Correction Method of Probe Unit

Abstract

To provide a correction method for a probe unit for correcting the linear expansion amount of a probe (stylus) to obtain an accurate measurement value.SOLUTION: With a probe offset initially obtained as a model, a correction method for a probe unit includes: a temperature data acquisition step of acquiring the temperature difference between a temperature during calibration and the current temperature in a measurement environment; a reference chip coordinate correction step of calculating a correction value of a reference chip coordinate value with the addition of linear expansion as a reference chip correction coordinate value; and a probe offset correction step of calculating a correction value of a probe offset value with the addition of linear expansion as a probe offset correction value.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to a method for controlling a shape measuring device, and more specifically, to a correction method for a probe unit that corrects the linear expansion of the probe unit so as to obtain an accurate measurement value even when there are fluctuations in the measurement environment temperature.

Background Art

[0002] A shape measuring device that detects the surface of a measurement object (workpiece) with a probe is widely used. In recent years, in response to the increasing complexity of the shape of the measurement object (workpiece), it has become possible to approach a workpiece with a complex shape while exchanging a plurality of probes (styli) or changing the posture of the probe with a probe having a rotational drive shaft.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] By using a plurality of probes (styli) or changing the posture by the rotational drive shaft of the probe itself, it becomes possible to efficiently measure even a workpiece with a complex shape. However, in exchange for this, the labor required to appropriately calibrate a plurality of types of probes (styli) and various modification forms of the probe increases. When the types of probes (styli) increase or when probes taking various postures are used, if calibration work is frequently performed for all probes and modified forms, there will be a problem that the measurement efficiency will not increase. On the other hand, when there are fluctuations in the measurement environment, measurement errors that cannot be overlooked will occur if calibration work is not appropriately carried out.

[0005] Therefore, an object of the present invention is to provide a correction method for a probe unit that can correct the linear expansion of the probe unit so as to obtain accurate measurement values even when there are fluctuations in the measurement environment temperature.

Means for Solving the Problems

[0006] The correction method for the probe unit of the present invention is A correction method for a probe unit that detects the surface of a measurement object with a measurement tip at the tip, The probe unit is A first chip that is a measurement chip in a standard form set as an initial standard specification, and A second chip that is a measurement chip in a modified form changed from the standard form, and can be switched and used, When calibrating the probe unit, by calibrating the first chip and the second chip respectively, the coordinate value of the first chip is obtained as a reference chip coordinate value, and the offset from the first chip to the second chip is obtained as a probe offset value. The measurement value when the second chip is used is obtained by taking into account the probe offset value in the reference chip coordinate value. The correction method for the probe unit is A temperature data acquisition step of acquiring the temperature difference between the temperature at the time of calibration and the current temperature of the measurement environment, A reference chip coordinate correction step of calculating a correction value of the reference chip coordinate value taking into account linear expansion as a reference chip correction coordinate value, A probe offset correction step of calculating a correction value of the probe offset value taking into account linear expansion as a probe offset correction value, A measurement value calculation step of obtaining a corrected measurement value when the second chip is used in the current measurement environment by taking into account the probe offset correction value in the reference chip correction coordinate value. It is characterized by this.

Brief Description of the Drawings

[0007]

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Figure 14

Embodiments for Carrying Out the Invention

[0008] Embodiments of the present invention will be illustrated and described with reference to the reference numerals attached to each element in the drawings. (First Embodiment) FIG. 1 is a diagram showing the overall configuration of a shape measurement system 100. Although the configuration of the shape measurement system 100 itself is known, it will be briefly described. The shape measurement system 100 includes a three-dimensional measuring machine 200, a motion controller 300 that controls the drive of the three-dimensional measuring machine 200, and a host computer 600 that controls the motion controller 300 and executes necessary data processing.

[0009] The three-dimensional measuring machine 200 includes a surface plate 210, a moving mechanism 220, and a probe unit 500.

[0010] The moving mechanism 220 includes a gantry-type Y slider 221 that is slidably provided in the Y direction on the surface plate 210, an X slider 222 that slides along the X-direction beam of the Y slider 221, a Z-axis column 223 fixed to the X slider 222, and a Z spindle 224 that moves up and down in the Z direction within the Z-axis column 223.

