JP2007190865A - Inkjet drawing device and discharge stability evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately obtain information including the speed and volume of liquid droplets in an inkjet drawing device by a simply structured device. <P>SOLUTION: The inkjet drawing device has at lest one channel 2 which discharges liquid droplets 5, a light source 31, and a light receiving section 32 which receives light from the light source. The course of the liquid droplets 5 intersects an optical path from the light source 31 to the light receiving section 32. The drawing device is provided with a transmissivity computation section 40d which computes transmissivity ai [ai is represented by (bo-bi)/bo] from the receiving amount of light bi in the light receiving section 32 in a period when a plurality of liquid droplets 5, 5, 5, 5 discharged from the channel 2 pass over the optical path and the receiving amount of light bo at the time when the liquid droplets do not pass over the optical path. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet drawing apparatus that discharges droplets by an ink jet method, and in particular, by ejecting a liquid such as ink toward an ejected object such as a recording sheet based on print data or the like. The present invention relates to an ink jet drawing apparatus that records images and figures.

  An ink jet drawing apparatus is an apparatus that can perform printing by ejecting droplets from an ejecting head onto an ejected object such as paper or a substrate with high accuracy and high density. The ink jet recording apparatus is used as a printer that records information such as characters or images output from a computer or the like on a recording medium such as paper. In addition, it is widely used for various purposes, such as being used when manufacturing electronic components.

  In an ink jet drawing apparatus, in order to perform good drawing, liquid ejection stability of an ejection head is evaluated. As the parameters for the ejection stability, the volume of the ejected droplets, the ejection speed, and the like are used.

Patent Document 2 describes a device that scans a head so that ejected liquid droplets intersect with a light emitting unit and a light receiving unit, continuously ejects liquid droplets, and outputs a pulse signal. Then, when evaluating the discharge state, a channel that does not discharge intentionally is included, and the channel that does not actually discharge is determined based on the timing of the pulse signal that does not discharge. Patent Document 3 determines the discharge speed based on the Doppler effect. An apparatus is described.

  Patent Document 1 evaluates the stability of ejected droplets by detecting the size and ejection speed of the droplets using an optical sensor unit having a light receiving surface as shown in FIG. 8 and a light source. An ejected droplet evaluation apparatus is described.

  The conventional optical sensor unit includes an optical sensor 131 having light receiving surfaces 130a to 130d that are equally divided in a matrix and photodetecting elements such as photodiodes having equal characteristics for each of the divided light receiving surfaces, and an upper side (130a. b) and the lower side (130c · d) each include a differential current-voltage conversion circuit 140 connected to the outputs of the photodetectors corresponding to the two light receiving surfaces. The light receiving surface 130 is irradiated with light from a light source (not shown), and a droplet 150 ejected from a head (not shown) travels so as to block this light.

  In this conventional technique, a change in the amount of light received by one ejected droplet is detected using an optical sensor having a plurality of light receiving surfaces and a plurality of light detection elements provided for each light receiving surface. To do.

  The speed of the liquid droplet is obtained based on the time difference between the output peaks among the plurality of light detection elements, and the volume of the liquid droplet is obtained by comparing the output value of each light detection element with a predetermined threshold value. .

Note that there is one droplet to be measured based on the measurement principle of Patent Document 1 (using a plurality of light detection elements and determining the speed of the liquid droplet based on the time difference between the output peaks of these light detection elements). Obviously.
JP 2001-71476 A (published on March 21, 2001) JP 2004-275801 A (released on October 7, 2004) Japanese Patent Laid-Open No. 4-27552 (published on January 30, 1992)

  However, the conventional inkjet drawing apparatus has a problem that there is room for improvement in the measurement accuracy of the discharge state and the apparatus becomes large.

  For example, in the apparatus of Patent Document 2, since it is only possible to determine whether or not to discharge, unstable discharge may be used for drawing.

  Further, the apparatus of Patent Document 3 has a problem that the configuration of the apparatus becomes very large.

