JP4447694B2

JP4447694B2 - Optical member support structure

Info

Publication number: JP4447694B2
Application number: JP21827199A
Authority: JP
Inventors: 谷口　　誠
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1999-08-02
Filing date: 1999-08-02
Publication date: 2010-04-07
Anticipated expiration: 2019-08-02
Also published as: JP2001042186A

Description

【０００１】
【発明の属する技術分野】
本発明は光学部材の支持構造に関するもので、特に熱的な環境が厳しい条件下でも安定した光学性能を発揮することが可能な光学部材の支持構造に関するものである。
【０００２】
【従来の技術】
従来、反射望遠鏡等の光学系においては、主鏡と副鏡を円筒状または三脚状の構造部材を介して保持し、光学部材間の光学距離を所望の値に保持する支持構造が取られている。従来の支持構造は単一の低膨張材で光学系を支持するシンプルな構造のものが殆どである。
【０００３】
【発明が解決しようとする課題】
しかしながら、人工衛星等に搭載される観測機器や光通信用光アンテナにおいては環境に対する要求が通常の場合より厳しく、使用される温度環境が著しく変化する。従って、従来の構造体により光学系を構成すると、前述の温度変化に伴って主鏡と副鏡の光学距離が変化し、長時間にわたって光学性能を維持することが困難であった。
【０００４】
また上述の温度変化に伴って光学部材その物の曲率変化が生じ、焦点位置の補正が必要となる場合、主鏡と副鏡の光学距離を前述の温度変化に応じて変化させると、焦点位置の補正が可能となる。しかしながら、単一材料の構成では光学距離の変化を適正にするには材質の選択による制約が大きく、光学性能の維持に適する補正量を得ることが困難であった。
【０００５】
本発明では、光学系の光学部材の支持構造を軽量、簡素化し、且つ主鏡と副鏡の光学距離を温度変化に関わらず一定に維持することを目的としている。
【０００６】
また、温度変化が光学部材その物の曲率の変化を伴う場合、全系の焦点移動を支持構造の構成により主鏡と副鏡の光学距離の変化量を調整して補正し、安定した光学性能を維持することを目的としている。
【０００７】
【課題を解決するための手段】
請求項１の発明の光学部材の支持構造は、光学部材の支持構造において、３つの第１部材を連結し第１光学部材を支持する第１三角形トラスと、前記第１三角形トラスとは位相が１８０°ずれて平行に配置され、３つの第２部材を連結し第２光学部材を支持する第２三角形トラスと、前記第１三角形トラスの各角部から、前記第１三角形トラスの各角部に対して最も近い前記第２三角形トラスの辺を含んで構成される２つの角部のうち一方に連結される第３部材と他方に連結される第４部材とを有し、前記第１、第３および第４部材によって構成される第３三角形トラスと、前記第２、第３および第４部材によって構成される第４三角形トラスと、を有し、温度変化が生じても前記第１三角形トラスの重心と前記第２三角形トラスの重心とを結ぶ距離を一定に維持するように前記第１、第２、第３、第４部材の長さおよび線膨張係数が設定されていることを特徴としている。
請求項２の発明は請求項１の発明において、前記第３および第４部材はそれぞれ長さが等しく、前記第１部材の線膨張係数が他の部材の線膨張係数と異なり、前記第２、第３および第４部材の線膨張係数が等しいことを特徴としている。
【０００８】
請求項３の発明の光学部材の支持構造は、
光学部材の支持構造において、
３つの第１部材を連結し第１光学部材を支持する第１三角形トラスと、
前記第１三角形トラスとは位相が１８０°ずれて平行に配置され、３つの第２部材を連結し第２光学部材を支持する第２三角形トラスと、
前記第１三角形トラスの各角部から、前記第１三角形トラスの各角部に対して最も近い前記第２三角形トラスの辺を含んで構成される２つの角部のうち一方に連結される第３部材と他方に連結される第４部材とを有し、前記第１、第３および第４部材によって構成される第３三角形トラスと、
前記第２、第３および第４部材によって構成される第４三角形トラスと、を有し、
温度変化による前記光学部材の曲率変化による焦点位置の変動を、前記温度変化に伴う前記第１、第２、第３、第４部材の寸法変化により補正するように、前記第１、第２、第３、第４部材の長さおよび線膨張係数が設定されていることを特徴としている。
請求項４の発明は請求項３の発明において、
前記第３および第４部材はそれぞれ長さが等しく、
前記第１、第２、第３、第４部材のうち前記第２または第３部材の線膨張係数が他の部材の線膨張係数と異なり、残りの部材の線膨張係数が等しいことを特徴としている。
請求項５の発明は請求項１乃至４のいずれか１項の発明において、
前記第１三角形トラスは主鏡である前記第１光学部材を支持し、
前記第２三角形トラスは副鏡である前記第２光学部材を支持し、
前記第１光学部材の反射面と前記第２光学部材の反射面とが対向するように配置されていることを特徴としている。
【０００９】
また、温度変化により光学部材に曲率変化が生じる場合は、材質の長さ及び線膨張係数の組合せを変えることにより主鏡と副鏡の光学距離を変化させ、温度変化に伴う焦点位置のずれを補正することができる。
【００１０】
【発明の実施の形態】
図1は本発明の実施形態1を示す図面である。同図において1は光学部材である主鏡、2は光学部材である副鏡である。主鏡1と副鏡2は、主鏡1の反射面と副鏡2の反射面とが対向するように配置されている。3は線膨張係数α_a、長さaの主鏡の支持部材、4は線膨張係数α_b、長さbの支持部材、5は線膨張係数α_c、長さcの支持部材、６は線膨張係数α_d、長さdの副鏡の支持部材である。本実施形態において部材4の長さbと部材5の長さcは等しく
