Method for estimating thermal deformation of machine tool and method for correcting thermal deformation using the same

Abstract

To provide a machine tool heat deformation estimation method that takes into consideration temperature changes at many locations on a machine tool, and can be applied even if procession conditions change.SOLUTION: A machine tool heat deformation estimation method includes: a test condition setting step S1 in which test condition for a work-piece is set by use of experimental design; a spindle-to-blade distance and temperature measurement step S2 in which a distance between a spindle and a blade and temperature changes at multiple locations are measured when performing an actual cutting test (simulation cutting test); a change tendency grouping step S3 in which change tendencies in measured temperatures at multiple locations are grouped; a measurement location narrowing-down step S4 in which a measurement location is narrowed down; an estimation equation setting step S5 in which heat deformation estimation equation is set; an experimental constant determination step S6 in which a measured temperature change amount corresponding to each item in the heat deformation equation is substituted to determine an experimental constant; and an experimental constant determination repeating step S7 in which combination of temperature tendency groups is changed, and the experimental constant determination step is repeated multiple times.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a thermal deformation estimation method for a machine tool that estimates the amount of thermal deformation of a workpiece caused by heat during machining, and a thermal deformation correction method that performs correction based on the amount of thermal deformation estimated using this thermal deformation estimation method. [Background technology]

[0002] As a method for estimating the amount of thermal deformation of a workpiece caused by heat during machining, a method has been proposed in which a first temperature sensor is provided in association with the main spindle, a second temperature sensor is provided in association with a ball screw mechanism that moves a moving member that moves integrally with the machining tool, and a third temperature sensor is provided for detecting the ambient temperature, and the amount of thermal deformation of the workpiece is estimated using the temperatures detected by the first to third temperature sensors (see, for example, Patent Document 1).

[0003] In this thermal deformation estimation method, the amount of thermal deformation of the spindle (H1) is calculated using a spindle thermal deformation correction formula, and this amount of thermal deformation of the spindle (H1) is expressed as the sum (H1 = C1 + C2) of the amount of thermal deformation of the bed of the machine tool and the amount of thermal deformation of the bearing means of the spindle (C2).

[0004] The thermal deformation amount of the bed (C1) is calculated by the following formula (1) using the initial temperature (T0) of the first temperature sensor, the ambient temperature (T1), and the temperature change amount (ΔTs) of the first temperature sensor: C1=[a1+(a2×T0)+(a3×T1)]×ΔTs ···(1) a1, a2, a3: coefficients The thermal deformation amount (C2) of the bearing means of the spindle is expressed by the following formula (2): C2=N×[b1+(b2×T0)+(b3×T1)]× {1-exp[(ln0.1)×t / 30)]} ···(2) b1, b2, b3: coefficients It is expressed as:

[0005] The amount of thermal deformation (H2) of the moving member is calculated using a moving member thermal deformation correction formula, and this amount of thermal deformation (H2) is calculated using the temperature change (ΔTb) of the second temperature sensor according to the following formula (3): H2 = Σpi × ΔTb (3) pi: coefficient It is expressed as:

[0006] The thermal deformation of the workpiece (HA) is the composite deformation (HA = H1 + H2) of the thermal deformation of the spindle (H1) and the thermal deformation of the moving parts (H2). By correcting with this composite deformation (HA), the effects of heat generated during machining can be suppressed and high-precision machining can be performed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4450722 Summary of the Invention [Problem to be solved by the invention]

[0008] The conventional method described above takes into consideration the thermal deformation of the spindle of the machine tool, i.e., the temperature change of the first temperature sensor, and the thermal deformation of the moving member (on which the machining tool is attached), i.e., the temperature change of the second temperature sensor, but in reality, it is expected that the location where the temperature change should be measured will differ depending on the model of the machine tool. Therefore, it is desired to realize a method for estimating the amount of thermal deformation that takes into consideration the temperature change of the location where it should be measured by the machine tool.

[0009] In addition, there are various machining conditions when machining a workpiece, such as the diameter of the workpiece, the axial machining length of the workpiece, the machining rotation speed of the workpiece, fluctuations in the machining environment temperature, whether or not cutting oil is used, and the material of the workpiece, and it is desirable to realize a method for estimating the amount of thermal deformation that can be applied even if these various machining conditions change.

[0010] The object of the present invention is to provide a method for estimating thermal deformation of a machine tool that takes into account a small number of temperature change measurement points suitable for estimating thermal deformation in each machine tool and can be applied to a wide range of machining conditions from a small number of experiments.

[0011] Another object of the present invention is to provide a method for correcting thermal deformation of a machine tool, which performs correction based on the amount of thermal deformation estimated using this thermal deformation estimation method. [Means for solving the problem]

[0012] The method for estimating thermal deformation of a machine tool of the present invention includes a test condition setting step for setting test conditions for a workpiece taking into consideration actual machining of the machine tool using an experimental design method; a spindle-to-cutter distance and temperature measurement step for measuring a spindle-to-cutter distance and temperature changes at multiple locations of the machine tool when a simulated cutting test and / or an actual cutting test based on the test conditions is performed on the workpiece; a change tendency grouping step for grouping locations showing similar trends based on the change trends of the measured temperatures at the multiple locations; a measurement location narrowing down step for selecting multiple temperature trend groups from the grouped multiple temperature trend groups and narrowing down one or two measurement locations from each selected temperature trend group; an estimation equation setting step for setting a thermal deformation estimation equation with the number of terms corresponding to the number of narrowed-down measurement locations; and a measurement method for measuring the thermal deformation of a workpiece by using the thermal deformation estimation equation to determine the change in the measured temperature corresponding to each term. Change in The actual measured value and The predicted change amount of the workpiece using the thermal deformation estimation formula an experimental constant determination step of determining an experimental constant so as to minimize the residual sum of squares; and an experimental constant determination repeat step of repeating the estimation formula setting step and the experimental constant determination step a plurality of times by changing the combination of the temperature tendency groups and / or the combination of the measurement points to be narrowed down in the measurement point narrowing down step; Repeat the above experimental constant determination After the step, the optimal measurement point suitable for the thermal deformation estimation formula is Combinations and Optimization The method includes an optimal experimental constant determination step for determining an experimental constant, and a thermal deformation amount estimation step for estimating the thermal deformation amount of the workpiece using the thermal deformation estimation formula, an optimal combination of measurement points, and the optimal experimental constant.

