JP4107345B2 - Inkjet recording head - Google Patents

Description

  The present invention relates to the configuration of a piezoelectric type ink jet printer head.

In a prior art on-demand type piezoelectric ink jet printer head, Japanese Patent Application Laid-Open No. 2001-246744 discloses a nozzle plate having a plurality of nozzles arranged in a row, and a pressure chamber for each nozzle. A base plate provided in a row in a direction, a manifold plate provided with a manifold chamber as a common ink chamber for replenishing each pressure chamber after storing ink from an ink supply source, and the manifold plate and the base plate It is disclosed that a cavity unit is configured by laminating a spacer plate interposed therebetween. In that case, an ink supply channel that communicates with the corresponding nozzle from each pressure chamber is formed so as to penetrate the manifold plate and the spacer plate. Further, the spacer plate is formed with an ink flow path communicating from the manifold chamber to each pressure chamber. A configuration is disclosed in which an active portion that can be selectively driven for each of the pressure chambers and a piezoelectric actuator that ejects ink are stacked on the upper surface of the base plate.
JP 2001-246744 A

  In the cavity unit configured as described above, a thin metal plate (plate) is formed so that a predetermined number of nozzles penetrate the plate thickness at predetermined intervals. Other plates (manifold plate, spacer plate) are also provided with ink supply channels and ink channels. In the manifold plate, a large range of manifold chambers that can supply ink to all the pressure chambers also penetrate the plate thickness. As these plates are formed and laminated, there are the following problems.

  That is, a predetermined number of nozzles, pressure chambers, and ink flow paths communicating between these plates must be previously formed in each plate, and the number of nozzles (the number of pressure chambers) is increased or decreased. In order to manufacture a product, the size of the plate must be determined from the beginning so as to correspond to this, so it was impossible to take a manufacturing process that responded to any change in the number of nozzles (number of pressure chambers). .

  Further, since the plurality of plates are stacked and joined, the stacking is liable to occur during this operation, and in particular, the ink supply flow path having a small diameter from the pressure chamber to the nozzle is smoothly communicated. There was a problem that became difficult.

  The present invention has been made in order to solve the above-described conventional problems, in which a pressure chamber and a common ink chamber are formed by laminating a plurality of plates in the arrangement direction of the pressure chambers, and a desired number of nozzles is achieved. Accordingly, by stacking the corresponding number of the plates, an ink jet recording head that can easily respond to the increase / decrease in the number of nozzles (the number of pressure chambers) and that does not fluctuate the ink flow performance even by the stacking operation. It is intended to provide.

In order to achieve this technical problem, the invention described in claim 1 includes a plurality of nozzles, a plurality of pressure chambers communicating with the nozzles via ink supply channels, and an arrangement of the plurality of pressure chambers. In an inkjet recording head that includes a common ink chamber that extends in a direction and communicates with each pressure chamber via an ink flow path, and ejects ink in the pressure chamber from the nozzle by an actuator provided corresponding to each pressure chamber, The opening serving as the common ink chamber is formed by penetrating in the plate thickness direction on the wide surface of the plate, while the pressure chamber, the ink supply channel, and the ink channel are arranged in the arrangement direction of the pressure chambers. Consists of a plurality of plates recessed in the plate thickness direction on the orthogonal surfaces, and the plates are stacked on the orthogonal surfaces so that the openings serving as the common ink chambers communicate with each other. And is characterized in that the combined and.

According to a second aspect of the present invention, in the ink jet recording head according to the first aspect, a part of each of the pressure chambers is opened to the side end surface in the stacking direction, and a part of the pressure chamber is opened. The part is covered with the actuator.

Furthermore, the invention according to claim 3 is the ink jet recording head according to claim 1 or 2 , wherein the actuator includes an active portion that can be selectively driven for each of the pressure chambers. They are arranged in parallel.

As described above, the invention described in claim 1 includes a plurality of nozzles, a plurality of pressure chambers communicating with the nozzles via ink supply channels, and the arrangement direction of the plurality of pressure chambers. In the ink jet recording head, each of the pressure chambers includes a common ink chamber that communicates with each pressure chamber via an ink flow path, and the actuator provided corresponding to each pressure chamber ejects ink in the pressure chamber from the nozzle. An opening serving as an ink chamber is formed by penetrating in the plate thickness direction on the wide surface of the plate, while the pressure chamber, the ink supply channel, and the ink channel are orthogonal to the arrangement direction of the pressure chambers. A plurality of plates recessed in the plate thickness direction on the surface, and the plates are laminated and joined on the orthogonal surfaces so that the openings serving as the common ink chamber communicate with each other. And it is characterized in Rukoto.

