JP2010152090A - Reflecting mirror system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflecting mirror system capable of holding geometrical position relation between a main mirror and a submirror at fixed relation even when an arbitrary temperature change or temperature distribution is generated in the reflecting mirror system, capable of minimizing a change in stress at a connection portion of members and capable of suppressing a deviation of an optical axis and reduction in reliability. <P>SOLUTION: The reflecting mirror system includes: a main mirror 1; a main mirror support part 2 for fixing the main mirror 1; a submirror 3; a submirror support part 4 for fixing the submirror 3; and a connection frame 5 for connecting the submirror support part 4 with the main mirror support part 2. In the system, configuration members of the main mirror 1, the submirror 3, the main mirror support part 2, the submirror support part 4, and the connection frame 5 are composed of materials having the same linear thermal expansion coefficient, a reflection surface of the main mirror 1 and a reflection surface of the submirror 3 are oppositely arranged on a common optical axis, and a main mirror connecting position 6 where the connection frame 5 is connected to the main mirror support part 2 and a submirror connecting position 7 where the connection frame 5 is connected to the submirror support part 4 are arranged point-symmetrically about the optical axis. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a telescope or an optical antenna used in space, for example, where thermal environmental changes are severe.

  In the case of an optical system used in a satellite or the like, the temperature change of the entire optical system in the space environment is very large. For this reason, if the optical system is thermally deformed and the relative position of the constituent members of the entire optical system changes, the movement of the focal point or the like may cause deterioration of the image. An adjustment mechanism for correcting the above is required. In the conventional reflector system, in order to maintain the geometric positional relationship between the primary mirror and the secondary mirror, a plurality of mirrors that support the primary mirror and extend in the radial direction with respect to the optical axis center of the primary mirror are provided. A first support means having a leg member; and a second support means having a plurality of frames for supporting the secondary mirror and connected to the distal ends of the legs of the first support means. The support member is constructed so that the linear expansion coefficient is different, and the member dimensions are selected so that the geometrical positional relationship between the primary mirror and the secondary mirror is constant even if the temperature changes (for example, patents) Reference 1).

JP 2001-318301 A (page 2, FIG. 1)

  In the conventional reflecting mirror system, when a temperature distribution is generated in a portion symmetrical to the optical axis of the primary mirror, the geometric positional relationship between the primary mirror and the secondary mirror can be kept constant. However, when used in a satellite or the like, sunlight is not always applied only to a portion that is symmetric with respect to the optical axis. If the temperature distribution occurs in a portion that is asymmetric with respect to the optical axis of the primary mirror, the first support is provided. Since the linear expansion coefficient of the means and the linear expansion coefficient of the second support means are different, it is difficult to keep the geometric positional relationship between the mirror and the secondary mirror constant. In addition, because it is made up of members with different linear expansion coefficients, the change in stress associated with temperature changes is large at the part where these members are connected, the optical axis shifts, and the reliability of the reflector is low. There was a problem of being lowered.

  The present invention has been made to solve the above-described problems. Even if any temperature change or temperature distribution occurs in the reflecting mirror system, the geometric positional relationship between the primary mirror and the secondary mirror is kept constant. At the same time, a change in stress at the connecting portion of the member can be suppressed to a minimum, and a shift of the optical axis and a decrease in reliability can be suppressed.

  In the reflecting mirror system according to the present invention, the primary mirror, the primary mirror support portion to which the primary mirror is fixed, the secondary mirror, the secondary mirror support portion to which the secondary mirror is fixed, the secondary mirror support portion and the primary mirror A reflecting mirror system comprising a connecting frame for connecting a support part, and a material having the same linear thermal expansion coefficient for the main mirror, sub mirror, main mirror support part, sub mirror support part and connecting frame constituent members The reflective surface of the primary mirror and the reflective surface of the secondary mirror are arranged facing each other with a common optical axis, and the primary mirror connection position where the coupling frame is connected to the primary mirror support portion, and the secondary mirror support portion The secondary mirror connection position to which the connecting frame is connected is a point-symmetrical position with respect to the optical axis.

