JP2008018658A - Apparatus for measuring liquid droplet speed - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly measure a speed of a liquid droplet ejected from a liquid ejecting head of an inkjet printer or the like. <P>SOLUTION: A fiber light guide 130 which guides light of an illuminant 220 with two strobe light sources is disposed on the same optical axis in a direction opposed to an area sensor camera 110 with respect to an inkjet head 120. The two strobe light sources are made to emit the light at predetermined time intervals t2 within a liquid droplet ejection spacing from a nozzle hole of the inkjet head 120. A position where the same liquid droplet ejected from the inkjet head 120 is illuminated twice by the two strobe light sources is photographed with multiple exposure by the area sensor camera 110. The liquid droplet speed is obtained from two position coordinates of the same liquid droplet photographed on the same screen by a personal computer for detection 270. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a droplet velocity measuring device that measures the velocity of droplets ejected from a liquid ejection head such as an ink jet printer.

Currently, inkjet printers are used not only for printing on ordinary paper media but also for printing other than paper media such as color filters, and high-resolution and high-quality printing is required.
In order to obtain such a high-quality print image, it is necessary to highly control the volume and ejection speed of the ejected ink droplets. For this reason, it is necessary to measure the ejection speed of the ejected droplets.

Conventionally, several methods have been proposed as methods for measuring the speed of droplets ejected from nozzle holes of a printer head or the like (Patent Document 1, Patent Document 2, and Patent Document 3).
JP-A-11-105307 JP-A-11-227172 JP 2006-110774 A

  The method of Patent Document 1 uses a center point in a shooting screen as a reference point, and calculates a droplet discharge speed from an error between a reference point of a photographed image and the position of the droplet when a certain time has elapsed after discharge. And use two cameras and strobe.

  On the other hand, in the method of Patent Document 2, the strobe light source emits a plurality of times with a time difference, the center position of the droplet is obtained from a plurality of images captured at the timing of each light emission, and the relative position between the plurality of droplet centers. And the discharge speed is obtained from the time difference between the respective timings.

  Furthermore, the method of Patent Document 3 illuminates two laser light sources from a direction substantially perpendicular to the droplet discharge direction. The two laser light sources are arranged at a predetermined interval with respect to the ejection direction, and are detected by detecting two laser light fluxes passing through the droplets by a photo sensor installed facing the laser light sources. The droplet discharge speed is obtained from the difference in timing at which the droplets of the two light beams cut off and the distance between the two laser beams.

  However, the method of Patent Document 1 determines a predetermined time during which a droplet falls from the nozzle hole to the vicinity of the reference position at the center of the screen, and obtains the droplet velocity from an error from the reference position at the predetermined time. The droplet velocity is measured based on the distance and time from the nozzle hole that is not present, and there is a possibility that a measurement error or error due to malfunction or the like may occur.

  The method of Patent Document 2 is a method for determining the center position of a droplet from a plurality of droplet images, and the target droplet is not continuously ejected from the same nozzle hole but is continuously ejected. The ejection speed is obtained using different droplets. In the case of different droplets, there is a problem in that individual discharged droplets do not always have the same drop characteristics and cannot accurately measure the droplet velocity.

  Further, in the method of Patent Document 3, two laser light sources emit light at different timings, the same droplet that cuts each laser beam is detected by a photosensor, and the droplet velocity is obtained from the time difference. However, in the case of a laser beam, since the beam is narrowed, there is a possibility that the droplet will be displaced from the laser beam when the droplet is not ejected approximately vertically, in which case the droplet velocity cannot be measured. There is a problem of becoming.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a droplet velocity measuring device capable of accurately measuring the velocity of droplets ejected from a liquid ejection head such as an ink jet printer. Is to provide.

  The present invention for solving the above-mentioned problems is a droplet velocity measuring device for measuring the velocity characteristics of droplets ejected from a printer head, and emits light that emits pulses twice or more within a droplet ejection interval time. And an exposure that starts exposure at the same time as the start of the first pulse emission or before the start of the pulse emission for an exposure time longer than the time from the start of the first pulse emission by the light emission means to the end of the last pulse emission. Means, and droplet velocity calculation means for calculating the velocity of the droplet from the position coordinates of two drop points of one droplet on the screen imaged by the imaging means, and the pulse emission interval. This is a droplet velocity measuring device.

