DE102009013043A1 - Thermal displacement correction for tool mesh - Google Patents

Abstract

The present invention relates to a method, an apparatus, and a computer readable medium that stores a program for correcting a thermal displacement error in a ball screw mechanism occurring during drive of a machine tool (M). A first heat value calculating section (51) calculates a first calorific value generated in a screw shaft (81) from a nut (8a) based on a rotational speed. A second heat value calculating portion (51) calculates a second calorific value generated in the propeller shaft (81) by a servo motor (71) based on a temperature increase. A temperature distribution calculating section (51) calculates a temperature distribution of a plurality of sections obtained by dividing the screw shaft (81) in a longitudinal direction from the first and second calorific values. A thermal shift value calculating section (51) calculates a thermal shift value of each of the temperature distribution sections. The correction amount calculating section (51) calculates a correction amount of process data for calculating a feed amount of the nut (8a) on the basis of the thermal shift amount.

Description

The The present invention relates to a thermal displacement correction for a machine tool, in particular the relates Invention on a correction method of a thermal displacement for a machine tool, a correction device for a thermal shift and a computer readable Medium, which is a program for a correction of a thermal Shift saves. In particular, the present invention relates The invention relates to a method and a device for correcting a failure due to thermal displacement of a ball screw mechanism, which occurs during operation of the machine tool, and on a computer-readable medium having a program for correcting such stores an error.

One Ball screw mechanism is widely used as a position mechanism for a machine tool. A temperature of the ball screw mechanism may due to a frictional resistance between a propeller shaft and a nut, a frictional resistance between the propeller shaft and each storage section and a heat generation of a servomotor increase. The ball screw mechanism can one thermal displacement (extension) due to the above mentioned temperature increase un subject. Today's NC machine tools are generally defined by a semi-closed feedback or loop system controlled. In the NC machine tool, the can use the half-closed feedback system the thermal displacement of the propeller shaft directly as a position error Pop up. As a countermeasure is a biasing method proposed. The bias method becomes a bias voltage to the propeller shaft for absorbing thermal expansion created. Recently, a thick screw shaft in an NC machine tool be used, and a feed rate of the NC machine tool can be very high. In such a case can be more heat be generated. Therefore, if the preload method is adopted will be needed, a very big voltage, to put on. Consequently, there may be a problem that the construction the ball screw mechanism is deformed, and a thrust bearing can burn or seize due to the creation of an unreasonable Force.

In a correction method of a thermal displacement for a screw shaft, as shown in the JP 1988-256 336 A is proposed, an unreasonable bias voltage is not applied to the propeller shaft, and a special measuring device is not necessary. In this method, the amount of thermal displacement during the process is corrected. More specifically, in the first process, a calorific value of the propeller shaft is obtained by a product of armature current of the servomotor and a voltage. In the second process, the temperature distribution is obtained from the heat values in a model in which the screw shaft is divided into a plurality of sections. In the third process, the amount of thermal displacement of the screw shaft is currently predicted based on the temperature distribution. In the fourth process, the amount of thermal displacement is input to a NC device as a gear error compensation.

The JP 1992-240 045 A that implies that in the JP 1988-256 336 A The above-mentioned method has a problem that the calorific value includes the acceleration / deceleration energy of the servomotor itself. In the correction method of the thermal shift amount used in the JP 1992-240 045 A is disclosed, the calorific value of each section of the screw shaft is calculated from the rotational speed of the servomotor. According to this method, the correction value calculated based on the rotation speed of the servomotor that is not affected by the acceleration / braking energy can approximate actual extension of the screw shaft.

In the in the JP 1992-260 045 A In the disclosed method, the calorific value of the servomotor is calculated only from the rotational speed. In this method, however, it is not considered that the calorific value may vary depending on a load of the servomotor. Further, the conditions of calculating the correction amount at an initial state of the operation of the servomotor and after a lapse of a fixed time are not disclosed. Therefore, in this method, the amount of correction calculated in a transient state that is the initial operation stage of the engine and the actual extension of the propeller shaft (thermal shift amount) may not approximate each other.

The inventor of the present invention actually operated a servomotor and measured a temperature of one end of a screw shaft. The inventor produced a thermal distribution model used in the JP 1992-240 045 A and conducted an experiment to compare an actual temperature of the end portion of the screw shaft and a temperature using the thermal distribution model was calculated by. As in 12 is shown, a mechanism for measuring the actual temperature of the end portion of the screw shaft includes a servomotor 201 , a screw shaft 203 , A mother 204 and a table 205 , The servomotor 201 and the screw shaft 203 are interconnected by a clutch 202 connected. The mother 204 is with the propeller shaft 203 connected with a thread and can move forward and backward (horizontal direction in 12 ) in response to the rotation of the propeller shaft 203 move. The table 205 is at the mother 204 attached and can be integral with the mother 204 move forward and backward. A solid camp 206 and a movable bearing 207 are installed in a support base that rotatably rotates the screw shaft 203 wearing.

The Conditions of the experiment were as follows.

(Condition 1)

A medium current through the servomotor 101 during the movement of the table 205 flowed, and the average rotational speed were constant. A temperature measuring section 208 (Measuring position) was on a fixed position 209 set, which was the end portion of the propeller shaft. The table 205 was repeatedly moved back and forth at a constant speed until the temperature reading reached the fixed section 209 stabilized.

(Condition 2)

The table 205 was moved to a position sufficiently remote from the fixed bearing 206 moved to prevent the heat generation of the mother 204 the temperature measuring section 208 affected. The servomotor 201 and the solid bearing 205 influenced the temperature of the temperature measuring section 208 ,

Next, the inventor of the present invention produced a thermal distribution model. Because the average current flowing through the servomotor 201 flows, and the average rotational speed is assumed to be constant, a heat input from the servomotor 201 considered constant at the end portion of the propeller shaft. Under such conditions, a heat conduction equation of a non-steady state, which was described in US Pat JP 1992-240 045 A is solved, whereby the temperature was calculated at all times.

