Numerical control device for a machine tool

Abstract

Numerical control device for a machine tool, wherein the numerical control device controls a machine tool having a main spindle (2) for mounting a tool, a table (3) holding a workpiece and a clamping device, three translational axes and one or more rotational axes, wherein the numerical control device comprises: a fault determination unit (19) which measures a position of a target mounted on any of the main spindle (2) and the table (3) using a measuring unit mounted on another of the main spindle (2) and the table (3) and determines an axis-dependent deformation fault parameter based on three-dimensional coordinate values ​​of a plurality of the measured positions of the target, an axis-dependent deformation error estimation unit (20) which calculates an estimated value of an axis-dependent deformation error caused by a deformation of the machine tool due to an operation of at least one of the translation axes and the rotation axes based on at least the axis-dependent deformation error parameter and a function of a geometric error of six degrees of freedom of the rotation axes, taking the instruction value of the rotation axes; an input unit (17) that receives a mass and a center of gravity position from at least one of the workpiece and the clamping device; a gravitational deformation estimation unit (18) which calculates an estimated value of a gravitational deformation error caused by the mass of at least one of the workpiece and the clamping device based on a function depending on at least one gravitational deformation error parameter, the mass and the center of gravity position received at the input unit (17) and the instruction values ​​of the rotation axes; a correction value calculation unit (16) that calculates correction values ​​for at least one of the translational and rotational axes with respect to an error in the position and orientation of the tool with respect to the workpiece, based on the estimated value of the axis-dependent deformation error, the estimated value of the gravitational deformation error, and the instruction values; and an addition unit (21) that adds the correction values ​​to the instruction values.

Description

[0001] The invention relates to a numerical control device and a numerical control method for correcting a deformation of a machine tool caused by the mass of a workpiece.

[0002] Fig. Figure 1 is a schematic representation of a five-axis CNC machining center comprising three translational and two rotational axes. Two degrees of freedom of translation of a main spindle head 2 along the X and Z axes, which are the translational axes and are perpendicular to each other, are possible with respect to a bed 1. One degree of freedom of rotation of a table 3 along the C axis, which is the rotational axis, is possible with respect to a slide 4. One degree of freedom of rotation of the slide 4 along the A axis, which is the rotational axis, is possible with respect to a pivot 5. The A and C axes are perpendicular to each other. Furthermore, one degree of freedom of translation of the pivot 5 along the Y axis, which is the translational axis and is perpendicular to the X and Z axes, is possible with respect to the bed 1.Accordingly, the main spindle head 2 can move in three degrees of freedom for translation and in two degrees of freedom for rotation with respect to the table 3. Servo motors, controlled by a numerical control system (not shown), drive the respective feed shafts. A workpiece is attached to the table 3, a tool is attached to the main spindle head 2 and rotated, and the relative position and orientation between the workpiece and the tool are controlled, thus ensuring machining.

[0003] For example, geometric errors between the respective axes, such as an error in the center position of the rotational axis (an offset from an assumed position) and an inclination error of the rotational axes (rectangularity and parallelism between the axes), affect the motion accuracy of this five-axis machine. These geometric errors degrade the machine's motion accuracy and thus reduce machining accuracy. While geometric errors can be reduced through adjustment, eliminating them entirely is difficult. Implementing a control system to correct these geometric errors enables high-precision machining.

[0004] Several methods have been proposed for measuring geometric error in a machine. However, these methods require expensive measuring equipment or multiple measuring devices. Measuring the error described above demands a certain level of technical skill. The publication of the unexamined Japanese patent application JP 2011-038902A discloses a system in which a probe is mounted on a tool holder in a machine, a target ball is installed on a table, the machine automatically performs a switching operation of an inclined axis and a rotational axis to a specified switching position, a center coordinate of the target ball is measured at each switching position, and then a geometric error is determined and corrected based on this result.

[0005] A deformation error caused by an external force, such as the gravity of a clamping device or a workpiece placed on the table 3, or by a displacement of the center of gravity of the slide 4, pivot 5, or the like, in accordance with operations of the translational and rotational axes, is also one of the factors affecting the motion accuracy in this five-axis machine. To reduce the deformation error, there is a method of increasing static stiffness by implementing a countermeasure, such as increasing the thickness of each component that makes up the machine. However, this method creates a problem due to the increase in the machine's mass itself, such as a reduction in speed and an increase in material costs.

