JP2009190280A - Liquid ejection inspecting method, liquid ejection inspecting apparatus, and printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a detection accuracy by reducing a rate of wrong detection of liquid ejection inspection, particularly to provide a liquid ejection inspecting method which enables reduction of a false positive rate, and to provide a liquid ejection inspecting apparatus, and a printer. <P>SOLUTION: At the time of inspecting the presence or absence of ejection of ink droplets from a nozzle on the basis of a current change amount at a head cap 63 by making the ink droplets ejected from the nozzle of a printing head 14 in a state that a potential difference is generated between the printing head 14 where the nozzle for ejecting the ink droplets is formed and the head cap 63 disposed oppositely to the printing head 14 via a gap, a threshold value for performing determination of the presence or absence of ejection according to the current change amount is set to be not smaller than a predetermined value (μ(N)+5.85σ(N)) based on a standard deviation σ(N) of the current change amount at the time of non ejection. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid discharge inspection method, a liquid discharge inspection apparatus, and a method for inspecting whether or not liquid droplets are discharged from a nozzle based on a current change amount in a head cap by discharging liquid droplets from a nozzle of a liquid discharge head, and The present invention relates to a printing apparatus including the same.

2. Description of the Related Art Generally, a printing apparatus such as an ink jet printer is configured to perform printing by ejecting ink droplets from a plurality of nozzles to desired positions by a print head mounted on a carriage that can reciprocate.
In this type of ink jet printer, a method for inspecting whether or not ink droplets are being ejected normally is a liquid ejection inspection in which the presence or absence of ejection is determined by detecting current changes caused by charged ink ejected from nozzles. A method is known (see, for example, Patent Document 1).
JP 2006-264243 A

In the liquid discharge inspection method as described above, “discharge” or “non-discharge” can be determined based on whether or not the magnitude of the detected current change exceeds a predetermined threshold. Regardless of whether it is determined as “non-ejection” or “discharge” despite non-ejection, it may occur probabilistically. The false detection rate for judging the rate as “false negative rate” and “non-ejection” as “ejection” is called “false positive rate”). If it is determined that “non-ejection” is “ejection”, a non-ejection state is not detected, and normal liquid ejection processing is performed with missing dots. For this reason, it is important to reduce the false positive rate for the purpose of the liquid discharge inspection for detecting defects in the liquid discharge portion.
For example, when the threshold is set so that the false positive rate = the false negative rate, the false positive rate and the false negative rate are reduced when the SN ratio when detecting a current change due to a change with time, an environmental change, or the like becomes small. Each will increase, which is not preferable.

  Therefore, an object of the present invention is to reduce the false detection rate of liquid discharge inspection and improve detection accuracy, and in particular, a liquid discharge inspection method, a liquid discharge inspection device, and printing capable of reducing a false positive rate To provide an apparatus.

A liquid discharge inspection method according to the present invention capable of solving the above-described problems includes a liquid discharge portion in which a nozzle for discharging a droplet is formed, and a liquid receiver disposed with a gap facing the liquid discharge portion. A liquid discharge for inspecting whether or not a liquid droplet is discharged from the nozzle on the basis of a current change amount in the liquid receiving portion in a state where a potential difference is generated between the liquid and the liquid receiving portion. An inspection method,
A threshold value for determining whether or not ejection is performed according to the current change amount is set to be a predetermined value or more based on a standard deviation of the current change amount during non-ejection.

In addition, the liquid ejection inspection apparatus according to the present invention includes a liquid ejection section in which nozzles for ejecting droplets are formed,
A liquid receiving portion that can be disposed with a gap facing the liquid ejection portion;
A detection unit for detecting a current change in the liquid receiving unit,
In a state where a potential difference is generated between the liquid discharge unit and the liquid receiving unit, the droplet is discharged from the nozzle, and the droplet is discharged from the nozzle based on the amount of current change detected by the detection unit. A liquid discharge inspection device for inspecting the presence or absence of
A threshold value for determining whether or not ejection is performed according to the current change amount is set to be equal to or greater than a predetermined value based on a standard deviation of the current change amount during non-ejection.

  According to the liquid discharge inspection method and the liquid discharge inspection apparatus of this configuration, the threshold for determining whether or not a liquid droplet is discharged from the liquid discharge portion is a standard for the amount of current change during non-discharge (that is, the noise level). Since it is set to be equal to or greater than a predetermined value based on the deviation, the false positive rate at which “non-ejection” is determined as “ejection” can be reliably maintained below a desired probability. Therefore, it is possible to improve the detection accuracy by reducing the false detection rate of the liquid discharge inspection, and to accurately detect the defect of the liquid discharge portion, so that the nozzle state of the liquid discharge portion can be kept good.

