JP4950443B2 - Calibration gauge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely calibrate in a short time for the calibration gauge to be used for a measurement device for measuring the surface precision such as the free curvature shape etc. <P>SOLUTION: The calibration gauge 100 is made in a mortar shape with the recess spherical surface 101. Because the mortar-shaped calibration gauge is provided with the recess spherical surface, the contact state of the touch probe is stabilized, a degradation in precision of the calibration of the touch probe caused by slip is eliminated. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a calibration gauge, and more particularly to a calibration gauge used for calibration of a measuring apparatus that measures shape accuracy such as a free-form surface shape.

  As a free-form surface measurement method for measuring the accuracy of the free-form surface in the direction perpendicular to the surface and quantifying it, and evaluating the accuracy of the free-form surface of a workpiece such as a mold, any coordinate position on the free-form surface is used. Information indicating the normal vector of the surface of the object to be measured at the coordinate position is obtained from the curved surface data of the free-form surface, and the obtained normal vector is obtained using a touch probe having a spherical or hemispherical probe. Set a position offset by a predetermined amount in the normal vector direction at the measurement point from the information shown, move the touch probe so that the center of the probe is located at the offset position, and move the touch probe from the offset position to the measurement point. The touch probe is brought into close contact with the surface of the object to be measured by moving it in the direction of the normal vector, and the contact position with the surface of the object to be measured from the offset position. There is movement amount or the measurement method for determining the equivalent thereto quantity values up (e.g., Patent Document 1).

Calibration of the measuring device (touch probe) in the shape measurement as described above is performed by fixing a reference sphere (calibration gauge) with a convex spherical surface to a work table of a three-axis processing machine as shown in Patent Document 1. any point in the convex spherical surface of the reference sphere feeler center of the touch probe relative to the reference sphere with respect to (the calibration point) a touch probe to be located in an offset position by a predetermined amount offset in the normal vector direction Move the axis, move the touch probe in the direction of the normal vector at an arbitrary point from the offset position, and bring the touch probe probe close to the surface of the reference sphere. From the offset position to the contact position with the surface of the reference sphere The amount of movement or equivalent quantity value is obtained.

  The shape dimension of the reference sphere is known, the distance in the normal vector direction from the offset position to any one point on the sphere of the reference sphere is known, and the difference value between this distance and the measured value of the above-mentioned movement amount The measurement value is corrected using the correction value as a correction value, and the calibration is repeated until the calibration difference value falls within the allowable value. CNC tuning is performed using this calibration difference value (error amount) as a calibration value at the time of shape measurement.

  In calibration with a reference sphere, different offset positions are created outside the reference sphere for each calibration point, and the touch probe is moved to the offset position for each point for each point (normal vector direction) calibration. It is necessary to let For this reason, the total path length of the touch probe in calibration is long, and time is required for calibration.

  Further, in the reference sphere, the spherical probe of the touch probe is not satisfactorily seated with respect to the convex sphere, and the phenomenon that the probe is slid with respect to the convex sphere is likely to occur, which causes a decrease in calibration accuracy.

JP 2002-267438 A

  The problem to be solved by the present invention is to enable calibration in a short time with high accuracy.

A calibration gauge according to the present invention includes a concave spherical surface for point measurement which is a complete hemispherical half of the whole sphere, and a hole made of a cylindrical portion concentric with the concave spherical surface, which is connected to the opening end side of the concave spherical surface. a calibration gauge it is.

The calibration gauge according to the present invention comprises a concave spherical surface for measuring a point which is a complete hemispherical half of the whole sphere, and a hole made of a cylindrical portion concentric with the concave spherical surface, which is connected to the opening end side of the concave spherical surface ; A calibration gauge having a projection having a convex spherical surface for measurement .

  According to the present invention, since the calibration gauge has a mortar shape having a concave spherical surface, the touch probe probe is satisfactorily seated on the concave spherical surface, and the touch probe calibration accuracy is not lowered due to slipping. The offset position set at the time of calibration can be set to one point of the center point of the concave sphere in any normal vector direction calibration, and the total path length of the touch probe in the calibration can be set using the calibration gauge by the convex sphere. It can be shorter than when used. This also shortens the time required for calibration.