[0011] The Y slider 221, the X slider 222, and the Z spindle 224 are each provided with a drive motor (not shown) and an encoder (not shown). Each drive motor is driven and controlled by a drive control signal from the motion controller 300. The encoder detects the amount of movement of each of the Y slider 221, the X slider 222, and the Z spindle 224, and outputs the detected value to the motion controller 300.

[0012] A scale coordinate system (Xs, Ys, Zs) is set for the three-dimensional measuring machine 200. FIG. 2 is a diagram illustrating the relationship between coordinate systems. The scale coordinate system includes an Xs axis, a Ys axis, and a Zs axis that are orthogonal to each other. The Zs axis is vertically upward. The origin Os of the scale coordinate system is determined by the origin of the scale of the encoder provided along the Xs axis, the origin of the scale of the encoder provided along the Ys axis, and the origin of the scale of the encoder provided along the Zs axis.

[0013] Also, a master gauge 211 (master ball) is installed at a predetermined position on the surface plate 210. The master gauge 211 is used for calibration and setting of the machine coordinate system (XM, YM, ZM). The master gauge 211 is a steel ball, a ceramic ball, or the like. The diameter (radius) of the master gauge 211 is known. That is, by measuring the coordinates of several points on the surface of the master gauge 211 with a probe, the center position of the master gauge 211 can be uniquely identified. At this time, the radius of the measuring tip and the length (shape) of the stylus are calibrated simultaneously.

[0014] The master gauge 211 is held at the tip of a column portion having a known height in the Z-axis direction from the upper surface of the surface plate 210. The machine coordinate system (X M is a parallel translation of the scale coordinate system (Xs, Ys, Zs) such that the center position of the master gauge 221 becomes the origin O M , Y M , Z M ).

[0015] As other coordinate systems, a probe coordinate system which is the coordinate system of a probe sensor built in the probe unit 500, and a work coordinate system (Xw, Yw, Zw) having a predetermined point (for example, a vertex) on the work surface as the origin and a predetermined surface of the work as the XwYw plane are also used, but they are not directly related to the present invention and are omitted.

[0016] A probe unit 500 is attached to the lower end of the Z spindle 224. FIG. 3 is an external view of the probe unit 500. FIG. 4 is a cross-sectional view of the probe unit 500.

[0017] The probe unit 500 includes a probe head main body 501 and a stylus 530 having a measurement tip (530A) at its tip.

[0018] The probe head main body 501 includes a probe fixing portion 502, a first rotation mechanism portion 510, and a second rotation mechanism portion 520.

[0019] The probe fixing portion 502 is attached to the lower end of the Z spindle 224. Also, a first rotation mechanism portion 510 is provided at the lower end of the probe fixing portion 502. The first rotation mechanism portion 510 includes a first housing 511, a first motor 512, and a first shaft 513. The first housing 511 is attached to the lower end of the probe fixing portion 502. The first motor 512 is installed inside the first housing 511, and the first shaft 513 is attached to the armature of the first motor 512. Now, let the rotation axis of the first shaft 513 be the first rotation axis A1. In this embodiment, the axial direction of the first rotation axis A1 is parallel to the Z-axis direction.

[0020] The second rotation mechanism portion 520 includes a second housing 521, a second motor 522, a second shaft 523, and a U-shaped connecting frame 524. The second housing 521 is connected to the first shaft 513. The second motor 522 is installed inside the second housing 521, and the second shaft 523 is attached to the armature of the second motor 522.

[0021] Now, let the rotation axis of the second shaft 523 be the second rotation axis A2. At this time, the first rotation axis A1 (the extension line thereof) and the second rotation axis A2 are orthogonal to each other. The U-shaped connecting frame 524 is attached to the second shaft 523 and is configured to rotate about the second rotation axis A2.

[0022] A stylus (530) is attached to the lower end of the U-shaped connecting frame 524. Now, the stylus 530 attached to the probe unit 500 in FIGS. 3 and 4 is a straight linear stylus 530. This straight stylus 530 is used as the reference stylus 530 for standard specifications. The axis A3 (extension line) of the reference stylus 530 is orthogonal to the second rotation axis A2.