  Further, as in Patent Document 1, when detecting the speed and volume of the liquid droplet by detecting that the liquid droplet has blocked the light, in order to increase the detection accuracy of the speed and volume of the liquid droplet, It is necessary to increase the rate of change (that is, the difference between the amount of received light when not ejected and the amount of received light when ejected). In the invention of Patent Document 1, since the object to be measured is a minute object such as one droplet, the change in the amount of received light is very small. Therefore, in the invention of Patent Document 1, in order to increase the detection accuracy, the light receiving surface must be made small, and the optical sensor must be positioned with respect to the ejection dots with high accuracy.

  Further, in Patent Document 1, in order to calculate the velocity of a droplet, it is necessary to detect and record a change in output of each photodetecting element over time. This increases the amount of data to be recorded and the time required for data processing.

  Moreover, in patent document 1, in order to obtain | require the speed of a droplet, several light-receiving surfaces are used. Therefore, a plurality of light receiving surfaces are also used to determine the size (volume) of the droplet. However, when the volume of a droplet is detected using a plurality of light receiving surfaces, the gap between the light receiving surfaces becomes noise, which makes accurate detection difficult (FIG. 9B).

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to obtain information including the velocity and volume of a droplet with high accuracy and a simple configuration.

In order to solve the above problems, an ink jet drawing apparatus according to the present invention includes at least one channel for ejecting droplets, a light source, and a light receiving unit that receives light from the light source, and the path of the droplets. A light source and a light receiving section so that a light path from the light source to the light receiving section intersects, and a plurality of liquid droplets ejected from the channel pass through the light path, and a light receiving amount bi at the light receiving section, And a transmittance calculating unit that calculates the transmittance ai [ai is represented by (b0−bi) / b0] from the received light amount b0 when the droplet does not pass on the optical path. As will be described later, the transmittance ai includes information on the volume and velocity of the droplet. Thus, from a single value, both the volume and velocity of the droplet can be obtained.

  And according to the said structure, since the several droplet is made into the object of a measurement, even if the light-receiving surface of a light-receiving part is enlarged, a high detection accuracy is obtained. Therefore, such a problem does not occur. If a light-receiving part having a large light-receiving surface can be used, the accuracy required for alignment between the droplet and the light source / light-receiving part is eased.

  In the present invention, it is only necessary to obtain the sum of the output values of the light receiving section within the capture time, and the change in the output amount with time within the capture time is not required. Therefore, the present invention requires a smaller amount of data to be recorded than that of Patent Document 1, and can reduce the recording capacity and the time required for data processing.

  In the present invention, one value (light shielding rate) including information on both the volume and velocity of the droplet is used, and this value is obtained from one light receiving unit. For this reason, the noise described above with respect to Patent Document 1 does not occur, and it can be said that more accurate information about the volume of the droplet can be obtained.

  In the present invention, channels that are not intentionally discharged are not set. A stable discharge channel can be determined, and not only non-discharge but also an unstable channel is not used for drawing, and the paper or substrate to be drawn is not soiled.

  Moreover, it is preferable that the said inkjet drawing apparatus is provided with the determination part which determines whether the said transmittance | permeability exists in a predetermined range.

  With this determination unit, it is possible to evaluate the discharge stability of the channel by a simple process of determining whether one value of the transmittance ai is within a predetermined range.

  The inkjet drawing apparatus includes a selection unit that selects a channel to be used for drawing, and the selection unit selects a channel whose transmittance is determined to be within the predetermined range by the determination unit. There may be.

  According to the above configuration, only the channel that can perform stable ejection is selected by the selection unit so as to be used for drawing.

  Moreover, it is preferable that the selection unit selects a channel for which the determination unit determines that the transmittance is within the predetermined range at least twice.

  For example, when fine bubbles are mixed in the channel, it may not be discharged. That is, even if such a channel is determined to be stable by the determination unit, it may be unstable in actual drawing. According to the above configuration, for example, if it is determined to be unstable by one discharge state evaluation, it is not used for drawing even if it is determined to be stable in the second determination thereafter. Only when it is determined to be stable twice or more by the evaluation of the discharge state, it is used for drawing. In this way, by using only the channel determined to be stably ejected twice or more for drawing, discharge failure during drawing can be greatly reduced.

