WO2021216063A1

WO2021216063A1 - Fluid ejection apparatus

Info

Publication number: WO2021216063A1
Application number: PCT/US2020/029325
Authority: WO
Inventors: Cristian DIEZ QUILEZ; Marta COMA VIVES; Andrei Alexandru DAFINOIU
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-04-22
Filing date: 2020-04-22
Publication date: 2021-10-28

Abstract

According to aspects of the present disclosure there are provided methods and apparatus for providing evacuation of gas from a fluid ejection device; the method comprising delivering printing fluid to the fluid ejection device at a predetermined flow rate to cause a pressure in a gas collection chamber to increase, and in response to the pressure increase, opening a pressure relief valve of a relief channel, the pressure relief valve coupled between the gas collection chamber and an exhaust vent.

Description

FLUID EJECTION APPARATUS

BACKGROUND

[0001] Thermal inkjet printing is a precise printing technique wherein individual printing fluid droplets are expelled from nozzles of a fluid ejection device to produce an accurate print image. A nozzle plate of the fluid ejection device may comprise a plurality of individual nozzles such that a large print image can be produced efficiently.

[0002] Each individual nozzle may comprise a nozzle chamber, which may include an associated actuator or resistor. The associated resistor is switched on or off by control circuitry to expel printing fluid droplets in order to build up the desired image on a print medium. Switching the associated resistor on causes heating of printing fluid in the nozzle chamber, resulting in formation of a bubble that causes the expulsion of a droplet of printing fluid onto the print medium. As the plurality of nozzles each expel printing fluid droplets onto the print medium, the print image is formed.

[0003] The control circuitry and plurality of resistors provide precise expulsion of the printing fluid droplets enabling accurate printed images to be produced. Thus, thermal inkjet systems are popular printing systems for home, personal, and business use.

[0004] Furthermore, thermal inkjet printing technology may be used in a variety of other contexts. For instance, thermal inkjet ejection devices may be used to eject binder fluids on a bed of build material in the context of an additive printing system. In another example, thermal inkjet ejection devices may be used to eject fluids for biomedical testing (e.g., fluid agents, reagents, and biological samples may be ejected in droplets, such as for testing). Etc. Therefore, the use of terms like "thermal inkjet printing" is not intended to limit the scope of the claims to the context of home and office printing devices. BRIEF INTRODUCTION OF THE DRAWINGS

[0005] Various features of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate features of the present disclosure, and wherein:

Figure 1 illustrates a device to evacuate gas from a gas collection chamber according to examples of the disclosure;

Figure 2 illustrates a system to provide gas evacuation from a fluid ejection apparatus according to examples of the disclosure;

Figure 3 illustrates a system to provide gas evacuation from a fluid ejection apparatus according to examples of the disclosure;

Figures 4a and 4b illustrate the relationship between pressure drop from inside a nozzle plate of a fluid ejection device and the flow rate of printing fluid out of nozzles of the nozzle plate.

Figure 5 illustrates a flow diagram comprising a first method of evacuating gas from a gas collection chamber;

Figure 6 illustrates a flow diagram comprising a second method of evacuating gas from a gas collection chamber.

DETAILED DESCRIPTION

[0006] In the following description, for purposes of explanation, numerous specific details of certain examples are set forth. Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples.

[0007] Further, reference in the specification to "a", "an" or similar language in relation to a particular feature, structure or characteristic described means a single feature/structure/characteristic or at least one feature/structure/characteristic. Thus, this wording should not be construed as limiting in its use. [0008] In a thermal inkjet system, printing fluid is supplied from a printing fluid reservoir into a chamber of a nozzle plate of a fluid ejection device. During printing, resistors in the nozzle plate are switched on, by applying a current, to heat the printing fluid, creating bubbles that expel printing fluid droplets onto a print medium.

[0009] However, heat generated by the resistors increases the temperature of printing fluid in the chamber, for example the operating temperature of a fluid ejection device may be up to 55°C. The increase in temperature of the printing fluid within the fluid ejection device, caused by heating in the resistors, decreases the solubility of gas in the printing fluid resulting in inadvertent release of dissolved gas from the printing fluid inside the fluid ejection device.

