The Driving Waveform Design Method of Power-Law Fluid Piezoelectric Printing Based on Iterative Learning Control.

In some applications of piezoelectric three-dimensional inkjet printing, the materials used are power-law fluids as they are shear thinning. Their time-varying viscosities affect the droplet formation, which is determined by the volume flow rate at the nozzle outlet. To obtain a fine printing effect, it is necessary to present a driving waveform design method that considers the shear-thinning viscosities of materials to control the volume flow rate at the nozzle outlet, which lays the foundation for the single and stable droplet generation during the printing process. In this research, we established the relationship between the driving waveform and the volume flow rate at the nozzle outlet by modifying a model that describes the inkjet mechanism of power-law fluid. The modified model was used to present a driving waveform design method based on iterative learning control. The iterative learning law of the method was designed based on the gradient descent algorithm and demonstrated its convergence. The driving waveform design method was verified to be practical and feasible by implementing drop generation experiments.

Stability Study of Multi-Level Grayscales Based on Driving Waveforms for Electrowetting Displays.

Electrowetting Display (EWD) is a new reflective display with an outstanding performance of color video playback. However, some problems still exist and affect its performance. For instance, oil backflow, oil splitting, and charge trapping phenomena may occur during the driving process of EWDs, which would decrease its stability of multi-level grayscales. Therefore, an efficient driving waveform was proposed to solve these disadvantages. It consisted of a driving stage and a stabilizing stage. First, an exponential function waveform was used in the driving stage for driving the EWDs quickly. Then, an alternating current (AC) pulse signal waveform was used in the stabilizing stage to release the trapped positive charges of the insulating layer to improve display stability. A set of four level grayscale driving waveforms were designed by using the proposed method, and it was used in comparative experiments. The experiments showed that the proposed driving waveform could mitigate oil backflow and splitting effects. Compared to a traditional driving waveform, the luminance stability was increased by 8.9%, 5.9%, 10.9%, and 11.6% for the four level grayscales after 12 s, respectively.

Research on Hydrodynamic Characteristics of Electronic Paper Pixels Based on Electrowetting.

In this paper, we propose a driving waveform with a complex ramp pulse for an electrowetting display system. The relationship between the contact angle and viscosity of inks was calculated based on the fluid-motion characteristics of different viscosities. We obtained the suitable range of viscosity and voltage in the liquid-oil-solid three-phase contact display system. We carried out model simulation and driving waveform design. The result shows that the driving waveform improves the response speed and aperture ratio of electrowetting. The aperture ratio of electrowetting pixels is increased to 68.69%. This research is of great significance to optimizing the structure of fluid material and the design of driving waveforms in electrowetting displays.

Toward Suppressing Oil Backflow Based on a Combined Driving Waveform for Electrowetting Displays.

Electrowetting display (EWD) is a new type of paper-like reflective display based on colored oil, which has gradually become one of the most potential electronic papers with low power consumption, fast response, and full color. However, oil backflow can occur in EWDs, which makes it difficult to maintain a stable aperture ratio. In order to improve the stability of the aperture ratio of EWDs, a new driving waveform was proposed based on analyzing the phenomenon of oil backflow. The driving waveform was composed of a shrinking stage and a driving stage. Firstly, a threshold voltage of oil splitting was calculated by analyzing the luminance curve of EWDs, which were driven by different direct current (DC) voltages. Then, an exponential function waveform, which increased from the threshold voltage, was applied to suppress oil splitting. Finally, a periodic signal combined with a reset signal with a DC signal was applied during the driving stage to maintain a stable aperture ratio display. Experimental results showed that the charge trapping effect could be effectively prevented by the proposed driving waveform. Compared with an exponential function waveform, the average luminance value was increased by 28.29%, and the grayscale stability was increased by 13.76%. Compared to a linear function waveform, the aperture ratio was increased by 10.44% and the response time was reduced by 20.27%.

Red Ghost Image Elimination Method Based on Driving Waveform Design in Three-Color Electrophoretic Displays.

Three-color electrophoretic displays (EPDs) are a new type of optoelectronic display device. However, they have the defect of red ghost images during gray scale transformation, which affects the accuracy of the gray scale display. In this paper, we proposed a new driving method for eliminating the red ghost images. A driving waveform was composed of an erasing stage, an activation stage, and a driving stage. First, the erasing stage was subdivided into a red erasing stage and an original erasing stage, the red erasing stage was used to eliminate residual red particles in the top of the microcapsules. Then, a high-frequency square wave was used as the activation stage for increasing the activity of the black and white particles. Meanwhile, the intensity of flickers could be decreased by the high-frequency square wave. Finally, the performance of the driving waveform was tested by a colorimeter. The experimental results showed that the driving waveform could effectively eliminate red ghost images by 80.43% and reduce the flicker intensity by 79.63%, compared with an existing driving waveform.

