Application Cases

Experiment Name: System Integration and Control Research in Piezoelectric Inkjet Printing Experiments

Experiment Purpose:

The stable ejection of droplets is a key factor in determining the quality of printed conductive lines. This paper focuses on the control research of experimental operating parameters to achieve the goal of uniform and stable droplet formation. Specifically, an industrial camera is used to periodically capture images to monitor whether the continuously ejected droplets are oscillating left and right and whether they deviate from the central axis of the piezoelectric nozzle. Based on the feedback of the droplet ejection situation, the center of gravity of the liquid in the liquid storage bottle is adjusted, and the pulse voltage parameters are improved to avoid the generation of satellite droplets and significantly enhance the droplet ejection effect. The entry pressure of the piezoelectric nozzle is quantitatively analyzed, and methods to effectively improve the efficiency of piezoelectric inkjet printing are explored. A new solution with viscosity and surface tension similar to that of silver nanofluid is formulated, and experimental research is conducted to comprehensively determine the regulation and control methods for printing this new solution.

Testing Equipment: Power amplifier, digital oscilloscope, function generator, computer, piezoelectric nozzle, etc.

Experiment Process:

Figure 1: Control Principle Diagram of Piezoelectric Inkjet Printing Experiment

The piezoelectric inkjet printing experimental system mainly consists of three modules: the piezoelectric drive module, the hydraulic supply module, and the optical camera module. The piezoelectric drive module provides the power source for the radial compression deformation of the piezoelectric nozzle. The hydraulic supply module provides an appropriate entry pressure for the piezoelectric nozzle to facilitate the ejection of stable-shaped droplets. The optical camera module observes whether the droplets oscillate left and right and whether the flight trajectory deviates from the central axis of the piezoelectric nozzle. Based on the observed droplet ejection situation, the control parameters of the piezoelectric drive module and the hydraulic supply module are adjusted to obtain droplets with stable ejection shapes. The control principle diagram of the piezoelectric inkjet printing experiment is shown in the figure above.

I. The insert plug of the piezoelectric print head is modified into a BNC interface, which can be connected to the high-voltage amplifier. At this point, a faint buzzing sound can be heard from inside the piezoelectric nozzle, indicating that it is working normally under the excitation of the pulse voltage.

II. The hydraulic supply module is set up to precisely control the meniscus of the liquid in the chamber by reasonably adjusting the entry pressure of the piezoelectric nozzle for the piezoelectric inkjet printing experiment. The printing solution used in this paper is ethanol liquid. The printing liquid is filled into the liquid conduit and the piezoelectric nozzle chamber. By adjusting the center of gravity of the liquid in the liquid storage bottle, the printing liquid neither retracts into the chamber nor overflows to form a meniscus.

Figure 2: Schematic Diagram of the Optical Camera Module

III. The optical camera module uses an industrial camera with a pixel size of 4.8μm and a frame rate of 210 frames per second. The experimental equipment required for droplet observation includes an industrial camera, a 1x magnifying lens, an LED light, and its controller. The schematic diagram of the optical camera module is shown in Figure 2. To ensure that the obtained droplet images are clear, the trigger pulse time for the industrial camera to take photos is usually very short. Therefore, this paper sets the trigger pulse time to 30μs.

Experimental Results:

Figure 3: Stable droplet formation entry pressure. (a) Relationship between entry pressure and voltage amplitude; (b) Droplet ejection speed corresponding to different entry pressures

Different voltage amplitudes are set to measure the maximum and minimum entry pressures corresponding to stable droplet formation, as shown in Figure 3(a). It can be seen from this figure that when the voltage amplitude increases from 25V to 50V, both the maximum and minimum entry pressures of the piezoelectric nozzle increase continuously, and the pressure difference between them decreases from 480Pa to 270Pa. This indicates that the higher the input voltage amplitude, the more difficult it is to modulate stable droplet ejection, and the higher the requirements for the test solution and other operating parameters.

Figure 3(b) describes the relationship between droplet speed and entry pressure under the action of a 30V excitation voltage. It can be seen that the droplet speed increases continuously with the decrease of entry pressure. When the entry pressure changes from -500Pa to -900Pa, the droplet speed increases from 0.28m/s to 1.03m/s. If the entry pressure continues to decrease at this time, the droplet ejection will become mist-like, which is not conducive to the stable formation of droplets. Therefore, reasonably controlling the entry pressure of the piezoelectric nozzle can not only obtain droplets with stable ejection shapes but also effectively increase the droplet exit speed.

Power Amplifier Recommendation: ATA-3080C

Figure: Specification Parameters of the ATA-3080C Power Amplifier

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