JP5601699B2 - Calibration device - Google Patents

Description

  The present invention relates to a zero point calibration technique of a two-point angle method probe for measuring a straight shape and a straight movement posture error.

  In order to accurately measure the shape of the object to be measured using the two-point angle probe using two angle sensors, it is necessary to remove the parabolic error caused by the zero point deviation (zero point error) of the two angle sensors. Therefore, it is necessary to calibrate the zero point error. Also, in measuring the posture error of movement, if there is a zero point error, it cannot be distinguished from a uniform change in posture, so here also the zero point calibration is required. Here, as a method for calibrating the zero point error, a method based on a known angle change along the straight line (hereinafter referred to as an angle shape), a measurement by the angle two-point method and a measurement by the improved inversion method are used in combination. A method for obtaining a zero point error, an angle width obtained by measuring two straight lines constituting the angle width by inverting the angle two-point method probe with reference to the angle width of a known angle shape There is a method of obtaining a change shape in the longitudinal direction and determining a zero point in comparison with a known angular width. These use the standard of the angle shape and angle width of a straight line obtained by another method.

  By using the above-mentioned known angular width reference, a dummy surface is placed opposite to the surface to be measured and the angular width is measured on the spot, and the probe is inverted to form the angular width by the angle two-point method. There is also a method of measuring the straight bus bars on both sides, which can be said to be a near real-time zero adjustment method.

  In addition, using a spirit level, the difference in inclination at both ends of the scanning motion trajectory is measured, and compared with the difference in inclination at both ends of the scanning motion trajectory obtained by the angle two-point method, a zero point is calculated. Methods are also known. A method of measuring the difference in inclination at both ends of the trajectory of the scanning motion by using an autocollimator and a reflecting mirror instead of the level is also established.

Kiyoo Satoshi, “Zero point error correction method of 3 point method and angle 2 point method”, Preprint of Precision Engineering Society Hokkaido Branch Lecture Meeting (September 2006, Sapporo) Satoshi Seino and Eiki Okuyama, "Advanced precision measurement using angle sensors", Precision Engineering Society Proceedings (March 2007, Tokyo)

  Here, in the method of calibrating the zero point error using a known reference, there is a problem of a change in the zero point until the probe is moved to the place where the measurement target is measured after the calibration and the actual measurement is performed. Even in the method of inverting the probe based on the angle width, it is difficult to determine an accurate zero point due to the influence of the zero point change during the measurement by the two-point angle method before and after the inversion.

  Further, for the purpose of measuring the rolling motion by the two-point angle method, it is extremely troublesome to obtain a reference mirror having a known rolling angle shape.

  On the other hand, the method of correcting the inclinations at both ends of the scanning motion locus is a highly accurate method if the environment is prepared. Also, in an environment where a level can be used, the zero point of a two-point probe for rolling measurement can be calibrated. However, with a spirit level, mechanical disturbance vibration that can be removed with the two-point angle probe becomes a measurement error, and with an autocollimator, air fluctuations cause an error. Is necessary for zero point detection.

  The present invention has been made in view of such problems of the conventional method. The zero point calibration of the angle two-point method probe can be performed quickly, accurately and easily while maintaining robustness with respect to the environment of the angle two-point method. This is made for the purpose of providing a calibration device and a straight shape measuring device that can be realized. It also has the purpose of contributing to the calibration of two-dimensional angle and two-point probes that measure rolling as well as pitching and yawing.

The calibration apparatus of the present invention is
A base holding two angle sensors to be calibrated;
Two or more polygonal mirrors in which two axial tilt angle widths (axial parallelism) sandwiching the center are calibrated at one or more predetermined rotational angle positions;
A rotating shaft that is rotatably supported with respect to the base and has the polygon mirror attached at a desired interval;
Two angle sensors to be calibrated are fixed relative to the polygonal mirror, and the tilt angles in the axial direction of the two or more polygonal mirrors are measured using the angle sensors at the predetermined rotation angle position. The first measurement value is obtained, and the axial tilt angles of the two or more polygon mirrors are measured by using each angle sensor at the rotation angle position rotated 180 degrees from the predetermined rotation angle position. The second measurement value is obtained, and the zero point of the angle sensor can be calibrated based on the first measurement value and the second measurement value.

