JP2010120150A - Estimation method for thermal deformation compensation of machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an estimation method for thermal deformation compensation for improving machining accuracy by applying the status temperature of a motor as a physical variable of independent displacement estimation calculation. <P>SOLUTION: A driving system operation value during movement of a numerical control lathe, a correction value changing by the number of spindle rotation, for example, is calculated and estimated as the traveling amount of a feed shaft based on a first estimation formula including the driving system operation value. The value obtained by calculating and estimating the correction value changing by the spindle motor stator temperature during movement of the numerical control lathe based on a second estimation formula including the spindle motor stator temperature as the movement amount of a feed shaft is added to the correction value, thus gaining the estimation value of thermal correction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an estimation method for correcting thermal deformation for correcting the thermal displacement of a machine tool to improve the processing accuracy of workpiece processing. More specifically, the present invention relates to an estimation method for correcting thermal deformation of a machine tool in which an estimation formula based on a stator temperature of a spindle motor or a temperature in the vicinity of a bearing is taken into account to improve the accuracy of a correction value.

  In a machine tool, heat is generated as the workpiece is processed. Therefore, thermal deformation is generated not only in the workpiece but also in the machine tool structure, and the shape accuracy and dimensional accuracy of the workpiece are deteriorated. For this reason, various techniques have been developed for reducing this influence as much as possible, that is, for correcting thermal deformation. This thermal deformation correction technology has conventionally had many techniques, such as a method for controlling the structure of a machine tool to be kept at a constant temperature, or a method for predicting and correcting thermal deformation due to a temperature change. Proposed.

  In this correction of thermal deformation, if it matches the actual measurement value, the machining accuracy will be improved. For this purpose, a calculation formula that approximates the actual measurement is set according to the characteristics of each machine tool, and the NC controller Calculation processing is performed to correct the feed value of each drive system. For example, the applicant of the present invention also analyzes machining accuracy or machine tool behavior caused by thermal deformation of the motion mechanism due to changes in ambient temperature, and corrects the amount of motion of the motion mechanism according to the analysis result. Therefore, a correction technique that can improve machining accuracy is proposed as a technique applied to a machining center and an NC lathe (see Patent Documents 1 and 2).

In addition, correction for machining error due to thermal displacement is detected by a temperature sensor, and machining error is corrected based on an equation that calculates a calculated temperature change that behaves the same as the thermal behavior of the machine tool's thermal displacement from this detected temperature change. The technique to do is also known (for example, refer patent document 3, 4, 5). Furthermore, a technique for detecting the spindle speed and performing thermal correction using an arithmetic expression is also known (see, for example, Patent Document 6). Furthermore, a technique for measuring and correcting the outer peripheral temperature of the motor stator with a partially attached sensor is also known (see, for example, Patent Document 7).
JP 2004-237394 A JP 2003-108206 A Japanese Patent No. 3792266 JP-A-8-300242 JP-A-9-108992 JP 2006-116663 A JP-A-9-85582

  As described above, with respect to accuracy correction accompanying thermal deformation in a machine tool, analysis is performed to correct the detected detection value by estimating the deformation using an arithmetic expression via detection means such as a temperature sensor. . Deformation during machine tool operation varies depending on the characteristics of the machine tool. For this reason, the deformation is corrected by controlling the drive system so that it becomes a numerical value that approximates the actual measurement value empirically, taking into account a predetermined coefficient that is different for each machine tool as a correction factor.

  However, in recent years, with the increase in speed, the influence of thermal deformation on machining accuracy has increased. For example, many spindles and the like have a so-called built-in type configuration in which a motor is directly incorporated into the spindle for speeding up. For this reason, the spindle and the like are directly influenced by the heat of the motor, and the amount of thermal deformation and the rate of change thereof are larger than those of a conventional machine tool having a general spindle configuration. These corrections are calculated by estimating a correction value assuming an arithmetic expression close to actual measurement. The normal correction is often performed by following only the change according to a predetermined factor, for example, when the acceleration / deceleration operation of the motor is large, when the rotation time under a certain condition is short, when the cutting load is involved, When the processing conditions are different at the time of start-up or during operation, it is not always possible to appropriately respond.

  In addition, the analysis itself is complicated, and it is not always an efficient estimation method to set an estimated value for correction, such as an analysis for each machine tool is necessary to perform accurately. Met. Therefore, especially in a machine tool that supports high speed, the estimated value often deviates greatly from the actual measurement value depending on the machine tool even if the conventional normal correction is performed. Therefore, especially in the built-in type NC lathe, even if the estimated value is output based on the set arithmetic expression, the numerical value often differs from the actually measured value over time.

The present invention has been conceived in order to solve the problem of correction in such a machine tool, and achieves the following object.
The object of the present invention is to capture the temperature of the stator of the motor incorporated in the main shaft or the temperature in the vicinity of the bearing as an independent factor of the arithmetic expression, that is, a physical variable, and approximate the estimated value of the thermal displacement of the main shaft to the actually measured value. Thus, the present invention provides an estimation method for correcting thermal deformation of a machine tool that can be corrected to improve the machining accuracy of the machine tool.

The present invention takes the following means in order to achieve the object.
The estimation method for correcting thermal deformation of a machine tool according to the first aspect of the present invention is a first estimation method including a correction value that varies depending on a driving system operating value when the feed system structure is moved in the machine tool, including the driving system operating value. Based on the equation, the step of calculating and estimating the amount of movement of the feed system structure, and the correction value that changes depending on the stator temperature of the spindle motor of the spindle during the movement of the feed system structure or the temperature in the vicinity of the bearing of the spindle, Based on a second estimation formula including a value of the stator temperature or the bearing vicinity temperature, a step of calculating and estimating the movement amount of the feed system structure, and an estimation result of the first estimation formula, The estimation result of the second estimation equation is added to obtain an estimated value corresponding to the correction value.

An estimation method for correcting thermal deformation of a machine tool according to a second aspect of the invention is characterized in that, in the first aspect, the drive system operating value is a value of a rotational speed of the spindle.
An estimation method for correcting thermal deformation of a machine tool according to a third aspect of the invention is characterized in that, in the first aspect, the drive system operating value is an output value of the spindle motor.
An estimation method for correcting thermal deformation of a machine tool according to a fourth aspect of the present invention is the first aspect, wherein the first estimation formula and the second estimation formula include a calculation formula that takes into account a delay associated with elapsed time. It is characterized by being.

An estimation method for correcting thermal deformation of a machine tool according to a fifth aspect of the present invention is characterized in that, in the first aspect, the machine tool is an NC lathe.
An estimation method for correcting thermal deformation of a machine tool according to a sixth aspect of the present invention is the method according to the first aspect, wherein the value of the rotational speed of the spindle and the estimated value of the movement amount of the feed system structure based on the stator temperature are: It is obtained by the following estimation formula.

