Actuator unit for an ink jet recording head and method of fabricating same

Abstract: Described is an actuator unit (10) for a laminated ink jet recording head including a first cover member (1) for forming a vibrating member having piezoelectric vibrators (4,4') on a surface thereof; a spacer (5) for forming pressure generating chambers (2,2') with a surface thereof sealed by the first cover member (1); a second cover member (6) having ink jetting outlets (7,7') and ink flowing inlets (8,8'), each ink jetting outlet (7,7') causing the corresponding pressure generating chamber (2,2') to communicate with a corresponding nozzle opening (30,30') of a flow path unit (20) at one end of the pressure generating chamber (2,2'), each ink flowing inlet (8,8') causing the corresponding pressure generating chamber (2,2') to communicate with a common ink chamber (26,26') of the flow path unit (20) at the other end of the pressure generating chamber (2,2'). The actuator unit is prepared by laminating and fixing the first cover member (1), the spacer (5) and the second cover member (6). A pitch (P1) at which the pressure generating chambers (2,2') are arranged is set to a value equal to or smaller than a pitch (P2) at which the nozzle openings (30,30') are arranged; widths (W1,W2) of partition walls (5a,5b) on outermost ends of pressure generating chambers (2,2') located on the outermost ends are set to a value equal to or greater than a width (W3) of a partition wall (5c) defining adjacent pressure generating chambers (2,2') and equal to or smaller than 1/2 of the nozzle opening arrangement pitch (P2). An increase in the distance between the adjacent pressure generating chambers (2,2') at the contact line between two actuator units is set to within a range of values substantially equal to the width of the partition wall.

Description: The invention relates to an actuator unit for an ink jet recording head and a method of fabricating such an actuator unit. Document EP-A-0 600 743 discloses an actuator unit for an ink jet recording head comprising: a plurality of pressure generating chambers communicating respectively with nozzle openings ; and pressure generating means for pressurizing respectively said plurality of pressure generating chambers ; wherein the width of partition walls on the outermost ends of said pressure generating chambers located at the outermost ends of said actuator is set more than a width of a partition wall defining adjacent pressure generating chambers. EP-A-0 572 230 discloses an ink jet recording head, in which piezoelectric vibration elements are stuck to one region of a resilient plate that constitute pressure generating chambers and in which ink droplets are produced by changing the volume of each pressure generating chamber while causing the corresponding piezoelectric vibration element to be flexibly displaced, is designed to displace a wide area of the pressure generating chamber. Therefore, the ink droplets can be produced stably. In order to improve the printing speed of such a recording head, attempts have been made to arrange a great number of nozzle openings per recording head. Since a head having a great number of nozzle openings has an extremely low yield, it is also designed to use a plurality of actuator units A, B, C and fix such actuator units in zigzag to a flow path unit D having nozzle openings and common ink chambers formed therein as shown in Fig. 11. However, for a color printing recording head that reguires at least three rows of nozzle openings, not only the width of the recording head is increased, but also ink jetting timing control becomes complicated since the positions of the nozzle openings that are driven to print an identical row of data are shifted in a carriage moving direction mutually. The present invention intends to overcome the aforementioned problems. The object is solved by the actuator unit for an ink jet recording head according to independent claims 1,2, and the method of fabricating an actuator unit according to independent claim 9. Further advantages, features, aspects and details of the invention are evident from the dependent claims, the description and the accompanying drawings. The claims are intended to be understood as a first non-limiting approach of defining the invention in general terms. The invention generally relates to an actuator unit for a laminated ink jet recording head and a method of fabricating such an actuator unit. The actuator unit has piezoelectric vibration elements, expandable and contractible pressure generating chambers, ink flowing inlets, and ink jetting outlets, and is adapted to construct a recording head while being laminated on a flow path unit having common ink chambers and nozzle openings formed therein. It is an aspect of the invention to provide an actuator units for a laminated ink jet recording head that can be arranged straight in paper feeding direction in pluralities. A second aspect of the invention is to provide a method of fabricating the actuator unit. According to the present invention, there is provided an actuator unit for a laminated ink jet recording head, a plurality of actuator units being brought into contact with each other at ends thereof and laminated on a flow path unit including nozzle openings, comprising: a first cover member having piezoelectric vibrators on the surface thereof; a spacer for forming pressure generating