13 shows an experimental value (actual value) of the thermal displacement at the fixed position 209 (please refer 12 ), and a calculated value based on the thermal distribution model. The vertical axis of the diagram represents the temperature of the end section of the propeller shaft (the fixed position 209 ), and the horizontal axis of the graph represents an elapsed time. The solid line represents the experimental value, and the broken line represents the calculated value. The results shown in the graph may lead to the following conclusion. The experimental value and the calculated value approximate each other after the temperature increase in the end portion of the screw shaft is stabilized. The temperature of the calculated value increases faster than the temperature of the experimental value during the duration of the transient state given before the temperature increase stabilizes. Therefore, in the above method, an accurate prediction may not be made.

It It is therefore an object of the present invention to provide a correction method a thermal displacement for a machine tool, a thermal displacement correcting device, and a computer readable medium, which is a program for a thermal displacement correction stores a correction value allows for an actual extension amount a propeller shaft in a transient state of one Start of operation of the machine tool for stabilization to approximate an increase in temperature.

These Task is solved by a correction method of thermal displacement for a machine tool Claim 1.

The machine tool for the thermal displacement correction method includes a ball screw mechanism for a feed drive provided with a screw shaft and a nut. A feed amount control calculates a feed amount of the nut by the screw shaft based on process data. A servomotor rotatively drives the propeller shaft. A speed controller controls a rotational speed of the servomotor based on the process data. The correction method includes a first step of calculating a first heat value, which in the screw shaft is generated due to a movement of the nut, based on the rotational speed. The method includes a second step of detecting a temperature increasing in the engine, and calculating a second heat value transmitted from the servo motor to the screw shaft based on the temperature rise. The correction method includes a third step of calculating a temperature distribution in a plurality of sections obtained by dividing the screw shaft in a longitudinal direction from the first and second heat values. The correction method includes a fourth step of calculating a thermal displacement amount of each of the plurality of temperature distribution sections. The correction method includes a fifth step of calculating a correction amount of the process data based on the thermal shift amount.

According to the Correction method of thermal displacement for a Machine tool can control the temperature distribution in the majority of Sections of the ball screw shaft are calculated by not only the first calorific value is used in the ball screw shaft generated due to the movement of the mother, but also a second heat value due to the temperature rise of the servomotor, and thus a correction amount is obtained. Therefore, the correction amount an actual length amount of the ball screw shaft approximate even in a transient state that occurs before the temperature of the servomotor is stabilized. A heat input from the servomotor to the ball screw shaft may be due to the temperature increase be influenced in the servo motor. The temperature increase in the Servo motor itself can influence drive components such as be assigned to a load. In particular, the temperature of the Servomotor constantly changing during a period, to the calorific value of the servomotor and a heat release value compensate each other. In the Korrektionsverfahren the thermal shift may be the second calorific value based on the temperature increase are used in the servomotor in calculating the correction value, whereby the correction amount, the change in temperature the servo motor follows can be obtained. In terms of Heat input unlike that of the servomotor to the ball screw shaft, For example, the thermal shift amount can be calculated for each the plurality of sections, adding the first heat value used in the ball screw shaft due to the movement the mother is generated. Therefore, in the correction process the thermal displacement of the correction amount with high accuracy be obtained without a separate provision of a sensor.

The Task is also solved by a correction device a thermal displacement for a machine tool according to claim 3.

The Correction device for thermal displacement for a machine tool includes a ball screw mechanism for a feed drive, with a propeller shaft and a mother is provided. A feed amount control is calculated a feed amount of the nut by the screw shaft on the Basis of process data. A servomotor drives rotationally the screw shaft. A speed control controls one Rotational speed of the servomotor based on the process data. The Contains thermal displacement correction device a speed detecting device, a temperature detecting section, a calculating portion of a first heat value, a Calculation section of a second heat value, a calculation section a temperature distribution, a calculating portion of a temperature shift amount and a calculating portion of a correction amount. The speed detection device detects the rotational speed. The temperature detection section detects a temperature increase in the servomotor. The calculation section of the first calorific value calculates a first calorific value, which is generated in the propeller shaft due to movement of the nut is, on the basis of the rotational speed, that of the speed detecting device is detected. The calculation section of the second heat value calculates a second calorific value from the servomotor is transmitted to the propeller shaft, on the basis the temperature increase generated by the temperature detecting section is detected. The calculation section of the temperature distribution calculates a temperature distribution in a plurality of sections, by dividing the screw shaft in a longitudinal direction are obtained from the first calorific value obtained by the calculating section of the first calorific value, and the second calorific value, that of the second heat value calculation section is calculated. The calculation portion of the thermal shift amount calculates a thermal shift amount of each of the plurality portions of the temperature distribution obtained by the calculating section the temperature distribution is calculated. The calculation section of the correction amount calculates a correction amount of the process data on the basis of the thermal shift amount generated by the calculation portion of the thermal shift amount is calculated is.

The Correction device of thermal displacement for a machine tool has the temperature detection section, which detects the temperature increase in the servomotor. Next will the temperature distribution in the plurality of sections of the ball screw shaft calculated using the second heat value on the Basis of the temperature increase, and thus the Kor rektionsbetrag receive. Therefore, the correction amount may be an actual Length of the ball screw shaft even in a transient state approximate, which is present before the temperature increase in the Servo motor is stabilized. With regard to heat input unlike those of the servomotor to the ball screw shaft of the thermal shift amount will be calculated for each the majority of sections where the calorific value is used which is in the ball screw shaft due to the movement of the nut is generated. Therefore, the correction amount can be with high accuracy can be obtained without separately providing a sensor.

The Temperature increase in the servomotor can be detected on the Basis of at least the rotational speed of the servomotor and the drive current value. In such a case, the correction amount be achieved with high accuracy by using an existing sensor is used without a separately provided sensor used becomes.

