JP4668020B2 - Liquid ejection head and image forming apparatus - Google Patents

Description

  The present invention relates to a liquid discharge head and an image forming apparatus, and more particularly, to a liquid discharge head using a laminated piezoelectric element and an image forming apparatus including the liquid discharge head.

  As an image forming apparatus such as a printer, a facsimile, a copying apparatus, and a multifunction machine of these, for example, an ink jet recording apparatus is known. The ink jet recording apparatus uses a liquid discharge head as a recording head, and is a recording medium such as recording paper (hereinafter referred to as “paper”, but the material is not limited to paper, and the recording medium, transfer paper, transfer material, Recording is also performed by ejecting ink droplets as a recording liquid (also referred to as image formation, printing, printing, printing, etc.).

For example, as an ink jet head as a liquid discharge head, a piezoelectric body, in particular, a laminated piezoelectric element in which piezoelectric layers and internal electrodes are alternately stacked is used as a pressure generating means for generating pressure for pressurizing ink that is liquid in a liquid chamber. Using the so-called piezo-type, in which an elastically deformable diaphragm that forms the wall surface of the liquid chamber is deformed by displacement in the d33 or d31 direction of the multilayer piezoelectric element, and the volume / pressure in the liquid chamber is changed to discharge droplets. Things are known.
JP 2003-051627 A JP-A-11-277745

In a liquid discharge head using such a laminated piezoelectric element, in order to efficiently transmit the displacement of the piezoelectric element to the diaphragm, it is opposed to the pressure chamber of the pressure transmitting member as described in Patent Document 3. The surface to be bonded is larger than the area of the multilayer piezoelectric element, and has a concave shape or a convex shape on the surface bonded to the pressure transmission member of the multilayer piezoelectric element, and the surface to be bonded to the multilayer piezoelectric element of the pressure transmission member In addition, there is a convex or concave shape in which concave portions are formed on both sides of the active portion on the end face of the laminated piezoelectric element joined to the pressure transmission member.
Japanese Patent No. 3486913

  By the way, in a liquid discharge head using a conventional multilayer piezoelectric element, for example, as described in Patent Document 3, the multilayer piezoelectric element is joined to the connecting portion of the diaphragm to transmit the displacement to the diaphragm. In such a configuration, the joint surface of the multilayer piezoelectric element moves while maintaining a flat surface, or if there are inactive portions at both ends, the inactive portion does not displace, so the joint surface It is recognized that the center part of the lens is deformed so as to have a convex shape.

  However, in reality, even if the laminated piezoelectric element is driven by joining the flat joint surface of the laminated piezoelectric element and the flat connecting portion of the diaphragm, the displacement of the laminated piezoelectric element becomes the displacement of the diaphragm. There is a problem that the displacement transmission efficiency or drive efficiency of the multilayer piezoelectric element is low due to insufficient transmission.

  Accordingly, the present inventors have sought the cause of the problem, and when the laminated piezoelectric element is displaced by applying voltage to the laminated piezoelectric element even though the joined surface of the laminated piezoelectric element is a flat surface, there is a depression in the bonded surface. Was found to have occurred.

  SUMMARY An advantage of some aspects of the invention is that it provides a liquid discharge head with improved displacement transmission efficiency and an image forming apparatus including the liquid discharge head.

In order to solve the above-described problem, a liquid discharge head according to the present invention includes:
A nozzle that ejects droplets of the recording liquid, a liquid chamber that communicates with the nozzle, a diaphragm that forms a wall surface of the liquid chamber, and a laminated piezoelectric element that displaces the diaphragm,
In the liquid discharge head, the multilayer piezoelectric element includes an active portion that generates a displacement in a vibration plate direction when a voltage is applied and an inactive portion that does not generate a displacement, and is connected to the vibration plate via a connecting portion. ,
When the direction along the longitudinal direction of the liquid chamber is the longitudinal direction,
The active portion of the long side direction of the length Lp ([mu] m) is longer than 1100 ([mu] m), is shorter than 1500 ([mu] m),
The length Lp (μm) in the longitudinal direction of the active part is in a relationship of Lp ≦ Lj + 500 with respect to the length Lj (μm) in the longitudinal direction of the connecting part,
The connecting part is connected only to the active part,
The multilayer when the piezoelectric element occurs a displacement, the multilayer piezoelectric element is a liquid discharge head characterized by having no dent in the longitudinal side direction central portion of the connecting surface between the connecting portion and the active portion.

