JP5740201B2 - Geometric error identification device - Google Patents

Description

  The present invention relates to a geometric error identification device for identifying a geometric error in a multi-axis machine tool such as a 5-axis control machining center.

Conventionally, as disclosed in, for example, Patent Document 1, in addition to the three orthogonal axes X, Y, and Z, the operation in a total of five axes including the C axis and A axis that are the rotation axes of the table A multi-axis machine tool such as a 5-axis control machining center that performs machining by controlling the machine is known. In such a multi-axis machine tool, there is a limit to improving the dimensional accuracy of each member and the assembly accuracy of the members, so it is necessary to identify so-called geometric errors such as inclination and position error between adjacent shafts. .
And as a method of identifying the geometric error in the 5-axis control machining center, three-axis circular interpolation motion measurement performed using a displacement sensor called a ball bar, that is, two linear axes and one rotary axis are synchronized. A method is generally known in which a geometric error is identified from a center deviation amount of a circular locus obtained by circular movement while maintaining a relative displacement between a predetermined point on the table and the spindle. However, this method requires a special measuring device called a ball bar, and the influence of the ball bar installation method on the identification accuracy is large, and there is a problem that high skill is required for accurate identification of geometric errors. .

  Therefore, instead of the ball bar, a touch probe (which is a general measuring instrument compared to the ball bar) and a target sphere serving as a measurement target are used, and the geometric error identification principle is the same as that of the above three-axis circular interpolation motion measurement. A geometric error identification method has been devised. For example, in the above 5-axis control machining center, the target sphere is set on the table, the table is indexed at multiple angles around the C axis and the A axis, and the position of the target sphere on the table is mounted on the main axis. The geometric error is identified from the center deviation amount of the arc locus drawn by a plurality of indexing conditions based on the measured position of the target sphere. That is, in this method, for example, the table is fixed at an arbitrary angle around the A axis and is indexed a plurality of times around the C axis, or conversely, the table is fixed at an arbitrary angle around the C axis. The measurement is repeated a plurality of times, the touch probe is brought into contact with the target sphere a plurality of times under the respective indexing conditions, and the center coordinates of the target sphere are calculated. When repeating such measurement, set the operating range of the axis (A-axis or C-axis) to be indexed multiple times, then set the number of measurement points arbitrarily, and make an equal pitch from the operating range and the number of measurement points Thus, the index angle pitch is calculated, and the center coordinates of the target sphere are measured under each index condition.

JP 2007-44802 A

  Here, it is generally known that a tilt error between three orthogonal axes (herein, a squareness error) becomes an elliptic component of ± 45 deg as a result of measurement using a ball bar. This also applies to the method using the touch probe, and the squareness error appears as an elliptic component of 45 deg in the circular locus obtained by the measurement. Therefore, in order to identify the squareness error with high accuracy, it is necessary to measure ± 45 deg points at which the influence of the squareness error greatly appears.

  However, conventionally, as described above, the index angle pitch is calculated at an equal pitch from the operation range and the number of measurement points, and the center coordinates of the target sphere are measured under each index condition. It is not always a measurement point. Therefore, when measurement is not performed at a point that is ± 45 deg, there is a problem that the accuracy of squareness error identification is lowered.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a geometric error identification device that can always accurately identify an inclination error between axes.

