PRINTHEAD ASSEMBLY

Abstract

The present disclosure provides a printhead assembly comprising: a plurality of printhead modules (100a), including a first printhead module, a second printhead module and a third printhead module. Each of the plurality of printhead modules (100a) comprises: a plurality of printhead nozzles (126) each provided with an actuator (118) for selectively ejecting print agent therefrom; at least one print agent manifold (122, 124) providing a fluid communication pathway between at least one print agent inlet and the plurality of printhead nozzles (126); and control circuitry (104) to control the actuators (118) of the printhead module (100a) to eject print agent from the printhead nozzles (126). The first printhead module is mounted to the third printhead module via the second printhead module.

Claims

1. A printhead assembly comprising: a plurality of printhead modules, including a first printhead module, a second printhead module and a third printhead module, each of the plurality of printhead modules comprising: a plurality of printhead nozzles each provided with an actuator for selectively ejecting print agent therefrom; at least one print agent manifold providing a fluid communication pathway between at least one print agent inlet and the plurality of printhead nozzles; and control circuitry to control the actuators of the printhead module to eject print agent from the printhead nozzles, wherein the first printhead module is mounted to the third printhead module via the second printhead module.

2. The printhead assembly of claim 1, wherein the actuator is a piezoelectric actuator.

3. The printhead assembly of claim 1, wherein the control circuitry comprises a CMOS circuit.

4. The printhead assembly of claim 1, wherein the at least one print agent manifold of the first printhead module is different from the at least one print agent manifold of the second printhead module.

5. The printhead assembly of claim 1, wherein the first printhead module is configured to be operatively coupled to a first print agent to be ejected by a first subset of the plurality of printhead nozzles of the first printhead module, and further operatively coupled to a second print agent to be ejected by a second subset of the plurality of printhead nozzles of the first printhead module, the second print agent different from the first print agent and the second subset distinct from the first subset.

6. The printhead assembly of claim 1, further comprising a first module connector for connecting the first printhead module to the second printhead module and a second module connector for connecting the second printhead module to the third printhead module.

7. The printhead assembly of claim 1, wherein the at least one print agent manifold of the second printhead module is arranged to receive the print agent at the at least one print agent inlet from at least one print agent outlet of the first printhead module in fluid communication with the at least one print agent inlet of the second printhead module, or wherein the at least one print agent manifold of the second printhead module is arranged to receive the print agent at the at least one print agent inlet from a print agent outlet defined in a further print agent manifold, different from the plurality of printhead modules.

8. The printhead assembly of claim 1, wherein the plurality of printhead modules are arranged in a tessellating pattern, and/or wherein the plurality of printhead modules each have a substantially identical external shape.

9. The printhead assembly of claim 1, wherein each printhead module comprises at least 100 printhead nozzles.

10. The printhead assembly of claim 1, wherein the third printhead module is electrically connected to the first printhead module via the second printhead module, such that control signals supplied to the first printhead module can be received by the control circuitry of the third printhead module.

11. A first printhead module for connection to a further printhead module having a substantially identical external shape as the first printhead module, the first printhead module comprising: a plurality of printhead nozzles each provided with an actuator for selectively ejecting print agent therefrom; at least one print agent manifold providing a fluid communication pathway between at least one print agent inlet and the plurality of printhead nozzles; control circuitry to control the actuators to eject print agent from the printhead nozzles; and a connection portion arranged to facilitate mounting of the first printhead module to the further printhead module.

12. A method of manufacturing a printhead module comprising: forming an integrated control circuit in a substrate; forming a plurality of piezoelectric actuators each in electrical communication with the integrated control circuit; forming a plurality of nozzle outlets, each associated with a respective one of the plurality of piezoelectric actuators; and forming at least one print agent manifold defining a fluid communication pathway between at least one print agent inlet and the plurality of nozzle outlets.

13. A method of manufacturing a printhead assembly, the method comprising: manufacturing a first printhead module, a second printhead module and a third printhead module, each according to the method of claim 12; and mounting the first printhead module to the third printhead module via the second printhead module.

14. A printer comprising the printhead assembly of claim 1, and one or more sources of print agent in fluid connection with the at least one print agent inlet of the at least one print agent manifold of each printhead module.