  In the present invention, the constituent members are made of a material having the same linear thermal expansion coefficient, and the primary mirror connection position where the coupling frame is connected to the primary mirror support part, and the secondary mirror where the coupling frame is connected to the secondary mirror support part By making the connection position point-symmetric with respect to the optical axis, the geometric positional relationship between the primary and secondary mirrors is kept constant even if any temperature change or temperature distribution occurs in the reflector. In addition, the change in stress at the connecting portion of the member can be suppressed to the minimum, and the shift of the optical axis and the decrease in reliability can be suppressed.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram of a reflector system according to Embodiment 1 for carrying out the present invention. In FIG. 1, the primary mirror 1 is fixed to the primary mirror support 2, and the secondary mirror 3 is fixed to the secondary mirror support 4. The primary mirror 1 and the secondary mirror 3 are arranged to face each other with a common optical axis. The primary mirror support portion 2 has a substantially triangular shape, and is connected to the connecting frame 5 by a primary mirror connection portion 6 near three vertices. The secondary mirror support part 4 has a larger circular shape than the secondary mirror 3 and is connected to the three connecting frames 5 by the secondary mirror connection part 7 on the side surface. The connection frame 5 has a spiral bent structure that is bent at a plurality of nodes. The primary mirror connecting portion 6 and the secondary mirror connecting portion 7 are configured so as to be point-symmetric with respect to the optical axis, that is, a position rotated by 180 degrees around the optical axis. Such a positional relationship is expressed as an antiphase positional relationship.

  The reflector system of the present embodiment will be described in further detail. The primary mirror 1 is a concave mirror having an outer diameter of 250 mm, an opening having an inner diameter of 70 mm in the center, and a focal length of 250 mm. The secondary mirror 3 is a convex mirror having an outer shape of 75 mm and a focal length of 500 mm. Since the primary mirror connecting portion 6 and the secondary mirror connecting portion 7 are in opposite phase positions, when the connecting frame 5 has a linear shape, the three connecting frames intersect at the center, This obstructs the optical path between the primary mirror and the secondary mirror of the reflecting mirror system, resulting in a decrease in light collection efficiency and a loss of part of the image. Therefore, the main mirror support part and the secondary mirror support part are 180 degrees by making the connection frame 5 have a spiral shape that bypasses the outside of the optical path so as not to block the optical path between the primary mirror and the secondary mirror. It is possible to connect at a shifted connection position of opposite phase.

  In the present embodiment, the constituent members of the primary mirror, secondary mirror, primary mirror support portion, secondary mirror support portion, and connecting frame are made of a material having the same linear thermal expansion coefficient, for example, a carbon fiber reinforced silicon carbide composite material (C / SiC).

  Next, the operation of the reflecting mirror system when the reflecting mirror system in the present embodiment is mounted on a satellite will be described.

  In a satellite equipped with a reflector system, the reflector system is shielded in the range that does not prevent the incidence of observation light in order to shield strong radiation from sunlight. When observing a celestial body, the direction of the reflector system is controlled so that light from the star to be observed enters the main mirror of the reflector system. In this case, if the reflector system is small and the direction can be controlled independently from the satellite body, the direction is controlled by the reflector system alone. If the reflector system is large and integrated with the satellite body, It is controlled in a desired direction by posture control. The light from the observation symmetry is reflected by the primary mirror 1, and the reflected light travels to the secondary mirror 3, and the light reflected by the secondary mirror 3 passes through the opening of the primary mirror 1 and passes through the back of the primary mirror 1. An image is formed on a light receiving portion (not shown) arranged corresponding to the opening. The information imaged on the light receiving unit is converted into a digital signal and transferred to the ground via a satellite communication device. The digital signal transferred to the ground is used for various kinds of information analysis such as image processing.

  Next, an operation when temperature distribution occurs in the reflecting mirror system in the present embodiment will be described. The primary mirror, secondary mirror, primary mirror support, secondary mirror support, and connecting frame components are made of materials with the same linear thermal expansion coefficient, so the temperature of the entire reflector system changes equally. Causes similar deformation, the geometrical positional relationship between the primary and secondary mirrors is kept constant, and the stress at the joints of the members hardly changes, and the optical axis shifts and reliability decreases. Can be suppressed.

