JP2016038674A - Correction value computing method and correction value computing program for machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a correction value computing method and a correction value computing program for a machine tool that efficiently compute a correction value of a translation axis.SOLUTION: A correction value computing method for a machine tool computes a correction value of a translation axis so as to correct a position error of a tool to a workpiece due to geometric error or to correct the position error and an attitude error of the tool. The method executes: a first coordinate value assigning step S3 of assigning a coordinate value at a correction reference point for turning processing to a command position of a translation axis when executing the turning processing; a second coordinate value assigning step S6 of assigning a coordinate value at a correction reference point for milling processing to the command position of the translation axis when executing the milling processing; and a correction value computing step S4 of computing a correction value on the basis of the command position of the translation axis where the coordinate value at the correction reference point for turning processing or for milling processing is assigned, a command position of a rotation axis and a geometric parameter.SELECTED DRAWING: Figure 4

Description

  According to the present invention, a spindle on which a tool is mounted and a table for holding a workpiece are moved relative to each other by two or more translation axes and one or more rotation axes, and the workpiece is rotated by the tool. In a machine tool capable of performing turning or milling a workpiece with a rotating tool, an error in the position of the tool relative to the workpiece due to a geometric error and an attitude of the tool The present invention relates to a correction value calculation method for a machine tool that calculates a correction value for the translation axis that corrects an error, and a correction value calculation program that causes a computer to execute the correction value calculation method.

  FIG. 1 is an example of the machine tool, and is a schematic view of a combined machining lathe having three translation axes and two rotation axes. The spindle head 2 is capable of translational motion with three degrees of freedom with respect to the bed 1 by means of X-axis, Y-axis, and Z-axis, which are translation axes orthogonal to each other, provided on the column 5. In addition, the spindle head 2 can move with one degree of freedom of rotation by the B axis, which is a rotation axis built in the tool post 4.

  Further, the main shaft portion 3 is provided on a main shaft base fixed to the bed 1 and is rotatable around a C axis which is a rotation shaft. A workpiece (not shown) can be attached to the main shaft portion 3. Each axis (X-axis, Y-axis, Z-axis, B-axis, C-axis) is driven by a servo motor (not shown) controlled by a numerical control device, and the workpiece is fixed to the main spindle portion 3 and the main spindle head. A tool (drill or the like) is attached to 2 and rotated, and the workpiece is milled with the rotating tool while controlling the relative position between the workpiece and the tool. In addition to this milling, a tool is fixed to the spindle head 2 and the workpiece rotated around the C axis is turned by the tool while controlling the relative position between the tool and the tool. be able to.

  Factors that affect the motion accuracy of the combined lathe described above include, for example, the error of the center position of the rotating shaft (deviation from the assumed position) and the tilt error of the rotating shaft (perpendicularity and parallelism between the axes). There is a geometric error (geometric error) between the axes. If there is a geometric error, the motion accuracy of the combined machining lathe deteriorates and the workpiece machining accuracy deteriorates. For this reason, it is necessary to reduce the geometric error by adjustment, but it is difficult to make it zero, and by performing control for correcting the geometric error, highly accurate turning and milling can be performed.

  As means for correcting geometric errors, methods as described in Patent Documents 1 and 2 have been proposed. In the method described in Patent Document 1, the position of the tool tip point due to the geometric error is converted by converting the position of the tool tip point into the position of each translational axis in consideration of the geometric error of the machine tool and setting them as command positions. Can be corrected. In the method described in Patent Document 2, the translational axis correction value calculated based on the rotational axis command value, the translational axis command value, and the geometric error is added to the translational axis command value, thereby translating. A command value for controlling the axis can be calculated. However, in the methods described in Patent Documents 1 and 2, when correcting the tilt error of the rotation axis, the translation axis is commanded to be corrected in accordance with the translation axis operation. The translation axis moves slightly. For example, when there is a parallelism error between the Z axis and the C axis as shown in FIG. 2, even if only the Z axis is operated, the X axis is slightly operated.

