JP2020009191A - Numerical controller of machine tool - Google Patents

Abstract

To provide a numerical controller for machine tools capable of implementing position correction that can highly precisely compensate an error in a relative position of a tool and a table despite simplicity in calculation of a correction quantity.SOLUTION: A numerical controller installed in a machine tool uses temperature information in a processing space, which is detected by a temperature sensor, to vary a lattice spacing and a tilt angle of lattices in spatial coordinates, which is used to calculate a correction quantity, according to a temperature difference between a time of setting spatial coordinates and a time of processing at the time of calculating the correction quantity. Therefore, although the correction quantity is calculated according to a simple method, an error in a relative position of a tool and a table can be highly precisely compensated. Eventually, processing precision of a machine tool can be upgraded greatly.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a numerical control device for a machine tool that can correct the relative positions of a tool and a table during machining of the machine tool.

  2. Description of the Related Art In machine tools, for the purpose of high value-added machining, improvement in accuracy of a five-axis machine is required. In the 5-axis machine, complicated shapes can be efficiently machined by inclining the workpieces and tools. Must be operated to change the relative position of the tool with respect to the workpiece. Therefore, the operating range of the linear axis tends to be larger in the 5-axis processing machine than in the 3-axis processing machine, and the accuracy of positioning of the linear axis in the entire processing space is an important point in increasing the processing accuracy. Become.

  Therefore, as a method for improving the positioning accuracy of the linear axis in the entire processing space, as in Patent Document 1, the processing space is divided into a grid shape, and the processing is performed by mapping the error amount of each linear axis at each grid point. There has been known a method of efficiently correcting the position of a blade edge in a space (so-called space correction). In this spatial correction, six component errors (that is, positioning error in the direction of the translational axis movement, straightness error in the horizontal and vertical directions, error of three translation components, and three component errors of Pitch, Yaw, and Roll) And a total of 21 error components obtained by adding a total of 18 components of the errors corresponding to the X-axis, Y-axis, and Z-axis of the straight-axis errors, and three square-angle errors between the straight-axis axes. The mapping of the error amount at each of the generated grid points is performed.

  According to such a space correction, there are a plurality of ball screw lead error corrections for correcting a positioning error of a linear axis, a straightness correction for correcting a linearity error of a linear axis, and a geometric error correction for correcting a square angle error between the linear axes. Since the position correction can be performed in accordance with the correction method, the position correction method can be simplified (simplified), and the number of measurements and the number of calculations for calculating the correction amount can be reduced. However, this spatial correction causes a correction error when thermal deformation of a tool or the like occurs due to a difference between the environmental temperature at the time of calculating the error map and the environmental temperature at the time of actual processing, thereby performing high-precision processing. You will not be able to do it. Therefore, as in Patent Document 2, a method of calculating thermal deformation by another correction method, adding the calculated correction amount to a correction amount that does not consider thermal deformation, and performing position correction using the combined correction amount is also proposed. Have been.

Japanese Patent No. 5030653 JP 2012-234424 A

  However, such a correction method as disclosed in Patent Document 2 in which a correction amount considering thermal deformation and a correction amount not considering thermal deformation are separately obtained and summed up, the calculation of the correction amount, which should be simplified, becomes complicated. As a result, there is a problem that the calculation load increases.

  An object of the present invention is to solve the problems in the conventional correction method as disclosed in Patent Document 2, and to accurately correct the error of the relative position between the tool and the table, despite the simple calculation of the correction amount. It is another object of the present invention to provide a position correction method capable of making the machining accuracy of a machine tool extremely good, and to provide a numerical control device for a machine tool capable of executing such position correction.

  In order to solve the above-mentioned problem, the invention according to claim 1 provides a machine tool having a tool and a table, in which a machining space is divided into a predetermined number of grids in advance and ideal space coordinates of each grid point are calculated. A numerical control device of a machine tool for setting and calculating a correction amount for correcting a relative position of a tool and a table with respect to its spatial coordinates, and according to a temperature difference between when setting spatial coordinates and when processing. And changing the grid interval and / or the tilt angle of the grid in the space coordinates for calculating the correction amount.

  According to a second aspect of the present invention, in the numerical control device for a machine tool according to the first aspect, the temperature of the processing space is detected by a temperature sensor installed in the machine tool, and the correction amount is set based on the detection result. It is characterized in that the lattice spacing in the spatial coordinates for calculation is changed.

  According to a third aspect of the present invention, in the numerical control device for a machine tool according to the first aspect, the temperature of the processing space is detected by a temperature sensor installed on the machine tool, and a correction amount is set based on the detection result. The tilt angle of the grid in the spatial coordinates for calculation is changed.

  According to a fourth aspect of the present invention, in the numerical control device for a machine tool according to any one of the first to third aspects, spatial coordinates can be arbitrarily set, and a predetermined grid point of the spatial coordinates is used as a reference. It is characterized in that it is possible to change the grid interval in space coordinates for calculating the correction amount.