[0023] (Standard form of the probe unit 500) As the initial standard specification of the probe unit 500, assume the probe unit 500 with the reference stylus 530 attached, and further assume that the axis A3 of the reference stylus 530 is parallel to the first rotation axis A1. (Or the axis A3 of the reference stylus 530 coincides with the first rotation axis A1.) This is defined as the standard form of the probe unit 500. That is, in the standard form, the rotation of the second rotation axis A2 is zero, and the axis A3 of the reference stylus 530 and the first rotation axis A1 are parallel to the Z-axis of the machine coordinate system. The reference stylus 530 has a measurement tip 530A at its lower end. The measurement tip is spherical and contacts the object to be measured. Now, the measurement tip 530A in the standard form will be referred to as the first tip 530A.

[0024] The extension line of the first rotation axis A1, the second rotation axis A2, and the extension line of the axis A3 of the stylus 530 intersect at one intersection point. For the following description, this intersection point will be named the rotation center Q.

[0025] Also, let the rotation angle of the first rotation axis A1 be represented by α1, and assume -180° ≤ α1 ≤ 180°. (If electrical connection can be made, there is no need to set a limit on the movable range, and the rotation operation itself can rotate any number of times.) In FIGS. 3 or 4, assume that the front is 0°, the counterclockwise rotation is positive when viewed from above, and the clockwise rotation is negative.

[0026] Let the rotation angle of the second rotation axis A2 be represented by α2, and assume that 0° ≤ α2 ≤ 90°. When the stylus 530 is vertically downward, it is defined as 0°. It is arbitrary which point is taken as the 0° reference.

[0027] The first motor 512 and the second motor 522 are, for example, stepping motors, and are assumed to drive in synchronization with the applied drive pulses. That is, it is assumed that the momentum (rotation angle) of the first rotation mechanism section 510 and the second rotation mechanism section 520 is proportional to the number of drive pulses.

[0028] The probe unit 500 supports the stylus 530 so that the stylus 530 can move in the axial directions of the Xp, Yp, and Zp axes within a certain range in order to detect the contact between the measurement tip (530A) and the work surface, and includes a probe sensor (not shown) for detecting the displacement of the stylus 530. (The Xp, Yp, and Zp axes are the coordinate axes of the probe coordinate system) The probe sensor outputs the detected value to the motion controller 300.

[0029] (Modified form of the probe unit) The probe unit 500 may be used as a modified form in which it is changed from the standard form according to the measurement object. As a modified form of the probe unit 500, for example, the stylus remains the reference stylus 530, and the first rotation mechanism section 510 (A1) and the second rotation mechanism section 520 (A2) can be rotationally driven as appropriate to lift the stylus or take a posture of rotational swing. Since the position of the measurement tip at this time is shifted from the position of the measurement tip (the first tip 530A) in the standard form, it will be referred to as the second tip 550A as the measurement tip in the modified form changed from the standard form.

[0030] Furthermore, as a case where it can become the "second tip 550A", there is also a case where the stylus is replaced from the reference stylus 530 with another non-standard stylus. The so-called irregular stylus mentioned here can be, for example, a bent L-shaped or cross-shaped stylus, or a straight-line stylus that is longer or shorter than the reference stylus 530. Note that one stylus (multi-stylus) may have a reference chip (first chip 530A) and a second chip 550A combined.

[0031] (Configuration of Motion Controller 300) Figure 5 is a functional block diagram of the motion controller 300 and the host computer 600. The motion controller 300 includes a measurement command acquisition unit 310, a counter unit 330, a drive command generation unit 340, and a drive control unit 350.

[0032] The measurement command acquisition unit 310 acquires measurement command data from the host computer 600.

[0033] The counter unit 330 counts the detection signals output from the encoder to measure the displacement of each slider, and counts the detection signals output from the probe sensor to measure the displacement of the probe unit 500 (stylus). The position information of the probe unit 500 or the measurement chip (550A) can be obtained from the measured displacements of the sliders 221, 222, 224 and the probe unit 500. Also, the pushing amount (or pushing direction) of the measurement chip (550A) can be obtained from the displacement of the stylus (550) measured by the counter unit 330 (the detection values (Px, Py, Pz) of the probe sensor). The drive command generation unit 340 generates a drive command to be given to the movement mechanism 220 based on the measurement command data from the host computer 600. The speed vector command for driving and controlling the movement mechanism 220 is described, for example, in Patent 5274782, Patent 6030339, Patent 6063161, etc.