  Such an operation may adversely affect machining accuracy such as flat machining (turning) and drilling (milling). For example, in the combined lathe of FIG. 1, as shown in FIG. 2, when the C axis is inclined by an angle β with respect to the Z axis due to a geometric error, the correction amount of the X axis changes due to the operation of the Z axis. In this state, when the outer periphery of the workpiece 20 is turned by the cutting tool 21 with the direction indicated by the thick dotted arrow in FIG. 2 as the feed direction, the tip point of the cutting tool 21 is angled with respect to the Z axis by correcting the X axis. Move parallel to a straight line inclined by β. When the Z-axis is a sliding guide, if the above-mentioned minute movement is performed, the shaft moves or does not move, so-called “slip feed” occurs, and the machining surface of the workpiece 20 is indented. It will deteriorate the properties. In addition, when drilling a workpiece 20 with a drill, the Z axis is sent in a direction inclined by an angle β with respect to the Z axis, which is the axial direction of the drill, and therefore a hole diameter abnormality occurs, There was an inconvenience that the life of the drill was also reduced.

  As means for preventing this, a method as described in Patent Document 3 has been proposed. In the method described in Patent Document 3, instead of the translation axis command value, the translation axis correction value is obtained using the coordinate value of the correction reference point, which is one point specified in advance in the translation axis command position space. The position error of the tool tip point due to the geometric error can be corrected by calculating and adding this correction value to the command value of the translation axis to obtain the command position. In the method described in Patent Document 3, although the translation axis correction value is changed in the case of the rotation axis operation, the translation axis correction value is not changed in the translation axis operation. In this way, the machining accuracy of the workpiece is improved.

JP 2004-272887 A JP 2012-220999 A JP 2012-221001 A

  However, in the above-described combined machining lathe, when the translation axis correction value is calculated by the method described in Patent Document 3 and the workpiece 20 is turned, the correction reference point is set on the central axis of the main spindle 3. On the other hand, when the correction value is calculated and the workpiece 20 is milled, the correction reference point is the machining point at which the workpiece is machined by a tool such as a drill unlike the turning process. It is desirable to specify a position close to. For example, as shown in FIG. 7, when performing drilling on the end surface of the workpiece 20 using the drill 22 without correcting the B-axis angle (B-axis correction value Δb = 0), the correction reference is used. Specify a point at the center of each drilling position. For this reason, in order to calculate the correction value, there is an inconvenience that correction reference points must be specified at different positions in the command position space of the translation axis for each machining (turning, milling). . Further, when the workpiece 20 is milled, correction using the correction reference point may not be performed. For example, as shown in FIG. 6 to be described later, when the drilling is performed on the end surface of the workpiece 20 by correcting the B-axis angle, the correction reference point is designated as a position close to the machining point. Even if not, by using the method disclosed in Patent Document 2, the tilt error of the rotation axis and the correction command of the translation axis are issued, and the workpiece 20 is punched. For this reason, it has been necessary to determine whether or not to specify a correction reference point for milling after determining whether or not the Z-axis is inclined with respect to the C-axis. For this reason, it is difficult to say that the translation axis correction value can be efficiently calculated in each machining.

  The present invention has been proposed in view of such circumstances, and is a machine tool that efficiently calculates a correction value of a translational axis that improves the machining accuracy of a workpiece in both turning and milling. It is an object of the present invention to provide a correction value calculation method and a correction value calculation program that causes a computer to execute the correction value calculation method.