[0013] In such a method for estimating thermal deformation of a machine tool, in the experimental constant determination repetition step, it is preferable to repeat the estimation equation setting step and the experimental constant determination step multiple times by changing the combination of temperature trend groups in the measurement point narrowing down step, the combination of measurement points to be narrowed down and / or the form of the thermal deformation estimation equation, and to determine, in the optimal experimental constant determination step, an optimal thermal deformation estimation equation suitable for the machine tool, as well as an optimal combination of measurement points suitable for this and optimal experimental constants.By doing this, it is possible to determine an optimal thermal deformation estimation equation suitable for the machine tool, as well as an optimal combination of measurement points and optimal experimental constants in this optimal thermal deformation estimation equation, thereby enabling the amount of thermal deformation of the machine tool to be accurately estimated.

[0014] In addition, in the experimental constant determination repeating step, at least any two of three or more thermal deformation estimation equations consisting of three, four or five or more terms are set, and the estimation equation setting step and the experimental constant determination step are repeated using the at least two thermal deformation estimation equations while changing the combination of temperature trend groups and / or the combination of measurement points to be narrowed down, so that the thermal deformation estimation equation can be expressed as a linear equation with an appropriate number of terms consisting of three, four or five or more terms, and can be provided as a relatively simplified thermal deformation estimation equation.

[0015] Furthermore, in such a method for estimating thermal deformation of a machine tool, it is preferable that in the change tendency grouping step, the temperature change amount on the reference side is divided by the maximum temperature change amount to make the temperature change amount on the reference side dimensionless, and then a coefficient is multiplied by the temperature change to be compared, and the sum of squared residuals between this coefficient-integrated temperature change and the dimensionless temperature change is calculated to calculate the similarity, and the temperature change tendencies are grouped based on the similarity.By grouping based on similarity in this manner, it is possible to avoid narrowing down the list to include a large number of locations where the temperature changes fluctuate in the same or similar manner.

[0017] In addition, in this method for estimating thermal deformation of a machine tool, the all-pairs method is used as the experimental design method, and the test conditions set in the test condition setting step include the diameter of the workpiece, the machining length of the workpiece, the number of times the workpiece is machined, fluctuations in the machining environment temperature, and whether or not cutting oil is used, making it possible to provide a general-purpose thermal deformation estimation formula that takes into account general machining conditions without being limited by the number of levels of each factor.

[0018] Further, the method for compensating for thermal deformation of a machine tool of the present invention includes a test condition setting step of setting test conditions for a workpiece taking into consideration actual machining of the machine tool using an experimental design method; a spindle-to-cutter distance and temperature measurement step of measuring a spindle-to-cutter distance and temperature changes at multiple locations of the machine tool when a simulated cutting test and / or an actual cutting test based on the test conditions is performed on the workpiece; a change tendency grouping step of grouping locations showing similar trends based on the change trends of the measured temperatures at the multiple locations; a measurement location narrowing down step of selecting multiple temperature trend groups from the grouped multiple temperature trend groups and narrowing down one or two measurement locations from each selected temperature trend group; an estimation equation setting step of setting a thermal deformation estimation equation with the number of terms corresponding to the number of narrowed down measurement locations; Change in The actual measured value and The predicted change amount of the workpiece using the thermal deformation estimation formula an experimental constant determination step of determining an experimental constant so as to minimize the residual sum of squares; an experimental constant determination repeat step of repeating the estimation formula setting step and the experimental constant determination step a plurality of times by changing the combination of the temperature tendency groups and / or the combination of the measurement points to be narrowed down in the measurement point narrowing down step; Experimental constant determination iterationThe method includes, after the step, an optimal experimental constant determination step for determining an optimal combination of measurement points and optimal experimental constants suitable for the thermal deformation estimation formula, a thermal deformation amount estimation step for estimating the thermal deformation amount of the workpiece using the thermal deformation estimation formula, the optimal combination of measurement points and the optimal experimental constants, a deformation amount difference calculation step for calculating the thermal deformation amount difference between the thermal deformation amount of the workpiece in the previous processing step and the thermal deformation amount of the workpiece in the current processing step, and a thermal deformation correction step for correcting the thermal deformation amount difference calculated in the deformation amount difference calculation step. Effect of the Invention

[0019] According to the method for estimating thermal deformation of a machine tool of the present invention, test conditions for a workpiece are set by using an experimental design method, taking into account the actual machining of the machine tool (test condition setting step), and the spindle-to-tool distance and temperature changes at multiple locations of the machine tool are measured when a simulated cutting test and / or an actual cutting test based on the test conditions are performed (spindle-to-tool distance and temperature measurement step), so that data on the spindle-to-tool distance and temperature changes at multiple locations under the set test conditions can be obtained. Then, locations showing similar trends are grouped based on the change trends of the measured temperature (change trend grouping step), multiple temperature trend groups are selected from these temperature trend groups, and one or two measurement locations are narrowed down from each selected temperature trend group (measurement location narrowing down step), so that the amount of thermal deformation can be estimated by narrowing down multiple locations with different temperature trends and taking into account the temperature changes at different locations. In addition, a thermal deformation estimation formula with the number of terms corresponding to the number of narrowed down measurement locations is set (estimation formula setting step), and the amount of change in the measured temperature corresponding to each term in this thermal deformation estimation formula is substituted. Then, the residual sum of squares between the actual measured value of the change in the workpiece and the predicted change in the workpiece using the thermal deformation estimation formula is minimized. The experimental constants are determined (experimental constant determination step), and the estimation formula setting step and the experimental constant determination step are repeated a number of times by changing the combination of temperature tendency groups and / or the combination of narrowed-down measurement points (experimental constant determination repeat step). RepeatAfter the step, an optimal combination of measurement points and optimal experimental constants suitable for the thermal deformation estimation formula are determined (optimal experimental constant determination step), and the amount of thermal deformation of the workpiece is estimated using this thermal deformation estimation formula, the optimal combination of measurement points, and the optimal experimental constants (thermal deformation amount estimation step). Therefore, the amount of thermal deformation of the workpiece can be estimated taking into account the temperature changes at a small number of different appropriate points of the machine tool, and the amount of thermal deformation can be accurately estimated with high precision using a relatively simple formula.