  In addition, when the temperature distribution occurs in the reflector system, the connection frame is configured to connect the primary mirror support unit and the secondary mirror instruction unit in opposite phases. Expansion and contraction are caused and the amount of deformation is offset, so that the lengths of the connecting frames become equal. For this reason, the positional relationship between the primary mirror support portion and the secondary mirror support portion is maintained in a parallel state, so that the geometrical positional relationship between the primary mirror and the secondary mirror is kept constant, and the shift of the optical axis can be suppressed. it can.

  As described above, in this embodiment, the constituent members are made of a material having the same linear thermal expansion coefficient, so that the change in stress at the connecting portion of the members can be minimized and the primary mirror can be suppressed. Arbitrary temperature change and temperature distribution in the reflector by setting the primary mirror connection position where the coupling frame is connected to the support part and the secondary mirror connection position where the coupling frame is connected to the secondary mirror support part. Even if this occurs, the geometric positional relationship between the primary mirror and the secondary mirror can be kept constant without a correction mechanism. As a result, even when a temperature change or a temperature distribution occurs in the reflecting mirror system, it is possible to suppress a deviation of the optical axis and a decrease in reliability.

  In this embodiment, an example in which a carbon fiber reinforced silicon carbide composite material (C / SiC) is used as a constituent member has been shown. However, since this composite material is lightweight and has a small linear expansion coefficient, it is used in a satellite or the like. It is a material suitable for the case. However, materials other than this material may be used. For example, a low thermal expansion glass material, an invar material, a beryllium alloy, or the like may be used.

Embodiment 2. FIG.
The second embodiment evaluates the relationship between the temperature distribution and the optical characteristics in the reflector system described in the first embodiment. FIG. 2 is a layout diagram for evaluating the optical characteristics of the reflecting mirror system in the present embodiment. In FIG. 2, an optical interferometer 9 is disposed at a position opposite to the secondary mirror of the primary mirror of the reflector system 8, and a reference mirror 10 is disposed at a position opposite to the optical interferometer 9 of the secondary mirror. As the optical interferometer 9, for example, a GPI-XP laser interferometer type shape measuring device manufactured by Zygo Corporation can be used. The positional relationship between the optical interferometer 9 and the reference mirror 10 is configured to be constant regardless of the temperature environment. Laser light emitted from the optical interferometer 9 passes through the opening 9 at the center of the primary mirror 1, is reflected by the secondary mirror 3 toward the primary mirror 1, and is further reflected by the primary mirror 1 to the reference mirror 10. Irradiated. The laser light applied to the reference mirror 10 is reflected by the reference mirror 10, traces the optical path in the reverse direction, and returns to the optical interferometer 9. The shapes of the primary mirror 1 and the secondary mirror 3 can be measured from the interference fringes between the laser light reflected and returned from the reference mirror 10 and the laser light emitted from the optical interferometer 9. In FIG. 2, the reflector system 8 is arranged in a constant temperature bath (not shown) so that the entire temperature can be adjusted to be constant in order to evaluate temperature characteristics. In addition, two opposing end portions P1 and P2 of the primary mirror support portion that supports the primary mirror 1 are defined, and two opposing end portions of the secondary mirror support portion that supports the secondary mirror 3 are denoted as P3 and P4. A heater and a thermocouple are attached to these four ends, and the temperature of these four ends can be changed independently.

  First, the wavefront aberration was 0.230λ (rms) as a result of measuring the wavefront aberration using the optical interferometer 9 while keeping the temperature of the entire reflector system 8 constant at 23 ° C. Here, the wavefront aberration is a disturbance of the concentric spherical wavefront that has passed through the optical system. Is done. Here, λ is the wavelength of the laser light of the optical interferometer 9, and for example, if the light source of the optical interferometer 9 is a He—Ne laser, λ = 632.8 nm. If the wavefront aberration is less than the Rayleigh limit (1 / 4λ), it is determined that there is no significant difference from the ideal image. Next, the wavefront aberration when the overall temperature of the reflector system 8 is 10 ° C. is 0.231λ (rms), and the wavefront aberration when the overall temperature of the reflector system 8 is 35 ° C. is 0.230λ ( rms). From this, it can be understood that the geometric positional relationship between the primary mirror and the secondary mirror of the reflecting mirror system does not change if the temperature of the entire reflecting mirror system is constant.

