JP2010036388A - Droplet amount measuring method and droplet discharging system employing thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system for efficiently observing volume of a droplet, which is discharged from a droplet discharging means so as to have various shapes. <P>SOLUTION: A droplet amount measuring method includes: acquisition of flying images of a plurality of droplets, which are discharged from a droplet discharging means and have various ligaments, a droplet amount curve, which is calculated by sweeping binary threshold values over respective images, calculation of threshold values, at which the droplet amount curve becomes equal to the droplet amounts measured with a weight acquiring means, a threshold value curve, which is calculated between a plurality of ligaments and the threshold values; and optimization of the binary threshold values in the image analysis of droplets having various flying shapes based on the threshold value curve in the order named. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for measuring a discharge amount of droplets discharged from a liquid discharge unit such as an ink jet recording head.

  In recent years, there has been a demand for high definition and high speed printing in ink jet technology. These techniques are based on a technique for increasing the density and miniaturization of droplet discharge nozzles in an ink jet recording head, or a technique for miniaturizing droplets using a head drive waveform. On the other hand, as characteristics of the ink jet recording head at the time of product evaluation, in order to ensure high print quality, characteristics for each nozzle such as a droplet flying speed and a discharge amount must be appropriately measured. This is because these characteristics depend on the dimensional variation of each nozzle in the head manufacturing process and directly affect the quality of the liquid droplet landing position deviation and the printing density unevenness during printing. Therefore, an increase in the number of nozzles accompanying an increase in the density of nozzles causes an increase in measurement time during product evaluation.

  Conventionally, the droplet velocity is based on the position of a droplet in an image captured intermittently by intermittently emitting a light source such as an LED in synchronization with the timing at which the droplet is ejected and the emission timing at the time of imaging. Thus, a method capable of measuring with high accuracy in a short time is known (for example, see Non-Patent Document 1).

  On the other hand, with respect to the droplet discharge amount, a droplet integration method that can be measured with relatively high accuracy has been used. In other words, in order to measure the droplet discharge amount of one droplet, a droplet is ejected a plurality of times per nozzle and collected in a container and measured by a weigh scale or the like on the ink supply container side connected to the head. This is a method of measuring the ink reduction amount with a weight meter or the like.

However, since the droplet to be measured is about several ng (10 ⁻⁹ g), the resolution of generally available high-precision weigh scales is about 1 × 10 ⁻⁵ g. In order to accurately measure the droplet weight, it is necessary to accumulate several tens of thousands to several hundred thousand shots per nozzle, and it takes a lot of time to measure the weight for each of the many accumulated nozzles. There was a problem that.

  A further problem is that with the demand for higher image quality of printed matter by the above-described ink jet recording apparatus, for example, as disclosed in Patent Document 1, attempts to miniaturize droplets ejected by controlling the piezoelectric element drive signal pulse waveform have been made. In such an attempt, the flying shape and the amount of liquid droplets ejected from each nozzle are usually varied based on variations in characteristics with respect to each nozzle. On the other hand, in order to obtain high-quality printing, it is necessary to measure the flying characteristics of the droplet with respect to the change in the waveform for each nozzle. There was a problem that.

  In response to this problem, methods as shown in the following four examples are disclosed as methods for efficiently measuring the droplet amount.

  For example, according to Patent Document 2, droplets are ejected from a nozzle of an ink jet recording head onto a movable transparent substrate, and the diameter of the droplet after landing is lined as transmitted light from a light source installed at the bottom of the substrate. This is a method of calculating the droplet amount from the correlation between the droplet diameter and the droplet amount, which is read by a type or area type CCD sensor and measured in advance.

  Further, according to Patent Document 3, a method is considered in which a discharged droplet is regarded as a rotationally symmetric body, a rotation center axis and a rotation radius are measured from captured image data, and are integrated and calculated from the tip to the end. It is.

Alternatively, according to Reference 4, the droplet velocity in a state where the ejected droplet has reached a constant velocity is observed, and the droplet radius is derived from the relational expression based on Stokes' law. The volume is calculated by That is, the specific basic formula is
^{Cd = Fd / (πr 2 ·} ρv 2/2) ··· ( Equation 1)
Fd = 6πμrv (Expression 2)
Re = 2rρv / μ (Expression 3)
Cd = Cd (Re) (Formula 4)
m (dv / dt) = mg−Fd = 0 (Expression 5)
m = (4/3) ρπr ³ (Expression 6)
It becomes. In the above formulas 1 to 6, Cd is a resistance coefficient in spherical particles, Fd is a resistance force acting on the spherical particles, r is a particle radius, ρ is a density of a fluid forming the particles, v is a particle density, etc. Final velocity after reaching a fast motion, μ is the viscosity of the gas around the particle, m is the mass of the particle, t is the time, g is the acceleration of gravity, π is the circumference, Re is the motion of the droplet particle in the gas Is the Reynolds number.

However, the function of the resistance coefficient Cd and the Reynolds number Re in Equation 4 is generally in the region of Re ≦ (0.1-10).
Cd = 24 / Re (Expression 7)
For the region of Re ≦ 1000, for example, according to the sample correlation equation described in Non-Patent Document 2,
Cd = (24 / Re) · (1 + 0.125Re ^0.72 ) (Expression 8)
It is known that Therefore, by solving Equations 1 to 6 for Cd, Fd, Re, m, r, and v, the droplet radius r can be obtained, whereby the droplet amount can be obtained.

