JP2012033203A - Numerical control machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a numerical control machine tool having a feeding spindle shaft capable of precisely correcting positional error and posture error.SOLUTION: The numerical control machine tool has a linear feed shaft and a spindle feed shaft and has a function to correct shift commands based on measured error data. The error data are multidimensional data including positional errors and posture errors. Error data storing means 25 stores a data table which is created by collecting a large amount of error data corresponding to the position and the rotation position of the linear feed shaft and the feeding spindle shaft. Correction data calculation means 26 that calculates correction data for correcting the shift command based on command position to the linear feed shaft and the feeding spindle shaft and the error data stored in the error data storing means. A posture error is corrected by calculating displacement amounts in three-dimensional coordinate values of a tool end position based on the posture error and tool dimensions, and correcting the shift command of the linear feed shaft based on displacement amount of the calculated three-dimensional coordinate values without rotating the feeding spindle shaft.

Description

  The present invention relates to a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft.

  In general, in a multi-axis machine tool, it is difficult to accurately position the position and posture of the feed shaft at a predetermined position and posture, and position and posture errors occur. For this reason, when high-precision machining is required, the feed axis is corrected in accordance with position and orientation errors. As a conventional example for correcting such a feed shaft error, those disclosed in Patent Documents 1 to 3 are known.

  In Patent Document 1, the misalignment (position misalignment of the shaft center) of two rotary feed shafts of a machine tool having two rotary feed shafts of A axis and B axis orthogonal to each other is measured in advance. It is disclosed that the coordinates of two rotary feed axes are obtained in consideration. The measured axis deviation is stored in advance in storage means such as a numerical controller, and is read from the storage means when the machining reference point of the workpiece is changed and a new machining reference point is obtained, so that the new machining reference point is accurately determined. Can be requested.

  In Patent Document 2, the machine position of a machine tool having two rotation feed axes, that is, an A axis and a C axis that are orthogonal to each other, is represented by 1) a position error and an attitude error with respect to the C axis, and 2) And 3) a method of obtaining by calculation based on a position error and an attitude error with respect to the main axis as a turning center. The position error and the posture error for the C axis, the A axis, and the main axis are errors obtained in advance when the rotary tool is in a predetermined positional relationship with respect to the work surface of the workpiece.

  Patent Document 3 discloses a method of correcting an error of a tool unit of a machine tool of a parallel link mechanism based on an error map. The error map has error data calculated by calculation from the difference between the command value and the detected value of the position and orientation of the tool unit tip corresponding to the lattice point of the work space at the tool unit tip.

Japanese Patent Publication No. 6-88192 JP 2004-272887 A JP-A-9-237112

  The correction method disclosed in Patent Document 1 corrects an axial deviation (position error) between two rotation feed axes of the A axis and the B axis, and does not correct an attitude error. For this reason, there was a limit in improving processing accuracy.

  The correction method disclosed in Patent Document 2 is a method for obtaining the machine position of the machine tool based on the position error and the attitude error when the position error and the attitude error regarding each axis are known in advance. If the posture error is not known, the machine position of the machine tool cannot be obtained accurately. For this reason, during the actual machining, the machine position of the machine tool cannot be obtained, and the machine position includes the position error and the attitude error of each axis, and highly accurate three-dimensional curved surface machining is performed. There was a problem that could not be done.

  The error map disclosed in Patent Document 3 uses table data for the position and orientation error of the tool unit tip driven by the parallel link mechanism, and has three orthogonal linear feed axes and a rotary feed axis. It was not directly applicable to machine tools.

  An object of the present invention is to provide a numerically controlled machine tool and a numerical control device that can accurately correct errors in the position and orientation of a machine tool having a rotary feed shaft.

