JPH08215983A - Thermal displacement correcting method of machine tool and device thereof - Google Patents

Abstract

PURPOSE: To provide a thermal displacement correcting method of a machine tool capable of accurately correcting thermal displacement and a device thereof. CONSTITUTION: The thermal characteristic of a temperature sensor S1 detecting temperature change of the machine body 10 of a machine tool 1 receiving influence of generated heat from a heat generating source is adjusted in sensitivity so as to nearly conform to the time constant of thermal displacement of a main spindle generated by receiving influence of generated heat from the heat generating source, and the thermal displacement corresponding to output of the temperature sensor is computed from output of the temperature sensor. An error gradually deviating computed thermal displacement from actual thermal displacement is computed in expectation of delay of output of the temperature sensor, and a moving quantity in the Z-axis direction is corrected using a total value adding the operation result to the computed thermal displacement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine tool thermal displacement correction method and apparatus.

[0002]

2. Description of the Related Art Machine tools have heat sources at various parts of the machine,
For example, rolling friction heat of the bearing of the main shaft and heat generated from the cutting portion are many. These heats are conducted to each part of the machine body and deform the machine body, and the deformation of the machine body greatly affects the processing accuracy. Therefore, there have been proposed various correction methods and devices for predicting the thermal displacement of the machine body due to these various causes and feeding back the error caused by the thermal displacement to the servo system to correct the error.

In a machine tool having such a correction function, it is important to accurately estimate the thermal displacement due to the operation of the machine, and various attempts have been made for that purpose. For example,
Prediction of thermal displacement from operating conditions such as spindle speed,
Alternatively, there is one that directly detects thermal displacement with a displacement sensor incorporated in the machine body.

The applicant of the present invention has proposed, in Japanese Patent Publication No. 6-22779 and Japanese Unexamined Patent Publication No. 3-79256, a thermal displacement correction method for a machine tool which calculates thermal displacement from a machine body temperature. The calculation of the thermal displacement in this method is basically based on the principle of the following equation (1). ΔL = L × coefficient of linear expansion × temperature change (1) Here, ΔL: thermal displacement of the airframe component, L: length of the airframe component.

[0005]

The processing accuracy after correction in the prior art is limited to about 20 to 30 [μm]. However, in recent years, machine tool users have generally requested that the accuracy after correction be suppressed to a processing error of 10 μm or less (that is, residual thermal displacement). This is because it is necessary to process a new material such as a ceramic material or a further downsized work piece with high precision.

Further, in the above-mentioned calculation method, the length L of the constituent part is estimated from the structure of the machine body, and the temperature change is calculated as the length L.
Since the temperature is detected from the center position of, the mounting position of the temperature sensor is limited. Furthermore, in order to accurately estimate the thermal displacement, the airframe needs to be divided into small components, and a large number of temperature sensors are required to calculate the temperature change of each part. Further, it is necessary to measure the length L of the machine body component and to confirm the linear expansion coefficient of each machine body constituent material. These have been obstacles in mounting a thermal displacement correction device for a machine tool that calculates thermal displacement from the machine body temperature.

On the other hand, in Japanese Patent Laid-Open No. 58-109250, a metal piece that is thermally similar to a machine tool is used, and its temperature is regarded as a temperature representative of the machine tool. There has been proposed a thermal displacement correction device that corrects thermal displacement of a machine tool by controlling. However,
In this case, a metal piece having thermal similarity must be prepared separately. Further, Japanese Laid-Open Patent Publication No. 60-9634 proposes a thermal displacement correction device using a temperature sensor having a thermal time constant that matches the characteristics of the Y-axis thermal displacement.
However, in this correction device, details of the temperature sensor having a thermal time constant matched to the characteristic of thermal displacement have not been clarified.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a thermal displacement correction method for a machine tool and a device therefor capable of highly accurately correcting a processing error due to heat. And Another object of the present invention is to eliminate the need to measure the length of the machine body component of the machine tool and to confirm the linear expansion coefficient of the machine body constituent material, and to measure the thermal displacement characteristics using an actual machine. Is to be simplified. Further, another object of the present invention is to greatly relax the restriction on the mounting position of the temperature sensor, and at the same time, to provide a thermal displacement correction method for a machine tool having a high degree of freedom in which thermal displacement can be accurately estimated with a small number of temperature sensors. It is to provide the device.

[0009]

In order to achieve the above object, the present invention detects a thermal displacement due to elongation in a predetermined axial direction or a thermal displacement due to a spindle inclination when a machine tool is given an arbitrary spindle rotational speed. At the same time, the temperature sensor detects a temperature change in an appropriate portion of the machine body. If the temperature change and the thermal displacement are the same in time series, the temperature change and the thermal displacement simply have a linear correlation, so that the thermal displacement of the machine tool can be easily estimated from the temperature change. Is assumed.

However, the "time constant" of the temperature change detected from the appropriate portion of the airframe is not necessarily the same as the "time constant" of the thermal displacement. Therefore, a method is required to change the thermal time constant of the temperature sensor so that the output characteristics of the temperature sensor installed at an appropriate location of the machine affected by the heat generated by the heat source match the characteristics of the thermal displacement of the machine tool. To be The "thermal displacement of machine tool" is the thermal displacement of the spindle, ideally the thermal displacement at the machining point of the tool, but in reality, for example, the spindle tip or the spindle tip may be temporarily It is the thermal displacement at an appropriate point of the test bar attached to the.

