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

Abstract

The thermal displacement correction method includes the steps of: providing a correction ball (44) fixed to a table (18), a probe (28) for measuring the position of the correction ball (44), and thermometers (48a-48d); setting a fixed coefficient in which the value multiplied by the temperature change amount corresponds to the thermal displacement of the position of the correction ball (44), and a variation coefficient multiplied by the fixed coefficient for weighting; the position of the correction ball (44) and the amount of temperature change are measured multiple times simultaneously in one cycle of temperature change. Calculating a plurality of predicted thermal displacement amounts (Z) by multiplying the product of the measured temperature change amount and the fixed coefficient by a plurality of variation coefficients; determining one variation coefficient, among the plurality of predicted thermal displacement amounts (Z), which has the smallest difference from the variation amount of the position of the correction ball (44) in one cycle; thermal displacement correction is performed on the basis of a predicted thermal displacement amount (Z) calculated from the fixed coefficient, the temperature change amount, and the determined variation coefficient.

Description

Technical Field

[0001] This invention relates to a method and system for correcting thermal displacement of machine tools. Background Technology

[0002] In machine tools, thermal displacement occurs due to internal heat generated during operation, machining heat, and room temperature variations in the factory where the machine tool is located. This thermal displacement can affect the accuracy of the machined dimensions, so minimizing thermal displacement is preferable. Consequently, in recent years, machine tools equipped with thermal displacement correction systems have been widely introduced.

[0003] However, the external environment during machine tool manufacturing and the setup environment of the factory where the machine tool is used are often different. Sometimes, the thermal displacement correction system set during manufacturing cannot properly correct the thermal displacement. In such cases, the thermal displacement correction system must be re-set in the machine tool's setup environment, leading to reduced machine tool efficiency or increased operating time and costs. Furthermore, Patent Document 1 discloses a correction method for thermal displacement using machine tool temperature measured over 24 hours. Here, the correction value is determined by assuming that the thermal displacement is proportional to the machine tool temperature. However, the actual extent to which the thermal displacement is corrected is unclear.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5392540 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The purpose of this invention is to provide a thermal displacement correction method and system that can obtain the optimal correction parameters with high precision and ease in the thermal displacement correction of machine tools.

[0009] Solution for solving the problem

[0010] According to the present invention, a method for thermal displacement correction of a machine tool is provided. The machine tool is set in an environment where periodic temperature changes occur, and a spindle on which a cutting tool is mounted and a worktable on which a workpiece is placed move relative to each other, and the workpiece is machined by the cutting tool. The method is characterized by comprising the following steps: equipping a measuring reference fixed relative to the worktable, a position measuring mechanism disposed on the spindle of the machine tool and measuring the position of the measuring reference, and a thermometer mounted on the machine tool; setting a fixed coefficient, which is a constant and whose value multiplied by the temperature change is equivalent to the thermal displacement of the position of the measuring reference, and a variation coefficient, which is a variable multiplied by the fixed coefficient for weighting and varies within a specified range; in the aforementioned environment... In the environment, during one cycle of temperature change, the position of the measurement reference using the position measuring mechanism and the temperature change using the thermometer are measured simultaneously multiple times. Multiple predicted thermal displacements are calculated by multiplying the measured temperature change by the fixed coefficient by multiple variation coefficients. The difference between the predicted thermal displacements and the change in position of the measurement reference over one cycle is calculated, and the variation coefficient that minimizes this difference is determined. Finally, thermal displacement correction is performed on the workpiece during processing in the aforementioned environment based on the predicted thermal displacement calculated using the product of the fixed coefficient, the temperature change, and the determined variation coefficient.

