JP2005061867A - Droplet weight measuring apparatus and droplet discharging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a droplet weight measuring apparatus capable of precisely detecting the weight of droplets discharged from a discharge head with a simple configuration, and to provide a droplet discharging apparatus. <P>SOLUTION: A QCM sensor 106 comprises a crystal 110, and electrodes 110a, 110b formed on both the surfaces of the crystal 110. A vibration voltage is applied from a vibration voltage oscillation section 111 to the electrode 110a to vibrate the crystal 110. A measurement section 112 and an arithmetic section 113 detect a change in the resonance frequency of the crystal 110 before and after droplets discharged from a discharge head 103 adhere to the electrode 110b, and measures the weight of droplets adhering to the electrode 110b. Then, the resolution of a detection means is set to 10% or smaller to the amount of droplets adhering to the electrode 110b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３６】
また、共振抵抗値をＲとし、電極１１０ｂに付着した液滴の粘度をηとすると、これらの関係は、下式（２）で表すことができる。
【００３７】
【数２】

【００３８】
演算部１１３は、測定部１１２から供給される電極１１０ｂへの液滴の付着前における共振周波数ｆｂｅｆｏｒｅ、付着後における共振周波数ｆａｆｔｅｒからその変化量Δｆｒｅｑ＝ｆｂｅｆｏｒｅ−ｆａｆｔｅｒを算出した後、変化量Δｆｒｅｑを上記式（１）に代入して、液滴の重量Ｉｍを算出する。また、演算部１１３は、測定部１１２から入力される電極１１０ｂに液滴の付着後の共振抵抗値Ｒを、上記式（２）に代入して、液滴の粘度ηを算出する。演算部１１３は、算出した液滴の粘度ηおよび重量Ｉｍを制御部１０１に出力する。なお、このように、液滴の重量Ｉｍは、共振周波数ｆのみで算出できるが、共振周波数ｆに加えて、共振抵抗Ｒも利用することで精度良く算出することができる。
【００３９】
［水晶振動子の基本周波数］
ＱＣＭセンサ１０６に使用する水晶１１０の基準周波数Ｆを分解能［ｎｇ／Ｈｚ］と周波数のバラツキ（変動）から検討した。図９は、水晶振動子の基準周波数Ｆ［ＭＨｚ］と分解能［ｎｇ／Ｈｚ］の関係を示す図である。同図に示すように、基準周波数Ｆ［ＭＨｚ］が高いほど分解能［ｎｇ／Ｈｚ］が高くなる。十分な測定精度を得るためには、分解能［ｎｇ／Ｈｚ］は液滴量に対して１０％以下とするのが好ましい。他方、基準周波数Ｆ［ＭＨｚ］が高いほど周波数のバラツキが大きくなる。図１０は、水晶振動子の基準周波数Ｆが５［ＭＨｚ］と、１０［ＭＨｚ］の場合の周波数のバラツキを説明するための図である。同図において、横軸は時間、縦軸は周波数変化［Ｈｚ］を示している。同図に示すように、基準周波数Ｆ＝５［ＭＨｚ］の水晶振動子の方が、基準周波数Ｆ＝１０［ＭＨｚ］の水晶振動子に比して、周波数のバラツキが小さくなる。図１１は、水晶振動子の基準周波数Ｆが５［ＭＨｚ］と、１０［ＭＨｚ］の周波数のバラツキを液滴量に換算したものを示している。同図に示すように、周波数のバラツキを液適量換算［ｎｇ］すると、基準周波数Ｆが５［ＭＨｚ］の場合は３．９８［ｎｇ］、１０［ＭＨｚ］の場合は１．７３［ｎｇ］となる。このように、ＱＣＭセンサ１０６に使用する水晶振動子の基準周波数Ｆは、分解能と周波数のバラツキの両者を考慮する必要がある。検討の結果、測定する液滴量を１滴〜数滴（例えば、液滴量が１．８〜２０ｎｇ）とした場合には、基準周波数Ｆ［ＭＨｚ］＝１〜３０［ＭＨｚ］の水晶振動子が分解能と周波数のバラツキの面から好ましいという結果が得られた。特に、基準周波数Ｆ［ＭＨｚ］＝５［ＭＨｚ］近傍が分解能と周波数の変動を両立でき、より好ましい。
【００４０】
［液滴重量の測定フロー］
図１２は、図１の液滴吐出装置１００の液滴重量の測定フローを示す図である。なお、吐出ヘッド１０３は、ＱＣＭセンサ１０６上になく待機位置にあるものとする。図１２において、まず、計測部１０７では、振動電圧発振部１１１は、ＱＣＭセンサ１０６の電極１１０ａに振動電圧を周波数掃引しながら印加する（ステップＳ１）。測定部１１２は、ＱＣＭセンサ１０６の電極１１０ｂに流れる電流を検出してインピーダンスの変化を検出し、ＱＣＭセンサ１０６の電極１１０ａに液滴の付着前の共振周波数ｆｂｅｆｏｒｅを算出して、演算部１１３に出力する（ステップＳ２）。なお、電極１１０ａに液滴の付着前の共振周波数ｆｂｅｆｏｒｅは、毎回測定しないで予め演算部１１３に記憶しておくことにしても良い。
【００４１】
つぎに、制御部１０１は、吐出ヘッド１０３から吐出された液滴が、水晶１１０の電極１１０ｂの略中央位置（図４の地点ＰＥ参照）に付着するような位置まで、ヘッドキャリッジ１０２により吐出ヘッド１０３を搬送する（ステップＳ３）。ここで、電極１１０ｂの略中央位置としているのは、電極１１０ｂの略中央位置に液滴を付着させた場合、検出精度が向上するためである。
【００４２】
続いて、制御部１０１は、標準駆動波形に従って、吐出ヘッド１０３に含まれるピエゾ素子１２２に駆動信号を供給して、吐出ヘッド１０３から電極１１０ｂのＰＥに向けて液滴を吐出させる（ステップＳ４）。この後、制御部１０１は、ヘッドキャリッジ１０２により吐出ヘッド１０３を待機位置まで搬送する（ステップＳ５）。ここで、吐出ヘッド１０３を待機位置まで搬送しているのは、吐出ヘッド１０３がＱＣＭセンサ１０６の上方にある場合には、吐出ヘッド１０３の浮遊容量や吐出ヘッド１０３がＱＣＭセンサ１０６に近づくことによる温度変化等の外乱によりＱＣＭセンサ１０６の出力が不安定になるからである。
【００４３】
この後、計測部１０７では、振動電圧発振部１１１は、ＱＣＭセンサ１０６の電極１１０ａに振動電圧を周波数掃引しながら印加する（ステップＳ６）。測定部１１２は、ＱＣＭセンサ１０６の電極１１０ｂに流れる電流を検出してインピーダンスの変化を検出し、ＱＣＭセンサ１０６の電極１１０ｂに液滴の付着後の共振周波数ｆａｆｔｅｒと、そのときの共振抵抗Ｒを算出して、演算部１１３に出力する（ステップＳ７）。
【００４４】
演算部１１３は、共振周波数ｆｂｅｆｏｒｅ、ｆａｆｔｅｒに基づいて、共振周波数の変化量Δｆｒｅｑ＝ｆｂｅｆｏｒｅ−ｆａｆｔｅｒを算出し、算出したΔｆｒｅｑを上述した式（１）を用いて液滴の重量Ｉｍを算出する（ステップＳ８）。また、演算部１１３は、共振抵抗Ｒに基づいて、上述した式（２）を用いて液滴の粘度η算出する。演算部１１３は、算出した液滴の重量Ｉｍおよび粘度ηを制御部１０１に出力する。制御部１０１は、算出された液滴の重量Ｉｍおよび液滴の粘度ηを表示部１０８に表示する（ステップＳ９）。
【００４５】
なお、制御部１０１は、算出した液滴の重量Ｉｍが所定値以下であるか否かを判断し、液滴の重量Ｉｍが所定値以下である場合には、吐出ヘッド１０３のノズル詰まりまたはインクのエンドの可能性があると判断して、”ノズル詰まりまたはインクのエンド”の可能性がある旨を表示部１０８に表示することにしても良い。また、制御部１０１は、以上のようにして測定した標準駆動波形の駆動信号で形成された液滴の重量Ｉｍに基づいて、吐出ヘッド１０３で描画対象物Ｗに描画を行う場合に、吐出ヘッド１０３に印加する駆動信号の駆動波形を変更する。
【００４６】
