JP4782950B2

JP4782950B2 - Liquid detector

Info

Publication number: JP4782950B2
Application number: JP2001220494A
Authority: JP
Inventors: 貞雄野田
Original assignee: Panasonic Electric Works SUNX Co Ltd
Current assignee: Panasonic Industrial Devices SUNX Co Ltd
Priority date: 2001-07-19
Filing date: 2001-07-19
Publication date: 2011-09-28
Anticipated expiration: 2021-07-19
Also published as: JP2003035588A

Description

【０００１】
【発明の属する技術分野】
本発明は、液体の液位や有無を光学的に検出する液体検出装置に関する。
【０００２】
【従来の技術】
この種の液体検出装置としては、例えば特開平8-320248号等に開示されたものがあるが、その基本的原理は、いずれも図７に示すように透光性の容器の側壁１に投光部２から光を照射し、側壁１の内側で反射した光を受光する位置に受光部３を設けた構成である。同図（Ａ）に示すように、投光部２からの光の照射域に液体が存在しない場合には、側壁１の内側で光が正反射して受光部３に到達するが、同図（Ｂ）に示すように、液体が存在すると、その正反射率が大きく減少するために、投光部２からの光の大部分は側壁１を貫通するようになって受光部３に到達しなくなる。従って、受光部３に入射する光量を計測することにより、液体の有無を判別できるのである。
【０００３】
【発明が解決しようとする課題】
ところで、投光部２からの光は容器の側壁１の外側でも反射するから、受光部３には容器の側壁１の内側で正反射した光（以下「内壁反射光４」）だけでなく、側壁１の外側で正反射した光（以下「外壁反射光５」）も入射することがある。この外壁反射光５は容器内の液体の有無にかかわらず常に受光部３に入射するからＳ／Ｎ比が低下し正確な液体検出を行うことができないおそれがある。
【０００４】
そこで、特開4-66820号では、容器の側壁面に対する投光部２及び受光部３の入射角θ（図７参照）を６０度以上にすると液体の有無による受光部３での受光量レベルの差が大きくなるという実験結果に基づいて、この入射角θを大きくすることでＳ／Ｎ比の向上を図ったものが開示されている。しかしながら、こうした構成では投光部２から出射された光が受光部３に直接入射することがあり、前記外壁反射光５と共にやはりＳ／Ｎ比低下の要因になり得る。
【０００５】
このような問題に対して、投光部２と受光部３との間に遮光部を設けたり、或いは投光部２からの光を絞ったりすることで、投光部２からの直接光や外壁反射光５が受光部３に入射するのを防止する方法が考えられる。実開昭51-51766号には、前者の方法が開示されている。図８に示すように、投光部２及び受光部３の間に非透光部材６Ａを設けて、投光部２からの直接光及び外壁反射光５の光路を遮断して、内壁反射光４のみ通過可能に構成されている。このような構成であれば受光部３には内壁反射光４のみが入射することになるからＳ／Ｎ比を向上させることができ、もってより正確な液体検出を行うことが可能になる。
【０００６】
ところで、正確な液体検出を行うためには、投光部２からの直接光や外壁反射光５による影響だけでなく、検出領域の範囲についても考慮する必要がある。即ち、容器に液体が供給されたり、液体を排出したりすると、液体内に気泡が生じて容器の側壁１の内側に付着する。気泡が付着した部分では液体がない場合と同様に投光部２からの光は側壁１の内側で正反射して受光部３に至ることになる。従って検出領域に液体が存在する場合でも気泡の付着によって受光部３での受光量レベルが液体がないときの受光量レベル側に近づいてしまう。逆に、検出領域に液体が存在しないときには、容器の側壁１の内側に水滴が付着して受光部３での受光量レベルが液体の存在するときの受光量レベル側に近づくこともある。従って、気泡や水滴の影響を避けるために検出領域をある程度広く確保する必要がある。
【０００７】