  The image forming apparatus according to the present invention includes the liquid discharge head according to the present invention.

According to the liquid ejection head according to the present invention, the length of the long side direction of the active section Lp ([mu] m) is longer than 1100 (μm), 1500 (μm ) is shorter than form, the longitudinal length of the active portion Lp (μm) has a relationship of Lp ≦ Lj + 500 with respect to the length Lj (μm) in the longitudinal direction of the connecting portion . The connecting portion is connected only to the active portion, and the stacked piezoelectric element is displaced. when multi-layer piezoelectric element since the structure without a recess in the longitudinal side direction central portion of the connecting surface of the connecting portion between the active portion, the displacement of the multilayer piezoelectric element can be directly transmitted to the diaphragm Displacement transmission efficiency is improved, and droplet discharge efficiency is improved.

  According to the image forming apparatus according to the present invention, since the liquid ejection head according to the present invention is provided, the driving efficiency is high, the droplet ejection characteristics are good, and a high-quality image can be stably formed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. A first embodiment of a liquid discharge head according to the present invention will be described with reference to FIGS. 1 is an exploded perspective view of the head, FIG. 2 is a cross-sectional view along the longitudinal direction of the head, FIG. 3 is an enlarged view of the main part of FIG. 2, and FIGS. It is sectional explanatory drawing which shows the different example along a hand direction.

  The liquid discharge head includes, for example, a flow channel plate 1 formed of a single crystal silicon substrate, a vibration plate 2 bonded to the lower surface of the flow channel plate 1, and a nozzle that is a nozzle forming member bonded to the upper surface of the flow channel plate 1. And a pressure fluid chamber 6 through which a nozzle 4 that ejects ink droplets communicates via a communication path 5, a fluid resistance portion 7, and a communication that communicates with the liquid chamber 6 via a fluid resistance portion 7. The recording liquid (for example, ink) is supplied from the common liquid chamber 8 formed in the frame member 17 through the supply port 10 formed in the diaphragm 2. The liquid chambers 6 are separated by a partition wall 6A.

  Then, on the outer side of the diaphragm 2 that forms the wall surface of the liquid chamber 6 (on the side opposite to the liquid chamber 6), corresponding to each pressurized liquid chamber 6, via a connecting portion 11 formed on the diaphragm 2. The upper end portion of the multilayer piezoelectric element 12 as pressure generating means is joined, and the lower end portion of the multilayer piezoelectric element 12 is joined and fixed to the support substrate 13. Note that the support substrate 13 may be divided for each row of the piezoelectric elements 12.

  The piezoelectric element 12 is formed by alternately stacking piezoelectric material layers 14 and internal electrodes 15a and 15b. In this case, the ink in the liquid chamber 6 is pressurized using a displacement in the d33 direction as the piezoelectric direction of the piezoelectric element 12. Although the piezoelectric elements 12 are arranged in two rows on one support substrate 13, a configuration in which a support substrate is provided for each row or a configuration in which three or more rows are arranged may be used.

  Further, the periphery of the flow path plate 1 and the vibration plate 2 is bonded and bonded to a frame member 17 formed by injection molding with, for example, epoxy resin or polyphenylene sulfite, and the frame member 17 and the support substrate 13 are bonded to a portion (not shown). They are fixed to each other with agents. The frame member 17 is formed with the above-described common liquid chamber 8 and a supply path (communication pipe) (not shown) for supplying recording liquid from the outside to the common liquid chamber 8. Further, it is connected to a recording liquid supply source such as a recording liquid cartridge (not shown). Although the frame member 17 is divided into two parts, it may be a single member.

