JP2004069380A - Apparatus for measuring coefficient of linear expansion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for measuring a coefficient of a linear expansion capable of accurately measuring and having a high operability. <P>SOLUTION: The apparatus for measuring a coefficient of a linear expansion includes a light wave interference measurement means 12 for measuring a length of an object to be measured having an already known preliminary value, and a temperature controlling means 14 for controlling a temperature of the object to a plurality of predetermined temperatures. The apparatus further includes a second and a third half mirrors 24 and 28 having an optical axis matched to the length measuring axis of the object 42, a first and second observation parts 32 and 34 for observing reference interference light and measured interference light formed by each of the half mirrors. The apparatus simultaneously observes the interference lights formed by the second and third half mirrors 24 and 28, measures the dimension of the object 42 at a predetermined temperature based on the preliminary value of the object 42 and an observed phase difference, and measures the coefficient of the linear expansion of the object 42 based on the dimensions at a plurality of different temperatures. <P>COPYRIGHT: (C)2004,JPO

Description

となる。ただし、Ｎ＝（Ｎ_４−Ｎ_３）＋（Ｎ_２−Ｎ_１）とした。
【００３３】
（式４）の（ε_２−ε_１）が第１スクリーン３２で観測される第１基準干渉縞と第１測定干渉縞の位相差であり、また、（ε_４−ε_３）が第２スクリーン３４で観測される第２基準干渉縞と第２測定干渉縞の位相差である。また、波長λは既知であり、被測定物の予備値と波長λより算出されるＮを用いて（式４）より被測定物の寸法Ｌ_Ｂが求められる。温度変更を繰り返して被測定物の寸法の測定を行ない、複数の温度での寸法から被測定物の線膨張係数を求めることができる。
【００３４】
図１に示すように、第１、２スクリーン３２、３４で形成された干渉縞をそれぞれ第１読取手段７０と第２読取手段７２によって観測することも可能である。この読取手段はＣＣＤカメラ、或いはその他の光電変換手段などにより干渉縞を読み取る。
これらの位相差は、図１のコンピュータ７４内の測定データ記憶手段７６へと送られ記憶される。さらに、その位相差から演算手段７８により上記の寸法Ｌ_Ｂが算出され、演算データ記憶手段８０に記憶される。また、コンピュータ７４と温度制御手段１４は接続され、被測定物の温度に関するデータ等の受け渡しを行なう。それらのデータは測定データ記憶手段７６に記憶される。
【００３５】
温度制御手段１４により被測定物４２の温度を変更し、上記と同様に寸法測定を行ない、その結果を演算データ記憶手段８０に記憶する。このように、異なる複数の温度での被測定物の寸法が演算データ記憶手段８０に記憶される。これらの異なる温度での寸法のデータや温度データを演算データ記憶手段８０、測定データ記憶手段７６から呼び出し、演算手段７８により所定の温度での線膨張係数を算出することができる。
【００３６】
以上の構成では、測定に単一波長のレーザ光を用いた例について説明した。しかし、本発明はこれに限定されるものではなく、もちろん複数の異なる波長を用いて測定を行なってもよい。
本発明は被測定物とベースプレートを密着させる必要がないので、密着型の光波干渉測定法を用いた場合と比較して作業が容易となり、測定時間が大幅に短縮される。また、密着のバラツキによる測定誤差がなく、高精度な測定が可能となる。
【００３７】
【発明の効果】
以上説明したように、本発明の線膨張係数測定装置は、非密着型の光波干渉測定手段と、被測定物の温度の維持及び温度の変更を行なう温度制御手段を備える。この結果、被測定物の線膨張係数の測定を高精度に行なうことが可能で、また作業性の向上および高速化が達成できる。
【図面の簡単な説明】
【図１】本発明の線膨張係数測定装置の概念図である。
【図２】可変温度槽（温度制御手段）の概略構成の説明図である。
【図３】温度コントローラの制御ブロック図である。
【符号の説明】
１０　本発明の線膨張係数測定装置
１２　光波干渉測定手段
１４　温度制御手段
１６　光照射部
１８　第１ハーフミラー（光分割部）
２４　第２ハーフミラー（第１干渉部）
２６　第１参照鏡（第１干渉部）
２８　第３ハーフミラー（第２干渉部）
３０　第２参照鏡（第２干渉部）
３２　第１スクリーン（第１観察部）
３４　第２スクリーン（第２観察部）
４２　被測定物[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for measuring a coefficient of linear expansion, and more particularly to an improvement of a mechanism for measuring a dimension thereof.