In order to achieve the above object, the invention according to claim 1 of the present invention is characterized in that a spindle on which a tool is mounted and a table for holding a workpiece are at least one rotation axis and a plane perpendicular to the rotation axis. In a multi-axis machine tool that processes the workpiece with the tool by moving relative to each other by two translation axes orthogonal to each other, a position of a target attached to one of the main shaft or the table is set around the rotation axis. And measuring the position of the target at each index angle using a touch probe attached to the main shaft or the other of the table, and a geometric error identification apparatus having a control device to identify the tilt error between the shaft, wherein the control device, calculate the plurality of index angle of around the rotational axis To Upon, while calculating a plurality of index angle at an equal pitch from the operating range and the measuring points and to be set to any around the rotation axis, bisecting between the two axes in the previous SL plane Rutotomoni determine a first index angle to position the target on the angle, the first index angle, it is determined whether the present in said plurality of index angle, the first index angle If there is not, the first indexing angle is added as a measurement point, the target is indexed at least to the first indexing angle, measurement is performed using the touch probe, and the tilt error is identified. It is characterized by.
In order to achieve the above object, the invention according to claim 2 of the present invention is such that a main shaft on which a tool is mounted and a table for holding a workpiece are orthogonal to at least one rotating shaft and the rotating shaft. In a multi-axis machine tool that processes the workpiece with the tool by relative movement with two translation axes orthogonal to each other in a plane to be rotated, the position of a target attached to one of the main shaft or the table is rotated. By indexing to a plurality of index angles around the axis and measuring the position of the target at each index angle using a touch probe attached to the main shaft or the other of the table, it is in the plane A geometric error identification device comprising a control device for identifying an inclination error between two axes, wherein the control device is configured to include the plurality of index angles around the rotation axis. In calculating the plurality of index angles at an equal pitch from the operation range around the rotation axis and the arbitrarily set number of measurement points, the two axes are divided into two equal parts on the plane. A first indexing angle at which the target is positioned on the angle to be measured, and determining whether the first indexing angle is present in the plurality of indexing angles; Is not present, the index angle closest to the first index angle among the plurality of index angles is replaced with the first index angle, and the target is indexed at least to the first index angle. Then, measurement using the touch probe is performed to identify the tilt error .
Furthermore , in order to achieve the above-mentioned object, the invention according to claim 3 of the present invention is such that a main shaft on which a tool is mounted and a table for holding a workpiece are at least one rotating shaft and orthogonal to the rotating shaft. In a multi-axis machine tool that processes the workpiece with the tool by relative movement with two translation axes orthogonal to each other in a plane to be rotated, the position of a target attached to one of the main shaft or the table is rotated. By indexing to a plurality of index angles around the axis and measuring the position of the target at each index angle using a touch probe attached to the main shaft or the other of the table, it is in the plane A geometric error identification device comprising a control device for identifying an inclination error between two axes, wherein the control device is configured to determine the plurality of indexes around the rotation axis. In calculating the degree, the plurality of index angles are calculated at an equal pitch from the operation range around the rotation axis and the arbitrarily set number of measurement points, while the distance between the two axes in the plane is second A first index angle at which the target is located on an angle to be divided is determined, and whether or not the first index angle is present in the plurality of index angles is determined, and the first index angle is If it does not exist, it is further determined whether or not an angle difference between the index angle closest to the first index angle and the first index angle among the plurality of index angles is within a predetermined allowable range. When the angle difference is not within the allowable range, the first index angle is included in the plurality of index angles, and the target is indexed to at least the first index angle to use the touch probe. Measure and identify the tilt error When the angular difference is within the allowable range, the first probe angle is not included in the plurality of index angles, and the touch probe is used without indexing the target to the first index angle. Measurement is performed to identify the tilt error.
The invention according to claim 4 is the multi-axis machine tool according to any one of claims 1 to 3 , wherein the translation axes are three orthogonal axes and the rotation axis is parallel to any one of the different translation axes. A geometric error identification device for identifying a tilt error between two orthogonal axes in a machine, wherein the first index angle is ± 45 deg and / or ± 135 deg.

  According to the present invention, when identifying an inclination error between two axes in a plane orthogonal to the axis to be rotated or swiveled, the target sphere is positioned on an angle that bisects the two axes in that plane. The first indexing angle to be obtained is obtained, the target sphere is indexed to at least the first indexing angle, measurement using the touch probe is performed, and the tilt error between the two axes is identified. Therefore, since measurement is always performed at the measurement points where the influence of the tilt error is most significant (including measurement points within the allowable range in claim 4), the accuracy of tilt error identification is extremely high. In addition, since the accuracy of identifying the tilt error is high, the accuracy of identifying the geometric error inherent to the C axis and the A axis, which are greatly affected by the tilt error, can be improved.