[0020] Furthermore, according to the thermal deformation compensation method for machine tools of the present invention, the amount of thermal deformation of the workpiece is estimated by the above-mentioned thermal deformation estimation method, and this estimated amount of thermal deformation is used to calculate the difference between the amount of thermal deformation of the workpiece in the previous machining process and the amount of thermal deformation of the workpiece in the current machining process (deformation amount difference calculation step), and compensation is made using this deformation amount difference (thermal deformation compensation step), so that thermal deformation can be compensated for relatively easily and the workpiece can be machined with high precision. [Brief description of the drawings]

[0021] [Figure 1] 1 is a front perspective view showing a schematic diagram of an example of an NC lathe to which a thermal deformation estimation method (thermal deformation correction method) according to the present invention is applied; [Diagram 2] FIG. 2 is a perspective view showing the NC lathe of FIG. 1 as viewed from the rear side. [Diagram 3] 2 is a diagram showing a flow of executing a thermal deformation estimation method applied to the NC lathe of FIG. 1 . [Figure 4] 4 is an explanatory diagram for explaining test conditions in a test condition setting step of the thermal deformation estimating method of FIG. 3; [Diagram 5] 5A and 5B are diagrams for explaining the similarity used when grouping temperature change trends, where FIG. 5A is a diagram showing the relationship between time and temperature change, and FIG. 5B is a diagram for explaining the calculation of the similarity. [Figure 6] A diagram showing the flow when applying the thermal deformation estimation formula to an NC lathe for machining. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of a thermal deformation estimation method and a thermal deformation correction method using the same according to the present invention will be described by applying it to an NC lathe as an example of a machine tool with reference to the accompanying drawings. First, an NC lathe will be outlined as an example of a machine tool to which the thermal deformation estimation method (thermal deformation correction method) is applied with reference to Figs. 1 and 2.

[0023] In Fig. 1 and Fig. 2, the NC lathe shown includes a lathe body 2 that is installed on the floor of a factory. The lathe body 2 includes a bed 3, a spindle unit 4 is provided on the left side of the bed 3, and a turret device 6 is attached to the right side of the bed 3. A spindle 7 is rotatably supported by the spindle unit 4, a drive pulley 8 is attached to the rear end of the spindle 7, and an output part of a spindle drive motor 10 and the drive pulley 8 are drivably connected via a drive belt (not shown). A chuck means 12 is attached to the spindle 7, and a workpiece (not shown) to be machined is detachably attached to the chuck means 12. As configured in this way, when the spindle drive motor 10 is operated, the spindle 7 is rotated in a predetermined direction via the drive belt and the drive pulley 8, and the rotation of the spindle 7 rotates the chuck means 12 (the workpiece attached thereto) integrally.

[0024] In this NC lathe, a moving member 14 is supported on the lathe body 2, a support table 16 is supported on the moving member 14, and a turret device 6 is attached to the support table 16. In this embodiment, the moving member 14 is movably supported on the lathe body 2 via a first support mechanism 18 extending in the lateral direction of the lathe body 2, i.e., in the axial direction (Z-axis direction) of the spindle 7, and is reciprocated in the Z-axis direction via the first support mechanism 18. The support table 16 is movably supported on the moving member 14 via a second support mechanism 20 extending in the front-rear direction (X-axis direction) of the lathe body 2, and is reciprocated in the X-axis direction via the second support mechanism 20. The first support mechanism 18 includes a first drive motor 22 for moving the moving member, and the second support mechanism 20 includes a second drive motor 24 for moving the support table 16.

[0025] The turret device 6 includes a turret body 26, a turret shaft (not shown) is rotatably supported by the turret body 26, and a turret 28 is attached to the turret shaft. A turret drive motor 25 is attached to the turret body 26, and the turret drive motor 25 is drivingly connected to the turret shaft. Because of this configuration, when the turret drive motor 25 rotates in a predetermined direction (or the opposite direction to the predetermined direction), the turret 28 is rotated in the predetermined direction (or the opposite direction to the predetermined direction) via the turret shaft. A plurality of tool attachment portions 30 are provided on the turret 28 at intervals in the circumferential direction, and machining tools (not shown) for machining the workpiece are attached to these tool attachment portions 30.

[0026] In this NC lathe, when a workpiece is machined, for example, the spindle 7 and the chuck means 12 (the workpiece attached thereto) are rotated in a predetermined direction by the spindle drive motor 10. Also, the support table 16 is moved in the X-axis direction (i.e., in a direction approaching the center of the workpiece) by the second drive motor 24, and the cutting depth during machining is set by this movement. Furthermore, the moving member 14 is moved in the Z-axis direction (i.e., in the axial direction of the workpiece) by the first drive motor 22, and the machining length in the axial direction of the workpiece is set by this movement. By operating the spindle drive motor 10 and the first and second drive motors 22, 24 in this manner and acting a machining tool (not shown) attached to the turret device 6 on the workpiece (not shown) held by the chuck means 12, machining of the workpiece is performed.

