JP2000135654A - Thermal displacement amount computing device and its method for machine tool, and thermal displacement correcting device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the processing size to the thermal displacement amount corresponding to the variations of the driving condition and the room temperature, in a simple structure and at a low cost. SOLUTION: This thermal displacement amount computing device of a machine tool is provided with a thermal event measuring means 16 to measure the thermal events such as the room temperature variation, the driving heat, and the processing heat, giving an influence to the displacement amount of a machine; a timepiece 4; a thermal event data memory means 11 to input the magnitude data of the measured thermal events and their generating time data, and to memorize those data in order; and a residual thermal displacement amount computing device 12 to compute the present residual thermal displacement amount, depending on the memorized past thermal event data, by an elapsed time coefficient (f) found by an experiment or a calculation. This thermal displacement amount operation device has a numerical value control and correcting means 13 to correct the processing size of a work depending on the found residual thermal displacement value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting thermal displacement of a machine tool such as a metal cutting machine, a press machine, and a sheet metal machine, and more particularly, to a method for compensating thermal displacement easily and with high accuracy with a relatively simple structure. The present invention relates to a method and a device for correcting thermal displacement of a machine tool, which can automatically perform the above.

[0002]

2. Description of the Related Art Machine parts such as metal cutting machines, press machines, and sheet metal machines are subject to thermal expansion due to changes in the outside air temperature, cutting heat during processing, processing heat during molding, or heat generated by a driving mechanism. And dimensional accuracy gradually decreases. Therefore, in order to always maintain the processing dimensional accuracy of the machine tool at a predetermined value or more, conventionally, a dimensional adjustment operation by an operator is required. Various techniques have been proposed for this dimension adjustment method.

For example, the dimensions of a work after processing are measured,
A displacement correction device for an NC machine tool is disclosed in which a measurement result is fed back to a control device of a machine tool as needed to correct machining command data, and thereafter, machining is performed based on the corrected machining command data. I have. Further, Japanese Patent Application Laid-Open No. 7-186003 and Japanese Patent Publication No. 6-92058 disclose that a thermal displacement of a machine tool is directly measured and fed back to a machining program, that is, machining command data is corrected according to the thermal displacement. A thermal displacement correction method is disclosed.

Japanese Patent Application Laid-Open No. Hei 9-108992 discloses that a temperature of a specific portion of a machine tool is measured, a thermal displacement of the machine tool is estimated based on the measured value, and the thermal displacement is fed back to a machining program. A machine tool with a correction device is disclosed. Further, Japanese Unexamined Patent Publication No. Sho 60-9947 discloses a thermal deformation correction device which feeds back to a machining program based on a relationship between an operation time and a thermal displacement amount under predetermined limited operating conditions. Have been.

[0005]

However, the above prior arts have the following problems. 1) The method of feeding back the measurement result of the workpiece dimensions after processing to the machine tool as needed is almost the best in terms of securing the processing accuracy, but is expensive because the workpiece dimensions must be measured with high precision. It is necessary to use simple measuring equipment, and the cost is high. In addition, there is a problem that it takes time to measure the dimensions for feedback, and it takes time and cost for the apparatus to input the measurement results to the machine tool. 2) JP-A-7-186003 and JP-B-6-920
In the method disclosed in Japanese Patent Application Laid-Open No. 58-58, it is often technically difficult to directly measure the thermal displacement of a machine tool in a predetermined direction, and thus this method may not be applicable. In addition, there is a problem that it is costly to solve this technical difficulty. 3) In the method disclosed in Japanese Patent Application Laid-Open No. 9-108992, it is technically difficult to accurately obtain a relational expression between a temperature or a temperature change amount of a specific portion and a thermal displacement amount of a machine,
In many cases, the improvement of working accuracy in practical use is insufficient. 4) According to the method disclosed in Japanese Patent Application Laid-Open No. 60-99547, it is effective when the operating conditions are fixed, but when the calorific value is not constant, such as when the work to be processed changes randomly, or when cutting is performed. It is difficult to apply this method, for example, when it is affected by both heat generation and changes in room temperature.

The present invention has been made in view of the above problems, and has a simple structure, can be manufactured at low cost, and can measure a thermal displacement and use a complicated relational expression between temperature and thermal displacement. Provided are a machine tool thermal displacement calculating device and a calculating method thereof, and a thermal displacement correcting device and a correcting method thereof, which are capable of correcting a processing dimension with respect to a thermal displacement amount in accordance with changes in operating conditions and room temperature without accompanying. It is intended to be.

[0007]

Before describing each means according to the present invention individually, first, a basic technique of a thermal displacement amount calculating method and a thermal displacement correcting method which are features of the present invention. The concept will be described with reference to FIGS.