[0002]
[Prior art]
The coefficient of linear expansion α due to a change in the temperature of a substance is given by the following (Equation 1).
α = (1 / L) · (ΔL / ΔT) (Equation 1)
Here, L is a dimension at a certain reference temperature (for example, 20 ° C.) of the object to be measured, and ΔL is a change in dimension that occurs when a temperature change of ΔT is given from the reference temperature. That is, in order to obtain the coefficient of linear expansion, the dimensions of the object under measurement at different temperatures must be measured. Therefore, in order to measure the linear expansion coefficient with high accuracy, it is necessary to have an accurate dimension measurement and precise temperature control of the object to be measured.
[0003]
As a measuring method for measuring a dimension with high accuracy, a light wave interference measurement represented by an edge measuring device such as a block gauge is generally used. In this method, one end surface of a block gauge is brought into close contact (ringing) with a base plate surface, inserted into one optical path of a Michelson interferometer, and the light of the other optical path is used as reference light, and the other end surface of the block gauge and the base plate are used. The interference with the light reflected from the surface is performed, and the dimensions of the block gauge are measured from the phase difference between these interference fringes and the preliminary value of the block gauge.
[0004]
[Problems to be solved by the invention]
However, in the method in which one side of the measurement surface of the block gauge is brought into close contact with the base plate, it is necessary to make close contact between the block gauge to be measured and the base plate, and in order to perform accurate measurement, it is necessary to minimize the variation in the close contact. Not be. However, this close contact work requires skill and is very troublesome.
In addition, the uncertainty of the dimension measurement due to the variation in close contact has hindered obtaining the linear expansion coefficient with high accuracy.
An object of the present invention is to increase the accuracy of measurement, facilitate the operation, and increase the speed when measuring the coefficient of linear expansion.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a linear expansion coefficient measuring apparatus of the present invention comprises a light wave interference measuring unit for determining a dimension between opposed end faces of a device under test, and a temperature capable of controlling the device under test to a plurality of predetermined temperatures. Control means.
The light wave interference measuring means includes a light irradiating unit for irradiating coherent light having a predetermined beam diameter and a wavelength, a light dividing unit for dividing the light irradiated from the light irradiating unit into two light beams, A first interference unit and a second interference unit having an optical axis coinciding with the measurement axis of the first and second observation units, and a first observation unit and a second observation unit for observing interference fringes of the first and second interference units, respectively. It is characterized by having.
[0006]
Here, one of the two light beams split by the light splitting unit is incident on the first interference unit, a part of the incident light is a first reference light, and the rest is the first interference unit. The light is reflected in the length measurement axis direction of the object to be measured.
Further, the other light beam of the two light beams split by the light splitting unit is incident on the second interference unit, a part of which is a second reference light, and the other is a light beam of the object to be measured by the second interference unit. The light is reflected in the measurement axis direction.
[0007]
A part of the light reflected from the first interference unit in the length-measuring axis direction of the DUT is reflected at one end of the DUT, returned to the first interference unit, and superimposed on the first reference light. The first interference light is measured, and the rest passes through the side of the object to be measured and is incident on the second interference unit, and is superimposed on the second reference light to become the second reference interference light.
Similarly, the light reflected from the second interference unit in the length-measuring axis direction of the measured object is partially reflected at the other end surface of the measured object, returns to the second interference unit, and returns to the second interference unit. The second interference light is superimposed and passes through the side of the object to be measured, enters the first interference unit, and is superimposed on the first reference light to become the first reference interference light.
[0008]
Further, the first observation unit observes the first reference interference light and the first measurement interference light formed by the first interference unit as a first reference interference fringe and a first measurement interference fringe, respectively.
Similarly, the second observation unit observes the second reference interference light and the second measurement interference light formed by the second interference unit as a second reference interference fringe and a second measurement interference fringe, respectively.
The phase difference between the first reference interference fringe and the first measurement interference fringe observed as described above, the phase difference between the second reference interference fringe and the second measurement interference fringe, and the preliminary Based on the values, the dimensions of the device under test maintained at a predetermined temperature by the temperature control means are measured at a plurality of temperatures, respectively, and the coefficient of linear expansion of the device under test is determined.
