JP2004249402A

JP2004249402A - Highly accurate processing method of machine tool

Info

Publication number: JP2004249402A
Application number: JP2003042895A
Authority: JP
Inventors: Harumitsu Senda; 治光千田
Original assignee: Okuma Corp; Okuma Machinery Works Ltd
Current assignee: Okuma Corp
Priority date: 2003-02-20
Filing date: 2003-02-20
Publication date: 2004-09-09

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for maintaining processing accuracy by providing a means for reflecting a change in a thermal displacement quantity caused by a change with the lapse of time of a machine tool. <P>SOLUTION: An approximate factor of a saturation time thermal displacement quantity or a thermal displacement time constant is predetermined, and is stored on a memory by an experiment for obtaining a thermal displacement quantity change when operating a heat source at respective operation speeds. A temperature rise value of a main spindle is calculated when setting rotation starting time as the origin in a state of sufficiently cooling the main spindle, and a difference from the reference temperature is calculated as the temperature rise value when a temperature is saturated in a temperature rise from the reference temperature (S-11). Then, a present thermal displacement quantity is determined from a predetermined relational expression of the the temperature rise value and thermal displacement (S-12). Afterwards, relational factors of a stored rotating speed and the thermal displacement quantity are compared, and when the factors are different, the memory of a storage device 10 is updated (S-13). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、工作機械において、熱変位を推定し補正するとともに、適宜加工を停止することで、加工精度を高いものとする方法に関するものである。
【０００２】
【従来の技術】
一般に工作機械は、機械の特性上各部に熱源（例えば主軸の転がり軸受け）を持っており、この熱源によって発生した熱が機械各部に伝わることで機体の熱変形を引き起す。この機体の熱変形は、加工精度に大きく影響することから、その防止策として、機体温度情報からの熱変位の推定を利用して、これを補正する方法が広く採用されている。ここで、当該熱変位の推定として、この出願と同一の出願人による特許文献１に示すものが知られている。
【０００３】
【特許文献１】
特開平９−２２５７８１号公報
【０００４】
このような熱変位の推定においては、回転数変化後の過渡状態から定常状態に至るまで、回転数と時間または推定回数に応じて演算式の係数を変化させながら主軸の熱変位を推定する。
【０００５】
【発明が解決しようとする課題】
上記熱変位の推定では、熱源に係る部分の使用の経過、環境の変化等の経時変化により熱変位量の変化が起きた場合でも、演算式の係数変化の仕方は変らないため、誤差判定が実状と合致しなくなる。
【０００６】
そこで、本発明の課題は、熱変位を推定する方法において、経時変化による熱変位量の変化への対応を可能にして、経時変化に関わらず加工精度を高度に維持することができる方法を提供することにある。
【０００７】
【課題を解決するための手段】
上記の課題を解決するために、本発明は、予め各運転速度における熱源運転時の熱変位量変化を得る実験により、飽和時熱変位量または熱変位時定数の近似係数を求めてメモリ上に記憶する予段階と、熱源温度の温度上昇値を得、温度上昇値から熱変位推定演算を求め、これを補正する補正段階と、運転速度変化時においてメモリ上の飽和時熱変位量および熱変位時定数から誤差値の変化を求め、誤差値が許容値になる時間を得て当該時間だけ加工停止する待機段階とを含み、熱変位が飽和する運転時において対応する温度上昇値から算出した熱変位量と、当該運転時の運転速度指令値とから、近似係数を算出して、少なくともメモリ上の対応する近似係数と異なる場合には、これをメモリ上に記憶し直すことを特徴とする（請求項１）。
【０００８】
また、本発明は、予め各運転速度における熱源運転時の熱変位量変化を得る実験により、飽和時熱変位量または熱変位時定数の近似係数を求めてメモリ上に記憶する予段階と、熱源温度の温度上昇値を得、温度上昇値から熱変位推定演算を求め、これを補正する補正段階と、運転速度変化時においてメモリ上の飽和時熱変位量および熱変位時定数から誤差値の変化を求め、誤差値が許容値になる時間を得て当該時間だけ加工停止する待機段階とを含み、少なくとも、熱変位が飽和する運転時において測定した熱変位量と、メモリ上の近似係数と当該運転時の運転速度指令値とから算出した熱変位量とが異なる場合には、測定熱変位量と運転速度指令値とから近似係数を算出してメモリ上に記憶し直すことを特徴とする（請求項２）。
【０００９】
以下に、本発明による熱変位推定方法の原理を、メモリを有する制御手段、主軸およびテーブルを備え、熱源を主軸としその運転を回転とした工作機械において説明する。工作機械の主軸熱変位変化は、主軸回転数（回転速度）が変化した後に発生する。このとき、熱変位が継続的に変化する過渡状態と熱変位変化がなくなり安定化した定常状態に分けることができる。
【００１０】
また、一般には回転速度が速くなるにつれて、熱変位量が大きくなる。その熱変位時定数は、主軸の構成、並びに主軸外筒冷却がなされる場合には、その冷却能力により主軸回転速度に対してほぼ一意的に決定されるが、主軸回転速度が上がって発熱量が増す場合と、回転速度が下がって発熱量が減る場合で時定数が異なることが多く、主軸回転速度によって変化する。また、主軸冷却装置の能力変化や軸受の劣化等の経時変化により回転速度に対する熱変位量は、変化する。
【００１１】
回転速度に起因した主軸飽和時熱変位量と時定数算出方法（実験あるいはシミュレーションの一部、予段階）について、回転速度を上げる場合から説明する。まず、主軸を、停止しており十分に熱変位が安定している状態において基準回転速度での回転を始めてこれを継続し、主軸とテーブル間の熱変位変化と時間を記録する。なお、熱変位の連続的な変化を記録するため、非接触式の変位計を用いるのが良い。
【００１２】
次に、この計測結果をもとに、最小二乗法等を用いて、次に示す［数１］によるカーブフィットを行い、基準回転速度における回転速度を上げた時の飽和時熱変位量（熱変位変化幅）、および熱変位時定数を求める。そして、基準回転速度を最高回転速度までにおいて例えば１０００〜２０００ｍｉｎ^−１刻みで変えて、次々と回転速度を上げた時の飽和時熱変位量、熱変位時定数を１０００〜２０００ｍｉｎ^−１刻みで計測し、求める。なお、測定例として、最高回転速度である１２０００ｍｉｎ^−１の回転数で主軸を回した場合の結果を図１に示し、この結果をカーブフィットしたものを［数２］で示す。
【００１３】
【数１】

