Patent Application
20050179739
1. Field of Invention
This invention relates to methods and apparatus used in thermal fluid jet printers.
2. Description of Related Art
A thermal fluid jet fluid ejecting head selectively ejects droplets of fluid from a plurality of drop emitters to create a desired image on an image receiving member, such as a sheet of paper. The fluid ejecting head typically comprises an array of the drop emitters that convey fluid to the image receiving member. In a carriage-type fluid jet fluid ejecting head, the fluid ejecting head moves back and forth relative to the image receiving member to print the image in swaths.
Alternatively, the array extends across the entire width of the image receiving member to form a full-width fluid ejecting head. Full-width fluid ejecting heads remain stationary as the image receiving member moves in a direction substantially perpendicular to the array of drop emitters.
A thermal fluid jet fluid ejecting head typically comprises a plurality of fluid passageways, such as capillary channels. Each channel has a drop emitter and is connected to a fluid supply manifold. Fluid from the manifold is retained within each channel. Then, in response to an appropriate signal applied to a resistive heating element in each channel, the fluid in a portion of the channel adjacent to the heating element is rapidly heated. Rapidly heating and vaporizing some of the fluid in the channel creates a bubble that causes a quantity of fluid, such as an ink droplet or a main ink droplet and smaller satellite drops, to be ejected from the emitter to the image receiving member. U.S. Pat. No. 4,774,530 to Hawkins, the disclosure of which is incorporated herein by reference in its entirety, shows a general configuration of a typical fluid jet fluid ejecting head.
U.S. Pat. No. 4,791,435 to Smith et al., the disclosure of which is incorporated herein by reference in its entirety, discloses an fluid jet system where a constant temperature of the fluid ejecting head is maintained by using the heating elements of the fluid ejecting head not only for ejecting ink but to maintain the temperature close to a predetermined value as well. The fluid ejecting head temperature is compared to thermal models of the fluid ejecting head to provide information for controlling the fluid ejecting head temperature. At low temperature, low energy pulses are sent to each channel, or nozzle, below the voltage threshold that would cause a drop of fluid to be ejected. Alternatively, the fluid ejecting head is warmed by firing some droplets of ink into an external chamber or “spittoon,” rather than onto the surface of the image receiving member.
European Patent Application 0 496 525 A1, the disclosure of which is incorporated herein by reference in its entirety, discloses fluid jet recording method and apparatus in which ink is ejected by thermal energy produced by a heat generating element of a recording head. In the EP 525 application, driving circuits apply plural driving pulses to the heat generating element for every ink droplet ejected. The plural driving pulses include a first driving pulse used to increase a temperature of the ink adjacent the heater without creating a bubble, and a second driving pulse subsequent to the first driving pulse to eject the ink. Additionally, a width of the first driving pulse is adjustable to change an amount of ejected ink.
European Patent Application 0 505 154 A2, the disclosure of which is incorporated herein by reference in its entirety, discloses thermal fluid jet recording method and apparatus which control an ink ejection quantity by changing driving pulses supplied to the recording head based on a variation in the temperature of the recording head. A preheat pulse is applied to the ink to control the ink temperature and is set to a value which does not cause an ink bubble to form. After a predetermined time interval, a main heat pulse is applied which forms an ink bubble to eject one or more droplets, such as a main droplet and satellite droplets, of ink from the ink channel.
This invention provides methods and apparatus for using a fluid ejecting head having a plurality of drop ejectors.
This invention separably provides systems and methods for varying the duration of pre-pulses.
This invention separably provides systems and methods for varying the duration of pre-pulses to sequentially pre-warm and fire fluid ejectors.
In various exemplary embodiments, a first set of pre-pulses are longer in duration than a second, subsequent set of pre-pulses, thereby maximizing drop volume for a given energy input.
In various exemplary embodiments, using a pulse train having multiple pre-pulses, longer pre-pulses are used initially, followed by smaller pre-pulses as the temperature of the ink layer rises. The longer pre-pulses initially result in a deeper energy penetration into the ink and consequently a larger, faster drop. This results in a more consistently controlled temperature of the ink/heater boundary layer, and reduces the possibility of early bubble nucleation.
In various exemplary embodiments, each ejector has a heating element actuatable in response to input or data signals to emit a quantity of fluid from the fluid ejecting head toward an image receiving member. Pulse trains comprising of a series of variable duration pre-pulses are used as the input signals. The pulse train can be determined based on, for example, the temperature of the fluid ejecting head.
In various exemplary embodiments, the sequential and cumulative firings of the pre-pulses and final or drop-forming pulses in the selected channels throughout the fluid ejecting head are performed in a manner to achieve the fastest possible drop velocities.