以上説明したように、実施の形態１の液滴吐出装置１００によれば、水晶１１０と、当該水晶１１０の両面に形成された電極１１０ａ、１１０ｂとでＱＣＭセンサ１０６を構成する。電極１１０ａに振動電圧発振部１１１から振動電圧を印加して水晶１１０を振動させる。測定部１１２および演算部１１３は、吐出ヘッド１０３から吐出される液滴が電極１１０ｂに付着する前後での水晶１１０の共振周波数の変化を検出して、当該電極１１０ｂに付着した液滴の重量を測定する。これにより、液滴重量測定装置を簡単かつ低コストの構成とすることができる。付言すると、ヒータ等を設ける必要がなく、温度制御等は不要である。また、ＱＣＭセンサ１０６の分解能を電極１１０ｂに付着する液滴量に対して、１０％以下とすることにより、液滴の重量の測定精度を向上させる。この結果、吐出ヘッドから吐出される液滴の重量を、簡単な構成で高精度に測定することが可能な液滴吐出装置を提供することができる。
【００４７】
また、水晶１１０の基準周波数Ｆを１ＭＨｚ〜３０ＭＨｚとすることにより、微少な液滴の重量も高精度に測定することができる。より好ましくは、水晶１１０の基準周波数Ｆを５ＭＨｚ近傍とすることにより、分解能と周波数の変動を完全に両立させることができる。なお、本実施の形態１の液滴吐出装置１００は、工業用のインクジェット装置として使用することができ、例えば、配線、カラーフィルタ、配向膜、マイクロレンズアレイ、エレクトロルミネセンス材料、および生体物質等のパターン形成に使用することができる。
【００４８】
（実施の形態２）
図１３は、本発明の実施の形態２にかかる液滴吐出装置３００の概略構成を示す図である。実施の形態２にかかる液滴吐出装置３００は、インクジェットプリンタとしたものである。実施の形態２にかかる液滴吐出装置３００は、用紙搬送路３０４の一部にＱＣＭセンサ３０１が設けられており、また、キャリッジ３０２に吐出ヘッドが搭載されている。この吐出ヘッドから吐出される液滴（インク滴）の重量の測定原理は、実施の形態１と同様であるのでその説明は省略する。実施の形態２にかかる液滴吐出装置３００は、印刷用紙上でキャリッジ３０２を往復動させながら微細なインク滴を吐出することによって、印刷用紙上にインクドットを形成して画像を印刷するインクジェットプリンタである。
【００４９】
図１３を参照して、液滴吐出装置３００が用紙に画像を印刷する動作を簡単に説明する。キャリッジ３０２には、インク滴を吐出するための吐出ヘッドが内蔵されている。キャリッジ３０２の上面側に装着されたインクカートリッジ３０８は吐出ヘッドにインクを供給する。印刷用紙は紙送りローラ３０３によってキャリッジ３０２の下側の所定位置に搬送される。印刷用紙が所定位置にセットされると、キャリッジ３０２は印刷用紙上を往復動しながら吐出ヘッドからインク滴を吐出させる。キャリッジ３０２は、図示するように２本のガイドレール３０５に導かれ、駆動ベルト３０６を介してキャリッジモータ３０７によって駆動される。このように、キャリッジ３０２を往復動させる動作は主走査と呼ばれる。
【００５０】
キャリッジ３０２の主走査に同期させて紙送りローラ３０３を駆動し、印刷用紙を主走査方向と直角方向に少しずつ移動させる。このように、主走査方向と交差する方向に、吐出ヘッドと印刷用紙とを相対的に移動させる動作は副走査と呼ばれる。こうして、キャリッジ３０２を主走査させながら印刷用紙を副走査させ、これにあわせてインク滴を適切なタイミングで吐出することで印刷用紙上にインクドットを形成し、これによって画像を印刷している。
【００５１】
このように、本発明の液滴吐出装置は、インクジェットプリンタにも好適に使用することが可能である。なお、インク滴の代わりに試料液体の重量を測定する場合には、インクカートリッジ３０８を取り外して、インクの代わりに試料液体が収納された容器をキャリッジ３０２に装着することにすれば良い。本発明は、上記した実施の形態１および実施の形態２に限定されるものではなく、発明の要旨を変更しない範囲で適宜変形して実施可能である。
【図面の簡単な説明】
【図１】本発明の実施の形態１にかかる液滴吐出装置の全体の概略構成を示す図である。
【図２】吐出ヘッドの詳細な構成を示す図である。
【図３】吐出ヘッドから吐出する液滴の大きさを変更する原理を説明するための図である。
【図４】ＱＣＭセンサの構成を示す平面図である。
【図５】水晶振動子の等価回路を示す図である。
【図６】計測部の概念図である。
【図７】帰還型の自励発振方式の概念図である。
【図８】水晶振動子のアドミッタンス線図である。
【図９】水晶振動子の基準周波数Ｆ［ＭＨｚ］と分解能［ｎｇ／Ｈｚ］の関係を示す図である。
【図１０】水晶振動子の基準周波数Ｆが５［ＭＨｚ］と、１０［ＭＨｚ］の周波数のバラツキを説明するための図である。
【図１１】水晶振動子の基準周波数Ｆが５［ＭＨｚ］と、１０［ＭＨｚ］の周波数のバラツキを液滴量に換算した図である。
【図１２】本発明の実施の形態１にかかる液滴吐出装置の液滴重量の測定フローを示す図である。
【図１３】本発明の実施の形態２にかかる液滴吐出装置の全体の概略構成を示す図である。
【符号の説明】
１００ 液滴吐出装置、１０１ 制御部、１０２ ヘッドキャリッジ、１０３Ｒ、１０３Ｇ、１０３Ｂ 吐出ヘッド、１０４Ｒ、１０４Ｇ、１０４Ｂ インクタンク、１０５ ステージ、１０６ ＱＣＭセンサ、１０７ 計測部、１０８ 表示部、１１０ 水晶、１１０ａ、１１０ｂ 電極、１１１ 振動電圧発振部、１１２ 測定部、１１３ 演算部、１２１ 圧力室、１２２ ピエゾ素子、１２３ノズル、１３１ 絶縁体、１３２ａ、１３２ｂ 支持体、１３３ａ、１３３ｂ端子、３００ 液滴吐出装置、３０１ ＱＣＭセンサ、３０２ キャリッジ、３０３ 紙送りローラ、３０４ 用紙搬送路、３０５ ガイドレール、３０６ 駆動ベルト、３０７ キャリッジモータ、３０８ インクカートリッジ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a droplet weight measuring device and a droplet discharging device, and in particular, a droplet weight measuring device capable of measuring the weight of a droplet discharged from a discharge head and a droplet discharging device equipped with the droplet weight measuring device. About.
[0002]
[Prior art]
For example, a droplet discharge device is used for forming a color filter, an alignment film, and the like of a liquid crystal display device. In addition, the droplet discharge device is used in various industrial fields. The droplet discharge device has a droplet discharge mechanism called a discharge head. A plurality of nozzles are regularly formed in the discharge head. In a droplet discharge device, a pattern made of a discharge material is drawn on a substrate which is a component of some product by discharging a droplet of the discharge material from these nozzles. As a device for measuring the weight of droplets ejected from the ejection head, for example, the following micro droplet weight device is known (for example, see Patent Document 1).
[0003]