[0034] (Configuration of Host Computer) The host computer 600 includes a CPU 611 (Central Processing Unit), memory, etc., and controls the three-dimensional measuring machine 200 via the motion controller 300. By executing a control program with the CPU 611511 (Central Processing Unit), the operation of this embodiment (probe temperature correction) is realized. An output device (display or printer) and an input device (keyboard or mouse) are connected to the host computer 600 as necessary.

[0035] The host computer 600 further includes a storage unit 620, a shape analysis unit 630, and a temperature correction unit 640.

[0036] The storage unit 620 stores design data (CAD data, NURBS data, etc.) regarding the shape of the measurement object (workpiece) W, measurement data obtained by measurement, and a control program for controlling the entire measurement operation. Also, in this embodiment, the storage unit 620 has a correction table storage unit 621 that stores calibration data (correction table) of the probe unit 500. The data stored in the correction table storage unit 621 is shown in FIG. 6. These calibration data (correction tables) stored in the correction table storage unit 621 will be described later.

[0037] The shape analysis unit 630 calculates the surface shape data of the measurement object based on the measurement data (sampling data) output from the motion controller 300, and performs shape analysis to obtain errors, distortions, etc. of the calculated surface shape data of the measurement object. Also, the shape analysis unit 630 generates measurement command data by performing conversions such as conversion to a PCC curve from design data (CAD data, NURBS data, etc.) including following path information.

[0038] Also, the shape analysis unit 630 generates calibration data based on the measurement data when the master gauge 211 is measured with the measurement tip in the standard form and the modified form. (This point will be described later.)

[0039] The temperature correction unit 640 obtains a correction value of the calibration data (correction table) according to the temperature difference ΔT between the calibration time and the workpiece measurement time. (This point will be described later.)

[0040] (Generation of correction table) First, when using the shape measurement system 100, it is necessary to perform calibration using the master gauge 211. The arithmetic processing for obtaining the calibration data from the measurement data of the calibration master gauge 211 is executed, for example, by the shape analysis unit 630.

[0041] (Calibration of the standard form (first chip 530A)) First, calibration is performed by the first chip 530A when the probe unit 500 is in the standard form. Thereby, together with the calibration of the electrical system (for example, encoder) of the three-dimensional measuring machine 200 and the probe unit 500 (for example, origin setting), the shape of the reference stylus 530 is also calibrated. As the calibration value (correction table) of the shape of the reference stylus 530, there are the distance L1 from the rotation center Q of the probe unit 500 to the center point of the first chip 530A (see FIG. 4), and the radius r1 of the first chip 530A (reference chip).

[0042] By calibration with the first chip 530A, a correction table S1 (S 1X , S 1Y , S 1Z ) for obtaining the center point of the first chip 530A is obtained. Here, let the center point coordinate values of the first chip 530A considering calibration be P 1c (P 1cX , P 1cY , P 1cZ ). Also, let the read values of the machine scale be M (M X , M Y , M Z ). The scale reading value of the machine mentioned here includes the reading value of the encoder of the three-dimensional measuring machine 200 and the reading value of the sensor of the probe unit 500, and it is assumed that the scale reading value of the machine indicates the coordinates of the rotation center Q of the probe unit 500. The center point coordinate value P of the first chip 530A taking calibration into account 1c is represented as follows by the correction table S1.

[0043] P 1c (P 1cX 、P 1cY 、P 1cZ ) = M(M X 、M Y 、M Z ) + S1(S 1X 、S 1Y 、S 1Z ) Since the shape of the reference stylus 530 is a straight line parallel to the Z-axis, S 1X = S 1Y = 0, and S 1Z = L1. P 1c (P 1cX 、P 1cY 、P 1cZ ) = M(M X 、M Y 、M Z ) + S1(0, 0, L1)

[0044] (Note that the surface of the work (object to be measured) is at a position shifted by a radius r in the approach direction from the center point coordinate value P of the first chip 530A. This is a well-known fact.) 1c

[0045] As a correction table for the first chip 530A, the radius r1 of the first chip 530A and the correction table S1 are stored in the correction table storage unit 621 (Fig. 6). At the same time, the environmental temperature Tr during the calibration operation is also stored in the correction table storage unit 621 as the reference temperature during calibration.