  One embodiment of a system for carrying out one embodiment of a calibration gauge and a calibration method of a measuring apparatus using the calibration gauge according to the present invention will be described with reference to FIG.

  The system includes a CAD / CAM machine 10 and a computer numerical controller (CNC) 20.

  The CAD / CAM machine 10 and the CNC 20 are connected so as to be capable of bidirectional communication by communication means 40 such as serial communication by RS2324 or the like, LAN, or the Internet. Note that the CAD / CAM machine 10 and the CNC 20 may exchange data offline.

  The CAD / CAM machine 10 is a dedicated computer or a general-purpose personal computer. The CAD / CAM machine 10 includes a man-machine interface, and by executing a computer program, a CAD / CAM data creation unit 11, a measurement program creation unit 12, a normal vector data extraction unit 13, and a calibration The execution program creation unit 14 is embodied.

  The CAD / CAM data creation unit 11 creates a numerical control machining program from the shape data, curved surface data (surface data), shape data, and curved surface data of the object to be measured (machined portion).

  The measurement program creation unit 12 creates a shape accuracy measurement program that performs shape accuracy measurement of the object to be measured. The shape accuracy measurement program uses the arbitrary coordinate position of the free-form surface (surface) of the object to be measured as the measurement point, and based on the data indicating the normal vector of the surface of the object at the measurement point, the normal vector direction from the measurement point Set the position offset by a predetermined amount, and move the touch probe so that the probe probe center is located at the offset position, and move the touch probe in the direction of the normal vector of the measurement point from the offset position. A computer language in which the CNC 20 can execute a procedure for bringing a probe probe close to and in contact with the surface of the object to be measured, and obtaining a movement amount from the offset position to the contact position with the surface of the object to be measured or a quantity value equivalent thereto. It is described.

The shape accuracy measurement program sequentially designates a plurality of measurement points S1, S2, S3... On the surface of the object to be measured by means of three orthogonal coordinate values (Xs, Ys, Zs), and each measurement point S1. , S2, S3... Describe the normal vector of the surface of the object to be measured. That is, the shape accuracy measurement program designates the measurement point fixed points S1, S2, S3,... On the surface of the object to be measured, by specifying the coordinate values (Xs, Ys, Zs) of the three orthogonal axes, and the designated measurement points S1, Each of S2, S3 has normal vector data of the surface of the object to be measured at each measurement point S1, S2, S3 .

The normal vector of the surface of the object to be measured at the measurement points S1, S2, S3... Is defined by the vectors i, j, and k in the X-axis, Y-axis, and Z-axis directions from the curved surface creation formula, There is a method of defining by the inclination angle B of the curved surface and the horizontal angle C at the measurement points S1, S2, S3. Here, by using the latter, the command format is expressed as follows.
Command format: G *** _ X *** _ Y ** _ Z *** _ B *** _ C ***

  When the object to be measured is a workpiece having a free-form surface shape machined by a CNC triaxial machine like a mold, the data indicating the normal vector, that is, the inclination angle B and the horizontal angle C For machining a free-form surface shape, it can be obtained from CAD / CAM curved surface data for creating a numerical control machining program used in a CNC triaxial machine.

  Thus, the measurement program creation unit 12 obtains the inclination angle B and the horizontal angle C from the CAD / CAM curved surface data created by the CAD / CAM data creation unit 11.

  Here, the shape accuracy measurement of the object to be measured by the shape accuracy measurement program will be described with reference to FIG.

Using a touch probe 60 having a spherical or hemispherical probe 61 as a three-dimensional shape measuring instrument, an offset position offset by a predetermined amount in the normal vector direction Ns at the measurement point S from the acquired data indicating the normal vector. set psof, so that its feeler center Tc is located offset position psof, a touch probe 60 is axially moved to move the touch probe 60 in the normal vector direction Ns measurement point S than offset position psof, touch The probe 61 of the probe 60 is brought into close contact with the surface of the workpiece W. The amount of movement from the offset position Psof to the contact position with the surface of the object to be measured or a quantity value equivalent thereto is obtained.