This device is equipped with a heater on a piezoelectric vibrating body with a diaphragm and a piezoelectric element bonded together, and does not peel off or evaporate even if hot melt ink (ink made by dissolving solid material) adheres to the piezoelectric vibrating body. A hot melt ink jet is sprayed in a state where the piezoelectric vibrator is controlled. When hot melt ink adheres, the electromechanical coupling coefficient of the piezoelectric vibrator changes, and the impedance of the piezoelectric element changes in proportion to the weight of the adhesion. The adhesion weight is calculated from the amount of change in impedance.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-248250
[Problems to be solved by the invention]
However, since the apparatus uses a piezoelectric vibrating body in which a diaphragm and a piezoelectric element are bonded together, the structure of the piezoelectric vibrating body is complicated and expensive. Further, since the heater for heating the piezoelectric vibrating body is provided to control the temperature of the piezoelectric vibrating body, there is a problem that the configuration becomes complicated and the control becomes complicated. In addition, since the weight of the droplet can be measured in a moment, no heater or temperature control is required. On the contrary, since heat applied to the diaphragm is transmitted to the piezoelectric element, the measurement accuracy is affected in the case of a piezoelectric element that is weak against heat, so that highly accurate weight measurement cannot be performed.
[0006]
The present invention has been made in view of the above problems, and a droplet weight measuring device and a droplet discharging device capable of measuring the weight of a droplet discharged from a discharge head with high accuracy with a simple configuration. The purpose is to provide.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems and achieve the object, according to the present invention, in a droplet weight measuring apparatus for measuring the weight of a droplet discharged from a discharge head, a piezoelectric vibrator having electrodes formed on both sides is used. Detecting means, an oscillating means for applying an oscillating voltage to the electrode to vibrate the piezoelectric vibrator, and a resonance frequency of the piezoelectric vibrator before and after the droplet ejected from the ejection head adheres to the electrode And a droplet weight measuring means for measuring the weight of the droplet attached to the electrode based on the detected change in the resonance frequency of the piezoelectric vibrator, and the resolution of the detecting means is It is characterized by being 10% or less with respect to the amount of droplets adhering to the electrode.
[0008]
The detection means includes a piezoelectric vibrator and electrodes formed on both surfaces of the piezoelectric vibrator. An oscillating voltage is applied from the outside to the electrodes formed on the piezoelectric vibrator to vibrate the piezoelectric vibrator. The resonance frequency of the piezoelectric vibrator changes before and after the liquid droplets ejected from the ejection head adhere to the electrodes formed on the piezoelectric vibrator. A change in the resonance frequency of the piezoelectric vibrator is detected, and the weight of the droplet attached to the electrode is measured. Thereby, the structure of a detection means can be made into a simple and low-cost structure. Further, the measurement accuracy of the weight of the droplet is improved by setting the resolution of the detection means to 10% or less with respect to the amount of the droplet attached to the electrode. As a result, it is possible to provide a droplet discharge device that can accurately measure the weight of droplets discharged from the discharge head with a simple configuration.