[0046] (Modeling of probe offset) ​If the probe unit 500 is modified and the workpiece is to be measured, these modifications also require calibration. That is, calibration work is also performed on the probe unit 500 in which the first rotation mechanism section 510 and the second rotation mechanism section 520 of the probe unit 500 are driven to lift (or swing) the stylus (530, 550) by a predetermined angle or the probe unit 500 in which the stylus is replaced with a deformed stylus (550). For the sake of explanation of the embodiment, the measurement tip in the modified form will be referred to as the second tip 550A. As illustrated in FIG. 7, the reference stylus 530 is replaced with the bent stylus 550, and further, when the first rotation mechanism section 510 and the second rotation mechanism section 520 are driven to lift and rotationally swing the stylus 550 by a predetermined angle, the measurement tip is defined as the second tip 550A.

[0047] In the present embodiment, as calibration data (correction table) for the second tip 550A, an offset value from the center of the first tip 530A to the center of the second tip 550A is obtained (FIG. 11). The offset value from the center of the first tip 530A to the center of the second tip 550A is defined as the probe offset value S 12 and will be so referred to.

[0048] By modeling the components of the probe unit 500, the probe offset value is expressed as follows. First, as illustrated in FIG. 8, it is assumed that the reference stylus 530 is replaced with the bent stylus 550. Here, as the bent stylus 550, an L-shaped stylus bent at 90° is illustrated, but the bending angle is not limited to 90°.

[0049] As shape parameters of the bent stylus 550, the portion from the rotation center Q to the bending point 551 is defined as the body axis 552, and the length of the body axis 552 is represented by L2. Also, the portion from the bending point 551 to the tip center is defined as the leg axis 553, and the length of the leg axis 553 is represented by L3.

[0050] Furthermore, the orientation of the leg axis 553 and the amount of bending are expressed by angular parameters. To represent the bending of the leg axis 553 of the bending stylus 550, an auxiliary coordinate system is introduced. The auxiliary coordinate system is shown in FIG. 9. Here, as the auxiliary coordinate system, a coordinate system composed of the I-axis, J-axis, and K-axis is introduced as a right-handed orthogonal coordinate system. With the rotations of the first and second rotation mechanism parts 520 of the probe head main body part 501 set to zero, the origin of the auxiliary coordinate system is at the bending point 551 of the bending stylus 550, the K-axis is parallel to the body axis 552 of the bending stylus 550, and the I-axis is parallel to the second rotation axis A2.

[0051] In this state, let the angle formed by the leg axis 553 and the K-axis (negative direction) be β1. Next, let the angle formed by the leg axis 553 and the KJ plane be β2. (The negative direction of the J-axis is set to 0 degrees, the positive direction of the J-axis is set to 180 degrees, and the right-handed rotation around the K-axis is defined as positive.)

[0052] It can also be rephrased as follows. First, rotate the measurement tip of the straight stylus parallel to the K-axis by β1 around the I-axis. Subsequently, rotate the measurement tip by β2 around the K-axis. Then, the measurement tip (530A) of the reference stylus 530 overlaps (or is in the same direction as) the measurement tip (550A) of the bending stylus 550.

[0053] Note that the chuck part for attaching the stylus (530, 550) to the probe head main body part 501 has a fitting such as a key and key groove, a protrusion and notch, or a partial flat surface that uniquely determines the attachment orientation of the stylus (530, 550). It is assumed that the bending direction and amount of the leg axis 553 of the bending stylus 550 are uniquely represented in the machine coordinate system.

[0054] For example, when the bending stylus 550 is an L-shaped stylus bent at 90°, and the length of the leg axis 553 is 1, the relationship between the bending direction of the L-shaped stylus and the angles β1 and β2 is shown in a table as in FIG. 10.

[0055] Then, as illustrated in FIG. 7, the first and second rotation mechanism parts 520 are rotated by the required angle, and the measurement chip (530A) is lifted and swung to the position to be calibrated. The rotation angles of the first and second rotation mechanism parts 520 in the modification to be calibrated are set as the reference angle (reference angle) α 1r , α 2r . The measurement chip of the probe unit 500 in this state is the second chip 550A.

[0056] Now, using the parameters introduced so far, the offset (probe offset) S 12 from the center of the first chip 530A to the center of the second chip 550A is expressed by the following formula.

[0057] S 12 =(S 12X , S 12Y , S 12Z ) Each element of the probe offset is expressed by the following formula.