  In this configuration, a cavity having the necessary number of nozzles (pressure chambers) is obtained by simply stacking the required number of plates having the same form (that is, the minimum unit of plates having nozzles, pressure chambers and common ink chambers as common elements) Units are easily obtained. Therefore, the manufacturing cost of the cavity unit having various numbers of nozzles can be greatly reduced.

  Moreover, even if the plate thickness of the plate is reduced, the overall cavity unit assembled so that a large number of nozzles (pressure chambers) are arranged in a row can be made compact while increasing its rigidity. There is an effect.

According to a second aspect of the present invention, in the ink jet recording head according to the first aspect, a part of each of the pressure chambers is opened to the side end surface in the stacking direction, and a part of the pressure chamber is opened. Since the portion is covered with the actuator, there is an effect that the actuator can be made compact.

Furthermore, the invention according to claim 3 is the ink jet recording head according to claim 1 or 2 , wherein the actuator includes an active portion that can be selectively driven for each of the pressure chambers. They are arranged in parallel. Therefore, the operation efficiency of the actuator that ejects ink in the pressure chamber can be increased by making the active portion of the actuator face the open portion of the pressure chamber.

  Embodiments of a piezoelectric ink jet recording head embodying the present invention will be described below with reference to the drawings. 1 to 6 show a first embodiment of the present invention. In these drawings, the cavity unit 1 includes a plurality of nozzles 11 arranged in a row, a plurality of pressure chambers 12 in a row parallel to the nozzles 11, and this pressure. And a common ink chamber 14 extending in the arrangement direction of the chambers 12. On the upper surface of the plate-type piezoelectric actuator 2 (FIG. 6) to be bonded to the cavity unit 1, a flexible flat cable 4 (FIG. 6) is laminated and bonded with an adhesive for connection with an external device. It is assumed that the ink is ejected downward from the nozzle 11 opened on the lower surface side of the cavity unit 1.

  As shown in FIGS. 1 to 4, the cavity unit 1 according to the first embodiment is configured by laminating a plurality of plates 10 and 20 in the arrangement direction of the pressure chambers 12. Each plate 10, 20 has a plane perpendicular to the arrangement direction of the pressure chambers 12 as a so-called plate surface, that is, a wide surface, and the arrangement direction of the pressure chambers 12 has a plate thickness. The wide surface of each of the plates 10 and 20 has a width L1 larger than the length of the pressure chamber 12, and a height L2 corresponding to the height from the pressure chamber 12 to the nozzle 11, and one plate (first plate). 10 has a plate thickness t1 corresponding to the width of the pressure chambers 12 (width in the arrangement direction), and the other plate (second plate) 20 has a plate thickness t2 corresponding to an interval separating the adjacent pressure chambers 12. .

The plates 10 and 20 are alternately formed by applying an adhesive (not shown) to the wide surfaces so that the wide surfaces (surfaces orthogonal to the arrangement direction of the pressure chambers 12) face each other. Are laminated and bonded. Further, the end plate 22 is joined to both end surfaces (wide surfaces) in the stacking direction of the plates 10 and 20 with an adhesive or the like, and the entire wide surfaces of the stacked end plates 10 and 20 are covered. (See FIG. 2).

  Further, the configuration will be described in detail. The first plate 10 having a substantially rectangular shape in a plan view has an opening 11 a that becomes one nozzle 11, an opening 12 a that becomes a pressure chamber 12 corresponding to the nozzle 11, and the pressure chamber 12. From the common ink chamber 14 to the pressure chamber 12, and an opening 15a serving as an ink flow path 15 communicating from the common ink chamber 14 to the pressure chamber 12. The first plate 10 is formed so as to be connected to each other on the wide surface of the first plate 10 so as to penetrate in the plate thickness direction.

