JP2012030338A - Method of measuring geometric error of multi-axis machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of measuring a geometric error for very effectively preventing, even when an improper geometric error is measured according to external disturbance, lowering of machining precision of a multi-axis machine tool caused by execution of correction based on such the improper geometric error.SOLUTION: In measurement of geometric errors, before an external disturbance presence checking step is executed to identify the geometric error, an A axis and a C axis are indexed under a plurality of conditions, the diameter of a target sphere 12 is measured, and variance on the measured values is calculated. When the variance exceeds a preset diameter variation permissible value Da, a measuring mistake is determined.

Description

  The present invention relates to a geometric error measurement method (identification method) for measuring and correcting a geometric error in a multi-axis machine tool.

  As machine tools, multi-axis machine tools such as a 5-axis machining center in which a rotary axis and a turning axis are added to a conventional 3-axis machining center for the purpose of performing highly efficient machining and workpieces with complicated shapes are known. Improvement of machining accuracy in such a multi-axis machine tool is desired.

  In multi-axis machine tools, as the number of axes increases, the assembly accuracy tends to deteriorate and the machining accuracy tends to deteriorate. However, there is a limit to the improvement in assembly accuracy, so there is a limit between adjacent axes. A correction system has been developed that measures so-called geometric errors such as tilt and position error and corrects the geometric errors to improve machining accuracy.

  Conventionally, as a method for measuring (identifying) geometric errors, a method for determining a geometric error based on the measurement results of a predetermined portion of a measurement object such as a displacement meter and a right angle score and setting a plurality of measurement objects, Although the method (patent document 1) which calculates | requires a geometric error using the measurement result when measuring simultaneous 2 axis | shaft and simultaneous 3 axis | shaft circular motion using a bar | burr was used, both require an expensive measuring device. In addition, there were problems such as the result being different depending on the skill of the measurer.

  Therefore, as a geometric error identification method that does not require an expensive measuring instrument and does not depend on the skill of the measurer, a touch probe is attached to the spindle of the machine tool, and a sphere serving as a target (measurement jig) is installed on the table. A measurement method that automatically performs the indexing operation of the swivel axis and rotation axis several times, measures the position of the target under each indexing condition, and automatically obtains (identifies) the geometric error based on the measurement results. Has been developed.

JP 2004-219132 A

  However, since the target used in the above-described measurement method becomes an object of interference when machining an actual workpiece, it is necessary to attach it to a table or the like when performing geometric error measurement and to remove it from the table when measurement is completed. A target fixed by a magnet has been developed for easy removal, but using such a target may cause the target to move during measurement. However, even if the target moves during measurement, a measurable state is maintained as long as it is within the measurement range of the touch probe, so that the amount of variation in the target position is also included in the measurement result. Then, if the geometric error is identified while the amount of variation in the target position is included, an unexpected error occurs in the identification result. If the geometric error correction system is used to correct such an identification result, In addition to being unable to improve accuracy, there can be situations where it is worsened.

  An object of the present invention is to solve the problems of the conventional measurement method described above, and to perform correction based on such inappropriate geometric error even when an inappropriate geometric error is measured based on disturbance. It is an object of the present invention to provide a geometric error measuring method capable of extremely effectively preventing a situation in which machining accuracy of a multi-axis machine tool is lowered due to execution.

  Among the present inventions, the invention described in claim 1 is for measuring a position of a target (measurement jig) installed on a table by a sensor provided on a main shaft in a machine tool having a plurality of linear axes and rotary axes. A geometric error measurement method for calculating and identifying a geometric error related to a straight axis and a rotation axis based on information on a measured position, wherein the straight axis or rotation is identified before the geometric error is identified. Step of confirming the presence or absence of disturbance error by determining the axis under a plurality of conditions, measuring the length of a predetermined part of the target, calculating the variation of those measured values, and determining that the measurement exceeds the predetermined value Is executed.

  According to a second aspect of the present invention, in the first aspect of the invention, the disturbance error presence / absence confirmation step performs the measurement of the length of a predetermined portion of the target at the initial setting position, and then performs a straight axis or rotation. Measure the length of the predetermined part of the target by indexing the axis to different positions, and measure each measured value after indexing the straight axis or rotating axis, and the measured value when checking the target installation position When the difference exceeds a preset measurement value fluctuation amount allowable value, it is determined that a measurement error has occurred.

  According to a third aspect of the present invention, in the first aspect of the present invention, the disturbance error presence / absence confirmation step performs measurement of the length of a predetermined portion of the target at an initial setting position, and then performs a straight axis or rotation. Measure the length of the predetermined part of the target by indexing the axis to different positions, and measure each measured value after indexing the straight axis or rotating axis, and the measured value when checking the target installation position When the difference exceeds the preset measurement value variation allowance, calculate the average value of each measured value after indexing the straight axis or rotary axis, and check the average value and the target installation position If the difference from the measured value exceeds the measured value fluctuation amount allowable value, a measurement error is determined.