【数２】

【００１４】
一方、回転速度を下げる場合について説明する。回転速度を上げた時と同様に、基準回転速度（例えば最高回転速度）の状態で主軸が十分に熱変位が安定している状態から主軸を停止させ、主軸とテーブル間の熱変位変化と時間を記録する。その後、飽和時熱変位量と熱変位時定数を、回転速度を上げた時と同様にして求める。これを各種基準回転速度において繰返す。
【００１５】
そして、熱変位量が主軸回転速度と関係があり［数３］の２次式近似とよく一致することを利用し、上記方法において求めた複数の飽和時熱変位量と基準回転速度（指令回転速度）とを次の［数３］に代入し、近似係数β，γをメモリに記憶する。
【００１６】
【数３】

【００１７】
また、上記方法において求めた熱変位時定数と指令回転速度を用いて、次の［数４］で表される近似式における近似係数１〜３を求める。［数４］は、熱変位が増大する場合と減少する場合で近似係数１〜３が異なるので、回転数を上げる場合と下げる場合とに分けて近似係数１〜３をそれぞれ算出し、メモリ上に記憶する。なお、運転時の近似係数１〜３の選択方法は［数５］で行う。
【００１８】
【数４】

【数５】

【００１９】
熱変位の推定演算方法について説明する（補正段階）。熱変位は継続的に変化するので、熱変位の推定は次の［数６］により演算する。このとき、回転数変化時の時間を基点とする。また［数６］から、［数７］に示す回転速度変化後の熱変位変化量と、［数８］に示すその変化時間を見積もることができる。必要とする加工精度が可能かの判定は、これらの式を用いて行う。
【００２０】
【数６】

【数７】

【数８】

【００２１】
次に、熱変位補正の推定誤差が、予め設定された誤差以内になる状態を判断する。熱変位補正にあたり、一般的な機械の温度計測値を用いる方法では、主軸温度と機体基準温度の差と、熱変位量との関係式を用いる。これは、飽和状態で温度上昇と熱変位量の関係が線形特性を有し、比較的容易に補償が可能であるためである。
【００２２】
例として、図２の運転条件での主軸温度上昇と、主軸とテーブル間の熱変位変化の計測結果を図３に示す。また、この結果に基づき次の［数９］によって温度上昇値から熱変位量を推定演算したときの推定誤差を図４に示す。この結果から、過渡状態において熱変位推定誤差が発生し、その誤差は回転速度変化後の熱変位変化量と熱変位変化時定数、並びに計測された温度の時定数の関数で表すことができると分かる。そこで、誤差の評価関数を［数１０］で表す。
【００２３】
【数９】

