Patent Grant
8025353
Embodiments of the present invention relate to droplet ejection, and more specifically to using an embedded waveform for variable drop size ejection.
Droplet ejection devices are used for a variety of purposes, most commonly for printing images on various media. They are often referred to as ink jets or ink jet printers. Drop-on-demand droplet ejection devices are used in many applications because of their flexibility and economy. Drop-on-demand devices eject one or more droplets in response to a specific signal, usually an electrical waveform, or waveform, that may include a single pulse or multiple pulses. Different portions of a multi-pulse waveform can be selectively activated to produce the droplets.
Droplet ejection devices typically include a fluid path from a fluid supply to a nozzle path. The nozzle path terminates in a nozzle opening from which drops are ejected. Droplet ejection is controlled by pressurizing fluid in the fluid path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical printhead has an array of fluid paths with corresponding nozzle openings and associated actuators, and droplet ejection from each nozzle opening can be independently controlled. In a drop-on-demand printhead, each actuator is fired to selectively eject a droplet at a specific target pixel location as the printhead and a substrate are moved relative to one another. Because drop-on-demand ejectors are often operated with either a moving target or a moving ejector, variations in droplet velocity lead to variations in position of drops on the media. These variations can degrade image quality in imaging applications and can degrade system performance in other applications. Variations in droplet volume and mass lead to variations in spot size in images, or degradation in performance in other applications.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which:
Described herein is a process and apparatus for driving a droplet ejection device with multi-pulse waveforms. In one embodiment, for ejecting a droplet from each nozzle in a printhead, the process includes generating a multi-pulse waveform that includes drive pulses in predetermined positions in the waveform. Next, the process includes applying the drive pulses to the actuator and causing the droplet ejection device to eject a first droplet of a fluid. The process also includes applying another multi-pulse waveform that includes the drive pulses in the predetermined positions, a subset of the drive pulses in the predetermined positions, the drive pulses in the predetermined positions with at least one additional embedded pulse between two pulses that are different than those used to eject the first droplet, a subset of the drive pulses in the predetermined positions with at least one additional embedded pulse between two pulses that are in their predetermined positions, or at least one additional embedded pulse without any of the drive pulses in the predetermined positions. This multi-pulse waveform is applied to the actuator and causes the droplet ejection device to eject a second droplet of the fluid. In some embodiments, the first and second droplets have different droplet sizes but these droplets are ejected at substantially the same effective drop velocity.
In another embodiment, the multi-pulse waveform includes three drive pulses fired during a time period to cause the droplet ejection device to eject an additional droplet of the fluid in response to the three drive pulses. Each ejected droplet discussed above can have a different droplet size with each droplet being ejected at substantially the same effective drop velocity.
The opposing surfaces of the body are covered with flexible polymer films 30 and 30′ that include a series of electrical contacts arranged to be positioned over the pumping chambers in the body. The electrical contacts are connected to leads, which, in turn, can be connected to flex prints 32 and 32′ including driver integrated circuits 33 and 33′. The films 30 and 30′ may be flex prints. Each flex print film is sealed to the body 20 by a thin layer of epoxy. The epoxy layer is thin enough to fill in the surface roughness of the jet body so as to provide a mechanical bond, but also thin enough so that only a small amount of epoxy is squeezed from the bond lines into the pumping chambers.
Each of the piezoelectric elements 34 and 34′, which may be a single monolithic piezoelectric transducer (PZT) member, is positioned over the flex prints 30 and 30′. Each of the piezoelectric elements 34 and 34′ have electrodes that are formed by chemically etching away conductive metal that has been vacuum vapor deposited onto the surface of the piezoelectric element. The electrodes on the piezoelectric element are at locations corresponding to the pumping chambers. The electrodes on the piezoelectric element electrically engage the corresponding contacts on the flex prints 30 and 30′. As a result, electrical contact is made to each of the piezoelectric elements on the side of the element in which actuation is effected. The piezoelectric elements are fixed to the flex prints by thin layers of epoxy.
The ink fill passage 26 is sealed by a portion 31 and 31′ of the flex print, which is attached to the exterior portion of the module body. The flex print forms a non-rigid cover over (and seals) the ink-fill passage and approximates a free surface of the fluid exposed to atmosphere.
Crosstalk is unwanted interaction between jets. The firing of one or more jets may adversely affect the performance of other jets by altering jet velocities or the drop volumes jetted. This can occur when unwanted energy is transmitted between jets.
In normal operation, the piezoelectric element is actuated first in a manner that increases the volume of the pumping chamber, and then, after a period of time, the piezoelectric element is deactuated so that it returns to its original position. Increasing the volume of the pumping chamber causes a negative pressure wave to be launched. This negative pressure starts in the pumping chamber and travels toward both ends of the pumping chamber (towards the orifice and towards the ink fill passage as suggested by arrows 33 and 33′). When the negative wave reaches the end of the pumping chamber and encounters the large area of the ink fill passage (which communicates with an approximated free surface), the negative wave is reflected back into the pumping chamber as a positive wave, traveling towards the orifice. The returning of the piezoelectric element to its original position also creates a positive wave. The timing of the deactuation of the piezoelectric element is such that its positive wave and the reflected positive wave are additive when they reach the orifice.