  The invention described in claim 4 is the invention described in any one of claims 1 to 3, wherein after the target installation position is measured at the initial setting position, each of the linear axis or the rotary axis after indexing is determined. After performing the measurement, determine the rectilinear axis or the rotation axis so that the target installation position becomes the initial setting position, and measure the target installation position again. When the deviation from the position exceeds a preset target position fluctuation amount allowable value, a measurement error is determined.

  The invention described in claim 5 is the invention described in any one of claims 1 to 3, wherein after the installation position of the target is measured under an arbitrary indexing condition of the linear axis or the rotary axis, the same indexing condition When the target installation position is measured again in, and the difference between the re-measured target installation position and the installation position at the previous measurement exceeds the preset target position variation tolerance, measurement is performed. It is characterized by judging a mistake.

  In the invention described in claim 6, in the invention described in any one of claims 1 to 5, each time the geometric error is identified, the geometric error calculated based on the identified geometric error is reduced. In addition to having a parameter update step for updating the correction parameter as a new correction parameter, the parameter update step is not executed when a measurement error is determined.

  In the invention described in claim 7, in the invention described in any of claims 1 to 6, when the measurement error is determined, the situation is notified and the position of the target or the length of the predetermined part is notified. This is characterized by interrupting the measurement.

  The invention described in claim 8 is the invention described in any one of claims 1 to 7, wherein the target is spherical, and the length of the predetermined portion of the target is the diameter of the sphere. It is characterized by this.

  According to the geometric error measuring method of the present invention, the position of the target (measurement jig) is shifted during the measurement of the geometric error, or a signal indicating that the touch probe has contacted the target due to unexpected vibration is issued. Even if an inappropriate geometric error (geometric error including an error due to disturbance) is identified due to the cause, the machining accuracy of the multi-axis machine tool is reduced by executing correction based on such inappropriate geometric error. The situation can be prevented very effectively.

It is explanatory drawing (perspective view) which shows a machining center. It is a block diagram which shows the control mechanism of a machining center. It is a conceptual diagram of a memory | storage means. It is explanatory drawing which shows the state which mounted | wore the spindle head with the touch probe, and mounted | worn the target with the table. It is explanatory drawing which shows a mode that a target sphere is measured in the some index position of C axis | shaft. It is explanatory drawing which shows a mode that a target sphere is measured in the some index position of A axis | shaft. It is explanatory drawing which shows the calculation method of the diameter of a target sphere. It is a flowchart which shows the content of the disturbance error existence confirmation process. It is a flowchart which shows the content of the remeasurement process of the diameter of a target sphere.

  Hereinafter, an embodiment of a geometric error measuring method according to the present invention will be described in detail with reference to the drawings.

<Configuration of multi-axis machine tool>
FIG. 1 shows a 5-axis control machining center (table turning type 5-axis machine) which is an example of a multi-axis machine tool (hereinafter simply referred to as a machining center M). The bed (base) 1 of the machining center M is provided with a trunnion 5 having a substantially U shape in front view so as to be slidable along the Y axis. The trunnion 5 has a cradle having a substantially U shape in front view. 4 is provided to be rotatable around the A axis (rotating axis). Further, the cradle 4 is provided with a disk-like table 3 so as to be rotatable about a C axis (rotary axis) orthogonal to the A axis. In addition, a spindle head 2 on which a tool can be mounted is provided on the bed 1 so as to be slidable along an X axis perpendicular to the Y axis and a Z axis perpendicular to the X and Y axes. . The spindle head 2 can rotate the mounted tool about the Z axis.

  The machining center M causes the spindle head 2 to approach the workpiece (workpiece) fixed to the table 3 in a state in which the tool mounted on the spindle head 2 is rotated. Various processes can be performed on the workpiece while controlling the relative position and the relative posture between the workpiece and the tool. Further, since the machining center M is configured as described above, the connection of the axes from the workpiece to the tool is in the order of C axis → A axis → Y axis → X axis → Z axis.

  FIG. 2 is a block diagram showing the control mechanism of the machining center M described above. Each servomotor for translating the trunnion 5 and the spindle head 2 and each servomotor for rotating the cradle 4 and the table 3 are shown. Is controlled by a control device (numerical control device) 21. Also connected to the control device 21 are an input means 31 for setting an index position (index condition) and the like, an output means 32 such as a monitor and a speaker for outputting a result of identification environment determination described later, and the like. Has been. Further, the control device 21 is provided with a storage means 22, and in the storage means 22, as shown in FIG. 3, a program storage area 23 for storing various programs, variables used for various calculations, and the like. Are provided, a variable storage area 24 for storing the above, an allowable value storage area 25 for storing various preset allowable values, and the like.