c＝b (1)
であり、部材4、部材5、部材6の線膨張係数は等しく
α_b＝α_c＝α_d (2)
で、部材3の線膨張係数α_aと異なっていることが特徴である。従って構造体を形成する三角形トラスのうち少なくとも一つの三角形では、該三角形を構成する3部材の少なくとも一つが異なる線膨張係数の材質で構成されている。本実施形態では主鏡を支持する部材の線膨張係数のみが他の部材と異なっていることが特徴である。また主鏡、副鏡を支持する構造は部材3、6とそれぞれ同一材質で作られている。
【００１１】
また、本発明の特徴である少なくとも一つが異なる線膨張係数の材質で構成されている三角形が複数個ある場合、該複数個の三角形の異なる部材の使い方は全系の対称性を崩さないように配置される。
【００１２】
本実施形態において、主鏡（第１光学部材）1は3本の部材（第１部材）3により支持され、副鏡（第２光学部材）2は3本の部材（第２部材）6により支持されている。主鏡1を支持する3本の部材3により形成される正三角形（第１三角形トラス）の平面と、副鏡2を支持する3本の部材6により形成される正三角形（第２三角形トラス）の平面は互いに平行で、それぞれの正三角形の重心を通る直線に垂直である。2つの正三角形（第１、第２三角形トラス）の頂点を結ぶ部材（第３部材）4と部材（第４部材）5により、立体的な骨組み構造が構成される。
第１三角形トラスの各角部Ｃから最も近い第２三角形トラスの辺を含んで構成される２つの角部のうち一方連結される部材４と他方に連結される部材５と部材６で第４三角形トラスを形成している。また部材３、部材４、部材５で第３三角形トラスを形成している。即ち、第１、第３、第４部材３、４、５によって形成されるのが第３三角形トラスを形成し、第２、第３、第４部材６、４、５によって形成されるのを第４三角形トラスを形成している。
【００１３】
上から観察すると部材3と部材6によって形成される2つの正三角形第１、第２三角形トラス）は重心が一致するとともに、大きさは異なるが相対角度関係が180度回転した位相関係を持つよう配置されている。一つの正三角形（第２三角形トラス）の頂点Ａは他の正三角形（第１三角形トラス）の近い方の2つの頂点Ｂ、Ｃと部材4、5により結合されている。
【００１４】
各部材の結合部は機構的、もしくは結合部にバネ性を持たせ、環境温度の変化による微小変形に対し回転方向に自由度を持たせている。
【００１５】
図1において部材3、4、５によって形成される頂点A、B、Cの三角形平面（第３三角形トラス）を1組の力学的平面とする。図2は該力学的平面を示したもので、三角形の高さhについては以下の式が成立する。
【００１６】
h ＝ (b²−a²/4 )^1/2 (3)
図3は本実施形態の骨組み構造の側面図を示したものである。一点鎖線は主鏡1を支持する部材3により形成される正三角形の平面と副鏡2を支持する部材6により形成される正三角形平面の重心を通る直線で、Hが光学的要求に対し最も重要な光学距離を示すパラメータである。簡単のため以降Hを光学距離と呼ぶことにする。
【００１７】
頂点A、B、Cにより形成される力学的平面と主鏡1を支持する正三角形の平面および副鏡２を支持する正三角形の平面との配置から、以下の関係式が成り立つ。
【００１８】
e ＝ 3^1/2( a−2d )/6 (4)
H＝ ( h²−e²)^1/2 (5)
これより
H ＝ ( ( 3b²−a²−d²＋ad ) /3 )^1/2 (6)
温度変化Tが生じると、各部材は温度変化にともない寸法変化を生じる。寸法変化後の部材3の長さをa'、部材4の長さをb'、部材5の長さをc'、部材6の長さをd'とすると
a'＝ a ( 1＋α_aT ) (7)
b'＝ b ( 1＋α_bT ) (8)
c'＝ b' ＝ b ( 1＋α_cT ) (9)
d'＝ d ( 1＋α_dT ) (10)
となる。従って各部材の寸法変化後の光学距離H'は次のようになる。
【００１９】
H'＝ ( ( 3b'²−a'²−d'²＋a'd' ) /3 )^1/2 (11)
(11)式でH＝H'となるように各部材の長さ及び線膨張係数を選択すると、温度変化が生じても光学距離Hが変化しない条件が導かれる。変化しない条件は
3 ( b²−b'²)−( a²−a'²)−( d²−d'²)＋( ad−a'd' )＝ 0 (12)
例えば部材3にチタン合金（線膨張係数 8.80E−6［/K］)、部材4、5、6にインバー合金（線膨張係数 1.20E−6［/K］)を使用し、部材3の長さを356.77mm、部材4及び5の長さを536.02mm、部材6の長さを50.00mmとすると、温度変化＋10Kに対する光学距離Hの変化量は＋2μmで、温度変化に関わらず光学距離Hをほぼ一定に保つことができることがわかる。
【００２０】
各部材の材質及び寸法には様々な組み合せが考えられるが、(12)式をほぼ満たす関係に導けば、環境変化に関わらず光学距離Ｈを一定に維持することができる。
【００２１】
また温度の上昇に伴い光学部材その物の曲率が変化する場合は、光学距離を所定の値変化させて、光学系の焦点位置の変化を補正できる。
【００２２】
例えば上述の長さの構成で部材3をより大きな線膨張係数をもつ材質に変更すると、温度の上昇に伴い光学距離が短くなる方向の変化を生じさせることができる。部材3にアルミ合金（線膨張係数 22.2E−6［/K］)を使用し、部材4、5、6はインバー合金（線膨張係数 1.20E−6［/K］)のままとすると、温度変化＋10Kに対する光学距離Hの変化量は−9μmとなる。
【００２３】
温度上昇に伴う光学部材の曲率変化による焦点位置の補正を光学距離を短くして対応する場合に本構成は適用できる。