It is a perspective explanatory view showing a multi-axis machine tool. It is explanatory drawing which showed the elliptical locus | trajectory resulting from the inclination error. It is explanatory drawing which showed the state which installed the target ball | bowl on the table. It is explanatory drawing which showed a mode that it measured after offsetting the rotation angle about the C axis of a table 90 degree | times when indexing a target ball | bowl around an A axis | shaft. It is explanatory drawing which showed the index condition list | wrist whose index angle pitch becomes equal pitch. It is explanatory drawing which showed a mode that the target ball | bowl was indexed turning about an A-axis. It is explanatory drawing which showed the example of correction of the index condition list. It is explanatory drawing which showed the other modification example of the index condition list. It is the flowchart figure which showed the control which concerns on the identification of inclination error.

  Hereinafter, a geometric error identification device according to an embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, identification of a geometric error (particularly, an inclination error between translation axes) in a 5-axis control machining center which is an example of a multi-axis machine tool will be described.

First, the multi-axis machine tool 1 will be described with reference to FIG. FIG. 1 is a perspective explanatory view showing a multi-axis machine tool 1. 1, the X axis, the Y axis, and the Z axis are three orthogonal axes (translation axes of the multi-axis machine tool 1), and the Y-axis direction is the front-rear direction and the X-axis direction in the multi-axis machine tool 1. Is the left-right direction, and the Z-axis direction is the up-down direction.
Y-axis guides 3 and 3 are formed on the upper surface of the bed 2 of the multi-axis machine tool 1, and a trunnion-structured AC axis unit 4 can move in the Y-axis direction on the Y-axis guides 3 and 3. is set up. The AC shaft unit 4 includes a cradle 5 formed in a U-shape that is wide in the left-right direction when viewed from the front, and the cradle 5 is driven by an A-axis drive mechanism (not shown) built in the left and right. Rotating and tilting is possible around the A axis (rotating axis) parallel to the X axis direction. Further, the AC shaft unit 4 includes a table 6 for placing a workpiece to be processed on the upper surface of the cradle 5, and the table 6 is a C-axis drive mechanism (not shown) built in the cradle 5. ) Can rotate 360 degrees around the C axis (rotation axis) parallel to the Z axis.

On the other hand, a gate-shaped cross rail 7 is fixed to the bed 2 so as to straddle the Y axis guides 3 and 3, and an X axis guide surface 8 is formed on the front surface of the cross rail 7. A ram saddle 9 is installed on the X-axis guide surface 8 so as to be movable in the X-axis direction. The ram saddle 9 is provided with a Z-axis guide surface 10, and a spindle head 12 having a main shaft 11 at the lower end is installed on the Z-axis guide surface 10 so as to be movable in the Z-axis direction. The ram saddle 9, the AC shaft unit 4, and the spindle head 12 are movable by a ball screw installed in parallel with each guide surface and a servo motor (not shown) connected to the ball screw. Further, the multi-axis machine tool 1 is provided with an NC device (control device) (not shown) including a geometric error identification device, and each axis of each member such as the AC shaft unit 4 and the spindle head 12 is controlled by the NC device. Driving in the direction is controlled.
The multi-axis machine tool 1 turns and rotates the workpiece fixed on the table 6 about the A axis and the C axis and moves it in the Y axis direction, while moving the main shaft 11 attached with the tool to the X axis. And by moving to the Z axis, multi-face machining is performed on the workpiece.

Here, the identification of the squareness error γ between the XY axes and the squareness error α between the YZ axes in the multi-axis machine tool 1 which is a main part of the present invention will be described.
When there is a squareness error γ [rad] between the XY axes on the XY plane of the multi-axis machine tool 1 as described above, if a circular locus of radius R as shown in FIG. 2 is drawn, the circular locus on the XY plane When the polar coordinate is θ [deg], the radius error ΔR is expressed by the following (formula 1) and is generally known to be an ellipse having a slope of ± 45 deg.

When the squareness error γ is to be identified using the touch probe and the target sphere 21, first, the target sphere 21 is fixed at a position away from the rotation center of the table 6 by R as shown in FIG. 3. Then, assuming that the A-axis turning center 22 is on the C-axis center line, the center coordinates [X ₀ Y ₀ Z ₀ of the target sphere 21 when the intersection of the C-axis center line and the A-axis turning center 22 is taken as the coordinate origin. A ₀ C ₀ ] is set as follows (Formula 2).