ところが、容器の中にはその側壁が極めて薄いものも多く、このような容器内の液体を、上述した非透光部材６Ａを用いた液体検出装置を使って検出する場合には、確保できる検出領域の面積に制約が生じるという新たな問題が発生する。このことについて、図９に示すように側壁１の厚さが異なる２種類（厚さｔ１＜ｔ２）の容器を例に挙げて詳説する。同図（Ａ）に示すように、容器の側壁１がある程度の厚み（ｔ２）があれば内壁反射光４の光路Ｒ１と、外壁反射光５の光路Ｒ２とはほどんど重複することがなく、外壁反射光５の光路Ｒ２を前記非透光部材６Ａ等で遮断しても検出領域Ｗ１に影響を与えることはない。ところが、同図（Ｂ）に示すように、側壁１が薄くなると（ｔ１）、内壁反射光４の光路Ｒ１と外壁反射光５の光路Ｒ２とが重なり合うことになる。ここで、同図（Ｃ）に示すように外壁反射光５の光路を遮断して内壁反射光４のみ通過する光路Ｒ３のみ開放するように非透光部材６Ｂを設けると、検出領域がＷ１からＷ２へと狭くなってしまうのである。従って、側壁１が薄いと、気泡や水滴の影響により正確な液体検出を行えないという問題が再び発生するのである。
【０００８】
本発明は、上記事情に鑑みてなされたもので、その目的は、液体収容容器内に付着する気泡及び水滴による影響を加味した検出領域を確保しつつ、外壁反射光等による影響を低減して正確な液体検出が可能な液体検出装置を提供するところにある。
【０００９】
【課題を解決するための手段】
上記目的を達成するため、請求項１の発明に係る液体検出装置は、光を透過可能であって、断面円弧状の液体収容容器に対して、外部から光を照射する投光部と、前記投光部からの光のうち前記液体収容容器の内壁面で反射して再び前記液体収容容器の外部に出射される内壁反射光を、受光レンズを通して受光する受光部とを備えて、前記液体収容容器のうち前記投光部からの光の照射部分の内壁面に接する液体の有無により変化する前記受光部での受光量に基づいて動作する液体検出装置において、前記受光レンズは、外向性コマ収差の特性を有する形状で形成されると共に、前記投光部から出射され前記液体収容容器の外壁面で反射して前記受光部側に向う外壁反射光の光束の中心が前記内壁反射光の光束の中心よりも前記受光レンズの中心から離れた位置を通過し、且つ、前記内壁反射光の光束の中心軸と前記受光レンズの中心軸とが平行になるように配置されているところに特徴を有する。
【００１１】
【発明の作用及び効果】
レンズの特性の１つとして、外向性コマ（彗星）収差が従来から知られている。即ち、レンズに対して、そのレンズ中心軸上の点（以下「軸上物点」）から照射された光は同じくレンズ中心軸上に焦点を結像する。これに対して、図１に示すように、レンズ中心軸Ｌ上以外の点（以下「軸外物点」）から照射された光は一点に集まらずに、レンズ中心から離れた位置に入射する光ほどレンズ１０の焦点から遠く離れる方向に発散し、彗星状にぼけた像１１を結ぶのである。この外向性コマ収差による影響は、照射点がレンズ１０の中心から離れるほど著しく大きくなる。なお、次式はレンズのコマ収差の大小の要因となるレンズ形状に関する式である。
【００１２】
「数１」
Ｓ＝（１／Ｒ1＋１／Ｒ2）・ｆ
Ｒ1：レンズの第１面（前面）の曲率半径
Ｒ2：レンズの第２面（後面）の曲率半径
ｆ：レンズの焦点距離
【００１３】
外向性コマ収差の特性を有するレンズとは、数１中のＳが１より小さいという条件を満たす形状のものをいう。
本発明は、この外向性コマ収差というレンズの特性に基づいて創作されたものである。
【００１４】
＜請求項１の発明＞
請求項１の構成によれば、受光レンズは、外向性コマ収差の特性を有する形状で形成されており、外壁反射光の光束の中心が内壁反射光のそれよりも受光レンズの中心から離れた位置を通過するように配置されている。従って、外壁反射光は、内壁反射光に比べて外向性コマ収差による影響が大きく受光レンズの焦点からより遠く離れる方向に発散する。これにより受光部には、例えば外向コマ収差の特性を有しない形状の受光レンズを使用する場合に比べて内壁反射光の占有率の高い光が入射することになり、もってＳ／Ｎ比の向上を図ることができる。
このような構成であれば、投光部及び受光部間に非透光部材を設けた従来の液体検出装置のように検出領域の範囲に制約が加わるということなく、気泡及び水滴の影響を加味した検出領域を確保しつつ、外壁反射光による影響を低減させることができ、もって正確な液体検出を行うことが可能になる。
【００１６】
【発明の実施の形態】
＜第１実施形態＞
本発明の第１実施形態を図２ないし図５によって説明する。
本実施形態に係る液体検出装置２０は、図２に示すように、投光用光ファイバＦ１からの光を投光レンズ２１を通して出射する投光部２２と、投光部２２から出射された光のうち液体収容容器の側壁２５で反射した光を受光レンズ２３を通して集光して受光用光ファイバＦ２に与える受光部２４とがケース２６内に収容された構成となっている。本実施形態では、液体検出装置２０は、液体収容容器の所定の側壁２５面上に、液体収容容器内の液面と平行な方向に投光部２２及び受光部２４が並ぶように配置され、例えばケース２６に貫通形成された取付穴Ｈ，Ｈに図示しないボルト等を通して図示しない支持部に固着される。液体検出の基本的原理は従来のものと同様であり、液体収容容器のうち投光部２２からの光の照射領域に液体が存在しない場合には、投光部２２からの光の一部は側壁２５内に入射して内壁で反射して再び外部に出射されて受光部２４に到達する。一方、液体収容容器の照射領域まで液体が満たされた場合には、内壁面での正反射率が大きく減少するために、投光部２２からの光の大部分は側壁２５を貫通し受光部２４に到達しなくなる。従って、受光用光ファイバＦ２の端部に接続された図示しないコントローラ部において受光部２４から伝送される受光量レベルを測定することで液体収容容器内の液体の有無を検出することができるのである。