[0006] Regarding such a problem, a geometric error in the three-dimensional measuring machine is described in the publication of the unexamined Japanese patent application JP 2005-214943A. In this process, workpieces with different masses are pre-loaded, and a compensation parameter for each workpiece's mass is derived from its measurement result and stored. A compensation parameter corresponding to the workpiece being measured is then retrieved from the stored parameters, if necessary, to correct a measured coordinate of that workpiece.

[0007] The publication of the unexamined Japanese patent application JP 2009 - 104 317 A proposes a device that corrects various errors by absorbing different errors, such as a deformation error due to an external force, a thermal displacement and a positioning error in the machine as geometric errors in a simpler configuration.

[0008] The deformation error described above varies depending on the assembly accuracy of each machine table. If the machine table has been used for a long time, its components will wear out, thus altering its deformation behavior. In this respect, if a deformation error is estimated based on a deformation error measured beforehand, as described in the publication of the unexamined Japanese patent application JP 2005-214943A, an error due to long-term change will occur.

[0009] According to the system described in the publication of the unexamined Japanese patent application JP 2011-038902A, it is possible to automatically determine the geometric error for long-term changes in the machine using a measuring device, such as a probe. However, it is not possible to determine a deformation error that changes depending on the position of an axis. When a large workpiece is inserted, it is sometimes impossible to take a measurement because the workpiece overlaps the machine. Furthermore, if the workpiece's center of gravity is eccentric from the center of the axis of rotation, its position changes depending on the position of the C-axis, thus altering the deformation behavior, and therefore it is not possible to determine the geometric error.

[0010] The publication of the unexamined Japanese patent application JP 2009-104317A assumes that the deformation error due to the external force is a function of, for example, the mass and center of gravity of the workpiece. However, as described above, the deformation behavior changes depending on variations in the machine table and the machine's operating conditions. Therefore, it is not possible to accurately estimate the deformation error solely based on the functions of the workpiece's mass and center of gravity.

[0011] German patent application DE 10 2016 008 043 A1 discloses a numerical control device for a machine tool with an axis-dependent deformation error estimation unit that calculates an estimated value of an axis-dependent deformation error caused by a deformation of the machine tool due to an operation of at least one of the translational and rotational axes, based on at least the axis-dependent deformation error parameter and instruction values ​​of at least one of the translational and rotational axes. The control device further comprises a correction value calculation unit that calculates correction values ​​of at least one of the translational and rotational axes with respect to an error in the position and orientation of the tool relative to the workpiece, based on the estimated value of the axis-dependent deformation error and the instruction values.

[0012] In DE 10 2015 113 890 A1, a machine tool with a workpiece position- and weight-dependent spring compensation is disclosed. The machine tool has an input unit that receives a mass and a center of gravity position of at least one of the workpiece and the clamping device, and a gravitational deformation estimation unit that calculates an estimated value of a gravitational deformation error caused by the mass of at least one of the workpiece and the clamping device based on at least one gravitational deformation error parameter, the mass and center of gravity position received at the input unit, and the instruction values.

[0013] Therefore, it is an object of the invention to provide a numerical control device and a numerical control method that ensures machining with high accuracy with respect to different workpieces by estimating a deformation error based on a mass and center of gravity position of a workpiece that are input, and determining the deformation error using a measuring device, such as a probe, in a state in which the workpiece has been introduced.

[0014] The problem is solved by a numerical control device according to claim 1. Advantageous further developments are the subject of the dependent claims.

[0015] To solve the problem described above, a numerical control device for a machine tool with the features of claim 1 is provided.

[0016] The invention can determine the deformation error with the measuring device even if the deformation behavior changes depending on the modification for each machine table and the machine's operating conditions. Even if a large workpiece has been introduced to make measurement difficult due to the superimposition, after the deformation error has been determined in a measurable state, for example, in a state where only the clamping device has been introduced, the deformation error is estimated from information about the mass and center of gravity position of a clamping device and a workpiece that was subsequently introduced, thus providing a more accurate estimate of the deformation error.Furthermore, if the workpiece's center of gravity is eccentric to the center of rotation, the deformation error, which changes depending on the position of the rotation axis, can be estimated based on the workpiece's mass and center of gravity position. The change in the deformation error as a function of the rotation axis position is also corrected by a correction based on the estimated deformation error. Moreover, the use of the measuring device can determine the deformation error, which was previously difficult to estimate.