In the liquid discharge inspection method according to the present invention, an intermediate value of the current change amount based on the standard deviation of the current change amount during non-discharge and the standard deviation of the current change amount during discharge is calculated,
If the intermediate value exceeds the predetermined value, the threshold is set to the intermediate value;
When the intermediate value is less than or equal to the predetermined value, the threshold value is preferably set to the predetermined value.

Further, in the liquid discharge inspection apparatus according to the present invention, an intermediate value of the current change amount based on the standard deviation of the current change amount during non-ejection and the standard deviation of the current change amount during discharge is calculated,
If the intermediate value exceeds the predetermined value, the threshold is set to the intermediate value,
When the intermediate value is less than or equal to the predetermined value, the threshold value is preferably set to the predetermined value.

  According to the liquid discharge inspection method and the liquid discharge inspection apparatus of this configuration, the intermediate value of the amount of current change in which the false positive rate = the false negative rate is calculated based on the standard deviation between the non-discharge time and the discharge time, and the value Is larger than the predetermined value, the false positive rate can be made smaller than the desired probability by setting the threshold value to an intermediate value. When the calculated intermediate value is less than or equal to the predetermined value, the false positive rate can be made lower than the desired probability by setting the threshold value to the predetermined value. Therefore, even if the SN ratio of the current change amount becomes small due to environmental changes or the like, the false positive rate can always be maintained below the desired probability.

In the liquid ejection inspection method according to the present invention, when the standard deviation of the current change amount during non-ejection is represented by σ (N), and the average value of the current change amount during non-ejection is represented by μ (N),
The predetermined value is preferably μ (N) + 5.85σ (N).

  According to the liquid discharge inspection method having this configuration, the threshold value is set to μ (N) + 5.85σ (N) or more, so that the false positive rate can be set to 1 / 50,000 or less.

In the liquid discharge inspection method according to the present invention, when the standard deviation of the current change amount at the time of discharge is represented by σ (S) and the average value of the current change amount at the time of discharge is represented by μ (S),
When the threshold value exceeds μ (S) −4σ (S), it is preferable to perform a cleaning process for the liquid ejection unit.

  According to the liquid ejection inspection method having this configuration, even if the false positive rate can be maintained below a desired probability, if the threshold exceeds μ (S) −4σ (S), “ejection” is determined as “non-ejection”. Since the false negative rate becomes greater than 1 / 100,000, the cleaning process of the liquid discharge unit returns the nozzle of the liquid discharge unit to a good state and improves the detection accuracy of the liquid discharge test again. be able to.

Further, a printing apparatus according to the present invention includes the liquid ejection inspection apparatus according to the present invention,
Ink is used as the liquid,
The liquid ejection unit is a print head that ejects ink droplets;
The liquid receiving portion is a head cap that can contact and separate from the print head.

  According to the printing apparatus having this configuration, it is possible to reliably maintain a false positive rate that determines “non-ejection” as “ejection” or less when the ink ejection inspection of the print head is performed. Therefore, it is possible to maintain good print quality by reducing the false detection rate of the ink ejection inspection to improve detection accuracy and accurately detecting defects such as missing dots in the print head.

Hereinafter, examples of embodiments of a liquid discharge inspection method, a liquid discharge inspection apparatus, and a printing apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is an external perspective view of a roll paper printer that is a printing apparatus according to an embodiment of the present invention. FIG. 2 is an external perspective view of the roll paper printer shown in FIG. 3 is a schematic side view showing the internal configuration of the roll paper printer shown in FIG. 1, and FIG. 4 is a perspective view of the roll paper printer shown in FIG. 1 with the printer case removed.

  The roll paper printer 1 of the present embodiment performs color printing on roll paper by an ink jet method using a plurality of types of color ink liquids, and as shown in FIG. A roll paper cover 3 and an ink cartridge cover 7 are provided on the front surface of the printer so as to be freely opened and closed. A recording paper discharge port 4 having a predetermined width corresponding to the width of the roll paper is formed on the front surface of the printer case 2a. A paper discharge guide 5 protrudes forward below the recording paper discharge port 4, and an opening / closing lever 6 for opening the roll paper cover 3 is disposed on the side of the paper discharge guide 5. A rectangular opening 2b for inserting and removing roll paper is formed below the paper discharge guide 5 and the opening / closing lever 6 in the printer case 2a. The opening 2b is sealed by the roll paper cover 3. .