[0009]
According to a preferred aspect of the present invention, it is desirable that the reference frequency F of the piezoelectric vibrator is 1 MHz to 30 MHz. Thereby, the weight of a minute droplet can be measured with high accuracy.
[0010]
Further, according to a preferred aspect of the present invention, it is desirable that the reference frequency F of the piezoelectric vibrator is in the vicinity of 5 MHz. As a result, both resolution and frequency fluctuation can be achieved.
[0011]
Further, according to a preferred aspect of the present invention, it is desirable to mount the above-described droplet weight measuring device on the droplet discharge device and the discharge head control means for discharging a droplet by applying a drive signal to the discharge head. . Thereby, the weight of the droplet discharged from the discharge head by the droplet discharge device can be measured with high accuracy.
[0012]
According to a preferred aspect of the present invention, the droplet discharge device is used for pattern formation of any one of a wiring, a color filter, an alignment film, a microlens array, an electroluminescent material, and a biological material. It is desirable to do. Thereby, the pattern formation of any one of wiring, a color filter, an alignment film, a microlens array, an electroluminescent material, and a biological substance can be performed using the droplet discharge device of the present invention.
[0013]
According to a preferred aspect of the present invention, it is desirable that the droplet discharge device is an ink jet printer. Thereby, the droplet discharge device of the present invention can be used as an ink jet printer.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of a droplet weight measuring device and a droplet discharge device equipped with the droplet weight measuring device according to the present invention will be described below with reference to the accompanying drawings.
(Embodiment 1)
The droplet discharge device according to the first exemplary embodiment of the present invention includes the following: [Entire configuration of droplet discharge device], [Discharge head], [QCM sensor], [Measurement principle of droplet weight], [Reference of crystal resonator] [Frequency] and [Droplet Weight Measurement Flow] will be described in this order.
[0015]
[Entire configuration of droplet discharge device]
FIG. 1 is a diagram showing an overall schematic configuration of a droplet discharge device 100 according to a first embodiment of the present invention. The droplet discharge device 100 according to the first embodiment has a configuration in which a sensor called QCM (Quartz-Crystal Microbalance) is mounted. The droplet discharge apparatus 100 of the present embodiment mainly includes a control unit 101, a head carriage 102, discharge heads 103R, 103G, and 103B, ink tanks 104R, 104G, and 104B, a stage 105, and a QCM sensor 106. The measuring unit 107 and the display unit 108 are provided.
[0016]
The control unit 101 includes a CPU (Central Processing Unit), a ROM, a RAM, and the like, and controls the entire droplet discharge device 100. Specifically, the control unit 101 controls the operation of drawing with the discharge heads 103R, 103G, and 103B on the drawing object W such as a substrate placed on the stage 105, and discharges from the discharge heads 103R, 103G, and 103B. The operation of measuring the weight of the droplets to be performed is controlled. The head carriage 102 conveys the ejection heads 103R, 103G, and 103B in the sub-scanning direction (X-axis direction) under the control of the control unit 101. The ejection heads 103 </ b> R, 103 </ b> G, and 103 </ b> B are carried by the head carriage 102 and move together with the head carriage 102, and eject liquid droplets from the nozzles according to a drive signal input from the control unit 101.
[0017]
The ink tanks 104R, 104G, and 104B are filled with R, G, and B inks, and supply the R, G, and B inks to the ejection heads 103R, 103G, and 103B, respectively. The stage 105 has a drawing object W such as a substrate placed thereon, and is conveyed in the main scanning direction (Y-axis direction) by a drive mechanism (not shown) according to the control of the control unit 101. The QCM sensor 106 includes a crystal resonator that is a piezoelectric resonator, and includes a crystal 110 and electrodes 110 a and 110 b formed on both surfaces of the crystal 110. The QCM sensor 106 is used when measuring the weight of droplets ejected from the ejection heads 103R, 103G, and 103B. The measurement unit 107 detects a change in the resonance frequency of the crystal 110 before and after the droplet is attached to the electrode 110b of the QCM sensor 106, measures the weight of the droplet attached to the electrode 110b, and controls the measurement result. Output to the unit 101. The display unit 108 includes, for example, an LCD monitor, and displays the measurement result of the weight of the droplets according to the control of the control unit 101.
[0018]
[Discharge head]
FIG. 2 is a diagram showing a detailed configuration of the ejection head 103R in FIG. As shown in FIG. 2, the ejection head 103 </ b> R includes a pressure chamber 121, a piezo element 122, and a nozzle 123. The pressure chamber 121 communicates with the ink tank 104R and temporarily stores the red ink supplied from the ink tank 104R. As is well known, the piezo element 122 is an element that transforms electro-mechanical energy at an extremely high speed by distorting the crystal structure when a voltage is applied. The piezo element 122 deforms the inner surface of the pressure chamber 121 according to the drive signal supplied from the control unit 101, and increases or decreases the pressure of the red ink in the pressure chamber 121. In the ejection head 103R, the red ink is ejected as a droplet IP from the nozzle 123 in accordance with the pressure increase / decrease of the red ink by the piezo element 122.
[0019]
The ejection head 103G has the same configuration as the ejection head 103R, and ejects the green ink supplied from the ink tank 104G as droplets in accordance with the drive signal supplied from the control unit 101. Similarly, the ejection head 103B ejects blue ink supplied from the ink tank 104B as droplets in response to a drive signal supplied from the control unit 101. In this embodiment, for convenience of explanation, red ink, green ink, and blue ink have their liquid properties (for example, viscosity characteristics according to temperature) substantially the same, and under the same conditions, It shall exhibit similar fluid behavior. Therefore, if the conditions for droplet ejection are exactly the same, the same amount of droplets is ejected regardless of which ink is used. In the following description, when it is not necessary to distinguish each of the ejection heads 103R, 103G, and 103B, the ejection head 103 is described, and similarly, each of the ink tanks 104R, 104G, and 104B is particularly distinguished. When it is not necessary to do this, it is described as an ink tank 104.