  The ink jet drawing apparatus may include a volume calculation unit that calculates the volume of the droplet from the transmittance ai.

  As described above, the transmittance ai includes information on the volume of the droplet. Thus, by obtaining the volume of the droplet, it is possible to quickly know how many dots should be ejected in order to obtain a desired figure, film thickness, and the like.

  Further, the ink jet drawing apparatus is provided in a head in which the channel is replaceable, and a display unit that displays to replace the head when the determination unit determines that the transmittance is out of a predetermined range It is preferable to provide.

  Conventionally, the total number of ejected dots per channel is counted, and head replacement is performed when a certain number of dots is exceeded. However, since the actual discharge state of the channel is not detected in this case, a head with unstable discharge may be used even if the number of dots is equal to or less than a specified value. However, according to the configuration of the present invention, the head replacement time is displayed from the actual channel ejection stability, so that the more accurate head replacement time can be known.

  The ink jet drawing apparatus preferably includes a suction unit that sucks air discharged from the channel from the traveling direction of the liquid by sucking air.

  According to the above-described configuration, ink can be prevented from being scattered by performing air suction from the bottom while discharging droplets. This can prevent the substrate to be drawn, the light receiving unit, the light source, the head, and the like from being soiled.

  The discharge stability evaluation method of the present invention is a discharge stability evaluation method for a channel for discharging a droplet, and includes a light irradiation step for irradiating light to the path of a droplet discharged from the channel, and a plurality of channels from the channel. A transmittance measuring step for measuring light transmittance in the path while the liquid droplets are ejected, and an evaluation step for evaluating that the ejection is stable when the transmittance is within a predetermined range. It is characterized by that.

  In order to solve the above problems, an ink jet drawing apparatus according to the present invention includes at least one channel for ejecting liquid droplets, a light source, and a light receiving unit that receives light from the light source, and the path of the liquid droplets. And the light path from the light source to the light receiving unit are provided so that the light source and the light receiving unit are provided, and the amount of light received by the light receiving unit while a plurality of liquid droplets discharged from the channel passes on the optical path. a transmissivity calculating unit that calculates transmissivity ai [ai is represented by (b0−bi) / b0] from bi and the received light amount b0 when the liquid droplet does not pass on the optical path; To do.

  Therefore, the ink jet drawing apparatus according to the present invention can obtain both the volume and the velocity of the droplet from one value of the transmittance ai by the simple configuration as described above. Further, by targeting a plurality of droplets, it is possible to accurately measure the ejection stability.

Embodiments of the present invention will be specifically described below with reference to the drawings.
[Embodiment 1]
The inkjet drawing apparatus of this Embodiment is demonstrated with reference to FIGS. The ink jet drawing apparatus of the present embodiment records characters or figures on an object by discharging droplets from a head. FIG. 1 is a block diagram illustrating a main part of the ink jet drawing apparatus according to the present embodiment, and FIG. 2 is a flowchart illustrating a discharge stability evaluation method according to the present embodiment.

  As shown in FIG. 1, the ink jet drawing apparatus according to the present embodiment includes a head 20, an optical sensor unit including a light emitting unit 31 and a light receiving unit 32, and a control system 40 that controls the head 2 and the optical sensor unit. .

  The inkjet head 20 is assumed to have an inkjet head 20 having a plurality of channels 2 separated by partition walls. The channel 2 is a minimum unit of the mechanism for ejecting ink, and includes one ink chamber 21 and one nozzle 22. A part of the wall separating the ink chambers 21 is formed of a piezoelectric body and a pair of electrodes provided so as to sandwich the piezoelectric body.

  When a droplet is ejected from the nozzle 22, a voltage is applied between the electrodes while a liquid such as ink is contained in the ink chamber 21. Then, the piezoelectric body is deformed and the volume of the ink chamber 21 is reduced, so that a droplet is ejected from the nozzle 22.