  The principle of measuring the sum at two opposing points of the inclination angle in the axial direction of the polygonal mirror surface necessary for the apparatus of the present invention will be described. As in the example of FIG. 1, in the polygonal mirror CP whose outer peripheral surface is a mirror surface, the sum of the inclination angles in the axial direction of the two surfaces facing each other across the center can be defined as the parallelism in the axial direction.

  In FIG. 2, three angle sensors A and B are used to indicate two axial tilt angles sandwiching the center of the polygonal mirrors CP1 and CP2 that are coaxially mounted in parallel with the rotation shaft SH that is rotatably supported. Shows the state to be measured. Here, a hexagonal mirror having six polygonal mirrors CP1 and CP2 having the same rectangular shape is shown as an example, but the present invention is not limited to this. The inclination of the tangent line in the axial direction in the cross section by the plane including the center of the rotation axis SH is expressed as positive when it is inclined inward to the right as shown in FIG. The output of one angle sensor that measures the tilt of the measurement point is the sum of the axial tilt angles of the mirror surface of the polygon mirror CP1 and the rigid tilt angle α (θ) of the polygon mirror CP1. At opposite measurement points, the sign of the rigid tilt angle α (θ) is reversed. The sum of the outputs of the two angle sensors A and B at the opposing measurement points cancels out the rigid inclination angle α (θ), and even if θ changes, the two opposite points on the mirror surface of the polygonal mirror CP1. Only the change in the sum of the tilt angles appears. The zero points of the two opposing angle sensors A and B do not necessarily coincide with each other. However, if the two angle sensors A and B do not change during calibration, they are opposed to each other without being affected by the shake of the rotating rotating shaft SH. Only the change in the sum of the tilt angles in the axial direction as the shape at two points can be extracted.

  As shown by the dotted line in FIG. 2, the polygon mirrors CP1 and CP2 are moved relative to each other while the mutual relationship between the pair of angle sensors A and B is maintained, and the axial inclination angle of the other polygon mirror CP2 is measured. The difference between the polygon mirrors in the sum of the axial tilt angles at the two opposing points of the polygon mirrors CP1 and CP2 can be detected. This is exactly the same relationship as when looking at the change in the sum of the outputs of the two sensors facing two opposite points when examining the change in the diameter of the disc. FIG. 2 shows a state in which two polygon mirrors CP1 and CP2 are fixed to one rotation axis SH. However, independent polygon mirrors CP1 and CP2 before being fixed to the rotation axis SH are replaced with a rotary table. It is also possible to perform measurement by placing them on top of each other (not shown) or by replacing them one after another.

  Further, the inclination in the direction along the circumference is calibrated with respect to a zero point calibration jig to which a polygon mirror whose axial inclination angle is calibrated by the above-described means is attached. In the apparatus shown in FIG. 7, the rotation shaft SH to which the polygonal mirrors CP1 and CP2 are attached is rotatably supported by the polygonal mirror bearing SPH with respect to the base BS. In addition, a rotation angle sensor (not shown) for detecting the rotation angle position of the rotation shaft SH is fixed to the base BS, and a rolling direction angle sensor SS3 for detecting a circumferential inclination is independently fixed. The polygon mirrors CP1 and CP2 that are detection targets of the angle sensor SS3 can be switched by moving the angle sensor SS3 relative to the base BS. By detecting and correcting the rolling angle when moving the movable sensor holder MSH with the electronic level EL attached to the movable sensor holder MSH, the two polygon mirrors CP1 and CP2 at the same rotational position of the rotary shaft SH Calibration is performed by knowing the relative rotation angle from the reading of the rolling direction angle sensor SS3. It is to be noted that the same effect can be obtained by mounting a level on the base and changing the polygon mirror as the target of the angle sensor while detecting the rolling angle of the base.