  In the machine tool correction value calculation method according to the first aspect of the present invention, the spindle on which the tool is mounted and the table holding the workpiece are relatively moved by two or more translation axes and one or more rotation axes. A machine tool capable of turning the workpiece rotated around the rotation axis by the tool or milling the workpiece by the rotating tool; A correction value calculation method for a machine tool that calculates a correction value of the translation axis that corrects an error in the position of the tool relative to the workpiece due to an error or an error in the position and an error in the posture of the tool, A determination step for determining whether to perform turning or the milling, and the determination of whether to perform the turning by the determination step; The first coordinate value substitution step of substituting the coordinate value of the turning correction reference point, which is one point designated in advance in the command position space, into the command position of the translation axis, and the milling by the determination step. A second coordinate value substituting step of substituting the coordinate value of the milling processing correction reference point, which is one point designated in advance in the command position space, into the command position of the translation axis when it is determined to perform , The command position of the translation axis obtained by substituting the coordinate value of the turning correction reference point in the first coordinate value substituting step, or the coordinate value of the milling machining correction reference point in the second coordinate value substituting step. The correction value is calculated based on the substituted command position of the translation axis, the command position of the rotation axis, and the geometric parameter representing the geometric error. A correction value calculation step that, characterized in that the run.

  A machine tool correction value calculation program according to a second aspect of the invention causes a computer to execute the machine tool correction value calculation method according to the first aspect.

According to the correction value calculation method for the machine tool according to the first aspect of the invention and the correction value calculation program for the machine tool according to the second aspect of the invention, when the determination step determines that the turning is performed, the correction value calculation step By using the command position of the translation axis into which the coordinate value of the correction reference point for turning is substituted, the error of the position of the tool with respect to the workpiece due to a geometric error or the error of the position and the error of the posture of the tool are corrected. The translation axis correction value can be calculated. In addition to this, when it is determined that the milling process is performed in the determination step, the correction value calculation step uses the translation axis command position into which the coordinate value of the milling process correction reference point is substituted, and the translation axis correction value. Can be calculated. Accordingly, the correction value can be automatically calculated according to each process (turning process, milling process), and thus the correction value can be calculated efficiently.
Further, during the turning process, the translation axis correction value calculated in the correction value calculation step is added to the translation axis command position to update the translation axis command position, and based on the updated command position, If the relative position of the tool with respect to the object is controlled, the correction value of the translation axis does not change even when the translation axis is operated by the updated command position, as in the method disclosed in Patent Document 3, and the rotation axis When the rotation axis is moved according to the command position, the translation axis correction value changes. As a result, even when the translation shaft is operated, the translation shaft does not move minutely, so that it is possible to prevent deterioration of the machined surface properties of the workpiece due to the minute operation during turning.
Further, at the time of milling, the translation axis correction value calculated in the correction value calculation step is added to the translation axis command position to update the translation axis command position. Based on the updated command position, If the relative position of the tool with respect to the workpiece is controlled, the geometric error can be corrected with sufficient accuracy in the vicinity of the milling machining correction reference point, and milling can be performed at a predetermined position of the workpiece. On the other hand, even if the translation axis command position is not updated using the translation axis correction value, the rotation axis operates based on the correction value and the translation axis is also corrected by the method disclosed in Patent Document 2. Therefore, milling can be accurately performed at a predetermined position of the workpiece by the tool. Therefore, during milling, both when controlling the relative position of the tool with respect to the workpiece based on the updated command position and when correcting the translational axis without updating the command position, Milling can be performed with high accuracy.

It is a mimetic diagram of the combined processing lathe of the embodiment of the present invention. It is a figure explaining the state which performs a turning process to a workpiece with a compound processing lathe by the conventional control method. It is a block diagram of the numerical controller which performs the control method of an embodiment. It is a flowchart of the process which calculates the correction value of the translation axis in a command value coordinate system. It is a figure explaining the state which performs a turning process to a workpiece with a compound processing lathe with the control method of an embodiment. It is a figure explaining the state which mills a workpiece with the complex processing lathe which can be controlled with the control method of an embodiment. It is a figure explaining the state which mills a workpiece with a compound processing lathe by the conventional control method.

