Compensation amount calculation device and compensation amount calculation method for thermal displacement of ball screw
Patent Information
- Application Number
- PCT/JP2025/015254
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-04-18
- Publication Date
- 2026-10-22
Smart Images
Figure JP2025015254_22102026_PF_FP_ABST
Abstract
Description
Device and method for calculating correction amount for thermal displacement of a ball screw
[0001] This disclosure relates to a device and method for calculating a correction amount for the thermal displacement of a ball screw, and more particularly to a device and method for calculating a correction amount for calculating a correction amount for the thermal displacement of a ball screw using a thermal displacement estimation formula for estimating the thermal displacement of a ball screw of a machine tool.
[0002] Techniques for determining thermal displacement in machine tools based on temperature information are described, for example, in Patent Documents 1 and 2. Patent Document 1 describes a thermal displacement correction device that can correct machining errors due to thermal displacement with high precision. Specifically, Patent Document 1 describes a thermal displacement correction device that detects the temperature change of the machine body affected by a heat source using a temperature sensor, calculates a calculated temperature change using the detected temperature change based on a differential equation that calculates a calculated temperature change that behaves approximately the same as the thermal behavior of the thermal displacement of the machine tool, and corrects machining errors based on the thermal displacement that changes in response to this calculated temperature change.
[0003] Patent Document 2 describes a machine tool that allows for relatively easy estimation of the thermal displacement of a support base, even when the temperature distribution of the support base supporting a bearing is complex. Specifically, Patent Document 2 describes a grinding machine comprising a grinding wheel base body that supports a rotating shaft member connected to a grinding wheel, an X-axis screw shaft and an X-axis nut member, and a connecting member that connects the grinding wheel base body 1 and the X-axis nut member, wherein the grinding wheel base connection portion of the connecting member that connects to the grinding wheel base body and the nut connection portion of the connecting member that connects to the X-axis nut member are located at different positions in the direction of the axis L1 of the X-axis screw shaft, the grinding wheel base connection portion is arranged so as to overlap with the position of the axis L2 of the rotating shaft member on axis L1 in a direction perpendicular to the direction of axis L1, and the connecting member is formed so that the direction of thermal displacement is along the direction of axis L1. Furthermore, Patent Document 2 describes a control device for a machine tool that includes a thermal displacement estimation unit that estimates the amount of thermal displacement in the axial direction of the screw shaft in the connecting member based on the detection result of a temperature sensor, and a movement amount correction unit that corrects the amount of movement of the nut member from the estimation result of the thermal displacement estimation unit.
[0004] JP 9-108992 A JP 2017-19022 A
[0005] In a machine tool, when the thermal displacement of a ball screw is estimated from temperature information, the estimation accuracy may decrease due to the influence of the thermal response characteristic of the ball screw with respect to ambient temperature changes.
[0006] Accordingly, there is a demand for a ball screw thermal displacement correction amount calculation device and a correction amount calculation method that can calculate the thermal displacement of the ball screw in consideration of the thermal response characteristic of the ball screw with respect to ambient temperature changes.
[0007] A representative first aspect of the present disclosure is a correction amount calculation device that calculates a thermal displacement correction amount for a ball screw of a machine tool using a thermal displacement estimation formula for estimating the thermal displacement of the ball screw, the correction amount calculation device comprising: a feed shaft operation information acquisition unit that acquires, from the machine tool, feed shaft operation information related to operation of a feed shaft including the ball screw; a temperature information acquisition unit that acquires, from the machine tool, temperature information related to the ball screw; a first variable determination unit that determines, based on the feed shaft operation information, a first variable included in the thermal displacement estimation formula and representing a thermal response characteristic of the ball screw that is not related to a change in ambient temperature of the ball screw; a second variable determination unit that determines, based on the feed shaft operation information, a second variable included in the thermal displacement estimation formula and representing a thermal response characteristic of the ball screw that is related to a change in ambient temperature of the ball screw; and a correction amount calculation unit that calculates the thermal displacement correction amount of the ball screw from the thermal displacement estimation formula, based on the feed shaft operation information, the temperature information, the first variable, and the second variable.
[0008] A typical second aspect of this disclosure is a method for calculating a correction amount, wherein the computer performs the following steps: acquiring feed axis operation information relating to the feed axis operation of a feed axis including a ball screw of the machine tool from the machine tool; acquiring temperature information relating to the ball screw from the machine tool; determining a first variable representing the thermal response characteristics of the ball screw that are independent of changes in ambient temperature, which is included in a thermal displacement estimation formula for estimating the thermal displacement of the ball screw based on the feed axis operation information; determining a second variable representing the thermal response characteristics of the ball screw that are related to changes in ambient temperature, which is included in the thermal displacement estimation formula, based on the feed axis operation information; and calculating a thermal displacement correction amount for the ball screw from the thermal displacement estimation formula based on the feed axis operation information, the temperature information, the first variable, and the second variable.
