Patent Publication Number: US-2022219458-A1

Title: Head device, liquid jetting apparatus, and head maintenance method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation of PCT International Application No. PCT/JP2020/036171 filed on Sep. 25, 2020 claiming priority under 35 U.S.C § 119(a) to Japanese Patent Application No. 2019-179130 filed on Sep. 30, 2019. Each of the above applications is hereby expressly incorporated by reference, in its entirety, into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a head device, a liquid jetting apparatus, and a head maintenance method. 
     2. Description of the Related Art 
     There is known an ink jet printing apparatus including an ink jet head. The ink jet printing apparatus performs a driving operation in which a meniscus is vibrated to such an extent that ink is not jetted from a nozzle, so that deterioration of the ink that is caused by the ink drying in the nozzle is suppressed. Such a driving operation is called a tickling operation, a meniscus shaking operation, and the like. 
     In the ink jet printing apparatus, a wiping operation is performed on a nozzle surface of the ink jet head to remove foreign substances such as ink mist adhering to the nozzle surface and to suppress a decrease in jetting performance that is caused by the foreign substances adhering to the nozzle surface. For the wiping operation, a wiping member such as a web sheet, to which a non-woven fabric or the like is applied, and a blade, to which rubber or the like is applied, is applied. 
     In a case where the tickling operation is performed during the wiping operation, the amount of ink drawn from the nozzle to the wiping member may be large in comparison with a case where the tickling operation is not performed. In the case of the ink jet head to which ink having a component that easily scrapes a liquid-repellent film formed on the nozzle surface is applied, deterioration of the liquid-repellent film is accelerated due to the wiping operation. 
     Described in JP2016-30366A is an ink jet printing apparatus including a wiper that wipes a nozzle surface. The apparatus described in JP2016-30366A drives a nozzle, with which the wiper is not in contact, in a case where the nozzle surface is wiped by means of the wiper so that the pressure of a pressure chamber communicating with a nozzle with which the wiper is in contact is reduced. Accordingly, a meniscus of the nozzle with which the wiper is in contact is pulled into the nozzle and ink leakage caused by the destruction of the meniscus is suppressed. 
     Described in JP4488342B is an ink jet printing apparatus including a wiper that wipes a nozzle surface. The apparatus described in JP4488342B performs a wiping operation while applying pulsation to ink to such an extent that the ink is not jetted, so that wiping failure such as unwiped residue is suppressed. 
     Described in JP2015-71231A is an ink jet printing apparatus including a maintenance device for an ink jet head. In the case of the apparatus described in JP2015-71231A, a negative pressure during maintenance of the ink jet head is set to fall within a range of −0.8 kilopascals to −0.1 kilopascals. 
     SUMMARY OF THE INVENTION 
     However, in the case of the invention described in JP2016-30366A, ink is jetted from a nozzle with which the wiper is not in contact and the ink jetted from the nozzle adheres to the wiper. In the case of the invention described in JP4488342B, ink adheres to the wiper at the time of the wiping operation. 
     In the case of the invention described in JP2015-71231A, ink leaks from a nozzle at the time of a wiping operation. The ink leaking from the nozzle adheres to a wiper. In such a case, particles contained in the ink may scrape a liquid-repellent film on a nozzle surface and the liquid-repellent film may be worn in a case where the wiping operation is performed by means of the wiper to which the ink adheres. 
     The present invention has been made in consideration of such circumstances and an object of the present invention is to provide a head device, a liquid jetting apparatus, and a head maintenance method with which it is possible to suppress wear of a liquid-repellent film on a nozzle surface that is caused by a wiping process with respect to the nozzle surface. 
     In order to achieve the above-described object, the following aspects of the invention are provided. 
     According to a first aspect, there is provided a head device including an ink jet head in which a liquid-repellent film is formed on a nozzle surface and a head control unit that controls the ink jet head. The head control unit applies a negative pressure to liquid in a nozzle, performs a non-jetting driving operation of causing the liquid in the nozzle to vibrate without being jetted, and stops the non-jetting driving operation for a wiping target nozzle with which a wiping member to be used in a wiping process comes into contact in a case where the wiping process with respect to the nozzle surface is to be performed. 
     According to the first aspect, the non-jetting driving operation for the wiping target nozzle is stopped. Accordingly, the liquid is restrained from being drawn out from the nozzle in contact with the wiping member to the nozzle surface and thus wear of the liquid-repellent film formed on the nozzle surface and a decrease in performance of the ink jet head can be suppressed. 
     As the wiping member, an absorbent member having a function of absorbing liquid may be applied. An example of the absorbent member is a web sheet. 
     The wiping of the nozzle surface may be performed by moving the ink jet head relative to the wiping member in a stopped state or by moving the wiping member relative to the ink jet head in a stopped state. 
     According to a second aspect, in the head device related to the first aspect, the head control unit may continue the non-jetting driving operation for a non-target nozzle with which the wiping member is not in contact. 
     According to the second aspect, the non-jetting driving operation for the non-target nozzle is performed. Accordingly, liquid is restrained from being dried in the non-target nozzle. 
     According to a third aspect, in the head device related to the first aspect, the ink jet head may include a plurality of head modules and have a structure in which the plurality of head modules are connected to each other and the head control unit may stop the non-jetting driving operation for a wiping target head module, to which the wiping target nozzle belongs, in a case where the wiping process is to be performed. 
     According to the third aspect, control of the non-jetting driving operation in accordance with the wiping process can be performed for each head module. 
     According to a fourth aspect, in the head device related to the third aspect, the head control unit may continue the non-jetting driving operation for a non-target head module other than the wiping target head module. 
     According to the fourth aspect, the non-jetting driving operation for the non-target head module is performed. Accordingly, liquid is restrained from being dried in a nozzle belonging to the non-target head module. 
     According to a fifth aspect, in the head device related to the third aspect, the head control unit may stop the non-jetting driving operation for the wiping target head module before a timing at which the wiping member starts to come into contact with the wiping target head module. 
     According to the fifth aspect, contact between the wiping member and ink in the nozzle can be suppressed more effectively. 
     Two adjacent head modules may be wiping target head modules. During the wiping process with respect to the wiping target head module for which the wiping process is performed first, the non-jetting driving operation for the wiping target head module for which the wiping process is performed later may be stopped. In other words, the non-jetting driving operation for the wiping target head module to be wiped next may be stopped at any timing at which the wiping member comes into contact with the wiping target head module to be wiped first. 
     According to a sixth aspect, in the head device related to the fifth aspect, the head control unit may stop the non-jetting driving operation for the wiping target head module at least 0.2 seconds before the timing at which the wiping member starts to come into contact with the wiping target head module. 
     According to the sixth aspect, it is possible to reliably stop the non-jetting driving operation for the wiping target head module before the wiping member comes into contact with the nozzle surface of the wiping target head module. 
     According to a seventh aspect, in the head device related to any one of the fourth to sixth aspects, the head control unit may perform the non-jetting driving operation for the wiping target head module after a timing at which contact between the wiping member and the wiping target head module ends. 
     According to the seventh aspect, contact between the wiping member and ink is reliably suppressed and liquid is restrained from being dried in a nozzle belonging to a head module for which the wiping process is finished. 
     According to an eighth aspect, in the head device related to the seventh aspect, the head control unit may perform the non-jetting driving operation for the wiping target head module at least 0.2 seconds after the timing at which the contact between the wiping member and the wiping target head module ends. 
     According to the eighth aspect, contact between the wiping member and the ink is more reliably suppressed and liquid is more reliably restrained from being dried in a nozzle belonging to the head module for which the wiping process is finished. 
     According to a ninth aspect, in the head device related to any one of the first to seventh aspects, a negative pressure setting unit that sets the negative pressure may set the negative pressure in a case of the wiping process to fall within such a range that the liquid is not drawn out from the nozzle in a case where the non-jetting driving operation is stopped. 