である。
ただし、
x：一定時間経過後のＸ軸方向の熱変位量（mm）、
y：一定時間経過後のＹ軸方向の熱変位量（mm）、
ｎ：主軸の回転速度（min^-1）、
ｔ：初期状態からの経過時間（min）、
Ｔ：式（３）によるステータ温度の推定値（℃）、
x₀：各主軸の回転速度に対するＸ軸方向の熱変位量の最大値（mm）、
y₀：各主軸の回転速度に対するＹ軸方向の熱変位量の最大値（mm）、
t_d：熱変位の時定数（min）、
t_s：温度の時定数（min）、
α_x：Ｘ軸に対する拡張項の補正係数、
α_y：Ｙ軸に対する拡張項の補正係数、
T_s：熱電対によるステータ温度の実測値（℃）、
β：各Ｘ，Ｙ主軸の回転速度に対するステータ温度の上昇の最大値（℃）、
T₀：ステータ温度の初期温度（℃）
である。 The estimated value x of the X axis feed axis and the estimated value y of the Y axis feed axis are

It is.
However,
x: Thermal displacement in the X-axis direction after a certain period of time (mm)
y: thermal displacement in the Y-axis direction after a certain time (mm)
n: Spindle speed (min ^-1 ),
t: elapsed time from the initial state (min),
T: Estimated value of stator temperature (° C) according to equation (3),
x ₀ : Maximum value (mm) of the amount of thermal displacement in the X-axis direction with respect to the rotational speed of each spindle.
y ₀ : maximum value (mm) of the amount of thermal displacement in the Y-axis direction with respect to the rotational speed of each spindle,
t _d : Thermal displacement time constant (min),
t _s : Time constant of temperature (min),
α _x : Correction coefficient of the expansion term with respect to the X axis,
α _y : correction coefficient for the expansion term with respect to the Y-axis,
T _s : Actual value (° C) of stator temperature measured by thermocouple,
β: Maximum value of the stator temperature rise (° C.) with respect to the rotational speed of each X, Y spindle,
T ₀ : Initial stator temperature (° C)
It is.

であり、

である。
ただし、
x：一定時間経過後のＸ軸方向の熱変位量（mm）、
x₀：各主軸回転速度に対するＸ軸方向の熱変位量の最大値（mm）、
x₁：主軸の回転速度が途中で変化する時間t₁（min）のときのＸ軸方向の熱変位量（mm）、
x₂：主軸の回転速度が途中で変化した後のＸ軸方向の熱変位量（mm）、
y：一定時間経過後のＹ軸方向の熱変位量（mm）、
y₀：各主軸回転速度に対するＹ軸方向の熱変位量の最大値（mm）、
y₁：主軸の回転速度が途中で変化する時間t₁（min）のときのＹ軸方向の熱変位量（mm）、
y₂：主軸の回転速度が途中で変化した後のＹ軸方向の熱変位量（mm）、
ｎ：主軸回転速度（min^-1）、
ｎ₁：主軸の回転速度が変化する前の値、
ｎ₂：主軸の回転速度が変化した後の値、
ｔ：初期状態からの経過時間（min）、
ｔ₁：主軸の回転速度が変化するときの値、
T_s：熱電対によるステータ温度の実測値（℃）、
t_d：熱変位の時定数（min）、
α_x：Ｘ軸に対する拡張項の補正係数、
α_y：Ｙ軸に対する拡張項の補正係数
である。 The estimation method for correcting the thermal deformation of the machine tool according to the seventh aspect of the present invention is the following estimation according to the first aspect of the present invention in which the estimated value of the thermal displacement when the rotational speed of the spindle changes after t ₁ (min) in the middle. It is obtained by a formula.
The estimated value x _{2 of} the X-axis feed axis and the estimated value y ₂ of the Y-axis feed axis are

And

It is.
However,
x: Thermal displacement in the X-axis direction after a certain period of time (mm)
x ₀ : Maximum value (mm) of the amount of thermal displacement in the X-axis direction for each spindle rotation speed,
x ₁ : Thermal displacement amount (mm) in the X-axis direction at time t ₁ (min) when the rotation speed of the spindle changes halfway,
x ₂ : Thermal displacement in the X-axis direction (mm) after the rotation speed of the spindle changes midway,
y: thermal displacement in the Y-axis direction after a certain time (mm)
y ₀ : Maximum value (mm) of the amount of thermal displacement in the Y-axis direction with respect to each spindle rotational speed,
y ₁ : thermal displacement amount (mm) in the Y-axis direction at time t ₁ (min) when the rotation speed of the spindle changes in the middle,
y ₂ : amount of thermal displacement in the Y-axis direction (mm) after the rotation speed of the spindle changes in the middle,
n: Spindle speed (min ^-1 )
n ₁ : Value before the spindle speed changes,
n ₂ : Value after the spindle rotation speed has changed,
t: elapsed time from the initial state (min),
t ₁ : Value when the rotational speed of the spindle changes,
T _s : Actual value (° C) of stator temperature measured by thermocouple,
t _d : Thermal displacement time constant (min),
α _x : Correction coefficient of the expansion term with respect to the X axis,
α _y is a correction coefficient for the expansion term with respect to the Y axis.

である。 Note that the estimated value x of the X-axis feed axis and the estimated value y of the Y-axis feed axis when stopped from a certain spindle rotational speed n are:

It is.

  An NC machine tool is generally controlled by an NC program by issuing an operation command signal to each spindle motor and each servo motor of a feed system according to an NC program. The machining accuracy of a workpiece by a machine tool is required to be high accuracy. A machine tool does not always maintain a certain condition in an operating state. For example, the cutting edge of a tool is worn or broken. For this reason, processing accuracy deteriorates. This deterioration in machining accuracy greatly affects not only the tool but also thermal deformation of the machine tool structure due to heat. For this reason, conventionally, the machining accuracy has been improved by correcting the operation amount of the feed servomotor for the thermal deformation of the spindle and the tool wear.

  Recently, as described above, machine tools corresponding to higher speeds have been developed, and a machine with a large rotation speed of the main spindle has been manufactured. The main shaft is generally configured such that the main shaft is rotatably supported by a bearing, and friction is generated by the rotation of the bearing. For example, the frictional heat causes an increase in the temperature of the main shaft, and the main shaft is deformed by thermal expansion accompanying the temperature increase. Furthermore, if it is a built-in type main shaft, the main shaft is thermally deformed by the influence of the heat of the motor itself. This deformation value becomes the thermal displacement of the main shaft, and this estimated value is calculated and used as a correction value. In the case of an NC lathe, the deformation value is a shift in the correlation position between the tool and the spindle that grips the workpiece rotatably. In the case of an NC lathe, the feed axes are usually two axes, the X axis and the Z axis. Recently, however, there is a lathe with a higher function and a Y-axis, and the present invention is intended for a machine tool having this function, particularly an NC lathe. The Y axis according to the present invention is an axis perpendicular to the X axis and the Z axis.