【００２４】
逆に上述の長さの構成で部材3をより小さな線膨張係数をもつ材質に変更すると、温度の上昇に伴い光学距離が長くなる方向の変化を生じさせることができる。即ち部材3にCFRP（線膨張係数 2.30E−6［/K］)を使用し、部材4、5、6をインバー合金（線膨張係数 1.20E−6［/K］)のままとすると、温度変化＋10Kに対する光学距離Hの変化量は＋7μmとなる。
【００２５】
温度上昇に伴う光学部材の曲率変化による焦点位置の補正を光学距離を長くしたい場合に本構成は適用できる。
【００２６】
以上示したように、光学部材の支持構造を構成する部材の材質及び寸法を組合せて光学距離の変化を最適化することにより、環境温度の変化に伴う光学性能変化が補正され、光学系を大幅に安定化することが可能となった。
【００２７】
また、本発明の光学部材の支持構造は骨組み構造となっているので、軽量且つ簡素な構造となっていることも特徴である。
【００２８】
本発明の実施形態2は実施形態1と同じ構造で部材4の長さbと部材5の長さcは等しく
c＝b (13)
であり、部材3、部材5、部材6の線膨張係数は等しく
α_a＝α_c＝α_d (14)
で、部材4の線膨張係数α_bと異なっていることが特徴である。従って実施形態2でも構造体を形成する三角形トラスのうち少なくとも一つの三角形では、該三角形を構成する3部材の少なくとも一つが異なる線膨張係数の材質で構成されている。本実施形態では主鏡と副鏡を支持する部材を結ぶ2種類の部材のうちの一方の線膨張係数のみが他の部材と異なっていることが特徴である。
【００２９】
温度変化Tが生じると、各部材は温度変化にともない寸法変化を生じる。寸法変化後の部材3の長さをa'、部材4の長さをb'、部材5の長さをc'、部材6の長さをd'とすると
a'＝ a ( 1＋α_aT ) (15)
b'＝ b ( 1＋α_bT ) (16)
c'＝ c ( 1＋α_cT ) (17)
d'＝ d ( 1＋α_dT ) (18)
となる。温度変化Tによる寸法変化後のhをh'とすると、h'は
h'＝ 2 ( s' ( s'−a') ( s'−b') ( s'−c') )^1/2/ a' (19)
ここでs'は
s'＝ ( a'＋b'＋c') /2 (20)
である。
【００３０】
図4は部材3、4、5によって形成される頂点A、B、Cの力学的平面が温度変化Tを受けて寸法変化した後の状態を示す。図4に示す様に頂点Aは元の位置から水平方向にuだけ移動する。uは
u ＝ ( 2a'²−b'²＋c'²) / (2a) (21)
である。
【００３１】
図5は温度変化Tを受けて寸法変化した後の骨組構造の上面図である。副鏡2を支持する部材6により形成される平面は主鏡1を支持する部材により形成される平面に対し光軸回りに回転する。なお、光軸と垂直方向のずれを持たずに回転成分のみになるのは、部材3、4、5という異なる線膨張係数の材質で構成されている同一形状の複数個の三角形の部材の使い方が、全系としての対称性を崩さないように組み合わされて配置されている結果である。
【００３２】
温度変化Tによる寸法変化後、副鏡2を支持する3本の部材6により形成される正三角形の外接円の半径Rは
R ＝ 3^1/2d' /3 (22)
である。
【００３３】
図6は温度変化Tを受けて寸法変化した後の骨組構造の側面図である。図6におけるe'は次の式で与えられる。
【００３４】
e'＝ 3^1/2a' /6 − ( R²−u²)^1/2 (23)
以上より、温度変化Tによる寸法変化後の光学距離H'は
H'＝ ( h'²−e'²) (24)
例えば部材3、5、6にインバー合金（線膨張係数 1.20E−6［/K］)、部材4にCFPR（線膨張係数 2.30E−6［/K］)を使用し、実施形態1と同じく部材3の長さを356.77mm、部材4及び5の長さを536.02mm、部材6の長さを50.00mmとすると、温度変化＋10Kに対する光学距離Hの変化量は＋89μmとなる。
【００３５】
本実施形態は温度の上昇に伴い光学部材その物の曲率が変化し、光学距離を長くなるように変化させて光学系の焦点位置の変化を補正する場合に適用できる。従来のように光学系の支持部材を単一材質のみで構成した場合は該単一材質の選択だけでは補正量が大きすぎたり、小さすぎたりして適正な系の構成ができないことがある。しかしながら本実施形態のように異なる線膨張係数を持つ材質を組み合わせることで、光学距離の補正量を調整することができる。
【００３６】
また、本実施形態で温度変化に伴い支持構造が変化すると、主鏡1に対し副鏡2が回転するが、カセグレン式光学系の様に光軸に対し軸対称な光学系では、該回転成分は光学性能に影響を与えない。
【００３７】
本発明の実施形態3も実施形態1と同じ構造で部材4の長さbと部材5の長さcは等しく
c＝b (25)
であり、部材3、部材4、部材5の線膨張係数は等しく
α_a＝α_b＝α_c (26)
で、部材6の線膨張係数α_dと異なっていることが特徴である。従って実施形態3でも構造体を形成する三角形トラスのうち少なくとも一つの三角形では、該三角形を構成する3部材の少なくとも一つが異なる線膨張係数の材質で構成されている。本実施形態では副鏡を支持する部材の線膨張係数のみが他の部材と異なっていることが特徴である。
【００３８】
温度変化Tが生じると、各部材は温度変化にともない寸法変化を生じる。寸法変化後の部材3の長さをa'、部材4の長さをb'、部材5の長さをc'、部材6の長さをd'とすると
a'＝ a ( 1＋α_aT ) (27)
b'＝ b ( 1＋α_bT ) (28)
c'＝ c ( 1＋α_cT ) (29)
d'＝ d ( 1＋α_dT ) (30)
となる。温度変化Tによる寸法変化後のhをh'とすると、h'は次のようになる。
【００３９】
h'＝ ( b'²−a'²/4 )^1/2 (31)