[0017] As described above, correcting the determined and estimated error ensures machining with higher accuracy in relation to the various workpieces. Fig. Figure 1 is a schematic representation of a five-axis control machining center. Fig. Figure 2 is a block diagram of a conventional numerical control device. Fig. Figure 3 is a block diagram of a numerical control device that performs a numerical control method of the invention. Fig. Figure 4 is a flowchart for determining a geometric error.

[0018] The following describes embodiments of the invention based on the drawings.

[0019] In an exemplary embodiment of the invention, Fig. 1. A five-axis control machining center (hereinafter referred to as a “five-axis machine”) is presented as an example. At this point, an embodiment is taken as a pivot-table type machining center whose axis configuration from a workpiece to a tool is a C-axis, A-axis, Y-axis, X-axis, and Z-axis. However, the invention does not limit the machine tool to a machining center and a five-axis machine, provided that a machine tool has three translational axes and at least one rotational axis.

[0020] Next, a description of a geometric error will be given.

[0021] The geometric error is defined as having a total of six components (δx, δy, δz, α, β, and γ) of relative translational errors in three directions and relative rotational errors in three directions between the respective axes. In the five-axis machine in this example, the axis connection from a workpiece (a material to be machined) attached to table 3 to a tool mounted on a main spindle of the main spindle head 2 has the sequence C-axis, A-axis, Y-axis, X-axis, and Z-axis. There are a total of 36 geometric errors to consider between the Z-axis and the tool and between the workpiece and the C-axis. However, a majority of these 36 errors exhibit redundant ratios.Thus, with these removed, the final geometric errors total 13 pieces: δx5, δy5, α5, β5, δy4, δz4, β4, γ4, γ3, α2, β2, α1 and β1, when the sequence of the respective geometric errors is represented as indices from one side of the tool. These geometric errors refer to the X-direction error of the C-axis center position, the offset error between the C- and A-axes, the angular offset error of the A-axis, the rectangularity between the C- and A-axes, the Y-direction error of the A-axis center position, the Z-direction error of the A-axis center position, the rectangularity between the A- and X-axes, the rectangularity between the A- and Y-axes, the rectangularity between the X- and Y-axes, the rectangularity between the Y- and Z-axes, the rectangularity between the Z- and X-axes, the rectangularity between the main spindle and the Y-axis, and the rectangularity between the main spindle and the X-axis.

[0022] Fig. Figure 2 represents an exemplary conventional numerical control device.

[0023] After an editing program 11 has been entered, an instruction value generator 12 creates an instruction value for each drive axis.

[0024] Next, a correction value calculator 16 calculates a correction value for each axis based on the generated instruction value. Then, a total value consisting of the instruction value and the correction value is transferred to the servo instruction value transfer calculator 13 to calculate a servo instruction value. The servo instruction values ​​for the respective axes are transferred to servo amplifiers 14a to 14e for the respective axes. The servo amplifiers 14a to 14e for the respective axes each control servo motors 15a to 15e to control the relative position and orientation of the main spindle head 2 with respect to the table 3.

[0025] This section describes a method for calculating the correction value in relation to the geometric error. To determine a tool center vector P... T To convert a vector in a workpiece coordinate system on the table 3 from a main spindle coordinate system on the main spindle head 2 to a workpiece coordinate system on the table 3, assuming that the length of a tool to be used is t and the instruction positions of the X, Y, Z, A and C axes are x, y, z, a and c respectively, the tool center vector in the workpiece coordinate system can be obtained by performing a homogeneous coordinate transformation using the following formula 1. That is, a tool center vector P I without the geometric error in the workpiece coordinate system P1=M5⋅M4⋅M3⋅M2⋅M1⋅PT where M5=[cos c−sin c00sin ccos c0000100001], M4=[10000cos a−sin a00sin acos a00001], M3=[1000010y00100001], M2=[100x010000100001], M1=[10000100001z0001], PT=[00−t1]

[0026] On the other hand, as in the following formula 2, a tool center vector P is used. R In the workpiece coordinate system, the geometric error is obtained by arranging the respective geometric error as transformation matrices between transformation matrices of the respective axes in Formula 1. Formula 2 is an approximation formula which, assuming that the geometric errors are minimal, assumes that the product of the geometric errors is 0. PR−ε6⋅M5⋅ε5⋅M4⋅ε4⋅M3⋅ε3⋅M2⋅ε2⋅M1⋅ε1⋅PT where εj=[1−γjβjδxjγj1−αjδyj−βjαj1δzj0001](j=1,2,…,6)