chambers, one surface thereof being sealed by the first cover member; and a second cover member laminated on the spacer and having ink jetting outlets communicating with one end of the pressure generating chambers and ink flowing inlets communicating with the other end of the pressure generating chambers; wherein a pitch at which the pressure generating chambers are arranged is set equal to or less than a pitch at which the nozzle openings are arranged and the width of partition walls on an outermost ends of the pressure generating chambers located at the outermost ends of the actuator is set equal to or more than a width of a partition wall defining adjacent pressure generating chambers and equal to or less than 1/2 the nozzle opening arrangement pitch. The distance between two pressure generating chambers that interpose the contact line of the two actuator units merely increases by a value substantially equal to the width of the partition wall that defines the pressure generating chambers. Therefore, the nozzle openings that are to communicate with these pressure generating chambers come to be arranged at least at positions corresponding to the pressure generating chambers. Hence, by slightly staggering the nozzle communication holes of the flow path unit that connect the pressure generating chambers to the corresponding nozzle openings, the two actuator units can be connected under such flow path conditions as to allow ink droplets to be jetted. The invention will be better understood by reference to the following descriptionsof embodiments of theinvention taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a top view showing an embodiment of the invention; Figs. 2(a) and 2(b) are sectional views showing the embodiment of the invention in the form of a structure in the vicinity of pressure generating chambers of a single actuator unit; Fig. 3 is a diagram showing an exemplary method of fabricating a spacer constituting the actuator unit; Fig. 4 is a diagram showing another exemplary method of fabricating a spacer constituting the actuator unit; Fig. 5 is a top view showing an exemplary actuator unit fabricated by the aforementioned method; Fig. 6 is a top view showing an embodiment of the invention when a recording head is formed using two actuator units; Figs. 7(a) and 7(b) are sectional views showing how nozzle openings and pressure generating chambers are connected around where the actuator units are connected to each other; Fig. 8 is a sectional view showing a laminated ink jet recording head, which is an embodiment of the invention, the recording head being formed using three actuator units of the invention; Fig. 9 is a sectional view showing pressure generating chambers and related portions thereof in one actuator unit in another embodiment of the ink jet print head of the invention; Fig. 10 is a sectional view showing pressure generating chambers and related portions thereof in one actuator unit in still another embodiment of the ink jet print head of the invention; and Fig. 11 is a diagram showing an example of a laminated ink jet recording head. Figs. 1 and 2 show an embodiment of the invention. In Figs. 1 and 2, reference numeral 1 denotes a first cover plate, which comprises a thin zirconia plate having a thickness of about 9 µm and has drive electrodes 3, 3' formed on a surface thereof in such a manner that the drive electrodes 3, 3' confront pressure generating chambers 2, 2' that will be described later. Piezoelectric vibrators 4, 4' made of PZT or the like are deposited on the drive electrodes 3, 3'. Reference numeral 5 denotes a spacer that defines the pressure generating chambers 2, 2'. The spacer 5 has through holes that will serve as the pressure generating chambers 2, 2' in such a manner that the through holes are arranged at a pitch equal to or less than a pitch P2. The pitch P2 is a pitch at which nozzle openings 30, 30' of a flow path unit 20, which will be described later, are arranged. The spacer 5 is also designed so that a width W3 of a partition wall 5c that defines one pressure generating chamber 2 from another pressure generating chamber 2' will become about 1/3 the width of each of the pressure generating chambers 2, 2'. Reference numeral 6 denotes a second cover body. On sides of the second cover body 6 toward which the pressure generating chambers 2, 2' confront each other are ink jetting outlets 7, 7' and on the sides thereof opposite to such sides are ink flowing inlets 8, 8'. The ink jetting outlets 7, 7' and the ink flowing inlets 8, 8' are formed so as to communicate with the pressure generating chambers 2, 2'. By the way, partition walls 5a, 5b positioned on both outermost ends of the spacer 5 as well as partition walls 6a, 6b on both outermost ends of the second cover body 6 are adequately rigid even if widths W1, W2 thereof are set to a value substantially equal to the width W3 of the partition wall 5c of the spacer 5 and of a partition wall 6c of the second cover body 6 that are formed inside. Therefore, the widths W1, W2 are set to values substantially equal to or more than the width W3 of the partition wall 5c of the pressure generating chamber 2 and substantially equal to or less than 1/2 a pitch P1 at which the pressure generating chambers 2 are arranged. Hereupon, the width W1 may be equal to the width W2 or W1 is less or more than the W2. These members 1, 5, 6 are assembled to an