Experimental-based feedforward control for a DoD inkjet printhead

Markets demand continuously for higher quality, higher speed, and more energy-efficient professional printers. Drop-on-Demand (DoD) inkjet printing is considered as one of the most promising printing technologies. It offers many advantages including high speed, quiet operation, and compatibility with a variety of printing media. Nowadays, it has been used as low-cost and efficient manufacturing technology in a wide variety of markets. Although the performance requirements, which are imposed by the current applications, are tight, the future performance requirements are expected to be even more challenging. These print requirements are related to the jetted drop properties, namely, drop velocity, drop volume, drop velocity consistency, productivity, and reliability. Meeting these performance requirements is restricted by several operational issues that are associated with the design and the operation of inkjet printheads. Major issues that are usually encountered are residual vibrations and crosstalk among ink channels. These result in a poor printing quality for high-speed printing. The main objective is to design a feedforward control strategy such that variations in the velocity and volume of the jetted drops are minimized. In this article, an experimental-based feedforward control scheme is proposed to improve the performance of a professional inkjet printer.     

Dynamic characteristics of a piezoelectric driven inkjet printhead fabricated using MEMS technology

To understand the residual vibration of the piezoelectric diaphragm in a piezo (PZT) driven inkjet printhead fabricated on silicon wafers by MEMS manufacturing process, the transfer function of the piezo velocity to sinusoidal input voltage is obtained in the experiments. The piezo velocity can be predicted using the obtained velocity transfer function with discrete Fourier transform of a trapezoidal waveform. In the low amplitude of voltage waveform, the spectrum shows a good agreement between the predicted and measured velocities of the piezo diaphragm. However, when the drop is ejected from the nozzle orifice with actual amplitude of the voltage waveform, the spectrum of the piezo velocity shows more complicated frequency components due to the reflected pressure waves and fluid motion inside the chamber. In this study it has been attempted to obtain the transfer function of the piezo velocity to the voltage input when the drops are fired. The simulated results of the piezo displacement with the various durations of the voltage waveform show a good agreement with the drop volume and velocity measured in experiments. In addition, it was found that suppressing the residual oscillations was closely related to eliminating the satellite drop formation, which was confirmed with the strobe stand drop visualization.     

Performance improvement of a drop-on-demand inkjet printhead using an optimization-based feedforward control method

The printing quality delivered by a drop-on-demand (DoD) inkjet printhead is 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. This paper proposes an optimization-based method to design the input actuation waveform for the piezo actuator in order to improve the damping of the residual oscillations. A discrete-time transfer function derived from the narrow-gap model is used to predict the response of the ink channel under the application of the piezo input. Simulation and experimental results are presented to show the applicability of the proposed method.     

A thermal inkjet printhead with a monolithically fabricated nozzleplate and self-aligned ink feed hole

A monolithic thermal inkjet printhead has been developed and demonstrated to operate successfully by combining monolithic growing of a nozzle plate on the silicon substrate and electrochemical etching of silicon for an ink feed hole. For the monolithic fabrication, a multiexposure and single development (MESD) technique and Ni electroplating are used to form cavities, orifices, and the nozzle plate. Electrochemical etching, as a back-end process, is applied to form an ink feed hole through the substrate, which is accurately aligned with the frontside pattern without any backside mask. The etch rate is nearly proportional to the current density up to 50 μm/min. Experiments with a 50-μm-diameter nozzle show ink ejection up to the operating frequency of 11 kHz with an average ink dot diameter of about 110 μm for 0.3-A, 5-μs current pulses     

Fabricating chambers of inkjet printhead by bonding SU-8 nozzle plate with suitable crosslinked degree

Microsystem Technologies - The process of fabricating chambers is becoming increasingly important for inkjet printhead. However, the majority of present fabrication methods suffer from some...     

Fabrication of chamber for piezo inkjet printhead by SU-8 photolithography technology and bonding method

The chamber is an important part of the inkjet printhead. However, the present fabrication methods of chamber suffer from a low alignment resolution between nozzle plates and piezoelectric structure and residual SU-8 removing problems during chamber fabricating process. In this paper, a SU-8 chamber was fabricated by using ultraviolet (UV) photolithography and SU-8 thermal bonding method. By this method, the infilling problem of the chamber during thermal bonding process was solved, and low alignment resolution problem of conventional UV exposure system during assembly process was avoided. The thickness of the SU-8 nozzle plate was optimized, and the influence of bonding parameters on the deformation of chamber was analyzed. The simulation results show that the optimal thickness of the SU-8 nozzle plate is 40 μm and the optimal bonding parameters are bonding temperature of 50 °C, bonding pressure of 160 kPa and bonding time of 6 min. The tensile test results show the bonding strength of the SU-8 chamber is 2.1 MPa by using the optimized bonding parameter.     