Therefore, in the present invention, by adjusting the thermal time constant of the temperature sensor, the characteristic of the thermal displacement of the machine tool and the output characteristic of the temperature sensor are made to substantially match, and the output of this temperature sensor is linear. The processing error is corrected by correcting the movement amount in the predetermined axis direction based on the thermal displacement obtained by the correlation. Also, for example, the heat generated from the main shaft bearing is
While raising the temperature near the heat source to which the temperature sensor is attached, the heat flow passing through the position near the heat source slowly raises the temperature of the structure other than this position. Therefore, the linear correlation between the temperature sensor output and the thermal displacement gradually includes an error after a long time due to the influence of the thermal displacement of the portion where the temperature change appears slowly. Therefore, considering the delay in the output of the temperature sensor,
Calculating a delay temperature change having the same thermal characteristics as the error,
The processing error is further corrected based on the thermal displacement obtained by the linear correlation with the delay temperature change.

That is, according to the thermal displacement correction method of the present invention, the thermal characteristics of the temperature sensor for detecting the temperature change of the machine body of the machine tool which is affected by the heat generation of the heat generation source are influenced by the heat generation of the heat generation source. Sensitivity is adjusted so as to approximately match the time constant of the generated spindle thermal displacement, and the thermal displacement corresponding to the output of the temperature sensor is calculated from the output of the temperature sensor, and the calculated thermal displacement and the actual thermal displacement gradually deviate. The moving error is calculated by considering the delay in the output of the temperature sensor, and the movement amount in the predetermined axis direction is corrected using the total value obtained by adding the calculation result to the calculated thermal displacement.

A thermal displacement compensating device for realizing this compensating method detects a temperature change of the machine body and detects a heat which is substantially equal to a time constant of a spindle thermal displacement caused by the heat generated by the heat source. A temperature sensor whose sensitivity is adjusted so as to have characteristics, a first thermal displacement calculating means for calculating a thermal displacement corresponding to the output of the temperature sensor from the output of the temperature sensor, and a first thermal displacement calculating means of the first thermal displacement calculating means. An error in which the output and the actual thermal displacement gradually deviate is calculated with a delay in the output of the temperature sensor, and the calculation result is added to the output of the first thermal displacement calculating means to calculate a total value. The second thermal displacement calculating means and the correcting means for correcting the movement amount in the predetermined axis direction by using the output of the second thermal displacement calculating means.

The output of the temperature sensor installed at an appropriate location of the machine body affected by the heat generated by the heat source includes the thermal characteristics of the machine body at the location where the temperature sensor is installed, as well as the thermal characteristics of the temperature sensor itself. Therefore, by adding a heat insulating material to the heat-sensitive portion of the temperature sensor and adjusting the sensitivity of the temperature sensor itself, it is possible to obtain from the temperature sensor an output that allows for a delay in the temperature change of the airframe. As a result of matching the thermal time constant of the output of the temperature sensor with the characteristic of the thermal displacement of the machine tool, the thermal time constant of the temperature sensor becomes a value larger than the initial thermal time constant of the temperature sensor itself. Therefore, as the mounting position of the temperature sensor, a location where the output characteristic of the temperature sensor is more sensitive than the thermal displacement characteristic is selected in advance. In this way, the temperature change of the temperature detected by the temperature sensor whose sensitivity is adjusted and the thermal displacement of the machine tool are directly associated with each other by a linear correlation.

The error between the thermal displacement and the actual thermal displacement, which appears from the output of the temperature sensor, which gradually appears over a long period of time, is a delayed response component of the thermal displacement. In the present invention, a "dummy method" is used as an example of a data processing method for matching the output data of the temperature sensor whose thermal time constant is adjusted with the thermal characteristics of the delayed response component. The dummy method detects the thermal displacement of the spindle when an arbitrary rotational speed of the spindle is applied to the machine tool, and at the same time, detects the temperature change of an appropriate portion having a time constant of the temperature change smaller than the time constant of the thermal displacement of the spindle. The behavior of the delayed temperature change that appears later than the detected temperature change is expected by setting a dummy heat capacity, and a fictitious delayed temperature change that has a time constant approximately the same as the time constant of the thermal displacement that appears late. This is a method of creating by the iterative calculation in which the change in the detected temperature is expected to be delayed. In the dummy method, when creating the lag temperature change, another lag temperature change is created once, and a lag having a time constant that is substantially the same as the time constant of the thermal displacement is created by allowing for further lag in this lag temperature change. A temperature change may be created.

By the way, when the delay response component does not have to be taken into consideration, the thermal displacement correction device includes the temperature sensor,
A first thermal displacement calculating means for calculating a thermal displacement corresponding to the output of the temperature sensor from the output of the temperature sensor, and a movement amount in the predetermined axial direction is corrected by using the output of the first thermal displacement calculating means. It may be provided with a correction means.

