JP2024112632A - Method and device for correcting errors in a machine tool - Google Patents

Abstract

To enable an automatic setting for the coordinates of a correction reference point in accordance with a processing scheme, and a highly precise processing without a burden for a worker.SOLUTION: When a command to start processing is input by an operator, a processing program is analyzed in step S1, and a processing scheme is determined in step S2. It is determined in step S3 whether or not the determined processing scheme is a predetermined processing scheme that is preset so as to utilize the coordinates of a predetermined correction reference point when the position of a tool is calculated. When the determined processing scheme does not match the set processing scheme, the coordinates of the commanded position in each axle are set to the coordinates for a correction value calculation in step S4, and when the determined processing scheme matches the set processing scheme, the coordinates of the correction reference point are set to the coordinates for the correction value calculation based on the processing program in step S5. The positional error of the tool is calculated in step S6, the correction value in each axle is calculated in step S7, and then the position of the tool is corrected in step S8.SELECTED DRAWING: Figure 5

Description

This disclosure relates to a method and apparatus for correcting geometric errors in machine tools.

FIG. 1 is a schematic diagram of a five-axis controlled machining center M (hereinafter referred to as a "five-axis machine") having three translational axes and two rotational axes.
The spindle head 2 is capable of translational movement with two degrees of freedom along the X-axis and Z-axis, which are translational axes and perpendicular to each other. The table 3 is capable of rotational movement with one degree of freedom relative to the cradle 4 along the C-axis, which is a rotational axis. The cradle 4 is capable of rotational movement with one degree of freedom relative to the trunnion 5 along the A-axis, which is a rotational axis and perpendicular to the C-axis. The trunnion 5 is capable of translational movement with one degree of freedom relative to the bed 1 along the Y-axis, which is a translational axis and perpendicular to the X-axis and Z-axis. Thus, the spindle head 2 has three translational degrees of freedom and two rotational degrees of freedom relative to the table 3. Each axis is driven by a servo motor controlled by a numerical control device, and the workpiece is fixed to the table 3, a tool is attached to the spindle head 2 and rotated, and the workpiece is machined into any shape.

The motion errors of this five-axis machine M include geometric errors between the axes (hereinafter referred to as "geometric errors"). These motion errors are transferred to the shape of the workpiece, and become a cause of shape and dimensional errors of the workpiece.
In response to this, technology has been developed that achieves high-precision machining by correcting and controlling geometric errors.
For example, the invention described in Patent Document 1 is an apparatus that, when controlling a machine, calculates a correction value for correcting the command position of each axis based on the geometric error present between the axes, i.e., the deviation of the center position of the rotation axis, the inclination error, and the command position of each axis, so that the relative relationship between the tool and the workpiece is the same as that of a machine with no errors, and drives each axis by adding the correction value to the command position.
However, in the invention described in Patent Document 1, when the tilt error of the rotation axis is corrected, the translation axis is commanded to be corrected in accordance with the movement of the translation axis, so that even if only one translation axis is moved, the other translation axes may move slightly, which may affect the machining accuracy. Therefore, Patent Document 2 discloses an invention in which, in the case of the movement of the rotation axis, the coordinate value of a preset correction reference point is used to calculate the correction value instead of the coordinate value of the command position of each axis. With this invention, even when the rotation axis is indexed to perform flat machining or hole drilling, the minute movements due to the correction value of each axis do not cause a decrease in the machining surface accuracy, quality, or tool life, and high-precision machining can be performed.

JP 2009-104317 A JP 2012-221001 A

The invention described in Patent Document 2 requires that a person specify in advance the coordinate values of the correction reference point used to calculate the correction value. In order to specify the coordinate values of this correction reference point, the worker must understand the processing content and be able to determine whether the processing method requires the specification of the coordinate values of the correction reference point, which creates a problem of a heavy burden on the worker. In particular, when drilling or flat processing is performed in multiple locations, it is necessary to specify the coordinate values each time, which increases the burden on the worker.

The present disclosure therefore aims to provide an error correction method and device for machine tools that can automatically set the coordinate values of the correction reference point according to the machining method, and can perform high-precision machining without placing a burden on the operator.