[0009] This is a block diagram of a ball screw thermal displacement correction amount calculation device according to the first embodiment of this disclosure. This is a block diagram of an example of the configuration of a machine tool feed axis. This is a block diagram of a partial configuration of a modified correction amount calculation device during machine learning. This is a block diagram of a partial configuration of a modified correction amount calculation device after machine learning. This is a flowchart of an example of the correction amount calculation method of the first embodiment. This is a block diagram of a ball screw thermal displacement correction amount calculation device according to the second embodiment of this disclosure. This is a diagram showing each section into which the movement range of the ball screw feed axis is divided. This is a diagram showing the correction amount for each section obtained by the section-by-section correction amount calculation unit and the sum of the correction amounts obtained by the correction amount calculation unit. This is a block diagram of a ball screw thermal displacement correction amount calculation device according to the third embodiment of this disclosure. This is a diagram showing a table that shows feed axis discrimination information and table position, and a combination of coefficients and time delays.
[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings.
[0011] (First Embodiment) Figure 1 is a block diagram showing a ball screw thermal displacement correction amount calculation device according to the first embodiment of the present disclosure. The correction amount calculation device 10 is connected to a machine tool 20. The machine tool 20 includes a control target 21 including a feed axis including a ball screw, and a control device 22 that controls the operation of the feed axis. The control device 22 outputs feed axis operation information to the correction amount calculation device 10. The control device 22 may be provided separately from the machine tool 20 and connected to the machine tool 20. The machine tool 20 outputs temperature information related to the ball screw from a temperature sensor (not shown) or the like to the correction amount calculation device 10. The correction amount calculation device 10 outputs the correction amount for the thermal displacement of the ball screw to the control device 22. The control device 22 corrects the feed axis operation based on the correction amount for the thermal displacement of the ball screw. The correction amount calculation device 10 may be provided inside the machine tool 20.
[0012] As shown in Figure 1, the correction amount calculation device 10 includes a temperature information acquisition unit 101, a feed axis operation information acquisition unit 102, a first variable determination unit 103, a second variable determination unit 104, and a correction amount calculation unit 105. The temperature information acquisition unit 101 acquires temperature information related to the ball screw of the machine tool 20 from the machine tool 20. The feed axis operation information acquisition unit 102 acquires feed axis operation information related to the feed axis operation of the machine tool 20 from the machine tool 20.
[0013] The first variable determination unit 103 determines, based on the feed axis operation information, a coefficient and an exponent (which become the first variable) that represent the thermal response characteristics of the ball screw that are not affected by the ambient temperature change of the ball screw, and which are included in the thermal displacement estimation formula. The second variable determination unit 104 determines, based on the feed axis operation information, a coefficient and a delay (which become the second variable) that represent the thermal response characteristics of the ball screw that are affected by the ambient temperature change of the ball screw, and which are included in the thermal displacement estimation formula. The delay is a time delay that takes into account the effect of the ambient temperature change.
[0014] The correction amount calculation unit 105 calculates the thermal displacement correction amount for the ball screw from the thermal displacement estimation formula based on the feed axis operation information, temperature information, the coefficient and exponent determined by the first variable determination unit 103, and the coefficient and delay determined by the second variable determination unit, and outputs the thermal displacement correction amount for the ball screw to the control device 22.
[0015] Figure 2 is a block diagram showing an example of the configuration of a machine tool's feed axis. The feed axis included in the controlled object 21 controlled by the control device 22, as shown in Figure 2, comprises a servo motor 201, a rotary encoder 202, a coupling 203, a ball screw 204, a nut 205, and a table 206. The coupling 203, ball screw 204, and nut 205 form a connecting mechanism that connects the servo motor 201 and the table 206. The control device 22 controls the machining of the workpiece mounted on the table 206 by moving the table 206 via the connecting mechanism using the servo motor 201.
[0016] The servo motor 201 is a motor having a rotating shaft, and its rotational angle position is detected by the rotary encoder 202. The detected position value is input to the control device 22 as position feedback.
[0017] The operation of the correction amount calculation device 10 will be explained in more detail below.
[0018] The temperature information acquisition unit 101 acquires the ambient temperature of the ball screw, which is temperature information related to the ball screw, from a temperature sensor (not shown) of the machine tool 20. The temperature sensor is installed in one or more locations where changes in the ambient temperature of the ball screw can be detected, and the temperature information may be one or more. For example, the temperature sensor is placed around the ball screw 204 shown in Figure 2, and on one or both of the nut 205 or the table 206, part of the machine tool structure. In this case, the temperature information related to the ball screw includes at least one of the ambient temperature of the ball screw 204 and the temperature of the part of the machine tool structure 20.