  The opening 12a serving as the pressure chamber 12 is formed in a state where its length direction is opened outward from the outer edge of the plate 10 along the width dimension L1 direction of the plate 10, and the pressure chamber 12 is directed toward the inside of the plate 10. As a depth. The opening 14a serving as the common ink chamber 14 is disposed so as to be surrounded by the entire periphery of the plate 10 on the side of the opening 11a serving as the nozzle 11 relative to the opening 12a, and the opening 12a, the opening 13a serving as the ink supply channel 13, and the plate 10 It is formed to have as large a cross-sectional area as possible while leaving a minimum partition wall width with respect to the outer periphery.

  Further, by setting the width dimension H2 of the opening 15a serving as the ink flow path 15 to be smaller than the width dimension H1 of the opening 13a serving as the ink supply flow path 13, the volume of the pressure chamber 12 is reduced by the operation of the piezoelectric actuator 2. Thus, the flow resistance of the ink on the ink flow path 15 side when the ink in the pressure chamber 12 is simultaneously pushed out to the nozzle 11 side (ink supply flow path 13) and the common ink chamber 14 (ink flow path 15). Increasing the ink ejection efficiency from the nozzle 11 increases.

  The opening 11 a serving as the nozzle 11 is open to one end face of the first plate 10.

  The second plate 20 has an opening 14b having substantially the same planar view shape (for example, a substantially rectangular shape in the embodiment) as the opening 14a serving as the common ink chamber 14 in the first plate 10. It is formed to penetrate in the thickness direction.

  The assembly method for making such a laminated structure will be described. As shown in FIG. 4, the first lead frame 100a, which is a material corresponding to the first plate 10, has a region where the first plate 10 is formed ( In the embodiment, a substantially rectangular shape in plan view) is secured at appropriate intervals in a matrix form of upper, lower, left and right. Within each formation region, an opening 11 a that becomes the nozzle 11, an opening 13 a that becomes the ink supply flow path 13, an opening 12 a that becomes the pressure chamber 12, an opening 15 a that becomes the ink flow path 15, and an opening 14 a that becomes the common ink chamber 14. Is formed so as to penetrate the plate thickness by punching or laser processing, plasma processing, etching processing or the like. At that time, as shown in FIG. 4, an intermittent boundary line 10a is formed so as to surround the formation region in the first lead frame 100a. That is, by connecting the plurality of tie bars 101 at appropriate intervals so as to straddle the boundary line 10a separating the inside and outside of the formation region, the plate portion in the formation region is prevented from being detached.

  In the second lead frame 100b, which is a material corresponding to the second plate 20, the formation region of the second plate 20 (in the embodiment, a substantially rectangular shape in plan view) is secured at appropriate intervals in the form of a matrix in the vertical and horizontal directions. . In each forming region, an opening 14b to be the common ink chamber 14 is formed so as to penetrate the plate thickness by punching, laser processing, plasma processing, or the like, as described above. In FIG. 4, the portion surrounded by the alternate long and short dash line is the formation region of the second plate 20.

  Adhesives are respectively applied (applied) to the wide surfaces of the first lead frame 100a and the second lead frame 100b as many as the required number of nozzles 11, and the first lead frame 100a and the second lead frame 100b are applied. Are aligned by a predetermined method such as inserting alignment pins (not shown) into the alignment holes formed in each lead frame, and the pressure is applied by alternately laminating them. In addition, adhesive bonding is performed. Next, when the stacked layer is punched (cut out) along the boundary line 10a, a block of the cavity unit 1 as shown in FIG. 2 is formed. Further, the end plate 22 is overlapped and joined to the laminated uppermost layer and lowermost layer. A third lead frame for constituting the end plate 22 is laminated and bonded to the uppermost layer and the lowermost layer of a laminate in which the first lead frame 100a and the second lead frame 100b are alternately laminated. The lead frame may be punched at once.

In the state shown in FIG. 2, the second plate 20 is located in contact with both the front and back wide surfaces of the first plate 10 (surfaces orthogonal to the arrangement direction of the pressure chambers 12), so that the opening 11 a of the nozzle 11 and the pressure are increased. The second plate 20 defines the surface on the wide surface side of each of the opening 12 a of the chamber 12, the opening 13 a serving as the ink supply channel 13, and the opening 15 a serving as the ink channel 15.

  In this way, in a state where the plurality of pressure chambers 12 are separated by the second plate 20, one surface thereof is formed open to one side in the stacking direction of the stacked plates 10, 20, opposite to the one side. On the side, the nozzle 11 is formed open. The openings 14 a and 14 b communicate with the nozzles 11 in the column direction to form a common ink chamber 14.

