WO2011024838A1

WO2011024838A1 - Method for thermal displacement correction in machine tool and thermal displacement correction device

Info

Publication number: WO2011024838A1
Application number: PCT/JP2010/064341
Authority: WO
Inventors: 治夫小林; 初倉橋
Original assignee: ブラザー工業株式会社
Priority date: 2009-08-28
Filing date: 2010-08-25
Publication date: 2011-03-03
Also published as: JP5397095B2; CN102481675B; JP2011045985A; CN102481675A

Abstract

The anterior shaft section and the nut-part mobile range of a ball screw shaft are segmented into five 80mm computation intervals, and the posterior shaft portion is treated as one computation interval. The amount of generated heat arising in the six computation intervals is computed every 50 ms on the basis of feed data and feed speed of a table. The temperature distribution of the six computation intervals is calculated every 6400 ms on the basis of amounts of generated heat (Q₁-Q₆) that are the cumulative values of 6400 ms of the computed amounts of generated heat, the total amount of generated heat (Q_T) that is the total of the amounts of generated heat (Q₁-Q₆), and an unsteady heat conduction equation. The magnitude of thermal displacement of the six computation intervals is computed every 6400 ms from the temperature distribution, and on the basis of the computed magnitudes of thermal displacement, correction amounts that correct the pitch error correction amount for the location of the break between each of fifteen correction intervals are computed every 6400 ms.

Description

Thermal displacement correction method and thermal displacement correction device for machine tool

The present invention relates to a thermal displacement correction method and a thermal displacement correction device for a machine tool. More particularly, the present invention relates to a method and apparatus for correcting an error caused by thermal displacement of a ball screw mechanism that occurs during operation of a machine tool.

The ball screw mechanism is widely used as a positioning mechanism for machine tools. The ball screw mechanism causes a pitch error between the amount of rotation of the ball screw shaft and the amount of movement of the nut due to manufacturing tolerances and the like. The thermal displacement correction device of the machine tool corrects the pitch error of the ball screw mechanism based on a preset pitch error correction amount table.

The temperature of the ball screw mechanism rises due to the frictional resistance between the ball screw shaft and the nut and the heat generated by the frictional resistance between the ball screw shaft and each bearing. The ball screw mechanism causes thermal expansion based on the above-described temperature rise, and generates thermal displacement (elongation). The thermal displacement of the ball screw shaft causes a positioning error of the machine tool. As a measure against the above, there is a pre-tension method. The pre-tension method applies pre-tension to the ball screw shaft and absorbs thermal expansion.

The machine tool uses a thick ball screw shaft and the feed speed is very fast. Therefore, since the amount of heat generation increases, when using the pre-tension method, the machine tool must apply a very large tension to the ball screw shaft. When a very large tension is applied to the machine tool, there is a problem that the ball screw mechanism is deformed. In the above case, there is a problem that an excessive force is applied to the thrust bearing and the ball screw mechanism is seized.

The methods for correcting the thermal displacement of the ball screw shaft proposed by Patent Documents 1 to 3 do not apply excessive tension to the ball screw shaft and do not require a special measuring device. The method corrects for thermal displacement during machine tool operation. Specifically, in the first step, the amount of heat generated in each section of the ball screw shaft is calculated based on the rotation speed of the servo motor. In the second step, the temperature distribution of the ball screw shaft is calculated based on the amount of heat generated using a model in which the nut movement range of the ball screw shaft is divided into a plurality of correction sections. The third step predicts the amount of thermal displacement of the ball screw shaft from time to time based on the temperature distribution. In the fourth step, the thermal displacement amount is given to the numerical control device (control unit) as a correction amount for correcting the pitch error correction amount. This method can approximate the calculated correction amount to the actual elongation of the ball screw shaft.

As shown in FIG. 8, for example, the correction section of the ball screw mechanism is a section in which the nut portion movement range (between X0 and X300 in the machine coordinates) 81b of the ball screw shaft 81 is equally divided by a length of 20 mm. Pitch error correction is performed for each correction section. The correction amount of the thermal displacement amount is calculated for each calculation section divided by the same set length as the correction section for pitch error correction. When the calculation interval is short, the number of calculation intervals increases. Therefore, the thermal displacement amount correction apparatus increases the processing load, and may not be able to calculate the thermal displacement correction amount within a predetermined time (calculation cycle). Since the above-mentioned length of 20 mm is short as the length of the calculation section, there is a case where the correction amount of the thermal displacement amount cannot be calculated.

The number of calculation sections decreases when the length of the calculation section is increased compared to when the set length of the calculation section is short. Therefore, the problem that the correction amount of the thermal displacement amount cannot be calculated does not occur. However, when the set length of the calculation section is increased, the calculation accuracy of the thermal displacement amount is lower than that when the set length of the calculation section is short. Therefore, in the case described above, there is a problem that the processing accuracy is lowered. Therefore, the thermal displacement amount correcting device needs to set the length of the calculation section to an appropriate length in order to suppress the load of the calculation process and achieve the target machining accuracy.

The conventional thermal displacement correction method sets the calculation interval as follows. The division position of the calculation section of the thermal shift correction amount is a position that coincides with the machine coordinate origin (X0). The length of the calculation section in the nut portion moving range 81b of the ball screw shaft 81 is an integral multiple of the length of the correction section for pitch error correction. FIG. 12 shows an example in which the length of the calculation section is 20 mm × 4 = 80 mm, and the origin X0 of the machine coordinates coincides with the break position of the calculation section.

In FIG. 12, the length of the front shaft portion 81a is 100 mm. The length of the nut portion moving range 81b is 300 mm. The length of the rear shaft portion 81c is 100 mm. In the above case, the length of the calculation section 1 is 80 mm. The length of the calculation section 2 is 20 mm. The length of the calculation section 3 to the calculation section 5 is 80 mm. The length of the calculation section 6 is 60 mm. The length of the calculation section 7 is 80 mm. The length of the calculation section 8 is 20 mm. The remainder that cannot be divided by the section length (80 mm) of the calculation section is in calculation section 2, calculation section 6, and calculation section 8.

