JP2006212765A - Machine tool thermal displacement compensation method - Google Patents

Abstract

【Task】
By comprehensively correcting the thermal displacement of both the machine tool feed screw and the workpiece, machining accuracy can be improved based on the actual size of the workpiece at the reference temperature.
[Solution]
First, in order to correct the positioning accuracy of the drive shaft 1 correctly, an absolute reference for the invar material R that hardly undergoes thermal expansion is provided, and an accurate positioning method is established by comparison with this absolute reference.
Secondly, the first machining is a correction based on the linear expansion coefficient specific to the material of the workpiece W, the length of the workpiece, and the temperature of the workpiece, considering the dimensions at the reference temperature that is the basis for workpiece accuracy judgment. It is reflected in the positioning at the time.
[Selection] Figure 19

Description

  The present invention relates to a thermal displacement correction method that realizes improvement of machining accuracy based on the actual size of a workpiece at a reference temperature by comprehensively correcting the thermal displacement of both the feed screw and the workpiece of the machine tool. .

Conventionally, although machine tools are required to have high precision positioning, the machine tools themselves have multiple potential factors that degrade positioning accuracy, and positioning errors can easily be caused by one or multiple factors. Will worsen.
Factors that cause positioning errors include various factors such as thermal expansion of the ball screw, which is a component of the drive system, and distortion and thermal deformation of the machine tool itself due to changes in ambient temperature. It is impossible to prevent.

  FIG. 1 shows a configuration of a general machine tool. A rotary motion of a servo motor 5 is transmitted by a ball screw 1 and converted into a linear motion by a nut 2 integrated with a machining table 3. The workpiece W on the table 3 can move relative to the spindle 7.

  As shown in FIG. 2, the ball screw 1 serving as a medium for transmitting the driving force of the servo motor 5 has a fixed side 10 connected to the servo motor 5 and a support anti-fixed side 11 at the other end. If 1 undergoes thermal expansion, it will extend in the direction of the non-fixed side 11.

The thermal expansion of the ball screw 1 varies depending on changes in the environmental temperature and the movement speed during processing. However, the thermal expansion caused by frictional heat has a particularly wide fluctuation range, and it is difficult to predict the expansion amount.
Since the above-described adverse effect deteriorates the positioning accuracy, as shown in FIG. 4, a positioning error corresponding to errors EX and EY occurs with respect to the position where the workpiece W should be positioned.

  On the other hand, as shown in FIG. 5, in the workpiece W, the ambient air temperature around the workpiece changes every moment, and the temperature of the cutting oil also varies depending on the machine tool and pump moving conditions. Errors CX and CY are generated due to thermal expansion.

As countermeasures against such positioning errors, there are no choice but to reduce the factors such as temperature changes or correct them after recognizing the errors themselves.
Originally, it is desirable to reduce the error factor itself, but for example, if you try to adjust the environmental temperature with advanced air conditioning equipment or temperature adjustment over the entire machine tool, the equipment cost and maintenance cost will rise, It is not rational from the viewpoint of energy saving.
Accordingly, it is common to perform accuracy correction based on error recognition after recognizing the occurrence of error as inevitable.

The speedup of machine tools in recent years is remarkable, but on the other hand, the problem of thermal displacement due to heat generation of ball screws and nuts that become the drive part is unavoidable, especially struggling with measures to prevent accuracy deterioration due to thermal expansion of ball screws. There are many.
In addition to the ball screw, there are various factors of positioning errors of machine tools, and they are often complex, so it is important to effectively suppress them while looking at cost performance.