  An embodiment of the present invention will be described with reference to FIGS. Below, the example which applied this invention to the combined processing lathe shown in FIG. 1 as embodiment is demonstrated. The complex machining lathe is controlled by a computer that executes a control program. The computer may be a numerical control device for the complex machining lathe or an independent control device connected thereto. A combination of these may also be used. In addition, this invention is not limited to the example applied to the said composite working lathe, For example, you may apply to the machine tool of 4 axes or less or 6 axes or more, and the main-axis part 3 rotates 2 degrees of freedom with a rotating shaft. The present invention may be applied to a composite machining lathe having a spindle or a complex machining lathe in which the spindle head 2 has two degrees of freedom of rotation by a rotation axis. The machine tool to which the present invention is applied may be a machining center or a grinding machine. Furthermore, the present invention may be applied not only to machine tools but also to industrial machines and industrial robots.

  FIG. 3 shows an example of a numerical control device for performing the control of the present embodiment. This numerical control device includes a command value generation unit 11, a correction value calculation unit 12, and a servo command value conversion unit 13. When the command value generating means 11 inputs a machining program G in which command coordinate values of each axis are described as a command to move the tool to a position to perform machining when machining the workpiece 20, FIG. A command value for each axis (B-axis, C-axis, X-axis, Y-axis, Z-axis) of the combined machining lathe shown is generated. This command value is sent to the correction value calculation means 12 and the servo command value conversion means 13. The correction value calculation means 12 calculates the correction value for each axis based on the command value generated by the command value generation means 11. This correction value is sent to the servo command value conversion means 13. The servo command value conversion means 13 that has received the command value and the correction value calculates the servo command value for each axis and sends it to the servo amplifiers 14a to 14e for each axis. The servo amplifiers 14a to 14e of the respective axes drive the servo motors 15a to 15e, respectively, to control the relative position and posture of the tool with respect to the workpiece 20 (see FIGS. 5 and 6).

In the present embodiment, the geometric error is defined as a total of six components (δx, δy, δz, α, β, γ) including three relative translation error components and three relative rotation error components between adjacent axes. In the combined machining lathe of the present embodiment, the axis configuration from the workpiece 20 to the tools 21 and 22 (see FIGS. 5 and 6) mounted on the spindle head 2 is C axis-Z axis-Y axis-X axis- B-axis. In this shaft configuration, there are 13 geometric errors excluding geometric errors in a redundant relationship. The 13 geometric errors are represented by δx ₁ , δz ₁ , α ₁ , β ₁ , α ₂ , γ ₂ , α ₃ , β ₄ with the order from the tool 21, 22 toward the workpiece 20 in the axis configuration as a subscript. , Γ ₄ , δx ₅ , δy ₅ , α ₅ , β ₅ . These geometric errors are, in order, B-axis center position X-direction error, B-axis center position Z-direction error, spindle head 2-B axis perpendicularity, B-axis origin error, B-Z axis perpendicularity, B -X axis perpendicularity, Z-X axis perpendicularity, XY axis perpendicularity, YZ axis perpendicularity, C axis center position X direction error, C axis center position Y direction error, CY It means the perpendicularity between axes and the perpendicularity between C-X axes. These 13 geometric errors are obtained in advance by actual measurement and stored in the storage means of the correction value calculation means 12. Note that δx, δy, δz, α, β, and γ are examples of geometric parameters of the present invention.

  Next, a translation axis correction value calculation method executed by the numerical controller shown in FIG. 3 will be described with reference to FIG. This numerical control device can calculate the correction value of the translation axis (X axis / Y axis / Z axis) in consideration of the above-mentioned geometric error by the correction value calculation program stored in the storage means of the correction value calculation means 12 It is said.