In order to achieve the above object, a first configuration of the present disclosure is a method for correcting a position of a tool relative to a workpiece in a machine tool having a table for holding a workpiece, a spindle for holding a tool, and three or more translation axes, the spindle being capable of relative translational movement with three or more degrees of freedom with respect to the table, the method comprising:
A program analysis step of analyzing a machining method from a machining program for machining the workpiece;
a machining method determination step of determining whether or not the machining method analyzed in the program analysis step coincides with a predetermined machining method that is preset as a method that uses coordinate values of a predetermined correction reference point when calculating the position of the tool;
a coordinate value setting step of setting a coordinate value of a command position in a command value coordinate system of the translation axis as a coordinate value for calculating a position of the tool when the analyzed machining method does not match the predetermined machining method, and setting a coordinate value of the correction reference point as a coordinate for calculating a position of the tool when the analyzed machining method matches the predetermined machining method;
a position error calculation step of calculating a position error of the tool caused by the geometric error based on a coordinate value of a command position in a command value coordinate system of the translation axis or a coordinate value of the correction reference point and a geometric error between each axis;
a correction value calculation step of converting the calculated position error of the tool into a command value coordinate system of the translation axes to calculate a correction value for the geometric error of each of the axes;
and a position correction step of correcting the position of the tool based on the calculated correction value.
Another aspect of the first configuration is characterized in that, in the above configuration, in the coordinate value setting step, if the analyzed machining method coincides with the specified machining method, the machining program is analyzed to set the coordinate value of the correction reference point.
In order to achieve the above object, a second configuration of the present disclosure is an apparatus for correcting a position of the tool relative to a workpiece in a machine tool having a table for holding a workpiece, a spindle for holding a tool, and three or more translation axes, the spindle being capable of relative translational movement with three or more degrees of freedom with respect to the table, the apparatus comprising:
a program analysis means for analyzing a machining method from a machining program for machining the workpiece;
a machining method determination means for determining whether or not the machining method analyzed by the program analysis means coincides with a predetermined machining method that is preset as a method using coordinate values of a predetermined correction reference point when calculating the position of the tool;
a coordinate value setting means for setting a coordinate value of a command position in a command value coordinate system of the translation axis as a coordinate value for calculating a position of the tool when the analyzed machining method does not match the predetermined machining method, and for setting a coordinate value of the correction reference point as a coordinate for calculating a position of the tool when the analyzed machining method matches the predetermined machining method;
a position error calculation means for calculating a position error of the tool caused by the geometric error based on a coordinate value of a command position in a command value coordinate system of the translation axes or a coordinate value of the correction reference point and a geometric error between each axis;
a correction value calculation means for calculating a correction value for a geometric error of each of the axes by converting the calculated position error of the tool into a command value coordinate system of the translation axes;
and a position correction means for correcting the position of the tool based on the calculated correction value.
Another aspect of the second configuration is characterized in that, in the above configuration, the coordinate value setting means analyzes the machining program and sets the coordinate value of the correction reference point when the analyzed machining method coincides with the specified machining method.

According to the present disclosure, it is possible to analyze the machining program, determine whether the machining method requires calculating the tool position using the coordinate value of the correction reference point, and automatically set the coordinate value of the correction reference point according to the machining method. Therefore, it is possible to perform high-precision machining without burdening the operator and without causing a decrease in the machining surface accuracy/quality or tool life when performing flat machining or drilling.

