JP5460427B2 - Measuring method and shape measuring device - Google Patents

Description

  The present invention relates to a precision measurement technique for obtaining a shape by scanning a sensor relative to a surface to be measured.

  Along with the increasing demands for improving the machining accuracy of large workpieces, there is also a need to improve the measurement accuracy of the machine tool straightness and the straight shape of the machined surface. A straight ruler is used as a reference for measuring the straightness of the machine. In measuring the shape of a workpiece, the machine's high-precision movement straightness is used as a reference. When the accuracy of these standards is insufficient, an inversion method or a multipoint method is used. The inversion method is disclosed in Non-Patent Document 1, and the multipoint method is disclosed in Patent Document 1.

Oswald Horikawa, Kaji Sato, Akira Shimokawabe, "Evaluation of roundness and absolute rotational motion accuracy by improved inversion method", Journal of Precision, 57-12 (1991) 2231-2236

JP 2007-178296 A

  By the way, there is a commercially available round shape measuring machine with high-precision rotational motion performance, but there is a limit to the size of the sample that can be mounted on the measuring machine, and the workpiece can be removed from the machine tool until the measuring machine. In many cases, it is difficult to carry.

  In particular, in the inversion method, it is necessary to invert both the sample to be measured and the sensor by 180 degrees, and the applicable range is limited. On the other hand, the three-point method requires at least three sensors, which causes difficulties in improving the environment for ensuring the stability of the sensor from the problem of sensor price.

  There is also a repetitive scanning type three-point method in which scanning measurement is repeated by sequentially rotating and shifting the sensor to three rotational angle positions instead of three sensors. In this case, there is a problem that the tolerance for the drift of the sensor becomes more severe.

  In view of the problems involved, the present invention proposes a new measurement principle that realizes high measurement accuracy by a repetitive scanning two-point method using only one sensor, and can be a measurement method and a portable type according to the principle. An object of the present invention is to provide a rotary scanning type shape measuring apparatus.

The measuring method of the present invention is a measuring method for measuring the shape of an object to be measured using a displacement sensor.
A first measurement step of measuring one of the measurement object and the displacement sensor while scanning the shape of the measurement object by rotating the other and fixing the other;
A shift step of shifting the object to be measured and the displacement sensor in a scanning direction by a desired angle around the rotation center while maintaining a relative positional relationship between the rotation center and the displacement sensor;
A second measuring step of measuring the shape of the object to be measured while scanning by fixing the one and rotating the other;
And a step of eliminating a motion error based on the measurement result of the first measurement step and the measurement result of the measurement step of the second measurement step.

  In the present invention, only one displacement sensor is used as in the reversal method, and instead of reversing both the object to be measured and the displacement sensor (180 degree rotation shift), only one of the rotational movement side is at most 30. It is possible to realize shape measurement by the sequential two-point method only by rotationally shifting by about 0 °.

  Further, in the present invention, the measurement target can be measured by mounting the measurement device on the measurement target or installing it in the vicinity of the measurement target, instead of mounting the measurement target on the measuring machine. The principle of the present invention will be described below with reference to the drawings.

  FIG. 1 (a) is a diagram for explaining a two-point method using two displacement sensors according to the prior art, and FIG. 1 (b) shows a method of shifting one displacement sensor according to the prior art. FIG. 2 is a diagram for explaining the present invention in which a displacement sensor is rotationally shifted and two rotational scanning measurements before and after the rotational shift are performed. 1 and 2, a disk-shaped object OB to be measured is placed on a table TB that can rotate around the rotation center O, and a displacement sensor S1 (S2) indicated by an arrow is arranged on the outer periphery of the object OB to be measured. Fixed with the sensitivity axis facing the surface. The displacement sensor is not particularly limited as long as it can measure the shape of the measurement target that intersects the sensitivity axis. In addition, in order to show relative rotation with table TB and to-be-measured object OB, the mark MK is attached | subjected to each.

In FIG. 1, the shape of the object to be measured at the position of the angle θ is f (θ), the motion error in the x direction at the position of the angle θ is ex (θ), and the motion error in the y direction at the position of the angle θ is ey ( θ). Here, in the conventional two-point method, two sensors S1 and S2 (see FIG. 1 (a)) arranged apart by an angle φ in the scanning direction, or separated by an angle φ in the scanning direction before and after the measurement. The outputs m1 (θ) and m2 (θ) of the sensor S1 arranged at the two positions have the following relationship.
m1 (θ) = f (θ) + ex (θ) (1)
m2 (θ) = f (θ + φ) + ex (θ) cos (φ) + ey (θ) sin (φ) (2)

Here, ex (θ) is deleted from the equations (1) and (2).
m2 (θ) / cos (φ) −m1 (θ) = f (θ + φ) −f (θ) + ey (θ) tan (φ) (3)
Thus, the effect of ey (θ) remains. That is, with the conventional two-point method, the component of the shake in the radial direction of the rotating shaft is included in the sensor output, so it can be said that it is difficult to measure with high accuracy.