  In step S1 in FIG. 4, the correction value calculation means 12 determines whether or not to turn the workpiece 20 (see FIG. 5). In step S <b> 1, as an example, the command value generation unit 11 acquires a machining program G and then transmits a signal corresponding to the command value in the machining program G to the correction value calculation unit 12. Then, the correction value calculation means 12 determines whether to turn the workpiece 20 or to mill the workpiece 20 based on the received signal. As an example of turning, as shown in FIG. 5, planar machining is performed on the outer periphery of a workpiece 20 that is attached to the spindle portion 3 and rotates around the C axis by a cutting tool 21 attached to the spindle head 2. On the other hand, as an example of milling, as shown in FIG. 6, drilling is performed on the workpiece 20 fixed to the spindle 3 by a drill 22 that is mounted on the spindle head 2 and rotates. Step S1 is an example of the determination step of the present invention. The main spindle 3 is an example of the table of the present invention.

If it is determined in step S1 that the workpiece 20 is to be turned, the correction value calculation means 12 determines whether or not to use the turning correction reference point in step S2. In the present embodiment, whether or not to use the turning correction reference point can be set by an operation unit provided in the numerical controller and operable by the operator. This turning correction reference point is an arbitrary point belonging to the same coordinate system (command value coordinate system) as the translation axis (X-axis / Y-axis / Z-axis). , A value within the range of the Z-axis command value, and a value set in advance and stored in the storage means of the numerical control device, or a value described in the machining program G for generating the command value or the like is used. In this embodiment, the coordinate values (x _T , y _T , z _T ) of the turning correction reference point are coordinate values on the central axis of the spindle 3 in the command value coordinate system when there is no geometric error. .

If it is determined in step S2 that the turning correction reference point is to be used, the correction value calculation means 12 substitutes the coordinate value of the turning correction reference point in the translation axis command position in step S3. In this embodiment, the correction value calculation means 12 adds the coordinate values (x _T , y _T ) of the turning correction reference point to the translation axis command values (x, y, z) sent from the command value generation means 11. , Z _T ). Step S3 is an example of the first coordinate value substitution step of the present invention.

After step S3, the correction value calculation means 12 calculates the correction value of the translation axis in the command value coordinate system at the time of turning as described below in step S4. When the tool tip point vector _PT on the tool coordinate system at the spindle head 2 is converted to the workpiece coordinate system at the spindle 3, the length vector of the tool 20 is set to t (t _X , t _Y , t _Z ), c is the command position on the C axis, b is the command position on the B axis, x is the command position on the X axis, y is the command position on the Y axis, and z is the command position on the Z axis. The matrix looks like [Equation 1]. The workpiece in the case where there is no geometric error by performing the homogeneous coordinate transformation using the tool tip point vector P _T and the transformation matrices M ₅ , M ₁ , M ₂ , M ₃ , M _{4 of} each axis. calculating a tool end point vector P _I of the coordinate system. When calculating the tool center point vector _{P I} is [number 1] command values x in, y, coordinates of turning correction reference point _{z (x T, y T,} z T) , respectively Assigned.

Further, in step S4, the matrix ε _j of [Equation 2] using the translation errors δx, δy, δz of the geometric errors and the rotation errors α, β, γ stored in the storage means of the correction value calculation means 12 is obtained. Let the transformation matrix be a geometric error. The correction value calculation means 12 uses the [Equation ₂ ] in which the matrix ε _j and the matrices ξ ₁ and ξ ₂ are arranged between the respective axes of [Equation 1], thereby eliminating the tool coordinate system in the case where there is a geometric error. Performs homogeneous coordinate transformation to the workpiece coordinate system when there is a geometric error. Thus, to calculate the tool center point vector P _R in the workpiece coordinate system when there is a geometric error. [Equation 2] is an approximate expression in which the product is regarded as zero on the assumption that the geometric error is minute. Δb and Δc are correction values for the B-axis and C-axis, respectively, and are obtained by [Equation 3]. A part of the posture error of the tool 21 with respect to the workpiece 20 can be corrected by the Δb and Δc. Further, by setting Δb and Δc to zero, a part of the posture error can be prevented from being corrected.

Subsequently, in step S4, the correction value calculation means 12 calculates the tool tip point position error ΔP _w = (δx, δy, δz) in the workpiece coordinate system by using [Equation 4]. In the present embodiment, by using the number 4, the difference between the tool center point vector P _I computed by Equation 2 and the tool center point vector P _R was calculated by Equation 1, the workpiece coordinate system computing a position error [Delta] P _w of the tool center point at.