[0027] In such an NC lathe, when cutting a workpiece, the temperature of the NC lathe rises due to heat generated from the spindle drive motor 10, the first and second drive motors 22, 24, heat generated by the rotation of the spindle 7, heat generated in the first and second support mechanisms 18, 20, etc., and this temperature fluctuation causes thermal deformation of the workpiece, which in turn reduces the machining accuracy of the workpiece. Therefore, the NC lathe of this embodiment is configured to estimate the amount of thermal deformation using the following thermal deformation estimation method, and to correct the thermal deformation using this estimated amount of thermal deformation by a thermal deformation correction method.

[0028] Next, a thermal deformation estimation method applied to this NC lathe will be described. In this embodiment, the thermal deformation estimation method includes various steps S1 to S7 shown in Fig. 3, and these steps S1 to S7 are executed according to the flow shown in Fig. 3.

[0029] In this thermal deformation estimation method, first, a test condition setting step S1 is performed. In this embodiment, the test conditions are planned by an experimental design method using an orthogonal array, an all pair method, etc. The factors and levels of the test conditions to which the experimental design method is applied are combined, for example, as shown in Table 1.

[0030] [Table 1] Referring to FIG. 4, the machining diameter (D) (mm) in Table 1 is the machining diameter at the end of machining of the workpiece, the machining length (L) (mm) is the machining range in the axial direction of the spindle, and the number of machining operations (N) is the number of rough machining operations in one cycle. In addition, the "temperature increase" in the ambient temperature (T) means machining is performed while maintaining the temperature at 20°C before the start of the test, at 25°C for 3 hours from the start of the test, and at 30°C thereafter, while the "constant temperature" means machining is performed while maintaining the temperature at 20°C at all times, and the "temperature decrease" means machining is performed while maintaining the temperature at 30°C before the start of the test, at 25°C for 3 hours from the start of the test, and at 20°C thereafter. The machining diameter (D), machining length (L), number of machining operations (N), and ambient temperature (T) under these test conditions can be set to appropriate values ​​depending on the model of the NC lathe, etc.

[0031] In addition, the number of times of processing is the number of times rough processing is performed, and one finish processing is performed after this rough processing, and after this finish processing, the spindle blade distance C between the tip of the processing tool K and the outer peripheral surface of the workpiece P is measured.

[0032] Then, the factors and levels in Table 1 are applied to the L9 orthogonal array as shown in Table 2, and the test conditions are determined as shown in Table 2. The test time (the time for tests with test numbers L1 to L9) is set to, for example, about 6 to 10 hours (e.g., 8 hours) assuming a typical test time, and processing stoppages for maintenance work etc. may be provided during this test period, for example, about 10 minutes 1 hour after the start of the test, about 60 minutes 3 hours after the start of the test, and about 20 minutes 5 hours after the start of the test.

[0033] [Table 2] Once the test conditions are set using the experimental design method in this way, step S2 of measuring the spindle-to-cutter distance and temperature is then executed. First to twenty-second temperature detection sensors SE1 to SE22 are attached to measure temperature changes corresponding to a plurality of locations on the NC lathe (22 locations in this embodiment, the first to twenty-second locations Ch1 to Ch22). As the first to twenty-second temperature detection sensors SE1 to SE22, for example, a commonly used T-type thermocouple can be used, and this T-type thermocouple detects the temperature states of the plurality of locations Ch1 to Ch22 on the NC lathe.

[0034] For example, the 1st to 22nd temperature detection sensors SE1 to SE22 are disposed at the 1st to 22nd locations Ch1 to Ch22 of the NC lathe, and the relationship between the 1st to 22nd locations Ch1 to Ch22 (locations where the 1st to 22nd temperature detection sensors SE1 to SE22 are disposed) and the parts of the NC lathe is as shown in Table 3. Some of the 1st to 22nd locations Ch1 to Ch22 that can be illustrated are shown in Figures 1 and 2. Note that the locations where the temperatures are measured can be set appropriately, and some of the 1st to 22nd locations Ch1 to Ch22 can be changed or some of these locations can be omitted, or other locations can be added to the 1st to 22nd locations Ch1 to Ch22.

[0035] [Table 3] In this embodiment, the NC lathe was installed in a simple air-conditioned room for testing, and Ch18 (ambient temperature) in Table 3 is the temperature of this simple air-conditioned room, and Ch19 (outside the air-conditioned room) is the temperature outside this simple air-conditioned room.

[0036] In this spindle-to-cutter distance and temperature measurement step S2, tests are performed with the test numbers in Table 2, and the temperatures of locations 1 to 22 Ch1 to Ch22 are measured at the end of one cycle of test machining for each workpiece, and the spindle-to-cutter distance C during test machining is measured. These measured temperatures and spindle-to-cutter distance C are then stored in a computer storage device (not shown) or the like.

[0037] The test in the spindle-to-cutter distance and temperature measurement step S2 may be an actual cutting test in which the workpiece P is actually cut, or may be a combination of the actual cutting test and a simulated cutting test (a test in which the workpiece P is not actually cut) in which the cutting tool is moved in the same manner as when the workpiece P is machined. In this case, for example, in the simulated cutting test, a dummy workpiece is used as the workpiece, and the cutting tool is moved in the same manner as in the actual cutting test to perform the simulated test. In addition, in the actual cutting test, the actual cutting test is performed in a combination of a case in which cutting fluid is used and a case in which cutting fluid is not used, and by combining the presence and absence of cutting fluid in this way, the amount of thermal deformation in cutting including cutting with cutting fluid and cutting without cutting fluid can be estimated.