[0027] Therefore, a positional error ΔP is assumed. W= (δx, δy, δz) at a tool center point in the tool coordinate system is expressed by the following formula 3. ΔPw=PR−PI

[0028] Furthermore, an error ΔP can occur. O with the instruction value by performing a coordinate transformation as in the following formula 4 with the position error ΔP W at the tool center point in the tool coordinate system. ΔPO=M4−1⋅M5−1⋅ΔPw

[0029] Accordingly, a correction value ΔP = (Δx, Δy, Δz) of the X, Y and Z axes is obtained in the following formula 5, which takes the instruction values ​​of the respective axes and the geometric error in the formula described above as previously measured and determined parameters (geometric parameters). ΔP=−ΔPO=M3⋅M2⋅M1⋅PT−M4−1⋅M5−1⋅ε6⋅M5⋅ε5⋅M4⋅ε4⋅M3⋅ε3⋅M2⋅ε2⋅M1⋅ε1⋅PT

[0030] If, as in Formula 6 below, a positional error is corrected, the correction values ​​Δa and Δc of the rotation axes, A-axis and C-axis, are obtained. The correction value ΔP = (Δx, Δy, Δz) of the X-, Y-, and Z-axes can be obtained at this time as in Formula 7 below. {Δc=−∑j=56γjΔa=−∑j=15αj ΔP=−ΔPO=M3⋅M2⋅M1⋅PT−M4−1⋅M5−1⋅ε6⋅ξC⋅M5⋅ε5⋅ξA⋅M4⋅ε4⋅M3⋅ε3⋅M2⋅ε2⋅M1⋅ε1⋅PT where ξC=[1−Δc00Δc10000100001], ξA=[100001−Δa00Δa100001]

[0031] Thus, the correction values ​​of the respective translation axes are added to the instruction values ​​of the respective corresponding translation axes in order to instruct, and thus the correction of the position error and the alignment error due to the geometric error at the tool center point is ensured.

[0032] On the other hand, if the deformation error exists due to the external force, it is assumed that the deformation error is a function f. G is the function that indicates this error with a curved line or a group of line segments. G The deformation error can be calculated as in the following formula 8 by adding an estimated value f. G_sim and a specific value f G_idt , which will be described later, will be obtained. fG=fG_sim+fG_idt

[0033] This deformation error can be treated as a partial geometric error. For example, if table 3 deforms under the load of the workpiece, its deformation error can be treated as a geometric error between the C-axis and the A-axis. A tool center vector W P DIn the workpiece coordinate system, if the deformation error exists, 9 can be obtained from the following formula. WPD=M5⋅ξG⋅M4⋅M3⋅M2⋅M1⋅TP−MD⋅TP where ξG−[1−fGCfGBfGXfGC1−fGAfGY−fGBfGA1fGZ0001]

[0034] Next, [the text] presents Fig. Figure 3 represents an exemplary numerical control device for carrying out a numerical control method in the invention. The instruction value generation means 12 and the servo instruction value transmission means 13 are to those in Fig. 2 identical. The machining program 11, the servo amplifiers 14a to 14e and the servo motors 15a to 15e have been omitted for the sake of simplifying the drawing.

[0035] In this numerical control device, each of the gravitational deformation estimator 18 and the axis-dependent deformation error estimator 20 calculates an estimated value of the deformation error based on the instruction value calculated by the instruction value generator 12 (one gravitational deformation estimator step and one axis-dependent deformation error estimator step). The correction value for the deformation error is obtained by adding the estimated values ​​of the respective deformation errors calculated in the gravitational deformation estimator 18 and the axis-dependent deformation error estimator 20, and inputting its total value into the correction value calculation tool 16 (one correction value calculation step).The calculated correction value is added to the instruction value in an addition element 21 as an addition means in order to be entered into the servo instruction value transfer means 13 (one addition step).

[0036] A description of a sequence of processes that input the mass and center of gravity position of the workpiece into the gravitational deformation estimator 18 and calculate the estimated value of the deformation error (hereinafter referred to as a "gravitational deformation error") based on the input mass and center of gravity position of the workpiece is provided.