[0010] Released gas may accumulate in nozzle chambers of the nozzle plate. If sufficient gas accumulates, printing fluid may be prevented from contacting the resistors inside each nozzle chamber (or from contacting a barrier layer between the resistors and the printing fluid), which can lead to a 'burnout' of the resistors, resulting in the failure of the drop ejection mechanism, and the end of life for the fluid ejection device.

[0011] A gas collection chamber may be used to collect gas in the fluid ejection device that is produced in this way, preventing gas from accumulating around the delicate resistors. However, once such a chamber is full, then any further gas released from heating the printing fluid may again accumulate in the nozzle chambers leading to burnout of the resistors. Thus, such a gas collection chamber may temporarily increase the lifespan of a fluid ejection device.

[0012] Some approaches to inhibit resistor burnout due to released gas include the use of 'degas' (0% air saturated) printing fluid along with 'air barrier' components within a printing fluid delivery system. These components attempt to prevent air entering the system and dissolving into the printing fluid thus maintaining the printing fluid at 0% air saturation. However, such air barrier components may be expensive and is may be difficult to provide a complete barrier to stop gases dissolving in the printing fluid. Further, degas printing fluid may be more expensive than regular printing fluid and may rely on enhanced air-tight storage facilities within a printing system, further increasing cost. [0013] Certain examples described herein provide methods and devices to exhaust accumulated gas from a fluid ejection device such as a printhead, which may increase the lifespan of the fluid ejection device or may allow a lifespan to be maintained while relaxing tolerances on air barrier components and air saturation level of the printing fluid.

[0014] Figure 1 illustrates a relief device 100 for exhausting gas from a fluid ejection device, such as a thermal inkjet ejection device. In the example shown in Figure 1, relief device 100 comprises a relief channel 101; a check valve 102; a filter 103; a vent 104 and an inlet 105.

[0015] The check valve 102 allows fluid to flow in one direction from the inlet 105 of the relief channel 101 to the vent 104. The check valve 102 opens when the pressure differential between the inlet 105 and the vent 104 is above a threshold amount and may close when this pressure differential is below the threshold amount. In some examples, the check valve 102 may be a single-use check valve and may open once, or 'crack', when the pressure differential reaches the threshold amount and may not close again. In some other examples, the check valve 102 may open and close in response to an actuator controlled by control circuitry. In some other examples, the check valve 102 may open when the pressure at the inlet 105 is greater than atmospheric pressure or some other threshold pressure above atmospheric pressure.

[0016] The filter 103 is a printing fluid impermeable filter that is permeable to gas such that, if the check valve 102 is open, gas is allowed to travel along the relief channel and exhaust through the vent 104, whereas printing fluid is not able to pass the printing fluid impermeable filter 103 and is retained within the relief channel. In some examples, filter 103 may comprise purge foam. In some examples, the filter 103 may form a gas impermeable seal upon contact with printing fluid.

[0017] Vent 104 allows gas to evacuate from a fluid ejection device to an external system. In some examples, vent 104 may be a vent to atmosphere.

[0018] Relief device 100 may be incorporated into a fluid ejection apparatus, such as a fluid ejection device, an inkjet printing system and/or a nozzle plate. [0019] Figure 2 illustrates an inkjet printing system 200 for ejecting printing fluid onto a print medium 207. In the example shown in Figure 2, the inkjet printing system 200 comprises a fluid ejection apparatus 201; a printing fluid reservoir 202; a printing fluid delivery system 203; and control circuitry 204. The fluid ejection apparatus 201 further comprises relief device 100; a gas collection chamber 205; and a nozzle plate 206. The nozzle plate comprises a plurality of nozzles, each nozzle may have an associated nozzle chamber and resistor.

[0020] The printing fluid delivery system 203 supplies printing fluid from a printing fluid reservoir 202 to the fluid ejection device 201. To inhibit printing fluid from leaking out of the nozzles of the fluid ejection device 201, the printing fluid within the fluid ejection device is maintained at a pressure lower than a pressure of the external environment, e.g. less than atmospheric pressure. Surface tension of the printing fluid within the plurality of nozzles prevents, or inhibits, air from entering the fluid ejection device 201 despite the lower internal pressure.

[0021] To control the pressure within the fluid ejection device 201, the printing fluid delivery system 203 comprises a pressure regulator to regulate the pressure of printing fluid supplied to the fluid ejection device 201, and therefore the pressure of the printing fluid within the fluid ejection device 201.