actuator unit 10 by molding a clay-like ceramic material into predetermined shapes and laminating and sintering the molded shapes without using an adhesive. The actuator unit 10 has a positioning through holes 11 and a positioning through recess in the middle in order to facilitate the assembling operation. When the spacer 5 that needs such thin partition walls 5a, 5b, 5c is to be formed of a green sheet 12 made of ceramic material, a groove 13 that extends as far as cutting lines C, C is formed along a boundary region so as to match the forming of the through holes serving as the pressure generating chambers 2 as shown in Fig. 3. Upon completion of sintering after drying the green sheet 12, the both end portions of the sintered sheet 12 are cut away along the cutting lines C which traverse both ends of the groove 13, so that the widths W1, W2 of the partition walls 5a, 5b of the pressure generating chambers 2, 2' positioned toward both outermost ends can be formed with the same accuracy as that of the width W3 of the partition wall 5c that defines the pressure generating chambers 2. It may be noted that by forming a projection 15 so as to coincide with the positioning through recess 14 on the other end as shown in Fig. 4 so that an actuator unit having the through recess 14 and the projection 15 can be prepared as shown in Fig. 5. The thus constructed actuator unit is advantageous in allowing two actuator units to be positioned relative to each other with ease when each actuator unit is to be set in a flow path unit. As shown in Figs. 6, 7(a) and 7(b), the flow path unit 20 is fixed to the thus constructed two actuator units 10, 10' by bringing outermost side walls 5b, 5b into contact with corresponding outermost side walls 5a, 5a and reinforcing the flow path unit 20 and two actuator units 10, 10' with fixing members 17, 17 so as to allow the fixing members 17, 17 to mount over a contact line 18. As a result, a recording head having the two actuator units 10, 10' arranged on a straight line in tandem can be completed. In this case, as shown in Figs. 7(a) and (b), the partition walls 5b, 5a of the respective actuator units 10, 10' confront one another at portions where the two adjacent pressure generating chambers 2a, 2b that are in contact with the contact line 18 are partitioned, the contact line 18 being a line with which the two actuator units 10, 10' come into contact. Therefore, the partition walls 5b, 5a are about twice as thick as each partition wall 5c that partitions other pressure generating chambers 2. However, by slightly shifting nozzle communication holes 28, 29 of the flow path unit 20 toward the nozzle openings 30, these pressure generating chambers 2, 2, 2a, 2b can be made to communicate with the nozzle openings 30, 30' that are arranged at the predetermined pitch P2. The flow path unit 20 to which these actuator units 10, 10' are fixed is formed by laminating an ink supply inlet forming substrate 21, a common ink chamber forming substrate 22, and a nozzle plate 23 with adhesive layers 24, 25 such as thermally fusible films. Ink supply inlets 27, 27' that not only connect common ink chambers 26, 26' to the pressure generating chambers 2, 2' but also serve as constrictions that utilize pressure effectively, are formed in the ink supply inlet forming substrate 21. The nozzle communication holes 28, 28' that introduce ink from the pressure generating chambers 2, 2' into the nozzle openings 20, 20' are also formed in the ink supply inlet forming substrate 21. Further, the common ink chamber forming substrate 22 is prepared by forming the common ink chambers 26, 26' and nozzle communication holes 29, 29'. The common ink chambers 26, 26' receive the ink from a not shown ink tank and distribute the received ink to the respective pressure generating chambers 2, 2'. The nozzle communication holes 29, 29' connect the pressure generating chambers 2, 2' to the nozzle openings 30, 30. The nozzle plate 23 is prepared by forming the nozzle openings 30, 30' so as to be arranged on a single line at the predetermined pitch P2. As described above, the distance between the two pressure generating chambers 2a, 2b located at the boundary at which the two actuator units 10, 10' are connected to each other is substantially twice the width of the partition wall 5c that defines the respective pressure generating chambers 2, 2 since the partition wall 5a abuts on the partition wall 5b. That is, a distance P3 between the pressure generating chambers 2a, 2b is larger than the distance P1 between other pressure generating chambers 2, 2. However, by forming the nozzle communication holes 28, 28' of the ink supply inlet forming substrate 21 and the nozzle communication holes 29, 29' of the common ink chamber forming substrate 22 so as to shift slightly toward the contact line 18, these pressure generating chambers 2a, 2b can be connected to each other without causing ink droplets to be jetted out into the nozzle openings 30, 30 at all times, i.e., without letting the ink stagnate in the nozzle openings 30, 30. Specifically, if the pressure generating chambers 2, 2' are arranged at a pitch P1 of about 0.03 cm (about 4/360 inches), then the width W3 of the partition wall 5c defining the pressure generating chambers 2 can be set to about 0.007 cm (about 1/360 inches) and this allows the distance P3 between the two pressure generating chambers 2a, 2b