On the other hand, in the measurement method of the present invention shown in FIG. 2, the object to be measured OB can be rotationally shifted around the rotation center O of the table TB by a rotation guide (not shown). Here, as shown in FIG. 2A, the shape of the measurement target OB fixed on the table TB is measured while rotating the table TB using one fixed displacement sensor S1. (4) Equation (first measurement step) is obtained. Next, as shown in FIG. 2B, the object to be measured OB is relatively rotated by the angle φ in the measurement direction (scanning direction) around the rotation center O of the table TB (shift step). In this state, the relative positional relationship between the rotation center O and the displacement sensor S1 is maintained. While maintaining this relationship, the same displacement sensor S1 is used to measure the shape of the object OB to be measured while rotating the table TB to obtain equation (5) (second measurement step).
m1 (θ) = f (θ) + ex (θ) (4)
m2 (θ) = f (θ + φ) + ex (θ) (5)

According to the present invention, since a rotational shift is given to the object OB to be measured, the motion error included in the sensor output is only the component in the same direction in two scans. Accordingly, as with the inversion method, if the motion error is repeatable, the sensitivity axis of the displacement sensor is obtained from the difference between the two measured values before and after the rotation shift (equations (4) and (5)) as shown in equation (6). By removing the motion error ex (θ) in the direction, a correct shape difference can be obtained.
m2 (θ) −m1 (θ) = f (θ + φ) −f (θ) (6)

  When this is sequentially added, the shape required for the measurement target OB is obtained. In FIG. 2, the measurement target OB is rotationally shifted as the structure in which the measurement target OB rotates around the rotation center of the table TB. However, in the case of the structure in which the displacement sensor rotates for scanning, The entire displacement detector including the displacement sensor may be rotationally shifted. What is important is that the same direction component of the radial motion error inherent to the rotation axis is detected by the displacement sensor before and after the rotation shift.

  In FIGS. 1 and 2, the object OB to be measured has a disk shape, but the object to be measured can be measured by rotational scanning regardless of whether it is an arc or hemisphere. Needless to say, it is not necessary to have a 360 degree circumference. Further, the present invention can also be applied to the case where plane unevenness such as a disk surface is scanned along a circle.

  The shape measuring apparatus of the present invention includes a rotation guide, a sensor holder that rotates around the rotation guide while maintaining a sensitivity axis of the displacement sensor in a direction perpendicular to a scanning circle, and the rotation guide and the sensor holder. It is preferable to have a shift mechanism that integrally rotates in a direction along the scanning circle.

  The shape measuring apparatus of the present invention can move at least the sensor holder (or the entire shape measuring apparatus) to relatively move the displacement sensor in a direction perpendicular to the axis of the rotational scanning circle, and the posture before and after the movement. Preferably, the change can be measured by an inclination posture detection device (for example, a level or an autocollimator) to correct the posture change accompanying the movement. In order to rotationally shift the displacement sensor and the measurement target, a structure in which the measurement target is installed via a rotatable table is also effective.

  In the shape measuring apparatus of the present invention, it is preferable that a plurality of displacement sensors are arranged so that displacement can be detected along concentric circles, and the shapes of a plurality of positions can be measured by one scan. A form in which the relative heights of the zero points of the plurality of displacement sensors are calibrated in advance and the obtained shapes along the plurality of concentric circles are associated with each other is also preferable. In the form of disk surface measurement, a structure in which a displacement sensor is also arranged at the center of the scanning circle to detect and remove a repetitive error in the axial movement of the rotating shaft during rotational scanning is preferable. A structure in which a plurality of displacement sensors are integrally held and an interpolation value related to a shape within the displacement sensor interval can be obtained by moving along the rotating arm is also preferable. At this time, it is also preferable to detect and correct a change in posture during movement with a level or an autocollimator.

  According to the present invention, only one displacement sensor is required, and a correct shape from which the rotational scanning error is removed can be measured within the range of repeatability of the scanning motion error.

  According to the present invention, it is possible to realize a shape measurement with high accuracy similar to the inversion method by performing a rotation shift without moving a large object to be measured from the machine tool.

  According to the present invention, it is possible to measure not only a perfect circular shape but also a circular arc shape or an aspherical shape with a partial rotational shift.

