Patent ID: 12222490

DESCRIPTION OF EMBODIMENTS

First Embodiment

A metrology system and telescope apparatus according to a first embodiment are described with reference toFIGS.1to6. The metrology system according to the first embodiment measures an amount of displacement of a structure of telescope apparatus1. Telescope apparatus1is apparatus including primary mirror including a primary mirror that reflects light or radio waves. The metrology system according to the present disclosure is applicable to the apparatus including primary mirror including a primary mirror that reflects light or radio waves, such as optical telescope apparatus, radio telescope apparatus, or antenna apparatus used in communication, radar, or the like. Further, the present disclosure is for apparatus including primary mirror including a metrology system. Herein, a case where the apparatus including primary mirror is a telescope apparatus is described.

With reference toFIGS.1to4, a configuration of the telescope apparatus according to the first embodiment is described. The telescope apparatus thus illustrated is in a state where the primary mirror is oriented at an elevation angle of 88 degrees.FIGS.1,2,3, and4are a schematic right side view, a schematic front view, a schematic rear view, and a schematic plan view of telescope apparatus1, respectively. Telescope apparatus1includes a primary mirror portion2, an elevation axis structural body3, an azimuth mount4, and a pedestal portion5. Primary mirror portion2includes a primary mirror6and a primary mirror supporting portion7that supports primary mirror6. Elevation axis structural body3is a member that supports primary mirror portion2and is rotatable around an elevation axis EL (also referred to as an EL axis or an elevation axis) that is a rotation axis that allows an elevation angle in an orientation direction to be changed. The orientation direction of telescope apparatus1is a direction in which primary mirror6(strictly speaking, a rotation axis RT of a paraboloid of revolution of a mirror surface) is oriented. Azimuth mount4supports elevation axis structural body3rotatably around elevation axis EL. Azimuth mount4is a member rotatable around an azimuth axis AZ (also referred to as an AZ axis or an azimuth axis) that is a rotation axis that allows an azimuth angle in the orientation direction to be changed. Pedestal portion5supports azimuth mount4rotatably around azimuth axis AZ. Pedestal portion5is fixed to a structure where telescope apparatus1is installed. The structure where telescope apparatus1is installed has a deep foundation in the ground. Primary mirror portion2and elevation axis structural body3each has a structure symmetrical with respect to a primary mirror center plane that is a plane including azimuth axis AZ and perpendicular to elevation axis EL.

In the drawings, elevation axis EL is indicated by a long dashed short dashed line. Azimuth axis AZ is indicated by a long dashed double-short dashed line. Rotation axis RT is indicated by a dashed line. Rotation axis RT is illustrated as a line segment between a secondary mirror and the primary mirror inFIGS.1and4.

Primary mirror portion2includes primary mirror6, primary mirror supporting portion7, a secondary mirror8, and a secondary mirror supporting portion9. Primary mirror6reflects observation light. Primary mirror supporting portion7is provided on a rear surface of primary mirror6existing on the contrary side to the mirror surface to support primary mirror6. Primary mirror supporting portion7is a structure in which rod-shaped members are joined together in a truss structure. Secondary mirror8is disposed at a focal point of primary mirror6. Secondary mirror8further collects the observation light collected by primary mirror6and reflects the observation light in a direction in which elevation axis structural body3is provided. The observation light collected by secondary mirror8enters an observation optical system (not illustrated) and is sent to an observation device. An end of the observation optical system on a side existing primary mirror portion2is disposed at a position near rotation axis RT and a rear surface of primary mirror supporting portion7. Secondary mirror supporting portion9supports secondary mirror8. Secondary mirror supporting portion9includes three supporting columns each having a truss structure. Secondary mirror supporting portion9is provided at a peripheral portion of primary mirror supporting portion7, which is located on an outer peripheral of primary mirror6, so as to be symmetrical with respect to the primary mirror center plane. The center supporting column is provided such that a center of a connecting portion of the center supporting column is present on the primary mirror center plane.