Thereafter, in step S4, the correction value calculation means 12 calculates the error ΔP ₀ of the command value of the translation axis in the command value coordinate system by using [Equation 5]. In the shaft configuration of this embodiment (C-axis-Z-axis-Y-axis-X-axis-B-axis), a command value is set between the C-axis that is the first rotation axis on the workpiece 20 side and the Z-axis that is the translation axis. There is a coordinate system. In this step S4, the homogeneous coordinate transformation from the workpiece coordinate system to the command value coordinate system is performed by using [Equation 5]. Thereby, the error ΔP ₀ of the command value of the translation axis in the command value coordinate system is calculated.

Subsequently, in step S4, the correction value calculation means 12 calculates the translation axis correction value ΔP = (Δx, Δy, Δz) in the command value coordinate system by using [Equation 6]. In this embodiment, by using [Equation 6], the value of the opposite sign of the command value error ΔP ₀ of the translation axis in the command value coordinate system is calculated as the translation axis correction value ΔP. Thus, step S4 is completed. Step S4 is an example of the correction value calculation step of the present invention.

  When the workpiece 20 is turned, the translational axes (X axis, Y axis, Z axis) calculated in step S4 are corrected in order to correct (cancel) the position error of the tool tip point due to the geometric error. The value ΔP is added to the command value (x, y, z) for each translation axis, and the command value for each translation axis is updated. In the turning process, the relative position of the bite tool 21 (see FIG. 5) with respect to the workpiece 20 is controlled based on the updated command value of each translation axis. When such control is performed, as shown in FIG. 5, the tip point of the cutting tool 21 can be positioned on a straight line parallel to the Z axis in the feed direction (the direction of the thick dotted line arrow in FIG. 5). Therefore, unlike the conventional example shown in FIG. 2, the tool bit 21 does not slightly move in the X-axis direction, and it is possible to prevent a dent or the like from being generated on the machining surface of the workpiece 20.

If it is determined in step S2 that the turning correction reference point is not used, the correction value calculation means 12 determines in step S4 that each command value x, y, z in [Expression 1] above. By using this [Equation 1] without substituting the coordinate values (x _T , y _T , z _T ) of the correction reference point for turning, the tool tip in the workpiece coordinate system when there is no geometric error calculating a point vectors _{P I.} After that, the same as step S4 in the case where the coordinate values (x _T , y _T , z _T ) of the turning correction reference points are substituted for the command values x, y, z in [Expression 1] described above. By this method, the translation axis correction value ΔP in the command value coordinate system is calculated.

If it is determined in step S1 in FIG. 4 that the workpiece 20 is to be milled, the correction value calculation means 12 determines in step S5 whether or not to use a milling correction reference point. In the present embodiment, it is possible to set whether or not to use the correction reference point for milling in the same manner as in the case of setting whether or not to use the correction reference point for turning in the above step S2. ing. The milling correction reference point is an arbitrary point similar to the turning correction reference point, and has the same coordinate value as the turning correction reference point. In the present embodiment, the coordinate values (x _M , y _M , z _M ) of the correction reference point for milling are set in the command value coordinate system when there is no geometric error, and the workpiece 20 by the drill 22 (see FIG. 7). The coordinate value of the point where the drilling position with respect to the center axis of the drill 22 coincides.

When it is determined in step S5 that the milling machining correction reference point is to be used, the correction value calculation means 12 substitutes the coordinate value of the milling machining correction reference point in the translation axis command position in step S6. In the present embodiment, the correction value calculation means 12 adds the coordinate values (x _M , y _M ) of the correction reference point for milling to the translation axis command values (x, y, z) sent from the command value generation means 11. , Z _M ). Step S6 is an example of the second coordinate value substitution step of the present invention.