15. A method of printing comprising: providing the printer of claim 14; and operating the control circuitry to eject print agent from at least one of the plurality of printhead nozzles of the plurality of printhead modules.

Description

DESCRIPTION OF THE DRAWINGS

[0071] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0072] FIG. 1 is a schematic diagram showing an arrangement of an actuator, printhead nozzle and control circuitry as disclosed herein;

[0073] FIG. 2 is an illustration of the arrangement shown in FIG. 1, including a plurality of printhead nozzles;

[0074] FIGS. 3a and 3b are block diagrams of control circuitry for a printhead as disclosed herein;

[0075] FIGS. 4a, 4b and 4c are graphical representations of actuator control signals for the circuitry described herein;

[0076] FIG. 5 shows an examples of a printhead module as disclosed herein;

[0077] FIG. 6 shows an arrangement of a plurality of the printhead modules shown in FIG. 5; and

[0078] FIG. 7 illustrated a method of manufacture of a printhead module.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

[0079] FIG. 1 is a schematic diagram showing an arrangement of an actuator, printhead nozzle and control circuitry as disclosed herein. With reference to FIG. 1, a droplet ejector assembly 100 (functioning as the printhead module) according to the invention comprises a silicon substrate 102 comprising control circuitry 104 on the first surface of the silicon substrate 102. The control circuitry 104 is typically an integrated circuit 104 in the form of a CMOS circuit 104. The person skilled in the art will appreciate that a CMOS circuit comprises both doped regions of the substrate and metallisation layers and interconnections formed on the first surface of the substrate. A plurality of layers shown generally as 112 are formed on the first surface 106 of the silicon substrate 102. Layer 112 is the CMOS metallization layer and comprises metal conductive traces and a passivation insulator such as SiO.sub.2, SiN, SiON. The droplet ejector assembly 100 further comprises a piezoelectric actuator 118 comprising a piezoelectric body 120 which in this example is formed of AlN or ScAlN but may be formed of another suitable piezoelectric material which is processable at a temperature of below 450 C. The piezoelectric actuator 118 forms a diaphragm with layers of materials such as silicon, silicon oxide, silicon nitride or derivatives thereof and has a passivation layer 160 (sometimes referred to as a nozzle defining layer 160) which prevents applied electrical potentials from contacting fluid.

[0080] At least one metallisation layer 112 includes interconnects, conducting signals from an external controller via a bond pad 180 to a first portion 105a of the control circuitry 104 and from second and third portions 105b, 150c of the control circuitry 104 to the piezoelectric actuator via electrical interconnects 108, in particular to first electrodes 140 and second electrodes 142 arranged to apply an electrical potential difference across and thereby actuate the piezoelectric body 120. An opening 120a is defined in the piezoelectric body 120 for passage of the electrical interconnect 108 between the second portion 105b of the control circuitry 104 and the second electrode 142.

[0081] The piezoelectric actuator 118 and accompanying passivation layer 160 defines a wall of a fluid chamber 122 which receives print agent, such as ink (in the case of an inkjet printer) or another printable fluid (for example in the case of an additive manufacturing printer) through a conduit 124 and which is in communication with a printhead nozzle 126 for ejecting liquid. The piezoelectric actuator 118 and the nozzle defining layer 160 further define a wall of the printhead nozzle 126. The conduit 124 forms at least part of a print agent manifold providing a fluid communication pathway between a print agent inlet (not shown in FIG. 1) and the printhead nozzle 126 (as well as further printhead nozzles, not shown in FIG. 1). The conduit 124 is defined by the silicon substrate 102, the metallisation layer 112 and the nozzle defining layer 160. A protective front surface 170 provides the external surface of the droplet ejector assembly 100, provided to cover and protect the piezoelectric actuator 118, and abutting against a surface 162 of the nozzle defining layer 160. The protective front surface 170 has apertures which define the nozzles 126. The piezoelectric actuator 118, chamber 122 and nozzle 126 together form a droplet ejector shown generally as 101.

[0082] Typically, the CMOS control circuit comprises patterned regions of doped silicon and metallisation layers. The number of metallisation layers depends on the complexity of the CMOS control circuit but three layers should suffice for many applications.