【数１０】

【００２４】
また［数１０］を用いての計算結果例を図５に示す。この図から［数１０］は極大値をもつ関数であることが分かる。そこで、次の［数１１］を満足する時間ｔ_ｂとしては、極大値を越えたものを求めることになる。そして、この時間ｔ_ｂだけ加工の停止をする（待機段階）。これにより、変位変化が許容値以内に収まり、加工精度の確保が可能になる。
【００２５】
【数１１】

【００２６】
そして、この熱変位推定演算を推定する工作機械の熱変位量の経時変化に合わせる調整方法について説明する。調整には、主軸回転速度と飽和時熱変位量の関係式を［数３］の近似式で表していることから近似係数βの調整（適宜の更新、記憶のし直し）をする。このとき、近似係数γが変化することは少ないので、近似係数βのみの調整で良い。
【００２７】
近似係数βの調整方法としては、主軸回転前と、回転し熱変位が飽和した状態とにおいての熱変位量を計測して調整する方法と、回転して熱変位が飽和した状態での計測温度上昇値から調整する方法がある。前者の方法においては、計測値と予めメモリに記憶した値を比較し、異なっていれば計測値から得た近似計数βをメモリに上書きして調整を行う。
【００２８】
また、後者のように温度計測を用いて調整する場合には、次の［数１２］に示すように、熱変位飽和状態で温度上昇値と熱変位量の関係が線形性を有することを利用し、［数７］のように予め実験（シミュレーション）により定数αを求め記憶しておき、主軸が停止し温度が安定している状態を基準として、主軸を最高回転速度で回転させた時の主軸の温度上昇値を計測する。その後、［数１２］を基に熱変位量を換算して、計測した主軸回転速度と熱変位量をもとに［数３］の近似係数βの調整を行う。この場合、機体等を基準温度にして、主軸の温度上昇値として算出してもよい。
【００２９】
【数１２】