  Further, an FPC cable 18 is connected to the piezoelectric element 12 by solder bonding, ACF (anisotropic conductive film) bonding or wire bonding in order to give a drive signal. The FPC cable 18 is selectively connected to each piezoelectric element 12. A drive circuit (driver IC) 19 for applying a drive waveform is mounted.

  Here, the flow path plate 1 is formed by anisotropically etching a single crystal silicon substrate having a crystal plane orientation (110), for example, with an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so Groove portions constituting the through hole, the fluid resistance portion 7, the communication portion 9 and the like serving as the pressurized fluid chamber 6 are formed.

  The diaphragm 2 is formed from a nickel (Ni) metal plate, and is manufactured by an electroforming method (electroforming). In the diaphragm 2, a portion corresponding to the pressurized liquid chamber 6 is a thin portion for facilitating deformation, and a connecting portion 11 for joining to the piezoelectric element 12 is provided in the central portion.

  In the lateral direction of the liquid chamber (the direction in which the nozzles 4 are arranged), as shown in FIG. 4, a bi-pitch structure in which the piezoelectric elements 12 and the column portions 22 are alternately arranged can be used, or as shown in FIG. Thus, it can also be set as the normal pitch structure which does not provide the support | pillar part 22. FIG.

  The nozzle plate 3 is formed from a nickel (Ni) metal plate, and is manufactured by an electroforming method (electroforming). In this nozzle plate 3, nozzles 4 having a diameter of 10 to 35 μm are formed corresponding to the respective pressure chambers 6, and bonded to the flow path plate 1 with an adhesive. A water-repellent layer formed of silicone resin is provided on the droplet discharge side surface of the nozzle plate 3 (surface in the discharge direction: discharge surface or surface opposite to the liquid chamber 6 side).

  In the liquid ejection head configured as described above, for example, when driven by a punching method, a drive pulse voltage of 20 to 50 V is selectively applied to the plurality of piezoelectric elements 2 according to an image recorded from a control unit (not shown). By applying the voltage, the piezoelectric element 12 to which the pulse voltage is applied is displaced to deform the vibration plate 2 in the direction of the nozzle plate 3, and pressurize the liquid in the liquid chamber 6 by changing the volume (volume) of the liquid chamber 6. Thus, droplets are ejected from the nozzles 4 of the nozzle plate 3. As the liquid droplets are discharged, the pressure in the liquid chamber 6 decreases, and a slight negative pressure is generated in the liquid chamber 6 due to the inertia of the liquid flow at this time. Under this state, the application of voltage to the piezoelectric element 12 is turned off, so that the diaphragm 2 returns to the original position and the liquid chamber 6 has the original shape, so that further negative pressure is generated. At this time, the liquid that has entered from the liquid supply pipe that leads to a liquid tank (not shown) is filled in the liquid chamber 6, and droplets are ejected from the nozzle 4 in response to the next drive pulse application.

Therefore, details of the multilayer piezoelectric element 12 will be described with reference to FIG.
As described above, the piezoelectric element 12 is formed by alternately stacking the piezoelectric material layers 14 and the internal electrodes 15a and 15b, and the internal electrodes 15a and 15b are interposed via the piezoelectric material layer 14 as shown in FIG. The opposed regions become active portions 31 that generate displacement by applying a voltage, and both ends in the longitudinal direction where the internal electrodes 15a and 15b are not opposed via the piezoelectric material layer 14 are displaced by applying a voltage. There is no inactive portion 32. And the connection part 11 of the diaphragm 2 is joined to the upper end surface of the active part 31.

  Here, if the length in the longitudinal direction of the active portion 31 of the piezoelectric element 12 (hereinafter also referred to as “active portion length”) Lp is increased, the total displacement of the piezoelectric element 12 increases, but in reality, the piezoelectric element 12 is connected to the connecting portion 11. Only the region contributes to the deformation of the diaphragm 2, that is, the pressure application to the pressurized liquid chamber 6.