  The control system 40 includes a control unit 40a, a light source drive unit 40b, a storage unit 40c, a transmittance calculation unit 40d, a stability determination unit 40e, a channel selection unit 40f, and a head drive unit 40g.

  The control unit 40a controls the overall operation of the ink jet drawing apparatus, and controls the light source driving unit 40b, the storage unit 40c, the head moving unit 40g, and the like according to commands from a host device or a built-in CPU (not shown). A control signal is supplied to each functional block in 40, or an output signal from these functional blocks is received and response processing for the functional block is performed.

  The light source driving unit 40 b drives the light source 31 to irradiate the light receiving unit 32 with light. Details of the light source 31 and the light receiving unit 32 will be described later. The light receiving unit 32 outputs an electrical signal (light reception amount signal) corresponding to the amount of received light to the storage unit 40c.

  The optical sensor unit moving unit 40k moves the optical sensor units (31, 32) based on a control signal from the control unit 40a.

  The storage unit 40c can store the received light amount signal output from the light receiving unit 32 and can output the stored received light amount signal to the transmittance calculating unit 40d. The storage unit 40c can also store the transmittance calculated by the transmittance calculator 40b.

  The transmittance calculating unit 40d receives the two received light amounts sent from the light receiving unit 32 via the storage unit 40c, that is, the light received while a plurality of droplets are ejected from the channel 2i and pass through the optical path of the light source 31. Based on the amount bi and the amount of light received b0 when the droplet is not ejected, that is, when the droplet does not pass on the optical path, the light transmittance ai [ai is (b0−bi ) / B0].

  The stability determination unit 40e determines whether or not the transmittance ai sent from the storage unit 40c is within a predetermined range.

  The channel selection unit 40f is a block for selecting the channel 2 used for drawing, and selects the channel 2 for which the transmittance ai is determined to be within the predetermined range by the stability determination unit 40e. Yes. Specifically, a drive signal is sent to the channel driver 40h so as to drive only the channels whose transmittance ai is within a predetermined range.

  The head drive unit 40g moves the head 20 to a desired position in accordance with a control signal from the control unit 40a.

  Further, the channel driving unit 40h drives each channel 2 in accordance with signals from the control unit 40 and the above-described channel selection unit 40f, and discharges droplets from the nozzles 22.

  Next, a method for evaluating the ejection stability of the channel using the ink jet drawing apparatus of the present embodiment will be described.

  The operation at the time of taking in the optical sensor unit and the amount of received light will be described in more detail with reference to FIG. FIG. 3 shows the positional relationship between the head 20 and the optical sensor unit (31, 32). (A) shows the position of the nozzle 22 when the head 20 is viewed from a line of sight perpendicular to the droplet discharge direction. It is a front view when the head 20 is seen from the formed surface. At this time, the number of nozzles 22, that is, the number of channels 2 is 48.

  The row of nozzles 22 is arranged in parallel to the optical path from the light source 31 to the light receiving unit 32. The nozzle pitch is 169.3 μm and the nozzle diameter is 20 μm. The light source 31 is a semiconductor laser having a wavelength of 650 nm and a light diameter of 1 mm. The light receiving unit 4 is a photodiode having a light receiving surface of 0.8 mm square. The light emitting unit and the light receiving unit are not limited to the semiconductor laser and the photodiode, and may be a general lamp and a sensor as long as they have a certain level of intensity and sensitivity. The dimensions shown above are not limited to this.

  Next, FIG. 4 will be described. When a droplet is ejected from the nozzle 22 of the channel 2i, the droplet 5 shields the laser beam. In this embodiment, a square light-receiving surface is used, and the transmittance ai is the number N of droplets that block light entering the light-receiving surface within the capture time, the area S0 of the light-receiving surface, and the light shielding per dot of the droplet 5 When the area is Sd, it is expressed by the following formula (1).

Furthermore, the following formula (2) is set depending on the light scattering rate of the droplet p, the driving frequency f, the discharge volume V (volume per one dot of the droplet 5), the length L of the light receiving surface, and the discharge speed v. To be rewritten.