  That is, pulse emission is performed twice or more within a discharge interval of a plurality of droplets that are continuously discharged, which is shorter than the droplet discharge interval and longer than the time from the start of the first pulse emission to the end of the last pulse emission. By photographing with the exposure time, one droplet is photographed twice or more on the same screen. The droplet velocity is calculated from the positional relationship of two times on the screen of the same droplet and the time interval of pulse emission.

  Here, the light emitting means includes two or more strobe light sources and a strobe delay generating means, and the strobe delay generating means emits the first strobe light source after a first predetermined time from the discharge timing from the printer head. Preferably, after the first strobe light source emits light, the second strobe light source emits light after a second predetermined time before the next droplet discharge.

The light emitting means includes one light emitter, a rotating light shielding plate having a slit, and a driving means for rotating the rotating light shielding plate, and the driving means is performed at least twice within a droplet discharge interval time. The rotating light-shielding plate may be rotated so that the light from the illuminant is applied to the droplet through the slit.
The rotating light shielding plate may have two or more slits. As a result, it is possible to irradiate the droplets with light rays through the slit twice within the droplet discharge interval.

  By adopting a structure comprising a rotating light shielding plate having a slit, the light emitter is not strobe light emission, it is only necessary to emit light constantly, and a cheaper light emitter can be used. It becomes possible to irradiate light to the same droplet twice or more within the droplet discharge interval, and it is possible to photograph the same droplet by multiple exposure on the same screen.

  According to the present invention, two or more dropping positions of the same droplet can be photographed by multiple exposure on the same screen, and an accurate droplet velocity can be measured.

Hereinafter, a first preferred embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a functional configuration diagram of the droplet velocity measuring apparatus 1.

FIG. 1A is a functional configuration diagram of a droplet velocity measuring device according to an embodiment. It comprises a head 120 of an inkjet printer, an area sensor camera 110, a strobe light source 220, a fiber light guide 130, and the like.
Droplets are ejected from the nozzle holes of the inkjet head 120 at predetermined intervals. For example, a droplet (n−1) 141, a droplet n142, and a droplet (n + 1) 143 are sequentially ejected from the nozzle holes of the head 120.

The strobe 220 is composed of two strobe light sources, and each strobe light source emits once within a predetermined droplet discharge interval. The emitted strobe light is guided to the fiber light guide 130.
The area sensor camera 110 and the fiber light guide 130 are disposed to face each other on the same optical axis below the inkjet head 120.
The area sensor camera 110 photographs the droplets ejected from the inkjet head 120 from the A direction. The fiber light guide 130 irradiates the droplet with strobe light in the anti-A direction.
The exposure time of the area sensor camera 110 is set to a time sufficient for the droplet n142 to pass through the Y direction imaging range. Even if the next droplet (n + 1) 143 enters the imaging range, the next droplet (n + 1) 143 is not reflected in the dark room because the strobe light is not emitted. It may be a long time (1/30 second = 33 ms).

  First, at the time of the first strobe light emission, the area sensor camera 110 takes an image of the droplet n142 at the position at the time of the first strobe light emission, and at the time of the second strobe light emission, the same droplet n142 is the second strobe light. The photograph is taken at the position (142 ') at the time of light emission.

  Examples of photographed images are shown in FIGS. 1 (b) and 1 (c). As shown in the figure, the area sensor camera 110 has a Y-direction imaging range 150 and an X-direction imaging range 160, where the Y direction is a perpendicular direction from the inkjet head 120, and the X direction is perpendicular to the Y direction. Thus, the direction is perpendicular to the paper surface of FIG.

As shown in FIGS. 1B and 1C, the positions (142 and 142 ′) of the same droplet at two time points are displayed in the captured image.
From the center coordinates of the droplets at these two time points, the distance dropped between the first flash emission and the second flash emission is obtained, and from the time interval between the first flash emission and the second flash emission, the speed of the droplet is calculated. Ask for.