[0022] Control circuitry 204 is coupled to the fluid ejection device 201 and the printing fluid delivery system 203 and controls operation of the fluid ejection device 201 and the printing fluid delivery system 203.

[0023] In some examples, the fluid ejection device 201 may further comprise the printing fluid reservoir 202; the printing fluid delivery system 203 and the control circuitry 204.

[0024] During printing operation, resistors in the nozzle plate 206 operate to heat the printing fluid, to generate bubbles that causes drops of printing fluid to be ejected from the nozzles. This heating causes the temperature of the printing fluid within the fluid ejection device 201 to increase, leading to release of dissolved gas from the printing fluid, due to the reduction of solubility of gas in the printing fluid with increasing temperature. The released gas accumulates in the gas collection chamber 205. [0025] The inkjet printing system 200 may determine if a predetermined amount of gas has accumulated in the gas collection chamber 205. For example, the system 200 may determine if a predetermined amount of gas has accumulated using a sensor situated either in the gas collection chamber 205 or at the inlet of the gas collection chamber. In some examples, the control circuitry 204 may monitor an amount of printing fluid consumed by the fluid ejection device 201. As the amount of gas released from a certain volume of printing fluid may be relatively constant, if it is determined that the amount of printing fluid consumed is over a threshold limit, it may be assumed that a certain amount of gas will have accumulated in the gas collection chamber 205.

[0026] In response to the determination that a predetermined amount of gas has accumulated in the gas collection chamber 205, printing system 200 performs a predetermined service operation. The service operation comprises causing the printing fluid delivery system 203 to deliver printing fluid to fluid ejection device 201 at a predetermined flow rate without activation of resistors in nozzle plate 206 to drive printing fluid through nozzles of the nozzle plate 206. This predetermined flow rate may be a greater flow rate than the flow rate of printing fluid delivered to the fluid ejection device 201 during printing operation.

[0027] Delivering printing fluid at the predetermined flow rate may comprise opening the pressure regulator within the printing fluid delivery system 203. The pressure regulator may be kept open during the predetermined service operation to allow printing fluid to freely flow into the fluid ejection device 201 increasing pressure within the device above the regulated pressure. The delivery of printing fluid at the predetermined flow rate causes the pressure in the fluid ejection device 201 to exceed a threshold pressure.

[0028] In response to the pressure in the fluid ejection device 201 exceeding the threshold pressure, pressure relief valve 102 in relief device 100 opens and gas that has accumulated in gas collection chamber 205 is exhausted via vent 104.

[0029] In some examples, the pressure relief valve 102 may be a single-use check valve, and once the pressure in the fluid ejection device 201 reaches a 'cracking pressure' the valve 'cracks' open and does not close again. In some examples, the pressure relief valve 102 may be opened by an actuator based on a control signal provided by the control circuitry 204 and may be closed once gas in the gas collection chamber 205 has been evacuated. In some examples, the pressure relief valve 102 may be a passive device that opens automatically due to a pressure differential across the device when the pressure in the fluid ejection device 301 exceeds the threshold pressure and then close once the pressure in the fluid ejection device 301 falls below the threshold pressure reducing the pressure differential across the relief valve 10. In some examples, this threshold pressure may be atmospheric pressure, or a predetermined pressure greater than atmospheric pressure.

[0030] The pressure relief valve 102 is closed during printing operation to isolate the exhaust vent 104 from the gas collection chamber 205 and thus maintain a lower internal pressure within the fluid ejection device 201 than the external pressure. Relief valve 102 may be selected to open under the specific conditions reached during the service operation.

[0031] Printing fluid impermeable filter 103 may form a gas impermeable seal upon contact with printing fluid. This is such that gas from the external environment cannot enter the fluid ejection device 201 through the exhaust vent 104 after the service operation has completed. Thus, the lower pressure within the fluid ejection device 201 is maintained even after the service operation has been performed. Check valve 102 may also maintain the lower pressure within the fluid ejection device 201 when closed. [0032] Figure 3 illustrates an inkjet printing system 300 to according to an example. Inkjet printing system 300 is similar to inkjet printing system 200 but further illustrates a pressure regulator 307; an air pump 308; an airbag 309 and a filter 310. In some examples, inkjet printing system 200 may comprise inkjet printing system 300. [0033] In the system of Figure 3, the airbag 309 is connected to pressure regulator 307 through a lever mechanism. Air pump 308 may be controlled to deliver air to airbag 309 to increase its size, resulting in pressure regulator 307 being held open by the lever mechanism. [0034] Fluid ejection device 301 may comprise a filter 310 to prevent, or inhibit, unwanted matter such as dust or dirt from entering delicate nozzle plate 306, while still allowing printing fluid to reach the nozzle plate 306.