     According to the ninth aspect, liquid is more reliably restrained from being drawn out from the wiping target nozzle to the nozzle surface. 
     According to a tenth aspect, in the head device related to the ninth aspect, the negative pressure setting unit may set the negative pressure in the case of the wiping process to −5000 kilopascals or more and −500 kilopascals or less. 
     According to the tenth aspect, contact between the wiping member and ink in a nozzle is more reliably suppressed. 
     According to an eleventh aspect, in the head device related to any one of the first to tenth aspects, at least one of liquid containing carbon black or liquid containing titanium oxide may be used for the ink jet head. 
     According to the eleventh aspect, wear of the liquid-repellent film can be suppressed in the ink jet head to which liquid containing a particle that easily scrapes the liquid-repellent film is applied. 
     An example of the liquid containing carbon black is black ink. An example of the liquid containing titanium oxide is white ink. 
     According to a twelfth aspect, there is provided a liquid jetting apparatus including an ink jet head in which a liquid-repellent film is formed on a nozzle surface, a head control unit that controls the ink jet head, and a wiping processing unit that performs a wiping process with respect to the nozzle surface. The head control unit applies a negative pressure to liquid in a nozzle, performs a non-jetting driving operation of causing the liquid in the nozzle to vibrate without being jetted, and stops the non-jetting driving operation for a wiping target nozzle with which a wiping member to be used in the wiping process comes into contact in a case where the wiping process with respect to the nozzle surface is to be performed by the wiping processing unit. 
     According to the twelfth aspect, the same effect as the effect of the first aspect can be achieved. 
     In the twelfth aspect, the same items as items specified in the second to eleventh aspects can be appropriately combined. In that case, components for processing or functions specified in the head device can be grasped as components of the liquid jetting apparatus for processing and functions corresponding thereto. 
     According to a thirteenth aspect, there is provided a head maintenance method of performing a wiping process with respect to a nozzle surface of an ink jet head in which a liquid-repellent film is formed on the nozzle surface, the method including a negative pressure applying step of applying a negative pressure to liquid in a nozzle and a non-jetting driving step of performing a non-jetting driving operation of causing the liquid in the nozzle to vibrate without being jetted. In the non-jetting driving step, the non-jetting driving operation is stopped for a wiping target nozzle with which a wiping member to be used in the wiping process comes into contact. 
     According to the thirteenth aspect, the same effect as the effect of the first aspect can be achieved. 
     In the thirteenth aspect, the same items as items specified in the second to eleventh aspects can be appropriately combined. In that case, components for processing or functions specified in the head device can be grasped as components of the head maintenance method for processing and functions corresponding thereto. 
     According to the aspects of the present invention, the non-jetting driving operation for the wiping target nozzle is stopped. Accordingly, the liquid is restrained from being drawn out from the nozzle in contact with the wiping member to the nozzle surface and thus wear of the liquid-repellent film formed on the nozzle surface and a decrease in performance of the ink jet head can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a head maintenance method according to an embodiment. 
         FIG. 2  is a schematic view of a modification example of the head maintenance method shown in  FIG. 1 . 
         FIG. 3  is a schematic diagram showing a tickling operation stoppage timing. 
         FIG. 4  is a schematic diagram showing a specific example of stoppage of the tickling operation. 
         FIG. 5  is a perspective view showing a configuration example of an ink jet head. 
         FIG. 6  is a plan view showing an example of the arrangement of nozzles of the ink jet head shown in  FIG. 5 . 
         FIG. 7  is a vertical cross-sectional view showing a three-dimensional structure of an ejector of the ink jet head shown in  FIG. 5 . 
         FIG. 8  is a block diagram showing a configuration example of an ink supply unit. 
         FIG. 9  is a front view of an ink jet printing apparatus. 
         FIG. 10  is a top view of the ink jet printing apparatus shown in  FIG. 9 . 
         FIG. 11  is a functional block diagram of the ink jet printing apparatus. 
         FIG. 12  is a flowchart showing the procedure for the head maintenance method according to the embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferable embodiments of the present invention will be described in detail with reference to the attached drawings. In the present specification, the same components will be given the same reference numerals and repetitive description thereof will be appropriately omitted. 
     [Head Maintenance Method] 
       FIG. 1  is a schematic view of a head maintenance method according to an embodiment. Head maintenance shown in  FIG. 1  is a wiping process of wiping nozzle surfaces  10 A of an ink jet head  10 . A liquid-repellent film  10 B is formed on each nozzle surface  10 A. 
     The ink jet head  10  has a structure in which a plurality of head modules  12  are connected to each other in a row along a longitudinal direction. The longitudinal direction of the ink jet head  10  is a direction parallel to a head movement direction shown in  FIG. 1 . 
     Here, the term “parallelism” in the present specification may also mean a state where two directions that intersect each other in the strict sense are substantially parallel to each other such that the same effect as a state of being parallel to each other is achieved. The same applies to the expression “being orthogonal to each other” and the expression “being orthogonal to each other” may also mean being substantially orthogonal to each other. Note that the number of head modules  12  shown in  FIG. 1  may be any number and the number of head modules  12  is not limited to that shown in  FIG. 1 . 
     A wiping device  20  brings a web sheet  22  caused to travel into contact with the nozzle surfaces  10 A of the ink jet head  10  to wipe the nozzle surfaces  10 A. The wiping device  20  includes a pressing roller  24  and a biasing unit  26 . 
     The wiping device  20  includes a storage unit that stores the web sheet  22  in a roll shape. The wiping device  20  includes a recovery unit that winds up and recovers the web sheet  22  that has been used. Note that the storage unit and the recovery unit are not shown. 
     The pressing roller  24  supports the web sheet  22  in a case where the web sheet  22  is brought into contact with the nozzle surface  10 A. The pressing roller  24  is driven to rotate in accordance with travel of the web sheet  22 . An arrow shown in  FIG. 1  shows a rotation direction of the pressing roller  24 . A traveling direction of the web sheet  22  that is in contact with the pressing roller  24  coincides with the rotation direction of the pressing roller  24 . 
     The biasing unit  26  applies, to the pressing roller  24 , a force toward the nozzle surfaces  10 A to bias the web sheet  22  toward the nozzle surfaces  10 A. An elastic member such as a spring may be applied to the biasing unit  26 . 
     In the head maintenance method shown in  FIG. 1 , the ink jet head  10  is moved in the head movement direction and the web sheet  22  of the wiping device  20 , of which the position is fixed, is caused to travel. At the position of the nozzle surfaces  10 A, the traveling direction of the web sheet  22  is opposite to a movement direction of the ink jet head  10 . Therefore, cleaning effectiveness with respect to the nozzle surfaces  10 A can be improved. 
     In the ink jet head  10 , a tickling operation is performed in a case where printing is not performed as in a maintenance process. Accordingly, ink in a nozzle is restrained from being dried in a case where printing is not performed. Note that no nozzle is shown in  FIG. 1 . Nozzles are given a reference numeral  122  and are shown in  FIG. 7 . 
     The tickling operation is a process of vibrating ink in a nozzle without the ink jetted from the nozzle. The expression “the jetting of ink” means a state where ink, of which the volume falls in a prescribed range, is split from the ink in the nozzle and is discharged from the nozzle in the form of a liquid droplet. The tickling operation may be realized by applying a drive voltage, which is lower than a drive voltage in the case of the jetting of ink, to pressure generating elements corresponding to respective nozzles. Note that the tickling operation in the embodiment corresponds to an example of a non-jetting driving operation. 
     The expression “the jetting of ink” may also mean causing ink mists, each of which has a volume lower than the prescribed range, to be discharged from the nozzles such that the plurality of ink mists are combined outside the nozzles and an ink droplet of which the volume falls in the prescribed range is formed. 