Primary mirror6is a parabolic mirror whose mirror surface is a paraboloid of revolution. Telescope apparatus1is a so-called offset telescope. When primary mirror6is oriented in the zenith direction, rotation axis RT of the paraboloid of revolution is parallel to azimuth axis AZ, and rotation axis RT is provided at a position apart from azimuth axis AZ. Rotation axis RT and azimuth axis AZ are present on the primary mirror center plane. Elevation axis EL is perpendicular to the primary mirror center plane, and rotation axis RT and elevation axis EL are in mutually twisted positions. When either rotation axis RT or elevation axis EL is moved in parallel so as to cause rotation axis RT and elevation axis EL to be present on the same plane, rotation axis RT and elevation axis EL are orthogonal to each other. When primary mirror6is oriented in a direction other than the zenith direction, rotation axis RT and azimuth axis AZ intersect. The position of the intersection of rotation axis RT and azimuth axis AZ is always apart from the position of the intersection of elevation axis EL and azimuth axis AZ. The intersection of elevation axis EL and azimuth axis AZ is referred to as an orientation direction change center.

In the offset telescope, the mirror surface of primary mirror2has a shape obtained by cutting out a portion of a parabolic mirror into a circle. The mirror surface of primary mirror6having a circular outer shape is asymmetrical in cross section when cut by a plane passing through the center of the outer circle and parallel to rotation axis RT, except a case where the cutting plane is orthogonal to the primary mirror center plane. That is, in the offset telescope, the mirror surface is asymmetrical with respect to the center of the circular shape. On the other hand, a normal primary mirror is obtained by cutting out the mirror surface into a circle such that rotation axis RT of the paraboloid passes through the center. The normal primary mirror has the center of the circular shape that coincides with rotation axis RT. Therefore, the normal primary mirror has an axisymmetric mirror surface. In the normal primary mirror, a cross-sectional shape in cross section cut by a plane including rotation axis RT is symmetrical regardless of where the cutting plane is located. Telescope apparatus having the normal primary mirror is referred to as an axisymmetric telescope apparatus.

A heat insulating material is provided on a surface of primary mirror supporting portion7and a surface of secondary mirror supporting portion9so as to suppress deformation caused by temperature change. Further, primary mirror supporting portion7includes a structure for cooling a periphery of primary mirror supporting portion7. The heat insulating material and the cooling structure are determined in consideration of an environment of a place where the telescope apparatus is installed.

In the offset telescope apparatus, regardless of in which direction primary mirror6is oriented, rotation axis RT is provided at a position apart from the orientation direction change center that is the intersection of azimuth axis AZ and elevation axis EL. Therefore, the end portion, on a side existing primary mirror portion2, of the observation optical system disposed near rotation axis RT is located at a position apart from the orientation direction change center. The offset telescope apparatus has a high degree of freedom in use of a space between the orientation direction change center and the rear surface of primary mirror6. In the axisymmetric telescope, since it is necessary to dispose the end portion, on the side existing primary mirror portion2, of the observation optical system near the orientation direction change center, the degree of freedom in using the space between the orientation direction change center and the rear surface of primary mirror6is low.

Elevation axis structural body3includes two sets of bearing portions10and counterweight portions11. The sets of bearing portions10and counterweight portions11are provided symmetrically on the rear surface of primary mirror supporting portion7. Bearing portions10hold an elevation axis member12(illustrated inFIGS.1and2) provided in azimuth mount4rotatably. Elevation axis member12and bearing portions10constitute elevation axis EL as a physical object. Counterweight portions11have such a weight that a center of gravity of primary mirror portion2and elevation axis structural body3are located near elevation axis EL. The center of gravity of primary mirror portion2and elevation axis structural body3are located on the primary mirror center plane. Counterweight portions11each has a shape like a fan having a center angle of about 135 degrees when viewed from the direction of elevation axis EL. Counterweight portions11are arranged at an interval of about 25% of a diameter of primary mirror6and in parallel to the primary mirror center plane.

