JP6910057B2 - How to correct thermal displacement of machine tools - Google Patents

Description

The present invention relates to a method for correcting thermal displacement for suppressing a machining error in a work due to thermal displacement of a machine tool, and particularly to a method for selecting and changing a correction coefficient based on the amount of change in environmental temperature.

式（１）で求めた補正値でＮＣ装置の指令値を補正している。
本出願人は更に補正精度を向上すべく、例えば特許文献１に補正式に時間遅れに起因する項を取り入れた技術を提案し、特許文献２に予知できない外乱の影響を抑えるべく、補正値に隣接設定値なる項を加える技術を提案している。
本発明は、さらに補正精度の向上を目的に環境温度の変化量に応じて、補正係数を選定、変更することを提案する。 When machining a workpiece with a machine tool such as a lathe or a multi-tasking machine, heat is generated in the driving part such as the spindle motor and the tool spindle motor, and the machining part such as turning and milling.
The machine temperature changes due to these generated heats, changes in room temperature, etc., and this temperature change causes thermal displacement of the machine itself, resulting in machining errors in the workpiece.
Generally, a coefficient ακ is multiplied by a detection value tκ detected by attaching a temperature sensor to a key point such as a bed, a spindle head, or a tool post of a machine tool, and a correction value δ is obtained from this and a constant β.

The command value of the NC device is corrected by the correction value obtained by the equation (1).
In order to further improve the correction accuracy, the applicant proposes, for example, a technique in which a term caused by a time delay is incorporated into the correction formula in Patent Document 1, and the correction value is set in order to suppress the influence of unpredictable disturbance in Patent Document 2. We are proposing a technique to add a term called an adjacent set value.
The present invention proposes to select and change the correction coefficient according to the amount of change in the environmental temperature for the purpose of further improving the correction accuracy.

Japanese Patent No. 4469681 Japanese Patent No. 4105598

An object of the present invention is to provide a method for correcting thermal displacement of a machine tool, which can select and change a correction coefficient (environmental parameter) based on the amount of change in environmental temperature.

The method for correcting the thermal displacement of a machine tool according to the present invention includes a recording unit that records changes in the environmental temperature over time, and is based on the amount of change in the environmental temperature during the previous operation, and heat due to the change in the environmental temperature at the start of the next operation. It is characterized by setting a displacement correction coefficient.
This set or changed correction coefficient is incorporated into the coefficient ακ of the equation (1) to perform thermal displacement correction.
If the environmental temperature changes significantly, a certain correction formula may not be sufficient, so when the machine tool starts operating, the amount of change in the environmental temperature during the previous operation is checked, and the correction coefficient can be changed. There is a feature in.
Here, the state of the previous operation means the previous operation when the machine tool is to be operated after being stopped for a predetermined period of time.
Therefore, although it differs depending on the operating system of the machine tool, in general, the amount of change in the environmental temperature on the day before the start of operation is the target.

In the present invention, the environmental temperature refers to a parameter indicating the environmental state of the machine tool, and examples thereof include the room temperature at which the machine tool is installed, the coolant (coolant) whose circulation is controlled, and the temperature of the drive unit. Be done.
According to the investigation by the present inventor, it has been clarified that the influence of the coolant is the largest, followed by the room temperature and the temperature of the milling motor.
Therefore, the present invention focuses on the amount of change in room temperature (A), the amount of change in coolant temperature (B), and the amount of change in temperature of the milling motor (C), and a coefficient table pre-coefficientd according to each change amount. Was created so that the correction coefficient of equation (1) could be selected or changed.

In the present invention, changes over time in the temperature of the coolant, room temperature, and temperature of the milling motor are recorded in a recording unit provided in a control unit or the like, and the amount of temperature change on the previous day is calculated during operation to match the changes. Since the correction coefficient of the thermal displacement correction formula can be selected or changed, the thermal displacement correction accuracy is improved and the tuning of the machine tool becomes easier.
In this case, the correction coefficient may be changed automatically, or may be changed based on the user's confirmation command.

