Ink Channel Research Articles

Robust Feedforward control for a Drop-on-Demand Inkjet Printhead

AbstractThe printing quality delivered by a Drop-on-Demand (DoD) inkjet printhead is mainly limited due to the residual oscillations in the ink channel. The maximal jetting frequency of a DoD inkjet printhead can be increased by quickly damping the residual oscillations and by bringing in this way the ink-channel to rest after jetting the ink drop. The inkjet channel model obtained is generally subjected to parametric uncertainty. This paper proposes a robust optimization-based method to design the input actuation waveform for the piezo actuator in order to improve the damping of the residual oscillations in the presence of parametric uncertainties in the ink-channel model. Experimental results are presented to show the efficacy of the proposed method.

Improving the Performance of an Inkjet Printhead using Model Predictive Control

AbstractInkjet printing is considered one of the most promising printing technologies that offers several advantages including high speed, quiet operation and compatibility with a variety of substrates. That makes it an important manufacturing technology serving a wide variety of markets. Though the performance criteria imposed by today's applications are quite tight already, the future performance requirements will be even more challenging. However, the attainable performance is limited by two operational issues that are generally encountered, namely residual vibrations and cross-talk. This paper presents an approach based on Model Predictive Control (MPC) with which an input waveform is designed to improve the printing quality of a piezoelectric inkjet printer. The narrow-gap model is employed to predict the response of the ink channel under the application of the piezo input. Simulation and experimental results are presented to investigate the performance of the proposed approach.

Acoustic measurement of bubble size and position in an ink jet printhead.

A bubble can be entrained in the ink channel of a piezo-driven ink jet printhead leading to malfunction. Here, an acoustic sizing method for the volume and position of the bubble is presented. The influence of the bubble on the channel acoustics is detected by the piezo-actuator operating in a sensing mode. The acoustic response is also modeled in a linearized bubble dynamics model and it is demonstrated how the size of the bubble and its position within the channel can be inferred from the inverse problem. The validity of the presented method is supported by time-resolved optical observations of the bubble dynamics visualized in a glass connection channel. The combined optical and acoustical recordings are compared to the model, where a very good agreement is found. [This work is part of the research program of the Technology Foundation STW and financially supported by Océ Technologies B.V.]

Manufacture of an Integrated Three-Dimensional Structure Nozzle Plate Using Microinjection Molding for a 1200-dpi Inkjet Printhead

This paper presents an integrated microtechnology for the fabrication of a 3-D structure nozzle plate for a 1200-dots-per-inch (dpi) inkjet printhead. The 3-D structure nozzle plate contains a fluidic channel, nozzle chamber, and 432 conical nozzles whose taper angle is about 9deg-11deg to vertical. When the integrated 3-D structure nozzle plate is packaged onto the printhead, there is no need for alignment between the nozzle and the ink chamber, as there is when conventional production methods are employed. Therefore, misalignment of the nozzle and ink chamber is avoided, thereby reducing the cost by up to 50%, as well as greatly improving the print quality. This paper demonstrated the integration of excimer laser technology and microinjection molding to fabricate a 3-D structure nozzle plate. Excimer laser technology was used to create the high aspect ratio pattern with a tapered angle structure, and then, high-hardness Ni-Co alloy microelectroforming technology was used to achieve micromold insertion of the nozzle plate. In the microinjection molding, a variotherm control system was utilized for rapid heating to the mold temperature, which must be close to the glass temperature to ensure a good replication of the nozzle plate. The experiment resulted in the fabrication of a 3-D structure nozzle plate 2.7 mm in width and 10.8 mm in length. The total thickness was not more than 80 plusmn2 mum (ink channels, nozzle chamber, and nozzle plate), and the diameter and pitch of the nozzle holes were 25 plusmn2 mum for the outlet, 43 plusmn2 mum for the inlet, 84 plusmn2 mum in pitch, and 30 plusmn2 mum for the ink channel. Using this 3-D structure nozzle plate improved the competitiveness of the inkjet printhead. We have demonstrated the manufacture of the main parts of the 3-D structure nozzle plate for a 1200-dpi printhead; the aforementioned fabrication process yields satisfactory results and can be applied to commercial production.

Effect of an entrained air bubble on the acoustics of an ink channel

Piezo-driven inkjet systems are very sensitive to air entrapment. The entrapped air bubbles grow by rectified diffusion in the ink channel and finally result in nozzle failure. Experimental results on the dynamics of fully grown air bubbles are presented. It is found that the bubble counteracts the pressure buildup necessary for the droplet formation. The channel acoustics and the air bubble dynamics are modeled. For good agreement with the experimental data it is crucial to include the confined geometry into the model: The air bubble acts back on the acoustic field in the channel and thus on its own dynamics. This two-way coupling limits further bubble growth and thus determines the saturation size of the bubble.