[0011] Furthermore, according to the present invention, a thermal displacement correction system for a machine tool is provided. This machine tool is installed in an environment where periodic temperature changes occur, and a spindle on which a cutting tool is mounted and a worktable on which a workpiece is placed move relative to each other, allowing the workpiece to be machined by the cutting tool. The thermal displacement correction system is characterized by comprising: a measuring reference fixed relative to the worktable; a position measuring mechanism disposed on the spindle of the machine tool for measuring the position of the measuring reference; a thermometer mounted on the machine tool; and a control unit electrically connected to the position measuring mechanism and the thermometer, which operates the position measuring mechanism and the thermometer in the environment, configured to simultaneously measure the position of the measuring reference and the position of the thermometer multiple times during one cycle of temperature changes. The control unit stores a fixed coefficient, which is a preset constant multiplied by the temperature change, and the value is equivalent to the thermal displacement of the position of the measurement reference. It also stores a variable, which is a preset variable multiplied by the fixed coefficient for weighting and varies within a specified range. Multiple predicted thermal displacements are calculated by multiplying the measured temperature change and the fixed coefficient by the multiple variable coefficients. The difference between the predicted thermal displacements and the change in position of the measurement reference over one cycle is calculated, and the variable coefficient that minimizes this difference is determined. Finally, thermal displacement correction is performed on the workpiece in the aforementioned environment based on the predicted thermal displacement calculated using the product of the fixed coefficient, the temperature change, and the determined variable coefficient.

[0012] The effects of the invention

[0013] According to the thermal displacement correction method and system of the present invention, the machine tool includes a measurement reference fixed relative to the worktable, a position measuring mechanism disposed on the spindle of the machine tool to measure the position of the measurement reference, and a thermometer mounted on the machine tool. Therefore, in an environment where temperature changes periodically, it is possible to simultaneously measure the position of the measurement reference using the position measuring mechanism and the temperature change using the thermometer multiple times during one cycle of temperature change. This allows for understanding the relationship between the temperature change in the actual operating environment of the machine tool and the change in the position of the measurement reference. Consequently, a variation coefficient reflecting the influence of the operating environment can be determined.

[0014] Furthermore, according to the thermal displacement correction method and system of the present invention, multiple predicted thermal displacements can be calculated by multiplying the measured temperature change by a fixed coefficient by a plurality of weighting coefficients, and the difference between these predicted thermal displacements and the change in position of the measured reference over one cycle can be calculated. The coefficient of variation that minimizes this difference is then determined. Therefore, by correcting the change in thermal displacement based on the predicted thermal displacement calculated according to the determined coefficient of variation, the change caused by thermal displacement can be minimized, enabling optimal thermal displacement correction. Moreover, since the coefficient of variation can be determined by comparing the change in position of the measured reference with the temperature change, the user can easily and accurately determine the coefficient of variation for thermal displacement correction without relying on repeated experiments or empirical rules. Attached Figure Description

[0015] Figure 1 This is a side view of a machine tool equipped with a thermal displacement correction system according to this embodiment.

[0016] Figure 2 This indicates a display example of the display involved in this embodiment.

[0017] Figure 3 This is a side view of the machine tool involved in a variation of this embodiment. Detailed Implementation

[0018] The thermal displacement correction system for a machine tool according to the embodiments will be described below with reference to the accompanying drawings. The same or corresponding elements are labeled with the same reference numerals, and repeated descriptions are omitted. To facilitate understanding, the scale of the drawings may sometimes be changed for illustration.

[0019] Figure 1 This is a perspective view of a machine tool 12 equipped with a thermal displacement correction system 10 according to this embodiment. The machine tool 12 includes a bed 14 that serves as a base and a column 16 erected on the upper surface of the bed 14. A worktable 18 for arranging and fixing a workpiece (not shown) as the workpiece to be processed is disposed on the upper surface of the bed 14.

[0020] A saddle 20 is disposed on the front surface of the column 16, and a Z-slider 22 is disposed on the front surface of the saddle 20. Furthermore, a spindle head 24 is disposed below the Z-slider 22, and a spindle 26 is mounted on the end side of the spindle head 24 (here, the lower side), configured to rotate relative to the spindle head 24 about an axis parallel to the Z-axis. The spindle 26 is configured to allow attachment and removal of a tool (not shown) for machining the workpiece while rotating with it.

[0021] Here, a probe 28, serving as a position measuring mechanism, is mounted on the end side of the main shaft 26. A contact portion 28a, capable of detecting contact with the object being measured, is disposed at the end of the probe 28. By obtaining the positions of the X-axis, Y-axis, and Z-axis when contact is detected, the position of the object being measured can be detected.

[0022] The machine tool 12 described in this embodiment is configured to change the relative position of the cutting tool with respect to the workpiece being machined. Machine tool coordinates, with a predetermined position as the origin, are pre-set on the machine tool 12, and these coordinates are mutually orthogonal linear axes, including the X-axis, Y-axis, and Z-axis.

