Inkjet printing system and related methods

Abstract

The present application discloses an inkjet printing system and method that dynamically control the meniscus pressure at a nozzle to more reliably deliver ink to a substrate. The system and method include: inferring an angle of a longitudinal axis of a printhead relative to a vertical reference axis based on an orientation signal from an orientation sensor; determining a target feed fluid pressure upstream of the nozzle and a target recirculation fluid pressure downstream of the nozzle at least in part based on the inferred angle of the longitudinal axis so as to maintain a target pressure differential across the nozzle; and controlling a variable feed pump speed and a variable recirculation pump speed to obtain the target feed fluid pressure and the target recirculation fluid pressure.

Description

Technical Field

[0001] The present disclosure generally relates to inkjet printing, and more particularly, to dynamically controlling the fluid pressure present at the meniscus of a printhead nozzle. Background Art

[0002] Inkjet printing systems are known that are capable of printing on complex three-dimensional surfaces, where the orientation of the printhead changes during operation. The system dynamically controls the backpressure within the printhead to maintain the ink within the nozzle at a desired meniscus level. However, using backpressure to supply ink to the nozzle may limit the speed at which ink can be supplied to the nozzle. Summary of the Invention

[0003] According to one aspect of the present disclosure, an inkjet printing system includes: an ink supply device; a printhead having nozzles configured to eject ink, the printhead defining a longitudinal axis and being supported to rotate about at least one degree of freedom relative to a vertical reference axis; a feed line fluidly coupled between the ink supply device and the nozzles; and a recirculation line fluidly coupled between the nozzles and the ink supply device independently of the feed line. A feed pump is disposed in the feed line and has a variable feed pump speed to generate a feed fluid pressure in the feed line between the feed pump and the nozzles, and a recirculation pump is disposed in the recirculation line and has a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzles. An orientation sensor determines the orientation of the longitudinal axis of the printhead and generates an orientation signal. A processor is operatively coupled to the feed pump, the recirculation pump, and the orientation sensor, and is programmed to infer an angle of the longitudinal axis relative to the vertical reference axis based on the orientation signal from the orientation sensor, determine a target feed fluid pressure and a target recirculation fluid pressure at least in part based on the inferred angle of the longitudinal axis to maintain a target pressure differential across the nozzles, and control the variable feed pump speed and the variable recirculation pump speed to obtain the target feed fluid pressure and the target recirculation fluid pressure.

[0004] According to another aspect of the present disclosure, an inkjet printing system includes: an ink supply device; a frame that is supported to rotate about at least one degree of freedom relative to a vertical reference axis; a printhead coupled to the frame and having nozzles configured to eject ink, the printhead defining a longitudinal axis; a feed line fluidly coupled between the ink supply device and the nozzles; and a recirculation line fluidly coupled between the nozzles and the ink supply device independently of the feed line. A feed pump is disposed in the feed line and has a variable feed pump speed to generate a feed fluid pressure in the feed line between the feed pump and the nozzles, and a recirculation pump is disposed in the recirculation line and has a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzles. At least one pressure sensor is coupled to the frame and is configured to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure, and an orientation sensor is provided to determine the orientation of the longitudinal axis of the printhead and generate an orientation signal. A processor is operatively connected to the feed pump, the recirculation pump, the at least one pressure sensor, and the orientation sensor, and is programmed to infer an angle of the longitudinal axis relative to the vertical reference axis based on the orientation signal from the orientation sensor, determine a target feed fluid pressure and a target recirculation fluid pressure at least in part based on the inferred angle of the longitudinal axis to maintain a target pressure differential across the nozzles, and control the variable feed pump speed and the variable recirculation pump speed respectively based on the feed line pressure signal and the recirculation line pressure signal to obtain the target feed fluid pressure and the target recirculation fluid pressure.

[0005] According to another aspect of the present disclosure, a method of dynamically controlling the ink flow rate through the nozzles of a printhead disposed in an inkjet printing system includes: determining the orientation of the longitudinal axis of the printhead based on an orientation signal from an orientation sensor; calculating an angle between the longitudinal axis of the printhead and a vertical reference axis; determining a target feed fluid pressure in a feed line supplying the nozzles and a target recirculation fluid pressure in a recirculation line returning from the nozzles at least in part based on the orientation of the longitudinal axis to obtain a target pressure differential at the nozzles; and controlling a variable feed pump speed of a feed pump disposed in the feed line and a variable recirculation pump speed of a recirculation pump disposed in the recirculation line to obtain the target feed fluid pressure and the target recirculation fluid pressure.

[0006] The features, functions, and advantages that have been discussed can be implemented independently in various embodiments or can be combined in other embodiments, and further details thereof can be seen with reference to the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic block diagram of an inkjet printing system according to the present disclosure.

[0008] Figure 2 is an enlarged perspective view of an exemplary actuator used in an Figure 1 inkjet printing system.

[0009] Figure 3 is Figure 1 a front view of an

[0010] Figure 4 inkjet printing system in a vertical position. Figures 1-3 is a schematic front elevation plan sectional view of a printhead of an

[0011] Figure 5 inkjet printing system in a first rotational position. Figure 4 is a schematic front elevation plan sectional view of a printhead of an

[0012] Figure 6 inkjet printing system in a second rotational position. Figure 4 and Figure 5 is a schematic front elevation plan sectional view of a printhead of an

[0013] Figure 7 inkjet printing system in a second rotational position, where the nozzles of the printhead are inverted.