Alternatively, according to Patent Document 5, the droplet velocity is observed at two locations until the ejected droplet moves at a constant velocity, preferably two locations immediately after ejection with a large degree of deceleration, and the Stokes law is taken into account. The droplet volume is calculated from the droplet radius determined from the equation of motion. That is, the specific basic formula is
dv / dt + kv = g (formula 9)
k≡6πμr / m (Formula 10)
m = (4/3) ρπr ³ (Expression 11)
It becomes. Further, the general solution v = v (t) of Equation 9 is as follows:
v = g / k + C · exp (−kt) (Equation 12)
It is. In the above formulas 9 to 12, v is a droplet velocity until reaching a constant velocity motion, k is a variable represented by formula 10, and other symbols g, m, μ, r, π, and ρ This is the same as Equations 1-6. Therefore, if the time t = t1, t2 at two places after the droplet discharge and the droplet velocity v = v1, v2 at each time are measured, and these are substituted into the equation 12 and made simultaneous, the constants C and k are obtained. Further, if the mass m is erased from the equations 10 and 11, the droplet radius r is obtained, whereby the droplet amount is obtained.

Japanese Patent No. 3275965 JP 2005-238787 A Japanese Patent Laid-Open No. 1993-149769 Japanese Patent Laid-Open No. 2003-028696 JP 2007-107933 A Supervised by Takeshi Amari “Inkjet Printer Technology and Materials”, CMC Publishing, 1998, P.A. 41-52 Asano Koichi “Basics and Applications of Mass Transfer” Maruzen, 2004, P.A. 115-116

  However, in the case of the method disclosed in Patent Document 2, since the contact angle of the droplet with respect to the substrate is affected by the surface roughness of the substrate surface and unevenness of the surface energy, it is always constant with respect to the entire surface of the substrate. In other words, there is a problem that the amount of droplets to be calculated varies.

  Further, in the case of the method disclosed in Patent Document 3, there is a problem in the method of extracting the contour when recognizing the image of the droplet. That is, since the size of the imaged droplet depends on the brightness of the image, an error occurs in the acquired size depending on the intensity of illumination. In addition, when the flying shape of the droplet is extremely stable, it is possible to acquire an image with a stable brightness level. However, it is difficult to accurately obtain the brightness level of the droplet because the image of the droplet that has been captured flies in an elongated shape on the column and unevenness in brightness occurs in the captured droplet image.

Further, in the case of the method disclosed in Patent Document 4, it is shown that a distance of about 50 to 70 mm is spent until the droplet moves at a constant speed. It is described that the droplet amount is calculated by Stokes' law for spherical particles because the droplet is deformed into a spherical shape by the surface tension while traveling the flight distance. However, in reality, since the diameter of the droplet to be measured is about 20 μm and the volume is about several pl, the final velocity v at which the velocity is constant is water when the droplet is water and the surrounding atmosphere is air. Density ρ = 1000 kg / m ³ , air viscosity μ = 1.8 × 10 ⁻⁵ Pa · s, and according to equations 1 to 6, v = about 12 mm / s. Therefore, if the temperature and humidity are not controlled after covering the surroundings of the device, it will be greatly affected by the surrounding environment, making it difficult to measure accurately and complicating the measuring device and adjustment. It was.

  In the case of the method disclosed in Patent Document 5, two or a plurality of droplet velocities are observed before the droplet moves at a constant velocity, and this is composed of an equation of motion based on Stokes' law. In this method, the droplet velocity is derived by solving the simultaneous equations. As shown in Equation 11, this method is based on the premise that the droplet has a spherical shape. That is, it can be said that this method is suitable when a sufficient amount of time has passed and the droplets have become spherical due to surface tension as in Patent Document 4. However, in general, the droplet immediately after being ejected from the ink jet recording head has not only a spherical shape (see FIG. 9A) but also a shape separated into a plurality of droplets (FIG. 9B). The relationship between the droplet radius r and the mass m is naturally unknown, since it flies in various shapes such as a shape (see FIG. 9C) that extends in a columnar shape due to its viscosity (see FIG. 9). Therefore, this method has a problem that it is difficult to calculate the amount of droplets having various flying shapes.

  In view of the above problems, the present invention provides a method for efficiently measuring the amount of droplets having various shapes, a droplet ejection system equipped with the method, and a droplet ejection system equipped with the same. It is for the purpose.

In order to achieve the above object, the first means of the present invention includes: an ink pressurizing chamber; a pressurizing chamber pressure varying means attached to the pressurizing chamber; and a nozzle opening for discharging droplets by the pressure varying means. In a droplet amount measuring method for measuring a droplet amount discharged from an ink jet recording head in which a plurality of nozzles composed of
A first step of acquiring flight characteristics of a plurality of droplets having different droplet lengths, and a droplet amount curve is calculated by sweeping a luminance level of a binarization threshold for each of the images. A second step, a third step of calculating a threshold value at which the droplet amount curve is equivalent to the droplet amount measured by the weight acquisition means, and a fourth step of calculating a threshold curve for a plurality of droplet lengths. And a fifth step of calculating an optimum threshold value based on the threshold curve and deriving the droplet amount.