Next, a thermal displacement correction method combining a temperature sensor whose sensitivity is adjusted so as to match the characteristics of thermal displacement and a dummy method is applied to a machining center using a spindle portion in a spindle head as a heat source. Take for example. First, the thermal displacement that changes in response to the temperature change of the temperature detected by the nose temperature sensor whose sensitivity is adjusted at the nose position of the spindle head is calculated. Next, calculate the delay response component of the thermal displacement that changes in response to the delay temperature change calculated with a delay in the temperature change of the temperature detected by the nose temperature sensor, and add this delay response component to the previously calculated thermal displacement. Add up to get the total value. Then, by giving the total value of thermal displacement calculated using the output of this nose temperature sensor as the offset amount of the axis movement amount of the servo system, the machining position is corrected, so the machining error due to heat is minimized. Can be held down.

[0018]

With the rotation of the main shaft of the machine tool, heat is generated from a heat source such as a main shaft bearing and a main shaft motor, and the heat is conducted to the components of the main body, resulting in a temperature change of the main body. Ordinary machine tools mainly use cast iron or steel as the structural material. Therefore, if the temperature of the airframe changes, thermal displacement proportional to the linear expansion coefficient of these structural materials occurs in each part. The thermal displacement of each of these parts is added to deteriorate the machining accuracy of the machine tool. In addition, the temperature change due to the rotation of the machine tool spindle appears early near the heat source,
The longer the distance from the heat source such as the head mounting portion and the column, the later the temperature appears, and the temperature change characteristics at each position differ. For this reason, the temperature change and the thermal displacement of any part of the airframe are not usually directly connected.

However, the time series data of the thermal displacement of the spindle when an arbitrary number of spindle revolutions is given to the machine tool and the time series data of the temperature change detected from the appropriate portion of the machine body affected by the heat generation of the heat source are used. By applying a step input response function of a single first-order lag element approximately, the time constant until the temperature change is saturated can be extracted respectively. The balance between the time constant of thermal displacement and the time constant of temperature change is representative of the time-dependent characteristics of the machine tool that are common over a wide range of the spindle rotational speed.

Therefore, when the detection sensitivity of the temperature sensor itself which has detected the time-series data of the temperature change is changed, it is possible to detect the temperature change as if the thermal characteristics of the machine body at the location where the temperature sensor is attached have changed. Series data is obtained. The detection sensitivity of the temperature sensor is adjusted so that the time constant extracted from the time series data substantially matches the time constant of the main spindle thermal displacement.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. For example, the numerical control (N
C) The machine tool is a vertical machining center (hereinafter referred to as MC) 1, but the present invention may be applied to other types of NC machine tools other than MC. A column 3 is erected on the bed 2, and a spindle head 5 having a spindle motor 4 is attached to the column 3 so as to be movable in the Z-axis direction. The column 3 can move on the bed 2 in the Y-axis direction. A spindle 6 is provided on the spindle head 5 in the Z-axis direction, and a tool 7 is attached to the tip of the spindle 6 which is driven to rotate by the spindle motor 4. The work 9 placed on the table 8 provided on the bed 2 is attached to the tool 7
By cutting. The table 8 moves on the bed 2 in the X-axis direction. The axis of the main shaft 6 is defined as the Z axis, and the directions orthogonal to the Z axis and forming the orthogonal coordinate system are defined as the X axis and the Y axis.

A temperature sensor for detecting a temperature change of the body 10 of the MC1, which is affected by the heat generated by the heat source, is attached to the MC1. In this embodiment, a nose temperature sensor S ₁ is attached to the nose position on the spindle front end side of the spindle head 5 to detect the temperature change at this nose position. The nose temperature sensor S ₁ can be adjusted in sensitivity so as to have a thermal characteristic that substantially matches the time constant of the thermal displacement of the spindle caused by the heat generated by the heat source. The temperature sensor S ₁ may be of any type, but a thermistor temperature sensor resistant to disturbance is desirable. Since the nose position is close to the main bearing of the main shaft 6 which is the main heat source, the temperature change immediately appears on the nose temperature sensor S _1, and the time constant of this temperature change is small.

Here, the principle of thermal displacement correction in the present invention will be described. According to the present invention, it is possible to correct the thermal displacement in each of the X, Y, and Z axial directions. Therefore, correction in the X-axis direction is usually unnecessary. Although it is necessary to correct the Y-axis and the Z-axis, both axes are treated in the same way, so the following description will be made taking the correction in the Z-axis direction as an example.

The calculation formula of the thermal displacement in the Z-axis direction is shown by the following formula. ΔZ = a · (ΔZ ₁ + ΔZ ₂ ) (2) where ΔZ: Z-axis thermal displacement a: overall correction coefficient (this coefficient a corrects the difference between the result of the equation (2) and the actual accuracy. ΔZ ₁ : Immediate response component of Z-axis thermal displacement ΔZ ₂ : Delayed response component of Z-axis thermal displacement.

That is, the arithmetic expression (2) includes an immediate response component ΔZ _{1 in} which the thermal displacement can be predicted immediately from the temperature change and a delayed response component ΔZ _{2 in} which the thermal displacement appears with a delay. The temperature change is calculated as a temperature difference obtained by subtracting the reference temperature from the temperature detected and output by the temperature sensor. As the “reference temperature”, the output of the temperature sensor at the first time when the power of the MC1 is turned on, or the average value of multiple additions of this output, or an absolute reference such as 20 [° C.] is adopted. Is stored in.
When there are a plurality of temperature sensors, the reference temperature for each temperature sensor is stored in the RAM 11.