  Deviation due to thermal deformation occurs in both the X-axis and the Y-axis, causing a machining error for the workpiece and degrading the machining accuracy. In the present invention, an estimation method particularly corresponding to high speed is used, and in particular, an estimated value for correction mainly by calculation processing of the NC controller is calculated using the spindle rotational speed as a factor. Furthermore, as an expansion correction means, the temperature of the motor stator or the temperature in the vicinity of the bearing is measured by a temperature sensor, and this is taken as a second physical variable to calculate an estimated value. Thus, the estimated value obtained by adding the second estimated value based on the motor stator temperature of the spindle to the first estimated value having the spindle rotational speed as a factor is input to the NC controller as a correction value, and the tool is controlled by NC drive control. The position was corrected to eliminate the processing error.

  An estimation method for correcting thermal deformation of a machine tool according to the present invention takes a stator temperature of a motor incorporated in a spindle or a temperature in the vicinity of a bearing as an independent factor of an arithmetic expression, that is, an estimated value of thermal displacement of the spindle. Is corrected by approximating the measured value to the actual measurement value, so that the machining accuracy of the machine tool can be improved.

  Embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2 are schematic explanatory views of a machine tool to which an estimation method for thermal deformation correction according to the present invention is applied. Except for FIG. 7, FIG. 3 to FIG. 30 are data diagrams showing comparisons between estimated values and measured values according to the present invention. FIG. 7 is an explanatory diagram showing an acceleration / deceleration cycle applied to the present invention. The machine tool shown in FIG. 1 is an NC lathe 1 in this embodiment. In this configuration, a headstock 3 is mounted and fixed on a bed 2 which is a table constituting the main body of the machine. The headstock 3 is provided with a rotating main shaft 5. The spindle 5 and the spindle stock 3 and the spindle stock 3 are rotatably supported by bearings 4 for attaching and rotating a workpiece or a tool.

  The built-in motor 6 for rotationally driving the main shaft 5 and a chuck 7 attached to the end of the main shaft 5 for gripping a tool or a workpiece 8. Since the workpiece 8 is held and fixed by the chuck 7, the workpiece 8 is rotationally driven together with the main shaft 5. The spindle 5 is directly rotated by a built-in motor 6 disposed in the spindle stock 3. A motor stator 6a, which is a fixed side of the built-in motor 6, is attached to the inner wall of the headstock 3 to which the built-in motor 6 is attached, and a temperature detection sensor 9 for detecting the temperature of the motor stator 6a. Is attached. On the other hand, a tool post 10 that moves relative to the spindle 5 is provided on the bed 2 at a position facing the spindle stock 3. The tool post 10 moves relative to the spindle 5 in the X-axis direction, the Z-axis direction, and the Y-axis direction.

  FIG. 1 illustrates an X axis and a Z axis that are orthogonal to each other. The Z axis is an axis parallel to the axis of the main shaft 5. Further, as shown in the figure, the Y-axis is an axis that is perpendicular to the X-axis and the Z-axis and is perpendicular to the paper surface. The tool post 10 is provided so as to move relative to the saddle 11 that moves relative to the spindle 5 in the Z-axis direction in the X-axis direction and the Y-axis direction. Accordingly, the tool post 10 itself moves relative to the main shaft 5 in the X-axis, Z-axis, and Y-axis directions. For this purpose, an X-axis servomotor 12 is provided on the X-axis, and a Y-axis servomotor (not shown) is provided on the Y-axis. The X axis is an axis parallel to the attachment surface of the workpiece 8. The X axis performs positioning and cutting motion of the tool post 10 in a direction perpendicular to the main shaft 5.

  The Y axis is configured on the X axis. In other words, the Y axis is configured as a composite Y axis on the X axis. Although not shown, the configuration of the tool post 10 in this embodiment is as follows. On the saddle 11, a temporary Y-axis second saddle that is moved by a Y-axis servomotor in a direction perpendicular to the Z-axis is provided. The X-axis is an axis that is moved on the second saddle by the X-axis servomotor in a direction perpendicular to the Z-axis and in an angular direction inclined to the temporary Y-axis. Therefore, the tool post 10 on the X axis is also movable in the X axis direction and the temporary Y axis direction. Thus, the Y axis is configured as a shaft that moves in the direction perpendicular to the X axis by NC control by combining the X axis and the provisional Y axis. Thus, the movement in the Y-axis direction is performed by the combined drive control of the X-axis servo motor and the temporary Y-axis servo motor.

  Further, a Z-axis servomotor 13 is provided on the Z-axis. The Z-axis servomotor 13 is driven to perform positioning and cutting motion of the tool post 10 in a direction parallel to the main shaft 5. A tool 14 is arranged and fixed on the tool post 10. In such a main body configuration, an NC device 15 is provided. The NC device 15 numerically controls the X-axis servomotor 12, Z-axis servomotor 13, and Y-axis servomotor of the feed system in accordance with the NC program. The NC lathe 1 described above has a known structure and function and is not special. The NC device 15 performs pre-programmed control.

  The NC device 15 is connected to a temperature detection sensor 9, a spindle rotation speed detection sensor 16 for detecting the rotation speed of the spindle 5, and a plurality of other drive or correction detection sensors 17. The temperature detection sensor 9 is installed as temperature detection of the stator portion of the spindle motor in the figure, but if it is installed near the bearing, the temperature near the bearing 4 can be directly detected. For the built-in motor 6, the output information signal is controlled. The NC device 15 itself receives analog signals from these sensors and converts the analog signals into digital signals by the A / D converter 23. The digital signal converted by the A / D converter 23 is taken into an estimated value calculating unit 18 for obtaining an estimated value, and is compared with the storage unit 19 and the calculating unit 20 to obtain an estimated value for correction. calculate.

  The correction unit 21 processes this estimated value and outputs a correction value. This correction value is input to the drive control unit 22, and is output as command information from the drive control unit 22 to the X-axis servomotor 12, the Z-axis servomotor 13, and the Y-axis servomotor. The present invention relates to a method for calculating and calculating the estimated value. That is, the command information is output to the X-axis servo motor 12 in the case of X-axis correction, and to the X-axis servo motor 12 and the Y-axis servo motor in the case of Y-axis correction.

  The present invention constructs a calculation formula for an estimated value, which is effective in comparison with an actual measurement value. Therefore, after setting the operating conditions, the calculation example of the calculated estimated value and the comparative example of the actual measurement value will be described mainly with reference to the data diagram. In this embodiment, the NC apparatus 1 described above and the dimension measuring apparatus shown in FIG. 2 collect data by measuring the amount of thermal displacement of the workpiece 8 only in the X and Y axis directions. Will be described. In this experiment, in order to eliminate the influence caused by the rotational accuracy of the spindle 5, a cylindrical workpiece 8 is gripped by a three-jaw chuck 7, and eddy current type non-contact displacement sensors Y1, Y2, X1, Further, the inner diameter hole surface to be measured of X2 and X2 was finished by self-cutting, and data was collected by measuring the inner peripheral surface of the inner diameter.