In various exemplary embodiments, the sequential and cumulative firings of the pre-pulses and final or drop-forming pulses in the selected channels throughout the fluid ejecting head are performed by loading image data from the printer controller into a print data array. The heating elements are then fired in a sequence controlled by pulse trains originating in a fluid ejecting head controller. The pulse trains are clocked to sequence the firing of the heating elements in a manner that results in the maximum possible drop volume range.
In various exemplary embodiments of this invention, using wave forms with variable length pre-pulses allows drop mass to be stable over substantial temperature and pulse train ranges. The fluid ejecting head circuit design reads these arbitrary wave forms.
Other objects, advantages and features of the invention will become apparent from the following detailed description taken in conjunction with the attached drawings, which disclose exemplary embodiments of the invention.
The invention will be described with reference to the following drawings in which like reference numerals refer to like elements and wherein:
For simplicity and clarification, the operating principles and design factors of various exemplary embodiments of the systems and methods according to this invention are explained with reference to one exemplary embodiment of a carriage-type fluid jet printer 2, as shown in
The basic explanation of the operation of the fluid jet printer 2 and the fluid ejecting head 30 is applicable for the understanding and design of any fluid ejection system that incorporates this invention. Although the systems and method of this invention are described in conjunction with the fluid jet printer 2 and the fluid ejecting head 30, the systems and methods according to this invention can be used with any other known or later-developed fluid jet ejection system.
The fluid ejecting head 4 is fixedly mounted on the support base 20, which reciprocally moves along the two parallel guide rails 22. According to various exemplary embodiments, support base 20 alternately moves reciprocally along a single shaft, with a slot to prevent rotation (not shown). The fluid ejecting head 4 is reciprocally moved by a cable 24 and a pair of pulleys 26, one of which is powered by a reversible motor 28. Alternatively, according to various other exemplary embodiments, fluid ejecting head 4 is moved by a motor driven belt (not shown). The fluid ejecting head 4 is generally moved across the receiving medium 8 perpendicularly to the direction that the receiving medium 8 is moved by the motor 10. Of course, any other known or later-developed structure usable to reciprocally move the carriage assembly 5 can be used in the thermal fluid jet printing device 2.
A silicon member having a plurality of ink channels is known as a “die module” or “chip”. Each die module can comprise hundreds, thousands, or more of the emitters 30, spaced 300 or more to the inch. An exemplary full-width thermal fluid jet fluid ejecting head has one or more die modules forming a full-width array extending across the full width of the receiving medium on which the image is to be printed. In fluid ejecting heads with multiple die modules, each die module includes its own ink supply manifold, or multiple die modules share a common ink supply manifold.
Each emitter 30 includes a capillary channel 32 terminating in an orifice or nozzle 34. The capillary channel 32 holds a quantity of fluid 36, such as ink, but not limited to ink, maintained within the capillary channel 32 until such time as a droplet of fluid is to be emitted. Each capillary channel 32 is connected to a supply of fluid from a fluid supply manifold (not shown). An upper substrate 38 is located adjacent to a thick film layer 44, which in turn is adjacent to a lower substrate 42.
Addressing electrodes 52 are sandwiched between the thick-film layer 44 and the lower substrate 42. The addressing electrodes 52 control and carry electrical current to one or more electrical heating elements 46 located within openings 54 in the thick film layer 44. Each of the ejectors 30 in the fluid ejecting head has its own heating element 46 and individual addressing electrode 52. In various exemplary embodiments, the addressing electrode 52 is protected by a passivation layer 40 and an insulating layer 50. Each addressing electrode 52 and associated heating element 46 is selectively controlled by control circuitry, as will be explained in detail below, to form and grow vapor bubbles in the fluid 36 due to heating the fluid 36 in contact with the heater element 46, with droplets 56 of the ink being subsequently ejected from the fluid ejecting head 4. Other known or later developed embodiments of the fluid ejecting head are also within the scope of this invention.
In operation, the thermal fluid jet fluid ejecting head applies a plurality of pulses to the heating element for each fluid droplet to be ejected. Zero or more variable length precursor pulses, i.e., warming pulses or pre-pulses, are applied by the heating element to warm the fluid adjacent to the heating element. Subsequently, a print pulse, i.e., a drive pulse, a firing pulse or a main pulse, is applied to the heating element. The print pulse causes the fluid droplet to be ejected. The pre-pulses are used to raise the temperature of the fluid adjacent to the heating element and additionally are used to control the volume of the fluid droplet. The pre-pulses do not contain enough energy to cause the fluid droplet to be emitted, and do not need to be applied at all if the fluid is initially at a sufficiently high temperature.