Since the design coordinate values (Xs, Ys, Zs) of the measurement point S and the coordinate values (Xsof, Ysof, Zsof) of the offset position Psof are known values, the offset position Psof and the measurement point S when the error is zero The distance in the normal vector direction, that is, the quantity value in the thickness direction is a known value, and the difference value between this known value (measurement reference value) and the measured value is directly the thickness of the measurement point S on the free-form surface f. The shape accuracy in the thickness direction is expressed as a quantity.

  By performing a comparison operation to determine whether or not the difference value is within a preset error tolerance value, OK or NG is output for each measurement point S, or the difference value is divided stepwise to obtain an error level. (VALUE) 0 to N can be output.

  When the workpiece W is a workpiece having a free-form surface shape machined by a CNC triaxial machine, as shown in FIG. 2, a touch probe 60 is attached to the spindle 51 of the CNC triaxial machine, and the CNC3 On the axis machine, the measurement of the free-form surface shape can be performed in the automatic mode using the CNC 20 (see FIG. 1) of the CNC triaxial machine.

  As a result, the CNC triaxial machine can function as a surface measuring CMM (Coordinating Measuring Machine) having a BC axis automatic offset function.

  This shape accuracy measurement can be equally performed even with a servo-controlled three-dimensional measurement dedicated machine having an orthogonal three-axis axis control system such as a surface straight measurement CMM provided with a BC axis automatic offset function.

  The normal vector data extraction unit 13 of the CAD / CAM machine 10 uses the shape accuracy measurement program created by the measurement program creation unit 12 to obtain normal vector data on the surface of the object to be measured at each measurement point S1, S2, S3. Extract.

  In this embodiment, since the normal vector is defined by the inclination angle B of the curved surface and the horizontal angle C, the normal vector data extraction unit 13 uses each measurement point S1, S2, S3 of the shape accuracy measurement program. ... (B *** _ C ***) of each measurement point S1, S2, S3, ... is extracted from each command format (G *** _ X *** _ Y *** _ Z *** _ B *** _ C **).

  Note that only one (B ** _ C **) is valid, and the same (B ** _ C **) is not duplicated.

  If the normal vector of the surface of the object to be measured at the measurement points S1, S2, S3,... Is defined by vectors i, j, k in the X axis, Y axis, and Z axis directions, The line vector data extraction unit 13 extracts vectors i, j, and k in the X-axis, Y-axis, and Z-axis directions.

  The calibration execution program creation unit 14 creates a calibration execution program. For each normal vector data (B ** _ C **) extracted by the normal vector data extraction unit 13, the calibration execution program calibrates the measuring apparatus only with respect to the normal vector direction indicated by the normal vector data. Describes the command to be executed.

As shown in FIG. 1, the calibration execution program is such that the center of the probe 61 of the touch probe 60 is recessed in the calibration gauge 100 with respect to the calibration gauge 100 installed at a predetermined position (predetermined coordinate position). The touch probe 60 is moved with respect to the spherical surface 101 so as to be located at an offset position Psof offset by a predetermined amount in the normal vector direction Nc for each extracted normal vector data (B ** _ C **). The probe 61 of the touch probe 60 is calibrated by moving the touch probe 60 from the offset position Psof in the normal vector direction Nc by three-axis synchronous control (three-axis simultaneous control) of the X, Y, and Z axes. brought close contact with the concave spherical surface 101 of the gauge 100, the calibration from the offset position Psof The procedure for determining the quantity value of the movement amount or its equivalent to the contact position between the concave spherical surface 101 of the over-di 100 are those described in available computer language execution CNC20.

  The CNC 20 is capable of three-axis synchronous control of the X axis, the Y axis, and the Z axis. The input / output unit 21, the program execution unit 22, the X axis control unit 23, the Y axis control unit 24, and the Z axis And an axis control unit 25.