  Next, the measurement range is set to 0 [deg] to 360 [deg], and the number of measurement points is set to eight. Then, since the indexing angle pitch is 45 deg, in the AC axis unit 4, the table 6 is fixed at an arbitrary angle (here, the angle at which the table 6 is horizontal) around the A axis, and the table 6 is rotated at the 45 deg pitch with the C axis. The coordinates of the target sphere 21 are measured with a touch probe attached to the spindle at each measurement point. Then, using the obtained measurement coordinates, coefficients A to E in the following (Expression 3), which is a relational expression related to the locus of the circle, are obtained by the least square method or the like. Then, since the coefficient D and the above (Equation 1) are correlated among the coefficients thus obtained, the perpendicularity error γ between the XY axes can be identified. In this case, θ indicating polar coordinates coincides with the indexing angle of the table 6 around the C axis.

Similarly, if the cradle 5 is indexed around the A axis while the C axis is fixed, the squareness error α between the YZ axes can be identified. Hereinafter, this identification will be described with reference to the flowchart of FIG.
The turning operation of the cradle 5 around the A axis in the AC axis unit 4 has a limited operating range, unlike the case where the table 6 is rotated around the C axis, and the cradle 5 is moved during the turning operation around the A axis. There is also a risk of interference with the ram saddle 9. Therefore, in order to avoid problems such as interference as much as possible, as shown in FIG. 4, a method of measuring after rotating the rotation angle of the table 6 around the C axis by 90 degrees is adopted. In this case, the center coordinates [X _i Y _i Z of the target sphere 21 when the turning angle around the A axis is determined as A _i and the rotation angle around the C axis is determined as C _i from the state of (Expression 2) above. _i ] is estimated by the following (formula 4).

  Then, first, an indexing condition list for identifying the perpendicularity error α between the YZ axes is created (S1). For example, in a state where the table 6 is indexed to −90 deg around the C axis, if the operation range of the cradle 5 around the A axis is set to −15 deg to +105 deg and the number of measurement points is set to 9 points, the index angle pitch is 15 deg. Thus, an indexing condition list as shown in FIG. 5 is created. Note that the turning or rotation angles of the indexing conditions A ′ axis and C ′ axis in FIG. 5 are machine command coordinates.

When the C ′ axis is determined as described above, Y _i and H exist. Therefore, if the A axis turning center is the coordinate origin in the YZ plane as shown in FIG. 6, the target is accompanied by turning around the A axis. locus drawn by the center of the sphere 21, so that the offset angle a ₀ radius RR is generated. Therefore, the offset angle _A0 is calculated from the fixed index angle information (that is, the rotation angle around the C axis) and the position of the target sphere 21 (S2). That is, the position _{Y i0} in the Y-axis direction in the rotation angle _{C i} of the turning angle 0 deg, about the C-axis of about A-axis from the (Equation 4) becomes the following (Equation 5). Further, the radius RR is expressed by the following (formula 6), and the offset angle A ₀ is expressed by the following (formula 7).

また、Ａ軸周りで旋回角度Ａ_ｉに割り出した際におけるＹＺ平面で見た実際の割出角度Ａ’は下記（式８）となる。

Further, the actual index angle A as seen in YZ plane definitive upon indexing the rotation angle A _i about A-axis' becomes the following (Equation 8).

Then, the index angle at which the perpendicularity error α is most easily identified, that is, the turning index angle _AE around the A axis where the actual index angle A ′ viewed in the YZ plane is ± 45 deg is calculated (S3). . That is, since A ′ = ± 45 deg in the above (Equation 8), the turning index angle A _E calculated in S3 = ± 45−A ₀ [deg]. Therefore, for example, when R = 200 mm, H = 50 mm, and C _i = 90 deg, the radius RR = 206.155 mm and the offset angle A ₀ = 13.633 deg in the YZ plane, so the actual index viewed in the YZ plane The turning index angle _AE around the A axis at which the angle A ′ is ± 45 deg is −58.633 deg in the above operating range.

Therefore, it is determined whether or not the turning index angle _AE exists in the index condition list created in S1 (S4). When the turning index angle _AE exists in the index condition list, the measurement operation, that is, the cradle 5 is sequentially indexed around the A axis according to the index condition list without correcting the index condition list. Then, the operation of measuring the coordinates of the target sphere 21 with the touch probe attached to the main axis at each measurement point is started (S7), and the perpendicularity error α between the YZ axes is identified based on the measurement result (S8).