[0020]
FIG. 3 is a diagram for explaining the principle of changing the size of the ejected droplet IP by controlling the drive waveform of the drive signal applied to the piezo element 122. In the figure, the horizontal axis represents time, and the vertical axis represents drive voltage. In the figure, during the period from time “0” to time “T1”, the drive signal supplied to the piezo element 122 takes a constant value “V _M ”, and at this time, the piezo element 122 is not deformed. In the subsequent period from time “T1” to time “T2”, the drive signal rises from “V _M ” to “V _H ”. In response to this, the piezo element 122 is deformed so that the ink in the pressure chamber 121 is depressurized, and the ink flows from the ink tank 104 into the pressure chamber 121.
[0021]
Next, the drive signal takes a constant value “V _H ” from time “T2” to time “T3”, and the drive signal continues from time “T3” to time “T4”. _Decrease from “V _H ” to “V _L ”. As the drive signal falls, the piezo element 122 is deformed so as to increase the pressure in the pressure chamber 121, and the red ink in the pressure chamber 121 is ejected in a state of being connected from the nozzle 123. In the following description, the period from time “T3” to time “T4” is referred to as a voltage drop period ΔT, and the amount of voltage “V _H −V _L ” that drops in the voltage drop period ΔT is expressed as a voltage drop. It will be referred to as the quantity ΔV.
[0022]
Next, between time “T4” and time “T5”, the drive signal takes a constant value “V _L ”. Subsequently, between time “T5” and time “T6”, the drive signal is “ It rises from “V _L ” to “V _M ”. Due to the increase in the drive signal, the piezo element 122 is deformed so that the pressure of the ink in the pressure chamber decreases, and the ink once ejected during the above-described voltage decrease period ΔT is pulled back, and a part of the piezoelectric element 122 becomes a droplet IP. Discharge.
[0023]
Here, for convenience of explanation, a technique for changing the droplet amount by adjusting the voltage drop period ΔT or the voltage drop amount ΔV in the drive waveform will be described. First, when the voltage drop period ΔT is shortened, the period for increasing the pressure of the solution is shortened, the momentum of ink ejected from the nozzle 123 within the voltage drop time ΔT is increased, and the amount of droplets can be increased. Conversely, if the voltage drop period ΔT is lengthened, the momentum of the ink ejected from the nozzle 123 is lowered, and the droplet amount can be reduced.
[0024]
On the other hand, when the voltage drop amount ΔV is increased, the ink pressure increase amount is increased, the amount of ink ejected from the nozzle 123 within the voltage drop time ΔT is increased, and the droplet amount can be increased. Conversely, when the voltage drop amount ΔV is reduced, the amount of ink ejected from the nozzle 123 is reduced, and the droplet amount can be reduced. Since these techniques can arbitrarily change the droplet amount without changing the mechanical configuration of the ejection head 103 such as the nozzle diameter, for example, a plurality of droplets from one nozzle 123 can be selectively selected. This technique is widely used in the case of discharging the ink.
[0025]
[QCM sensor]
FIG. 4 is a plan view showing the configuration of the QCM sensor 106 of FIG. The crystal 110 has a substantially square shape, and a pair of electrodes 110a and 110b are attached to both surfaces thereof so as to face each other. The pair of electrodes 110a and 110b can be made of a metal such as Au or Pt. Further, the insulator 131 holds the crystal 110 in a freely oscillating manner by the conductive supports 133a and 133b. The support 133a is electrically connected to the electrode 110a and electrically connected to the terminal 132a fixed to the insulator 131. Similarly, the support 133b is electrically connected to the electrode 110b and is electrically connected to the terminal 132b fixed to the insulator 131. Moreover, in the same figure, PE has shown the approximate center position of the electrode 110b.
[0026]
FIG. 5 shows an equivalent circuit of the crystal 110. As shown in FIG. 5, the crystal 110 is electrically equivalent to an electric circuit composed of a resistor R1, capacitors C1 and Co, and a coil L1. Here, Co is an equivalent electrode capacitance that is a capacitance component generated by the electrodes 110 a and 110 b provided on both surfaces of the crystal 110. The crystal 110 has an electrical natural frequency. When the electrodes 110a and 110b provided on both sides of the crystal 110 are connected to a power source, the circuit starts oscillating at the natural frequency, and the crystal 110 also has the same frequency as the oscillation frequency. Vibrate. The oscillation frequency is mainly determined by the angle at which the crystal 110 is cut out with respect to the crystal growth axis and the thickness of the crystal 110, and the vibration form of the crystal 110 is determined by the angle at which the thin plate is cut out. In the QCM, a crystal 110 cut out at a predetermined angle called AT cut is usually used, and the vibration form of the AT cut crystal 110 is a thickness-shear vibration, that is, the front and back surfaces of the crystal 110 are crystal. In the direction perpendicular to the thickness direction of 110, the vibrations are caused to deviate from each other.
[0027]
If the external force acting on the crystal 110 is constant, the quartz crystal 110 vibrates at a constant resonance frequency. However, when the external force changes due to a droplet attached to the electrode 110b, the resonance frequency changes according to the amount of change. It has the characteristic. In other words, when a droplet adheres to the electrode 110b, the crystal 110 has a characteristic that it vibrates at a resonance frequency corresponding to the weight and viscosity of the droplet. In addition, the crystal 110 has a characteristic that when a liquid adheres to the electrode 110b, the resonance resistance value changes according to the viscosity of the adhering liquid. As will be described later, the measurement unit 107 calculates the weight and viscosity of the droplet by using the characteristics of the crystal 110.
[0028]
[Measurement principle of drop weight]
FIG. 6 shows a conceptual diagram of the measurement unit 107 of FIG. The measurement unit 107 in this embodiment uses an external oscillation method. In FIG. 6, the measurement unit 107 excites the crystal 110 by applying an oscillation voltage Vin (corresponding to the oscillation voltage oscillation unit 111) to one electrode 110 a of the crystal 110 with the oscillator 150. The RF voltmeter 151 (corresponding to the measurement unit 112) measures the current Iq = (Vq / RL) flowing from the other electrode 110b of the excited crystal 110. Thus, the electrical impedance of the crystal 110 with respect to the frequency can be obtained from the relationship between the applied vibration voltage and the current flowing through the crystal 110. The impedance changes greatly near the resonance frequency. Therefore, the measurement unit 107 measures the impedance while sweeping the frequency of the applied oscillating voltage, and obtains the frequency at which the impedance is minimized. This frequency is the series resonance frequency (fs), and the resistance component at this time is the resonance resistance.