The flex print has electrodes 50 on the side 51 of the flex print that comes into contact with the piezoelectric element. The flex print electrodes and the piezoelectric element electrodes overlap sufficiently for good electrical contact and easy alignment of the flex print and the piezoelectric element. The flex print electrodes extend beyond the piezoelectric element (in the vertical direction in
A cavity plate is illustrated in more detail in
In one embodiment, the PZT member 234 ejects one or more droplet sizes of a fluid from the pumping chambers. The drive electronics 233 are coupled to the PZT member 234. During operation of the ink jet module 210, the drive electronics 233 drive the PZT member 234 with a first multi-pulse waveform that includes drive pulses in predetermined positions to cause the PZT member 234 to eject a first droplet with a first droplet size of the fluid in response to the drive pulses of the multi-pulse waveform. The first multi-pulse waveform may include three drive pulses in their predetermined positions to cause the droplet ejection device to eject the first droplet of the fluid.
The drive electronics 233 also drive the PZT member 234 with a second multi-pulse waveform having different pulses than the first multi-pulse waveform, that includes at least two drive pulses, where such drive pulses including zero or more drive pulses of the drive pulses that are in predetermined positions and one or more additional pulses that are located in the second multi-pulse waveform at locations embedded between predetermined positions of two of the drive pulses, to cause the actuator to eject a second droplet of the fluid. Each of the ejected droplets can have a different droplet size and each droplet can be ejected at substantially the same effective drop velocity.
The second multi-pulse waveform may include one embedded drive pulse to cause the droplet ejection device to eject the second droplet of the fluid. The second multi-pulse waveform may also include two embedded drive pulses and no drive pulses in the predetermined locations to cause the droplet ejection device to eject the second droplet of the fluid. In one embodiment, a third waveform is applied to the actuator with the third waveform having one or more drive pulses fired to cause the droplet ejection device to eject a third droplet of the fluid with a third droplet size in response to applying the third waveform to the actuator.
The process can repeat through the above processing blocks to apply another waveform to the actuator at processing block 808 and cause the droplet ejection device to eject a second droplet with a second droplet size of the fluid in response to this other multi-pulse waveform having different pulses than the first multi-pulse waveform, which includes at least two drive pulses that include zero or more drive pulses of the drive pulses that are in predetermined positions and one or more additional pulses that are located in the second multi-pulse waveform at locations embedded between predetermined positions of two of the drive pulses at processing block 810. In one embodiment, each embedded pulse is embedded in between the predetermined positions of two drive pulses. In some embodiments, the first and second droplets have different droplet sizes yet are ejected at substantially the same effective drop velocity. Additionally, a time period from initiation to termination of each multi-pulse waveform can be approximately the same even though each multi-pulse waveform may have different types and quantities of pulses in predetermined positions and/or embedded pulses.
In one embodiment, a first multi-pulse waveform can potentially have any combination of three drive pulses having predetermined locations in the waveform. In this embodiment, the drive pulses are fired to cause the droplet ejection device to eject a first droplet. A second multi-pulse waveform can include one or more embedded pulses, which are then fired to cause the droplet ejection device to eject a second droplet of the fluid in response to the embedded pulses. Each embedded pulse is embedded between predetermined positions of two drive pulses. A third waveform can include one or more drive pulses in predetermined positions or one or more embedded pulses that are then fired to cause the droplet ejection device to eject a third droplet of the fluid in response to the one or more drive pulses. The first, second, and third droplets each have different droplet sizes with each droplet having substantially the same effective drop velocity.
In some embodiments, the droplet ejection device ejects additional droplets of the fluid in response to the pulses of the multi-pulse waveform or in response to pulses of additional multi-pulse waveforms. A waveform may include a series of sections that are concatenated together. Each section may include a fixed time period (e.g., 1 to 3 microseconds) and a certain number of samples having a duration (e.g., 0.125 microseconds) and associated amount of data. The time period of a sample is long enough for control logic of the drive electronics to enable or disable each jet nozzle for the next waveform section. The waveform data is stored in a table as a series of address, voltage, and flag bit samples and can be accessed with software. A waveform provides the data necessary to produce a single sized droplet and various different sized droplets.
The spacing between the pulses of a multi-pulse waveform effectively define a frequency for the waveform, though the spacing is not necessarily constant. The effective pulse frequency can be calculated as follows:
Frequency=1/Time,
where Time is the time between the pulses.
The individual pulse widths, in each section of the waveform, may be determined separately from the pulse frequency.