These Task is also solved by a computer readable medium, this is a correction program for a thermal shift for a machine tool stores, according to claim 5.

The Machine tool of thermal displacement correction program The computer readable medium includes a ball screw mechanism for a feed drive, with a propeller shaft and a mother is provided. A feed amount control is calculated a feed amount of the nut by the screw shaft on the Basis of process data. A servomotor drives rotationally the screw shaft. A speed control controls one Rotational speed of the servomotor based on the process data. Contains the thermal displacement correction program Commands that cause a control of the machine tool a first step of calculating a first heat value, which is generated in the propeller shaft due to the movement of the nut is based on the rotational speed; a second step detecting a temperature rise in the servomotor and calculating a second heat value supplied from the servomotor to the Screw shaft is transmitted, based on the temperature increase; a third step of calculating a temperature distribution in a plurality of sections obtained by dividing the propeller shaft in a longitudinal direction, from the first and the second heat value; a fourth step of calculating a thermal shift amount of each of the plurality of Sections from the temperature distribution; and a fifth Step of calculating a correction amount of the process data based on the thermal shift amount.

According to the computer-readable medium containing a thermal correction program Shift stores, calculates the control of the machine tool the temperature distribution in the plurality of sections of the ball screw shaft using not only the first heat value, the is generated by the nut on the ball screw shaft, but also of the second heat value based on the temperature increase in the servomotor. Thus, the correction amount can be obtained. Therefore, the correction amount can be an actual length amount approximate the ball screw shaft, even in a transient state, which takes place before the temperature of the servomotor stabilizes is.

Further Features and benefits of the invention result from the following description of exemplary embodiments based on the figures. From the figures show:

1 an overall perspective view of a machine center M according to an embodiment of the present invention;

2 a front view around a main spindle head 5 and an automatic tool changer 7 of the machine center M;

3 a structure diagram of a ball screw mechanism;

4 a block diagram of a control system of the machine center M;

5 an explanatory view in a case where a propeller shaft is divided into sections for obtaining a heat value;

6 an explanatory view of a data field of a calculation circuit 19 a temperature distribution;

7 an explanatory view showing a relationship between an engine body temperature and an elapsed time when a rotational speed of a motor and a current are constant;

8A to 8D Illustrative views for explaining a method for calculating the engine body temperature, wherein 8A is a graph of a relationship between an elapsed time and the engine body temperature from 0 to t1 after the start of the drive, 8B is a diagram of a relationship between the elapsed time and the engine body temperature from t1 to t2 after the start of the drive, 8C is a diagram of a relationship between the elapsed time and the engine body temperature from t2 to t3 after the start of the drive, and 8D FIG. 12 is a graph of a relationship between the elapsed time and the engine body temperature from 0 to t3 after the start of the drive; FIG.

9 a view for explaining a temperature of each section and the heat value that is input for each section;

10 a view showing a temperature increase rate at the time 0, t1 and t2;

11 a flowchart of a position correction control of the machine center M;

12 a schematic view of an experimental device for measuring a temperature of an end portion of the screw shaft; and

13 a graph showing a calculated value calculated according to the prior art method and an experimental value represented by the in 12 shown experimental device is shown.

preferred Embodiments of the present invention will be below described with reference to the drawings.

First Embodiment

A construction of a machine center M (machine tool) will be described with reference to FIG 1 to 4 described. This in 1 Machine Center M shown is a machine tool that applies a desired machine process (eg, "grinding", "painting", "stirring", "drilling" and "cutting") to a workpiece while performing a relative movement between the workpiece and a tool is caused. The machine center M contains a base 1 which is a cast iron base, a machine body 2 who is based on 1 is provided, and a splash cover (not shown) attached to an upper portion of the base 1 is attached. The machine body 2 can perform a cutting process of the workpiece. The spray cover may have a box-shaped shape and the machine body 2 and the base 1 Cover from above.

The base 1 is a cast product having a substantially rectangular solid shape that is elongated in a y-axis direction. The four corners of the lower section of the base 1 each have height adjustable feet.

Next is the machine body 2 described. As in 1 is shown contains the machine body 2 a column 4 , a main spindle head 5 , a main spindle (not shown), a tool changer 7 and a table 8th , The pillar 4 is on an upper surface of a pillar pedestal 3 attached in a back part of the base 1 is provided and extends vertically upwards. The main spindle head 5 can along a front surface of the column 4 be moved up and down and rotatably supports the main spindle, which is provided inside. The tool changer 7 is on the right side of the main spindle head 5 intended. The tool changer 7 can replace a tool holder attached to the upper end of the main spindle with another tool holder. The tool holder can with a tool 6 Be provided, The table 8th is based 1 provided, and the workpiece can be removed on the table 8th be attached. The pillar 4 has on its side of the rear surface a box-like control box 9 on. The control box 9 contains a numerical control device 50 for controlling the activities of the machine center M.

Next is a moving mechanism of the table 8th described. An x-axis motor 71 (please refer 4 ) and a y-axis motor 72 (please refer 4 ), which are servomotors, can set the table 8th in the x-axis direction (the horizontal direction of the machine body 2 in 1 ) and in the y-axis direction (the depth direction of the machine body 2 ) move. The moving mechanism of the table 8th is structured as follows. A rectangular shaped support base 10 is on the bottom of the table 8th and has on its upper surface a pair of x-axis guide rails extending along the x-axis direction. The pair of x-axis guide rails movably carry the table 8th , As in 3 is shown is a nut part 8a on the bottom surface of the table 8th intended. The nut part 8a is with an x-axis screw shaft 81 bolted, different from the x-axis engine 71 extends, whereby a ball screw mechanism is provided. A solid camp 91a at the support base 10 fastened, carries an end section 81a the x-axis screw shaft 81 on one side closer to the x-axis motor 71 , A movable warehouse 91b carries the opposite end portion 81b ,