When generated heat (hereinafter referred to as a thermal event) which causes a thermal displacement of a machine tool occurs,
Generally, the thermal effects cause the machine to deform in a relatively short period of time, then reduce the effects over a longer period of time, and become negligible after a predetermined time. The relationship between the amount of thermal displacement and the elapsed time with respect to this thermal event is, for example, a curve as shown in FIG. 1, and the inventor of the present application has obtained a curve when a predetermined thermal event is generated for a specific machine tool. The curve is determined experimentally. As shown in the figure, for example, when the temperature suddenly changes in a step-like manner, it is considered that a thermal event has occurred. Due to the influence of this thermal event, the displacement amount of the machine during a relatively short predetermined time t1 from the time of occurrence is considered. Gradually increase,
After that, it gradually decreases for a longer time than when it increases. Then, after a predetermined time t2 from the start of the decrease, there is no influence of the thermal event at all. Such a response curve can be interpreted as a step response of a thermal displacement to a thermal event.

The following events can be considered as thermal events. 1) When the room temperature (the temperature around the machine that has an effect of giving thermal displacement to the machine) rises or falls by a certain amount or more at a certain time. When the drive motor generates heat 3) When a certain amount of cutting heat is generated by processing the workpiece at a certain time Here, the degree of influence of these thermal events, that is, the magnitude of the thermal displacement and its influence Is unique to each machine, and can be easily obtained experimentally or by calculation (simulation).

In general, in a machine tool, as shown in FIG. 2, such various thermal events occur successively in a time series with different magnitudes, and a thermal displacement at a certain point in time is generated. The amount can be considered to be generated by adding all the effects of the past thermal events. Therefore, the present inventor approximates a response curve corresponding to each thermal event with a predetermined time function f (t) (hereinafter referred to as an elapsed time coefficient in an embodiment described later), and The magnitude data and the occurrence time data are stored, and the influence of each thermal event in the past is calculated by the time function f (t) of the response curve based on the magnitude data and the occurrence time data of the past thermal event. It is noted that it is possible to calculate and estimate to what extent each of them remains at the present moment, and to calculate and estimate the amount of thermal influence currently remaining (that is, the amount of generated thermal displacement) as the sum of them.
Then, it is possible to correct the processing dimension based on the estimated amount of thermal displacement.

As described above, in order to achieve the above-mentioned object, the invention according to claim 1 provides a machine tool thermal displacement amount calculating apparatus for calculating a displacement amount due to heat generation of a machine. Thermal event measuring means 16 for measuring thermal events such as room temperature change, operating heat and processing heat which affect
And a clock 4 for measuring the current time, thermal event data storage means 11 for inputting measured thermal event size data and its occurrence time data, and sequentially storing these data, Based on the obtained elapsed time coefficient f representing the effect of the unit generated heat on the thermal displacement of the machine, based on the past thermal event size data and its occurrence time data stored in the thermal event data storage means 11. , And a remaining thermal displacement calculating means 12 for calculating the current remaining thermal displacement.

According to the first aspect of the present invention, the time function f representing the effect of the predetermined unit generated heat on the thermal displacement of the machine.
Is adopted, the amount of thermal displacement remaining at the present time for each thermal event is calculated based on the magnitude of past thermal events (change in room temperature, operating heat and processing heat, etc.) and the elapsed time from the occurrence thereof. You. And as the sum of these,
The current residual thermal displacement due to all past thermal events is determined. As a thermal event, a change in room temperature is based on a driving current value and a driving time of the spindle motor, and a processing heat is calculated based on a driving current value that can represent a calorific value of a machine tool. Since it can be easily obtained as a predetermined unit calorific value which is measured and set in advance for each work type, if there is at most one simple thermal event measuring device, a clock and a controller (computer, etc.) Thus, a thermal displacement calculating device can be configured. Thereby, it can be compact and inexpensive. Also, since it is only necessary to measure the change in room temperature around the machine, the operating heat of the machine, the processing heat, etc., it is possible to measure with high accuracy compared to the conventional method of measuring the thermal deformation itself, and the amount of thermal displacement is easy Measurement with high accuracy. In addition, since changes in various heat values are captured as a heat source of a thermal event, random processing in which the heat value is not constant as described in the section of the prior art, that is, operating conditions and room temperature change. Even when machining, the amount of thermal displacement can be accurately measured.

According to a second aspect of the present invention, there is provided a thermal displacement compensating apparatus for a machine tool for compensating a work size of a workpiece based on a displacement due to heat generation of the machine. An arithmetic unit and numerical control correcting means 13 for correcting the work size of the workpiece based on the residual thermal displacement obtained by the thermal displacement calculating unit are provided.