  The principle of the present invention will be described. FIG. 3 is a diagram for explaining the mathematical principle of the present invention. Two polygonal mirrors CP1 and CP2 whose relative difference of the sum of the inclination angles of two points facing each other at 180 degrees are fixedly arranged on the sensor holder HL at an interval equal to the interval between the sensors SS1 and SS2 of the angle two-point probe. Thus, the sensors SS1 and SS2 face the mirror surfaces of the polygon mirrors CP1 and CP2, respectively, and can measure the tilt angle in the axial direction. In the polygon mirrors CP1 and CP2, the change in the parallelism in the axial direction is calibrated in advance at a predetermined rotational angle position. A rotation angle sensor (not shown) can measure the rotation angle position of the rotation shaft SH.

  FIG. 3A shows a state in which the rotation axis SH is at the position of the rotation angle θ = 0 degree for performing the first measurement, and the rotation axis SH is rotated to a position of the rotation angle θ = 180 degrees for performing the second measurement opposite thereto. This state is shown in FIG. 3A and 3B, the sensitivity axis directions of the probes of the angle sensors SS1 and SS2 are in a horizontal plane, and the influence of the deflection due to the gravity of the rotation axis SH does not appear in the figure.

  Hereinafter, the zero point calibration of the angle sensor will be described. Here, due to an error in attaching the polygonal mirrors CP1 and CP2 with respect to the rotation axis SH, the axis of the polygonal mirror CP2 is inclined closer to each other in FIG. 3A by an angle Δφ with respect to the axis of the polygonal mirror CP1. In 3 (b), it is assumed that they are inclined to the side away from each other by the same amount. Further, it is assumed that the zero point position of the angle sensor SS2 is inclined by the angle α with respect to the zero point position of the angle sensor SS1. At this time, the rotation angle position of the rotation shaft SH is θ, and the outputs of the two angle sensors SS1 and SS2 are μA (θ) and μB (θ), respectively.

First, in the state shown in FIG. 3A, if the differential output (first measurement value) of the angle two-point probe by the two angle sensors SS1 and SS2 is μ (0), the geometric relationship
μ (0) = μA (0) −μB (0) = Δφ + α (1)
It can be expressed. However, the inclination angle difference between the measurement surfaces of the polygon mirrors CP1 and CP2 is corrected by using a calibration value, and is omitted in the equation.

Next, in the state shown in FIG. 3B in which the rotation shaft SH has rotated 180 degrees from the state shown in FIG. 3A, the differential output of the angle two-point method probe by the two angle sensors SS1 and SS2 (second) (Measured value of) is μ (π),
μ (π) = μA (π) −μB (π) = − Δφ + α (2)
It can be expressed.

Since P0 is the average value of both, if Δφ is eliminated from the equations (1) and (2), P0 (position shift) can be obtained by the following equation.
α = {μ (0) + μ (π)} / 2 (3)

  By moving the angle sensor SS2 by the obtained α, the zero point positions of the angle sensors SS1 and SS2 on both sides can be matched. In this way, obtaining the deviation amount α and correcting the attitude deviation of the angle sensor is called zero point adjustment of the angle two-point probe.

  Next, a case where the sensitivity axes of the angle sensors SS1, SS2 are oriented in the vertical direction will be considered. In this case, the axis bends due to the influence of gravity, and this deflection causes the disc CP2 to be tilted by an angle β with respect to the disc CP1.

  First, in the state shown in FIG. 4 (a) and the state shown in FIG. 4 (b), the polygon mirrors CP1 and CP2 are rotated by 180 degrees, but unlike the inclination due to attachment, the deflection of the rotation axis S due to gravity is rotated. Since the posture is the same before and after, the influence of the deflection of the mutual inclination angles of the polygon mirrors CP1 and CP2 cannot be removed from the sum of the outputs before and after the inversion, and appears twice. The difference in the apparent zero point when the sensitivity axis of the angle sensor is in the horizontal direction versus the vertical direction indicates the influence of the deflection of the axis due to gravity, and if this is measured in advance, It can also be used for correction in zero point adjustment.