Toward Suppressing Charge Trapping Based on a Combined Driving Waveform with an AC Reset Signal for Electro-Fluidic Displays.

Digital microfluidic technology based on the principle of electrowetting is developing rapidly. As an extension of this technology, electro-fluidic displays (EFDs) have gradually become a novel type of display devices, whose grayscales can be displayed by controlling oil film in pixels with a microelectromechanical system (MEMS). Nevertheless, charge trapping can occur during EFDs' driving process, which will produce the leakage current and seriously affect the performance of EFDs. Thus, an efficient driving waveform was proposed to resolve these defects in EFDs. It consisted of a driving stage and a stabilizing stage. Firstly, the response time of oil film was shortened by applying an overdriving voltage in the driving stage according to the principle of the electrowetting. Then, a direct current (DC) voltage was designed to display a target luminance by analyzing leakage current-voltage curves and a dielectric loss factor. Finally, an alternating current (AC) reset signal was applied in the stabilizing stage to suppress the charge trapping effect. The experiment results indicated that compared with a driving waveform with a reset signal and a combined driving waveform, the average luminance was improved by 3.4% and 9.7%, and the response time was reduced by 29.63% and 51.54%, respectively.

Design of Driving Waveform for Shortening Red Particles Response Time in Three-Color Electrophoretic Displays.

Three-color electrophoretic displays (EPDs) have the advantages of multi-color display and low power consumption. However, their red particles have the disadvantage of long response time. In this paper, a driving waveform, which is based on electrophoresis theory and reference gray scale optimization, was proposed to shorten the response time of red particles in three-color EPDs. The driving waveform was composed of erasing stage, reference gray scale forming stage, red driving stage, and white or black driving stage. Firstly, the characteristics of particle motion were analyzed by electrophoresis theory and Stokes law. Secondly, the reference gray scale of the driving waveform was optimized to shorten the distance between red particles and a common electrode plate. Finally, an experimental platform was developed to test the performance of the driving waveform. Experimental results showed that the proposed driving waveform can shorten the response time of red particles by 65.57% and reduce the number of flickers by 66.67% compared with the traditional driving waveform.

Design of Driving Waveform Based on a Damping Oscillation for Optimizing Red Saturation in Three-Color Electrophoretic Displays.

At present, three-color electrophoretic displays (EPDs) have problems of dim brightness and insufficient color saturation. In this paper, a driving waveform based on a damping oscillation was proposed to optimize the red saturation in three-color EPDs. The optimized driving waveform was composed of an erasing stage, a particles activation stage, a red electrophoretic particles purification stage, and a red display stage. The driving duration was set to 360 ms, 880 ms, 400 ms, and 2400 ms, respectively. The erasing stage was used to erase the current pixel state and refresh to a black state. The particles' activation stage was set as two cycles, and then refreshed to the black state. The red electrophoretic particles' purification stage was a damping oscillation driving waveform. The red and black electrophoretic particles were separated by changing the magnitude and polarity of applied electric filed, so that the red electrophoretic particles were purified. The red display stage was a low positive voltage, and red electrophoretic particles were driven to the common electrode to display a red state. The experimental results showed that the maximum red saturation could reach 0.583, which was increased by 27.57% compared with the traditional driving waveform.

Design of Driving Waveform for Shortening Response Time of Black Particles and White Particles in Three-Color Electrophoretic Displays.

The shortage of color in traditional electrophoretic displays (EPDs) can be compensated by three-color EPDs. However, the response time of black particles and white particles is increased. A new driving waveform based on the principle of three-color EPDs and electrophoresis theory was proposed to shorten the response time of black particles and white particles. The proposed driving waveform consisted of an erasing stage, an activation stage, a red driving stage, and a white or a black driving stage. The activation stage was mainly optimized in this paper. Firstly, the motion characteristics of the particles were analyzed using Stokes law and electrophoresis theory. Secondly, an optimal high frequency oscillation voltage was tested in order to improve the activity of the particles. Then, the influence of oscillation period and oscillation times on the activation stage were analyzed for optimizing the reference grayscale. According to the luminance of pixels, an oscillation period of 30 ms and an oscillation time of 30 were determined. The experimental results showed that the response time of black particles was shortened by 45%, and the response time of white particles was shortened by 40% compared with a traditional driving waveform.