  In the program storage area 23, a correction parameter calculation program for calculating a correction parameter used for correcting the geometric error based on the identified geometric error, or a correction parameter after calculation every time the correction parameter is calculated. A parameter update program or the like for automatically updating as a new correction parameter is stored. Further, the allowable value storage area 25 stores a preset diameter fluctuation amount allowable value (threshold value) Da, a preset position fluctuation amount allowable value (threshold value) Pa, and the like.

<Machining center geometric error>
Next, the geometric error of the machining center M will be described. Here, it is assumed that the geometric error is composed of a total of six components (δx, δy, δz, α, β, γ) in the three directions of the relative translation error between the axes and the three directions of the relative rotation error. Each geometric error is indicated with two sandwiched axis names. For example, a translation error in the Y direction between the C axis and the A axis is expressed as δy _CA , and a rotation error around the Z axis between the Y axis and the X axis is expressed as γ _YX . The symbol indicating the tool is T.

Since the connection of the axes from the workpiece to the tool in the machining center M is the order of the C axis, A axis, Y axis, X axis, and Z axis, there are a total of 60 geometric errors when considering the gap between the Z axis and the tool. If one exists in the redundant relationship but the other is excluded, the final geometric error is δx _CA , δy _CA , α _CA , β _CA , δy _AY , δz _AY , β _AY , γ _AY. , Γ _YX , α _XZ , β _XZ , α _ZT , β _ZT in total. Of these, five of γ _YX , α _XZ , β _XZ , α _ZT , and β _ZT are geometric errors related to the linear axis, and the XY inter-axis perpendicular angle and the Y-Z inter-axis perpendicular angle, respectively. , Z-X axis perpendicularity, tool-Y axis perpendicularity, tool-X axis perpendicularity. The other eight are geometric errors related to the rotation axis, which are the C-axis center position X-direction error, the CA-axis offset error, the A-axis angle offset error, the CA-axis perpendicularity, and the A-axis center position, respectively. The Y-direction error, the A-axis center position Z-direction error, the A-X axis perpendicularity, and the A-Y axis perpendicularity. Therefore, the geometric error in the machining center M is the sum of δx _CA , δy _CA , α _CA , β _CA , δy _AY , δz _AY , β _AY , γ _AY , γ _YX , α _XZ , β _XZ , α _ZT , β _ZT . It is identified by determining 13 parameters.

<Identification method of geometric error>
The above-described geometric error identification method will be described below. When identifying the geometric error, as shown in FIG. 4, the touch probe 11 is attached to the spindle head 2 instead of the tool, and the target sphere 12 as a target is fixed to the table 3 (attached to the base of the target sphere 12). Fixed by a magnet etc.). The touch probe 11 has a sensor (not shown) that senses that the target sphere 12 has been touched, and can emit a signal using infrared rays, radio waves, or the like when the touch is sensed. Yes. On the other hand, the control device 21 of the machining center M stores, as a measurement value, the current position of each axis at the moment of receiving a signal emitted from the touch probe 11 by the connected receiver (or when the delay is taken into consideration). 22 can be stored. Then, in accordance with a command from the control device 21, the center position of the target sphere 12 is measured by the touch probe 11 in a predetermined index state of the A axis and the C axis, and a geometric error is identified (measured) based on the measured value. ).

  Here, the relationship between the measured value of the center position of the target sphere 12 and the geometric error will be described. The center position of the target sphere 12 is a table coordinate system (the coordinate system on the table 3 in which the intersection of the A axis and the C axis is the origin in an ideal state with no geometric error, and the X axis is parallel to the X axis of the machining center M) ) And (R, 0, H). The center position measurement value (x, y, z) of the target sphere 12 when there is no geometric error can be expressed by the following [Equation 1], where a is the A-axis angle and c is the C-axis angle.

On the other hand, the measurement value (x ′, y ′, z ′) of the center position of the target sphere 12 when there is a geometric error including the error (δx _WC , δy _WC , δz _WC ) of the mounting position of the target sphere 12. The matrix relational expression is the following [Equation 2]. However, the approximation is made assuming that the geometric error is minute.

  When this [Equation 2] is expanded, the following [Equation 3] is obtained. Here, in order to simplify the equation, the product of geometric errors is assumed to be minute and approximated to zero.

