JP2007152666A - Liquid droplet observing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid droplet observing device which can more clearly photograph fine liquid droplets being discharged from a liquid jetting head. <P>SOLUTION: This liquid droplet observing device 1 comprises a control section 3, a light-emitting section 5, and a photographing section 6. In this case, the control section 3 has a driving signal-generating circuit 37 which generates a driving signal and controls the discharge of ink droplets by a recording head 2 by feeding a discharging pulse in the driving signal from the driving signal-generating circuit to a piezoelectric oscillator. The light-emitting section 5 irradiates a flying region A of the ink droplets which have been discharged from the nozzle opening of the recording head with light by making an LED 4 emit the light. The photographing section 6 is confront-arranged on the opposite side from the light-emitting section across the flying region, and photographs the ink droplets flying in the flying region with the light-emitting section as a light source. The control section synchronizes the discharge of the ink droplets by the recording head and the light emission by the light-emitting section, and also, sets the light-emitting frequency at a maximum value which can be synchronized with the discharging motion within a range for which the maximum driving frequency in the design of the light-emitting section as the upper limit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a droplet observation apparatus that observes droplets ejected from a liquid jet head such as an ink jet recording head.

  Examples of the liquid ejecting head for ejecting the liquid in the pressure chamber as droplets from the nozzle opening include, for example, an ink jet recording head used in an image recording apparatus such as a printer, and a color material ejecting head used for manufacturing a color filter such as a liquid crystal display. There are an electrode material ejecting head used for forming electrodes such as an organic EL (Electro Luminescence) display and an FED (surface emitting display), and a bioorganic matter ejecting head used for manufacturing a biochip (biochemical element).

  This type of liquid ejecting head is required to land extremely fine droplets at a desired position on an ejection target such as recording paper with high accuracy. For this reason, in the manufacturing process of the liquid ejecting head, the droplets are ejected from the liquid ejecting head and the flying droplets are imaged by the camera. Based on the captured images, the nozzle opening is clogged, the flying direction, The flight speed, liquid volume, etc. are inspected. For example, in the micro-droplet observation device disclosed in Patent Document 1, a strobe light emitting unit and a CCD camera are arranged in a state of facing each other with a flying region of a droplet ejected from a liquid ejecting head interposed therebetween. A droplet that is flying is imaged by a CCD camera while synchronizing the light emission cycle and the droplet discharge cycle.

Japanese Patent Laid-Open No. 2001-239744 (page 9, FIG. 1)

  By the way, as the light source of the strobe, for example, a xenon tube that has excellent followability with respect to a change in electric input and can blink at a relatively high frequency is preferably used. However, with a xenon tube, it is difficult to make the luminance constant. For example, when the luminance is too high, there is a problem that it is impossible to capture very fine droplets as clearly as several pl. Further, when the xenon tube is caused to emit light, it is necessary to drive it with a driving pulse set to a high voltage of several tens of kV using a pulse starter. Therefore, when discharging droplets at a higher frequency, the xenon tube There has been a problem that a malfunction occurs in the drive circuit of the liquid jet head due to radiation noise caused by high-frequency drive pulses during light emission.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a droplet observation apparatus that can capture fine droplets ejected from a liquid ejecting head more clearly. It is in.

In order to achieve the above object, a droplet observation apparatus of the present invention includes a pressure chamber communicating with a nozzle opening, and a nozzle of a liquid ejecting head having pressure generating means for causing a pressure fluctuation in the liquid introduced into the pressure chamber. A droplet observation device for observing a droplet discharged from an opening,
A drive signal generating circuit for generating a drive signal for driving the pressure generating means; and supplying the drive signal from the drive signal generating circuit to the pressure generating means, thereby ejecting droplets by the liquid ejecting head. A control unit to control;
A light emitting unit that has a solid light emitting element and emits light to a flying region of a liquid droplet ejected from a nozzle opening of the liquid jet head by causing the solid light emitting element to emit light;
The light emitting unit is disposed opposite to the opposite side across the flying region of the droplet, and includes an imaging unit that captures images of the flying droplet in the flying region by multiple exposure,
The control unit synchronizes the ejection of droplets by the liquid ejecting head and the light emission of the solid state light emitting element by the light emitting unit, and the light emission frequency is within a range where the maximum driving frequency in the design of the light emitting unit is the upper limit. A maximum value that can be synchronized with the discharge of droplets is set.