If the result of determination in S4 is that the turning index angle A _E does not exist in the indexing condition list, the turning index angle A _E and the nearest turning index angle in the indexing condition list created in S1 It is determined whether the difference is within a predetermined allowable range (S5). For example, if the allowable range is set to ± 1 deg, the nearest turning index angle in the indexing condition list (in FIG. 5) created by turning index angles _AE and S1 is −60 deg. The difference between the two angles exceeds the allowable range, and NO is determined in S5. If it is determined that it is out of the allowable range in this way, the indexing condition list created in S1 is corrected (S6). For example, to add turning index angle _{A E} as measured point in the middle (between -45deg and -60Deg) operation path as shown in FIG. 7, the turning index angle _{A E} 8 The closest turning index angle −60 deg is replaced with the turning index angle _AE . Then, the measurement operation is started according to the corrected index condition list (S7), and the squareness error α between the YZ axes is identified based on the measurement result (S8). If the result of determination in S5 is within the allowable range, the measurement operation is started in S7 without correcting the index condition list.

  According to the geometric error identification device having the above-described configuration, the index condition list is corrected by the method described above in identifying the squareness error, and the influence of the squareness error is exerted on the biaxial plane forming a right angle. Since the measurement at the point of ± 45 deg that appears most (or the measurement point within the allowable range) is always executed, the accuracy of squareness error identification is extremely high. Further, since the accuracy of perpendicularity error identification is high, the accuracy of identification of geometric errors inherent to the C-axis and A-axis, which are greatly affected by the squareness error, can be improved.

  The geometric error identification device according to the present invention is not limited to the aspect of the above embodiment, and the configuration related to the creation and correction control of the index condition list is within the scope of the present invention. Thus, it can be changed as necessary.

For example, in the above embodiment, when the calculated turning index angle _AE does not exist in the index condition list, it is determined whether the index condition list is within an allowable range that does not need to be corrected. However, without making such a determination, the index condition list can always be corrected when it does not exist.
In the above embodiment, when the indexing condition list is corrected, the turning index angle _AE is newly added to the indexing condition list in the middle of the operation path. However, the position to be added can be changed as appropriate. For example, it may be added to the end of the index condition list.

  Furthermore, in the above-described embodiment, a method for identifying an inclination error (perpendicularity error) between orthogonal axes in the multi-axis machine tool 1 having three orthogonal axes as translation axes is described. Therefore, measurement of ± 45 deg is performed. For example, the guide surface in the X-axis direction is inclined at a predetermined angle from the vertical plane in the front-rear direction, and in addition to the X-axis and the Z-axis, the X-axis and the Y-axis In a multi-axis machine tool having a Ys axis obtained by synthesizing the Ys axis (the Ys axis is in the front-rear direction) as a translation axis, in order to accurately identify the angle error between the XYs axes, instead of ± 45 deg, XYs It is better to measure at an angle that bisects between the axes. In other words, the measurement points that must be measured in order to improve the accuracy of the tilt error are not limited to ± 45 deg points, and are changed according to the multi-axis machine tool that is the target of identifying the tilt error. The

Furthermore, in the above embodiment, since the cradle operating range is -15 deg to +105 deg, the turning index angle around the A axis at which the actual index angle A ′ viewed in the YZ plane in S3 is ± 45 deg. Although only A _E is calculated, the turning index angle A _E is calculated using ± 135 deg instead of ± 45 deg according to the operating range of the cradle, or the turning index angle _AE is calculated using both. There is no problem even if you do.
Needless to say, how to set the allowable range and how many measurement points are set are not limited to those of the above-described embodiment.

In addition, the multi-axis machine tool targeted by the geometric error identification device according to the present invention is not limited to the multi-axis machine tool of the above embodiment. For example, two or more rotation axes are provided on the main shaft side. Or a rotation axis provided on each of the main shaft side and the table side, or only one rotation shaft is provided on either the main shaft side or the table side. It may be a thing. That is, not only a machining center-based machine tool called a 5-axis machine, but also a multi-task machine based on a lathe. In such a case, the translation axes may be two axes, or the translation guide axes may be in a relationship where the actual guide surfaces are inclined rather than orthogonal as long as they can be configured for control.
In addition, the A-axis that is one of the rotation axes is not limited to the cradle turning axis, and may be a rotation axis that can rotate 360 degrees, and the geometric error can be identified even if the arrangement of the target and the touch probe is changed. Is possible.

