【発明の詳細な説明】（産業上の利用分野）本発明は物体までの絶対距離を測定するアブソリュート
測長方法およびアブソリュート測長器に関し、特に、Ｆ
Ｍヘテロダイン測長法を使用したアブソリュー；・測長
方法ならびに、アブソリュート測長器に関する。Detailed Description of the Invention (Industrial Application Field) The present invention relates to an absolute length measuring method and an absolute length measuring device for measuring the absolute distance to an object, and particularly relates to an absolute length measuring device for measuring an absolute distance to an object.
Absolute using M-heterodyne length measurement method: -Relates to a length measurement method and an absolute length measurement device.
（従来の技術）近年、サブナノメートルの精度を要求される電子部品や
製造装置の要求か高まり、この産業界の要請に応しるべ
く、距離計測や形状計測に用いられる干渉計の分野で、
高精度な干渉縞計測技術の研究開発が活発化している。(Prior art) In recent years, the demand for electronic components and manufacturing equipment that requires sub-nanometer precision has increased, and in order to meet this industrial demand, in the field of interferometers used for distance measurement and shape measurement,
Research and development of high-precision interference fringe measurement technology is gaining momentum.
現在実用化されている、レーザ変位計に代表されるイン
クリメンタル式の測長器（すなわち、干渉縞の数を積算
する方式の測長器）の構成の一例を第９図に示す。FIG. 9 shows an example of the configuration of an incremental length measuring device (that is, a length measuring device that integrates the number of interference fringes), which is currently in practical use and is typified by a laser displacement meter.
このレーザ変位計は、レーザ光源４０からレーザー光を
出射し、被測定対象物体４３に変位し６を与え、この光
路差に起因する干渉縞をフォトダイオード４４で検出し
、その数（Ｍ）を計数し、演算回路４５により所定の演
算を行って、相対的に距離り、を検出するものである。This laser displacement meter emits a laser beam from a laser light source 40 to give a displacement of 6 to an object to be measured 43, detects interference fringes caused by this optical path difference with a photodiode 44, and calculates the number (M) of the interference fringes. The calculation circuit 45 performs a predetermined calculation to detect the relative distance.
また、絶対距離を測定する測長法として、ＦＭヘテロダ
イン計測法があり、最近、光源として半導体レーザを使
用し、注入電流を変化させることによりレーザ光をＦＭ
変調しく中心波長８３０ｎ■）、ヘテロダイン検波によ
り得られたビート信号の位相偏位を測定することにより
、粗面散乱体に対して約５００１の絶対距離を約５０μ
ｍの精度で測定でき、かつ相対距離を約１０ｎ■の高精
度で測定可能な測長器についての報告がなされている（
ｖＯＦＳ４−８［半導体レーザによる距離の高分解能
ＦＭヘテロダイン測定法」、小林、日中、伊藤、大高、
福井大学工学部 Ｊａｎｕａｒｙ １２−１！ｌ、 １
９８７． Ｊａｐａｎ ５ｏｃｉｅｔｙ ｏｒ Ａｐｐ
ｌｉｅｄ ｐｈｙｓｉｃｓ）。In addition, there is the FM heterodyne measurement method as a length measurement method for measuring absolute distance.
By measuring the phase deviation of the beat signal obtained by modulating the center wavelength of 830n) and heterodyne detection, the absolute distance of about 5001 to the rough scatterer can be calculated by about 50μ.
There has been a report on a length measuring device that can measure with an accuracy of m and a relative distance with a high accuracy of about 10 n.
vOFS4-8 [High-resolution FM heterodyne measurement method of distance using semiconductor laser], Kobayashi, Naka, Ito, Otaka,
Fukui University Faculty of Engineering January 12-1! l, 1
987. Japan 5ociety or App
led physics).
（発明が解決しようとする課題）上述した従来の技術のうち、レーザ変位計等のインクリ
メンタル式のものは、変位を与えなければ距離が測定で
きず、高精度のレール等が必要となる。また、第１０図
のように物体の形状測定等において、例えば、主面アか
ら主面イへと測定物を移動させた場合には、段差の部分
において信号が瞬時的に失われ、それだけで測定が不能
となってしまう。光路が遮られて信号を失った場合も同
様である。(Problems to be Solved by the Invention) Among the conventional techniques described above, incremental type ones such as a laser displacement meter cannot measure distance unless displacement is applied, and a highly accurate rail or the like is required. In addition, when measuring the shape of an object as shown in Figure 10, for example, when moving the object to be measured from main surface A to main surface B, the signal is momentarily lost at the step part, which causes Measurement becomes impossible. The same applies when the optical path is blocked and the signal is lost.
また、従来のＦＭヘテロダイン測長器では、第１１図の
上側の図に示すように、相対距離はレーザ光の波長レベ
ル（ナノメータオーダー）の測定が可能であるが、絶対
距離については５０μｍ程度が限界であり、相対距離の
測定と比較して精度がかなり低い。Furthermore, with the conventional FM heterodyne length measuring instrument, as shown in the upper part of Figure 11, relative distances can be measured at the wavelength level of laser light (nanometer order), but absolute distances can be measured at about 50 μm. It is limited and has much lower accuracy compared to relative distance measurements.