  The second means of the present invention is the first means, wherein the first step sweeps the strength of the pressure variable means for a plurality of (m) levels for one nozzle or a plurality of nozzles (n). By doing so, the droplet length of the flying droplet, the ejection amount, and the image data are obtained.

  According to a third means of the present invention, in the first means, the second step analyzes the droplet image acquired for each minimum resolution of the luminance level at the binarization threshold value, or interpolates the resolution. By dividing the image into a plurality of sections by means and analyzing the image after increasing the resolution in a pseudo manner, or by thinning out the resolution to an appropriate number and then performing an interpolation process using an approximate expression, a droplet volume curve is obtained. It is characterized by being calculated.

  According to a fourth means of the present invention, in the first means, the fourth step sweeps the strength of the pressure variable means for a plurality of (m) levels for one nozzle or a plurality of nozzles (n). The threshold curve is calculated by approximating the (n × m) pieces of data obtained by performing the approximation using a linear expression or an approximate expression such as a polynomial.

  The fifth means of the present invention is characterized in that the optimum threshold value is calculated by installing the threshold value optimization method of the first to fourth means in the droplet amount measurement program.

  According to a sixth means of the present invention, in the droplet discharge system, the droplet amount measurement program of the fifth means is installed.

  According to a seventh means of the present invention, the droplet discharge system of the sixth means is an ink jet recording head characteristic evaluation device, an ink jet recording head property correction device, an ink jet recording head drive waveform optimization device, or an ink jet. It is a type recording device.

  The droplet amount measuring method according to the present invention has an effect of improving the detection accuracy of the droplet size in the conventional droplet image processing method, and enables analysis of droplet amounts having various flying shapes. Therefore, there is an effect that it is possible to measure the flight characteristics of droplets for each nozzle formed in a large number in an ink jet recording head or the like in a short time.

  Further, by configuring a droplet discharge system such as an ink jet recording apparatus equipped with the program based on the present method, the droplet flight characteristics in a droplet discharge means such as an ink jet recording head are measured. There is an effect that high-quality printing can be carried out by sorting out or correcting the characteristics.

The droplet amount measuring method and droplet discharge system according to the present invention will be described below based on the flowchart shown in FIG.
[Step 1] Droplet characteristics acquisition step One nozzle for obtaining a threshold curve, or a plurality (n) of representative nozzles, and a driving voltage V = V (n, m) for a plurality of voltage levels (m). 3 are measured, that is, the flying speed v, the droplet length L, and the droplet weight wr. At this time, with respect to the flying speed v = v (n, m) and the droplet length L = L (n, m), the binarization threshold is such that noise in the acquired flying image does not affect the droplet. When b = b0, the former is a value obtained by dividing the position coordinate in the flying direction at the pixel at the leading end of the flying droplet by the time interval td from ejection to image acquisition, and the latter is from the leading end to the end of the droplet. It is defined as a distance obtained by multiplying a value obtained by counting pixels by a size per pixel, and both are calculated by image processing. In addition, it is preferable that the droplet position at the time of measurement is set to about 1 mm between the head and the print medium in a normal ink jet recording apparatus.

On the other hand, with respect to the droplet weight, the weight wr = wr (n, m), which is integrated for the number of discharges set arbitrarily, is measured by the weight measuring device.
[Step 2] Droplet Volume Curve Calculation Step Subsequently, a plurality of pieces of image data D = D (n, m, b) when the binarization threshold value b is swept from bmin to bmax with respect to the acquired original image. To get. The droplet volume is calculated by integrating the pixels corresponding to the droplet portion of the data D obtained with respect to the threshold value b at the time of sweeping from the leading end to the end of the droplet. With respect to the droplet weight wi obtained by multiplying this by the droplet density, a droplet amount curve wi = wi (n, m, b) with respect to the threshold value b is calculated.

  As shown in FIG. 3, this curve is shown as a biaxial curve with the horizontal axis indicating the threshold value b and the vertical axis indicating the droplet volume (unit: pl). This curve means that after increasing gradually with the luminance level of the flying droplet, the binarization threshold level increases rapidly as it approaches the luminance level in the observation region other than the droplet.

According to the method of claim 3, the image data D acquired in step 1 may be called for each luminance level to calculate the droplet volume, or each luminance level may be further determined if it is obtained with higher accuracy. The droplet volume may be calculated after dividing into a plurality of sections and performing interpolation processing.
[Step 3] Droplet Amount Equivalent Threshold Calculation Step The threshold b = b (n, m) when the droplet amount wr obtained in step 1 is equivalent to the droplet amount curve wi obtained in step 2 is shown in FIG. Is calculated by a droplet amount equivalent threshold value calculation auxiliary line 902. As a result, it is possible to reduce the variation in the size of the droplets on the image data caused by the illumination intensity, which was a problem of the Patent Document 3.
[Step 4] Threshold Curve Calculation Step The droplet length L consisting of n × m obtained by repeating steps 1 to 3 for a plurality (n) of representative nozzles and a plurality (m) of driving voltages. And the threshold value b are interpolated by the approximate curve b = b (L) described in claim 4. As a result, it is possible to reduce variations in brightness level in droplet pixels generated in droplet image data having different droplet lengths imaged by a light source such as a strobe as described in the problem of Patent Document 3.
[Step 5] Optimal Threshold Calculation Step After calculating the droplet length L for the measurement target nozzle in the same manner as in Step 1, the threshold b is set based on the threshold curve b = b (L) calculated in Step 4 above. calculate. In other words, the droplets ejected from the plurality of nozzles, which is a problem of the Patent Document 4 and Patent Document 5, are not limited to be spherical, and droplets having various shapes can be obtained. The discharge amount can be measured in a short time.