[0038] In the actual cutting test and the simulated cutting test, the cutting tool K is moved, for example, from the origin O in FIG. 4 in the X-axis direction and then moved in the Z-axis direction. In the actual cutting test, the cutting tool K acts on the workpiece P to perform actual cutting, and in the simulated cutting test, the cutting tool K is moved without acting on a dummy workpiece (not shown) to perform simulated cutting. After one cycle of the actual cutting test and the simulated cutting test is completed, the cutting tool K is returned to the origin. In this returned state, the temperatures at the 1st to 22nd locations Ch1 to Ch22 are detected by the 1st to 22nd temperature detection sensors SE1 to SE22, and the spindle-to-cutter distance (C) (see FIG. 4) is measured.

[0039] In this way, the temperature change trends of the temperature changes at the 1st to 22nd locations Ch1 to Ch22 of the NC lathe (i.e., changes in the detected temperatures of the 1st to 22nd temperature detection sensors SE1 to SE22) are grouped (change trend grouping step S3), and the measurement locations are narrowed down from the multiple grouped groups (measurement location narrowing down step S4).

[0040] In the change tendency grouping step S3, a parameter called similarity is defined, and using this parameter, the smaller the similarity value, the more similar the temperature change tendency is, and grouping is performed. When calculating this similarity, two temperature measurement points to be compared are selected under certain test conditions (in this embodiment, the test with the test number in Table 2), and in this embodiment, any two are selected from the 1st to 22nd points Ch1 to Ch22, and one of the two selected measurement points is used as a reference object and the other is used as a comparison object to calculate the similarity.

[0041] To explain this similarity with reference to Figure 5, for example, as shown in Figure 5(a), the temperature of measurement point A of the reference object (for example, the first point Ch1) changes as shown by the solid line ΔT1, and the temperature of measurement point B of the comparison object (for example, the second point Ch2) changes as shown by the dashed line ΔT2.

[0042] To calculate this similarity, first, as shown in Figure 5(b), the temperature change (ΔT1) at measurement point A (first location Ch1) of the reference object is divided by its maximum temperature change (ΔTmax) to make the temperature change at measurement point A (reference point) dimensionless.

[0043] Next, the coefficient α (℃) is applied to the temperature change at the measurement point B (second point Ch2) to be compared. -1 ), and the sum of squared residuals between this value and the temperature change at measurement point A, which has been made dimensionless, is calculated. The sum of these sums of squared residuals for all the tests under consideration (in this embodiment, all the tests with the test numbers in Table 2) is defined as the similarity between measurement point A (first location Ch1) and measurement point B (second location Ch2) to calculate the similarity. The coefficient α is a value determined so as to minimize the similarity.

[0044] The results of this similarity for all combinations of measurement points, that is, the 1st to 22nd measurement points Ch1 to Ch22, are shown in Table 4 as a list.

[0045] [Table 4] Since the similarity defined in this way is the sum of the residual sum of squares of the temperature change amounts of the two measurement points used in the comparison (the measurement point of the reference subject and the measurement point of the comparison subject), the smaller this similarity is, the higher the correlation between the temperature change trends of the two measurement points. In this way, the similarity trend is determined for all measurement points.

[0046] When grouping the temperature change trends, the similarity between two measurement points, excluding the same temperature measurement points, is extracted in ascending order of value, and groups are formed by removing overlapping combinations. A threshold value is set for this grouping, and grouping is performed based on this threshold value. Note that an appropriate value can be set for this threshold value.

[0047] When the temperature change trends at the 1st to 22nd locations Ch1 to Ch22 are grouped based on the similarity as described above, the results are as shown in Table 5, for example, and in this embodiment, the temperature change trends are classified into 1st to 9th groups (G1 to G9).

[0048] [Table 5] Then, the measurement locations are narrowed down from the temperature change tendency groups, which in this embodiment are the first to ninth groups G1 to G9 (measurement location narrowing down step S4). In this narrowing down, the number of measurement locations is selected corresponding to the number of terms in the thermal deformation estimation formula to be set. For example, when setting a thermal deformation estimation formula with four terms, four measurement locations are selected, and when setting a thermal deformation formula with three terms (or five terms), three measurement locations (or five measurement locations) are selected.

[0049] In this narrowing down, one or two measurement points are narrowed down from one group, and when three or more measurement points are narrowed down from one group, the emphasis is on the temperature change of the selected specific group, and the temperature change of the entire NC lathe is not considered, which is undesirable. In addition, in this narrowing down, it is desirable to include the second group G2 which includes the largest number of measurement points (10 in this case), and by including this second group G2, the temperature change of the representative measurement points of the NC lathe is considered, making it possible to more accurately estimate the amount of thermal deformation of the workpiece P.

[0050] Considering the above, in this embodiment, the second group G2 including the most (in this case, 10) measurement points, the third group G3 including the second most (in this case, 5) measurement points, and the remaining seven groups (groups including one measurement point), for example, the fifth and seventh groups G5 and G7 are selected. Note that, for the remaining seven groups, any two groups may be selected from groups including measurement points that measured temperatures related to the NC lathe (i.e., measurement points other than the 19th measurement point Ch19), and for example, the fourth and sixth groups G4 and G6 may be selected instead of the fifth and seventh groups G5 and G7.

[0051] Then, the measurement location is narrowed down by one from the selected groups (the second group G2, the third group G3, the fifth group G5, and the seventh group G7). In this embodiment, for the second group G2, the sixth measurement location Ch6 is narrowed down from the ten measurement locations, for the third group G3, the twelfth measurement location Ch12 is narrowed down from the five measurement locations, for the fifth group 5G, the eighth measurement location Ch8 is narrowed down, and for the seventh group G7, the fourteenth measurement location Ch14 is narrowed down, and in this manner, a combination of measurement locations is selected.

[0052] Since the second group G2 includes 10 measurement points that show the same or similar temperature change trends, instead of the sixth measurement point Ch6, a combination of measurement points may be selected by narrowing down the combination to any one of the remaining nine measurement points, for example, the second measurement point Ch2, the twenty-second measurement point Ch22, the fifth measurement point Ch5, the eleventh measurement point Ch11, the eighteenth measurement point Ch18, the twentieth measurement point Ch20, the twenty-first measurement point Ch21, the ninth measurement point Ch9, and the fifteenth measurement point Ch15.

