JP2004233152A - Weighing instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a weighing instrument, for performing weighing with high accuracy and with a wide measurement range by removing sliding portions in a support part to eliminate resistance, and having little measurement error caused by temperature since heat generation is little even at the long-time continuous measurement. <P>SOLUTION: This weighing instrument is equipped with a magnet unit 2 comprising electromagnets 6a and 6b installed so as to confront a guide 4 of magnetic substance via a gap and a permanent magnet 7 disposed so that the gap is included in a magnetic circuit of generated magnetic flux, a levitation body 3 levitated by attraction produced between the guide 4 and the magnet unit 2, a sensor 12 for detecting a physical quantity in the magnetic circuit, a control means 11 for controlling an excitation current passed through the electromagnets so that the levitation body is stably levitated relative to the guide based on the detected physical quantity while the stationary values of the excitation current flowing through the electromagnets are converged at zero whether or not external force exists acting on the levitation body, and a means 30 for calculating the weight of a measuring object from the physical quantity. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

ただし、μ０は真空中の透磁率、Ｓは磁気回路の断面積、ｚはギャップ長２９の検出値、Ｈｍはギャップ１０に生じる磁界の強さ、ｌｍは永久磁石７の長さ、μｓはギャップ部分以外の非透磁率である。この式における吸引力ｆとギャップ長ｚとの関係を表す概略図を図５に示す。
【００３６】
以上のような関係から、磁気浮上系においてゼロパワー制御がなされている場合には、磁石ユニット２とガイド４との間のギャップ１０の大きさ、すなわちギャップ長２９は浮上部の総重量をパラメータとする関数となる。このとき浮上部の重量が小さい場合には、それに釣り合うための吸引力は小さくなるため、ギャップ長２９が広がる。一方、浮上部の重量が大きい場合には、それに釣り合うための吸引力が大きくなるため、ギャップ長２９が狭くなる。
【００３７】
本実施の形態では、この関係を用いて、秤量演算装置３０において被測定物の重量を演算する。ここで、秤量演算装置３０は、ギャップセンサ１５の出力値に対してフィルタリング等の前処理を行う信号処理器５１と、その出力を導入して、上記関係式を用い、ギャップ長２９と磁石ユニット２に用いられている永久磁石７の磁気力により発生する吸引力、すなわち浮上体３と被測定物の重量との和を演算する浮上部重量演算器５２と、その浮上部重量演算器５２の出力から、浮上体３の重量を減ずる減算器５３とから構成されている。
【００３８】
これにより、秤量演算装置３０において、ギャップセンサ１５の出力値から被測定物の重量を演算し、その結果を出力装置５４に表示させることができる。なお、実際の浮上部重量演算器５２で用いる関係式においては、上式の各変数に対して、実験等で得られた補正を加え、浮上部の重量を演算しても何ら差し支えない。
【００３９】
また、上述の関係式より、吸引力ｆは、ギャップ長ｚの２乗に反比例することがわかる。したがって、被測定物の重量が比較的小さく、ギャップ長ｚが大きい場合には、被測定物の重量変化に対するギャップ長ｚの変化率が大きくなり、測定の精度が高くなる。一方、被測定物の重量が比較的大きく、ギャップ長ｚが小さい場合には、吸引力ｆの変化率が比較的大きくなるため、秤量台の磁気浮上剛性が高まることになり、その結果、比較的大きな荷重まで測定することが可能となる。したがって磁気浮上系では、このような非線形特性を有することによって、線形特性の秤量手段を有する従来の秤量装置に比べて、比較的広い測定レンジを得ることができる。
【００４０】
さらに、本実施の形態の秤量装置においては、測定を行っているときでも、コイル９に流れる電流は、被測定物の重量にかかわらず、定常状態で零に収束し、被測定物を浮上させる吸引力は永久磁石７の磁気力のみで釣り合わせることになる。したがって、長時間測定を行った場合でもコイル９に電流がほとんど流れることはなく、コイル９による発熱を大きく低減させることができる。これにより、コイル９の発熱に起因する温度変化によって、永久磁石７の特性が変化することを防ぐことができ、従来の秤量装置において問題となっていた、長時間連続測定時のコイル発熱による測定誤差の発生を抑制することができる。
【００４１】
なお、この構成において浮上制御する際に用いるギャップ長２９を検出する手段は、磁石ユニット２とガイド４との間のギャップの大きさを直接、もしくは間接的に検出できるものであればいかなる方式でもよく、渦流式センサ、光学式センサ、音波式センサ等のギャップセンサを用いることで実現できる。
【００４２】
また、本実施の形態では浮上部の重量を測定する秤量演算装置３０にギャップ長２９の値ｚを導入することとしているが、その検出手段としては、前記ギャップ長２９の検出手段と同様のセンサを用いることができ、かつ、浮上制御に用いるギャップセンサ１５と同一のものを利用してもよい。
【００４３】