  According to the above configuration, since the solid-state light emitting element that can be driven at a lower voltage is used as the light source, unnecessary radiation noise can be suppressed and malfunction of the drive circuit can be prevented. Further, the ejection of the liquid droplet by the liquid ejecting head and the light emission of the solid state light emitting element by the light emitting unit are synchronized, and the light emission frequency is within the range where the maximum driving frequency in the design of the light emitting unit is the upper limit. Since the maximum value that can be synchronized with the discharge is set, the solid-state light emitting element can emit light with as high luminance as possible while synchronizing the discharge of the droplet and the light emission of the light emitting unit. As a result, a fine droplet can be imaged more clearly by the imaging unit, and as a result, the droplet can be observed with higher accuracy.

In the above configuration, when the droplet discharge interval is T and the number of discharges for one light emission is N, the light emission frequency F of the solid state light emitting element is expressed by the following formula (1).
F = 1 / (T × N) (1)
It is desirable to set based on

  In the above configuration, a light emitting diode can be employed as the solid state light emitting device.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. In the embodiments described below, various limitations are made as preferred specific examples of the present invention. However, the scope of the present invention is not limited to the following description unless otherwise specified. However, the present invention is not limited to these embodiments.

FIG. 1 is a schematic diagram illustrating the configuration of a droplet observation apparatus to which the present invention is applied. As shown in the figure, the droplet observation apparatus 1 according to the present embodiment is an observation target of an ink jet recording head (hereinafter simply referred to as a recording head) 2 that is a kind of liquid ejecting head. The recording head 2 is mounted on an ink jet printer (image recording apparatus) that discharges liquid ink in the form of droplets and records characters and images on an ejection target such as recording paper. The droplet observation device 1 includes a control unit 3 that performs overall control of the entire device, a light-emitting diode that is a kind of solid-state light-emitting element as a light-emitting source, that is, a light-emitting unit 5 that has an LED (Light Emitting Diode) 4, An imaging unit 6 composed of a CCD (Charge Coupled Device) camera and an LCD (Liquid Crystal)
And a display device 7 composed of a CRT (Cathode-Ray Tube) or the like.

  Here, before describing each part of the droplet observation apparatus 1, the structure of the recording head 2 to be observed will be described with reference to FIG. The illustrated recording head 2 includes an actuator unit 13 in which a plurality of piezoelectric vibrators 10, a fixing plate 11 thereof, a flexible cable 12, and the like are unitized, a head case 14 that accommodates the actuator unit 13 therein, and a head case 14 is provided with a flow path unit 15 joined to the front end surface of 14. The head case 14 is a block-shaped member made of synthetic resin in which an accommodation chamber 16 for accommodating the actuator unit 13 is formed. The accommodating chambers 16 are empty portions that penetrate the height direction of the head case 14 and are individually formed by the same number as the number of actuator units 13 accommodated. The actuator unit 13 is housed in a state in which the tip surface of the piezoelectric vibrator 10 faces the opening on the flow channel unit joint surface side of the housing chamber 16, and the fixing plate 11 is placed on the inner wall surface of the case that partitions the housing chamber 16. It is glued.

  A piezoelectric vibrator 10 (a kind of pressure generating element) of this embodiment is a laminated piezoelectric vibrator configured by alternately laminating piezoelectric bodies and internal electrodes, and has an extremely narrow width of about several tens of μm. It is cut into comb teeth. The piezoelectric vibrator 10 expands and contracts in a direction orthogonal to the electric field direction according to a potential difference between the piezoelectric body and the internal electrode. Each piezoelectric vibrator 10 is mounted on the fixed plate 11 in a so-called cantilever state. That is, the base end side portion of each piezoelectric vibrator 10 is joined onto the fixed plate 11, so that the free end portion protrudes outward from the edge of the fixed plate 11. And the front end surface of each piezoelectric vibrator 10 is joined to the island part 31 of the flow path unit 15 mentioned later. Further, the flexible cable 12 is electrically connected to each piezoelectric vibrator 10 on the surface of the base end side portion that is opposite to the fixed plate 11.

