Model-free optimization based feedforward control for an inkjet printhead

Inkjet is an important technology in document printing and many new industrial applications. As inkjet developments are moving towards higher productivity and quality, it is required to achieve small droplet size which is fired at a high jetting frequency. Inkjet printers are now widely used to form conductive traces for circuits, as well as color filters in LCD and plasma displays, what makes the printing quality an important issue. In this paper, an optimization-based feedforward control is proposed to improve the printing quality of the piezoelectric inkjet printer. A novel optimized input pulse is proposed and a model-free optimization is applied to obtain the optimal parameters of the proposed pulse. The proposed optimal pulse is applied to the inkjet printhead and the system performance is investigated

Performance improvement of professional printing systems : from theory to practice

Performance Improvement of Professional Printing Systems: from theory to practice Markets demand continuously for higher quality, higher speed, and more energy-efficient professional printers. In this thesis, control strategies have been developed to improve the performance of both professional inkjet and laser printers. Drop-on-Demand (DoD) inkjet printing is considered as one of the most promising printing technologies. It offers several 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. Several requirements are related to the jetted drop properties, namely, drop velocity, drop volume, drop velocity consistency, productivity, and reliability. Meeting the performance requirements is restricted by several operational issues that are associated with the design and operation of inkjet printheads. Major issues that are usually encountered are residual vibrations in and crosstalk among ink channels. This results in a poor printing quality for high-speed printing. Given any arbitrary bitmap, the main objective is to design actuation pulses such that variations in the velocity and volume of the jetted drops are minimized. Several model-based feedfoward control techniques using an existing model are implemented to generate appropriate input pulses for the printhead. Although the implementation of the model-based techniques shows a considerable improvement of the printhead performance compared with the current performance, further improvements are still necessary. We observe that besides the pulse shape the state of the ink surface at the nozzle plate (speed, position) at the start of the pulse influences the drop velocity considerably. This state at firing depends also on previous pixels in the bitmap of the image. Consequently, any pulse design has to guarantee almost the same initial state when firing a drop. Based on these facts, a model-free optimization scheme is developed to minimize the drop velocity variations taking into account the bitmap information. Experimental results show the effectiveness of the optimized pulses. Laser printing systems are highly depending on the appropriate combination of several design factors so as to become functional in a desired working range. The physical printing process involves multiple temperature set points at different places, precise electro-magnetic conditions, transfer of toner through certain pressures and layouts, and many other technical considerations. In the laser printing system there are several challenging issues and unknown disturbances. They originate from different sources, such as the printer itself (unknown phenomena appear, disturbances that are not foreseen, wear, contamination, failures, bugs), the environment of the system (power supply variations, temperature, humidity, vibrations), and the printing media (weight, coating, thermal properties, humidity characteristics, and initial temperature). These issues have a negative effect on the stability and performance of the laser printing system. The objective is to design a control scheme to achieve printing quality requirements and a high productivity. Good printing quality means that the fusing temperature should track a certain reference signal at different operating conditions. Based on the printing system behavior, we propose two different control schemes to cope with the large parameter variations and disturbances, namely, a Model Reference Adaptive Controller (MRAC) and a nonlinear (scheduled) observer-based output feedback control scheme. Both control techniques yield considerable performance improvements compared with the present industrial controller

Adjoint-based optimization for inkjet printing

In this thesis the flow inside inkjet printhead microchannels is analysed using a two- parameter low Mach number expansion of the compressible Navier–Stokes equations and a reduced order model for the free surface flow inside the inkjet nozzle. The channel flow is separated into equations for an incompressible flow with no acoustic oscillations and equations for thermoviscous acoustic oscillations with no mean flow. This thesis concerns two types of optimal control problems. The optimal control problem of the first type is finding a velocity profile of the piezo-electric actuator that eliminates residual oscillations after a droplet is ejected. The cost function is the sum of the acoustic energy in the channel and the surface energy of the spherical cap of ink at the end of the nozzle at a given time. This problem is approached by obtaining the sensitivity of the total energy inside an inkjet microchannel with respect to boundary forcing using the adjoint method. Using gradient-based optimization algorithms, optimal waveforms are found that minimize the objective value at various final times and for geometries with increasing complexity. Physical interpretation to the optimal waveforms profiles is provided, and the exploited mechanisms are revealed. The optimal control problem of the second type is finding a shape of the inkjet printhead channel that maximises dissipation of the acoustic oscillations, without increasing the pressure drop required to drive the steady flow. Similarly, the adjoint approach is used to obtain the sensitivity of the acoustic flow eigenvalues with respect to boundary deformations in Hadamard form. Knowing the shape sensitivity of the incompressible flow viscous dissipation, the constrained optimization problem is solved to find a design that has the same viscous dissipation for the steady flow but a 40% larger decay rate for the oscillating flow. The final shape is not straightforward and would have been difficult to achieve through physical insight or trial and error. It could be improved further by adapting the parameters that describe the shape, but in this case the improvement would be small. The method is general and could be applied to many different applications in microfluidics. In summary, the methods in this thesis are promising techniques in the design and optimization of inkjet printheads. The discussed numerical techniques and the gained physical understanding can be used to automatically find the optimal design parameters, or, at a minimum, accelerate the experimental trial and error processes.This project has received funding from the European Unions Horizon 2020 research and innovation programme under Grant Agreement No. H2020-MSCA-ITN-2015