[0009]
Further, the temperature control means includes an adiabatic heat retaining unit serving as a container for accommodating the object to be measured, a heating unit to heat the object to be measured, and a heating control unit to control heating by the heating unit, The heat-insulating heat-insulating section was provided with a heat-insulating layer and a window through which the measurement light was transmitted on a side surface in the measurement optical axis direction.
Furthermore, in order to keep the inside of the heat insulating and heating unit at a reduced pressure or a vacuum state, the heat insulating and heating unit has a sealed structure, and a vacuum valve for connecting a vacuum pump or the like for reducing the inside of the heat and heat insulating unit to a reduced or vacuum state. It is preferred to attach
[0010]
It is preferable that the temperature control unit includes a fine movement control unit for adjusting the position of the measured object. It is also preferable that the heating unit and the fine movement control unit are formed of a material having a small coefficient of thermal expansion.
Half mirror included in the first interference portion from said light splitting part, wherein one end of the object to be measured, the optical path length to the half mirror included in the first interference portion and L _1, the second from the light splitting unit half mirror included in the interference portion, the optical path length to the half mirror included in the first interference portion and L _2, a half mirror included in the second interference portion from said light splitting part, the other end of the object to be measured the optical path length to the half mirror included in the second interference portion and L _3, a half mirror included in the first interference portion from the light splitting unit, the optical path length to the half mirror included in the second interfering portion It is referred to as _{L 4.}
[0011]
In this case, the dimension L _B of the object to be measured is represented by Equation 2] below.
(Equation 2)
_{L B = λ / 2 {N} + (ε 4 -ε 3) + (ε 2 -ε 1)},
_{However, N = N 4 -N 3 +} N 2 -N 1,
L ₁ : λ (N ₁ + ε ₁ ),
L ₂ : λ (N ₂ + ε ₂ ),
L ₃ : λ (N ₃ + ε ₃ ),
L ₄ : λ (N ₄ + ε ₄ ),
λ: wavelength of the light,
N _{i (i} = 1~4): natural number part of the quotient when the optical path length L _i divided by the wavelength λ of the light,
ε _i (i = 1 to 4): a phase which is a fraction of a quotient when the optical path length L _i is divided by the wavelength λ of the light,
(Ε ₂ −ε ₁ ): phase difference between the first reference interference fringe and the first measurement interference fringe observed by the first observation unit,
(Ε ₄ −ε ₃ ): phase difference between the second reference interference fringe and the second measurement interference fringe observed by the second observation unit.
[0012]
Further, the linear expansion coefficient measuring device reads the phase difference between the reference interference fringe and the measured interference fringe observed by each of the observation units, and reads each phase difference of the interference fringe obtained by the reading unit. Comprising: a calculating means for obtaining a dimension between both end faces of the DUT at a predetermined temperature from a preliminary value between both end faces of the DUT, and a storage means for storing the dimension of the DUT determined by the calculation means. It is also possible. Here, the coefficient of linear expansion of the measured object is calculated from the dimensions of the measured object at different temperatures stored by the storage means.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention uses a non-contact light wave interference measurement method in which the temperature of an object to be measured is changed by temperature control means, and the linear expansion coefficient due to the temperature change is obtained from the dimensions of the object to be measured at each temperature.
Hereinafter, an embodiment of a linear expansion coefficient measuring apparatus according to the present invention will be described with reference to the drawings. In the present embodiment, an end device such as a block gauge having a rectangular cross section is assumed as the object to be measured. However, the present invention is not limited to this, and the surface accuracy and parallelism of both surfaces may be good enough to allow interferometric measurement. It can be applied to other measured objects.
[0014]
FIG. 1 is a conceptual diagram of one embodiment of the linear expansion coefficient measuring apparatus of the present invention. The linear expansion coefficient measuring device 10 of FIG. 1 includes a light wave interference measuring unit 12 and a temperature control unit 14. The device under test 42 is placed at the place where the temperature control means 14 is installed.
In addition, the light wave interference measuring means 12 includes a light irradiating section 16, a first half mirror 18 (a light dividing section) that divides the irradiated light, and a second half mirror 24 (a second half mirror 24) that is spaced apart by a predetermined distance. 1st interference part), the third half mirror 28 (second interference part), the first reference mirror 26 (first interference part), and the second reference mirror 30 (second interference part) corresponding to the second and third half mirrors 24 and 28, respectively. 2 interference section), a first screen 32 (first observation section), and a second screen 34 (second observation section). The second half mirror 24 and the third half mirror 28 are arranged such that the optical axis of the measurement light connecting them coincides with the length measurement axis of the device under test 42. The first screen 32 and the second screen 34 are provided corresponding to the second and third half mirrors 24 and 28, respectively.