  In the flow path unit 15, the nozzle substrate 19 is disposed on one surface of the flow path substrate 18 with the flow path substrate 18 interposed therebetween, and the vibration plate 20 is disposed on the other surface opposite to the nozzle substrate 19. It is composed by bonding. The nozzle substrate 19 in the flow path unit 15 is a thin plate made of stainless steel in which a plurality of nozzle openings 21 are opened in a row at a pitch corresponding to the dot formation density. In the present embodiment, for example, 180 nozzle openings 21 are formed in a row at a pitch of 180 dpi, and these nozzle openings 21 constitute a nozzle row.

  The flow path substrate 18 is formed with a plurality of empty portions that become pressure chambers 22 and groove portions that become ink supply ports 23 at the same pitch as the nozzle openings 21 of the nozzle substrate 19, and empty portions that become common ink chambers 24. It is the formed plate-shaped member. The pressure chamber 22 is formed as a long and narrow chamber in a direction orthogonal to the direction in which the nozzle openings 21 are arranged (nozzle row direction). The ink supply port 23 is a groove having a narrow channel width that communicates between the common ink chamber 24 and the pressure chamber 22. Further, a nozzle communication port 25 for communicating the nozzle opening 21 and the pressure chamber 22 is penetrated in the plate thickness direction in an end region opposite to the ink supply port 23 in the pressure chamber 22. Is provided.

  The diaphragm 20 has a double structure in which an elastic film 27 made of an elastic film such as PPS resin is laminated on the surface of a metal support plate 26 such as stainless steel. The diaphragm 20 is provided with a diaphragm portion 28 that seals one opening surface of the pressure chamber 22 and a compliance portion 29 that seals one opening surface of the common ink chamber 24. . The diaphragm portion 28 is manufactured by annularly etching a portion of the support plate 26 corresponding to the pressure chamber 22, and the island portion 31 where the elastic portion 30 only of the elastic film 27 and the piezoelectric vibrator 10 are joined. And are provided. In addition, the compliance unit 29 removes the support plate 26 corresponding to the common ink chamber 24 by etching, and uses only the elastic film 27.

  In the recording head 2 having the above-described configuration, ink from an ink cartridge (one type of liquid storage member) (not shown) is once introduced into the common ink chamber 24 and then distributed from the common ink chamber 24 to each pressure chamber 22. The Then, when an ejection pulse in the drive signal is supplied to the piezoelectric vibrator 10 using a later-described ejection timing pulse as a trigger, the piezoelectric vibrator 10 expands and contracts in the longitudinal direction of the element, and accordingly, the island portion 31 is moved to the pressure chamber 22. The volume of the pressure chamber 22 changes due to the displacement of the island portion 31. As a result, pressure fluctuations occur in the ink in the pressure chamber 22, and ink drops (that is, a kind of liquid droplets) are ejected from the nozzle openings 21 by controlling the pressure fluctuations by the expansion and contraction of the piezoelectric vibrator 10.

  Next, the control unit 3 of the droplet observation apparatus 1 will be described. The control unit 3 in this embodiment includes a CPU 34 that controls each unit according to a control program stored in the ROM 33, a ROM 33 that stores a control program for various data processing, a RAM 35 that stores various data, and an imaging A display control unit 36 that displays an image captured by the unit 6 on the display device 7, a drive signal generation circuit 37 that generates a drive signal for driving the piezoelectric vibrator 10 of the recording head 2, and a reference clock pulse signal Input / output of data between the oscillation circuit 38 for generating the signal, the frequency dividing circuit 39 for dividing the reference clock pulse signal generated by the oscillation circuit 38, and the connected devices (the recording head 2, the light emitting unit 5, and the imaging unit 6). The interface (I / F) unit 36 for performing the above is provided in a mutually connected state. The control unit 3 comprehensively controls the ink droplet ejection operation by the recording head 2, the light emission operation by the light emitting unit 5, and the imaging operation by the imaging unit 6.