  Therefore, the present inventors set the active portion length Lp of the piezoelectric element 12 to two types of 1400 μm and 1600 μm, and the longitudinal length of the inactive portion 32 (hereinafter also referred to as “inactive portion length”) Lu is fixed at 150 μm. The displacement distribution of the contact surface (connecting surface) between the piezoelectric element 12 and the connecting portion 11 when the piezoelectric element 12 was driven was measured. The result is shown in FIG.

  As can be seen from FIG. 7, in this example, when the active portion length Lp is 1400 μm, the contact surface (upper end surface) of the piezoelectric element 12 is a flat surface without a depression even after displacement, whereas when the active portion length Lp is 1600 μm. It can be seen that the vicinity of the center connected to the connecting portion 11 is recessed and the amount of displacement is reduced. As described above, when the piezo-electric element 12 is driven and the connecting surface with the linking part 11 is depressed, the displacement of the piezo-electric element 12 cannot be efficiently transmitted to the diaphragm 2.

  In order to confirm this, a numerical simulation was performed on the pressure value generated in the liquid chamber 6 using the active portion length Lp of the piezoelectric element 12 as a parameter. The result is shown in FIG. As can be seen from FIG. 8, the liquid chamber pressure has a peak at a certain active portion length Lp. That is, when the active portion length Lp is shorter than the length at which the liquid chamber pressure reaches the peak value, the active portion length Lp is not sufficient, and therefore the total displacement amount of the piezoelectric element 12 increases as the active portion length Lp increases. Therefore, the pressure increases, but if the length exceeding the peak value is exceeded, as shown in FIG. 7, a depression is generated near the center of the connecting surface and the displacement is reduced, so that the liquid chamber pressure does not increase.

Therefore, by setting the active portion length Lp of the piezoelectric element 12 to such a length that does not cause a depression on the connecting surface when driven, the displacement transmission efficiency is improved, and the droplet ejection efficiency or the driving efficiency is improved. Even if the length of the active portion of the piezoelectric element is made longer than the length when the liquid chamber pressure reaches the peak value, the cost is increased due to the increase in size, and the characteristics are rather lowered.
As described above, when the multilayer piezoelectric element is displaced, the coupling surface between the coupling part and the multilayer piezoelectric element is flat, and the coupling region has a configuration in which the central part in the longitudinal direction has no depression. The displacement of the piezoelectric element can be transmitted to the diaphragm as it is, so that the displacement transmission efficiency is improved and the droplet discharge efficiency is improved.

Next, the relationship between the active portion length Lp of the piezoelectric element 12 and the longitudinal length of the connecting portion 11 (hereinafter referred to as “connecting portion length”) Lj will be described.
The active part length Lp at which the above-described liquid chamber pressure exhibits a peak value varies depending on the connecting part length Lj. Therefore, an experiment was conducted on a configuration in which the pressure when the relationship between the active portion length Lp and the connecting portion length Lj was changed reached a peak value.

  Here, the difference between the active part length Lp and the connecting part length Lj, that is, (Lp−Lj) is used as a parameter, the connecting part length Lj and the inactive part length Lu are fixed, and the change in the liquid chamber pressure when the active part length Lp is changed. Evaluation was made and the value of (Lp−Lj) was determined from the active part length Lp when the pressure was maximum. The result is shown in FIG.

  As can be seen from FIG. 9, when the connecting portion length Lj is lengthened, the optimum value of (Lp−Lj) decreases, but when it is shortened, it becomes constant at a certain value. The maximum value of (Lp−Lj) at this time is about 500 μm from FIG. Since it is not practical to make the inactive portion length Lu shorter than this, the value of (Lp−Lj) is preferably 500 μm at the maximum. If (Lp−Lj) is further increased, only problems such as an increase in cost and a decrease in driving efficiency due to an increase in size occur, and there is no merit. Making (Lp−Lj) smaller than this value lowers the driving efficiency, but there is a cost merit due to downsizing.

  Accordingly, it is preferable that the active portion length Lp (μm) of the piezoelectric element is in a relationship of Lp ≦ Lj + 500 (μm) with respect to the connecting portion length Lj (μm) in the long direction. As a result, it is possible to achieve harmony between miniaturization of the head due to miniaturization of the piezoelectric element and improvement of driving efficiency.