図3において温度変化Tを受けて寸法変化した後のeの値をe'とすると、e'は次の式で与えられる。
【００４０】
e'＝ 3^1/2( a'−2d' ) /6 (32)
以上より、温度変化Tによる寸法変化後の光学距離H'は
H'＝ ( h'²−e'²) (33)
例えば部材3、4、5にインバー合金（線膨張係数 1.20E−6［/K］)、部材6にCFPR（線膨張係数 2.30E−6［/K］)を使用し、実施形態1と同じく部材3の長さを356.77mm、部材4及び5の長さを536.02mm、部材6の長さを50.00mmとすると、温度変化＋10Kに対する光学距離Hの変化量は＋61μmとなる。
【００４１】
本実施形態は温度の上昇に伴い光学部材その物の曲率が変化し、光学距離を長くなるように変化させて光学系の焦点位置の変化を補正する場合に適用できる。従来のように光学系の支持部材を単一材質のみで構成した場合は該材質の選択だけでは補正量が大きすぎたり、小さすぎたりして適正な補正を実現できないことがある。しかしながら本実施形態のように異なる線膨張係数を持つ材質を組み合わせることで、光学距離の補正量を最適化することができる。
【００４２】
【発明の効果】
以上説明したように、本発明の光学部材の支持構造においては該支持構造体を形成する三角形トラスのうち少なくとも一つの三角形において、該三角形を構成する3部材のうち少なくとも一つを異なる線膨張係数の材質で構成することを特徴としている。各部材の長さと線膨張係数を選択することにより光学部材間の光学距離を温度変化に関わらず一定に保ったり、あるいは該温度変化により光学部材に曲率変化が生じた場合には光学距離を所定の値だけ変化させて、焦点位置等の光学性能の変化を補正することが可能となった。
【００４３】
本発明ではハード対応で自然に光学性能変化を補正できるため、センサ等の処理系対応が不要で、安定し且つ安価な系を達成することが可能である。ハード的に自然に補正が行えるため、極めて広範囲な温度変化にも対応することができ、宇宙空間の様な厳しい条件にも適用する系を構成することが可能となった。また、支持構造体自体も骨組構造として構成されるため、軽量で簡素な構造とすることができる。
【図面の簡単な説明】
【図１】本発明の実施形態１の光学部材の支持構造を示す斜視図、
【図２】部材3、4、5により形成される力学的平面を示す図、
【図３】本発明の実施形態1の骨組み構造の側面図、
【図４】本発明の実施形態2において部材3、4、5により構成される力学的平面が温度変化Tにより寸法変化した状態を示す平面図、
【図５】温度変化で寸法変化した後の実施形態2の骨組み構造の上面図、
【図６】温度変化で寸法変化した後の実施形態2の骨組み構造の側面図
【符号の説明】
1 主鏡、
2 副鏡、
3 主鏡支持部材、
4 支持部材、
5 支持部材、
6 副鏡支持部材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a support structure for an optical member, and particularly relates to a support structure for an optical member that can exhibit stable optical performance even under severe thermal conditions.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an optical system such as a reflective telescope, a support structure has been adopted in which a primary mirror and a secondary mirror are held via a cylindrical or tripod-like structural member, and an optical distance between the optical members is maintained at a desired value. Yes. Most conventional support structures have a simple structure in which the optical system is supported by a single low expansion material.
[0003]
[Problems to be solved by the invention]
However, with respect to observation equipment and optical communication antennas mounted on artificial satellites or the like, environmental requirements are more severe than usual, and the temperature environment in which they are used changes significantly. Therefore, when the optical system is configured by the conventional structure, the optical distance between the primary mirror and the secondary mirror changes with the temperature change described above, and it is difficult to maintain the optical performance for a long time.