  The drive signal generation circuit 37 receives data indicating the amount of change in the voltage value of the ejection pulse supplied to the piezoelectric vibrator 10 of the recording head 2 and a timing signal that defines the timing for changing the voltage of the ejection pulse. Based on the data and the timing signal, for example, a drive signal including an ejection pulse DP as shown in FIG. 3 is generated. The ejection pulse DP illustrated in FIG. 3 includes a first charging element PE1 that raises the potential with a relatively gentle gradient from the reference potential (intermediate potential) VM to the maximum potential VH, and a first that maintains the maximum potential VH for a certain period of time. The hold element PE2, the discharge element PE3 that drops the potential with a steep gradient from the highest potential VH to the lowest potential VL, the second hold element PE4 that maintains the lowest potential VL for a short time, and the potential from the lowest potential VL to the reference potential VM And a second charging element PE5 that restores.

  When the ejection pulse DP is applied to the piezoelectric vibrator 10, ink droplets are ejected as follows. That is, when the first charging element PE1 is supplied, the piezoelectric vibrator 10 contracts and the pressure chamber 22 expands. After the expansion state of the pressure chamber 22 is maintained for a very short time, the discharge element PE3 is applied and the piezoelectric vibrator 10 is rapidly expanded. Along with this, the volume of the pressure chamber 22 contracts to a reference volume (the volume of the pressure chamber 22 when the reference potential VM is applied to the piezoelectric vibrator 10) or less, and the meniscus exposed to the nozzle opening 21 faces outward. Pressurized rapidly. Thereby, an ink droplet of a predetermined liquid amount is ejected from the nozzle opening 21. Thereafter, the second hold element PE4 and the second charging element PE5 are sequentially supplied to the piezoelectric vibrator 10, and the pressure chamber 22 returns to the reference volume so as to converge the meniscus vibration accompanying the ejection of the ink droplets in a short time. To do.

  The oscillation circuit 38 in the control unit 3 generates a reference clock pulse that serves as a reference for control timing of each unit. The reference clock pulse is set to a frequency of about several MHz to several hundred MHz, for example. The frequency dividing circuit 39 divides the reference clock pulse output from the oscillation circuit 38 to output a timing pulse having a frequency corresponding to the control of each unit. For example, the frequency dividing circuit 39 divides the reference clock pulse to generate a pulse of several kHz to several hundred kHz, and discharge timing that defines the timing of supplying the drive signal (discharge pulse DP) to the piezoelectric vibrator 10. It outputs to the recording head 2 as a pulse. The frequency dividing circuit 39 divides the reference clock pulse to generate a pulse of several hundred Hz to several kHz, and outputs the pulse to the light emitting unit 5 as a light emission timing pulse that defines the light emission timing of the LED 4 by the light emitting unit 5. To do. In the droplet observation apparatus 1, the ejection operation of the recording head 2 is controlled using the ejection timing pulse, and the ejection operation of the LED 4 by the light emitting unit 5 is controlled using the light emission timing pulse. (Ejection cycle) and the light emission operation (light emission cycle) by the light emitting unit 5 can be synchronized.

  The light emitting unit 5 includes an LED 4 serving as a light source at the time of image capturing by the image capturing unit 6, and is disposed in a state where the optical axis L of the LED 4 is directed to the flying region A of the ink droplet ejected from the nozzle opening 21 of the recording head 2. Has been. The light emitting unit 5 is configured to receive the light emission timing pulse from the control unit 3 and cause the LED 4 to emit light using the light emission timing pulse as a trigger. That is, the light emitting unit 5 causes the LED 4 to emit light in synchronization with the ejection operation of the recording head 2 at the light emission frequency defined by the light emission timing pulse. Solid-state light emitting devices represented by LEDs can be driven at a lower voltage than when a xenon tube is used as a light source, so that it is difficult for unnecessary radiation noise to occur when light is emitted at high frequencies. It is possible to prevent the malfunction of the driving circuit that performs the operation. The light emitting section 5 has a design maximum drive frequency in order to cause the LED 4 to emit light with a light amount of a certain level or more. The maximum drive frequency is, for example, several kHz, and the light emission drive at a frequency higher than this cannot be followed by the drive circuit of the light emitting unit 5, and the light quantity of the LED 4 cannot be obtained sufficiently.