In order to achieve the above object, a numerically controlled machine tool according to claim 1 has a linear feed shaft and a rotary feed shaft, and errors in the relative position and relative attitude between the spindle and the work table are preliminarily determined. A numerically controlled machine tool having a function of positioning and measuring a shaft and the rotary feed shaft at a predetermined position and posture, and correcting a movement command based on the measured error data,
The error data is multidimensional data including a position error and an attitude error, and is a data table created by collecting a large number of the error data corresponding to the position and rotation angle of the linear feed shaft and the rotary feed shaft. Error data storage means for storing
Correction data calculation means for calculating correction data for correcting the movement command from the command position for the linear feed axis and the rotary feed axis and the error data stored in the error data storage means,
In the correction of the posture error, a deviation amount of the three-dimensional coordinate value of the tool tip position is calculated from the posture error and the tool dimension, and the rotary feed shaft is rotated based on the calculated deviation amount of the three-dimensional coordinate value. And the movement command of the linear feed axis is corrected.

  According to a second aspect of the present invention, in the numerically controlled machine tool according to the first aspect, the position error is an error in a relative position between the main shaft and the work table, and the rotary feed shaft rotates at a predetermined rotation. It is an error represented by a three-dimensional coordinate value when positioned at an angle, and the posture error is a relative posture error between the spindle and the work table, and the first rotary feed shaft orthogonal to each other It is an error represented by an inclination angle when the second rotary feed shaft is positioned at a predetermined rotation angle.

  According to a third aspect of the present invention, in the numerically controlled machine tool according to the second aspect, the measurement interval of the rotation angle in the first rotary feed shaft and the second rotary feed shaft is at an adjacent measurement point. The posture error difference is set to be a predetermined value.

  As described above, according to the numerically controlled machine tool of the present invention, the data table stored in the error data storage means includes an error including both a position error and an attitude error, which are errors generated when the rotary feed shaft operates. Since the data is included, the machine tool can be positioned at the target position with high accuracy by correcting the movement command based on the error data.

  Further, since the measurement interval between the measurement points for measuring the posture error is set so that the difference in posture error between adjacent measurement points becomes a predetermined value, the measurement interval can be widened when the difference is small. For this reason, the amount of data can be reduced while maintaining the accuracy of correction, and the burden on the memory can be reduced.

  Further, in a 5-axis machine tool having X, Y, and Z linear feed axes and A and C rotary feed axes, an attempt is made to correct the posture error in the B-axis direction by rotating the A and C axes. In this case, the rotational feed axis must be swiveled greatly each time correction is performed, which will adversely affect the machining, but by moving the tool tip position deviation amount to the destination with a movement command of a three-dimensional coordinate value, The posture error in the B-axis direction can be corrected without rotating the rotary feed shaft. Thereby, the so-called singularity problem can be avoided.

  In addition, according to the numerically controlled machine tool of the present invention, it is possible to reliably correct errors in the relative posture and relative position between the spindle and the work table that are generated by operating the rotary feed shaft, and perform highly accurate machining. It can be carried out.

It is a block diagram which shows one Embodiment of the numerical control apparatus which concerns on this invention. FIG. 2 is a side view of a machining center to which the numerical control device of FIG. 1 is applied. It is explanatory drawing which shows the coordinate system of the machining center of FIG. It is explanatory drawing which shows the lattice point of three-dimensional coordinate space. It is explanatory drawing which shows the two-dimensional data sheet linked | related with each lattice point of FIG. It is explanatory drawing showing the two-dimensional coordinate system which looked at the three-dimensional coordinate system of FIG. 3 by A view. It is explanatory drawing showing the two-dimensional coordinate system which looked at the three-dimensional coordinate system of FIG. 3 by B view. It is explanatory drawing showing the two-dimensional coordinate system which looked at the three-dimensional coordinate system of FIG. 3 by C view. It is a flowchart which shows an example of the correction method using an error map. It is explanatory drawing explaining the correction method of FIG. It is explanatory drawing explaining the angle correction vector of FIG. 10, (a) is a figure of XY plane, (b) is a figure of XZ plane, (c) is a figure of YZ plane. It is explanatory drawing explaining the position correction vector of FIG.

  Specific examples of embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows, as an example, an embodiment of a numerical control device according to the present invention applied to a 5-axis horizontal machining center (numerical control machine tool) in which a spindle head is inclined. In FIG. 1, the functional configuration of the numerical control device of the present embodiment is shown in a block diagram. 2 shows the basic configuration of the machining center, and FIG. 3 shows three orthogonal linear feed axes X, Y, Z and two rotary feed axes A, C. In FIG. 3, the rotary feed axis B-axis is not shown, but the A-axis functions as the B-axis by rotating the C-axis by 90 °.