By the way, when the temperature change of the environment in which the machine tool is installed is relatively slow, the thermal deformation of the whole machine tool due to the room temperature change is substantially similar to that of the tool 7 and the workpiece 9. Change. That is, since a processing error due to heat does not occur in such a slow room temperature change, the result of predicting the thermal displacement from the temperature change including the room temperature change is different from the actual thermal displacement. Therefore, in this case, the momentary temperature detected by the temperature sensor separately provided on the bed of the machine tool is adopted as the reference temperature, and the value obtained by subtracting this reference temperature from the temperature output from each temperature sensor is used. Used as a temperature change. By doing so, even if there is a change in room temperature, accurate thermal displacement correction can be performed.

Next, the immediate response component ΔZ ₁ is calculated by the following equation. ΔZ ₁ = b · ΔT ₁ (3) where ΔT ₁ : detection sensitivity adjusted nose temperature sensor S
Temperature change obtained by subtracting the reference temperature from the output of ₁ [° C] b: Internal correction coefficient [± μm / ° C]. In addition, in order to calculate the immediate response component ΔZ ₁ , it suffices that at least one temperature sensor is installed, but it is added as appropriate according to the number of heat sources. Further, the temperature sensor may be installed at a place other than the nose position as long as it is a place sensitive to the heat generated by the heat source.

On the other hand, the equation for calculating the delay response component ΔZ ₂ is as follows. ΔZ ₂ = c · Y ₁ (4) Here, Y _{1 is} a delay temperature change calculated by using a temperature change ΔT ₁ [° C.] c is an internal correction coefficient [± μm / ° C.].

It should be noted that the temperature information used in the calculation of the delay response component ΔZ ₂ may be at least one, but may be appropriately added depending on the number of heat sources. Also, as temperature information,
Instead of using the output of the nose temperature sensor S _{1 described above,} the output of a temperature sensor separately installed at an appropriate location of the machine that is affected by the heat generated by the heat source may be used. For example, FIG. 1 shows a case where the head temperature sensor S ₂ may be attached to a position near the column 3 of the spindle head 5. When the detection sensitivity of the separately installed head temperature sensor S ₂ is not adjusted, the equation for calculating the delay response component ΔZ ₂ is as follows. ΔZ ₂ = c · Y ₂ (5) Here, Y _{2 is} a delay temperature change [° C.] calculated using the temperature change obtained by subtracting the reference temperature from the output of the head temperature sensor S ₂ that does not adjust the detection sensitivity. .

[0030] Alternatively, the detection sensitivity of the head temperature sensor S _2, by adjusting to match substantially to the time constant of the response delay component [Delta] Z _2, the delay response component [Delta] Z _2, calculates the previous immediate response component [Delta] Z ₁ It is also possible to calculate from the following equation in the same manner as the equation (3). ΔZ ₂ = c · ΔT ₂ (6) Here, ΔT ₂ : detection sensitivity adjusted head temperature sensor S
It is the temperature change [° C] obtained by subtracting the reference temperature from the output of ₂ .

Since the handling of the equations (5) and (6) is the same as the above equations (4) and (3), the detailed explanation of the equations (5) and (6) is given by the equation (4). , (3) will be used instead. Hereinafter, the case where the nose temperature sensor S ₁ is used will be mainly described, but regarding the calculation of the delay response component ΔZ ₂ , the thermal displacement correction can be similarly performed even if the temperature change is detected by the head temperature sensor S ₂ .

FIG. 1 is a block diagram showing an embodiment of the present invention. As shown, the output signal of the nose temperature sensor S ₁ (and head temperature sensor S ₂ ) is
(And the circuit 25), A / of the thermal displacement correction device 12
The analog signal input to the D converter 13 is converted into a digital signal here. The digital signal from the A / D converter 13 is input to the arithmetic storage unit 14 where the thermal displacement is calculated.

Correcting means 2 based on the calculated thermal displacement
By 1, the amount of movement in the predetermined axis direction is corrected. Correction means 2
The output signal of No. 1 is transmitted to the numerical controller 16 via the programmable controller 15, is fed back to the servo system, and the position is corrected. That is, the correction means 21
The calculation result is output to the external offset means that externally offsets the movement command value of the numerical controller 16. As a result, for example, the origin position of the Cartesian coordinate system is offset, and the numerical controller 16 controls the trajectory of the tool 7 of the MC1 and the like. The programmable controller 15 receives an instruction from the numerical controller 16 and manages the operation sequence of MC1. The programmable controller 15 may include the thermal displacement correction device 12.

The detected value of the nose temperature sensor S ₁ (and the head temperature sensor S ₂ ) is calculated by the calculation storage unit 14 via the A / D converter 13, and the command causes
Nose temperature sensor S ₁ (and head temperature sensor S ₂ )
It is written in the memory address in the RAM 11 designated for. Further, the RAM 11 stores temperature data sampled by the nose temperature sensor S ₁ (and the head temperature sensor S ₂ ) at regular intervals. This temperature data is displayed on the display unit of the numerical controller 16. The ROM 17 stores a program for calculating the thermal displacement according to the present invention, a correction coefficient, and the like. The clock 18 is for determining the temperature detection time of the nose temperature sensor S ₁ (and the head temperature sensor S ₂ ).