[0053] Furthermore, for the third group G3, similarly to the second group G2, instead of the 12th measurement point Ch12, a combination of measurement points may be selected by narrowing down the combination to, for example, any one of the third measurement point Ch3, the seventh measurement point Ch7, the 13th measurement point Ch13, and the 16th measurement point Ch16.

[0054] Once the measurement locations have been narrowed down to four in this manner, a thermal deformation estimation equation is then set to obtain the amount of thermal deformation ΔD (i.e., the amount of change in machining diameter) of the workpiece P caused by the thermal deformation of the lathe body 2 (bed 3) (estimation equation setting step S5). In this embodiment, since the measurement locations have been narrowed down to four, a thermal deformation estimation equation with the number of terms corresponding to the number of measurement locations, i.e., a four-term thermal deformation estimation equation, is set. In this case, the predicted amount ΔD1 of the amount of change in machining diameter of the workpiece P caused by the thermal deformation of the lathe body 2 (bed 3) is calculated using the following equation (1): ΔD1=a1×ΔT1+a2×ΔT2+a3×ΔT3+a4×ΔT4 (1) In this formula (1), ai (i = 1 to 4) is an empirical constant, and ΔTi (i = 1 to 4) is the temperature change at each measurement point.

[0055] For example, when the number of measurement points is narrowed down to three, the thermal deformation estimation formula (i.e., the predicted amount ΔD2 of the change in the machining diameter of the workpiece P caused by the thermal deformation of the lathe body 2) is expressed by the following formula (2): ΔD2=a1×ΔT1+a2×ΔT2+a3×ΔT3 (2) It can be expressed as:

[0056] Next, the measured temperature (specifically, the measured temperature change) is substituted into the above formula (1), and the experimental constants a1 to a4 are determined so that the residual sum of squares between the actual value of the machining diameter change of the workpiece P and the machining diameter change prediction amount ΔD1 of the workpiece P using the above formula (1) is minimized (experimental constant determination step S6). In this embodiment, for example, the temperature change amount of the sixth measurement point Ch6 of the second group G2 is substituted for the temperature change amount ΔT1, for example, the temperature change amount of the twelfth measurement point Ch12 of the third group G3 is substituted for the temperature change amount ΔT2, for example, the temperature change amount of the eighth measurement point Ch8 of the fifth group G5 is substituted for the temperature change amount ΔT3, and for example, the temperature change amount of the fourteenth measurement point Ch14 of the seventh group G7 is substituted for the temperature change amount ΔT4. The calculation of this residual sum of squares can be performed, for example, by a simple numerical solution.

[0057] Then, the empirical constants a1 to a4 of the thermal deformation estimation formula are determined using the calculation results (empirical constant determination step S7). The empirical constants determined in this manner are, for example, as shown in Table 6.

[0058] [Table 6] By using the experimental constants a1 to a4 shown in Table 6, the above formula (1) can be expressed as the following formula (3): ΔD1=5.37×ΔT1+0.50×ΔT2-4.83×ΔT3+ 0.26×ΔT4 (3) In this way, it is possible to determine a thermal deformation estimation equation for calculating a predicted change in machining diameter ΔD1 (ΔD3) of the workpiece P due to the thermal deformation of the lathe body 2 (bed 3) when the above-mentioned NC lathe is used.

[0059] In order to determine more optimal experimental constants, the combination of temperature tendency groups and / or the combination of narrowed-down measurement points in the measurement point narrowing-down step S4 are changed and the estimation formula setting step S5 and the experimental constant determination step S6 are repeated multiple times (for example, about 10 to 30 times) (repeated experimental constant determination step S7). In the second round, for example, for the second group G2, the second measurement point Ch2 is narrowed down, for example, for the third group G3, the seventh measurement point Ch7 is narrowed down, for example, for the fourth group G4, the fourth measurement point Ch4 is narrowed down, and for example, for the sixth group G6, the tenth measurement point Ch10 is narrowed down, and thus the combination of measurement points is changed (measurement point narrowing-down step S4). After narrowing down the four measurement points for the second round in this way, the thermal deformation amount ΔD (i.e., the amount of change in machining diameter) of the workpiece P caused by the thermal deformation of the lathe body 2 (bed 3) is next obtained (estimation formula setting step S5). In this case, the predicted change in machining diameter of the workpiece P caused by the thermal deformation of the lathe body 2 (bed 3) is calculated by the following formula (1): ΔD1=a1×ΔT1+a2×ΔT2+a3×ΔT3+a4×ΔT4 (1) The measured temperature (specifically, the measured temperature change) is substituted into this formula (1), and the experimental constants a1 to a4 are determined so that the residual sum of squares between the actual value of the machining diameter change of the workpiece P and the predicted machining diameter change amount ΔD1 of the workpiece P using the above formula (1) is minimized. In the case of this second round, for example, the temperature change amount of the second measurement point Ch2 of the second group G2 is substituted for the temperature change amount ΔT1, for example, the temperature change amount of the seventh measurement point Ch7 of the third group G3 is substituted for the temperature change amount ΔT2, for example, the temperature change amount of the fourth measurement point Ch4 of the fourth group G4 is substituted for the temperature change amount ΔT3, and for example, the temperature change amount of the tenth measurement point Ch10 of the sixth group G6 is substituted for the temperature change amount ΔT4. The calculation of this residual sum of squares can also be calculated using a simple numerical solution, as described above. Then, the experimental constants a1 to a4 of the second round are determined using this calculation result (experimental constant determination step S6).

