JP2012220999A - Correction value operation method and program of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and the like in a machine tool, capable of correcting a position error of a tool tip point due to a geometrical error as well as correcting an attitude error of the tool and capable of operating a correction value of a rotation axis independent of a rotation axis instruction value with a small calculation amount.SOLUTION: A correction value operation method of a machine tool, for correcting a position error and an attitude error of a tool with respect to a workpiece due to a geometric error in a machine tool having two or more translation axes and one or more rotation axes, includes: a rotation axis correction value operation step (S3) for operating a correction value of the rotation axes by using a geometric parameter representing the geometric error; and a translation axis correction value operation step (S4) for operating a correction value of the translation axes by using a command value of each of the rotation axes and a command value of each of the translation axes, and the geometric parameter.

Description

  The present invention relates to a method or program for calculating a correction value for correcting a geometric error of a machine tool having a translation axis and a rotation axis.

  FIG. 1 is a schematic diagram of a machine tool (5-axis control machining center, 5-axis machine) having three translation axes and two rotation axes, which is an example of the machine tool. The spindle head 2 is a translational axis and can move in two translational degrees of freedom relative to the bed 1 by means of an X axis and a Z axis orthogonal to each other. The table 3 can move with one degree of freedom of rotation with respect to the cradle 4 by a C-axis which is a rotation axis. The cradle 4 can move with one degree of freedom of rotation with respect to the trunnion 5 by the A axis that is the rotation axis, and the A axis and the C axis are orthogonal to each other. The trunnion 5 is a translational axis and is capable of translational movement with one degree of freedom with respect to the bed 1 by the Y axis perpendicular to the X axis and the Z axis. Each axis is driven by a servomotor (not shown) controlled by a numerical control device, and a workpiece (workpiece) is fixed to the table 3, a tool is attached to the spindle head 2, and the workpiece is rotated. Machining is performed by controlling the relative position of the tool.

  Factors affecting the motion accuracy of the 5-axis machine include, for example, an error in the center position of the rotating shaft (deviation from the assumed position), an inclination error of the rotating shaft (perpendicularity and parallelism between the shafts), etc. There is a geometric error (geometric error) between the axes. If there is a geometric error, the motion accuracy of the machine tool is deteriorated, and the processing accuracy of the workpiece is deteriorated. For this reason, it is necessary to reduce the geometric error by adjustment, but it is difficult to make it zero, and high-precision machining can be performed by performing control for correcting the geometric error.

  As means for correcting geometric errors, methods as described in Patent Documents 1 and 2 below have been proposed. In Patent Document 1, the position of the tool tip point is converted into the position of each translation axis in consideration of the geometric error of the machine tool, and the command tip position is used to correct the tool tip point position error due to the geometric error. can do. On the other hand, in the case of Patent Document 2, the difference between the position of the tool tip point with respect to the workpiece when there is a geometric error and the position when there is no geometric error is controlled as a correction value for the translation axis, thereby causing a geometric error. The position error of the tool tip can be corrected.

  In the correction means of Patent Document 1, the position error of the tool tip point is corrected, but in reality, not only the position error of the tool tip point but also the posture error of the tool occurs due to the geometric error. For example, in the 5-axis machine shown in FIG. 1, when the work 7 is flattened by attaching a square end mill 6 to the spindle head 2 as shown in FIG. 2, the rotational geometric error α around the X axis causes the spindle head 2 to move. On the other hand, when the table 3 is inclined, a posture error of the front end surface of the square end mill 6 occurs. Here, if plane processing is performed with the direction from the front to the back of FIG. 2 as the feed direction and the thick arrow P direction as the pick direction, the positioning command value in the pick direction in the square end mill 6 is a plurality of points spaced apart from each other. It becomes a set of. Then, in these correction means, although the tool tip point is corrected from each positioning command value to a point Q inclined by the inclination α with respect to the Y axis, there is an interval in the positioning command value. Q also has an interval, and a step is generated on the processed surface as shown in FIG.