[0019] The feed axis operation information acquisition unit 102 acquires feed axis operation information related to feed axis operation from the control device 22. The feed axis operation information includes at least one of the feed axis identification information of the machine tool 20, position, speed, acceleration, and torque. The feed axis identification information is, for example, information that identifies one of the X axis, Y axis, and Z axis.
[0020] The first variable determination unit 103 determines coefficients and indices that represent the thermal response characteristics of the ball screw, which are independent of ambient temperature changes, based on, for example, the X-axis as feed axis discrimination information and the speed of the X-axis, which are feed axis operation information. Specifically, the first variable determination unit 103 determines the values of the coefficients A and B and indices a and b (which become the first variables) of the thermal displacement estimation formula for estimating thermal displacement, shown in Equation 1 (Equation 1 below), as variables that represent the thermal response characteristics of the ball screw, which are independent of ambient temperature changes.
[0021] The second variable determination unit 104 determines a coefficient and a delay that represent the thermal response characteristics of the ball screw related to ambient temperature changes, based on, for example, the X-axis as feed axis discrimination information and the speed of the X-axis, which are feed axis operation information. Specifically, the second variable determination unit 104 determines the values of the coefficient C and delay D (which becomes the second variable) of the thermal displacement estimation formula for estimating thermal displacement, shown in Equation 1, as variables that represent the thermal response characteristics of the ball screw related to ambient temperature changes.
[0022] In this specification, when the term "variable" is used, it includes the variables δ(t), δ(t-1), V(t), F(t), F(t-1), T(t), T(t-D), coefficients A, B, C, exponents a, b, and lag D in Formula 1 and Formula 2 described later, and also includes the variables δ(t-1, n), V(t, n), δ(t-1, n-1), δ(t-1, n+1), and coefficient E in Formula 2.
[0023] The variables included in Equation 1 are explained below. In Equation 1, the variable δ(t) represents the amount of elongation (axial displacement) of the ball screw at time t, and the variable δ(t-1) represents the amount of elongation of the ball screw at time (t-1) prior to time t. The variable δ(t) mainly represents the amount of axial deformation due to thermal expansion or mechanical load, and the variable δ(t-1) indicates that the current amount of elongation depends on the past state. The variable V(t) represents the ball screw feed rate at time t. The variable V(t) indicates that high-speed rotation or high-speed feed increases heat generation and affects elongation. The variable F(t) is a quantity that shows the effect of the change in ambient temperature at time t. The variable F(t-1) is a quantity that shows the effect of the change in ambient temperature at time (t-1) prior to time t. The variable T(t) is the ambient temperature at time t, and the variable T(t-D) is the ambient temperature D time (delay) before time t.
[0024] In Equation 1, coefficient A is the velocity-dependent coefficient, a constant that determines the effect of the ball screw's feed rate on elongation. Coefficient B is the damping coefficient with respect to past elongation, a constant that scales the ball screw's natural contraction and elastic restoring force. The exponent a represents the nonlinearity with respect to velocity; for example, if a > 1, it means that thermal expansion increases exponentially as the velocity increases. The exponent b represents the nonlinearity of the damping characteristics; for example, if b > 1, it means that the damping effect becomes stronger the larger the past elongation.
[0025] In Equation 1, coefficient C is the sensitivity coefficient to ambient temperature changes, and delay D is the time delay that takes into account the effect of ambient temperature changes. Coefficient C and delay D are coefficients and time that represent the thermal response characteristics. Coefficient C and delay D can be determined from the cumulative ambient temperature change. Since the cumulative temperature change is time-series information, it is necessary to refer to past temperatures, and the number of reference points and period of past temperatures are determined as appropriate.
[0026] The thermal displacement estimation formula shown in Equation 1, by including a quantity F(t) that indicates the effect of ambient temperature changes, has the following effects: (1) Consideration of temperature change history: Since the ambient temperature T(t-D) D seconds ago is considered, it is possible to reflect the effects of rapid temperature changes or temperature fluctuation patterns. (2) Reflection of cumulative effects: By using the ambient temperature D seconds ago, the current elongation can be calculated from past elongation, and the cumulative effect of elongation over time can be accurately represented. (3) Reflection of material properties: By adjusting the coefficient C, the thermal expansion characteristics of different metallic materials can be reflected. (4) Consideration of delay effect: By adjusting the delay D, the delay time until the temperature change affects the elongation of the metallic rod can be considered, and the delay in heat conduction in large metallic structures or parts with complex shapes can be represented.
[0027] The correction amount calculation unit 105 stores the thermal displacement estimation formula shown in Equation 1, and calculates the thermal displacement correction amount for the ball screw from the thermal displacement estimation formula in Equation 1 based on the feed axis operation information, temperature information, variables (coefficient and exponent) determined by the first variable determination unit 103, and variables (coefficient and lag) determined by the second variable determination unit 104, and outputs the thermal displacement correction amount for the ball screw to the control device 22.