[0083] Although only one printhead nozzle 126 and piezoelectric actuator 118 is shown in FIG. 1, it will be understood that a plurality of printhead nozzles 126 and corresponding piezoelectric actuators 118 are typically provided. Each piezoelectric actuator 118 is configured to control ejection of print agent from the respective printhead nozzle 126.

[0084] FIG. 2 shows an illustration of the arrangement shown in FIG. 1, including a plurality of printhead nozzles. With reference to FIG. 2 specifically, which shows a printhead module 100a having multiple droplet ejectors 101 (individual piezoelectric actuators, fluid chambers and droplet ejection outlets), flexible cable interconnect 138 with a limited number of signal conductors connects an external controller through wires to the printhead module 100a that comprises multiple droplet ejectors shown as 101, for ejecting different print agents, for example ink of different colours. The piezoelectric actuators 118, the control circuitry 104 and the printhead nozzles 126, forming multiple droplet ejectors 101, are typically formed from a single CMOS/actuator substrate, though the print agent manifold of each printhead module 100a may be at least partly defined by at least one further component provided in fluid communication with the printhead nozzles 126. In these examples, as well as the main portion of CMOS control circuit 104, the CMOS control circuit includes separate circuit elements 104 associated with each droplet ejector, which may for example comprise a latch and an ejector transistor for each piezoelectric actuator.

[0085] FIG. 3a is a block diagram of the control circuitry fora printhead assembly. In this example, actuator control is distributed between a machine controller 220 and the control circuitry (e.g., CMOS circuit) 104 within the printhead module 100a. They are connected in part by conductors extending through a single or multiple flexible cable interconnects 138. Multiple actuators 120 are controlled by the application of potentials to their electrodes 140, 142. The machine controller comprises at least a processor 200, such as a microprocessor or microcontroller which has memory 202 storing relevant data and program code. A wired or wireless electronic interface 204 receives input data from an external device driver. One skilled in the art will appreciate that the machine controller may be distributed between a number of separate components or functional modules, such as one component which converts an image into a pixelated pattern for printing using a dither matrix, for example, and a separate component which converts the pixelated pattern into a print pattern for the different nozzles.

[0086] The machine controller may comprise at least one waveform generator and a voltage amplifier 208 which provides a continuous pattern of actuator control pulses (shown in FIG. 4) to the printhead through one or more drive signal conductors 210. A ground conductor 212 also extends from the machine controller to the droplet ejector assembly 100. (Ground connections within printhead not shown for clarity). The processor 200 generates digital control signals 214 typically as a serial bus, and also transmits clock signals 216 to the printhead which serve to synchronise printing with movements of the printhead. The connector also provides voltage levels associated with the operational voltage of CMOS control electronics.

[0087] Within the printhead module 100a, contact pads 136 are connected to the conductors of the flexible connector and signals are routed through patterned metallised layer 112 to the CMOS control circuit 104 and from the CMOS control circuit to the electrodes 140, 142 which actuate individual piezoelectric bodies 120 within respective piezoelectric actuators. The control circuit 104 on substrate 102 comprises ejection switch circuit 220, including ejection transistors having outputs which are in direct electrical connection with the electrodes 140, 142 (i.e. without a further intervening switching semiconductor junction). The ejection switch circuit switches the actuator control pulse signals and if one of the electrodes remains connected to ground, the ejection switch circuit may be as simple as single transistor per actuator, or a single transistor per electrode to switch the signal applied to that electrode. The ejection switch circuit may be distributed around the substrate with a portion (e.g. a transistor or transistor and latch) proximate each droplet ejector.

[0088] The ejection switch circuit does not carry out power amplification. Instead it switches the actuator control pulses, determining whether each pulse is relayed to the respective actuator or not, for each pulse. Voltage amplification is carried out in the machine controller by amplifier 208.

[0089] The ejection switch circuit is controlled by latch and shift transistors 222, which receive and store digital data from a control circuit 224 which processes received data, for example converting received serial data, storing these in registers 226 and using the received data to determine which actuators are to actuate during each successive actuator firing events. The control circuit 228 also stores trim data used to customise the precise timing of voltage switching for each actuator, which is typically determined during a calibration step on set-up, and may store configuration data 230 which indicates the physical layout of nozzles, security information and or nozzle actuation count history information. The control circuit 224 also receives data from sensors 232, 234, 236, some of which are associated with individual actuators, for example nozzle fill levels sensors, and some of which sense parameters relevant to the function of the printhead as a whole, for example temperature sensors.