When identifying the geometric error, first, the A axis is determined in a state where the upper surface of the table 3 is perpendicular to the spindle head 2 (Z axis) (A axis angle a = 0 °), and the C axis angle c is set to 0. The center positions of the target spheres 12 at n locations for one round are measured by calculating at an arbitrary angle pitch from °. For example, if the angular pitch is 30 °, 12 measurements are performed from 0 ° to 330 ° as shown in FIG. 5 (hereinafter, this measurement is referred to as index measurement). As a result, when i = 1 to n, n spherical center position measurement values (x _i ′, y _i ′, z _i ′) are obtained, and the measurement values draw a circular locus. The A-axis and C-axis indexing positions (indexing conditions) in geometric error identification are stored in advance in the storage unit 22 of the control device 21.

Here, the radius of the measurement value on the XY plane, that is, the distance from the center position of the C axis to each center position measurement value is R when there is no geometric error, and the radius error when there is a geometric error. ΔR _XY is added. This ΔR _XY can be calculated as shown in the following [Equation 4] by modifying and approximating [Equation 3].

Substituting [Equation 3] into [Equation 4], the following [Equation 5] is obtained. Therefore, ΔR _XY is a circular locus including zero-order (radius error), first-order (center deviation), and second-order (elliptical shape) components.

Also, the sine-cosine function of n to the divided angle theta ₁ through? _N at regular intervals 360 ° has the following properties: [Expression 6].

Then, paying attention to the secondary sine component of [Equation 5], the property of [Equation 6] is used. The [Delta] R _xyi corresponding to each center position measurement values, C axis angle c 2 order sine components r _b2 by taking the average by multiplying quadratic sine value of _i is obtained when the indexing respectively, deform it Then, the following [Equation 7] is obtained, and the XY inter-axis perpendicular angle γ _YX can be obtained.

Further, the primary component is extracted. By _multiplying ΔR _XYi by the primary cosine value or sine value of the C-axis angle c _i, a primary cosine component r _a1 and a primary sine component r _b1 are obtained, which are transformed into the following [Equation 8] Is obtained.

  [Formula 3] is obtained by transforming [Formula 3] and obtaining the average of the X coordinate x ′ and the Y coordinate y ′ of each center position measurement value. This [Equation 9] is for obtaining the center of the circular locus, that is, the primary component, and can be used instead of [Equation 8].

On the other hand, as can be seen from the equation Z coordinates of the center position measurement values of the number 3], Z coordinate values 0 next to the C-axis angle c _i, is a circle having a primary cosine-sine component. In order to extract the primary component of this circle, the following [Equation 10] is obtained by multiplying the Z coordinate of each center position measurement value by the cosine value and sine value of the C-axis angle c _i when calculated. It is done. β _AY can be obtained from another method or from the measurement and formula described later and substituted to obtain β _CA and α _CA which are geometrical errors related to the C axis inclination error.

Next, the A-axis is tilted at any angle a _t other than 0 °, to measure the center position of the target ball 12 in one round n locations with indexing at any angle pitch C axis angle c from 0 ° (Indexing measurement). As before, the center position measurement value draws a circular locus, but the radius, that is, the distance from the intersection of the A axis and the C axis to each center position measurement value is R when there is no geometric error, When there is a geometric error, a radius error ΔR is added. ΔR is expressed by the following [Equation 11] obtained by modifying and approximating [Equation 3].

Substituting [Equation 3] into this [Equation 11] yields the following [Equation 12] ( _note that detailed equations of r _a0 , r _a1 , r _b1 , and r _a2 are omitted).

Similar to [Equation 5], [Equation 12] is a circular locus including 0-secondary components. Focusing on the quadratic sine component and multiplying ΔR _i corresponding to each center position measurement value by the quadratic sine value of the C-axis angle c _{i obtained} respectively, the following [Equation 13] is obtained. It is done. By substituting [Equation 7] or γ _YX obtained by another method for this [Equation 13], β _XZ can be obtained.

  Here, depending on the index angle of the A axis, it may not be possible to measure for one round due to interference between the spindle head 2 and the table 3 or the like, or the limitation of the movable range of each axis. [Equation 13] cannot be used when there is no center position measurement value for one round. In that case, the following [Equation 14] is obtained by solving the coefficient of [Equation 12] by the method of least squares using a plurality of center position measurement values.

Next, as shown in FIG. 6, indexing the C-axis angle c _t to 90 ° or -90 °, to measure the center position of the target ball 12 m locations by indexing the A-axis to any of a plurality of angles ( Indexing measurement). In many cases, the A-axis cannot mechanically rotate once, and even if it can, it cannot be measured by the touch probe 11, and therefore, measurement is performed within a certain angular range instead of one round. Focusing on the X coordinate of the center position measurement value, the following [Expression 15] is obtained from [Expression 3].

