JP2012221000A - Correction value operation method and program of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a correction value operation method and the like for correcting a position error of a tip point of a tool and an attitude error of the tool while avoiding a forcible operation of a rotation axis due to a change of a correction value of the rotation axis when the rotation axis is in a clamp state.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 with a clamp mechanism, includes: a rotation axis correction value updating operation step (S3-S5) for operating and updating a correction value of the rotation axes by using a geometric parameter representing the geometric error when the clamp mechanism is not in the clamp state and maintaining the correction value of the rotation axes to the previous one when the clamp mechanism is in the clamp state; and a translation axis correction value operation step (S6) 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

  Many of the rotary shafts of machine tools often have a clamp mechanism in order to ensure rigidity during processing. The correction parameter for correcting the tool posture changes or changes, and the correction value of the rotary axis changes. However, when the rotary axis is clamped by the clamp mechanism, the rotary axis is corrected despite being clamped. Since the rotary shaft tends to operate depending on the value, a large load is applied by twisting the rotary shaft, etc., causing a rotation error due to deformation of the member, resulting in a decrease in accuracy. In addition, the motor that drives the rotating shaft may cause overheating, which may cause machine failure.

  Therefore, in the present invention, in the first to third and fourth aspects of the present invention, the correction value of the rotating shaft is changed when the rotating shaft is in a clamped state, and the rotating shaft is prevented from operating forcibly. It is an object of the present invention to provide a correction value calculation method and program for correcting errors and tool posture errors.

  In order to achieve the above object, a first aspect of the present invention is directed to a machine tool having two or more translation axes and one or more rotation axes provided with a clamp mechanism, and is subject to geometric error. A correction value calculation method for the machine tool, which corrects an error in the position and orientation of a tool with respect to a workpiece, and uses the geometric parameter representing the geometric error when the clamp mechanism is not in a clamped state. A rotation axis correction value update calculation step for calculating and updating a rotation axis correction value and maintaining the rotation axis correction value at a previous one when the clamp mechanism is in a clamped state; and A translation axis correction value calculation step of calculating a correction value of the translation axis using the command value and the command value of 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.

  The invention according to claim 3 is the above invention, wherein, in the translational axis correction value calculation step, when the geometric parameter relating to the error in the posture of the tool is changed when the clamp mechanism is in a clamped state. The translation axis correction value for correcting the change in the tool position error caused by the change is calculated.

  In order to achieve the above object, a fourth aspect of the present invention 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, it is possible to correct the position error of the tool tip point without generating an excessive load on the rotating shaft by holding the rotating shaft correction value without being updated while the rotating shaft is clamped. It becomes possible.

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).

  In the 5-axis machine, a clamp mechanism (not shown) is provided on both the A and C axes. The clamping mechanism clamps the rotating shaft during processing or before and after the processing in order to ensure rigidity during processing. The clamp mechanism is controlled to be clamped or unclamped by a computer. In addition, it can be made not to comprise a clamping mechanism in any one of A axis | shaft and C axis | shaft. In a machine tool having a different number of rotation axes, all the rotation axes may be provided with clamp shafts, or only some of the rotation axes may be provided with a clamp mechanism.

  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, steps S3 to S5 are repeated by the number n of the rotation axes. In step S3, a new correction value for the i-th (i = 1 to n) rotation axis is calculated. The calculation will be described later.

  Next, in step S4, it is determined whether or not the i-th rotation axis is in a clamped state. If the i-th rotation axis is not in a clamped state (in an unclamped state), the process proceeds to step S5 and the i-th rotation axis correction value is stepped. Update to the new correction value calculated in S3. On the other hand, in the clamped state, the rotation axis correction value is not updated and remains the previously calculated value. After calculating the rotation axis correction values for all the rotation axes, the translation axis correction values are calculated in step S6. A series of correction value calculation is performed for each period of updating the correction value, and during that time, the correction value is stored in a storage means (not shown). The initial value of the correction value for each axis is 0. The determination of the clamp state in step S4 may be performed based on the presence or absence of a clamp command, or may be performed using a sensor (a signal state in the clamp mechanism).