In order to eliminate the influence of expansion and contraction of the inner diameter hole, four displacement sensors are attached to the tip of the measuring jig manufactured using the low thermal expansion casting (linear expansion coefficient 0.8 × 10 ^-6 / K). Two Y1, Y2, X1, and X2 are arranged symmetrically with respect to the X and Y axes, respectively, and the gap between the opposing bore holes is measured, and the X axis and Y axis directions of the main shaft axis are measured. The amount of displacement was calculated. The reference side of the measuring jig was fixed to a tailstock (not shown), and the relative displacement between the two was measured. A specific method for calculating the estimated value of the thermal displacement amount of the main shaft 5 is as follows. The calculation of the estimated value will be described assuming that it is applied to the NC lathe 1 described above. On the X axis and the Y axis, the estimation equations for calculating the estimated value for estimating the thermal displacement amount of the main shaft 5 are as shown in the following equations (1) and (2).

ただし、
x：一定時間経過後のＸ軸方向の熱変位量（mm）、
y：一定時間経過後のＹ軸方向の熱変位量（mm）、
ｎ：主軸の回転速度（min^-1）、
ｔ：初期状態からの経過時間（min）、
Ｔ：式（３）によるステータ温度の推定値（℃）、
x₀：各主軸の回転速度に対するＸ軸方向の熱変位量の最大値（mm）、
y₀：各主軸の回転速度に対するＹ軸方向の熱変位量の最大値（mm）、
t_d：熱変位の時定数（min）、
t_s：温度の時定数（min）、
α_x：Ｘ軸に対する拡張項の補正係数、
α_y：Ｙ軸に対する拡張項の補正係数、
T_s：熱電対によるステータ温度の実測値（℃）、
β：各Ｘ，Ｙ主軸の回転速度に対するステータ温度の上昇の最大値（℃）、
T₀：ステータ温度の初期温度（℃）
である。 The estimated value x of the X-axis feed axis and the estimated value y of the Y-axis feed axis are as follows.

However,
x: Thermal displacement in the X-axis direction after a certain period of time (mm)
y: thermal displacement in the Y-axis direction after a certain time (mm)
n: Spindle speed (min ^-1 ),
t: elapsed time from the initial state (min),
T: Estimated value of stator temperature (° C) according to equation (3),
x ₀ : Maximum value (mm) of the amount of thermal displacement in the X-axis direction with respect to the rotational speed of each spindle.
y ₀ : maximum value (mm) of the amount of thermal displacement in the Y-axis direction with respect to the rotational speed of each spindle,
t _d : Thermal displacement time constant (min),
t _s : Time constant of temperature (min),
α _x : Correction coefficient of the expansion term with respect to the X axis,
α _y : correction coefficient for the expansion term with respect to the Y-axis,
T _s : Actual value (° C) of stator temperature measured by thermocouple,
β: Maximum value of the stator temperature rise (° C.) with respect to the rotational speed of each X, Y spindle,
T ₀ : Initial stator temperature (° C)
It is.

The right side of the equations (1) and (2) is composed of two terms, the first term and the second term, and the first term is also a model equation generally known from the past (basic estimation). model). Specifically, x ₀ (n) and y ₀ (n) of the basic estimation model are maximum values (mm) of displacement amounts in the X-axis and Y-axis directions with respect to the spindle rotation speed, and are derived from actual measurement values. In general, the displacement x, y during spindle no-load operation increases with the spindle rotation speed n from the start of spindle rotation. When the spindle rotation speed is constant, it converges to a steady value after a certain period of time. To do. Therefore, the displacement amount in the steady state with respect to the spindle rotational speed is expressed by using the displacement time constant t _d (n) of the first-order lag system as the displacement characteristic in the transient state.

This basic estimation model can accurately estimate the amount of displacement of the main shaft 5 when the main shaft rotation speed is constant. For example, FIG. 3 and FIG. 4 show data when the rotational speed of the main shaft is constant. The vertical axis in the figure indicates the amount of displacement in the X axis or Y axis, and the horizontal axis indicates the elapsed time. The actual measurement values in the figure are data obtained by measuring the displacement amount of the X axis or the Y axis when the main shaft 5 is rotated at a constant rotational speed of 800 min ⁻¹ , 2000 min ⁻¹ , or 3200 min ⁻¹ . The calculated values in the figure are estimated values calculated by the basic estimation model under the same conditions. This calculation will be described later in detail. As is apparent from this graph, the actual measurement value and the calculated value are in good agreement.

  Therefore, when the spindle rotational speed is constant, the displacement amount of the X axis and the Y axis can be accurately estimated only by the first estimation formula, and the feed system can be controlled. However, in actual machining, there are not a few cases where acceleration and deceleration operations due to changes in the rotational speed of the main shaft 5 and activation / deceleration are complicated in a short time. In such a case, the heat generation of the main shaft motor increases, and the estimated value of the thermal displacement amount of the main shaft has a large difference from the actual measurement value only with the basic estimation model of the first-order lag system. Therefore, an extended estimation model in which the stator temperature of the spindle motor is added as a parameter to the basic estimation model is newly defined by the above-described equations (1) and (2).

  The estimation formulas of the formulas (1) and (2) are obtained by adding the first estimation formula including the drive system operating value and the second estimation formula including the temperature value of the motor stator 6a. The first estimation formula is the first term on the right side of formula (1) and formula (2). The second estimation expression is composed of the second term on the right side of Expression (1) and Expression (2). The derivation of the first estimation formula and the second estimation formula will be described below using measured values of experimental data (sometimes referred to as measured values) and calculated values. The first estimation formula is a conventionally known formula (see the above-described basic estimation model), and the second estimation formula is a correction formula based on the amount of thermal displacement for correcting the first estimation formula. is there. The calculation of the correction formula will be described later.

  The second estimation formula includes the temperature of the motor stator 6a of the main shaft motor 6 as a parameter, but can also be calculated by the temperature in the vicinity of the main shaft bearing. In this embodiment, the temperature is calculated using the temperature of the motor stator 6a of the spindle motor 6. Next, a comparison data diagram between the calculated value and the actual measurement is shown by the relationship between the displacement amount and the rotation speed of the spindle. In order to determine each parameter of the basic estimation model, experiments were conducted under the following conditions. As experimental conditions, the maximum values of thermal displacement in the X and Y axis directions were measured for 180 minutes of operation time including the steady state for each of the main spindle rotational speeds of 800 rpm, 2000 rpm, and 3200 rpm. FIG. 5 is an example about the X axis, and FIG. 6 is an example about the Y axis. 5 and 6, the vertical axis represents the maximum displacement amount in the X-axis direction or the Y-axis direction, and the horizontal axis represents the rotational speed of the main shaft 5.