interposing the contact line 18 therebetween to be set to about 0.04 cm (about 6/360 inches). That is, the distance P3 becomes wider merely by about 0.014 cm (about 2/360 inches) than the pitch P1 of the pressure generating chambers 2, 2' other than the outermost pressure generating chambers. If the nozzle communication holes 28, 28' of the ink supply inlet forming substrate 21 and the nozzle communication holes 29, 29' of the common ink chamber forming substrate 22 of the flow path unit 20 are arranged so as to position toward the contact line 18, the ink can be driven out of the nozzle openings 30 smoothly without stagnation in the pressure generating chambers 2, 2' since steps between the upper and lower communication holes 28, 29, 28', 29' are reduced. As a result, a plurality of actuator units 10 can be arranged in tandem on a straight line with respect to the nozzle openings 30, 30 pitched at a predetermined interval so as to communicate with the nozzle openings 30, 30. While the case where the recording head is constructed by connecting two actuator units in tandem has been described in the aforementioned embodiment, a recording head may be constructed by connecting three or more actuator units 10, 10', 10" to the flow path unit 20 having nozzle openings at the predetermined pitch P2 by making the pitch P1 at which the pressure generating chambers are arranged slightly smaller than the pitch P2 at which the nozzle openings 30 formed in the flow path unit 20 are arranged as shown in Fig. 8. That is, assuming that the nozzle arrangement pitch is P2, that the distance between the ends of the adjacent actuator units is P3, and that the number of pressure generating chambers in a single row of a single actuator unit is N, then the pressure generating chamber arrangement pitch P1 may be set as follows. P1 = P2 - (P3 - P2) / (N - 1) The pressure generating chambers in the middle of the actuator units 10, 10', 10", e.g., pressure generating chambers 41, 42 of the actuator unit 10' in the middle are positioned on vertical lines of nozzle openings 51, 52 to which such pressure generating chambers 41, 42 are to be connected, whereas the pressure generating chambers 44, 45, 46 positioned on a right side of the pressure generating chambers 42 in Fig. 8 are gradually deviated from the centerlines of nozzle openings 54, 55, 56 to which the pressure generating chambers 44, 45, 46 are to be connected. However, if the nozzle opening arrangement pitch P2 is set to 0.03 cm (4/360 inch) as described above and the number of nozzle openings in a row to which the actuator units 10, 10', 10" are connected is set to 32, then a displacement between the nozzle opening arrangement pitch P2 and the pitch P1 at which the pressure generating chamber 2, 2' are arranged is about 4.6 µm. Therefore, if the pitch P4 at which the nozzle communication holes 28, 28, 28 ·· ·· of the ink supply inlet forming substrate 21 and a pitch P5 at which the nozzle communication holes 29, 29, 29 ·· ·· of the common ink chamber forming substrate 22 are given as P4 = P2 - 2 (P3 - P2) / 3 (N - 1) P5 = P2 - (P3 - P2) / 3 (N - 1), then, ink is allowed to flow smoothly from the pressure generating chambers 2 to the corresponding nozzle openings 30. By making the pressure generating chamber arrangement pitch P1 slightly smaller than the nozzle opening arrangement pitch P2, the pressure generating chambers located in the middles of the actuator units 10, 10', 10" are caused to communicate with the nozzle openings substantially straight. Further, if the communication holes of the flow path unit 20 are gradually shifted slightly toward a side end, an increase in the thickness due to the two partition walls 5a', 5b" of the two pressure generating chambers 46, 47 and due to the two partition walls 5a and 5b' of the pressure generating chambers 50, 57 can be absorbed merely by shifting the positions of the communication holes of the flow path units confronting the actuator units within the ranges of the regions in which the respective actuator units confront. Therefore, four or more actuator units can be connected in tandem. While the case where a plurality of actuator units are connected in a row has been described in the aforementioned embodiment, it is apparent that an ink jet recording head for a multi-nozzle color printer can be constructed simply by arranging a number of actuator units in tandem in a carriage moving direction. In the aforementioned actuator unit, the pressure generating portion comprises the first cover plate 1, the piezoelectric vibrators 4 and the drive electrodes 3 as shown in Figs. 1 and 2. Alternatively, the pressure generating portion which comprises piezoelectric vibrating plates 100, lower electrodes 101 and upper electrodes 102 so as to seal a surface of the space may be applied as shown in Fig. 9. Furthermore, the pressure generating portion comprising cover plates 106, electrically conductive layer 103, heating elements 104 and protective layer 105 may be used as shown in Fig. 10. Other constitutions which make the pressure in the pressure generating chamber change may be used for the present invention. Therefore, the recording head provided with the actuator unit has a great number of nozzle openings on a single straight line and such recording head can be fabricated with a high yield. In addition, the width of a color printing recording head can be reduced.