     Regarding a wiping target head module  12 A which is the target of the wiping process with respect to the nozzle surface  10 A, the tickling operation is stopped for all nozzles of the wiping target head module  12 A. For the head modules  12  other than the wiping target head module  12 A, performance of the tickling operation is continued. For the head module  12  after being subjected to the wiping process with respect to the nozzle surface  10 A, performance of the tickling operation is restarted. 
     Regarding the ink jet head  10 , the wiping process with respect to the nozzle surfaces  10 A is performed in order from the head module  12  that is positioned at a downstream end in the head movement direction. The tickling operation is switched on and off for each head module  12 . 
     Accordingly, ink is restrained from being drawn out from a nozzle of the wiping target head module  12 A to a nozzle surface and thus wear of the liquid-repellent film  10 B that is caused by contact between a pigment contained in the ink and the liquid-repellent film  10 B may be suppressed. 
     Particularly, black ink containing carbon black and white ink containing titanium oxide may accelerate wear of the liquid-repellent film  10 B in comparison with ink containing other pigments. The head maintenance method in the present embodiment is suitable for the ink jet head  10  to which black ink containing carbon black is applied and the ink jet head  10  to which white ink containing titanium oxide is applied. 
     Note that, a nozzle belonging to the wiping target head module  12 A in the embodiment corresponds to an example of a wiping target nozzle. The head module  12  other than the wiping target head module  12 A in the embodiment corresponds to an example of a non-target head module other than a wiping target head module. A nozzle belonging to the head module  12  other than the wiping target head module  12 A in the embodiment corresponds to an example of a non-target nozzle with which a wiping member is not in contact. 
       FIG. 2  is a schematic view of a modification example of the head maintenance method shown in  FIG. 1 . As shown in  FIG. 2 , a nozzle for which the tickling operation is not stopped may be set for the wiping target head module  12 A. In a tickling continuation region  12 B shown in  FIG. 2 , a nozzle for which the tickling operation is not stopped is disposed. For a nozzle belonging to the tickling continuation region  12 B, the tickling operation is continued without being stopped. 
     The tickling continuation region  12 B may be defined in accordance with the position of the wiping device  20  at the wiping target head module  12 A, which is derived based on the moving speed of the ink jet head  10  and a timing at which the wiping of the wiping target head module  12 A is started. Here, the term “speed” may also mean a speed indicating the absolute value of a speed. Note that a nozzle belonging to the tickling continuation region  12 B in the embodiment corresponds to an example of a non-target nozzle with which the wiping member is not in contact. 
       FIG. 3  is a schematic diagram showing a tickling operation stoppage timing.  FIG. 3  shows that transition of performance or stoppage of the tickling operation is made in order of a timing t 11 , a timing t 12 , a timing t 13 , and a timing t 14  in chronological order. 
     “ON” of the head module  12  denotes performance of the tickling operation. “OFF” denotes stoppage of the tickling operation. Note that a quadrangular shape with a reference numeral “ 22 A” denotes a web sheet contact region. The web sheet contact region  22 A is a region where the web sheet  22  comes into contact with the nozzle surface  10 A. 
     Regarding the ink jet head  10  shown in  FIG. 3 , the planar shape of each head module  12  is a parallelogram and a boundary line between the head modules  12  adjacent to each other is inclined with respect to a wiping direction. Note that the wiping direction has the same meaning as the movement direction of the ink jet head  10 . 
     For each head module  12 , the tickling operation is stopped before the web sheet  22  starts to pass by the head module  12 . At the timing t 11 , the tickling operation for the wiping target head module  12 A is stopped and the tickling operation for a non-wiping target head module  12 C to be wiped next to the wiping target head module  12 A is stopped. 
     That is, for the non-wiping target head module  12 C to be wiped next to the wiping target head module  12 A, the tickling operation is stopped during a wiping process for the wiping target head module  12 A to be wiped before the wiping of the non-wiping target head module  12 C. 
     In other words, the tickling operation for the non-wiping target head module  12 C to be wiped next may be stopped at any timing at which the web sheet  22  is in contact with the wiping target head module  12 A. 
     At the timing t 12  and the timing t 13 , the web sheet  22  comes into contact with two wiping target head modules  12 A adjacent to each other in accordance with movement of the ink jet head  10 . The non-wiping target head module  12 C, which is a target to be wiped next at the timing t 11 , is the wiping target head module  12 A at the timing t 12  and the timing t 13 . In other words, at the timing t 12  and the timing t 13 , two adjacent head modules  12  are the wiping target head modules  12 A. 
     At the timing t 14 , the tickling operation for the wiping target head module  12 A that is positioned on an upstream side in the head movement direction and is one of the two wiping target head modules  12 A adjacent to each other at the timing t 12  and the timing t 13  is restarted. 
     At the timing t 14 , after the web sheet  22  completely passes by the wiping target head module  12 A, the tickling operation for the head module  12  that is not a target to be wiped and is the wiping target head module  12 A at an earlier time is restarted. In this manner, it is possible to reliably avoid contact between the web sheet  22  and ink in the nozzles throughout the wiping process with respect to the nozzle surfaces  10 A. 
       FIG. 4  is a schematic diagram showing a specific example of stoppage of the tickling operation. The drawing shows stoppage and restart of the tickling operation in any module in chronological order. A timing t 21  is a timing that is at least 0.2 seconds before a contact start timing t s . The contact start timing t s  is a timing at which contact between the wiping target head module  12 A and the web sheet  22  is started. 
     A timing t 22  is a timing that is 0.2 seconds before the contact start timing t s . Before the timing t 22 , the tickling operation for the wiping target head module  12 A is stopped. That is, the tickling operation for the wiping target head module  12 A is stopped at least 0.2 seconds before the contact start timing t s . 
     A timing t 23  is the contact start timing t s . A timing t 24  is a contact end timing t e . A timing t 2  is a timing that is 0.2 seconds after the contact end timing t e . At the timing t 25 , stoppage of the tickling operation for the wiping target head module  12 A is maintained. 
     A timing t 26  is any timing that is at least 0.2 seconds after the contact end timing t e . For the head module  12  that is the wiping target head module  12 A at an earlier time, the tickling operation is restarted at any timing that is at least 0.2 seconds after the contact end timing t e . 
     That is, for each head module  12 , the tickling operation is stopped before a timing that is 0.2 seconds before the contact start timing t s , at which contact between the web sheet  22  and the head module  12  is started, and is restarted after a timing that is 0.2 seconds after the contact end timing t e , at which contact between the web sheet  22  and the head module  12  ends. 
     A wiping process period for one head module  12  may be set to any period between 1.0 second and 5.0 seconds. A period preceding a tickling operation end timing with respect to the contact start timing t s  may be set to any period between 4.0% and 20% of the wiping process period for one head module  12 . The same applies to a tickling operation restart delay period with respect to the contact end timing t e . 
     [Internal Pressure Control of Ink Jet Head] 
     A negative pressure is applied to ink inside the ink jet head  10  in the present embodiment. A negative pressure in the case of the wiping process for the nozzle surfaces  10 A is set within such a range that no ink is drawn out from a nozzle to a nozzle surface in a case where the tickling operation is stopped. Examples of the negative pressure in the case of the wiping process for the nozzle surfaces  10 A include a range of equal to or larger than −5000 kilopascals and equal to or smaller than −500 kilopascals. 
     The negative pressure in the case of the wiping process for the nozzle surfaces  10 A may be increased relative to a negative pressure in the case of printing and may coincide with the negative pressure in the case of printing. The expression “to increase the negative pressure” means “to increase the absolute value of the negative pressure” and has the same meaning as “to decrease a pressure”. 
     [Effect] 
     According to the head maintenance method in the embodiment, the following effects can be achieved. 