A pair of y-axis guide rails resting on the top surface of the base 1 are provided and extend along the longitudinal direction, movably carry the support base 10 thereon. The x-axis motor 71 who is in the support base 10 is provided, can the table 8th move and drive in the x-axis direction along the x-axis guide rails. The y-axis engine 72 who is in the base 1 is provided, can the table 8th move and drive in the y-axis direction along the y-axis guide rails. The y-axis movement mechanism has the same ball screw mechanism (see 3 ) on how the x-axis movement mechanism.

telescopic covers 11 and 12 telescopically expanding and contracting cover the x-axis guide rails on the left and right sides of the table 8th , A telescope cover 13 and a rear y-axis cover covers the y-axis guide rails in front of and behind the support base 10 , These telescopic covers 11 . 12 and 13 and the rear y-axis cover constantly cover the x-axis guide rails and the y-axis guide rails even when the table is up 8th in the x-axis direction or in the y-axis direction. Therefore prevent the telescopic covers 11 . 12 and 13 and the rear y-axis cover that shavings, a cooling liquid, etc. sprayed or scattered from the machine area fall on each guide rail.

Next, a raising / lowering mechanism of the main spindle head 5 described. A guide rail (the illustration is omitted) extending in the up and down direction on one side of the front surface of the pillar 4 extends, leads the main spindle head 5 via a linear guide (the illustration is omitted) in a raising / lowering way. A mother (the illustration is omitted) connects the main spindle head 5 with a z-axis screw shaft (the illustration is omitted), which is on the side of the front surface of the column 4 is provided and extends in the upward and downward direction. A z-axis engine 73 (please refer 4 ) can rotate and drive the z-axis screw shaft in the normal and in the reverse direction, resulting in the main spindle head 5 moved up and down. A z-axis control section may be the z-axis motor 73 in accordance with a control signal from a CPU 51 the numerical control device 50 drive. The z-axis engine 73 is driven, whereby the main spindle head moves up and down and drives.

As in 1 and 2 is shown is the tool changer 7 with a tool magazine 14 and a tool change arm 15 Mistake. The tool magazine 14 can store a plurality of tool holders that hold the tool 6 hold. The tool change arm 15 can hold, advance and replace one tool holder attached to the main spindle and another tool holder. In the tool magazine 14 is a plurality of tool pots (the illustration is omitted) and a feed mechanism (the illustration is omitted) is provided. The tool pot carries the tool holder. The feed mechanism pushes the tool pot in the tool magazine 14 in front.

4 shows an electrical structure of the machine center M. the control device 50 as a control section includes a microcomputer. The control device 50 is with an input / output interface 54 , a CPU 51 , a ROM 52 , a ram 53 , Spindle control sections 61a to 64a and 75a , Servo amplifiers 61 to 64 , Differentiators 71b to 74b etc. provided. The servo amplifiers 61 to 64 are consistent with the x-axis motor 71 , the y-axis motor 72 , the z-axis motor 73 and the main spindle motor 74 connected. The spindle control section 75a is with a magazine engine 75 connected.

The x-axis motor 71 and the y-axis motor 72 are respectively provided for moving the table in the x-axis direction and the y-axis direction. The magazine engine 75 is for turning and moving the tool magazine 14 intended. The main spindle motor 74 is for turning the main spindle see. Hereinafter, the x-axis motor 71 , the y-axis engine 72 , the z-axis motor 73 and the main spindle motor 74 together as the engines 71 to 74 designated. These engines 71 to 74 indicate according to encoder 71a to 74a on.

The spindle rod sections 61a to 64a can each have a move instruction amount from the CPU 51 receive and a current command (a command value of a motor torque) to each of the servo amplifiers 61 to 64 output. The servo amplifiers 61 to 64 can each receive the current command and a drive current to each of the motors 71 to 74 output. The spindle control sections 61a to 64a may each have a position feedback signal from each of the encoders 71a to 74a received to perform a position feedback control. The differentiators 71b to 74b may each be the position feedback signal from each of the encoders 71a to 74a is output, differentiate to convert the differentiated position feedback signals into velocity feedback signals, and thus the velocity feedback signals to the spindle control sections 61a to 64a output.

The spindle control sections 61a to 64a may each perform the speed feedback control based on the speed feedback signal from each of the differentiators 71b to 74b is issued. current detectors 61b to 64b can correspondingly capture the drive current coming from the servo amplifiers 61 to 64 to the engines 71 to 74 is issued. The current detectors 61b to 64b can according to the drive current to the spindle control sections 61a to 64a rückkoppeln. The spindle control sections 61a to 64a can accordingly perform a current (torque) control in response to the feedback drive current.

The spindle control section 75a can get the motion command from the CPU 51 for driving the magazine engine 75 receive.

The RAM 53 can z. For example, a parameter associated with a mechanical structure, a parameter associated with physical properties, and heat dissipation coefficients (rate) η _N , η _B , which will be described later. Examples of the parameter associated with the mechanical structure include a length and a diameter of the screw shaft 81 and a reference position to be described later. Examples of the parameter associated with the physical properties include a density, a specific heat, a linear expansion coefficient, a heat capacity, a heat transfer coefficient and γ used in the formulas (3) (4) to be described later , As in 6 shown points the RAM 53 a data area storing thermal values (abbreviated to "CV" in the drawing) corresponding to sections 1 to n of a mother moving section to be described later, a data area corresponding to a total heat value and a data area corresponding to a total rotational speed of the servomotor.

When Next, a description will be made about a method for calculating a thermal shift amount, the is used in the numerical control of the machine center M. To facilitate a ball screw mechanism of an x-axis as an example, basically the same thing also correct for a ball screw mechanism of a y-axis and a ball screw mechanism of a z-axis. In this calculation method the heat values of three areas of the propeller shaft, d. H. a front bearing portion, a mother terbewegungsabschnitts and a rear bearing section. The mothers move section is divided into a plurality of sections. The heat value Each of the plurality of sections is obtained.