  Both ends of the common ink chamber 14 are sealed by the end plates 22 and 22 and are in a sealed state. Accordingly, when ink is supplied from an ink supply source such as an external ink tank to the cavity unit 1 through the tube or the like through the ink supply hole 23 provided on the side surface of the end plate 22, the opening 14a and the opening 14b are continuously connected. Ink can be supplied to each pressure chamber 12 and thus to each nozzle 11 through a portion (corresponding to the common ink chamber 14). In addition, since the openings 14a and 14b occupy a large area on the wide surfaces of the first plate 10 and the second plate 20, even if the first plate 10 and the second plate 20 are alternately stacked, the openings 14a and 14b are common. The entire opening 14a and the opening 14b that become the ink chamber 14 are not blocked. On the other hand, since the nozzle 11, the ink supply channel 13, the pressure chamber 12, and the ink channel 15 are integrally formed on one plate (the first plate 10), the position is shifted when the second plate 20 is joined. However, the distribution of ink is not hindered.

  If an adhesive relief groove (not shown) is formed in advance on the wide surface of each lead frame (plate), the excess adhesive is used for the nozzle 11, the ink supply channel 13, the pressure chamber 12, and the ink channel. 15 and the common ink chamber 14, it is possible to prevent the spaces in the portions (particularly, the nozzle 11, the ink supply channel 13 and the ink channel 15) having a particularly small cross-sectional area from being blocked by the adhesive.

  In the embodiment, the first plate 10, the second plate 20, and the end plate 22 are each made of 42% nickel alloy steel plate. The plate thickness of the first and second plates 10 and 20 defines the arrangement interval of the nozzles 11 in the column direction, that is, the dot interval of the ink jet by the nozzles 11. For example, if the thicknesses of the first and second plates 10 and 20 are each 169 μm, this corresponds to a spacing of 75 inkjet dots per inch (25.4 mm).

  As described above, when the openings 11 a, 12 a, 13 a, 14 a, and 15 a serving as the nozzle 11, the ink supply channel 13, the pressure chamber 12, and the ink channel 15 are formed through the first plate 10, the nozzle 11, the ink The supply flow path 13 and the ink flow path 15 have the same width in the plate thickness direction of the pressure chamber 12 and the plate. In order to make the width smaller than the pressure chamber 12, these are formed by half-etching or the like. The first plate 10 and the recess are formed.

  FIG. 5 is an exploded perspective view of the piezoelectric actuator 2, and FIG. 6 is a perspective view of the piezoelectric actuator 2 and the flexible flat cable 4. As shown in FIG. 5, the piezoelectric actuator 2 has a structure in which a plurality of (in the embodiment, four) piezoelectric sheets 31 (indicated by reference numerals 31a to 31d individually) and a top sheet 32 are laminated. Of the piezoelectric sheets 31, the lowermost piezoelectric sheet 31 a and the upper surfaces (wide surfaces) of the odd-numbered piezoelectric sheets 31 c counting upward are narrowed for each pressure chamber 12 in the cavity unit 1. The individual electrodes 33 are formed in a row along the row direction (first direction, long side direction) of the nozzle 11, and each individual electrode 33 has a second direction (short side) orthogonal to the first direction. And one end of each individual electrode 33 is exposed at the edge of one long side of each piezoelectric sheet 31. On the upper surfaces (wide surfaces) of the even-numbered piezoelectric sheets 31b and 31d from the bottom, a common electrode 34 common to the plurality of pressure chambers 11 overlaps with all the individual electrodes 33 in plan view. It is formed with a large area. A partial lead portion 34 a of the common electrode 34 extends in the direction opposite to the direction in which one end of the individual electrode 33 extends and is exposed at the edge of the other long side of the piezoelectric sheet 31. In the embodiment, the width dimension of each individual electrode 33 is formed slightly smaller than the width dimension of the corresponding pressure chamber 12.

  On the other hand, on the upper surface of the uppermost topsheet 32, as shown in FIG. 5, along the edge of the long side, the surface electrode 35 for each of the individual electrodes 33 and the common electrode 34 are provided. A surface electrode 36 is formed by printing.

