives, and the distance X _j is sequentially stored. However, by plotting for each ΔX, the uneven shape of the target surface L can be detected, and the straightness can be measured and evaluated. At the same time, the reflectance distribution α _j of the target surface L and the scanning locus (movement shift of the moving body 5 ′) Y _i of the sensor 4 ′ can be measured.

The present invention is not limited to the dependency of the surface reflectance α _j of the optical sensor 4 ', but can be similarly applied to the case where other sensors are proportionally affected by the physical property value of the target surface L. . Further, in the present embodiment, an alternating voltage is applied to the piezo element 7 to generate the reference displacement ΔY in the initial state (i = 0), but the distance between the sensor and the target surface L is changed by some actuator. It is only necessary to be able to fluctuate up and down by ΔY.

[0018]

As described above, according to the present invention, the distance from the reference horizontal plane to the target surface and the scanning locus of the sensor (error of the moving body) are successively increased without being affected by the physical property value of the target surface. Sequential calculation can be performed by the point method, and stricter straightness measurement and evaluation can be performed.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of a straightness measuring device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a straightness measuring method in the straightness measuring device.

FIG. 3 is a schematic perspective view of a conventional straightness measuring device.

FIG. 4 is an explanatory diagram of a straightness measuring method in a conventional straightness measuring device.

[Explanation of symbols]

 1 1st guide body 2 2nd guide body 3 Measurement object 4'Optical sensor (non-contact sensor) 5'Movable body 6 Horizontal groove 7 Piezo element L Target surface

Claims (1)

[Claims] 1. A movable body that is movable in a horizontal direction is provided so as to face a measurement surface of an object to be measured, and three non-contact type sensors that measure a distance to the measurement surface are horizontally mounted on the movable body. Are arranged at equal heights in the same direction, and a changing means for changing the distance between the three sensors of the moving body and the measurement surface is provided, and in the initial state, the changing means is driven to change the distance between the three means.
The distance detection signals of the sensors of the pedestals are input, and thereafter, the distance detection signals of the three sensors are input for each movement of the sensor of the moving body, and the distance detection signals of the three sensors are sequentially input at each of the intervals by the multipoint method. A straightness measuring device comprising a calculating device for calculating and storing a distance from a reference horizontal plane and evaluating straightness based on a transition of the distance.