That is, it can be said that [Equation 15] indicates an arc including 0th and 1st order components. However, 90 ° C-axis angle _{c t,} Mixing changed and -90 °, also adds zero-order component which is dependent on _{c t.} The following [Equation 16] is obtained by obtaining the coefficient of each component of [Equation 12] by using the least square method or the like as a variable. Therefore, the geometric errors γ _AY and β _AY related to the tilt error of the A axis can be obtained by obtaining and substituting β _XZ by the above method or another method.

Next, attention is paid to the Y and Z coordinates of the center position measurement value. The radius error of the circular locus due to the geometric error, that is, the error ΔR _YZ of the distance from the center of the A axis to the sphere center can be obtained from the following [ _Equation 17].

Substituting [Equation 3] into this [Equation 17] gives the following [Equation 18]. Detailed expressions of r _a0 and r _c0 are omitted.

Therefore, ΔR _YZ is an arc locus including 0-second order components, and the following [Equation 19] is obtained by solving the coefficient of each component by the least square method or the like.

Here, obtaining the coefficient of [Equation 18] is the same as obtaining the radius and center position of the arc and the size of the elliptic component included in the arc. In general, the accuracy of obtaining the center position and elliptical component of an arc becomes worse as the arc angle is smaller. Therefore, as shown in FIG. 6, indexed to both the C-axis 90 ° (the center position of the target ball 12 _e p1 _{to e p4)} and -90 ° (the center position of the target ball 12 _e n1 _{to e n4)} To measure. Thereby, the arc angle can be widened and the identification accuracy can be increased. When it is not necessary to obtain α _XZ , the calculation may be performed by ignoring the secondary components r _a2 and r _b2 as 0 in [Equation 19].

  From the above, by measuring the center position of the target sphere 12 at a plurality of positions by the above-described method and calculating using the above-described mathematical formula, in addition to the eight geometric errors related to the rotation axes (A-axis and C-axis), the linear axis It is possible to identify eleven geometric errors in total with respect to (Y axis, X axis, Z axis). The remaining two need to be identified by another method.

<Check for disturbance error>
In the machining center M, the geometric error is identified by the above-described method in the control device 21. At this time, whether or not an error due to disturbance (positional displacement of the target sphere, etc.) is included in the identified geometric error. A disturbance error presence / absence confirmation process (hereinafter simply referred to as a confirmation process) is executed (this process is referred to as a disturbance error presence / absence confirmation step). In the confirmation process, the spindle head 2 of the machining center M is moved along one of the linear axes (Y axis, X axis, Z axis) by the following method at each index position of the A axis and the C axis. The diameter of the target sphere 12 is measured by bringing the touch probe 11 into contact with the target sphere 12 five times in total. Then, the measured value of the diameter of the target sphere 12 and the installation position of the target sphere 12 are compared, and based on the result, it is determined whether or not an error due to disturbance is included in the identified geometric error. .

<Measurement method of target sphere diameter>
FIG. 7 schematically illustrates an example of a method for measuring the diameter of the target sphere. When measuring the diameter of the target sphere 12, first, the spindle head 2 is moved in the X-axis direction to bring the touch probe 11 into contact with the target sphere 12. Then, using the result (TP1) measured by contacting the target sphere 12 from the + X direction and the result (TP2) measured by contacting the target sphere 12 from the -X direction (TP2), the target sphere 12 is expressed by the following formula 1. calculating the center position X _S in the X-axis direction. When measuring TP1 and TP2, the spindle head 2 is kept at the same position in the Y-axis and the Z-axis. The position of the spindle head 2 at that time on the Z-axis is _{denoted as ZTP1234} .
X _S = (X _TP1 + X _TP2 ) / 2... 1

Next, the spindle head 2 is moved along the X-axis direction to the center position Xs of the target sphere 12 in the X-axis direction, and then the spindle head 2 is kept at the same position in the X-axis and the Z-axis. The touch probe 11 is brought into contact with the target sphere 12 by moving in the Y-axis direction. Then, using the result (TP3) measured by contacting the target sphere 12 from the + X direction and the result (TP4) measured by contacting the target sphere 12 from the −X direction, the target sphere 12 is expressed by the following equation 2. calculating the center position Y _S in the Y-axis direction.
Y _S = (Y _TP3 + Y _TP4 ) / 2... 2

At this time, the radius R _XY of the target sphere 12 measured by Z _{TP 1234} (that is, the position of the spindle head 2 in the Z-axis direction at the time of X _S , Y _S measurement) is obtained by the following expression 3.
R _XY = (Y _TP3 −Y _TP4 ) / 2... 3