[0014] It should be understood that the figures are not necessarily drawn to scale and sometimes schematically illustrate the disclosed embodiments. It should be further understood that the following detailed description is merely exemplary in nature and is not intended to limit the invention or its application and use. Thus, although the present disclosure is depicted and described as certain illustrative embodiments for purposes of explanation, it should be understood that the present disclosure may be implemented in a variety of other types of embodiments as well as in a variety of other systems and environments. DETAILED DESCRIPTION

[0015] The following detailed description is the best presently contemplated mode of carrying out the invention. Since the scope of the invention is best defined by the appended claims, the description should not be regarded as limiting, but merely for the purpose of illustrating the general principles of the invention.

[0016] An inkjet printing system and method are disclosed herein that are particularly suitable for printing on complex three-dimensional surfaces such as the surface of an aircraft 10 ( Figures 4-6 ). The inkjet printing system includes a printhead having nozzles from which ink is ejected. More specifically, the systems and methods disclosed herein dynamically manage the feed fluid pressure upstream of the nozzles and the recirculation fluid pressure downstream of the nozzles at least in part based on the orientation of the printhead. The feed flow rate and the recirculation flow rate are controlled such that a target fluid pressure is maintained at the meniscus of the nozzles, independent of the orientation of the printhead.

[0017] Reference Figure 1 , the inkjet printing system 20 includes a printhead 22 coupled to a frame 24. The frame 24 is supported for rotation about at least one degree of freedom relative to a vertical reference axis 26. In some embodiments, the frame is supported for rotation about three degrees of freedom, such as rotation about orthogonal X, Y, and Z axes, and the vertical reference axis 26 may be parallel to the Z axis, as Figure 1 shown.

[0018] The inkjet printing system 20 may further include a frame actuator 30 for actuating the frame 24 about at least one degree of freedom relative to the vertical reference axis 26. For example, Figure 2 the frame actuator 30 shown in operates to rotate the frame 24 about the X, Y, and Z axes. In this embodiment, the frame actuator 30 includes a microwheel actuation device 32 having a plurality of microactuator elements. For example, the microwheel actuation device 32 includes a first microwheel 34 rotatably coupled to a first electric motor 36 and a second microwheel 38 rotatably coupled to a second electric motor 40. The first electric motor 36 and the second electric motor 40 independently drive the first microwheel 34 and the second microwheel 38, respectively. However, it should be understood that fewer or greater numbers of microwheels and electric motors may be incorporated into the microwheel actuation device 32 as needed.

[0019] In some embodiments, the circumference of the first microwheel 34 has a first wheel surface 42, and the circumference of the second microwheel 38 has a second wheel surface 44. Additionally, each of the first wheel surface 42 and the second wheel surface 44 includes wheel microtextures 46 that engage microtextures on the surface of a gimbal 48. The frame 24 may include a frame base 50 that pivots and / or rotates about the gimbal 48 such that operating the first electric motor 36 and the second electric motor 40 sequentially or simultaneously will cause the frame 24 to rotate. Although the frame actuator 30 is shown as a gimbal-type actuator in Figure 2 , it should be understood that other types of frame actuators, such as gear-driven arms or robotic arms, may be used without departing from the scope of the present application. Additionally, although the illustrated frame actuator 30 provides movement along three axes, it should be understood that the frame actuator is capable of moving along more or fewer than three axes.

[0020] Reference Figure 3, the inkjet printing system 20 includes a bulk ink supply device 52 for supplying ink to the nozzles 54 of the printhead 22. More specifically, a feed line 56 fluidly couples the ink supply device 52 to the nozzles 54, and ink is supplied to the nozzles 54 through this feed line. A recirculation line 58 fluidly couples the nozzles 54 to the ink supply device 52 independently of the feed line 56, and ink is removed from the nozzles 54 through this recirculation line. A feed pump 60 is disposed in the feed line 56 and has a variable feed pump speed to generate a feed line fluid pressure in the feed line 56 between the feed pump 60 and the nozzles 54. Similarly, a recirculation pump 62 is disposed in the recirculation line 58 and has a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line 58 between the recirculation pump 62 and the nozzles 54. Thus, it should be understood that the feed pump 60 and the recirculation pump 62 can be operated to generate a fluid pressure at the nozzles 54.

[0021] The printhead 22 is coupled to the frame 24 and can pivot with the frame. As shown in reference Figures 3-6 Best shown, the printhead 22 generally includes a housing 70 that defines an internal ink passage 72. The internal ink passage 72 is fluidly connected between each of the nozzles 54 and the feed line 56 and the recirculation line 58. Additionally, the printhead 22 defines a longitudinal axis 66 that extends through the nozzles 54 and indicates the orientation of the nozzles 54.

[0022] An orientation sensor 100 is provided for determining the orientation of the printhead 22. In the exemplary embodiment shown in Figure 3 shown, the orientation sensor 100 is an accelerometer coupled to the frame 24. Alternatively, the orientation sensor 100 can be coupled to any structure mounted on the frame 24, such as the printhead 22. The accelerometer can determine the orientation of a reference associated with the printhead 22, such as the longitudinal axis 66, relative to a fixed reference frame, such as the vertical reference axis 26. In this embodiment, the orientation sensor 100 generates an orientation signal indicating the angle between the longitudinal axis 66 and the vertical reference axis 26. Depending on the device, orientation feedback can be provided by the CNC machine tool at any time based on the given position of the end effector.