（第２の実施の形態）次に、本発明の第２の実施の形態の秤量装置について説明する。第１の実施の形態では、ギャップ長２９、及び励磁電流の検出結果に直接フィードバックゲインを乗ずる制御手法としてきたが、浮上演算回路１３に状態観測器を用いることによって浮上系の状態を推定し、その結果を用いて制御回路を構成することもできる。第２の実施の形態は、この原理を採用したことを特徴とする。
【００４４】
図６は、浮上演算回路１３内の制御電圧演算回路１９の部分に、状態観測器４０を導入したときの構成図である。この図６に示すように、状態観測器４０を含む制御電圧演算回路１９は、ギャップ長偏差Δｚ、励磁電流偏差Δｉを導人し、ギャップ長偏差Δｚ、Δｚの時間微分値Δｚ′、励磁電流偏差Δｉ、及び外力ｕを演算して出力する状態観測器４０と、Δｚを導入しフィードバックゲインＦ１をΔｚに乗じるゲイン補償器２１と、Δｚ′を導入してフィードバックゲインＦ２を乗じるゲイン補償器２２と、Δｉを導入してフィードバックゲインＦ３を乗じるゲイン補償器２３と、ｕを導入してフィードバックゲインＦ４を乗じるゲイン補償器４１と、ゲイン補償器２１〜２３及びゲイン補償器４１の出力を入力し、これらの総和を演算する加算器４２と、加算器４２の出力値を目標値から減じる減算器２８とで構成されている。
【００４５】
上記のような状態観測器４０を用いた浮上制御に関しては、例えば特許第３１５２７７５号に示された制御手法を採用する。
【００４６】
この第２の実施の形態の秤量装置では、上記回路構成の状態観測器を導入することによって、浮上系の状態を推定しながら制御を施し、より安定した浮上系を構築することが可能になる。なお、上記のような状態観測器４０を用いた浮上制御を行っている場合には、被測定物の重量を演算する秤量演算装置３０に導入する値として、上述のギャップ長２９を用いるほかに、コイル９に流れる励磁電流の検出値を用いることもできる。
【００４７】
本実施の形態では磁気浮上系においてはゼロパワー制御を採用しているため、定常状態では励磁電流が零となるが、被測定物の重量の変化、もしくは荷重が印加された際の過渡状態においては、励磁電流がその荷重変化に応じて流れることになる。その際、ギャップ長２９と励磁電流を前記状態観測器４０に導入することによって、その出力値として浮上体３に加わる外乱荷重ｕ”を得ることができる。
【００４８】
このような構成においては、このｕ”は被測定物の重量を示すことになるため、このような状態観測器４０を用いることによって、ギャップ長２９、及び励磁電流の検出器を導入して被測定物の重量を演算する秤量演算装置３０を得ることができる。また、この状態観測器４０を用いることにより、浮上系が過渡状態にあるときでも外乱推定を行うことができるため、被測定物を積載したとき、もしくは被測定物の重量が変化した場合などにおいて、浮上系の安定を待つことなく秤量演算を行い、短時間で測定結果を推定することができる。
【００４９】
さらに、上記のように状態観測器４０を用い、その出力値の１つである荷重推定を秤量の手段として用いる場合には、別途秤量演算装置３０を分離して設置する必要はなく、図示のように状態観測器４０と秤量演算装置３０を同一の制御ブロックとし、浮上制御装置１１の内部に秤量演算装置３０を含めるような構成としても構わない。
【００５０】
（第３の実施の形態）次に、本発明の第３の実施の形態の秤量装置について説明する。第３の実施の形態では、秤量演算装置３０に導入する値として、ギャップ長２９の値ｚを直接用いるのではなく、積分補償器２６の出力値を用いることもできる。以下に、第３の実施の形態として、積分補償器２６の出力値を秤量演算手段に用いる場合について、図７を参照しながら説明する。
【００５１】
浮上演算回路１３において、励磁電流の値ｉとギャップ長２９の値ｚを導入し、適当な演算を施すことによって浮上体３を磁気浮上させているが、この際、励磁電流の検出値は、浮上制御とともに、励磁電流目標値との差分Δｉに積分補償器２６を乗じて電圧指令値ｅを演算するために、電流目標値が零のときには定常状態において励磁電流が零となり、浮上演算回路１３全体でゼロパワー制御が構成される。このとき、積分補償器２６の出力値は、ゼロパワーで磁気浮上しているときの、基準ギャップ長ｚ０からの偏差を打ち消すのに相当する値が出力されていることになる。したがって、この積分補償器２６の出力値は、ギャップ長２９を検出することと等価となり、前述と同様の秤量演算手段で、被測定物の重量を測定することができる。この場合には、積分補償器２６の出力を秤量演算装置３０に導入し、浮上部重量演算器５２によって積分補償器２６の出力値から浮上部全体の重量を演算し、減算器５３で浮上体３の重量を減じたものを出力装置５４で表示する構成となる。
【００５２】
なお、積分補償器２６の出力値は検出信号を積分した値となるため、必然的に検出信号の高調波成分がフィルタリングされることになり、検出信号中のノイズや高調波成分が取り除かれたものとなる。したがって、この積分補償器２６の出力値を秤量演算に用いると信号ノイズが小さく、秤量演算が容易となるだけではなく、被測定物の重量の推定も迅速に行うことができる。
【００５３】
以下に、被測定物が秤量台５に積載されたときの応答の例を用いて、重量推定の原理を説明する。被測定物が秤量台５に積載された際に、励磁電流の値が図８（ａ）のような波形を示したとすると、積分補償器２６の出力値は図８（ｂ）のような波形となり、ほぼ１次系のステップ応答とみなすことができる。この際、積分補償器２６の出力値としては、励磁電流の検出値に含まれる高調波成分やノイズ成分を取り除いたものが得られるため、その応答は比較的滑らかなものとなる。
【００５４】
ここで、積分補償器２６の出力値を１次系とみなし、一定時間間隔τで検出した出力値の差分をΔｖとすれば、その応答特性から、各時間での差分出力値Δｖｎの変化率、すなわちΔｖｎ＋１／Δｖｎは一定の値を示す。さらに、応答の最終値ｖ∞の値は、ある点における出力値ｖｎと、そのときの検出時間間隔τ、そしてシステム全体の応答時定数Ｔを用いて、
【数２】

の関係から求めることができる。なお、応答の時定数Ｔは、装置の構造、及び浮上演算回路１３の各設定値より既知の値であるため、応答を１次系と見なせる波形が得られた時点、すなわち差分出力値の変化率が一定となった時点において、系の安定を待つことなく、過渡応答中に被測定物の重量を予測することができる。
【００５５】
以上のようにして、過渡応答中に重量を予測する場合には、図７に示したように、その出力値を浮上部重量演算器５２の出力値を直接出力装置５４に引き渡すか、浮上部重量推定演算器５５の出力を表示するかを選択するために、出力切換器５６を設け、自動もしくは手動で出力値を切り替える構成としてもよい。
【００５６】
（第４、５の実施の形態）これまで説明した実施の形態それぞれにおいては、磁気回路中の物理量検出手段として、励磁電流検出、及びギャップ長２９を検出する手段を用いたが、ギャップセンサ１５、電流検出器１６の代わりに、浮上体３の加速度を検出する加速度センサ、もしくは磁束の大きさを検出するホール素子を用いてもよい。