また、熱変位の時定数t_dに関しては、主軸回転速度ｎに関する２次の多項式で近似可能で、次の式で近似できる。

The measured values in FIGS. 5 and 6 can be approximated by the following equation as a cubic polynomial with respect to the spindle rotational speed n using the least square method.

Further, the time constant t _d of the thermal displacement can be approximated by a quadratic polynomial relating to the spindle rotational speed n, and can be approximated by the following equation.

  The measurement results of the thermal displacement amounts of the X axis and the Y axis in a state where the room temperature is maintained at 23 ° C., and these equations 10 to 12 were substituted into the first estimation equation and calculated, as shown in FIG. 3 and FIG. It is a graph of a calculation result. The wavy lines in the figure are calculated values, in other words, estimated values. Hereinafter, similarly, a calculation value (estimated value) is represented by a wavy line. The solid line in the figure is the measured value, in other words, the actually measured value. Hereinafter, similarly, a measurement value is represented by a solid line. As is clear from this graph, the actual measurement value and the calculated value by the first estimation formula are in good agreement.

  The following experiment was performed to determine each parameter of the extended estimation model. The extended estimation model is obtained by adding the second estimation formula in addition to the basic estimation model including the first estimation formula described above. Here, experimental results for determining each parameter of the second estimation formula are shown. FIG. 7 illustrates one cycle in which the NC lathe 1 operates. One cycle defined in this example is an acceleration time from when the NC machine tool is unloaded and the spindle motor 6 is started from a stopped state until the rotation speed of the spindle 5 reaches the set rotation speed. These are the time of constant rotation speed rotating at the set constant rotation speed, the deceleration time for decelerating until the rotation speed of the main spindle 5 stops, and the stop time for stopping the motor 6.

Next, the relationship between the estimated value for each cycle time and the operating value of the spindle motor 6 is as shown in Table 1 below. The cycle time in this experiment refers to one cycle shown in FIG. The breakdown of the cycle time is that the stop time of the spindle 5 is fixed at 2 seconds during one cycle, the acceleration time to each set rotation speed, the deceleration time (time for loading the current in the reverse rotation direction), and these The rest of the time is the rotation time at a constant rotation speed. The thermal displacement was measured during the stop time in the cycle at a position stopped at this fixed position and stopped at this fixed position in order to eliminate the influence of the deflection accuracy of the spindle 5.

  The first column of Table 1 is the cycle time, the second column is the maximum displacement amount in the X-axis direction, the third column is the maximum displacement amount in the Y-axis direction, the fourth column is the maximum value of the stator temperature rise, and the fifth column is the spindle. The output voltage of the motor 6 and the sixth column are the average output of the spindle motor 6. The data shown in Table 1 is for the case where the rotational speed of the motor 6 is 3200 rpm. The cycle time Const in Table 1 is the case where rotation is performed at a constant rotational speed of 3200 rpm without accel / deceleration. According to Table 1, the change in the temperature of the motor stator 6a, the change in the output voltage of the spindle motor 6, and the average output of the spindle motor 6 are proportional to the maximum displacement amount in the X-axis direction and the maximum displacement amount in the Y-axis direction. is doing.

  Among these, FIG. 8 shows a data diagram of the relationship between the maximum displacement amount in the X-axis direction and the average output of the spindle motor 6. In the figure, the amount of displacement in the X-axis direction is on the vertical axis, and the average output of the spindle motor 6 is on the horizontal axis. The relationship between the maximum displacement amount in the Y-axis direction and the average output of the spindle motor is shown in FIG. In the figure, the amount of displacement in the Y-axis direction is on the vertical axis, and the average output of the spindle motor 6 is on the horizontal axis. 8 and 9 show the relationship between the average output of the spindle motor and the amount of displacement of the spindle after 3 hours (180 min) from the start of the motor operation. From the graphs of FIG. 8 and FIG. 9, it can be understood that the relationship between the average output of the motor 6 and the amount of displacement of the X axis and the Y axis is a substantially linear relationship.

  FIG. 10 shows the results of measuring the temperature rise until the stator temperature reaches a steady state. The measurement was performed using a thermocouple sensor attached to the stator. At this time, the rotation speed of the main shaft 5 is constant rotation of 800 rpm, 2000 rpm, and 3200 rpm. From this graph, the maximum temperature rise value in the steady state with respect to the spindle rotational speed increases with the rotational speed. FIG. 11 is a diagram showing the relationship of the maximum temperature rise of the motor stator 6 a with respect to the rotational speed of the main shaft 5. FIG. 11 shows the maximum temperature rise value of the stator with respect to each rotational speed from the measured values of FIG.

この近似式用いて、式（３）による、ステータ温度Tの計算結果を図１０にも図示している。この計算では、t_sは、基本推定モデルのt_dの値を用いた。 The maximum value β of the stator temperature rise for each spindle rotation speed shown in FIG. 11 can be approximated as a third-order polynomial related to the spindle rotation speed n using the least square method, and is given by the following equation: .

FIG. 10 also shows the calculation result of the stator temperature T according to the expression (3) using this approximate expression. In this calculation, t _s is the value of t _d of the basic estimation model.

  In actual machining, there are not a few cases where acceleration and deceleration operations due to changes in the rotational speed of the spindle and start / stop are performed in a short time. In such a case, the heat generation of the spindle motor increases, and the deviation from the actual measurement value increases only with the basic estimation model of the first-order lag system. Therefore, an extended estimation model in which the stator temperature of the spindle motor is added as a parameter to the basic estimation model is newly defined by the above-described equations (1) and (2). In addition, it is known that the stator temperature when the spindle rotation speed is constant also increases with time and converges to a steady value after the passage of time, so the maximum value is a function of each rotation speed, It can be expressed by the following equation as a product form with a first-order lag function relating to elapsed time.

ここで、
ｎ：主軸回転速度（min^-1）、
ｔ：初期状態からの経過時間（min）、
T₀：モータステータの初期温度（℃）、
t_s：温度の時定数（min）、
β：各主軸回転速度に対するステータ温度上昇の最大値（℃。）
である。

here,
n: Spindle speed (min ^-1 )
t: elapsed time from the initial state (min),
T ₀ : initial temperature of motor stator (° C),
t _s : Time constant of temperature (min),
β: Maximum value of stator temperature rise for each spindle speed (° C)
It is.

The temperature time constant t _{s in} this equation is the same as the thermal displacement time constant t _d described above.
t _s (n) = t _d (n). . . Formula (15)

As described above, α _x and α _y in the above-described expressions (1) and (2) are not determined, and all other parameters are determined. α _x and α _y can be determined from the following measurement results. Experiments were performed for acceleration / deceleration cycles of 10 sec, 20 sec, and 40 sec at spindle speeds of 800 min ⁻¹ , 2000 min ⁻¹ , and 3200 min ⁻¹ , respectively. In this experiment, the amount of displacement in the X-axis direction and the Y-axis direction was measured, and the temperature of the stator was measured.