  Next, wavefront aberration when temperature distribution occurs in the reflecting mirror system will be described. Wavefront aberration was measured by changing the temperatures of the ends of the primary and secondary mirrors, P1, P2, P3, and P4. Table 1 shows the relationship between the temperature at each end and the wavefront aberration. Table 1 also shows the wavefront aberration when the temperature of the entire reflecting mirror system is constant.

  In Table 1, when the primary mirror support is 30 ° C. and the secondary mirror support is 20 ° C., the wavefront aberration is 0.231 λ (rms), and the geometric positional relationship between the primary mirror and the secondary mirror is the entire reflector system. It can be seen that there is almost no change from when the temperature is constant. Further, even when a temperature distribution that is not symmetrical with respect to the optical axis occurs, such as one end of the primary mirror support and the secondary mirror support is 15 ° C. and the other end is 25 ° C., the wavefront aberration Is 0.231λ (rms), and it can be seen that the geometrical positional relationship between the primary mirror and the secondary mirror is almost the same as when the temperature of the entire reflecting mirror system is constant.

  As described in the present embodiment, when the temperature distribution does not occur in the reflector system and the entire temperature changes constantly, the constituent members of the reflector system are made of a material having the same linear thermal expansion coefficient. Therefore, since the entire reflecting mirror system is deformed in a similar shape, the geometric positional relationship between the primary mirror and the secondary mirror is kept constant. Also, when temperature distribution occurs in the reflector system, the primary mirror connection position and secondary mirror connection position of the connecting frame are configured in opposite phases, so the secondary mirror can tilt when viewed from the primary mirror. In addition, the geometric positional relationship between the primary mirror and the secondary mirror is kept constant.

  As described above, in this embodiment, the constituent members are made of a material having the same linear thermal expansion coefficient, so that the change in stress at the connecting portion of the members can be minimized and the primary mirror can be suppressed. By setting the primary mirror connection position where the connection frame is connected to the support part and the sub mirror connection position where the connection frame is connected to the secondary mirror support part to a position opposite in phase to each other, Expansion and contraction are caused and the amount of deformation is offset, so that the lengths of the connecting frames become equal. Therefore, even if an arbitrary temperature change or temperature distribution occurs in the reflecting mirror, the geometrical positional relationship between the primary mirror and the secondary mirror can be kept constant without a correction mechanism, and stress at the connecting portion of the member can be maintained. The change can be suppressed to the minimum, and the shift of the optical axis and the decrease in reliability can be suppressed.

It is a schematic diagram of the reflecting mirror system in Embodiment 1 of this invention. It is an arrangement plan when evaluating the optical characteristic of the reflecting mirror system in Embodiment 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary mirror 2 Primary mirror support part 3 Secondary mirror 4 Secondary mirror support part 5 Connection frame 6 Primary mirror connection part 7 Secondary mirror connection part 8 Reflective mirror system 9 Optical interferometer 10 Reference mirror 11 Opening part

Claims (2)

A primary mirror and a primary mirror support to which the primary mirror is fixed;
A secondary mirror and a secondary mirror support to which the secondary mirror is fixed;
A reflecting mirror system comprising a connecting frame for connecting the sub mirror support part and the primary mirror support part,
The primary mirror, the secondary mirror, the primary mirror support part, the secondary mirror support part, and the constituent members of the connection frame are made of a material having the same linear thermal expansion coefficient,
The reflective surface of the primary mirror and the reflective surface of the secondary mirror are arranged to face each other with a common optical axis,
A primary mirror connection position where the coupling frame is connected to the primary mirror support;
The secondary mirror connection position where the coupling frame is connected to the secondary mirror support is a point-symmetrical position with respect to the optical axis. 3. The reflector system according to claim 2, wherein the constituent member is a carbon fiber reinforced silicon carbide composite material.

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