[0015]
The operation of the above components will be described below. First, the temperature control means 14 has a function of changing the temperature of the device under test 42 and a function of maintaining the temperature of the device under test 42 constant. The temperature of the device under test 42 can be controlled to a plurality of predetermined temperatures by the temperature control means 14.
Next, each component of the light wave interference unit 12 will be described. The light irradiation unit 16 includes a light source 36, a collimator lens 38, a reflection mirror 40, and the like, and irradiates a laser beam having a predetermined beam diameter and wavelength. As will be described later, since the laser beam needs to be reflected at the end face of the device under test 42 and to pass through the side of the device under test, the beam diameter of the laser beam needs to have a certain size. It is. For this reason, it is more desirable that the beam diameter be larger than the cross-sectional area of the measured object.
[0016]
The first half mirror 18 splits the laser light emitted from the light irradiation unit 16 into two light beams, and each light beam enters the second half mirror 24 and the third half mirror 28. The first reference mirror 26 and the second reference mirror 30 reflect the light transmitted through the second and third half mirrors 24 and 28, respectively, and use the light as reference light to interfere with the measurement light at the second and third half mirrors 24 and 28. Let it. As described above, the pair of the first reference mirror 26 and the second half mirror 24 and the pair of the second reference mirror 30 and the third half mirror 28 function as an interference unit that causes the measurement light and the reference light to interfere with each other. Further, the first half mirror 18, the second half mirror 24, and the third half mirror 28 constitute an annular interferometer. The first and second screens 32 and 34 observe the interference light formed by the second and third half mirrors 24 and 28 as interference fringes, respectively.
[0017]
Using the optical interference measuring means 12 having the above-described configuration, the dimensions of the DUT 42 maintained at a constant temperature by the temperature control means 14 are measured. Further, the temperature of the DUT 42 is changed by the temperature control means 14 and the measurement at that temperature is repeated to obtain the dimensions of the DUT 42 at a plurality of different temperatures. Is calculated.
[0018]
Next, the optical path of the laser light in the light wave interference measuring means 12 will be described in order. The laser light emitted from the light irradiating unit 16 is split into two light beams by the first half mirror 18 and travels to the second half mirror 24 and the third half mirror 28, respectively. The light incident on the second half mirror 24 is split into light reflected in the length-measuring axis direction and light transmitted through the second half mirror 24 and traveling toward the first reference mirror 26. The light directed to the first reference mirror 26 is reflected by the first reference mirror 26, returns to the second half mirror 24, and becomes the first reference light. A part of the light traveling in the length measurement axis direction is reflected on the left end face 42a of the measured object 42 in the figure and returns to the second half mirror 24, and the rest passes through the measured object 42 and is located on the third half mirror. 28.
[0019]
Similarly, of the two light beams split by the first half mirror 18, the light incident on the third half mirror 28 is the light reflected in the length measurement axis direction and the light transmitted through the third half mirror 28 and the second reference mirror 30. The light is split into The light directed to the second reference mirror 30 is reflected by the second reference mirror 30, returns to the third half mirror 28, and becomes the second reference light. A part of the light traveling in the length measurement axis direction is reflected by the right end surface 42b of the measured object 42 in the drawing and returns to the third half mirror 28, and the rest passes by the measured object 42 and is returned to the second half mirror. 24.
In the second half mirror 24, the light that has traveled along the optical path described above interferes with the first reference light coming from the first reference mirror 26 and the light passing by the side of the object 42 to be measured, and the first reference light The first reference light becomes the interference light, and the light reflected by the left end surface 42a of the device under test 42 interferes with the first reference light to become the first measurement interference light. These interference lights are observed as interference fringes on the first screen 32, and the phase difference between the first reference interference fringe and the first measurement interference fringe is read.
[0020]
Similarly, in the third half mirror 28, the light passing by the side of the DUT 42 and the second reference light from the second reference mirror 30 interfere with each other to become second reference interference light, and the DUT 42 The light reflected by the right end face 42b of the light beam and the second reference light from the second reference mirror 30 interfere with each other to become the second measurement interference light. These interference lights are observed as a second reference interference fringe and a second measurement interference fringe on the second screen 34, respectively, and the phase difference between the reference interference fringe and the measurement interference fringe is read.