【００３０】
【発明の実施の形態】
以下、本発明を立形マシニングセンタに具体化した実施形態を図面に基づいて説明する。図６は当該実施形態の概略を示すものであるが、横形マシニングセンタの場合も同様のシステムを採用できる。
【００３１】
立形マシニングセンタは、周知のように、主軸ヘッド１、コラム２、主軸３、ベッド４、移動テーブル５等から構成されている。主軸３にはその発熱温度を測定する第１温度センサ６が取り付けられ、ベッド４には基準温度を測定する第２温度センサ７が取り付けられている。温度測定装置８は各温度センサ６，７からのアナログ信号をデジタル信号に変換して数値化する。熱変位推定演算判定器９は、数値化された温度データと、メモリを有する記憶装置１０に予め記憶された補正パラメータとに基づき熱変位量を推定して補正量を算出する。
【００３２】
また、記憶装置１０には、主軸３の主軸回転速度、熱変位および時定数の情報が記憶されており、該記憶情報と主軸３の運転状況を基に、熱変位推定演算判定器９にて、今後の熱変位変化量を予測し、回転速度変化情報を基に加工継続か否かを判定し、ＮＣ装置１１は、その情報に従って加工を行う。また、熱変位推定演算判定器９において、主軸３の温度上昇値の情報から熱変位量を換算し、記憶装置１０に格納されている主軸回転速度と熱変位の情報の更新を行う。
【００３３】
図７は熱変位推定方法の一実施形態を示すフローチャートである。熱変位推定演算判定器９は、主軸回転速度の変化の検出を把握すると（Ｓ−１）、回転速度変化直前の熱変位量を［数６］により算出する（Ｓ−２）。このときの推定演算熱変位量ＥＳＴ_０は、先回の回転数変化時のものを用い、時間ｔは回転変化前の回転速度での運転時間を用いる。この計算結果を推定演算熱変位量ＥＳＴ_０として更新記録する。
【００３４】
次に、熱変位推定演算判定器９は、回転速度変化があってからの時間を計測するために、時間ｔのカウントを開始する（Ｓ−３）。この時間ｔは、熱変位変化量を演算するのに用いる。熱変位推定演算判定器９は、［数３］を用い、指令された回転速度での飽和時熱変位量の算出（Ｓ−４）を行う。
【００３５】
更に、熱変位推定演算判定器９は、熱変位時定数の算出を、熱変位が増大する場合と減少する場合で異なる時定数を［数５］により定めたうえで（Ｓ−５）、［数４］により行う（Ｓ−６）。即ち、熱変位推定演算判定器９は、熱変位時定数を、熱変位の方向に基づいて選択演算する。
【００３６】
続いて、熱変位推定演算判定器９は、待機時間の算出をする（Ｓ−７）。ここでは、熱変位補正の推定誤差が、予め設定された誤差以内になる時間を算出する。主軸熱変位の補正システムとして一般的に温度を用いる方法では、主軸熱変位変化の過渡状態で補正誤差を生じることが多く、その補正誤差は、回転数変化後から飽和までの熱変位変化量、熱変位時定数、計測している温度の時定数と密接な関係がある。そこで、誤差量の時間変化関数を［数１０］で求める。
【００３７】
例として、図５の誤差曲線を有する場合で、許容値が５μｍ、即ち誤差量が５μｍである時間ｔを算出する。（Ａ_Ｓ−ＥＳＴ_０）＝２０μｍ，Ｔ_Ｓ＝１２ｍｉｎ，Ｔ_Ｔ＝３ｍｉｎの場合、ｔ＝１．３１ｍｉｎと１６．４３ｍｉｎを得る。ここで、１．３１ｍｉｎは、この時間後に誤差が拡大するため、１６．４３ｍｉｎを待機時間として算出する。
【００３８】
待機時間中は、加工停止指令とともに、必要があれば待機時間を含めたメッセージの表示を行う（Ｓ−８）。待機方法としては、回転速度変化後の時間で［数６］［数１０］を用いて誤差量を継続的に計算し、その結果が予め設定した値に達するまでとしてもよい。
【００３９】
そして、待機後と判断された場合（Ｓ−９でＹｅｓ）、熱変位推定演算判定器９は、ＮＣ装置１１に対し、加工開始を指令する（Ｓ−１０）。
【００４０】
熱変位推定演算に使用する主軸回転速度と熱変位量の経時変化に関する調整方法について、主に図８に基づき説明する。なお、当該調整は、加工毎に行ってもよいし、所定加工回数毎に行ってもよいし、所定時間経過後の最初の加工において行ってもよい。また、調整のための運転を個別にするようなものであってもよい。
【００４１】
主軸３の温度上昇値を回転の開始時を基点とする場合には、主軸３が十分冷えた状態で、基準温度からの温度上昇とする場合には、温度が飽和したときの基準温度との差を温度上昇値として算出する（Ｓ−１１）。
【００４２】
続いて立形マシニングセンタにおいて予め求めておいた、温度上昇値と熱変位の関係式から現在の熱変位量を求める（Ｓ−１２）。その後、記憶されている回転速度と熱変位量の関係係数を比較し、異なっていれば、記憶装置１０のメモリにおける更新（記憶のし直し）を行う（Ｓ−１３）。なお、常時関係係数を更新するものであってもよい。
【００４３】
本説明は、マシニングセンタにおいて説明を行ったが、同様に回転工具により加工を行うターニングセンタについても適用できる。また、主軸の熱変位により加工寸法が変化する旋盤においても同様の手法にて、適用可能である。
【００４４】
【発明の効果】
以上のように、本発明によれば、安定までの時間を推定することで精度確保の待ち時間を最小化し、加工の効率化をおこなうことができ、その推定に用いる熱変位情報の更新が成されるので、高精度な推定が維持される。また、熱変位補正機能を有する場合においても、熱変位推定誤差の生じ易い主軸回転数変化後の過渡状態での推定補償誤差量を推定することで、加工精度の向上を効率的に図れるという優れた効果を奏する。
【図面の簡単な説明】
【図１】主軸の変位変化の経時変化を示す特性図である。
【図２】主軸の回転速度の経時変化を示す特性図である。
【図３】主軸の変位変化と温度上昇の経時変化を示す特性図である。
【図４】温度上昇値により熱変位を推定した誤差の経時変化を示す特性図である。
【図５】評価関数の経時変化を示す特性図である。
【図６】本発明の方法が実施される立形マシニングセンタの概略図である。
【図７】本発明による熱変位推定方法の一実施形態を示すフローチャートである。
【図８】本発明による熱変位調整方法の一実施形態を示すフローチャートである。
【符号の説明】
１・・主軸ヘッド、２・・コラム、３・・主軸、４・・ベッド、５・・移動テーブル、６・・第１温度センサ、７・・第２温度センサ、８・・温度測定装置、９・・熱変位推定演算判定器、１０・・記憶装置、１１・・ＮＣ装置。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for estimating and correcting a thermal displacement in a machine tool and appropriately stopping the processing, thereby increasing the processing accuracy.
[0002]
[Prior art]
Generally, a machine tool has a heat source (for example, a rolling bearing of a main shaft) in each part due to the characteristics of the machine, and the heat generated by this heat source is transmitted to each part of the machine to cause thermal deformation of the body. Since the thermal deformation of the fuselage greatly affects the processing accuracy, a method for preventing the thermal deformation is widely adopted as a preventive measure by using the estimation of the thermal displacement from the fuselage temperature information. Here, as the estimation of the thermal displacement, the one shown in Patent Document 1 by the same applicant as the present application is known.
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 9-225781
In the estimation of the thermal displacement, the thermal displacement of the spindle is estimated from the transient state after the change in the rotational speed to the steady state while changing the coefficient of the arithmetic expression according to the rotational speed and the time or the estimated number of times.
[0005]
[Problems to be solved by the invention]
In the above estimation of the thermal displacement, even if the amount of thermal displacement changes due to the aging of the portion related to the heat source, the environmental change, etc., the method of changing the coefficient of the arithmetic expression does not change. It will not match the actual situation.
[0006]