  In the above description, the principle has been explained on the condition that the mutual difference in axial parallelism between the opposing mirror surfaces of two polygonal mirrors at one angular position has been calibrated. If the mutual difference in directional parallelism is calibrated, the average value of the zero point calibration results between the angle sensors may be used as the calibration value using the calibration values of the axial parallelism at the plurality of rotational angle positions. it can. At that time, for example, instead of the sensor readings at the two rotation angle positions corresponding to the pair of mirror surfaces of the formula (3), the average value of the readings at the plurality of rotation angle positions is used. If the rotational angle positions where the mutual difference in the axial parallelism is calibrated are sufficiently large and the mutual difference in the two polygon mirrors with the average axial parallelism over one rotation is calibrated, the angle sensor For the adjustment of the zero point error, the average axial parallelism difference (the average value of the sum of the tilt angles) can also be used.

  Therefore, even if the average tilt angle obtained by the method of measuring the tilt angle of the polygon mirror with one angle sensor is used as a calibration value instead of the sum of the tilt angles of the two opposing surfaces of the polygon mirror, a similar calibration device can be used. Needless to say, it can be configured. When using any of these methods, the same rotation angle position as the inclination angle reading position at the time of correcting the inclination angle of the polygon mirror is reproduced, and the zero sensor at the same position is read by the angle sensor. This is preferable from the viewpoint of accuracy.

  According to the present invention, since only the difference in angle between the opposing mirror surfaces that does not require a special reference in measurement is used, a highly accurate and stable zero point calibration apparatus for the angle two-point probe can be configured. Further, according to the present invention, since the difference in average inclination angle of the inclination angle for one rotation of the polygon mirror by one angle sensor can be substituted for the difference in inclination angle average value formed by the opposing mirror surfaces, the angle two-point method can be simply used. A zero-point calibration device for the probe can be configured.

  According to the present invention, the movement of the zero point when the sensitivity axis of the angle sensor for detecting the tilt in the axial direction is set in the vertical direction with respect to the zero point in the horizontal plane (the deflection of the rotation axis). The influence of δ) can be corrected.

  Furthermore, in the calibration apparatus of the present invention, the rotary shaft is supported at two points, and when the deflection of the rotary shaft is caused by gravity, the polygon mirror is provided at two places where the inclination angles due to the deflection in the direction of gravity are equal. Each is attached.

  Further, as shown in FIGS. 3A to 3B, the calibration device of the present invention is configured so that the two angle sensors to be calibrated are relatively positioned with respect to the polygon mirror so that the sensitivity axis is in the horizontal direction. The circumference of the two or more polygonal mirrors is fixed at the predetermined rotation angle position by using each angle sensor to obtain a first measurement value, and 180 degrees with respect to the predetermined rotation angle position. A second measured value is obtained by measuring the axial inclination of the mirror surfaces of the two or more polygon mirrors rotated by a degree using each angle sensor, and the first measured value and the second measured value Based on the above, it is fundamental to obtain the attitude deviation of one angle sensor.

  Further, two angle sensors to be calibrated are fixed relative to the polygon mirror so that the sensitivity axis is in the vertical direction, and the two or more polygon mirrors are tilted in the axial direction at the predetermined rotation angle position. Is measured using each angle sensor to obtain a third measurement value, and the axial tilt angles of the two or more polygon mirrors rotated 180 degrees with respect to the predetermined rotation angle position are A fourth measurement value is obtained by measurement using a sensor, and the deflection of the rotating shaft is determined based on the deviation between the third measurement value, the fourth measurement value, and the tilt angle output of the one angle sensor. It is characterized in that the amount of inclination angle can be obtained. The “sensitivity axis” refers to an axis that passes through a point detected by the sensor in the case of an angle sensor and indicates a direction of an inclination angle detected by the sensor.

  In addition, with respect to the angle sensor in the direction for detecting the inclination of the mirror surface in the circumferential direction of the polygon mirror, there is no influence of shaft deflection.

  The straight shape measuring apparatus according to the present invention is characterized by using an angle sensor constituted by the calibration apparatus described above.