  According to the present invention, since the measurement accuracy can be maintained if the stability of a single displacement sensor is taken into consideration, it is not necessary to consider a subtle difference in characteristics between displacement sensors as in the multipoint method.

  According to the present invention, even for a large object to be measured that is difficult to reverse, a motion error can be removed by the rotational shift of the displacement detector.

  The displacement sensor or table has a built-in encoder, measures the relative rotation angle between the object to be measured and the displacement sensor, and outputs the average value of the displacement sensor reading at the scanning interval according to the given command. Is also preferable.

  It is also preferable that an index (mark MK) or the like that can be used to confirm the desired rotational shift amount is provided on the measurement target or the table (or the displacement sensor side).

  A structure for correcting a movement error caused by a posture with respect to gravity is also preferable.

  It is also preferable to employ a displacement detection unit that controls the displacement sensor in the sensitivity axis direction so as to keep the output of the displacement sensor constant while performing rotational scanning.

(A) is a figure for demonstrating the two-point method using two displacement sensors by a prior art, and FIG.1 (b) demonstrates the method of shifting one displacement sensor by a prior art. FIG. It is a figure for demonstrating this invention which rotationally shifts a displacement sensor and performs two rotational scanning measurement before and behind a rotation shift. It is a perspective view which shows the measuring apparatus concerning 1st Embodiment. It is a perspective view which shows the measuring apparatus concerning 2nd Embodiment. It is a perspective view which shows the measuring apparatus concerning 3rd Embodiment. It is a figure which shows the state which correct | amends a measurement result from the reading of a spirit level.

  Hereinafter, a measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a perspective view showing the shape measuring apparatus according to the first embodiment. In FIG. 3 (a), the shape measuring device for measuring the outer peripheral shape of the disk-shaped object OB to be measured is installed in the detection unit holding base BS installed in the measurement target OB and the detection unit holding base BS. A rotation guide (shaft) RG, a cylindrical scanning rotation portion SR that is fitted to the rotation guide RG and relatively rotates about the rotation axis X, and a sensor holder SH that extends in a bowl shape from the scanning rotation portion SR; A displacement sensor S1 attached to the end of the sensor holder SH and having a sensitivity axis directed toward the measurement target OB. The detection unit holding base BS is a shift mechanism that integrally rotates the rotation guide RG and the sensor holder SH, and rotates and shifts relative to the measurement target OB in the direction along the scanning circle. A rotation shift position display mark MK is formed on the measurement target OB, the detection unit holding base BS, and the scanning rotation unit SR.

  A measuring method using the shape measuring apparatus will be described. First, in the state of FIG. 3A, when the scanning rotation unit SR is relatively rotated around the rotation guide RG, the sensor S1 simultaneously rotates around the measurement target OB and detects the unevenness on the outer periphery. Therefore, the output of the displacement sensor S1 is output in synchronization with a signal of an encoder (not shown) (detecting the relative rotation angle of the scanning rotation unit SR). By obtaining the output, the measurement result of equation (4) can be obtained.

  Next, when the object to be measured OB and the detection unit holding base BS are rotationally displaced (shifted) by a predetermined angle in the scanning direction without changing the crossing position of the rotation axis X, the state shown in FIG. . Thereafter, when the scanning rotation unit SR is relatively rotated around the rotation guide RG, the sensor S1 rotates around the object to be measured OB and acquires the output thereof, whereby the measurement result of the equation (5) is obtained. can get. From equations (4) and (5), equation (6) is obtained, and a difference for obtaining only the shape of the object OB to be measured is obtained. Note that the eccentric state between the object to be measured OB and the rotation guide RG changes before and after the rotation shift, but the influence of the eccentricity is excluded from the perfect circle shape as a component that coincides with the rotation period.

  FIG. 4 is a perspective view showing a shape measuring apparatus according to the second embodiment. The present embodiment is different from the sensor holder SH only in that the sensitivity axis is provided in parallel with the rotation guide RG so that the displacement sensor S1 measures the shape of the upper surface of the measurement target OB. The measuring method is the same as that of the shape measuring apparatus shown in FIG. If the arm length of the sensor holder SH is variable so that the radius from the rotation axis X to the sensitivity axis of the sensor S1 can be arbitrarily changed, the upper surface of the object OB to be measured can be used as long as it does not interfere with the detection unit holding base BS. The shape can be measured.