[0029]
FIG. 7 shows a conceptual diagram of a feedback self-oscillation method (conventional method) used when measuring the resonance frequency of the crystal 110. The external oscillation system of this embodiment will be described in comparison with the feedback self-excited oscillation system shown in FIG. In FIG. 7, in the feedback self-excited oscillation method, the oscillation circuit including the crystal 110 is set in a resonance state, and the resonance frequency that is changed when a droplet is attached to the electrode is measured by the frequency counter 160. Then, based on the measured resonance frequency, the weight of the substance attached to the electrode surface of the crystal resonator is measured. However, as described above, the resonance frequency of the quartz crystal 110 also changes depending on the viscoelasticity of the adhered substance. For this reason, when a substance having both viscoelastic properties adheres, it cannot be determined whether the change has occurred due to either of the influences. On the other hand, it is known that resonance resistance is mainly proportional to viscoelasticity. The measurement unit 107 of the present embodiment measures both the resonance frequency and the resonance resistance to determine whether the change is due to weight or viscoelasticity.
[0030]
FIG. 8 shows an admittance diagram of the crystal 110. The frequency characteristics of the crystal resonator impedance represented by the equivalent circuit in FIG. 5 above were measured and plotted on an impedance plane with the G (conductance) component on the X axis and the B (susceptance) component on the Y axis. Is. As shown in the figure, the entire curve is shifted on the B axis by ωCo due to the influence of the equivalent electrode capacitance Co. Since the resonance point of the feedback self-excited oscillation system is a point where the phase shift is “0”, that is, a point where the B component is “0”, it is indicated by fr in FIG. Because of Co, the resonance point shifts from fs (series resonance frequency), which is the resonance point of the original crystal resonator, to fr (generally speaking, fr is referred to as the resonance frequency).
[0031]
Here, the proportional relationship between the weight and the frequency holds true for fs. Therefore, in the feedback self-excited oscillation method based on fr, an error occurs in the relationship between weight and frequency. Specifically, as shown in (a) of the figure, while the load is small and G is large (while the resonance resistance R is small), the radius of the circle is large, so there is not much difference between the values of fs and fr. . On the other hand, as shown in (b) of the figure, when the load increases and G becomes extremely small (R becomes large), both of them become large by deviation. For this reason, in the feedback self-excited oscillation method that measures fr as the resonance frequency, linearity deteriorates as the load increases. On the other hand, in the method of measuring fs by the external oscillation method as in the present embodiment, such linearity degradation does not occur.
[0032]
Further, when the load increases and the state becomes as shown in (c) of the figure, the fr point disappears, so that the conventional feedback self-oscillation method cannot oscillate. On the other hand, in the external oscillation system according to the present embodiment, fs is measured and thus there is no influence of the equivalent electrode capacitance Co. Therefore, even in this case, the resonance point can be found. That is, the external oscillation method of the present embodiment enables measurement with a heavy load as compared with the feedback self-excited oscillation method. Further, in the feedback self-excited oscillation method, it is necessary to tune the oscillation circuit according to the frequency to be used in order to obtain both stable and accurate oscillation. For this reason, it is difficult to cope with a wide range of oscillation frequencies with the same oscillation circuit. On the other hand, in the external oscillation system of the present embodiment, an oscillating voltage for oscillating the crystal 110 is generated externally, so that a wide range of frequencies can be handled without changing the circuit.
[0033]
Next, the measuring unit 107 in FIG. 1 will be described in detail. The oscillating voltage oscillator 111 applies an oscillating voltage to one electrode 110 a of the QCM sensor 106 to vibrate the crystal 110. At that time, the frequency of the oscillating voltage is changed little by little from the low frequency to the high frequency to sweep the frequency. The measurement unit 112 measures the current Iq = (Vq / RL) flowing from the other electrode 110b of the QCM sensor 106, and the electrical impedance of the crystal 110 with respect to the frequency from the relationship between the applied vibration voltage and the current flowing through the crystal 110. Is calculated. Then, the measurement unit 112 calculates a frequency (the above-described series resonance frequency fs) at which the measured impedance is minimum as the resonance frequency value, and calculates the impedance at this time as the resonance resistance value. The measurement unit 112 outputs the calculated resonance frequency value and resonance resistance value to the calculation unit 113. In this case, the measurement unit 112 outputs the resonance frequency fbefore before adhesion of the droplet to the electrode 110b and the resonance frequency after after adhesion to the calculation unit 113. The calculation unit 113 calculates the weight of the droplet based on the resonance frequencies fbefore and after input from the measurement unit 112 as described below, and based on the resonance resistance input from the measurement unit 112. Calculate the viscosity of the droplet.
[0034]
Here, when the weight of the droplet attached to the electrode 110b is Im, and the amount of change Δfreq of the resonance frequency before and after the attachment of the droplet, the amount of droplet Im and the amount of change Δfreq of the resonance frequency before and after the attachment of the droplet. Can be expressed as in the following formula (1).
[0035]
[Expression 1]

[0036]
Further, when the resonance resistance value is R and the viscosity of the droplet attached to the electrode 110b is η, these relationships can be expressed by the following equation (2).
[0037]
[Expression 2]

[0038]
The calculation unit 113 calculates the change amount Δfreq = fbefore-fafter from the resonance frequency fbefore before adhesion of the droplet to the electrode 110b supplied from the measurement unit 112 and the resonance frequency after adhesion, and then calculates the change amount Δfreq. Substituting into the above equation (1), the droplet weight Im is calculated. Further, the calculation unit 113 calculates the viscosity η of the droplet by substituting the resonance resistance value R after the droplet adheres to the electrode 110b input from the measurement unit 112 into the above equation (2). The calculation unit 113 outputs the calculated droplet viscosity η and weight Im to the control unit 101. As described above, the droplet weight Im can be calculated only by the resonance frequency f, but can be accurately calculated by using the resonance resistance R in addition to the resonance frequency f.