As described above, the phase difference between the first reference interference fringe and the second measurement interference fringe simultaneously observed on the first screen 32 and the second screen 34, and the position of the second reference interference fringe and the second measurement interference fringe. and phase difference, based on the preliminary value of the measured object 42, the dimensions L _B of the object to be measured is measured. The relationship between the phase difference and the dimensions of the device under test will be described later.
[0021]
The coefficient of linear expansion due to a change in the temperature of the device under test can be determined, for example, as follows. First keeping the temperature control means 14 to the reference temperature T with the measured object 42, the size L _B of the object 42 at that temperature is measured by the optical interference measuring means as described above. Next, the temperature of the DUT 42 is changed from the reference temperature T by the temperature control means 14 and is maintained at the temperature T ′ (= T + ΔT). The temperature T to 'similar dimensions of the workpiece 42 also in measurement as described above poured, the length L _B' and. By substituting the change amount of the temperature variation ΔT and dimensions (Equation _{1) ΔL B (= L B} '-L B), the linear expansion coefficient of the DUT 42 at a reference temperature T is determined.
The above is the basic configuration of the linear expansion coefficient measuring device of the present invention. Since the light wave interference measurement means is configured as described above, it is not necessary to bring the device under test into close contact with the base plate. Therefore, the operation becomes easy, and a measurement error due to a variation in ringing is removed, so that highly accurate measurement can be performed.
[0022]
Since the first reference interference fringe and the first measurement interference fringe are simultaneously observed on the first screen 32 and the second reference interference fringe and the second measurement interference fringe are simultaneously observed on the second screen 34, the measurement time Is shortened.
Further, in the present invention, an annular interferometer is constituted by the first half mirror 18, the second half mirror 24, and the third half mirror 28, but the second half mirror 24 and the third half mirror 28 are spatially separated. Therefore, there is no possibility that the clockwise light and the counterclockwise light interfere with each other, and an appropriate measurement can be performed.
[0023]
FIG. 2 is a diagram showing one embodiment of the temperature control means in the present invention. The temperature control means shown in the figure is configured as a box-shaped variable temperature tank 44 in which an object 42 to be measured is accommodated. The wall (insulated heat retaining section) 46 of the variable temperature tank 44 is a heat insulating layer formed of a heat insulating material or a member having a heat insulating structure, and the walls 46 on both sides in the measurement optical axis direction transmit light. It is provided with a window 48 made of glass or the like. This window 48 is at least larger than the beam diameter of the laser beam used. The device under test 42 is installed on a heat equalizing plate 52 (heating unit), and the heating control unit includes a heater 50, a temperature controller 56, a power supply 57, and the like. The heater 50 (heating control unit) heats the soaking plate 52 (heating unit), and the temperature sensor 54 and the heater 50 attached to the measured object 42 are connected to a temperature controller 56 (heating control unit).
[0024]
As described above, since the variable temperature tank 44 (temperature control means) is a heat insulating layer, the mutual influence between the temperature environment inside the variable temperature layer 44 and the temperature environment outside the variable temperature layer 44 is reduced. For this reason, the optical devices such as the light wave interference unit provided outside the variable temperature layer 44 are hardly affected by the temperature, and the measurement at a high temperature becomes possible. In addition, since the temperature environment inside the variable temperature layer 44 is stabilized, the temperature of the device under test 42 can be easily kept constant.
[0025]
Further, the temperature sensor 54 attached to the measured object 42 senses the temperature of the measured object 42 and transmits the information to the temperature controller 56, so that the temperature controller 56 can appropriately control the heating by the heater 50. FIG. 3 is a control block diagram of the temperature controller 56. The temperature information sensed by the temperature sensor 54 attached to the device under test 42 is sent to a comparator 58, where it is compared with a set temperature. The result is sent to the characteristic compensating element 60, and the operation amount of the heater 50 is calculated according to the thermal characteristics of the heater 50, the heat equalizing plate 52, and the device under test 42, and the operation amount is sent to the amplifier 62 to Heat 50.
[0026]
As described above, since the heating amount is adjusted according to the temperature change of the device under test, the temperature of the device under test can be kept stable, and the device under test can be set to various temperatures. As a result, precise temperature control becomes possible, and the object to be measured 42 can be uniformly heated because the temperature is heated via the heat equalizing plate 52.