【００１７】
さて、本実施形態では、受光レンズ２３は外向性コマ収差の特性を有する形状をなしている。即ち次式においてＳが１より小さいという条件を満たす形状である。
【００１８】
「数２」
Ｓ＝（１／Ｒ1＋１／Ｒ2）・ｆ
Ｒ1：レンズの第１面（前面）の曲率半径
Ｒ2：レンズの第２面（後面）の曲率半径
ｆ：レンズの焦点距離
なお、本実施形態の受光レンズ２３は例えばＲ1＝∞、Ｒ2＝-2.34ｍｍ、ｆ＝4ｍｍのレンズを用いた。（Ｓ＝-1.709＜１だから外向性コマ収差の特性を有することになる。）
【００１９】
次に前記受光部２４と投光部２２との配置関係について図４に基づいて説明する。なお、同図は説明を簡単にするために、投光部２２から出射された光のうち液体収容容器の外壁で正反射される外壁反射光Ｍ２、及び内壁で正反射される内壁反射光Ｍ１についてはそれらの光束の中心の光路のみを矢印で示してある。同図に示すように、受光レンズ２３は、そのレンズ中心軸Ｌ１が内壁反射光Ｍ１の光束の中心軸にほぼ一致させるように配置されている。
【００２０】
次いで本実施形態に係る液体検出装置２０の作用効果について説明する。
投光用及び受光用の光ファイバＦ１，Ｆ２の端部に接続された図示しないコントローラ部を起動させると、投光用光ファイバＦ１から投光レンズ２１を介して略平行光が液体収容容器の側壁２５に照射される。すると、この平行光の一部は内壁に向うが、他の一部はやはり外壁面で反射して受光部２４側に向うことになる。照射領域に液体がない場合、内壁に向った光は正反射して受光部２４側に向う。ここで、受光レンズ２３はそのレンズ中心軸Ｌ１が内壁反射光Ｍ１の光束の中心軸にほぼ一致させるように配置されている。従って、内壁反射光Ｍ１は、図５（Ａ）に示すように、ほとんど外向性コマ収差の影響を受けることなく焦点位置に結像する。一方、同図（Ｂ）に示すように、受光レンズ２３上において、外壁反射光Ｍ２の光束の中心の照射点は内壁反射光Ｍ１のそれよりもレンズ中心軸Ｌ１から離れた位置になる。従って、外向性コマ収差の影響を受けて焦点から反れた位置に彗星状の像を結ぶことなる。
【００２１】
このように、受光レンズ２３上において、外壁反射光Ｍ２の光束中心の照射点を、内壁反射光Ｍ１のそれよりレンズ中心軸Ｌ１から離れた位置にすることで、受光レンズ２３を通過する外壁反射光Ｍ２を焦点から反れた位置に発散させて、もって受光用光ファイバＦ２に入射する光における内壁反射光Ｍ１の占有率を高くすることができる。従って、コントローラ部で測定される受光量は液体収容容器内の液体の有無によって大きく変化することになり、精度のよい液体検出が可能になる。また、投光部及び受光部間に非透光部材を設けた従来の液体検出装置のように検出領域の範囲に制約が加わるということなく、気泡及び水滴の影響を加味した検出領域を確保しつつ、外壁反射光Ｍ２による影響を低減させることができ、もって正確な液体検出を行うことが可能になる。
【００２２】
＜関連技術＞
図６は本発明に係る関連技術を示す。前記実施形態との相違は、受光レンズ２３を内壁反射光Ｍ１の光束中心方向に対して傾けて配置したところにあり、その他の点は前記第１実施形態と同様である。従って、第１実施形態と同一符号を付して重複する説明を省略し、異なるところのみを次に説明する。
【００２３】
例えば液体収容容器の側壁２５が極めて薄い場合、内壁反射光Ｍ１の光速中心と、外壁反射光Ｍ２の光束中心との間隔Ｄ１が極めて狭くなり、両反射光の受光レンズ２３における照射点距離Ｄ２も狭くなる。このような場合には外向性コマ収差による影響の差がそれ程生じないために受光用光ファイバＦ２に入射する外壁反射光Ｍ２の光量を低減させることができないこともある。ここで、前述したように、外向性コマ収差による影響は照射点が受光レンズ２３の中心から離れるほどより著しく大きくなる。そこで、本関連技術では、図６に示すように、受光レンズ２３を内壁反射光Ｍ１の光束中心方向に対して液体収容容器側又は投光部２２側（本関連技術では液体収容容器側）に角度αだけ傾けて配置することで、内壁及び外壁の両反射光Ｍ１，Ｍ２の受光レンズ２３上における各照射点をレンズ中心からより遠くに離すと共に、前記照射点距離Ｄ２が広くなるように構成してある。
【００２４】