[0023] The machine tool 12 described in this embodiment is vertical, with the Z-axis extending vertically. The X-axis and Y-axis are set on a plane perpendicular to the Z-axis, which is, in this case, a horizontal plane. In the machine tool 12 described in this embodiment, the worktable 18 is configured to move along the Y-axis direction (machine tool front-to-back direction). Furthermore, the saddle 20 is configured to move along the X-axis direction (machine tool left-to-right direction). Moreover, the Z-slider 22 is configured to move along the Z-axis direction (machine tool up-and-down direction). Thus, the machine tool 12 is configured to allow relative movement between the spindle 26 (for mounting tools, not shown) and the worktable 18 (for the workpiece, not shown) along the X, Y, and Z axes.

[0024] Machine tool 12 has a pair of X-axis guideways 30a and 30b formed on the front surface of column 16 to enable relative movement of the tool and workpiece along the X-axis direction. A saddle 20 is mounted on the X-axis guideways 30a and 30b and configured to reciprocate along the X-axis direction. Furthermore, machine tool 12 has an X-axis motor 32 that moves the saddle 20 via a ball screw mechanism or the like. Therefore, spindle 26 can move together with the saddle 20 along the X-axis direction.

[0025] The machine tool 12 has a pair of Y-axis guideways 34a and 34b disposed on the upper surface of the bed 14 for relative movement of the tool and the workpiece along the Y-axis direction. The worktable 18 is supported by the Y-axis guideways 34a and 34b via guide blocks 36 and is configured to reciprocate along the Y-axis direction. In addition, the machine tool 12 has a Y-axis motor 38 for moving the worktable 18 along the Y-axis guideways 34a and 34b.

[0026] Machine tool 12 has a pair of Z-axis guideways 40a and 40b formed on the front surface of the saddle 20 to enable relative movement of the tool and workpiece along the Z-axis direction. A Z-slider 22 is mounted on the Z-axis guideways 40a and 40b and configured to reciprocate along the Z-axis direction. Furthermore, machine tool 12 has a Z-axis motor 42 for moving the Z-slider 22 via a ball screw mechanism or the like. Therefore, the tool and spindle 26 can move together with the spindle head 24 along the Z-axis direction. Moreover, inside the spindle head 24, a drive motor (not shown) is arranged for rotating the spindle 26 about an axis along the Z-axis direction.

[0027] A calibration ball 44 with a known radius is fixed on the upper surface of the worktable 18 as a measurement reference. The thermal displacement correction system 10 has a control unit 46 that operates the machine tool 12 and moves the spindle 26 and the worktable 18 relative to each other. The control unit 46 operates the machine tool 12, causing the probe 28 to move from the reference position toward the calibration ball 44 on the worktable 18, so that the contact portion 28a of the probe 28 contacts the calibration ball 44 from multiple directions. The position of the calibration ball 44 relative to the reference position can be determined based on the position of the X-axis, Y-axis, and Z-axis at the time of contact. In addition, the following description describes the case where the calibration ball 44 is used as a measurement reference, but it is not limited to this. Workpieces with known dimensions, ring gauges with known inner diameter, outer diameter, and height, and cylindrical objects with known radius and height can also be used as measurement references.

[0028] The machine tool 12 is equipped with multiple thermometers, specifically four thermometers: 48a, 48b, 48c, and 48d. Specifically, thermometer 48a is located inside the column 16, and thermometer 48b is located inside the saddle 20. Additionally, thermometer 48c is located inside the spindle head 24, and thermometer 48d is located inside the bed 14.

[0029] Four thermometers 48a, 48b, 48c, and 48d are electrically connected to the control unit 46 of the thermal displacement correction system 10, configured to store the measured temperature data in the storage unit 50 of the thermal displacement correction system 10. Furthermore, the control unit 46 is electrically connected to the probe 28. Therefore, it is configured to record the position data of the calibration ball 44 measured by the probe 28 in the storage unit 50.

