JP6656945B2 - Compensation method for thermal displacement of machine tools - Google Patents

Compensation method for thermal displacement of machine tools Download PDF

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JP6656945B2
JP6656945B2 JP2016029314A JP2016029314A JP6656945B2 JP 6656945 B2 JP6656945 B2 JP 6656945B2 JP 2016029314 A JP2016029314 A JP 2016029314A JP 2016029314 A JP2016029314 A JP 2016029314A JP 6656945 B2 JP6656945 B2 JP 6656945B2
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thermal displacement
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啓太 佐々木
啓太 佐々木
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中村留精密工業株式会社
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本発明は、ワークの加工における工作機械の熱変形によって生ずるワークの加工誤差を補正する方法に関する。   The present invention relates to a method for correcting a processing error of a work caused by thermal deformation of a machine tool in processing the work.

工作機械は環境の温度変化、ワークを加工する際に発生する駆動熱、加工熱等により機械温度が変化し、機械温度の変化により熱変形が起こり、その熱変形がワークの加工誤差として現れる。
例えば、旋盤やマシニングセンタ等の工作機械においては、主軸の回転により軸受部等にて熱が発生し、工具による加工部でも熱が発生する。
これらの熱はベッド,コラム,主軸台,刃物台等に伝達され、工作機械の運転に伴って機械温度が局部的又は全体的に上昇し、それが熱変形となりワークの加工に誤差を与える。
The machine temperature of a machine tool changes due to environmental temperature changes, driving heat generated during processing of a workpiece, processing heat, and the like, and thermal deformation occurs due to a change in the machine temperature, and the thermal deformation appears as a processing error of the workpiece.
For example, in a machine tool such as a lathe or a machining center, heat is generated in a bearing or the like due to rotation of a main shaft, and heat is also generated in a machined portion by a tool.
The heat is transmitted to a bed, a column, a headstock, a tool rest, and the like, and the temperature of the machine locally or entirely rises with the operation of the machine tool, which causes thermal deformation and causes an error in machining of the work.

そこで、工作機械及びワークの熱変形による加工誤差を補正するために、従来は主軸台や刃物台の温度を計測し、これらの機械温度とワークに生ずる加工誤差との関係を予め計測し、この計測値から機械温度による加工誤差の補正式を求めてNC装置に登録しておき、実際にワークを加工するときにNC装置から出力される指令値を、そのときの機械温度を前記補正式に代入して得られた演算結果により刃物台の位置を補正することにより、加工誤差を小さくすることが行われている。   Therefore, in order to correct a processing error due to thermal deformation of a machine tool and a work, conventionally, the temperature of a headstock or a tool post is measured, and the relationship between the machine temperature and the processing error generated in the work is measured in advance. A correction formula for the processing error due to the machine temperature is obtained from the measured value and registered in the NC device, and a command value output from the NC device when actually processing a workpiece is converted into a machine temperature at the time by the correction formula. A processing error is reduced by correcting the position of a tool post based on a calculation result obtained by substitution.

しかし、工作機械が大型になり、例えばフレーム等に大型の鋳物構造物等を採用している場合に、従来の工作機械のベッドや構成部品のリアルタイムでの温度測定値に基づく補正では、機械温度の測定部位からワークの加工誤差に直接影響を及ぼす部位にまで熱伝達する時間的ズレを考慮していないため、必ずしも加工精度向上につながらない課題があった。
また従来は、補正精度の向上を目的に例えば主軸台,カップリングケース,フレーム等の複数の部位の温度を測定し、その差分を用いて変位に似せたカーブを生成し、補正値を求めることも行われているが、それでは測定点が多くなるとともに係数が大きいものになるため、イレギュラーな温度変化があった場合に補正値が急変して補正精度が不安定になる問題があった。
However, when the machine tool becomes large and, for example, employs a large casting structure or the like for a frame or the like, the correction based on the real-time temperature measurement values of the bed and the components of the conventional machine tool requires a machine temperature. Since the time lag of heat transfer from the measurement site to the site directly affecting the processing error of the work is not taken into account, there is a problem that the processing accuracy is not necessarily improved.
Conventionally, in order to improve the correction accuracy, the temperature of a plurality of parts such as a headstock, a coupling case, a frame, etc. is measured, and a difference-like curve is generated by using a difference between the temperatures to obtain a correction value. However, since the number of measurement points increases and the coefficient increases, the correction value suddenly changes when an irregular temperature change occurs, and the correction accuracy becomes unstable.

本出願人は、特許文献1において主軸回転数と機械温度の検出値の積の履歴値を用いた補正項を含む補正式を提案している。
この方法により、ワークの加工誤差の精度向上を達成させているものの、熱移動の遅れに関しては改善の余地が残されている。
The present applicant has proposed a correction formula including a correction term using a history value of a product of a spindle speed and a detected value of a machine temperature in Patent Document 1.
Although this method achieves an improvement in the accuracy of the processing error of the work, there is room for improvement in the delay of the heat transfer.