  The imaging unit 6 is constituted by a CCD camera having an objective lens 42 and a CCD imaging device 43, and on the optical axis L of the light emitting unit 5, the objective lens 42 is opposite to the light emitting unit 5 across the flight region A. Are opposed to each other in a state of facing the flying region A side. The imaging unit 6 employs a relatively high-resolution CCD imaging device 43 having an XGA (1024 × 768 pixels) or SXGA (1280 × 1024 pixels) size, for example, in order to cope with imaging of smaller ink droplets. Yes. Then, under the control of the control unit 3, the imaging unit 6 images the ink droplets flying in the flying region A by multiple exposure using the light emitting unit 5 as a light source. The image data captured by the imaging unit 6 is output to the control unit 3.

  The droplet observation apparatus 1 configured as described above continuously ejects ink droplets from the nozzle opening 21 at the ejection frequency Fd defined by the ejection timing pulse, and uses the light emission timing pulse in synchronization with the ejection of the recording head 2. While the LED 4 of the light emitting unit 5 is caused to emit light at the specified light emission frequency Fe, the ink droplets flying in the flying region A are imaged by the imaging unit 6. In the image captured in this way, as shown in FIG. 4, the ink droplets (main ink droplet Dm and satellite ink droplet Ds associated therewith) are emitted from the light emitting unit 5 against a background that is relatively high in brightness and close to white. Since the light from the light is blocked, the image is captured in a color close to black. In this example, imaging is performed in a state where ink droplets are simultaneously ejected from the nozzle openings 21 constituting the nozzle row. Based on the captured image, inspections such as the presence / absence of clogging (dot missing) of the nozzle opening 21, the flying direction of the ink droplet, the flying speed, and the liquid amount (particle diameter) are performed. For example, paying attention to a single ink drop, the flying speed of the ink drop can be determined by examining how far the ink drop flew at a certain time using a plurality of images taken continuously. Can be sought.

Here, since the LED 4 as the light source can be driven with low power as described above, there is an advantage that it is difficult to generate radiation noise in light emission driving at a high frequency. On the other hand, xenon that has been suitably used in the past is used. There is a drawback that the amount of light is lower than that of the tube. For this reason, in order to capture a clear image of ink droplets that are flying at several m / s, including satellite ink droplets Ds that are finer than the main ink droplets Dm, the imaging unit 6 is performing one exposure (one frame). It is important that the LED 4 emits as much light as possible by the light emitting unit 5. Therefore, the control unit 3 synchronizes the ejection period of the ink droplets by the recording head 2 and the light emission period of the LED 4 by the light emitting unit 5 and then sets the light emission frequency Fe (that is, the frequency of the light emission timing pulse) to the light emitting unit 5. The maximum drive frequency Fm is set to a maximum value within a range having an upper limit. Specifically, when the ejection interval of the ink droplets by the recording head 2 is T (= 1 / Fd) and the number of ejections for one light emission is N, the light emission frequency Fe of the LED 4 is expressed by the following equation (1). Set based on.
Fe = 1 / (T × N) (1)
The number N of ejections in the equation (1) is expressed by the following equation (2), where n is the number of times after the decimal point when the ejection frequency Fd is divided by the maximum drive frequency Fm of the light emitting unit 5 and a is the remainder. Sought by.
N = n + a (2)

For example, the discharge frequency Fd is 6840 × ¹⁰ 3 Hz ink droplets, when the maximum driving frequency Fm of the light-emitting portion 5 is 1000Hz, n = Fd / Fm = 6840 × 10 3 / 1000Hz = 6000 (a = 840) , and the The ejection number N for one light emission is N = n + a = 6000 + 840 = 6840 Hz based on the above equation (2). Further, the discharge interval T is T = 1 / Fd≈1.462 × 10 ⁻⁷ sec. Therefore, the light emission frequency Fe of the LED 4 is determined as Fe = 1 / (T × N) = 1 / (1.462 × 10 ⁻⁷ × 6840) ≈1000 Hz based on the above equation (1).