[0035] As described above with reference to Figure 2, in order to exhaust accumulated gas from gas collection chamber 305, the inkjet printing system 300 performs a predetermined service whereby printing fluid delivery system 303 delivers printing fluid to fluid ejection device 301 at a predetermined flow rate.

[0036] Delivering printing fluid at the predetermined flow rate includes controlling the air pump 308 to increase pressure in the airbag 309 such that the pressure regulator 307 is kept open. This allows printing fluid to freely flow into the fluid ejection device 301 increasing pressure of the printing fluid within the fluid ejection device 301.

[0037] During the predetermined service operation, the delivery of printing fluid at the predetermined flow rate causes the pressure in the fluid ejection device 301 to exceed the threshold pressure.

[0038] In response to the pressure in the fluid ejection device 301 exceeding the threshold pressure, pressure relief valve 102 in relief device 100 opens and gas that has accumulated in gas collection chamber 305 is exhausted via vent 104. The pressure relief valve 102 may open automatically in response to a pressure differential across the pressure relief valve 102, once the pressure in the fluid ejection device 301 exceeds the threshold pressure, and may close once the pressure in the fluid ejection device 301 falls below the threshold pressure. This threshold pressure may be atmospheric pressure or a predetermined pressure above atmospheric pressure.

[0039] The pressure relief valve 102 is closed during printing operation and may open under the specific conditions reached during the predetermined service operation. Printing fluid impermeable filter 103 may form a gas impermeable seal upon contact with printing fluid.

[0040] Figure 4a illustrates an example relationship between flow rate of printing fluid supplied by the printing fluid delivery system 303 and a pressure drop from inside fluid ejection apparatus 301 to outside nozzle plate 306. An increase in printing fluid pressure inside the fluid ejection apparatus 301 leads to printing fluid flowing out through the nozzle plate 306. As illustrated, the pressure within the fluid ejection device 301 follows a predictable relationship with the flow rate of the supplied printing fluid. For example, the dependency may follow a pressure loss curve which has a linear component and a quadratic component. While the particular values of pressure and flow rate may be specific to each individual printing system or fluid ejection device, a similar relationship may be measured for each individual arrangement.

[0041] Figure 4b illustrates that the dependency between flow rate of printing fluid supplied to the fluid ejection device 301 and pressure within the fluid ejection device can be used to control the pressure within the fluid ejection device and to generate a pressure greater than a threshold pressure sufficient to cause the relief valve 102 to open. In the example illustrated by Figure 4b the threshold pressure is three PSI and is reached at a flow rate of approximately 100 cm³/min. By delivering printing fluid to the fluid ejection device at a rate of 100 cm³/min or greater during the service operation, a pressure greater than 3 PSI is achieved in the fluid ejection device causing the pressure relief valve 102 to open, and allowing gas that has accumulated inside fluid ejection device 301 to be evacuated.

[0042] Figure 5 illustrates a method 500 of evacuating gas from a fluid ejection device. The method may be performed by the inkjet printing system 200, 300 and/or by control circuitry 204. In some examples, Figure 5 may illustrate a method of the service operation that inkjet printing system 300 may perform to evacuate gas in gas collection chamber 305.

[0043] According to the method of Figure 5, at block 510, inkjet printing system 300 delivers printing fluid to the fluid ejection device 301 at a predetermined flow rate to cause a pressure in the fluid ejection device 301 to exceed a threshold pressure. [0044] At block 520, in response to the pressure in the fluid ejection device 301 exceeding the threshold pressure, the inkjet printing system 300 opens a pressure relief valve 102 of a relief channel 101, coupled between a gas collection chamber 305 of the fluid ejection device 301 and an exhaust vent 104, to evacuate gas from the gas collection chamber 305. [0045] Figure 6 illustrates a method 600 of evacuating gas that has accumulated in a fluid ejection device, for example by using a system 200, B00 as illustrated in Figures 2 and 3. In some examples, Figure 6 may illustrate a method of the service operation that inkjet printing system 300 may perform to evacuate gas in gas collection chamber 305. The method may be performed by the inkjet printing system 200, 300 and/or by control circuitry 204.