[0028] In this embodiment, when the correction amount calculation unit 105 calculates thermal displacement, it estimates the influence of frictional heat generated by the feed axis operation on thermal displacement from feed axis identification information and feed axis operation information such as speed, and also estimates the influence of ambient temperature changes on thermal displacement obtained from temperature information.
[0029] (Method for determining coefficients, exponents and lag) The first variable determination unit 103 and the second variable determination unit 104 can determine the coefficients A, B, exponents a, b, C, and lag D of the thermal displacement estimation formula shown in Equation 1, based on feed axis operation information, by any of the following methods (1) to (3). The first variable determination unit 103 stores a table showing the correspondence between the feed axis operation information and the determined coefficients A, B, a, and b. The second variable determination unit 104 stores a table showing the correspondence between the feed axis operation information and the determined coefficients C and lag D. (1) Collection and analysis of experimental data The values of coefficients A, B, exponents a, b, C, and lag D are estimated by statistically analyzing the collected data on the amount of ball screw elongation and the collected data on the change in ambient temperature when at least one of the feed axis position, velocity, acceleration, and torque, which constitute feed axis operation information, is changed.
[0030] (2) Utilization of machine learning The optimal values of coefficients A, B, exponents a, b, C, and lag D in the thermal displacement estimation formula shown in Equation 1 are estimated using the collected data. The method for determining each coefficient, exponent, and lag using machine learning will be described later.
[0031] (3) Use software to simulate the heat conduction or deformation of the numerically simulated ball screw, and adjust the values of coefficient A, coefficient B, exponent a, exponent b, coefficient C, and lag D while comparing the simulation results with the measured data.
[0032] The thermal response characteristics shown by coefficients A, B, exponents a, b, C, and lag D in Equation 1 vary depending on the design (diameter or pitch) and material of the ball screw. Changes in the diameter or pitch of the ball screw affect the surface area and the contact surface with the surroundings, which in turn affects heat dissipation. A larger surface area improves heat dissipation efficiency and can potentially suppress temperature rise. Generally, chromium-molybdenum steel (SCM420, SCM415) is used for the screw shaft and nut, but stainless steel (SUS440C) is used for special environment applications, and the thermal response characteristics of these materials differ. When determining coefficients A, B, exponents a, b, C, and lag D using the three methods described above, the design (diameter or pitch) and material of the ball screw are reflected. For example, if the surface area and contact surface with the surroundings change due to the ball screw design, coefficient C will change because it is affected by the ambient temperature.
[0033] The method for determining the coefficients, exponents, and lags of the first variable determination unit 103 and the second variable determination unit 104 may be a combination of the three methods described above as appropriate. For example, the coefficients, exponents, and lags of the first variable determination unit 103 and the second variable determination unit 104 may be determined by utilizing machine learning as described in method (2), or the coefficients and exponents of the first variable determination unit 103 may be determined by collecting and analyzing experimental data as described in method (1), and the coefficients and lags of the second variable determination unit 104 may be determined by utilizing machine learning as described in method (2).
[0034] (Method for evaluating the calculated coefficients, indices, and delays) The calculated coefficients, indices, and delays may be inserted into the thermal displacement estimation formula of Equation 1, and the difference between the estimated thermal displacement obtained using the thermal displacement estimation formula and the actual thermal displacement of the collected data may be used as the evaluation value of the coefficients, and the coefficients, indices, and delays may be evaluated based on the evaluation value. If the obtained evaluation value is greater than the threshold, the coefficients, indices, and delays can be recalculated using one of the three methods for calculating the coefficients, indices, and delays described above. If the obtained evaluation value is less than or equal to the threshold, the first variable determination unit 103 stores a table showing the correspondence between the feed axis operation information and coefficients A, B, indices a and b, and the second variable determination unit 104 stores a table showing the correspondence between the feed axis operation information and coefficients C and delay D.
[0035] (Modified Correction Amount Calculation Device for Determining Coefficients, Exponents, and Lag Using Machine Learning) Figure 3 is a block diagram showing a partial configuration of a modified correction amount calculation device during machine learning. Figure 4 is a block diagram showing a partial configuration of a modified correction amount calculation device after machine learning. The correction amount calculation device shown in Figures 3 and 4 has a machine learning unit 106 added to the correction amount calculation device 10 shown in Figure 1. In Figures 3 and 4, the temperature information acquisition unit 101 is omitted.
[0036] During machine learning, the machine learning unit 106 acquires temperature information from the temperature information acquisition unit 101, feed axis operation information from the feed axis operation information acquisition unit 102, and the calculated thermal displacement correction amount of the ball screw from the correction amount calculation unit 105. The temperature information, feed axis operation information, and thermal displacement correction amount become input data. The machine learning unit 106 stores measured data of the ball screw elongation amount as labels for cases where at least one of the feed axis position, velocity, acceleration, and torque, which constitute the feed axis operation information, is changed.