Among known examples, the temperature change of the machine is detected by a temperature sensor, and based on the differential equation that calculates the calculated temperature change that behaves almost the same as the thermal behavior of the thermal displacement of the machine tool from this detected temperature change, The calculated temperature change is calculated using the detected temperature change, and the processing error is corrected based on the thermal displacement that changes corresponding to the calculated temperature change (for example, see Patent Document 1),
The position of the feed axis is monitored, the average movement speed and movement frequency of the feed axis per position correction unit time are obtained, and the correction amount is obtained and updated with an approximate expression based on this speed and frequency, and the position correction amount for the command position is determined from this correction amount. And the command position is corrected by the position correction amount (see, for example, Patent Document 1).
As described above, there are documents that deal with the expansion of the ball screw, but all are accuracy corrections that do not have an invariant absolute reference inside.
Like the correction method described above, inferences that depend only on predictions from measurement results lack reliability, and there are limitations such as inability to operate without limiting the usage conditions to some extent.
In addition, thermal expansion occurs not only in machine tools but also in processed workpieces, but there is no method for maintaining comprehensive accuracy including processed workpieces as products.
JP-A-9-108992 Japanese Patent Laid-Open No. 10-138091

  The problem to be solved by the present invention and its purpose are to provide a highly accurate simple device based on a comparison with the absolute reference for the thermal displacement of the ball screw, which is considered to be the most effective in taking measures against positioning errors of machine tools. It is intended to provide a thermal displacement correction method that makes it possible to stably operate a comprehensive and highly accurate accuracy correction by correcting and managing the thermal displacement of a workpiece to be processed based on a reference temperature.

  The most important aspect of the present invention is that an invar material having extremely low expansion characteristics with respect to a temperature change is set as an absolute reference, and the thermal expansion amount of the workpiece with respect to the reference temperature is taken into account while performing positioning correction based on this. It is a feature.

In the thermal displacement correction method for a machine tool according to claim 1 of the present invention, an invar material that is a low expansion material is joined to a fixed side of a linear drive shaft of the machine tool in a positional relationship parallel to the moving direction of the drive shaft,
In the Invar material, two detection sensors for detecting the detection piece are arranged at a precise interval,
On the other hand, on the moving side of the drive shaft, a detection piece that can be detected by the detection sensor is provided,
In the relative movement between the fixed side and the moving side of the drive shaft,
First, when checking the accuracy of the machine tool, the coordinate values when the two detection sensors detect the detection piece are stored in advance, and this is used as an absolute reference.
When using a machine tool, the difference between the coordinate value of each of the two detection values detected by the two detection sensors and the absolute reference is regarded as a positioning error from the absolute reference,
By placing a point indicating the error value and the above two coordinate values on a two-dimensional coordinate where one is the coordinate value of the drive axis and the other is an error, and setting a linear approximation formula passing between the two points,
Immediately before the control device executes the drive axis movement command, the coordinate value of the movement destination is substituted into the linear approximation formula in advance, the positioning error at the movement destination is obtained, and the movement correction for canceling this error is added. The position control of the machine tool is corrected so as to be the true coordinate value of the movement destination.

  A second aspect of the present invention is characterized in that three or more detection sensors according to the first aspect are arranged.

  According to a third aspect of the present invention, the detection sensor and the detection piece described in the first aspect are replaced, and the movement of two detection pieces is captured by one detection sensor.

  A fourth aspect of the present invention is characterized in that three or more detection pieces according to the third aspect are arranged.

In the thermal displacement correction method for a machine tool according to claim 5 of the present invention, the invar material is joined so as to be integrated with the machining table of the machine tool,
Instead of two detection sensors on both ends of the above Invar material, two round pockets are processed at precise intervals,
On the other hand, an automatic tool changeable touch sensor is called on the spindle of the machine tool by a tool change command,
First, at the accuracy inspection of a machine tool, the touch sensor is moved to the center of each perfect circle part of the invar material by NC program and macro program, and a plurality of points are placed on the inner side walls of the two perfect circle pockets. By measuring and computing this, the center coordinates of each perfect pocket are calculated and stored in advance, and this is the absolute reference,
By measuring the center coordinates of the two round pockets with a touch sensor when using a machine tool, the positional deviation from the absolute reference in the center coordinates of each round pocket is regarded as a positioning error.
By placing a point indicating the error value and the above two coordinate values on a two-dimensional coordinate where one is the coordinate value of the drive axis and the other is an error, and setting a linear approximation formula passing between the two points,
Immediately before executing the movement command of the drive axis, the coordinate value of the movement destination is substituted in advance in the above linear approximation formula to determine the positioning error at the movement destination, and the value obtained by adding movement correction to cancel this error is the true value. It is characterized in that the positioning control of the machine tool is corrected so as to be the coordinate value of the movement destination.