[0039]
[Basic frequency of crystal unit]
The reference frequency F of the crystal 110 used for the QCM sensor 106 was examined from the resolution [ng / Hz] and frequency variation (variation). FIG. 9 is a diagram showing the relationship between the reference frequency F [MHz] and the resolution [ng / Hz] of the crystal resonator. As shown in the figure, the higher the reference frequency F [MHz], the higher the resolution [ng / Hz]. In order to obtain sufficient measurement accuracy, the resolution [ng / Hz] is preferably 10% or less with respect to the droplet amount. On the other hand, frequency variation increases as the reference frequency F [MHz] increases. FIG. 10 is a diagram for explaining frequency variation when the reference frequency F of the crystal resonator is 5 [MHz] and 10 [MHz]. In the figure, the horizontal axis represents time, and the vertical axis represents frequency change [Hz]. As shown in the figure, the variation in frequency is smaller in the crystal resonator having the reference frequency F = 5 [MHz] than in the crystal resonator having the reference frequency F = 10 [MHz]. FIG. 11 shows a result of converting the variation in frequency of 5 [MHz] and 10 [MHz] as the reference frequency F of the crystal resonator into the amount of droplets. As shown in the figure, when the variation in frequency is converted to an appropriate amount [ng], when the reference frequency F is 5 [MHz], 3.98 [ng] and 10 [MHz] are 1.73 [ng]. It becomes. As described above, the reference frequency F of the crystal resonator used in the QCM sensor 106 needs to consider both resolution and frequency variation. As a result of the examination, when the droplet amount to be measured is 1 to several droplets (for example, the droplet amount is 1.8 to 20 ng), the crystal vibration of the reference frequency F [MHz] = 1 to 30 [MHz] The result that the child is preferable in terms of the resolution and frequency variation was obtained. In particular, the vicinity of the reference frequency F [MHz] = 5 [MHz] is more preferable because it can achieve both resolution and frequency fluctuation.
[0040]
[Drop weight measurement flow]
FIG. 12 is a diagram showing a measurement flow of the droplet weight of the droplet discharge device 100 of FIG. It is assumed that the ejection head 103 is not on the QCM sensor 106 but is in a standby position. In FIG. 12, first, in the measurement unit 107, the oscillating voltage oscillation unit 111 applies the oscillating voltage to the electrode 110a of the QCM sensor 106 while sweeping the frequency (step S1). The measurement unit 112 detects a current flowing through the electrode 110b of the QCM sensor 106 to detect a change in impedance, calculates a resonance frequency fbefore before the droplets are attached to the electrode 110a of the QCM sensor 106, and outputs the resonance frequency fbefore to the calculation unit 113. Output (step S2). Note that the resonance frequency fbefore before the droplets adhere to the electrode 110a may be stored in advance in the calculation unit 113 without being measured each time.
[0041]
Next, the control unit 101 causes the head carriage 102 to eject the ejection head to a position where the droplet ejected from the ejection head 103 adheres to a substantially central position of the electrode 110b of the crystal 110 (see point PE in FIG. 4). 103 is conveyed (step S3). Here, the reason why the approximate center position of the electrode 110b is used is that the detection accuracy is improved when a droplet is attached to the approximately center position of the electrode 110b.
[0042]
Subsequently, the control unit 101 supplies a drive signal to the piezo element 122 included in the discharge head 103 according to the standard drive waveform, and discharges droplets from the discharge head 103 toward the PE of the electrode 110b (step S4). . Thereafter, the control unit 101 conveys the ejection head 103 to the standby position by the head carriage 102 (step S5). Here, the reason why the ejection head 103 is transported to the standby position is that when the ejection head 103 is above the QCM sensor 106, the floating capacity of the ejection head 103 and the ejection head 103 approaching the QCM sensor 106. This is because the output of the QCM sensor 106 becomes unstable due to a disturbance such as a temperature change.
[0043]
Thereafter, in the measurement unit 107, the oscillating voltage oscillation unit 111 applies the oscillating voltage to the electrode 110a of the QCM sensor 106 while sweeping the frequency (step S6). The measurement unit 112 detects a change in impedance by detecting a current flowing through the electrode 110b of the QCM sensor 106, and calculates the resonance frequency after the droplet is attached to the electrode 110b of the QCM sensor 106 and the resonance resistance R at that time. Calculate and output to the calculation unit 113 (step S7).
[0044]
The calculation unit 113 calculates the resonance frequency change amount Δfreq = fbefore−fafter based on the resonance frequencies f before and after, and calculates the weight Im of the droplet using the above-described equation (1) ( Step S8). In addition, the calculation unit 113 calculates the viscosity η of the droplet based on the resonance resistance R using the above-described equation (2). The calculation unit 113 outputs the calculated droplet weight Im and viscosity η to the control unit 101. The control unit 101 displays the calculated droplet weight Im and droplet viscosity η on the display unit 108 (step S9).
[0045]
The control unit 101 determines whether or not the calculated droplet weight Im is equal to or smaller than a predetermined value. If the droplet weight Im is equal to or smaller than the predetermined value, nozzle clogging or ink in the ejection head 103 is detected. It is also possible to display on the display unit 108 that there is a possibility of “nozzle clogging or ink end”. Further, the control unit 101 uses the ejection head 103 to draw on the drawing object W based on the weight Im of the droplet formed by the drive signal having the standard drive waveform measured as described above. The drive waveform of the drive signal applied to 103 is changed.
[0046]
As described above, according to the droplet discharge device 100 of the first embodiment, the QCM sensor 106 is configured by the crystal 110 and the electrodes 110a and 110b formed on both surfaces of the crystal 110. The crystal 110 is vibrated by applying a vibration voltage from the vibration voltage oscillator 111 to the electrode 110a. The measurement unit 112 and the calculation unit 113 detect a change in the resonance frequency of the crystal 110 before and after the droplet ejected from the ejection head 103 adheres to the electrode 110b, and determine the weight of the droplet adhered to the electrode 110b. taking measurement. Thereby, a droplet weight measuring apparatus can be made a simple and low-cost configuration. In addition, it is not necessary to provide a heater or the like, and temperature control or the like is not necessary. In addition, by setting the resolution of the QCM sensor 106 to 10% or less with respect to the amount of droplets attached to the electrode 110b, the accuracy of measuring the weight of the droplets is improved. As a result, it is possible to provide a droplet discharge device that can accurately measure the weight of droplets discharged from the discharge head with a simple configuration.