A servo-controlled capacitive pressure sensor using a capped-cylinder structure microfabricated by a three-mask process

A silicon-micromachined servo-controlled capacitive pressure sensor is described. The use of a capped-cylinder shape with pick-off electrodes external to a sealed cavity permits this device to be fabricated in only three masking steps. Device behavior is evaluated experimentally and by finite element analysis. A fabricated device with 2 mm diameter, 9.7 /spl mu/m structural thickness and 10 /spl mu/m cavity height provides a measured sensitivity of 0.516 V/kPa over a dynamic range of 20-100 kPa gauge pressure, with a nonlinearity of <3.22% of full scale. The open-loop sensitivity of this device averaged over a dynamic range of 0-250 kPa is -408 ppm/kPa. A voltage bias applied to the servo-electrode can be used to tune both the open-loop and servo-controlled sensitivity by more than 30%. An alternative design in which the Si electrode is segmented to relieve residual stress provides 10-20% more open-loop sensitivity with similar structural dimensions. Fabricated devices are sealed within a metal package filled with an inert dielectric liquid. This enhanced open-loop sensitivity by a factor of about 1.7, and in servo-controlled operation, reduced restoring voltage by a similar factor. Measurements and analysis of temperature responses of these devices are presented.     

A silicon-glass-based microfabricated wide range thermal distribution gas flow meter

Recently, there has been high demand on miniaturizations of bio-instruments and wide range gas flux measurement in the field of chemistry and mechanics. This paper presents the design, fabrication, and characterization of a silicon-glass-based thermal distribution gas flow meter (20 mm × 10 mm × 1.6 mm) with a wide detection range. To facilitate the fabrication and maintain the stability of the sensor, a platinum (Pt) thin film was adopted as the heater and thermometers. Both the thermal property and temperature sensitivity of Pt thin film were characterized. SiO₂ passivation layers were deposited on top of the Pt film to prevent thermal and electrical shift of sensitive elements. Three pairs of thermometers were constructed beside the heater. Sensitivity and gas flux range of the gas flow meter can be increased by alternate use of these three sensor pairs. We also introduced a specific hardware control circuit system for real-time gas flux monitoring through the connection with a computer interface. The proposed gas flow sensor device was capable of measuring gas flux within the range of 0.8-2800 ml/min, thus demonstrating the potential for a wide range of applications.     

Performance of a 7-mm microfabricated car

A 7-mm-scale miniature car was manufactured as a conceptional model of a micromachine. The car consists of a chassis, a shell body, and an electromagnetic motor whose diameter is 1.0 mm. The motor consists of a core shaft, a coil, and a cylindrical permanent magnet magnetized by a special tool. The car runs at the maximum speed of 100 mm/sec by electric power. This is the smallest wheel driven mechanism in the world. The moving characteristics are investigated in detail by a high-speed video camera. Through the experiments, problems of the moving mechanism for micromachines are studied     

Development of a microfabricated electrochemical-cantilever hybrid platform

The design and fabrication of a combined electrochemical-cantilever microfluidic system is described. A chip integrating cantilevers with electrodes into a microchannel is presented with the accompanying polymer flow cell. Issues such as electrical and fluid connections are addressed, electromechanical behavior in ionic solution is investigated, and two uses of the system are demonstrated. First, all cantilevers are functionalized with cysteine, to facilitate detection of Cu²⁺ ions, then one cantilever is electrochemically cleaned in situ to generate a reference cantilever for differential measurements. Two concentrations of Cu²⁺ ions are successfully measured in this way. Clean cantilevers are used to probe a solution with and without [Fe(CN)₆]^3−/4− redox couple present, demonstrating the combined voltammetric and deflection readout.     