[0058] S 12X =-L3·Cos(α 1r )·Sin(β1)·Sin(β2)-Sin(α 1r ){L3·Cos(-α 2r )·Sin(β1)·Cos(β2)+Sin(-α 2r )(L3·cos(β1)+L2)}

[0059] S 12Y =-L3·Sin(α 1r )·Sin(β1)·Sin(β2)+Cos(α 1r ){L3·Cos(-α 2r )·Sin(β1)·Cos(β2)+Sin(-α 2r )(L3·Cos(β1)+L2)}

[0060] S 12Z = L3·Sin(α 1r )·Sin(β1)·Cos(β2) - Cos(-α 2r )(L3·Cos(β1)+L2)+L1

[0061] Among these, the angular values α 1r , α 2r , β1, and β2 are known values. That is, α 1r , α 2r are the rotation angles of the first and second rotation mechanism parts 520 of the probe head main body 501, and the values obtained by a sensor (for example, a rotary encoder) are trusted. (Alternatively, it is assumed that the first and second rotation mechanism parts 520 of the probe head main body 501 have been calibrated separately.) β1 and β2 are the specifications of the (bent) stylus. Note that the angles are trusted because it is considered that the angles are not affected by temperature.

[0062] On the other hand, L1, L2, and L3 are obtained from calibration data. L1 is obtained from the calibration value of the first chip 530A. Regarding L2 and L3, they will be described later.

[0063] The model formula of the probe offset S 12 is stored in the temperature correction unit 640.

[0064] (Calibration of the modified form (second chip 550A)) Now, measure the master gauge 211 with the second chip 550A to obtain calibration data (correction table) for the second chip.

[0065] The correction table S2 (S 2X , S 2Y , S 2Z ) for obtaining the center point of the second chip 550A is obtained by calibrating the second chip 550A. Now, the center point coordinate value of the second chip 550A considering calibration is P 2c (P 2cX, P 2cY , P 2cZ ) is represented by Also, let the reading value of the machine scale be M (M X , M Y , M Z ) is represented by The reading value of the machine scale here includes the reading value of the encoder of the three-dimensional measuring machine 200 and the reading value of the sensor of the probe unit 500, and the reading value of the machine scale is assumed to indicate the coordinates of the rotation center Q of the probe unit 500. The center point coordinate value P of the second chip 550A taking calibration into account 2c is represented as follows by the correction table S2. This relationship is illustrated in FIG. 11.

[0066] P 2c (P 2cX , P 2cY , P 2cZ ) = M(M X , M Y , M Z ) + S2(S 2X , S 2Y , S 2Z )

[0067] Therefore, the offset (probe offset) S from the center of the first chip 530A to the center of the second chip 550A 12 is obtained as the difference between the correction table S2(S 2X , S 2Y , S 2Z ) for obtaining the center point of the second chip 550A and the correction table S1(S 1X , S 1Y , S 1Z ) for obtaining the center point of the first chip 530A. That is, the value of the probe offset S 12 is as follows.

[0068] S 12 (S 12X , S 12Y , S 12Z ) = S2(S 2X , S 2Y , S 2Z ) - S1(S1X , S 1Y , S 1Z )

[0069] First, the probe offset S 12 was obtained in advance as a model. Therefore, substituting S 12 (S 12X , S 12Y , S 12Z ) into the previous model equation and solving the simultaneous equations, the calibration values of L2 and L3 can be obtained. In the correction table storage unit 621, as the correction table for the second chip 550A, L2, L3, and the probe offset S 12 at the time of calibration are stored. (As described above, the temperature at the time of calibration is also stored in the correction table storage unit 621.)

[0070] When there is no temperature correction as described later, when measuring the measurement target (workpiece) with the second chip 550A, in obtaining the center point of the second chip 550A, the shape analysis unit 630 takes into account the probe offset S 12 from the center point of the first chip 530A.

[0071] P 2c (P 2cX , P 2cY , P 2cZ ) = P 1c (P 1cX , P 1cY , P 1cZ ) + S 12 (S 12X , S 12Y , S 12Z )

[0072] Note that the center point P 1c of the first chip 530A is obtained from the machine reading M and the correction table S1 as described above.

[0073] Furthermore, by taking into account the approach direction and the chip diameter, the position of the surface of the measurement object can be obtained. Since this itself is well-known, it will be omitted.