The pitch error correction amount is corrected by the following method using the thermal displacement amount calculated for each calculation section. The thermal displacement correction device corrects the pitch error correction amount of X0 using the sum of the thermal displacement amounts of calculation interval 1 and calculation interval 2 as the thermal displacement amount at position X0. The thermal displacement correction device calculates the thermal displacement amounts at the positions X20, X40, X60, and X80 based on the fact that the length of the calculation section 3 is four times the length of the correction section as follows. The thermal displacement correction device equally divides ¼ of the thermal displacement amount in the calculation section 3 to the positions X20, X40, X60, and X80, and calculates the thermal displacement amount at each position. The thermal displacement correction device corrects the pitch error correction amount at each position using the thermal displacement amount. For other calculation sections, the pitch error correction amount is corrected in the same manner as described above.

JP 63-256336 A JP-A-4-240045 JP 7-299701 A

In the above division method, the lengths of the calculation section 2, the calculation section 6, and the calculation section 8 are shorter than the section length (80 mm) of the calculation section. In the division method, the number of computation sections increases due to

computation sections

2 and 8 having the minimum length (20 mm) among the remainders that cannot be divided by the section length of the computation sections. Therefore, the calculation cycle for calculating the amount of thermal displacement must be set small according to the number of calculation sections. Therefore, the calculation processing load of the thermal displacement correction device increases.

In the method shown in FIG. 13, calculation interval 2 in FIG. 12 is added to calculation interval 1, calculation interval 6 is added to calculation interval 5, and calculation interval 8 is added to calculation interval 7. In the method shown in FIG. 13, the lengths (80 mm) of the calculation section 2 and the calculation section 3 are lengths for determining a calculation cycle for calculating the thermal displacement amount. Therefore, the method shown in FIG. 13 can suppress the processing load of the thermal displacement correction device. The range from the front shaft portion 81a of the ball screw shaft 81 to the nut portion moving range 81b affects the calculation accuracy of the thermal displacement amount. Each of the calculation section 1 and the calculation section 4 is longer than the length of the calculation section. Therefore, since the calculation accuracy of the thermal displacement amount is lowered, the target machining accuracy may not be achieved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal displacement correction method for a machine tool and a thermal displacement correction device for the same that can suppress the calculation processing load of the numerical control device and perform highly accurate thermal displacement correction. is there.

A method of correcting a thermal displacement amount of a machine tool according to claim 1 comprises: a feed drive ball screw mechanism including a shaft and a nut; a servo motor that rotationally drives the shaft into which the nut of the ball screw mechanism is screwed; and the servo motor. In a thermal displacement correction method for a machine tool having a control unit controlled based on control data, a fixed side end connected to the shaft and the servo motor, a movable side end opposite to the fixed side end, When calculating the amount of thermal displacement of the shaft during operation of the machine tool, a plurality of calculation sections obtained by dividing the total length of the shaft by a fixed length from the fixed side end and the movable side end And a heat generation amount and a temperature distribution in each calculation section are calculated.

The thermal displacement amount correction method according to claim 1 divides the entire length of the shaft into a fixed length calculation section from the fixed side end, and sets the length of the calculation section including the movable side end to a certain length or more. Calculate calorific value and temperature distribution for each calculation section. In the thermal displacement amount correction method, the delimitation position of the thermal displacement amount correction calculation section does not need to coincide with the delimitation position of the pitch error correction correction section. Therefore, the thermal displacement amount correction method can lengthen the calculation cycle for calculating the thermal displacement amount by setting the section length of the calculation section to be longer, and can reduce the processing load on the thermal displacement amount correction apparatus. In addition, when the calculation section including the movable side end portion is longer than the other calculation sections, there is a higher possibility that an error occurs when the temperature distribution is calculated compared to the other calculation sections. The movable side end is away from the servo motor which is a heat source. Therefore, there is no problem because the error in the temperature distribution of the calculation section including the movable side end portion has less influence than the other calculation sections.

The thermal displacement correction method can perform highly accurate thermal displacement correction by setting the length of the calculation section so as not to become unnecessarily long. In the thermal displacement correction method, by setting the section length of the calculation section to an appropriate size, it is possible to achieve the target machining accuracy while suppressing the calculation processing load in the thermal displacement correction device. .

The thermal displacement correction method for a machine tool according to claim 2 divides a nut movement range, which is a range in which the nut can move, of a total length of the shaft into a plurality of correction sections shorter than the calculation section. A pitch error correction amount for correcting a pitch error for each correction section is corrected using the thermal displacement amount.

According to the thermal displacement correction method of claim 2, the calculation cycle for calculating the thermal displacement can be lengthened, and the calculation processing load in the thermal displacement correction device can be reduced.

A method for correcting a thermal displacement amount of a machine tool according to claim 3 includes: a feed drive ball screw mechanism including a shaft and a nut; a servo motor that rotationally drives the shaft into which the nut of the ball screw mechanism is screwed; and the servo motor. A control unit that controls based on the control data, and divides a nut movement range, which is a range in which the nut can move, of a total length of the shaft into a plurality of correction sections, and a pitch error for each of the plurality of correction sections In the method of correcting a thermal displacement amount of a machine tool to be corrected, a fixed side end connected to the servo motor on the shaft and a movable side end opposite to the fixed side end are provided in advance, and the total length of the shaft is increased. , Including a plurality of calculation sections divided into a fixed length calculation section longer than the correction section from the fixed side end section and the movable side end section, and a calculation greater than the fixed length A first step for calculating the heat generation amount for each calculation section at predetermined time intervals based on the rotation speed of the servo motor and control data for each of the calculation sections; Based on the total calorific value accumulated for a predetermined period of time and the unsteady heat conduction equation, a second step of calculating a temperature distribution for each calculation interval for each predetermined period, and based on the temperature distribution, Based on the third step of calculating the thermal displacement amount for each calculation interval for each predetermined period, and the correction amount for correcting the pitch error correction amount for each correction interval based on the thermal displacement amount for each calculation interval, And a fourth step for calculating every predetermined period.