According to the invention described in claim 2, according to claim 1,
Based on the current residual thermal displacement calculated by the described thermal displacement calculating device, the processing size is corrected by calculating the thermal displacement correction amount of each axis position command value of the NC control, so that it is easy and accurate. Can be corrected. Therefore, the thermal displacement of the machine tool can be corrected by the compact thermal displacement compensating device including the sensor and the computing device for computing the thermal displacement amount and the compensation amount.

According to a third aspect of the present invention, there is provided a method for calculating a thermal displacement of a machine tool for calculating a displacement due to heat generation of a machine. A step of measuring the thermal event and sequentially storing the magnitude data of the thermal event and its occurrence time data, and the elapsed time indicating the effect of the unit generated heat on the thermal displacement of the machine, obtained in advance by experiment or calculation Calculating a current remaining thermal displacement amount based on the stored past thermal event size data and its occurrence time data using a coefficient f.

According to the third aspect of the present invention, the time function f representing the effect of the predetermined unit generated heat on the thermal displacement of the machine.
Then, based on the magnitude of past thermal events (room temperature change, operation heat, processing heat, etc.) and the elapsed time, the amount of thermal displacement remaining at the present time for each thermal event is calculated, and the total The current residual thermal displacement due to all the thermal events is calculated. Since the change in room temperature is measured by a thermometer, the measuring device for the thermal event may be a simple one, and the operating heat and the processing heat are measured each time by measuring in advance under predetermined operating conditions for each type of work. Since there is no need, there is no need for a thermal event measurement device. Therefore, the thermal displacement calculating device can be configured compactly and inexpensively. In addition, the measurement of thermal events (such as changes in room temperature, operating heat, and processing heat) is more accurate and easier than conventional measurement of thermal deformation itself. Thermal displacement can be easily and accurately measured. Furthermore, since various changes in the calorific value are captured as the heat source of the thermal event, it is possible to cope with random machining in which the calorific value is not constant as described in the section of the related art.

According to a fourth aspect of the present invention, there is provided a machine tool thermal displacement correction method for correcting a work dimension of a work based on a displacement amount due to heat generation of a machine. A step of measuring thermal events such as operating heat and processing heat and sequentially storing the magnitude data of the thermal events and the time of occurrence thereof; and Based on the elapsed time coefficient (f) representing the effect on the current thermal event magnitude data based on the stored past thermal event size data and its occurrence time data, a step of calculating the current remaining thermal displacement amount, this calculated A numerical control correction step of correcting the work dimension of the work based on the residual thermal displacement.

According to the invention described in claim 4, according to claim 3,
The described thermal displacement amount calculation method (a step of sequentially storing thermal event data and a step of calculating a current residual thermal displacement amount based on the past thermal event data by an elapsed time coefficient (f)) Since the processing dimension is corrected based on the obtained current residual thermal displacement amount, the processing size can be corrected easily and accurately without a large-scale apparatus. Therefore, the thermal displacement of the machine tool can be corrected compactly and at low cost.

[0019]

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

First, a first embodiment showing a method of obtaining a correction value for a thermal displacement due to a thermal event of a change in room temperature will be described with reference to FIGS. FIG. 3 is a block diagram showing a hardware configuration of the thermal displacement compensator. In the figure, a room temperature sensor 3 is for indirectly detecting the amount of thermal displacement of the machine tool 2, and is installed at a specific position near the machine tool 2, which strongly affects the thermal displacement of the machine tool 2. It is assumed that the room temperature at the position is provided so as to equivalently represent the amount of thermal displacement of the machine tool 2. The room temperature sensor 3 outputs a room temperature detection signal to the controller 10. The clock 4 measures the current time and outputs time data to the controller 10. The controller 10 is composed of, for example, a computer device mainly composed of a microcomputer or the like. The controller 10 receives a room temperature detection signal from the room temperature sensor 3 and performs a predetermined arithmetic processing described later based on the room temperature detection signal to perform thermal displacement. The amount is estimated, and the estimated thermal displacement data is transmitted to the NC control device 1. NC
The control device 1 controls the start, stop, rotation speed, position, and the like of the spindle motor of the machine tool 2 and each axis drive motor that drives a table on which a workpiece is placed and movable, for example, in three orthogonal directions. And controls these operating sequences. The NC control device 1 stores a machining program for machining a work in advance, and controls the drive and sequence of each of the motors according to the machining program. At this time,
The NC controller 1 corrects and obtains a position command value for each axis motor in the machining program based on the thermal displacement amount data input from the controller 10 using a predetermined correction formula described later. Each axis motor is controlled.

FIG. 4 is a functional block diagram of the thermal displacement compensator according to the present embodiment. In FIG.
0 is a thermal event measuring means 16, a thermal event data storing means 11, a residual thermal displacement calculating means 12, a numerical control correcting means 13, and a data storing address updating means 14
And storage time determination means 15.