[0090] FIG. 3b is a further block diagram for control circuitry for a printhead assembly. The control circuitry is substantially similar to that described in relation to FIG. 3a, but the electrical signals (e.g. the actuator control pulses via drive signal conductors 210, the digital control signals 214 and the clock signals 216) are transferred to the printhead modules 100a, 100b, 100c together. In other words, the electrical signals 210, 214, 216 are transferred to the third printhead module 100c via the first printhead module 100a and the second printhead module 100b. In this way, it will be understood that electrical connection between the machine controller 220 and the plurality of printhead modules 100a, 100b, 100c can be provided even where the machine controller 220 is only directly electrically connected to the first printhead module 100a.

[0091] Each printhead module 100a, 100b, 100c includes control circuitry 104 and a plurality of (e.g. at least two) actuators 120, and the electrical signals can provide actuation of any combination of one or more of the actuators 120 on any of the plurality of printhead modules 100a, 100b, 100c via the control circuitry 104 on each printhead module 100a, 100b, 100c. Each of the electrical signals 210, 214, 216 is electrically connected to the control circuitry 104 of each of the printhead modules 100a, 100b, 100c.

[0092] The electrical signals typically comprise address information indicative of the particular printhead module 100a, 100b, 100c, as well as the particular actuator 120 on the given printhead module 100a, 100b, 100c, to be operated to cause ejection of print agent from the printhead nozzle associated with the operated actuator 120.

[0093] FIGS. 4(a), 4(b) and 4(c) show three possible drive waveforms generated by waveform generator or voltage amplification 206 in alternative embodiments. The x axis is time (in milliseconds) and the y axis is potential per m thickness of actuator. As the piezoelectric bodies are made of a non-ferroelectric material in this example the pulses may be applied in either direction. In FIG. 4(a) the signals have a default voltage of 0 and in each pulse are switch to a positive potential and back to zero after a predetermined period of time. In FIG. 4(b) the signals have a default voltage of 0 and are switched first to a positive potential (to cause the piezoelectric actuator to deform in one direction) and then to a negative potential (to cause the piezoelectric actuator to deform in the opposite direction) before returning to zero. In FIG. 4(c) the signals have a default voltage of 200V and are switched to a voltage of 200V (causing the electric fields in the piezoelectric body to reverse in direction) before returning to 200V.

[0094] During operation, the processor 200 receives printing data, such as bitmaps, in digital form through interface 204 and processes this data by known means to send a sequence of printing instructions through serial connection 216 to each printhead module. These printing instructions may be as detailed as instructions for each printhead module as to whether and when to eject a droplet during printing cycles. In one embodiment, the waveform generator generates repeating voltage pulses suitable for application to the electrodes of individual piezoelectric actuators. These are periodic with a time spacing which determines the time between droplet ejection events on the printhead. Alternatively, the voltage amplification, 208, may provide and maintain a single voltage level of multiple voltage levels to the printhead assembly. The ejection transistors within the printhead module will switch these voltages according to the CMOS control circuit.

[0095] As the waveform generator or generators are not located on the printhead and is used to drive numerous piezoelectric actuators, it or they can generate a significant amount of heat without causing problems. There are not substantial substrate space limitations so it or they may be relatively complex circuits adapted to carefully control the shape of the waveform, with selected, and optionally variable, slew rates, and the power amplifier may be selected to produce the desired voltage up to the maximum possible current requirement in the event that all actuators which may be actuated simultaneously be actuated together.

[0096] The control circuit 224 on an individual printhead substrate receives the printing instructions through serial connection 216 and processes these (for example converting from serial to parallel instructions). With reference to the clock signals 214, it is determined whether each individual piezoelectric actuator should be actuated to eject a droplet during each printing cycle and this data is loaded into latches 222. At an appropriate time during each printing cycle, the latched data is passed to the ejection switch circuit which thereby either switch the received printing waveform to the electrodes of the respective actuator element, causing it to carry out a droplet ejection cycle, or to not do so in which case both electrodes of the respective actuator element remain connected to ground and the droplet ejector does not carry out a droplet ejection cycle.