α _x , α _y are calculated by the least squares method based on the relationship between the stator temperature rise during acceleration / deceleration cycles and the measured displacement, respectively, with multiple correlation coefficients of 0.82 (for α _x ) and 0.94 (for α _y The result calculated as) is as follows.
α _x = 0.27 · 10 ⁻³ . . . Formula (16)
α _y = 0.99 · 10 ^-3 . . . Formula (17)

  These formulas 13-17 show the figure which applied the thermal displacement in an acceleration / deceleration cycle also to a 2nd estimation formula as a correction | amendment of a 1st estimation formula, and compared this estimation result and measured value for every rotational speed. . FIGS. 12a and 13a are data diagrams showing the results of calculating the displacement amounts in the X-axis direction and the Y-axis direction in the case of a 10-second cycle using the extended estimation model, and the actual measurement results over time. FIGS. 12b and 13b are data diagrams that display the actual measurement results of data diagrams in which the displacement amounts in the X-axis direction and the Y-axis direction in the case of the 10 sec cycle are calculated only by the first estimation formula. FIG. 14 is a diagram showing the result of measuring the temperature of the stator during this actual measurement.

12a, 12b, 13a, and 13b, the vertical axis indicates the amount of displacement in the X-axis direction or the Y-axis direction, and the horizontal axis indicates time. The vertical axis of the graph in FIG. 14 indicates the stator temperature, and the horizontal axis indicates time. FIGS. 12 a, 12 b, 13 a, 13 b, and 14 are cases where the rotational speed of the main shaft 5 is 800 min ⁻¹ , 2000 min ⁻¹ , and 3200 min ⁻¹ . In the graphs showing the results calculated only with the first estimation equation shown in FIGS. 12b and 13b, the deviation from the actually measured value increases as the rotational speed increases. In other words, it can be said that the greater the difference between the measured temperature of the stator and the reference temperature (estimated temperature under the constant rotation speed of the stator << calculated by equation (3) >>), the greater the correction effect by the second estimated equation.

  Similarly, FIG. 15a, FIG. 16a, FIG. 15b, FIG. 16b, and FIG. 17 are data diagrams in the case of 20 sec cycle, and FIG. 18a, FIG. 19a, FIG. 18b, FIG. FIG. According to these data, when the calculation is performed using only the first estimation formula, there is a discrepancy between the calculated value and the actually measured value, particularly when the spindle rotation speed increases. Therefore, it can be understood that if the estimated value is calculated only by the first estimation formula, an insufficient result is obtained and a machining error is caused. From these data diagrams, it can be seen that the calculation result by the extended estimation model shows a value closer to the measured value than the calculation using only the first estimation equation.

[Changes in spindle speed and acceleration / deceleration conditions]
In the above description, the transient characteristics of the X-axis and Y-axis thermal displacements from the initial state to the steady state with respect to the rotational speed and the acceleration / deceleration cycle have been described. However, in reality, the time for which the spindle rotates at a constant rotation speed is short, and the rotation speed often changes while the thermal displacement changes transiently. It is required that the above estimation model can be applied to any combination of the above. Accordingly, FIG. 21 shows a theoretical form of an extended thermal displacement estimation example when the operating conditions change during the operation.

  The vertical axis in FIG. 21 indicates the amount of thermal displacement of the main axis, and the horizontal axis indicates the operation time. First, the spindle rotation speed of the spindle 5 of the NC lathe 1 is set to the first rotation speed at the time of start-up, and is set to the second rotation speed at the change point to operate.

ただし、
x：一定時間経過後のＸ軸方向の熱変位量（mm）、
x₀：各主軸回転速度に対するＸ軸方向の熱変位量の最大値（mm）、
x₁：主軸の回転速度が途中で変化する時間t₁（min）のときのＸ軸方向の熱変位量（mm）、
x₂：主軸の回転速度が途中で変化した後のＸ軸方向の熱変位量（mm）、
y：一定時間経過後のＹ軸方向の熱変位量（mm）、
y₀：各主軸回転速度に対するＹ軸方向の熱変位量の最大値（mm）、
y₁：主軸の回転速度が途中で変化する時間t₁（min）のときのＹ軸方向の熱変位量（mm）、
y₂：主軸の回転速度が途中で変化した後のＹ軸方向の熱変位量（mm）、
ｎ：主軸回転速度（min^-1）、
ｎ₁：主軸の回転速度が変化する前の値、
ｎ₂：主軸の回転速度が変化した後の値、
ｔ：初期状態からの経過時間（min）、
ｔ₁：主軸の回転速度が変化するときの値、
T_s：熱電対によるステータ温度の実測値（℃）、
t_d：熱変位の時定数（min）、
α_x：Ｘ軸に対する拡張項の補正係数、
α_y：Ｙ軸に対する拡張項の補正係数
である。 The calculation formula in this example is as follows. The symbols are according to the figure. The estimated value x of the X-axis feed axis and the estimated value y of the Y-axis feed axis are expressed by the following equations.

However,
x: Thermal displacement in the X-axis direction after a certain period of time (mm)
x ₀ : Maximum value (mm) of the amount of thermal displacement in the X-axis direction for each spindle rotation speed,
x ₁ : Thermal displacement amount (mm) in the X-axis direction at time t ₁ (min) when the rotation speed of the spindle changes halfway,
x ₂ : Thermal displacement in the X-axis direction (mm) after the rotation speed of the spindle changes midway,
y: thermal displacement in the Y-axis direction after a certain time (mm)
y ₀ : Maximum value (mm) of the amount of thermal displacement in the Y-axis direction with respect to each spindle rotational speed,
y ₁ : thermal displacement amount (mm) in the Y-axis direction at time t ₁ (min) when the rotation speed of the spindle changes in the middle,
y ₂ : amount of thermal displacement in the Y-axis direction (mm) after the rotation speed of the spindle changes in the middle,
n: Spindle speed (min ^-1 )
n ₁ : Value before the spindle speed changes,
n ₂ : Value after the spindle rotation speed has changed,
t: elapsed time from the initial state (min),
t ₁ : Value when the rotational speed of the spindle changes,
T _s : Actual value (° C) of stator temperature measured by thermocouple,
t _d : Thermal displacement time constant (min),
α _x : Correction coefficient of the expansion term with respect to the X axis,
α _y is a correction coefficient for the expansion term with respect to the Y axis.

実測結果からは、主軸回転速度から停止したときの熱変位の時定数は、起動時の５倍であったため、この式８、９の熱変位の時定数は５倍になっている。 Note that the estimated value x of the X-axis feed axis and the estimated value y of the Y-axis feed axis when stopped from a certain spindle rotational speed n are expressed by the following equations.

From the actual measurement results, the time constant of the thermal displacement when stopping from the spindle rotational speed was five times that at the time of startup, so the time constant of the thermal displacement of the equations 8 and 9 is five times.