Further, the variable temperature bath 44 may have a closed structure. At this time, the variable temperature tank 44 is provided with a vacuum valve 64 to which a vacuum pump or the like is attached so as to reduce the pressure or vacuum inside. By maintaining the inside of the variable temperature layer 44 in a reduced pressure or vacuum state, the fluctuation of the measurement light due to the fluctuation of the density of the air is reduced, and more accurate measurement can be performed. Further, the heat insulating effect of the variable temperature layer 44 is further enhanced.
[0027]
It is also preferable to provide a fine movement control unit 66 for performing optical alignment on the heat equalizing plate 52 serving as a mounting table for the sample 42. The fine movement control unit 66 shown in FIG. 2 is provided with a support member 68, and the heat equalizing plate 52 is installed on the support member 68.
[0028]
By adjusting the adjustment knob 65 of the fine movement control unit 66, it is possible to appropriately set the angle of the object 42 with respect to the measurement optical axis, the position in the height direction, and the like. Further, in order to prevent the position of the DUT 42 from changing in the height direction with respect to the measurement optical axis due to a temperature change, the support member 68 between the heat equalizing plate 52 and the fine movement control unit 66 has a small thermal expansion coefficient. It is desirable to be made of a material. In addition to the support member 68, it is preferable to use a material having a small coefficient of thermal expansion for members inside the variable temperature tank 44, such as the heat equalizing plate 52 and the fine movement control unit 66. By using a member made of a material having a small coefficient of thermal expansion, the deformation of the member supporting the DUT 42 due to a temperature change can be suppressed to a small degree. Increase.
[0029]
The position control of the DUT 42 by the fine movement control unit 66 can be set from outside the variable temperature bath 44. For this reason, the fine movement control drive section 67 provided outside the variable temperature chamber 44 is connected to the adjustment knob 65 of the fine movement control section 66, and electrically controls a motor or the like that drives the adjustment knob 65, and The position of 42 is set. Further, the adjustment knob 65 of the fine movement control unit 66 may be provided outside the variable temperature bath 44 so that the adjustment can be manually performed from the outside.
[0030]
Next, the relationship between the phase difference read by the light wave interference measuring means and the dimensions of the device under test will be described with reference to FIG.
From the first half mirror 18 to the second half mirror 24, further toward the left end in the drawing surface 42a of the object 42, where the optical path length of the optical path reflected light is returned to the second half mirror 24 again as L ₁ . Further, an optical path length from the first half mirror 18 to the third half mirror 28, which is reflected there, passes by the measured object 42, and enters the second half mirror 24 is defined as L ₂ . Similarly, the optical path length _{L 3} is the first half mirror 18, the third half mirror 28, a right end face 42b, the optical path length proceeding to the third half mirror 28 of the object 42. Optical path length L ₄ are, directed from the first half mirror 18 to the second half mirror 24, where it is reflected to the optical path length to be incident to the third half mirror 28 passes through the side of the object 42.
[0031]
The optical path length between the first half mirror 18 and the second half mirror 24 is a, the optical path length between the second half mirror 24 and the left end surface 42a of the device under test 42 in the drawing is b, and the first half mirror is b. The optical path length between the mirror 18 and the third half mirror 28 is c, and the optical path length between the third half mirror 28 and the right end surface 42b of the device under test 42 in the drawing is d.
The above optical path length _L i (i = _1~4) of the optical path length a, b, c, expressed using a _{d L 1 = a + 2b,} L 2 = b + c + d + L B,
_{L 3 = c + 2d, L} 4 = a + b + d + L B,
It becomes. A From these equations, b, c, Erasing the d dimension L _B of the workpiece 42 is represented by the following equation (2).
_{L B = 1/2 {(} L 4 -L 3) + (L 2 -L 1)} ... ( Equation 2)
[0032]
The above optical path lengths L ₁ , L ₂ , L ₃ , and L ₄ are expressed as follows using the wavelength λ of the laser light used for measurement.
L _i = λ (N _i + ε _i ) (i = 1 to 4) (Equation 3)
Here, N _i is an integer portion of the quotient obtained by dividing the optical path length L _i at the wavelength lambda, epsilon _i is the fractional part of the quotient (phase). Substituting (Equation 3) into (Equation 2)

It becomes. _However, was _{N = (N 4 -N 3)} + (N 2 -N 1).