[0030] Furthermore, the storage unit 50 of the control unit 46 is configured to pre-record fixed coefficients Za, Zb, Zc, Zd and variable coefficients A, B, C, D set by the user. The fixed coefficients Za, Zb, Zc, Zd are constants determined based on the shape of the machine tool 12 or the coefficient of linear expansion of the components constituting the machine tool. They are constants (coefficients) where the value obtained by multiplying by the temperature change is equivalent to the change in position of the correction ball 44 caused by thermal displacement, i.e., the change in position of the correction ball 44 is set as a function of the temperature change. The fixed coefficients are defined as axial components in the X-axis, Y-axis, and Z-axis directions. Figure 1 The fixed coefficients Za, Zb, Zc, and Zd shown represent the components along the Z-axis, i.e., the axis of the main spindle 26. Here, the fixed coefficients Za, Zb, Zc, and Zd are defined by decomposing each influencing factor for the amount of variation. Specifically, they are defined as follows: Za corresponds to the variation caused by thermal displacement (i.e., thermal expansion and contraction) of the column 16; Zb corresponds to the variation caused by thermal expansion and contraction of the main spindle 26; Zc corresponds to the variation caused by thermal expansion and contraction of the worktable 18; and Zd corresponds to the variation caused by thermal expansion and contraction of the bed 14. Therefore, the variation in the position of the correction ball 44 caused by thermal displacement, i.e., the predicted thermal displacement Z, is calculated by adding together the values ​​obtained by multiplying each of these four fixed coefficients Za, Zb, Zc, and Zd by the temperature change.

[0031] Furthermore, the influence of these four fixed coefficients Za, Zb, Zc, and Zd on the predicted thermal displacement Z varies depending on the machine tool 12's installation environment or usage conditions. Therefore, they are defined by weighting and summing them together. Specifically, the product of the four fixed coefficients Za, Zb, Zc, and Zd with the temperature change is multiplied by the four weighting coefficients A, B, C, and D, and the resulting values ​​are summed to calculate the predicted thermal displacement Z. Thus, as... Figure 1 As shown, the predicted thermal displacement Z in the Z-axis direction can be calculated using the following formula.

[0032] Z=Za×A+Zb×B+Zc×C+Zd×D (1)

[0033] Furthermore, in equation (1), for convenience, fixed coefficients Za, Zb, Zc, and Zd are shown as values ​​that are converted into the amount of position change of the correction ball 44 by multiplying by the temperature change. The four variation coefficients A, B, C, and D are variables that vary within a specified range. Multiple values ​​for each of the variation coefficients A, B, C, and D are preset and recorded in the storage unit 50.

[0034] In the following explanation, as a representative example, the predicted thermal displacement Z in the Z-axis direction will be explained. However, the predicted thermal displacement X in the X-axis direction and the predicted thermal displacement Y in the Y-axis direction can also be processed in the same way as the predicted thermal displacement Z in the Z-axis direction and can be calculated by the following formula.

[0035] X=Xa×E+Xb×F+Xc×G+Xd×H (2)

[0036] Y=Ya×I+Yb×J+Yc×K+Yd×L (3)

[0037] Here, the fixed coefficients Xa, Xb, Xc, Xd and Ya, Yb, Yc, Yd are fixed coefficients corresponding to the changes in the X-axis and Y-axis directions caused by thermal expansion and contraction of the column 16, spindle 26, worktable 18 and bed 14. The variation coefficients E, F, G, H and I, J, K, L are variation coefficients corresponding to the fixed coefficients Xa, Xb, Xc, Xd and Ya, Yb, Yc, Yd respectively. In addition, similar to equation (1), for equations (2) and (3), for convenience, the fixed coefficients Xa, Xb, Xc, Xd and Ya, Yb, Yc, Yd are shown as values ​​converted by multiplying by the temperature change to correspond to the changes in the position of the correction ball 44.

[0038] like Figure 1 as well as Figure 2 As shown, the thermal displacement correction system 10 includes a display 52 that is electrically connected to the control unit 46 and the storage unit 50. Figure 2 This illustrates a display example of display 52. ​​Display 52 shows the time-varying temperature changes (sequence) at temperature measurement positions A-01, A-02, and A-03 of the machine tool 12. Here, the position and temperature of the calibration ball 44 are measured over several days, with one cycle set to 24 hours. Setting one cycle to 24 hours is to appropriately account for the influence of external environmental changes, such as diurnal temperature variations, on thermal displacement. By performing measurements over multiple consecutive cycles (several days), the reliability of the measurement data can be improved.