Design and Fabrication of Printed DNA Droplets Arrangement and Detection Inkjet System

This article describes the aims to establish a thermal bubble printhead with simultaneously driving multi-channel for DNA droplet arrangement. It proposed a monolithic CMOS/MEMS system with multi-level output voltage ESD protection system for protected inkjet printhead. High-voltage power, low-voltage logic, and CMOS/MEMS architecture were integrated in inkjet chip. It used bulk micromachining technology (MEMS). On-chip high-voltage electrostatic discharge (HV-ESD), protection design in smart power technology of monolithic inkjet chip is a challenging issue. The nozzle jets interleaving scanning sequence is controlled spatially on the elements to avoid the strong interference with DNA droplets caused by the excitation of the neighbor driven elements. A heating element, disposed on the substrate, includes a conductor loop which does not encompass the heating elements on the substrate. The configuration of the heater jet significantly reduces both electromagnetic and capacitance interference caused by the heating elements. The simulation and experience result have shown in the research. It is reduced nearly half the time compared to the case with traditional scanning sequence. This experiment develops new controlled structure designs of chip for inkjet printheads. A bubble inkjet(TIJ) device is designed, several of the architectures may be adjusted just a small microns to improve and optimize the DNA drop nucleation and generation efficiency. The DNA droplet ejection behavior of the multiplexer inkjet printhead within 60-μm orifice size has been measured beyond 5 kHz operation system, 12 pL capacity of ejected DNA droplet volume

Learning for Advanced Motion Control

Iterative Learning Control (ILC) can achieve perfect tracking performance for mechatronic systems. The aim of this paper is to present an ILC design tutorial for industrial mechatronic systems. First, a preliminary analysis reveals the potential performance improvement of ILC prior to its actual implementation. Second, a frequency domain approach is presented, where fast learning is achieved through noncausal model inversion, and safe and robust learning is achieved by employing a contraction mapping theorem in conjunction with nonparametric frequency response functions. The approach is demonstrated on a desktop printer. Finally, a detailed analysis of industrial motion systems leads to several shortcomings that obstruct the widespread implementation of ILC algorithms. An overview of recently developed algorithms, including extensions using machine learning algorithms, is outlined that are aimed to facilitate broad industrial deployment.Comment: 8 pages, 15 figures, IEEE 16th International Workshop on Advanced Motion Control, 202

Methods for Fabricating Printed Electronics with High Conductivity and High Resolution

Flexible and printable electronics are attractive techniques which are believed to be widespread and occupy huge market. However, low conductivity, nozzle clog because of the accumulation of nano-particles and relative high cost (expensive silver/copper nanoparticle inks) limit its appeal. In this thesis, two new effective and convenient methods of fabricating copper patterns with high conductivity and strong adhesion on flexible photopaper and polymer substrates (PET) are demonstrated, solving all those problems. Functional photopaper and PET substrate was prepared with inkjet printing of a palladium salt solution and hyperthermal hydrogen induced cross-linking (HHIC) polyelectrolytes onto its surface respectively, followed by electroless deposition of copper, creating high quality flexible copper patterns on different substrates. The developed technique was successfully applied for fabricating functional flexible circuits such as radio frequency identification devices (RFID) antenna, micro-inductive coil and complex circuit board

Effect of Process Parameters on the Performance of Drop-On-Demand 3D Inkjet Printing: Geometrical-Based Modeling and Experimental Validation

As additive manufacturing has evolved, 3D inkjet printing (IJP) has become a promising alternative manufacturing method able to manufacture functional multi-material parts in a single process. However, issues with part quality in terms of dimensional errors and lack of precision still restrict its industrial and commercial applications. This study aims at improving the dimensional accuracy of 3D IJP parts by developing an optimization-oriented simulation tool of droplet behavior during the drop-on-demand 3D IJP process. The simulation approach takes into consideration the effect of droplet volume, droplet center-to-center distance, coverage percentage of jetted droplets, the contact angle of the ink on the solid substrate and coalescence performance of overlapping droplets, in addition to the number of printed layers. Following the development of the simulation tool using MATLAB, its feasibility was experimentally validated and the results showed a good agreement with a maximum deviation of 2.25% for horizontal features. In addition, the simulated horizontal features are compared with the results of “Inkraster” software, which also illustrates droplet behavior, however, only in 2D. For vertical features, a dial gauge indicator is used to measure the sample height, and the validation results show that the simulation tool can predicate the height of the sample with an average error of 10.89% for a large droplet diameter and 8.09% for a small diameter. The simulation results were found to be in a good agreement with the dimensions of the printed parts. The developed tool was then used to elucidate the effect of resolution of processed TIFF image and droplet diameter on the dimensional accuracy of 3D IJP parts