  According to the sixth aspect of the present invention, the invar material is joined to the machining table of the machine tool so as to be inclined, thereby simultaneously detecting the positioning error in the biaxial direction and applying the biaxial positioning correction to the positioning control of the machine tool. It is characterized by that.

  The seventh aspect of the present invention is characterized in that the invar material is integrated in a jig.

  The eighth aspect of the present invention is characterized in that the invar material is incorporated into a base plate of a jig and integrated with the base plate.

According to a ninth aspect of the present invention, there is provided a thermal displacement correction method for a machine tool according to the first to eighth aspects, wherein the workpiece is fixed near the center of the invar material,
A contact-type temperature sensor is attached to the above workpiece, and this measures the temperature of the workpiece,
Based on the temperature measurement result of the workpiece and the linear expansion coefficient specific to the workpiece, the dimension at the reference temperature of 20 ° C. is set as the actual dimension, and a correction value for correcting to the actual dimension is as follows:
Calculate based on the calculation formula of correction value = workpiece length x (reference temperature-workpiece temperature) x linear expansion coefficient.
The correction value is further superimposed on the positioning correction.

  A tenth aspect of the present invention is characterized in that, in the ninth aspect, the temperature sensor is a non-contact type temperature sensor.

  According to an eleventh aspect of the present invention, in the tenth aspect, the non-contact type temperature sensor is integrated with the touch sensor.

  According to a twelfth aspect of the present invention, in the tenth aspect, the non-contact type temperature sensor is integrated with the main shaft.

The thermal displacement correction method according to the present invention includes the above-described configuration conditions and operates as follows.
First, since the thermal displacement correction for the ball screw is performed based on an invar material that is extremely difficult to thermally expand, it is a very direct method.
In other words, in the case of thermal displacement correction that greatly depends on predictions and inferences, the usage of machine tools varies greatly depending on the user, so there is no guarantee that these predictions and inferences will be appropriate for all users, and the reality is often Inadequate correction may cause adverse effects.
However, the method for correcting the thermal displacement of the ball screw according to the present invention is extremely effective because the invar material with extremely small thermal expansion is used as an absolute reference, so there is no ambiguity and the device configuration and data processing are simple. And operational reliability is high.
In addition, the simple device configuration and processing system facilitate mounting on a machine tool, so that it can be mounted on a machine tool at a low cost.

Secondly, since the workpiece placed on the machining table is also thermally expanded, no matter how much the positioning accuracy of the machine tool is improved, accuracy cannot be guaranteed at the product level without taking measures for accuracy of the workpiece.
However, the thermal displacement correction method according to the present invention is for further canceling the thermal expansion of the workpiece with respect to the above-described positioning correction so as to obtain the workpiece size at the reference temperature, that is, the actual size by adding the workpiece temperature measurement. Apply overlay correction.
In order to maintain the accuracy of the final product level by eliminating the positioning error of the machine tool by the thermal displacement correction of the first drive shaft and superimposing the correction of the thermal expansion of the second workpiece on the positioning correction. Position control can be reflected in advance during machining.

  As described above, the present invention is a comprehensive thermal displacement correction method that aims to maintain the accuracy of the product itself, rather than partially or locally responding to errors due to thermal displacement. The present invention makes it possible with a simple machine configuration and control, and has the advantage of being able to provide thermal displacement correction that is low in cost and easy to mount and highly reliable.

In the first embodiment of the present invention, in the first embodiment, in order to correct the positioning accuracy of the drive shaft correctly, an absolute reference of invar material that hardly undergoes thermal expansion is provided, and an accurate positioning method is established by comparison with this absolute reference. To do.
As a result, the drive system is free from errors due to thermal displacement, and the movement command of the drive shaft is directly reflected in unmatched positioning.