本発明はこのような問題点に鑑みてなされたものであり
、その目的は、アブソリュート測長の精度を光源の波長
以下の精度、すなわち、ｌｏｎｍ程度まで飛躍的に向上
させることにある。The present invention has been made in view of these problems, and its purpose is to dramatically improve the accuracy of absolute length measurement to less than the wavelength of the light source, that is, to the order of lonm.
（課題を解決するための手段）本発明のアブソリュート測長方法は、レーザ光源と、特
定の周波数域において光吸収のピークを有する光吸収用
セルと、被測定対象である物体からの反射光と参照光と
の干渉位相を測定する第１の干渉計と、第１の長さ基準
および該第１の長さ基準より短い第２の長さ基準のそれ
ぞれを光路差とする第２および第３の干渉計とを用意し
、まず、ＦＭ変調された前記レーザ光を前記物体に向け
て照射し、前記第１および第２の干渉計がら得られる干
渉次数を測定し、次に、前記光吸収用セルの吸収ピーク
の周波数に前記レーザ光源の周波数を固定し、この状態
で前記第１．第２および第３の干渉計のそれぞれにより
干渉位相を測定し、ＦＭ変調期間において前記第１およ
び第２の干渉計により測定された干渉次数と、前記吸収
ピークの周波数における前記レーザ光源の波長と、前記
第１の長さ基準とを用いて下記第１式より干渉次数Ｎを
求め、Ｎ−整数（（Ｌｍ、、、・Ｎ、）／ （λ５．．・ＮＮ
Ｌ）１・・・・・・・・・（１）周波数安定化期間において前記第２および第３の干渉計
（３０，２１，２２，２７，２ｇ 、２３，２４，２５
．２６）のそれぞれにより測定された干渉位相（θＮＬ
＋ θＳＬ）を用いて、下記第２式より空気の絶対屈
折率ｎａｂ、を求め、ｎ ｍｈｏ −ｎ 。＋ ［ＮＸ ＋ （（θＮＬ−θ
ｏ）／２π｝ ・ （λｇｓｓ ／ Ｌ ｌｅ□）］
・・・・・・・・・（２）但し、ｎｏおよびθｏは、
絶対空気屈折率部（３２）を校正した時の空気の屈折率
の値と第２の干渉計から得られる位相の初期値であり、
Ｎｘは第３の干渉計から得られる位相信号θＳＬより決
定した第２の干渉計の干渉次数であり、次に、前記干渉次数Ｎ、空気の絶対屈折率ｎ１ｂ１．第
１の干渉計により測定された干渉位相（θｍ）、前記吸
収ピークの周波数における前記レーザ光源（１）の波長
（λ□、）を下記第３式に代入し、Ｌ□−（Ｎ＋ （θ□／２π｝）（λｇｍ＋ ／ ｎ
ａｂ８） ・・・
・・・・・・（３）これにより、前記物体（６）までの
絶対距離（Ｌｍ、）を求めることを特徴とする。(Means for Solving the Problems) The absolute length measurement method of the present invention includes a laser light source, a light absorption cell having a light absorption peak in a specific frequency range, and a light reflected from an object to be measured. a first interferometer that measures the interference phase with the reference light, and second and third interferometers that use a first length reference and a second length reference shorter than the first length reference as optical path differences, respectively. an interferometer is prepared, first, the FM modulated laser beam is irradiated toward the object, the interference order obtained from the first and second interferometers is measured, and then the light absorption The frequency of the laser light source is fixed to the frequency of the absorption peak of the first cell. The interference phase is measured by each of the second and third interferometers, and the interference order measured by the first and second interferometers during the FM modulation period and the wavelength of the laser light source at the frequency of the absorption peak are determined. , the interference order N is determined from the first equation below using the first length standard, and N - integer ((Lm,,,・N,)/(λ5...・NN
L) 1... (1) During the frequency stabilization period, the second and third interferometers (30, 21, 22, 27, 2g, 23, 24, 25
．． 26), the interference phase (θNL
+ θSL), the absolute refractive index nab of air is determined from the second equation below, and n mho −n is obtained. + [NX + ((θNL-θ
o)/2π} ・(λgss/L le□)]
・・・・・・・・・(2) However, no and θo are
These are the value of the refractive index of air when the absolute air refractive index section (32) is calibrated and the initial value of the phase obtained from the second interferometer,
Nx is the interference order of the second interferometer determined from the phase signal θSL obtained from the third interferometer, and next, the interference order N, the absolute refractive index of air n1b1 . Substituting the interference phase (θm) measured by the first interferometer and the wavelength (λ□, ) of the laser light source (1) at the frequency of the absorption peak into the third equation below, L□−(N+ (θ □/2π})(λgm+/n
ab8)...
(3) This is characterized in that the absolute distance (Lm, ) to the object (6) is determined.