In the present embodiment, the thermal event measuring means 16 outputs room temperature data detected by the room temperature sensor 3 to the thermal event data storage means 11 as thermal event information. The storage time determination unit 15 receives the current time data from the clock 4 and compares the current time data with the calculation time for each of the predetermined calculation unit times dh. A storage command is output to the event data storage means 11 and a calculation command is output to the residual thermal displacement calculation means 12. When the storage command is input from the storage time determination unit 15, the thermal event data storage unit 11 reads the thermal event data (room temperature data) from the thermal event measurement unit 16 and stores the thermal event data in the thermal event table as shown in FIG. It is stored at a predetermined address A (the storage address of the latest data) as room temperature data T1 at the current time. In the thermal event table, room temperature data measured in the past is stored in time series as shown in FIG.
For each of (A + 1), (A + 2),..., Room temperature data a predetermined time before the current time is stored. In the present embodiment, since the room temperature is measured and stored at predetermined calculation time intervals, the address itself indicates the elapsed time from the present time. However, the present invention is limited to such a data storage method. Instead, for example, the occurrence time when a thermal event occurs may be stored as it is.

Upon receiving the calculation command from the storage time determining means 15, the remaining thermal displacement calculating means 12 calculates the remaining thermal displacement based on the following equation (1). This residual thermal displacement is calculated as the sum of the current influences of all past thermal events (here, changes in room temperature). Therefore, the processing dimension of the machine tool (ie, (The amount of movement of each axis) can be corrected. Therefore, the amount of residual thermal displacement is used as a correction coefficient H when correcting the processing dimension. This correction coefficient H is output to the numerical control correction means 13.

(Equation 1) Here, the elapsed time coefficient f (t) expresses the amount of thermal displacement at the time of a step response in which the room temperature instantaneously rises once as a function of time, and is experimentally obtained. The calculation unit time dh is a predetermined calculation interval time set in advance.
Further, tp (i) represents time-series thermal event data (here, room temperature data) stored in the memory area at the address i of the thermal event table, i represents a parameter representing elapsed time, and tp (1) = T1 (latest room temperature data).

In the elapsed time coefficient f (t), the magnitude of the thermal event generated at a certain point in time (when the elapsed time parameter is i) is the amount of change in the room temperature at that point in time (“tp (i + 1)
−tp (i−1)) / 2 ”, and the residual thermal displacement at this time due to a thermal event of this magnitude is“ f ((i−1) × d
h) × (tp (i + 1) −tp (i−1)) / 2 ”. Therefore, the amount of residual thermal displacement due to all past thermal events is integrated, that is, in the above equation (Equation 1), i
= 2 to n, the residual thermal displacement at the present time due to the influence of all the past thermal events is obtained.

The numerical control correction means 13 obtains the position correction values Xs, Ys, Zs for each axial direction of the machining table from the following equations 2 to 4 based on the input correction coefficient H,
It is transmitted to the control device 1 by communication or the like. These position correction values Xs, Ys, Zs indicate the parallel shift amounts of the absolute coordinates of each axis.

Xs = Kx × H

## EQU3 ## Ys = Ky × H

Here, Kx, Ky, and Kz are coefficients for converting the correction coefficient H into position correction values Xs, Ys, and Zs corresponding to the respective axial directions.

The NC control device 1 calculates the position correction values Xs, Xs, transmitted from the numerical control correction means 13 for each calculation unit time dh.
Ys and Zs are input, and this position correction value is added to the target position of each axis stored in advance in the machining program to calculate a corrected position command. The timing at which the correction calculation of the position command is performed is, for example, before the start of processing for each work when the total processing time of one work is short enough not to be affected by the amount of thermal displacement during that time. In addition, if the time is long enough to be affected by the amount of thermal displacement during the processing during that time, it is preferable that the time is set to be a predetermined short time or a short step.

After the correction value calculation at each calculation time is completed, the data storage address updating means 14 updates the address of each data in the thermal event table by shifting one by one. That is, as shown in the following Expressions 5 to 7, data having the oldest occurrence time among the data in the thermal event table is erased, and all other data is moved to the address corresponding to the past time by one calculation unit time dh. Each is transferred and stored. And always, the latest thermal event data tp
Prepare to store (1) at address A.