このような構成であれば、受光レンズ２３を通過する外壁反射光Ｍ２は内壁反射光Ｍ１に比べて外向性コマ収差の影響を強く受けて受光レンズ２３の焦点からより遠くの位置に彗星状の像を結ぶことになる。従って、受光レンズ２３を傾けない場合に比べて受光用光ファイバＦ２に入射する外壁反射光Ｍ２をより多く低減させることができる。
【００２５】
＜他の実施形態＞
本発明は、前記実施形態及び前記関連技術に限定されるものではなく、例えば、以下に説明するような実施形態も本発明の技術的範囲に含まれ、さらに、下記以外にも要旨を逸脱しない範囲内で種々変更して実施することができる。
（１）上記各実施形態では、受光レンズ２３は、内壁反射光Ｍ１の光束中心がレンズ中心に入射するように配置したが、請求項１に記載でいうように「外壁反射光の光束の中心が内壁反射光の光束の中心よりも受光レンズの中心から離れた位置を通過するように」配置すれば本発明の効果を得ることができる。また、外向性コマ収差による影響は、照射点がレンズの中心から離れるほど著しく大きくなるという特性を生かして、受光レンズを、内壁反射光の光束中心が受光レンズの中心軸から離れた位置を通過するように配置してもよい。このように配置することで、内壁反射光と外壁反射光との外向性コマ収差による影響差を大きくすることができ、もって受光部に入射する外壁反射光の低減を図ることができる。
【図面の簡単な説明】
【図１】外向性コマ収差を説明するための概略図
【図２】本発明の第１実施形態に係る液体検出装置の平断面図
【図３】その正面図
【図４】投光部及び受光部の配置関係を説明するための概略図
【図５】内壁反射光及び外壁反射光の外向性コマ収差による影響を説明するための模式図
【図６】本発明の関連技術に係る液体検出装置の投光部及び受光部の配置関係を説明するための概略図
【図７】従来の液体検出装置の原理を示す断面図
【図８】非透光部材を設けた従来の液体検出装置の断面図
【図９】液体収容容器の側壁の厚さと検出領域の広狭との関係を示す模式図
【符号の説明】
２０…液体検出装置
２１…投光レンズ
２２…投光部
２３…受光レンズ
２４…受光部
２５…側壁
Ｄ２…照射点距離
Ｌ１…レンズ中心軸
Ｍ１…内壁反射光
Ｍ２…外壁反射光[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid detection apparatus that optically detects a liquid level and presence / absence of a liquid.
[0002]
[Prior art]
This type of liquid detection device is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-320248. However, the basic principle of this type of liquid detection device is that it is applied to the side wall 1 of a translucent container as shown in FIG. In this configuration, the light receiving unit 3 is provided at a position to receive light from the light unit 2 and receive the light reflected from the inside of the side wall 1. As shown in FIG. 4A, when no liquid is present in the light irradiation area from the light projecting unit 2, the light is regularly reflected inside the side wall 1 and reaches the light receiving unit 3. As shown in (B), when liquid is present, its regular reflectance is greatly reduced, so that most of the light from the light projecting unit 2 penetrates the side wall 1 and reaches the light receiving unit 3. Disappear. Therefore, the presence or absence of the liquid can be determined by measuring the amount of light incident on the light receiving unit 3.