  The program execution unit 22 executes a numerical control machining program, a shape accuracy measurement program, and a calibration execution program by user designation. Regardless of which program is executed, the program execution unit 22 generates an X-axis command, a Y-axis command, and a Z-axis command by the X-axis control unit 23, the Y-axis control unit 24, and the Z-axis control unit 25. The axis command is output to the X-axis servo motor 31, the Y-axis servo motor 32, and the Z-axis servo motor 33.

  Position detectors 34, 35, and 36 such as rotary encoders are connected to the X-axis servo motor 31, the Y-axis servo motor 32, and the Z-axis servo motor 33, respectively. The position detectors 34, 35, and 36 detect the motor positions of the servo motors 31 to 33 for each axis. The motor position signals of the position detectors 34, 35, and 36 are input to the CNC 20 as position signals for feedback servo control, shape accuracy measurement, and calibration.

  In addition, the position signal at the time of each control can also use the output signal of a linear sensor by providing a linear sensor with respect to each axis | shaft of an X-axis, a Y-axis, and a Z-axis.

  At the time of measuring the shape accuracy and at the time of calibration, a touch probe 60 is used instead of a tool instead of a tool 51 on the spindle 51 of a CNC three-axis processing machine that is moved in the direction of each axis by an X-axis servo motor 31, a Y-axis servo motor 32, and a Z-axis servo motor 33 Install. An on / off signal indicating contact of the probe 61 of the touch probe 60 is input to the CNC 20 via the programmable logic controller (PLC) 26.

  Calibration for measuring the shape accuracy by the touch probe 60 is performed by the program execution unit 22 of the CNC 20 executing the calibration execution program.

  This calibration is performed by measuring the offset position displaced from the surface of the object to be measured at the measurement points S1, S2, S3... Specified in the normal vector direction Nc of the surface of the object to be measured and the measuring point S1, This is calibration of a measuring device that measures the surface shape accuracy by measuring the distance in the normal vector direction Nc from the surface of the object to be measured at S2, S3, and so on, at each measurement point S1, S2, S3,. Calibration is performed only for the normal vector direction Nc of the surface of the object to be measured.

  In the present embodiment, the calibration is performed on the same machine as the shape accuracy measurement by attaching a calibration gauge 100 having a hemispherical concave spherical surface 101 to a predetermined machine coordinate position.

In this calibration, the center of the probe 61 of the touch probe 60 with respect to the calibration gauge 100 is in the normal vector direction with respect to one point (measurement points S1, S2, S3...) Of the concave spherical surface 101 of the calibration gauge 100. The touch probe 60 is moved together with the spindle 51 by the X-axis servo motor 31, the Y-axis servo motor 32, and the Z-axis servo motor 33 so as to be positioned at the offset position Psof offset by a predetermined amount to Nc, and the touch probe 60 is moved to the offset position. The probe 61 of the touch probe 60 is moved closer to the concave spherical surface 101 of the calibration gauge 100 by moving in the normal vector direction Ns of the one point from Psof, and the concave spherical surface 101 of the calibration gauge 100 from the offset position Psof . There is a movement amount to the contact position Calibrate the measuring device seeking the quantity value equivalent to the same.

Since the shape dimension of the calibration gauge 100 is known, the distance in the normal vector direction from the offset position Psof to any one point of the concave spherical surface 101 of the calibration gauge 100 is known, and this distance and the above-described movement amount The difference value of the measured values is taken into the CNC 20 as a calibration difference value, and the shape accuracy measurement by the CNC 20 is tuned.

  Then, as a guarantee of the calibration result, the calibration reflecting the calibration difference value is performed in the same manner, and the above calibration is repeated until the calibration difference value falls within the allowable value.

In this calibration, the actual measurement points S1, S2, S3 ... normal vector direction and same phase, because calibration Direct method cracking line, actually the normal vector direction of the calibration required in the shape accuracy measurement Thus, the calibration for guaranteeing a high shape accuracy measurement result is performed accurately and in a short time without unnecessarily increasing the number of calibration points.