Tp (n) = tp (n-1)

Tp (n-1) = tp (n-2)

Tp (2) = tp (1)

Next, the procedure of the correction calculation processing of the controller 10 according to the present embodiment will be described with reference to the flowchart shown in FIG. In the following, each step number is represented by adding S. First, in S1, the current time is read from the clock 4 and it is checked whether or not the calculated time has been reached (storage time determination means 15). If not, repeat the same process and wait until the calculation time is reached. When it has reached, in S2, the current room temperature data detected by the thermal event measuring means 16 by the room temperature sensor 3 is input and stored in tp (1) of the thermal event data table (thermal event data storage means 11). . At this time, the calculation time may be stored. Next, in S3, based on all past room temperature data stored in the thermal event table and the time of occurrence thereof (here, the calculation time at each time point), the current residual thermal displacement amount, That is, the correction coefficient H is calculated (remaining thermal displacement calculating means 12). In general, the elapsed time t in the elapsed time coefficient f (t) can be obtained based on the formula “current time−past time”. Here, thermal event data is stored for each calculation unit time dh. Therefore, it is obtained by the formula “(i−1) × dh”. Then, in S4, based on the obtained correction coefficient H, a position correction value Xs, Ys, Zs of each axis, that is, a correction amount of the processing dimension is calculated by Expressions 2 to 4, and then in S5, the position correction value Xs,
Ys and Zs are transmitted to the NC control device 1 (numerical control correction means 13). Next, in S6, the next calculation time is obtained by adding the calculation unit time dh to the current calculation time, and is set (stored) at a predetermined address in the memory. Thereafter, in S7, the oldest room temperature data is deleted, and other data is sequentially transferred and stored so as to be shifted to the address corresponding to the time one calculation unit time dh older, and the area for storing the latest data (address A) To secure. Then, go back to the first S1,
The above processing is repeated.

According to the present embodiment, when a change in room temperature occurs, it is determined that a thermal event has occurred, and the amount of residual thermal displacement according to the magnitude of the change in room temperature and the elapsed time is determined by the elapsed time coefficient f ( The calculation is performed based on a simple calculation expression such as t). The elapsed time coefficient f (t) is experimentally obtained as a step response of a thermal displacement when a unit thermal event (a change in room temperature of 1 ° C.) instantaneously occurs, that is, a residual thermal displacement. The calculation can be performed based on the elapsed time coefficient f (t) only by measuring the room temperature and the elapsed time. Therefore, with a compact device configuration,
The amount of residual thermal displacement can be calculated accurately with a simple calculation formula. This makes it possible to manufacture a thermal displacement correction device that can easily correct the processing dimension of a machine tool with respect to the thermal displacement, which has been difficult in the past, at a very low cost.

Next, a second embodiment will be described. This embodiment shows an example in which a thermal displacement amount for a thermal event due to operating heat is corrected. FIG. 7 shows the hardware configuration of the present embodiment, and the same components as those in FIG. As shown in the figure, a heat value of a machine tool is assumed as a thermal event, and this heat value is used as the operating heat of each drive motor (spindle motor and each table drive shaft motor). The NC control device 1 transmits drive current value data of each drive motor and its drive time data to the controller 10. The controller 10 calculates the total operation heat based on the input drive current value data and the drive time data for each drive motor, and stores the operation heat as a thermal event together with the occurrence time. Then, predetermined arithmetic processing described later is performed, and each axis correction value is obtained based on the calculated residual thermal displacement amount, and is output to the NC control device 1.

Each function will be described with reference to the functional block diagram of this embodiment shown in FIG. Here, FIG.
The same reference numerals are given to the same functional components. In the present embodiment, the thermal event measuring means 16 measures the operating heat of the machine tool, and based on the driving current value data for each driving motor and the driving time data inputted from the NC control device 1, the total. Calculate the operating heat. The calculated total operation heat data is output to the thermal event data storage means 11. As in the previous embodiment, when the storage command from the storage time determination unit 15 is input, the thermal event data storage unit 11 converts the operating heat data from the thermal event measurement unit 16 into thermal event data at the current time. It is stored at a predetermined address (corresponding to address A in the previous embodiment) of the target event table. Similar to the previous embodiment, the residual thermal displacement calculating means 12 calculates the residual thermal displacement based on the thermal event data (operating heat) stored in the thermal event table and the time of occurrence by the following equation (8). (Correction coefficient H) is calculated and obtained. Then, the residual thermal displacement data is output to the numerical control correcting means 13. Here, the elapsed time coefficient f
(t) represents the thermal displacement as a function of the elapsed time t when the unit heat generation Q1 is continuously generated for the calculation unit time dh, as shown in FIG. 9, and is obtained experimentally. . The elapsed time t is generally obtained based on a formula “current time−past time”. In the present embodiment, when a predetermined amount or more of heat is generated at a certain point in time, it is determined that the event is a thermal event, and the relationship between the amount of heat generation and the thermal event is shown in FIG. Note that the other functional components are the same as those in the previous embodiment, and thus description thereof will be omitted.