  As described above, the steps 1 to 5 are the threshold optimization steps in the present invention, and it is preferable to automate these by describing the processing steps in an arbitrary program language as shown in the fifth aspect. .

  Furthermore, it is preferable to construct a system in which the method is mounted as shown in the sixth aspect.

  Further, as described in claim 7, an ink jet recording head characteristic evaluation apparatus that applies the method to all nozzles, and a droplet amount calculated by the method is fed back to an ink pressurizing chamber pressure variable means. An ink jet recording head characteristic correcting device for correcting the variable amount of pressure by performing the operation, and an ink jet recording head for generating a waveform having optimum characteristics for printing by feeding back the droplet amount to the drive waveform generating means It is preferable to construct a drive waveform optimizing device or an ink jet recording device equipped with the above-described device.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

  First, an outline of an ink jet recording head and an ink jet recording apparatus will be described below. FIG. 10 is an apparatus configuration diagram illustrating the configuration and operation of the ink jet recording apparatus used in the embodiment of the present invention, and FIG. 11 is a partial perspective view illustrating the structure and operation of the recording head.

  The ink jet recording apparatus includes an ink jet recording head 10 and an ink jet recording head driving device 20. Further, the ink jet recording head 10 includes an ink flow path unit 101, a head housing 102 that holds the unit, and a piezoelectric element unit 103. Among these, as shown in FIG. 11, the ink flow path unit 101 is configured by attaching an orifice plate 130, an ink flow path forming plate 142, and a diaphragm forming plate 122 in this order.

  The piezoelectric element unit 103 is configured by sticking a rod-shaped piezoelectric element 110 to a piezoelectric element supporting substrate 113 in a comb shape. With this structure, the recording head 10 includes n nozzles. Each nozzle has n nozzle openings 131 arranged in rows at a predetermined pitch on the orifice plate 130 of FIG. An ink pressurizing chamber 140 having an opening end at the nozzle opening 131, an ink inlet 145 for supplying ink to the ink pressurizing chamber 140, and a common ink chamber 150 for supplying ink to the ink inlet 145 are configured. . In addition, at least one wall surface of the ink pressurizing chamber 140 is formed of the diaphragm 120 by attaching the diaphragm forming plate 122. One end of the rod-like piezoelectric element 110 of the piezoelectric element unit 103 is attached to the surface of the diaphragm 120 opposite to the ink pressurizing chamber 140. That is, the tip of the rod-shaped piezoelectric element 110 is abutted against the diaphragm 120 and attached to the diaphragm via the adhesive layer. Each nozzle has the same structure.

  The rod-like piezoelectric element 110 of each nozzle element is attached to the piezoelectric element support substrate 113 by bonding or the like, and constitutes a piezoelectric element unit 103. There are columnar piezoelectric element support substrate fixing portions 114 on both sides of the piezoelectric element support substrate 113 in the piezoelectric element arrangement direction, and the bottom surfaces thereof are fixed to the ink flow path unit 101 by bonding or the like. On the other hand, since the ink flow path unit 101 is adhesively fixed to the head housing 102 in the vicinity of the adhesive fixing portion, the bottom surface of the piezoelectric element support substrate fixing portion 114 is fixed to the head housing 102. .

  The rod-like piezoelectric element 110 has a laminated structure as shown in FIG. 11, and a plurality of layered piezoelectric elements 111 are laminated via layered electrodes 112. The layered electrodes 112 are connected to a common electrode 1121 and individual electrodes 1122 formed on the side surfaces of every other bar-shaped piezoelectric element. The common electrode 1121 and the individual electrode 1122 are connected to the common electrode 1121 and the individual electrode 1122 formed on the upper surface of the piezoelectric element support base 113, and further connected to the flexible cable terminal 161 of the flexible cable 160.

  The ink jet recording head 10 having the above structure is driven by a signal from the recording head driving device 20 via the flexible cable 160.

  The recording head driving device 20 includes a recording data signal generation circuit 302, a piezoelectric element driving data signal generation circuit 303, a piezoelectric element driving switching circuit 304, a timing signal generation circuit 301, and an electric element driving signal pulse generation circuit 305.

  For example, in accordance with recording signal input data from a host device such as a personal computer, a recording data signal is generated by a recording data signal generation circuit 302. Based on the data signal and a timing signal from the timing signal generation circuit 301, A piezoelectric element drive data signal creation circuit 303 creates a piezoelectric element drive data signal. The piezoelectric element drive data signal creation circuit 303 controls the switching element 3041 of the piezoelectric element drive switching circuit 304. The switching element driving circuit 3042 is connected to the piezoelectric element driving signal pulse generation circuit 305 via the one switching element, and the switching element driving circuit 3042 controlled by the piezoelectric element driving data signal is turned on and off. Thereby, the piezoelectric element of each nozzle is driven by the piezoelectric element drive signal pulse.

