Patent Grant
8282193
Ink jet printers generally use an array of jets, which may also be referred to as drop emitters or nozzles. As the printing surface passes the array, or the array passes over the printing surface, the jets drop ink onto it, forming an image. The drop of ink is typically forced out of the jet or aperture by activation of an electromechanical transducer. The transducer receives an activation signal at the correct time, and it actuates to force the ink out of the apertures.
The drops then fall onto the printing substrate in a pattern determined by the activation signals received by the transducers, the patterns of the drop ultimately form the printed image. In some printers, the printing surface is the paper or other print surface that is the final surface upon which the image is formed. In other printers, the printing surface is an intermediate transfer surface, such as a drum or a belt, from which the image is then transferred to the final print surface. In either case, the timing of the activation of the jets determines the positions in which the drops fall on the printing surface.
In some printers, an effect exists that causes a subset of the jet array, such as the outer row or rows of jets, single jets, groups of jets in a particular area, edge jets, etc. to slow down over the initial months of use at operating temperatures. The velocity of the jet in its flight from the print head to the printing surface slows. Due to the movement between the printing surface and the jet array, this causes a drift in the dot position, degrading the overall print quality. This degradation or print quality may result in service calls because of fuzzy or blurred edges and lines in the printed images, requiring printhead replacement, or other action to remedy the issue.
This is merely an example of a printing system. Other variations exist. For example, the print head may move relative to the printing surface, with the printing surface fixed in place. Alternatively, the printing system may be a direct printing system, where the print head prints directly onto the final printing substrate. Any discussion of particular examples here is not intended to limit the scope of the claims and no such limitation should be assumed.
In
The distance 34 is the height different of the array of jets between the first and third rows. The distance 32 is the distance difference between how far the first row of ink drops from the first row of jets travels to contact the printing surface and how far the third row of ink drops from the third row of jets travels to contact the printing surface. Each jet typically operates by activating a transducer that causes a drop of ink to be ejected from the jet.
In
When the print system controller 10, which may be a microcontroller, microprocessor, or any other component that is capable of executing instructions, determines that the jet needs to expel an ink drop 49 through the aperture 47, the controller generates an electrical signal. This signal is received by the electrodes 43 that then cause the transducer 41 to operate. When the transducer operates in this embodiment, it causes the membrane 37 to flex. This in turn causes the ink in the chamber 35 to travel down the ink outlet 45 and ultimately be expelled through the aperture. It must be noted that the term ‘transducer’ as used here means any type of actuator that causes ink to expel ink drop through the aperture 47. A transducer is any device that converts an electrical signal to some sort of mechanical action. For example, a piezoelectric transducer receives an electrical signal that causes the transducer to vibrate against a diaphragm, which in turn causes the membrane to pull ink into a chamber and then expel it out the jet. In a bubble jet printer, the transducer is a resistor that receives a signal, heats up and causes a bubble to form in the ink, pushing ink out the jet. These are just examples, with the understanding that any device that causes ink to exit the aperture is considered a transducer.
It has been discovered that the velocity of drops from the outer rows of the jets slow down over the first few months of operation. This causes a greater delay in the drops reaching the printing surface, moving the corresponding row of ink drops to be further ‘up’ on the drum than they would otherwise be, because the drum is moving down past the array. This causes the ink drops from the outer rows of jets to be separated from the other rows of ink drops by a different gap than the other rows of ink drops are separated from each other, leading to objectionable artifacts in the print image such as blurry or fuzzy lines. This discussion will refer to this phenomenon as ‘thermal drift.’
One solution to the problem of thermal drift involves determining the vertical position of the rows. In this discussion, ‘vertical’ is in the direction of movement, so in the array of
This adjustment may not make sense without an explicit understanding of the terminology. A ‘pixel’ or picture element, as used here, corresponds to an ink drop position on the printed image. A pixel distance then, has the dimensions of an ink drop. The vertical position of the pixels in each row is averaged across the array to determine the average spacing between rows. If a row is more than a half of a pixel off where the average spacing would otherwise dictate where that row would be, the entire row may be moved a full pixel distance in the opposite direction. In other words, if a row was a half a pixel distance or more too low, the row could be ‘moved’ a full pixel distance up. The example of a movement corresponding to a full pixel is just for ease of understanding, the distance of movement may be a partial pixel distance as well.
In this approach, the jets themselves are not moved. To ‘move’ a row actually means to adjust the firing interval for that row to fire the jets in that row at a time that is either an interval earlier or later than they would otherwise be fired. On an individual pixel level, each individual jet's timing was adjusted as needed to keep the pixels within some partial pixel distance, such as a half pixel, of the average for the rows. However, if these movements are done without consideration to the effects of thermal drift, then the end result may not be optimal.
It is possible to use the idea of adjusting the pixel firing interval to move rows up or down as needed, in conjunction with manufacturing the arrays of jets to accommodate thermal drift.
In array 50, the array has jets for four different colors, magenta (M), cyan (C), yellow (Y) and black (K). In this particular embodiment, the array of jets is divided into two groups each group having two colors, shown here as group 66 have magenta and cyan, and group 64 having black and yellow. This is only an example, and the principles of the invention shown here apply to any configuration of colors or just monochrome printing, such as black. For example, there could be two groups, one for a first color and one for a second color, or one group for a first and second color and one group for a third color.
The array shown here has the outer rows 56, a black row at the bottom of the array, and row 52, a magenta row at the top of the array, offset from the position they would have if the rows were evenly spaced. Looking at the position of row 56, one can see that the gap 60 between the apertures of row 56 and the apertures of row 58 is larger than the gap 62, which is what the gap between the apertures in rows 58 and 56 would be if the rows were evenly spaced.
In this instance, row 56 has been offset in a positive direction, meaning in the direction of the movement between the print head and the printing surface. Referring back to
Similar to the movement of row 56, row 52 has also been offset in a positive direction. Note that in the case of the upper, outer row, the offset results in a smaller gap between the rows, where the offset results in a larger gap for the lower outer row.
Unlike the approach mentioned above, this approach actually manufactures the array of jets with this offset positioning. The positions of the jets are actually altered in their physical locations on the aperture plate of the print head. In one example, the jets were located in a position that is 35-45% of a pixel distance different than where they would have been located with even spacing.
The physical adjustment to the array can be combined with instructions executed by the print system controller that differ from the instructions used in the previous approach.
It is possible that a group may need to be ‘moved’ as discussed above to meet a particular print specification. If this needs to occur, it occurs at 74. The individual jets may then be moved as needed to ensure that they fire within a partial pixel of the average position of the group at 78. This occurs whether groups have been moved or not. The previous approach, of moving groups a pixel up or down depending upon whether the group is at least a half pixel from the average, may be applied to the non-offset groups of the array, as needed.
This approach will generally result in the printing system initially adjusting for the physically offset groups to make them closer to their ideal position. Over time, due to the thermal drift, the groups will end up as if they were offset in the other direction, but not enough to be objectionable. They start out too positive to begin with, which is adjusted for by the controller, and end up being slightly too negative, but ideally both situations will be within the operating specifications. This reduces the number of service call and print head replacements. In addition, the controller adjustments could be altered over time to maintain optimal print quality. These alterations may be performed automatically with software instructions that cause the controller to make the alterations or may be adjusted by service personnel in the field.
It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6969146 | Brookfield et al. | Nov 2005 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20110234670 A1 | Sep 2011 | US |