  When the open / close lever 6 is operated, the roll paper cover 3 is unlocked. When the paper discharge guide 5 is pulled forward after unlocking, as shown in FIG. 2, the roll paper cover 3 is opened until it becomes almost horizontal forward with the lower end as a center. When the roll paper cover 3 is opened, the roll paper storage unit 11 formed inside the printer is opened, and the recording paper transport path from the roll paper storage unit 11 to the recording paper discharge port 4 is opened. The roll paper can be easily replaced from the front. In FIG. 2, the exterior portion of the roll paper cover 3 and the opening / closing lever 6 are not shown.

  As shown in FIG. 3, a roll paper storage unit 11 is formed in the center of the main body frame 10 in the width direction inside the roll paper printer 1. The roll paper storage unit 11 stores the roll paper 12 in a direction along the roll paper width direction in the printer width direction.

  A head unit frame 13 is horizontally attached to the upper end of the main body frame 10 above the roll paper storage unit 11. The head unit frame 13 includes a print head 14 that is an inkjet head, a linear scale 15 and an encoder sensor 16 for detecting the position of the print head 14, a carriage 17 on which the print head 14 and the encoder sensor 16 are mounted, and a carriage 17. A carriage guide shaft 18 for guiding the movement of the printer in the printer width direction is arranged. A carriage transport mechanism including a carriage motor 19 and a timing belt 20 for reciprocating the carriage 17 along the carriage guide shaft 18 is disposed.

  The print head (liquid ejection unit) 14 is mounted on the carriage 17 so that the nozzle surface 14a that ejects ink droplets faces downward. The encoder sensor 16 is disposed on the upper end surface 14 b of the print head 14. The carriage guide shaft 18 is stretched horizontally in the printer width direction, and the linear scale 15 is stretched parallel to the carriage guide shaft 18 above the print head 14.

  A platen 21 that extends horizontally in the printer width direction with a certain gap is disposed below the print head 14. The printing position of the print head 14 is defined by the platen 21. A tension guide 22 curved downward is attached to the rear end of the platen 21. The tension guide 22 is biased upward by a spring, and the recording paper 12 a drawn from the roll paper 12 stored in the roll paper storage unit 11 is printed in a state where a predetermined tension is applied by the tension guide 22. It is pulled out along the recording paper conveyance path passing through the position.

  On the rear side of the platen 21, a rear paper feed roller 23 is stretched horizontally in the printer width direction. A rear paper pressing roller 24 having a predetermined width is pressed against the rear paper feeding roller 23 through the recording paper 12a with a predetermined pressing force. A front paper feed roller 25 is disposed at a front end side portion of the platen 21. A front paper pressing roller 26 is pressed against the front paper feeding roller 25 from above via the recording paper 12a. The rear paper feed roller 23 and the front paper feed roller 25 are driven by a paper feed motor 27 mounted on the main body frame 10.

  While the carriage 17 is reciprocatingly moved along the carriage guide shaft 18, printing is performed on the surface of the portion of the recording paper 12 a that is fed from the roll paper 12 and positioned at the printing position by the print head 14 mounted on the carriage 17. Is done. The printing position is controlled based on the detection signal of the encoder sensor 16. After a series of line printing in the width direction of the recording paper 12a is completed, the rear paper feeding roller 23 and the front paper feeding roller 25 are rotationally driven to feed the recording paper 12a by a predetermined pitch. After this, the next line is printed. Thus, the recording paper 12a is printed by the print head 14 while being intermittently sent out at a predetermined pitch. For example, a scissors-type recording paper cutting device 28 is disposed at the recording paper discharge port 4 from which the recording paper 12a after printing is discharged. The recording paper cutting device 28 cuts the recording paper 12a positioned between them in the width direction.

  The platen 21, the tension guide 22, the rear paper feed roller 23, and the front paper feed roller 25 are configured to open and close together with the roll paper cover 3.

  When the ink cartridge cover 7 shown in FIGS. 1 and 2 is opened, the inner cartridge mounting portion 9 (see FIG. 4) is opened, and the ink cartridge 8 can be attached to and detached from the cartridge mounting portion 9. become.