More particularly, in the thermal fluid jet printing process according to this invention, when a signal is applied from a power source to the addressing electrode using the control circuitry, the heating element is energized. This very rapidly raises the temperature of the heating element, as well as the temperature of the fluid that is in physical contact with the heater element. The ink increases in temperature until the ink is above its boiling point. As temperature of the ink continues to increase, the fluid in the neighborhood of the heating element may become superheated, i.e., heated beyond the normal boiling temperature of the fluid, if the heating element is energized with sufficient magnitude and/or duration. At this point, the fluid immediately adjacent to the heating element will vaporize, creating a bubble 57 (item 57 in
The vapor bubble begins to expand under the influence of the high initial vapor pressure, which can be, in various exemplary embodiments, several tens or hundreds of atmospheres, and continues to expand due to inertial effects.
As the size of the vapor bubble grows, the pressure in the vapor bubble decreases, due in part to the increase in the volume of the vapor bubble. However, the pressure in the vapor bubble decreases as well due to cooling caused by the fluid lying at the initially expanding interface with the vapor bubble. This cooling occurs due to the fluid evaporating at the bubble-fluid interface, as well as to heat conducting from the vapor bubble into the surrounding fluid.
Following initial growth of the vapor bubble, the heating element loses contact with the fluid. Accordingly, subsequent growth of the vapor bubble is essentially unaffected by the temperature of the heating element. Thus, the eventual size of the vapor bubble, and thus the size of the droplet of the fluid ejected from the nozzle, depends on the energy stored in the layer of superheated fluid that was in contact with the heating element when the vapor bubble nucleated. With higher fluid ejecting head and ink temperatures, there is more energy stored in the superheated fluid next to the heater element when the ink temperature reaches the nucleation value.
In addition, the viscosity of the fluid depends on the temperature of the fluid. In particular, higher fluid temperatures lead to lower viscosity, and similarly reduced resistance to flow. Thus, high temperatures cause more energy to be stored in the superheated layer in the fluid, and cause lower resistance to the impulsive flow involved in ejecting the fluid droplets. As a result, drop volumes increase with fluid ejecting head temperature.
Only a small fraction of the energy dissipated in the heater element is utilized in nucleating the vapor bubble and producing the fluid droplet. The remainder of the heat flows into the die and the rest of the fluid ejecting head or print head, raising their temperature. Thus, continued use of the thermal inkjet fluid ejecting head causes the temperature of the thermal inkjet fluid ejecting head to increase. Unless some device, structure or apparatus is provided to prevent drop masses from changing, drop masses will increase with continued use of the thermal inkjet fluid ejecting head, thus degrading print quality. In addition, thermal inkjet fluid ejecting heads are used within a range of ambient temperatures. Variations in the ambient temperature exacerbate the variations in droplet masses due to the self-heating effect described above.
Simply changing pulse width or voltage in response to changes in fluid ejecting head temperature is a costly method of maintaining a constant drop volume as the temperature of the thermal inkjet fluid ejecting head changes. This occurs due to the de-coupling of the heater element from the fluid by the vapor bubble once the vapor bubble forms and due to the existence of a minimal or threshold voltage below which no droplet is produced.
The energy input to the heating element can be varied to provide different energy amounts stored in the layer of superheated fluid at the time of vapor bubble nucleation, by breaking the heating pulses into two or more segments. Following this technique, energy is supplied to the heater element and the fluid via one or more pre-pulses that locally heat the fluid. In various exemplary embodiments, the fluid is heated to temperatures above the normal boiling point of the fluid, to provide some superheat in the fluid, but not to the temperature required for a vapor bubble to form and grow. With the fluid next to the heater element thus pre-heated, a relatively short off time allows the heat to diffuse deeper into the fluid, while the temperature of the fluid next to the heater decreases. A subsequent main or firing pulse, possibly having a longer duration, is then provided to the heater element to re-heat the fluid next to the heater element to the nucleation temperature, where a vapor bubble forms, causing a droplet of the fluid to be ejected.
In order to create such an optimum waveform, various elements may be considered. In various exemplary embodiments, these elements include, for example, the geometry of the fluid ejecting head,—the amount of fluid to be ejected depending on a print mode, the geometry of the channel, the geometry of the heating element, the properties of the fluid, and the like. The geometry of the heating element may include, for example, the type of the heating element, the area of the heating element, the shape of the heating element, and the layer structure of the heating element. One or more of the above elements may be utilized to determine which pre-pulses to use.