Optical measurement of flow field and concentration field inside a moving nanoliter droplet

Droplets-based method has been employed to enhance mixing in microfluidic systems. This paper presents experimental studies of the recirculating flow field inside a moving droplet and the characterization of the mixing of two aqueous droplets. In the first part, the velocity field inside the moving water droplet was measured using the micro-particle image velocimetry (micro-PIV) technique. The PIV measurements showed that recirculation flow exists inside the droplet. However, the findings suggested that the outer layer of droplets move at a faster velocity than the central part. The result is different from what is reported by other researchers. In the second part, two water droplets, a de-ionized (DI) water droplet and another DI water droplet with fluorescent dye, were brought together by the carrier fluid to form a bigger droplet. The mixing between the two aqueous droplets was characterized by the fluorescent dye concentration distribution.     

The effect of visualizing the flow of multimedia content among and inside devices

This study introduces a user interface, referred to as the flow interface, which provides a graphical representation of the movement of content among and inside audio/video devices. The proposed interface provides a different frame of reference with content-oriented visualization of the generation, manipulation, storage, and display of content as well as input and output. The flow interface was applied to a VCR/DVD recorder combo, one of the most complicated consumer products. A between-group experiment was performed to determine whether the flow interface helps users to perform various tasks and to examine the learning effect of the flow interface, particularly in regard to hooking up and recording tasks. The results showed that participants with access to the flow interface performed better in terms of success rate and elapsed time. In addition, the participants indicated that they could easily understand the flow interface. The potential of the flow interface for application to other audio video devices, and design issues requiring further consideration, are discussed.     

The microstructure of CVD diamond for high-density thermal inkjet

The microstructure for high-density thermal inkjet (TIJ) is proposed to overcome the defect due to the limit of the nozzle density in conventional TIJs. To bring high-density TIJ, the heat transfer of diamonds by means of placing heaters on sidewall of ink inlet is used in order to minimize the area occupied by the heaters. In addition, manifold, inlet, pressure chamber and nozzle concerning the flow of ink are placed in-line. To demonstrate feasibility, TIJ for bubble visualization test is designed and fabricated. Diamond is deposited on the sidewall of inlet with Hot Filament CVD (HFCVD). The trench filling method and the side deposition method are executed for the vertical sidewall of diamond. To solve the problem for direct CVD deposition on Pt layer, Ta film is utilized as a passivation layer in the fabrication processing. The generated bubble confirms the possibility of the bubble formation by heat transfer of diamond.This work was supported by the Research Institute for Applied Science and Technology, Sogang University.     

Micro-PIV investigation of the internal flow transitions inside droplets traveling in a rectangular microchannel

This paper discusses the studies on the internal flow field of droplets traveling in a rectangular microchannel by means of microparticle image velocimetry, specifically concentrating on the effects of capillary number, viscosity ratio and interfacial tension. The flow topology is predominantly dependent on the capillary number. It shows that the evident transitions from three pairs of recirculation zones at lower capillary numbers to one pair of recirculation zones near the sidewalls with low velocity in the central area at intermediate capillary numbers, then to a pair of recirculation zones closest to the axial centerline with high velocity in the central area at higher capillary numbers. There are two critical capillary numbers increasing with viscosity ratio in the evolution of flow features. Droplet size only influences two velocity components values other than the flow topology within intervals separated by the critical values. The equilibrium mechanism of viscous friction force and Marangoni stress dominate the internal topological transition in a surfactant added system. The obtained internal fluid phenomena inside droplets are beneficial to provide a guideline for screening of biochemical reaction conditions in the device.     

Experimental and numerical study of the recirculation flow inside a liquid meniscus focused by air

The internal motions inside a liquid meniscus in the so-called liquid cone-jet mode, which can occur upon stimulation by a coflowing gas sheath in flow focusing, are explored by both numerical simulation and experimental visualization. The results for low viscosity liquids show that, as in previous numerical simulations, a recirculating cell inside the meniscus appears when the injected liquid flow rate is reduced. Thus, as the flow rate is reduced not only the average residence time of particles in the meniscus becomes longer, but the appearance of a recirculation cell provides a natural platform for the efficient micro-mixing of different species before they are ejected through the issuing jet. The numerical results were confirmed with experimental visualization of the flow inside the meniscus using a dyed liquid. However, when the viscosity of the liquid is increased the recirculating cell disappears. In this case, viscous stresses organize the streamlines and direct the flow to the meniscus tip, which prevents the recirculating cell from being formed even for very small injected rate of liquid flow.     