Therefore, in Patent Document 2, a tool posture vector ^T V _G = [i j k] for a workpiece when there is a geometric error is obtained, and correction values Δa and Δc of the rotation axes (A axis and C axis) are obtained as a vector ^T V. It is assumed that the posture error of the tool can be corrected by calculating by the following [Equation 1] using the _G and A axis command value a and correcting the rotation axis command value.

JP 2004-272887 A JP 2009-104317 A

However, in the case of Patent Document 2, it is not possible to calculate when the A-axis command value a is 0 according to the above [Equation 1]. For this reason, there is a problem that the correction value cannot be correctly derived and exception processing needs to be performed. This is because the five-axis machine has a configuration of three translation axes and two rotation axes, and therefore cannot cope with all errors in six spatial degrees of freedom (three translational degrees of freedom and three degrees of freedom of rotation) due to geometric errors. Depending on the reason. Further, the calculation of the above-described tool posture vector ^T V _G requires almost the same amount of calculation as the calculation of the correction value of the position error of the tool tip point, and the amount of calculation increases when correcting the tool posture error. There is a problem.

  Therefore, in the present invention, in the first to eighth and ninth aspects, in a machine tool such as a 5-axis machine, it is possible to correct a position error of a tool tip point due to a geometric error and a tool posture error, In addition, it is an object of the present invention to provide a method and program that can calculate a rotation axis correction value that does not depend on the rotation axis command value with a small amount of calculation.

  In order to achieve the above-mentioned object, the invention according to claim 1 is a machine tool having two or more translation axes and one or more rotation axes, and the position of the tool relative to the workpiece due to geometric errors and A correction value calculation method for the machine tool, which corrects a posture error, a rotation axis correction value calculation step for calculating a correction value of the rotation axis using a geometric parameter representing the geometric error, and A translation axis correction value calculation step of calculating a correction value for the translation axis using the command value for each rotation axis, the command value for each translation axis, and the geometric parameter.

  The invention according to claim 2 is the above invention, wherein, in the translation axis correction value calculation step, the translation axis correction value is further calculated using the rotation axis correction value. It is.

  According to a third aspect of the present invention, in the above-mentioned invention, in the translation axis correction value calculation step, the rotation axis is corrected by the correction value of the rotation axis, so that the rotation axis is assumed to occur. The correction value of the translation axis for further correcting the error is calculated.

According to a fourth aspect of the present invention, in the above invention, the translational axis correction value calculation step has no geometric error by using the command value of each rotary shaft and the command value of each translational axis. The ideal tool position calculating step for calculating the ideal tool position, the command value for each rotary axis, the command value for each translation axis, the geometric parameter, and the rotation calculated in the rotation axis correction value calculating step An actual tool position calculating step for calculating an actual tool position when there is a geometric error using an axis correction value; and a tool position for calculating a difference between the ideal tool position and the actual tool position. An error calculation step, and a tool position coordinate conversion step for converting the coordinates of the difference,
It is characterized by including.

  The invention according to claim 5 is the above invention, wherein in the rotation axis correction value calculation step, a sum of a plurality of geometric parameters in the same rotation direction as the rotation axis or an inverse sign of the sum is corrected for the rotation axis. It is characterized by a value.

  Invention of Claim 6 is the said invention, The said machine tool has one said rotating shaft, In the said rotating shaft correction value calculation step, all the said of the same rotation direction as the said rotating shaft A geometric parameter sum or an inverse sign of the sum is used as a correction value for the rotation axis.

  The invention according to claim 7 is the above invention, wherein the machine tool has two rotation axes, and is considered as a chain of axes from a tool to a workpiece in the rotation axis correction value calculation step. The sum of the geometric parameters in the same rotation direction as the first rotation axis between the tool and the second rotation axis or the reverse sign of the sum is used as the correction value for the first rotation axis, and the 1 The sum of the geometric parameters in the same rotation direction as the second rotation axis between the second rotation axis and the workpiece or the reverse sign of the sum is used as a correction value for the second rotation axis, To do.