  Then, side electrodes for connection are applied so that the exposed portions of the individual electrodes 33 at the same position in the vertical direction of the piezoelectric sheet 31 in the piezoelectric actuator 2 are electrically connected to the surface electrode 35 in the top sheet 32. Similarly, a side electrode for connection is applied so that the exposed portions (leading portions 34a) of the common electrode 34 of the piezoelectric sheet 31 are electrically connected to the surface electrode 36 of the top sheet 32 (FIG. 6). reference).

An adhesive sheet made of a synthetic resin material that is non-ink-permeable and electrically insulating as an adhesive layer on the entire lower surface (the wide surface facing the pressure chamber 12) of the plate-type piezoelectric actuator 2 having the above-described configuration. 37 is attached in advance (see FIG. 3), and then bonded to the cavity unit 1 so that each individual electrode 33 in the piezoelectric actuator 2 corresponds to each pressure chamber 12 in the cavity unit 1. The flexible flat cable 4 is overlapped and bonded to the upper surface of the piezoelectric actuator 2 so that various wiring patterns (not shown) in the flexible flat cable 4 are connected to the surface electrodes. 35 and 36 are electrically joined.

  In this configuration, the piezoelectric sheet 31 between any individual electrode 33 and the common electrode 34 among the individual electrodes in the piezoelectric actuator 2 is selectively applied with a voltage, so that distortion in the stacking direction due to the piezoelectric is caused. It becomes the active portion 38 of the piezoelectric element that is generated (see FIG. 2). As the internal volume of the pressure chamber 12 corresponding to the selected individual electrode 33 is reduced by the distortion of the active portion 38, the ink in the pressure chamber 12 is ejected from the nozzle 11 in the form of droplets. Predetermined printing is performed.

As shown in FIG. 7 and FIG. 8, the second embodiment is a configuration in which a large number (group) of first plates 40 having the same form are stacked, and both end faces of the stack are sealed with end plates 41. An opening 42a to be the common ink chamber 42 is formed by penetrating in the plate thickness direction on the wide surface of each first plate 40, while each first plate 40 has an opening 43a to be one nozzle 43 and a pressure. An opening 44 a serving as a chamber 44, an opening 45 a serving as an ink supply channel 45 communicating the pressure chamber 44 and the nozzle 43, and an opening 46 a serving as an ink channel 46 communicating from the common ink chamber 42 to the pressure chamber 44. Are recessed in the thickness direction on the wide surface of the first plate 40.

  Then, the first plates 40 are laminated and bonded at their wide surfaces so that the openings 42a serving as the common ink chambers 42 communicate with each other, and the wide surfaces at both ends of the group of the stacked first plates 40 are end plates. Seal at 41. As a result, the open surface on the wide surface side of the openings 43a, 45a, 44a, 46a, which is recessed on one surface (wide surface) of one of the first plates 40, is the other first plate that contacts the wide surface. A nozzle 43, an ink supply channel 45, a pressure chamber 44, and an ink channel 46 are formed by being defined on the back surface of 40. Also in this case, the arrangement interval of the nozzles 43 (inkjet dot interval) is regulated by the thickness of the first plate 40.

  The piezoelectric actuator is connected to the surface of the stacked body of the first plate 40 in the stacking direction through the adhesive sheet 37 that is impermeable to ink and electrically insulated from the surface where the plurality of pressure chambers 44 are open (exposed). It is the same as that of the said 1st Embodiment to cover 2 and to join. The operations and effects exhibited by the second embodiment are substantially the same as those of the first embodiment.

  The end plate 41 is preferably provided with an ink supply hole 23 for connecting a pipe for supplying ink from an external ink supply source.

  9A and 9B show the nozzle 11 (43), the ink supply channel 13 (45), the pressure chamber 12 (44), and the ink channel (15 (15) in the first and second embodiments. 46) and modified examples of the arrangement pattern of the common ink chambers 14 (42) In these modified examples, the side of the first plate 10 (40) orthogonal to the one end face where the nozzle 11 (43) opens. A part of the pressure chamber 12 (44) is opened (exposed) on the end face side, and the part is covered with the piezoelectric actuator 2.