Azimuth mount4includes elevation axis member12, a mount base portion13, an elevation axis structural body supporting portion14, and a working scaffold15. Mount base portion13is supported by pedestal portion5. On an upper side of mount base portion13, a motor, a gear mechanism, and the like for rotating elevation axis structural body3and keeping elevation axis structural body3at a specified angle are installed. The motor, the gear mechanism, and the like are not illustrated. Elevation axis structural body supporting portion14is a member that is provided on the upper side of mount base portion13and supports elevation axis structural body3. Elevation axis structural body supporting portion14has, from its lower side, a cylindrical portion, a truncated cone portion, and an approximately cylindrical portion in a horizontal direction. The approximately cylindrical portion of elevation axis structural body supporting portion14has a truncated cone shape with a radius that decreases toward each end in the horizontal direction. Elevation axis member12is provided horizontally on each side surface of the approximately cylindrical portion. Elevation axis member12is a member constituting elevation axis EL. Elevation axis member12is a cylindrical member. Center axes of two elevation axis members12coincide with each other and coincide with elevation axis EL. Each elevation axis member12is disposed so as to be inserted into a corresponding bearing portion10. Elevation axis members12are not visible when telescope apparatus1is viewed from the outside. Working scaffold15is a scaffold attached to mount base portion13. A person stands on working scaffold15to perform work such as maintenance.

In telescope apparatus1, elevation axis members12are provided in azimuth mount4, and bearing portions10are provided in elevation axis structural body3. The metrology system according to the present disclosure is also applicable to telescope apparatus in which elevation axis members12are provided in elevation axis structural body3, and bearing portions10are provided in azimuth mount4.

Pedestal portion5is fixed to the structure. Inside pedestal portion5, a bearing portion that supports mount base portion13rotatably, a motor that rotates mount base portion13, and the like are provided. The bearing portion is provided between mount base portion13and pedestal portion5. The bearing portion includes a bearing that makes mount base portion13rotatable with less friction relative to pedestal portion5.

Telescope apparatus1may or may not include a metrology system30that measures the amount of displacement of the structure of telescope apparatus1. Telescope apparatus1can be corrected (compensate for) an error in the orientation direction and be scanned. As a method for correcting (compensating for) an error in the orientation direction, a known technique disclosed in PTL 2 or the like can be applied.

With reference toFIGS.5to9, a structure of metrology system30according to the first embodiment is described. Metrology system30is provided inside elevation axis structural body supporting portion14.FIGS.5to9are drawn as if elevation axis structural body supporting portion14on a front side in a direction perpendicular to the paper surface does not exist.FIGS.5and6are a perspective view (partial transparent perspective view) and a front view (partial transparent perspective view) of metrology system30, respectively.FIGS.5and6illustrate a state before working scaffold15is installed on mount base portion13.FIG.7is an enlarged front view of a portion including the elevation axis base portion included in metrology system30.FIG.8is an enlarged front view of a portion of metrology system30where a displacement meter is disposed.FIG.9is a plan view of metrology system30.FIG.9is a plan view of a side where mount base portion13is provided as viewed from a virtual cross section of a lower side of a branch portion31B.

To illustrate the structure and operation of metrology system30, an XYZ coordinate system is defined as follows: A Z axis extending in a vertical direction is defined to coincide with azimuth axis AZ. An X axis is defined on a horizontal plane. A Y axis is defined to be orthogonal to the X axis on the horizontal plane. The Y axis is parallel to a direction in which primary mirror6is oriented at an elevation angle of zero degrees. A positive direction of the Y axis is a direction from a side where secondary mirror8is provided to a side where secondary mirror8is not provided. A positive direction of the X axis is a direction obtained by rotating the positive direction of the Y axis clockwise by 90 degrees.