FIG. 1B shows a case where the droplet n142 has dropped in the vertical direction. In this case, since the X coordinate of the position 142 and the position 142 ′ is the same, the drop distance L is obtained from the difference of the Y coordinates. .
On the other hand, FIG. 10C is a diagram when the droplet n142 is ejected in an oblique direction.
In this case, the X-coordinates of the position 142 and the position 142 ′ are different and advance by L2 in the X direction and L1 in the Y direction. This makes it possible to measure the ejection direction as well as the droplet velocity perpendicular to the inkjet head 120.
In this case, the droplet velocity is calculated from the distance between the position 142 and the position 142 ′, that is, (L1 ² + L2 ² ) ^1/2 .

FIG. 2 is a system configuration diagram of the droplet velocity measuring apparatus 1.
The droplet velocity measuring device 1 includes an inkjet head 120, a head transport stage 210, a uniaxial stage controller 215, an area sensor camera 110, an inspection personal computer 270, a display device 280, a strobe 220, a fiber light guide 130, a pulse generator 230, It consists of a sequencer 240 and the like.

The inkjet printer head 120 is provided with a plurality of nozzle holes in a direction perpendicular to the paper surface, and the droplet velocity measuring device 1 shoots a droplet discharged from one of the nozzle holes and adjusts the velocity. taking measurement.
The head transport stage 210 is a transport stage for moving the inkjet head 120 in a direction perpendicular to the paper surface. The nozzle holes provided in the head 120 are placed on the optical axes of the area sensor camera 110 and the fiber light guide 130. Transport. This makes it possible to measure the speed of the ejected droplets for each nozzle hole provided in the head 120.
The head transport stage 210 is driven and controlled by a uniaxial stage controller 215.

  The inspection personal computer 270 includes, for example, a control unit 271 including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a storage unit 273 including a RAM and a hard disk device, and an external device. An input / output interface 275 that is an interface with the bus 277 is used.

Area sensor camera 110 and display device 280 are connected to inspection personal computer 270 via input / output interface 275.
Camera control information such as shutter speed and shutter timing is sent from the inspection personal computer 270 to the area sensor camera 110 via the input / output interface 275, and the area sensor camera 110 sends the captured image data via the input / output interface 275. Send to inspection PC 270.
Image data sent from the area sensor camera 110 is stored in the storage unit 273 and displayed as a captured image 285 on the display device 280.

  The uniaxial stage controller 215 is connected to the inspection personal computer 270 via the input / output interface 275, receives the instruction signal from the inspection personal computer 270, and drives the head conveyance stage 210.

  The pulse generator 230 controls the discharge interval of droplets discharged from the nozzle holes of the inkjet head. That is, droplets are ejected from the nozzle holes at pulse intervals generated by the pulse generator 230.

The pulse signal generated by the pulse generator 230 is also input to the sequencer 240.
The sequencer 240 includes a strobe delay device 250 and a camera trigger device 260.

The strobe 220 includes two strobe light sources 221 and 223.
The strobe delay device 250 receives the pulse signal from the pulse generator 230, generates a trigger signal for causing the strobe light source 221 and the strobe light source 223 to emit light sequentially at a predetermined delay time, and sends the trigger signal to each of the strobe light sources 221 and 223.
The strobe 220 is connected to the fiber light guide 130, guides the light emission of the strobe light sources 221 and 223, and irradiates the droplets ejected from the head 120 with strobe light. This fiber light guide 130 has two inputs and one output, and the input side is connected to two strobe light sources 221 and 223. The output is one and is directed to the ejected droplets from the head 120.

  The camera trigger device 260 receives the droplet discharge trigger pulse generated by the pulse generator 230 and generates a camera shooting trigger pulse. The generated trigger pulse enters the inspection personal computer 270 via the input / output interface 275 and is sent to the area sensor camera 110 as camera control information.