[0074] (Temperature correction) If the temperature of the measurement environment is stable and the same during the calibration operation and the actual workpiece measurement, there is no drift in the measurement value due to the environmental temperature change. However, if the temperature of the measurement environment fluctuates, temperature drift occurs. In this embodiment, it is aimed to correct the linear expansion of the probe (stylus), which has not been conventionally dealt with, by the temperature correction unit 640. For example, as illustrated in FIG. 13, assuming that the body axis 552 and the leg axis 553 of the bent stylus 550 each extend as the environmental temperature rises, the position of the measurement tip (second tip 550A) will shift accordingly. At this time, when trying to obtain the position of the second tip 550A taking into account the probe offset S 12 from the first tip 530A, since the probe offset is fluctuating, the correct center position of the second tip 550A cannot be obtained. FIG. 14 is a diagram exemplifying the fluctuation of the probe offset so that it becomes easy to understand by virtually overlapping the positions of the first tip 530A in the state before linear expansion and the state after linear expansion.

[0075] FIG. 12 is a flowchart showing the procedure of the temperature correction process. First, the temperature correction unit 640 first acquires the temperature of the measurement environment (ST110). A temperature sensor may be attached to the three-dimensional measuring machine 200, or the temperature may be obtained from a temperature sensor in the measurement room. The temperature correction unit 640 acquires the difference ΔT between the temperature at the time of calibration and the current temperature of the measurement environment as temperature data.

[0076] Subsequently, the temperature correction unit 640 performs temperature correction on the correction table S1 for the first tip. Since the first tip 530A is a tip attached to the tip of the linear reference stylus 530, the temperature correction of the correction table S1 for the first tip 530A means taking into account the expansion and contraction of the linear expansion amount of the length L1 of the reference stylus 530. Let the linear expansion coefficient be k1, and the length of the reference stylus 530 at the current temperature T be L 1T and.

[0077] L 1T = L1 + ΔL1 = L1(1 + k1ΔT) S 1T (S 1TX 、S 1TY 、S 1TZ ) = S 1T (0, 0, L 1T )

[0078] The temperature correction unit 640 stores the corrected table S for the first chip in the correction table storage unit 621 in combination with the temperature data at the time of correction. 1T

[0079] Furthermore, the temperature correction unit 640 corrects the temperature of the probe offset S. 12 The probe offset S 12 is modeled, so by taking into account the linear expansion of L1, L2, and L3, the temperature-corrected probe offset S 12T is obtained.

[0080] Let the linear expansion coefficient of the bending stylus 550 be k2, and let the lengths of the body axis 552 and the leg axis 553 at the current temperature T be L 2T 、L 3T . L 2T = L2 + ΔL2 = L2(1 + k2ΔT) L 3T = L3 + ΔL3 = L3(1 + k2ΔT)

[0081] The offset table S after temperature correction 12T is obtained by substituting the temperature-corrected L 1T 、L 2T 、L 3T into the model.

[0082] The offset table S after temperature correction 12T =(S 12TX 、S 12TY 、S 12TZ )

[0083] S 12TX = -L3T ·Cos(α 1r )·Sin(β1)·Sin(β2)-Sin(α 1r ){L 3T ·Cos(-α 2r )·Sin(β1)·Cos(β2)+Sin(-α 2r )(L 3T ·cos(β1)+L 2T )}

[0084] S 12TY =-L 3T ·Sin(α 1r )·Sin(β1)·Sin(β2)+Cos(α 1r ){L 3T ·Cos(-α 2r )·Sin(β1)·Cos(β2)+Sin(-α 2r )(L 3T ·Cos(β1)+L 2T )}

[0085] S 12TZ =L 3T ·Sin(α 1r )·Sin(β1)·Cos(β2)-Cos(-α 2r )(L 3T ·Cos(β1)+L 2T )+L 1T

[0086] The temperature correction unit 640 stores the offset table S after temperature correction in the correction table storage unit 621 in combination with the temperature data at the time of correction. 12T (Calculation of corrected measurement value)