[0023] The inkjet printing system 20 also includes at least one pressure sensor for determining the actual pressure of the ink upstream and downstream of the nozzles 54. In Figure 3In the example shown, at least one pressure sensor includes a feed pressure sensor 102 configured to generate a feed line pressure signal indicative of the actual pressure of the ink supplied to the nozzle 54 through the feed line 56. The at least one pressure sensor also includes a recirculation pressure sensor 104 configured to generate a recirculation line pressure signal indicative of the actual pressure of the ink removed from the nozzle 54 through the recirculation line 58. The feed pressure sensor 102 and the recirculation pressure sensor 104 are housed in a pressure manifold 105.

[0024] In operation, the printhead 22 receives ink from the ink supply device 52 and selectively discharges ink droplets from the nozzle 54 onto the surface 10. As Figures 4-6 Best shown, the nozzle 54 defines a desired meniscus level 112 at which the ink exists in the nozzle 54 to accurately discharge ink droplets. The desired meniscus level 112 has a position fixed relative to the pressure manifold 105 housing the feed pressure sensor 102 and the recirculation pressure sensor 104. For example, the desired meniscus level 112 of the nozzle 54 is spaced a distance D1 from the feed pressure sensor 102 and the recirculation pressure sensor 104 along the longitudinal axis 66.

[0025] The inkjet printing system 20 also includes a controller 120 for controlling the operation of the printhead 22. More specifically, the controller 120 includes a processor 122 that can execute logic stored in the data memory 124 to control the operation. The controller 120 is operatively coupled to the feed pump 60, the recirculation pump 62, the orientation sensor 100, the feed pressure sensor 102, and the recirculation pressure sensor 104. The controller 120 can represent any kind of computing device or controller, or can also be part of another device, such as a device fully included within a server, and a portion of the controller 120 can be elsewhere or located within other computing devices.

[0026] The processor 122 is programmed to dynamically control the pressure differential between the feed line pressure and the recirculation line pressure based at least in part on the orientation of the printhead 22. More specifically, the processor 122 can be programmed to infer the angle A of the longitudinal axis 66 relative to the vertical reference axis 26 based on the orientation signal from the orientation sensor 100 ( Figures 4-6) Additionally, the processor 122 can determine the target feed pressure and the target recirculation pressure at least partially based on the inferred angle of the longitudinal axis to maintain a target differential pressure at the nozzle 54. Further still, the processor 122 can control the variable feed pump speed and the variable recirculation pump speed to obtain the target feed pressure and the target recirculation pressure, thereby providing a target differential pressure at the nozzle 54 regardless of the orientation of the printhead 22. In an example where a feed pressure sensor 102 and a recirculation pressure sensor 104 are provided, the processor is also programmed to control the variable feed pump speed and the variable recirculation pump speed based on the feed line pressure signal and the recirculation line pressure signal, respectively. In some examples, the target differential pressure is in the range of approximately +2 millibars (mb a r) to -2 mb a r.

[0027] Additionally, the processor 122 can be programmed to calculate a head pressure adjustment to the target feed pressure and the target recirculation pressure. The head pressure adjustment is based on the meniscus level 112 of the nozzle 54 and the distances D1 along the longitudinal axis 66 between the feed pressure sensor 102 and the recirculation pressure sensor 104 and the orientation of the printhead 22. Since the distance D1 is predetermined and substantially fixed, and the angle of the longitudinal axis 66 is determined by the orientation sensor 100, the head pressure adjustment can be calculated using simple trigonometric functions.

[0028] It should be understood that the head pressure adjustment will vary according to the orientation of the printhead 22. More specifically, the cosine of the angle A is equal to the head pressure adjustment divided by the distance D1. In other words, the head pressure adjustment is equal to the product of the distance D1 and the cosine of the angle A. Thus, when the printhead 22 is oriented such that the longitudinal axis 66 is vertical, the angle A is zero, and the cosine of 0 is 1, so the head pressure adjustment is equal to the distance D1. As Figure 5 shown, when the printhead 22 is rotated to the angle A1, then the head pressure adjustment is equal to the distance D1 multiplied by the cosine of the angle A1. For example, if the angle A1 is 20° and the distance D1 is 2 inches (5.08 cm), then the head pressure adjustment is 1.88 inches of water column (4.68 mbar). This head pressure adjustment is then applied to the preliminary feed and recirculation pressure calculations to arrive at the target feed pressure and the target recirculation pressure.

[0029] Furthermore, it should be noted that when the printhead 22 is inverted to the angle A2, as Figure 6 shown, the head pressure adjustment will have a negative value. Therefore, the head pressure adjustment for the inverted printhead 22 will require an increase in the preliminary feed and recirculation pressure calculations to obtain the target feed and recirculation pressures.

[0030] Figure 7FIG. 0 is a flow chart showing an exemplary method 200 for dynamically controlling the feed and recirculation pressures through printhead 22. Method 200 begins at block 202 by determining the orientation of the longitudinal axis 66 of printhead 22 based on an orientation signal from orientation sensor 100. At block 204, method 200 continues by calculating the angle between the longitudinal axis 66 of printhead 22 and the vertical reference axis 26. At block 206, a target feed pressure for the ink supplied to nozzle 54 and a target recirculation pressure for the ink removed from nozzle 54 are determined at least in part based on the inferred angle of the longitudinal axis 66 to obtain a target differential pressure at nozzle 54. At block 208, method 200 includes controlling a variable feed pump speed of a feed pump disposed in the feed line supplying nozzle 54 and a variable recirculation pump speed of a recirculation pump disposed in the recirculation line returning from nozzle 54 to obtain the target feed pressure and the target recirculation pressure.