  An object of the present invention is to efficiently obtain the weight of the droplets 30 ejected from the nozzle openings 131 of the ink jet recording head 10 by controlling the piezoelectric element drive signal pulses.

  On the other hand, as described above, with the demand for high image quality of printed matter by an ink jet recording apparatus, there has been an attempt to miniaturize the normal-size droplet 30 to be ejected by controlling the piezoelectric element drive signal pulse waveform. Has been done. The normal size droplet 30 here means that the pulse width PW of the piezoelectric element drive signal pulse waveform as shown in FIG. 12 is set according to the pulse width at which the ink oscillation system Helmholtz resonance of the nozzle occurs. It represents a droplet ejected by a waveform characterized by.

  According to Patent Document 1, the piezoelectric element drive signal pulse waveform is contracted as shown in the shape of FIG. 13 so that the central region of the meniscus of the nozzle opening is raised and ink is ejected from the nozzle opening. The shrinking process that starts to discharge, and the outer edge of the meniscus in which the pressure generating chamber is expanded until the speed at the nozzle opening at the rear end of the ink that has started to discharge becomes zero, and the central region is raised by the contracting process The droplet 30 to be ejected is miniaturized by an expansion process for drawing the part.

  However, since the waveform due to the miniaturization attempt as shown in FIG. 13 is twice or more than the waveform for obtaining a droplet of a normal size, the parameters regarding the timing and the piezoelectric element driving voltage are increased. is there. On the other hand, when determining the timing in each step and the piezoelectric element driving voltage, manufacturing variations in members such as the ink flow path unit 101, the piezoelectric element 110, and the nozzle opening 131 that constitute the ink jet recording head 10, Furthermore, considering the variation in the physical properties of the ink used in the ink jet recording apparatus, in order to perform high-quality printing, characteristics must be measured for a wide variety of combinations of heads, nozzles, inks, and waveforms. Don't be. Therefore, since it takes a long time to measure the flying characteristics of the droplet, particularly the droplet discharge amount, it takes a lot of time to design the drive signal pulse waveform.

  Therefore, the present inventor has devised the present invention in order to efficiently measure the droplet discharge amount, and configured an ink jet type recording head characteristic observation apparatus as follows to measure the droplet amount. . In addition, this invention is not limited to a following example, A device can be arbitrarily comprised according to a measurement object and measurement environment.

  First, the apparatus configuration will be described below with reference to FIG. The apparatus is divided into two systems, a mechanism system 801 that is a first system and a control system 802 that is a second system.

  A mechanism system 801 as a first system includes an inkjet recording head 10, a droplet 30 ejected from the head 10, an illumination light source 601 for acquiring a flying image of the droplet 30, and a magnifying lens 602. , An optical sensor 603, an ink supply source 206 for supplying ink to the head, an ink supply pipe 207, an ink collecting member 208 for collecting ejected ink, and the weight of the ink collecting unit 208 A weight measuring device 701 for measuring the position of the nozzle and a movable stage 501 for selecting a nozzle position in the head. The detailed configuration of the system 801 will be described below.

  As the head 10, a piezoelectric element drive type ink jet head (trade name: GEN3E2, number of nozzles: 128) manufactured by Ricoh Printing Systems Co., Ltd. is used. 30 is attached to the stage 501 so as to fly vertically downward. The stage 501 is movable in the X, Y, and Z directions in order to adjust the nozzle position of the head 10 and the focal position of the sensor 603. Each of the stages 501 has three axes via a ball screw by a stepping motor. It is the structure which carries out a linear motion operation.

  The sensor 603 is a CCD black and white camera (number of pixels: 380,000 pixels) manufactured by Toshiba Terry Inc., to which a magnifying lens 602 of about 5 times is attached, and an illumination light source that opposes the sensor 30 with a droplet 30 flying vertically downward. An image is picked up from the horizontal direction by the illumination light of the LED used in 601. With the above optical system, a rectangular area from the nozzle surface of the head 10 to a point of about 1 mm corresponding to the gap between the head and the print medium in the ink jet recording apparatus is imaged.

  As the weight measuring device 701, an electronic balance (trade name: SAG285 high-precision weighing module, minimum display unit: 0.00001 g) manufactured by METTLER TOLEDO is used, and a plurality of flying droplets 30 installed on the upper portion of the device are used. The weight of the ink collecting member 208 that collects the ink is measured.

Further, tripropylene glycol methyl ether (trade name: Dawanol TPM, chemical formula: CH ₃ O (C ₃ H ₆ O) ₃ H, specific gravity: 1.0) manufactured by Dow Chemicals Co., Ltd. is used for the ink of the droplets 30 to be discharged. What adjusted the viscosity to 10 mPa * s was used.