  FIG. 3 is an explanatory diagram of the timing of each part of the droplet velocity measuring apparatus.

  The pulse generator 230 generates a discharge interval trigger of droplets discharged from the nozzle holes of the inkjet head 120, that is, a discharge frequency (the uppermost pulse train in FIG. 3). For example, when the ejection frequency is M (kHz), droplets are ejected at 1 / M (msec) intervals. For example, when M = 20, droplets are ejected from the nozzle holes at intervals of 50 μsec.

  The camera trigger device 260 receives the discharge interval trigger M (kHz) as an input, generates a camera drive trigger (camera trigger), and inputs it to the inspection personal computer 270. The inspection personal computer 270 receives the camera trigger and outputs a camera control signal such as a shutter speed to the area sensor camera 110.

  On the other hand, the strobe delay device 250 receives the discharge interval trigger M (kHz) as an input and generates the strobe light emission timing. That is, the light emission timing of the first strobe light source 221 is set to time t1 after the discharge interval trigger, and the light emission timing of the second strobe light source 223 is set to time t1 + t2 after the discharge interval trigger. In practice, however, the strobe emits strobe light for a time t4 after time t3 from the strobe delay trigger.

The inspection personal computer 270 inputs the camera trigger and sets the exposure time and the like. At this time, the exposure time is from the start of light emission of the first strobe light source 221 until the end of light emission of the second strobe light source 223. Longer than the time t5.
The exposure start timing may be the same as the time when the first strobe light source 221 emits light, that is, after the time t3 has elapsed from the strobe delay trigger. However, in FIG. It is said.

  These camera control information generation programs are stored in the ROM of the control unit 271 of the inspection personal computer 270, and the shutter speed and the like are set by the CPU executing this program.

A zoom lens 170 is attached to the area sensor 110.
Upon receiving the camera control information from the inspection personal computer 270, the area sensor camera 110 opens and discharges the droplet n (142) discharged from the nozzle hole of the inkjet head 120 after the time t1 has elapsed from the camera trigger. The positions of the droplets (142 and 142 ′) at the time of the strobe light emission at the later times t1 + t3 and t1 + t2 + t3 are subjected to multiple photographing.

The captured image 285 is displayed on the display 280.
The storage unit 273 of the inspection personal computer 270 or the ROM of the control unit 271 stores a program for calculating the droplet velocity from the two photographed droplet positions (142 and 142 ′). By doing so, the drop velocity is determined.

  That is, the difference L (L1 and L2) between the two droplet positions is obtained from the coordinates of the two droplet positions (142 and 142 ') on the photographed image 285. The droplet velocity is calculated by dividing the difference L by t2, which is the time difference between the first and second strobe emission.

Next, a second preferred embodiment will be described.
FIG. 4A is a functional block diagram of the second preferred embodiment. The second preferred embodiment is the same as the first preferred embodiment except for the pulse emission method.

  The area sensor camera 110 photographs the droplet n142 ejected from the nozzle hole of the inkjet head 120. A light emitter 410 and a rotating light shielding plate 420 are provided on the side facing the area sensor camera 110 with respect to the inkjet head 120.

  The area sensor camera 110 and the light emitter 410 are installed on the same optical axis. Further, the rotary light shielding plate 420 is provided with slits 421 and slits 422, and the optical axis of the light emitter 410 is cut vertically, so that the slit 421 and the slit 422 pass on the optical axis of the light emitter 410 during rotation. A rotating light shielding plate 420 is disposed.

  In such a configuration, the light emitter 410 does not need to emit strobe light, and can be formed of, for example, an LED.

FIG. 5 is a system configuration diagram of the droplet velocity measuring apparatus 1 according to the second embodiment, and FIG. 4B is a diagram illustrating timing.
The difference from the first embodiment is a light source 410, a rotating light shielding plate 420, and their drive circuits (440, 430).

  As the light source, an LED light source 410 or the like can be used, and it may remain lit during the measurement period as shown in FIG. The LED light source 410 is turned on / off via the light emitter drive circuit 440 by a signal from the inspection 270.