  The ink cartridge 8 contains a plurality of color ink packs in a cartridge case. In the case of the roll paper printer 1 of the present embodiment, the ink cartridge 8 is pulled out by a predetermined distance in front of the cartridge mounting portion 9 in conjunction with the operation of opening the ink cartridge cover 7.

When each ink pack in the ink cartridge 8 is mounted on the cartridge mounting portion 9, the ink supply needle provided on the cartridge mounting portion 9 side is inserted and connected to the ink supply port of the ink pack. An ink channel 31 fixed in the printer case 2 a is connected to the ink supply needle of the cartridge mounting portion 9, and one end of a flexible ink supply tube 33 is connected to the ink channel 31. .
The other end of the ink supply tube 33 is connected to the carriage 17 and communicates with the print head 14 via a damper unit and a back pressure adjustment unit.

  As shown in FIG. 4, the upper position of the cartridge mounting portion 9 that is out of the printing area is a standby position (maintenance area) of the carriage 17 that reciprocates. A head maintenance mechanism 40 that performs a maintenance operation of the print head 14 exposed on the lower surface of the carriage 17 is disposed below the standby position.

  As shown in FIG. 5, the head maintenance mechanism 40 includes a head cap mechanism 60 for sealing the nozzle formation surface of the print head 14, a wiper mechanism 50 for wiping the nozzle formation surface, and a head cap mechanism 60. And an ink suction mechanism 70 for sucking the residual ink.

  The head cap mechanism 60, the wiper mechanism 50, and the ink suction mechanism 70 are driven by a pump motor (not shown) via a power transmission mechanism 80. These parts are attached to a housing 41 that can be attached to and detached from the printer body.

The wiper mechanism 50 and the head cap mechanism 60 are provided side by side in the reciprocating direction of the carriage 17, and the ink suction mechanism 70 is provided on the rear side of the head cap mechanism 60 (right rear side in FIG. 5).
A power transmission mechanism 80 is arranged so that the head cap mechanism 60, the wiper mechanism 50, and the ink suction mechanism 70 can be interlocked.

  The power transmission mechanism 80 is constituted by a gear train composed of a plurality of gears. The head cap mechanism 60 and the wiper mechanism 50 are moved in the direction along the reciprocating direction of the print head 14 and up and down by the driving force from the pump motor and the guide of the housing 41. The ink suction mechanism 70 is operated while moving forward and backward in the direction.

  The ink suction mechanism 70 is a tube pump in which one end of the tube 72 is connected to the head cap mechanism 60 and the other end is connected to the waste ink introducing portion of the ink cartridge 17. When the ink suction mechanism 70 is driven, Ink is sucked from the nozzles of the print head 14 via the head cap mechanism 60 and discharged into the waste ink storage chamber of the ink cartridge 8.

The head cap mechanism 60 includes a slider 64 and a head cap (liquid receiving portion) 63 fixed to the cap holder 62. The slider 64 is formed in a case shape, and is supported by the housing 41 so as to approach or separate from the nozzle formation surface of the print head 14.
A cap holder 62 having a head cap 63 fixed to the tip portion is held in the upper end recess of the slider 64 so as to move forward and backward with respect to the slider 64.

  The wiper mechanism 50 includes a slider 52 and a wiper 51. The slider 52 is formed in a box shape, and a slide portion 53 is supported and guided by a guide portion 44 provided in the housing 41 so as to slide in the same direction as the slider 64 of the head cap mechanism 60. A wiper 51 made of a rubber plate material, which is an elastic material, is embedded in the tip portion of the slider 52.

  The slider 52 can move between a position where the wiper 51 is most retracted inside the head maintenance mechanism 40 (retracted position) and a wiping position where the wiper 51 performs a process of wiping off dirt on the nozzle forming surface. It is like that. The wiping position is such that the tip of the wiper 51 contacts and rubs against the nozzle forming surface of the print head 14. Thereby, the wiper 51 can wipe off foreign matters such as ink adhering to the nozzle formation surface. Depending on the type of ink, the wiper 51 may be formed of soft plastic or the like.

  As shown in FIG. 6, the head cap 63 is formed of a box-shaped rubber having an opening with a size capable of sealing the nozzle forming surface 14 a of the print head 14, and the upper edge is formed with a nozzle. The lip portion 96 can be in close contact with the surface 14a.