  Next, a control system 802 as a second system includes a signal source 300 that drives the head 10 and the illumination light source 601, a piezoelectric element drive switching circuit 304 that constitutes the drive signal source 300, and a piezoelectric element drive signal. A pulse generation circuit 305, a piezoelectric element drive signal pulse amplification circuit 306, a drive data generation circuit 303 for generating these drive data, a stage control circuit 502 for controlling the operation of the movable stage 501, and Image data acquisition circuit 404 for acquiring image data acquired by the camera 603 into an information processing apparatus 400 such as a commercially available personal computer, and weight data for acquiring weight data acquired by the weight measuring apparatus 701 into the apparatus 400 An acquisition circuit 402 and a pixel data corresponding to the droplet of the image data; A droplet amount curve calculation circuit 405 for calculating a droplet amount curve by sweeping a binarization threshold value in the data collector, and an optimum threshold value calculation for calculating an optimum threshold value from the droplet amount curve data and the weight data A circuit 406; a data input unit 403 such as a keyboard and a mouse for an observer to input data to the device 400; and a data display unit 402 such as a display for outputting a result calculated by the device 400; , And a data storage device 401 such as a hard disk for holding all the data described above in the device 400. The above-described system 802 is controlled by a droplet amount measurement program developed based on the present invention. The detailed configuration of the system 802 will be described below.

  As the stage control circuit 502, a stepping motor controller (trade name: MPL-16) manufactured by Merek is used to drive the stage 501 in three directions.

  For the image data acquisition circuit 404, a frame grabber board (trade name: CT-3000A) manufactured by Cybertech Co., Ltd. is used to acquire image data from the camera 603 as a grayscale image having a luminance level of 8 bits and 256 gradations.

  The weight data acquired by the weight measuring device is acquired by connecting an interface unit provided in the device and an RS-232C communication port provided in the personal computer.

  The above-described program (compiler: Borland C ++ Builder) built on MicroSoft's Windows (registered trademark) is composed of a plurality of windows, setting drive conditions, setting stage moving conditions, and image acquisition conditions for each window. , And display condition setting, weight acquisition condition setting input, execution of each processing command, and control of each process. Further, the program can be simply provided through a recording medium such as a CD-ROM or a network such as the Internet.

  Next, specific measurement steps will be described below with reference to the flowchart of FIG.

[Pre-Process] Measurement Condition Input Measurement conditions in this example will be described with reference to FIG. That is, m = 3 in the voltage level number 907, and V = 16, 19, and 22V are input to the set voltage 909 for each level number 908. Further, a representative nozzle n = 2 (end No. 1 nozzle and center No. 64 nozzle) for optimizing the threshold value is input by a nozzle selection unit (not shown). In addition, the threshold curve approximate expression setting unit 914 interpolates the threshold curve with the following quadratic expression, and the droplet discharge number setting unit 913 uses the weight measuring device 701 to measure the weight. Was set to 600,000.

b = a ₂ · L ² + a ₂ · L + a ₀ (Expression 13)
However, a ₂ , a ₂ , a ₀ are coefficients, as described above, b is a threshold value, and L is a droplet length. Further, on the image display section shown in FIG. 7, the size of the rectangular area indicated by the white dotted line in the figure is changed, and the analysis area 31 is set so that noise components are not superimposed on the image to be analyzed. An appropriate initial value b = b0 of the threshold value is set. However, in this example, the color tone is set so that the luminance of the droplet portion 30 is white (= 255) and the luminance of the other region is black (= 0). In this example, as shown in the droplet amount curve shown in FIG. 3 described above, it is known that the curve gradually increases with respect to the threshold region of about 60 to 80, while the flying droplet is a flying tip. Since the brightness level at the head and rear ends is high, it is found that the threshold value does not need to be particularly strict in analyzing the droplet velocity at the tip and the droplet length from the tip to the rear end. Therefore, b0 = 70 is set in this example.

  Further, supplementing the image in FIG. 7, the position coordinates of the upper left pixel of the screen are (x, y) = (0, 0), and the position coordinates of the lower right pixel are (x, y) = (640, 480) ( (Unit: pix), the x-axis is taken in the right direction and the y-axis is taken in the downward direction. The white portion on the left side of the image represents the nozzle surface of the head 10, and the white circular portion in the dotted rectangle indicates the droplet 30 in the process of flying from the left side of the screen to the right side (actually vertically downward). is there.

  In addition, after adjusting the magnification of the lens, the size s (unit: μm / pix) per pixel of the acquired image is corrected in advance by a dimension calibration unit. In this example, the size s = 2.8 μm / pix.

  Further, the frequency of 5 kHz was set in a droplet discharge frequency setting unit (not shown).

[Step 1] Droplet characteristics acquisition step A level 1 driving voltage V (1, 1) = 16 V per nozzle was applied to the head 30 to discharge droplets. Weight data wr (1, 1) per droplet obtained by the weight measuring device 701 = 10.5 ng, and droplet length L (1, 1) calculated by image processing on the droplet = 25.3 μm Are displayed on the droplet length display unit 911 and the droplet amount equivalent threshold value display unit 912 in FIG. The droplet length L was calculated by the following formula 14.

L = s (x _t −x _b ) / t _d (Equation 14)
However, _{x t} droplet tip in the x direction pixel position coordinates (pix), _{x b} is the rear end in the x direction pixel position coordinates (pix), _{t d} is the time interval (in this example from the droplet ejection to the image acquisition , T _d = 120 μs), and s is the pixel size (μm / pix).