     [1] 
     In a case where the ink jet head  10  in which the liquid-repellent films  10 B are formed on the nozzle surfaces  10 A is wiped, the tickling operation is stopped for a nozzle with which the web sheet  22  comes into contact. Accordingly, ink is restrained from being drawn out from the nozzle to a nozzle surface due to contact between the nozzle and the web sheet  22  in a case where the nozzle surfaces  10 A are wiped and thus wear of the liquid-repellent films  10 B is suppressed. 
     [2] 
     The tickling operation is continued for nozzles that are not in contact with the web sheet  22 . Accordingly, ink in the nozzles that are not in contact with the web sheet  22  is restrained from being dried. 
     [3] 
     In the ink jet head including the plurality of head modules, the tickling operation is stopped for all of nozzles of the wiping target head module  12 A. Accordingly, ink is restrained from being drawn out from the nozzles of the wiping target head module  12 A to a nozzle surface due to contact between the web sheet  22  and the nozzles. 
     [4] 
     For the head module  12  that is not a wiping process target, the tickling operation is continued. Accordingly, ink in nozzles of the head module  12  not to be wiped is restrained from being dried. 
     [5] 
     For the head module  12  that is a target to be wiped next to the wiping target head module  12 A, the tickling operation is stopped before the web sheet  22  comes into contact with the head module  12 . Accordingly, it is possible to more effectively restrain ink from being drawn out from nozzles to the nozzle surface  10 A due to contact between the web sheet  22  and the ink in the nozzles. 
     [6] 
     For the wiping target head module  12 A, the tickling operation is restarted at any timing after a timing at which the web sheet  22  has passed by the wiping target head module  12 A. Accordingly, ink in nozzles of the wiping target head module  12 A is restrained from being dried after the end of a wiping process with respect to the nozzle surface  10 A. 
     [7] 
     For the wiping target head module  12 A, the tickling operation is stopped before a timing that is 0.2 seconds before a timing at which the web sheet  22  comes into contact with the wiping target head module  12 A and is restarted after a timing that is 0.2 seconds after a timing at which the state of the web sheet  22  changes from a state of being in contact with the wiping target head module  12 A to a state of not being in contact with the wiping target head module  12 A. Accordingly, the tickling operation for the wiping target head module  12 A can be stopped before the web sheet  22  comes into contact with the nozzle surface  10 A of the wiping target head module  12 A. 
     [8] 
     For the wiping target head module  12 A, a negative pressure is set within such a range that no ink is drawn out from nozzles to a nozzle surface in the case of the wiping process with respect to the nozzle surface  10 A. Accordingly, ink can be restrained from leaking or being erroneously jetted from the nozzles. 
     [9] 
     White ink containing titanium oxide as a pigment and black ink containing carbon black as a pigment are applied. Accordingly, in a case where a possibility that wear of the liquid-repellent films  10 B is accelerated is high, the wear of the liquid-repellent films  10 B can be suppressed. 
     [Configuration Example of Ink Jet Head] 
       FIG. 5  is a perspective view showing a configuration example of an ink jet head. The ink jet head  10  shown in the drawing has a structure in which the plurality of head modules  12  are connected to each other in a row along the longitudinal direction of the ink jet head  10 . The plurality of head modules  12  are integrated and supported by means of a head frame  100 . 
     The ink jet head  10  is a line head in which a plurality of nozzles are arranged in a paper width direction over a length corresponding to the total length of paper. Note that no nozzle is shown in  FIG. 5 . Nozzles are given a reference numeral  122  and are shown in  FIG. 6 . The paper width direction is a direction orthogonal to a paper transportation direction in a printing apparatus. 
     The planar shape of the nozzle surface  10 A of the head module  12  is a parallelogram. Dummy plates  102  are attached to both ends of the head frame  100 . The planar shape of the nozzle surfaces  10 A of the ink jet head  10  including the head modules  12  and the dummy plates  102  is rectangular as a whole. 
     A flexible substrate  104  is attached to the head module  12 . The flexible substrate  104  is a wiring member that transmits a drive voltage supplied to the head module  12 . One end of the flexible substrate  104  is electrically connected to the head module  12  and the other end thereof is electrically connected to a drive voltage supply circuit. Note that the drive voltage supply circuit is not shown. 
       FIG. 6  is a plan view showing an example of the arrangement of nozzles of the ink jet head shown in  FIG. 5 . A central portion of the nozzle surface  10 A of the head module  12  includes a belt-shaped nozzle arrangement portion  120 . The nozzle arrangement portion  120  functions substantially as the nozzle surface  10 A. 
     A plurality of nozzles  122  are arranged at the nozzle arrangement portion  120 . Each of the nozzles  122  includes a nozzle opening  124  formed in the nozzle surface  10 A. A structure example of the nozzle  122  will be described later. In the following description, “the arrangement of the nozzles  122 ” may be replaced with “the arrangement of the nozzle openings  124 ”. 
     The planar shape of the head module  12  shown in  FIG. 6  is a parallelogram including end surfaces that are close to long sides extending along a direction V that is inclined with respect to the paper width direction denoted by a reference numeral “X” at an angle β and end surfaces that are close to short sides extending along a direction W that is inclined with respect to the paper transportation direction denoted by a reference numeral “Y” at an angle α. 
     In the head module  12 , the plurality of nozzles  122  are arranged in a matrix shape in a row direction along the direction V and a column direction along the direction W. The nozzles  122  may be arranged along a row direction along the paper width direction and a column direction diagonally intersecting the paper width direction. 
     In the case of the ink jet head  10  in which the plurality of nozzles  122  are arranged in a matrix shape, a projection nozzle row obtained by projecting each nozzle  122  in the matrix arrangement along a nozzle row direction can be considered to be equivalent to one nozzle row in which the nozzles  122  are arranged at approximately equal intervals at a density at which the maximum recording resolution in the nozzle row direction is achieved. The projection nozzle row is a nozzle row obtained by orthographically projecting each nozzle  122  in the matrix arrangement along the nozzle row direction. 
     The expression “approximately equal intervals” means substantially equal intervals as jetting points recordable in the printing apparatus. For example, the concept of “equal intervals” also includes a case where an interval or the like that is made slightly different in consideration of at least one of a manufacturing error or movement of liquid droplets on a substrate attributable to landing interference is included. The projection nozzle row corresponds to a substantial nozzle row. In consideration of the projection nozzle row, each nozzle  122  can be associated with a nozzle number denoting a nozzle position in an order in which projection nozzles are arranged along the nozzle row direction. 
     In the present embodiment, the line-type ink jet head  10  has been described as an example. However, application to a serial-type ink jet head is also possible. 
       FIG. 7  is a vertical cross-sectional view showing a three-dimensional structure of an ejector of the ink jet head shown in  FIG. 5 . An ejector  130  includes the nozzle  122 , a pressure chamber  132  leading to the nozzle  122 , and a piezoelectric element  134 . The nozzle opening  124  communicates with the pressure chamber  132  via a nozzle flow path  136 . The pressure chamber  132  communicates with a common tributary flow path  140  via an individual supply path  138 . 
     A vibration plate  142  constituting a top surface of the pressure chamber  132  includes a conductive layer that corresponds to a lower electrode of the piezoelectric element  134  and functions as a common electrode. Note that the conductive layer is not shown. The pressure chamber  132 , a wall portion of another flow path portion, the vibration plate  142 , and the like can be made of silicon. 
     The material of the vibration plate  142  is not limited to silicon and the vibration plate  142  can be formed of a non-conductive material such as resin. The vibration plate  142  itself may be made of a metal material such as stainless steel to be a vibration plate serving as a common electrode also. 