  Referring to FIG. 2, the machining center 1 includes a base 2 installed on a floor, a column 3 erected on the base 2 so as to be linearly movable in the Z-axis direction, and a Y-axis that is perpendicular to the column 3. And a headstock 5 that can move in the direction. The headstock 5 is provided with a bracket 5a that can be rotated and fed by a servo motor 30 (see FIG. 1) in a C-axis direction around an axis parallel to the Z-axis. In the bracket 5a, the spindle head 4 is provided such that it can be rotated and fed by a servo motor 30 (see FIG. 1) in the A-axis direction around an axis parallel to the X-axis.

  The machining center 1 is provided with a work table 6 that is erected on the base 2 at a position facing the spindle head 4 and that can move linearly in the X-axis direction that is perpendicular to the paper surface. A work 7 is held on the work table 6 via the scale 8.

  Referring to FIG. 3, the C axis and the A axis are shown together with the orthogonal triaxial coordinate system shown in FIG. The A axis is a rotational feed around an axis parallel to the X axis, and the spindle head 4 is rotatable in the A axis direction with respect to the bracket 5a. In the illustrated example, a contact-type measurement probe 9 for measuring the position and angle is mounted at a position where the tool is mounted. The measurement probe 9 is a general one, and includes, for example, a transducer made of a differential transformer and a ceramic contact 10. The contact 10 can be displaced in three axial directions orthogonal to each other. The displacement in the axial direction of the contact 10 is detected by each transducer and converted into an electric signal. Note that the measuring instrument and measuring method for measuring the position and angle of the feed shaft are not particularly limited, and it is also possible to measure using a laser length measuring instrument or another measuring instrument.

  As shown in FIG. 1, the numerical controller 20 of the present embodiment that controls the machining center 1 has a function of correcting the position error and the posture error of the five-axis feed axes, and decodes the machining program 21. Then, pre-processing calculation means 22 for calculating a movement command for each feed axis, and interpolation based on the movement command for linearly or circularly interpolating the feed on each feed axis X, Y, Z, A, C Interpolating means 23 for calculating pulses, command position recognizing means 24 for recognizing command positions that are the movement destination positions of the respective feed axes X, Y, Z, A, and C by acquiring the interpolated pulses, Error data storage means 25 for storing an error map (data table) 32 created by collecting a large number of error data 34 related to the position and attitude of the rotary feed axes A and C, including the attitude error, and a command Place And correction data calculation means 26 for calculating correction data for correcting the command position from the error data 34 read from the error data storage means 25, and correction for correcting the command position based on the correction data and obtaining a correction pulse. Pulse calculation means 27 and addition means 28 for outputting a pulse obtained by adding the interpolation pulse and the correction pulse to the servo amplifier 29 are provided. The servo motors 30 of the feed axes X, Y, Z, A, and C are driven by the drive current amplified by the servo amplifier 29 to move the feed axes X, Y, Z, A, and C. Yes.

  Next, the error map 32 will be described. As shown in FIG. 4, the error map 32 is associated with each lattice point 31 in the orthogonal coordinate system. That is, the linear feed axes X, Y, and Z are associated with predetermined positions in the axial directions. A matrix-like two-dimensional array data sheet 33 as shown in FIG. 5 is associated with each lattice point 31 in the orthogonal coordinate system. The error map 32 is composed of a number of two-dimensional array data sheets 33 associated with the respective lattice points 31 in the orthogonal coordinate system.

  Each two-dimensional array data sheet 33 is composed of a large number of error data 34 measured at points where the A axis and the C axis intersect at an arbitrary angle, with the horizontal axis being the A axis and the vertical axis being the C axis. ing. The error data 34 is composed of a position error 35a and an attitude error 35b. The position error 35 a is a position error represented by a three-dimensional coordinate value generated when the rotary feed axes A and C are positioned at predetermined positions, and the posture error 35 b is a difference between the spindle head 4 and the work table 6. It is an error in the relative posture, and is an error represented by an inclination angle generated when the rotation feed axes A and C orthogonal to each other are positioned at a predetermined rotation angle.