【００５７】
図９は、本発明の第４の実施の形態として、ギャップセンサ１５の代わりに加速度センサ３１、及び２つの積分器３２を用いた場合の構成を示している。このように、加速度センサ３１の検出値を２回積分したものをギャップ長２９の値ｚとして演算する構成をとることもできる。この場合には、特にセンサの設定位置を浮上体３の加速度が検出できる範囲で任意に決定できるという利点がある。
【００５８】
また図１０は、本発明の第５の実施の形態として、電流検出器１６の代わりに磁束の大きさを検出するホール素子で成る磁束検出器３３を用いた例を示している。この場合には、磁束の大きさを検出することにより、磁気回路中に発生する吸引力の大きさを得ることができ、それによりフィードバック制御を施すことができる。ただし、この場合には励磁電流の値を直接的に導入することができないため、励磁電流を積分補償器２６に導入してゼロパワー制御をかけることができない。このように電流信号を直接導入しない場合には、図示のようにパワーアンプ１４に導入する指令値ｅに対して、同様の積分補償器３４を導入してフィードバックすることにより、パワーアンプ１４からの出力を零に収束させることで、特許第２７９３２４０号「浮上式搬送装置」にも示されているようなゼロパワー制御を実現することができる。
【００５９】
（第６の実施の形態）以上述べてきた各実施の形態においては磁石ユニット２を台枠１に取りつけ、ガイド４を浮上体３に設置した場合について説明してきたが、磁石ユニット２、及びガイド４の設置箇所は限定されるものではなく、その配置を逆にし、図１１に示すように、台枠１にガイド４を設置し、磁石ユニット２を浮上体３に設置しても何ら差し支えない。このように構成したのが本発明の第６の実施の形態である。
【００６０】
この第６の実施の形態の秤量装置でも、これまで説明してきた各実施の形態と同様に浮上制御装置１１、秤量演算装置３０を構成することによって、被測定物の重量測定が可能となる。
【００６１】
以上、本発明を適用した秤量装置の具体的な構成について、第１〜第６の実施の形態として詳細に説明したが、本発明に係る秤量装置は、以上の例に限定されるものではなく、本発明の要旨を逸脱しない範囲で種々変更可能である。
【００６２】
【発明の効果】
以上のように本発明によれば、被測定物を積載する秤量台は浮上体に設置され磁気浮上されているため、台枠等と接触部を持つことなく被測定物の重量を測定することが可能となる。したがって、従来の秤量装置における支点部等に起因する抵抗等の影響がなくなるため、測定誤差を発生することなく、高精度な秤量が行える。
【００６３】
また、本発明によれば、浮上体が非線形を有するばね定数で支持されており、被測定物の重量が大きくなると浮上体を支持する浮上剛性が上がるため、従来の線形ばね定数で支持される構成と比べて、測定範囲を広くとることが可能である。
【００６４】
また、本発明によれば、定常状態において、被測定物を含む浮上部を浮上させる磁気吸引力を永久磁石の吸引力のみで発生させ、さらに電磁石に流れる励磁電流の定常値を、浮上体に積載された被測定物の重量の大きさにかかわらず零にすることができるため、上記電磁石のコイルには、浮上部に対して被測定物の重量が変化した際に過渡的な電流が流れるのみとなり、コイルで消費される電力を従来に比べて減少させることができ、これにより、コイルに流れる電流を軽減させることが可能になり、コイル部における発熱を軽減し、長時間秤量を行った場合でも温度変化が少なく、安定した測定精度を得ることができる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態の秤量装置の斜視図。
【図２】上記第１の実施の形態の秤量装置の断面図。
【図３】上記第１の実施の形態の秤量装置における磁石ユニットの斜視図。
【図４】上記第１の実施の形態の秤量装置における浮上制御装置及び秤量演算装置のブロック図。
【図５】上記第１の実施の形態の秤量装置における磁石ユニットのギャップ長と吸引力の関係を示す図。
【図６】本発明の第２の実施の形態の秤量装置における浮上制御装置及び秤量演算装置のブロック図。
【図７】本発明の第３の実施の形態の秤量装置における浮上制御装置及び秤量演算装置のブロック図。
【図８】上記第３の実施の形態の秤量装置において出力波形から重量推定する手法を示す図。
【図９】本発明の第４の実施の形態の秤量装置における浮上制御装置及び秤量演算装置のブロック図。
【図１０】本発明の第５の実施の形態の秤量装置における浮上制御装置及び秤量演算装置のブロック図。
【図１１】本発明の第６の実施の形態の秤量装置の断面図。
【図１２】従来の秤量装置の基本構成を示す断面図。
【符号の説明】
１…台枠
２…磁石ユニット
３…浮上体
４…ガイド
５…秤量台
６ａ…電磁石
６ｂ…電磁石
７…永久磁石
８…継鉄
９…コイル
１０…ギャップ
１１…制御装置
１２…センサ部
１３…浮上演算回路
１４…パワーアンプ
１５…ギャップセンサ
１６…電流検出器
１７…減算器
１８…減算器
１９…制御電圧演算回路
２０…微分器
２１…ゲイン補償器
２２…ゲイン補償器
２３…ゲイン補償器
２４…電流偏差目標値発生器
２５…減算器
２６…積分補償器
２７…加算器
２８…減算器
２９…ギャップ長
３０…秤量演算装置
３１…加速度センサ
３２…積分器
３３…磁束検出器
４０…状態観測器
４１…ゲイン補償器
４２…加算器
５１…信号処理器
５２…浮上部重量演算器
５３…減算器
５４…出力装置
５５…浮上部重量推定器
５６…出力切換器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a weighing device using electromagnetic force.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a weighing device using an electromagnetic force, an electromagnetic force-balanced electronic balance has been widely used. FIG. 12 shows a basic configuration of a conventional electronic balance. Generally, a conventional electronic balance employs a method of measuring the weight of an object to be measured by balancing the electromagnetic force with the weight of the object, as disclosed in Japanese Patent No. 3289463, for example.