  A comparison example between the estimated value and the actual measurement value based on this is shown in FIGS. 23 and 24 as an example of a 10-second cycle of the rotation pattern shown in FIG. FIG. 23 shows changes in the amount of displacement in the X-axis direction and the Y-axis direction. The vertical axis of the graph in FIG. 23 indicates the amount of displacement, and the horizontal axis indicates time. The rotation pattern shown in FIG. 22 is a case where the spindle rotation speed changes randomly with a constant acceleration / deceleration cycle, and shows a change when a 10 sec cycle is performed every 30 min. FIG. 24 shows the temperature change of the motor stator 6a. The vertical axis of the graph in FIG. 24 indicates temperature, and the horizontal axis indicates time.

  The graph of FIG. 24 shows the room temperature at the time of measurement, the calculated value of the motor stator 6a of the main shaft 5, and the measured value. As can be seen from the graph of FIG. 23, the estimated error in the amount of thermal displacement in the X-axis and Y-axis directions is about 0.0018 mm, 0.0036 mm, and 240 min at about 90 min. It has become. According to this, the trend of the change in the displacement amount shown in FIG. 23 is substantially the same as the tendency of the change in the estimated value and the actually measured value.

  Similar to FIGS. 22, 23, and 24, FIG. 26 and FIG. 27 show data diagrams when the rotation pattern shown in FIG. 25 is a random acceleration / deceleration cycle pattern. As shown in FIG. 25, this random cycle is a pattern in which both the acceleration / deceleration cycle and the spindle rotational speed change randomly, and is changed randomly every 30 minutes. Also in this example, the change trend of the displacement amount shown in FIG. 26 forms a mountain at the change point of 60 min and the change point of 180 min, for example, and the tendency of the change of the estimated value and the actual measurement value substantially coincides with the operating condition. Even if changes, it can be confirmed that it is following.

  In a short cycle, the stator tends to rise in temperature, and the amount of displacement also changes accordingly. As can be seen from the graph of FIG. 26, the estimated error in the amount of thermal displacement in the X-axis and Y-axis directions is 0.0017 mm, 0.0036 mm, and max. It is 0.0035mm. FIG. 29 and FIG. 30 show data diagrams when the rotation pattern shown in FIG. 28 is a random acceleration / deceleration cycle pattern. As shown in FIG. 29, this random cycle is a case where only the spindle rotational speed changes randomly, and shows a change made every 30 min.

  FIG. 30 shows the temperature change of the motor stator 6a. The vertical axis of the graph in FIG. 30 indicates temperature, and the horizontal axis indicates time. The graph of FIG. 30 shows the measured values of the room temperature at the time of measurement and the temperature of the motor stator 6a of the main shaft 5. As can be seen from the graph of FIG. 29, the estimated error in the amount of thermal displacement in the X-axis and Y-axis directions decreases instantaneously around 210 min due to the stop of the spindle rotation. If the difference between the estimated value and the estimated value is an estimation error, the maximum is 0.0037 mm and 0.0020 mm, respectively. In other sections, the error can be estimated with high accuracy except that the error of the thermal displacement amount in the Y-axis direction around 120 min is 0.0015 mm at the maximum.

  In the case of the rotation patterns of FIGS. 22 and 28, the change in the spindle rotational speed is the same, but only the acceleration / deceleration cycle is different. In the case of the pattern of FIG. 22, the heat generation of the motor increases, and the maximum thermal displacement amounts in the X-axis and Y-axis directions have increased to 1.53 times and 1.87 times, respectively. It is corrected.

  As described above, the estimated value obtained by adding the second estimated expression taking into account the temperature of the motor stator 6a to the first estimated expression is a value very close to the actually measured value. It can be confirmed by the data diagram. Therefore, it can be said that the estimation method of the present invention is an effective correction method based on the actual measurement. Although the embodiment has been described above, it goes without saying that the present invention is not limited to this embodiment. Although the machine tool of the embodiment has been described as an NC lathe, it is needless to say that it can be applied to, for example, an NC grinder and a machining center.

FIG. 1 is a schematic explanatory diagram of an NC lathe to which an estimation method for thermal deformation correction is applied. FIG. 2 is a schematic explanatory diagram of an NC lathe to which an estimation method for thermal deformation correction is applied, and FIG. 2 (a) is a diagram conceptually showing a main shaft 5 to which a workpiece 8 is attached. (B) is a conceptual diagram showing the X-axis and the Y-axis. FIG. 3 is a data diagram showing the amount of displacement of the X axis when the spindle rotation speed is constant (only the first estimation equation). FIG. 4 is a data diagram showing the amount of displacement of the Y-axis when the spindle rotation speed is constant (only the first estimation formula). FIG. 5 is an X-axis data diagram showing a change in the maximum displacement amount in the X-axis direction with respect to each spindle rotational speed. FIG. 6 is a Y-axis data diagram showing changes in the maximum displacement amount in the Y-axis direction with respect to each spindle rotational speed. FIG. 7 is an explanatory diagram for explaining the concept of the cycle. FIG. 8 is a data diagram showing the relationship between the amount of X-axis displacement and the average spindle motor output. FIG. 9 is a data diagram showing the relationship between the displacement amount of the Y axis and the average output of the spindle motor. FIG. 10 is a data diagram showing changes in the stator temperature for each spindle rotational speed. FIG. 11 is a data diagram showing a change in the maximum value of the temperature rise of the stator with respect to each spindle rotational speed. FIG. 12a is an X-axis data diagram showing the displacement amount of each spindle rotational speed in the case of a 10-sec acceleration / deceleration cycle, and is a data diagram showing an estimated value and an actual measurement value by an extended estimation formula. FIG. 12B is an X-axis data diagram showing the displacement amount of each spindle rotational speed in the case of a 10-second acceleration / deceleration cycle, and is a data diagram showing an estimated value and an actual measurement value based on a basic estimation equation. FIG. 13a is a data diagram of the Y axis showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 10 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by an extended estimation formula. FIG. 13b is a data diagram of the Y axis showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 10 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by a basic estimation formula. FIG. 14 is a diagram showing data obtained by actually measuring the temperature of the stator when the amount of displacement of each spindle rotational speed is an acceleration / deceleration 10 sec cycle. FIG. 15a is an X-axis data diagram showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 20 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by an extended estimation formula. FIG. 15B is an X-axis data diagram showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 20 sec cycle, and is a data diagram showing an estimated value and an actual measurement value based on a basic estimation formula. FIG. 16a is a data diagram of the Y-axis showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 20 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by an extended estimation formula. FIG. 16b is a data diagram of the Y-axis showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 20 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by a basic estimation formula. FIG. 17 is a diagram showing data obtained by actually measuring the temperature of the stator when the amount of displacement of each spindle rotational speed is a 20-second acceleration / deceleration cycle. FIG. 18a is an X-axis data diagram showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 40 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by an extended estimation formula. FIG. 18b is an X-axis data diagram showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 40 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by a basic estimation formula. FIG. 19a is a Y-axis data diagram showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 40 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by an extended estimation formula. FIG. 19b is a data diagram of the Y axis showing the displacement amount of each spindle rotational speed in the case of an acceleration / deceleration 40 sec cycle, and is a data diagram showing an estimated value and an actual measurement value by a basic estimation formula. FIG. 20 is a diagram showing data obtained by actually measuring the temperature of the stator when the displacement amount of each spindle rotational speed is 40 sec acceleration / deceleration cycle. FIG. 21 is a data diagram showing an estimation example of thermal displacement when the operating condition changes midway. FIG. 22 is a pattern diagram when the rotation speed of the spindle changes randomly with a constant acceleration / deceleration cycle of 10 sec. FIG. 23 is an X-axis and Y-axis data diagram showing changes in thermal displacement when the rotation speed of the spindle changes randomly with a constant acceleration / deceleration cycle of 10 sec. FIG. 24 is a data diagram showing changes in the spindle stator temperature when the rotation speed of the spindle changes randomly with a constant acceleration / deceleration cycle of 10 sec. FIG. 25 is a pattern diagram in the case where both the acceleration / deceleration cycle and the spindle rotation speed change randomly. FIG. 26 is an X-axis and Y-axis data diagram showing changes in thermal displacement when both the acceleration / deceleration cycle and the spindle rotation speed change randomly. FIG. 27 is a data diagram showing changes in the spindle stator temperature when both the acceleration / deceleration cycle and the spindle rotation speed change randomly. FIG. 28 is a pattern diagram in the case where only the spindle rotational speed changes randomly. FIG. 29 is an X-axis and Y-axis data diagram showing changes in thermal displacement when only the spindle rotation speed in FIG. 28 changes randomly. FIG. 30 is a data diagram showing changes in the spindle stator temperature when only the spindle rotational speed in FIG. 28 changes randomly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... NC lathe 2 ... Bed 3 ... Spindle stand 4 ... Bearing 5 ... Spindle 6 ... Built-in motor 9 ... Stator temperature detection sensor 15 ... NC apparatus 16 ... Spindle speed detection sensor 18 ... Estimated value calculation part