Depending on the accuracy required, the improvement of the positioning accuracy of the drive system according to the first embodiment may be sufficient. However, if higher accuracy is desired, the thermal expansion of the workpiece on the processing table should be taken into consideration. Therefore, higher accuracy is required.
Therefore, in the second embodiment, the present invention provides a dimension at a reference temperature that is a basis for determining the accuracy of a workpiece from the linear expansion coefficient specific to the material of the workpiece, the length of the workpiece, and the temperature of the workpiece. The correction with the eyes on is reflected in the positioning during processing.

When the thermal displacement correction methods according to the first and second embodiments are combined, the accuracy standard of the product and the positioning correction at the time of machining are very directly correlated, and the accuracy of the product is greatly improved.
The present invention will now be described in order with each embodiment.

FIG. 6 shows a first embodiment of the present invention, in which position sensors 14, 14 ′ are attached to the invar material R attached to the fixed side of the drive shaft (ball screw 1) at a precise interval L2. The detection piece 15 attached to the moving side of the drive shaft (processing table 3) is captured by the two position sensors 14 and 14 ′, and the detection signal is transmitted to the control device 12 through the signal line 13.
At this time, the coordinate values at the time when the detection sensors 14 and 14 'on the ball screw fixing side capture the detection piece 15 and the coordinate values held in advance during the accuracy inspection of the machine tool are respectively compared to obtain an error, and an invar material is obtained. Assuming that R is unchanged, an approximate linear equation of error is set, and the positioning of subsequent machining is corrected.

FIG. 7 shows the invar material R with four detection sensors 14, 14 ′, 14 ″, 14 ′ ″ attached thereto.
This is for performing positioning correction more precisely in each section from each error in each detection sensor arranged at precise intervals L3, L4, and L5.
Usually, even a correction between two points shown in FIG. 6 can be expected to have a sufficient effect. However, when a highly accurate positioning correction is required in a certain section, or the movable range is very long, depending on each part of the ball screw. This is a method for dealing with a case where a difference in thermal expansion has to be taken into consideration.

  FIG. 8 is an example in which the first embodiment shown in FIG. 6 is mounted on each of the XYZ axes of the machine tool, and enables general orthogonal three-axis positioning correction. .

The method for detecting each position of the invar material R is to perform positioning correction based on the measurement by the detection sensor and the detection piece, but the one shown in FIG. 9 is the center position of the two perfect circle pockets P1 and P2. This is a method of performing positioning correction by detecting each with the probe 17.
For example, an invar material R having round pockets P1, P2 at both ends is fixed on the processing table 3, and a touch sensor S capable of automatic tool change is called on the spindle 7 for the round pockets P1, P2, and the tip The probe 17 is used for measurement.

FIG. 10 shows the measurement of the perfect circle pocket. If the four-point measurement in FIG. 10A and the three-point measurement in FIG. 10B are used, the center of the circle can be obtained mathematically by two-dimensional coordinates. Is possible.
If a one-dimensional center is sufficient, the two-point measurement shown in FIG. 10C may be sufficient.
Although the measurement points are set according to the actual measurement stability, the cycle time allowable for the measurement, and the like, four-point measurement is basically desirable.

FIG. 11 shows a case in which the invar material R processed with the perfect circular pockets P1 and P2 at both ends is installed in parallel with the drive shaft to be corrected. In this case, only one axis can be corrected for positioning. is there.
However, as shown in FIG. 12, when the invar material R is tilted, sections L3 and L4 are formed in the two-axis directions, and the centers of the perfect circle pockets P1 and P2 are measured in two-dimensional coordinates. By correcting the positioning in the direction, it is possible to cope with the correction in the biaxial direction without increasing the number of measurements.

FIG. 13 shows an embodiment in which the invar material R is mounted on the processing table 3 as in FIG. 9.
The figure is shown enlarged for the sake of clarity, but in reality, the diameter of the perfect circular pocket, the invar material, etc. are mounted in a compact manner, and consideration is given to interference during processing.
Further, as long as it is possible to measure even the perfect circle pockets P1 and P2, a jig or a workpiece may be mounted on the central portion of the invar material R. Therefore, it may be buried in the processing table 3 as shown in FIG. By doing so, the use of the processing table is not hindered.