[0003]
In the conventional electromagnetic balance of the electromagnetic force balance type, a weighing table 103 for loading an object to be measured is provided at one end of a lever 102 rotatably installed around a fulcrum 101. A magnetic circuit 106 for generating a load for balancing the weight of the loaded object to be measured and a force coil 105 are disposed on the opposite side of the lever 102 with respect to the lever 102. The magnetic circuit 106 is formed by a permanent magnet 107, the force coil 105 is disposed in a static magnetic field formed by the magnetic circuit 106, and an electromagnetic force is generated by flowing a current through the force coil 105. The weight of the measured object loaded on one end of the lever 102 and the electromagnetic force are balanced. Here, the current flowing through the force coil 105 is controlled by performing an appropriate calculation so as to correct the inclination of the lever 102 detected by the displacement sensor 108 provided at the end of the lever 102 to zero. is there.
[0004]
In the conventional electronic balance, in the above configuration, the weight of the object to be measured is balanced with the electromagnetic force of the force coil 105, and the magnitude of the current flowing through the force coil 105 in an equilibrium state is determined. Find the weight of
[0005]
[Patent Document 1]
Japanese Patent No. 2712161
[0006]
[Patent Document 2]
Japanese Patent No. 2793240
[0007]
[Patent Document 3]
Japanese Patent No. 2967822
[0008]
[Patent Document 4]
Japanese Patent No. 3152775
[0009]
[Patent Document 5]
Japanese Patent No. 3289463
[0010]
[Problems to be solved by the invention]
However, in the case of the conventional weighing device having the above-described configuration, since the lever is rotatably joined around the fulcrum, the fulcrum is accompanied by resistance during operation. At this time, if any resistance is generated at the fulcrum, the force transmitted to the opposite side of the lever is affected, which causes a measurement error. Therefore, in order to reduce the resistance at the fulcrum, it is necessary to make the contact part fine and precise, but the load due to the object to be measured must be supported by the fulcrum, so there is a limit in strength, and there are constraints in design. It was.
[0011]
In the conventional weighing device, when the object to be measured is loaded on a weighing platform and weighing is performed, a current is always applied to the coil to generate a force against the weight of the object to be measured, and the electromagnetic force is applied. Must occur. Therefore, in a conventional weighing device, if an object to be measured is left standing on a weighing platform and the measurement is continued, an electromagnetic force must be generated to balance the object with the object to be measured. Generates heat, and the permanent magnet is rapidly heated. Since the magnitude of the magnetic flux of the permanent magnet changes depending on the temperature, in such a state, the measurement result changes over time, which has been a problem in continuous measurement.
[0012]
The present invention has been made in view of the conventional problems as described above, and eliminates a contact portion in a support portion and removes resistance, thereby enabling weighing with high accuracy and a wide measurement range. In addition, an object of the present invention is to provide a weighing device that generates less heat even during long-time continuous measurement and has a small measurement error due to temperature.
[0013]
[Means for Solving the Problems]
The weighing device according to the first aspect of the present invention is a weighing device, wherein at least a part of the guide is formed of a magnetic material, an electromagnet is installed so as to face the guide via a gap, and a magnetic circuit configured by generated magnetic flux forms the gap. A magnet unit composed of a permanent magnet arranged so as to include, a floating body levitated by an attractive force generated between the guide and the magnet unit, and a detecting means for detecting a physical quantity in the magnetic circuit; The floating body is stably levitated with respect to the guide based on the physical quantity detected by the detecting means, and the steady value of the exciting current flowing through the electromagnet is converged to zero regardless of the presence or absence of an external force acting on the floating body. Control means for controlling the exciting current flowing through the electromagnet, and the weight of the DUT placed on the floating body based on the physical quantity of the detection means. It is obtained by a weighing calculation means for calculation.
[0014]
According to a second aspect of the present invention, in the weighing apparatus of the first aspect, the control means includes an integration compensator for integrating the detected value of the exciting current with a predetermined gain. .
[0015]
According to a third aspect of the present invention, in the weighing device of the first aspect, the control unit includes an exciting unit that excites the electromagnet based on an input signal, and an integration compensator that integrates the input signal with a predetermined gain. And means for feeding back the output value of the integration compensator to the input signal.
[0016]
According to a fourth aspect of the present invention, in the weighing device of the first to third aspects, the physical quantity detecting means is means for detecting the size of the gap.
[0017]
The invention according to claim 5 is the weighing device according to claim 4, wherein the means for detecting the size of the gap is an eddy current sensor.
[0018]
According to a sixth aspect of the present invention, in the weighing device of the first to third aspects, the physical quantity detecting means is means for detecting a magnitude of an exciting current flowing through the coil.
[0019]
According to a seventh aspect of the present invention, in the weighing device of the first to third aspects, the physical quantity detecting means is means for detecting the acceleration of the floating body.
[0020]
The invention according to claim 8 is the weighing device according to any one of claims 1 to 3, wherein the physical quantity detecting means is means for detecting a magnetic flux in the gap.
[0021]
According to a ninth aspect of the present invention, in the weighing device of the eighth aspect, a hall element is used as the means for detecting the magnetic flux.
[0022]
According to a tenth aspect of the present invention, in the weighing device of the fourth or fifth aspect, the physical quantity of the detection means input to the weighing calculation means is a detected value of the gap.
[0023]
According to an eleventh aspect of the present invention, in the weighing device of the sixth aspect, the physical quantity of the detection means input to the weighing calculation means is a detected value of the exciting current.