Claims (7)

A correction value that varies depending on the drive system operating value when the feed system structure is moved in the machine tool is calculated and estimated as a movement amount of the feed system structure based on the first estimation formula including the drive system operating value. Process,
Based on the second estimation formula including the value of the stator temperature or the bearing vicinity temperature, the correction value that changes depending on the stator temperature of the spindle motor of the spindle during the movement of the feed structure or the temperature near the bearing of the spindle, Calculating and estimating the amount of movement of the feed structure, and
An estimation method for correcting thermal deformation of a machine tool, comprising: adding an estimation result of the first estimation formula and an estimation result of the second estimation formula to obtain an estimation value corresponding to the correction value. In the estimation method for thermal deformation correction of the machine tool according to claim 1,
The drive system operating value is a value of a rotational speed of the spindle. An estimation method for correcting thermal deformation of a machine tool. In the estimation method for thermal deformation correction of the machine tool according to claim 1,
The driving system operating value is an output value of the spindle motor. An estimation method for correcting thermal deformation of a machine tool. In the estimation method for thermal deformation correction of the machine tool according to claim 1,
The estimation method for correcting thermal deformation of a machine tool, wherein the first estimation formula and the second estimation formula include a calculation formula that takes into account a delay associated with an elapsed time. In the estimation method for thermal deformation correction of the machine tool according to claim 1,
The machine tool is an NC lathe. An estimation method for correcting thermal deformation of a machine tool. In the estimation method for thermal deformation correction of the machine tool according to claim 1,
The estimated value for the rotational deformation of the spindle and the estimated value of the amount of movement of the feed system structure based on the stator temperature is obtained by the following estimation formula: Method.
The estimated value x of the X axis feed axis and the estimated value y of the Y axis feed axis are

It is.
However,
x: Thermal displacement in the X-axis direction after a certain period of time (mm)
y: thermal displacement in the Y-axis direction after a certain time (mm)
n: Spindle speed (min ^-1 ),
t: elapsed time from the initial state (min),
T: Estimated value of stator temperature (° C) according to equation (3),
x ₀ : Maximum value (mm) of the amount of thermal displacement in the X-axis direction with respect to the rotational speed of each spindle.
y ₀ : maximum value (mm) of the amount of thermal displacement in the Y-axis direction with respect to the rotational speed of each spindle,
t _d : Thermal displacement time constant (min),
t _s : Time constant of temperature (min),
α _x : Correction coefficient of the expansion term with respect to the X axis,
α _y : correction coefficient for the expansion term with respect to the Y-axis,
T _s : Actual value (° C) of stator temperature measured by thermocouple,
β: the maximum value of the stator temperature rise (° C.) with respect to the rotational speed of each X, Y spindle,
T ₀ : Initial stator temperature (° C)
It is. In the estimation method for thermal deformation correction of the machine tool according to claim 1,
An estimated value for thermal deformation correction of a machine tool, wherein the estimated value of thermal displacement when the rotational speed of the spindle changes after t ₁ (min) in the middle is obtained by the following estimation formula.
The estimated value x _{2 of} the X-axis feed axis and the estimated value y ₂ of the Y-axis feed axis are

And

It is.
However,
x: Thermal displacement in the X-axis direction after a certain period of time (mm)
x ₀ : Maximum value (mm) of the amount of thermal displacement in the X-axis direction for each spindle rotation speed,
x ₁ : Thermal displacement amount (mm) in the X-axis direction at time t ₁ (min) when the rotation speed of the spindle changes halfway,
x ₂ : Thermal displacement in the X-axis direction (mm) after the rotation speed of the spindle changes midway,
y: thermal displacement in the Y-axis direction after a certain time (mm)
y ₀ : Maximum value (mm) of the amount of thermal displacement in the Y-axis direction with respect to each spindle rotational speed,
y ₁ : Thermal displacement in the Y-axis direction (mm) at time t ₁ (min) during which the spindle speed changes midway
y ₂ : Thermal displacement amount in the Y-axis direction (mm) after the rotation speed of the spindle changes midway
n: Spindle speed (min ^-1 )
n ₁ : Value before the spindle speed changes,
n ₂ : Value after the spindle rotation speed has changed,
t: Elapsed time from the initial state (min)
t ₁ : Value when the rotational speed of the spindle changes,
T _s : Actual value (° C) of stator temperature measured by thermocouple,
t _d : Thermal displacement time constant (min),
α _x : Correction coefficient of the expansion term with respect to the X axis,
α _y : correction coefficient for the expansion term with respect to the Y axis, and
Note that the estimated value x of the X-axis feed axis and the estimated value y of the Y-axis feed axis when stopped from a certain spindle rotational speed n are:

It is.

Images