  FIG. 15 shows an example in which the invar material R is tilted and further embedded in the processing table 3, and the two-axis simultaneous positioning correction is possible and the use of the processing table is not hindered.

FIG. 16 is an embodiment equipped with an example of an additional device that is not affected by chips or cutting oil when measuring the perfect circular pocket P.
Except at the time of measurement, the upper surface of the perfect circle pocket P is closed with the cover 18 to prevent intrusion of chips and cutting oil. Only when the measurement is performed, the cover open signal is received from the signal line 13 and the drive unit 19 (for example, an electromagnetic actuator) , The air actuator) is used to rotate the cover 18 around the rotation axis 20 to open the perfect circular pocket P, and the probe 17 of the touch sensor S can be used for measurement.
Thereby, the measurement surface of the perfect circle pocket P used as a measurement reference is kept clean.

FIG. 17 shows an example in which a jig F is mounted on the processing table 3 of the machine tool.
In the present embodiment, a planar invar material R is placed on the processing table 3, and blocks R1 and R2 are prepared with round pockets P1 and P2 for measurement near the diagonal points of the invar material. The jig F is placed within the range, and the positioning correction of the jig F and the workpiece W is performed.
Although FIG. 17 shows a plate-like invar material R, the use of the invar material as shown in FIG. 15 is also possible.

By the way, the above-described embodiments for positioning correction are only corrections for the drive shaft (ball screw 1), and the thermal expansion of the workpiece is not taken into consideration.
In other words, when the positioning correction of the drive system is not sufficient, when processing a workpiece that has a large linear expansion coefficient and is likely to thermally expand, when the workpiece temperature changes with time due to the surrounding environmental temperature during mass production, etc. When it is necessary to consider the occurrence of errors due to thermal expansion, it is necessary to separately manage accuracy based on the actual size at the reference temperature of the workpiece.
In order to cope with this, the thermal displacement according to the second embodiment in which the correction of the thermal expansion of the workpiece based on the reference temperature of the workpiece is added to the positioning correction of the drive shaft based on the absolute reference of invar material. A correction method is provided.

FIG. 18 is an embodiment showing a method for measuring the temperature of the workpiece for correcting the thermal expansion of the workpiece W.
A contact type temperature sensor 22 such as a thermocouple is attached to the workpiece W, the change in the temperature of the workpiece W over time is detected, and the reference temperature is determined by the linear expansion coefficient specific to the workpiece W material, the workpiece W temperature measurement, and the workpiece W length. The amount of workpiece expansion with respect to (20 ° C.) is obtained by calculation and added to positioning correction to comprehensively improve positioning accuracy.

  In FIG. 18, the temperature sensor 22 is attached to the side surface of the workpiece W, but it is also possible to incorporate a temperature sensor in the workpiece pressing portion of the clamper 12 for fixing the workpiece W on the jig F. If a temperature sensor is attached to the clamper, the measurement data can be stabilized by measuring the temperature of the workpiece more diversified or by averaging a plurality of measurement results.

Further, instead of the contact-type temperature sensors 14, 14 ′, 14 ″, 14 ′ ″, FIG. 19 shows a modified example using a non-contact-type temperature sensor 23.
That is, the temperature of the workpiece W is measured by attaching a non-contact type temperature sensor 23 such as a radiation thermometer capable of measuring the temperature by the amount of infrared rays in the vicinity of the workpiece W.
Since the non-contact type temperature sensor 23 can be installed away from the workpiece W and the jig F, the degree of freedom of mounting is higher than that of the contact type.
Further, if the temperature sensor 23 is incorporated in the touch sensor S as shown in FIG. 20 (a) or incorporated in the main shaft 7 as shown in FIG. 20 (b), the temperature can be measured while freely changing the measurement location. Is also possible.

As described above, the thermal displacement correction apparatus for executing the thermal displacement correction method of the present invention has been described.
Next, details of the thermal displacement correction method according to the first embodiment of the present invention will be described.
The explanation will be based on the configuration of one axis, but the basic idea is the same for two axes, and the basic idea is the same for the detection sensor and detection piece, the perfect circle pocket and the touch sensor. is there.