  In the present invention, it is possible to use two inclined angles defined in the axial direction of two polygonal mirrors having a small angle change over time or due to environmental changes, or one long rod-shaped polygonal mirror, as an angle width reference. it can. In order not to increase the number of necessary sensors, it is preferable to calibrate the tilt angle difference between two circular sections of two polygon mirrors or rod-shaped polygon mirrors in advance. In the present invention, the polygonal mirror used for calibration is not scanned in the axial direction, and a calibration rotary shaft having a minimum length can be used. It is preferable to have a structure in which a calibration device can be installed in the vicinity of the probe so that the two-point angle method probe can easily and quickly access the calibration rotary shaft.

  The present invention is a polygon mirror which is made of a material having a sufficiently small coefficient of thermal expansion and whose inclination angle is calibrated at a predetermined rotational angle position, and two or more polygons at a desired interval. It is preferable that the apparatus includes a single rotation shaft to which a mirror is attached and a signal generation unit that can detect the predetermined rotation angle position of the rotation shaft.

  In the present invention, it is preferable to minimize the influence of the deflection due to gravity by supporting the rotating shaft at two points and attaching the polygonal mirrors at two positions on the axis where the inclination due to the deflection due to gravity is equal.

  The present invention preferably includes one or more angle sensors fixed toward the polygon mirror in order to detect a reproduction error of the deflection deformation of the shaft that occurs during rotation of the rotating shaft. The angle sensor is a two-dimensional angle sensor that can detect the tilt angle in the circumferential direction in addition to the tilt in the axial direction of the polygonal mirror, and at the same time when performing the operation for obtaining the zero point of the tilt angle in the axial direction. It is possible to detect the angle in the circumferential direction and calibrate the deviation of the zero point of the angle sensor of the circumferential inclination angle from the difference of the average value of one rotation of the angle sensor output of each circumferential inclination angle. It is preferable that it is possible. Furthermore, the angle sensor is a two-dimensional angle sensor that can detect a tilt angle in the circumferential direction in addition to the tilt in the axial direction of the polygon mirror, and determines the predetermined rotation angle position from the angle in the circumferential direction. It is preferable that it is.

  In the present invention, when measuring the tilt angle in the axial direction with the two angle sensors facing each other with the two polygon mirrors attached to the rotation shaft, the average is obtained by measuring at two positions rotated by 180 degrees. Then, calibrate the difference in apparent diameter between the vertical and horizontal directions, and correct the influence of tilt due to the deflection due to gravity in the sensitivity direction of the probe when calibrating the zero point of the angle two-point probe. Is preferable.

  The present invention is preferably attached to a column holding an angle two-point method probe that moves relative to a table on which an object to be measured is mounted, and moves relative to the table integrally with the probe.

  In the present invention, when the probe has a sensitivity axis in a horizontal plane that is not affected by the deflection due to gravity, the difference between the two-point angle readings obtained by the two-point angle probe of 180 degrees is obtained. The zero point is calibrated based on the theoretical differential output determined from the difference between two pre-calibrated tilt angles using the average value of the dynamic output, so the influence of drift of the angle sensor output during calibration is Can provide technology that is difficult to receive.

  In the present invention, the deflection amount of the rotation axis due to gravity when the sensitivity axis of the probe is placed in a direction other than the horizontal direction is detected from the difference from the zero point obtained in the horizontal direction, and the apparent difference due to the difference in the direction of the probe sensitivity axis is detected. The change in diameter difference can be corrected to calibrate the zero point in any direction.

  In the present invention, since a level or an autocollimator is not required for zero-point calibration of the two-point angle method probe, the robustness inherent to the two-point method that is hardly affected by disturbance vibration or air fluctuation can be maintained.

  In the present invention, since the object to be measured is not used for zero point calibration, the angle two-point method can be applied to an object to be measured which has an arbitrary shape and cannot be rotated, and its shape can be measured.

  In the present invention, the rotation axis for zero point calibration can be relatively easily held and used beside the two-point angle method probe, so that the zero point calibration can be repeated quickly as necessary even during the measurement operation. .