[0003]
[Problems to be solved by the invention]
By the way, since the light from the light projecting part 2 is reflected also outside the side wall 1 of the container, the light receiving part 3 is not only the light regularly reflected inside the side wall 1 of the container (hereinafter referred to as “inner wall reflected light 4”), The light regularly reflected from the outside of the side wall 1 (hereinafter referred to as “outer wall reflected light 5”) may also be incident. Since the outer wall reflected light 5 is always incident on the light receiving unit 3 regardless of the presence or absence of liquid in the container, the S / N ratio may be lowered and accurate liquid detection may not be performed.
[0004]
Therefore, in Japanese Patent Laid-Open No. 4-66820, when the incident angle θ (see FIG. 7) of the light projecting unit 2 and the light receiving unit 3 with respect to the side wall surface of the container is set to 60 degrees or more, the light reception level at the light receiving unit 3 depending on the presence or absence of liquid. Based on the experimental result that the difference between the two increases, the incident angle θ is increased to improve the S / N ratio. However, in such a configuration, the light emitted from the light projecting unit 2 may be directly incident on the light receiving unit 3, which may cause a decrease in the S / N ratio together with the outer wall reflected light 5.
[0005]
For such a problem, by providing a light shielding part between the light projecting part 2 and the light receiving part 3, or by narrowing the light from the light projecting part 2, direct light from the light projecting part 2 or A method for preventing the outer wall reflected light 5 from entering the light receiving unit 3 can be considered. Japanese Utility Model Publication No. 51-51766 discloses the former method. As shown in FIG. 8, a non-translucent member 6A is provided between the light projecting unit 2 and the light receiving unit 3 to block the optical path of the direct light from the light projecting unit 2 and the outer wall reflected light 5, thereby reflecting the inner wall reflected light. Only 4 can pass. With such a configuration, only the inner wall reflected light 4 is incident on the light receiving unit 3, so that the S / N ratio can be improved, and more accurate liquid detection can be performed.
[0006]
By the way, in order to perform accurate liquid detection, it is necessary to consider not only the influence of the direct light from the light projecting unit 2 and the external wall reflected light 5 but also the range of the detection region. That is, when liquid is supplied to or discharged from the container, bubbles are generated in the liquid and adhere to the inside of the side wall 1 of the container. The light from the light projecting unit 2 is regularly reflected inside the side wall 1 and reaches the light receiving unit 3 as in the case where there is no liquid at the part where the bubbles are attached. Accordingly, even when liquid is present in the detection region, the light reception level at the light receiving unit 3 approaches the light reception level when there is no liquid due to the attachment of bubbles. Conversely, when no liquid is present in the detection region, water droplets may adhere to the inside of the side wall 1 of the container, and the received light amount level at the light receiving unit 3 may approach the received light amount level side when liquid is present. Therefore, in order to avoid the influence of bubbles and water droplets, it is necessary to secure a wide detection area to some extent.
[0007]
However, many containers have very thin sidewalls, and when the liquid in such a container is detected using the above-described liquid detection device using the non-translucent member 6A, detection that can be secured. There arises a new problem that the area of the region is restricted. This will be described in detail by taking two types of containers (thickness t1 <t2) having different thicknesses as shown in FIG. 9 as an example. As shown in FIG. 5A, if the side wall 1 of the container has a certain thickness (t2), the optical path R1 of the inner wall reflected light 4 and the optical path R2 of the outer wall reflected light 5 do not overlap each other. Even if the optical path R2 of the outer wall reflected light 5 is blocked by the non-translucent member 6A or the like, the detection region W1 is not affected. However, as shown in FIG. 5B, when the side wall 1 becomes thin (t1), the optical path R1 of the inner wall reflected light 4 and the optical path R2 of the outer wall reflected light 5 overlap each other. Here, when the non-translucent member 6B is provided so as to block only the optical path R3 through which only the inner wall reflected light 4 passes by blocking the optical path of the outer wall reflected light 5 as shown in FIG. It becomes narrower to W2. Therefore, if the side wall 1 is thin, the problem that accurate liquid detection cannot be performed due to the influence of bubbles and water droplets occurs again.