     A piezoelectric unimorph actuator is composed of a structure in which the piezoelectric element  134  is laminated on the vibration plate  142 . A drive voltage is applied to an individual electrode  144 , which is an upper electrode of the piezoelectric element  134 , so that a piezoelectric body  146  is deformed and the volume of the pressure chamber  132  is changed with the vibration plate  142  being bent. A change in pressure accompanied by a change in volume of the pressure chamber  132  acts on ink, so that the ink is jetted from the nozzle opening  124 . 
     In a case where the piezoelectric element  134  returns to an original state after the ink is jetted, the pressure chamber  132  is filled with new ink from the common tributary flow path  140  through the individual supply path  138 . An operation of filling the pressure chamber  132  with ink is called a refilling operation. 
     The shape of the pressure chamber  132  as seen in plan view is not particularly limited and may be various shapes such as a quadrangular shape, other polygonal shapes, a circular shape, and an elliptical shape. A cover plate  148  shown in  FIG. 7  is a member that maintains a movable space  150  of the piezoelectric element  134  and seals the periphery of the piezoelectric element  134 . 
     A supply side ink chamber and a recovery side ink chamber are formed above the cover plate  148 . The supply side ink chamber is connected to a supply side common main flow path via a communication path. The recovery side ink chamber is connected to a recovery side common main flow path via the communication path. 
     Note that the supply side ink chamber, the recovery side ink chamber, the communication path, the supply side common main flow path, and the recovery side common main flow path are not shown. The ejector shown in  FIG. 7  has the same meaning as a jetting element, a printing element, and the like. 
     [Ink Supply Unit] 
       FIG. 8  is a block diagram showing a configuration example of an ink supply unit. An ink supply unit  200  shown in the drawing supplies ink to each head module  12  and circulates ink for each head module  12 . 
     Each head module  12  is connected to a supply manifold  230  via a supply individual flow path  210 . The supply individual flow path  210  includes a supply flow path damper  212  and a supply flow path valve  214 . Note that, in  FIG. 8 , only a part of the supply individual flow path  210  and the like is given a reference numeral. 
     The supply flow path damper  212  suppresses pulsation of ink passing through the supply individual flow path  210 . The supply flow path valve  214  performs the supplying and blocking of ink passing through the supply individual flow path  210  in accordance with a command signal transmitted from a control unit. 
     Each head module  12  is connected to a circulation manifold  232  via a circulation individual flow path  220 . The circulation individual flow path  220  includes a circulation flow path damper  222  and a circulation flow path valve  224 . 
     The circulation flow path damper  222  suppresses pulsation of ink passing through the circulation individual flow path  220 . The circulation flow path valve  224  performs the supplying and blocking of ink passing through the circulation individual flow path  220  in accordance with a command signal transmitted from the control unit. 
     The supply manifold  230  is a primary storage flow path for ink supplied from an ink tank  240 . The circulation manifold  232  is a primary storage flow path for ink through which ink is circulated from the ink jet head  10  to the ink tank  240 . 
     The supply manifold  230  and the circulation manifold  232  communicate with each other via a first bypass flow path  242  and a second bypass flow path  250 . The first bypass flow path  242  includes a first valve  244 . The second bypass flow path  250  includes a second valve  252  and a damper  254 . 
     The supply manifold  230  includes a supply pressure sensor  234 . The circulation manifold  232  includes a circulation pressure sensor  236 . A head control unit that controls the ink jet head  10  operates a supply pump  260  and a circulation pump  262  based on the result of pressure detection of the supply pressure sensor  234  and the circulation pressure sensor  236  and internal pressure settings of the ink jet head  10  to control the internal pressure of the ink jet head  10 . Note that the internal pressure of the ink jet head  10  includes the negative pressure described above. 
     [Specific Example of Liquid-Repellent Film] 
     As the liquid-repellent film  10 B of the nozzle surface  10 A shown in  FIG. 1 , a liquid-repellent film containing a linear fluorine-containing silane coupling agent can be applied. The liquid-repellent film can be produced by using silicon as the material of a nozzle plate, forming a first organic film while using a silicon compound, which is a silicon compound containing no fluorine atom and is represented by Expression 1 or Expression 2, as a raw material, forming an inorganic oxide film on the first organic film, and forming a second organic film on the inorganic oxide film while using a linear fluorine-containing silane coupling agent as a raw material. The second organic film is liquid-repellent against ink. 
       X 3 - n R 2   n Si—R 1 —Z  Expression 1
 
     However, in Expression 1, n=0, 1, or 2. 
       HN(SiR 3 R 4 R 5 ) 2   Expression 2
 
     X in Expression 1 is any of halogen excluding fluorine, a methoxy group, an ethoxy group, an acetoxy group, or a 2-methoxyethoxy group, and R 2  is an alkyl group having 1 to 3 carbon atoms. 
     R 1  is C m H 2m , where m is a natural number of 1 to 20. Z is a group containing any of a methyl group, a vinyl group, an amino group, an epoxy group, a methacrylic group, an acryloyl group, a mercapto group, an isocyanate group, an acylthio group, or a ureide group. R 3 , R 4 , and R 5  in Expression 2 are alkyl groups having 1 to 3 carbon atoms. 
     The silicon compound has a boiling point that is equal to or higher than 20° C. and equal to or lower than 350° C. The linear fluorine-containing silane coupling agent is a compound represented by Expression 3. 
       X 3 - n R 7   n Si—R 6 —Z  Expression 3
 
     However, in Expression 3, n=0, 1, or 2. 
     In Expression 3, X is any of halogen, a methoxy group, an ethoxy group, an acetoxy group, or a 2-methoxyethoxy group, R 7  is an alkyl group having 1 to 3 carbon atoms, and R 6  is a C p H 2p  group where p is a natural number of 1 to 20 or a group containing a linear fluorocarbon chain and C q H 2q  where q is a natural number of 1 to 20. Z is a group containing any of a methyl group, a vinyl group, an amino group, an epoxy group, a methacrylic group, an acryloyl group, a mercapto group, an isocyanate group, an acylthio group, a ureide group, or a trifluoromethyl group. 
     A self-assembled monolayer may be applied to at least one of the first organic film or the second organic film. In a step of forming the first organic film, the first organic film can be formed by applying a vapor phase method. As the inorganic oxide film, a silicon oxide film may be applied. 
     In a step of forming the inorganic oxide film, the inorganic oxide film can be formed by applying the vapor phase method. In a step of forming the second organic film, the second organic film can be formed by applying the vapor phase method. 
     The thickness of the first organic film and the thickness of the second organic film may be equal to or larger than 0.5 nanometers and equal to or smaller than 30 nanometers. The thickness of the first organic film and the thickness of the second organic film are preferably equal to or larger than 0.5 nanometers and equal to or smaller than 10 nanometers. The thickness of the first organic film and the thickness of the second organic film are more preferably equal to or larger than 0.5 nanometers and equal to or smaller than 5 nanometers. 
     As the thickness of the liquid-repellent film  10 B, the thickness of the second organic film liquid-repellent against ink can be applied. The thickness of the liquid-repellent film  10 B may be a thickness obtained by adding the thickness of the first organic film to the thickness of the second organic film. That is, the thickness of the liquid-repellent film  10 B may be equal to or larger than 5 nanometers and equal to or smaller than 60 nanometers. 
     [Configuration Example of Ink Jet Printing Apparatus] 
     Next, a liquid jetting apparatus to which the head maintenance method according to the embodiment is applied will be described. In the following description, an ink jet printing apparatus will be described as the liquid jetting apparatus. 
     [Overall Configuration of Ink Jet Printing Apparatus] 
       FIG. 9  is a front view of an ink jet printing apparatus.  FIG. 10  is a top view of the ink jet printing apparatus shown in  FIG. 9 . An ink jet printing apparatus  300  includes a paper transportation unit  302 , a printing unit  304 , and a maintenance unit  306 . The paper transportation unit  302  includes a printing drum  310 . The ink jet printing apparatus  300  includes a paper feeding unit and a paper discharging unit. The paper feeding unit supplies paper to be used for printing to the paper transportation unit  302 . The paper discharging unit accumulates paper on which printing has been performed. Note that the paper feeding unit and the paper discharging unit are not shown. 