  The head cap 63 has a storage recess 94, and a storage material 95 having a multilayer structure for absorbing waste ink is stored in the storage recess 94. The absorption material 95 is held by a pressing member (not shown). The upper surface is a position lower than the tip position of the lip portion 96.

  One end of a tube from the ink suction mechanism 70 is connected to the head cap 63, and the pump motor of the ink suction mechanism 70 is driven while the lip portion 96 is in close contact with the nozzle forming surface 14a. Then, the inside of the head cap 63 is depressurized, and ink is sucked from the ink nozzles of the print head 14 and discharged into the waste ink storage chamber of the ink cartridge 8.

  In addition, a metal shaft 97 as a current inspection detector is erected in the housing recess 94 of the head cap 63, and the metal shaft 97 can be electrically connected to the absorber 95. A lead wire 98 is connected to the lower end of the metal shaft 97, and a signal can be taken out through the lead wire 98.

  In the roll paper printer 1, the print head 14 is cleaned by the head maintenance mechanism 40. This cleaning is performed at a predetermined timing or at the time of a user's operation. The head cap 63 is brought into close contact with the nozzle forming surface 14a of the print head 14, and the inside is sucked by the ink suction mechanism 70 for printing. An ink suction process for sucking thickened ink from the ink nozzles of the head 14 and a wiping process for wiping dirt on the nozzle formation surface 14a of the print head 14 with the wiper 51 are performed.

  Further, in the roll paper printer 1 provided with the head maintenance mechanism 40, a predetermined amount of ink from the ink nozzles of the print head 14 is started before or periodically to form an ink meniscus at the ink nozzles of the print head 14. A flushing process for ejecting ink into the head cap 63 and a capping process for protecting the head cap 63 by closely contacting the nozzle forming surface 14a of the print head 14 are performed after the suspension of printing in order to prevent clogging of the ink nozzles.

  Further, in the roll paper printer 1, the head maintenance mechanism 40 performs an ink discharge inspection for inspecting whether ink droplets are normally discharged from the ink nozzles of the print head 14. That is, the head maintenance mechanism 40 also has a function of an ink discharge inspection device (liquid discharge inspection device).

Next, an ink ejection inspection method (liquid ejection inspection method) using the head maintenance mechanism 40 will be described with reference to a flowchart shown in FIG. 7 and a detection signal distribution graph shown in FIG.
FIG. 8 shows a signal distribution of current change and its change. The horizontal axis of the graph of FIG. 8 indicates the magnitude (absolute value) ΔV of the current change signal, N is a detection signal (that is, noise) during non-ejection, S is a detection signal during ejection, and μ (N ) Is the average value of N, μ (S) is the average value of S, σ (N) is the standard deviation of N, and σ (S) is the standard deviation of S.

When the ink ejection inspection is started, the head cap 63 is raised and disposed at a height at which a slight gap is provided with respect to the nozzle formation surface 14a of the print head 14, and the head cap 63 is The print head 14 moves upward (step S01).
In this state, a gap of a predetermined dimension A is formed between the nozzle formation surface 14 a of the print head 14 and the tip of the lip portion 96 of the head cap 63, and the nozzle formation surface 14 a of the print head 14 and the head cap 63 The gap with the upper surface of the absorbent 95 is set to a predetermined dimension B that is narrow enough to satisfactorily perform ink ejection inspection (see FIG. 6).

  In this state, a voltage is applied between the print head 14 and the head cap 63 with a predetermined potential difference (step S02). Then, with the voltage applied, the voltage value actually applied to the head cap 63 is measured, and the average value μ (S) of the detection signal value at the time of ejection is estimated from the value (step S03).

It should be noted that when the roll paper printer 1 is manufactured at the factory, the values of μ (S) and μ (N) obtained by actual inspection, and the values of σ (S) and σ (N) obtained by the preliminary evaluation are obtained. Stored inside the printer.
Since the detection signal intensity at the time of ejection is proportional to the voltage value applied to the head cap 63, by measuring this voltage value, the average value μ () of the detection signal intensity based on μ (S) of the factory measurement value The value of S) can be estimated.

In order to determine whether or not ink droplets are ejected, it is determined based on whether or not the magnitude of the detected current change signal is greater than a predetermined threshold. The false detection rate (false positive rate and false negative rate) changes depending on what criteria this threshold is set.
Here, the setting of the threshold value will be described with reference to FIGS.
In FIG. 8A, the S / N ratio is comparatively large and the state of the print head 14 is good, such as shortly after the print head 14 is cleaned. FIG. 8B is an example in which the SN ratio is slightly reduced due to an annular change, a use state, or the like, and FIG. 8C is an example in which the SN ratio is further reduced.