After step S6, the correction value calculation means 12 calculates the correction value of the translation axis in the command value coordinate system at the time of milling as described below in step S4. In step S4, by using the [Equation 1] obtained by substituting the coordinate values (x _M , y _M , z _M ) of the correction reference point for milling into the command values in the above [Equation 1], calculating a tool end point vector P _I in the workpiece coordinate system in the absence of errors. After that, the same as step S4 in the case where the coordinate values (x _T , y _T , z _T ) of the turning correction reference points are substituted for the command values x, y, z in [Expression 1] described above. By this method, the translation axis correction value ΔP in the command value coordinate system is calculated.

When performing milling the workpiece 20 corrects the positional error [Delta] P _w of the tool center point according to geometric errors (cancel) for each translation axis which is calculated by the step S4 (X axis · Y axis · Z axis) Is added to the command value (x, y, z) of each translation axis, and the command value of each translation axis is updated. And in the said milling process, the relative position of the drill 22 with respect to the workpiece 20 is controlled based on the command value of each updated translation axis. By performing such control, the tip point of the drill 22 can be positioned at a point where the drilling position of the workpiece 20 and the center axis of the drill 22 coincide. Thereby, when drilling the workpiece 20 with the drill 22, no deviation occurs between the drilling position and the center axis of the drill 22. When the drill 22 is advanced toward the workpiece 20 from this positioning state, it is possible to perform drilling at a predetermined position of the workpiece 20. However, when drilling the workpiece 20 with the drill 22 as shown in FIG. 6, the command value for each translation axis is not updated using the correction value ΔP calculated in step S4. This is because, without updating each translation axis, the method disclosed in Patent Document 2 above operates the B axis based on the correction value of the B axis that is the rotation axis, and the X axis that is the translation axis. This is because the correction command is also issued, so that the drill 22 can be precisely drilled at a predetermined position of the workpiece 20.

If it is determined in step S5 that the milling machining correction reference point is not used, the correction value calculation means 12 applies the milling machining values to the command values x, y, z in the above [Equation 1]. By using this [Equation 1] without substituting the coordinate values (x _M , y _M , z _M ) of the correction reference point, the tool tip point vector P _{I in} the workpiece coordinate system when there is no geometric error is used. Is calculated. After that, the same as step S4 in the case where the coordinate values (x _M , y _M , z _M ) of the milling processing correction reference point are assigned to the command values x, y, z in [Equation 1] described above. By this method, the translation axis correction value ΔP in the command value coordinate system is calculated.

  In both the turning process and the milling process of the present embodiment, as in the method disclosed in Patent Document 3 above, even when the translation axis is operated by the command value (x, y, z), the translation axis The correction value ΔP does not change, and the translation axis correction value ΔP changes when the rotation axis is operated according to the rotation axis command values c and b. Thereby, even when the translational axis is operated, each translational axis does not operate minutely. Therefore, in the plane machining shown in FIG. 5, the occurrence of a dent or the like on the machining surface of the workpiece 20 due to the minute movement is prevented. Further, when drilling the workpiece 20, the geometric error can be corrected with sufficient accuracy in the vicinity of the milling correction reference point, and the workpiece 20 can be drilled at a predetermined position. However, as shown in FIG. 6, drilling is performed on the workpiece 20 with the drill 22 with the direction of the thick dotted arrow in FIG. When performing, the command value of each translational axis is not updated using the correction value ΔP calculated in step S4. Even in this case, the B-axis operates based on the correction value of the rotation axis (B-axis), and the translation axis (X-axis) is also commanded to be corrected, so that the drill 22 can accurately place the workpiece 20 at a predetermined position. This is because drilling can be performed well.