  The invention according to claim 8 is the above invention, wherein the machine tool has three rotation axes, and is considered as a chain of axes from a tool to a workpiece in the rotation axis correction value calculation step. The sum of the geometric parameters in the same rotation direction as the first rotation axis between the tool and the second rotation axis or the reverse sign of the sum is used as the correction value for the first rotation axis, and the 1 The sum of the geometric parameters in the same rotation direction as the second rotation axis or the reverse sign of the sum between the second rotation axis and the third rotation axis is used as a correction value for the second rotation axis, The sum of the geometric parameters in the same rotational direction as the third rotational axis between the second rotational axis and the workpiece or the inverse sign of the sum is used as a correction value for the third rotational axis. It is a feature.

  In order to achieve the above object, the invention described in claim 9 is a machine tool correction value calculation program for causing a computer to execute the machine tool correction value calculation method.

  According to the present invention, a correction value for a rotation axis that does not depend on the rotation axis command value is calculated with a small amount of calculation by a simple calculation method with a small amount of calculation, resulting from a geometric error of a machine tool such as a 5-axis machine In addition to correcting the position error of the tool tip point, it is also possible to correct the tool posture error caused by the geometric error.

It is a schematic diagram of a 5-axis control machining center. It is a schematic diagram of the plane process by the attitude | position error of the tool which concerns on a prior art example. It is a block diagram of the control apparatus which performs the control method of this invention. It is a flowchart of the correction value calculation in this invention. It is a table | surface of the start position and end position of the geometric parameter used for the correction value calculation of the rotating shaft of this invention.

  Hereinafter, as an example of an embodiment according to the present invention, correction in the 5-axis machine shown in FIG. 1 will be described based on the drawings as appropriate. The correction is performed by a computer that executes a correction program. The computer may be a numerical control device of a 5-axis machine, or an independent control device connected to the computer. A combination of these may be used. In addition, the said form is not limited to the following example, For example, you may apply to the machine tool of 4 axes or less, or 6 axes or more, and it replaces with the table 3 having 2 degrees of freedom of rotation by a rotating shaft, The spindle head 2 may have two degrees of freedom of rotation, and the spindle head 2 and the table 3 may each have one degree of freedom or more of rotation. Further, as a machine tool, a lathe, a compound processing machine, a grinding machine, or the like can be employed instead of the machining center (FIG. 1).

  FIG. 3 shows an example of a numerical controller 10 for performing the control method of the present invention. When the machining program G is input, the command value generation unit 11 generates a command value for each drive axis. The correction value calculation means 12 calculates the correction value of each axis based on the command value generated by the command value generation means 11, and the servo command value conversion means 13 that receives the total value of the command value and the correction value, The servo command value for each axis is calculated and sent to the servo amplifiers 14a to 14e for each axis. The servo amplifiers 14a to 14e for each axis drive the servo motors 15a to 15e, respectively, to control the relative position and posture of the spindle head 2 with respect to the table 3.

  Next, the geometric error will be described. The geometric error is defined as a total of six components (δx, δy, δz, α, β, γ) in three directions of relative translation error and three directions of relative rotation error between the axes. The connection of the axis from the workpiece 7 fixed to the table 3 of the 5-axis machine to the tool fixed to the spindle head 2 is the order of C axis, A axis, Y axis, X axis, Z axis, Considering between the tools and between the workpiece 7 and the C axis, there are a total of 36 geometric errors. However, since there are a plurality of 36 geometric errors in a redundant relationship, they are excluded as the final geometric error.

Then, the final geometric error, expressed as a subscript order from the tool side of the axis name and the geometric _{errors, δx 5, δy 5, α} 5, β 5, δy 4, δz 4, β 4, γ ₄ , γ ₃ , α ₂ , β ₂ , α ₁ , β ₁ in total. These are, in order, C-axis center position X-direction error, C-A axis offset error, A-axis angle offset error, C-A axis squareness, A-axis center position Y-direction error, and A-axis center position Z, respectively. Direction error, A-X axis perpendicularity, A-Y axis perpendicularity, XY axis perpendicularity, Y-Z axis perpendicularity, Z-X axis perpendicularity, Main axis-Y axis perpendicularity , The perpendicularity between the main axis and the X axis. The numerical controller 10 includes storage means (not shown) for storing these geometric errors.