Metrology system30includes an elevation axis base portion31, an inclinometer32, an azimuth axis base portion33and a displacement meter34. Long-term monitoring of a change in the direction of elevation axis EL is performed using elevation axis base portion31and inclinometer32. The change in the direction of elevation axis EL is caused by displacement due to heat generated in primary mirror portion2, elevation axis structural body3, and azimuth mount4, displacement due to aging, or the like. Displacement meter34monitors displacement of elevation axis base portion31relative to azimuth axis base portion33in the short term. The short term means a short period of time as compared with a time required for monitoring displacement due to heat, displacement due to aging, or the like. The short term can also be said to be instantaneous. Elevation axis base portion31, inclinometer32, azimuth axis base portion33, and displacement meter34are housed in azimuth mount4.

Elevation axis base portion31include a main body portion31A and branch portion31B. Main body portion31A is provided along the elevation axis, passing through a position where elevation axis EL and azimuth axis AZ intersect. Branch portion31B extends downward from main body portion31A. Main body portion31A included in elevation axis base portion31have two ends fixed to elevation axis structural body supporting portion14. Main body portion31A is also referred to as a reference pole portion. Main body portion31A has a shape in which three cylinders having the same radius and each having a flange are connected so that their center axes coincide with each other. Branch portion31B that branches downward is connected to the center cylinder of main body portion31A. Branch portion31B extends along azimuth axis AZ. Branch portion31B is a cylinder having a flange at its lower end. Branch portion31B is provided so that its center axis coincides with azimuth axis AZ. Lower end of branch portion31B is closed flat. A heat insulating material is attached to elevation axis base portion31as a measure against thermal expansion in order to reduce the amount of expansion or contraction caused by temperature change.

Inclinometer32is provided at a position on an upper side of elevation axis base portion31through which azimuth axis AZ passes. Inclinometer32measures an inclination angle of main body portion31A that is a portion of elevation axis base portion31extending along elevation axis EL. Inclinometer32detects a direction of gravity and detects the inclination angle from a difference between the direction of gravity and a direction in which inclinometer32is installed.

Inclinometer32converts the displacement of elevation axis base portion31into an angle (inclination angle) of rotation around the X axis and an angle of rotation around the Y axis, and outputs the converted angles. Inclinometer32detects the amount of displacement (θX, θY) of elevation axis base portion31.

Inclinometer32is formed in elevation axis base portion31and is disposed on azimuth axis AZ. Elevation axis base portion31is provided along elevation axis EL. It is therefore possible to detect a deviation in the orientation direction of primary mirror6. Since displacement due to heat or displacement due to aging occurs mainly on an axis other than the Z axis (azimuth axis AZ), inclinometer32that detects the amount of displacement (θX, θY) of elevation axis base portion31can detect displacement due to heat or displacement due to aging.

When an inclinometer having an automatic reversal measurement function is used as inclinometer32, it is possible to correct a temperature drift during long-term monitoring. Inclinometer32having the automatic reversal measurement function includes a turntable, and a sensor that detects the direction of gravity is installed on the turntable. By rotating the turntable by 180 degrees at intervals of fixed time and measuring the inclination angle, the effect of the temperature drift can be removed from the inclination angle.

Main body portion31A (reference pole portion) of elevation axis base portion31is installed so as to represent the center axis of elevation axis EL. That is, elevation axis base portion31is fixed to elevation axis structural body supporting portion14so that the center axis of main body portion31having a cylindrical shape coincides with elevation axis EL. Therefore, inclinometer32can measure the amount of displacement of elevation axis EL. In a case where the center axis of main body portion31having a cylindrical shape is apart from elevation axis EL, the inclination angle measured by inclinometer32is different from the inclination angle of elevation axis EL.