The arithmetic storage unit 14 stores the temperature change Δ of the temperature detected by the nose temperature sensor S ₁ whose detection sensitivity is appropriately adjusted.
With T _1, the first thermal distortion calculating means for calculating an immediate response component [Delta] Z ₁ of thermal displacement which corresponds to the temperature change [Delta] T ₁ 1
9, the delay temperature change Y ₁ appearing later than the temperature change [Delta] T _1, the delay temperature calculating means 22 for calculating expected to delay in the temperature change [Delta] T _1, the thermal displacement by using the delay temperature change Y ₁ Second thermal displacement calculating means 20 for calculating the delay response component ΔZ ₂ is provided. The second thermal displacement calculation means 20 adds the calculated delayed response component ΔZ ₂ to the immediate response component ΔZ ₁ calculated by the first thermal displacement calculation means 19. The correction unit 21 corrects the movement amount in the Z-axis direction using the added total value of the thermal displacements.

FIG. 2 is an enlarged sectional view showing a state in which the nose temperature sensor S ₁ is installed. As shown in the drawing, a recess 31 is formed in the detected portion 30 of the machine body 10 affected by the heat source (for example, the nose position of the spindle head 5 in this embodiment). Nose temperature sensor S as a temperature sensor
Reference numeral ₁ denotes a fixing member 32 for fixing the temperature sensor S ₁ to the detected portion 30, a rod-shaped heat sensitive portion 33 attached to the fixing member 32 and inserted into the recess 31, and a surface of the heat sensitive portion 33. And a paper 34 as a heat insulating material for adjusting the thermal characteristics of the temperature sensor S ₁ to a required value. The heat insulating material may be rubber, synthetic resin material, metal pieces, paint, or the like.

Male screw portion 36 of base 35 of fixing member 32
The nose temperature sensor S ₁ is detachably fixed to the detected portion 30 by screwing the screw into the female screw portion 37 of the recess 31. By increasing or decreasing the amount of the paper 34 wound around the heat-sensitive portion 33, the time constant of the temperature change detected by the nose temperature sensor S ₁ can be calculated in the Z-axis direction at the spindle position (preferably, the machining point by the tool 7). The time constant of thermal displacement of is adjusted to be approximately the same value. A filler 3 such as silicon grease having a large thermal conductivity is provided in the void in the recess 31.
Since 9 is filled, the temperature of the detected part 30 is quickly detected by the heat sensitive part 33 via the filler 39. The head temperature sensor S _{2 with} adjustable sensitivity has substantially the same structure as the nose temperature sensor S ₁ . The recess 3
You may adjust the thermal conductivity of the filler 39 interposed between 1 and the heat sensitive part 33. That is, the thermal characteristics of the temperature sensor S ₁ can be adjusted to a required value by using the filler 39 as the heat insulating material together with or instead of using the paper 34. For example, it is preferable to use a filler obtained by adding an appropriate amount of Styrofoam powder to silicon grease.

The specific procedure of this embodiment will be described below with reference to FIGS. FIG. 3 is a flowchart showing the operation of the present embodiment, FIG. 4 is a graph showing changes over time in Z-axis thermal displacement, and FIG. 5 is a graph showing changes over time in a typical example of Z-axis thermal displacement and nose temperature change T (change in sample temperature). The graph shown in FIG. 6 is a graph showing the standard relationship between sample temperature change and Z-axis thermal displacement. FIG. 7 is a graph showing the Z-axis thermal displacement with respect to the nose temperature change, FIG. 8 is a graph showing the Z-axis thermal displacement with respect to the nose temperature change when the Z-axis thermal displacement contains a delayed response component, and FIG. 9 is the delayed temperature. It is a graph explaining the method of calculating a change.

First, the time constant of the thermal displacement of the spindle in MC1, for example, in the Z-axis direction is calculated in advance based on the data shown in FIG. In FIG. 4, the horizontal axis represents time and the vertical axis represents thermal displacement in the Z-axis direction. When calculating the time constant of the thermal displacement in the Z-axis direction, MC1 is set to the spindle rotation speed S (for example, S = 10,
000 [min ^-1 ]) for continuous operation. Then, the thermal displacement in the Z-axis direction at the tip portion of the spindle 6 or at an appropriate portion of the test bar temporarily attached to the tip portion of the spindle 6 is measured as time series data 40. When the main axis is tilted due to heat generation, it is preferable to measure the thermal displacement at the root portion and the tip portion of the test bar, for example.

Since the data 40 (marked with "○" in the figure) usually includes the influence of the room temperature change, the room temperature correction data 4 having the saturation value Z _max corrected for the influence of the room temperature change 4
Calculate 1 (marked with "●" in the figure). The "time constant" is "the time required for the output to reach 63.2% of the saturation value Z _max when a stepwise input is applied in the linear first-order delay system". Therefore, in the room temperature correction data 41,
By applying the step input response function of the first-order lag element by the least squares method, the thermal displacement time constant τ _{z in} the Z-axis direction (for example, τ _z
= 0.57 [h]) is obtained.