The invar material R shown in FIG. 21 is obtained by processing perfect circular pockets P1 and P2 at both ends. However, the distance between the centers of the perfect circular pockets P1 and P2 is not changed regardless of temperature change. Is regarded as an absolute reference, and is regarded as a master gauge MG for positioning correction of the present invention.
The master gauge MG by the invar material R is preferably placed in the area where the workpiece W is placed, mainly in the vicinity of the center of the processing table 3. In this case, the machine origin on the fixed side of the ball screw 1 is O1, and each perfect circle The center coordinates of the pockets P1 and P2 are M1 and M2, respectively.

First, referring to FIG. 22, a thermal displacement correction method according to the first embodiment of the present invention will be described.
The machine coordinates of M1 and M2 are measured at the time of accuracy inspection of the machine tool, and are registered in advance as parameters of the control device 12.
Next, immediately before actual machining, the machine coordinates of M1 and M2 are measured again, and respective errors are obtained.
The measurement points M1 and M2 measured again include errors due to temperature expansion of the ball screw of the machine tool or thermal expansion due to frictional heat due to operation, etc. Therefore, an approximate straight line of error at each point at the measurement points M1 and M2 FIG. 22 is a graph of Expression G2.
This is basically a graph of such a linear line because the ball screw extends to the anti-fixed side with respect to the fixed side by thermal expansion.

The reality is a line graph with minute changes as shown in G1, but considering the resolution of positioning of a general machine tool, the approximation linear equation G2 is also approximated with necessary and sufficient accuracy.
At the stage of this graph, the error at any point other than M1 and M2 can be obtained by the above approximate linear equation. After this approximate linear equation is established, the coordinate value of the movement command of the machining program is preliminarily determined. What is necessary is just to correct | amend the error calculated | required from the said approximate linear formula.
For example, in the case of a movement command for moving to X = 165.5, an error at X = 165.5 is obtained in advance by an approximate linear equation immediately before executing this movement command, and it is temporarily 5 microns in the plus direction. If so, minus 5 microns for offsetting this is reflected in the movement command, so that the actual movement command becomes X = 165.495.

  With the above, the accurate positioning accuracy of the drive shaft (ball screw 1) itself can be obtained. However, if the temperature expansion of the workpiece W is ignored, the effect of the accurate positioning accuracy of the drive shaft is reduced. FIG. 23 shows a thermal displacement correction method according to the second embodiment for further reflecting expansion in positioning correction.

As shown in the linear expansion coefficient 53, the workpiece has a linear expansion coefficient peculiar to the material. By grasping this numerical value and the temperature change of the work, it is possible to predict a change in the size of the work. is there.
In addition, since the thermal expansion of the workpiece occurs in the entire workpiece, it is necessary to set the reference position for thermal expansion. However, the workpiece center is set near the master gauge center M3, and the workpiece thermal expansion is based on the master gauge center M3. Correct.

The value to be corrected is as shown in Equation 51. The temperature at which the workpiece has a normal dimension is the reference temperature (20 ° C.), and the linear expansion coefficient is applied to the difference between the temperature measured by the temperature sensor and the reference temperature. Since the numerical value is an error due to thermal expansion per 1 m of the workpiece, if the workpiece size is further increased, the thermal expansion amount of the workpiece to be actually corrected can be obtained.
Therefore, as shown in Expression 52, when the correction value is added to the measured value, the actual workpiece dimension can be obtained from the apparent dimension.

The graph A1 is a graph for correcting the positioning of the ball screw described in the above description. When the above equation 51 is superimposed on the graph A1 with the center M3 as a base point, a graph A2 serving as a superimposition correction value is set. Can do.
From this graph A2, it is possible to obtain a positioning correction value in consideration of the thermal expansion of the workpiece at an arbitrary coordinate.

As described above, according to the above embodiments, the following effects are obtained.
That is, the present invention is a comprehensive thermal displacement correction method aiming at maintaining the accuracy of the product itself, rather than partially or locally corresponding to the error due to thermal displacement. There is an advantage that it can be realized by the configuration and control, and it is possible to provide a highly reliable thermal displacement correction that is easy to implement while being low in cost.