  In setting the threshold, first, as shown in FIG. 8A, an intermediate value based on σ (S) and σ (N) is calculated as the threshold so that the false positive rate = false negative rate. For example, threshold = μ (S) + 6.85σ (S) = μ (N) −6.85σ (N) (step S04). Note that σ (S), σ (N), and μ (N) may be calculated using factory measured values or by actually performing ejection.

  In the present invention, in order to keep the false positive rate determined as “ejection” low despite non-ejection, the standard deviation σ () is set so that the threshold value is sufficiently larger than the average value of signals at the time of non-ejection. N) is set to be a predetermined value or more based on N). In the present embodiment, this predetermined value is set as μ (N) + 5.85σ (N). In this case, the false positive rate can be 1 / 50,000 or less.

  Therefore, it is determined whether or not the SN threshold value exceeds a predetermined value (μ (N) + 5.85σ (N)) (step S05), and the intermediate threshold value is μ (N) + 5.85σ ( If greater than N), the threshold value is set to an intermediate value (step S06). Thereby, a false positive rate can be made still smaller than a desired probability (1 / 750,000).

  As shown in FIG. 8B, when the threshold value of the intermediate value of SN is equal to or smaller than a predetermined value (μ (N) + 5.85σ (N)), the threshold value is set to a predetermined value (step S07). . Thereby, a false positive rate can be made into a desired probability (1 / 750,000) or less. Therefore, even if the SN ratio of the current change amount becomes small due to environmental changes or the like, the false positive rate can always be maintained below the desired probability.

  Thus, by setting the threshold value to a predetermined value (μ (N) + 5.85σ (N)) or higher, the false positive rate can be maintained below a desired probability, but the false negative rate can also be suppressed to a certain level or lower. preferable. If the threshold value exceeds μ (S) −4σ (S), the false negative rate becomes greater than 1 / 100,000. Therefore, after step S06 or step S07 in which the threshold value is fixed to a predetermined value (μ (N) + 5.85σ (N)) or more, it is determined whether the threshold value is equal to or less than μ (S) −4σ (S). (Step S08).

In step S08, if the threshold value is μ (S) −4σ (S) or less (see FIG. 8B), it is determined that the desired false negative rate and false positive rate can be secured, and the ink ejection test is started. (Step S09).
In the ink ejection test, charged ink droplets (droplets) are ejected from the ink nozzles of the print head 14. In this way, a signal of a current change caused by the charged ink landing on the absorber 95 is taken out from the metal shaft 97 for current inspection through the lead wire 98, and the current change is based on the current change. The ejection state of the ink droplets from the ink nozzle can be inspected based on whether or not the signal exceeds the threshold value.

  If the threshold value exceeds μ (S) −4σ (S) in step S08 (see FIG. 8C), the head cap 63 is raised to cap the nozzle forming surface 14a, and a cleaning operation (abnormal process). Is performed (step S10). As a result, the nozzles of the print head 14 can be returned to a good state, and the detection accuracy of the ink ejection test can be made good again.

  As described above, according to the ink ejection inspection method and the ink ejection inspection device of the present embodiment, the threshold value for determining whether or not ink droplets are ejected from the print head 14 is the amount of current change during non-ejection. Since it is set to a predetermined value (μ (N) + 5.85σ (N)) or more based on the standard deviation σ (N), a false positive rate that determines “non-ejection” as “ejection” is surely desired. Or less (1 / 750,000). Therefore, it is possible to maintain a good nozzle state of the print head 14 by reducing the false detection rate of the ink ejection test to improve the detection accuracy and accurately detecting the defect of the print head 14.

The roll paper printer 1 equipped with the ink ejection inspection device (head maintenance mechanism 40) that performs the above-described ink ejection inspection method performs "non-ejection" as "ejection" when performing the ink ejection inspection of the print head 14. The false positive rate that is judged can be reliably maintained below a desired probability. Therefore, it is possible to improve the detection accuracy by reducing the false detection rate of the ink ejection inspection, and it is possible to maintain a good print quality by accurately detecting defects such as missing dots of the print head 14.
The frequency at which the ink ejection inspection is performed is set as appropriate. As an example of the high frequency, it can be performed each time printing is performed on a piece of recording paper 12a, that is, every time the recording paper cutting device 28 is operated. According to this, good print quality can always be maintained.