また、本発明のアブソリュート測長器は、出力光の周波
数を所定範囲で連続的に変化させることができる光源と
、該光源の周波数安定化手段と、前記物体からの反射光
と参照光との干渉位相を測定する干渉位相測定手段と、
第１の長さ基準と該第１の長さ基準より短い第２の長さ
基準を具備し、該第１の長さ基準を光路差として得られ
る干渉位相と、第２の長さ基準を光路差として得られる
干渉位相とをそれぞれ測定する、基準長さを用いた干渉
位相測定手段と、前記干渉位相測定手段および基準長さ
を用いた干渉位相測定手段から得られる干渉位相測定信
号を入力とし、位相偏位を利用して前記絶対距離を算出
する演算部とを有し、前記周波数安定化手段は、特定の
周波数域において光吸収のピークを有し、前記光源の出
力光を人力とする光吸収用セルと、該光吸収用セルを通
過した光の強度を測定する光センサと、該光センサの出
力の低下により前記光源の出力光の周波数が前記光吸収
用セルの吸収ピークの周波数に達したことを検出し、制
御信号を前記光源に帰還させる手段とを具備し、周波数
を連続的に変化させている前記光源の周波数が前記吸収
ピークの周波数と一致すると、該光源の周波数を吸収ピ
ークの周波数に固定するようになっていることを特徴と
する。Further, the absolute length measuring device of the present invention includes a light source capable of continuously changing the frequency of output light within a predetermined range, a frequency stabilizing means for the light source, and a means for adjusting the frequency of the reflected light from the object and the reference light. an interference phase measuring means for measuring an interference phase;
A first length reference and a second length reference shorter than the first length reference are provided, and an interference phase obtained by using the first length reference as an optical path difference and a second length reference are provided. An interference phase measurement means using a reference length that measures the interference phase obtained as an optical path difference, and an interference phase measurement signal obtained from the interference phase measurement means and the interference phase measurement means using the reference length are input. and an arithmetic unit that calculates the absolute distance using phase deviation, and the frequency stabilizing means has a peak of light absorption in a specific frequency range, and the frequency stabilizing means has a peak of light absorption in a specific frequency range, and the frequency stabilizing means has a peak of light absorption in a specific frequency range, and the output light of the light source is controlled manually. a light absorption cell that measures the intensity of light that has passed through the light absorption cell; and a light sensor that measures the intensity of the light that has passed through the light absorption cell; means for detecting that the frequency has been reached and returning a control signal to the light source, and when the frequency of the light source whose frequency is continuously changed matches the frequency of the absorption peak, the frequency of the light source is fixed at the absorption peak frequency.
（作用）ＤＢＲレーザ等の注入電流を変化させて発振周波数を広
い範囲に渡り連続的に変化させ、周波数がＲｂ（ルビジ
ュウム）等のガスセルの光吸収ピ一りの周波数になると
、負帰還をかけて発振周波数をその吸収ピーク周波数に
固定し、安定化させる。(Function) The oscillation frequency is continuously changed over a wide range by changing the injection current of a DBR laser, etc. When the frequency reaches the same frequency as the light absorption peak of a gas cell such as Rb (rubidium), negative feedback is applied. to fix the oscillation frequency at its absorption peak frequency and stabilize it.
ＦＭ変調期間には絶対モードの測定を行い、安定化期間
には相対モードの測定を行う。すなわち、第１１図の下
側の図に示すように、絶対モードでの測定精度を相対モ
ードのレベルまで高め、相対モードの測定と合体させる
。Absolute mode measurement is performed during the FM modulation period, and relative mode measurement is performed during the stabilization period. That is, as shown in the lower diagram of FIG. 11, the measurement accuracy in the absolute mode is increased to the level of the relative mode, and is combined with the measurement in the relative mode.
測長は、マイケルソンの干渉計等と、第１および第２の
基準長さを利用した干渉計とにより行う。The length measurement is performed using a Michelson interferometer or the like and an interferometer that uses the first and second reference lengths.
レーザ光の広範囲に渡る連続的なＦＭ変調と、Ｒｂ等の
ガスセルによる波長の安定化ならびに波長の絶対値の保
障と、高精度の基準長さ（基準ギャップ）の採用により
、干渉次数Ｎを高精度に特定でき、これによって絶対モ
ードによる測定精度を光源の波長レベルにまで向上でき
、さらに、ＦＭ変調期間に連続する相対モードによる測
定と２種類の基準長さの採用によって、空気の絶対屈折
率ｎ＊ｂ＊ｈ干渉位相θｍを高精度に測定でき、結果的
に、アブソリュート測長のレベルを相対測長のレベル、
すなわち、光源の波長以下（１０ｎｍオーダ）のレベル
にまで高めることが可能となる。The interference order N is increased by continuous FM modulation of the laser beam over a wide range, stabilization of the wavelength by a gas cell such as Rb, guarantee of the absolute value of the wavelength, and adoption of a highly accurate reference length (reference gap). This improves the measurement precision of the absolute mode to the level of the wavelength of the light source.Furthermore, by using the continuous relative mode during the FM modulation period and using two types of reference lengths, the absolute refractive index of the air can be determined. The n*b*h interference phase θm can be measured with high precision, and as a result, the level of absolute length measurement can be changed to the level of relative length measurement,
In other words, it becomes possible to increase the wavelength to a level that is below the wavelength of the light source (on the order of 10 nm).