  FIG. 5 (a) shows a perspective view of a shape measuring apparatus using a spirit level for posture detection. This shape measuring apparatus is an example in which two displacement sensors S1, S2 having different rotation radii (r1, r2) are attached to a sensor holder SH and simultaneously scanned for rotation, and shape measurement is performed at different positions on concentric circles. More specifically, the pair of leg portions of the gate-shaped detection unit holding base BS is slidably mounted on the measurement surface of the measurement target OB. In the center of the horizontal beam portion of the detection unit holding base BS, a level LV that is an inclination posture detection device and a rotation guide RG are fixedly arranged, and the rotation guide RG rotatably supports the scanning rotation shaft SR. The center of a horizontal bar-shaped sensor holder SH is attached to the lower end of the scanning rotating shaft SR. Displacement sensors S1 and S2 are attached to the sensor holder SH with different radii of rotation (r1, r2) so as to face the surface to be measured. As described above, by rotating the scanning rotation axis SR, different positions on the concentric circles on the surface to be measured can be measured.

  FIG. 5 (b) shows whether the detection unit holding base BS moves by d for each sensor holder SH on the surface to be measured OB (along the direction orthogonal to the axis of the rotational scanning circle). An example in which the shape is measured by the above-described method by performing rotational scanning at a point will be described. The points where the scanning circles at the two points overlap are points on the same measurement plane, so the height can be matched, but the rotation around the intersection axis c connecting the intersections cannot be constrained, so the shape is not fixed. Therefore, it is necessary to correct the inclination of the detector holding base BS before and after the detector holding base BS is moved by d. For this purpose, the reading of the level LV is used in this embodiment. By detecting the level LV, it is possible to detect the posture of the detection unit holding base BS, and it is possible to perform accurate shape measurement by correcting the posture change. Needless to say, a combination of an autocollimator and a reflecting mirror may be used instead of the level LV. Although only two displacement sensors are shown, the density of concentric circles may be increased by using more sensors, or the rotation radius of the displacement sensor is changed by shifting the sensor holder in the radial direction. Thus, the structure may be such that the rotational scanning is repeated. Further, in FIG. 5 (a), the detection unit holding base BS is placed on the surface to be measured, but it may be structured so as to straddle the object to be measured OB in FIG. 5 (a).

  The role of the level of the present invention will be described with reference to FIG. In the embodiment of FIG. 5, when the rotational scanning measuring device is moved and rotationally scanned, the scanning reference circle CL2 after the movement is different from the scanning reference circle CL1 before the movement due to the inclination of the rotation axis accompanying the movement in FIG. It tilts like a). Here, the inclination (rolling) around the movement axis can be corrected by making the heights of the intersections of the scanning circles before and after the movement equal, assuming that the heights at the same point on the surface to be measured are the same. However, since the inclination in the moving direction (pitching θp) occurs around a straight line connecting the crossing points, it cannot be corrected by just aligning the heights. Therefore, it is necessary to correct this inclination by an external reference. If the inclination of the entire apparatus before and after the movement is measured with a level LV as in the present invention, the difference is determined by the scanning reference circle CL1. Since this corresponds to the inclination θp of CL2, the correct shape can be obtained by correcting this inclination as shown in FIG. 6 (b).

  Although not shown in the figure, in the shape measuring apparatus for measuring the outer circumference of the cylinder as shown in FIG. 3, a plurality of displacement sensors are arranged in the cylinder axis direction, or a plurality of sensor holders are moved in the cylinder axis direction. A form that obtains a perfect circle shape in a cross section perpendicular to the axis is also preferable.

BS Detection unit holding base MK Rotation shift position display mark OB Object to be measured RG Rotation guide S1 Displacement sensor SH Sensor holder SR Scanning rotation unit X Rotation axis

Claims (3)

In a measurement method for measuring the shape of a measurement object using a displacement sensor,
A first measurement step of measuring one of the measurement object and the displacement sensor while scanning the shape of the measurement object by rotating the other and fixing the other;
A shift step of shifting the object to be measured and the displacement sensor in a scanning direction by a desired angle around the rotation center while maintaining a relative positional relationship between the rotation center and the displacement sensor;
A second measuring step of measuring the shape of the object to be measured while scanning by fixing the one and rotating the other;
A measurement method comprising the step of eliminating a motion error based on a measurement result of the first measurement step and a measurement result of the measurement step of the second measurement step. A shape measuring device using the measuring method according to claim 1,
A rotation guide,
A sensor holder that rotates around the rotation guide while maintaining a sensitivity axis of the displacement sensor in a direction perpendicular to a scanning circle;
A shape measuring apparatus comprising: a shift mechanism that integrally rotates the rotation guide and the sensor holder and that shifts in a direction along a scanning circle.   By moving at least the sensor holder, the displacement sensor can be relatively moved in a direction perpendicular to the axis of the rotational scanning circle, and a change in posture before and after the movement is measured by an inclination posture detecting device, and accompanying the movement 3. The shape measuring apparatus according to claim 2, wherein the posture change can be corrected.