[0024]
A twelfth aspect of the present invention is the weighing device according to the second or third aspect, wherein the physical quantity of the detection means input to the weighing calculation means is an output value of the integration compensator.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0026]
(First Embodiment) FIG. 1 is a perspective view of a weighing device according to a first embodiment of the present invention, and FIG. 2 is a sectional view of a mechanism of the weighing device. The underframe 1 has a substantially box-like shape having an opening on the upper surface, and the magnet unit 2 is installed inside the upper surface. Inside the underframe 1, a floating body 3 is included. At each end of the floating body 3, a guide 4 made of a ferromagnetic material is installed at a position facing the magnet unit 2 installed on the underframe 1. On the upper surface of the floating body 3, a weighing platform 5 for loading the object to be measured is provided. When the object to be measured is placed on the weighing platform 5, a sum of the floating body 3 and the object to be measured is obtained. The structure is such that the weight of the entire floating part increases.
[0027]
As shown in FIG. 3, the magnet unit 2 installed on the underframe 1 is composed of two electromagnets 6a and 6b and a permanent magnet 7 inserted between the end side surfaces of the electromagnets 6a and 6b. And is formed in a U-shape as a whole. Each of the electromagnets 6a and 6b includes a yoke 8 formed of a ferromagnetic material and a coil 9 wound around the yoke 8. The coils 9 are connected in series in such a direction that magnetic fluxes formed by the electromagnets 6a and 6b are added to each other. The guide 4 is arranged at a position facing the magnet unit 2. A gap 10 is formed between the magnet unit 2 and the guide 4. Therefore, a predetermined attractive force is generated between the magnet unit 2 and the guide 4 in accordance with the magnetic flux caused by the electromagnets 6a and 6b and the permanent magnet 7 and the size of the gap 10. Thereby, the floating body 3 can be floated.
[0028]
The weighing device of the present embodiment has a levitation control device 11 for controlling the attraction force of each magnet unit having a configuration as shown in FIG.
[0029]
The levitation control device 11 includes a sensor unit 12 that detects a physical quantity in a magnetic circuit formed by the magnet unit 2, and a levitation operation circuit that calculates electric power to be supplied to each coil 9 based on a signal from the sensor unit 12. 13 and a power amplifier 14 that supplies electric power to each coil 9 based on a signal from the floating operation circuit 13. In the present embodiment, the sensor unit 12 includes a gap sensor 15 for detecting the size of the gap 10 and a current detector 16 for detecting a current value of each coil 9.
[0030]
The levitation operation circuit 13 in the levitation control device 11 includes a subtractor 17 that calculates a gap length deviation signal Δz obtained by subtracting the gap length design value z0 from the gap length signal z obtained by the gap sensor 15, and a current detector A subtracter 18 for calculating a current deviation signal Δi obtained by subtracting the current design value i0 from the excitation current detection signal i obtained in step 16 and outputs of the gap length deviation signal Δz and the current deviation signal Δi are introduced. And a control voltage calculation circuit 19 for calculating an electromagnet control voltage e for causing the levitation body 3 to magnetically levitate stably. Then, the calculation result of the control voltage e is given to the power amplifier 14, and the exciting current resulting from the voltage e is supplied to the coil 9.
[0031]
Here, the control voltage operation circuit 19 includes a differentiator 20 that introduces Δz and calculates and outputs a time differential value Δz ′ of Δz, a gain compensator 21 that introduces Δz and multiplies the feedback gain F1 by Δz, A gain compensator 22 for introducing Δz ′ and multiplying the feedback gain F2 by Δz ′, a gain compensator 23 for introducing Δi and multiplying the feedback gain F3 by Δi, a current deviation target value generator 24 and a current compensator A subtractor 25 that subtracts from the target value of the deviation target value generator 24, an integration compensator 26 that integrates the output value of the subtractor 25 and multiplies the integration result by a feedback gain, and outputs the gain compensators 21, 22, and 23 It comprises an adder 27 for inputting and calculating the sum of these, and a subtractor 28 for subtracting the output value of the adder 27 from the output value of the integration compensator 26.
[0032]
Thus, a magnetic levitation system based on so-called zero power control is configured. The control principle of the control voltage calculation circuit 19 is, for example, a method disclosed in Japanese Patent No. 2967822 “floating-type transfer device”, whereby stable magnetic levitation control of the levitation body 3 is possible.
[0033]
In this case, when the levitation body 3 flies stably and is in a steady state, the current flowing through the coil 9 becomes zero due to the action of the integration compensator 26, and the attraction required for levitation is all the magnetic force generated by the permanent magnet 7. Served by. The same applies to the case where the weight of the floating body 3 and the entire levitation composed of the object to be measured loaded on the levitation body 3 changes, and a load change caused by the weight change of the object to be measured in the levitation occurs. In this case, current flows transiently through the coil 9 to make the gap length 29 of the gap 10 a predetermined value, but when the state is again stabilized, the current flows through the coil 9 by using the above-described control method. The current becomes zero, and a gap length 29 is formed in which the total weight of the floating portion at that time and the attractive force generated by the magnetic force of the permanent magnet 7 are balanced.
[0034]
Zero power control is performed as described above, and when the floating body 3 is stably floating and the exciting current is zero, if the influence of the leakage magnetic flux and the like is ignored, the gap length z and the attractive force f Can be expressed by the following equation.
[0035]
(Equation 1)

Here, μ0 is the magnetic permeability in a vacuum, S is the cross-sectional area of the magnetic circuit, z is the detected value of the gap length 29, Hm is the strength of the magnetic field generated in the gap 10, lm is the length of the permanent magnet 7, and μs is the gap. Non-permeability other than the part. FIG. 5 is a schematic diagram showing the relationship between the suction force f and the gap length z in this equation.