[0037] First, an input device 17 located in the numerical control unit inputs a mass and a center of gravity position of the workpiece into the gravitational deformation estimation device 18 (a workpiece information preservation step). The input device 17 includes a method for inputting the mass mw and the center of gravity position vw of the workpiece, which were entered manually or automatically identified.

[0038] The gravitational deformation estimator 18 calculates the gravitational deformation error in accordance with a function f. G_sim (a, c, mw, v W ) based on the input mass and center of gravity position, and the instruction value generated in instruction value generator 12. The function f G_sim (a, c, m W , v W The deformation error is a function that takes into account the instruction values ​​of the A-axis and the C-axis, the mass mw, and the center of gravity position v. WThis function is taken as a gravitational deformation error parameter. It is obtained beforehand, for example, from an actually measured value and an analytical value.

[0039] Next, a description of a sequence of processes that the function f will be given. G_idt of the deformation error (hereinafter referred to as an “axis-dependent deformation error function”) in the axis-dependent deformation error estimation tool 20 based on the geometric error determined in the error determination tool 19 and the estimated value of the deformation error, and the estimated value of the deformation error (hereinafter referred to as an “axis-dependent deformation error”) is calculated.

[0040] Fig. 4 is a sequence of a process which performs a measurement in the error determination device 19 using the measuring device to determine the geometric error.

[0041] First, before measuring the geometric error, a starting and reference position of a target ball installed on a table is determined by a probe attached to the main spindle as a measuring instrument (S1-1).

[0042] Next, for a number selected in a measurement condition, a switching measurement is performed to determine the geometric error, (S1-2).

[0043] Next, in accordance with the switching conditions of a pivot axis (the A-axis) and a rotation axis (the C-axis) set in advance by the input means 17 and the like (S1-3), switching operations of the A-axis as an inclined axis and of the C-axis as the rotation axis are performed (S1-4).

[0044] Then, a process (S1-5) to measure a coordinate of the target ball under the respective switching conditions is repeated (S1-6). The geometric error is determined from this result (S1-7).

[0045] The following describes details of steps S1-7.

[0046] Under one measurement condition, it is assumed that one of the rotation axes is fixed and the other is switched to a plurality of angles, and the center position of the target ball is measured. Difference vectors of the measured values ​​at the ball's center position with respect to the instruction value under this measurement condition can be decomposed into a radial directional component, an axial directional component, and a tangential directional component of a switching axis. These respective components can be approximated, for example, by a least-squares method as Fourier series of a zero-order component (radius error), a first-order component (center deviation), and a second-order component (elliptical shape), namely an arc with an error.

[0047] A radial directional component dRri , an axial directional component dRa i and a tangential directional component dRt i the measured values ​​at a k-th switching angle θ ijk The rotation of a j-th axis of rotation can be expressed under a measurement condition i as the following formula 10. dRri=ra0i+ra1i*cos(θijk)−rb1isin(θijk)+ra2i*cos(2θijk)+rb2i*sin(2θijk)dRai=aa0i+aa1i*cos(θijk)−ab1isin(θi jk)+aa2i*cos(2θijk)+ab2i*sin(2θijk)dRti=ta0i+ta1i*cos(θijk)−tb1isin(θijk)+ta2i*cos(2θijk)+tb2i*sin(2θijk)

[0048] The deformation error is treated as a geometric error between the C-axis and the A-axis. An axis-dependent deformation error is assumed if the A-axis angle is α. G_idt (a) to be. If it is assumed that a fixed axis is the A-axis, the switching axis is the C-axis, and the A-axis angle under the measurement condition ia iis, will be, if the geometric error between the C-axis and the A-axis under measurement condition i, i.e., the A-axis angle a i is an axis-dependent deformation error f G_idt (a i ) as determined in the following formula 11. Here, H is a coordinate in the Z-direction of the target ball's center point in a table coordinate system (a coordinate system on the table which, in an ideal state without geometric error, assumes an intersection of the A- and C-axes as its origin and whose X-axis is parallel to the X-axis of the machine). fG_idt X(ai)=−ra1i−fG_idt_B(ai)*H fG_idt Y(ai)=rb1i+fG_idt_A(ai)*H fG_idt Z(ai)=aa0i fG_idt A(ai)=ab1i fG_idt B(ai)=aa1i fG_idt C(ai)=ta0i

[0049] Under a plurality of measurement conditions, as in Formula 11, a geometric error of six degrees of freedom is determined using a function of the geometric error of six degrees of freedom by assuming the instruction value of the A-axis as one variable, thus giving the axis-dependent deformation error f G_idt (a i ) with respect to each A-axis angle a i is obtained under the majority of measurement conditions. An axis-dependent deformation error function f G_idt (a) is obtained by interpolating the axis-dependent deformation error f G_idt (a i ) with respect to each A-axis angle a i with the straight line and the curved line and by approximating the discrete value with, for example, a trigonometric function.