[0004]
If the curvature of the optical member itself changes with the temperature change described above and the focus position needs to be corrected, if the optical distance between the primary mirror and the secondary mirror is changed according to the temperature change, the focus position Can be corrected. However, in the case of a single material configuration, there is a great restriction on the selection of the material in order to properly change the optical distance, and it has been difficult to obtain a correction amount suitable for maintaining optical performance.
[0005]
An object of the present invention is to make the support structure of the optical member of the optical system light and simple, and to keep the optical distance between the primary mirror and the secondary mirror constant regardless of the temperature change.
[0006]
In addition, when the temperature change is accompanied by a change in the curvature of the optical member itself, the focus shift of the entire system is corrected by adjusting the amount of change in the optical distance between the primary and secondary mirrors by the structure of the support structure, and stable optical performance The purpose is to maintain.
[0007]
[Means for Solving the Problems]
In the optical member support structure according to the first aspect of the present invention, in the optical member support structure, the first triangular truss connecting the three first members to support the first optical member and the first triangular truss are in phase. A second triangular truss connected in parallel by three 180 ° members and supporting the second optical member, and each corner of the first triangular truss from each corner of the first triangular truss A third member connected to one of the two corners including the side of the second truss truss closest to the fourth member and a fourth member connected to the other, A third triangular truss constituted by third and fourth members and a fourth triangular truss constituted by the second, third and fourth members, and the first triangle even if a temperature change occurs. The center of gravity of the truss and the center of gravity of the second triangular truss Said department distance to maintain constant first, second, third, length and the linear expansion coefficient of the fourth member is characterized by being set.
According to a second aspect of the present invention, in the first aspect, the third and fourth members are equal in length, the linear expansion coefficient of the first member is different from the linear expansion coefficient of the other members, and the second, The third and fourth members have the same linear expansion coefficient.
[0008]
The support structure of the optical member of the invention of claim 3 is:
In the support structure of the optical member,
A first triangular truss that connects the three first members and supports the first optical member;
The first triangular truss is arranged in parallel with a phase difference of 180 °, a second triangular truss that connects the three second members and supports the second optical member;
The first triangular trusses are connected to one of the two corners including the side of the second triangular truss that is closest to each corner of the first triangular truss. A third triangular truss having three members and a fourth member connected to the other, and constituted by the first, third and fourth members;
A fourth triangular truss configured by the second, third and fourth members;
The first, second, so as to correct the variation of the focal position due to the change in curvature of the optical member due to the temperature change by the dimensional change of the first, second, third and fourth members accompanying the temperature change. The length and the linear expansion coefficient of the third and fourth members are set.
The invention of claim 4 is the invention of claim 3,
The third and fourth members are each equal in length,
Of the first, second, third, and fourth members, the second or third member has a different linear expansion coefficient from the other members, and the remaining members have the same linear expansion coefficient. Yes.
The invention of claim 5 is the invention of any one of claims 1 to 4,
The first triangular truss supports the first optical member which is a primary mirror,
The second triangular truss supports the second optical member which is a secondary mirror,
The reflective surface of the first optical member and the reflective surface of the second optical member are arranged to face each other.
[0009]
In addition, if the curvature of the optical member changes due to temperature changes, the optical distance between the primary and secondary mirrors is changed by changing the combination of the material length and the linear expansion coefficient, and the focal position shifts due to temperature changes. It can be corrected.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a drawing showing Embodiment 1 of the present invention. In the figure, 1 is a primary mirror which is an optical member, and 2 is a secondary mirror which is an optical member . The primary mirror 1 and the secondary mirror 2 are arranged so that the reflective surface of the primary mirror 1 and the reflective surface of the secondary mirror 2 face each other. 3 is a support member for the primary mirror having a linear expansion coefficient α _a and length a, 4 is a support member having a linear expansion coefficient α _b and length b, 5 is a support member having a linear expansion coefficient α _c and length c, 6 is This is a support member for a secondary mirror having a linear expansion coefficient α _d and a length d. In this embodiment, the length b of the member 4 and the length c of the member 5 are equal.
c ＝ b (1)
And the linear expansion coefficients of member 4, member 5, and member 6 are equal α _b = α _c = α _d (2)
Thus, the member 3 is different from the linear expansion coefficient α _a of the member 3. Therefore, in at least one of the triangular trusses forming the structure, at least one of the three members constituting the triangle is made of a material having a different linear expansion coefficient. The present embodiment is characterized in that only the linear expansion coefficient of the member that supports the primary mirror is different from that of the other members. The structure for supporting the primary and secondary mirrors is made of the same material as the members 3 and 6, respectively.
[0011]
In addition, when there are a plurality of triangles made of materials having different linear expansion coefficients, at least one of the features of the present invention, the usage of the different members of the plurality of triangles does not break the symmetry of the entire system. Be placed.
[0012]
In the present embodiment, the primary mirror (first optical member) 1 is supported by three members (first member) 3 and the secondary mirror (second optical member) 2 is supported by three members (second member) 6. It is supported. The plane of an equilateral triangle (first triangle truss) formed by three members 3 supporting the primary mirror 1 and an equilateral triangle (second triangle truss) formed by three members 6 supporting the secondary mirror 2 The planes are parallel to each other and perpendicular to a straight line passing through the center of gravity of each equilateral triangle. A member (third member) 4 and a member (fourth member) 5 connecting the apexes of two equilateral triangles (first and second triangle trusses) constitute a three-dimensional framework structure.