  The numerical control device for a machine tool according to the present invention changes the error map of the space correction by thermal deformation (that is, directly reflects the deformation due to heat generated during processing on the error map in the space correction). Although the correction amount is calculated by the method, the error of the relative position between the tool and the table can be corrected with high accuracy, and the processing accuracy of the machine tool can be made extremely good.

FIG. 1 is an explanatory view (perspective view) showing a machine tool (a vertical machining center) equipped with a numerical controller. FIG. 3 is a block diagram illustrating a control mechanism of the numerical controller. It is an explanatory view showing a coordinate position of a processing space. 5 is a flowchart illustrating the contents of a correction process performed by the numerical controller. It is explanatory drawing which shows the deformation | transformation state in the YZ-axis direction of a processing space (a has shown the ideal state, b has shown the state which inclined occurred).

Hereinafter, an embodiment of a numerical control device according to the present invention will be described in detail with reference to the drawings.
<Configuration of machine tool and numerical controller>
FIG. 1 shows a machine tool (three-axis machining center) equipped with a numerical controller according to the present invention, and FIG. 2 is a block diagram showing a control mechanism of the numerical controller. The machine tool M includes a bed 4 serving as a base, a cross rail (column) 3 fixed to the bed 4, a spindle 1 on which a cutting tool 15 can be mounted, a spindle head 2 for fixing the spindle 1, and a front side of the bed 4. Numerical control device, which is constituted by a saddle 5 slidably mounted on the upper part, a table 6 for mounting a work (workpiece) slidably mounted on the upper part of the saddle 5, and the like, and connected thereto. The operation is controlled by C (see FIG. 2). The bed 4 of the machine tool M is provided with a temperature sensor 7 for measuring the ambient temperature of the processing space and a measuring device (such as a laser tracker) 8 for measuring the relative displacement between the spindle 1 and the table 6. Have been.

  In such a machine tool M, the spindle head 2 for fixing the spindle 1 can be moved vertically (Z-axis direction) with respect to the cross rail 3 by a built-in first drive device (motor) 9. The saddle 5 can be moved in the front-rear direction (Y-axis direction) with respect to the bed 4 by a built-in second driving device (motor) 10. Further, the table 6 can be moved in the left-right direction (X-axis direction) with respect to the saddle 5 by a built-in third driving device (motor) 11. The machine tool M controls the relative position between the cutting tool 15 mounted on the spindle 1 and the workpiece as described above so that the workpiece can be machined into a desired shape. Has become.

  As shown in the block diagram of FIG. 2, the numerical controller C includes a CPU 12, a storage unit 13, a timer (not shown), an input unit (keyboard, touch panel, etc.), an output unit (monitor, etc.), an input unit for the input unit, An interface 14 for connecting the output means to the CPU 12 is provided. The numerical controller C includes a first drive unit 9 for moving the spindle head 2 up and down, a second drive unit 10 for moving the saddle 5 back and forth, and a third drive unit 11 for moving the table 6 left and right. , Temperature sensor 7, measuring device 8, and the like via interface 14. Then, the machine tool M calculates a correction amount using the temperature detected by the temperature sensor 7 and the measurement value by the measuring device 8 according to a program stored in the storage unit 13 of the numerical controller C, and calculates the correction amount. , The first drive device 9, the second drive device 10, and the third drive device 11 are driven and controlled.

<Position correction by numerical controller>
When the position is corrected by the numerical controller C, the working space of the machine tool M (movable area of the tool mounted on the main spindle 1) is divided into grids at predetermined intervals, and the ideal space of each grid point is set. Set the coordinates (see FIG. 3). In the spatial coordinates, an error amount [EXi, EYi, EZi] can be set at each grid point [Xi, Yi, Zi]. Here, the distance between the grid points in the set space coordinates is [Lx, Ly, Lz].

  The correction amount is calculated based on the relative displacement between the spindle 1 and the table 6 measured by the measuring device 8. When the machine tool M is positioned at the coordinates of each grid point of the spatial coordinates set as described above, the relative relationship between the main shaft 1 and the table 6 is changed from the target by the positioning error of the linear axis, the straightness error, the attitude error, and the like. Error occurs. Errors can be obtained in each axis direction, and these errors are used as correction amounts.

  Hereinafter, an example of position correction by the numerical controller C will be described with reference to the flowchart of FIG. When performing position correction, first, reference is made to a reference temperature To which is a reference for setting a correction amount (S1). As the reference temperature To, a temperature serving as a reference at the time of creating an error map, such as a set environmental temperature at the time of measuring the correction amount or a temperature (for example, 20 ° C.) in consideration of the object temperature correction of the measuring device 8 is adopted. can do. Here, assuming that an error map is set in consideration of the object temperature correction of the measuring device 8, To = 20 ° C.

  Next, current temperature information of each part of the machine tool M and / or a part other than the processing space is obtained (S2). Here, the temperature detected by the temperature sensor 7 installed on the bed 4 is acquired as the representative temperature T of the machine tool M. Then, the error map is corrected using the acquired temperature information (S3). Here, the correction of the error map means that the distance [Lx, Ly, Lz] between the lattice points at the time of creating the error map has changed due to a temperature change ΔT = (T−To) from the time of measuring the correction amount. The idea is to correct the expansion or contraction due to temperature changes. For example, when the linear expansion coefficient α of the casting is used, the corrected error map [Xi ′, Yi ′, Zi ′] is given by the following equation 1.