     Regarding the printing drum  310 , a plurality of adsorption holes are formed in a paper supporting region on which paper is supported. The plurality of adsorption holes are connected to a suction pump via gas flow paths. A rotary supporting shaft  312  of the printing drum  310  is connected to a rotary shaft of a motor via a connection member. 
     In the ink jet printing apparatus  300 , the rotary shaft of the motor is rotated in a prescribed rotation direction based on a control signal so that the printing drum  310  is rotated in a prescribed rotation direction and paper supported on the paper supporting region of the printing drum  310  is transported along a prescribed transport path. Note that in  FIGS. 9 and 10 , the paper supporting region, the adsorption holes, the gas flow paths, the suction pump, and the connection member are not shown. 
     The printing unit  304  performs printing on paper transported by means of the paper transportation unit  302 . The printing unit  304  includes ink jet heads that jet cyan ink, magenta ink, yellow ink, and black ink, respectively. 
     An ink jet head  10 C shown in  FIG. 10  jets cyan ink. An ink jet head  10 M jets magenta ink. An ink jet head  10 Y jets yellow ink. An ink jet head  10 K jets black ink. 
     In the following description, a term “the ink jet head  10 ” will be used as a generic term indicating the ink jet head  10 C and the like or a term indicating any one of the ink jet head  10 C and the like in a case where the ink jet head  10 C and the like do not need to be distinguished from each other. 
     A drop-on-demand method is applied to the ink jet head  10 . Regarding the ink jet head  10 , the jetting of ink is controlled based on a jetting drive voltage supplied from a printing control unit shown in  FIG. 11 . In addition, regarding the ink jet head  10 , the tickling operation is controlled based on a drive voltage for the tickling operation which is supplied from the printing control unit. 
     The maintenance unit  306  includes a head moving mechanism  320 , a wiping unit  322 , and a cap unit  324 . The head moving mechanism  320  collectively moves the ink jet head  10 C and the like. 
     The head moving mechanism  320  includes a horizontal moving mechanism  330 . The horizontal moving mechanism  330  includes guide rails  332 , a ball screw  334 , a nut  336 , a motor  338 , and a pair of frames  340 . The head moving mechanism  320  includes a raising and lowering mechanism. The raising and lowering mechanism collectively raises and lowers the ink jet head  10 C and the like. The raising and lowering mechanism is not shown. 
     The horizontal moving mechanism  330  causes the ink jet head  10 C and the like to reciprocate between a printing position and a capping position within a plane parallel to a horizontal plane along a horizontal direction. The printing position is a position directly above the printing drum  310  and is the position of the ink jet head  10 C and the like in the case of a printing operation. The capping position is a position directly above the cap unit  324  and is the position of the ink jet head  10 C and the like in the case of a capping operation. 
     The ink jet head  10 C and the like are integrally supported by means of the frame  340 . The frame  340  is connected to the nut. The motor  338  is operated to rotate the ball screw  334 . The frame  340  connected to the nut  336  moves in the horizontal direction and the ink jet head  10 C and the like move in the horizontal direction within the plane parallel to the horizontal plane. As the motor, a control type motor of which rotation and stoppage can be controlled by means of a command signal like a stepping motor and a servomotor is applied. 
     The wiping unit  322  includes a wiping device  20 C, a wiping device  20 M, a wiping device  20 Y, and a wiping device  20 K shown in  FIG. 10 . The wiping device  20 C wipes the nozzle surfaces  10 A of the ink jet head  10 C. The wiping device  20 M, the wiping device  20 Y, and the wiping device  20 K wipe the nozzle surfaces  10 A of the ink jet head  10 M, the nozzle surfaces  10 A of the ink jet head  10   y , and the nozzle surfaces  10 A of the ink jet head  10 K, respectively. 
     The wiping device  20  shown in  FIG. 1  and the like corresponds to any one of the wiping device  20 C, the wiping device  20 M, the wiping device  20 Y, and the wiping device  20 K shown in  FIG. 10 . The wiping unit  322  in the embodiment corresponds to an example of a wiping processing unit. 
     The cap unit  324  includes a cap  360 C, a cap  360 M, a cap  360 Y, and a cap  360 K. The cap  360 C caps the ink jet head  10 C. The cap  360 M, the cap  360 Y, and the cap  360 K cap the ink jet head  10 M, the ink jet head  10 Y, and the ink jet head  10 K, respectively. 
     The frame  340  and the ink jet head  10 C and the like denoted by broken lines in  FIG. 9  show the ink jet head  10 C and the like in a state of being capped by means of the cap  360 C. 
     [Description on Functional Block of Ink Jet Printing Apparatus] 
       FIG. 11  is a functional block diagram of the ink jet printing apparatus. The ink jet printing apparatus  300  includes a system controller  400 . The system controller  400  functions as an overall control unit that collectively controls each part of the ink jet printing apparatus  300 . In addition, the system controller  400  functions as a calculation unit that performs various calculation processes. 
     The system controller  400  may execute a program to control each part of the ink jet printing apparatus  300 . Furthermore, the system controller  400  functions as a memory controller that controls the reading and writing of data in a memory such as a read only memory (ROM) and a random access memory (RAM). 
     The ink jet printing apparatus  300  includes a communication unit  402  and an image memory  404 . The communication unit  402  includes a communication interface (not shown). The communication unit  402  can transmit and receive data to and from a host computer  403  connected to the communication interface. 
     The image memory  404  functions as a temporary storage unit for various data including image data. Data is read and written from and in the image memory  404  through the system controller  400 . Image data loaded from the host computer  403  via the communication unit  402  is temporarily stored in the image memory  404 . 
     The ink jet printing apparatus  300  includes a transportation control unit  410 , a printing control unit  412 , a head movement control unit  414 , a maintenance control unit  416 , and a pressure control unit  418 . The transportation control unit  410  controls the operation of the paper transportation unit  302  in accordance with a command from the system controller  400 . 
     The printing control unit  412  controls the operation of the printing unit  304  in accordance with a command from the system controller  400 . That is, the printing control unit  412  controls the jetting of ink of the ink jet head  10  shown in  FIG. 1  and the like. 
     The printing control unit  412  includes an image processing unit. The image processing unit forms dot data based on input image data. The image processing unit includes a color separation processing unit, a color conversion processing unit, a correction processing unit, and a halftone processing unit. Note that the image processing unit, the color separation processing unit, the color conversion processing unit, the correction processing unit, and the halftone processing unit are not shown. 
     The color separation processing unit performs color separation processing on the input image data. For example, in a case where the input image data is represented by RGB, the color separation processing unit decomposes the input image data into data for each of RGB colors. Here, R represents red. G represents green. B represents blue. 
     The color conversion processing unit converts image data for each color obtained through the decomposition into red, green, and blue into cyan, magenta, yellow, and black corresponding to ink colors. 
     The correction processing unit performs correction processing on image data for each color obtained through the conversion into cyan, magenta, yellow, and black. Examples of the correction processing include gamma correction processing, density unevenness correction processing, abnormal recording element correction processing, and the like. 
     The halftone processing unit converts, for example, image data represented by a multi-gradation number such as 0 to 255 into dot data represented by a binary value or a multiple value of a ternary value or more that is less than the number of gradations of the input image data. 
     A predetermined halftone processing rule is applied to the halftone processing unit. Examples of the halftone processing rule include a dither method, an error diffusion method, and the like. The halftone processing rule may be changed depending on image recording conditions, the content of the image data, and the like. 