[Step 2] Droplet Volume Curve Calculation Step In parallel with the weight acquisition process in Step 1, the droplet flight image data D is acquired, and as shown in FIG. 3, the binarization threshold value b is set to the minimum sweep threshold value. Liquid for droplet flying image data D = D (1, 1, b) when the level is swept one by one from bmin (= 60) as the unit 904 to bmax (= 107) as the sweep threshold maximum value setting unit 906 A drop volume curve 901 was calculated. The droplet amount was calculated by the following equation 15.

wi = Σ _i (ρ · s · π (s (y _r −y _c )) ² ) (Equation 15)
However, [rho is the density of the ink 30, y _r is y-direction pixel position coordinates corresponding to the droplet outer edge on each x-coordinate (pix), y _c is the y-direction pixel on the droplet center axis on the x-coordinate location coordinates (pix), i is a suffix showing each x coordinate from x _t to x _b, [pi is circle ratio, and the other symbols are the same as the above equation 14.

[Step 3] Droplet Equivalent Equivalent Threshold Calculation Step The threshold value at the intersection of the weight data wr acquired in step 1 and the curve 901 acquired in step 2 is calculated by a droplet amount equivalent threshold calculation auxiliary line 902, as shown in FIG. The threshold value b (1, 1) = 82 is shown in the droplet amount equivalent threshold value display unit 912.

  As described above, data acquisition at n = 1 and m = 1 is completed. A process similar to this is No. The test was performed for 64 nozzles and m = 2 and 3, and the relationship between the length L of n × m = 6 droplets and the threshold value b was determined.

[Step 4] Threshold Curve Calculation Step FIG. 5 shows the results of calculating the coefficients a ₂ , a ₁ and a ₀ by the least square method by applying the data to the above equation 13. As described above, as the droplet length L increases, that is, as the droplet expands in a columnar shape as shown in FIG. The brightness level tends to decrease. It is a feature of the present invention that the threshold value b is corrected by an approximate curve as shown in FIG.

[Step 5] Optimal threshold calculation step In realizing high-quality printing, it is important to know the variation in the amount of droplets flying from each nozzle in the head 10. According to the present invention, the droplet length L discharged from each nozzle was analyzed, and the droplets flew from each nozzle by the threshold curve which is a function of the droplet length L calculated in step 4 and the binarization threshold b. The optimal threshold for droplets with various shapes was calculated. Further, the ejection amount of each droplet was calculated from the image data binarized by the threshold value by the above formula 15. The time required for image processing for calculating droplet amount data per nozzle depends on the performance of the personal computer that is the information processing apparatus 400, but in this example, a commercially available CPU 2 GHz, memory 1 GB. In the case of a computer having the above, measurement can be performed in about 1 second.

[Post-Processing] Measurement Result Output FIG. 8 shows an example in which droplet amount data is acquired by applying the present invention to all nozzles of the head 30 and displayed as a graph 916. Further, FIG. 8 shows a droplet velocity (unit: m / s) which is a characteristic of a flying droplet, a degree of bending at the time of droplet flying (unit: deg), ligament (synonymous with the above-described droplet length, unit : Μm) is also calculated by image processing at the same time and is shown in the figure.

  When 600,000 shots are ejected at 5 kHz in the conventional droplet integration method described above, it takes 2 minutes × 128 nozzles = 4 hours for acquiring the droplet amount data for one nozzle.

  On the other hand, in the case of the present invention, the time required for the threshold optimization process is 2 minutes × 6 data = 12 minutes, and the liquid acquisition amount data acquisition time per nozzle obtained by image processing is 1 second × 128 nozzles = 2 minutes. It will be completed in 14 minutes.

  FIG. 6 is an example comparing the result of measuring an appropriate amount of the liquid according to the present invention and the actual value of weight. The two don't have to match completely, but there is an approximate match. Note that the measurement accuracy can be improved by electrically subdividing the acquired image luminance level or by appropriately selecting the performance of the CCD camera.

  The present invention is not limited to the ink jet recording head characteristic observation apparatus in the above-described embodiment, and can be applied to various droplet discharge systems described in the seventh aspect.