[0046] According to the method of Figure 6, at block 610, control circuitry 204 monitors printing fluid consumed associated with fluid ejection device 201. At block 620, control circuitry 204 then determines whether the monitored printing fluid consumed is greater than a threshold amount, or volume, of print fluid. If the monitored printing fluid consumed is not greater than the threshold amount then control circuitry 204 continues to monitor the printing fluid consumed.

[0047] If the monitored printing fluid consumed is greater than the threshold amount then, at block 630, control circuitry 204 controls printing fluid delivery system 203 to deliver printing fluid to the fluid ejection device 201 at a predetermined flow rate, for example determined using a relationship as illustrated in Figures 4a and 4b. In some examples, this predetermined flow rate may be greater than the flow rate of printing fluid delivered during normal printing operations.

[0048] The delivery of printing fluid at the predetermined flow rate to the fluid ejection device 201 causes the pressure in the fluid ejection device 201 to exceed a threshold pressure. At block 640, pressure relief valve 102 opens once the threshold pressure has been exceeded and closes if the pressure in the fluid ejection device 201 falls below the threshold pressure, thus allowing gas to evacuate from gas collection chamber 205. In some examples, the pressure relief valve 102 may be a single-use check valve configured to 'crack' once a threshold pressure differential has been exceeded. In some other examples, control circuitry 204 may open the pressure relief valve 102. [0049] At block 650, control circuitry 204 then controls printing fluid delivery system 203 to stop delivery of printing fluid to the fluid ejection device 201 at the predetermined flow rate. In some examples, this may be performed after gas from the gas collection chamber 205 has been evacuated, after a predetermined amount of time has passed, after a predetermined amount of printing fluid has been delivered at the predetermined flow rate, or other such similar variable. The predetermined amount of printing fluid may be a volume greater than or equal to the volume of the gas collection chamber 205.

[0050] Once the fluid delivery system 203 stops delivery of the printing fluid , the pressure of the printing fluid within the fluid ejection device 201 drops until the pressure relief valve 102 closes, having evacuated most or all of the accumulated gas from the gas collection chamber. In some examples, control circuitry 204 may close the pressure relief valve 102.

[0051] In some examples, the single-use check valve 102 does not close once gas from the gas collection chamber 205 has been evacuated. If printing fluid contacts the printing fluid impermeable filter 103, the filter 103 forms a gas impermeable seal. No damage is caused to the fluid ejection device 201 since printing fluid can still flow through the nozzle plate and out of the nozzles. Forming the gas impermeable seal allows the environment of the fluid ejection device 201 to be separated from the external environment. In this instance, the pressure in the fluid ejection device 201 may be kept at a pressure below a pressure of the external environment once normal printing operations resume.

[0052] Thus, the methods disclosed in Figures 5 and 6 enable printing system 200,300 to evacuate gas from gas collection chamber 205, 305. This frees up capacity for further gas that may be produced due to the thermal increase of printing fluid during printing such that the gas produced does not accumulate in nozzle chambers next to resistors. Thus, burnout of the resistors may be avoided and the lifetime of fluid ejection device 201, 301 may be increased.

[0053] Certain methods and systems as described herein may be implemented by a processor that processes program code that is retrieved from a non-transitory storage medium. In particular, methods 500 and 600 illustrated in Figures 5 and 6 may be implemented in the form of computer program code stored on computer readable media and executable by a processor to perform the described methods. The computer- readable media may be any media that can contain, store, or maintain programs and data for use by or in connection with an instruction execution system (e.g., non- transitory computer readable media). Computer-readable media can comprise any one of many physical media such as, for example, electronic, magnetic, optical, electromagnetic, or semiconductor media. More specific examples of suitable machine- readable media include, but are not limited to, a hard drive, a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory, or a portable disc.

[0054] All of the features disclosed in this specification (including any accompanying claims, abstract, and drawings) may be combined in any combination, except combinations where some of such features are mutually exclusive. Each feature disclosed in this specification, including any accompanying claims, abstract, and drawings, may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example of a generic series of equivalent or similar features.