[0037] The machine learning unit 106 learns coefficients A, B, exponents a, b, C, and lag D such that the difference between the measured data of ball screw elongation with respect to temperature information and feed axis movement information and the thermal displacement correction amount calculated by the correction amount calculation unit 105 is less than or equal to a predetermined threshold. The machine learning unit 106 outputs the coefficients A, B, exponents a, b, C, and lag D obtained through learning to the first variable determination unit 103 and the second variable determination unit 104, and terminates the learning operation.
[0038] The machine learning unit 106 does not perform the operation of calculating the thermal displacement correction amount after machine learning. In Figure 4, the path connected to the machine learning unit 106 is shown as a dashed line, indicating that the machine learning unit 106 does not function after learning.
[0039] The machine learning unit 106 may determine the coefficients, exponents, and lags of the first variable determination unit 103 and the second variable determination unit 104. Alternatively, if method (2) using the machine learning unit 106 is combined with method (1) or method (3), the machine learning unit 106 may determine the coefficients and exponents of the first variable determination unit 103 or the coefficients and lags of the second variable determination unit 104.
[0040] Next, an example of the correction amount calculation method according to the first embodiment of the present disclosure will be described. FIG. 5 is a flowchart illustrating an example of the correction amount calculation method according to the first embodiment. In the following description, an example in which the correction amount calculation method of the present disclosure is executed by the correction amount calculation device 10 will be described, but the correction amount calculation method of the present disclosure can also be executed by a configuration other than the correction amount calculation device 10.
[0041] In step S11, the temperature information acquisition unit 101 acquires temperature information related to the ball screw of the machine tool 20 from the machine tool 20.
[0042] In step S12, the feed shaft operation information acquisition unit 102 acquires feed shaft operation information related to the feed shaft operation of the machine tool 20 from the machine tool 20.
[0043] In step S13, the first variable determination unit 103 determines, based on the feed shaft operation information, coefficients A and B and exponents a and b that represent the thermal response characteristics of the ball screw independent of ambient temperature changes.
[0044] In step S14, the second variable determination unit 104 determines, based on the feed shaft operation information, a coefficient C and a delay D that represent the thermal response characteristics of the ball screw related to ambient temperature changes.
[0045] In step S15, the correction amount calculation unit 105 calculates the thermal displacement correction amount of the ball screw from the thermal displacement estimation formula of Formula 1, based on the feed shaft operation information, the temperature information, the coefficients A and B and exponents a and b determined by the first variable determination unit, and the coefficient C and delay D determined by the second variable determination unit, and then the process ends.
[0046] According to the correction amount calculation device and the correction amount calculation method of the present embodiment described above, the thermal displacement of the ball screw is calculated in consideration of the thermal response characteristics determined by the design, material, or the like of the ball screw with respect to ambient temperature changes, so that the estimation accuracy of the thermal displacement can be improved.
[0047] (Second Embodiment) FIG. 6 is a block diagram illustrating a correction amount calculation device for thermal displacement of a ball screw according to the second embodiment of the present disclosure. The correction amount calculation device 11 of the present embodiment shown in FIG. 6 is configured such that the correction amount calculation unit 105 of the correction amount calculation device 10 shown in FIG. 1 includes a section-specific correction amount calculation unit 107, a section detection unit 108, and a total correction amount calculation unit 109. In FIG. 6, illustration of the machine tool 20 is omitted.
[0048] In the present embodiment, the first variable determination unit 103 determines the values of coefficients A, B and exponents a, b of Mathematical Formula 2 described later, and also determines the value of a coefficient E representing the thermal response characteristic of the ball screw that is not affected by ambient temperature changes.
[0049] The section detection unit 108 detects sections of the feed shaft of the ball screw from feed shaft operation information. For example, the section detection unit 108 detects sections obtained by dividing the movement range of the X-axis from the reference position from the feed shaft operation information output from the control device 22, and outputs each detected section to the correction amount calculation unit 105. FIG. 7 is a diagram illustrating each section obtained by dividing the movement range of the feed shaft of the ball screw. In FIG. 7, X1, X2, X3, ... represent each divided section.