  Next, a correction value calculation method for geometric errors, which is executed by the numerical control apparatus 10, will be described. FIG. 4 is a flowchart of the correction value calculation.

  In step S1, it is determined whether to correct the tool posture error. When the tool posture error is not corrected, the correction value of the rotation axis is not calculated in step S2 and is set to zero. On the other hand, when correcting the tool posture error, the correction value of the rotation axis is calculated in step S3. The calculation in step S3 will be described later. Finally, in step S4, the translation axis correction value is calculated.

Prior to the description of the calculation in step S3, the method for calculating the translational axis correction value in step S4 will be described. In order to convert the tool tip point vector _PT on the spindle coordinate system at the spindle head 2 to the workpiece coordinate system on the table 3, the length of the tool to be used is t, and X, Y, Z, A, C If the command positions of the axes are x, y, z, a, and c, respectively, they can be obtained by performing homogeneous coordinate conversion using the following [Equation 2]. That is, determine the tool center point vector P _I in the workpiece coordinate system in the absence of geometric errors.

On the other hand, as shown in the following [Equation 3], each geometric error is arranged as a transformation matrix between the transformation matrices of the respective axes of the above [Equation 2], so that the tool in the workpiece coordinate system when there is a geometric error. Request tip point vector _{P R.} Note that [Equation 3] is an approximate expression in which the product is regarded as 0 on the assumption that the geometric error is minute.

Accordingly, the position error ΔP _W = (δx, δy, δz) of the tool tip point in the workpiece coordinate system is expressed by the following [Equation 4].

Furthermore, the position error [Delta] P _W of the tool center point in the workpiece coordinate system, by the coordinate transformation as shown in the following Equation 5, it is possible to obtain the error [Delta] P _O in the command value.

  Therefore, the correction value ΔP = (Δx, Δy for the X, Y, and Z axes is obtained by the following [Equation 6] using the command value of each axis and the geometric error of the above formula as a parameter (geometric parameter) measured and identified in advance. , Δz).

  By adding the correction value ΔP of each translation axis obtained in this way to the corresponding translation axis command value and commanding it, the position error of the tool tip point due to the geometric error can be corrected.

In addition, when correcting the tool posture, which will be described later, it is necessary to correct the command value of the rotary axis. When the rotary axis is operated by this correction value of the rotary axis, the position of the tool tip point with respect to the workpiece also moves. The translational axis correction value is corrected by the amount of movement of the tool tip position based on the axis correction value. In other words, it is necessary to correct the translation axis correction value for the movement of the tool tip position, which is an error assumed to occur in the translation axis by commanding the correction of the rotation axis. To make this modification, using a rotating axis corrected command value obtained by adding the correction value to the rotation axis command value when obtaining the tool end point vector P _R in the workpiece coordinate system when there is a geometric error. That is, instead of the above [Equation 3], the following [Equation 7] is used. Here, Δa is an A-axis correction value, and Δc is a C-axis correction value. [Equation 8] approximating [Equation 7] may be used.

  Next, the rotation calculation of the rotation axis in step S3 will be described.

  Considering the connection order of the axes from the tool to the workpiece, the A axis is closer to the tool side than the C axis, so the A axis is called the first rotation axis and the C axis is called the second rotation axis. Further, the A axis is fourth and the C axis is fifth when viewed from the tool side. When the number of these orders is associated with the position of each rotation axis, the position Loc1 of the first rotation axis is 4, and the position Loc2 of the second rotation axis is 5. Further, the position Loc3 of the third rotation axis is not considered because there are only two rotation axes. Further, the order of geometric errors from the tool side is also associated with the position of the geometric error and represented by 1 to 6.