特許第4271611号公報Japanese Patent No. 4271611

本発明は、工作機械の熱変形に起因する加工点の熱変位即ちワークの加工誤差を小さくできる熱変位の補正方法の提供を目的とする。   SUMMARY OF THE INVENTION An object of the present invention is to provide a method for correcting a thermal displacement at a processing point due to thermal deformation of a machine tool, that is, a thermal displacement that can reduce a processing error of a work.

本発明に係る工作機械の熱変位の補正方法は、機械温度の測定データの履歴値と熱移動の遅れ値に基づいて演算した補正値により、NC装置の送り指令を補正することでワーク加工中の工具位置を補正することを特徴とする。
本明細書で熱変位とは、工作機械が熱変形したことにより生じる工具位置の変位をいう。
ここで熱移動の遅れ値とは、温度センサー等により所定のインターバルを設けて測定された過去のデータを逐次、データベースに格納しておき、ワークの加工時に、どれくらい過去の温度測定値に基づいて補正値を計算するのかを決める係数をいう。
In the method for correcting a thermal displacement of a machine tool according to the present invention, a work command is corrected by correcting a feed command of an NC device by a correction value calculated based on a history value of measured data of a machine temperature and a delay value of a heat transfer. The tool position is corrected.
In this specification, the term “thermal displacement” refers to a displacement of a tool position caused by a thermal deformation of a machine tool.
Here, the delay value of the heat transfer means that the past data measured at predetermined intervals by a temperature sensor or the like is sequentially stored in a database, and based on the past temperature measurement value during processing of the workpiece. A coefficient that determines whether to calculate a correction value.

本発明において、前記機械温度の測定データの履歴値は工作機械を構成する構造物又は/及び構成部分の温度の測定データの履歴値であってもよい。
ここで構造物とは、工作機械のフレーム,ベッド,テーブル,コラム等の機械的構造物をいい、構成部分とは主軸台,刃物台,ワーク支持台等の工作機械に備えた部品等からなる部分をいう。
In the present invention, the history value of the measurement data of the machine temperature may be a history value of the measurement data of the temperature of a structure or / and a component of the machine tool.
Here, the structure refers to a mechanical structure such as a frame, a bed, a table, and a column of a machine tool, and the constituent part includes components provided in the machine tool such as a headstock, a tool rest, and a work support. Part.

本発明に係る熱変位の補正方法は、ワークの加工時よりも所定の時間だけ過去の測定温度データに対して熱移動の遅れ値に対応した係数を用いて演算した補正値により、NC装置の送り指令を補正したので、従来の補正方法に比較してワークの加工精度が向上する。   The thermal displacement correction method according to the present invention is based on a correction value calculated by using a coefficient corresponding to a delay value of heat transfer with respect to measured temperature data in the past for a predetermined period of time from the time of processing a workpiece. Since the feed command is corrected, the processing accuracy of the workpiece is improved as compared with the conventional correction method.

また本発明において、工作機械を構成する相互に異なる部位、例えば主軸台の前後、フレームの各部位、カップリングケース等にそれぞれ温度センサー等の温度測定手段を取り付け、所定の時間的間隔を空けて測定した温度測定データを逐次格納しておき、ワークの加工方法や加工内容に応じて、温度変化と熱変形との相関が強い測定部位の過去の温度測定値を採用してもよい。
このようにすると、従来の複数の部位の差分による補正に比較して補正係数を小さくすることができ、温度の変動による補正値の急変が少なくなり、熱変位の補正が安定する。
Further, in the present invention, temperature measuring means such as a temperature sensor is attached to each of the different parts constituting the machine tool, for example, the front and rear of the headstock, each part of the frame, the coupling case, etc., at predetermined time intervals. The measured temperature measurement data may be sequentially stored, and a past temperature measurement value of a measurement site having a strong correlation between a temperature change and thermal deformation may be adopted according to a processing method and processing content of the work.
By doing so, the correction coefficient can be reduced as compared with the conventional correction based on the difference between a plurality of parts, and a sudden change in the correction value due to a temperature change is reduced, and the correction of the thermal displacement is stabilized.

本発明における熱移動の遅れを考慮した温度測定値の例を示す。4 shows an example of a temperature measurement value in the present invention in which a delay in heat transfer is considered. 従来のリアルタイム温度測定値の例を示す。5 shows an example of a conventional real-time temperature measurement value.