Further, inclinometer32is installed at a position on an upper side of main body portion31A through which azimuth axis AZ passes. Azimuth axis AZ is present at a center position of main body portion31A in the horizontal direction. Therefore, inclinometer32can measure the amount of displacement of elevation axis EL caused by displacement of elevation axis structural body3and azimuth mount4(mainly, elevation axis structural body supporting portion14) due to a load of primary mirror portion2. When measuring the amount of displacement of elevation axis EL, inclinometer32can eliminate the influence of bending or local deformation of main body portion31A included in elevation axis base portion31. In a case where main body portion31A included in elevation axis base portion31bends, when inclinometer32is installed at a position other than the center of main body portion31A, inclinometer32also measures an inclination angle influenced by the bending of main body portion31A in addition to the amount of displacement of elevation axis EL. Measuring the displacement including the inclination angle influenced by the bending means that inclinometer32cannot measure the amount of displacement of elevation axis EL accurately.

Inclinometer32is disposed at a position where the inclination of elevation axis EL can be measured as accurately as possible. As a result, the deviation of the orientation direction of telescope apparatus1can be corrected by exerting the maximum correction effect.

Azimuth axis base portion33has a lower end fixed to mount base portion13. Azimuth axis base portion33is provided separately from elevation axis structural body supporting portion14. Azimuth axis base portion33has an upper cylindrical portion33A on its upper side and a frame structure portion33B on its lower side. Upper cylindrical portion33A is also referred to as a metrology pole. Frame structure portion33B is also referred to as a metrology tower. The upper side of azimuth axis base portion33is a side adjacent to branch portion31B. The lower side of azimuth axis base portion33is a side on which mount base portion13is provided. Upper cylindrical portion33A is a cylinder having flanges at both ends. An upper flange of upper cylindrical portion33A has a circular shape. A lower flange of upper cylindrical portion33A has an equilateral triangular outer shape. A center of gravity of the equilateral triangle and a center axis of the cylinder of upper cylindrical portion33A coincide with azimuth axis AZ. Upper and lower ends of upper cylindrical portion33A are closed flat. A heat insulating material is attached to upper cylindrical portion33A as a measure against thermal expansion in order to reduce the amount of expansion or contraction caused by temperature change. Frame structure portion33B is a member having a frame structure in which rod-shaped members are connected.

Displacement meter34is provided between branch portion31B and upper cylindrical portion33A. Displacement meter34measures the amount of displacement of branch portion31B relative to upper cylindrical portion33A. Displacement meter34is preferably an optical encoder as disclosed in PTL 3. A rotary encoder and a linear encoder of other types such as a mechanical type, a magnetic type, or an electromagnetic induction types can be used. Rather than measuring the amount of one-dimensional displacement, a displacement meter that measures the amount of two-dimensional or three-dimensional displacement may be used.

Frame structure portion33B has an equilateral triangular outer shape as viewed from above as illustrated inFIG.9. The three vertices of the triangle of frame structure portion33B are arranged immediately inside the circular cross section of elevation axis structural body supporting portion14. The three sides of the triangle of frame structure portion33B are arranged at angles of 15 degrees, 75 degrees, and 135 degrees relative to the positive direction of the X axis. As illustrated inFIG.6, frame structure portion33B includes three rod members fixed vertically to mount base portion13at positions of the vertexes of the triangle. The three vertical rod members are connected by three rod members provided horizontally at different height positions. There are three sets of three horizontal rod members. Frame structure portion33B further includes three rod members extending obliquely to connect joint portions between the vertical rod members and the horizontal rod members. Six rod members extend obliquely from the horizontal rod members at the highest position to connect to the vertices of the triangle at the lower end of upper cylindrical portion33A. Frame structure portion33B has the rod members connected to form triangles, so that it is possible to make the frame structure portion33B lightweight and strong. The structure in which upper cylindrical portion33A and frame structure portion33B are combined enables a reduction in weight of azimuth axis base portion33as compared with a case where azimuth axis base portion33has a cylindrical structure in its entirety.

With reference toFIGS.7to9, the layout and structure of displacement meter34are described. As illustrated in an enlarged view of a main portion inFIG.7, between branch portion31B and upper cylindrical portion33A, displacement meters34are disposed in parallel to the Z direction and displacement meters34are disposed in parallel to the horizontal plane. Displacement meter34is a linear encoder that measures the amount of one-dimensional displacement. The linear encoder measures the amount of displacement of one object relative to the other object. In order for the linear encoder to measure the amount of displacement, one object is provided with a scale with divisions, and the other object is provided with a sensor that reads the divisions on the scale. The linear encoder measures the amount of displacement between one object and the other object by reading the divisions on the scale with the sensor.