     The printing control unit  412  includes a waveform generation unit, a waveform storage unit, and a drive circuit which are not shown. The waveform generation unit generates the waveform of drive voltage. The waveform storage unit stores the waveform of the drive voltage. The drive circuit generates a drive voltage having a drive waveform corresponding to the dot data. The drive circuit supplies the drive voltage to the ink jet head  10 . 
     That is, a jetting timing and an ink jetting amount for each pixel position are determined based on dot data generated through processing performed by using the image processing unit. A drive voltage corresponding to the jetting timing and the ink jetting amount for each pixel position and a control signal for determining a jetting timing for each pixel are generated. The drive voltage is supplied to the ink jet head  10  and ink is jetted from the ink jet head  10 . The ink jetted from the ink jet head  10  forms dots. 
     The head movement control unit  414  operates the head moving mechanism  320  in cooperation with the maintenance control unit  416  in accordance with a command from the system controller  400 . The head movement control unit  414  may include a raising and lowering control unit that controls the raising and lowering mechanism and a horizontal movement control unit that controls the horizontal moving mechanism  330 . The head movement control unit  414  in the embodiment corresponds to an example of a component of the head control unit. 
     The maintenance control unit  416  operates the maintenance unit  306  in accordance with a command from the system controller  400 . The maintenance control unit  416  may include a wiping control unit that controls the wiping unit  322  and a cap control unit that controls the cap unit  324 . The maintenance control unit  416  may include the head movement control unit  414 . 
     The maintenance control unit  416  raises and lowers the wiping unit  322  in accordance with the position of the ink jet head  10  in a head movement path. That is, the maintenance control unit  416  raises the wiping unit  322  to a wiping processing position at which the web sheet  22  of the wiping unit  322  comes into contact with the nozzle surfaces  10 A of the ink jet head  10  in a period of time in which the ink jet head  10  passes through a wiping position of the wiping unit  322 . After the ink jet head  10  passes through the wiping position of the wiping unit  322 , the wiping unit  322  is lowered from the wiping processing position to a standby position. 
     The maintenance control unit  416  derives the position of the ink jet head  10  in the head movement path by using the moving speed of the ink jet head  10  and an elapsed period of time from the start of movement of the ink jet head  10 . 
     The maintenance control unit  416  controls the tickling operation for the ink jet head  10  in cooperation with the printing control unit  412 , in accordance with the position of the ink jet head  10  in the head movement path. 
     That is, the maintenance control unit  416  performs the tickling operation of the ink jet head  10  in cooperation with the printing control unit  412  in a case where the ink jet printing apparatus  300  is switched to a maintenance mode. 
     In the maintenance mode, the maintenance control unit  416  controls stoppage and restart of the tickling operation for each head module  12  in cooperation with the printing control unit  412 . The printing control unit  412  and the maintenance control unit  416  in the embodiment correspond to an example of components of the head control unit. 
     The pressure control unit  418  adjusts the internal pressure of the ink jet head  10  in accordance with a command transmitted from the system controller  400 . That is, the pressure control unit  418  controls the operation of a pump  420  based on the result of pressure detection that is transmitted from a pressure sensor  440 . 
     The pressure control unit  418  controls the operation of the pump  420  based on the result of pressure detection that is transmitted from the pressure sensor  440 . The pump  420  shown in  FIG. 11  corresponds to the supply pump  260  and the circulation pump  262  shown in  FIG. 9 . In addition, the pressure sensor  440  corresponds to the supply pressure sensor  234  and the circulation pressure sensor  236 . The pressure control unit  418  in the embodiment corresponds to an example of the head control unit. In addition, the pressure control unit  418  corresponds to an example of a negative pressure setting unit. 
     The ink jet printing apparatus  300  includes an operation unit  430 . The operation unit  430  includes an operation member such as an operation button, a keyboard, and a touch panel. The operation unit  430  may include a plurality of types of operation members. Note that the operation member is not shown. 
     Information input via the operation unit  430  is sent to the system controller  400 . The system controller  400  executes various processes in accordance with the information sent from the operation unit  430 . 
     The ink jet printing apparatus  300  includes a display unit  432 . The display unit  432  includes a display device such as a liquid crystal panel and a display driver. The display device and the display driver are not shown. The display unit  432  causes the display device to display various information such as various setting information and abnormality information of the apparatus in accordance with a command from the system controller  400 . 
     The ink jet printing apparatus  300  includes a parameter storage unit  434 . The parameter storage unit  434  stores various parameters used in the ink jet printing apparatus  300 . The various parameters stored in the parameter storage unit  434  are read via the system controller  400  and set for each part of the apparatus. 
     The ink jet printing apparatus  300  includes a program storage unit  436 . The program storage unit  436  stores programs used for each part of the ink jet printing apparatus  300 . The various programs stored in the program storage unit  436  are read via the system controller  400  and executed in each part of the apparatus. 
     Each control unit such as the system controller  400  and the transportation control unit  410  shown in  FIG. 11  executes a prescribed program by using hardware described below to realize the functions of the ink jet printing apparatus  300 . Various processors can be applied to the hardware of each control unit. Examples of the processors include a central processing unit (CPU) and a graphics processing unit (GPU). The CPU executes a program to function as various processing units. 
     The CPU is a general-purpose processor. The GPU is a processor specialized in image processing. As the hardware of the processors, an electric circuit in which electric circuit elements such as semiconductor elements are combined with each other is applied. Each control unit includes a ROM in which a program or the like is stored and a RAM which is a work area for various operations. 
     Two or more processors may be applied with respect to one control unit. The two or more processors may be the same types of processors or different types of processors. In addition, one processor may be applied with respect to a plurality of control units. 
     Paper applied to the ink jet printing apparatus  300  may be a sheet of paper or continuous paper. As the paper, not only a paper medium but also a resin sheet, a metal sheet, and the like can be applied. The paper transportation unit  302  of the ink jet printing apparatus  300  may perform plane transportation of paper by using a transportation belt or the like. 
     In the present embodiment, the ink jet printing apparatus  300  that prints an image on paper has been described as an example of a liquid jetting apparatus. However, the functions of the ink jet printing apparatus  300  according to the present embodiment can be realized also in a pattern forming apparatus that forms a pattern on a substrate or the like by using liquid having functionality. 
     [Procedure for Head Maintenance Method] 
       FIG. 12  is a flowchart showing the procedure for the head maintenance method according to the embodiment. In the case of a switch to the maintenance mode, the maintenance mode of the ink jet printing apparatus  300  is performed. 
     In maintenance of the ink jet head  10 , a wiping process with respect to the nozzle surfaces  10 A, a suction process performed by using the cap unit  324 , and a purging process performed by using the cap unit  324  may be performed.  FIG. 12  shows the procedure for the wiping process with respect to the nozzle surfaces  10 A in the maintenance of the ink jet head  10 . 
     The wiping process with respect to the nozzle surfaces  10 A of the ink jet head  10  is started. In a maintenance negative pressure setting step S 10 , the maintenance control unit  416  shown in  FIG. 11  sets a negative pressure corresponding to the wiping process with respect to the nozzle surfaces  10 A in cooperation with the pressure control unit  418 . After the maintenance negative pressure setting step S 10 , the process proceeds to a tickling operation start step S 12 . Note that the maintenance negative pressure setting step S 10  in the embodiment corresponds to an example of the negative pressure applying step. 
     In the tickling operation start step S 12 , the maintenance control unit  416  starts the tickling operation for all of the head modules  12  in cooperation with the printing control unit  412 . After the tickling operation start step S 12 , the process proceeds to a wiping target determination step S 14 . The tickling operation start step S 12  described in the embodiment corresponds to an example of a non-jetting driving step. 
     In the wiping target determination step S 14 , the maintenance control unit  416  determines, for each of all of the head modules  12  provided in the ink jet head  10 , whether or not the head module  12  is the wiping target head module  12 A, in a prescribed order. 