Prior to the description of the calculation in step S3, the method for calculating the translational axis correction value in step S6 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. It is necessary to correct the translational axis correction value by the amount of movement of the tool tip position based on the axis correction value. 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 calculation of the new correction value for the rotating shaft 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 new correction value of the rotational axis is the geometric parameter between the geometric error start position ls * and the end position le * in FIG. 5 in the same rotational direction as the rotational axis (A axis is α *, B axis Is the reverse sign of the total value of β * and C-axis is 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 new 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 new correction value Δa _{temp for the} A axis and the new correction value Δc _{temp for the} C axis are obtained by the following [Equation 9].

  If the rotating shaft is not in the clamped state, each new correction value is substituted into the corresponding rotating shaft correction value in step S5. For example, if both the A and C axes are not in the clamped state, the following processing shown in [Expression 10] is performed.

  The tool posture error due to the geometric error can be corrected by adding the correction values of the respective rotation axes thus obtained to the corresponding command values. 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.

On the other hand, if the rotating shaft is in a clamped state, even if the geometric parameters (α _* , β _* , γ _* ) of the rotating system are changed (* indicates an arbitrary suffix), a step is performed for the rotating shaft being clamped. Since S5 is not executed, the translation axis correction value is calculated using the rotation axis correction value calculated and stored last time as it is. That is, the translation axis correction value is calculated in a state where the rotation axis correction value is maintained as before. Since the geometric parameter used for the calculation of the translation axis correction value has been updated, the tool posture error remains, but the tool tip point position error is corrected including its influence.

Furthermore, when there is a deformation error due to the weight of the trunnion 5 itself or the workpiece 7, an A-axis angle error, a displacement that varies depending on the position and / or angle of another axis, etc., the geometry that changes these errors. Treat as error. In this case, a value calculated by interpolating between the points with a straight line or a curve using data of a plurality of points given in advance, or a value calculated from the model formula is substituted into the geometric parameter. For example, the rotational error about the A-axis by the weight of the workpiece 7 (A-axis angle error), treated as geometric errors alpha ₄ that varies, with deformation model formula weight and center of gravity etc. of the workpiece 7 is variable, the correction value the values calculated for each calculation cycle, and assigned to the alpha _4.

In addition, when processing is performed with the A-axis being indexed at a certain angle, the A-axis is clamped to increase the rigidity. Since the weight and center of gravity of the workpiece 7 As the machining progresses is changed, the rotational error about the A-axis is changed, alpha ₄ is changed. At this time, since the A axis is being clamped, the correction value of the rotation axis is not updated, and only the correction value of the translation axis is updated. As a result, the tool orientation error remains only alpha ₄ variation, but the tool center point position error is accurately corrected.

  When it is desired to correct the tool posture error, the unclamping of the A-axis is performed once, the rotation axis correction value is updated, and the rotation axis moves by the amount of change to correct the tool posture error. At this time, the translation axis correction value is also updated at the same time, the translation axis is operated, and the tool tip point position error generated by the rotation axis operation is corrected.

In the above, the correction value (temporary value, Δa _temp or Δc _temp ) of the rotation axis is continuously calculated even during clamping. However, the calculation of the correction value of the rotation axis may be temporarily stopped during clamping.

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

Claims (4)

In a machine tool having two or more translation axes and a rotation axis having one or more clamp mechanisms, the machine tool corrects errors in the position and orientation of the tool relative to the workpiece due to geometric errors. The correction value calculation method of
When the clamp mechanism is not in the clamped state, the correction value of the rotary shaft is calculated and updated using the geometric parameter representing the geometric error, and when the clamp mechanism is in the clamped state, the rotary shaft A rotation axis correction value update calculation step for maintaining the correction value of
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,
When the geometric parameter related to the error in the tool posture is changed when the clamp mechanism is in the clamped state, the translational axis for correcting the change in the error in the tool position caused by the change is changed. The correction value calculation method for a machine tool according to claim 1, wherein the correction value is calculated.   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 3.

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