Finally, after the spindle head 2 is moved along the Y-axis direction to the center position Ys of the target sphere 12 in the Y-axis direction, the spindle head 2 is kept at the same position in the X-axis and the Y-axis. The measurement result (TP5) is obtained by moving the touch probe 11 from the + Z direction along the Z-axis direction and bringing the touch probe 11 into contact with the target sphere 12. At this time, if the radius of the target sphere 12 is R ₀ , the following expression 4 is established.
R ₀ ² = R _XY ² + [R ₀ + (Z _TP5 −Z _TP1234 )] ² ... 4

Therefore, the measured diameter D ₀ of the target sphere 12 is obtained by the following formula 5.
D ₀ = [R _XY ² + (Z _TP5 −Z _TP1234 ) ² ] / (Z _TP5 −Z _TP1234 ) 5

  As described above, in order to identify (measure) the geometric error, it is necessary to obtain the center position of the target sphere 12. Therefore, when the center position and the diameter of the target sphere 12 are measured at each index position. Is controlled by the control device 21 so that the number of movements of the spindle head 2 (touch probe 11) is minimized.

<Contents of disturbance error checking process>
Hereinafter, the content of the disturbance error presence / absence confirmation process executed in the control device 21 will be specifically described with reference to the flowchart of FIG.

In the disturbance error presence / absence confirmation processing, first, the installation position and the diameter of the target sphere 12 are measured before the measurement of the diameter of the target sphere 12 under each of the A-axis and C-axis indexing conditions (hereinafter, this measurement is referred to as the installation position). This is called confirmation measurement.) Then, the center position XYZ (X _S , Y _S , Z _S ) and diameter (hereinafter referred to as a reference value Ds) of the target sphere 12 obtained by the measurement correspond to the index positions of the A axis and C axis at the time of measurement. And recorded in the storage means 22 (S1-a).

  Next, measurement of the installation position of the target sphere 12 under each indexing condition for identifying the geometric error (hereinafter referred to as indexing measurement) is executed a predetermined number of times (S1-b). In each measurement, first, the indexing operation of the A axis and the C axis set in the measurement condition is executed (S1-c). Since the position of the target sphere 12 varies depending on the indexing operation, the above-described method (that is, the spindle head 2 is changed to one of the Y axis, X axis, and Z axis of the machining center M) for each indexing operation. The center position and the diameter of the target sphere 12 are measured by a method of moving the touch probe 11 to the target sphere 12 multiple times), and the measurement results are recorded in the storage means 22 (S1-d). .

As described above, after the measurement of the center position and the diameter of the target sphere 12 at the predetermined index position, it is evaluated whether or not the measured diameter is likely. In this evaluation, a reference value Ds, which is a measurement result of the diameter of the target sphere 12 at the time of installation position confirmation measurement, and a preset diameter fluctuation amount allowable value Da (threshold) are called from the storage unit 22 (S1). -E, S1-f). Then, according to the following expression 6, it is determined whether or not the difference between the diameter value Dm of the target sphere 12 measured after the indexing operation and the reference value Ds is within the range of the diameter variation allowable value Da. (S1-g).
Ds−Da / 2 <Dm ≦ Ds + Da / 2 (6)
(However, Ds is a reference value, Da is a diameter variation allowable value, Dm is a measured value after indexing operation)

  If the above relationship is satisfied, it is determined that there is no problem in the measurement result (an error due to disturbance is not included). On the other hand, if the relationship of the above equation 6 is not satisfied, it is determined that an error due to disturbance such as a positional deviation of the target sphere 12 has occurred during measurement, and the diameter variation NG flag is validated (S1-h). And such a determination is implemented for every index measurement.

Further, after all the above indexing measurements are completed, the A axis and the C axis are again indexed to the installation position of the target sphere 12 at the installation position confirmation measurement, and the center position XYZ (X _F , Y of the target sphere 12 is determined. _{F 1} , Z _F ) and diameter are measured (S1-i) (hereinafter referred to as re-measurement step).

As described above, after re-measuring the center position and the diameter of the target sphere 12 at the installation position of the target sphere 12 at the time of installation position confirmation measurement, the amount of variation ΔXYZ between the measurement values at the time of installation position confirmation measurement and at the time of re-measurement. Is calculated by the following equation 7.
ΔXYZ = √ [(X _F −X _S ) ² + (Y _F −Y _S ) ² + (Z _F −Z _S ) ² ]... 7

  Thereafter, a preset position fluctuation amount allowable value Pa (threshold value) of the target sphere 12 stored in the storage means 22 is called, and the calculated fluctuation amount ΔXYZ and the called position fluctuation amount allowable value Pa are called. Are compared (S1-j).