[0039] In addition, Figure 2The display 52 shows the variation ED1 of the position of the calibration ball 44 measured by the probe 28 over one cycle, and a histogram CP1 showing the X-axis, Y-axis, and Z-axis components of the variation ED1. For easy visual identification, the displacement ED1 in the display 52 is not a numerical value, but is displayed as a circle with a radius equivalent to the displacement ED1 on the image of the measuring mechanism. Furthermore, the display 52 shows the corrected variation ED2 obtained by correcting the displacement ED1 using one of the multiple sets of variation coefficients A to L recorded in the storage unit 50, and a histogram CP2 showing the X-axis, Y-axis, and Z-axis components of the corrected variation ED2. The corrected variation ED2 is calculated by subtracting this predicted thermal displacement Z from the product of one of the multiple sets of variation coefficients A, B, C, and D pre-set and recorded in the storage unit 50, fixed coefficients Xa to Xd, Ya to Yd, Za to Zd, and the measured temperature change. To facilitate visual identification, the corrected variation ED2 on the display 52 is not a numerical value, but is displayed on the image of the measuring mechanism as a circle with a radius equivalent to the corrected variation ED2. Therefore, based on the variation ED1 and the corrected variation ED2 displayed on the display 52, the user can easily determine the optimal set of variation coefficients A to L for thermal displacement correction from a set of multiple variation coefficients A to L.

[0040] Next, the thermal displacement correction method and the function and effect of the thermal displacement correction system 10 will be explained by describing the thermal displacement correction using the thermal displacement correction system 10 in this embodiment.

[0041] According to the thermal displacement correction system 10 of this embodiment, in the setting environment of the machine tool 12, during a period of 24 hours defined as one cycle, at multiple time points selected by the user so that the effect of temperature changes can be understood, the position of the correction ball 44 using the probe 28 and the amount of temperature change using thermometers 48a, 48b, 48c, and 48d can be measured simultaneously.

[0042] In addition, by multiplying the measured temperature change by the fixed coefficients Za, Zb, Zc, and Zd by a set of multiple variation coefficients A, B, C, and D, multiple predicted thermal displacements Z are calculated. The difference between the multiple predicted thermal displacements Z and the change in position of the measured calibration ball 44 over one period is calculated, and a set of variation coefficients A, B, C, and D with the smallest difference can be determined.

[0043] Furthermore, the thermal displacement correction during the processing of the workpiece (illustration omitted) in the set environment can be performed based on the predicted thermal displacement Z calculated by multiplying the fixed coefficients Za, Zb, Zc, Zd, the temperature change, and the determined set of one variable coefficients A, B, C, D.

[0044] According to the thermal displacement correction method and thermal displacement correction system 10 of this embodiment, the machine tool 12 includes: a correction ball 44 fixed relative to the worktable 18; a probe 28 arranged along the axis of the spindle 26 of the machine tool 12 and used to measure the position of the correction ball 44; and thermometers 48a, 48b, 48c, and 48d mounted on the machine tool 12. Therefore, in an environment where temperature changes periodically, the position of the correction ball 44 measured by the probe 28 and the temperature change measured by the thermometers 48a, 48b, 48c, and 48d can be measured simultaneously multiple times within a 24-hour period of temperature change. This allows for the understanding of the relationship between the temperature change in the actual operating environment of the machine tool 12 and the position change of the correction ball 44. Consequently, a set of variation coefficients A, B, C, and D reflecting the influence of the operating environment can be determined.

[0045] Furthermore, according to the thermal displacement correction method and thermal displacement correction system 10 of this embodiment, the measured temperature change and the fixed coefficients Za, Zb, Zc, Zd are multiplied by a set of multiple variation coefficients A, B, C, D used for weighting, respectively, to calculate multiple predicted thermal displacement amounts Z. The difference between these values ​​and the measured change in the position of the correction ball 44 over one cycle is calculated, and a set of variation coefficients A, B, C, D that minimizes this difference can be determined. Therefore, by correcting the variation based on the predicted thermal displacement amount Z calculated from the determined set of variation coefficients A, B, C, D, the variation caused by thermal displacement can be minimized, and optimal thermal displacement correction can be performed. Furthermore, by comparing the measured change in the position of the correction ball 44 with the temperature change, the variation coefficients A, B, C, D can be determined. Therefore, the user can easily and accurately determine a set of variation coefficients A, B, C, D for thermal displacement correction without relying on repeated experiments or empirical rules.