  Next, if the difference (Lp−Lj) between the active portion length Lp and the connecting portion length Lj of the piezoelectric element is made too small, the mutual interference characteristics are deteriorated due to the extreme miniaturization of the piezoelectric element, that is, the supporting force is reduced by the supporting portion 22. Such a problem occurs.

Therefore, the mutual interference characteristics were compared by changing the configurations of the piezoelectric element, the pressurized liquid chamber, and the connecting portion. The result is shown in FIG. here,
Configuration 1: Pressurized liquid chamber length 1500 μm Connection portion length 1200 μm Inactive portion length 300 μm
Configuration 2: Pressurized liquid chamber length 1300 μm Connection portion length 1200 μm Inactive portion length 150 μm

Configuration 3: Pressurized liquid chamber length 1100 μm Connection portion length 1100 μm Inactive portion length 150 μm
It was.

  Here, as an index indicating the mutual interference, a value obtained by dividing the maximum pressure value of the pressurized liquid chamber by the displacement amount of the flow path plate 1 in the driving direction of the piezoelectric element 12 is used. That is, if the value is large, the vibration of the flow path plate 1 is small even at the same pressure, indicating that mutual interference hardly occurs.

  As can be seen from FIG. 10, in any configuration, when (Lp−Lj) is 300 μm or less, the mutual interference characteristics deteriorate. Therefore, the value of (Lp−Lj) is preferably 300 μm or more, that is, Lp ≧ 300 + Lj.

  In the piezoelectric element, when the active part length Lp is shortened, the ratio of the active part length Lp to the total length, that is, the value obtained by adding the active part length Lp and the inactive part length Lu decreases. That is, the ratio of the displacement generation region to the size of the piezoelectric element is reduced. Therefore, if the piezoelectric element is too small, the structure becomes inefficient. As shown in FIG. 7, if the active part length Lp is too long, the flatness of the displacement of the active part 31 is impaired, and a dent is generated near the center connected to the connecting part 11 to reduce the displacement.

In addition to these two points, the maximum displacement amount of the piezoelectric element was considered as a parameter indicating the performance of the piezoelectric element, and the following evaluation parameters were defined.
Evaluation parameter = dimensional efficiency x flatness x maximum displacement

Here, dimensional efficiency = active part length / (active part length + inactive part length)
Flatness = Displacement at the center of the piezoelectric element / maximum displacement of the piezoelectric element

  FIG. 11 shows an evaluation result when the active portion length Lp of the piezoelectric element 12 is changed using this evaluation parameter. From this, it can be seen that when the active part length Lp becomes 1100 (μm) or less and 1500 (μm) or more, the value of the evaluation parameter rapidly decreases. That is, the active part length Lp of the piezoelectric element 12 is preferably in the range of 1100 μm <Lp <1500 μm.

  Next, since the displacement of the active part 31 is suppressed by extending the inactive part 32, the inactive part length Lu of the piezoelectric element 12 is reduced in driving efficiency, but in FIG. Therefore, the supporting force increases and the displacement of the flow path plate 1 decreases. That is, the mutual interference characteristic is improved.

  Therefore, in order to evaluate both, the characteristic when the inactive part length Lu was changed was evaluated using the index indicating the mutual interference used previously. The result is shown in FIG.

  As can be seen from FIG. 12, when the length of the inactive portion length Lu is changed, it can be seen that there is a maximum value at a certain value. If the value is larger than this value, the mutual interference characteristic is deteriorated, and the merit of extending the inactive portion length Lu is lost. Therefore, it is preferable that the inert length Lu be equal to or less than a value that takes this maximum value. From FIG. 12, it is preferable that the inactive portion length Lu (μm) is approximately −0.5 × active portion length Lp (μm) +950 (μm) or less.