  As a result of comparing the fluctuation amount ΔXYZ with the position fluctuation amount allowable value Pa, if the fluctuation amount ΔXYZ is less than or equal to the position fluctuation amount allowable value Pa, there is no problem in the measurement result (including an error due to disturbance). Judgment) On the other hand, when the fluctuation amount ΔXYZ exceeds the position fluctuation amount allowable value Pa, it is determined that an error due to disturbance such as a positional deviation of the target sphere 12 has occurred during measurement (measurement error has occurred), and the installation position fluctuation The NG flag is validated (S1-k).

  Further, when the diameter variation NG flag is valid, there is a possibility that a measurement error has occurred during the measurement of the installation position confirmation of the target sphere 12, and therefore the diameter variation NG flag is reconfirmed (S1- l).

FIG. 9 is a flowchart showing the processing contents in the reconfirmation of the diameter variation NG flag. When reconfirming the diameter variation NG flag, first, the diameter of the target sphere 12 in all the indexing measurements from the storage means 22. The measurement result is called (S2-a), and the maximum value Dm _max and the minimum value Dm _min are acquired from these measurement results (S2-b). When the difference between the maximum value Dm _max and the minimum value Dm _min satisfies the following expression 8, it is determined that there is no measurement error (S2-c).
| Dm _max −Dm _min | <Da 8
(However, Dm _max is the maximum value of the diameter, Dm _min is the minimum value of the diameter, and Da is the allowable value of the diameter variation.)

On the other hand, if the difference between the maximum value Dm _max and the minimum value Dm _min exceeds the diameter variation allowable value Da, it is determined that a measurement error has occurred during the installation position check measurement of the target sphere 12. In that case, the average value Dm _av of all the measured values is calculated using a statistical method (S2-d), and among all the measured values Dm, the measured value that does not satisfy the following formula 9 (that is, the average value) The diameter variation NG flag is enabled (S2-e) (hereinafter referred to as an average value comparison step) for the measured value in which the difference from Dm _av exceeds the diameter variation allowable value Da.
Dm _av −Da / 2 ≦ Dm ≦ Dm _av + Da / 2... 9
(However, Dm _av is an average value, Dm is a measured value, and Da is a diameter variation allowable value.)

  Thereafter, it is determined whether or not the diameter variation NG flag is valid, and after determining that the diameter variation NG flag is not valid (that is, no measurement error has occurred), the geometric error is determined by the method described above. Identification is performed (S1-m). Then, based on a correction parameter calculation program stored in the storage unit 22, a correction parameter used for correcting the identified geometric error is calculated.

  After executing the identification of the geometric error, the diameter variation NG flag and the installation position variation NG flag are checked again (S1-n). Based on the program, the calculated correction parameter is automatically updated as a new correction parameter, and then a series of processing ends (S1-o).

  On the other hand, if there is a diameter variation NG flag or an installation position variation NG flag, an alarm or message is output by the output means 32 (S1-p). In this case, since the identification result may include an error, a series of processing is performed without executing the automatic update of the correction parameter based on the parameter update program regardless of the contents of the initial setting. Exit.

<Effects of geometric error measurement method>
In the geometric error measurement method in the above embodiment, before identifying the geometric error, the A-axis and the C-axis are calculated under a plurality of conditions, the diameter of the target sphere 12 is measured, and the variation of these measured values is calculated. When the variation exceeds the diameter variation allowable value Da, which is a preset threshold value, a disturbance error presence / absence confirmation step for determining a measurement error is executed, so an inappropriate geometric error (an error based on the disturbance is detected). A situation in which the machining accuracy of the machining center M is reduced due to the execution of the correction based on the included geometric error can be prevented very effectively.

<Example of changing geometric error measurement method>
The geometric error measurement method according to the present invention is not limited to the above-described embodiment, and can be appropriately changed as necessary without departing from the gist of the present invention. For example, the measurement method according to the present invention is not limited to the method using a spherical target (measurement jig) as in the above-described embodiment, and the rectangular parallelepiped shape is used by using a target having another shape such as a rectangular parallelepiped shape. The presence or absence of a disturbance error may be confirmed based on variations in measured values of the length of a predetermined side of the target and the distance between predetermined surfaces.

  Further, the geometric error measurement method according to the present invention is not limited to the method of continuing the processing even when it is determined that the NG flag is present in the disturbance error presence / absence confirmation processing as in the above-described embodiment, and when the NG flag is present. It is also possible to change to the one that outputs the fact that a measurement error exists and immediately terminates all the processes.

  Further, according to the geometric error measuring method of the present invention, as in the above embodiment, the difference between the target sphere diameter Dm and the reference value Ds measured after each indexing operation in the disturbance error presence / absence confirmation processing is the diameter variation tolerance. If the target sphere is not within the range of the value Da, the target sphere is returned to the position at the time of installation position check measurement and the diameter is measured again. It is also possible to change to the one that measures the diameter again.