  Thus, by determining the light emission frequency Fe based on the above equation (1), it is possible to cause the LED 4 to emit light with as high luminance as possible while synchronizing the light emission with the ejection of the ink droplets. Thereby, a fine ink droplet can be imaged more clearly by the imaging part 6, As a result, it becomes possible to test | inspect the flying speed of an ink droplet, etc. with high precision based on the imaged image. .

  By the way, the present invention is not limited to the above embodiment, and various modifications can be made based on the description of the scope of claims.

  In each said embodiment, although the example which uses LED4 as a light emission source of the light emission part 5 was shown, it is not restricted to this. For example, other solid-state light emitting elements that can be driven at a low voltage, such as a semiconductor laser, can be used.

  In the above description, the recording head 2 has been described as an example of a liquid jet head to be observed for droplets. However, the present invention is for observing droplets (functional droplets) ejected from other liquid jet heads. Can also be applied. For example, a color material ejecting head used for manufacturing a color filter such as a liquid crystal display, an electrode material ejecting head used for forming an electrode such as an organic EL (Electro Luminescence) display, an FED (surface emitting display), a biochip (biochemical element) The present invention is also suitable for observing droplets ejected from a bio-organic matter ejecting head or the like used in the production of

It is a schematic diagram explaining the structure of a droplet observation apparatus. FIG. 3 is a cross-sectional view of a main part illustrating the configuration of a recording head. It is a figure explaining the structure of an ejection pulse. It is a figure which shows an example of the image imaged by the imaging part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Droplet observation apparatus, 2 ... Recording head, 3 ... Control part, 4 ... LED, 5 ... Light emission part, 6 ... Imaging part, 7 ... Display apparatus, 10 ... Piezoelectric vibrator, 18 ... Channel substrate, 19 ... Nozzle substrate, 20 ... vibration plate, 21 ... nozzle opening, 22 ... pressure chamber, 33 ... ROM, 34 ... CPU, 35 ... RAM, 37 ... drive signal generation circuit, 38 ... oscillation circuit, 39 ... frequency divider circuit, 40 ... I / F section, 42 ... objective lens, 43 ... CCD image sensor

Claims (3)

A droplet observation apparatus for observing droplets ejected from a nozzle opening of a liquid ejecting head having a pressure chamber communicating with the nozzle opening and pressure generating means for causing a pressure fluctuation in the liquid introduced into the pressure chamber. And
A drive signal generating circuit for generating a drive signal for driving the pressure generating means; and supplying the drive signal from the drive signal generating circuit to the pressure generating means, thereby ejecting droplets by the liquid ejecting head. A control unit to control;
A light emitting unit that has a solid light emitting element and emits light to a flying region of a liquid droplet ejected from a nozzle opening of the liquid jet head by causing the solid light emitting element to emit light;
The light emitting unit is disposed opposite to the opposite side across the flying region of the liquid droplet, and includes an imaging unit that images the liquid droplet flying in the flying region using the light emitting unit as a light source.
The control unit synchronizes the ejection of droplets by the liquid ejecting head and the light emission of the solid state light emitting element by the light emitting unit, and the light emission frequency is within a range where the maximum driving frequency in the design of the light emitting unit is the upper limit. A droplet observation apparatus characterized in that it is set to a maximum value that can be synchronized with droplet ejection. The control unit sets the emission frequency F of the solid state light emitting element to the following formula (1), where T is the droplet discharge interval and N is the number of discharges for one light emission.
F = 1 / (T × N) (1)
The droplet observation device according to claim 1, wherein the droplet observation device is set based on   The droplet observation apparatus according to claim 1, wherein the solid state light emitting element is a light emitting diode.

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