  As described above, the driving efficiency is improved by shortening the inactive portion length Lu, but if it is shortened to some extent, it does not change any more. The result of evaluating this is shown in FIG. Here, the pressure in the liquid chamber 6 when an ink jet head is manufactured by changing the active part length Lp and the inactive part length Lu is evaluated.

  As can be seen from FIG. 13, regardless of the active portion length Lp, the pressure value does not change when the inactive portion length Lu is 100 μm or less. That is, when the inactive portion length Lu is set to 100 μm or less, the mutual interference characteristic is deteriorated and the driving efficiency is not improved. Therefore, the inactive portion length Lu of the piezoelectric element is preferably 100 μm or more.

  By the way, as described above, in order to reduce the size of the piezoelectric element, when the inactive part length cannot be extended more than necessary, the end part of the inactive part 32 (the end part opposite to the side in contact with the active part 31). ) Actually causes displacement. Therefore, for example, as shown in FIG. 14, if this region is connected to the flow path plate 1 via the diaphragm thick part 2A, the flow path plate 1 is pushed up by the displacement generated in the inactive portion 32, Interference characteristics deteriorate.

  Therefore, it is preferable that the piezoelectric element 12 and the diaphragm 2 are connected only by the active part 31 and not by the inactive part 32. When it is necessary to arrange the diaphragm thick part 2A other than the connecting part 11 for the convenience of assembly, the diaphragm thick part 2A and the inactive part 32 are not connected (connected) as shown in FIG. Like that.

  Next, an example of an image forming apparatus provided with the liquid ejection head according to the present invention will be described with reference to FIGS. FIG. 16 is an explanatory side view for explaining the overall configuration of the image forming apparatus, and FIG. 17 is an explanatory plan view of the main part of the apparatus.

  In this image forming apparatus, a carriage 103 is slidably held in a main scanning direction by a guide rod 101 and a guide rail 102 that are horizontally mounted on left and right side plates (not shown), and a driving pulley 106A is driven by a main scanning motor 104. And the driven pulley 106B are moved and scanned in the direction indicated by the arrow (main scanning direction) via the timing belt 105.

  For example, four independent ink jet recording liquid droplets (ink droplets) of black (K), cyan (C), magenta (M), and yellow (Y) are recorded on the carriage 103. The recording head 107 composed of the liquid ejection heads 107k, 107c, 107m, and 107y is arranged in a direction along the main scanning direction, and is mounted with the droplet ejection direction facing downward. In addition, although the independent liquid discharge head is used here, it is also possible to employ a configuration in which one or a plurality of heads having a plurality of nozzle rows for discharging recording liquid droplets of each color are used. Further, the number of colors and the arrangement order are not limited to this.

  The carriage 103 is equipped with a sub tank 108 for each color for supplying each color ink to the recording head 107. Ink is supplied to the sub tank 108 from a main tank (ink cartridge) (not shown) via an ink supply tube 109.

  On the other hand, as a sheet feeding unit for feeding a recording medium (sheet) 112 loaded on a sheet stacking unit (pressure plate) 111 such as a sheet feeding cassette 110, the sheets 112 are separated and fed from the sheet stacking unit 111 one by one. Opposite to the half-moon roller (feed roller) 113 and the feed roller 113 to be fed, a separation pad 114 made of a material having a large friction coefficient is provided, and this separation pad 114 is urged toward the feed roller 113 side.

  As a transport unit for transporting the paper 112 fed from the paper feed unit below the recording head 107, a transport belt 121 for electrostatically attracting and transporting the paper 112, and a paper feed unit A counter roller 122 for transporting the paper 112 fed through the guide 115 while sandwiching it between the transport belt 121 and the paper 112 fed substantially vertically upward is changed by about 90 ° and copied on the transport belt 121. A conveying guide 123 for adjusting the pressure and a tip pressure roller 125 urged toward the conveying belt 121 by a pressing member 124. Further, a charging roller 126 which is a charging unit for charging the surface of the conveyance belt 121 is provided.