(Calculation of the total heat value)

As in 5 is shown, the mother moving portion whose length is represented by L, divided into n section. In the present embodiment, the portion in which the nut is present is determined every fixed time (for example, 50 ms), and the calorific value (a first calorific value) is obtained from an actual rotational speed (feed rate) of the servomotor. The obtained heat value is in the data area of the RAM 53 saved. The calorific value can be calculated using the following formula: Q = K 1 × F T (1) where Q represents the heat value, F represents the feed rate and K ₁ and T represent corresponding coefficients.

In the present embodiment, the calorific value due to the motion of the nut in each section is calculated for each fixed time during a fixed period. In the present embodiment, the calorific value becomes 128 calculated for every 50 ms for a duration of 6400 ms. The calculated values are summed for each section and the sum in the data area of the RAM 53 stored corresponding to each of the sections 1 to n. The RAM 53 Also stores a total heat value Q _TTL , which is the sum of the heat values 1 to n in the sections 1 to n, which are generated in the duration of 6400 ms, and a total rotation speed N _TTL in other data areas.

(Distribution of total heat value: 1)

The present method of distributing the total heat value Q _TTL is based on the same method as that described in US Pat JP 1992-240 045 A is disclosed. More specifically, it is assumed that there is no heat transfer between the nut moving portion, the front bearing portion and the rear bearing portion, and that these portions are thermal and approximately independent of each other. In addition, it is considered that a ratio of the heat value of each heat source with respect to the total heat value is substantially constant regardless of the change in the feed speed.

In the present embodiment, based on the above method, a calorific value Q _{N of} a moving portion and a calorific value Q _{B of} a rear bearing portion are calculated from the following formula: Q N = η N × Q TTL Q B = η B × Q TTL wherein the ratio η _{N represents} a ratio of the heat value of the nut moving portion to the total heat value, and the ratio η _{B represents} a ratio of the heat value of the rear bearing portion to the total heat value. As mentioned in the above method, the ratios η _N and η _{B are} fixed. Therefore, Q _N and Q _B can be measured with an actual engine, and the ratios η _N and η _B can be previously calculated.

(Distribution of the heat value for each section of the mother's movement section)

Next, in the present embodiment, the calorific value is obtained for each portion of the nut moving portion. The one in the RAM 53 stored heat value is a total of the heat value calculated for every 50 ms for the duration of 6400 ms. Therefore, a mean heat value is obtained every 50 ms for each section, and thereafter the existence probabilities X ₁ , ..., X _i , ..., and X _{n of} the nut in each section are calculated from the average heat value and the total heat value Q _TTL by using the following formula:

After the existence probabilities X ₁ ,..., X _i ,..., And X _{n of} the mother in each section are obtained, the distribution heat values Q _N1 ,..., Q _Ni ,..., And Q _Nn are given for each of the portions 1 to n are calculated from the existence probabilities and the heat values Q _{N of} the mother motion portion by using the following formulas:

(Distribution of total heat value: 2)

Next, a heat value Q _{F of} the front bearing is calculated. The calorific value Q _{F of} the front bearing portion is associated with heat input due to an increase in temperature in the servomotor. Therefore, in the present embodiment, the temperature of a body of the servomotor is calculated. Then, an amount of heat input at the end portion of the screw shaft, ie, the heat value Q _{F of} the front bearing (a second heat amount) may be obtained from a difference between the calculated temperature of the servo motor body and the temperature of the end portion of the screw shaft.

A method of calculating the temperature of the servo motor body will be described. The temperature change in the servomotor in a case where the rotational speed of the servomotor and the drive current are constant will be explained with reference to FIG 7 described. When the drive of the engine center M is started, an engine body temperature θ _{M is} increased, a curve 150 is drawn, and is saturated at a fixed temperature. The temperature at saturation is referred to as a saturation temperature L _1a . The saturation temperature L _1a can be represented by the following formula: L 1a = K 2 × ω + K 3 × i 2 (2) wherein K ₂ and K ₃ respectively represent a constant specific to the servomotor, ω is a motor rotation speed, and i is a drive current of the servomotor.

The curve 150 representing the increase in engine body temperature θ _M can be represented by the following formula: Θ M = L 1a × {1 - exp (-γ × t)} (3) where γ represents a constant specific to the servomotor and t represents a time elapsing from the start of the drive. When the engine center M is stopped after the engine body temperature Θ _{M has reached} the saturation temperature L _1a (at the time when t = 8 hours in) 7 ), the engine body temperature can decrease Θ _M , a curve 151 is drawn. The curve 151 can be represented by the following formula: Θ M = L 1a × exp (-γ × t) (4) where γ represents a constant specific to the servo motor and t represents a time elapsing from the stop of the drive.

An engine body temperature Θ _M1a after "a" minutes passed from the start of the engine center M drive can be represented by the following formula based on the formula (3): Θ M1a = L 1a × {1 - exp (-γ × a / 60)}.

An engine body temperature Θ _M-1a after "a" minutes passed from the stop of the engine center M drive can be represented by the following formula based on the formula (4): Θ M-1a = L 1a × exp (-γ × a / 60).

To now the temperature change in the servo motor is described been assuming that the rotational speed of the servomotor and the drive current are constant. The rotational speed and the Driver power of the servomotor, however, do not always need in the actual drive of the machine center M constant to be. In particular, need in a transient state at the initial operating state, the rotational speed and the drive current is not constant. Therefore, at the present embodiment, the saturation temperature of the servomotor using formula (2) from an actual one Rotational speed and an actual drive current (In particular, each average value of the rotational speed and of the drive current measured during 50 ms) for every predetermined elapsed time (in particular 6400 ms) is taken. The temperature change in the servo motor body then becomes the saturation temperature using formulas (3) and (4) and the elapsed time. The temperature changes obtained will be added together, reducing the actual temperature of the servo motor body can be calculated.