[0055] The present teachings are not restricted to the details of any foregoing examples. Any novel combination of the features disclosed in this specification (including any accompanying claims, abstract, and drawings) may be envisaged. The claims should not be construed to cover merely the foregoing examples, but also any variants that fall within the scope of the claims.

[0056] Examples

[0057] According to example 1, there is provided a fluid ejection apparatus comprising: a nozzle; an actuator associated with the nozzle, the actuator to heat a printing fluid to cause a drop of the printing fluid to be ejected from the nozzle; a gas collection chamber associated with the actuator; and a relief channel coupled between the gas collection chamber and a vent, the relief channel comprising: a check valve to allow fluid flow along the relief channel from the gas collection chamber to the vent when a pressure in the gas collection chamber is raised above atmospheric pressure; and a printing fluid impermeable filter to block flow of printing fluid through the relief channel, wherein the filter is gas permeable. [0058] Example 2, there is provided the apparatus of example 1, wherein the gas collection chamber is to collect gas emitted from the printing fluid in response to heating of the printing fluid by the associated actuator.

[0059] Example 3, there is provided the apparatus of example 1 or 2, wherein the filter is to form a gas impermeable seal upon contact with printing fluid.

[0060] Example 4, there is provided the apparatus of any of examples 1 to 3, wherein the vent comprises a vent to atmosphere.

[0061] Example 5, there is provided the apparatus of any of examples 1 to 4, wherein the gas collection chamber comprises a gas sensor to monitor the amount of gas in the gas collection chamber.

[0062] According to example 6, there is provided a method of evacuating gas from a fluid ejection device, the method comprising: delivering printing fluid to the fluid ejection device at a predetermined flow rate to cause a pressure in the fluid ejection device to exceed a threshold pressure; in response to the pressure in the fluid ejection device exceeding the threshold pressure, opening a pressure relief valve of a relief channel, coupled between a gas collection chamber of the fluid ejection device and an exhaust vent, to evacuate gas from the gas collection chamber.

[0063] Example 7, there is provided the method of example 6, further comprising: monitoring accumulation of gas in the gas collection chamber; and wherein the delivering printing fluid to the fluid ejection device is performed in response to a monitored accumulation of gas being greater than a threshold amount.

[0064] Example 8, there is provided the method of example 6 or 7, further comprising: monitoring printing fluid consumed associated with the fluid ejection device; and wherein the delivering printing fluid to the fluid ejection device is performed in response to a monitored printing fluid consumed being greater than a threshold amount.

[0065] Example 9, there is provided the method of any of examples 6 to 8, wherein the pressure release valve is closed during normal printing operations of the fluid ejection device to isolate the exhaust vent from the gas collection chamber. [0066] Example 10, there is provided the method of any of examples 6 to 9, further comprising: opening a pressure regulator regulating the pressure in the fluid ejection device, while delivering printing fluid to the fluid ejection device at the predetermined flow rate.

[0067] According to example 11, there is provided an inkjet printing system comprising: a fluid ejection device further comprising: a nozzle; a actuator associated with the nozzle, the actuator to heat a printing fluid to cause a drop of the printing fluid to be ejected from the nozzle; a gas collection chamber associated with the actuator; and a relief channel coupled between the gas collection chamber and a vent to atmosphere, the relief channel comprising: a check valve to allow fluid flow along the relief channel from the gas collection chamber to the vent when a pressure in the gas collection chamber is raised above atmospheric pressure; and a printing fluid impermeable filter to block flow of printing fluid through the relief channel, wherein the filter is gas permeable; and a printing fluid delivery system to supply printing fluid from a printing fluid reservoir to the fluid ejection device; and control circuitry coupled to the fluid ejection device and the printing fluid delivery system.

[0068] Example 12, there is provided the printing system of example 11, the control circuitry to: monitor printing fluid consumed associated with the fluid ejection device; in response to a monitored printing fluid consumed being greater than a threshold amount, control the printing system to perform a service operation.

[0069] Example 13, there is provided the printing system of example 11 or 12, wherein during the service operation the control circuitry is to control the printing fluid delivery system to deliver printing fluid to the fluid ejection device at a predetermined flow rate to cause the pressure in the gas collection chamber to exceed a threshold pressure.