  In the third embodiment shown in FIG. 10, a stack of a plurality of (in the illustrated embodiment, two) second plates 20 having only the openings 14b is prepared. On the other hand, the first plate 50 in which the openings 11a, 13a, 12a and 14a are formed to penetrate in the plate thickness direction, the first plate 51 in which the openings 12a and 14a are formed to penetrate in the plate thickness direction, and the openings 12a and 15a. , 14a are prepared by stacking three sheets with the first plate 52 penetratingly formed in the plate thickness direction, and these are alternately stacked as shown in FIG. Thereby, the dimension of the pressure chamber 12 in the arrangement direction of the pressure chambers is equal to the thickness of the three first plates 50, 51, 52. On the other hand, the nozzle 11 can be made smaller with a width corresponding to the plate thickness of the first plate 50, and the arrangement interval (pitch) P of the nozzles 11 in the arrangement direction of the pressure chambers is the first of the three plates. The sum of the plate thicknesses of the plates 50, 51, 52 and the plate thicknesses of the two second plates 20 can be a large pitch. In addition, the ink supply channel 13 and the ink channel 15 can be shifted in the arrangement direction of the pressure chambers. In these cases, the thickness of the plurality of first plates 50 to 52 and the second plate 20 may be the same, or may be different from each other.

  In each of the embodiments, in the first plate, the pressure chamber 12 (44) and the common ink chamber 14 (42) are connected to the ink supply channel 13 (45) and the ink channel 15 (46). It can be drawn in an arbitrary curved shape along the wide surface of each plate, whereby flow disturbance is reduced in a portion where the flow direction of ink changes, and stable ejection characteristics can be exhibited.

  In each embodiment, similarly to a known ink jet recording head, a plurality of nozzles are drilled in one plate, a nozzle plate is bonded to the surface of the plates 10 and 20 in the stacking direction, and each of the openings 11a and You may make it communicate with a nozzle. In this case, the ink supply channel 13 may be extended to the edge of the plate 10.

  In the present invention, an actuator such as a heating element may be used as the actuator without using a piezoelectric element.

It is a perspective view which shows the shape of each opening of the 1st plate and 2nd plate by 1st Embodiment of this invention. It is a perspective view of the cavity unit which laminated | stacked the 1st plate and 2nd plate of 1st Embodiment alternately. It is an expanded side sectional view of a cavity unit. It is a partial expansion perspective view which shows the assembly of a cavity unit. It is a disassembled perspective view of a piezoelectric actuator. It is a perspective view of a piezoelectric actuator. It is a perspective view which shows the shape of each opening of the plate in 2nd Embodiment. It is a perspective view which shows the cavity unit which laminated | stacked the 1st plate in 2nd Embodiment. (A) And (b) is a modification of arrangement | positioning of each opening in a cavity unit, respectively. It is a sectional side view at the time of laminating | stacking several 1st plate and 2nd plate and comprising a cavity unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cavity unit 2 Piezoelectric actuators 10 and 40 1st plate 11 Nozzle 12 Pressure chamber 12a Opening 13 and 45 used as a pressure chamber Ink supply flow path 13a and 45a Opening 14 and 42 used as an ink supply flow path Supply ink chambers 14a and 14b, 42a Openings 15 and 46 serving as supply ink chambers Ink channels 15a and 46a Openings 20 serving as ink channels 20 Second plate

Claims (3)

  A plurality of nozzles, a plurality of pressure chambers communicating with each nozzle via an ink supply channel, and a common ink extending in the arrangement direction of the plurality of pressure chambers and communicating with each pressure chamber via an ink channel An ink jet recording head that ejects ink in the pressure chamber from the nozzle by an actuator provided corresponding to each pressure chamber, and the opening serving as the common ink chamber is formed in the plate thickness direction on the wide surface of the plate. On the other hand, the pressure chamber, the ink supply flow path, and the ink flow path are formed of a plurality of plates that are recessed in the plate thickness direction on a surface orthogonal to the arrangement direction of the pressure chambers. An ink jet recording head, wherein the plates are laminated and bonded on the orthogonal surfaces so that the openings serving as the common ink chambers communicate with each other. 2. The ink jet recording head according to claim 1, wherein a part of each of the pressure chambers is opened to a side end surface in the stacking direction, and a portion where the part of the pressure chamber is opened is covered with the actuator. 3. The ink jet recording head according to claim 1, wherein an active portion that can be selectively driven for each of the pressure chambers is arranged in the actuator in parallel with the arrangement of the pressure chambers.