A method of calculating the actual temperature of the servo motor body will be described below with reference to FIG 8th described. In the following description, it is assumed that times t1, t2 and ... (minutes) have elapsed from the start of driving the machine center M. Namely, each time between times 0, t1, t2, and... Is considered as the elapsed time in each processing.

In the present embodiment, it is assumed that the engine body temperature Θ _M according to the formula (3) increases during the elapsed time and thereafter decreases according to the formula (4). As in 8A is shown, the engine body temperature Θ _{Mt1 increases} on the basis of the elapsed time between the times 0 and t1 from the time 0 to the time t1, and then decreases after the time t1 has passed, thereby forming a curve 301 is drawn. A value Θ _Mt1-1 at the time t1 of the engine body temperature Θ _Mt1 can be calculated as follows according to the formula (3): Θ Mt1-1 = L t1 × {i - exp (-γ × t1 / 60)} where L _{t1 represents} a saturation temperature obtained from the actual rotational speed and the actual drive current of the servomotor between time 0 and time t1. The engine body temperature Θ _Mt1 decreases according to the formula (4) after the time t1, and therefore, a value Θ _Mt1-2 at the time t2 of the engine body temperature Θ _Mt1 can be calculated as follows: Θ Mt1-2 = Θ Mt1-1 × exp {-γ × (t 2 -t 1) / 60}.

Accordingly, the values Θ _Mt1-3 and Θ _Mt1-4 at the times t3 and t4 of the engine body temperature Θ _Mt1 can be calculated as follows: Θ Mt1-3 = Θ Mt1-1 × exp {-γ × (t3-t1) / 60} Θ Mt1-4 = Θ Mt1-1 × exp {-γ × (t4-t1) / 60}.

As in 8B is shown, the engine body temperature Θ _{Mt2 increases} on the basis of the elapsed time between the times t1 and t2 from the time t1 to the time t2, and then decreases after the time t2 has elapsed, thereby forming a curve 302 is drawn. The saturation temperature L _t2 can be calculated from the actual rotational speed and the actual drive current of the servomotor between times t1 and t2. Therefore, engine body temperatures Θ _Mt2-1 , Θ _Mt2-2, and Θ _Mt2-3 at times t2, t3, and t4 can be respectively calculated by using formulas (3) and (4). Θ Mt2-1 = L t2 × [1 -exp {-γ × (t2-t1) / 60}] Θ Mt2-2 = Θ Mt2-1 × exp (-γ × (t3-t2) / 60} Θ Mt2-3 = Θ Mt2-1 × exp {-γ × (t4-t2) / 60}.

As in 8C is shown, the engine body temperature Θ _{Mt3 increases} on the basis of the elapsed time between times t2 and t3 from time t2 to time t3, and then decreases after time t3 has elapsed, thereby forming a curve 303 is drawn. The engine body temperature Θ _Mt3-1 , Θ _mt3-2 and Θ _Mt3-3 at times t3, t4 and t5 can be calculated as in the case of Θ _Mt1 and Θ _{Mt2, respectively} .

The values of engine body temperatures Θ _Mt1 , Θ _Mt2 , Θ _Mt3 and ... at any time, as described above ben, are added to calculate the actual engine temperature Θ. It is z. For example, assume that the engine body temperatures Θ _Mt1 , Θ _Mt2 and Θ _Mt3 , as indicated by the curves 301 . 302 and 303 are shown (see 8A to 8C ), on the basis of each elapsed time for times t1, t2, t3 and .... In such a case, a value X ₁ at the time t1 of the engine body temperature Θ is equal to Θ _Mt1-1 . A value X ₂ at the time t2 of the engine body temperature Θ is equal to Θ _Mt1-2 + Θ _Mt2-1 . A value X ₃ at time t3 of engine body temperature Θ is equal to Θ _Mt1-3 + Θ _Mt2-2 + Θ _Mt3-1 . Accordingly, the engine body temperature Θ can be calculated at any time. As a result, the engine body temperature change can be obtained as indicated by a curve 304 (please refer 8D ) is shown.

In the present embodiment, the calorific value Q _{F of} the front bearing is calculated by using the engine body temperature Θ calculated as described above, according to the following formula (5): Q F = K 4 (Θ - Θ s ) (5) wherein K _{4 represents} a coefficient and Θ _s the temperature of the end portion of the screw shaft on the servomotor side (the end portion 81a in the example of 3 ).

(Calculation of the temperature distribution)

After the heat value for each heat source has been calculated as described above, the CPU calculates 51 the temperature distribution from the heat values. The temperature distribution can be obtained by solving the following equation of the heat conduction in the non-stationary weight state under the initial conditions of {θ} _{t = 0} and d {θ} / dt _{t = 0} : [C] d {θ} / dt + [H] {θ} + {Q} = 0 (6) where [C] represents a heat capacity matrix, [H] represents a heat conduction matrix, {θ} represents the temperature distribution, {Q} represents the heat value, and t represents a time.

More accurate, the drive of the machine center M is started (t = 0), and the temperature distribution when the time t1, t2 and ... (minutes) has passed is calculated.

When the mother moving section is divided into sections, as in FIG 5 4, the temperature of each section and the calorific value input for each section can be represented as in FIG 9 is shown. The following formula (7) can be represented as follows by 9 is used:

The temperature distribution {θ} of each section of the screw shaft at the time t0 and the engine body temperature Θ are already known. Therefore, the heat value Q _{F of} the front bearing can be calculated from the formula (5). The distribution heat values Q _N1 to Q _Nn in each section of the nut moving section and the calorific value Q _{B of} the rear bearing can also be obtained from the formula (1). The calculated values are assigned to the right side of formula (7). That is, as in 10 ₂ , the rate (d {θ} _{t = 0} / dt), that is, a slope of the temperature increase in each section of the screw shaft can be obtained. In the present embodiment, the temperature {θ} in each section can be calculated at t = t1 based on the obtained inclination by using the following formula: {Θ} t = t1 = {θ} t = 0 + (d {8} t = 0 / dt) × t1.