Of the two corners that include the side of the second triangle truss that is closest to each corner C of the first triangular truss, the member 4 that is connected to one side, the member 5 that is connected to the other, and the member 6 are the fourth. A triangular truss is formed. The member 3, member 4, and member 5 form a third triangular truss. That is, the first, third, and fourth members 3, 4, and 5 form the third triangular truss, and the second, third, and fourth members 6, 4, and 5 form. A fourth triangular truss is formed.
[0013]
When viewed from above , the two equilateral triangle trusses 1 and 2 formed by member 3 and member 6 have the same center of gravity and different phase, but the relative angular relationship seems to have a phase relationship rotated 180 degrees. Has been placed. A vertex A of one equilateral triangle (second triangle truss) is connected to two vertices B and C closer to the other equilateral triangle (first triangle truss) by members 4 and 5.
[0014]
The connecting portion of each member is mechanical or has a spring property in the connecting portion, and has a degree of freedom in the rotation direction with respect to minute deformation due to a change in environmental temperature.
[0015]
In FIG. 1, the triangular planes (third triangular trusses) of vertices A, B, and C formed by members 3, 4, and 5 are defined as a set of mechanical planes. FIG. 2 shows the mechanical plane, and the following formula is established for the height h of the triangle.
[0016]
^{^{h = (b 2 -a 2/}} 4) 1/2 (3)
FIG. 3 shows a side view of the framework structure of the present embodiment. The alternate long and short dash line is a straight line passing through the center of the equilateral triangle formed by the member 3 supporting the primary mirror 1 and the equilateral triangle plane formed by the member 6 supporting the secondary mirror 2, and H is the most suitable for optical requirements. This is a parameter indicating an important optical distance. For simplicity, H will be referred to as the optical distance.
[0017]
From the arrangement of the mechanical plane formed by the vertices A, B, and C, the plane of the regular triangle that supports the primary mirror 1, and the plane of the regular triangle that supports the secondary mirror 2, the following relational expression is established.
[0018]
e = 3 ^1/2 (a−2d) / 6 (4)
H = (h ² −e ² ) ^1/2 (5)
Than this
H = ((3b ² −a ² −d ² + ad) / 3) ^1/2 (6)
When the temperature change T occurs, each member undergoes a dimensional change with the temperature change. The length of the member 3 after the change in dimension is a ′, the length of the member 4 is b ′, the length of the member 5 is c ′, and the length of the member 6 is d ′.
a '= a (1 + α _a T) (7)
b '= b (1 + α _b T) (8)
c '= b' = b ( 1 + α c T) (9)
d '= d (1 + α _d T) (10)
It becomes. Accordingly, the optical distance H ′ after the dimensional change of each member is as follows.
[0019]
H '= ((3b' ² -a ' ² -d' ² + a'd ') / 3) ^1/2 (11)
When the length and linear expansion coefficient of each member are selected so that H = H ′ in the expression (11), a condition that the optical distance H does not change even when the temperature changes is derived. Conditions that do not change
3 (b ² −b ′ ² ) − (a ² −a ′ ² ) − (d ² −d ′ ² ) + (ad−a′d ′) = 0 (12)
For example, titanium alloy (linear expansion coefficient 8.80E-6 [/ K]) is used for member 3, Invar alloy (linear expansion coefficient 1.20E-6 [/ K]) is used for members 4, 5, and 6, and the length of member 3 If the length is 356.77 mm, the length of members 4 and 5 is 536.02 mm, and the length of member 6 is 50.00 mm, the change in the optical distance H with respect to the temperature change + 10K is +2 μm, and the optical distance H is set regardless of the temperature change. It can be seen that it can be kept almost constant.
[0020]
Various combinations of the material and dimensions of each member are conceivable. However, if a relationship that substantially satisfies the equation (12) is derived, the optical distance H can be maintained constant regardless of environmental changes.
[0021]
Further, when the curvature of the optical member itself changes as the temperature rises, the change in the focal position of the optical system can be corrected by changing the optical distance by a predetermined value.
[0022]
For example, when the member 3 is changed to a material having a larger linear expansion coefficient with the above-described length configuration, a change in a direction in which the optical distance is shortened with an increase in temperature can be caused. If aluminum alloy (linear expansion coefficient 22.2E-6 [/ K]) is used for member 3, and members 4, 5, and 6 are left as Invar alloy (linear expansion coefficient 1.20E-6 [/ K]), the temperature The change amount of the optical distance H with respect to the change + 10K is −9 μm.
[0023]
This configuration can be applied to the case where the correction of the focal position due to the change in the curvature of the optical member due to the temperature rise is handled by shortening the optical distance.
[0024]
Conversely, when the member 3 is changed to a material having a smaller linear expansion coefficient with the above-described length configuration, a change in the direction in which the optical distance becomes longer as the temperature rises can be caused. That is, if CFRP (linear expansion coefficient 2.30E-6 [/ K]) is used for member 3 and members 4, 5, and 6 are left as Invar alloy (linear expansion coefficient 1.20E-6 [/ K]), the temperature The change amount of the optical distance H with respect to the change + 10K is +7 μm.