Next, the procedure of the correction calculation processing in this embodiment will be described with reference to the flowchart shown in FIG. First, in S11, the current time is read from the clock 4 and it is checked whether or not the calculated time has been reached (storage time determination means 15). If not, repeat the same process and wait until it reaches. When it has reached, in S12, the current operating heat (here, the heat generated by the motor) is input from the thermal event measuring means 16 and stored in tp (1) (latest thermal event data) of the thermal event table. (Thermal event data storage means 11). At this time, the calculation time may be stored. Next, in step S13, based on all past operating heat data stored in the thermal event table and its generation time (here, the calculation time at each time point), the current residual thermal displacement amount is calculated according to equation (8). That is, the correction coefficient H is calculated (remaining thermal displacement calculating means 12). Elapsed time coefficient f
In general, the elapsed time t in (t) can be obtained based on the equation “current time−past time”. Here, since thermal event data is stored for each calculation unit time dh, the equation It is determined by “(i−1) × dh”. Then, in S14, based on the obtained correction coefficient H,
After calculating the position correction values Xs, Ys, and Zs of each axis by the formulas (2) to (4), the position correction values Xs, Ys, and Zs are set to N in S15.
It is transmitted to the C control device 1 (numerical control correction means 13). Next, in S16, the next calculation time is obtained by adding the calculation unit time dh to the current calculation time, and is stored at a predetermined address in the memory. Thereafter, in S17, the oldest operating heat data is deleted, and the other data is sequentially transferred and stored so as to be shifted to an address corresponding to one calculation unit time dh older, and an area for storing the latest data is secured. I do. Then, the process returns to the first step S11 and the above processing is repeated.

According to the present embodiment, it is determined that a thermal event has occurred when operating heat is generated by driving the spindle motor, the table drive motor, or the like for a predetermined time or more, and the thermal event is determined according to the magnitude of the operating heat and the elapsed time. The remaining thermal displacement is calculated based on an arithmetic expression such as an elapsed time coefficient f (t). The elapsed time coefficient f (t) in the present embodiment is an experimental value as a step response of a thermal displacement amount when a unit heat value (a unit thermal event amount) continues for a calculation unit time dh, that is, a residual thermal displacement amount. Is required. Then, the operation heat, that is, the amount of generated heat is calculated from the drive current value of the spindle motor, the table drive motor, and the like, and the elapsed time is simply measured.
It can be calculated based on the elapsed time coefficient f (t). Therefore, with a compact device configuration, the amount of residual thermal displacement can be calculated easily and accurately with a simple calculation formula. This makes it possible to manufacture a thermal displacement correction device that can easily correct the processing dimension of a machine tool with respect to the thermal displacement, which has been difficult in the past, at a very low cost.

Next, a third embodiment will be described. This embodiment shows an example in which the amount of thermal displacement is corrected for a thermal event due to processing heat. In the case where the processing cycle time per workpiece is short and substantially the same processing is always repeated (for example, Automotive engine parts). In this case, the processing heat represents the cutting heat of the machine tool, for example, the processing heat generated at the cutting edge during the processing,
Heat input to the tool itself, heat input to part of the work,
Another part receives heat to the machine tool via the chips.
Therefore, this cutting heat is a factor that affects the thermal displacement of the machine tool.

FIG. 12 shows a hardware configuration of the present embodiment. The same components as those in FIG. 3 are denoted by the same reference numerals and description thereof will be omitted. As shown in the figure, assuming the processing heat of the machine tool as a thermal event, in the present embodiment, this processing heat,
It is determined based on a preset amount of processing heat generated at the time of processing per workpiece to be processed. The NC control device 1 stores machining calorie data for each workpiece type and transmits the machining calorie data to the controller 10 after the work machining is completed. The controller 10 stores the input processing calorie data for each work as a thermal event together with the occurrence time. Then, predetermined arithmetic processing described later is performed,
Each axis correction value is calculated based on the calculated residual thermal displacement, and N
Output to C control device 1.

FIG. 13 is a block diagram showing a functional configuration according to this embodiment, and each function will be described with reference to FIG. The thermal event measuring means 16 outputs a preset amount of processing heat for each work to the thermal event data storage means 11. FIG. 13 shows an example in which machining calorie data is input from the NC control device 1, but may be stored in advance in the thermal event measuring means 16 of the controller 1. As in the previous embodiment, when the storage command from the storage time determination unit 15 is input, the thermal event data storage unit 11 converts the processing calorie data from the thermal event measurement unit 16 into thermal event data at the current time. At a predetermined address of the target event table. Similar to the previous embodiment, the residual thermal displacement calculating means 12 calculates the residual thermal displacement based on the thermal event data (the amount of processing heat) stored in the thermal event table and the time of occurrence by the following equation (9). (Correction coefficient H) is calculated and obtained. Then, the residual thermal displacement data is output to the numerical control correcting means 13. Here, the elapsed time coefficient f (t)
Represents the amount of thermal displacement as a function of the elapsed time t when the unit cutting heat Q2 is continuously generated for the calculation unit time dh, as shown in FIG. 14, and is obtained experimentally. When the thermal time constant is short, the elapsed time coefficient f (t)
May be expressed by an exponential function (EXP function) as shown in the following Expression 10.