  From this equation, it can be seen that the transmittance ai [ai = (b0−bi) / b0] includes the discharge volume V and the discharge speed v. When the discharge volume V and the discharge speed v change, the transmittance ai also changes. It can be seen that the transmittance ai increases as the discharge volume V increases and the discharge speed v decreases as the drive frequency is equal. In other words, an unstable channel with a low discharge speed v is measured with a large transmittance ai.

  Further, the discharge volume V in this embodiment is 5 pl, and the droplet diameter is 21.2 μm.

  Based on FIG. 2, the ejection state evaluation method will be described. First, when the ejection state evaluation operation is started (start), the control unit 40a moves the head 20 or the optical sensor unit (31, 32) to the ejection state position via the head moving unit 40g or the optical sensor moving unit 40b. Let (S1).

  Next, the signal of the light receiving unit 32 is measured in a state where no droplet is ejected (S2). This value is stored in the storage unit 40c as a threshold value (b0).

  Next, the discharge state of channels 1 to 48 is measured (S3). Discharge is started from the beginning of the channel group to be discharged (from channel 1 in the figure) (S3-1). Next, the received light signal is captured, and this value (b1) is stored in the storage unit (S3-2). Next, the discharge is stopped (S3-3). Then, the head 20 or the optical sensor unit is moved to the measurement position of the next channel (S3-4).

  A series of discharge-take-stop operations (FIG. 5) and movement are repeated up to the channel 48. When the reception of the received light amount to the last channel is completed, the movement of the head 20 or the optical sensor unit (31, 32) is stopped. Next, the transmittance calculating unit 40d calculates the transmittance ai [ai = (b0−bi) / b0] from each received light amount (S4).

  Next, it is determined whether or not the channel is stably ejected by determining whether or not the transmittance ai is within the following range (3) by the stability determination unit 40e (S5).

  With the above operation, it is possible to determine the discharge state with high accuracy in a very short time without requiring high-precision positioning or complicated data processing.

  That is, as described above, by measuring the transmittance while ejecting droplets continuously, it is not necessary to synchronize the ejection start signal and the received light capture signal, and the measurement becomes very simple. In addition, since a plurality of ejection dots block the light receiving unit, noise is reduced and detection accuracy is increased. Further, by setting not only the lower limit value but also the upper limit value, unstable discharge with a low discharge speed can be detected, and a stable channel can be selected by a very simple method.

  This is a method for setting the lower limit value and the upper limit value of the determination condition, but this greatly varies depending on the specifications required for the apparatus. In the present embodiment, a stable discharge channel is determined by obtaining a lower limit value and an upper limit value as stable discharge within 25% with respect to a discharge speed of 8 m / s, that is, conditions satisfying 6 m / s to 10 m / s.

  The acquisition time per channel is about 5 ms, and it takes only 0.34 s to evaluate the discharge state of 48 channels even considering the data communication speed. In this way, it is possible to evaluate the stable discharge state in a very short time. In addition, since data processing is simple, processing does not take time. This take-in time may be shorter or longer than 5 ms, but if it is too short, noise increases and accurate evaluation of the discharge state cannot be performed. If it is too long, noise will be reduced, but short-term evaluation will not be possible. Of course, the upper limit value and the lower limit value are not limited to the above numerical values.

  Further, as will be described later, the transmittance when the channel of the unused (initial state) head is used may be measured, and the upper limit value and the lower limit value may be determined based on the initial transmittance. In this way, by using the initial transmittance as a reference, it is possible to detect head deterioration due to use.

  The transmittance obtained by the present embodiment is shown in FIG. FIG. 6 also shows the transmittance range in which ejection is stable. It can be seen from FIG. 6 that there are unstable discharge channels even when the transmittance is large.

  As described above, since the transmittance ai includes the discharge speed v and the discharge volume V, if the discharge speed is known, the discharge volume can be obtained from the transmittance ai. The ink jet drawing apparatus of the present embodiment includes a volume calculation unit 40n (FIG. 1). By providing a camera or the like that can observe the droplet 5, the ejection speed v of the droplet 5 can be obtained by this camera. By storing the discharge speed v in the storage unit 40c and calculating it together with the transmittance ai, the volume per droplet can be obtained.