     In the wiping target determination step S 14 , the result of the determination is No in a case where the maintenance control unit  416  determines that the head module  12  that is the target of the determination is not the wiping target head module  12 A. In a case where the result of the determination is No, the wiping target determination step S 14  is repeated until the result of the determination in the wiping target determination step S 14  becomes Yes. 
     Meanwhile, in the wiping target determination step S 14 , the result of the determination is Yes in a case where the maintenance control unit  416  determines that the head module  12  that is the target of the determination is the wiping target head module  12 A. In a case where the result of the determination is Yes, the process proceeds to a tickling operation stoppage step S 16 . 
     In the tickling operation stoppage step S 16 , the maintenance control unit  416  stops the tickling operation for the wiping target head module  12 A in cooperation with the printing control unit  412 . After the tickling operation stoppage step S 16 , the process proceeds to a wiping step S 18 . The tickling operation stoppage step S 16  described in the embodiment corresponds to an example of the non-jetting driving step. 
     In the wiping step S 18 , the maintenance control unit  416  performs a wiping process with respect to the nozzle surface  10 A of the wiping target head module  12 A. After the wiping step S 18 , the process proceeds to a wiping end determination step S 20 . In the wiping end determination step S 20 , the maintenance control unit  416  determines whether or not the wiping process with respect to the wiping target head module  12 A is finished. In the wiping end determination step S 20 , the result of the determination is No in a case where the maintenance control unit  416  determines that the wiping process with respect to the wiping target head module  12 A is not finished. In a case where the result of the determination is No, the wiping end determination step S 20  is repeated until the result of the determination in the wiping end determination step S 20  becomes Yes. 
     Meanwhile, in the wiping end determination step S 20 , the result of the determination is Yes in a case where the maintenance control unit  416  determines that the wiping process with respect to the wiping target head module  12 A is finished. In a case where the result of the determination is Yes, the process proceeds to a tickling operation restart step S 22 . 
     In the tickling operation restart step S 22 , the maintenance control unit  416  restarts the tickling operation for the wiping target head module  12 A of which the wiping process is finished, in cooperation with the printing control unit  412 . After the tickling operation restart step S 22 , the process proceeds to an all-module wiping end determination step S 24 . 
     In the all-module wiping end determination step S 24 , the maintenance control unit  416  determines whether or not the wiping process with respect to the nozzle surface  10 A is finished for all of the head modules  12 . In the all-module wiping end determination step S 24 , the result of the determination is No in a case where the maintenance control unit  416  determines that the wiping process with respect to the nozzle surface  10 A is not finished for all of the head modules  12 . In a case where the result of the determination is No, the process proceeds to the wiping target determination step S 14  and steps of the wiping target determination step S 14  to the all-module wiping end determination step S 24  are repeatedly performed until the result of the determination in the all-module wiping end determination step S 24  becomes Yes. 
     Meanwhile, in the all-module wiping end determination step S 24 , the result of the determination is Yes in a case where the maintenance control unit  416  determines that the wiping process with respect to the nozzle surface  10 A is finished for all of the head modules  12 . In a case where the result of the determination is Yes, the process proceeds to a tickling operation end step S 26 . 
     In the tickling operation end step S 26 , the maintenance control unit  416  ends the tickling operation for all of the head modules  12  in cooperation with the printing control unit  412 . After the tickling operation end step S 26 , the process proceeds to a printing negative pressure setting step S 28 . 
     In the printing negative pressure setting step S 28 , the maintenance control unit  416  sets a negative pressure of the ink jet head  10  to a negative pressure in a printing mode in cooperation with the pressure control unit  418 . After the printing negative pressure setting step S 28 , a prescribed end process is performed and the maintenance control unit  416  ends the wiping process with respect to the nozzle surfaces  10 A. 
     [Example of Application to Head Device] 
     A head device may be configured by applying a portion of components of the ink jet printing apparatus  300  described with reference to  FIGS. 9 to 11 . That is, the head device according to the embodiment includes the ink jet head  10  and the head control unit. 
     The head control unit includes the system controller  400 , the communication unit  402 , the printing control unit  412 , and the pressure control unit  418  shown in  FIG. 11 . The head device performs tickling operation control of the ink jet head  10  in cooperation with a maintenance device of the ink jet head  10 . 
     [Example of Application to Program Invention] 
     A program corresponding to the head device, the ink jet printing apparatus, and the head maintenance method disclosed in the present specification can be configured. That is, it is possible to configure a program that causes a computer to realize the functions of each part shown in  FIG. 11  and the like and the functions of each part shown in  FIG. 12 . 
     For example, it is possible to configure a program that causes a computer to realize a negative pressure setting function corresponding to the maintenance negative pressure setting step S 10  and the printing negative pressure setting step S 28  shown in  FIG. 12  and a tickling operation switching function corresponding to the tickling operation start step S 12 , the tickling operation stoppage step S 16 , and the tickling operation end step S 26 . 
     Regarding the embodiment of the present invention described above, the configuration requirements can be appropriately changed, added, or deleted without departing from the spirit of the present invention. The present invention is not limited to the embodiments described above, and various modifications can be made by a person having ordinary knowledge in the art within the technical idea of the present invention. 
     EXPLANATION OF REFERENCES 
     
         
         
           
               10 : ink jet head 
               10 A: nozzle surface 
               10 B: liquid-repellent film 
               10 C: ink jet head 
               10 M: ink jet head 
               10 Y: ink jet head 
               10 K: ink jet head 
               12 : head module 
               12 A: wiping target head module 
               12 B: tickling continuation region 
               12 C: non-wiping target head module to be wiped next 
               20 : wiping device 
               20 C: wiping device 
               20 M: wiping device 
               20 Y: wiping device 
               20 K: wiping device 
               22 : web sheet 
               22 A: web sheet contact region 
               24 : pressing roller 
               26 : biasing unit 
               100 : head frame 
               102 : dummy plate 
               104 : flexible substrate 
               120 : nozzle arrangement portion 
               122 : nozzle 
               124 : nozzle opening 
               130 : ejector 
               132 : pressure chamber 
               134 : piezoelectric element 
               136 : nozzle flow path 
               138 : individual supply path 
               140 : supply side common tributary flow path 
               142 : vibration plate 
               144 : individual electrode 
               146 : piezoelectric body 
               148 : cover plate 
               150 : movable space 
               200 : ink supply unit 
               210 : supply individual flow path 
               212 : supply flow path damper 
               214 : supply flow path valve 
               220 : circulation individual flow path 
               224 : circulation flow path valve 
               230 : supply manifold 
               232 : circulation manifold 
               236 : circulation pressure sensor 
               240 : ink tank 
               242 : first bypass flow path 
               244 : first valve 
               250 : second bypass flow path 
               252 : second valve 
               254 : damper 
               260 : supply pump 
               262 : circulation pump 
               300 : ink jet printing apparatus 
               302 : paper transportation unit 
               304 : printing unit 
               306 : maintenance unit 
               310 : printing drum 
               312 : rotary supporting shaft 
               320 : head moving mechanism 
               322 : wiping unit 
               324 : cap unit 
               330 : horizontal moving mechanism 
               332 : guide rail 
               334 : ball screw 
               336 : nut 
               338 : motor 
               340 : frame 
               360 C: cap 
               360 M: cap 
               360 Y: cap 
               360 K: cap 
               400 : system controller 
               402 : communication unit 
               403 : host computer 
               404 : image memory 
               410 : transportation control unit 
               412 : printing control unit 
               414 : head movement control unit 
               416 : maintenance control unit 
               418 : pressure control unit 
               430 : operation unit 
               432 : display unit 
               434 : parameter storage unit 
               436 : program storage unit 
             S 10  to S 28 : each step in head maintenance method