It is a figure for demonstrating the parallelism of the axial direction of the polygonal mirror of this invention. It is a figure explaining the method to measure the change of the axial parallelism of the polygon mirror used for this invention. It is a figure which shows the calibration apparatus concerning embodiment of this invention. It is a figure explaining the method of the influence of the deflection of the axis | shaft by gravity. It is a figure which shows the calibration apparatus concerning embodiment of this invention. It is a figure which shows the straight shape measuring apparatus using calibrated angle sensor SS1-SS2. It is a figure which shows the fundamental structure when calibrating the difference of the inclination angle of the circumferential direction between the some polygonal mirrors used for this invention.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 is a diagram showing a calibration apparatus according to an embodiment of the present invention. In FIG. 5, the lower ends of the plate-like supporters SP1 and SP2 are fixed on the base BS so as to be spaced apart in parallel. The support bases SP1 and SP2 have V-shaped cutouts VL1 and VL2 at their upper edges, which serve as bearings. A rotation shaft SH is placed in the notches VL1 and VL2, and the rotation shaft SH is supported by the support bases SP1 and SP2 so as to be horizontally rotatable at two points.

  Two polygonal mirrors CP1 and CP2 are coaxially fixed to the outer periphery of the rotation shaft SH. Note that the intervals and positions of the notches VL1 and VL2 are such that the inclination angles due to the gravity of the rotation axis SH at the fixed points of the two polygonal mirrors CP1 and CP2 are equal (that is, when the two fixed points are connected, they become a horizontal line). It is also possible to attach a weight to the outside of the support position of the rotating shaft.

  Further, on the base BS, a sensor holder HL is held along the polygonal mirrors CP1 and CP2. The sensor holder HL holds two angle sensors SS1, SS2. The two angle sensors SS1, SS2 are arranged so as to face the outer peripheries of the two polygonal mirrors CP1, CP2, respectively. Although not shown, a rotation angle sensor for detecting the rotation angle position of the rotation shaft SH may be provided. In order to set the sensitivity axes of the angle sensors SS1, SS2 in the vertical direction, the sensor holder HL may be moved right above the rotation axis and the sensor axis may be directed in the vertical direction. The angle sensors SS1 and SS2 are, for example, optical sensors that can detect the angle of the surface to be measured from the deviation between the emitted light and the reflected light by emitting a light beam to the surface to be measured and entering the reflected light. Good but not limited to it.

  According to the present embodiment, the calibration of the difference between the zero points of the two angle sensors SS1, SS2 can be performed by the calibration method described with reference to FIG.

  Means for giving rotation to the rotating shaft SH can be effective manually or by an electric motor. In the case of electric drive, it may be a continuous rotation method or a method of repeating rotation and stop on a step at a predetermined rotation angle interval. In the former case, it is necessary to separately generate a trigger signal for determining the timing of data recording. In the latter case, it is only necessary to be programmed so as to perform sampling at rest.

  It should be noted that, instead of using two polygon mirrors, a necessary length of polygon mirror or two or more disks may be used to calibrate the difference in axial parallelism between two predetermined axial positions. Needless to say, it is good. Two or more polygon mirrors are enough. Furthermore, a polygon mirror may be mounted on the rotation axis so as to be movable in the axial direction, and a spacer may be inserted between adjacent polygon mirrors to arbitrarily set the interval between the polygon mirrors.

  FIG. 6 is a view showing a straight shape measuring apparatus using the angle sensors SS1 and SS2 calibrated in this way. As shown in FIG. 6, a sample SP to be measured is placed on a moving stage STX that goes straight with respect to a column CL, and at the same time, a calibrated angle two-point probe (sensor) is placed on a surface within the horizontal plane of the sample SP to be measured. The two sensors SS1 and SS2) attached in parallel to the column CL by the holder HL are opposed to each other, and the surface shape of the sample SP to be measured is measured while moving the moving stage STX. Since the sensors SS1 and SS2 are configured by the above-described method, the surface shape of the sample SP to be measured and the pitching when the moving stage STX moves can be accurately measured. When the two sensors SS1 and SS2 have a function of detecting a minute inclination angle around the x axis, it is possible to measure the rolling of the movement and also measure the yawing. As a result, the straightness of the sample SP to be measured is obtained. The shape can be measured.