  Here, the conveyance belt 121 is an endless belt, is stretched between the conveyance roller 127 and the tension roller 128, and the conveyance roller 127 is rotated from the sub-scanning motor 131 via the timing belt 132 and the timing roller 133. By doing so, it is configured to circulate in the belt conveyance direction (sub-scanning direction). A guide member 129 is disposed on the back side of the conveyance belt 121 in correspondence with the image forming area formed by the recording head 107.

  In addition, a slit disk 134 is attached to the shaft of the transport roller 127, and a sensor 135 for detecting the slit of the slit disk 134 is provided, and the encoder 136 is configured by the slit disk 134 and the sensor 135. .

  The charging roller 126 is arranged so as to contact the surface layer of the conveyor belt 121 and rotate following the rotation of the conveyor belt 121, and applies 2.5N to both ends of the shaft as a pressing force.

  Further, an encoder scale 142 having slits is provided on the front side of the carriage 103, and an encoder sensor 143 including a transmission type photosensor for detecting the slits of the encoder scale 142 is provided on the front side of the carriage 103. An encoder 144 for detecting the position of the carriage 103 in the main scanning direction is configured.

  Further, as a paper discharge unit for discharging the paper 112 recorded by the recording head 107, a separation unit for separating the paper 112 from the conveying belt 121, a paper discharge roller 152 and a paper discharge roller 153, and paper discharge A paper discharge tray 154 for stocking the paper 112 to be printed.

  A double-sided paper feeding unit 155 is detachably mounted on the back. The double-sided paper feeding unit 155 takes in the paper 112 returned by the reverse rotation of the transport belt 121, reverses it, and feeds it again between the counter roller 122 and the transport belt 121.

  Further, as shown in FIG. 10, a maintenance / recovery mechanism 156 for maintaining and recovering the state of the nozzles of the recording head 107 is arranged in the non-printing area on one side of the carriage 103 in the scanning direction.

  The maintenance / recovery machine 156 includes a cap 157 for capping each nozzle surface of the recording head 107, a wiper blade 158 which is a blade member for wiping the nozzle surface, and a discharge unit for discharging the thickened recording liquid. An empty discharge receiver 159 for receiving droplets when performing empty discharge for discharging droplets that do not contribute to recording is provided.

  In the image forming apparatus configured as described above, the sheets 112 are separated and fed one by one from the sheet feeding unit, and the sheet 112 fed substantially vertically upward is guided by the guide 115, and includes the conveyance belt 121 and the counter roller 122. The leading end is guided by the conveying guide 123 and pressed against the conveying belt 121 by the leading end pressure roller 125, and the conveying direction is changed by approximately 90 °.

  At this time, a positive voltage output and a negative output are alternately repeated from the AC bias supply unit to the charging roller 126 by a control circuit (not shown), that is, a charging voltage pattern in which an alternating voltage is applied and the conveying belt 121 alternates. That is, plus and minus are alternately charged in a band shape with a predetermined width in the sub-scanning direction which is the circumferential direction. When the paper 112 is fed onto the conveyance belt 121 charged alternately with plus and minus, the paper 112 is attracted to the conveyance belt 121 by electrostatic force, and the paper 112 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 121. Is done.

  Therefore, by driving the recording head 107 according to the image signal while moving the carriage 103 in the forward and backward directions, ink droplets are ejected onto the stopped paper 112 to record one line, and the paper 112 is After transporting a predetermined amount, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper 112 has reached the recording area, the recording operation is finished, and the paper 112 is discharged onto the paper discharge tray 154.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 112 is fed into the double-sided paper feeding unit 155 by rotating the conveyor belt 121 in the reverse direction. The paper 112 is reversed (with the back surface being the printing surface), and is fed again between the counter roller 122 and the conveyor belt 121. The timing is controlled, and the sheet is conveyed onto the conveyor bell 121 as described above. After recording on the back side, the paper is discharged onto the paper discharge tray 154.