Furthermore, to obtain the optimum waveform, the following factors may also be considered: desired velocity of a drop, desired volume of drop, pre-pulse modeling, and actual collected data generated using empirical tests, as is described later with reference to
This heater temperature characteristic or behavior is achieved by using an initial pulse, for example, a pre-pulse, which facilitates the rising part of the temperature from time 0 until time 0.5. When the initial pulse is removed at time 0.5, the heating element starts to cool, and then the heating element is re-activated with a second pre-pulse at time 1, which is typically going to be a shorter pre-pulse than the initial pre-pulse since the heating element is at a higher temperature when the second pre-pulse is activated. This second pre-pulse heats up the heating element toward the critical nucleation temperature Te. The second pre-pulse is then deactivated at time 1.5. Next, the heating element is re-activated with a third pre-pulse at time 1.8, which heats up the heating element again toward the critical nucleation temperature Te. The third pre-pulse is then deactivated at time 2.3. The heating element again starts to cool, and a fourth, fifth, etc., pre-pulses are applied similarly until it is time to shoot the main firing pulse at time 4.5. Then, at time 4.5, the temperature of the heating element is spiked so that the nucleation temperature Te is exceeded, thereby nucleating a vapor bubble, which produces the fluid droplet.
One of the phenomena that typically needs to be considered when designing a pulse train to drive a thermal fluid jet heater is interference. This refers to the nucleation of small vapor bubbles during the pre-pulse phase, also known as early nucleation. When early nucleation occurs the vapor bubbles resulting from applying the main pulse can actually be smaller than without a pre-pulse. This is because when the main pulse is applied the vapor bubbles generated during the pre-pulse phase end up thermally isolating the ink from the heater. Even if the small early nucleation bubbles have collapsed by the time the main pulse is applied, the disturbance of the temperature gradient next to the heater surface of the heating element is large enough to cause a detrimental effect on the vapor bubble size.
Open pool experiments coupled with thermal simulations show that early nucleation typically occur at heater surface temperatures well below the nucleation temperature of the ink (˜300° C.). This is believed to be due to the presence of crevices and impurities on the heater surface that act as early nucleation sites where bubble growth tends to start.
Another constraint of more practical nature that needs to be taken into account in designing pulse trains is the fact that the pulse train is made out of digital bits or ticks of an electronic clock of a finite size. Typical ticks are of the order of 0.1 μs in duration.
As the purpose of the pre-pulses is to have an efficient jetting mechanism, it is advantageous to only put in the least amount of energy necessary to form the correct drop mass and the correct drop speed. As shown in
According to various exemplary embodiments, the present invention is utilized to maintain a constant drop volume, and, in addition, the present invention is utilized to control drop volume. Thus, smaller drops may be fired when smaller drops are desired, and larger drops may be created when larger drops are desired.
For example, for the type 1 pre-pulse train, there is only a single duration pre-pulse. For the type 2 pre-pulse train, for example, the first pre-pulse is twice as long as any other pre-pulse in the type 2 pulse train. For type 3, for example, the first pre-pulse P1 is 0.3 micro-seconds, the second pre-pulse P2 is 0.2 micro-seconds, and the remaining pre-pulses P3 through P6 are all 0.1 micro-second in length. For type 4 for example, the first pre-pulse P1 is 0.4 micro-seconds, the second pre-pulse P2 is 0.3 micro-seconds, the third pre-pulse P3 is 0.2 micro-seconds in length, and the remaining pre-pulses P4 through P6 are all 0.2 micro-second in length. For type 5 for example, the first pre-pulse P1 is 0.5 micro-seconds, the second pre-pulse P2 is 0.4 micro-seconds, the third pre-pulse P3 is 0.3 micro-seconds in length, the fourth pre-pulse is 0.2 microseconds in length, and the remaining pre-pulses P5 and P6 are both 0.1 micro-second in length. For type 6 for example, the first pre-pulse P1 is 0.6 micro-seconds, the second pre-pulse P2 is 0.5 micro-seconds, the third pre-pulse P3 is 0.4 micro-seconds in length, the fourth pre-pulse is 0.3 microseconds in length, the fifth pre-pulse is 0.2 micro-seconds in length, and the sixth pre-pulse is 0.1 micro-second in length.
The optimum enable wave trains are generally optimum when used in conjunction with initially low temperature fluid ejecting heads, and are generally in the fastest section (shown as the lightest section in
The determined optimum enable wave train is stored in a look-up table for retrieval by the fluid ejecting head circuitry.
While the invention has been described in relation to preferred embodiments, many modifications and variations are apparent from the description of the invention, and all such modifications and variations are intended to be within the scope of the present invention as defined in the appended claims.