[0031] As described above, a method for spraying surface 10 can be performed using an inkjet printing system 20 having a printhead 22 coupled to a frame 24, where printhead 22 has nozzles 54. The method includes: providing ink to printhead 22, selectively ejecting ink droplets from nozzles 54 onto surface 10, actuating frame 24 in at least one degree of freedom while providing ink to printhead 22, and dynamically controlling the differential pressure at nozzles 54.

[0032] To actuate frame 24, frame 24 is rotated about the X, Y, and Z axes. For example, such actuation can include independently driving first idler wheel 34 and second idler wheel 38 using first electric motor 36 and second electric motor 40. In a particular example, when frame 24 includes a frame base 50 that pivots and / or rotates about gimbal 48, the actuation includes pivoting frame 24 by sequentially or simultaneously operating first electric motor 36 and second electric motor 40. In such an example, gimbal 48 moves relative to frame 50 when motors 36, 40 are operated.

[0033] To provide ink, ink is provided or supplied from a bulk ink supply device 52 to nozzles 54 of printhead 22. For example, ink is supplied to nozzles 54 through a feed line 56 fluidly coupled to ink supply device 52 and nozzles 54. Additionally, ink can be removed from nozzles 54 through a recirculation line 58 that is fluidly coupled to nozzles 54 and ink supply device 52 independently of feed line 56.

[0034] When ink is supplied to the printhead 22, a feed line fluid pressure is generated in the feed line 56 between the feed pump 60 and the nozzle 54 using a feed pump 60 disposed in the feed line 56, wherein the feed pump 60 has a variable feed pump speed. Similarly, a recirculation fluid pressure is generated in the recirculation line 58 between the recirculation pump 62 and the nozzle 54 using a recirculation pump 62 disposed in the recirculation line 58, wherein the recirculation pump 62 has a variable recirculation pump speed. Additionally, by the operation of the feed pump 60 and the recirculation pump 62, the supplied ink also generates a fluid pressure at the nozzle 54.

[0035] Dynamically controlling the pressure differential also includes determining the actual pressures of the ink upstream and downstream of the nozzle 54. For example, for the determination, a feed line pressure sensor 102 generates a feed line pressure signal indicative of the actual pressure of the ink supplied to the nozzle 54 through the feed line 56. Similarly, a recirculation pressure sensor 104 generates a recirculation line pressure signal indicative of the actual pressure of the ink removed from the nozzle 54 through the recirculation line 58. The variable feed pump speed and the variable recirculation pump speed are controlled based on the feed line pressure signal and the recirculation line pressure signal.

[0036] Dynamic control also includes determining the orientation of the printhead 22. More specifically, this orientation is determined by using an orientation sensor 100 to determine the orientation of a reference 66 associated with the printhead 22 relative to a fixed reference frame 26. Further details are described below.

[0037] Dynamically controlling the pressure differential includes dynamically controlling the pressure differential between the feed line pressure and the recirculation line pressure at least in part based on the orientation of the printhead 22. This orientation can be determined by inferring the angle A of the longitudinal axis 66 of the printhead 22 relative to the vertical reference axis 26 based on an orientation signal from the orientation sensor 100. The target feed pressure and the target recirculation pressure for maintaining the target pressure differential at the nozzle 54 can be determined at least based on the inferred angle A of the longitudinal axis 66 of the printhead 22. The variable feed pump speed and the variable recirculation pump speed are controlled to obtain the target feed pressure and the target recirculation pressure, thereby providing the target pressure differential at the nozzle 54 regardless of the orientation of the printhead 22.

[0038] Dynamic control can also include calculating a head pressure adjustment for the target feed pressure and the target recirculation pressure. Such calculation can include varying the head pressure adjustment according to the orientation of the printhead 22. The head pressure adjustment can then be applied to the preliminary feed and recirculation pressure calculations to arrive at the target feed pressure and the target recirculation pressure.

[0039] In addition, the present disclosure includes implementations according to the following examples:

[0040] Example A1. A method of spraying a surface using an inkjet printing system having a print head coupled to a frame, the print head having nozzles, the method comprising: providing ink to the print head; selectively discharging ink droplets from the nozzles onto the surface; actuating the frame in at least one degree of freedom while the ink is being provided to the print head; and dynamically controlling the pressure differential at the nozzles.

[0041] Example A2. The method according to Example A1, wherein actuating further comprises rotating the frame about the X, Y, and Z axes.

[0042] Example A3. The method according to Example A1 or A2, wherein actuating further comprises independently driving a first micro-wheel and a second micro-wheel using a first electric motor and a second electric motor.

[0043] Example A4. The method according to any one of Examples A1 to A3, wherein the frame comprises a frame base pivotally and / or rotatably mounted about a gimbal, and wherein actuating further comprises pivoting the frame by sequentially or simultaneously operating the first electric motor and the second electric motor.

[0044] Example A5. The method according to any one of Examples A1 to A4, wherein providing ink further comprises providing ink from a bulk ink supply device to the nozzles of the print head.

[0045] Example A6. The method according to any one of Examples A1 to A5, wherein providing ink further comprises supplying ink to the nozzles through a feed line fluidly coupled to the ink supply device and the nozzles.

[0046] Example A7. The method according to any one of Examples A1 to A6, further comprising removing ink from the nozzles through a recirculation line fluidly coupled to the nozzles and the ink supply device independently of the feed line.

[0047] Example A8. The method according to any one of Examples A1 to A7, wherein providing ink further comprises generating a feed line fluid pressure in the feed line between the feed pump and the nozzles using a feed pump disposed in the feed line, wherein the feed pump has a variable feed pump speed.

[0048] Example A9. The method according to any one of Examples A1 to A8, wherein providing ink further comprises generating a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzles using a recirculation pump disposed in the recirculation line, wherein the recirculation pump has a variable recirculation pump speed.