[0050] The section-specific correction amount calculation unit 107 detects sections obtained by dividing the movement range of the X-axis from the reference position from the feed shaft operation information output from the control device 22, and calculates the correction amount for each detected section from the feed shaft operation information such as speed and temperature information. The section-specific correction amount calculation unit 107 may calculate the correction amount for each section from the feed shaft operation information and the temperature information, using each section output from the section detection unit 108. The correction amount for each divided section is obtained by Mathematical Formula 2 (Formula 2 below). In Equation 2, the variables δ(t, n) and δ(t-1, n) represent the elongation in interval n at time t and time t-1, V(t, n) represents the ball screw feed rate (which becomes the table speed) at time t and interval n, and the variables T(t) and T(t-D) represent the ambient temperature at time t and time t-D. The coefficient E is multiplied by the value obtained by subtracting twice the elongation in interval (n-1) from the sum of the elongation in interval (n-1) and the elongation in interval (n+1) at time (t-1). The coefficient E is a coefficient that expresses the effect of elongation due to axial heat conduction of the ball screw by using the difference in thermal displacement between adjacent intervals in the calculation. The term using the coefficient E allows us to consider the non-uniformity of the axial temperature distribution of the ball screw and the effect of elongation due to heat conduction (if one part is hotter than another part, this effect can be expressed). The coefficients A and B, exponents a and b, coefficient C, and lag D in equation 2 can be determined in the same manner as in the first embodiment. Coefficient E can also be determined in the same manner using the method for determining coefficients A and B, exponents a and b, coefficient C, and lag D described in the first embodiment.
[0051] The correction amount sum calculation unit 109 calculates the thermal displacement correction amount by summing the correction amounts for each section from the reference position to the movement range of the feed axis, based on the correction amount for each section and the sections of the feed axis. Figure 8 shows the correction amount for each section obtained by the section-by-section correction amount calculation unit 107 and the sum of the correction amounts obtained by the correction amount sum calculation unit 109.
[0052] According to the ball screw thermal displacement correction amount calculation device and correction report calculation method of this embodiment, the estimation accuracy can be improved when the heat distribution is non-uniform (occurring when the table is moved locally, for example).
[0053] (Third Embodiment) Figure 9 is a block diagram showing a correction amount calculation device for the thermal displacement of a ball screw according to the third embodiment of the present disclosure. The correction amount calculation device 12 of this embodiment shown in Figure 9 has a storage unit 110 added to the configuration of the correction amount calculation device 10 shown in Figure 1. In Figure 6, the machine tool 20 is omitted from the description.
[0054] The storage unit 110 stores a table describing multiple feed axis operation information sets with different conditions, and multiple different coefficients C and delay D related to the thermal displacement estimation formula of Equation 1, corresponding to each of the multiple feed axis operation information sets. For example, the storage unit 110 stores a table showing multiple different feed axis discrimination information sets and table positions (feed axis positions), and multiple different coefficients C and delay D corresponding to the multiple feed axis discrimination information sets and table positions, as shown in Figure 10. The feed axis discrimination information and table positions become the feed axis operation information. As shown in Figure 10, the coefficients C and delay D are set to different values corresponding to the feed axis discrimination information sets and table positions (feed axis positions).
[0055] The second variable determination unit 104 determines coefficients C and lag D representing the thermal response characteristics of the ball screw by referring to the storage unit 110 based on the feed axis operation information. For example, if the feed axis discrimination information is the X axis and the table position is 500 mm (center), then coefficients C2 and lag D2 are determined by referring to the storage unit 110.
[0056] (Method for determining coefficient C and lag D) Coefficients C and lag D can be determined by the following methods: (1) Collection of experimental data Measure the amount of thermal displacement of the ball screw and the change in ambient temperature at different table positions, observe the time lag of the amount of thermal displacement in response to the change in ambient temperature at each position, and estimate the value of lag D. (2) Utilization of machine learning Use the collected data to model the relationship between the table position and coefficients C and lag D, and predict the values of coefficients C and lag D at any position through a machine learning model. (3) Thermal conduction simulation Model the thermal conduction characteristics of the ball screw, simulate the temperature distribution at each position, and estimate the values of coefficients C and lag D for each position.
[0057] According to the ball screw thermal displacement correction amount calculation device and correction report calculation method of this embodiment, the estimation accuracy is improved by taking into account the effect of ambient temperature changes for each table position.
[0058] Each component included in the correction amount calculation device of each embodiment and modified example described above can be implemented by hardware, software, or a combination thereof. Furthermore, the correction amount calculation method performed by the cooperation of each component included in the correction amount calculation device of each embodiment and modified example described above can also be implemented by hardware, software, or a combination thereof. Here, implementation by software means implementation by a computer reading and executing a program.
[0059] To realize the components included in the correction amount calculation device through hardware, software, or a combination thereof, the correction amount calculation device is equipped with a arithmetic processing unit such as a CPU (Central Processing Unit). The arithmetic processing unit functions as an execution unit. The correction amount calculation device is also equipped with auxiliary storage devices such as an HDD (Hard Disk Drive) that store various control programs such as application software or an OS (Operating System), and main memory such as RAM (Random Access Memory) for storing data temporarily required for the arithmetic processing unit to execute the program.