  The correction value of the rotation axis is a geometric parameter between the geometric error start position ls * and the end position le * in FIG. 5 in the same rotation direction as the rotation axis (A axis is α *, B axis is β * and C-axis are opposite signs of the total value of γ *). Here, * indicates that the number corresponding to the rotation axis is included among the numbers indicating the positions. That is, the correction value of the first rotation axis is the reverse sign of the total value from ls1 to le1, and the second rotation axis is the total value from ls2 to le2. If there is a third rotation axis, the length is from ls3 to le3.

  As shown in FIG. 5, the geometric parameter selected as the correction value varies depending on the number of rotation axes. When there are two rotation axes, the correction value for the first rotation axis is from the first (ls1 = 1) to the geometric parameter of the position of the second rotation axis (le1 = Loc2). The value is from one workpiece side position (ls2 = Loc1 + 1) to the final position (le2 = 6) of the position of the first rotation axis. Therefore, in the case of a 5-axis machine, the A-axis correction value Δa and the C-axis correction value Δc are obtained by the following [Equation 9].

  Then, by adding the obtained correction values of the respective rotation axes to the corresponding command values and instructing them, it is possible to correct the tool posture error due to the geometric error. Further, based on this rotation axis correction value, the translation axis correction value is calculated as described above, and the obtained correction value for each translation axis is added to the corresponding command value and commanded. The position error of the tool tip point due to can also be corrected at the same time.

  If the position of the rotation axis, the correspondence between the rotation axis and the geometric error component, and the start position / end position are associated and set in advance, only the addition of the right side of [Equation 9] is performed when calculating the actual correction value. Therefore, the calculation amount is very small.

  Next, functions and effects of the present invention will be described using mathematical expressions.

The machine has 14 geometric errors δx ₅ , δy ₅ , α ₅ , β ₅ , γ ₅ , δy ₄ , δz ₄ , β ₄ , γ ₄ , γ ₃ , α ₂ , β ₂ , α ₁ , β _1. Suppose it exists. For the sake of simplification, the following equations are approximated by treating the product of geometric errors as 0, assuming that the geometric error is very small.

  The position error (δx, δy, δz) of the tool tip point in the workpiece coordinate system is the following [Equation 10] obtained by modifying [Equation 4].

On the other hand, the tool posture error in the workpiece coordinate system can be obtained from the fact that _PT in [Equation 2] and [Equation 3] is changed to V _T = [0 0 1 0] t. Therefore, the tool posture error (δi, δj, δk) is expressed by the following [Equation 11].

  Examine the effect of tool posture error correction by rotating axis correction command. First, tool posture errors (δi ′, δj ′, δk ′) when the rotation axis is commanded to be corrected are expressed by the following [Equation 12].

  On the other hand, assuming that the geometric error is known, the correction value of the rotation axis calculated by [Equation 9] using the value as a geometric parameter is the following [Equation 13].

  When [Equation 13] is substituted into [Equation 12], as shown in [Equation 14], tool posture errors (δi ″, δj ″, δk ″) after the rotation axis correction command are obtained.

  According to [Equation 14] and the like, the tool posture error after the rotation axis correction command is reduced by correcting the geometric error of the α system, and high-accuracy machining is possible. However, the effect of the geometric error of the β system remains. This is because it is theoretically impossible to correct all three degrees of freedom of the posture error with the two rotation axes.

  Next, the effect of correcting the tool tip position error based on the rotation axis and translation axis correction command according to the present invention will be discussed. The position error (δx ′, δy ′, δz ′) of the tool tip point in the workpiece coordinate system when commanded with the correction values of the rotation axis and translation axis taken into consideration is the following [Expression 15] It becomes.

  On the other hand, assuming that the geometric error is known, the translation axis correction values (Δx, Δy, Δz) calculated by [Equation 6] with [Equation 7] substituted as the geometric parameter are the following [ Equation 16].