Therefore, an object of the present invention is to provide a method for estimating thermal displacement, which is capable of responding to a change in the amount of thermal displacement due to aging, and which can maintain a high processing accuracy regardless of aging. Is to do.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention obtains an approximate coefficient of the thermal displacement at the time of saturation or the thermal displacement time constant by performing an experiment to obtain a thermal displacement at the time of operating the heat source at each operating speed in advance. A preliminary stage to be stored, a temperature rise value of the heat source temperature, a thermal displacement estimation calculation obtained from the temperature rise value, a correction stage to correct the same, and a saturation thermal displacement amount and a thermal displacement in the memory when the operating speed changes. Calculating a change in the error value from the time constant, obtaining a time when the error value becomes an allowable value, and stopping machining for the time, and performing a heat operation calculated from the corresponding temperature increase value during the operation in which the thermal displacement is saturated. It is characterized in that an approximation coefficient is calculated from the displacement amount and the operation speed command value at the time of the operation, and when at least different from the corresponding approximation coefficient in the memory, the approximation coefficient is stored in the memory again ( Claim 1).
[0008]
The present invention also provides a preliminary step of obtaining an approximate coefficient of the thermal displacement at the time of saturation or the thermal displacement time constant by performing an experiment for previously obtaining a change in the thermal displacement during the operation of the heat source at each operation speed, and storing the approximate coefficient in the memory. Obtain the temperature rise value of the temperature, calculate the thermal displacement estimation calculation from the temperature rise value, and correct it, and change the error value from the saturation thermal displacement amount and the thermal displacement time constant in the memory when the operating speed changes. And obtaining a time when the error value becomes an allowable value and stopping the machining for the time, at least, the amount of thermal displacement measured at the time of operation when the thermal displacement is saturated, the approximate coefficient on the memory and the When the thermal displacement calculated from the operation speed command value during operation is different from the thermal displacement, the approximation coefficient is calculated from the measured thermal displacement and the operation speed command value and stored in the memory again ( Claim 2).
[0009]
Hereinafter, the principle of the thermal displacement estimating method according to the present invention will be described for a machine tool including a control unit having a memory, a main shaft and a table, having a heat source as a main shaft and rotating the operation. The change in the spindle thermal displacement of the machine tool occurs after the spindle rotation speed (rotation speed) changes. At this time, it can be divided into a transient state in which the thermal displacement continuously changes and a stable steady state in which the thermal displacement does not change.
[0010]
In general, the thermal displacement increases as the rotation speed increases. The thermal displacement time constant is almost uniquely determined with respect to the spindle rotation speed by the configuration of the spindle and the cooling capacity when the spindle outer cylinder is cooled. In many cases, the time constant is different between when the rotation speed increases and when the heat generation amount decreases because the rotation speed decreases, and the time constant changes depending on the main shaft rotation speed. Further, the amount of thermal displacement with respect to the rotation speed changes due to a change with time such as a change in the performance of the spindle cooling device and deterioration of the bearing.
[0011]
A method of calculating the amount of thermal displacement at the time of spindle saturation caused by the rotation speed and the time constant (part of an experiment or a simulation, preliminary stage) will be described from the case where the rotation speed is increased. First, in a state where the spindle is stopped and the thermal displacement is sufficiently stabilized, rotation at the reference rotational speed is started and continued, and the change in thermal displacement between the spindle and the table and the time are recorded. In order to record a continuous change in thermal displacement, a non-contact type displacement meter is preferably used.
[0012]
Next, based on the measurement results, a curve fit by the following [Equation 1] is performed using the least squares method or the like, and the amount of thermal displacement at saturation (heat) when the rotation speed at the reference rotation speed is increased. Displacement change width) and thermal displacement time constant. Then, the reference rotational speed is changed up to the maximum rotational speed, for example, in increments of 1000 to 2000 min ⁻¹ , and the amount of thermal displacement at saturation and the thermal displacement time constant when the rotational speed is increased one after another are measured in increments of 1000 to 2000 min ^−1. And ask. As a measurement example, the result when the main shaft is rotated at a rotation speed of 12000 min ^-1 which is the maximum rotation speed is shown in FIG. 1, and the result obtained by curve fitting is shown by [Equation 2].
[0013]
(Equation 1)