[0060] The correction amount calculation device then reads application software or an operating system from an auxiliary storage device, expands the read application software or an operating system into the main storage device, and performs calculations based on this application software or an operating system. Furthermore, it controls various hardware components of the correction amount calculation device based on these calculation results. This realizes the functional blocks of each embodiment and modified example. The correction amount calculation method can also be realized with a configuration similar to that of the correction amount calculation device.
[0061] The components included in the correction amount calculation device can be realized by hardware, including electronic circuits. When the correction amount calculation device is configured as hardware, some or all of the functions of each component included in the correction amount calculation device can be implemented using integrated circuits (ICs) such as ASICs (Application Specific Integrated Circuits), gate arrays, FPGAs (Field Programmable Gate Arrays), and CPLDs (Complex Programmable Logic Devices).
[0062] Programs can be stored and supplied to a computer using various types of non-transitor computer-readable media. Non-transitor computer-readable media include various types of tangible storage media. Examples of non-transitor computer-readable media include magnetic recording media (e.g., hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memory (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (random access memory)). Furthermore, the program may be supplied to the computer by various types of temporary computer-readable media.
[0063] According to the correction amount calculation device and correction amount calculation method of this disclosure, including the embodiments and modified examples described above, the accuracy of estimating thermal displacement can be improved by calculating the thermal displacement of the ball screw while considering the thermal response characteristics of the ball screw determined by the design or material of the ball screw in response to ambient temperature changes.
[0064] While the embodiments and modifications described above are preferred embodiments of the present invention, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention.
[0065] Regarding the above embodiment, the following additional information is disclosed. (Addendum 1) A correction amount calculation device (10, 11, 12) that calculates a correction amount for the thermal displacement of a ball screw (204) using a thermal displacement estimation formula for estimating the thermal displacement of a ball screw of a machine tool (20), comprising: a feed axis operation information acquisition unit (102) that acquires feed axis operation information related to the feed axis operation of a feed axis including the ball screw from the machine tool; a temperature information acquisition unit (101) that acquires temperature information related to the ball screw from the machine tool; a first variable determination unit (103) that determines a first variable that represents the thermal response characteristics of the ball screw, which are included in the thermal displacement estimation formula and are independent of changes in ambient temperature of the ball screw, based on the feed axis operation information; and a second variable determination unit (104) that determines a second variable that represents the thermal response characteristics of the ball screw, which are included in the thermal displacement estimation formula and are related to changes in ambient temperature of the ball screw, based on the feed axis operation information. A correction amount calculation device comprising: a correction amount calculation unit (105) that calculates the thermal displacement correction amount of the ball screw from the thermal displacement estimation formula based on the feed axis operation information, the temperature information, the first variable, and the second variable;
[0066] (Note 2) The correction amount calculation device described in Note 1, wherein the second variable determination unit (104) determines, as the second variable, a coefficient relating to the ambient temperature change of the ball screw (204) and a delay due to the influence of the ambient temperature change of the ball screw.
[0067] (Note 3) The correction amount calculation device according to Note 1 or 2, wherein the feed axis operation information includes identification information of the feed axis of the machine tool (20) and at least one of position, velocity, acceleration, and torque.
[0068] (Note 4) The correction amount calculation device according to any one of Notes 1 to 3, wherein the temperature information relating to the ball screw (204) includes at least one of the ambient temperature of the ball screw and the temperature of a part of the structure of the machine tool (20).
[0069] (Note 5) The correction amount calculation device according to any one of Notes 1 to 4, further comprising a machine learning unit (106) that calculates at least one of the first and second variables relating to the thermal displacement estimation formula, which are determined by the first variable determination unit (103) and the second variable determination unit (104), by machine learning.
[0070] (Note 6) The correction amount calculation device according to any one of Notes 1 to 5, comprising: a section-by-section correction amount calculation unit (107) that calculates a correction amount for each section obtained by dividing the movement range of the feed shaft of the ball screw from the feed shaft operation information and the temperature information; a section detection unit (108) that detects the sections of the feed shaft of the ball screw from the feed shaft operation information; and a total correction amount calculation unit (109) that calculates the sum of the correction amounts for each section from the reference position of the ball screw to the movement range of the feed shaft as the thermal displacement correction amount, based on the correction amount for each section and the sections of the feed shaft.
[0071] (Note 7) A correction amount calculation device according to any one of Notes 1 to 6, comprising a storage unit (110) that stores a plurality of feed axis operation information items having different conditions and a plurality of different second variables corresponding to each of the plurality of feed axis operation information items, wherein the second variable determination unit (104) determines the second variable corresponding to the feed axis operation information acquired by the feed axis operation information acquisition unit (102) by referring to the storage unit.