（実施例）次に、本発明の実施例について図面を参照して説明する
。(Example) Next, an example of the present invention will be described with reference to the drawings.
実施例１第１図は本発明のアブソリュート測長器の一実施例の構
成を示す図である。Embodiment 1 FIG. 1 is a diagram showing the configuration of an embodiment of an absolute length measuring device of the present invention.
本実施例のアブソリュート測長器３５は、測長用光源１
と、この光源１の駆動電流を連続的に変化させるための
電流スィーパ（低出力インピーダンスのアンプを利用し
た可変電流源回路） １Ｂと、光源１の出力光強度を一
定に保つための定電流源Ｉ８と、ＦＭモードと周波数安
定化モードとを切換えるスイッチＩ７と、光学系２．
３．４．１０と、周波数安定化部３１と、干渉位相測定
部３ｏと、空気の絶対屈折率補正部３２と、位相測定部
３３と、制御処理部３４とを有している。The absolute length measuring device 35 of this embodiment has a length measuring light source 1.
1B, a current sweeper (variable current source circuit using a low output impedance amplifier) for continuously changing the driving current of light source 1, and a constant current source for keeping the output light intensity of light source 1 constant. I8, a switch I7 for switching between FM mode and frequency stabilization mode, and optical system 2.
3.4.10, a frequency stabilization section 31, an interference phase measurement section 3o, an air absolute refractive index correction section 32, a phase measurement section 33, and a control processing section 34.
以下、各部の構成と機能を説明する。The configuration and functions of each part will be explained below.
測長月光源１光源１としてＤＢＲ半導体レーザを使用している。ＤＢ
Ｒ半導体レーザは、出力光強度を決定する活性領域と周
波数を制御するＤＢＲ領域とを具備し、注入電流Ｉ６は
定電流源Ｉ８て一定に保たれ、周波数制御電流ＩＣはス
ィーパ１６の吸込み量の変化にしたがって所定範囲に渡
７て連続的に変化する。これによってＦＭ変調がなされ
る。Length measurement moon light source 1 A DBR semiconductor laser is used as the light source 1. DB
The R semiconductor laser includes an active region that determines the output light intensity and a DBR region that controls the frequency.The injection current I6 is kept constant by a constant current source I8, and the frequency control current IC is controlled by the amount of absorption by the sweeper 16. It changes continuously over a predetermined range 7 according to the change. This performs FM modulation.
周波数安定化部３１ＤＢＲ半導体レーザ１から出射された光はコリメータレ
ンズ２で平行光とされ、アイソレータ３およびハーフミ
ラ−４を経てハーフミラ−１ｏて分割され、さらにハー
フミラ−１１で再分割される。Frequency Stabilizer 31 The light emitted from the DBR semiconductor laser 1 is made into parallel light by a collimator lens 2, passed through an isolator 3 and a half mirror 4, divided by a half mirror 1o, and further divided by a half mirror 11.
分割された光の一方はリファレンス用フォトダイオード
（光センサ）１２により検波され、他方の光はＲｈ（ル
ビジュウム）ガスセル１３を通過後に透過光モニタ用フ
ォトダイオード（光センサ）１４て検波される。フォト
ダイオード１２．１４の検出出力の差を比較器１５ｂで
検出し、この結果は制御処理部３４に送られる。光源１
の出力光の周波数が、ガスセル１３の吸収ピークの周波
数となって吸収が生じ、フォトダイオード１４の出力が
急激に低下すると、制御処理部３４はこれを検出し、ス
イッチエフをアンプＬ５ａ側に切換え、アンプ１５ａの
出力をＤＢＲ半導体レーザ１に帰還させる。これにより
、周波数（位相）の負帰還ループが構成され、レーザ光
の周波数はガスセル１３の吸収ピークの周波数に固定（
安定化）される。One of the divided lights is detected by a reference photodiode (light sensor) 12, and the other light is detected by a transmitted light monitor photodiode (light sensor) 14 after passing through a Rh (rubidium) gas cell 13. A comparator 15b detects the difference between the detection outputs of the photodiodes 12 and 14, and the result is sent to the control processing section 34. light source 1
When the frequency of the output light becomes the frequency of the absorption peak of the gas cell 13 and absorption occurs, and the output of the photodiode 14 suddenly decreases, the control processing unit 34 detects this and switches the switch F to the amplifier L5a side. , the output of the amplifier 15a is fed back to the DBR semiconductor laser 1. This constitutes a frequency (phase) negative feedback loop, and the frequency of the laser beam is fixed at the absorption peak frequency of the gas cell 13 (
stabilized).
干渉位相測定部３０マイケルソンの干渉計から構成されており、ハーフミラ
−４を透過した光は、さらにハーフミラ−７で分割され
、分割光は反射ミラー５と被測定対象（反射ミラー）７
でそれぞれ反射され、フォトダイオード８上で合波され
、干渉位相が得られる。Interference phase measuring section 30 Consists of a Michelson interferometer, the light transmitted through the half mirror 4 is further divided by the half mirror 7, and the divided light is sent to the reflecting mirror 5 and the object to be measured (reflecting mirror) 7.