[0008]
The present invention has been made in view of the above circumstances, and its purpose is to reduce the influence of the reflected light from the outer wall while securing a detection region that takes into account the influence of bubbles and water droplets adhering to the liquid container. A liquid detection apparatus capable of accurate liquid detection is provided.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a liquid detection device according to the invention of claim 1 is capable of transmitting light, and projects a light projecting unit that irradiates light from the outside to a liquid container having a circular arc cross section. A light receiving portion that receives light reflected from the inner wall surface of the liquid container and reflected by the inner wall surface of the liquid container and is emitted to the outside of the liquid container again through a light receiving lens. In the liquid detection device that operates based on the amount of light received by the light receiving unit that varies depending on the presence or absence of liquid in contact with the inner wall surface of the portion irradiated with light from the light projecting unit, the light receiving lens includes outward coma aberration The center of the luminous flux of the outer wall reflected light that is emitted from the light projecting portion and reflected by the outer wall surface of the liquid container and directed toward the light receiving portion is the luminous flux of the inner wall reflected light. Of the light receiving lens Passes through the heart away, and has a feature in that the center axis of the light beam of the inner wall reflected light and the center axis of the light receiving lens are arranged in parallel.
[0011]
[Action and effect of the invention]
As one of the characteristics of the lens, extroverted coma (comet) aberration has been conventionally known. That is, the light emitted from a point on the lens central axis (hereinafter referred to as “on-axis object point”) is focused on the lens central axis. On the other hand, as shown in FIG. 1, light emitted from points other than the lens center axis L (hereinafter referred to as “off-axis object point”) does not converge on one point but enters a position away from the lens center. The light diverges away from the focal point of the lens 10 and forms a comet-like blurred image 11. The influence of the outward coma aberration becomes remarkably larger as the irradiation point is further away from the center of the lens 10. The following expression is an expression related to the lens shape that causes the coma aberration of the lens.
[0012]
"Number 1"
S = (1 / R1 + 1 / R2) · f
R1: radius of curvature of the first surface (front surface) of the lens R2: radius of curvature of the second surface (rear surface) of the lens f: focal length of the lens
The lens having the characteristic of outward coma is a lens having a condition that satisfies the condition that S in Equation 1 is smaller than 1.
The present invention was created on the basis of this lens characteristic called outward coma.
[0014]
<Invention of Claim 1>
According to the configuration of the first aspect, the light receiving lens is formed in a shape having the characteristic of outward coma, and the center of the light flux of the outer wall reflected light is further away from the center of the light receiving lens than that of the inner wall reflected light. It is arranged to pass through the position. Therefore, the outer wall reflected light is more influenced by outward coma than the inner wall reflected light and diverges in a direction farther away from the focus of the light receiving lens. As a result, light having a higher occupancy ratio of the inner wall reflected light is incident on the light receiving portion than when a light receiving lens having a shape having no outward coma characteristics is used, for example, so that the S / N ratio is improved. Can be achieved.
With such a configuration, the influence of bubbles and water droplets is taken into consideration without adding restrictions to the range of the detection region as in the conventional liquid detection device in which a non-translucent member is provided between the light projecting unit and the light receiving unit. Thus, it is possible to reduce the influence of the reflected light from the outer wall while securing the detection area, and thus it is possible to perform accurate liquid detection.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 2, the liquid detection device 20 according to this embodiment includes a light projecting unit 22 that emits light from the light projecting optical fiber F <b> 1 through the light projecting lens 21, and light emitted from the light projecting unit 22. Among them, a light receiving portion 24 that collects the light reflected by the side wall 25 of the liquid container through the light receiving lens 23 and applies the light to the light receiving optical fiber F <b> 2 is housed in the case 26. In the present embodiment, the liquid detection device 20 is arranged on the predetermined side wall 25 of the liquid storage container so that the light projecting unit 22 and the light receiving unit 24 are aligned in a direction parallel to the liquid level in the liquid storage container. For example, the mounting holes H are formed through the case 26 and are fixed to a support portion (not shown) through bolts (not shown). The basic principle of liquid detection is the same as the conventional one. When no liquid is present in the light irradiation area of the light projecting unit 22 in the liquid container, a part of the light from the light projecting unit 22 is The light enters the side wall 25, is reflected by the inner wall, is emitted to the outside again, and reaches the light receiving unit 24. On the other hand, when the liquid is filled up to the irradiation region of the liquid container, the regular reflectance at the inner wall surface is greatly reduced. Therefore, most of the light from the light projecting unit 22 penetrates the side wall 25 and passes through the light receiving unit. 24 will not be reached. Therefore, the presence or absence of liquid in the liquid container can be detected by measuring the received light amount level transmitted from the light receiving unit 24 in a controller unit (not shown) connected to the end of the light receiving optical fiber F2. .