According to the thermal displacement correction method of claim 3, the same effect as that of claim 1 is obtained. The thermal displacement correction method can lengthen the calculation cycle for calculating the thermal displacement, and can reduce the calculation processing load in the numerical controller. In the thermal displacement correction method, by setting the section length of the calculation section to an appropriate size, it becomes possible to achieve the target machining accuracy while suppressing the calculation processing load in the thermal displacement correction device. .

A thermal displacement correction device for a machine tool according to claim 4 comprises: a feed driving ball screw mechanism including a shaft and a nut; a servo motor that rotationally drives the shaft into which the nut of the ball screw mechanism is screwed; and the servo motor. A control unit that controls based on the control data, and divides a nut movement range, which is a range in which the nut can move, of a total length of the shaft into a plurality of correction sections, and a pitch error for each of the plurality of correction sections In the thermal displacement correction device for a machine tool to be corrected, the shaft has a fixed side end connected to the servo motor and a movable side end opposite to the fixed side end, and the rotation of the servo motor A speed detection device for detecting speed, and a plurality of calculation sections and a plurality of calculation sections obtained by dividing the entire length of the shaft into calculation sections having a fixed length longer than the correction section from the fixed side end. A calculation section that includes the movable side end and is equal to or longer than the predetermined length is set, and for each calculation section, a heat generation amount for each calculation section is determined based on a rotation speed of the servo motor and control data. Based on a calorific value computation unit that computes every time, a total calorific value obtained by accumulating the calorific value for each computation interval for a predetermined period, and an unsteady heat conduction equation, a temperature distribution for each computation interval is calculated for the predetermined period. A temperature distribution calculation unit that calculates each time, a thermal displacement amount calculation unit that calculates a thermal displacement amount for each of the calculation intervals for each predetermined period based on the temperature distribution, and a thermal displacement amount for each of the calculation intervals. A correction amount calculation unit that calculates a correction amount for correcting the pitch error correction amount for each correction section for each predetermined period.

According to the thermal displacement correction device of claim 4, the same effect as that of claim 1 is obtained. Since the thermal displacement correction device includes the speed detection device, the calorific value calculation device, the temperature distribution calculation device, the thermal displacement amount calculation device, and the correction amount calculation device, the same effect as in the third aspect is obtained.

1 is an overall perspective view of a machine tool. The front view centering on the spindle head and tool changer of a machine tool. The block diagram of an X-axis ball screw mechanism. The block diagram of the control system of a machine tool. Explanatory drawing of the several calculation area which divided | segmented the full length of the ball screw shaft. Explanatory drawing of memory | storage data, such as the total emitted-heat amount of several calculation area. Explanatory drawing of the distribution calorific value and temperature distributed to the some calculation area. Explanatory drawing of the correction area for pitch error correction amount. Explanatory drawing which shows the thermal displacement amount in each section division position from a fixed bearing. The flowchart of the thermal displacement amount correction control program. The flowchart of a correction amount calculation processing program. FIG. 5 is a diagram corresponding to FIG. FIG. 5 is a view corresponding to FIG. 5 of another prior art.

Hereinafter, modes for carrying out the present invention will be described.

The configuration of the machine tool M will be described with reference to FIGS. The lower right of FIG. 1 is the front of the machine tool M. In the machine tool M, the workpiece (not shown) and the tool 6 move relative to each other in the XYZ rectangular coordinate system independently, so that a desired machining (for example, “milling”, “drilling”, Etc.) can be applied. The X-axis direction, Y-axis direction, and Z-axis direction of the machine tool M (machine main body 2) are the left-right direction, front-rear direction, and vertical direction of the machine tool M (machine main body 2), respectively.
As shown in FIG. 1, the machine tool M includes a base 1, a machine body 2, and a cover (not shown) as main components. The base 1 is a substantially rectangular parallelepiped casting that is long in the Y-axis direction. The machine body 2 is provided on the upper part of the base 1. The machine body 2 cuts the workpiece. The cover is fixed to the upper part of the base 1. The cover has a box shape covering the machine body 2 and the upper part of the base 1.

The machine body 2 will be described. The machine body 2 includes a column 4, a spindle head 5, a spindle 5A, a tool changer (ATC) 7, and a table 8 as main components. The column 4 has a substantially prismatic shape and is fixed to a column seat portion 3 provided at the rear portion of the base 1. The spindle head 5 can be moved up and down along the column 4. The spindle head 5 rotatably supports the spindle 5A. The tool changer 7 is provided on the right side of the spindle head 5. The tool changer 7 exchanges the tool holder on which the tool 6 at the tip of the spindle 5A is mounted and the tool holder accommodated in the tool magazine 14. The table 8 is provided on the upper part of the base 1. The table 8 fixes the work so as to be detachable. The control box 9 is box-shaped. The control box 9 is provided on the back side of the column 4. The numerical control device 50 (see FIG. 4) is provided inside the control box 9. The numerical controller 50 controls the operation of the machine tool M. The numerical control device 50 has a function as a thermal displacement correction device.

The moving mechanism of the table 8 will be described with reference to FIG. 1 and FIG. An X-axis motor 71 that is a servomotor drives the table 8 to move in the X-axis direction. A Y-axis motor 72, which is a servo motor, drives the table 8 to move in the Y-axis direction. The X-axis motor 71 is provided on the support base 10. The Y-axis motor 72 is provided on the base 1. The support base 10 is provided below the table 8. The support base 10 includes a pair of X-axis feed guides (not shown) extending along the X-axis direction on the upper surface thereof. A pair of X-axis feed guides movably support the table 8 thereon.