(Equation 2)

[0014]
On the other hand, a case where the rotation speed is reduced will be described. In the same way as when the rotation speed is increased, the spindle is stopped from a state where the thermal displacement of the spindle is sufficiently stable at the reference rotational speed (for example, the maximum rotational speed), and the change in thermal displacement between the spindle and the table and time Record Thereafter, the amount of thermal displacement at the time of saturation and the thermal displacement time constant are obtained in the same manner as when the rotational speed is increased. This is repeated at various reference rotational speeds.
[0015]
Using the fact that the amount of thermal displacement is related to the spindle rotational speed and agrees well with the quadratic approximation of [Equation 3], the plurality of thermal displacement amounts at saturation and the reference rotational speed (command rotational speed) obtained by the above method are used. ) Is substituted into the following [Equation 3], and the approximate coefficients β and γ are stored in the memory.
[0016]
[Equation 3]

[0017]
Further, using the thermal displacement time constant and the command rotational speed obtained in the above method, approximate coefficients 1 to 3 in an approximate expression expressed by the following [Equation 4] are obtained. [Equation 4] is different from the approximation coefficients 1 to 3 when the thermal displacement increases and decreases. Therefore, the approximation coefficients 1 to 3 are calculated for the case where the rotational speed is increased and the case where the thermal displacement is decreased, respectively. To memorize. The method of selecting the approximation coefficients 1 to 3 during operation is performed by [Equation 5].
[0018]
(Equation 4)

(Equation 5)

[0019]
A method for estimating thermal displacement will be described (correction stage). Since the thermal displacement changes continuously, the estimation of the thermal displacement is calculated by the following [Equation 6]. At this time, the time when the rotation speed changes is set as a base point. Further, from [Equation 6], it is possible to estimate the amount of change in thermal displacement after a change in the rotational speed shown in [Equation 7] and the change time shown in [Equation 8]. The determination as to whether the required processing accuracy is possible is made using these equations.
[0020]
(Equation 6)

(Equation 7)

(Equation 8)

[0021]
Next, a state is determined in which the estimated error of the thermal displacement correction is within a preset error. In correcting thermal displacement, a general method using measured temperature values of a machine uses a relational expression between a difference between a spindle temperature and a body reference temperature and a thermal displacement amount. This is because the relationship between the temperature rise and the amount of thermal displacement has a linear characteristic in a saturated state and can be compensated relatively easily.
[0022]
As an example, FIG. 3 shows a measurement result of a temperature rise of the spindle under the operating conditions of FIG. 2 and a change in thermal displacement between the spindle and the table. FIG. 4 shows an estimation error when the thermal displacement amount is estimated and calculated from the temperature rise value by the following [Equation 9] based on the result. From this result, a thermal displacement estimation error occurs in the transient state, and the error can be represented by a function of the thermal displacement change amount after the rotation speed change, the thermal displacement change time constant, and the time constant of the measured temperature. I understand. Therefore, the error evaluation function is represented by [Equation 10].
[0023]
(Equation 9)

(Equation 10)

[0024]
FIG. 5 shows an example of calculation results using [Equation 10]. From this figure, it can be seen that [Equation 10] is a function having a maximum value. Therefore, the time t _b that satisfies the following Equation 11], thus obtaining what exceeds the maximum value. Then, the time t _b just stop working (waiting stage). As a result, a change in displacement falls within an allowable value, and processing accuracy can be ensured.
[0025]
[Equation 11]