本発明に係る熱変位の補正方法の例を以下具体的に説明するが、本発明はこれに限定されない。
図1に工作機械の高速回転する主軸台前部に取り付けた温度センサーによる測定温度Tに、ワークの加工時に対して60分前の測定温度を採用した例を示す。
熱変位の補正値δは、δ=α×T+β(定数)の式で求められる。
式中の添字は、測定温度箇所を表す。
αは、採用した過去の測定温度Tと、熱変位と、その測定温度T温度の関係を一次関数で近似した場合の傾き(補正係数)をいう。
図1に示した例の場合に、NC装置の制御プログラムの演算部には温度データの格納部を有し、主軸台に取り付けた温度センサーによる測定値を例えば3分毎に逐次格納する。
格納するデータ数は、例えば最大240分前まで等、実用性、記録容量等を考慮して、順次所定時間以上過去のものは順送り消去してもよい。
また、図1は加工現在に対する60分前の過去の測定データを用いたが、どれだけ過去の測定データを用いるかは、予め計測して選定するのがよい。
さらには、何らかの理由により履歴を消失した場合は、残っている他の測定データを用いて補間してもよい。
An example of the method for correcting thermal displacement according to the present invention will be specifically described below, but the present invention is not limited thereto.
The measured temperature T 0 by a temperature sensor attached to the headstock front rotating at a high speed of the machine tool in FIG. 1 shows an example employing a measurement temperature of 60 minutes ago against during processing of the workpiece.
The correction value δ 0 of the thermal displacement is obtained by an equation of δ 0 = α 0 × T 0 + β 0 (constant).
The suffix in the formula indicates a measurement temperature point.
α 0 refers to the slope (correction coefficient) when the relationship between the adopted past measured temperature T 0 , thermal displacement, and the measured temperature T 0 temperature is approximated by a linear function.
In the case of the example shown in FIG. 1, the arithmetic unit of the control program of the NC device has a storage unit for temperature data, and sequentially stores values measured by a temperature sensor attached to the headstock, for example, every three minutes.
The number of data to be stored may be sequentially deleted for a predetermined time or more in consideration of practicality, recording capacity, and the like, for example, up to 240 minutes before.
Although FIG. 1 uses the past measurement data 60 minutes before the current processing, how much past measurement data is used is preferably measured and selected in advance.
Further, when the history is lost for some reason, interpolation may be performed using other remaining measurement data.

図2は、工作機械の各測定部位でのリアルタイム測定温度の変化のグラフを示す。
曲線1は、主軸台の後部に温度センサーを取り付けた場合であり、同様に曲線2はカップリングケース、曲線3はフレームの油圧タンク横部、曲線4はフレームの後部中央に温度センサーを取り付けた例である。
このように、リアルタイムの測定温度による補正は熱移動が考慮されていないので、加工初めの時から測定温度が上昇し、実際に熱変形が生じる前に補正量が加えられる。
よって、図1に示した本発明による補正方法よりも精度が悪い。
FIG. 2 shows a graph of a change in the real-time measured temperature at each measurement site of the machine tool.
Curve 1 shows the case where the temperature sensor was attached to the rear part of the headstock. Similarly, curve 2 shows the coupling case, curve 3 shows the side of the hydraulic tank of the frame, and curve 4 shows the case where the temperature sensor was attached to the center of the rear part of the frame. It is an example.
As described above, since the correction based on the measured temperature in real time does not consider heat transfer, the measured temperature increases from the beginning of the processing, and the correction amount is added before actual thermal deformation occurs.
Therefore, the accuracy is lower than the correction method according to the present invention shown in FIG.

なお、本発明においては上記にて例を挙げたように、工作機械の各部位での測定温度を一定のインターバルにて逐次格納部に格納した過去の測定温度データのうち、遅れ係数に基づく過去のデータに対する補正係数を予め定めて、格納部に記憶させるのもよい。
このようにすると、ワークの加工方法や加工条件によって適した部位と、遅れ係数を選定して補正値を求めることもできる。
例えば、主軸台後部は補正式δ=α×T+β、フレーム後部中央部の補正式δ=α×T+βのように、それぞれ演算式を格納登録しておき、ワークの加工時に読み出して選択指令を出し、プログラムの実行に用いることができる。
In the present invention, as described above, among the past measured temperature data stored in the storage unit at regular intervals at predetermined intervals, the measured temperature at each part of the machine tool is determined based on the past coefficient based on the delay coefficient. May be determined in advance and stored in the storage unit.
In this case, a correction value can be obtained by selecting a part suitable for the processing method and processing conditions of the work and a delay coefficient.
For example, arithmetic expressions are stored and registered in the headstock rear portion, such as a correction formula δ 1 = α 1 × T 1 + β 1 , and a correction formula δ 2 = α 2 × T 2 + β 2 in a frame rear center portion. It can be read out at the time of machining a workpiece and issue a selection command to be used for executing a program.

Claims (1)

機械温度の測定データの履歴値と熱移動の遅れ値に基づいて演算した補正値により、NC装置の送り指令を補正することでワーク加工中の工具位置を補正するものであり、
工作機械を構成する構造物の異なる部位又は/及び構成部品毎に、前記測定データの履歴値と熱移動の遅れ値に基づいた補正値を演算する複数の演算式を格納部に格納してあり、
前記複数の演算式から加工条件に適した演算式の選択手段を有していることを特徴とする工作機械の熱変位の補正方法。
The tool position during work machining is corrected by correcting the feed command of the NC device with the correction value calculated based on the history value of the measurement data of the machine temperature and the delay value of the heat transfer ,
A plurality of arithmetic expressions for calculating a correction value based on the history value of the measurement data and the delay value of the heat transfer are stored in the storage unit for each of different parts or / and components of the structure constituting the machine tool. ,
A method for correcting thermal displacement of a machine tool, comprising: means for selecting an arithmetic expression suitable for machining conditions from the plurality of arithmetic expressions .
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