A Driving Method for Reducing Oil Film Splitting in Electrowetting Displays.

Electrowetting displays (EWDs) are one of the most potential electronic papers. However, they have the problem of oil film splitting, which could lead to a low aperture ratio of EWDs. In this paper, a driving waveform was proposed to reduce oil film splitting. The driving waveform was composed of a rising stage and a driving stage. First, the rupture voltage of oil film was analyzed by testing the voltage characteristic curve of EWDs. Then, a quadratic function waveform with an initial voltage was applied at the rising stage to suppress oil film splitting. Finally, a square wave was applied at the driving stage to maintain the aperture ratio of EWDs. The experimental results show that the luminance was increased by 8.78% and the aperture ratio was increased by 4.47% compared with an exponential function driving waveform.

A Fast-Response Driving Waveform Design Based on High-Frequency Voltage for Three-Color Electrophoretic Displays.

Three-color electrophoretic displays (EPDs) have the characteristics of colorful display, reflection display, low power consumption, and flexible display. However, due to the addition of red particles, response time of three-color EPDs is increased. In this paper, we proposed a new driving waveform based on high-frequency voltage optimization and electrophoresis theory, which was used to shorten the response time. The proposed driving waveform was composed of an activation stage, a new red driving stage, and a black or white driving stage. The response time of particles was effectively reduced by removing an erasing stage. In the design process, the velocity of particles in non-polar solvents was analyzed by Newton's second law and Stokes law. Next, an optimal duration and an optimal frequency of the activation stage were obtained to reduce ghost images and improve particle activity. Then, an optimal voltage which can effectively drive red particles was tested to reduce the response time of red particles. Experimental results showed that compared with a traditional driving waveform, the proposed driving waveform had a better performance. Response times of black particles, white particles and red particles were shortened by 40%, 47.8% and 44.9%, respectively.

A Separated Reset Waveform Design for Suppressing Oil Backflow in Active Matrix Electrowetting Displays.

The electrowetting display (EWD) is a kind of reflective paper-like display. Flicker and grayscale distortion are caused by oil backflow, which is one of the important factors restricting the wide application of EWDs. The charge embedding caused by the electric field force in the dielectric layer is the cause of oil backflow. To suppress oil backflow, a separated reset waveform based on the study of oil movement is proposed in this paper. The driving waveform is divided into two parts: a reset waveform and a grayscale waveform. The reset waveform generated by a reset circuit can be used to output various voltages. The grayscale waveform is set as a traditional PWM waveform. The reset waveform is composed of a charge-releasing stage and oil-moving back stage. Two phases are contained in the charge releasing stage. The overdriving voltage is used during the first phase to reverse the voltage of all pixels. The trapped charges can then be released from the dielectric layer during the second phase. A higher voltage is used during the oil-moving back stage to drive the oil faster in the pixel. By comparing the experimental data, the oil backflow time is extended 761 times by the reset waveform. The four grayscales can be maintained by the reset waveform after driving for 300 s.

Driving Waveform Design of Electrowetting Displays Based on an Exponential Function for a Stable Grayscale and a Short Driving Time.

The traditional driving waveform of the electrowetting display (EWD) has many disadvantages, such as the large oscillation of the target grayscale aperture ratio and a long time for achieving grayscale. Therefore, a driving waveform based on the exponential function was proposed in this study. First, the maximum driving voltage value of 30 V was obtained by testing the hysteresis curve of the EWD pixel unit. Secondly, the influence of the time constant on the driving waveform was analyzed, and the optimal time constant of the exponential function was designed by testing the performance of the aperture ratio. Lastly, an EWD panel was used to test the driving effect of the exponential-function-driving waveform. The experimental results showed that a stable grayscale and a short driving time could be realized when the appropriate time constant value was designed for driving EWDs. The aperture ratio oscillation range of the gray scale could be reduced within 0.95%, and the driving time of a stable grayscale was reduced by 30% compared with the traditional driving waveform.

Driving Waveform Design with Rising Gradient and Sawtooth Wave of Electrowetting Displays for Ultra-Low Power Consumption.

As a kind of paper-like display technology, power consumption is a very important index for electrowetting displays (EWDs). In this paper, the influence of driving waveforms on power consumption of the EWDs is analyzed, and a driving waveform with rising gradient and sawtooth wave is designed to reduce the power consumption. There are three stages in the proposed driving waveform. In the initial stage, the driving voltage is raised linearly from the threshold to the maximum value to reduce the invalid power consumption. At the same time, the oil breakup can be prohibited. And then, a section of sawtooth wave is added for suppressing oil backflow. Finally, there is a section of resetting wave to eliminate the influence of charge leakage. Experimental results show that the power consumption of the ultra-low power driving waveform is 1.85 mW, which is about 38.13% lower than that of the conventional used square wave (2.99 mW), when the aperture ratio is 65%.