As shown in FIG. 3, the nut portion 8 a is arranged on the lower surface of the table 8. The nut portion 8a is screwed with the X-axis ball screw shaft 81 to constitute an X-axis ball screw mechanism. The X-axis ball screw shaft 81 is connected to the X-axis motor 71 via the coupling 17. The fixed bearing 18 is fixed to the support base 10. The fixed bearing 18 supports a fixed-side end portion 81e of the X-axis ball screw shaft 81 on the X-axis motor 71 side (fixed side). The movable bearing 19 supports the movable side end 81f. The movable end 81f is on the opposite side (movable side) of the fixed end 81e. The movable bearing 19 is movable along the axial direction of the X-axis ball screw shaft 81.

A pair of Y-axis feed guides (not shown) are provided on the upper side of the base 1. The pair of Y-axis feed guides extends along the Y-axis direction of the base 1. The Y-axis feed guide supports the support 10 so as to be movable. The table 8 moves in the X-axis direction along the X-axis feed guide when the X-axis motor 71 is driven. The support base 10 is moved in the Y-axis direction along the Y-axis feed guide when the Y-axis motor 72 is driven. The Y-axis moving mechanism is a ball screw mechanism, similar to the X-axis moving mechanism.

Covers

11 and 12 cover the X-axis feed guide on the left and right sides of the table 8. The

covers

11 and 12 can be expanded and contracted. The cover 13 and the Y-axis rear cover (not shown) cover the Y-axis feed guide on both the front and rear sides of the support base 10, respectively. The

covers

11, 12, 13 and the Y-axis rear cover always cover the X-axis feed guide and the Y-axis feed guide regardless of whether the table 8 moves in either the X-axis direction or the Y-axis direction. The

covers

11, 12, 13 and the Y-axis rear cover prevent chips and coolant liquid scattered from the machining area from falling on the rails of the respective feed guides.

The lifting mechanism of the spindle head 5 will be described with reference to FIG. 1 and FIG. The column 4 supports a Z-axis ball screw shaft (not shown) extending in the vertical direction. A nut portion (not shown) is screwed with the Z-axis ball screw shaft. The nut portion supports the spindle head 5. A Z-axis motor 73 (see FIG. 4) rotates the Z-axis ball screw shaft in forward and reverse directions. The spindle head 5 is driven up and down in the Z-axis direction by a Z-axis motor 73 (see FIGS. 2 and 4) that rotates the Z-axis ball screw shaft in the forward and reverse directions. The axis control unit 63a (see FIG. 4) drives the Z-axis motor 73 based on a control signal from the CPU 51 (see FIG. 4) of the numerical controller 50. The spindle head 5 is driven up and down by driving a Z-axis motor 73.

1 and 2, the tool changer 7 includes a tool magazine 14 and a tool change arm 15. The tool magazine 14 stores a plurality of tool holders (not shown) that support the tool 6. The tool exchange arm 15 grasps a tool holder attached to the main shaft 5A and another tool holder, and conveys and exchanges them. The tool magazine 14 includes a plurality of tool pots (not shown) and a transport mechanism (not shown) inside. The tool pot supports the tool holder. The transport mechanism transports the tool pot in the tool magazine 14.

The electrical configuration of the numerical control device 50 will be described with reference to FIG. The numerical controller 50 as a control unit of the machine tool M includes a microcomputer. The numerical controller 50 includes an input / output interface 54, a CPU 51, a ROM 52, a flash memory 53, axis controllers 61a to 64a and 75a, servo amplifiers 61 to 64, differentiators 71b to 74b, and the like. The axis controllers 61a to 64a are connected to the servo amplifiers 61 to 64, respectively. The servo amplifiers 61 to 64 are connected to an X-axis motor 71, a Y-axis motor 72, a Z-axis motor 73, and a main shaft motor 74, respectively. The shaft control unit 75 a is connected to the magazine motor 75.

The X-axis motor 71 and the Y-axis motor 72 are motors for moving the table 8 in the X-axis direction and the Y-axis direction, respectively. The Z-axis motor 73 is a motor for driving the spindle head 5 up and down in the Z-axis direction. The magazine motor 75 is a motor for rotating the tool magazine 14. The main shaft motor 74 is a motor for rotating the main shaft 5A. The X-axis motor 71, Y-axis motor 72, Z-axis motor 73, and main shaft motor 74 are provided with encoders 71a to 74a, respectively.

The axis controllers 61a to 64a receive the movement command amount from the CPU 51 and output a current command (motor torque command value) to the servo amplifiers 61 to 64. The servo amplifiers 61 to 64 receive a current command and output a drive current to the motors 71 to 74. The axis controllers 61a to 64a receive position feedback signals from the encoders 71a to 74a and perform position feedback control. Differentiators 71b to 74b differentiate the position feedback signals output from the encoders 71a to 74a and convert them into speed feedback signals. Differentiators 71b to 74b output speed feedback signals to the axis controllers 61a to 64a.

The axis controllers 61a to 64a receive the speed feedback signals from the differentiators 71b to 74b and control the speed feedback. Current detectors 61b to 64b detect drive currents output from servo amplifiers 61 to 64 to motors 71 to 74, respectively. The current detectors 61b to 64b feed back the detected drive current to the axis controllers 61a to 64a. The shaft controllers 61a to 64a perform current (torque) control based on the drive current fed back by the current detectors 61b to 64b. The shaft control unit 75 a receives the movement command amount from the CPU 51 and drives the magazine motor 75.

The ROM 52 is a main control program for executing a machining program for the machine tool M, a control program for thermal displacement correction control (see FIG. 10), and a control program for correction amount calculation processing for calculating the correction amount of the pitch error correction amount ( (See FIG. 11). Stores the parameters related to the flash memory 53 is a mechanical structure, and parameters related to the physical properties, heat distribution coefficient (ratio) eta _N, and eta _F, and eta _B, the pitch error correction amount table or the like. The parameter relating to the mechanical structure is, for example, the length and diameter of the ball screw shaft 81. Parameters relating to physical properties are, for example, density and specific heat. The flash memory 53 also appropriately stores a plurality of machining programs for machining various workpieces. The flash memory 53 stores the calculation result of the CPU 51.