[0025]
This configuration can be applied to a case where it is desired to lengthen the optical distance for the correction of the focal position due to the change in the curvature of the optical member accompanying the temperature rise.
[0026]
As described above, by optimizing changes in the optical distance by combining the materials and dimensions of the members that make up the support structure of the optical member, changes in the optical performance due to changes in the environmental temperature are corrected, and the optical system is greatly improved. It became possible to stabilize.
[0027]
Moreover, since the support structure of the optical member of the present invention has a framework structure, it is also characterized by a lightweight and simple structure.
[0028]
The second embodiment of the present invention has the same structure as the first embodiment, and the length b of the member 4 is equal to the length c of the member 5.
c ＝ b (13)
And the linear expansion coefficients of member 3, member 5, and member 6 are equal to each other, α _a = α _c = α _d (14)
Thus, the linear expansion coefficient α _b of the member 4 is different. Therefore, also in Embodiment 2, in at least one of the triangular trusses forming the structure, at least one of the three members constituting the triangle is made of a material having a different linear expansion coefficient. The present embodiment is characterized in that only one of the two types of members connecting the members supporting the primary mirror and the secondary mirror is different from the other members.
[0029]
When the temperature change T occurs, each member undergoes a dimensional change with the temperature change. The length of the member 3 after the change in dimension is a ′, the length of the member 4 is b ′, the length of the member 5 is c ′, and the length of the member 6 is d ′.
a '= a (1 + α _a T) (15)
b '= b (1 + α _b T) (16)
c '= c (1 + α _c T) (17)
d '= d (1 + α _d T) (18)
It becomes. If h 'is h' after dimensional change due to temperature change T, h '
h '= 2 (s'(s'-a')(s'-b')(s'-c')) ^1/2 / a' (19)
Where s'
s '= (a' + b '+ c') / 2 (20)
It is.
[0030]
FIG. 4 shows a state after the mechanical planes of the vertices A, B, and C formed by the members 3, 4, and 5 are subjected to a temperature change T and undergo dimensional changes. As shown in FIG. 4, the vertex A moves from the original position in the horizontal direction by u. u is
u = (2a ' ² −b' ² + c ' ² ) / (2a) (21)
It is.
[0031]
FIG. 5 is a top view of the frame structure after the dimensions change due to the temperature change T. FIG. The plane formed by the member 6 that supports the secondary mirror 2 rotates around the optical axis with respect to the plane formed by the member that supports the primary mirror 1. Note that the only component that has no rotational deviation from the optical axis in the vertical direction is the use of multiple triangular members of the same shape made of materials with different linear expansion coefficients of members 3, 4, and 5. However, this is a result of being arranged in combination so as not to break the symmetry of the entire system.
[0032]
After the dimension change due to the temperature change T, the radius R of the circumscribed circle of the equilateral triangle formed by the three members 6 supporting the secondary mirror 2 is
R = 3 ^1/2 d '/ 3 (22)
It is.
[0033]
FIG. 6 is a side view of the frame structure after the size is changed due to the temperature change T. FIG. E ′ in FIG. 6 is given by the following equation.
[0034]
e '= 3 ^1/2 a' / 6 − (R ² −u ² ) ^1/2 (23)
From the above, the optical distance H ′ after the dimensional change due to the temperature change T is
H '＝ (h' ² −e ' ² ) (24)
For example, invar alloy (linear expansion coefficient 1.20E-6 [/ K]) is used for members 3, 5 and 6, and CFPR (linear expansion coefficient 2.30E-6 [/ K]) is used for member 4, as in the first embodiment. If the length of the member 3 is 356.77 mm, the lengths of the members 4 and 5 are 536.02 mm, and the length of the member 6 is 50.00 mm, the change amount of the optical distance H with respect to the temperature change +10 K is +89 μm.
[0035]
This embodiment can be applied to the case where the curvature of the optical member changes with increasing temperature and the change in the focal position of the optical system is corrected by changing the optical distance to be longer. When the support member of the optical system is composed of only a single material as in the prior art, the correction amount may be too large or too small just by selecting the single material, and an appropriate system may not be constructed. However, the optical distance correction amount can be adjusted by combining materials having different linear expansion coefficients as in this embodiment.
[0036]
In the present embodiment, when the support structure changes with temperature change, the secondary mirror 2 rotates relative to the primary mirror 1, but in an optical system that is axially symmetric with respect to the optical axis, such as a Cassegrain optical system, the rotational component Does not affect the optical performance.
[0037]
Embodiment 3 of the present invention also has the same structure as Embodiment 1, and the length b of member 4 is equal to the length c of member 5.
c ＝ b (25)
And a, member 3, member 4, the linear expansion coefficient of the member 5 is equal _{_{_{α a = α b = α c}}} (26)
Thus, the characteristic is that the linear expansion coefficient α _d of the member 6 is different. Therefore, also in Embodiment 3, in at least one of the triangular trusses forming the structure, at least one of the three members constituting the triangle is made of a material having a different linear expansion coefficient. The present embodiment is characterized in that only the linear expansion coefficient of the member that supports the secondary mirror is different from the other members.
[0038]
When the temperature change T occurs, each member undergoes a dimensional change with the temperature change. The length of the member 3 after the change in dimension is a ′, the length of the member 4 is b ′, the length of the member 5 is c ′, and the length of the member 6 is d ′.
a '= a (1 + α _a T) (27)
b '= b (1 + α _b T) (28)
c '= c (1 + α _c T) (29)
d '= d (1 + α _d T) (30)
It becomes. If h ′ is h ′ after dimensional change due to temperature change T, h ′ is as follows.