[0046] Furthermore, according to the thermal displacement correction method and thermal displacement correction system 10 involved in this embodiment, thermometers 48a, 48b, 48c, and 48d are installed at multiple locations on the machine tool 12. Therefore, temperature changes can be measured at locations close to areas prone to thermal displacement, such as the column 16, saddle 20, spindle head 24, and bed 14, allowing for high-precision understanding of the correlation between temperature changes and variations. Consequently, a set of variation coefficients A, B, C, and D optimal for thermal displacement correction can be obtained with high precision.

[0047] Furthermore, according to the thermal displacement correction method and thermal displacement correction system 10 of this embodiment, the position of the known-sized correction ball 44 fixed to the worktable 18 can be measured using the probe 28 mounted on the spindle 26. Therefore, the position of the correction ball 44 can be measured with high precision, and the influence of the position measurement of the correction ball 44 on the thermal displacement of the machine tool 12 can be accurately determined. Thus, a set of variation coefficients A, B, C, and D optimal for thermal displacement correction can be obtained with high precision.

[0048] Furthermore, according to the thermal displacement correction method and thermal displacement correction system 10 involved in this embodiment, one measurement cycle is 24 hours, and the measurement of the position of the correction ball 44 and the amount of temperature change is performed for one or more cycles. Therefore, the influence of temperature fluctuations on a 24-hour basis can be taken into account, and the correlation between the amount of temperature change and the fluctuation can be accurately grasped. As a result, a set of variation coefficients A, B, C, and D that are optimal for thermal displacement correction can be obtained with high accuracy.

[0049] Furthermore, according to the thermal displacement correction method and thermal displacement correction system 10 of this embodiment, the machine tool 12 includes a storage unit 50 for storing data of fixed coefficients Za, Zb, Zc, Zd and a set of multiple variable coefficients A, B, C, D. Additionally, a display 52 electrically connected to the storage unit 50 is provided, which displays: the variation in the position of the measured correction ball 44 over one period (24 hours); and the corrected variation when the variation is corrected based on a predicted thermal displacement Z calculated using a set of variable coefficients A, B, C, D selected from the sets of multiple variable coefficients A, B, C, D. Therefore, the user can determine a set of variable coefficients A, B, C, D from the sets of multiple variable coefficients A, B, C, D based on the variation ED1 and the corrected variation ED2 displayed on the display 52. ​​Thus, the optimal set of variable coefficients A, B, C, D for thermal displacement correction can be easily obtained.

[0050] As explained above, the thermal displacement correction system 10 of this embodiment can obtain the optimal variation coefficients A, B, C, and D with high precision and ease in the thermal displacement correction of the machine tool 12.

[0051] (Modified Example)

[0052] Hereinafter, a modified example of the thermal displacement correction system 10 according to this embodiment will be described. Reference numerals that are the same as or correspond to those in this embodiment will not be repeated.

[0053] like Figure 3As shown, according to the thermal displacement correction system 70 involved in the modified example, the machine tool 72 is horizontal, and the axial direction (Z-axis direction) of the spindle 26 extends along the front-to-back direction of the machine tool, with the vertical direction being the Y-axis direction. Therefore, the X-axis and Z-axis are set on a plane perpendicular to the Y-axis, which in this case is a horizontal plane.

[0054] A pair of Y-axis guideways 74a and 74b are formed on the front surface of the column 16, and a slider 76 is slidably mounted on the Y-axis guideways 74a and 74b along the Y-axis direction. Furthermore, the machine tool 72 has a Y-axis motor 78 for moving the slider 76 along the Y-axis direction via a ball screw mechanism or the like. The column 16 is configured to slide along the X-axis direction via an X-axis motor (not shown). Therefore, the slider 76 is configured to slide along both the Y-axis (vertical direction) and the X-axis (machine tool left-right direction). Consequently, the spindle head 24 and the spindle 26, whose axes extend along the Y-axis direction, are configured to slide along both the Y-axis (vertical direction) and the X-axis (machine tool left-right direction) in response to the sliding of the slider 76.

[0055] The machine tool 72 has a pair of Z-axis guideways 80a and 80b disposed on the upper surface of the bed 14 for relative movement of the tool and the workpiece along the Z-axis direction. The worktable 18 is supported by the Z-axis guideways 80a and 80b via guide blocks 36 and is configured to perform reciprocating movement along the Z-axis direction. In addition, the machine tool 72 has a Z-axis motor 82 for moving the worktable 18 along the Z-axis guideways 80a and 80b.