It is a figure for demonstrating the apparatus structure of this invention. It is a flowchart for demonstrating the droplet amount measuring method in this invention. It is a figure for demonstrating an example of the droplet amount curve displayed on the droplet amount measurement program in the Example of this invention. It is a figure for demonstrating an example of the coefficient calculation result of the threshold curve displayed on the droplet amount measurement program in the Example of this invention. It is a figure for demonstrating an example of the threshold curve in the Example of this invention. It is a figure for demonstrating an example of the droplet amount calculation result by the droplet amount measurement method and the measurement result by the conventional droplet integration method in the Example of this invention. It is a figure for demonstrating an example of the droplet flight image displayed on the droplet amount measurement program in the Example of this invention. It is a figure for demonstrating an example of the measurement result of the droplet characteristic displayed on the droplet amount measurement program in the Example of this invention. (A) is a figure for demonstrating an example of the flying droplet which shows the spherical shape in the Example of this invention, (b) is the flying droplet which shows the shape isolate | separated into two droplets in the Example of this invention. FIG. 4C is a diagram for explaining an example of flying droplets showing a shape extending in a columnar shape in the embodiment of the present invention. FIG. 2 is a configuration diagram for explaining a configuration of an ink jet recording head and a recording apparatus using the same in an embodiment of the present invention. FIG. 2 is a configuration diagram for explaining a structure of an ink jet recording head in an embodiment of the present invention. It is a figure for demonstrating an example of the piezoelectric element drive signal pulse waveform of the inkjet recording head in the Example of this invention. It is a figure for demonstrating an example of the piezoelectric element drive signal pulse waveform of the inkjet recording head in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inkjet recording head 20 Inkjet recording head drive device 30 Droplet 31 Analysis area 40 Recording medium 101 Ink flow path unit 102 Head housing 103 Piezoelectric element unit 110 Piezoelectric element 111 Layered piezoelectric element 112 Layered electrode 1121 Common electrode 1122 Individual electrode 113 Piezoelectric element support substrate 114 Piezoelectric element support substrate fixing part 120 Diaphragm 122 Diaphragm forming plate 130 Orifice plate 131 Nozzle opening 140 Ink pressurizing chamber 142 Ink flow path forming plate 145 Ink inflow hole 150 Common ink chamber 160 Flexible cable 161 Flexible cable terminal 201 Housing 202 X-axis linear motion stage 203 Y-axis linear motion stage 204 Z-axis linear motion stage 205 Head base 206 Ink supply source 207 Ink supply tube 208 Collecting member 300 Driving signal source 301 Timing signal generating circuit 302 Recording data signal generating circuit 303 Piezoelectric element driving data signal generating circuit 304 Piezoelectric element driving switching circuit 3041 Switching element 3042 Switching element driving circuit 305 Piezoelectric element driving signal pulse generating circuit 306 Piezoelectric Element drive signal pulse amplification circuit 400 Information processing device 401 Data storage device 402 Data display device 403 Data input device 404 Image data acquisition circuit 405 Drop volume curve calculation circuit 406 Optimal threshold calculation circuit 501 Movable stage 502 Movable stage control circuit 601 Illumination light source 602 Magnifying lens 603 Optical sensor 701 Weight measuring device 702 Weight data acquisition circuit 801 Mechanism system 802 Control system 901 Drop volume curve 902 Drop volume equivalent threshold calculation auxiliary line 903 Drop volume actual measurement value 904 Sweep threshold minimum value setting unit 905 Droplet volume equivalent threshold value display unit 906 Sweep threshold maximum value setting unit 907 Voltage level number setting unit 908 Level number 909 Setting voltage setting unit 910 Droplet weight actual value display unit 911 Liquid Droplet length display unit 912 Droplet amount equivalent threshold value display unit 913 Droplet ejection number setting unit 914 Threshold curve approximation formula setting unit 915 Droplet flight characteristic acquisition data display unit 916 Droplet velocity / droplet weight characteristic graph

Claims (7)

Inkjet recording comprising a plurality of nozzles each composed of an ink pressurizing chamber, a pressurizing chamber pressure varying means attached to the pressurizing chamber, and a nozzle opening for discharging droplets by the pressure varying means. In the droplet amount measuring method for measuring the droplet amount discharged from the head,
A first step of acquiring flight characteristics of a plurality of droplets having different droplet lengths, and a droplet amount curve is calculated by sweeping a luminance level of a binarization threshold for each of the images. A second step, a third step of calculating a threshold value at which the droplet amount curve is equivalent to the droplet amount measured by the weight acquisition means, and a fourth step of calculating a threshold curve for a plurality of droplet lengths. And a fifth step of calculating an optimum threshold based on the threshold curve and deriving a droplet amount.   2. The droplet amount measuring method according to claim 1, wherein the first step sweeps a plurality of (m) levels of the strength of the pressure variable means with respect to one nozzle or a plurality of nozzles (n). A droplet amount measuring method, characterized in that the droplet length, ejection amount, and image data of a flying droplet are acquired by the above method.   2. The droplet amount measuring method according to claim 1, wherein the second step analyzes the droplet image acquired for each minimum resolution of the luminance level at the binarization threshold value, or the resolution is calculated by an interpolation processing unit. Divide into a plurality of sections and analyze the image after increasing the resolution in a pseudo manner, or calculate the droplet volume curve by thinning out the resolution to an appropriate number and then performing interpolation using an approximate expression A method for measuring the amount of liquid droplets.   2. The droplet amount measuring method according to claim 1, wherein the fourth step sweeps a plurality of (m) levels of the strength of the pressure varying means with respect to one nozzle or a plurality of nozzles (n). A method for measuring a droplet amount, characterized in that a threshold curve is calculated by approximating (n × m) pieces of data acquired by (1) by an approximate expression such as a linear expression or a polynomial expression.   A drop amount measurement program for calculating an optimum threshold by mounting the threshold optimization method according to claim 1.   A droplet discharge system, comprising the droplet amount measurement program according to claim 5.   The droplet discharge system according to claim 6 is an ink jet recording head characteristic evaluation device, an ink jet recording head property correction device, an ink jet recording head drive waveform optimization device, or an ink jet recording device. A droplet discharge system.

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