The pitch error correction amount table is a table for correcting pitch errors of the ball screw mechanisms of the X axis, the Y axis, and the Z axis. The pitch error of the ball screw mechanism is caused by manufacturing tolerances. In this embodiment, the pitch error between the rotation amount of the ball screw shaft 81 and the movement amount of the nut portion 8a is corrected based on a preset pitch error correction amount table. When the thermal displacement correction method of the present embodiment corrects the thermal displacement, the pitch error correction amount is corrected using the calculated thermal displacement. The present embodiment is an example in which the thermal displacement of the X-axis ball screw shaft 81 is corrected. However, the same applies to the Y-axis ball screw mechanism and the Z-axis ball screw mechanism.

As shown in FIG. 8, the nut portion 8 a is movable in the nut portion moving range 81 b within the entire length of the X-axis ball screw shaft 81. Pitch error correction is performed for each correction section. The correction sections set in the nut portion movement range 81b are a plurality of sections that are shorter than a calculation section described later. Specifically, the plurality of correction sections are 15 sections with a set length of 20 mm. The pitch error correction amount for correcting the pitch error is a value obtained by the following procedure in the adjustment stage after the machine tool M is manufactured. The nut portion 8a moves from the position X0 to the position X300 for each correction section at intervals of 20 mm in the X-axis direction according to the command value. In this embodiment, an error with respect to the movement command value, that is, an error which is (target value−actual movement amount) is accurately measured. In this embodiment, a table of pitch error correction amounts is created based on the measurement results. In this embodiment, the created table is stored in advance in the flash memory 53 and shipped. In the present embodiment, a table of pitch error correction amounts is similarly created for the Y-axis and Z-axis directions.

熱 Explain how to calculate thermal displacement. The amount of thermal displacement is generated along with the numerical control during the operation of the machine tool M. As shown in FIG. 5, the present embodiment calculates the amount of heat generated in three regions of the front shaft portion 81a of the ball screw shaft 81, the nut portion movement range 81b, and the rear shaft portion 81c of the ball screw shaft 81. In the present embodiment, the heat generation amount of six calculation sections obtained by dividing the ball screw shaft 81 over the entire length in the length direction is calculated based on the heat generation amount of the three regions.

[Calculation of total calorific value]
The lengths of the front shaft portion 81a and the rear shaft portion 81c of the ball screw shaft 81 shown in FIG. 5 are each 100 mm. The length of the nut portion moving range 81b is 300 mm. The overall length of the ball screw shaft 81 is 500 mm. The length of the calculation section is 80 mm. Therefore, when the end of the nut portion moving range 81b on the movable bearing 19 side is divided at equal intervals from the fixed side end 81e by the length of the calculation section, it coincides with the calculation section 5. The rear shaft portion 81c is divided into two sections of 80 mm and 20 mm when divided by calculation sections. In the present embodiment, the calculation section including the movable side end 81f is set to be equal to or greater than the calculation section of 80 mm. Therefore, the length of the calculation section 6 is 100 mm.

In the present embodiment, at every predetermined time (for example, 50 ms), based on the X-axis feed data (control data) of the machining program, it is determined in which calculation section the nut portion 8a exists. In this embodiment, the calorific value is calculated according to the following equation based on the feed speed of the table 8. The feed speed of the table 8 is determined based on the actual rotational speed of the X-axis motor 71. The actual rotational speed of the X-axis motor 71 is determined based on the detection signal of the encoder 71a. The data area of the flash memory 53 stores the calculated heat generation amount. The calorific value is calculated according to the following equation.

Q = K ₁ × F ^T
Q is a calorific value. F is the feed speed of the table 8. K ₁ and T are respectively predetermined constants.

In the present embodiment, the amount of heat generated by the movement of the nut portion 8a in each calculation section is calculated 128 times every 50 ms for a predetermined period (for example, 6400 ms) using the above formula. In the present embodiment, the calorific values calculated during a predetermined period are totaled for each computation interval, and calorific values Q ₁ to Q ₆ for each computation interval are calculated. As shown in FIG. 6, in this embodiment, the heat generation amounts Q ₁ to Q ₆ are stored in the flash memory 53 in association with the calculation sections 1 to 6. In this embodiment, the total calorific value Q _T is calculated and stored in the flash memory 53. The total heat generation amount Q _T is a heat generation amount obtained by adding the heat generation amounts Q ₁ to Q ₆ .

[Distribution of total calorific value]
The distribution method of the total calorific value Q _T shown below is based on the same method as that of Japanese Patent Publication No. 1992-240045. That is, it is considered that the nut portion movement range 81b, the front shaft portion 81a, and the rear shaft portion 81c of the ball screw shaft 81 do not conduct heat to other portions, and are thermally independent. The ratio of each heat generating portion to the total heat generation amount Q _T is substantially constant regardless of the change in the feed rate.

The CPU 51 calculates the distributed heat generation amount of each heat generating part according to the following equation.
Q _F = η _F × Q _T
Q _N = η _N × Q _T
Q _B = η _B × Q _T
The calorific value Q _F is the calorific value of the front shaft portion 81 a due to the rotation of the fixed bearing 18. The heat generation amount Q _N is the heat generation amount of the nut portion moving range 81b. The heat generation amount Q _B is the heat generation amount of the rear shaft portion 81 c due to the rotation of the movable bearing 19. Ratio eta _F is the ratio of the calorific value Q _F with respect to the total heat generation amount Q _T. Ratio eta _N is the ratio of the calorific value Q _N to the total heat generation amount Q _T. Ratio eta _B is the ratio of the calorific value Q _B to the total heat generation amount Q _T. The ratios η _F , η _N , and η _B are constant as shown in the method. Therefore, the ratios η _F , η _N, and η _B are values calculated in advance by measuring Q _F , Q _N , and Q _B using an actual machine.