In view of the above restrictions, a waveform that produces several different drop sizes, has coalesced drops at each drop size, fires drops of each size at the same effective velocity, has good sustainability, and meets other requirements is described herein. Further, it is impractical to simply add extra pulses to the beginning or ending of a waveform because a wider waveform, when fired in a variable-drop-size mode, will not be able to fire to as high of a frequency in comparison to a waveform that does not have the extra pulses as illustrated in
One resulting application of this waveform in
For various droplet sizes, the waveform 100 may not maintain the same effective drop velocity for each droplet size. For example, pulse 120 firing alone, can produce a first droplet size with an effective target velocity. Pulses 110, 120, and 130 firing together, may produce a second droplet size with a similar effective target velocity. Pulses 120 and 130, firing together, may produce a third droplet size with an effective velocity several meters per second faster than the other drops because the low velocity sub-drop from pulse 110 is not present to slow the velocity of the total drop.
However, the waveform 1100 is able to maintain the same effective drop velocity for each droplet size. For example, pulse 1120 firing alone, can produce a first droplet size (e.g., 30 ng) with an effective target velocity (e.g., 8 m/s). If the pulses 1120 and 1130 are fired at a reduced voltage and embedded in the waveform 1100, the combination of embedded pulses 1115 and 1125 produces a second droplet at the desired weight (e.g., 50 ng) at the target velocity (e.g., 8 m/s). In this case, the multi-pulse waveform 1100 has two additional embedded drive pulses fired during the same time period 1140 to cause the droplet ejection device to eject one additional droplet of the fluid in response to the two additional embedded drive pulses. Pulses 1110, 1120, and 1130 firing together, may produce a third droplet size (e.g., 80 ng) with a similar effective target velocity. The three droplets can have different droplet sizes with each droplet being ejected at substantially the same effective drop velocity during the time period 1140.
In one embodiment, the first droplet size is greater than the second droplet size which is greater than the third droplet size. In other embodiments, the first droplet size is less than the second droplet size which is less than the third droplet size. Also, the time period during which the pulses fire can be between forty and sixty microseconds in duration. In one embodiment, the effective drop velocity for each droplet is approximately 8 m/s with a range from 6 m/s to 11 m/s in order for different droplet sizes to land on a target with the same relative timing to that of the driving pulse or pulses that fire to eject each droplet.
For certain embodiments, other types of pulses, drop shaping sub-pulses, or completely different pulses can be embedded into the waveform of
Embedding portions of the waveform (e.g., pulse 1115 and 1125) within itself provides greater flexibility in the development of the waveform, permits improved drop formation for each drop size, and enables improved control over the drop velocities. Pre-pulses and post pulses applied to portions of a waveform can be used to improve drop formation, velocity frequency response, and mass frequency response. Other combinations of pulses 1110-1130 can be used to form other drop sizes and other drop velocities. For example, pulse 1115 or 1120 could be used to form a small drop having a particular drop velocity, and pulses 1115 and 1120 or 1120 and 1125 could be used to form a medium drop having the same drop velocity as the small drop, and pulses 1115, 1120, and 1125 or pulses 1115, 1120, and 1130 could be combined to form a large drop having a similar velocity as the small and medium drops.
The process can repeat through the above processing blocks to apply another waveform to the actuator at processing block 1308 and cause the droplet ejection device to eject a second droplet with a second droplet size of the fluid in response to this other multi-pulse waveform having different pulses than the first multi-pulse waveform, which includes at least two drive pulses that include zero or more drive pulses of the drive pulses that are in predetermined positions and zero or more additional pulses that are located in the second multi-pulse waveform at locations embedded between predetermined positions of two of the drive pulses at processing block 1310. In one embodiment, each embedded pulse is embedded in between the predetermined positions of two drive pulses. In some embodiments, the first and second droplets have different droplet sizes yet are ejected at substantially the same effective drop velocity.
In one embodiment, a first multi-pulse waveform can potentially have any combination of drive pulses and one or more additional embedded pulses in the waveform (e.g., pulses 1115, 1120, and 1125 or pulses 1115, 1120, and 1130). In this embodiment, the drive pulses are fired to cause the droplet ejection device to eject a first droplet. A second multi-pulse waveform can include zero or more drive pulses with predetermined positions and zero or more embedded pulses (e.g., pulses 1115 and 1120 or 1120 and 1125), which are then fired to cause the droplet ejection device to eject a second droplet of the fluid in response to the embedded pulses. Each embedded pulse is embedded between predetermined positions of two drive pulses. A third waveform can include one or more drive pulses in predetermined positions and/or one or more embedded pulses (e.g., pulse 1115 or 1120) that are then fired to cause the droplet ejection device to eject a third droplet of the fluid in response to the one or more drive pulses. The first, second, and third droplets each have different droplet sizes with each droplet having substantially the same effective drop velocity.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
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