As illustrated inFIG.8, displacement meter34includes a scale member34A and a sensor portion34B. Scale member34A has a scale that is a rod-shaped member with divisions. Sensor portion34B includes a ring-shaped member into which the rod-shaped member is inserted, and a sensor that reads the divisions on the rod-shaped member. In the drawing, the sensor is represented by a circle below the rod-shaped member. When the rod-shaped member is inserted into the ring-shaped member, the rod-shaped member moves only in a determined direction. In metrology system30, scale member34A is attached to branch portion31B, and sensor portion34B is attached to upper cylindrical portion33A. Alternatively, scale member34A may be attached to upper cylindrical portion33A, and sensor portion34B may be attached to branch portion31B. For each displacement meter34, member to which scale member34A is attached may be different, and member to which sensor portion34B is attached may be different.

As illustrated inFIGS.8and9, metrology system30includes four displacement meters34having rod-shaped members arranged in a horizontal direction (perpendicular to the Z axis) and eight displacement meters34having rod-shaped members arranged in a vertical direction (parallel to the Z axis). Displacement meters34having rod-shaped members arranged in the horizontal direction are referred to as horizontally arranged displacement meter34. Displacement meters34having rod-shaped member arranged in the vertical direction are referred to as vertically arranged displacement meters34. Four horizontally arranged displacement meters34are arranged on an upper surface of upper cylindrical portion33A, two of four horizontally arranged displacement meters34extending in the X-axis direction, and the other two extending in the Y-axis direction. Eight vertically arranged displacement meters34each has sensor portion34B attached to a side surface of a corresponding one of eight ribs provided on the flange at the upper end of upper cylindrical portion33A. The eight ribs are provided at intervals of 45 degrees in the horizontal plane. Straight lines connecting two ribs facing each other include a straight line parallel to the X axis or the Y axis.

From the amount of displacement measured by displacement meter34, the amount of displacement of branch portion31B along the X axis, the Y axis, and the Z axis relative to upper cylindrical portion33A is calculated. The amount of displacement of branch portion31B relative to upper cylindrical portion33A is calculated by considering the amount of displacement generated by translational motion of a center of gravity G0of branch portion31B (δX, δY, δZ) and the amount of displacement generated by rotational motion around center of gravity G0(θX, θY, θZ). For each displacement meter34j, the amount of displacement (δX, δY, δZ) generated by translational motion and the amount of displacement (θX, θY, θZ) generated by rotational motion around center of gravity G0are calculated from an amount of displacement Δjmeasured by each displacement meter34jby considering a direction vector used for measuring the amount of displacement and a position vector of each displacement meter34relative to center of gravity G0. The amount of displacement that affects a change in the orientation direction of telescope apparatus1greatly is the amount of displacement (θX, θY, θZ) generated by rotational motion. Displacement meter34detects the amount of rotational displacement (θX, θY, θZ) of elevation avis base portion31including branch portion31B.

The amount of displacement Δjmeasured by horizontally arranged displacement meters34is generated mainly as an amount of displacement (0, 0, θZ) generated by rotational motion around the Z axis and amounts of displacement (δX, δY, 0) generated by translational motion on the XY plane. The amount of displacement Δjmeasured by vertically arranged displacement meters34is generated mainly as amounts of displacement (θX, θY, 0) generated by rotational motion around the X axis and the Y axis and an amount of displacement (0, 0, θZ) generated by translational motion in the Z-axis direction. Depending on the direction in which displacement meter34is installed, which of the amounts of displacement generated by rotational motion around the X axis and the Y axis is measured mainly by displacement meter34is changed.