[Nut movement range calorific value distribution]
In the present embodiment, the heat generation amount Q _N of the nut portion movement range 81b is distributed to six calculation sections. In the present embodiment, the distribution ratios X ₁ to X ₆ are calculated according to the following equation based on the calorific values Q ₁ to Q ₆ and the total calorific value Q _T. The distribution ratios X ₁ to X ₆ are ratios for distributing the calorific value Q _N to the calorific values of the six calculation sections. The heat generation amounts Q ₁ to Q ₆ and the total heat generation amount Q _T are respectively stored in the data area.

X ₁ = calorific value Q ₁ / Q _{T of} calculation section 1
:
X ₆ = calorific value Q ₆ / Q _{T in} calculation section 6
In this embodiment, after calculating the distribution ratios X ₁ to X ₆ of the six calculation sections, the distribution heat generation amount of the six calculation sections is calculated according to the following equation using the distribution ratio and the heat generation amount Q _N of the nut movement range 81b. Q _N1 to Q _N6 are calculated.

Q _N1 = X ₁ × Q _N
:
Q _N6 = X ₆ × Q _N
Based on FIG. 5, the temperature of each part and the calorific value of each calculation section can be expressed as shown in FIG.

[Calculation of temperature distribution]
In the present embodiment, after calculating the heat generation amounts of the six calculation sections, the temperature distribution is calculated based on the heat generation amounts of the respective calculation sections. The temperature distribution can be calculated by solving the following unsteady heat conduction equation. However, the initial condition is {θ} _{t = 0} = {θ ₀ }, and θ ₀ is the initial temperature.

[C] d {θ} / dt + [H] {θ} + {Q} = 0
[C] is a heat capacity matrix. [H] is a heat conduction matrix. {Θ} is a temperature distribution. {Q} is the calorific value. t is time.

[Calculation of thermal displacement]
As shown in FIG. 7, the present embodiment calculates temperatures θ ₁ to θ _{6 in six} calculation sections of the ball screw shaft 81. In this embodiment, based on the calculated temperatures θ ₁ to θ ₆ , the thermal displacement amounts at the six calculation section break positions of the ball screw shaft 81 (positions corresponding to θ ₁ to θ ₆ in FIG. 7) are calculated. The amount of thermal displacement at the six calculation section break positions is calculated according to the following equation.

ΔL = ∫ ^L ₀ β × θ (L) dL (1)
ΔL is the amount of thermal displacement. β is the coefficient of linear expansion of the ball screw shaft material. The integration symbol indicates integration over a range of 0 to L. L shows the length to the calculation section delimitation position regarding six calculation sections. Specifically, the above equation shows the integration over a range of 0 to 80, 0 to 160, 0 to 240,.

[Calculation of correction amount]
In this embodiment, after calculating the thermal displacement amounts at the six calculation section break positions of the ball screw shaft 81, the correction amounts for correcting the pitch error correction amounts at the 16 correction section break positions are calculated. The nut portion movement range 81b of the present embodiment is a section of X0 to X300 (300 mm range). The length of each correction section is 20 mm. Therefore, in this embodiment, correction amounts at 16 positions of X0, X20, X40,..., X300 are calculated. The correction amounts at the 16 correction section break positions can be calculated in accordance with FIG. 9 and the [correction amount calculation formula] described later.

With reference to FIG. 9, the case where the correction amount for correcting the pitch error correction amount is calculated will be described. The vertical axis of the upper graph in FIG. 9 indicates the amount of thermal displacement based on the position of the fixed bearing 18. The horizontal axis of the graph on the upper side of the drawing indicates the position of each part of the ball screw shaft 81 with respect to the fixed bearing 18. The horizontal axis on the lower side of the drawing indicates the delimiting positions (X0, X20..., X300) of the 16 correction sections.
D _F1 is a thermal displacement amount in the calculation section 1.
D _F2 is the total amount of thermal displacement in the calculation section 1 and the calculation section 2.
:
D _F6 is the total amount of thermal displacement in the calculation interval 1 to the calculation interval 6.

As shown in FIG. 9, the present embodiment calculates the correction amount at the delimiter positions (X0, X20,..., X300) of the 16 correction sections according to the following equation.
[Correction amount calculation formula]
X0 correction amount = (thermal displacement amount in computation section 1) + (thermal displacement amount in computation section 2) × {(length between the left break position in computation section 2 and X0) / (length of computation section 2) }
Correction amount of X20 = (thermal displacement amount in calculation section 1) + (thermal displacement amount in calculation section 2) × {(length between left separation position of calculation section 2 and X20) / (length of calculation section 2) }-(X0 correction amount)
Correction amount of X40 = (thermal displacement amount of computation section 1) + (thermal displacement amount of computation section 2) × {(length between left delimiter position of computation section 2 and X40) / (length of computation section 2) }-(X20 correction amount)
Correction amount of X60 = (thermal displacement amount of calculation section 1) + (thermal displacement amount of calculation section 2) × {(length between left delimiter position of calculation section 2 and X60) / (length of calculation section 2) }-(X40 correction amount)
Correction amount of X80 = (thermal displacement amount of computation section 1) + (thermal displacement amount of computation section 2) + (thermal displacement amount of computation section 3) × {(length between left separation position of computation section 3 and X80 ) / (Length of calculation section 3)} − (correction amount of X60)
:
X300 correction amount = (thermal displacement amount in computation section 1) + (thermal displacement amount in computation section 2) + (thermal displacement amount in computation section 3) + (thermal displacement amount in computation section 4) + (in the computation section 5) Thermal displacement amount) + (Thermal displacement amount in the calculation section 6) × {(Length between the left separation position of the calculation section 6 and X300) / (Length of the calculation section 6)} − (Correction amount of X280)

Referring to FIG. 10, the procedure of the thermal displacement correction control executed by the numerical controller 50 will be described. In the figure, Si (i = 1, 2,...) Indicates each step. The thermal displacement amount correction control will be briefly described because there are many portions that overlap with the contents described above. Machining according to numerical control for an actual workpiece is executed in parallel with thermal displacement correction control.