[0060] In this way, the combination of temperature trend groups and / or the combination of narrowed-down measurement locations in the measurement location narrowing-down step S4 are changed, and the estimation formula setting step S5 and the empirical constant determination step S6 are repeated multiple times to perform the empirical constant determination repetition step S7. Note that the number of repetitions in the empirical constant determination repetition step S7 can be any number of times, and may be performed for all combinations of temperature trend groups and narrowed-down measurement locations.

[0061] Then, an optimal experimental constant determination step S8 is performed to determine the optimal combination of measurement points and optimal experimental constants suitable for the thermal deformation estimation formula. In determining the optimal experimental constants, the thermal deformation amount ΔD (i.e., the amount of change in machining diameter) of the workpiece P is calculated using the thermal deformation estimation formula into which the experimental constants determined by each of the multiple combinations are substituted, and the thermal deformation estimation formula that is closest to the thermal deformation amount of the workpiece due to actual machining is determined from these calculated thermal deformation estimation formulas, and the experimental constants in this thermal deformation estimation formula become the optimal experimental constants.

[0062] When the optimal empirical constants are determined in this manner, the optimal measurement locations are also determined, and a thermal deformation estimation formula using the optimal empirical constants is also determined, making it possible to accurately estimate the amount of thermal deformation of the workpiece P using this thermal deformation estimation formula, the optimal combination of measurement locations, and the optimal empirical constants (thermal deformation amount estimation step S9). When using this thermal deformation estimation formula (3), it is not necessary to provide the first to twenty-second temperature detection sensors SE1 to SE22 at the first to twenty-second measurement locations Ch1 to Ch22 described above, and it is sufficient to provide temperature detection sensors at the measurement locations narrowed down when determining this thermal deformation estimation formula (3).

[0063] For example, if the measurement points of temperature fluctuation adopted in the thermal deformation estimation formula determined as the optimal experimental constants are, for example, the 6th measurement point Ch6, the 12th measurement point Ch12, the 8th measurement point Ch8, and the 14th measurement point Ch14, then it is sufficient to provide a 6th temperature detection sensor SE6 corresponding to the 6th measurement point Ch6, a 12th temperature detection sensor SE12 corresponding to the 12th measurement point Ch12, an 8th temperature detection sensor SE8 corresponding to the 8th measurement point Ch8, and a 14th temperature detection sensor SE14 corresponding to the 14th measurement point Ch14.After determining this thermal deformation estimation formula (3), the predicted amount of change in the machining diameter of the workpiece P can be accurately calculated with a relatively simple configuration.

[0064] The thermal deformation estimation formula (3) obtained in this way can be applied to the correction of thermal deformation of the workpiece P, and when it is actually applied to an NC lathe for machining, it can be performed as follows, for example, along the flow shown in Fig. 6. First, one cycle of a predetermined machining (for example, cutting) is performed on the workpiece (machining step S11).

[0065] When this processing cycle is completed, the temperatures at four measurement points (in this case, for example, the sixth measurement point Ch6, the twelfth measurement point Ch12, the eighth measurement point Ch8 and the fourteenth measurement point Ch14) are measured by temperature detection sensors (in this case, the sixth temperature detection sensor SE6, the twelfth temperature detection sensor SE12, the eighth temperature detection sensor SE8 and the fourteenth temperature detection sensor SE14) (temperature measurement step S12).

[0066] Next, the measured temperatures at the four measurement points are used to calculate the predicted amount of thermal deformation of the workpiece (predicted amount calculation step S13). When using the thermal deformation estimation formula (3), the temperature change amounts (ΔT1 to ΔT4) at the four measurement points are calculated, and these temperature change amounts (ΔT1 to ΔT4) are substituted into the thermal deformation formula (3) to perform calculations, thus calculating the predicted amount of thermal deformation in the current processing cycle. The current predicted amount of thermal deformation (estimated amount of thermal deformation) is registered in a storage device or the like, as it will be used in the next processing cycle.

[0067] Then, the difference between the predicted amount of thermal deformation in the previous machining cycle and the predicted amount of thermal deformation in the current machining cycle is calculated (prediction difference calculation step S14), and the thermal deformation is corrected so that this predicted difference is reflected in the next machining cycle (thermal deformation correction step S15). That is, this predicted difference is added to the machining conditions for machining the workpiece, and thermal deformation correction is performed in this manner. Then, in the next machining cycle, the machining cycle is performed under the machining conditions after thermal deformation correction, and machining (cutting) of the workpiece is performed while repeatedly performing thermal deformation correction in this manner, and by machining in this manner, high-precision machining with reduced thermal deformation is possible.

[0068] In the above-described embodiment, an example has been described in which thermal deformation correction is performed for each cycle of processing the workpiece, but such thermal deformation correction may also be performed for multiple cycles of the workpiece (for example, an appropriate number of cycles, for example, three cycles).

[0069] We verified whether the thermal deformation estimation formula determined as described above could actually be applied to, for example, an NC lathe, and obtained the results shown in Tables 7 and 8.

[0070] [Table 7]

[0071] [Table 8] Table 7 shows the results when cutting oil is not used, and Table 8 shows the results when cutting oil is used. It was confirmed that the effect of thermal correction can be obtained by using the above thermal deformation estimation formula both when cutting oil is used and when it is not used.

[0072] The above describes one embodiment of the thermal deformation estimating method and thermal deformation correcting method for a machine tool according to the present invention. However, the present invention is not limited to such an embodiment, and various modifications and alterations are possible without departing from the scope of the present invention.

[0073] For example, in the above-described embodiment, in the experimental constant determination repeat step S7, the combination of temperature trend groups and / or the combination of narrowed-down measurement points are changed to determine the optimal combination of measurement points and optimal experimental constants for the thermal deformation estimation formula. However, instead of such a configuration, in the experimental constant determination repeat step S7, the combination of temperature trend groups, the combination of measurement points and / or the form of the thermal deformation estimation formula may be changed to determine the optimal thermal deformation estimation formula suitable for the machine tool and the optimal combination of measurement points and optimal experimental constants suitable for this. When this is done, the amount of thermal deformation (change in machining diameter) of the workpiece can be estimated with higher accuracy.