Since the nose position is close to the heat source, the temperature changes rapidly. Therefore, the nose temperature sensor S ₁ has a paper 3
When the temperature change is detected in the state where 4 is not wound, as shown in FIG. 5, when the sample temperature change T at the nose position is based on the time constant τ _z of the Z-axis thermal displacement E at the tip of the main shaft, etc. Data with a smaller constant τ _S is obtained. The balance of the values of the time constant τ _{z of} the Z-axis thermal displacement E extracted here and the time constant τ _S of the sample temperature change T represents the thermal characteristics peculiar to each machine tool, and the spindle rotational speed. Even if operating conditions change, there is no change. Therefore, once both time constants τ _z ,
It is sufficient to perform the work of calculating τ _S.

However, when the relationship between the sample temperature change T and the Z-axis thermal displacement E is represented based on the data of FIG. 5, for example, an arcuate curve 42 is obtained as shown in FIG. That is, in this case, since the sample temperature change T and the Z-axis thermal displacement E do not have a simple linear relationship, it is not possible to immediately estimate the thermal displacement from the temperature change of the temperature detected from the nose position at any time.

Therefore, the thermal sensation part 33 of the nose temperature sensor S _{1 is} previously set so that the time constant τ _{S of the} temperature change detected by the nose temperature sensor S ₁ becomes substantially the same value as the time constant τ _Z of the spindle thermal displacement. A sheet of paper 34 is wound around the sheet to adjust the sensitivity. In this way, since the nose temperature change ΔT ₁ detected by the nose temperature sensor S ₁ has the same time constant as the main spindle thermal displacement, the nose temperature variation ΔT ₁ is the Z axis thermal displacement as indicated by the straight line 43 in FIG. It has a linear relationship. The slope b of the straight line 43 represents the correlation between the nose temperature change ΔT ₁ and the Z-axis thermal displacement.

Next, the procedure of this embodiment will be described with reference to the flow chart. As shown in FIGS. 1 and 3, the MC 1 is activated to start cutting the workpiece 9 with the tool 7 (step 101). The temperature change ΔT ₁ at the nose position is detected by the nose temperature sensor S ₁ (step 102), and the detection result is input to the first thermal displacement calculating means 19 and the delay temperature calculating means 22. The first thermal displacement calculation means 19 calculates the thermal displacement corresponding to the output of the nose temperature sensor S ₁ , that is, the immediate response component ΔZ ₁ by using the equation (3) (step 103).

Although this method alone can correct the thermal displacement with high accuracy, the column 3 and the like have a large mass and are apart from the main shaft 6, which is a main heat source, so that the temperature change appears with a delay. . This delay temperature change Y ₁ is, for example, in the region B where a long time has elapsed in FIG.
An error is given to the linear correlation between T ₁ and the Z-axis thermal displacement. Therefore, as indicated by the temperature change line 43a, an error occurs in which the immediate response component ΔZ ₁ output from the first thermal displacement calculation means 19 and the actual thermal displacement gradually deviate. Therefore, the delay temperature calculation means 22 to which the nose temperature change ΔT ₁ is input calculates the delay temperature change Y ₁ from the nose temperature change ΔT ₁ (step 104).

As a method of calculating the delay temperature change Y ₁ , there is the above-mentioned "dummy method". The behavior of the delay temperature change Y ₁ appearing after the nose temperature change ΔT ₁ is set by setting the dummy heat capacity C. Anticipate. Specifically, it is obtained by an approximate solution of the differential equation (7). C · dY ₁ / dt + Y ₁ = ΔT ₁ (7)

The horizontal axis of FIG. 9 represents time, and the vertical axis represents delay temperature change. From FIG. 9, the following equation is obtained. Y ₁ = Y ₀ + (dY ₀ / dt + dY ₁ / dt) / 2 · Δt (8)

From equation (7), dY ₁ / dt and dY ₀ / d
When t is calculated and substituted into the equation (8), the delay temperature change Y
_The formula for calculating ₁ is the following formula (9). This equation (9) is a temperature conversion equation, and the symbol C corresponds to its coefficient. The delay temperature change Y ₁ calculated by the equation (9) is a virtual created temperature change. Y ₁ = [ΔT ₀ + ΔT ₁ + (C / Δt) · Y ₀ −Y ₀ ] / [(C / Δt) +1] (9) where Δt: calculation interval [min] ΔT ₁ : nose temperature sensor Temperature change input of nose temperature detected by S ₁ [° C] ΔT ₀ : Previous temperature change input [° C] Y ₁ : Delayed temperature change output [° C] Y ₀ : Previous delayed temperature change output [° C] C: This is the dummy heat capacity [min].

FIG. 10 shows a sample temperature change T, which is a typical example of the temperature change of the temperature detected by the nose temperature sensor S ₁ before adjusting the detection sensitivity, and a delay temperature showing the same thermal behavior as the delay response component. A simulated example 50 of change (temperature change A, time constant τ _B ) is shown. Further, in FIG. 10, equation (9)
The delay temperature change Y ₁ created by using the temperature change ΔT ₁ of the nose temperature is indicated by the mark "○". Temperature change A
Is based on the assumption that the saturation value T _max becomes equal to the sample temperature change T after a long time has passed, and the mark “◯” indicates the case where the measurement interval, that is, the calculation interval Δt is 1.0 [min]. In this way, the time capacity τ _B (τ _B
It is possible to create a delayed temperature change Y ₁ that behaves in the same manner as the temperature change A of> τ _S ).