  For example, a case where a color filter is drawn by an ink jet apparatus is taken as an example. When a 2 μm color filter is to be applied to one cell (471 × 137.5 μm), the total discharge amount is 996 pl when the pigment component of the ink is 13%. If the discharge volume of channel 1 is determined to be 5.2 pl, it can be seen that a desired film thickness can be obtained by discharging 192 drops in channel 1. As described above, an ink jet apparatus capable of quickly obtaining a desired film thickness by a simple method can be provided.

  In the past, the total number of ejected droplets per channel was counted and, for example, display was performed so that the head was replaced when the lifetime exceeded 1 × 10 10. However, the life of the head is exclusively the life of the actuator (for example, the life of a piezoelectric element when the head is a piezo type, and the life of a heat generating portion when Bubble Jet (registered trademark) is used). In other portions, for example, the discharge state often deteriorates due to, for example, the water-repellent surface of the nozzle or the fixation of ink inside the head. In that case, it is not known that the discharge state is deteriorated in the conventional ink jet drawing apparatus. Therefore, in the conventional apparatus, it is possible to recognize the deterioration only by drawing as a result of poor drawing quality. That is, the life of the head is determined by drawing.

  From equation (2), it can be seen that if the discharge volume V or the discharge speed v changes, the transmittance ai also changes. When the ink jet drawing apparatus 1 according to the present embodiment is used, the stability determination unit 40e can determine the ejection stability of the channel as described above. Therefore, when the stability determination unit 40e determines that the stability of the channel is deteriorated (out of a predetermined range), the stability determination unit 40e displays on the display unit 6 to replace the head. The structure to be made may be sufficient. At this time, the stability determination unit 40e compares, for example, the initial transmittance of the head stored in the storage unit 40c with the transmittance of the head in use, for example, N% or more than the initial transmittance. It may be configured to display on the display unit 6 so that the head is replaced when the head is displaced.

  Thus, according to the ink jet drawing apparatus 1 of the present embodiment, it is possible to confirm the deterioration of the head without actually drawing. The comparison of the transmittance may be performed for each channel or by comparison with an average value of all the channels. By determining the replacement of the head in this way, it is possible to quickly determine the deterioration of the head, and no unnecessary drawing is performed, which contributes to labor reduction and cost reduction.

  In addition, the ink jet drawing apparatus according to the present embodiment can prevent ink from being scattered by performing air suction from the bottom with the suction device 7 during discharge during discharge state evaluation (S3). Accordingly, it is possible to prevent the substrate to be drawn from being soiled, the light source 31 and the light receiving unit 32 from being soiled, and the head 20 from being dirty.

  In the flow of FIG. 4, S10 may be provided after S5, and S10 may be a step in which the channel selection unit 40f selects a channel determined to be stable in S5.

  In this way, only the channel determined to be stable ejection is used for drawing, so that clean drawing can be obtained without soiling the substrate. If the discharge channel is selected only because the transmittance is larger than a certain level, even an unstable channel may be used for drawing, but according to the present embodiment, the transmittance is in a certain range. Since the channel is determined to be stable, this is not the case and a good image can be obtained.

  Further, S11 may be provided after S5, and S11 may be a step of confirming whether or not the measurement (S3) to determination (S4) are performed twice in each channel. When it is confirmed in S12 that the above steps have been performed twice, in a further step S13, the channel selection unit 40f selects the channel determined to be stable twice in S5. Also good.

[Embodiment 2]
FIG. 7 is a front view showing the positional relationship between the head 20 and the optical sensor units (31, 32) according to another embodiment of the present invention. In this embodiment, the row of nozzles 22 is arranged perpendicular to the optical path from the light source 31 to the light receiving unit 32. Other than that, the configuration is the same as that of the first embodiment.

  A discharge state evaluation method when the ink jet drawing apparatus of the present embodiment is used will be described with reference to FIG.