, and are multiplexed on the photodiode 8 to obtain an interference phase.
絶対屈折率測定部３２ハーフミラ−ＩＯで分割された他方の光は、ハーフミラ
−１９で再び分割され、ハーフミラ−２１と反射ミラー
２２により、長い長さ基準Ｌ１゜。１と短い長さ基準Ｌ
ｍｂ。１．（それぞれ、基準ギャップ２７．２６によ
り提供される）に導かれ、それぞれの長さに対応した干
渉信号をフォトダイオード２８および２５で得る。基準
ギャップ２７．２６は熱膨張係数の小さいスーパーイン
バーやゼロデユア−等の材料で構成されている。Absolute refractive index measuring section 32 The other light split by the half mirror IO is split again by the half mirror 19, and is measured by the half mirror 21 and the reflecting mirror 22 to a long length reference L1°. 1 and short length standard L
mb. 1. (provided by reference gaps 27, 26, respectively), and interference signals corresponding to their respective lengths are obtained at photodiodes 28 and 25. The reference gaps 27 and 26 are made of a material with a small coefficient of thermal expansion, such as Super Invar or Zerodure.
信号処理部位相測定部３３は、３つのフォトダイオード８゜２８．
２５からの検出出力を受けてそれぞれの位相を求め、制
御処理部８４は位相偏位より、測長器３５のレーザ光出
射端部から被測定対象である物体６までの距離り、を求
め、出力（例えば、デイスプレィ機器に表示）する。The signal processing part phase measuring section 33 includes three photodiodes 8°28.
25, the control processing unit 84 calculates the distance from the laser beam emitting end of the length measuring device 35 to the object 6 to be measured from the phase deviation. Output (for example, display on a display device).
動作第２図は本実施例の動作フローと、これに対応する構成
部分の様子ならびに物理量の算出過程をまとめて示す図
である。この図では、理解を容易とするために上部、中
部、下部をそれぞれレーザ光源部、測定部、演算部にわ
け、かつ、中央より左部をＦＭ変調期間、右部をガスセ
ルの周波数に安定化した期間に分け、表形式で記載して
いる。Operation FIG. 2 is a diagram collectively showing the operation flow of this embodiment, the state of the corresponding components, and the calculation process of physical quantities. In this figure, for ease of understanding, the upper, middle, and lower parts are divided into the laser light source section, measurement section, and calculation section, respectively, and the left part from the center is the FM modulation period, and the right part is stabilized at the gas cell frequency. It is divided into periods and listed in table format.
また、第３図には時間（１）に対する各部の波形が示さ
れている。Further, FIG. 3 shows waveforms of various parts with respect to time (1).
まず、時ｔＡｔｌ−ｔ２（期間Ｔａ）にはＤＢＲ半導体
レーザ１の出力光は連続的にＦＭ変調されており（ステ
ップ５０）、第３図の最上部の図のように周波数ｆは直
線的に増加していく。この期間において、マイケルソン
の干渉計３０と、長い基準長さＬｌ。ｎ、（基準ギャッ
プ２７）を基準とした干渉計のそれぞれ（すなわち、フ
ォトダイオード８２８）から干渉位相が測定され、これ
により干渉次数Ｎ、とＮＮＬとが特定される（ステップ
５１）。本実施例では、第３図の上から３番目および第
４番目の図のように、Ｎｆｆ１とＮＮＬとはそれぞ゛れ
、３４８および３．５である。First, at time tAtl-t2 (period Ta), the output light of the DBR semiconductor laser 1 is continuously FM modulated (step 50), and the frequency f is linearly modulated as shown in the top diagram of FIG. It will increase. During this period, the Michelson interferometer 30 and the long reference length Ll. The interference phase is measured from each of the interferometers (that is, the photodiode 828) using n, (reference gap 27) as a reference, and thereby the interference orders N and NNL are specified (step 51). In this embodiment, as shown in the third and fourth figures from the top of FIG. 3, Nff1 and NNL are 348 and 3.5, respectively.
時刻ｔ２にＤＢＲ半導体レーザ１の出力光の周波数がＲ
ｂガスセルの吸収ピークの周波数と一致し、第３図の上
から２番目の図に示されるようにフォトダイオード１４
の出力が急激に低下すると、スイッチ１７が切替わり、
周波数がこの吸収ピークの周波数に安定化される（ステ
ップ５２）。この安定化期間は時刻ｔ３まで続き（期間
Ｔｂ）、時刻ｔ３に１回のサイクルが終了する。この安
定化期間に、フォトダイオード８．２８．２５のそれぞ
れにより、干渉位相θｍ、θ９０．θ９．が求められる
（ステップ５３）。At time t2, the frequency of the output light of the DBR semiconductor laser 1 becomes R.
b coincides with the absorption peak frequency of the gas cell, and as shown in the second diagram from the top of FIG. 3, the photodiode 14
When the output of the switch 17 suddenly decreases, the switch 17 switches.