This delay temperature change Y ₁ and delay response component ΔZ
_{Since 2} is a straight line 51 having a linear relationship as shown in FIG. 11, the above equation (4) is established. Actually, it is not necessary to take the procedure of extracting the temperature change Y ₁ . For example,
Using the sample temperature change T, the dummy heat capacity C of the equation (9) and the internal correction coefficient c of the equation (4) are appropriately selected. The result of the repeated calculation is the Z-axis thermal displacement (the line including the region B) in FIG. The best values of the heat capacity C and the coefficient c are determined so as to match the error obtained by subtracting 43a) from the straight line 43. The heat capacity C and the coefficient c determined here are values unique to each machine tool, and this work may be performed once. The second thermal displacement calculation means 20 calculates the delay response component ΔZ ₂ by substituting the delay temperature change Y ₁ calculated by the delay temperature calculation means 22 into the equation (4) in which the internal correction coefficient c is fixed. (Step 105). Then, by using the equation (2), the second thermal displacement calculation means 20 uses the delay response component ΔZ ₂ calculated as described above to obtain the immediate response component Δ.
It is added to Z ₁ to calculate the total value, that is, the Z-axis thermal displacement ΔZ (step 106).

The vertical axis in FIG. 12 is the measured Z-axis thermal displacement, and the horizontal axis is the nose temperature change ΔT ₁ and the delay temperature change Y _1.
Z estimated using the procedure up to step 106
Axial thermal displacement ΔZ. For the calculation of this thermal displacement ΔZ, the following equation in which the overall correction coefficient a of equation (2) is 1 is used. ΔZ = b · ΔT ₁ + c · Y ₁ (10)

The actually measured Z-axis thermal displacement on the vertical axis shown in FIG. 12 and the value of the Z-axis thermal displacement ΔZ on the horizontal axis obtained by the equation (10) are substantially coincident with each other on the straight line 52 having an inclination of 45 °. To do. This means that both have the same value. Therefore, the Z-axis thermal displacement ΔZ can be calculated with sufficiently high accuracy based on the temperature data of the nose temperature sensor S ₁ installed at the location affected by the heat generation of the main bearing.

In this way, the processing error is corrected by correcting the movement amount in the Z-axis direction by the correction means 21 based on the Z-axis thermal displacement ΔZ calculated in step 106 (step 107). The workpiece 7 can be cut with high precision by the tool 7. After that, it is determined whether or not the correction is completed (step 108).
C1 is stopped (step 109), and the entire procedure ends. If the correction is not completed, the process returns to step 102.

In this embodiment, repetitive calculation is performed. Therefore, as shown in FIG. 1, the thermal displacement correction device 12 preferably includes the storage means 23. This storage means 23 simultaneously stores the last final calculation result of the delay temperature calculation means 22 and the power-off time until the MC1 power is turned off and then turned on again to restart the operation. ing. The storage means 23 exchanges data with the delay temperature calculation means 22. By doing so, even if the calculation of the delay temperature change is interrupted by turning off the power supply of the MC1, the history of the calculation of the thermal displacement correction is saved, and therefore the repeated calculation becomes effective.

According to the experiment conducted by the present inventor, the thermal displacement before correction was about 40 to 50 [μm], but in the present invention, the target value of the thermal displacement after correction can be brought close to zero. it can. That is, when the thermal displacement is corrected according to the present invention, the residual thermal displacement can be reduced to ± 5 [μm] or less. Even when the thermal displacement before correction is 100 μm or more, the residual thermal displacement after correction is ± 5 according to the present invention.
It has been confirmed that the size can be reduced to [μm] or less. As described above, according to the present invention, the thermal displacement can be corrected with high accuracy. Further, even when the intermittent operation is performed, according to the present invention, the residual thermal displacement after correction can be set to ± 5 [μm] or less.

As described above, according to the present invention, by using the output of the temperature sensor whose sensitive time constant is adjusted,
The thermal displacement characteristic peculiar to the machine becomes the detection characteristic of the temperature sensor as it is. Therefore, since the output of the temperature sensor is immediately reflected in the estimation of the thermal displacement, the complicated calculation of the thermal displacement prediction using the temperature sensor output becomes unnecessary. In addition, since the delay response component that appears with the passage of a long time may be calculated from time to time at large intervals, the calculation frequency may be low and the calculation amount may be small. It will be reduced. When the dummy method is used, the temperature change of the machine body may be detected by a temperature sensor separately provided on the column, bed, cross rail, etc. of the machine tool. Further, the correlation in the present embodiment only needs to have a certain correspondence relationship, and may be a case other than the primary correlation.