[0039]
^{h '= (b' 2 -a} '2/4) 1/2 (31)
In FIG. 3, when the value of e after the change in size due to the temperature change T is e ′, e ′ is given by the following equation.
[0040]
e '= 3 ^1/2 (a'-2d') / 6 (32)
From the above, the optical distance H ′ after the dimensional change due to the temperature change T is
H '＝ (h' ² −e ' ² ) (33)
For example, Invar alloy (linear expansion coefficient 1.20E-6 [/ K]) is used for members 3, 4, and 5, and CFPR (linear expansion coefficient 2.30E-6 [/ K]) is used for member 6, as in the first embodiment. If the length of the member 3 is 356.77 mm, the lengths of the members 4 and 5 are 536.02 mm, and the length of the member 6 is 50.00 mm, the change amount of the optical distance H with respect to the temperature change + 10K is +61 μm.
[0041]
This embodiment can be applied to the case where the curvature of the optical member changes with increasing temperature and the change in the focal position of the optical system is corrected by changing the optical distance to be longer. When the support member of the optical system is composed of only a single material as in the prior art, the correction amount may be too large or too small just by selecting the material, and appropriate correction may not be realized. However, the correction amount of the optical distance can be optimized by combining materials having different linear expansion coefficients as in the present embodiment.
[0042]
【The invention's effect】
As described above, in the support structure of the optical member of the present invention, at least one of the triangular trusses forming the support structure, and at least one of the three members constituting the triangle is different in linear expansion coefficient. It is characterized by comprising. By selecting the length and linear expansion coefficient of each member, the optical distance between the optical members is kept constant regardless of the temperature change, or when the curvature change occurs in the optical member due to the temperature change, the optical distance is set to a predetermined value. It is possible to correct changes in the optical performance such as the focal position by changing only the value of.
[0043]
In the present invention, the change in optical performance can be naturally corrected with hardware support, so that a processing system such as a sensor is not required, and a stable and inexpensive system can be achieved. Since correction can be performed naturally in terms of hardware, it is possible to cope with a wide range of temperature changes, and it is possible to construct a system that can be applied to harsh conditions such as outer space. Further, since the support structure itself is also configured as a framework structure, it can be a light and simple structure.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a support structure for an optical member according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing a mechanical plane formed by members 3, 4 and 5;
FIG. 3 is a side view of the framework structure of Embodiment 1 of the present invention,
FIG. 4 is a plan view showing a state in which a mechanical plane constituted by members 3, 4, and 5 in the second embodiment of the present invention changes in size due to a temperature change T;
FIG. 5 is a top view of the framework structure of Embodiment 2 after the dimensions change due to a temperature change;
FIG. 6 is a side view of the framework structure of the second embodiment after the dimensions change due to a temperature change.
1 primary mirror,
2 Secondary mirror,
3 Primary mirror support member,
4 Support member,
5 support members,
6 Secondary mirror support member

Claims

In the optical member support structure, the first triangular truss that connects the three first members to support the first optical member, and the first triangular truss are arranged in parallel with a phase shift of 180 °. A second triangular truss that connects the members and supports the second optical member; and from each corner of the first triangular truss, the side of the second triangular truss that is closest to each corner of the first triangular truss A third triangle having a third member connected to one of the two corners including the fourth member connected to the other and a fourth member connected to the other; A truss and a fourth triangular truss constituted by the second, third and fourth members, and the center of gravity of the first triangular truss and the center of gravity of the second triangular truss even if a temperature change occurs. wherein the distance which connects to maintain a constant first The support structure of the second, third, optical member length and the linear expansion coefficient of the fourth member, characterized in that it is set.

The third and fourth members are equal in length, the linear expansion coefficient of the first member is different from that of the other members, and the linear expansion coefficients of the second, third and fourth members are equal. The support structure for an optical member according to claim 1.

In the optical member support structure, the first triangular truss that connects the three first members to support the first optical member, and the first triangular truss are arranged in parallel with a phase shift of 180 °. A second triangular truss that connects the members and supports the second optical member; and from each corner of the first triangular truss, the side of the second triangular truss that is closest to each corner of the first triangular truss A third triangle having a third member connected to one of the two corners including the fourth member connected to the other and a fourth member connected to the other; A truss and a fourth triangular truss configured by the second, third, and fourth members, and a variation in focal position due to a change in curvature of the optical member due to a temperature change is caused by the temperature change. Dimensions of the first, second, third and fourth members The support structure of an optical member, characterized in that to correct the first, second, third, length and the linear expansion coefficient of the fourth member is set by reduction.

The third and fourth members are equal in length, and the linear expansion coefficient of the second or third member of the first, second, third, and fourth members is different from the linear expansion coefficient of other members. The support structure for an optical member according to claim 3, wherein the remaining members have the same linear expansion coefficient.

The first triangular truss supports the first optical member, which is a primary mirror, and the second triangular truss supports the second optical member, which is a secondary mirror. The reflective surface of the first optical member and the second optical truss 5. The optical member support structure according to claim 1, wherein the optical member support structure is disposed so as to face a reflection surface of the optical member. 6.