Claims: An actuator unit (10) for an ink jet recording head comprising: a plurality of pressure generating chambers (2, 2') communicating respectively with nozzle openings (30, 30'); and pressure generating means for pressurizing respectively said plurality of pressure generating chambers (2, 2'); wherein the pitch P1 at which said pressure generating chambers (2, 2') are arranged is set less than the pitch P2 at which said nozzle openings (30, 30') are arranged, and the width (W1, W2) of partition walls (5a, 5b) on the outermost ends of said pressure generating chambers (2, 2') located at the outermost ends of said actuator (10) is set equal to or more than a width (W3) of a partition wall (5c) defining adjacent pressure generating chambers (2, 2') and equal to or less than 1/2 the nozzle opening arrangement pitch. An actuator unit (10) for an ink jet recording head comprising: a plurality of pressure generating chambers (2, 2') communicating respectively with nozzle openings (30, 30'); and pressure generating means for pressurizing respectively said plurality of pressure generating chambers (2, 2'); wherein the pitch P1 at which said pressure generating chambers (2, 2') are arranged is set equal to or less than the pitch P2 at which said nozzle openings (30, 30') are arranged, and the width (W1, W2) of partition walls (5a, 5b) on the outermost ends of said pressure generating chambers (2, 2') located at the outermost ends of said actuator (10) is set more than a width (W3) of a partition wall (5c) defining adjacent pressure generating chambers (2, 2') and equal to or less than 1/2 the nozzle opening arrangement pitch. The actuator unit (10) according to claim 1 or 2, wherein a plurality of actuator units (10, 10', 10'') are brought into contact with each other at ends thereof and laminated on a flow path unit (20) including nozzle openings (30, 30'). The actuator unit (10) according to one of the preceding claims, further comprising: a first cover member (1) having piezoelectric vibrators (4, 4') on the surface thereof; a spacer (5) for forming said pressure generating chambers (2, 2'), one surface thereof being sealed by said first cover member (1); and a second cover member (6) laminated on said spacer (5) and having ink jetting outlets (7, 7') communicating with one end of said pressure generating chambers (2, 2') and ink flowing inlets (8, 8') communicating with the other end of said pressure generating chambers (2, 2'). The actuator unit (10) according to one of the preceding claims, wherein the pressure generating chamber arrangement pitch P1 is given as follows: P1 = P2 - (P3 - P2) / (N-1); wherein P3 is a pressure generating chamber arrangement pitch of adjacent outermost pressure generating chambers of one and another adjacent actuator unit brought into contact with each other, and N is a number of pressure generating chambers in an arrangement row of pressure generating chambers in one actuator unit. The actuator unit (10) according to one of the preceding claims, wherein the pressure generating chamber arrangement pitch P1 is set substantially equal to 0.03 cm (4/360 inches) and the width of the partition defining the pressure generating chambers (2, 2') is set substantially equal to about 0.007 cm (about 1/360 inches). The actuator unit (10) according to one of the preceding claims, wherein a positioning through recess (14) is formed on one end in a pressure generating chamber arrangement direction. The actuator unit (10) according to one of claims 1 to 6, wherein a positioning through recess (14) is arranged on one end in a pressure generating chamber arrangement direction and a projection (15) engageable with said through recess (14) is formed on the other end. A method of fabricating an actuator unit for an ink jet recording head according to claims 1 or 2 comprising the steps of: forming cutting lines on both ends of a green sheet made of ceramic; forming through holes serving as pressure generating chambers of the actuator unit in the green sheet; forming a groove in a boundary region to separate a plurality of spacers of the actuator unit, wherein the groove extends as far as the cutting lines and vertically to the arrangement direction of the through holes and have a width such that the width of partition walls on outermost ends of the pressure generating chambers located at the outermost ends of the actuator unit can be set; sintering the green sheet; and cutting away both end portions of the green sheet from the cutting line.

Inventors: KAMOI KAZUMI, KATAKURA TAKAHIRO, SHINADA SATOSHI, KAMOI, KAZUMI, KATAKURA, TAKAHIRO, SHINADA, SATOSHI
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1996
Main classification: B41J2
IPC codes: B41J2