[0074] In this case, in the experimental constant determination repeating step, it is preferable to set at least any two of three or more thermal deformation estimation equations consisting of three, four or five or more terms, and to repeat the estimation equation setting step and the experimental constant determination step using the at least two thermal deformation estimation equations while changing the combination of temperature trend groups and / or the combination of measurement points to be narrowed down, to determine the thermal deformation estimation equation with the optimal number of terms, the optimal combination of measurement points, and the optimal experimental constants.

[0075] In addition, for example, in the above-mentioned embodiment, in the step of measuring the spindle-to-cutlery distance and temperature in the thermal deformation estimation method, the spindle-to-cutlery distance and the temperature change at the measurement point are measured by an actual cutting test alone or a combination of an actual cutting test and a simulated cutting test, but the present invention is not limited to such a configuration and may be performed by a simulated cutting test alone. In this case, the spindle-to-cutlery distance is measured using a dummy workpiece. [Explanation of symbols]

[0076] 2. Lathe body 3 Beds 4 Main shaft 6 Turret device 7 Spindle 14 Moving parts 16 Support Table 18 First support mechanism 20 Second support mechanism 26 Turret body Ch1~Ch22 measurement points K processing tool P Workpiece SE1~SE22 Temperature detection sensors

Claims

1. a test condition setting step for setting test conditions for a workpiece taking into consideration actual machining of the machine tool using an experimental design method; a spindle-to-cutter distance and temperature measurement step for measuring the spindle-to-cutter distance and temperature changes at multiple locations of the machine tool when a simulated cutting test and / or an actual cutting test based on the test conditions is performed on the workpiece; a change tendency grouping step for grouping locations showing similar trends based on the change tendency of the measured temperatures at the multiple locations; a measurement location narrowing down step for selecting multiple temperature trend groups from the grouped multiple temperature tendency groups and narrowing down one or two measurement locations from each selected temperature trend group; an estimation equation setting step for setting a thermal deformation estimation equation with a number of terms corresponding to the number of narrowed-down measurement locations; a step of repeating the estimation formula setting step and the experimental constant determination step a plurality of times by changing the combination of the temperature trend groups and / or the combination of the measurement points to be narrowed down in the measurement point narrowing down step, and a step of determining an optimal combination of measurement points and an optimal experimental constant suitable for the thermal deformation estimation formula after the experimental constant determination repetition step; and a step of estimating the amount of thermal deformation of the workpiece using the thermal deformation estimation formula, the optimal combination of measurement points, and the optimal experimental constant.

2. The thermal deformation estimation method described in claim 1, characterized in that in the experimental constant determination repeating step, the estimation equation setting step and the experimental constant determination step are repeated multiple times by changing the combination of temperature trend groups in the measurement point narrowing down step, the combination of narrowed down measurement points and / or the form of the thermal deformation estimation equation, and in the optimal experimental constant determination step, an optimal thermal deformation estimation equation suitable for the machine tool, an optimal combination of measurement points suitable for this, and the optimal experimental constants are determined.

3. The thermal deformation estimation method for a machine tool as described in claim 2, characterized in that in the empirical constant determination repeating step, at least any two of three or more thermal deformation estimation equations consisting of three, four, or five or more terms are set, and the estimation equation setting step and the empirical constant determination step are repeated using at least two thermal deformation estimation equations while changing the combination of the temperature trend groups and / or the combination of the measurement points to be narrowed down.

4. A method for estimating thermal deformation of a machine tool as described in any one of claims 1 to 3, characterized in that in the change tendency grouping step, the temperature change amount on the reference side is divided by the maximum temperature change amount to make the temperature change amount on the reference side dimensionless, and then a coefficient is multiplied by the temperature change to be compared, and the sum of squared residuals between this coefficient-integrated temperature change and the dimensionless temperature change is calculated to calculate a similarity, and the temperature change tendencies are grouped based on the similarity.

5. The method for estimating thermal deformation of a machine tool as described in claim 1, characterized in that the machine tool is an NC lathe, the experimental design method is an all-pairs method, and the test conditions set in the test condition setting step include the diameter of the workpiece, the machining length of the workpiece, the number of times the workpiece is machined, fluctuations in the machining environment temperature, and whether or not cutting oil is used.

6. a test condition setting step of setting test conditions for a workpiece taking into consideration actual machining of a machine tool using an experimental design method; a spindle-to-cutter distance and temperature measurement step of measuring a spindle-to-cutter distance and temperature changes at a plurality of locations of the machine tool when a simulated cutting test and / or an actual cutting test based on the test conditions is performed on the workpiece; a change tendency grouping step of grouping locations showing similar trends based on the change trends of the measured temperatures at the plurality of locations; a measurement location narrowing down step of selecting a plurality of temperature tendency groups from the plurality of grouped temperature tendency groups and narrowing down one or two measurement locations from each selected temperature tendency group; an estimation equation setting step of setting a thermal deformation estimation equation having a number of terms corresponding to the number of narrowed-down measurement locations; and a residual between an actual value of the change in the workpiece and a predicted amount of change in the workpiece using the thermal deformation estimation equation by substituting an amount of change in the measured temperature corresponding to each term in the thermal deformation estimation equation. a thermal deformation estimation step for estimating an amount of thermal deformation of the workpiece using the thermal deformation estimation formula, the optimal combination of measurement points, and the optimal experimental constant; a deformation amount difference calculation step for calculating a difference in the amount of thermal deformation of the workpiece in a previous machining process and a thermal deformation amount of the workpiece in a current machining process; and a thermal deformation correction step for correcting the difference in the amount of thermal deformation calculated in the deformation amount difference calculation step.

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