  In addition, the geometric error measuring method according to the present invention, as in the above-described embodiment, is used when the repositioning of the installation position is performed in the disturbance error presence / absence confirmation process, and the variation amount is regarded as a scalar and the positional variation allowable value Pa. (Scalar) is not limited to confirming the presence or absence of disturbance error, and the amount of change is captured by each component in the Y-axis direction, X-axis direction, and Z-axis direction, and the position variation allowable value Pa in the Y-axis direction It is also possible to change to a component that confirms the presence or absence of a disturbance error by comparison with the component, the X-axis direction component, and the Z-axis direction component.

  On the other hand, the method of identifying the geometric error obtained from the target installation position (center position) at each indexing position is not limited to the method of the above embodiment, and it depends on the axis configuration of the multi-axis machine tool, the shape of the target, and the like. It can be changed as appropriate.

  Further, the measurement of the target installation position (center position) and diameter is not limited to the method of bringing the touch probe into contact with the target as in the above embodiment, and a method using a laser displacement meter that can measure the distance in a non-contact manner, It is also possible to change to a method of obtaining the center position and diameter of the target from the measured values of each displacement sensor by bringing three or more displacement sensors into contact with the target at the same time.

  Since the geometric error measurement method according to the present invention has excellent effects as described above, it can be suitably used as a geometric error measurement method (identification method) in various multi-axis machine tools.

M ·· Machining center 1 ·· Bed 2 ·· Spindle head 3 ·· Table 4 · Cradle 5 ·· Trunnion 11 ·· Touch probe 12 ·· Target ball 21 ·· Control device

Claims (8)

In a machine tool having a plurality of linear axes and rotary axes, the position of the target installed on the table is measured by a sensor provided on the main axis, and the geometry related to the linear axes and rotary axes is determined based on information about the measured positions. A geometric error measurement method for calculating and identifying an error,
Before the geometric error is identified, the straight axis or the rotation axis is calculated under a plurality of conditions, the length of a predetermined part of the target is measured, and the variation of these measured values is calculated. The variation exceeds the predetermined value. A geometric error measuring method, comprising: performing a disturbance error presence / absence confirmation step that determines that a measurement error has occurred. The disturbance error presence confirmation step includes
After executing the measurement of the length of the predetermined part of the target at the initial setting position, the linear axis or the rotation axis is determined at a plurality of different positions and the length of the predetermined part of the target is measured,
A measurement error is determined when the difference between each measured value after indexing the straight axis or rotating shaft and the measured value at the time of confirming the installation position of the target exceeds a preset allowable value for the measured value fluctuation amount. The geometric error measuring method according to claim 1, wherein the geometric error is measured. The disturbance error presence confirmation step includes
After executing the measurement of the length of the predetermined part of the target at the initial setting position, the linear axis or the rotation axis is determined at a plurality of different positions and the length of the predetermined part of the target is measured,
When the difference between each measured value after the indexing of the rectilinear axis or rotating axis and the measured value at the time of confirming the installation position of the target exceeds a preset measured value fluctuation amount allowable value, the rectilinear axis or Calculate the average value of each measured value after indexing the rotation axis,
The measurement error is determined when a difference between the average value and a measured value at the time of confirming the installation position of the target exceeds the measured value fluctuation amount allowable value. Method of measuring geometric errors. After measuring the target installation position at the initial setting position, perform each measurement after indexing the linear axis or rotary axis, and then set the linear axis or rotary axis so that the target installation position becomes the initial setting position. Determine the target installation position again,
The measurement error is determined when a difference between the re-measured target installation position and the initial setting position exceeds a preset target position variation allowable value. Item 4. A method for measuring a geometric error according to any one of Items 1 to 3. After measuring the installation position of the target under any indexing condition of the linear axis or the rotation axis, measure the target installation position again under the same indexing condition,
The measurement error is determined when the deviation between the re-measured target installation position and the installation position at the previous measurement exceeds a preset target position variation allowable value. Item 4. A method for measuring a geometric error according to any one of Items 1 to 3. Each time a geometric error is identified, it has a parameter update step for updating a correction parameter of the geometric error calculated based on the identified geometric error as a new correction parameter.
6. The geometric error measuring method according to claim 1, wherein when the measurement error is determined, the parameter updating step is not executed.   The geometric error measurement method according to claim 1, wherein when the measurement error is determined, the situation is notified and measurement of the position of the target or the length of the predetermined part is interrupted. .   The geometric error measuring method according to claim 1, wherein the target is spherical, and the length of a predetermined portion of the target is a diameter of the sphere.

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