The frequency is stabilized to the frequency of this absorption peak (step 52). This stabilization period continues until time t3 (period Tb), and one cycle ends at time t3. During this stabilization period, the interference phases θm, θ90. θ9. is determined (step 53).
この場合の干渉位相θｍ等は第４図に示すように、フォ
トダイオードの出力信号のエンベロープを求め、全体の
振幅すと、この振幅の中心位置からの変位量ａを求め、
ＣＯ３−’ （ａ／ｂ）を計算することにより算出され
る。なお、短い長さ基準を光路差とした干渉位相θＮ、
より、後述する空気の絶対屈折率ｎ、６．を特定する際
に必要となる干渉次数Ｎｘか求められる。In this case, the interference phase θm, etc., as shown in Figure 4, is obtained by finding the envelope of the output signal of the photodiode, calculating the overall amplitude, and finding the displacement a of this amplitude from the center position.
It is calculated by calculating CO3-' (a/b). In addition, the interference phase θN with the short length reference as the optical path difference,
Therefore, the absolute refractive index n of air, which will be described later, is 6. The interference order Nx required for specifying is determined.
次に、制御処理部３４は下記式による演算を行い、絶対
距離Ｌ□を測定する。まず、下記第１式より干渉次数Ｎ
を求め（ステップ５４）、Ｎ−整数（（Ｌｌ。□・Ｎｆｆ１）／ （λ１□ ・Ｎ
ＮＬ） ！・・・・・・・・・（１）次に、干渉位相春〒千〇礼、θ３．を用いて、下記第２
式より空気の絶対屈折率ｎ、１．を求める（ステップ５
５）。Next, the control processing unit 34 calculates the following formula to measure the absolute distance L□. First, from the first equation below, the interference order N
(Step 54), N-integer ((Ll.□・Nff1)/(λ1□・N
NL)!・・・・・・・・・(1) Next, the interference phase spring 〒1000, θ3. Using the following 2nd
From the formula, the absolute refractive index of air is n, 1. (Step 5)
5).
ｎ ｓｂａ −ｎ 。＋ ［ＮＸ ＋ （（θＮ
Ｌ−θｏ）／２π｝ （λ１゜、／Ｌ１゜、、、）
］ ・・・・・・・・・（２）但し、ｎｏおよび
θｏは、絶対空気屈折率部（３２）を校正した時の空気
の屈折率の値と第２の干渉計から得られる位相の初期値
であり、ＮＸは第３の干渉計から得られる位相信号θＳ
Ｌより決定した第２の干渉計の干渉次数である。このと
き、干渉次数Ｎ、は、高精度ゆえに複数の干渉縞が現れ
る、長い長さ基準Ｌ ＋６ｎＭを使用した干渉計単独で
は特定できないが、精度の低い、短い長さ基準Ｌ ａｈ
。、１を利用した干渉計の測定結果を重ねることにより
、決定することができる（第５図）。nsba-n. + [NX + ((θN
L-θo)/2π} (λ1゜, /L1゜,,,)
] ・・・・・・・・・(2) However, no and θo are the value of the refractive index of air when the absolute air refractive index section (32) is calibrated and the phase obtained from the second interferometer. is the initial value, and NX is the phase signal θS obtained from the third interferometer.
This is the interference order of the second interferometer determined from L. At this time, the interference order N, cannot be determined by an interferometer alone using the long length standard L +6nM, where multiple interference fringes appear due to its high accuracy, but the short length standard L ah, which has low accuracy.
. , 1 can be determined by overlapping the measurement results of interferometers using 1 (FIG. 5).
次に、ステップ５４で求めた干渉次数Ｎ、ステップ５５
で求めた空気の絶対屈折率ｎ。、、干渉計３０により測
定された干渉位相θｏ、前記吸収ピークの周波数におけ
る前記レーザ光源１の波長λ１．。Next, the interference order N obtained in step 54, step 55
The absolute refractive index of air, n. ,, the interference phase θo measured by the interferometer 30, the wavelength λ1 of the laser light source 1 at the frequency of the absorption peak. .
（既知）を下記第３式に代入し、Ｌ、−（Ｎ＋ （θｍ／２π｝） ・（λｇ＠＠ ／
ｎ ＠１１、） ・・・
・・・・・・（３）これにより、前記物体（６）までの
絶対距離り、を求める（ステップ５６）。(known) into the third equation below, L, -(N+ (θm/2π}) ・(λg@@ /
n @11,) ・・・
(3) From this, the absolute distance to the object (6) is determined (step 56).
第３式において、干渉次数Ｎ、ならびにθヨ／２πより
決まる端数位相εの精度が極めて高いために、絶対距離
り、、をナノメータのオーダーで高精度に測定できる。In the third equation, since the precision of the interference order N and the fractional phase ε determined by θ y /2π is extremely high, the absolute distance , can be measured with high precision on the order of nanometers.
実施例２第６図は本発明の第２の実施例の構成を示す図、第７図
はその動作を説明するための時間に対する各部の波形を
示す図である。Embodiment 2 FIG. 6 is a diagram showing the configuration of a second embodiment of the present invention, and FIG. 7 is a diagram showing waveforms of various parts with respect to time to explain its operation.