[0070] Example 14, there is provided the printing system of any of examples 11 to 13, wherein the printing fluid delivery system further comprises: a pressure regulator to regulate pressure in the fluid ejection device; and the control circuitry further to open the pressure regulator during delivery of the printing fluid at the predetermined flow rate. [0071 ] Example 15, there is provided the printing system of any of examples 11 to

14, wherein the fluid ejection device comprises a page wide array fluid ejection device.

Claims

1. A fluid ejection apparatus comprising: a nozzle; an actuator associated with the nozzle, the actuator to heat a printing fluid to cause a drop of the printing fluid to be ejected from the nozzle; a gas collection chamber associated with the actuator; and a relief channel coupled between the gas collection chamber and a vent, the relief channel comprising: a check valve to allow fluid flow along the relief channel from the gas collection chamber to the vent when a pressure in the gas collection chamber is raised above atmospheric pressure; and a printing fluid impermeable filter to block flow of printing fluid through the relief channel, wherein the filter is gas permeable.

2. The apparatus of claim 1, wherein the gas collection chamber is to collect gas emitted from the printing fluid in response to heating of the printing fluid by the associated actuator.

3. The apparatus of claim 1, wherein the filter is to form a gas impermeable seal upon contact with printing fluid.

4. The apparatus of claim 1, wherein the vent comprises a vent to atmosphere.

5. The apparatus of claim 1, wherein the apparatus comprises a gas sensor to monitor an amount of gas in the gas collection chamber.

6. A method of evacuating gas from a fluid ejection device, the method comprising: delivering printing fluid to the fluid ejection device at a predetermined flow rate to cause a pressure in the fluid ejection device to exceed a threshold pressure; and in response to the pressure in the fluid ejection device exceeding the threshold pressure, opening a pressure relief valve of a relief channel, coupled between a gas collection chamber of the fluid ejection device and an exhaust vent, to evacuate gas from the gas collection chamber.

7. The method of claim 6, further comprising: monitoring accumulation of gas in the gas collection chamber; and wherein the delivering printing fluid to the fluid ejection device is performed in response to a monitored accumulation of gas being greater than a threshold amount.

8. The method of claim 6, further comprising: monitoring printing fluid consumed associated with the fluid ejection device; and wherein the delivering printing fluid to the fluid ejection device is performed in response to a monitored printingfluid consumed beinggreaterthan a threshold amount.

9. The method of claim 6, wherein the pressure release valve is closed during normal printing operations of the fluid ejection device to isolate the exhaust vent from the gas collection chamber.

10. The method of claim 6, further comprising: opening a pressure regulator regulating the pressure in the fluid ejection device, while delivering printing fluid to the fluid ejection device at the predetermined flow rate.

11. An inkjet printing system comprising: a fluid ejection device further comprising: a nozzle; an actuator associated with the nozzle, the actuator to heat a printing fluid to cause a drop of the printing fluid to be ejected from the nozzle; a gas collection chamber associated with the actuator; and a relief channel coupled between the gas collection chamber and a vent to atmosphere, the relief channel comprising: a check valve to allow fluid flow along the relief channel from the gas collection chamber to the vent when a pressure in the gas collection chamber is raised above atmospheric pressure; and a printing fluid impermeable filter to block flow of printing fluid through the relief channel, wherein the filter is gas permeable; and a printing fluid delivery system to supply printing fluid from a printing fluid reservoir to the fluid ejection device; and control circuitry coupled to the fluid ejection device and the printing fluid delivery system.

12. The printing system of claim 11, the control circuitry to: monitor printing fluid consumed associated with the fluid ejection device; and in response to a monitored printing fluid consumed being greater than a threshold amount, control the printing system to perform a service operation.

13. The printing system of claim 12, wherein during the service operation the control circuitry is to control the printing fluid delivery system to deliver printing fluid to the fluid ejection device at a predetermined flow rate to cause the pressure in the gas collection chamber to exceed a threshold pressure.

14. The printing system of claim 13, wherein the printing fluid delivery system further comprises: a pressure regulator to regulate pressure in the fluid ejection device; and the control circuitry further to open the pressure regulator during delivery of the printing fluid at the predetermined flow rate.

15. The printing system of claim 11, wherein the fluid ejection device comprises a page wide array fluid ejection device.