[0049] Example A10. The method according to any one of Examples A1 to A9, wherein providing ink further comprises generating a fluid pressure at the nozzles by operating the feed pump and the recirculation pump.

[0050] Example A11. The method according to any one of Examples A1 to A10, wherein the dynamic control further includes determining the actual pressures of the ink upstream and downstream of the nozzle.

[0051] Example A12. The method according to Example A11, wherein determining the actual pressures further includes using a feed pressure sensor to generate a feed line pressure signal indicative of the actual pressure of the ink supplied to the nozzle through the feed line.

[0052] Example A13. The method according to Example A11 or A12, wherein determining the actual pressures further includes using a recirculation pressure sensor to generate a recirculation line pressure signal indicative of the actual pressure of the ink removed from the nozzle through the recirculation line.

[0053] Example A14. The method according to any one of Examples A1 to A13, wherein the dynamic control further includes controlling a variable feed pump speed and a variable recirculation pump speed based on the feed line pressure signal and the recirculation line pressure signal.

[0054] Example A15. The method according to any one of Examples A1 to A14, wherein the dynamic control further includes determining the orientation of the print head.

[0055] Example A16. The method according to Example A15, wherein determining the orientation further includes using an orientation sensor to determine the orientation of a reference associated with the print head relative to a fixed reference frame.

[0056] Example A17. The method according to any one of Examples A1 to A16, wherein dynamically controlling the pressure difference further includes dynamically controlling the pressure difference between the feed line pressure and the recirculation line pressure at least in part based on the orientation of the print head.

[0057] Example A18. The method according to Example A17, further including inferring the angle of the longitudinal axis of the print head relative to a vertical reference axis (26) based on an orientation signal from the orientation sensor.

[0058] Example A19. The method according to any one of Examples A1 to A18, wherein the dynamic control further includes determining a target feed pressure and a target recirculation pressure at least in part based on the inferred angle of the longitudinal axis of the print head to maintain a target pressure difference at the nozzle.

[0059] Example A20. The method according to Example A19, further including controlling a variable feed pump speed and a variable recirculation pump speed to obtain the target feed pressure and the target recirculation pressure, thereby providing a target pressure difference at the nozzle regardless of the orientation of the print head.

[0060] Example A21. The method according to any one of Examples A1 to A20, wherein the dynamic control further comprises calculating a head pressure adjustment for a target feed pressure and a target recirculation pressure.

[0061] Example A22. The method according to Example A21, wherein the calculating further comprises varying the head pressure adjustment based on the orientation of the printhead.

[0062] Example A23. The method according to Example A22, further comprising applying the head pressure adjustment to a preliminary feed and recirculation pressure calculation to derive a target feed pressure and a target recirculation pressure.

[0063] Example B1. An inkjet printing system, comprising: an ink supply device; a printhead having nozzles configured to eject ink and supported for rotation about at least one degree of freedom; a feed pump disposed in a feed line and having a variable feed pump speed for generating a feed fluid pressure in the feed line between the feed pump and the nozzles; a recirculation pump disposed in a recirculation line and having a variable recirculation pump speed for generating a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzles; an orientation sensor for determining the orientation of the printhead; and a processor operatively coupled to the feed pump, the recirculation pump, and the orientation sensor, the processor being programmed to control the variable feed pump speed and the variable recirculation pump speed based on the orientation of the printhead to obtain a target feed fluid pressure and a target recirculation fluid pressure.

[0064] Example B2. The system according to Example B1, further comprising: a feed line fluidly coupled between the ink supply device and the nozzles; and a recirculation line fluidly coupled between the nozzles and the ink supply device independently of the feed line.

[0065] Example B3. The system according to Example B2, wherein the printhead defines a longitudinal axis, and wherein the processor is further configured to: infer an angle of the longitudinal axis relative to a vertical reference axis based on an orientation signal from the orientation sensor; and determine the target feed fluid pressure and the target recirculation fluid pressure at least in part based on the inferred angle of the longitudinal axis to maintain a target pressure differential across the nozzles.

[0066] Example B4. An inkjet printing system, comprising: an ink supply device; a printhead having nozzles configured to discharge ink, the printhead defining a longitudinal axis and being supported for rotation about at least one degree of freedom relative to a vertical reference axis; a feed line fluidly coupled between the ink supply device and the nozzles; a recirculation line fluidly coupled between the nozzles and the ink supply device independently of the feed line; a feed pump disposed in the feed line and having a variable feed pump speed to generate a feed fluid pressure in the feed line between the feed pump and the nozzles; a recirculation pump disposed in the recirculation line and having a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzles; an orientation sensor for determining the orientation of the longitudinal axis of the printhead and generating an orientation signal; and a processor operatively coupled to the feed pump, the recirculation pump, and the orientation sensor, the processor being programmed to: infer an angle of the longitudinal axis relative to the vertical reference axis based on the orientation signal from the orientation sensor; and determine a target feed fluid pressure and a target recirculation fluid pressure at least in part based on the inferred angle of the longitudinal axis to maintain a target differential pressure across the nozzles; and control the variable feed pump speed and the variable recirculation pump speed to obtain the target feed fluid pressure and the target recirculation fluid pressure.

[0067] Example B5. The inkjet printing system according to any one of Examples B1 to B4, further comprising at least one pressure sensor configured to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure.

[0068] Example B6. The inkjet printing system according to Example B5, wherein the at least one pressure sensor includes a feed line pressure sensor and a recirculation line pressure sensor.

[0069] Example B7. The inkjet printing system according to Example B6, wherein the processor is further operatively coupled to the at least one pressure sensor and is further programmed to control the variable feed pump speed and the variable recirculation pump speed based on the feed line pressure signal and the recirculation line pressure signal, respectively.

[0070] Example B8. The inkjet printing system according to any one of Examples B1 to B7, wherein the nozzles define a desired meniscus level for holding ink in the nozzles.

[0071] Example B9. The inkjet printing system according to Example B8, wherein the desired meniscus level of the nozzles is spaced a distance D1 from the at least one pressure sensor along the longitudinal axis of the printhead.

[0072] Example B10. The inkjet printing system according to Example B9, wherein when determining the target feed fluid pressure and the target recirculation fluid pressure, the processor is further programmed to calculate the head pressure based on the inferred angle of the longitudinal axis and the distance D1, and to adjust the target feed pressure and the target recirculation pressure based on the head pressure.

[0073] Example B11. The inkjet printing system according to any one of Examples B1 to B10, wherein the orientation sensor includes an accelerometer.

[0074] Example B12. The inkjet printing system according to any one of Examples B1 to B11, further comprising a frame supported to rotate about at least one degree of freedom.

[0075] Example B13. The inkjet printing system according to Example B12, wherein the printhead is coupled to the frame.

[0076] Example C1. An inkjet printing system, comprising: an ink supply device; a frame supported to rotate about at least one degree of freedom; a printhead coupled to the frame and having nozzles configured to eject ink; a feed pump disposed in a feed line and having a variable feed pump speed to generate a feed fluid pressure in the feed line between the feed pump and the nozzles; a recirculation pump disposed in a recirculation line and having a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzles; at least one pressure sensor configured to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure; an orientation sensor for determining the orientation of the printhead and generating an orientation signal; and a processor operably coupled to the feed pump, the recirculation pump, the at least one pressure sensor, and the orientation sensor, the processor being programmed to control the variable feed pump speed and the variable recirculation pump speed based on the feed line pressure signal and the recirculation line pressure signal.

[0077] Example C2. The system according to Example C1, wherein the at least one degree of freedom is relative to a vertical reference axis.

[0078] Example C3. The system according to Example C1 or C2, wherein the printhead defines a longitudinal axis; and the orientation sensor determines the orientation of the longitudinal axis of the printhead.

[0079] Example C4. The system according to any one of Examples C1 to C3, wherein the at least one pressure sensor is coupled to the frame.

[0080] Example C5. The method according to any one of Examples C1 to C4 further includes: a feed line fluidly coupled between the ink supply device and the nozzle; and a recirculation line fluidly coupled between the nozzle and the ink supply device independently of the feed line.

[0081] Example C6. The system according to Example C5, wherein the processor is further programmed to: infer an angle of a longitudinal axis of the printhead relative to a vertical reference axis based on an orientation signal from an orientation sensor; determine a target feed fluid pressure and a target recirculation fluid pressure at least in part based on the inferred angle to maintain a target pressure differential across the nozzle; and obtain the target feed fluid pressure and the target recirculation fluid pressure by controlling a variable feed pump speed and a variable recirculation pump speed.

[0082] Example C7. An inkjet printing system includes: an ink supply device; a frame supported for rotation about at least one degree of freedom relative to a vertical reference axis; a printhead coupled to the frame and having a nozzle configured to eject ink, the printhead defining a longitudinal axis; a feed line fluidly coupled between the ink supply device and the nozzle; a recirculation line fluidly coupled between the nozzle and the ink supply device independently of the feed line; a feed pump disposed in the feed line and having a variable feed pump speed to generate a feed fluid pressure in the feed line between the feed pump and the nozzle; a recirculation pump disposed in the recirculation line and having a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzle; at least one pressure sensor coupled to the frame and configured to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure; an orientation sensor for determining an orientation of the longitudinal axis of the printhead and generating an orientation signal; and a processor operably coupled to the feed pump, the recirculation pump, the at least one pressure sensor, and the orientation sensor, the processor being programmed to: infer an angle of the longitudinal axis relative to the vertical reference axis based on the orientation signal from the orientation sensor; determine a target feed fluid pressure and a target recirculation fluid pressure at least in part based on the inferred angle of the longitudinal axis to maintain a target pressure differential across the nozzle; and control the variable feed pump speed and the variable recirculation pump speed respectively based on the feed line pressure signal and the recirculation line pressure signal to obtain the target feed fluid pressure and the target recirculation fluid pressure.

[0083] Example C8. The inkjet printing system according to any one of Examples C1 to C7, wherein the nozzle defines a desired meniscus level for holding ink in the nozzle.

[0084] Example C9. The inkjet printing system according to Example C8, wherein a desired meniscus level of the nozzle is spaced apart from at least one pressure sensor by a distance D1 along a longitudinal axis of the printhead.

[0085] Example C10. The inkjet printing system according to Example C9, wherein, when determining a target feed fluid pressure and a target recirculation fluid pressure, the processor is further programmed to calculate a head pressure based on an inferred angle of the longitudinal axis and the distance D1, and to adjust the target feed pressure and the target recirculation pressure based on the head pressure.

[0086] Example C11. The inkjet printing system according to any one of Examples C1 to C10, wherein at least one pressure sensor includes a feed line pressure sensor and a recirculation line pressure sensor.

[0087] Example C12. The inkjet printing system according to any one of Examples C1 to C11, wherein the orientation sensor includes an accelerometer.

[0088] Example D1. A method for dynamically controlling an ink flow rate through a nozzle of a printhead disposed in an inkjet printing system, the method comprising: determining an orientation of a longitudinal axis of the printhead based on an orientation signal from an orientation sensor; calculating an angle between the longitudinal axis of the printhead and a vertical reference axis; determining at least in part a target feed fluid pressure in a feed line supplying the nozzle and a target recirculation fluid pressure in a recirculation line returning from the nozzle based on the orientation of the longitudinal axis to obtain a target pressure difference at the nozzle; and controlling a variable feed pump speed of a feed pump disposed in the feed line and a variable recirculation pump speed of a recirculation pump disposed in the recirculation line to obtain the target feed fluid pressure and the target recirculation fluid pressure.

[0089] Example D2. The method according to Example D1, wherein at least one pressure sensor is provided to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure, and wherein the variable feed pump speed and the variable recirculation pump speed are controlled based on the feed line pressure signal and the recirculation line pressure signal, respectively.

[0090] Example D3. The method according to Example D2, wherein the nozzle defines a desired meniscus level for holding ink in the nozzle, the desired meniscus level of the nozzle is spaced apart from at least one pressure sensor by a distance D1 along the longitudinal axis of the printhead, wherein determining the target feed fluid pressure and the target recirculation fluid pressure further includes calculating a head pressure based on the orientation of the longitudinal axis and the distance D1, and adjusting the target feed pressure and the target recirculation pressure based on the head pressure.

[0091] Example D4. The method according to Example D2 or D3, wherein at least one pressure sensor includes a feed line pressure sensor and a recirculation line pressure sensor.

[0092] Example D5. The method according to any one of Examples D1 to D4, wherein the orientation sensor includes an accelerometer.

[0093] Example D6. The method according to any one of Examples D1 to D5, wherein the feed line fluidly couples the nozzle to the ink supply device, and wherein the recirculation line fluidly couples the nozzle to the ink supply device independently of the feed line.

[0094] Descriptions of different advantageous arrangements have been given for purposes of illustration and description, and the description is not intended to be exhaustive or limited to the embodiments in the disclosed form. Many modifications and variations will be obvious to those of ordinary skill in the art. Additionally, different advantageous embodiments may describe different advantages compared to other advantageous embodiments. The selected one or more embodiments are chosen and described to explain the principles of the embodiments, practical applications, and to enable other ordinary skilled artisans in the art to understand the disclosure. Various modifications suitable for a particular purpose are envisioned.

Claims

1. An inkjet printing system (20), comprising: an ink supply device (52); a printhead (22) having nozzles (54) configured to eject ink and supported for rotation about at least one degree of freedom; a feed pump (60) disposed in a feed line (56) and having a variable feed pump speed to generate a feed fluid pressure in the feed line (56) between the feed pump (60) and the nozzles (54); a recirculation pump (62) disposed in a recirculation line (58) and having a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line (58) between the recirculation pump (62) and the nozzles (54); an orientation sensor (100) for determining the orientation of the printhead (22); and a processor (122) operatively coupled to the feed pump (60), the recirculation pump (62), and the orientation sensor (100), the processor (122) being programmed to control the variable feed pump speed and the variable recirculation pump speed based on the orientation of the printhead (22) to obtain a target feed fluid pressure and a target recirculation fluid pressure.

2. The inkjet printing system (20) according to claim 1, further comprising at least one pressure sensor (102, 104) configured to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure, and Among them, the processor (122) is further operatively coupled to the at least one pressure sensor (102, 104) and further programmed to control the variable feed pump speed and the variable recirculation pump speed based on the feed line pressure signal and the recirculation line pressure signal, respectively.

3. The inkjet printing system (20) according to claim 1, wherein, The nozzles (54) define a desired meniscus level (112) for holding ink in the nozzles (54), wherein the desired meniscus level (112) of the nozzles (54) is spaced a distance (D1) from the at least one pressure sensor (102, 104) along a longitudinal axis (66) of the printhead (22).

4. The inkjet printing system (20) according to claim 3, wherein, When determining the target feed fluid pressure and the target recirculation fluid pressure, the processor (122) is further programmed to calculate a head pressure based on an inferred angle (A) of the longitudinal axis (66) and the distance (D1) and to adjust the target feed fluid pressure and the target recirculation fluid pressure based on the head pressure.

5. The inkjet printing system (20) according to any one of claims 1 to 4, further comprising: a feed line (56) fluidly coupled between the ink supply device (52) and the nozzles (54); and a recirculation line (58) fluidly coupled between the nozzles (54) and the ink supply device (52) independently of the feed line (56), Wherein, the printhead (22) defines a longitudinal axis (66), and wherein the processor (122) is further programmed to: Infer an angle (A) of the longitudinal axis (66) relative to a vertical reference axis (26) based on an orientation signal from the orientation sensor (100); and Determine the target feed fluid pressure and the target recirculation fluid pressure at least in part based on the inferred angle (A) of the longitudinal axis (66) to maintain a target pressure differential across the nozzle (54).

6. The inkjet printing system according to claim 2, wherein, The at least one pressure sensor includes a feed line pressure sensor and a recirculation line pressure sensor.

7. The inkjet printing system according to claim 1, wherein, The orientation sensor includes an accelerometer.

8. An inkjet printing system, comprising: An ink supply device; A frame supported for rotation about at least one degree of freedom relative to a vertical reference axis; A printhead coupled to the frame and having a nozzle configured to eject ink, the printhead defining a longitudinal axis; A feed line fluidly coupled between the ink supply device and the nozzle; A recirculation line independently fluidly coupled between the nozzle and the ink supply device relative to the feed line; A feed pump disposed in the feed line and having a variable feed pump speed to generate a feed fluid pressure in the feed line between the feed pump and the nozzle; A recirculation pump disposed in the recirculation line and having a variable recirculation pump speed to generate a recirculation fluid pressure in the recirculation line between the recirculation pump and the nozzle; At least one pressure sensor coupled to the frame and configured to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure; An orientation sensor for determining an orientation of the longitudinal axis of the printhead and generating an orientation signal; And A processor operatively coupled to the feed pump, the recirculation pump, the at least one pressure sensor, and the orientation sensor, the processor being programmed to: Infer an angle of the longitudinal axis relative to the vertical reference axis based on the orientation signal from the orientation sensor; Determine a target feed fluid pressure and a target recirculation fluid pressure at least in part based on the inferred angle of the longitudinal axis to maintain a target pressure differential across the nozzle; And Control the variable feed pump speed and the variable recirculation pump speed respectively based on the feed line pressure signal and the recirculation line pressure signal to obtain the target feed fluid pressure and the target recirculation fluid pressure.

9. The inkjet printing system according to claim 8, wherein, The nozzle defines a desired meniscus level for holding ink in the nozzle.

10. The inkjet printing system according to claim 9, wherein, The desired meniscus level of the nozzle is spaced a distance (D1) from the at least one pressure sensor along the longitudinal axis of the printhead.

11. The inkjet printing system according to claim 10, wherein, When determining the target feed fluid pressure and the target recirculation fluid pressure, the processor is further programmed to calculate a head pressure based on an inferred angle of the longitudinal axis and the distance (D1), and to adjust the target feed pressure and the target recirculation pressure based on the head pressure.

12. The inkjet printing system according to claim 8, wherein, The at least one pressure sensor includes a feed line pressure sensor and a recirculation line pressure sensor.

13. The inkjet printing system according to claim 8, wherein, The orientation sensor includes an accelerometer.

14. A method of dynamically controlling the ink flow rate through a nozzle of a print head disposed in an inkjet printing system, the method comprising: determining an orientation of a longitudinal axis of the print head based on an orientation signal from an orientation sensor; calculating an angle between the longitudinal axis of the print head and a vertical reference axis; determining a target feed fluid pressure in a feed line supplying the nozzle and a target recirculation fluid pressure in a recirculation line returning from the nozzle at least partially based on the orientation of the longitudinal axis to obtain a target pressure differential at the nozzle; and controlling a variable feed pump speed of a feed pump disposed in the feed line and a variable recirculation pump speed of a recirculation pump disposed in the recirculation line to obtain the target feed fluid pressure and the target recirculation fluid pressure.

15. The method according to claim 14, wherein, Providing at least one pressure sensor to generate a feed line pressure signal indicative of an actual feed line pressure and a recirculation line pressure signal indicative of an actual recirculation line pressure, and wherein controlling the variable feed pump speed and the variable recirculation pump speed is based on the feed line pressure signal and the recirculation line pressure signal, respectively.

16. The method according to claim 15, wherein, The nozzle defines a desired meniscus level that holds ink in the nozzle, the desired meniscus level of the nozzle being spaced a distance (D1) from the at least one pressure sensor along the longitudinal axis of the print head, and wherein determining the target feed fluid pressure and the target recirculation fluid pressure further includes calculating a head pressure based on the orientation of the longitudinal axis and the distance (D1), and adjusting the target feed pressure and the target recirculation pressure based on the head pressure.

17. The method according to claim 15, wherein, The at least one pressure sensor includes a feed line pressure sensor and a recirculation line pressure sensor.

18. The method according to claim 14, wherein, The orientation sensor includes an accelerometer.

19. The method according to claim 14, wherein, The feed line fluidly couples the nozzle to an ink supply device, and wherein the recirculation line fluidly couples the nozzle to the ink supply device independently of the feed line.

20. A method of spraying a surface (10) using an inkjet printing system according to any one of claims 1 to 13, the inkjet printing system having a print head (22) coupled to a frame (24), the print head (22) having nozzles (54), the method comprising: providing ink to the print head (22); selectively ejecting ink droplets from the nozzles (54) onto the surface (10); actuating the frame (24) with at least one degree of freedom while ink is being provided to the print head (22); and dynamically controlling the pressure differential at the nozzles (54).

21. The method according to claim 20, wherein, The steps of dynamic control further include controlling the variable feed pump speed and the variable recirculation pump speed based on the feed line pressure signal and the recirculation line pressure signal.

22. The method according to claim 20, wherein, The step of dynamically controlling the pressure difference further includes dynamically controlling the pressure difference between the feed line pressure and the recirculation line pressure at least in part based on the orientation of the printhead (22).

23. The method according to claim 20, wherein, The steps of dynamic control further include: Determining a target feed pressure and a target recirculation pressure at least in part based on an inferred angle (A) of the longitudinal axis (66) of the printhead (22) to maintain a target pressure difference at the nozzle (54); and Controlling the variable feed pump speed and the variable recirculation pump speed to obtain the target feed pressure and the target recirculation pressure, thereby providing the target pressure difference at the nozzle (54) regardless of the orientation of the printhead (22).

24. The method according to any one of claims 20 to 23, wherein, The steps of dynamic control further include calculating a head pressure adjustment to the target feed pressure and the target recirculation pressure, wherein the calculating step further includes: Changing the head pressure adjustment according to the orientation of the printhead (22); and Applying the head pressure adjustment to the preliminary feed and recirculation pressure calculations to derive the target feed pressure and the target recirculation pressure.

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