Displacement meter34detects the amount of displacement of elevation axis base portion31including branch portion31B relative to azimuth axis base portion33including upper cylindrical portion33A. Azimuth axis base portion33is fixed firmly to mount base portion13, and mount base portion13and pedestal portion5are fixed firmly to the structure. Therefore, displacement meter34can measure the amount of displacement of elevation axis EL that is generated when primary mirror portion2, elevation axis structural body3, and azimuth mount4are deformed temporarily by wind (wind pressure) or the like. Displacement meter34can detect an amount of temporary rotational displacement (θX, θY, θZ) of elevation axis base portion31caused by wind (wind pressure) or the like. Since displacement meter34is installed on a side of branch portion31B adjacent to azimuth axis base portion33, and elevation axis base portion31is provided along elevation axis EL, a deviation in the orientation direction of telescope apparatus1can be detected from the rotational amount of displacement (θX, θY, θZ) of elevation axis base portion31.

Azimuth mount4and pedestal portion5are fixed firmly to the ground where telescope apparatus1is installed. Further, azimuth axis base portion33is fixed firmly to mount base portion13included in azimuth mount4. Azimuth axis base portion33is fixed to mount base portion13separately from elevation axis structural body supporting portion14. Therefore, the position of azimuth axis base portion33relative to the ground is fixed. Further, elevation axis structural body supporting portion14houses azimuth axis base portion33therein, but elevation axis structural body supporting portion14and azimuth axis base portion33are not connected. Therefore, azimuth axis base portion33is not affected by displacement or deformation of elevation axis structural body supporting portion14. On the other hand, elevation axis base portion31is fixed to elevation axis structural body supporting portion14. Displacement meter34is installed between azimuth axis base portion33and elevation axis base portion31. Therefore, displacement meter34can measure the amount of displacement of elevation axis structural body supporting portion14relative to the ground.

Elevation axis base portion31, inclinometer32, azimuth axis base portion33, and displacement meter34are housed in azimuth mount4. That is, azimuth mount4is a cover (casing) of elevation axis base portion31, inclinometer32, azimuth axis base portion33, and displacement meter34. Therefore, the measurement accuracy of inclinometer32and displacement meter34can be maintained high. A disturbance caused by wind or the like is not applied directly to elevation axis base portion31and azimuth axis base portion33. Therefore, the amount of displacement of elevation axis EL corresponds to the amount of displacement of elevation axis base portion31. Further, inclinometer32and displacement meter34are disposed in an environment with less temperature fluctuation. Therefore, in the amount of displacement measured by inclinometer32and displacement meter34, an error resulting from temperature change or the like is reduced.

Inclinometer32is used in long-term monitoring of displacement due to heat, displacement due to aging, or the like, and any inclinometer32longer in sampling period than displacement meter34may be used. On the other hand, displacement meter34is used in short-term monitoring of displacement caused by wind (wind pressure) or the like. Therefore, a sampling period of displacement meter34is shorter than a sampling period of inclinometer32.

The metrology system and the telescope apparatus according to the first embodiment can detect a deviation in the orientation direction of primary mirror6by measuring the amount of displacement of elevation axis base portion31. For example, the use of the method disclosed in PTL 2 in processing displacement that is measured by displacement meter34and fluctuates in the short term allows the telescope to be oriented in an intended direction even in a case where there is displacement that fluctuates in the short term. Further, it is possible to grasp an error between a command value for the orientation direction and a direction in which the primary mirror is oriented actually by processing a long-term fluctuation measured by inclinometer32and to orient the primary mirror in the commanded orientation direction even in a telescope having an error in the orientation direction caused by the displacement due to aging or the like.

Inclinometer32may be disposed on azimuth axis AZ between the orientation direction change center, which is the intersection of azimuth axis AZ and elevation axis EL, and the rear surface of primary mirror6. Offset telescope apparatus1has a sufficient space between elevation axis base portion31and the rear surface of primary mirror6, so that inclinometer32is disposed easily. Also in an axisymmetric telescope apparatus, the inclinometer is disposed in the space between the elevation axis base portion and the rear surface of the primary mirror.