[0072] (Note 8) A method for calculating a correction amount, wherein the computer performs the following steps: acquiring feed axis operation information relating to the feed axis operation of a feed axis including a ball screw (204) of a machine tool (20) from the machine tool; acquiring temperature information relating to the ball screw from the machine tool; determining a first variable representing the thermal response characteristics of the ball screw that are not affected by changes in ambient temperature, which is included in a thermal displacement estimation formula for estimating the thermal displacement of the ball screw based on the feed axis operation information; determining a second variable representing the thermal response characteristics of the ball screw that are affected by changes in ambient temperature, which is included in the thermal displacement estimation formula, based on the feed axis operation information; and calculating a thermal displacement correction amount for the ball screw from the thermal displacement estimation formula based on the feed axis operation information, the temperature information, the first variable, and the second variable.
[0073] 10, 11, 12 Correction Amount Calculation Device 20 Machine Tool 21 Controlled Object 22 Control Device 101 Temperature Information Acquisition Unit 102 Feed Axis Operation Information Acquisition Unit 103 First Variable Determination Unit 104 Second Variable Determination Unit 105 Correction Amount Calculation Unit 106 Machine Learning Unit 107 Interval-Specific Correction Amount Calculation Unit 108 Interval Detection Unit 109 Correction Amount Sum Calculation Unit 110 Storage Unit
Claims
1. A correction amount calculation device for calculating a thermal displacement correction amount for a ball screw of a machine tool using a thermal displacement estimation formula for estimating the thermal displacement of the ball screw of the machine tool, comprising: a feed axis operation information acquisition unit that acquires feed axis operation information related to the feed axis operation of a feed axis including the ball screw from the machine tool; a temperature information acquisition unit that acquires temperature information related to the ball screw from the machine tool; a first variable determination unit that determines a first variable included in the thermal displacement estimation formula, which represents the thermal response characteristics of the ball screw that are not affected by changes in ambient temperature of the ball screw, based on the feed axis operation information; a second variable determination unit that determines a second variable included in the thermal displacement estimation formula, which represents the thermal response characteristics of the ball screw that are affected by changes in ambient temperature of the ball screw, based on the feed axis operation information; and a correction amount calculation unit that calculates the thermal displacement correction amount for the ball screw from the thermal displacement estimation formula based on the feed axis operation information, the temperature information, the first variable, and the second variable.
2. The correction amount calculation device according to claim 1, wherein the second variable determination unit determines, as the second variable, a coefficient relating to the change in ambient temperature of the ball screw and a time delay due to the influence of the change in ambient temperature of the ball screw.
3. The correction amount calculation device according to claim 1 or 2, wherein the feed axis operation information includes identification information of the feed axis of the machine tool and at least one of position, velocity, acceleration, and torque.
4. The correction amount calculation device according to any one of claims 1 to 3, wherein the temperature information relating to the ball screw includes at least one of the ambient temperature of the ball screw and the temperature of a part of the structure of the machine tool.
5. The correction amount calculation device according to any one of claims 1 to 4, further comprising a machine learning unit that calculates at least one of the first and second variables relating to the thermal displacement estimation formula, which are determined by the first variable determination unit and the second variable determination unit, by machine learning.
6. The correction amount calculation device according to any one of claims 1 to 5, comprising: a section-by-section correction amount calculation unit that calculates a correction amount for each section obtained by dividing the movement range of the feed shaft of the ball screw from the feed shaft operation information and the temperature information; a section detection unit that detects sections of the feed shaft of the ball screw from the feed shaft operation information; and a total correction amount calculation unit that calculates the sum of the correction amounts for each section from the reference position of the ball screw to the movement range of the feed shaft as the thermal displacement correction amount, based on the correction amount for each section and the sections of the feed shaft.
7. A correction amount calculation device according to any one of claims 1 to 6, comprising a storage unit that stores a plurality of feed axis operation information having different conditions and a plurality of different second variables corresponding to each of the plurality of feed axis operation information, wherein the second variable determination unit determines the second variable corresponding to the feed axis operation information acquired by the feed axis operation information acquisition unit by referring to the storage unit.
8. A method for calculating a correction amount, wherein the computer performs the following steps: acquiring feed axis operation information relating to the feed axis operation of a feed axis including a ball screw of the machine tool from the machine tool; acquiring temperature information relating to the ball screw from the machine tool; determining a first variable representing the thermal response characteristics of the ball screw that are not affected by changes in ambient temperature, which is included in a thermal displacement estimation formula for estimating the thermal displacement of the ball screw based on the feed axis operation information; determining a second variable representing the thermal response characteristics of the ball screw that are affected by changes in ambient temperature, which is included in the thermal displacement estimation formula, based on the feed axis operation information; and calculating a thermal displacement correction amount for the ball screw from the thermal displacement estimation formula based on the feed axis operation information, the temperature information, the first variable, and the second variable.