The thermal displacement correction method using the positioning method according to the present invention is not limited to a machine tool, but is effective for any feeding device that requires precise positioning accuracy on a linear movement axis. Is an extremely effective means for stabilizing and stabilizing.
Moreover, since generation | occurrence | production of the inferior goods originating in the defect of processing precision is suppressed by this invention, more stable physical distribution can be established in the manufacturing line which consists of a machine tool.

It is a block diagram of the machine tool used as a prior art example. It is an external view explaining fixation of the ball screw used as a prior art example. It is an external view explaining the elongation of the ball screw used as a prior art example. It is explanatory drawing which shows the position shift by the thermal displacement of the ball screw used as a prior art example. It is explanatory drawing which shows the thermal expansion of the workpiece | work used as a prior art example. It is the 1st Embodiment of this invention and is the attachment schematic of an apparatus. It is the 1st Embodiment of this invention and is the attachment schematic of an apparatus. It is a 1st embodiment of the present invention, and is a mounting diagram of a detection sensor, a detection piece, etc. 1 is a schematic diagram of a touch sensor according to a first embodiment of the present invention. FIG. It is explanatory drawing which shows a motion of a touch sensor. It is the schematic which shows the shaping example of the invar material for touch sensors. It is the schematic which shows the inclination arrangement | positioning for touch sensors. It is the schematic which shows mounting of the measurement by a touch sensor. It is the schematic which shows mounting of the measurement by a touch sensor. It is the schematic which shows mounting of the measurement by a touch sensor. It is a block diagram of the protective cover for a perfect circle pocket. It is the schematic which shows the structure combined with the jig | tool. It is the schematic which shows the 2nd Embodiment of this invention and shows the measuring method of workpiece | work temperature. It is the schematic which shows the 2nd Embodiment of this invention and shows the measuring method of workpiece | work temperature. It is the schematic which shows the 2nd Embodiment of this invention and shows mounting of the measuring apparatus of workpiece | work temperature. It is the schematic of a master gauge. It is explanatory drawing of the approximate linear type | formula of an error which shows 1st Embodiment. It is explanatory drawing of superposition correction | amendment which shows 2nd Embodiment.

Explanation of symbols

1 Ball screw (drive shaft)
2 Nut 3 Processing table 4 Coupling 5 Servo motor 6 Encoder 7 Spindle 8 Automatic tool changer 9 Control panel 10 Ball screw fixed side 11 Ball screw non-fixed side 12 Controller 13 Signal line 14 Position sensor 14 'Position sensor 14''Position sensor 14 '''Position sensor 15 Detection piece 16 Column 17 Probe 18 Cover 19 Cover drive unit 20 Cover rotating shaft 21 Clamper 22 Temperature sensor (contact type)
23 Temperature sensor (non-contact type)
24 Tool 51 Calculation Formula for Obtaining Correction Value 52 Calculation Formula for Obtaining Actual Dimensions 53 Example of Linear Expansion Coefficient 100 Machine Tool 101 Machine Tool A1 Graph (Correction Amount Obtained from Comparison with Reference Value)
A2 graph (correction amount taking into account workpiece temperature and linear expansion)
CX X-direction thermal expansion CY Y-direction thermal expansion EX X-direction error EY Y-direction error F Jig G1 Error plot G2 Error approximate straight line L1 Ball screw length L2 Sensor spacing L3 Sensor spacing L4 Sensor spacing Interval L5 Sensor interval M1 Measurement point M2 Measurement point M3 Master gauge center MG Master gauge (Invar material)
O1 Machine origin (fixed side)
P True circle pocket P1 True circle pocket P2 True circle pocket R Invar materials R1, R2 Block S with a true circle processed Touch sensor W Workpiece θ Tilt angle

Claims (12)