  In the method of FIG. 8, the same operation as in FIG. 4 is performed until the threshold value (b0) is measured. Thereafter, the head 20 or the optical sensors (31, 32) are moved in the direction of the arrow in FIG. 7 (S20). The speed at this time is a speed at which the droplet 5 blocks the middle of the light receiving surface. In this embodiment, the evaluation time per channel is 7 ms, and the head moving speed is 24.19 mm / s.

  Next, discharge is started from the beginning of the channel group to be discharged, that is, from channel 1 (S21-1). Next, the received light signal is captured, and this value (b1) is stored in the storage unit (S21-2). Next, the discharge is stopped (S21-3). This series of discharge-take-in operation is repeated up to channel 48.

  Next, the movement of the head 20 or the optical sensor unit is stopped (S22). For each channel, the transmittance ai is measured (S23), and the discharge state is determined (S24), whereby it can be determined whether the channel is stably discharged.

  In this way, it is possible to determine the discharge state with high accuracy in a very short time without requiring highly accurate positioning or complicated data processing.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The ink jet drawing apparatus and the ejection state evaluation method of the present invention are suitably used for a printing apparatus using an ink jet system such as a color printer.

It is a block diagram which shows the principal part of the inkjet drawing apparatus which concerns on one Embodiment of this invention. It is a flowchart which shows the evaluation method of the discharge stability which concerns on one Embodiment of this invention. The positional relationship between the head 20 and the optical sensor unit (31, 32) is shown. (A) is a view when the head 20 is viewed from a line of sight perpendicular to the droplet discharge direction, and (b) is a surface on which the nozzle 22 is formed. It is a front view when the head 20 is seen from. It is a front view which shows the positional relationship of a laser beam, a light-receiving surface, and a droplet. It is drawing which shows the time concerning a series of operation | movement of discharge-take-in-stop. It is a scatter diagram which shows the transmittance | permeability obtained by one Embodiment of this invention. It is a front view showing the positional relationship of the head 20 and optical sensor unit (31, 32) which concerns on other embodiment of this invention. It is a flowchart which shows the evaluation method of the discharge stability which concerns on other embodiment of this invention. (A) And (b) is a front view which shows the optical sensor unit of the conventional discharge stability evaluation apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet drawing apparatus 20 Head 21 Channel 22 Nozzle 31 Light source 32 Light-receiving part 40 Control system

Claims (8)

The light source and the light receiving unit include at least one channel for discharging the droplet, a light source, and a light receiving unit that receives light from the light source, so that the path of the droplet intersects the light path from the light source to the light receiving unit. Part is provided,
From the amount of light received by the light receiving unit bi while the plurality of droplets ejected from the channel pass on the optical path and the amount of received light b0 when the droplet does not pass on the optical path, the transmittance ai [ai is (B0−bi) / b0] is further provided, and a transmissivity calculating unit is further provided.   The inkjet drawing apparatus according to claim 1, further comprising a determination unit that determines whether or not the transmittance is within a predetermined range. It has a selection part that selects the channel used for drawing,
The ink jet drawing apparatus according to claim 2, wherein the selection unit selects a channel whose transmittance is determined by the determination unit to be within the predetermined range.   The inkjet drawing apparatus according to claim 3, wherein the selection unit selects a channel that has been determined by the determination unit two or more times when the transmittance is within the predetermined range.   The inkjet drawing apparatus according to claim 1, further comprising a volume calculation unit that calculates a volume of the droplet from the transmittance ai. The channel is provided in a replaceable head,
The inkjet drawing apparatus according to claim 2, further comprising: a display unit configured to display the head to be replaced when the determination unit determines that the transmittance is out of a predetermined range.   The inkjet drawing apparatus according to claim 1, further comprising: a suction unit that sucks air droplets discharged from the channel from the traveling direction of the liquid droplets by sucking air. A method for evaluating the discharge stability of a channel for discharging droplets,
A light irradiation step of irradiating light to a path of a droplet discharged from the channel;
A transmittance measuring step for measuring the transmittance of light in the path while a plurality of droplets are ejected from the channel;
And an evaluation step of evaluating that the ejection is stable when the transmittance is within a predetermined range.

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