FIG. 1 is a schematic diagram of a five-axis controlled machining center. FIG. 2 is a block diagram showing a control configuration of a numerical control device. FIG. 2 is a functional block diagram of a numerical control device that generates servo command values for each axis. 1 is a schematic diagram illustrating an example of drilling a hole in a workpiece. 1 is a flow chart of an error correction method.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings.
In this embodiment, the case of drilling will be described as an example, and the machine tool to which the invention is applied will be described as a five-axis machine M shown in FIG.
2 is a block diagram showing an example of the control configuration of the numerical control device 11 of the five-axis machine M. The numerical control device 11 is an example of the error correction device of the second configuration of the present disclosure, and is configured to include a CPU, a recording means 12 connected to the CPU, and a display means 13, and controls the servo motors 27a to 27e of each axis. The numerical control device 11 is provided with an input means 14 for setting a machining program for the workpiece, a geometric error to be described later, a machining method that requires the position of a tool to be calculated using the coordinate values of a correction reference point, and the like. The machining program and the geometric error are non-temporarily recorded in the recording means 12. The machining method that requires the position of a tool to be calculated using the coordinate values of a correction reference point is also non-temporarily recorded in the recording means 12.

FIG. 3 is a functional block diagram of a numerical control device 11 that generates servo command values for each axis.
When a command to process a workpiece is input to the numerical control device 11, first, a processing program 21 is read from the recording means 12, and a command value generating means 22 generates coordinate values of a command position for each translation axis.
Next, the program analysis means 23 judges whether or not the machining method of the machining program 21 is a machining method that requires calculation of the tool position using the coordinate values of the correction reference point, and sets the coordinate values.
Next, a correction value for each axis is calculated by a correction value calculation means 24 based on the generated coordinate value of the command position or the coordinate value of the correction reference point, and the sum of the coordinate value of the command position and the correction value is sent to a servo command value conversion means 25 to calculate a servo command value, and the servo command value for each axis is sent to the servo amplifiers 26a to 26e of each axis. The servo amplifiers 26a to 26e of each axis drive servo motors 27a to 27e, respectively, to control the relative position of the spindle head 2 (tool) with respect to the table 3. Thus, the numerical control device 11 functions as a program analysis means, a machining method determination means, a coordinate value setting means, a position error calculation means, a correction value calculation means, and a position correction means of the present disclosure.

Next, the geometric error will be described. The geometric error is defined as a total of six components (δx, δy, δz, α, β, γ) consisting of three relative translation errors and three relative rotation errors between adjacent axes.
In the case of the five-axis machine M of this example, the six geometric error components exist between each axis, between the C-axis and the workpiece, and between the Z-axis and the tool, so there are a total of 36 geometric errors. However, if redundant errors are excluded from the 36, there are only 13. If the axes between which geometric errors exist are expressed as subscripts in the order from the tool side, the 13 geometric errors are α ₁ , β ₁ , α ₂ , β ₂ , γ ₃ , δ _{y 4} , δ _{z 4} , β ₄ , γ ₄ , δ _{x 5} , δ _{y 5} , α ₅ , and β ₅ . These are, in order, the perpendicularity between the tool and the Y axis, the perpendicularity between the tool and the X axis, the perpendicularity between the Y and Z axes, the perpendicularity between the Z and X axes, the perpendicularity between the X and Y axes, the Y direction error of the A axis central position, the Z direction error of the A axis central position, the perpendicularity between the A and X axes, the perpendicularity between the A and Y axes, the X direction error of the C axis central position, the Y direction error of the C axis central position, the A axis origin error, and the perpendicularity between the C and A axes. These geometric errors are measured in advance and recorded in the recording means 12.

Next, an error correction method of the numerical control device 11 according to the first configuration of the present disclosure will be described with reference to the flowchart of Fig. 5, taking as an example the case of machining the hole 1 shown in the schematic diagram of Fig. 4. This error correction method is executed based on an error correction program pre-recorded in the recording means 12.
First, the operator presets in the recording means 12 a predetermined machining method that requires the use of coordinate values of a predetermined correction reference point when calculating the position of a tool. This machining method may be multiple.
When an operator inputs a command to start machining, the numerical control device 11 reads and analyzes the machining program 21 recorded in the recording means 12 in step (hereinafter simply referred to as "S") 1, and determines the machining method in S2 (S1, S2: program analysis steps).
In this analysis, it is analyzed whether the processing is hole drilling, plane machining, shape machining, etc. For example, in the case of hole drilling, it is judged whether it is a hole drilling cycle in which the tool 6 is positioned from a standby position P1 away from the workpiece 7 to a position P2 directly above hole 1 as shown in Fig. 4, cuts and positions the tool 6 at a position P3, performs hole drilling, returns to the position P2 directly above, and moves to a position P4 directly above the next hole 2. Alternatively, it may be judged to be hole drilling when there is information on the tool 6 used for processing (e.g., a drill) and a cutting positioning command.