When the CPU 51 starts the thermal displacement correction control, the CPU 51 executes initial setting in step S1. In step S1, the CPU 51 sets a matrix necessary for calculation according to the finite element method based on setting data such as parameters. The CPU 51 sets an initial temperature in step S1. The CPU 51 executes processing such as clearing the related memory area of the flash memory 53 in step S1. As shown in FIG. 5, the CPU 51 divides the extended range of the ball screw shaft 81 into six calculation sections 1 to 6 in step S2.

The CPU 51 sets 0 to the counter I in step S3. In step S4, the CPU 51 reads the X-axis feed data and the detection signal of the encoder 71a. In step S5, the CPU 51 calculates the amount of heat generated every 50 ms in the calculation sections 1 to 6, and stores the calculated amount of heat generated in the flash memory 53. In step S6, the CPU 51 adds “1” to the counter I. In step S7, the CPU 51 determines whether or not the counter value of the counter I is larger than “127”. When the determination in step S7 is No, the CPU 51 returns to step S4 and repeats the processing from step S4 to step S6. When the determination at Step S7 is Yes, the CPU 51 proceeds to the process at Step S8. CPU51 calculates a total heat generation amount Q _T of the calorific value Q ₁ to Q _6, the calorific value Q ₁ to Q ₆ between 6,400ms arithmetic section 1 every 6 in step S8, the result of computation is stored into the flash memory 53 To do.

In step S < _b > 9, the CPU 51 calculates the calorific values Q _F , Q _N , and Q _B of each unit described above and stores the calculation results in the flash memory 53. The CPU 51 calculates the calorific values Q _N1 to Q _N6 distributed to the calculation sections 1 to 6 and stores the calculation results in the flash memory 53. The CPU 51 calculates the heat generation amount for the calculation sections 1 to 6 shown in FIG. 7 and stores the calculation result in the flash memory 53. In step S 10, the CPU 51 calculates the temperatures θ ₁ to θ ₆ in the calculation sections 1 to 6 based on the heat generation amounts of the respective parts shown in FIG. 7 and stores the calculation results in the flash memory 53.

In step S11, the CPU 51 calculates the amount of thermal displacement at the calculation section break positions for the six calculation sections based on the equation (1), and stores the calculation results in the flash memory 53. In step S12, the CPU 51 calculates the correction amounts at the 16 correction section break positions as described above based on the correction amount calculation formula described above. In step S13, the CPU 51 executes a correction process for the pitch error correction amount set in advance for the 16 correction section break positions using the correction amount calculated in step S12. The CPU 51 executes a feed amount correction process using the corrected pitch error correction amount. In step S14, the CPU 51 determines whether or not to end the thermal displacement amount correction process. When the determination result is No, the CPU 51 returns to step S3 and repeatedly executes step S3 and subsequent steps. The thermal displacement correction control ends when the determination result in step S14 is Yes.

The correction amount calculation process will be described with reference to FIG. The correction amount calculation process is a process of calculating a correction amount for correcting the pitch error correction amount in step S12. In the figure, Si (i = 20, 21...) Indicates each step. When starting the correction amount calculation process, the CPU 51 sets the counter n to 0 (S20). The CPU 51 calculates the correction amount ΔM _n of the position Xn according to the following equation (S21).

First, the CPU 51 calculates the correction amount ΔM ₀ of the position X0 according to ΔM _n = D _F + ΔD _n × {(Xn−X _F ) / L _n } −ΔM _n−20, n = 0. The above expression is a simple expression of the above-described correction amount calculation expression. _DF is the total amount of thermal displacement generated in the calculation section on the fixed side with respect to the position Xn. ΔD _n is the amount of thermal displacement generated in the calculation interval including the position Xn. X _F is the left delimiter position of the calculation section including the position Xn. L _n is the length of the calculation interval including the position Xn. ΔM ₋₂₀ used when calculating ΔM ₀ is set to 0.

The CPU 51 adds 20 to n in step S22. In step S23, the CPU 51 determines whether n is 320 or not. If n is not 320 (S23: No), the CPU 51 determines that the calculation for the correction amount up to the position X300 has not ended, returns to step S21, and calculates the correction amount ΔM _n for the position Xn. CPU51 is until calculates a correction amount .DELTA.M ₃₀₀ position X300 to run repeatedly to S23 S21. When the CPU 51 calculates the correction amount ΔM ₃₀₀ (S21), n = 320 in step S22. The determination in step S23 is Yes. CPU51 complete | finishes the process of FIG. 11, and transfers to step S14 of FIG.

Encoder 71a corresponds to “speed detection device”. The CPU 51 that executes Steps S3 to S7 corresponds to a “heat generation amount calculation unit”. The CPU 51 that executes Steps S8 to S10 corresponds to a “temperature distribution calculation unit”. The CPU 51 that executes step S11 corresponds to a “thermal displacement amount calculation unit”. The CPU 51 executing step S12 corresponds to a “correction amount calculation unit”.

The operation and effect of the thermal displacement correction method for the machine tool M and the thermal displacement correction device (numerical control device 50) described above will be described. The calculation section is a section obtained by dividing the entire length of the ball screw shaft 81 of the ball screw mechanism by a fixed length longer than the correction section from the fixed side end portion 81e. The length of the calculation section including the movable side end portion 81f is not less than a certain length. CPU51 calculates the emitted-heat amount and temperature distribution of several calculation area. The CPU 51 calculates the thermal displacement amount at the break position of the plurality of calculation sections based on the calculation result. The CPU 51 calculates a correction amount for correcting the pitch error correction amount. Therefore, the thermal displacement correction method and the thermal displacement correction device (numerical control device 50) have the following effects.