本実施例は、第１の実施例のスイッチ１７を除去し、周
波数を吸収ピークの周波数に安定化させる機構をなくし
たものである。その代わりに、フォトダイオード１４の
検出出力を直接に位相測定部３３に入力し、スィーパＩ
Ｂで周波数掃引しながら、時刻ｔ３およびｔ５に得られ
る吸収ピークをトリガーとして端数位相θｍ等を測定す
る。本実施例によれば、周波数安定化機構をなくした分
だけ、構成が簡素化でき、複雑なシーケンスが不要とな
り、さらに高速測定が可能となるという効果がある。In this embodiment, the switch 17 of the first embodiment is removed, and the mechanism for stabilizing the frequency at the absorption peak frequency is eliminated. Instead, the detection output of the photodiode 14 is directly input to the phase measuring section 33, and the sweeper I
While sweeping the frequency at B, the fractional phase θm and the like are measured using the absorption peaks obtained at times t3 and t5 as triggers. According to this embodiment, since the frequency stabilization mechanism is eliminated, the configuration can be simplified, a complicated sequence is unnecessary, and high-speed measurement is possible.
実施例３本発明は上述の実施例に限定されるものではなく、種々
変形が可能である。Embodiment 3 The present invention is not limited to the above-described embodiment, and various modifications are possible.
例えば、周波数可変光源としてはＤＢＲレーザの他、色
素レーザやＴｉドープのサファイヤレーザ等の波長が連
続的に可変のレーザを使用してもよい。また、ＦＭ変調
回路を付加し、電圧駆動タイプのレーザを外部変調して
もよい。For example, as the frequency variable light source, in addition to a DBR laser, a laser whose wavelength is continuously variable, such as a dye laser or a Ti-doped sapphire laser, may be used. Furthermore, an FM modulation circuit may be added to externally modulate the voltage-driven laser.
また、測定対象物体６の面を鏡面とする必要は必ずしも
なく、直前にレンズを設置し、粗面での計測や形状計測
をしてもよい。Further, the surface of the object 6 to be measured does not necessarily have to be a mirror surface, and a lens may be installed just in front of the object 6 to perform measurement or shape measurement on a rough surface.
また、ＦＭ測長により干渉次数Ｎを決定する方式として
、長い長さ基準と干渉位相の比をとるのではなく、第８
図に示すように、ガスの複数の吸収線を利用してトリガ
ー信号を得、この２本の吸収線のタイミング間のレーザ
の周波数変移ΔＦを測定してもよい。In addition, as a method for determining the interference order N by FM length measurement, instead of taking the ratio of the long length reference and the interference phase,
As shown in the figure, a trigger signal may be obtained using a plurality of absorption lines of the gas, and the frequency shift ΔF of the laser between the timings of these two absorption lines may be measured.
（発明の効果）以上説明したように本発明は、ガスセルを用いた波長の
安定化と絶対値の保障、少なくとも２種類の高精度の基
準ギャップ（基準長さ）の採用、ならびにＦＭ変調波に
よる絶対モードによる測定とそれに続く周波数を固定し
ての相対モードでの測定システムの採用、ならびに空気
の絶対屈折率の測定（屈折率の補正）により、下記の効
果が得られる。(Effects of the Invention) As explained above, the present invention stabilizes the wavelength using a gas cell and guarantees the absolute value, employs at least two types of highly accurate reference gaps (reference lengths), and uses FM modulated waves. By adopting an absolute mode measurement followed by a relative mode measurement system with a fixed frequency, and by measuring the absolute refractive index of air (refractive index correction), the following effects can be obtained.
（１）従来不可能であった、使用する光源の波長以下の
レベルの絶対距離の測定が可能となる。(1) It becomes possible to measure absolute distances at a level below the wavelength of the light source used, which was previously impossible.
（２）しかも、ｌＯｎｍオーダーのレベルまでの測定が
可能であり、アブソリュート測長のレベルを相対測長の
レベルと同程度とすることが可能となる。(2) Moreover, it is possible to measure up to a level on the order of 1 Onm, and it is possible to make the level of absolute length measurement comparable to the level of relative length measurement.
（３）これにより、例えば、極めて高精度な形状測定器
の提供か可能となり、今後、サブナノメートルの精度を
要求される電子部品や製造装置分野の産業界の要請に応
え、各種の機器への適用、応用が期待される。(3) This makes it possible, for example, to provide extremely high-precision shape measuring instruments, which will meet the demands of the electronic parts and manufacturing equipment industries that require sub-nanometer precision in the future. Applications and application are expected.