Further, Q _F at t = t1 can be calculated according to the formula (5) from the temperature of the end portion of the propeller shaft T _S of {θ} _{t = t1} and the engine body temperature Θ calculated using the formulas (3) and (4) is. The calculated value is then assigned to the formula (7), whereby d {θ} _{t = t1} / dt can be obtained. As a result, the temperature at each section at t = t2 can be calculated from the following formula: {Θ} t = t2 = {θ} t = t1 + (d {θ} t = t1 / dt) × (t2 - t1).

The Temperatures can be up to t = t3 and at other times the similar way are obtained.

(Calculation of thermal shift amount)

After the temperature distribution of the screw shaft as described above is obtained, the thermal shift amount can be calculated from the temperature distribution. The thermal shift amount can be calculated from the following formula (8): ΔL = ∫ L 0 β × θ (L) dL (8) where ΔL represents the amount of thermal shift and β represents a linear expansion coefficient of a material of the screw shaft.

Next, a specific procedure of the numerical control of the machine center M will be described with reference to FIG 11 shown flowchart described. The CPU 51 sets a matrix necessary for the calculation using the finite element method based on setting data such as parameters. As in 5 is shown divides the CPU 51 the mother moving section of the screw shaft in finite number of sections, causing the CPU 51 Regions in a heat distribution model forms (S1).

Next is the CPU 51 the initial temperature {θ} _{t = 0} for each section in the heat distribution model set in step S1. The initial temperature {θ} _{t = 0} can be set individually for each section. If the temperature of the engine center M can be treated as equal to the ambient temperature θ _air , the initial temperatures {θ} _{t = 0} can be set to the ambient temperature θ _air for all sections. On the other hand, if there is a temperature difference between each section due to e.g. As the drive of the machine center M, the CPU can 51 set the initial temperature for each section. The CPU 51 stores the initially set temperature {θ} _{t = 0} and a reference position in the RAM 53 (S2)

The CPU 51 identifies the section that represents the current position of the nut part 8a contains, for every 50 ms and calculates the total of the heat value due to the movement of the nut 8a for each section based on the data of the feed rate and the formula (1) (S3). After a fixed time (6400 ms) has passed, the CPU calculates 51 the calorific value Q _{N of} the nut moving portion from the ratio η _{N of} the calorific value Q _N of the nut moving portion with respect to the total calorific value Q _TTL which is the sum of the calorific values of all the portions. The CPU 51 calculates the existence probability of the mother for each section from the total heat value Q _TTL and the mean heat value for each section. The CPU 51 distributes a value obtained by multiplying the heat value Q _{N of} the mother moving section and the likelihood of existence as a heat value due to the movement of the nut to each of the sections obtained by the division in step S1 (S4).

The CPU 51 calculates the saturation temperature based on the formula (2) by using the current passing through the servo motor and the motor rotation speed. The CPU 51 wins the temperature increase in the servo motor body based on the saturation temperature and the formulas (3) and (4) (S5). The CPU 51 calculates the heat input at the portion adjacent to the servomotor, that is, the heat value of the front bearing from the temperature increase in the servo motor body and the temperature of the end portion of the screw shaft in which the formula (5) is used (S6).

The CPU 51 The temperature distribution in each section is obtained by using the heat value of each section obtained in steps S4 and S6 and the non-stationary state heat conduction equation (6) (7). The CPU 51 calculates the thermal shift amount of each section from the temperature distribution obtained in step S7 by using formula (8) (S8). The CPU 51 calculates the amount of thermal displacement from the reference position stored in step S2, that is, a correction amount to be used in a process control (S9). If a correction mode is ON, the CPU sends 51 a feed amount signal corresponding to the correction amount calculated in step S9 to the spindle control section 61a (S10). If the CPU 51 the editing until the step S10 has ended, the CPU returns 51 to step S3 and continues the calculation periodically (each after the expiration of 6400 ms).

The CPU 51 that performs the processing in step S3 corresponds to a calculation portion of a first heat value. The CPU 51 which executes the processing in step S5 corresponds to a temperature detecting section. The CPU 51 , which carries out the processing in step S6, corresponds to a calculation section of a second heat value. The CPU 51 which executes the processing in step S7 corresponds to a calculation section of a temperature distribution. The CPU 51 which executes the processing in step S8 corresponds to a thermal shift amount calculating section. The CPU 51 which executes the processing in step S9 corresponds to a calculation portion of a correction amount.

Second Embodiment

When Next, a second embodiment will be described. The second embodiment is different from the first one Embodiment in that the temperature increase in the Servo motor is not calculated from the current and the rotational speed but by using a temperature sensor attached to the Servo motor is attached, and a room temperature sensor, which is a Room temperature measures.

The temperature Θ _{M0 of} the servo motor body is detected by the temperature sensor (the illustration is omitted) separated into the x-axis motor 71 is installed, and a room temperature θ _atm is _detected by the room temperature sensor (illustration is omitted) which detects the ambient temperature installed in the machine center M. The temperature Θ _{M0 of} the servo motor body and the room temperature θ _atm become the CPU 51 Posted.

The CPU 51 calculates the temperature increase Θ in the servo motor body using the following formula: Θ = Θ M0 - θ atm ,

The heat value Q _{F of} the front bearing is assigned to heat input due to the temperature increase in the servomotor. Therefore, the CPU calculates 51 the heat value Q _{F of} the front bearing from the temperature increase Θ in the servo motor body using the following formula: Q F = K 5 (Θ - Θ S ) where K _{5 represents} a coefficient and Θ _{S represents} the temperature increase in the end portion of the screw shaft from the time t = 0. When the above calculation is used, the detection accuracy of the amount of heat input to the end portion of the screw shaft, which is calculated using a thermal displacement correction algorithm, can be increased. Therefore, the second embodiment can realize further improvement of accuracy of thermal displacement correction. In the second embodiment, the temperature sensor and the room temperature sensor correspond to the temperature detection section.