F (t) = EXP ｛-(time (1) -time
(i)) / ta｝ ta is a thermal time constant, which is experimentally obtained. Also, tim
e (i) represents each calculation time data, i is a calculation time parameter, time (1) represents the current time, and time (1)
i) represents the calculation time of (i-1) times before. heat
(I) represents the amount of heat generated (the amount of processing heat) at each calculation time.

Then, the present inventor performs a simulation, and when the elapsed time coefficient f (t) is an exponential function, the processing heat amount per processing cycle of the predetermined work is represented by the following equation (11). It has been confirmed that it can be represented by a simple formula.

[Equation 11] Processing heat amount = Amount of change over time due to continuous processing × Cycle time / Time constant Here, as shown in FIG. That is, the time constant ta is the time constant of the thermal displacement amount curve (substantially a first-order lag function) at this time. The cycle time is a machining repetition cycle time per piece when the workpiece is actually machined.

Note that other functional components are the same as those of the above-described embodiment, and thus description thereof will be omitted.

Next, the procedure of the correction calculation processing in this embodiment will be described with reference to the flowchart shown in FIG. First, in S21, processing of a work is started. next,
In S22, the current amount of processing heat is input from the thermal event measuring means 16 and stored in tp (1) (latest thermal event data) of the thermal event table (thermal event data storage means 11). At this time, the current calculation time read from the clock 4 may also be stored. Next, in S23, based on all past machining calorie data stored in the thermal event table and its generation time (here, the calculation time at each time point), the current residual thermal displacement amount is calculated according to Expression 9. That is, the correction coefficient H is calculated (the residual thermal displacement calculating means 1).
2). When the thermal time constant is short, the elapsed time coefficient f (t) may be calculated as an exponential function represented by Expression 10. Then, in S24, based on the obtained correction coefficient H, the position correction values Xs, Ys, Zs of the respective axes are calculated by Expressions 2 to 4.
, The position correction values Xs, Ys, Zs are obtained in S25.
Is transmitted to the NC control device 1 (the numerical control correction means 1).
3). Next, in S26, the oldest machining calorie data is deleted, and other data is sequentially stored in the address corresponding to the oldest time by one.
The data is transferred so as to be shifted one by one and stored, and an area for storing the latest data is secured. Then, returning to the first step S21, the above processing is repeated.

According to the present embodiment, it is determined that a thermal event has occurred when a predetermined amount or more of cutting heat (ie, processing heat) has been generated by processing a workpiece for a predetermined time or longer, and the magnitude of the processing heat and the elapsed time are determined. Is calculated based on an arithmetic expression such as an elapsed time coefficient f (t). The elapsed time coefficient f (t) is basically obtained experimentally as a step response of the thermal displacement amount when the unit processing heat (unit thermal event amount) continues for the calculation unit time dh, similarly to the previous embodiment. Although it is determined, when the thermal time constant is short, it may be approximately expressed by an exponential function.
Then, a work 1 set in advance for each work type
The residual heat displacement can be calculated on the basis of the elapsed time coefficient f (t) simply by reading the processing heat generated during the individual processing as the amount of generated heat and measuring the elapsed time. Therefore, with a compact device configuration, the amount of residual thermal displacement can be calculated easily and accurately with a simple calculation formula. In particular, the machining cycle time per work is short,
The calculation method according to the present embodiment is very effective when almost the same processing is repeated at all times. This makes it possible to manufacture a thermal displacement correction device that can easily correct the processing dimension of a machine tool with respect to the thermal displacement, which has been difficult in the past, at a very low cost.

As described above, according to the present invention, the amount of residual thermal displacement of a machine tool can be calculated by measuring the magnitude of a thermal event such as a change in room temperature, operating heat, and processing heat and the time of occurrence thereof. Processing dimensions can be corrected. Since the operating heat and the processing heat are generally known from experiments, actual measurements, and experiences, and need not be measured each time, the heat generated by the operating heat and the processing heat is obtained only by the clock function of the NC controller 1 or the controller 10. Displacement correction is possible. Also, in the case of thermal displacement correction due to a change in room temperature, only a temperature sensor may be added in terms of hardware. Therefore, the processing dimensions can be corrected with high accuracy without using a large-scale apparatus or increasing costs.