Since upper cylindrical portion33A included in azimuth axis base portion33and elevation axis base portion31have a cylindrical shape, upper cylindrical portion33A and elevation axis base portion31have no direction dependency in deformation such as expansion or contraction caused by temperature change. This prevent upper cylindrical portion33A and elevation axis base portion31from being deformed locally, and allows inclinometer32and displacement meter34to measure the amount of displacement of elevation axis EL accurately.

It is possible to monitor displacement due to heat, displacement due to aging, or the like over the long term using displacement meter34instead of inclinometer32. For this purpose, the followings are required. (a) Azimuth axis base portion33is fixed to a foundation separated from telescope apparatus1. (b) Elevation axis base portion31and azimuth axis base portion33are made of a material having a low thermal expansion coefficient, such as an invar alloy. Inclinometer32measures the direction of gravity, so that no matter where inclinometer32is installed, inclinometer32can measure the inclination angle of a member on which inclinometer32is installed. Therefore, the above-described measures necessary for the long-term monitoring of displacement due to heat, displacement due to aging, or the like by displacement meter34are not required.

The metrology system may include only inclinometer32without displacement meter34. In such a metrology system without displacement meter34, the elevation axis base portion does not have branch portion31B. The elevation axis base portion is provided along the elevation axis, and passes through a position where elevation axis EL and azimuth axis AZ intersect. The metrology system including only inclinometer32can measure long-term displacement of elevation axis EL and correct an error in the orientation direction of the telescope apparatus caused by the displacement due to aging or the like. Regardless of whether displacement meter34is provided, the metrology system including inclinometer32is applicable to telescope apparatus in which the elevation axis base portion can be disposed at a position along elevation axis EL.

Instead of displacement meter34that measures the plurality of amounts of one-dimensional displacement, a displacement meter capable of measuring the amount of two-dimensional or three-dimensional displacement may be used. The use of the displacement meter capable of measuring the amount of two-dimensional or three-dimensional displacement allows a reduction in the number of displacement measuring components. The displacement meter capable of measuring the amount of two-dimensional or three-dimensional displacement is disposed appropriately considering the amount of displacement to be measured.

Herein, a case where the metrology system according to the present disclosure is applied to telescope apparatus has been described. The metrology system according to the present disclosure is applicable to not only telescope apparatus but also apparatus including primary mirror that includes a primary mirror portion including a primary mirror and a primary mirror supporting portion that supports the primary mirror, an elevation axis structural body that supports the primary mirror portion, and being rotatable around an elevation axis that allows an elevation angle in an orientation direction in which the primary mirror is oriented to be changed, an azimuth mount being rotatable around an azimuth axis that allows an azimuth angle in the orientation direction to be changed, and to support the elevation axis structural body rotatably around the elevation axis, and a pedestal portion that supports the azimuth mount rotatably around the azimuth axis. The metrology system according to the present disclosure is capable of measuring the amount of displacement of a structure of the apparatus including primary mirror, particularly the amount of displacement of the elevation axis. Examples of the apparatus including primary mirror may include an antenna apparatus and the like.

A modification of the embodiment, omission of some components, or any desired combination of a modification and omission is possible.

REFERENCE SIGNS LIST

1: telescope apparatus (apparatus including primary mirror),2: primary mirror portion,3: elevation axis structural body,4: azimuth mount,5: pedestal portion,6: primary mirror,7: primary mirror supporting portion,8: secondary mirror,9: secondary mirror supporting portion,10: bearing portion,11: counterweight portion,12: elevation axis member,13: mount base portion,14: elevation axis structural body supporting portion,15: working scaffold,30: metrology system,31: elevation axis base portion,31A: main body portion (reference pole portion),31B: branch portion,32: inclinometer,33: azimuth axis base portion,33A: upper cylindrical portion (metrology pole),33B: frame structure portion (metrology tower),34: displacement meter,34A: scale member,34B: sensor portion