[0056] An angle plate 84 is erected on the upper surface of the worktable 18, and a calibration ball 44 is fixed on the side of the angle plate 84 facing the spindle 26 along the Z-axis. The calibration ball 44 is fixed on the side facing the probe 28.

[0057] Multiple thermometers, specifically three thermometers 86a, 86b, and 86c, are installed inside the machine tool 72. The first thermometer 86a is installed inside the bed 14, and the second thermometer 86b is installed inside the column 16. Additionally, the third thermometer 86c is installed inside the spindle head 24. These three thermometers 86a, 86b, and 86c are electrically connected to the control unit 46 of the thermal displacement correction system 10, and are configured to record the measured temperature data into the storage unit 50 of the thermal displacement correction system 10.

[0058] According to the thermal displacement correction method and thermal displacement correction system 70 of this embodiment, the measured temperature change and the fixed coefficients Za, Zb, Zc, Zd are multiplied by a set of multiple variation coefficients A, B, C, D used for weighting, respectively, to calculate multiple predicted thermal displacement amounts Z. The difference between these predicted thermal displacement amounts and the measured change in position of the correction ball 44 over one period is calculated, and the set of variation coefficients A, B, C, D with the smallest difference can be determined. Therefore, by correcting the variation based on the predicted thermal displacement amount Z calculated according to the determined set of variation coefficients A, B, C, D, the variation caused by thermal displacement can be minimized, and optimal thermal displacement correction can be performed. Furthermore, by comparing the measured change in position of the correction ball 44 with the temperature change, a set of variation coefficients A, B, C, D can be determined. Therefore, the user can easily and accurately determine the set of variation coefficients A, B, C, D for thermal displacement correction without relying on repeated experiments or empirical rules.

[0059] The embodiments of the thermal displacement correction systems 10 and 70 for machine tools 12 and 72 have been described above, but the present invention is not limited to the embodiments described above. Various modifications of the above embodiments are included in the embodiments of the present invention within the scope that can be conceived by those skilled in the art.

[0060] Explanation of reference numerals in the attached figures

[0061] 10 Thermal displacement correction system

[0062] 12 machine tools

[0063] 18 workbenches

[0064] 26 spindles

[0065] 28 probes (position determination mechanism)

[0066] 44. Calibration ball (measurement standard)

[0067] 46 Control Department

[0068] 48a First Thermometer

[0069] 48b Second Thermometer

[0070] 48c third thermometer

[0071] 48d fourth thermometer

[0072] 50 storage units

[0073] 52 monitors

[0074] 70 Thermal Displacement Correction System

[0075] 72 machine tool

[0076] 86a First Thermometer

[0077] 86b No. 2 thermometer

[0078] 86c No. 3 thermometer

[0079] A~D variation coefficient

[0080] E~H variation coefficient

[0081] I~L variation coefficient

[0082] ED1 change

[0083] ED2 Correction Change

[0084] Xa~Xd fixed coefficients

[0085] Ya~Yd fixed coefficient

[0086] Za~Zd fixed coefficient

[0087] Z Predicted thermal displacement

Claims

1. A method for thermal displacement correction of a machine tool, wherein the machine tool is set in an environment where periodic temperature changes occur, and a spindle on which a cutting tool is mounted and a worktable on which a workpiece is placed move relative to each other, and the workpiece is machined by the cutting tool, characterized in that, The above-mentioned thermal displacement correction method includes the following steps: The machine tool is equipped with a measuring reference fixed relative to the worktable, a position measuring mechanism disposed on the spindle of the machine tool and measuring the position of the measuring reference, and a thermometer installed on the machine tool. A fixed coefficient is set as a constant and its value after multiplying by the temperature change is equivalent to the thermal displacement of the position of the above-mentioned measurement reference, and a variation coefficient is set as a variable multiplied by the above-mentioned fixed coefficient for weighting and varies within a specified range. In the above-described environment, during one cycle of temperature change, the position of the measurement reference using the position measuring mechanism and the temperature change using the thermometer are measured simultaneously multiple times. Multiple predicted thermal displacements are calculated by multiplying the measured temperature change by the fixed coefficient by multiple variation coefficients. For each of the aforementioned predicted thermal displacements, the difference between its variation and the measured position of the aforementioned measurement reference over one cycle is calculated, and the variation coefficient is determined when this difference is minimized; and Based on the predicted thermal displacement calculated by multiplying the fixed coefficient, the temperature change, and the determined variation coefficient, thermal displacement correction is performed on the workpiece during processing in the aforementioned environment.