[0033]
(Ε ₂ −ε ₁ ) in (Equation 4) is the phase difference between the first reference interference fringe and the first measurement interference fringe observed on the first screen 32, and (ε ₄ −ε ₃ ) is the second difference. This is the phase difference between the second reference interference fringe and the second measurement interference fringe observed on the screen 34. The wavelength λ is known, the dimension L _B of the object to be measured than with N calculated from the pre-value and the wavelength λ of the DUT (Equation 4) is obtained. The dimensions of the measured object are measured by repeating the temperature change, and the linear expansion coefficient of the measured object can be obtained from the dimensions at a plurality of temperatures.
[0034]
As shown in FIG. 1, the interference fringes formed by the first and second screens 32 and 34 can be observed by the first reading unit 70 and the second reading unit 72, respectively. This reading means reads the interference fringes using a CCD camera or other photoelectric conversion means.
These phase differences are sent to and stored in the measurement data storage means 76 in the computer 74 of FIG. Further, the by calculation means 78 from the phase difference above dimensions L _B is calculated and stored in operation data storage section 80. Further, the computer 74 and the temperature control means 14 are connected and exchange data relating to the temperature of the device under test. Those data are stored in the measurement data storage means 76.
[0035]
The temperature of the DUT 42 is changed by the temperature control means 14, the dimension is measured in the same manner as described above, and the result is stored in the arithmetic data storage means 80. As described above, the dimensions of the device under test at a plurality of different temperatures are stored in the arithmetic data storage unit 80. The dimensional data and temperature data at these different temperatures are called from the operation data storage unit 80 and the measurement data storage unit 76, and the operation unit 78 can calculate the linear expansion coefficient at a predetermined temperature.
[0036]
In the above configuration, an example in which laser light of a single wavelength is used for measurement has been described. However, the present invention is not limited to this, and the measurement may of course be performed using a plurality of different wavelengths.
In the present invention, since there is no need to bring the object to be measured into close contact with the base plate, the work becomes easier and the measurement time is greatly reduced as compared with the case where the contact type light wave interference measurement method is used. In addition, there is no measurement error due to variations in close contact, and highly accurate measurement can be performed.
[0037]
【The invention's effect】
As described above, the linear expansion coefficient measuring apparatus of the present invention includes the non-contact type optical wave interference measuring means and the temperature control means for maintaining and changing the temperature of the device under test. As a result, the coefficient of linear expansion of the object to be measured can be measured with high accuracy, and workability can be improved and the speed can be increased.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a linear expansion coefficient measuring device of the present invention.
FIG. 2 is an explanatory diagram of a schematic configuration of a variable temperature bath (temperature control means).
FIG. 3 is a control block diagram of a temperature controller.
[Explanation of symbols]
10 Linear expansion coefficient measuring apparatus 12 of the present invention 12 Light wave interference measuring means 14 Temperature control means 16 Light irradiation unit 18 First half mirror (light splitting unit)
24 Second half mirror (first interference unit)
26 First Reference Mirror (First Interference Unit)
28 Third half mirror (second interference section)
30 Second reference mirror (second interference unit)
32 1st screen (1st observation part)
34 second screen (second observation unit)
42 DUT

Claims (7)

In a linear expansion coefficient measuring apparatus comprising: a light wave interference measuring unit for determining a dimension between opposed end faces of the device under test, and a temperature control device capable of controlling the device under test to a plurality of predetermined temperatures,
The light wave interference measuring means,
A light irradiating unit that irradiates light having a predetermined beam diameter and wavelength,
A light splitting unit that splits the light emitted from the light emitting unit into two light beams,
A first interference unit and a second interference unit having an optical axis coinciding with the length measurement axis of the device under test;
A first observation unit and a second observation unit for observing interference fringes of the first interference unit and the second interference unit, respectively;
With
One of the two light beams split by the light splitting unit is incident on the first interference unit, and a part of the light beam becomes the first reference light, and the rest of the light beam is measured by the first interference unit. Reflected in the measurement axis direction,
The other light beam of the two light beams split by the light splitting unit is incident on the second interference unit, and a part of the light beam becomes a second reference light, and the rest of the two light beams is generated by the second interference unit. Reflected in the measurement axis direction,
Part of the light reflected from the first interference unit in the length-measuring axis direction of the object to be measured is reflected at one end of the object to be measured, returns to the first interference unit, and is superimposed on the first reference light. 1 measurement interference light, the remainder passes through the side of the object to be measured, enters the second interference unit, is superimposed on the second reference light, and becomes the second reference interference light,
Part of the light reflected from the second interference section in the length-measuring axis direction of the object to be measured is reflected at the other end surface of the object to be measured, returns to the second interference section, and is superimposed on the second reference light. It becomes the second measurement interference light, and the rest passes through the side of the object to be measured and enters the first interference unit, is superimposed on the first reference light, and becomes the first reference interference light,
The first observation unit observes the first reference interference light and the first measurement interference light formed by the first interference unit as a first reference interference fringe and a first measurement interference fringe, respectively;
The second observation unit observes the second reference interference light and the second measurement interference light formed by the second interference unit as a second reference interference fringe and a second measurement interference fringe, respectively.