第１図は本発明のアブソリュート測長器の第１の実施例
の構成を示す図、第２図は本実施例の動作フローと、これに対応する構成
部分の様子ならびに物理量の算出過程をまとめて示す図
（この図では、理解を容易とするために上部、中部、下
部をそれぞれレーザ光源部。測定部、演算部にわけ、かつ、中央より左部をＦＭ変調
期間、右部をガスセルの周波数に安定化した期間に分け
、表形式で記載している）、第３図は第１図の時間に対
する各部の波形を示す図、第４図は端数位相（θｍ等）の算出方法を説明するため
の図、第５図は空気の絶対屈折率（ｎａｂｓ）の算出方法（こ
のときに必要となる干渉次数ｎｘの求める方法を含む）
を説明するための図、第６図は本発明のアブソリュート測長器の第２の実施例
の構成を示す図、第７図は第６図の各部の時間に対する波形を示す図、第８図は本発明の他の変形例を説明するための図、第９図は従来例（インクリメンタル式の変位計）の構成
を示す図、第１Ｏ図は第９図の従来例の問題点を示す図、第１１図
は他の従来例（絶対距離の測長器）と本発明のアブソリ
ュート測長器との性能の比較を示す図である。１・・・ＤＢＲ半導体レーザ２・・・コリメータレンズ３・・・アイソレーション ４・・・ハーフミラ−５
・・・反射ミラー（ＣＣ）６・・・被測定対象物体（反射ミラー（ＣＣ））７・・
・ハーフミラ−８・・・フォトダイオード（光センサ）１（１，１１・
・・ハーフミラ−１２・・・フォトダイオード１３・・・Ｒｂ（ルビジュウム）ガスセル１４・・・フ
ォトダイオード１５ａ・・・アンプ１５ｂ・・・比較器（差動アンプ）１６・・・電流スィーパ−１７・・・スイッチ１９、２
１．２４・・・ハーフミラ−２０、２２，２３・・・反射ミラー２６、２７・・・基準ギャップ２５、２８・・・フォトダイオード３０・・・干渉位相測定部３２・・・絶対屈折率測定部３４・・・制御処理部３５・・・アブソリュート測長器３６・・・吸収測定部Ｌｌ。、１・・・長い長さ基準り、、。、・・・短い長さ基準３１・・・周波数安定化部３３・・・位相測定部第４図ｔ２ｔコ第５図Fig. 1 is a diagram showing the configuration of the first embodiment of the absolute length measuring device of the present invention, and Fig. 2 summarizes the operation flow of this embodiment, the appearance of the corresponding components, and the calculation process of physical quantities. (In this figure, for ease of understanding, the upper, middle, and lower parts are the laser light source section. The measurement section and the calculation section are divided into the FM modulation period and the right section, respectively. Figure 3 shows the waveforms of each part versus time in Figure 1. Figure 4 explains how to calculate the fractional phase (θm, etc.). Figure 5 shows the method for calculating the absolute refractive index (nabs) of air (including the method for calculating the interference order nx, which is necessary at this time).
FIG. 6 is a diagram showing the configuration of the second embodiment of the absolute length measuring device of the present invention. FIG. 7 is a diagram showing waveforms of each part of FIG. 6 versus time. FIG. 8 is a diagram for explaining another modification of the present invention, FIG. 9 is a diagram showing the configuration of a conventional example (incremental displacement meter), and FIG. 1O is a diagram showing problems in the conventional example of FIG. 9. , FIG. 11 is a diagram showing a comparison of performance between another conventional example (absolute distance measuring device) and the absolute length measuring device of the present invention. 1... DBR semiconductor laser 2... Collimator lens 3... Isolation 4... Half mirror 5
... Reflection mirror (CC) 6 ... Object to be measured (reflection mirror (CC)) 7 ...
・Half mirror 8... Photodiode (light sensor) 1 (1, 11・
...Half mirror 12...Photodiode 13...Rb (rubidium) gas cell 14...Photodiode 15a...Amplifier 15b...Comparator (differential amplifier) 16...Current sweeper 17. ...Switch 19, 2
1.24...Half mirror 20, 22, 23...Reflection mirror 26, 27...Reference gap 25, 28...Photodiode 30...Interference phase measuring section 32...Absolute refractive index measurement Section 34... Control processing section 35... Absolute length measuring device 36... Absorption measuring section Ll. , 1...Long length standard,,. ...Short length reference 31...Frequency stabilization section 33...Phase measurement section Fig. 4 t2t Fig. 5
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2086435AJP2725434B2 (en) | 1990-03-30 | 1990-03-30 | Absolute length measuring method and absolute length measuring device using FM heterodyne method |
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2086435AJP2725434B2 (en) | 1990-03-30 | 1990-03-30 | Absolute length measuring method and absolute length measuring device using FM heterodyne method |
| Publication Number | Publication Date |
|---|---|
| JPH03285102Atrue JPH03285102A (en) | 1991-12-16 |
| JP2725434B2 JP2725434B2 (en) | 1998-03-11 |
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2086435AExpired - Fee RelatedJP2725434B2 (en) | 1990-03-30 | 1990-03-30 | Absolute length measuring method and absolute length measuring device using FM heterodyne method |
| Country | Link |
|---|---|
| JP (1) | JP2725434B2 (en) |
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| JP2001041706A (en)* | 1999-07-27 | 2001-02-16 | Mitsubishi Heavy Ind Ltd | Optical frequency domain reflection measuring device and optical frequency domain reflection measuring method |
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