<Effect of this embodiment>
In the correction value calculation method and the correction value calculation program for the combined machining lathe according to the present embodiment, when the correction value calculation means 12 determines to perform turning in step S1, the coordinate value of the turning correction reference point is determined in step S4. Using the translation axis command value into which (x _T , y _T , z _T ) is substituted, the translation axis correction value ΔP for correcting the tool tip point position error ΔP _w due to the geometric error can be calculated. In addition to this, when it is determined in step S1 that milling is to be performed, in step S4, the translation axis command value into which the coordinate values (x _M , y _M , z _M ) of the milling processing correction reference point are substituted, The correction value ΔP can be calculated. As a result, the correction value ΔP can be automatically calculated according to each process (turning, milling), so that the correction value ΔP can be calculated efficiently.

  The present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing a part of the configuration without departing from the spirit of the invention. In the embodiment described above, the translation axis correction value ΔP is calculated using [Equation 6]. However, instead of [Equation 6], the C-axis command position c and the C-axis correction value are calculated from this [Equation 6]. The translation axis correction value ΔP may be calculated by using [Expression 7] excluding elements related to Δc. For example, in the turning process shown in FIG. 5, since the C axis rotates at a high speed, if the translation axis correction value ΔP changes accordingly, the translation axis vibrates. However, if the translation axis correction value ΔP is calculated using [Equation 7] excluding the elements related to the command position c of the C axis and the correction value Δc of the C axis, the correction even if the C axis rotates at high speed. Since the value ΔP does not change, there is an advantage that the vibration of the translation axis can be suppressed. Further, since the correction of the angle of the C-axis is meaningless in turning, there is an advantage that the correction value ΔP can be calculated efficiently.

  In addition, for example, depending on the machine tool model, workpiece dimensions, etc., it may be determined whether or not to calculate the translation axis correction value ΔP using the turning correction reference point in advance during turning. Good. As an example, when the Z axis is a slip guide, the correction value ΔP is calculated using the turning correction reference point, but when the Z axis is a rolling guide, the correction value is used without using the turning correction reference point. In a machine tool with semi-closed control, the correction value ΔP is calculated using a turning correction reference point. However, with a fully closed control machine tool, a correction value ΔP is used without using a turning correction reference point. May be calculated. If the Z-axis movement range is equal to or greater than the predetermined range, the correction value ΔP is calculated using the turning correction reference point. If the Z-axis movement range is less than the predetermined range, the turning correction reference point is calculated. The correction value ΔP may be calculated without using a point. Then, the numerical controller determines whether the Z-axis is sliding guide or rolling guide, determines whether it is semi-closed control or full-closed control, and the Z-axis movement range is greater than or less than a predetermined range. It is possible to automatically determine whether there is any.

  2 .... Spindle head, 3 .... Spindle part, 20..Workpiece, 21..Bite tool, 22 .... Drill.

Claims (2)

A main spindle on which a tool is mounted and a table for holding a workpiece are relatively moved by two or more translation axes and one or more rotation axes, and the workpiece is rotated about the rotation axis by the tool. In a machine tool capable of turning the workpiece or milling the workpiece with the rotating tool, an error in the position of the tool relative to the workpiece due to a geometric error or the A correction value calculation method for a machine tool that calculates a correction value for the translational axis that corrects a position error and a tool posture error,
A determination step for determining whether to perform the turning or the milling;
When it is determined that the turning is performed in the determination step, the coordinate value of the turning correction reference point, which is one point specified in advance in the command position space of the translation axis, is set as the command position of the translation axis. A first coordinate value substituting step for substituting
When it is determined in the determination step that the milling process is to be performed, the coordinate value of the milling process correction reference point, which is one point specified in advance in the command position space, is substituted into the command position of the translation axis. A second coordinate value substitution step;
The command position of the translation axis obtained by substituting the coordinate value of the turning correction reference point in the first coordinate value substituting step or the coordinate value of the milling machining correction reference point in the second coordinate value substituting step A correction value calculation step for calculating the correction value based on the command position of the translation axis, the command position of the rotation axis, and a geometric parameter representing the geometric error;
A correction value calculation method for a machine tool, characterized in that   A machine tool correction value calculation program which causes a computer to execute the machine tool correction value calculation method according to claim 1.

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