[0017]
In the present embodiment, the light receiving lens 23 has a shape having the characteristic of outward coma. That is, the shape satisfies the condition that S is smaller than 1 in the following equation.
[0018]
"Number 2"
S = (1 / R1 + 1 / R2) · f
R1: radius of curvature of the first surface (front surface) of the lens R2: radius of curvature of the second surface (rear surface) of the lens f: focal length of the lens The light receiving lens 23 of the present embodiment has R1 = ∞, R2 = −, for example. A lens of 2.34 mm and f = 4 mm was used. (S = -1.709 <1, so that it has the characteristic of outward coma.)
[0019]
Next, the arrangement relationship between the light receiving unit 24 and the light projecting unit 22 will be described with reference to FIG. For the sake of simplicity, FIG. 6 shows that the outer wall reflected light M2 that is regularly reflected by the outer wall of the liquid container and the inner wall reflected light M1 that is regularly reflected by the inner wall out of the light emitted from the light projecting unit 22. For, only the optical path at the center of the luminous flux is indicated by an arrow. As shown in the figure, the light receiving lens 23 is arranged such that the lens central axis L1 thereof substantially coincides with the central axis of the light beam of the inner wall reflected light M1.
[0020]
Next, functions and effects of the liquid detection device 20 according to the present embodiment will be described.
When a controller unit (not shown) connected to the ends of the projecting and receiving optical fibers F1 and F2 is activated, substantially parallel light is transmitted from the projecting optical fiber F1 through the projecting lens 21 to the liquid container. The side wall 25 is irradiated. Then, a part of the parallel light is directed to the inner wall, while the other part is also reflected by the outer wall surface and is directed to the light receiving unit 24 side. When there is no liquid in the irradiated area, the light directed toward the inner wall is specularly reflected and travels toward the light receiving unit 24 side. Here, the light receiving lens 23 is arranged so that the lens central axis L1 thereof substantially coincides with the central axis of the light beam of the inner wall reflected light M1. Therefore, as shown in FIG. 5A, the inner wall reflected light M1 forms an image at the focal position with almost no influence of outward coma. On the other hand, as shown in FIG. 5B, on the light receiving lens 23, the irradiation point at the center of the light beam of the outer wall reflected light M2 is located farther from the lens center axis L1 than that of the inner wall reflected light M1. Therefore, a comet-like image is formed at a position deviated from the focal point due to the influence of outward coma.
[0021]
In this way, on the light receiving lens 23, the irradiation point at the light beam center of the outer wall reflected light M2 is positioned farther from the lens center axis L1 than that of the inner wall reflected light M1, so that the outer wall reflection passing through the light receiving lens 23 is achieved. The light M2 is diverged to a position deviated from the focal point, so that the occupation ratio of the inner wall reflected light M1 in the light incident on the light receiving optical fiber F2 can be increased. Therefore, the amount of received light measured by the controller unit varies greatly depending on the presence or absence of liquid in the liquid container, and liquid detection with high accuracy becomes possible. In addition, a detection area that takes into account the influence of bubbles and water droplets is ensured without the restriction of the range of the detection area as in the conventional liquid detection device in which a non-translucent member is provided between the light projecting part and the light receiving part. However, the influence of the outer wall reflected light M2 can be reduced, so that accurate liquid detection can be performed.
[0022]
< Related technologies >
FIG. 6 shows a related technique according to the present invention . The difference from the above embodiment is that the light receiving lens 23 is arranged to be inclined with respect to the center of the light flux of the inner wall reflected light M1, and the other points are the same as in the first embodiment. Therefore, the same reference numerals as those in the first embodiment are attached and the redundant description is omitted, and only different points will be described next.
[0023]
For example, when the side wall 25 of the liquid container is extremely thin, the distance D1 between the light velocity center of the inner wall reflected light M1 and the light beam center of the outer wall reflected light M2 is extremely narrow, and the irradiation point distance D2 of the both reflected lights on the light receiving lens 23 is also the same. Narrow. In such a case, since the difference in influence due to outward coma does not occur so much, the light amount of the outer wall reflected light M2 incident on the light receiving optical fiber F2 may not be reduced. Here, as described above, the influence due to the outward coma aberration becomes remarkably larger as the irradiation point moves away from the center of the light receiving lens 23. Therefore, in this related technology , as shown in FIG. 6, the light receiving lens 23 is placed on the liquid container side or the light projecting unit 22 side (the liquid container side in this related technology ) with respect to the direction of the center of the inner wall reflected light M1. Arrangement is made such that each irradiation point on the light receiving lens 23 of both the inner wall and outer wall reflected light M1, M2 is further away from the center of the lens and the irradiation point distance D2 is widened by inclining the angle α. It is.