  The liquid discharge inspection method and the liquid discharge inspection apparatus according to the present invention include a color material discharge head and an organic EL display used for manufacturing a color filter such as a liquid crystal display, including the ink jet printer exemplified in the above embodiment. , Electrode material discharge heads used for electrode formation such as FED (surface emitting display), liquid organic discharge heads used for biochip manufacturing liquid discharge devices using liquid discharge heads, samples as precision pipettes, etc. It can also be applied to a discharge device or the like.

1 is an external perspective view of a roll paper printer that is a printing apparatus according to an embodiment of the present invention. FIG. 2 is an external perspective view showing a state in which a roll paper cover of the roll paper printer shown in FIG. 1 is opened. FIG. 2 is a schematic side view showing an internal configuration of the roll paper printer shown in FIG. 1. FIG. 2 is a perspective view of a state in which a printer case is removed from the roll paper printer illustrated in FIG. 1. It is a perspective view of a head maintenance mechanism. FIG. 4 is a cross-sectional view of a part of the head maintenance mechanism. 3 is a flowchart of an ink discharge inspection method. It is a graph which shows distribution of the signal of the current change at the time of an ink discharge test | inspection, and its change.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Roll paper printer (printing apparatus), 14 ... Print head, 14a ... Nozzle formation surface, 40 ... Head maintenance mechanism, 63 ... Head cap (liquid receiving part), 97 ... Metal shaft (detection part).

Claims (7)

A liquid is discharged from the nozzle in a state in which a potential difference is generated between a liquid discharge portion in which a nozzle for discharging liquid droplets is formed and a liquid receiving portion disposed so as to face the liquid discharge portion with a gap. A liquid discharge inspection method for inspecting whether or not a droplet is discharged from the nozzle based on a current change amount in the liquid receiving portion by discharging a droplet,
A liquid ejection inspection method, characterized in that a threshold for determining whether ejection is present or not in accordance with the amount of current change is set to be equal to or greater than a predetermined value based on a standard deviation of current variation during non-ejection. The liquid discharge inspection method according to claim 1,
Calculate the intermediate value of the current variation based on the standard deviation of the current variation during non-ejection and the standard deviation of the current variation during ejection,
If the intermediate value exceeds the predetermined value, the threshold is set to the intermediate value;
When the intermediate value is less than or equal to the predetermined value, the threshold value is set to the predetermined value. In the liquid discharge inspection method according to claim 1 or 2,
When the standard deviation of the current change amount during non-ejection is represented by σ (N), and the average value of the current change amount during non-ejection is represented by μ (N),
The liquid discharge inspection method, wherein the predetermined value is μ (N) + 5.85σ (N). In the liquid discharge inspection method according to any one of claims 1 to 3,
When the standard deviation of the current change amount at the time of discharge is expressed as σ (S) and the average value of the current change amount at the time of discharge is expressed as μ (S)
When the threshold value exceeds μ (S) −4σ (S), a cleaning process for the liquid discharge unit is performed. A liquid ejection part in which nozzles for ejecting liquid droplets are formed;
A liquid receiving portion that can be disposed with a gap facing the liquid ejection portion;
A detection unit for detecting a current change in the liquid receiving unit,
In a state where a potential difference is generated between the liquid discharge unit and the liquid receiving unit, the droplet is discharged from the nozzle, and the droplet is discharged from the nozzle based on the amount of current change detected by the detection unit. A liquid discharge inspection device for inspecting the presence or absence of
A liquid ejection inspection apparatus, characterized in that a threshold for determining whether or not ejection is performed according to the amount of current change is set to be equal to or greater than a predetermined value based on a standard deviation of current variation during non-ejection. . In the liquid discharge inspection apparatus according to claim 5,
An intermediate value of the current change amount based on the standard deviation of the current change amount during non-discharge and the standard deviation of the current change amount during discharge is calculated,
If the intermediate value exceeds the predetermined value, the threshold is set to the intermediate value,
When the intermediate value is less than or equal to the predetermined value, the threshold value is set to the predetermined value. A liquid ejection inspection device according to claim 5 or 6,
Ink is used as the liquid,
The liquid ejection unit is a print head that ejects ink droplets;
The printing apparatus, wherein the liquid receiving portion is a head cap that can contact and separate from the print head.

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