[0050] An example of the approximation using the trigonometric function is described. If it is assumed that an x-direction component fG_idt Since x (a) of the axis-dependent deformation error function can be expressed in a first-order trigonometric function, the x-direction component f G_idt x (a) of the axis-dependent deformation error function as in the following formula 12 using X-direction components δx a and δx b an axis-dependent deformation error parameter can be expressed. fG_idt X(a)=δxa(1−cos(a))+δxb sin(a)

[0051] Formula 12 can be solved using, for example, the method of least squares by identifying an X-direction-axis-dependent deformation error f. G_idt x (a i ) with respect to a plurality of A-axis angles a i for the X-direction axis-dependent deformation error parameter δx a and δx bFive components other than the X-direction component are calculated simultaneously to determine the axis-dependent deformation error parameters of six degrees of freedom.

[0052] Thus, the axis-dependent deformation error estimator 20 calculates the estimated value of the axis-dependent deformation error based on the axis-dependent deformation error parameter determined in the error determination agent 19 and the instruction value. The estimated value is combined with the estimated value of the gravitational deformation error calculated in the gravity deformation estimator 18 to input its total value into the correction value calculation agent 16, obtaining the correction value to be added to the instruction value.

[0053] Thus, according to the numerical control device and the numerical control method of the five-axis machine described above, the estimated value of the axis-dependent deformation error caused by the deformation of the five-axis machine, such that the translational and / or rotational axes are operating, is calculated by the axis-dependent deformation error estimator 20 based on the axis-dependent deformation error parameter and the instruction value of the translational and / or rotational axis. The mass and center of gravity position of the workpiece are inputted to the input device 17. The estimated value of the gravitational deformation error caused by the mass of the workpiece is calculated by the gravitational deformation estimator 18 based on the gravitational deformation error parameter, the mass, and the center of gravity position received at the input device 17, and this instruction value.The correction value of the translational axis and / or the rotational axis with respect to the error of the position and / or orientation of the tool relative to the workpiece is calculated by the correction value calculation tool 16 based on the estimated value of the axis-dependent deformation error, the estimated value of the gravitational deformation error, and this instruction value. The correction value is added to the instruction value by the adder term 21.

[0054] Thus, even if the deformation behavior changes depending on a modification for each machine table and a usage condition of the machine, the deformation error can be determined with the measuring device.

[0055] For example, if a large workpiece is introduced to make measurement difficult due to an overlap, the deformation error is determined in a measurable state, such as a state in which only the clamping device is present. After the deformation error is determined, information about the mass and center of gravity position of a clamping device and any workpiece introduced from that point onward is obtained. Based on this information, the deformation is estimated more accurately. Furthermore, if the center of gravity of the workpiece is eccentric from the center of the rotation axis (C-axis), the deformation error, which changes depending on the position of the C-axis, can be estimated based on the mass and center of gravity position of the workpiece.The change in deformation error depending on the position of the C-axis is also corrected by a correction based on the estimated deformation error. Furthermore, the use of the measuring device can determine the deformation error, which was previously difficult to estimate.

[0056] As described above, correcting the determined and estimated error ensures machining with higher accuracy in relation to the various workpieces.

[0057] As another embodiment, a description of an example is given, which is achieved by determining an axis-dependent deformation error, wherein the gravitational deformation error f G_sim in a state where the clamping device and the workpiece are placed on the table, except when the axis-dependent deformation error is identified when the clamping device and the workpiece are not placed on the table.

[0058] The error caused by gravitational deformation f G_sim The positional errors of the tool centers in the X, Y, and Z axis directions caused by the following formula 13 are obtained. ΔPO_G_sim=M3⋅M2⋅M1⋅PT−M4−1⋅ξG_sim⋅M4⋅M3⋅M2⋅M1⋅PT where ξG_sim=[1−fG_simCfG_simBfG_simXfG_simC1−fG_simAfG_simY−fG_simBfG_simA1fG_simZ0001]

[0059] Accordingly, in the error determination instrument 19, after subtracting the positional errors of the tool centers in the X, Y, and Z axes obtained in formula 13 from the measured value of the sphere center position, the calculation is performed in accordance with formulas 10, 11, and 12. Thus, the axis-dependent deformation error parameter, which corresponds to the gravitational deformation error f, can be determined. G_sim excludes, can be determined.