[0024]
With such a configuration, the outer wall reflected light M2 passing through the light receiving lens 23 is more influenced by outward coma than the inner wall reflected light M1, and has a comet-like shape at a position farther from the focus of the light receiving lens 23. I will connect the statue. Therefore, the outer wall reflected light M2 incident on the light receiving optical fiber F2 can be reduced more than when the light receiving lens 23 is not tilted.
[0025]
<Other embodiments>
The present invention is not limited to the above- described embodiment and the related technology . For example, the embodiments described below are also included in the technical scope of the present invention, and further, other than the following, the gist is not deviated from. Various modifications can be made within the range.
(1) In each of the above embodiments, the light receiving lens 23 is arranged so that the light beam center of the inner wall reflected light M1 is incident on the center of the lens. However, as described in claim 1, “the center of the light beam of the outer wall reflected light” The effect of the present invention can be obtained if it is arranged so as to pass through a position farther from the center of the light receiving lens than the center of the light flux of the inner wall reflected light. Also, the effect of outward coma aberration takes advantage of the characteristic that the irradiation point becomes farther away from the center of the lens, passing through the light receiving lens through the position where the center of the reflected light from the inner wall is away from the center axis of the light receiving lens. You may arrange so that. By arranging in this way, it is possible to increase the difference in influence due to the outward coma aberration between the inner wall reflected light and the outer wall reflected light, thereby reducing the outer wall reflected light incident on the light receiving unit.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining outward coma aberration. FIG. 2 is a cross-sectional plan view of a liquid detection device according to a first embodiment of the present invention. FIG. 3 is a front view thereof. FIG. 5 is a schematic diagram for explaining the arrangement relationship of the light receiving parts. FIG. 5 is a schematic diagram for explaining the influence of outward coma on the inner wall reflected light and the outer wall reflected light. FIG. 6 is a liquid detection according to the related art of the present invention. FIG. 7 is a cross-sectional view illustrating the principle of a conventional liquid detection device. FIG. 8 is a cross-sectional view of the conventional liquid detection device provided with a non-translucent member. Sectional view [Fig. 9] Schematic diagram showing the relationship between the thickness of the side wall of the liquid container and the width of the detection region
DESCRIPTION OF SYMBOLS 20 ... Liquid detection apparatus 21 ... Light projection lens 22 ... Light projection part 23 ... Light reception lens 24 ... Light reception part 25 ... Side wall D2 ... Irradiation point distance L1 ... Lens central axis M1 ... Inner wall reflected light M2 ... Outer wall reflected light

Claims

光を透過可能であって、断面円弧状の液体収容容器に対して、外部から光を照射する投光部と、
前記投光部からの光のうち前記液体収容容器の内壁面で反射して再び前記液体収容容器の外部に出射される内壁反射光を、受光レンズを通して受光する受光部とを備えて、
前記液体収容容器のうち前記投光部からの光の照射部分の内壁面に接する液体の有無により変化する前記受光部での受光量に基づいて動作する液体検出装置において、
前記受光レンズは、外向性コマ収差の特性を有する形状で形成されると共に、前記投光部から出射され前記液体収容容器の外壁面で反射して前記受光部側に向う外壁反射光の光束の中心が前記内壁反射光の光束の中心よりも前記受光レンズの中心から離れた位置を通過し、且つ、前記内壁反射光の光束の中心軸と前記受光レンズの中心軸とが平行になるように配置されていることを特徴とする液体検出装置。A light projecting unit that is capable of transmitting light and irradiates light from the outside with respect to the liquid container having a circular arc cross section ;
A light receiving unit that receives light reflected from the inner wall surface of the liquid storage container out of the light from the light projecting part and is emitted to the outside of the liquid storage container again through a light receiving lens;
In the liquid detection device that operates based on the amount of light received by the light receiving unit that varies depending on the presence or absence of liquid in contact with the inner wall surface of the portion irradiated with light from the light projecting unit in the liquid container,
The light receiving lens is formed in a shape having a characteristic of outward coma, and is reflected from the outer wall surface of the liquid container and is reflected from the outer wall surface of the liquid container and is reflected by the outer wall reflected light toward the light receiving unit. The center passes through a position farther from the center of the light receiving lens than the center of the light beam of the inner wall reflected light , and the central axis of the light beam of the inner wall reflected light and the center axis of the light receiving lens are parallel to each other. A liquid detection apparatus characterized by being arranged .