[0097] Sensors 232, 234, 236 are monitored during printing. The precise timing of switching the received printing waveform to the electrodes of the respective actuator element can be varied responsive to a measure of temperature using a temperature sensitive CMOS element.

[0098] Each nozzle may have slightly different ejection characteristic behaviour (drop volume, velocity) based on variance in wafer manufacturing (on a single waferor between wafer lots), due to printhead assembly, due to actuation lifetime. This data can be used to alter the drive waveform for specific nozzles by the CMOS control circuitfor examplechanging the actuation pulse duration or switching to a different levelor to switch certain nozzles to different drive waveforms.

[0099] The viscosity and surface tension of some inks is highly sensitive to temperaturethis ultimately changes the droplet ejection characteristics. Certain print patterns will result in certain nozzles firing continuously whereas others fire sporadically. This will result in a variable heat pattern. The monitored temperature can be used by the control circuit to modify waveforms and/or feedback control information to the controller for appropriate action such as reducing print speed etc.

[0100] The shift registers move the droplet fire pattern information through to the latch registers. Thus, the shift registers interface with the serial connection, and move all print data to the latch registers in a given print cycle. The latch registers interface with the ejection registers to initiate a print command.

[0101] FIG. 5 shows a printhead module 300 as disclosed herein, and to be connected to a plurality of other printhead modules (as shown in FIG. 6). The printhead module 300 includes a print agent inlet 310, in the form of a plurality of print agent inlets 310. Print agent enters the printhead module 300 through the print agent inlet 310, and can be internally routed in one or more print agent manifolds (not shown in FIG. 5), to a plurality of printhead nozzles as described hereinbefore. In this example, the print agent inlet 310 is on a lateral side of the printhead module 300. The printhead module 300 further includes a print agent outlet 320, through which print agent not expelled from the printhead module 300 through the printhead nozzles, can be relayed to further printhead modules connected to thereto. In other words, the print agent outlet 320 is configured to align with the print agent inlet 310 of a further printhead module.

[0102] The printhead nozzles are provided in a print region 340, from which print agent is to be controllably ejected in operation of the printhead module 300.

[0103] The or each of the print agent manifolds may be specific to the particular printhead module 300. The surface properties of the print agent manifolds may be configured to match the print agent to be supplied thereto.

[0104] Control and/or power signals are provided to the printhead module 300 via a flexible interconnect 330.

[0105] FIG. 6 shows an arrangement 400 of a plurality of printhead modules 300, connected together in an assembled arrangement. In the present example, there are four rows of printhead modules 300, each row including five printhead modules 300, though it will be understood that other configurations are possible.

[0106] Although only five printhead modules 300 are labelled in FIG. 6 for clarity, it will be understood that FIG. 6 includes a total of 20 printhead modules 300.

[0107] From FIG. 6, it will be seen that the plurality of printhead modules 300 tesselate perfectly, meaning that there are no gaps therebetween, thereby providing a particularly space-efficient arrangement of printhead modules 300. However, in other examples, there may be spaces between some portions of the printhead modules 300.

[0108] The arrangement 400 includes a first row 410, a second row 420, a third row 420 and a fourth row 440. The second row 420 is offset from the first row 410, such that the print regions 340 of the printhead modules 300 in the first row 410 laterally only partially overlap the print regions 340 of the printhead modules 300 in the second row 420. The third row 430 and the fourth row 440 are offset in a similar way to the first row 410 and the second row 420, such that the print regions 340 of the third row 430 are substantially laterally matched with the print regions 340 of the first row 410, and the print regions 340 of the fourth row 440 are substantially laterally matched with the print regions 340 of the second row 420. Thus, in some examples, the fourth row 440 can provide redundancy for the second row 420, and the third row 430 can provide redundancy for the first row 410. In other examples, different print agents can be provided to the printhead nozzles of the corresponding printhead modules in the overlapping rows.

[0109] The arrangement 400 of printhead modules shown in FIG. 6 can be used to provide redundancy in the printhead modules 300.

[0110] It will be understood that the shape of the printhead module 300 is not limited to that shown, and could be in any suitable shape to be connected to further printhead modules 300.