  1 .... multi-axis machine tool, 4 .... AC axis unit, 5 .... cradle, 6 .... table, 21 ... target ball.

Claims (4)

The main shaft on which the tool is mounted and the table for holding the workpiece are moved relative to each other by at least one rotation axis and two translation axes orthogonal to each other in a plane orthogonal to the rotation axis. In a multi-axis machine tool machined with a tool, the position of a target attached to one of the spindle or the table is determined at a plurality of index angles around the rotation axis, and attached to the other of the spindle or the table. A geometric error identification device comprising a controller for identifying a tilt error between two axes in the plane by measuring a position of the target at each index angle using a touch probe. ,
In calculating the plurality of index angles around the rotation axis, the control device calculates the plurality of index angles at an equal pitch from an operation range around the rotation axis and an arbitrarily set number of measurement points. While calculating
The first index angle look Rutotomoni of said target between said two shafts before Symbol plane bisecting the angle position, the first indexing angle is present in the plurality of index angle When the first index angle does not exist, the first index angle is added as a measurement point, and the target is indexed to at least the first index angle, and the touch probe A geometric error identification device characterized in that measurement is performed to identify the tilt error. The main shaft on which the tool is mounted and the table for holding the workpiece are moved relative to each other by at least one rotation axis and two translation axes orthogonal to each other in a plane orthogonal to the rotation axis. In a multi-axis machine tool machined with a tool, the position of a target attached to one of the spindle or the table is determined at a plurality of index angles around the rotation axis, and attached to the other of the spindle or the table. A geometric error identification device comprising a controller for identifying a tilt error between two axes in the plane by measuring a position of the target at each index angle using a touch probe. ,
In calculating the plurality of index angles around the rotation axis, the control device calculates the plurality of index angles at an equal pitch from an operation range around the rotation axis and an arbitrarily set number of measurement points. While calculating
A first index angle at which the target is positioned on an angle that bisects the two axes in the plane is obtained, and whether the first index angle exists in the plurality of index angles If the first index angle does not exist, the index angle closest to the first index angle among the plurality of index angles is replaced with the first index angle, A geometric error identification device characterized by identifying the tilt error by performing measurement using the touch probe by determining the target at least at the first index angle. The main shaft on which the tool is mounted and the table for holding the workpiece are moved relative to each other by at least one rotation axis and two translation axes orthogonal to each other in a plane orthogonal to the rotation axis. In a multi-axis machine tool machined with a tool, the position of a target attached to one of the spindle or the table is determined at a plurality of index angles around the rotation axis, and attached to the other of the spindle or the table. A geometric error identification device comprising a controller for identifying a tilt error between two axes in the plane by measuring a position of the target at each index angle using a touch probe. ,
In calculating the plurality of index angles around the rotation axis, the control device calculates the plurality of index angles at an equal pitch from an operation range around the rotation axis and an arbitrarily set number of measurement points. While calculating
A first indexing angle at which the target is positioned on an angle that bisects the two axes in the plane is obtained, and whether the first indexing angle exists in the plurality of indexing angles. If the first index angle does not exist, an angle difference between the index angle closest to the first index angle and the first index angle among the plurality of index angles is predetermined. If the angle difference is not within the allowable range, the first index angle is included in the plurality of index angles, and at least the first index angle is included. While measuring the target and performing measurement using the touch probe to identify the tilt error, if the angle difference is within the allowable range, the first index angle is set to the plurality of index angles. Do not include, index the target at the first index angle And without it performs measurement using the touch probe, geometric error identification device and identifying the slope error. A geometric error identification device for identifying an inclination error between two orthogonal axes in a multi-axis machine tool in which the translation axes are orthogonal three axes and the rotation axis is parallel to any one of the different translation axes;
The geometric error identification device according to claim 1 , wherein the first index angle is ± 45 deg and / or ± 135 deg.

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