[0036]
From the above relationship, when the zero power control is performed in the magnetic levitation system, the size of the gap 10 between the magnet unit 2 and the guide 4, that is, the gap length 29 is a parameter of the total weight of the levitation. Is a function. At this time, if the weight of the floating part is small, the suction force for balancing it is small, and the gap length 29 is widened. On the other hand, if the weight of the floating part is large, the suction force for balancing the weight becomes large, so that the gap length 29 becomes narrow.
[0037]
In the present embodiment, the weight of the measured object is calculated in the weighing calculation device 30 using this relationship. Here, the weighing operation device 30 introduces the signal processor 51 for performing pre-processing such as filtering on the output value of the gap sensor 15 and the output thereof, and uses the above relational expression to calculate the gap length 29 and the magnet unit. A floating weight calculator 52 for calculating the attractive force generated by the magnetic force of the permanent magnet 7 used in the lifter 2, that is, the sum of the weight of the floating body 3 and the object to be measured; It comprises a subtractor 53 for reducing the weight of the floating body 3 from the output.
[0038]
This allows the weighing calculation device 30 to calculate the weight of the measured object from the output value of the gap sensor 15 and display the result on the output device 54. In addition, in the relational expression used in the actual levitation weight calculator 52, the weight of the levitation may be calculated by adding a correction obtained by an experiment or the like to each variable of the above expression.
[0039]
Further, it can be seen from the above relational expression that the suction force f is inversely proportional to the square of the gap length z. Therefore, when the weight of the object to be measured is relatively small and the gap length z is large, the rate of change of the gap length z with respect to the change in the weight of the object to be measured increases, and the accuracy of the measurement increases. On the other hand, when the weight of the object to be measured is relatively large and the gap length z is small, the rate of change of the suction force f is relatively large, so that the magnetic levitation rigidity of the weighing platform is increased. It is possible to measure up to an extremely large load. Therefore, the magnetic levitation system having such non-linear characteristics enables a relatively wide measurement range to be obtained as compared with a conventional weighing device having weighing means having linear characteristics.
[0040]
Furthermore, in the weighing device of the present embodiment, even when the measurement is being performed, the current flowing through the coil 9 converges to zero in a steady state regardless of the weight of the object to be measured, and the object to be measured is levitated. The attraction force is balanced only by the magnetic force of the permanent magnet 7. Therefore, even when the measurement is performed for a long time, almost no current flows through the coil 9, and the heat generated by the coil 9 can be greatly reduced. Thus, it is possible to prevent the characteristics of the permanent magnet 7 from being changed due to a temperature change caused by the heat generated by the coil 9, which is a problem in the conventional weighing device, and is a problem due to the heat generated by the coil during long-time continuous measurement. The occurrence of errors can be suppressed.
[0041]
In this configuration, the means for detecting the gap length 29 used for levitation control may be any method that can directly or indirectly detect the size of the gap between the magnet unit 2 and the guide 4. Often, this can be achieved by using a gap sensor such as an eddy current sensor, an optical sensor, or a sound wave sensor.
[0042]
Further, in the present embodiment, the value z of the gap length 29 is introduced into the weighing operation device 30 for measuring the weight of the flying height, but the detecting means is the same as the sensor for detecting the gap length 29. And the same sensor as the gap sensor 15 used for levitation control may be used.
[0043]
(Second Embodiment) Next, a weighing device according to a second embodiment of the present invention will be described. In the first embodiment, the control method of directly multiplying the detection result of the gap length 29 and the exciting current by the feedback gain has been described. However, the state of the levitation system is estimated by using a state observer in the levitation arithmetic circuit 13, A control circuit can also be configured using the result. The second embodiment is characterized by adopting this principle.
[0044]
FIG. 6 is a configuration diagram when the state observer 40 is introduced into the control voltage operation circuit 19 in the levitation operation circuit 13. As shown in FIG. 6, the control voltage calculation circuit 19 including the state observer 40 guides the gap length deviation Δz and the excitation current deviation Δi, and calculates the gap length deviation Δz, the time differential value Δz ′ of Δz, the excitation current A state observer 40 that calculates and outputs the deviation Δi and the external force u, a gain compensator 21 that introduces Δz and multiplies the feedback gain F1 by Δz, and a gain compensator 22 that introduces Δz ′ and multiplies the feedback gain F2. And a gain compensator 23 that introduces Δi and multiplies the feedback gain F3, a gain compensator 41 that introduces u and multiplies the feedback gain F4, and outputs of the gain compensators 21 to 23 and the gain compensator 41. , And a subtractor 28 for subtracting the output value of the adder 42 from the target value.
[0045]
For the levitation control using the state observer 40 as described above, for example, a control method disclosed in Japanese Patent No. 3152775 is adopted.
[0046]
In the weighing device according to the second embodiment, by introducing the state observer having the above circuit configuration, control is performed while estimating the state of the levitation system, and a more stable levitation system can be constructed. . In the case where the levitation control using the state observer 40 as described above is performed, in addition to using the above-described gap length 29 as a value to be introduced into the weighing operation device 30 that calculates the weight of the measured object. Alternatively, the detected value of the exciting current flowing through the coil 9 can be used.
[0047]
In the present embodiment, zero power control is employed in the magnetic levitation system, so the excitation current is zero in a steady state, but in a transient state when a change in the weight of the measured object or a load is applied. Means that the exciting current flows according to the change in the load. At this time, by introducing the gap length 29 and the exciting current into the state observer 40, a disturbance load u ″ applied to the floating body 3 can be obtained as an output value.
[0048]
In such a configuration, u ″ indicates the weight of the object to be measured. Therefore, by using such a state observer 40, a gap length 29 and a detector for the exciting current are introduced and the object is measured. It is possible to obtain the weighing calculation device 30 that calculates the weight of the measured object.In addition, by using this state observer 40, it is possible to perform disturbance estimation even when the levitation system is in a transient state. When is loaded, or when the weight of the measured object changes, the weighing operation can be performed without waiting for the stabilization of the floating system, and the measurement result can be estimated in a short time.