2. The thermal displacement correction method as described in claim 1, characterized in that, It also includes the step of installing multiple of the above-mentioned thermometers at multiple locations on the above-mentioned machine tool.

3. The thermal displacement correction method as described in claim 2, characterized in that, The aforementioned measurement reference is composed of any one of the following: the surface of the workpiece, the upper surface and inner circumference of an object with a ring shape, the surface of a spherical object, or the upper surface and outer circumference of a cylindrical object. The aforementioned position measuring mechanism is a probe held on the aforementioned main shaft.

4. The thermal displacement correction method as described in claim 3, characterized in that, One cycle is 24 hours, and the location of the measurement reference and the measurement of the temperature change are carried out in one or more cycles.

5. The thermal displacement correction method according to any one of claims 1 to 4, characterized in that, It also includes the following steps: The aforementioned machine tool is equipped with a storage unit for storing data of the aforementioned fixed coefficients and multiple of the aforementioned variable coefficients; The display connected to the storage unit shows: the change in the position of the measurement reference for one cycle; and the corrected change when the change is corrected based on the predicted thermal displacement calculated using one of the multiple change coefficients. as well as The user determines one of the aforementioned variation coefficients from among the plurality of aforementioned variation coefficients based on the displayed variation amount and the aforementioned corrected variation amount.

6. A thermal displacement correction system for a machine tool, wherein the machine tool is set in an environment where periodic temperature changes occur, causing a spindle on which a cutting tool is mounted and a worktable on which a workpiece is placed to move relative to each other, and the workpiece is machined by the cutting tool, characterized in that, The above-mentioned thermal displacement correction system has the following features: The measurement reference is fixed relative to the aforementioned worktable; A position measuring mechanism is disposed on the spindle of the machine tool to measure the position of the measuring reference. A thermometer, which is installed on the aforementioned machine tool; as well as The control unit is electrically connected to the position measuring mechanism and the thermometer, and operates the position measuring mechanism and the thermometer in the aforementioned environment. It is configured to simultaneously measure the position of the measuring reference and the amount of temperature change using the thermometer multiple times during one cycle of temperature change. The aforementioned control unit The storage includes a fixed coefficient that is a pre-set constant multiplied by the aforementioned temperature change and corresponds to the thermal displacement of the aforementioned measurement reference position, and a variable coefficient that is a pre-set variable multiplied by the aforementioned fixed coefficient for weighting and varies within a specified range. Multiple predicted thermal displacements are calculated by multiplying the measured temperature change by the fixed coefficient by multiple variation coefficients. For each of the above-mentioned predicted thermal displacements, the difference between the variation of the position of the above-mentioned measurement reference over one cycle is calculated, and the variation coefficient is determined when the difference is minimized. as well as Based on the predicted thermal displacement calculated by multiplying the fixed coefficient, the temperature change, and the determined variation coefficient, thermal displacement correction is performed on the workpiece during processing in the aforementioned environment.

7. The thermal displacement correction system as described in claim 6, characterized in that, The aforementioned thermometers are installed in multiple locations on the aforementioned machine tool.

8. The thermal displacement correction system as described in claim 7, characterized in that, The aforementioned measurement reference is composed of any one of the following: the surface of the workpiece, the upper surface and inner circumference of an object with a ring shape, the surface of a spherical object, or the upper surface and outer circumference of a cylindrical object. The aforementioned position measuring mechanism is a probe held on the aforementioned main shaft.

9. The thermal displacement correction system as described in claim 8, characterized in that, One cycle is 24 hours, and the location of the measurement reference and the measurement of the temperature change are carried out in one or more cycles.

10. The thermal displacement correction system according to any one of claims 6 to 9, characterized in that, The above-mentioned machine tools have: A storage unit for storing data of the aforementioned fixed coefficients and multiple of the aforementioned variable coefficients; and A display electrically connected to the aforementioned storage unit displays: the amount of variation of the measured reference position over one cycle; and the corrected amount of variation when the amount of variation is corrected based on the predicted thermal displacement calculated using one of the plurality of variation coefficients. Users can determine one of the above-mentioned variation coefficients from among the multiple variation coefficients based on the displayed variation amount and the above-mentioned corrected variation amount.

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