BS Base CL Column CP1, CP2 Polyhedral mirror
SH Sensor holder
MSH Movable sensor holder SC Straight ruler SH Rotating shaft SP1, SP2 Support base SS1-SS2 Angle sensor STX Moving stage VL1, VL2 Notch

Claims (6)

A base holding two angle sensors to be calibrated;
Two or more polygon mirrors in which the sum of the axial tilt angles (axial parallelism) of two points on the mirror surfaces facing each other across the center is calibrated at a predetermined rotational angle position;
A rotating shaft that is rotatably supported with respect to the base and has the polygon mirror attached at a desired interval;
Two angle sensors to be calibrated are fixed relative to the polygonal mirror, and the axial inclination angles of the mirror surfaces of the two or more polygonal mirrors at the predetermined rotation angle position are determined using the angle sensors. A first measurement value is obtained by measurement, and the tilt angles in the axial direction of the mirror surfaces of the two or more polygon mirrors at the rotation angle position rotated 180 degrees from the predetermined rotation angle position are measured using each angle sensor. A calibration apparatus characterized in that a second measurement value is obtained by measurement, and the mutual zero point positions of the angle sensors can be calibrated based on the first measurement value and the second measurement value.   The mutual difference between the average values over one turn of the sum of the axial tilt angles (axial parallelism) at the two opposing points of the mirror surfaces of the two or more polygon mirrors is calibrated, and the two sensors 2. The calibration apparatus according to claim 1, wherein the zero point position is calibrated using an average of the sum of the inclination angles.   The rotating shaft is supported at two points, and when the deflection of the rotating shaft occurs due to gravity, the polygon mirrors are respectively attached at two locations where the axial inclination angles due to the deflection are equal. The calibration apparatus according to claim 1 or 2. Two angle sensors to be calibrated are fixed relative to the polygon mirror so that the sensitivity axis is in a horizontal plane, and the mirror surfaces of the two or more polygon mirrors are inclined in the axial direction at the predetermined rotation angle position. An angle is measured using each angle sensor to obtain a first measurement value, and an axial inclination angle of the mirror surface of the two or more polygon mirrors rotated by 180 degrees with respect to the predetermined rotation angle position is determined. , Using each angle sensor to obtain a second measurement value, and based on the first measurement value and the second measurement value, obtain a shift of the zero point of the angle sensor from each other,
Furthermore, two angle sensors to be calibrated are fixed relative to the polygon mirror so that the sensitivity axis is in the vertical direction, and the axial direction of the mirror surfaces of the two or more polygon mirrors at the predetermined rotation angle position A tilt angle is measured using each angle sensor to obtain a third measurement value, and an axial tilt angle of the mirror surface of the two or more polygon mirrors rotated 180 degrees with respect to the predetermined rotation angle position Is measured using each angle sensor to obtain a fourth measurement value, and based on the third measurement value, the fourth measurement value, and the deviation of the zero point between the two angle sensors, The calibration apparatus according to claim 1, wherein an axial inclination angle of the polygonal mirror due to the deflection of the rotation shaft can be obtained.   The angle sensor is a two-dimensional angle sensor capable of detecting a tilt angle in the circumferential direction in addition to the tilt in the axial direction of the polygonal mirror, and in an operation for obtaining a zero point of the tilt angle in the axial direction, At the same time, the angle in the circumferential direction is detected, and the zero point of the angle sensor in the circumferential direction is determined from the difference in the average value for one rotation of the angle sensor output in each circumferential direction that has been calibrated in advance. The calibration apparatus according to claim 4, wherein the deviation can be calibrated.   The angle sensor is a two-dimensional angle sensor capable of detecting a tilt angle in the circumferential direction in addition to the tilt in the axial direction of the polygon mirror, and determines the predetermined rotation angle position from the angle in the circumferential direction. The calibration apparatus according to claim 1, wherein