Next, in S3, it is determined whether or not the processing method determined in S2 coincides with a predetermined processing method preset in the recording means 12 (processing method determination step).
Therefore, if the determined machining method does not match the preset machining method, the coordinate values of the command position of each axis are set to the coordinate values x, y, z for calculating the correction value in S4. On the other hand, if the determined machining method matches the preset machining method, the coordinate values of the correction reference point are set to the coordinate values x, y, z for calculating the correction value based on the machining program 21 in S5 (S4, S5: coordinate value setting step).
For example, in the case of the drilling process shown in FIG. 4, the correction reference points are directly above positions P2 and P4, which are the starting points for cutting feed, and the coordinate values are the X-axis, Y-axis, and Z-axis coordinate values of directly above positions P2 and P4.
Next, in S6, the position error of the tool 6 is calculated based on the coordinate values set in S4 or S5 and the geometric errors between the axes (position error calculation step).
Next, in S7, a correction value for each axis is calculated (correction value calculation step), and in S8, the position of the tool 6 is corrected (position correction step).

Next, the method of calculating the position error of the tool 6 in S6 and the method of calculating the correction value for each axis in S7 will be described in detail using mathematical expressions.
First, a method for calculating the correction values ΔCc and ΔCa for the rotation axes C and A will be described. The correction values ΔCc and ΔCa can be calculated from the following equation 2 using a conversion matrix ε _j (the following equation 1) of the geometric error due to six geometric error components (δx, δy, δz, α, β, γ).
Here, the subscript j indicates the axis-to-axis relationship in which a geometric error exists, in order from the tool side.

The transformation matrices of the rotational axes C and A and the translational axes X, Y, and Z, and the tool tip vector ^T P in the spindle coordinate system can be expressed by the following equation 3.

The tool tip vector ^W P _I in the workpiece coordinate system when there is no geometric error can be determined by the following equation 4 using the transformation matrix of equation 3 and the tool tip vector.
Here, c and a are the coordinate values of the command position of the rotation axis, and x, y, and z are the coordinate values of the command position of the translation axis set in S4 or the coordinate values of the correction reference point set in S5.

Furthermore, the tool tip vector ^W _PG in the workpiece coordinate system when a geometric error exists can be determined by the following equation 5 using the geometric error conversion matrix ε _j (equation 1).

_A position error vector Δe of the tip of each tool in the workpiece coordinate system due to a _geometric error can be calculated from the difference between ^WPG and ^WPI by the following equation 6.

The correction value of the translation axis due to the position error can be treated as the inverse sign of the position error converted into the command coordinate system. The correction value vector ΔComp is shown in the following equation 7.

In this manner, the error correction method and numerical control device 11 of the above-described form analyze the machining method from the machining program 21 for machining the workpiece 7, and determine whether or not the analyzed machining method coincides with a predetermined machining method that is preset as one that uses the coordinate values of a predetermined correction reference point when calculating the position of the tool 6.
Then, when the machining methods do not match, the coordinate values of the command position in the command value coordinate system of the translational axes are set, and when the machining methods match, the coordinate values of the correction reference point are set, and the position error of the tool 6 caused by the geometric error is calculated from the set coordinate values and the geometric error between each axis. The calculated position error of the tool 6 is converted into the command value coordinate system of the translational axes to calculate a correction value for the geometric error of each axis, and the position of the tool 6 is corrected based on the calculated correction value.
According to this configuration, it is possible to analyze the machining program 21, judge whether the machining method requires calculating the position of the tool 6 using the coordinate value of the correction reference point, and automatically set the coordinate value of the correction reference point according to the machining method. Therefore, it is possible to perform high-precision machining without imposing a burden on the operator and without causing a decrease in the machining surface accuracy/quality or tool life when performing hole drilling.

