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The Capillary Lock Actuator: A novel bistable microfluidic actuator for cost-effective high-density actuator arrays suitable for large-scale graphical tactile displays

Periodic Reporting for period 2 - CaLA (The Capillary Lock Actuator: A novel bistable microfluidic actuator for cost-effective high-density actuator arrays suitable for large-scale graphical tactile displays)

Reporting period: 2020-11-01 to 2022-04-30

The aim of the project is the development of a tactile display for the visually impaired as an all-in-one and portable device alternative to the Braille system, audio aids, screen reader, and text-to-speech devices. To date, display technology for sighted users has seen astonishing improvements and evolved to high-resolution screens even on mobile devices. However, the market still lacks such portable devices with text and graphical options translated from Braille. This is due to challenges in creating a tactile display, which effectively is an actuator array with thousands of individually addressable actuators. In contrast, for sighted people, creating large-scale displays, which effectively are arrays of millions of individually addressable light emitters (LEDs), has been evolved owing to advanced control electronics.
The impact of this research project on society stems from the potential to generate a device that supports the interaction of the visually impaired with all aspects of today’s modern information technologies. According to the World Health Organization (WHO) over 285 million people are reported as visually impaired globally, 2.55 million of whom in Europe. A Braille line costs around 10.000 € which corresponds to a prize of 125 € per character and 20 € per actuator. Charts, diagrams or maps can be neither processed by a screen reader nor by a Braille line. Windows, menus, icons or pictograms that are routinely used by sighted people in operating a computer, therefore, remain inaccessible to visually impaired users, which results in many problems at study centers or at work. Where graphical and online content (images, pictograms, and webpages) become increasingly important, the inability to perceive information visually is the primary inhibitor for inclusion.
The main objective of this research is a revolution in microactuator array technology with a fundamentally new concept termed the Capillary Lock Actuator (CaLA). CaLA is a novel bistable massively parallelizable microfluidic microactuator, which overcomes many of the limitations currently associated with microactuators. It can be operated with low-voltage control signals and requires virtually no power for actuation. The project will use CaLA actuator arrays for setting up the very first portable tactile graphic display with 30.000 individually addressable taxels thereby significantly outperforming the state-of-the-art. It will be based on manufacturing techniques for highly complex microstructures in glass invented at the research group of the grant consolidator, the NeptunLab of Freiburg University.
Based on the work packages provided in the grant proposal, we made progress in different aspects of the project including system design (WP 1), where we fixed the primary microfluidics design (WP 1.1) with simulations for the fluid dynamics, calculations on the capillary pressure and fixed the channel design after a few iterations. We also faced some challenges for generating reproducible actuation plugs in the microactuators and solved the problem by designing an additional segment generator. To have consistent segment plugs in the array of actuators, we applied the design of the segment generator on all the actuators. The milestone achieved was a fixed design for the actuator and the segment generator. The actuation and triggering effects (WP 1.2) were tested at different voltage ranges and patterns and the implementation of Electrowetting on Dielectrics (EWOD) was studied.
Following the manufacturing of the actuators by 3D printing and stereolithographic techniques (WP 2), we ran more tests on the bonding of the membrane to close the microfluidic actuator chips and added additional layers for the haptic surface as well as the electronic units. Extensive research has been carried out on the electronics, design of the PCBs, and microcontrollers meeting the requirements of a compact tactile display. Different designs, fluidic and electronic interconnections, and communication protocols were studied to develop fast-responsive microcontrollers to be integrated with the actuators (covered in WP 2.1).
A breakthrough in the project and material implemented in the tactile display was achieved from developing novel technologies in the manufacturing of glass. The technology of fused silica glass manufacturing was initiated at NeptunLab and for the first time, and the achievement of manufacturing via injection molding was published in Science journal (Publication 1). This technology will be key for the future mass-market manufacturing.
Another achievement in the project was the electrode manufacturing with novel methodologies (WP 2.2) which is reported in the publication section. We did research on Platinum (Pt) as an interesting material owing its high conductivity and achieved its 3D microstructuring through two-photon lithography (TPL) (Publication 2).
A milestone in the project was to maintain the approval from the Ethics Committee of the University of Freiburg for running the prototype tests, i.e. the first user studies. This was followed by an important aspect of the project in form of the tests on the primary prototypes and haptic surface of the tactile display. Significant progress was achieved in the design and manufacturing of the movable structures, which act as an interlayer between the actuators and the haptic bulging membrane. The various prototypes were studied at Karlsruhe Institute of Technology’s (KIT) Study Center for the Visually Impaired (SZS). The visually impaired staff at SZS provided effective feedback on the haptic surface and pin design optimization.
The injection molding of fused silica glass yielded a novel pathway for mass-market compatible structuring of glass at significantly reduced energy consumption: up to 80% less in comparison with conventional glass manufacturing. This development is a significant step in the modern manufacturing methods for glass with a significant impact for many applications in academia and industry.
Building on the feedback of the first prototypes from SZS, we currently aim at developing a technology for the tactile displays, which could be used by everybody, not only the visually impaired but also the sighted people. To this effect we currently study the potential to include visual output as well as haptic input - both of which were not originally foreseen in the project proposal.
Sustainability of the IM process for fabrication of fused silica glass components.
Injection molding of fused silica glass using thermoplastic nanocomposites.
Microstructuring of platinum using lithography and two-photon lithography
Structuring platinum using organic–inorganic photoresins.