[0026]
An adjustment method for adjusting the thermal displacement amount of the machine tool for estimating the thermal displacement estimating operation according to the temporal change will be described. In the adjustment, the approximation coefficient β is adjusted (appropriate updating and re-storing) because the relational expression between the spindle rotation speed and the thermal displacement at the time of saturation is expressed by the approximate expression of [Equation 3]. At this time, since the approximation coefficient γ rarely changes, adjustment of only the approximation coefficient β is sufficient.
[0027]
As a method of adjusting the approximation coefficient β, there are a method of measuring and adjusting the amount of thermal displacement before and after rotation of the spindle and a state where the thermal displacement is saturated, and a method of measuring the temperature when rotating and the thermal displacement is saturated. There is a way to adjust from the rising value. In the former method, the measured value is compared with a value stored in the memory in advance, and if different, the approximate count β obtained from the measured value is overwritten in the memory to perform adjustment.
[0028]
Further, when the adjustment is performed by using the temperature measurement as in the latter case, as shown in the following [Equation 12], the relationship between the temperature rise value and the amount of thermal displacement in the thermal displacement saturated state has linearity. Then, as shown in [Equation 7], a constant α is obtained and stored in advance by an experiment (simulation) and stored when the spindle is stopped and the temperature is stable. Measure the temperature rise of the spindle. After that, the thermal displacement amount is converted based on [Equation 12], and the approximation coefficient β of [Equation 3] is adjusted based on the measured spindle rotational speed and thermal displacement amount. In this case, the temperature may be calculated as the temperature rise value of the main shaft with the body or the like as the reference temperature.
[0029]
(Equation 12)

[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is embodied in a vertical machining center will be described with reference to the drawings. FIG. 6 shows an outline of the embodiment, but a similar system can be adopted in the case of a horizontal machining center.
[0031]
As is well known, the vertical machining center includes a spindle head 1, a column 2, a spindle 3, a bed 4, a moving table 5, and the like. The main shaft 3 is provided with a first temperature sensor 6 for measuring the heat generation temperature, and the bed 4 is provided with a second temperature sensor 7 for measuring a reference temperature. The temperature measuring device 8 converts analog signals from the temperature sensors 6 and 7 into digital signals and converts them into numerical values. The thermal displacement estimating operation determining unit 9 estimates the thermal displacement amount based on the digitized temperature data and the correction parameter stored in the storage device 10 having a memory in advance, and calculates the correction amount.
[0032]
The storage device 10 stores information on the spindle rotation speed, the thermal displacement, and the time constant of the spindle 3. The amount of thermal displacement change in the future is predicted, and it is determined whether or not to continue processing based on the rotational speed change information, and the NC apparatus 11 performs the processing according to the information. The thermal displacement estimator 9 determines the amount of thermal displacement from the information on the temperature rise value of the spindle 3 and updates the information on the spindle rotational speed and the thermal displacement stored in the storage device 10.
[0033]
FIG. 7 is a flowchart illustrating an embodiment of the thermal displacement estimation method. When detecting the change in the spindle rotational speed (S-1), the thermal displacement estimating / determining unit 9 calculates the thermal displacement amount immediately before the rotational speed change by (Equation 6) (S-2). At this time, the estimated operation thermal displacement amount EST ₀ is the value at the time of the previous rotation speed change, and the time t is the operation time at the rotation speed before the rotation change. This calculation result is updated and recorded as the estimated thermal displacement amount EST ₀ .
[0034]
Next, the thermal displacement estimating operation determining unit 9 starts counting the time t in order to measure the time after the rotation speed has changed (S-3). This time t is used to calculate the amount of change in thermal displacement. The thermal displacement estimating operation determining unit 9 calculates the thermal displacement amount at the time of the commanded rotational speed at the time of the saturation using the [Equation 3] (S-4).
[0035]
Further, the thermal displacement estimation calculation / determination unit 9 calculates the thermal displacement time constant according to [Equation 5] with different time constants when the thermal displacement increases and decreases (S-5), Equation 4] (S-6). That is, the thermal displacement estimation calculation determining unit 9 selects and calculates the thermal displacement time constant based on the direction of the thermal displacement.
[0036]
Subsequently, the thermal displacement estimating operation determining unit 9 calculates a standby time (S-7). Here, a time is calculated in which the estimated error of the thermal displacement correction is within a preset error. In a method that generally uses temperature as a correction system for the spindle thermal displacement, a correction error often occurs in a transient state of the spindle thermal displacement change, and the correction error includes a thermal displacement change amount from a rotation speed change to saturation, There is a close relationship with the thermal displacement time constant and the time constant of the temperature being measured. Therefore, a time change function of the error amount is obtained by [Equation 10].
[0037]
As an example, when the error curve shown in FIG. 5 is provided, the time t at which the allowable value is 5 μm, that is, the amount of error is 5 μm, is calculated. When (A _S -EST ₀ ) = 20 μm, T _S = 12 min, and T _T = 3 min, t = 1.31 min and 16.43 min are obtained. Here, since the error increases at 1.31 min after this time, 16.43 min is calculated as the standby time.
[0038]
During the standby time, a message including the standby time is displayed together with the machining stop command if necessary (S-8). As a standby method, the error amount may be continuously calculated using [Equation 6] and [Equation 10] at the time after the rotation speed is changed, and the error amount may be calculated until the result reaches a preset value.
[0039]
Then, when it is determined that the state is after standby (Yes in S-9), the thermal displacement estimation calculation determination unit 9 instructs the NC device 11 to start machining (S-10).
[0040]
A method for adjusting the rotational speed of the spindle and the amount of thermal displacement over time used in the thermal displacement estimation calculation will be described mainly with reference to FIG. The adjustment may be performed for each processing, may be performed every predetermined number of times, or may be performed in the first processing after a lapse of a predetermined time. Further, the operation for adjustment may be performed individually.
[0041]
When the temperature rise value of the main shaft 3 is set as the starting point of the rotation, the main shaft 3 is in a sufficiently cooled state, and when the temperature is raised from the reference temperature, when the temperature rises from the reference temperature, the difference between the temperature and the reference temperature when the temperature is saturated. The difference is calculated as a temperature rise value (S-11).
[0042]
Subsequently, the current thermal displacement amount is determined from the relational expression between the temperature rise value and the thermal displacement, which has been determined in advance in the vertical machining center (S-12). Thereafter, the stored relationship coefficient between the rotational speed and the thermal displacement is compared, and if different, the memory in the storage device 10 is updated (stored again) (S-13). It should be noted that the relationship coefficient may be constantly updated.
[0043]
Although the description has been made with reference to the machining center, the present invention can be similarly applied to a turning center that performs machining with a rotary tool. Further, the present invention can be applied to a lathe in which a processing dimension changes due to a thermal displacement of a spindle by a similar method.
[0044]
【The invention's effect】
As described above, according to the present invention, by estimating the time until stabilization, the waiting time for ensuring accuracy can be minimized, and the efficiency of machining can be improved, and the thermal displacement information used for the estimation can be updated. Therefore, a highly accurate estimation is maintained. In addition, even in the case where the thermal displacement correction function is provided, it is possible to efficiently improve the machining accuracy by estimating the amount of compensation error in a transient state after a change in the spindle rotational speed at which a thermal displacement estimation error is likely to occur. Has the effect.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing a change over time in a displacement change of a main shaft.
FIG. 2 is a characteristic diagram showing a change over time in a rotation speed of a main shaft.
FIG. 3 is a characteristic diagram showing a change in displacement of a main shaft and a change with time in temperature rise.
FIG. 4 is a characteristic diagram showing a change with time of an error in estimating a thermal displacement based on a temperature rise value.
FIG. 5 is a characteristic diagram showing a temporal change of an evaluation function.
FIG. 6 is a schematic diagram of a vertical machining center in which the method of the present invention is implemented.
FIG. 7 is a flowchart illustrating an embodiment of a thermal displacement estimation method according to the present invention.
FIG. 8 is a flowchart illustrating an embodiment of a thermal displacement adjusting method according to the present invention.
[Explanation of symbols]
1. spindle head, 2. column, 3. spindle, 4. bed, 5. moving table, 6. first temperature sensor, 7. second temperature sensor, 8. temperature measuring device, 9 ··························································································· NC device.