The numerical controller 50 does not require that the calculation section break position and the correction section break position match. Therefore, the numerical controller 50 can lengthen the calculation cycle for calculating the thermal displacement amount by setting the length of the calculation section to be long. The numerical control device 50 can reduce the processing load on the numerical control device 50.

The numerical control device 50 can perform highly accurate thermal displacement correction by setting the section length of the computation section so as not to become unnecessarily long. The numerical control device 50 can suppress the calculation processing load in the numerical control device 50 and achieve the target machining accuracy by setting the section length of the calculation section to an appropriate size.

A modified example in which the above embodiment is partially modified will be described.
1) In the above embodiment, the case where the thermal displacement correction device and the thermal displacement correction method of the present invention are applied to the thermal displacement correction of the X-axis ball screw mechanism has been described. The present invention can also be applied to the correction of thermal displacement of the Y-axis ball screw mechanism and the Z-axis ball screw mechanism.
2) In the above embodiment, the numerical controller 50 divides the front shaft portion 81a of the ball screw shaft 81 and the nut portion moving range 81b into five calculation sections at intervals of 80 mm (four times the set length of the correction section). The calculation interval may be longer than the correction interval. For example, the calculation section may have a length other than four times, such as 1.5 times and 3 times the set length of the correction section.

3) In the above embodiment, the machine tool M includes the X-axis motor 71 on the front shaft portion 81 a side of the ball screw shaft 81. When the machine tool M is provided with the X-axis motor 71 on the rear shaft portion 81c side of the ball screw shaft 81, the numerical control device 50 performs thermal displacement of the six calculation sections of the ball screw shaft 81 in the same manner as in the above embodiment. The amount can be calculated.
4) In the above embodiment, the calculation cycle for calculating the heat generation amount is 50 ms as an example, but the calculation cycle is not limited to 50 ms. The predetermined period of 6400 ms is an example. The predetermined period is not limited to 6400 ms. For example, the predetermined period may be in seconds instead of ms.

Claims

A machine tool comprising: a feed drive ball screw mechanism including a shaft and a nut; a servo motor that rotationally drives the shaft into which the nut of the ball screw mechanism is screwed; and a control unit that controls the servo motor based on control data. In the thermal displacement correction method of
A fixed side end connected to the shaft with the servo motor, and a movable side end opposite to the fixed side end are provided in advance,
When calculating the amount of thermal displacement of the shaft during operation of the machine tool, the plurality of calculation sections obtained by dividing the total length of the shaft by a fixed length from the fixed side end and the movable side end, and A method of correcting a thermal displacement amount of a machine tool, wherein the heat displacement amount and temperature distribution of each calculation section are calculated by setting the calculation sections of a certain length or more.
A nut movement range that is a range in which the nut can move in the entire length of the shaft is divided into a plurality of correction sections shorter than the calculation section, and a pitch error correction amount for correcting a pitch error for each of the plurality of correction sections is obtained. The method for correcting a thermal displacement amount of a machine tool according to claim 1, wherein the thermal displacement amount is corrected using the thermal displacement amount.
A feed drive ball screw mechanism including a shaft and a nut; a servo motor that rotationally drives the shaft into which the nut of the ball screw mechanism is screwed; and a control unit that controls the servo motor based on control data; In the thermal displacement correction method for a machine tool, the nut movement range, which is the range in which the nut can move, of the total length of the shaft is divided into a plurality of correction sections, and the pitch error correction is performed for each of the plurality of correction sections.
A fixed side end connected to the shaft with the servo motor, and a movable side end opposite to the fixed side end are provided in advance,
The total length of the shaft is set to a calculation section that includes a plurality of calculation sections and a movable end section that are divided into calculation sections having a fixed length longer than the correction section from the fixed side end and the fixed length or more. And
For each of the calculation sections, a first step of calculating a calorific value for each calculation section at predetermined intervals based on the rotation speed of the servo motor and control data;
A second step of calculating a temperature distribution for each calculation interval for each predetermined period based on a total heat generation amount obtained by accumulating the heat generation amount for each calculation interval for a predetermined period and an unsteady heat conduction equation;
A third step of calculating a thermal displacement amount for each of the calculation sections for each of the predetermined periods based on the temperature distribution;
A fourth step of calculating a correction amount for correcting a pitch error correction amount for each correction section for each predetermined period based on the thermal displacement amount for each calculation section;
A method for correcting the amount of thermal displacement of a machine tool equipped with
A feed drive ball screw mechanism including a shaft and a nut; a servo motor that rotationally drives the shaft into which the nut of the ball screw mechanism is screwed; and a control unit that controls the servo motor based on control data; In a thermal displacement correction device for a machine tool that divides a nut movement range, which is a range in which the nut can move, of a total length of the shaft into a plurality of correction sections, and corrects a pitch error for each of the plurality of correction sections,
The shaft has a fixed side end connected to the servo motor, and a movable side end opposite to the fixed side end,
A speed detection device for detecting the rotational speed of the servo motor;
The total length of the shaft is set to a calculation section that includes a plurality of calculation sections and a movable end section that are divided into calculation sections having a fixed length longer than the correction section from the fixed side end and the fixed length or more. And
For each calculation section, a heat generation amount calculation unit that calculates a heat generation amount for each calculation section every predetermined time based on the rotation speed of the servomotor and control data;
Based on the total calorific value obtained by accumulating the calorific value for each calculation section for a predetermined period and an unsteady heat conduction equation, a temperature distribution calculation unit that calculates the temperature distribution for each calculation period for each predetermined period;
Based on the temperature distribution, a thermal displacement amount calculation unit that calculates a thermal displacement amount for each of the calculation sections for each predetermined period;
A correction amount calculation unit for calculating a correction amount for correcting a pitch error correction amount for each correction section for each predetermined period based on the thermal displacement amount for each calculation section;
Thermal displacement correction device for machine tools equipped with