[0049]
Further, when the state observer 40 is used as described above and the load estimation, which is one of the output values, is used as the weighing means, it is not necessary to separately install the weighing operation device 30 separately. As described above, the configuration may be such that the state observation device 40 and the weighing operation device 30 are the same control block, and the weighing operation device 30 is included inside the levitation control device 11.
[0050]
(Third Embodiment) Next, a weighing device according to a third embodiment of the present invention will be described. In the third embodiment, instead of directly using the value z of the gap length 29 as the value to be introduced into the weighing operation device 30, the output value of the integral compensator 26 can be used. Hereinafter, as a third embodiment, a case where the output value of the integration compensator 26 is used for the weighing calculation means will be described with reference to FIG.
[0051]
In the levitation operation circuit 13, the levitation body 3 is magnetically levitated by introducing the value i of the exciting current and the value z of the gap length 29 and performing an appropriate operation. At this time, the detected value of the exciting current is In addition to the levitation control, the difference .DELTA.i from the exciting current target value is multiplied by the integral compensator 26 to calculate the voltage command value e. Therefore, when the current target value is zero, the exciting current becomes zero in a steady state. Zero power control is constituted as a whole. At this time, the output value of the integration compensator 26 is a value equivalent to canceling the deviation from the reference gap length z0 when the magnetic levitation is performed at zero power. Therefore, the output value of the integral compensator 26 is equivalent to detecting the gap length 29, and the weight of the measured object can be measured by the same weighing calculation means as described above. In this case, the output of the integral compensator 26 is introduced into the weighing calculation device 30, the weight of the entire levitation is calculated from the output value of the integration compensator 26 by the levitation weight calculator 52, and the levitation body is calculated by the subtractor 53. 3 is displayed on the output device 54 with the weight reduced.
[0052]
Since the output value of the integration compensator 26 is a value obtained by integrating the detection signal, the higher harmonic component of the detection signal is necessarily filtered, and the noise and the higher harmonic component in the detection signal are removed. It will be. Therefore, when the output value of the integral compensator 26 is used for the weighing operation, the signal noise is small, the weighing operation is easy, and the weight of the object to be measured can be quickly estimated.
[0053]
Hereinafter, the principle of weight estimation will be described using an example of a response when an object to be measured is loaded on the weighing platform 5. Assuming that the value of the exciting current has a waveform as shown in FIG. 8A when the object to be measured is loaded on the weighing platform 5, the output value of the integration compensator 26 has a waveform as shown in FIG. And can be regarded as a step response of a primary system. At this time, the output value of the integration compensator 26 is obtained by removing harmonic components and noise components included in the detection value of the exciting current, and the response is relatively smooth.
[0054]
Here, assuming that the output value of the integration compensator 26 is a primary system and the difference between the output values detected at a constant time interval τ is Δv, from the response characteristics, the change rate of the difference output value Δvn at each time is obtained. That is, Δvn + 1 / Δvn indicates a constant value. Furthermore, the value of the final value of the response v∞ is calculated using the output value vn at a certain point, the detection time interval τ at that time, and the response time constant T of the entire system.
(Equation 2)

From the relationship. Since the time constant T of the response is a known value from the structure of the apparatus and each set value of the floating operation circuit 13, the time when a waveform that can be regarded as a primary system of the response is obtained, that is, the change in the difference output value When the rate becomes constant, the weight of the measured object can be predicted during the transient response without waiting for the stability of the system.
[0055]
As described above, when the weight is predicted during the transient response, as shown in FIG. 7, the output value is transferred to the output value of the floating weight calculator 52 directly to the output device 54, or the floating value is calculated. In order to select whether to display the output of the weight estimation calculator 55, an output switch 56 may be provided to automatically or manually switch the output value.
[0056]
(Fourth and fifth embodiments) In each of the embodiments described so far, the means for detecting the exciting current and the means for detecting the gap length 29 are used as the physical quantity detecting means in the magnetic circuit. Instead of the current detector 16, an acceleration sensor for detecting the acceleration of the levitation body 3 or a Hall element for detecting the magnitude of the magnetic flux may be used.
[0057]
FIG. 9 shows a configuration according to a fourth embodiment of the present invention in which an acceleration sensor 31 and two integrators 32 are used instead of the gap sensor 15. As described above, a configuration may be adopted in which the value obtained by integrating the detection value of the acceleration sensor 31 twice is calculated as the value z of the gap length 29. In this case, in particular, there is an advantage that the set position of the sensor can be arbitrarily determined within a range where the acceleration of the floating body 3 can be detected.
[0058]
FIG. 10 shows an example in which a magnetic flux detector 33 composed of a Hall element for detecting the magnitude of a magnetic flux is used instead of the current detector 16 as the fifth embodiment of the present invention. In this case, by detecting the magnitude of the magnetic flux, the magnitude of the attraction force generated in the magnetic circuit can be obtained, whereby feedback control can be performed. However, in this case, since the value of the exciting current cannot be directly introduced, the exciting current cannot be introduced into the integration compensator 26 to perform zero power control. When the current signal is not directly introduced as described above, a similar integration compensator 34 is introduced and fed back to the command value e introduced to the power amplifier 14 as shown in the figure, so that By converging the output to zero, it is possible to realize zero power control as disclosed in Japanese Patent No. 2,793,240 “floating type transport device”.
[0059]
Sixth Embodiment In each of the embodiments described above, the case where the magnet unit 2 is mounted on the underframe 1 and the guide 4 is installed on the floating body 3 has been described. The installation location of 4 is not limited, and the arrangement may be reversed. As shown in FIG. 11, the guide 4 may be installed on the underframe 1 and the magnet unit 2 may be installed on the floating body 3 without any problem. . This is the configuration of the sixth embodiment of the present invention.
[0060]
In the weighing device according to the sixth embodiment as well, by configuring the levitation control device 11 and the weighing operation device 30 in the same manner as in each of the embodiments described above, the weight of the object to be measured can be measured.