[0087] (Calculation of corrected measurement value) Assume that the measured environmental temperature has changed from the temperature at the time of calibration by ΔT to the temperature T. When measuring the shape of the object to be measured (workpiece) in this temperature environment using the bending stylus 550, the shape analysis unit 630 obtains a temperature-corrected measurement value using the temperature-corrected correction table. The operation of obtaining the measurement value is executed by the shape analysis unit 630 as follows. The machine reading M (M X , M Y , MZ ) By taking into account the correction table S for the first chip 1T , the center coordinates of the temperature-corrected first chip 530A can be (virtually) obtained. Then, by taking into account the offset table S after temperature correction for the center coordinates of the first chip 530A 12T , the center coordinates of the temperature-corrected second chip 550A in the modified form to be calibrated can be (virtually) obtained (see Fig. 13). Furthermore, as for the sampling of the measured values, since there are the rotation angles α1 and α2 of the first and second rotation mechanism parts 520, the reference angle α 1r , α 2r , the center of the current measurement chip is at the position rotated by the rotation amounts (α1 - α 1r ) and (α2 - α 2r ) from it. Furthermore, the surface of the workpiece (object to be measured) is at a position taking into account the approach direction and the chip diameter.

[0088] Note that, so far, it is the correction of the linear expansion of the probe unit 500. However, hereafter, further taking into account (subtracting) the linear expansion of the scale of the encoder, for example, the measured values corrected to the temperature at the time of calibration or the specified regulated temperature (such as 20 degrees or 25 degrees) may be obtained.

[0089] According to the present embodiment described above, it is possible to correct the linear expansion of the probe (stylus) that has not been dealt with conventionally and obtain accurate measured values. Also, even if there is a temperature change in the measurement environment, accurate measured values can be obtained by the temperature correction of the probe unit 500 of the present embodiment. Therefore, it is not necessary to frequently calibrate all the probes (styli) and all the modified forms, and the number of calibrations can be considerably reduced. Also, even if calibration work is to be performed, the number of calibrations for all the probes and all the modified forms can be reduced. As for the regular calibration, only the calibration of the reference stylus 530 may be performed, and the calibration of the others (such as the second chip) may be performed as needed as appropriate.

[0090] Note that the present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the gist thereof. In the above embodiment, the biaxial probe unit 500 has been exemplified, but the probe unit 500 itself does not necessarily require a rotational drive shaft. The present invention is considered to be widely applicable to cases where measurement is performed using a measurement tip having an offset from the first tip 530A of the reference stylus 530.

Explanation of Reference Numerals

[0091] 100 Shape measurement system 200 Three-dimensional measuring machine 210 Surface plate 211 Master gauge 220 Moving mechanism 221 Y slider 222 X slider 223 Z-axis column 224 Z spindle 300 Motion controller 310 Measurement command acquisition unit 330 Counter unit 340 Drive command generation unit 350 Drive control unit 500 Probe unit 501 Probe head main body 502 Probe fixing part 510 First rotation mechanism part 511 First housing 512 First motor 513 First shaft 520 Second rotation mechanism part 521 Second housing 522 Second motor 523 Second shaft 524 U-shaped connecting frame 530 Reference stylus 530A Measurement tip (first tip) 550 Bent stylus 550 Stylus 550A Measurement Chip (Second Chip) 551 Buckling Point 552 Trunk Axis 553 Leg Axis 600 Host Computer 611 CPU 620 Storage Unit 621 Correction Table Storage Section 630 Shape Analysis Section 640 Temperature Correction Section.

Claims

【Claim 1】 A method for correcting a probe unit that detects the surface of an object to be measured by a measurement tip at the tip, wherein the probe unit, a first chip which is a measurement chip in a standard form set as an initial standard specification, a second chip which is a measurement chip in a modified form changed from the standard form, and can be switched and used, when calibrating the probe unit, by calibrating the first chip and the second chip respectively, the coordinate value of the first chip is obtained as a reference chip coordinate value and the offset from the first chip to the second chip is obtained as a probe offset value, the measured value when the second chip is used is obtained by taking into account the probe offset value in the reference chip coordinate value, the correction method of the probe unit, a temperature data acquisition step of acquiring a temperature difference between the temperature at the time of calibration and the current temperature of the measurement environment, a reference chip coordinate correction step of calculating a correction value of the reference chip coordinate value taking into account the linear expansion when the probe unit is in the standard form as a reference chip correction coordinate value, a probe offset correction step of calculating a correction value of the probe offset value taking into account the linear expansion when the probe unit is in the standard form and the linear expansion when the probe unit is in the modified form as a probe offset correction value, and a measurement value calculation step of obtaining a corrected measurement value when the second chip is used in the current measurement environment by adding the probe offset correction value to the reference chip correction coordinate value. A method for correcting a probe unit, characterized in that.

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