Since the present invention does not use the length of the conventional airframe component, the length of the airframe is not limited, and the length measurement and the rotational speed of the airframe component are variously changed. It is not necessary to actually measure the data. Therefore, the thermal displacement and the temperature change only have to be measured once under a certain number of rotations, and the actual measurement work of the thermal displacement characteristic extraction using an actual machine is simplified. Further, the work of confirming the linear expansion coefficient of the airframe constituent material is unnecessary.

Further, since the temperature sensor may be mounted at any position, the restriction on the mounting position of the temperature sensor is relaxed, and at the same time, thermal displacement is caused by only a small number of temperature sensors (for example, one for one heat source). Can be expected with high accuracy and can be made highly flexible. In addition, the temperature is corrected based on the temperature of the aircraft, and the room temperature is not directly detected. Therefore, even if the room temperature suddenly changes, for example, by opening the door of the room in winter or operating the cooler in summer, the effect of room temperature is eliminated, and the correction accuracy can be maintained with high accuracy. Further, the thermal displacement correction method and its apparatus of the present invention are applied to other types of machines in which thermal displacement adversely affects the accuracy and performance of the machine, for example, automatic control machines such as printing machines, presses, and laser processing machines. Also has the same effect. This automatic control machine is controlled by an automatic control device such as an NC device. In the drawings, the same reference numerals indicate the same or corresponding parts.

[0059]

Since the present invention is configured as described above, it is possible to correct the thermal displacement with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a state in which a nose temperature sensor is installed.

FIG. 3 is a flowchart showing the operation of this embodiment.

FIG. 4 is a graph showing changes with time of Z-axis thermal displacement.

FIG. 5 is a graph showing changes with time of Z-axis thermal displacement and sample temperature change.

FIG. 6 is a graph showing the relationship between sample temperature change and Z-axis thermal displacement.

FIG. 7 is a graph showing Z-axis thermal displacement with respect to change in nose temperature.

FIG. 8 is a graph showing the Z-axis thermal displacement with respect to the change in the nose temperature when the Z-axis thermal displacement includes a delayed response component.

FIG. 9 is a graph illustrating a method of calculating a delay temperature change.

FIG. 10 is a graph showing sample temperature change, delay temperature change, and created delay temperature change.

FIG. 11 is a graph showing a delay response component with respect to a delay temperature change.

FIG. 12 is a graph showing Z-axis thermal displacement with respect to thermal displacement estimated from changes in nose temperature and delay temperature.

[Explanation of symbols]

1 Vertical Machining Center (Machine Tool) 6 Spindle 7 Tool 10 Machine Body 12 Thermal Displacement Correcting Device 19 First Thermal Displacement Calculating Means 20 Second Thermal Displacement Calculating Means 21 Correcting Means 30 Detected Part 31 Recessed Part 32 Fixing Member 33 Heat Sensitive Part 34 Paper (heat insulating material) S ₁ Nose temperature sensor (temperature sensor) S ₂ Head temperature sensor (temperature sensor)

Claims (4)

[Claims] 1. A thermal characteristic of a temperature sensor for detecting a temperature change of a machine body of a machine tool which is affected by heat generation of a heat source is substantially equal to a time constant of a spindle thermal displacement generated by the heat generation of the heat source. The sensitivity is adjusted so that the thermal displacement corresponding to the output of the temperature sensor is calculated from the output of the temperature sensor, and the error in which the calculated thermal displacement and the actual thermal displacement are gradually deviated is the output of the temperature sensor. A method for correcting thermal displacement of a machine tool, characterized in that the amount of movement in a predetermined axis direction is corrected using a total value obtained by adding the calculated result to the calculated thermal displacement. 2. A temperature characteristic of a machine body of a machine tool that is affected by heat generation of a heat source is detected, and has a thermal characteristic that is substantially equal to a time constant of a spindle thermal displacement that is caused by the heat of the heat source. Using a temperature sensor whose sensitivity is adjusted, a first thermal displacement calculation means for calculating a thermal displacement corresponding to the output of the temperature sensor from the output of the temperature sensor, and an output of the first thermal displacement calculation means. A thermal displacement correction device for a machine tool, comprising: a correction unit that corrects a movement amount in a predetermined axis direction. 3. A temperature characteristic of a machine body of a machine tool that is affected by heat generated by a heat source is detected, and has thermal characteristics that substantially match a time constant of spindle thermal displacement that occurs due to the heat generated by the heat source. A temperature sensor whose sensitivity is adjusted, first thermal displacement calculating means for calculating thermal displacement corresponding to the output of the temperature sensor from the output of the temperature sensor, and output of the first thermal displacement calculating means and actual heat. An error in which the displacement is gradually deviated is calculated with a delay in the output of the temperature sensor, and the calculation result is added to the output of the first thermal displacement calculation means to calculate a total value. A thermal displacement compensating device for a machine tool, comprising: a thermal displacement computing means; and a compensating means for compensating a movement amount in a predetermined axial direction by using an output of the second thermal displacement computing means. 4. The temperature sensor, a fixing member for fixing the temperature sensor to a detected portion of the machine body having a concave portion, and a fixing member attached to the fixing member and inserted into the concave portion. 4. A heat-sensitive part, and a heat insulating material, which is applied to the surface of the heat-sensitive part in an appropriate amount to adjust the thermal characteristics of the temperature sensor to a required value.
A thermal displacement compensating device for a machine tool according to.