Driving Waveform Design of Electrophoretic Display Based on Optimized Particle Activation for a Rapid Response Speed.

Electrophoretic displays (EPDs) have excellent paper-like display features, but their response speed is as long as hundreds of milliseconds. This is particularly important when optimizing the driving waveform for improving the response speed. Hence, a driving waveform design based on the optimization of particle activation was proposed by analyzing the electrophoresis performance of particles in EPD pixels. The particle activation in the driving waveform was divided into two phases: the improving particle activity phase and the uniform reference grayscale phase. First, according to the motion characteristics of particles in improving the particle activity phase, the real-time EPD brightness value can be obtained by an optical testing device. Secondly, the derivative of the EPD brightness curve was used to obtain the inflection point, and the inflection point was used as the duration of improving particle activity phase. Thirdly, the brightness curve of the uniform reference grayscale phase was studied to set the driving duration for obtaining a white reference grayscale. Finally, a set of four-level grayscale driving waveform was designed and validated in a commercial E-ink EPD. The experimental results showed that the proposed driving waveform can cause a reduction by 180 ms in improving particle activity phase and 120 ms in uniform reference grayscale phase effectively, and a unified reference grayscale can be achieved in uniform reference grayscale phase at the same time.

Aperture Ratio Improvement by Optimizing the Voltage Slope and Reverse Pulse in the Driving Waveform for Electrowetting Displays.

Electrowetting display (EWD) performance is severely affected by ink distribution and charge trapping in pixel cells. Therefore, a multi structural driving waveform is proposed for improving the aperture ratio of EWDs. In this paper, the hysteresis characteristic (capacitance-voltage, C-V) curve of the EWD pixel is tested and analyzed for obtaining the driving voltage value at the inflection point of the driving waveform. In the composition of driving waveform, a voltage slope is designed for preventing ink dispersion and a reverse pulse is designed for releasing the trapped charge which is caused by hysteresis characteristic. Finally, the frequency and the duty cycle of the driving waveform are optimized for the max aperture ratio by a series of testing. The experimental results show that the proposed driving waveform can improve the ink dispersion behavior, and the aperture ratio of the EWD is about 8% higher than the conventional driving waveform. At the same time, the response speed of the driving waveform can satisfy the dynamic display in EWDs, which provides a new idea for the design of the EWD driving scheme.

Improving Electrophoretic Particle Motion Control in Electrophoretic Displays by Eliminating the Fringing Effect via Driving Waveform Design.

Electrophoretic display is realized by controlling colored nanoparticles moving in micrometer spaces via electrophoresis. The quality of information display is therefore affected by the unsynchronized particle moving speed and the mismatched electric signal according to the crosstalk of the electric field and inhomogeneous material distribution. In this work, we analyzed the mechanism of a fringe phenomenon that affected the information display quality of electrophoretic displays (EPDs). Electrical driving waveforms (voltage signals) are designed to reduce the fringe phenomenon. By using the optimizing driving waveform, we proposed that the fringe phenomenon is quantified as gray value that can be diminished by 25.5, while keeping a response time of 200 ms.

Reliability of a MEMS Actuator Improved by Spring Corner Designs and Reshaped Driving Waveforms.

In this paper, we report spring corner designs and driving waveforms to improve the reliability for a MEMS (Micro-Electro-Mechanical System) actuator. In order to prevent the stiction problems, no stopper or damping absorber is adopted. Therefore, an actuator could travel long distance by electromagnetic force without any object in moving path to absorb excess momentum. Due to long displacement and large mass, springs of MEMS actuators tend to crack from weak points with high stress concentration and this situation degrades reliability performance. Stress distribution over different spring designs were simulated and a serpentine spring with circular and wide corner design was chosen due to its low stress concentration. This design has smaller stress concentration versus displacement. Furthermore, the resonant frequencies are removed from the driving waveform based on the analysis of discrete Fourier transfer function. The reshaped waveform not only shortens actuator switching time, but also ensures that the spring is in a small displacement region without overshooting so that the maximum stress is kept below 200 MPa. The experimental results show that the MEMS device designed by theses principles can survive 500 g (gravity acceleration) shock test and pass 150 million switching cycles without failure.