  Substituting [Equation 16] into [Equation 15], the following [Equation 17] is obtained. This is the tool tip position error (δx ″, δy ″, δz ″) after the translation axis and rotation axis correction command.

  Therefore, the effect of the β system geometric error cannot be completely corrected for the tool posture error, but the error remains, but the tool tip point position error disappears due to the correction of all geometric errors including the β system geometric error, Processing accuracy can be improved.

1 bed 2 spindle head 3 table 4 cradle 5 trunnion 6 square end mill (tool)
7 Workpiece (Workpiece)

Claims (9)

In the machine tool having two or more translation axes and one or more rotation axes, the correction value calculation method for the machine tool corrects errors in the position and orientation of the tool relative to the workpiece due to geometric errors. And
A rotation axis correction value calculating step of calculating a correction value of the rotation axis using a geometric parameter representing the geometric error;
A translation axis correction value calculation step of calculating a correction value of the translation axis using the command value of each rotation axis and the command value of each translation axis and the geometric parameter;
A method for calculating a correction value for a machine tool, comprising: In the translation axis correction value calculation step,
2. The correction value calculation method for a machine tool according to claim 1, wherein the correction value for the translation axis is calculated using the correction value for the rotation axis. In the translation axis correction value calculation step,
The correction value of the translation axis for further correcting an error assumed to occur in the translation axis is calculated by correcting the rotation axis with the correction value of the rotation axis. Or the correction value calculation method of the machine tool of Claim 2. The translation axis correction value calculation step includes:
An ideal tool position calculating step of calculating an ideal tool position when there is no geometric error using the command value of each rotary axis and the command value of each translation axis;
When there is a geometric error using the command value for each rotation axis, the command value for each translation axis, the geometric parameter, and the correction value for the rotation axis calculated in the rotation axis correction value calculation step An actual tool position calculating step for calculating the actual tool position;
A tool position error calculating step for calculating a difference between the ideal tool position and the actual tool position;
A tool position coordinate conversion step for coordinate conversion of the difference;
The correction value calculation method for a machine tool according to any one of claims 1 to 3, further comprising: In the rotation axis correction value calculation step,
5. The machine tool according to claim 1, wherein a sum of the plurality of geometric parameters in the same rotation direction as the rotation axis or an inverse sign of the sum is used as a correction value of the rotation axis. Correction value calculation method. The machine tool has one axis of rotation,
The machine tool according to claim 5, wherein, in the rotation axis correction value calculation step, a sum of all the geometric parameters in the same rotation direction as the rotation axis or an inverse sign of the sum is used as a correction value of the rotation axis. Machine correction value calculation method. The machine tool has two rotation axes,
In the rotation axis correction value calculation step,
Considering the chain of axes from the tool to the workpiece, the sum of the geometric parameters in the same rotation direction as the first rotation axis or the reverse sign of the sum between the tool and the second rotation axis is the 1 The correction value for the second rotation axis,
The sum of the geometric parameters in the same rotation direction as the second rotation axis between the first rotation axis and the workpiece or the reverse sign of the sum is used as a correction value for the second rotation axis. 6. The machine tool correction value calculation method according to claim 5, The machine tool has three rotation axes,
In the rotation axis correction value calculation step,
Considering the chain of axes from the tool to the workpiece, the sum of the geometric parameters in the same rotation direction as the first rotation axis or the reverse sign of the sum between the tool and the second rotation axis is the 1 The correction value for the second rotation axis,
The correction value of the second rotation axis is the sum of the geometric parameters in the same rotation direction as the second rotation axis or the opposite sign of the sum between the first rotation axis and the third rotation axis. age,
The sum of the geometric parameters in the same rotational direction as the third rotational axis between the second rotational axis and the workpiece or the inverse sign of the sum is used as a correction value for the third rotational axis. 6. The machine tool correction value calculation method according to claim 5,   A machine tool correction value calculation program for causing a computer to execute the machine tool correction value calculation method according to any one of claims 1 to 8.

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