[0061]
As described above, the specific configuration of the weighing device to which the present invention is applied has been described in detail as the first to sixth embodiments, but the weighing device according to the present invention is not limited to the above examples. Various changes can be made without departing from the spirit of the present invention.
[0062]
【The invention's effect】
As described above, according to the present invention, since the weighing table for loading the object to be measured is installed on the floating body and magnetically levitated, the weight of the object to be measured can be measured without having a contact portion with the underframe or the like. Becomes possible. Therefore, there is no influence of resistance or the like due to the fulcrum portion or the like in the conventional weighing device, so that highly accurate weighing can be performed without generating a measurement error.
[0063]
Further, according to the present invention, the floating body is supported by a non-linear spring constant, and when the weight of the measured object increases, the floating rigidity supporting the floating body increases, so that the floating body is supported by the conventional linear spring constant. Compared with the configuration, it is possible to widen the measurement range.
[0064]
Further, according to the present invention, in a steady state, a magnetic attraction force for levitating the levitation including the object to be measured is generated only by the attraction force of the permanent magnet, and furthermore, a steady value of the excitation current flowing through the electromagnet is generated by the levitation body Since the load can be reduced to zero regardless of the weight of the loaded DUT, a transient current flows through the coil of the electromagnet when the weight of the DUT changes relative to the floating part. Only the power consumed by the coil can be reduced as compared with the conventional case, thereby making it possible to reduce the current flowing through the coil, reduce the heat generation in the coil portion, and perform weighing for a long time. Even in this case, the temperature change is small, and stable measurement accuracy can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view of a weighing device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the weighing device according to the first embodiment.
FIG. 3 is a perspective view of a magnet unit in the weighing device according to the first embodiment.
FIG. 4 is a block diagram of a levitation control device and a weighing operation device in the weighing device according to the first embodiment.
FIG. 5 is a diagram illustrating a relationship between a gap length of a magnet unit and an attractive force in the weighing device according to the first embodiment.
FIG. 6 is a block diagram of a levitation control device and a weighing operation device in a weighing device according to a second embodiment of the present invention.
FIG. 7 is a block diagram of a levitation control device and a weighing operation device in a weighing device according to a third embodiment of the present invention.
FIG. 8 is a diagram showing a method for estimating weight from an output waveform in the weighing device according to the third embodiment.
FIG. 9 is a block diagram of a levitation control device and a weighing operation device in a weighing device according to a fourth embodiment of the present invention.
FIG. 10 is a block diagram of a levitation control device and a weighing operation device in a weighing device according to a fifth embodiment of the present invention.
FIG. 11 is a sectional view of a weighing device according to a sixth embodiment of the present invention.
FIG. 12 is a sectional view showing a basic configuration of a conventional weighing device.
[Explanation of symbols]
1: Underframe
2 ... Magnet unit
3… Floating body
4. Guide
5 ... weighing platform
6a ... electromagnet
6b ... electromagnet
7 ... permanent magnet
8. Yoketsu
9 ... coil
10 gap
11 ... Control device
12 ... Sensor part
13 Floating operation circuit
14. Power amplifier
15 gap sensor
16 ... Current detector
17 ... Subtractor
18 ... Subtractor
19 ... Control voltage operation circuit
20 ... differentiator
21 ... Gain compensator
22 ... Gain compensator
23 ... Gain compensator
24 ... Current deviation target value generator
25 ... Subtractor
26 ... Integral compensator
27 ... Adder
28 ... Subtractor
29 ... Gap length
30 ... weighing calculation device
31 ... Acceleration sensor
32 ... Integrator
33 ... Magnetic flux detector
40… State observer
41 ... Gain compensator
42 ... Adder
51 ... Signal processor
52… Floating weight calculator
53 ... Subtractor
54 ... Output device
55… Floating part weight estimator
56 Output switch

Claims (12)

A guide formed at least in part of a magnetic material, an electromagnet installed so as to face the guide via a gap, and a permanent magnet arranged so that the magnetic circuit formed by the generated magnetic flux includes the gap. Magnet unit to be
A floating body that is levitated by an attractive force generated between the guide and the magnet unit,
Detecting means for detecting a physical quantity in the magnetic circuit;
Based on the physical quantity detected by the detection means, the floating body is stably levitated with respect to the guide, and the steady value of the exciting current flowing through the electromagnet converges to zero regardless of the presence or absence of an external force acting on the floating body. Control means for controlling an exciting current flowing through the electromagnet so as to cause
A weighing device comprising: a weighing operation unit configured to calculate a weight of an object to be measured loaded on the floating body based on a physical quantity of the detection unit. 2. The weighing device according to claim 1, wherein the control unit includes an integration compensator that integrates the detection value of the excitation current with a predetermined gain. The control unit includes: an exciting unit that excites the electromagnet based on an input signal; an integration compensator that integrates the input signal with a predetermined gain; and an output value of the integration compensator fed back to the input signal. 2. The weighing device according to claim 1, further comprising: a weighing device. The weighing device according to any one of claims 1 to 3, wherein the physical quantity detecting means is means for detecting the size of the gap. The weighing device according to claim 4, wherein the means for detecting the size of the gap is an eddy current sensor. The weighing device according to any one of claims 1 to 3, wherein the means for detecting the physical quantity is means for detecting a magnitude of an exciting current flowing through a coil of the electromagnet. The weighing device according to any one of claims 1 to 3, wherein the physical quantity detecting means is means for detecting acceleration of the floating body. The weighing device according to any one of claims 1 to 3, wherein the physical quantity detecting means is a means for detecting a magnetic flux in the gap. 9. The weighing device according to claim 8, wherein a Hall element is used as the means for detecting the magnetic flux. The weighing device according to claim 4, wherein a physical value of the detection unit input to the weighing calculation unit is a detected value of the gap. 7. The weighing device according to claim 6, wherein the physical quantity of the detection means input to the weighing calculation means is a detected value of the exciting current. 4. The weighing device according to claim 2, wherein the physical quantity of the detection means input to the weighing calculation means is an output value of the integration compensator.

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