  Further, during printing (recording) standby, the carriage 103 is moved to the maintenance / recovery mechanism 155 side, and the nozzle surface of the recording head 107 is capped by the cap 157 so that the nozzles are kept in a wet state. To prevent. In addition, the recording liquid is sucked from the nozzle in a state where the recording head 107 is capped by the cap 157 (referred to as “nozzle suction” or “head suction”), and a recovery operation is performed to discharge the thickened recording liquid or bubbles. Wiping is performed by the wiper blade 158 in order to clean and remove ink adhering to the nozzle surface of the recording head 107 by this recovery operation. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 107 is maintained.

  As described above, since the image forming apparatus includes the recording head constituted by the liquid discharge head according to the present invention, the droplet discharge efficiency is high, a high-quality image can be stably formed, and the apparatus itself can be downsized. Also, the cost can be reduced.

  In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to an image forming apparatus having a printer configuration. However, the present invention is not limited to this. For example, the present invention may be applied to an image forming apparatus such as a printer / fax / copier multifunction machine. it can. Further, the present invention can be applied to an image forming apparatus using a recording liquid or a fixing processing liquid that is a liquid other than ink.

It is an exploded perspective view showing an example of a liquid discharge head concerning the present invention. It is sectional explanatory drawing along the longitudinal direction of the head. FIG. 3 is an enlarged view of a main part of FIG. 2. It is sectional explanatory drawing of the bipitch structure along the liquid chamber transversal direction of the head. It is sectional explanatory drawing of the normal pitch structure along the liquid chamber transversal direction of the head. It is principal part expanded sectional explanatory drawing of the piezoelectric element part of the head. It is explanatory drawing explaining the relationship between active part length and displacement. It is explanatory drawing explaining the relationship between an active part length and a liquid chamber pressure. It is explanatory drawing explaining the difference of the active part length used as a diaphragm connection part length and a pressure maximum, and a connection part length. It is explanatory drawing with which it uses for description of the relationship between the difference of active part length, a connection part length, and mutual interference. It is explanatory drawing with which it uses for description of the relationship between active part length and an evaluation parameter. It is explanatory drawing with which it uses for description of the relationship between an inactive part length and a mutual interference. It is explanatory drawing with which it uses for description of the relationship between an inactive part length and a liquid chamber pressure. FIG. 5 is a cross-sectional explanatory view illustrating a liquid discharge head configuration in which a diaphragm thick wall portion and an inactive portion of a piezoelectric element are connected. FIG. 5 is a cross-sectional explanatory view illustrating a liquid discharge head configuration that does not connect a thick plate portion of a diaphragm and an inactive portion of a piezoelectric element. 1 is an overall configuration diagram illustrating an example of an image forming apparatus according to the present invention. Similarly it is principal part plane explanatory drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Flow path plate 2 ... Vibration plate 3 ... Nozzle plate 4 ... Nozzle 6 ... Liquid chamber 11 ... Connection part 12 ... Piezoelectric element 31 ... Active part 32 ... Inactive part 103 ... Carriage 107 ... Recording head

Claims (2)

A nozzle that ejects droplets of the recording liquid, a liquid chamber that communicates with the nozzle, a diaphragm that forms a wall surface of the liquid chamber, and a laminated piezoelectric element that displaces the diaphragm,
In the liquid discharge head, the multilayer piezoelectric element includes an active portion that generates a displacement in a vibration plate direction when a voltage is applied and an inactive portion that does not generate a displacement, and is connected to the vibration plate via a connecting portion. ,
When the direction along the longitudinal direction of the liquid chamber is the longitudinal direction,
The active portion of the long side direction of the length Lp ([mu] m) is longer than 1100 ([mu] m), is shorter than 1500 ([mu] m),
The length Lp (μm) in the longitudinal direction of the active part is in a relationship of Lp ≦ Lj + 500 with respect to the length Lj (μm) in the longitudinal direction of the connecting part,
The connecting part is connected only to the active part,
The multilayer when the piezoelectric element occurs a displacement, the multilayer piezoelectric element is a liquid discharge head characterized by having no dent in the longitudinal side direction central portion of the connecting surface between the connecting portion and the active portion. An image forming apparatus comprising a liquid ejection head for ejecting recording liquid droplets of the recording liquid, comprising the liquid ejection head according to claim 1 .

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