[0111] FIG. 7 shows a flowchart illustrating a method of manufacturing a printhead module. The method 500 of manufacturing a printhead module comprises forming 510 an integrated circuit (e.g. the CMOS control circuit 104, 134 and the metal interconnect layer 112) on the substrate 102. The CMOS circuit is formed by standard CMOS processing methodologies including ion implantation on a p-type or n-type substrate and the interconnect later is also formed by standard processes such as ion implantation, chemical vapour deposition, physical vapour deposition, etching, chemical-mechanical planarization and/or electroplating.

[0112] Additional layers of material are formed on the substrate, including the electrodes 140 and 142, with an intervening piezoelectric body using successive thin film deposition techniques. Thus, the method 500 further comprises forming 520 a plurality of actuators (typically piezoelectric actuators), each to be in electrical communication with the integrated circuit. Each step must avoid damage to the CMOS control circuit. The piezoelectric body is formed of a material such as AlN or ScAlN which may be deposited at a temperature below 450 C. by PVD (including low-temperature sputtering). Electrodes are formed of, for example titanium, platinum, aluminium, tungsten or alloys thereof.

[0113] The method 500 further comprises forming 530 a nozzle outlet associated with each actuator. In other words, a plurality of nozzle outlets are formed. Each nozzle outlet is associated with a respective one of the plurality of actuators. Each nozzle outlet extends through the substrate. Typically, each nozzle outlet further extends through one or more further layers on the substrate. The method 500 also comprises forming 540 a print agent manifold for routing print agent therethrough towards the plurality of nozzle outlets. The print agent manifold may be formed before or after the formation of the nozzle outlets. The print agent manifold may be formed before or after the formation of the plurality of actuators. The print agent manifold is a fluid channel defining a fluid communication pathway between a print agent inlet of the printhead module, and the plurality of nozzle outlets. Fluid channels and apertures through the substrate may be formed using etching procedures such as DRIE. Channel defining layer 128 may be formed using DRIE etch and wafer bonding of silicon MEMS substrates. The nozzle defining layer can be formed of metal, silicon MEMS wafer or a plastics material by deposition on or adhesion to the channel defining later. Each droplet ejector chip is connected to the machine controller via a flexible interconnect. In contrast to prior art devices according to FIG. 1, the number of discrete conductors in the flexible interconnect is limited, for example 4 to 16 conductors.

[0114] The material from the which the piezoelectric body is formed cannot be and is not PZT due to the requirement to avoid damaging the CMOS control circuit upon which the piezoelectric actuator, including the piezoelectric body is formed. Accordingly, the piezoelectric actuator has a piezoelectric constant d.sub.31 which is much lower, usually at least one and potentially two orders of magnitude, less than PZT depending on its precise composition.

[0115] It will be understood that the printhead modules may have alternative configurations from those described herein.

[0116] The flexible interconnect may be mounted to an edge of a printhead assembly and used to drive several or many individual printhead modules, for example printhead modules for different colours of ink (or other materials in the case of an additive printer) or droplet ejectors for different colours of ink (or other materials) may all be formed in a single continuous substrate in an individual printhead module.

[0117] In an alternative embodiment, instead of the machine controller including a waveform generator and the waveform being conducted to the printhead modules and the CMOS control circuit thereon, the CMOS control circuit actuates the piezoelectric actuators, causing droplet ejection, by switching the voltage applied to one or more of the electrodes of each piezoelectric actuator, for example between ground and a fixed voltage, or between multiple fixed voltage levels, one or more of which may be ground.

[0118] In this case, the flexible connector 138 contains one or more electrical conductors carrying a fixed voltage from the machine controller to the printhead module. In summary, there is provided a printhead assembly comprising: a plurality of printhead modules (100a), including a first printhead module, a second printhead module and a third printhead module. Each of the plurality of printhead modules (100a) comprises: a plurality of printhead nozzles (126) each provided with an actuator (118) for selectively ejecting print agent therefrom; at least one print agent manifold (122, 124) providing a fluid communication pathway between at least one print agent inlet and the plurality of printhead nozzles (126); and control circuitry (104) to control the actuators (118) of the printhead module (100a) to eject print agent from the printhead nozzles (126). The first printhead module is mounted to the third printhead module via the second printhead module.