Vortex structure of steady flow in a rectangular cavity

The vortex structure of the two-dimensional steady flow in a lid-driven rectangular cavity at different depth-to-width ratios and Reynolds numbers is investigated using a lattice Boltzmann method. The aspect ratio varies from 0.1 to 7 and the Reynolds number ranges from 0.01 to 5000. The effects of the aspect ratio and Reynolds number on the size, center position and number of vortices are determined together with the flow pattern in the cavity. The present results not only confirm the vortex structure of Stokes flow reported by previous researchers, but also reveal some new evolution features of the vortices and their structure with the Reynolds number. When the Reynolds number approaches 0, the flow shows a characteristic feature of symmetric vortex structure. On the other hand, as the Reynolds number increases, the sizes and center positions of the vortices in the near-lid region appear to be strongly affected by the inertia force, resulting in an asymmetric vortex structure in this region. The influence of the inertia force decreases along the depth for the deep cavity flow. It is found that there is a critical value of the aspect ratio, which depends on the Reynolds number. When the critical value is exceeded, flow pattern in a certain region of cavity becomes symmetric again. These large symmetric vortices are similar in shape, and their sizes approach a constant.     

Influence of dynamic boundary conditions on the computed flow patterns inside a coaxial rotating disk-cylinder system

In this paper, numerical solutions for the steady axisymmetric flow of an isothermal viscous fluid driven by moderate disk and/or cylinder coaxial rotation are presented. The influence of the two possible types of dynamic boundary conditions for the solid walls on the meridional flow features is discussed in detail using the computed Stokes streamfunction, angular momentum and vorticity distributions. Results show a clear dependence between the computed-generated flow patterns and the boundary conditions used.     

Turbulent boundary layer structure of flow over a smooth-curved ramp

The effects of a convex-curved wall followed by a recovery over a flat surface on a turbulent boundary layer structure are addressed via large-eddy simulation (LES). The curved wall constitutes a smooth ramp formed by a portion of circular arc. The statistically two-dimensional upstream boundary layer flow is realistically fed by an injected inflow boundary condition. The inflow is extracted from a simultaneously simulated flat-plate boundary layer which is computed based on a compressible rescaling method. After flowing over the curved surface the flow is allowed to recover its realistic condition by passing over a downstream flat surface. The Reynolds number introduced at the inlet section of the computational domain which starts 4 times the ramp length (L_r) upstream of the curved surface is Re_δo=U_∞δ_o/ν=9907. The Reynolds number is based on the inflow boundary layer thickness δ_o, the free-stream velocity U_∞ and the kinematic viscosity ν.Mean flow predictions obtained using the present LES with the rescaling–recycling inflow condition agree well with the available experimental data from literature. The Reynolds stress components match the experimental one. However, small deviation occurs due to the smaller-domain height used in the present simulation. The experiments showed that there is a generated pressure gradient on the upper wall and this in return affects the turbulence energy on the other wall. The numerical data as well as the experiments show an enhancement of the turbulent stresses in the adverse pressure gradient region. The increased level of turbulent stresses is accompanied with large peaks aligned with the inflection point of the velocity profiles. The high stress levels are nearly unchanged by reattachment process, decaying only after the mean velocity recovered and the high production of turbulence near the outer layer drops. The recovery of the outer layer is due to the turbulent eddies generated by the separation region. Numerical visualizations show strong elongation and lifting of eddies in the region of the adverse pressure gradient generated by the curved wall. Computations of two-point correlations are also performed to represent the formation and deformation of the turbulent eddies before, over and after the curved wall. Different effects on the eddy size and its structure angle are presented.     

输浆管道液—固两相流静电场特性研究

利用有限元方法建立了输浆管道内液-固两相流(矿浆)的静电场模型,以检测灵敏度为媒介,对液-固两相流的软场特性进行深入研究,分析了矿浆的流速、固体颗粒大小、结垢、浓度对软场特性的影响,得出了如下结论:在矿浆流速越低、矿浆固体颗粒越大和结垢层越厚时,灵敏度分布越不均匀;矿浆浓度的变化越大,对灵敏度影响越大。这一结论为输浆管道液-固两相流的可视化检测提供了技术支撑。