  Alternatively, in addition to the expansion or contraction of the error map due to the temperature change, there is a case where the spatial coordinates are inclined as shown in FIG. The inclination is caused by a temperature change from the time of measurement of the correction amount, for example, the cross rail 3 falling down, or a change in the level of the machine tool M from the measurement of the correction amount. Even when the spatial coordinates have such an inclination, the error map is corrected in the same manner as the expansion or contraction of the error map.

  An example of correction of an error map in a case where a tilt occurs in the space coordinates as shown in FIG. 5B (when a squareness error φ occurs in the YZ plane) is shown. Here, assuming that the squareness error φ is sufficiently small and the shape creation theory is used, the corrected error map [Xi ′, Yi ′, Zi ′] is given by the following equation 2.

  Then, similarly to the correction of the error map, the correction amount [EXi, EYi, EZi] set for each grid point is corrected (S4). With such correction, the correction amount [EXi ', EYi', EZi '] is given by the following Expression 3.

  With the series of processes described above, it is possible to perform spatial correction taking into account deformation due to heat generated during processing and changes in squareness, and it is possible to process a workpiece with high accuracy while using a simple correction method Become.

<Effects of the numerical controller>
As described above, when calculating the correction amount, the numerical controller C sets the grid interval and the grid inclination angle in the space coordinates for calculating the correction amount in accordance with the temperature difference between the setting of the space coordinate and the processing. In order to calculate the correction amount by changing the error map of the space correction by thermal deformation (ie, by directly reflecting the deformation due to heat generated during processing on the error map in the space correction), In spite of calculating the correction amount by any method, the error of the relative position between the tool 1 and the table 6 can be corrected with high accuracy, and the processing accuracy of the machine tool M can be made extremely good.

<Modification example of numerical controller>
The configuration of the numerical control device according to the present invention is not limited to the aspect of the above-described embodiment at all, and the configuration such as the shape and structure of the processing device (CPU and the like), the storage unit, the temperature sensor, the measuring device, and the like, Modifications can be made as needed without departing from the spirit of the present invention. Further, the machine tool equipped with the numerical control device is not limited to the three-axis (vertical) machining center as in the above embodiment, but may be changed to another machine tool such as a five-axis machine or a lathe.

  For example, the numerical control device according to the present invention is not limited to the above-described embodiment, in which the correction amount is calculated with the detected temperature of each part of the machine tool obtained by the temperature sensor as one of the representative temperatures, and Temperature sensors are installed near the measuring instruments, and the temperature change for each component in each axial direction is obtained based on the detected temperature obtained by those temperature sensors, and the temperature change for each component in each axial direction is calculated for each error. It may be used for correcting the map and the correction amount.

  Further, the numerical control device according to the present invention is not limited to the one that corrects only the processing space of the machine tool as in the above-described embodiment, and the numerical control device may use any coefficient in consideration of the linear expansion coefficient and the like of the workpiece. It is also possible to change it to one that corrects the space including. Furthermore, the numerical control device according to the present invention is not limited to the one that sets the origin of the error map at the corner of the processing space and calculates the correction amount, as in the above-described embodiment, but is adapted to the thermal deformation behavior of the machine tool. It is also possible to change the error map to one that corrects the error map with reference to an arbitrary grid point in the processing space. In addition, the numerical control device according to the present invention is not limited to the one using the shape generation theory for calculating the squareness error as in the above embodiment, but is changed to one that calculates the squareness error geometrically. It is also possible.

Machine tool (3-axis machining center)
C · · · Numerical controller 1 · · · spindle 6 · · · table 7 · · · temperature sensor 8 · · · measuring instrument

Claims (4)

In a machine tool equipped with a tool and a table, the working space is divided into a predetermined number of grids in advance to set ideal space coordinates of each grid point, and the relative positions of the tool and the table with respect to the space coordinates are set. A numerical control device of a machine tool for calculating a correction amount for correction,
A numerical control device for a machine tool, wherein a grid interval and / or a tilt angle of a grid in a space coordinate for calculating a correction amount is changed according to a temperature difference between a time of setting a space coordinate and a time of machining.   The temperature sensor according to claim 1, wherein the temperature of the processing space is detected by a temperature sensor installed in the machine tool, and a lattice interval in space coordinates for calculating a correction amount is changed based on the detection result. Numerical control equipment for machine tools.   2. The method according to claim 1, wherein the temperature of the processing space is detected by a temperature sensor installed in the machine tool, and a tilt angle of a grid in space coordinates for calculating a correction amount is changed based on the detection result. A numerical control device for a machine tool as described in the above.   The space coordinates can be arbitrarily set, and a grid interval in space coordinates for calculating a correction amount can be changed with reference to a predetermined grid point of the space coordinates. A numerical control device for a machine tool according to any one of the above.

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