[0060] The gravitational deformation error calculated in the gravitational deformation estimator 18 and the axis-dependent deformation error calculated in the axis-dependent deformation error estimator 20 are summed as in formula 8 to input their total value into the correction value calculation tool 16. This calculates the correction values ​​for the tool center position error and the tool center position error. The calculated correction value is added to the instruction value to correct the tool center position error and the tool center position error.

[0061] In the configuration described above and in the other embodiment, the mass and center of gravity position of the workpiece are entered. However, it can be a mass and center of gravity position that includes the workpiece and the clamping device, or it can be a mass and center of gravity position of only the clamping device.

[0062] It is explicitly stated that all features disclosed in the description and / or the claims are intended to be disclosed separately and independently of one another for the purpose of the original disclosure as well as for the purpose of limiting the claimed invention, irrespective of the combination of features in the embodiments and / or the claims. It is explicitly stated that all ranges of values ​​or specifications of groups of units disclose every possible intermediate value or possible intermediate unit for the purpose of the original disclosure as well as for the purpose of limiting the claimed invention, in particular as limits of ranges of values.

Claims

[1] Numerical control device for a machine tool, wherein the numerical control device controls a machine tool having a main spindle (2) for mounting a tool, a table (3) holding a workpiece and a clamping device, three translational axes and one or more rotational axes, wherein the numerical control device comprises: a fault determination unit (19) which measures a position of a target mounted on any of the main spindle (2) and the table (3) using a measuring unit mounted on another of the main spindle (2) and the table (3) and determines an axis-dependent deformation fault parameter based on three-dimensional coordinate values ​​of a plurality of the measured positions of the target, an axis-dependent deformation error estimation unit (20) which calculates an estimated value of an axis-dependent deformation error caused by a deformation of the machine tool due to an operation of at least one of the translation axes and the rotation axes based on at least the axis-dependent deformation error parameter and a function of a geometric error of six degrees of freedom of the rotation axes, taking the instruction value of the rotation axes; an input unit (17) that receives a mass and a center of gravity position from at least one of the workpiece and the clamping device; a gravitational deformation estimation unit (18) which calculates an estimated value of a gravitational deformation error caused by the mass of at least one of the workpiece and the clamping device based on a function depending on at least one gravitational deformation error parameter, the mass and the center of gravity position received at the input unit (17) and the instruction values ​​of the rotation axes; a correction value calculation unit (16) that calculates correction values ​​for at least one of the translational and rotational axes with respect to an error in the position and orientation of the tool with respect to the workpiece, based on the estimated value of the axis-dependent deformation error, the estimated value of the gravitational deformation error, and the instruction values; and an addition unit (21) that adds the correction values ​​to the instruction values. [2] Numerical control device for the machine tool according to claim 1, wherein the error determination unit (19) takes one of the rotational axes as a motion axis and another axis of the rotational axes as a fixed axis, positions the fixed axis at two or more fixed positions, positions the motion axis at a plurality of positions at the respective fixed positions, measures a position of the target with the measuring unit to obtain respective coordinate values ​​of the position of the target, calculates a radial component error, an axial component error and a tangential component error from the plurality of coordinate errors at the respective fixed positions, calculates a six-degrees-of-freedom error with respect to the motion axis at the respective fixed positions from the calculated radial component error,the calculated axial component error and the calculated tangential component error are determined, and the axis-dependent deformation error parameter is determined based on the majority of coordinate values ​​at the respective fixed positions from the determined error of six degrees of freedom. [3] Numerical control device for the machine tool according to claim 1, wherein the error determination unit (19) calculates an estimated value of a position error of the tool with respect to the workpiece caused by the gravitational deformation error from a difference between an estimated position of the tool when the gravitational deformation error exists, with respect to the workpiece and an ideal position of the tool with respect to the workpiece without the gravitational deformation error, and determines the axis-dependent deformation error parameter using a coordinate value obtained by subtracting the estimated value of the position error from a coordinate value measured by the measuring unit.

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