The temperature control means based on a phase difference between the first reference interference fringe and the first measurement interference fringe, a phase difference between the second reference interference fringe and the second measurement interference fringe, and a preliminary value of the device under test; A linear expansion coefficient measuring apparatus, wherein dimensions of the object to be measured maintained at a predetermined temperature are measured at a plurality of temperatures. The linear expansion coefficient measuring device according to claim 1,
The temperature control means,
Adiabatic heat retaining unit serving as a container for accommodating the object to be measured,
A heating unit for heating the object to be measured,
A heating control unit that controls heating by the heating unit,
The linear thermal expansion coefficient measuring device, wherein the thermal insulation section includes a thermal insulation layer and a window through which the measurement light passes on a side surface in a measurement optical axis direction. The linear expansion coefficient measuring device according to claim 2,
A linear expansion coefficient measuring device, characterized in that the heat insulating and heat retaining section has a closed structure and a vacuum valve in order to keep the inside of the heat insulating and heat retaining section under reduced pressure or vacuum. In the linear expansion coefficient measuring device according to any one of claims 2 to 3,
A linear expansion coefficient measuring device, wherein the temperature control means includes a fine movement control unit for adjusting a position of an object to be measured. The linear expansion coefficient measuring device according to claim 4,
A linear expansion coefficient measuring device, wherein members constituting the heating unit and the fine movement control unit are formed of a material having a small thermal expansion coefficient. The linear expansion coefficient measuring device according to any one of claims 1 to 5,
Half mirror included in the first interference portion from said light splitting part, one end of the object to be measured, the optical path length to the half mirror included in the first interference portion and L _1,
Half mirror included in the second interference portion from the light dividing unit, an optical path length to the half mirror included in the first interference portion and L _2,
Half mirror included in the second interference portion from said light splitting part, the other end of the object to be measured, the optical path length to the half mirror included in the second interference portion and L _3,
Half mirror included in the first interference portion from the light dividing unit, an optical path length to the half mirror included in the second interference portion and L _4,
The linear expansion coefficient measurement apparatus, characterized in that the dimension L _B of the object to be measured is expressed by Equation 1] below.

_{However, N = N 4 -N 3 +} N 2 -N 1,
L ₁ : λ (N ₁ + ε ₁ ),
L ₂ : λ (N ₂ + ε ₂ ),
L ₃ : λ (N ₃ + ε ₃ ),
L ₄ : λ (N ₄ + ε ₄ ),
λ: wavelength of the light,
N _{i (i} = 1~4): natural number part of the quotient when the optical path length L _i divided by the wavelength λ of the light,
ε _i (i = 1 to 4): a phase which is a fraction of a quotient when the optical path length L _i is divided by the wavelength λ of the light,
(Ε ₂ −ε ₁ ): phase difference between the first reference interference fringe and the first measurement interference fringe observed by the first observation unit,
(Ε ₄ −ε ₃ ): phase difference between the second reference interference fringe and the second measurement interference fringe observed by the second observation unit. In the linear expansion coefficient measuring device according to any one of claims 1 to 6,
Reading means for reading a phase difference between a reference interference fringe and a measurement interference fringe observed by the first observation unit and the second observation unit;
Calculating means for determining a dimension between both end faces of the DUT at a predetermined temperature from each phase difference of the interference fringes obtained by the reading means and a preliminary value between both end faces of the DUT,
Storage means for storing the dimensions of the measured object obtained by the calculation means,
A linear expansion coefficient measuring apparatus characterized in that a linear expansion coefficient of a measured object is obtained from dimensions of the measured object at a plurality of different temperatures stored in the storage means.

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