Claims

A preliminary step of obtaining an approximate coefficient of the thermal displacement at the time of saturation or the thermal displacement time constant by an experiment to obtain the thermal displacement during the heat source operation at each operating speed in advance,
A correction step of obtaining a temperature rise value of the heat source temperature, obtaining a thermal displacement estimation calculation from the temperature rise value, and correcting this;
When the operating speed changes, the change in error value is determined from the amount of thermal displacement at the time of saturation and the thermal displacement time constant on the memory.
When an approximation coefficient is calculated from the thermal displacement amount calculated from the corresponding temperature rise value during the operation in which the thermal displacement is saturated and the operation speed command value during the operation and is different from at least the corresponding approximation coefficient in the memory. A high-precision machining method for a machine tool, wherein the method is stored again in a memory.

A preliminary step of obtaining an approximate coefficient of the thermal displacement at the time of saturation or the thermal displacement time constant by an experiment to obtain the thermal displacement during the heat source operation at each operating speed in advance,
A correction step of obtaining a temperature rise value of the heat source temperature, obtaining a thermal displacement estimation calculation from the temperature rise value, and correcting this;
When the operating speed changes, the change in error value is determined from the amount of thermal displacement at the time of saturation and the thermal displacement time constant on the memory.
At least, when the thermal displacement amount measured during the operation in which the thermal displacement is saturated and the thermal displacement amount calculated from the approximation coefficient on the memory and the operating speed command value during the operation are different, the measured thermal displacement amount is A high-precision machining method for a machine tool, wherein an approximation coefficient is calculated from an operation speed command value and stored in a memory.