The flowchart of the system for automatically selecting and changing the environmental parameters according to the present invention is shown. A recording example of changes in environmental temperature over time is shown. An example of warning of temperature change of coolant is shown. A comparative example of the amount of change over time in processing to which the present invention is applied is shown.

A configuration example of the present invention will be described below based on the flowchart shown in FIG.
In the NC machine tool, the NC control unit or the like has a recording unit for changing the environmental temperature with time.
The value measured by the temperature sensor attached to the machine tool is sent to this recording unit.
In the flowchart shown in FIG. 1, an example is shown in which (A): temperature change at room temperature, (B): temperature change of coolant (coolant), and (C): temperature change of milling motor are used as the environmental temperature.
The graph is shown in FIG.

When the machine tool is started, the value of the amount of temperature change on the previous day is calculated and compared with a predetermined threshold value of each temperature.
For example, the amount of change in room temperature RT is _{less than 1} ° C, the _{amount of change in coolant temperature is less than CT 1} ° C, and the amount of change in milling motor temperature is less than _{MT 1 ° C.}
If neither of them exceeds the threshold value, the machine tool machining program proceeds.
If any of the temperatures exceeds the threshold value, the process proceeds to the selection of the correction coefficient.
At this time, for example, if the amount of change in room temperature exceeds RT _{1 and} exceeds RT ₂ ° C, or the amount of change in coolant temperature exceeds CT _{1 and} exceeds CT ₂ ° C, a warning display is also output.
An example thereof is shown in FIG.

制御部には、図１の表中に示したようにＸ＝０〜７の８つの区分に分けた係数テーブル表が記憶され、その中から式（１）の係数ακの組み合せを選定する。
この場合に、Ｘの式で求められた値の小数点第１位が０を超える場合に、クーラントの係数を２倍にして適用する。
さらに、補正式（１）の差分から定数βを修正する。
なお、この修正は自動制御してもよく、ユーザーの確認指令に基づいて実行してもよい。
制御部には、係数を変更した日付，時刻が記録される。
なお、表中隣接ｍとは本出願人による特許文献２に示した隣接設定値に対応する。 Next, from the amount of change in each temperature, one of the values "0", "1", and "1.1" is used for A, B, and C in the formula (2) according to the classification of A, B, and C in the table. To find the value of X.
In the table, CT ₃ is larger than _{CT 1 and} smaller than _{CT 2.}

As shown in the table of FIG. 1, the control unit stores a coefficient table table divided into eight categories of X = 0 to 7, and selects a combination of the coefficients ακ of the equation (1) from the table.
In this case, when the first decimal place of the value obtained by the formula of X exceeds 0, the coolant coefficient is doubled and applied.
Further, the constant β is corrected from the difference in the correction formula (1).
Note that this modification may be automatically controlled or executed based on a user confirmation command.
The control unit records the date and time when the coefficient was changed.
The adjacent m in the table corresponds to the adjacent set value shown in Patent Document 2 by the applicant.

FIG. 4 shows the amount of change over time in the machining dimensions of the workpiece with and without the application of the environmental parameters in which the optimum combination of coefficients was selected from the coefficient table based on the flowchart shown in FIG.
According to the present invention, it was confirmed that the processing error is reduced.

Claims (3)

Equipped with a recording unit that records changes in environmental temperature over time
It compares the environmental temperature and the environmental temperature of the next operation at the start of the previous operation, the correction method for a machine tool thermal displacement and sets the correction coefficient of thermal displacement due to the temperature difference. The method for correcting thermal displacement of a machine tool according to claim 1, wherein the environmental temperature includes a temperature difference of a coolant of the machine tool. The temperature difference between the environmental temperature include the temperature difference between the temperature difference and the milling motor room in addition to the temperature difference of the cooling fluid, and characterized in that based on the respective temperature differences, selecting a respective correction factor 2. The method for correcting thermal displacement of a machine tool according to claim 2.

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