In the above embodiment, the timing for setting the coordinate values for calculating the tool position is after the machining method determination step, but the timing is not limited to this, and the coordinate values may be set at an earlier stage, for example, at the same time as determining the machining method.
In the above embodiment, a five-axis machine is used as an example of a machine tool for drilling, but the machine tool may be a three-axis translational machining center, a multitasking machine, or a lathe. The machining method using the coordinate values of the correction reference point may also be used for plane machining. In particular, if the coordinate values of the correction reference point are used for plane machining or drilling, which are performed by indexing rotation axes such as the A-axis and C-axis, a decrease in machining accuracy can be prevented.
In the above embodiment, an example has been described in which the error correction device of the present disclosure is provided in the numerical control device, but the error correction device may be provided separately from the numerical control device.

1: Bed, 2: Spindle head, 3: Table, 4: Cradle, 5: Trunnion, 6: Tool, 7: Workpiece, 11: Numerical control device, 12: Recording means, 13: Display means, 14: Input means, 21: Machining program, 22: Command value generation means, 23: Program analysis means, 24: Correction value calculation means, 25: Servo command value conversion means.

Claims (4)

1. A method for correcting a position of a tool relative to a workpiece in a machine tool having a table for holding a workpiece, a spindle for holding a tool, and three or more translation axes, the spindle being capable of relative translational movement with three or more degrees of freedom relative to the table, comprising:
A program analysis step of analyzing a machining method from a machining program for machining the workpiece;
a machining method determination step of determining whether or not the machining method analyzed in the program analysis step coincides with a predetermined machining method that is preset as a method that uses coordinate values of a predetermined correction reference point when calculating the position of the tool;
a coordinate value setting step of setting a coordinate value of a command position in a command value coordinate system of the translation axis as a coordinate value for calculating a position of the tool when the analyzed machining method does not match the predetermined machining method, and setting a coordinate value of the correction reference point as a coordinate for calculating a position of the tool when the analyzed machining method matches the predetermined machining method;
a position error calculation step of calculating a position error of the tool caused by the geometric error based on a coordinate value of a command position in a command value coordinate system of the translation axis or a coordinate value of the correction reference point and a geometric error between each axis;
a correction value calculation step of converting the calculated position error of the tool into a command value coordinate system of the translation axes to calculate a correction value for the geometric error of each of the axes;
a position correcting step of correcting a position of the tool based on the calculated correction value;
1. A method for correcting errors in a machine tool, comprising: The method for correcting errors in a machine tool according to claim 1, characterized in that in the coordinate value setting step, if the analyzed machining method matches the predetermined machining method, the machining program is analyzed to set the coordinate value of the correction reference point. 1. A machine tool having a table for holding a workpiece, a spindle for holding a tool, and three or more translation axes, the spindle being capable of relative translational movement with three or more degrees of freedom with respect to the table, the machine tool comprising:
a program analysis means for analyzing a machining method from a machining program for machining the workpiece;
a machining method determination means for determining whether or not the machining method analyzed by the program analysis means coincides with a predetermined machining method that is preset as a method using coordinate values of a predetermined correction reference point when calculating the position of the tool;
a coordinate value setting means for setting a coordinate value of a command position in a command value coordinate system of the translation axis as a coordinate value for calculating a position of the tool when the analyzed machining method does not match the predetermined machining method, and for setting a coordinate value of the correction reference point as a coordinate for calculating a position of the tool when the analyzed machining method matches the predetermined machining method;
a position error calculation means for calculating a position error of the tool caused by the geometric error based on a coordinate value of a command position in a command value coordinate system of the translation axis or a coordinate value of the correction reference point and a geometric error between each axis;
a correction value calculation means for calculating a correction value for a geometric error of each of the axes by converting the calculated position error of the tool into a command value coordinate system of the translation axes;
a position correction means for correcting a position of the tool based on the calculated correction value;
An error correction device for a machine tool comprising: The error compensation device for a machine tool according to claim 3, characterized in that the coordinate value setting means analyzes the machining program and sets the coordinate value of the compensation reference point when the analyzed machining method coincides with the specified machining method.

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