Invar material, which is a low expansion material, is joined to the fixed side of the linear drive shaft of the machine tool in a positional relationship parallel to the moving direction of the drive shaft,
In the Invar material, two detection sensors for detecting the detection piece are arranged at a precise interval,
On the other hand, on the moving side of the drive shaft, a detection piece that can be detected by the detection sensor is provided,
In the relative movement between the fixed side and the moving side of the drive shaft,
First, when checking the accuracy of the machine tool, the coordinate values when the two detection sensors detect the detection piece are stored in advance, and this is used as an absolute reference.
When using a machine tool, the difference between the coordinate value of each of the two detection values detected by the two detection sensors and the absolute reference is regarded as a positioning error from the absolute reference,
By placing a point indicating the error value and the above two coordinate values on a two-dimensional coordinate where one is the coordinate value of the drive axis and the other is an error, and setting a linear approximation formula passing between the two points,
Immediately before the control device executes the drive axis movement command, the coordinate value of the movement destination is substituted into the linear approximation formula in advance, the positioning error at the movement destination is obtained, and the movement correction for canceling this error is added. A machine tool thermal displacement correction method, comprising: correcting a machine tool positioning control so as to be a true coordinate value of a movement destination.   A method for correcting thermal displacement of a machine tool, comprising three or more detection sensors according to claim 1.   The method according to claim 1, wherein the detection sensor and the detection piece are replaced, and the movement of the two detection pieces is captured by one detection sensor.   A method for correcting a thermal displacement of a machine tool, comprising three or more detection pieces according to claim 3. Joining Invar material with the machining table of the machine tool,
Instead of two detection sensors on both ends of the above Invar material, two round pockets are processed at precise intervals,
On the other hand, an automatic tool changeable touch sensor is called on the spindle of the machine tool by a tool change command,
First, at the accuracy inspection of a machine tool, the touch sensor is moved to the center of each perfect circle part of the invar material by NC program and macro program, and a plurality of points are placed on the inner side walls of the two perfect circle pockets. By measuring and computing this, the center coordinates of each perfect pocket are calculated and stored in advance, and this is the absolute reference,
By measuring the center coordinates of the two round pockets with a touch sensor when using a machine tool, the positional deviation from the absolute reference in the center coordinates of each round pocket is regarded as a positioning error.
By placing a point indicating the error value and the above two coordinate values on a two-dimensional coordinate where one is the coordinate value of the drive axis and the other is an error, and setting a linear approximation formula passing between the two points,
Immediately before executing the movement command of the drive axis, the coordinate value of the movement destination is substituted in advance in the above linear approximation formula to determine the positioning error at the movement destination, and the value obtained by adding movement correction to cancel this error is the true value. A method for correcting a thermal displacement of a machine tool, comprising correcting the positioning control of the machine tool so as to obtain a coordinate value of a movement destination.   6. The invar material is tilted and joined to a machining table of a machine tool, so that a positioning error in two axes is detected at the same time, and a two-axis positioning correction is applied to positioning control of the machine tool. A thermal displacement correction method for a machine tool as described.   The thermal displacement correction method for a machine tool according to claim 6, wherein the invar material is integrated in a jig and integrated.   The thermal displacement correction method for a machine tool according to claim 6, wherein the invar material is incorporated in a base plate of a jig and integrated with the base plate. In the above Claims 1 to 8, the workpiece is fixed near the center of the invar material,
A contact-type temperature sensor is attached to the above workpiece, and this measures the temperature of the workpiece,
Based on the temperature measurement result of the workpiece and the linear expansion coefficient specific to the workpiece, the dimension at the reference temperature of 20 ° C. is set as the actual dimension, and a correction value for correcting to the actual dimension is as follows:
Calculate based on the calculation formula of correction value = workpiece length x (reference temperature-workpiece temperature) x linear expansion coefficient.
A method for correcting a thermal displacement of a machine tool, wherein the correction value is further superimposed on a positioning correction.   10. The thermal displacement correction method for a machine tool according to claim 9, wherein the temperature sensor is a non-contact type temperature sensor.   11. The workpiece temperature measuring apparatus according to claim 10, wherein a non-contact type temperature sensor is integrated with a touch sensor.   11. The workpiece temperature measuring apparatus according to claim 10, wherein a non-contact type temperature sensor is integrated with the main shaft.

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