Similar to the first embodiment, the pulse generator 230 generates a droplet ejection frequency M (kHz). The ejection frequency M is sent to the inkjet head 120, ejects droplets, and is input to the sequencer 240. The camera trigger generation circuit 260 of the sequencer 240 generates a camera drive trigger (camera trigger).
The camera trigger is input to the inspection personal computer 275 via the input / output interface 275, and the inspection personal computer 275 sends camera control information such as camera trigger and shutter speed to the area sensor camera 110.

The sequencer 240 is provided with a rotation light blocking plate rotation speed generation circuit 510.
The rotation light shielding plate rotation speed generation circuit 510 receives the ejection frequency M and generates the rotation frequency of the rotation shielding plate 420.
For example, when the rotation frequency is made lower than the discharge frequency and longer than the exposure time of the area sensor camera 110, the slit 421 and the slit 422 pass on the optical axis of the light emitter 410 once in the discharge interval, It becomes possible to irradiate the droplet n142 with light emitted from the light emitter 410.

The inspection personal computer 270 opens the shutter with the camera trigger as an input. The shutter speed is controlled to close the shutter before the next droplet discharge timing.
As a result, imaging data in which light from the light emitter 410 is irradiated twice on the same droplet through the slit 421 is taken into the inspection personal computer from the area sensor camera 110 via the input / output interface 275, and the captured image 285 is displayed on the display 280. Is displayed.

  The method for calculating the droplet velocity from the two positions (142 and 142 ') of the droplet n142 displayed in the captured image 285 is the same as in the first embodiment.

  As described above, it is possible to accurately measure the speed of the liquid droplets by irradiating the same liquid droplet twice within one liquid droplet discharge interval and by taking multiple images of the image on the same image. .

  The present invention is not limited to the embodiment described above, and various modifications are possible, and these are also included in the technical scope of the present invention.

Functional block diagram of the droplet velocity measuring apparatus 1 according to the first embodiment System configuration diagram of the droplet velocity measuring device 1 Timing explanatory diagram of the droplet velocity measuring apparatus 1 Functional block diagram of the droplet velocity measuring apparatus 1 according to the second embodiment The system block diagram of the droplet velocity measuring apparatus 1 which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ......... Droplet velocity measuring apparatus 110 ......... Area sensor camera 120 ......... Inkjet head 130 ......... Fiber light guide 141, 142, 143 ......... Droplet 210 ......... Head conveyance stage 220 ... ... Strobe light source 230 ... ... Pulse generator 240 ... ... Sequencer 250 ... ... Strobe delay device 260 ... ... Camera trigger device 270 ... ... Inspection personal computer 280 ... ... Display device

Claims (4)

A droplet velocity measuring device for measuring velocity characteristics of droplets ejected from a printer head,
A light emitting means for emitting pulses two or more times within a droplet discharge interval time;
An imaging unit that starts imaging at an exposure time longer than the time from the start of the first pulse emission by the light emission unit to the end of the last pulse emission, and at the same time as the start of the first pulse emission or before the start of the pulse emission,
Droplet velocity calculating means for calculating the velocity of the droplet from the position coordinates of two drop points of one droplet on the screen imaged by the imaging means, and the pulse emission interval;
A droplet velocity measuring apparatus comprising: The light emitting means comprises two or more strobe light sources and strobe delay generating means,
The strobe delay generating means causes the first strobe light source to emit light after a first predetermined time from the discharge timing from the printer head, and after the first strobe light source emits light, a second predetermined time before discharging the next droplet. 2. The droplet velocity measuring apparatus according to claim 1, wherein the second strobe light source is made to emit light later. The light emitting means comprises one light emitter, a rotating light shielding plate having a slit, and a driving means for rotating the rotating light shielding plate,
2. The rotating light shielding plate according to claim 1, wherein the driving unit rotates the rotating light shielding plate so that the droplets are irradiated with light from the light emitter through the slits at least twice within a droplet discharge interval time. Droplet velocity measuring device.   The droplet speed measuring device according to claim 3, wherein the rotary light shielding plate has two or more slits.

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