[0047]
Further, by setting the reference frequency F of the crystal 110 to 1 MHz to 30 MHz, the weight of a minute droplet can be measured with high accuracy. More preferably, by setting the reference frequency F of the crystal 110 to around 5 MHz, it is possible to achieve both the resolution and the frequency fluctuation completely. The droplet discharge device 100 according to the first embodiment can be used as an industrial inkjet device, such as a wiring, a color filter, an alignment film, a microlens array, an electroluminescent material, and a biological material. Can be used for pattern formation.
[0048]
(Embodiment 2)
FIG. 13 is a diagram showing a schematic configuration of a droplet discharge device 300 according to the second embodiment of the present invention. The droplet discharge device 300 according to the second embodiment is an ink jet printer. In the droplet discharge device 300 according to the second exemplary embodiment, a QCM sensor 301 is provided in a part of the sheet conveyance path 304, and a discharge head is mounted on the carriage 302. The principle of measuring the weight of the droplets (ink droplets) ejected from the ejection head is the same as that in the first embodiment, and a description thereof will be omitted. The droplet discharge device 300 according to the second embodiment is an inkjet printer that prints an image by forming ink dots on a print sheet by discharging fine ink droplets while reciprocating a carriage 302 on the print sheet. It is.
[0049]
With reference to FIG. 13, the operation of the droplet discharge device 300 for printing an image on a sheet will be briefly described. The carriage 302 has a built-in discharge head for discharging ink droplets. An ink cartridge 308 mounted on the upper surface side of the carriage 302 supplies ink to the ejection head. The printing paper is conveyed to a predetermined position below the carriage 302 by the paper feed roller 303. When the printing paper is set at a predetermined position, the carriage 302 ejects ink droplets from the ejection head while reciprocating on the printing paper. The carriage 302 is guided to two guide rails 305 as shown in the figure, and is driven by a carriage motor 307 via a drive belt 306. Thus, the operation of reciprocating the carriage 302 is called main scanning.
[0050]
The paper feed roller 303 is driven in synchronization with the main scanning of the carriage 302 to move the printing paper little by little in the direction perpendicular to the main scanning direction. In this way, the operation of relatively moving the ejection head and the printing paper in the direction crossing the main scanning direction is called sub-scanning. In this way, the printing paper is sub-scanned while main-scanning the carriage 302, and ink droplets are ejected at an appropriate timing to form ink dots on the printing paper, thereby printing an image.
[0051]
Thus, the droplet discharge device of the present invention can be suitably used for an ink jet printer. In the case where the weight of the sample liquid is measured instead of the ink droplet, the ink cartridge 308 may be removed and a container storing the sample liquid instead of the ink may be attached to the carriage 302. The present invention is not limited to the first embodiment and the second embodiment described above, and can be appropriately modified and implemented without changing the gist of the invention.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall schematic configuration of a droplet discharge device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a detailed configuration of an ejection head.
FIG. 3 is a diagram for explaining the principle of changing the size of droplets ejected from an ejection head.
FIG. 4 is a plan view showing a configuration of a QCM sensor.
FIG. 5 is a diagram showing an equivalent circuit of a crystal resonator.
FIG. 6 is a conceptual diagram of a measurement unit.
FIG. 7 is a conceptual diagram of a feedback self-oscillation method.
FIG. 8 is an admittance diagram of a crystal resonator.
FIG. 9 is a diagram illustrating a relationship between a reference frequency F [MHz] and a resolution [ng / Hz] of a crystal resonator.
FIG. 10 is a diagram for explaining variation in frequency when the reference frequency F of the crystal resonator is 5 [MHz] and 10 [MHz].
FIG. 11 is a diagram in which a variation in frequency when the reference frequency F of a crystal resonator is 5 [MHz] and 10 [MHz] is converted into a droplet amount.
FIG. 12 is a diagram showing a flow of measuring a droplet weight of the droplet discharge device according to the first embodiment of the present invention.
FIG. 13 is a diagram illustrating an overall schematic configuration of a droplet discharge device according to a second embodiment of the present invention.
[Explanation of symbols]
100 droplet discharge device, 101 control unit, 102 head carriage, 103R, 103G, 103B discharge head, 104R, 104G, 104B ink tank, 105 stage, 106 QCM sensor, 107 measurement unit, 108 display unit, 110 crystal, 110a, 110b electrode, 111 oscillating voltage oscillation unit, 112 measuring unit, 113 calculating unit, 121 pressure chamber, 122 piezo element, 123 nozzle, 131 insulator, 132a, 132b support, 133a, 133b terminal, 300 droplet discharge device, 301 QCM sensor, 302 carriage, 303 paper feed roller, 304 paper transport path, 305 guide rail, 306 drive belt, 307 carriage motor, 308 ink cartridge

Claims (6)

In a droplet weight measuring apparatus that measures the weight of droplets discharged from the discharge head,
Detection means comprising a piezoelectric vibrator having electrodes formed on both sides;
Oscillating means for applying a vibration voltage to the electrode to vibrate the piezoelectric vibrator;
A change in the resonance frequency of the piezoelectric vibrator before and after the droplet discharged from the discharge head adheres to the electrode is detected, and at least based on the detected change in the resonance frequency of the piezoelectric vibrator, Droplet weight measuring means for measuring the weight of the adhered droplet;
With
A droplet weight measuring apparatus, wherein the detection means has a resolution of 10% or less with respect to a droplet amount attached to the electrode. The droplet weight measuring apparatus according to claim 1, wherein a reference frequency F of the piezoelectric vibrator is 1 MHz to 30 MHz. The droplet weight measuring apparatus according to claim 2, wherein the reference frequency F of the piezoelectric vibrator is in the vicinity of 5 MHz. The droplet weight measuring device according to any one of claims 1 to 3,
A discharge head control means for discharging a droplet by applying a drive signal to the discharge head;
A droplet discharge apparatus comprising: 5. The droplet discharge device is used for pattern formation of any one of a wiring, a color filter, an alignment film, a microlens array, an electroluminescent material, and a biological material. Droplet discharge device. The droplet discharge device according to claim 4, wherein the droplet discharge device is an inkjet printer.

Images