  Here, the measurement interval of the rotation angle between the A axis that is the first rotation feed axis and the C axis that is the second rotation feed axis is set so that the difference between the posture errors 35b at the adjacent measurement points becomes a predetermined value. Has been. In other words, the measurement interval is widened when the difference in posture error 35b between adjacent measurement points is small, and the measurement interval is narrowed when the difference changes greatly. It is possible to reduce the amount of data by increasing the measurement interval of the part with a small error difference and reduce the memory load, and to maintain the accuracy of correction by narrowing the measurement interval of the part where the error difference greatly changes. it can.

  Each of FIGS. 6 to 8 is a diagram showing a position error 35a and a posture error 35b as viewed from the respective arrow directions. FIG. 6 is a view as seen from the view A in FIG. 3, and shows a position error 35a (X, Y) and a posture error 35b (K). FIG. 7 is a view as seen from the view B in FIG. 3, and shows a position error 35a (Y, Z) and an attitude error 35b (I). FIG. 8 is a view as seen from the C view of FIG. 3, and shows a position error 35a (X, Z) and an attitude error 35b (J).

  Thus, since the error data 34 includes both the position error 35a and the attitude error 35b, which are errors generated by the operation of the rotary feed axes A and C, the movement command is based on the error data 34. Is corrected to the correct value, the tool tip can be positioned at the target position with high accuracy.

Next, a movement command correction method using the error map 32 described above will be described.
First, the movement command of the machining program 21 is decoded by the preprocessing arithmetic means 22 to obtain the movement vector of each feed axis X, Y, Z, A, C at a predetermined interpolation cycle. Subsequently, the command position recognition means 24 adds this movement vector to the current position to recognize the command positions of the feed axes X, Y, Z, A, and C at a predetermined interpolation cycle. When the angles of the rotational feed axes A and C at the command position are the measurement points of the A axis and the C axis of the two-dimensional array data sheet 33, the error data 34 is acquired as it is. When the angle of the rotary feed axes A and C at the command position corresponds to the angle between adjacent measurement points on the A axis and / or C axis of the two-dimensional array data sheet 33 (in the case of an intermediate position between measurement points), Error data is calculated by interpolation such as interpolation.

  Correction data is calculated based on the acquired error data 34 at the command position that is the position of the movement destination (correction data calculation means 26). The obtained correction data is added to the command position including the error to obtain a new command position for each interpolation cycle. Finally, the obtained correction data is similarly compared with the correction data obtained at the current position, and the difference amount is added to the movement vector of each feed axis in a predetermined interpolation cycle. In this way, the movement command including the error is corrected, and the position of each feed axis can be accurately obtained.

  Next, a method for correcting the movement command by expressing the correction value calculated by the correction data calculating means 26 as a three-dimensional coordinate value will be described. This method has a problem that when the C-axis is 0 ° and there is a posture error in the B-axis direction that the machine does not originally have, the rotary feed shaft is rotated greatly in order to correct the posture error in the B-axis direction. A correction method capable of avoiding the so-called “singularity” problem is provided. The B axis is a rotary feed shaft around an axis parallel to the Y axis.

  FIG. 9 shows a flowchart of this correction method. Formula 1 shows a calculation formula for obtaining a position correction vector based on the posture and posture error of the tool 40, the position and position error of the tool 40, and the protrusion length of the tool 40 by this method.

  First, in step S0, the command position is recognized from the movement command of the machining program. In step S <b> 1, error data 34 corresponding to the command position is acquired from the error map 32. In step S2, a position correction vector is calculated from the position error 35a of the error data 34. As shown in FIG. 12, the position correction vector is a vector for translating the tool 40 held by the spindle head to the movement destination. On the other hand, from the attitude error 35b of the error data 34, an attitude correction value is calculated in step S5. In step S6, the posture correction value obtained in step S5 is added to the command posture obtained in step S3 to obtain a corrected posture. In step S7, a corrected command position is obtained from the corrected posture and the protruding length of the tool 40.