Entrapped air bubbles in piezo-driven inkjet printing: Their effect on the droplet velocity

Air bubbles entrapped in the ink channel are a major problem in piezo-driven inkjet printing. They grow by rectified diffusion and eventually counteract the pressure buildup at the nozzle, leading to a breakdown of the jetting process. Experimental results on the droplet velocity udrop as a function of the equilibrium radius R0 of the entrained bubble are presented. Surprisingly, udrop(R0) shows a pronounced maximum around R0=17μm before it sharply drops to zero around R0=19μm. A simple one-dimensional model is introduced to describe this counterintuitive behavior which turns out to be a resonance effect of the entrained bubble.

Minimizing residual vibrations and cross-talk for inkjet printheads using ILC designed simplified actuation pulses

The attainable performance of inkjet printheads is severely limited by residual vibrations and cross-talk. Both effects are inseparably linked with the actuation of an ink channel. Residual vibrations occur each time a droplet has been jetted and, while actuating a channel, fluid-mechanics in neighboring channels are excited also. These phenomena affect the performance negatively, e.g. in terms of drop-consistency and achievable jetting frequencies. Previous work has shown that Iterative Learning Control (ILC) can be applied to design input wave forms (pulses) that leave the droplet formation undisturbed while minimizing these operational issues. However, the resulting pulses are usually too complex to be implemented on the Application Specific Integrated Circuit (ASIC) of a printhead. In this paper, the ILC control framework is adjusted with a modified algorithm that allows for the design of pulses with predefined complexity. It is demonstrated that this modified ILC using only piece-wise affine command signals operates without a severe loss of performance compared to unconstrained ILC. This paper shows the modeling required for ILC, the design of the controller, and the accompanying experimental results that show the minimization of residual vibrations as well as cross-talk.

Combination of thick resist and electroforming technologies for monolithic inkjet application

This paper reports a novel method for fabricating a monolithic inkjet chip by combination of thick resist photolithography and electroforming technologies. It integrates two-step photolithography process by two kinds of thick photoresists, SU-8 and JSR, and one-step nickel electroplating process to form the channels, chambers and nozzles of monolithic inkjet chip. The nickel nozzle plate can be replaced by SU8 material as second thick SU8 resist is used. The first thick resist of SU8 for both kinds of nozzle plates, nickel and SU8, is used for the structure formation of ink channel and chamber. Followed the nickel or SU8 nozzle plates are fabricated on SU8 chambers. The nickel nozzle plate is performed by second thick resist JSR and electroforming process while the SU8 nozzle plate is only by second thick SU8 resist process. A light-absorbing polymer layer is coated between two thick resist layers for protecting the first SU8 layer from overheating during the metal seed layer deposition or over-exposure during the second thick resist lithography process. A prototype of monolithic inkjet chip with a 300 dpi resolution has been successfully demonstrated.

Simulation on the Ejection Performance of Thermal Bubble Inkjet Printhead for Top and Back Shooting Design

There are many parameters that influence droplet ejection performance, i.e. printing quality, of inkjet print head such as ejection velocity and directionality of ink droplet. Ink droplet with larger ejection velocity from an inkjet print head nozzle exit will be less affected by the surrounded air disturbance and keep a good directionality. The printing quality of a thermal bubble inkjet print head is also affected by bubble growth dynamics. It depends on the proper geometry and size designs of micro-fluidic ink channel within the inkjet print head such as nozzle orifice, ink firing chamber and heaters. This work used computational fluid dynamics (CFD) method to study the parameters and effects on droplet ejection performance of thermal bubble inkjet print head for both top and back shooting type of thermal bubble nucleation. The numerical scheme, volume of fluid (VOF) method, has been used to deal with the interface between surrounded air and droplet liquid.

Increased Inkjet Printing Frequency From ‘Offset Channel’ Printheads

The request for increased print throughput in inkjet printing can be met by increasing the print frequency, while maintaining high ink drop volumes. A modified ink channel geometry, termed ‘offset-channels’ is presented, which combines both, short, stiff channel walls and large channel cross sections, respectively. Features of this printhead are high resonance frequencies of the channel walls, and high ink drop volumes up to the highest print frequencies. A Chevron-type version of the offset-channel actuator allows operating the printhead at low driving voltages.

Large Drop Volumes From Xaar-Type Inkjet Printheads

While the trend for high resolution, photo quality printing demands inkjet drop volumes of a few picoliters, there are other applications that require large drop volumes for low resolution, high optical density printing. By modification of standard Xaar-type piezo inkjet printheads ink drops of more than 150 pl volume could be produced. Controlled drop formation was obtained, channel starvation did not occur, and the printhead appeared robust against misfiring, so that no channels were lost when printing even odd pattern for extended times.In a further development step each ink channel was equipped with four nozzles, arranged in a square. In this fashion ,square dots’ were printed, which perfectly filled the square pixels of a 185 dpi raster. Consequently high quality line pattern could be printed on several inkjet papers at optical densities larger than 2 in a single pass.