  The calibration gauge 100 used in this embodiment is a mortar-shaped calibration gauge having a hemispherical concave spherical surface 101 as shown in FIG. The calibration gauge 100 has a cylindrical portion 102 having a height (axial length) h with the same radius as the radius of the concave spherical surface 101 concentrically with the concave spherical surface 101 on the opening end side of the concave spherical surface 101. The calibration gauge 100 has a horizontal upper surface 103 around the open end of the cylindrical portion 102.

In this calibration gauge 100, the offset position Psof can be set to one point of the center point Gc of the concave spherical surface 101 in any normal vector direction calibration.

As a result, the program description for setting the offset position Psof can be simplified, and the total path length of the touch probe 60 in calibration can be made shorter than when a calibration gauge using a convex spherical surface is used. This also shortens the time required for calibration.

  Further, in the calibration gauge using the convex spherical surface, the spherical probe 61 of the touch probe 60 is not satisfactorily seated with respect to the convex spherical surface, and the phenomenon that the probe 61 slides with respect to the convex spherical surface is likely to occur. If it is 101, the probe 61 sits better with respect to the concave spherical surface 101, and the calibration accuracy of the touch probe 60 is not lowered due to slipping.

The offset position Psof is set, that is, the coordinates ( Xsof , Ysof , Zsof ) of the center point Gc of the concave spherical surface 101 of the calibration gauge 100 are set by the CNC 20 using the touch probe 60 and automatic centering of the inner diameter by G code By executing the (orthogonal two-direction approach) macro program, the cylindrical portion 102 of the calibration gauge 100 is automatically centered to obtain coordinate values ( Xsof , Ysof ), and the touch probe 60 is used. A coordinate value ( Zsof ) can be obtained by measuring the Z-axis positions of four orthogonal points on the horizontal upper surface 103 and subtracting the height h from the average value.

Thus, the use of the concave spherical calibration gauge 100 facilitates the setting of the offset position Psof , and this also shortens the time required for calibration.

  Another embodiment of the calibration gauge according to the present invention will be described with reference to FIG. 4, parts corresponding to those in FIG. 3 are denoted by the same reference numerals as those in FIG. 3, and description thereof is omitted.

  The calibration gauge 105 according to this embodiment has a hemispherical convex spherical surface 104 in addition to the hemispherical concave spherical surface 101 equivalent to the calibration gauge 100 shown in FIG.

  In this calibration gauge 105, the concave spherical surface 101 and the convex spherical surface 104 can be used properly depending on whether the surface of the object to be measured at the measurement point is concave or convex.

1 is a system configuration diagram showing one embodiment of a system for carrying out one embodiment of a calibration cage and a calibration method of a measuring apparatus using the calibration cage according to the present invention. FIG. It is explanatory drawing which shows the actual example of a free-form surface shape measurement. It is a longitudinal section showing one embodiment of a calibration gauge by this invention. It is a longitudinal cross-sectional view which shows other embodiment of the calibration gauge by this invention.

Explanation of symbols

10 CAD / CAM machine 11 CAD / CAM data creation unit 12 Measurement program creation unit 13 Normal vector data extraction unit 14 Calibration execution program creation unit 20 CNC
21 Input / output unit 22 Program execution unit 23 X-axis control unit 24 Y-axis control unit 25 Z-axis control unit 26 Programmable logic controller 31 X-axis servo motor 32 Y-axis servo motor 33 Z-axis servo motor 34, 35, 36 Position detector 40 communication means 51 spindle 60 touch probe 61 probe 100 calibration gauge 101 concave spherical surface 102 cylindrical portion 103 horizontal upper surface 104 convex spherical surface 105 calibration gauge

Claims (2)

A concave measuring spherical surface for point measurement which is a complete hemispherical half of the whole sphere, and a hole made of a cylindrical portion concentric with the concave spherical surface, which is connected to the opening end side of the concave spherical surface ,
A calibration gauge characterized by that. A hole made up of a concave spherical surface for point measurement, which is a perfect hemispherical half of the whole sphere, and a cylindrical portion concentric with the concave spherical surface, which is connected to the opening end side of the concave spherical surface ;
A projection having a convex spherical surface for point measurement ,
Calibration gauge that wherein the.

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