  In step S4, a command position before correction is obtained from the command posture obtained in step S3 and the protrusion length of the tool 40. In step S8, the posture correction vector is calculated by subtracting the uncorrected command position obtained in step S4 from the corrected command position obtained in step S7. As shown in FIG. 11, the posture correction vector is a vector for rotating the tool 40 held on the spindle to the movement destination with the base end as a fulcrum. Finally, in step S9, as shown in FIG. 10, the posture vector obtained in step S8 and the position correction vector obtained in step S2 are added.

  In this way, the tool tip position is moved to the destination by the movement command of the three-dimensional coordinate value, that is, the position correction vector, thereby correcting the posture error 35b in the B-axis direction without rotating the rotary feed shaft. And the so-called singularity problem of the tool 40 held on the spindle head can be avoided.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, it can deform | transform and implement variously. In the present embodiment, a method of correcting the movement command with reference to the error map 32 every predetermined interpolation cycle is described. However, when interpolation is not performed, for example, each feed axis X, Y, Z, When moving A and C, that is, when a start point and an end point are commanded, correction can be made with reference to the error map 32. In this case, in FIG. 1, the movement command of the machining program is decoded by the pre-processing calculation means 22, the movement vector of each feed axis in a predetermined cycle is obtained, and then interpolation is not performed by the interpolation means 23. The recognition means 24 adds this movement vector to the current position to recognize the command position of each feed axis X, Y, Z, A, C. Error data 34 at the command position is acquired from the error map 32, correction data is calculated based on the acquired error data 34, and this correction data is added to the end point of the movement command to obtain a new command position. Finally, the obtained correction data is added to the movement vector of each feed axis in a predetermined cycle.

  The error map 32 of this embodiment is a database of error data 34 when the rotary feed axes A and C are operated. However, the position error when the linear feed axes X, Y and Z are operated. It is also possible to create an error map by creating a database of error data including attitude errors.

  Further, in the present embodiment, the example in which the main shaft side rotates to the A and C axes has been described, but the work table side may be configured to rotate.

DESCRIPTION OF SYMBOLS 1 Machining center 20 Numerical control apparatus 22 Preprocessing calculating means 23 Interpolating means 24 Command position recognition means 25 Error data storage means 26 Correction data calculating means 27 Correction pulse calculating means 31 Lattice point 32 Error map 33 Two-dimensional array data sheet 34 Error data 35a Position error 35b Posture error

Claims (3)

It has a linear feed axis and a rotary feed axis, and measures the error of the relative position and relative orientation between the spindle and the work table by positioning the linear feed axis and the rotary feed axis at a predetermined position and orientation in advance. A numerically controlled machine tool having a function of correcting a movement command based on the error data,
The error data is multidimensional data including a position error and an attitude error, and is created by collecting a large number of the error data corresponding to the position and rotation angle of the linear feed shaft and the rotary feed shaft. Error data storage means for storing the table;
Correction data calculation means for calculating correction data for correcting the movement command from the command position for the linear feed axis and the rotary feed axis and the error data stored in the error data storage means,
In the correction of the posture error, a deviation amount of the three-dimensional coordinate value of the tool tip position is calculated from the posture error and the tool dimension, and the rotary feed shaft is rotated based on the calculated deviation amount of the three-dimensional coordinate value. A numerically controlled machine tool characterized by correcting a movement command of the linear feed axis. The position error is an error of a relative position between the spindle and the work table, and is an error represented by a three-dimensional coordinate value when the rotary feed shaft is positioned at a predetermined rotation angle.
The posture error is an error in the relative posture between the main shaft and the work table, and is an inclination angle when the first rotary feed shaft and the second rotary feed shaft orthogonal to each other are positioned at a predetermined rotation angle. The numerically controlled machine tool according to claim 1, wherein the error is expressed by:   The measurement interval of the rotation angle in the first rotary feed shaft and the second rotary feed shaft is set so that a difference in the posture error between adjacent measurement points becomes a predetermined value. Numerically controlled machine tools.

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