Next, a modified embodiment in which the above embodiments are partially modified will be described. In the first embodiment described above, the temperature increase Θ in the servo motor body is calculated by using the formulas (3) and (4). The temperature increase Θ in the servo motor body can also be calculated on the basis of a primary deceleration system in which the temperature increase in the servomotor is discretized by using the following formulas: L Tn = K 6 × ω + K 7 × i 2 Θ n = (1 - K 8th ) Θ n-1 + L Tn (9) where K ₆ , K ₇ and K _{8 are} coefficients specific to the servomotor.

When the temperature increase in the servomotor is calculated only from the rotational speed, the formula (2) can be changed as follows: L 1a = K 9 × ω.

Alternatively, when the temperature increase in the servomotor is calculated only from the drive current value, the formula (2) can be changed as follows: L 1a = K 10 × i 2 where K ₉ and K _{10 are} coefficients specific to the servomotor.

Further, when the temperature increase in the servo motor body is calculated only from the rotational speed using the discretized primary deceleration system, the formula (9) can be changed as follows: L Tn = K 11 × ω.

Alternatively, when the temperature increase in the servo motor body is calculated only from the drive current value, the formula (9) may be changed as follows: L Tn = K 12 × i 2 where K ₁₁ and K _{12 are} coefficients specific to the servomotor.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 1988-256336 A [0003, 0004]
• - JP 1992-240045 A [0004, 0004, 0006, 0010, 0055]
• JP 1992-260045 A [0005]

Claims (5)

A thermal displacement correcting method for a machine tool (M), the machine tool (M) comprising: a ball screw mechanism for a feed drive provided with a screw shaft (10); 81 ) and a mother ( 8a ), a feed amount control which determines a feed amount of the nut ( 8a ) through the propeller shaft ( 81 ) calculated on the basis of process data, a servomotor ( 71 ), the rotationally the screw shaft ( 81 ), and a speed controller which controls a rotational speed of the servomotor ( 71 ) on the basis of the process data, the method comprising: a first step of calculating a first heat value stored in the propeller shaft (FIG. 81 ) due to a movement of the mother ( 8a ) is generated based on the rotational speed; a second step of detecting a temperature increase in the servomotor ( 71 ) and calculating a second heat value received from the servomotor ( 71 ) to the propeller shaft ( 81 ), based on the temperature increase; a third step of calculating a temperature distribution in a plurality of sections by dividing the propeller shaft (14) 81 ) are obtained in a longitudinal direction from the first and second heat values; a fourth step of calculating a thermal shift amount of each of the plurality of sections from the temperature distribution; and a fifth step of calculating a correction amount of the process data based on the thermal shift amount. Correction method according to claim 1, wherein the temperature increase in the servomotor ( 71 ) is detected on the basis of at least the rotational speed and a drive current value of the servomotor ( 71 ). A thermal displacement correcting device for a machine tool (M), said machine tool (M) comprising: a ball screw mechanism for a feed drive provided with a screw shaft (10); 81 ) and a mother ( 8a ), a feed amount control which determines a feed amount of the nut ( 8a ) through the propeller shaft ( 81 ) calculated on the basis of process data, a servomotor ( 71 ), the rotationally the screw shaft ( 81 ), and a speed controller which controls a rotational speed of the servomotor ( 71 ) on the basis of the process data, the apparatus comprising: a speed detecting device that detects the rotational speed; a temperature detecting portion that detects a temperature increase in the servomotor (FIG. 71 ) detected; a calculation section ( 51 ) of a first calorific value that calculates a first calorific value in the propeller shaft ( 81 ) due to a movement of the mother ( 8a ) based on the rotational speed detected by the speed detecting device; a calculation section ( 51 ) of a second calorific value that calculates a second calorific value received from the servomotor ( 71 ) to the propeller shaft ( 81 ), based on the temperature increase detected by the temperature detecting section; a calculation section ( 51 ) a temperature distribution that calculates a temperature distribution in a plurality of sections that are divided by dividing the propeller shaft (FIG. 81 ) are obtained in the longitudinal direction, from the first heat value obtained by the calculating section ( 51 ) of the first calorific value and the second calorific value calculated by the calculating section ( 51 ) of the second calorific value is calculated; a calculation section ( 51 ) of a thermal shift amount that calculates a thermal shift amount of each of the plurality of sections from the temperature distribution calculated by the calculating section (16) 51 ) of the temperature distribution is calculated; and a calculation section ( 51 ) of a correction amount that calculates a correction amount of the process data based on the thermal shift amount calculated by the calculating portion ( 51 ) of the thermal shift amount. The correction device according to claim 3, wherein the temperature detecting section detects the temperature increase based on at least the rotational speed and a drive current value of the servomotor. 71 ) detected. A computer-readable medium storing a thermal displacement correction program for a machine tool (M), the machine tool (M) comprising: a ball screw mechanism for a feed drive coupled to a screw shaft (10); 81 ) and a courage ter ( 8a ), a feed amount control which determines a feed amount of the nut ( 8a ) through the propeller shaft ( 81 ) calculated on the basis of process data, a servomotor ( 71 ), the rotationally the screw shaft ( 81 ), and a speed controller which controls a rotational speed of the servomotor ( 71 ) on the basis of the process data, the program having instructions for causing a control of the machine tool (M) to execute: a first step of calculating a first heat value present in the propeller shaft ( 81 ) due to the movement of the mother ( 8a ) is generated based on the rotational speed; a second step of detecting a temperature increase in the servomotor ( 71 ) and calculating a second heat value received from the servomotor ( 71 ) to the propeller shaft ( 81 ), based on the temperature increase; a third step of calculating a temperature distribution in a plurality of sections formed by dividing the screw shaft (10); 81 ) are obtained in a longitudinal direction from the first and second heat values; a fourth step of calculating a thermal shift amount of each of the plurality of sections from the temperature distribution; and a fifth step of calculating a correction amount of the process data based on the thermal shift amount.