In the above-described embodiment, the case where the thermal events such as the change in room temperature, the operating heat, and the processing heat occur independently has been described. However, in practice, these thermal events occur in combination. In this case, the amount of residual thermal displacement due to each thermal event alone, that is, the correction coefficient H, is calculated, and the actual correction coefficient H is obtained by summing them, and the correction value of the processing dimension may be calculated based on the sum. . In the description so far, the numerical control correction means 13 is
Although the example provided in the above is shown, it may be provided in the NC control device 1. Further, the thermal event measuring means 16 may be provided in the NC control apparatus 1. For example, when the processing heat is a thermal event, the processing heat data stored in the NC control apparatus 1 is used for one workpiece. It may be transmitted to the controller 10 for each processing.

[Brief description of the drawings]

FIG. 1 shows a relationship between a thermal displacement amount and an elapsed time with respect to a thermal event according to the present invention.

FIG. 2 is an explanatory diagram of occurrence of a thermal event according to the present invention.

FIG. 3 is a block diagram illustrating a hardware configuration of the thermal displacement correction device according to the first embodiment.

FIG. 4 is a functional configuration block diagram of the thermal displacement correction device of the first embodiment.

FIG. 5 is an explanatory diagram of a thermal event table.

FIG. 6 is a flowchart of a correction calculation process according to the first embodiment.

FIG. 7 is a block diagram illustrating a hardware configuration of a thermal displacement correction device according to a second embodiment.

FIG. 8 is a functional configuration block diagram of a thermal displacement correction device according to a second embodiment.

FIG. 9 is an explanatory diagram of a relationship between a thermal event (operating heat) and a thermal displacement amount according to the second embodiment.

FIG. 10 is an explanatory diagram of a relationship between a heat value and a thermal event according to the second embodiment.

FIG. 11 is a flowchart of a correction calculation process according to the second embodiment.

FIG. 12 is a block diagram illustrating a hardware configuration of a thermal displacement correction device according to a third embodiment.

FIG. 13 is a functional configuration block diagram of a thermal displacement correction device according to a third embodiment.

FIG. 14 is an explanatory diagram of a relationship between a thermal event (cutting heat) and a thermal displacement amount according to the third embodiment.

FIG. 15 is an explanatory diagram of a relationship between a heat value and a thermal event according to the third embodiment.

FIG. 16 is a flowchart of a correction calculation process according to the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 NC controller 2 Machine tool 3 Room temperature sensor 4 Clock 10 Controller 11 Thermal event data storage means 12 Remaining thermal displacement calculation means 13 Numerical control correction means 14 Data storage address update means 15 Storage time determination means 16 Thermal event measurement means

Claims (4)

[Claims] An apparatus for calculating a thermal displacement of a machine tool, which calculates a displacement due to heat generation of a machine, wherein a thermal event measuring a thermal event such as a change in room temperature, an operating heat, and a working heat which affects the displacement of the machine. Event measurement means (1
6), a clock (4) for measuring the current time, and thermal event data storage means (11) for inputting measured thermal event size data and its occurrence time data and sequentially storing these data. The magnitude of the past thermal event stored in the thermal event data storage means (11) is determined by the elapsed time coefficient (f) which indicates the effect of the unit generated heat on the thermal displacement of the machine, which is obtained in advance by experiment or calculation. And a residual thermal displacement calculating means (12) for calculating a current residual thermal displacement based on the data and the time of occurrence thereof. 2. On the basis of a displacement amount due to heat generation of a machine,
A thermal displacement compensating device for a machine tool for compensating a processing dimension of a workpiece, wherein the thermal displacement computing device for a machine tool according to claim 1 and a residual thermal displacement calculated by the thermal displacement computing device, Numerical control correction means (1
3) A device for correcting thermal displacement of a machine tool, comprising: 3. A method for calculating a thermal displacement of a machine tool, which calculates a displacement due to heat generation of a machine, comprising: measuring a thermal event such as a change in room temperature, an operating heat, and a processing heat which affects the displacement of the machine; A step of sequentially storing the magnitude data of the thermal event and the time data of the occurrence thereof, and an elapsed time coefficient (f) indicating the effect of the unit generated heat on the thermal displacement of the machine, which is obtained in advance by experiment or calculation. Calculating a current residual thermal displacement amount based on the stored past thermal event size data and its occurrence time data. 4. On the basis of a displacement amount due to heat generation of a machine,
In the method of correcting thermal displacement of a machine tool, which corrects the processing dimensions of a workpiece, thermal events such as room temperature change, operating heat, and processing heat that affect the amount of machine displacement are measured, and the magnitude data and The step of sequentially storing the occurrence time data, and the magnitude of the stored past thermal event is determined by an elapsed time coefficient (f) indicating the effect of the unit generated heat on the thermal displacement of the machine, obtained in advance by experiment or calculation. And a numerical control correction step of correcting the work dimension of the work based on the calculated remaining thermal displacement based on the calculated remaining thermal displacement based on the calculated remaining thermal displacement. A method for correcting thermal displacement of a machine tool, characterized in that: