The present disclosure generally relates to inkjet printing and, more particularly, to controlling pressure of ink held in an ink reservoir used during inkjet printing.
Drop on demand printing systems typically maintain a slight backpressure within the printhead to retain ink at a desired meniscus level within a nozzle. The backpressure should be high enough to prevent ink from leaking from the nozzle when the system is not actively ejecting ink, but not so high that air is drawn into the printhead through the nozzle. In conventional systems, the backpressure is typically set at a static pressure level. In some systems, multiple static pressure levels may be provided based on the type of printing mode being used. Systems that provide one or more static pressure levels, however, do not adequately manage backpressure in inkjet systems that are configured to print on complex, three-dimensional surfaces, where backpressure requirements may change as the printhead is placed at different attitudes relative to the surface to be printed.
In accordance with one aspect of the present disclosure, a controller is provided for dynamically controlling pressure in an ink reservoir of an inkjet assembly having an ink reservoir defining an ink-receiving chamber and a control chamber for receiving a control fluid from a control fluid source, and an orientation sensor configured to determine an orientation of the ink reservoir and generate an orientation signal. The controller comprises a processor operably coupled to the control fluid source and the orientation sensor, the processor programmed to determine a desired pressure for the control chamber based, at least in part, on the orientation signal, and control the control fluid source to adjust an actual pressure level in the control chamber to the desired pressure for the control chamber.
In accordance with another aspect of the present disclosure, an inkjet printing system includes an ink reservoir defining an ink-receiving chamber and a control chamber, a control fluid source fluidly communicating with the control chamber, and an orientation sensor configured to determine an orientation of the ink reservoir and generate an orientation signal. A processor is operably coupled to the control fluid source and the orientation sensor, the processor programmed to determine a desired pressure for the control chamber based, at least in part, on the orientation signal, and control the control fluid source to adjust an actual pressure level in the control chamber to the desired pressure for the control chamber.
In accordance with a further aspect of the present disclosure, an inkjet printing system having a dynamically controlled ink backpressure includes a frame supported for rotation in at least one degree of freedom relative to a vertical reference axis, an ink reservoir coupled to the frame and defining a longitudinal axis and comprising a control chamber and an ink-receiving chamber, a control fluid source fluidly communicating with the control chamber to deliver a control fluid across a range of pressure levels, and an orientation sensor for determining an orientation of the ink reservoir and generating an orientation signal. A processor is operably coupled to the control fluid source and the orientation sensor, the processor programmed to determine a desired pressure for the control chamber based, at least in part, on the orientation signal, and control the control fluid source to adjust an actual pressure level in the control chamber to the desired pressure for the control chamber.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings.
It should be understood that the drawings are not necessarily drawn to scale and that the disclosed embodiments are sometimes illustrated schematically. It is to be further appreciated that the following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses thereof. Hence, although the present disclosure is, for convenience of explanation, depicted and described as certain illustrative embodiments, it will be appreciated that it can be implemented in various other types of embodiments and in various other systems and environments.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Inkjet printing systems and methods are disclosed herein that are particularly suited for printing on complex, three dimensional surfaces, such as a surface 10 of an aircraft (
More specifically with reference to
The inkjet printing system 20 may further include a frame actuator 30 for actuating the frame 24 in the at least one degree of freedom relative to the vertical reference axis 26. For example, the exemplary frame actuator 30 illustrated at
The inkjet assembly 22 is coupled to, and pivotable with, the frame 24. As best shown with reference to
As best shown in
A control fluid is supplied to the control chamber 74 to control a pressure of the ink disposed in the ink-receiving chamber 76. With continued reference to
Additionally, an orientation sensor 100 is provided for determining an orientation of the inkjet assembly 22. In the exemplary embodiment shown in
The inkjet assembly 22 further includes a pressure sensor 102 for determining an actual pressure level in the control chamber 74. As best shown in
The printhead 62 receives ink from the ink reservoir 60 and selectively discharges ink droplets onto the surface 10. As best shown in
The inkjet assembly 22 also includes a controller 120 for controlling operation of the inkjet assembly. More specifically, the controller includes a processor 122 that may execute logic stored in data storage 124 to control the operations. The controller 120 is operably coupled to the first valve 92, the second valve 96, the orientation sensor 100, and the pressure sensor 102. The controller 120 may be representative of any kind of computing device or controller, or may be a portion of another apparatus as well, such as an apparatus included entirely within a server and portions of the controller 120 may be elsewhere or located within other computing devices.
The processor 122 is programmed to dynamically control pressure in the control chamber 74 based on orientation of the ink reservoir 60. More specifically, the processor 122 may be programmed to infer an angle A of the longitudinal axis 66 relative to the vertical reference axis 26 based on the orientation signal from the orientation sensor 100.
Additionally, the processor 122 is programmed to calculate an effective water column height along the vertical reference axis 26 based on the inferred angle A of the longitudinal axis 66 of the ink reservoir 60 and the distance D1 between the desired meniscus level 112 of the nozzle 110 and the ink top surface level 114. With the distance D1 being predetermined and substantially fixed, and the angle of the longitudinal axis 66 being determined from the orientation sensor 100, the effective water column may be calculated using simple trigonometry.
The processor 122 further may be programmed to determine a desired pressure for the control chamber 74 based, at least in part, on the effective water column height H. The effective water column height H may be directly converted into a pressure value, such as inches of water column, that may be used to determine how much backpressure is needed to maintain ink at the desired meniscus level 112. More specifically, the desired pressure for the control chamber 74 must take into account the pressure equivalent to the effective water column height H to maintain a predetermined pressure at the meniscus. Stated mathematically, the predetermined pressure at the meniscus PM is equal to the sum of the desired pressure for the control chamber PC and the effective water column pressure PEWC. The desired pressure for the control chamber PC depends on several factors, but is primarily related to the distance between the ink reservoir 60 and the printhead 62. For systems used to print on aircraft, for example, the desired pressure for the control chamber PC is expected to be within a range of approximately +10 inches water column to −10 inches water column. The predetermined pressure at the meniscus PM is selected to have a value that holds the ink at the desired meniscus level 112. For example, the predetermined pressure at the meniscus PM may be within a range of approximately +0.5 inches water column to approximately −0.5 inches water column.
Additionally, the above equation may be rearranged to solve for the desired pressure for the control chamber PC, wherein desired pressure for the control chamber PC is equal to the predetermined pressure at the meniscus PM minus the effective water column pressure PEWC. For example, if the predetermined pressure at the meniscus PM is negative 0.25 inches water column, and the effective water column height H is 2 inches (and therefore the effective water column pressure PEWC is 2 inches water column), then the desired pressure for the control chamber PC is negative 2.25 inches water column.
It will be appreciated that the effective water column pressure PEWC will change according to the orientation of the ink reservoir 60. More specifically, the cosine of angle A is equal to the effective water column height divided by the distance D1. Stated another way, the effective water column height is equal to the product of the distance D1 and the cosine of angle A. Thus, when the ink reservoir 60 is oriented so that the longitudinal axis 66 is vertical, the angle A is zero and the cosine of zero is 1, and therefore the effective water column pressure PEWC is equal to the distance D1. When the ink reservoir 60 is rotated to an angle A1, as shown in
Furthermore, it is noted that when the ink reservoir 60 is inverted to angle A2, as shown in
The processor 122 may further be programmed to adjust a pressure level at the control chamber 74 to achieve the desired pressure for the control chamber. More specifically, the processor 122 may operate the control fluid source 88, such as by selectively opening and closing the first valve 92 and the second valve 96, to change the pressure inside the control chamber 74. The processor may employ a simple feedback loop based on the pressure signal from the pressure sensor 102 to determine when the desired pressure for the control chamber 74 is reached.
The description of the different advantageous arrangements has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may describe different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure. Various modifications, as are suited to the particular use, are contemplated.
Number | Date | Country | |
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Parent | 15624351 | Jun 2017 | US |
Child | 15987100 | US |