TACMON2

 

Development of a very low-cost Interactive Graphical Tactile Display capable of displaying textual and graphical information as an advanced user interface for the visually impaired (TACMON2)

 Project duration: X 2012 -  II 2015

 www.tacmon.eu

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General project description

The aim of TACMON2 is to develop an innovative technology for the low-cost realization of a large area Interactive Graphical Tactile Display as a computer periphery for visually impaired people, providing them a new dimension of access also to graphical oriented electronic information and to a wider range of PC applications. The proposed Graphical Tactile Display will consist of a fine matrix of tactile (haptic) accessible for the human touch sense, thus for visually impaired people. The concept of the cost reduction is the application of technologies, which allow the batch production of the actuator matrix on the surface without the need for individual assembly of actuators for each tactile dot.

The TACMON2 technology is innovative in the combination of the applied technologies realizing an electrostatic pneumatic hybrid actuator system. A proof of concept has been successfully demonstrated based on silicon MEMS technology. The aim of the current project is a significant cost reduction by transferring the proofed concept from silicon base to LTCC (Low Temperature Co-fired Ceramics) based technology, as well as by developing a compact and integrated pneumatic support system realized in polymer technology.

TACMON2 proposal intends to increase SME competitive advantage in the special needs sector by offering an innovative and cost-effective. There are 7.4 million visually impaired people in the European Union. High unemployment amongst the visually impaired is a serious social and economic problem for the EU. There is a need for effective assistive technology to facilitate employment of the visually impaired and for industry to better be able to meet anti-discrimination legislation, as well as to avoid the increasing exclusion from the increasingly visual/graphical oriented of information and communication technologies. The EU must quickly address the needs of sector SMEs that provide technological solutions for the disabled.

Working principle

The whole display will consist of hybrid PDMS/LTCC actuators, an electronic dots driving system and a pneumatic system. In order to display the graphical and textual data on the tactile matrix surface, each actuator has to be able to move and to be clamped separately by activating the electrostatic clamping force where it is necessary. Therefore, a complex electrical driving system is developed by integrating a central control unit, a custom made high voltage power supply and matrix driver electronics. The TACMON2 project requires the use of a pneumatic system to provide a vacuum of 50 kPa (absolute pressure of 50 kPa) and a pressure of 100 kPa (absolute pressure of 200 kPa) for the correct operation of the LTCC chips (in order to obtain the required stroke of the pins). The pneumatic system will be composed of a pneumatic base board, an air distribution manifold and an embedded controller. These parts will be described in the following sections.
The principle of the whole display can be explained in fig. 1 and 2. Each of the chips consists of 36 tactile dots which can be independently addressed. The pressurized air or vacuum from the pneumatic system are connected to a gas inlet in the chip as it is presented in fig. 1. Then the gas is evenly distributed inside the chip thanks to the buried manifold and connected to the gas nozzles. Therefore all of the dots can be at once inflated (deflected) and deflated. However, the independent actuation of dots can be achieved only if some additional driving mechanism is used. The electrostatic force was chosen in this particular case. Each of the dots has two additional electrodes; one deposited on the PDMS membrane and the second on the LTCC. The electrodes are protected from an electrical short circuit by a thin dielectric layer deposited directly on the LTCC electrode. If electrical potential will occur between these two electrodes the membrane can be electrostatically clamped. The mechanism of the actuation is described in more detail in fig. 2. When the atmospheric pressure (100 kPa) is supplied to the chip and the electrical potential between electrodes is zero, the dot is not inflated as it is presented in fig. 2a. It is an ideal state of actuation – the device is turned off. When the dot is pressurized to 200 kPa (absolute pressure) and clamping is off (electrical potential between electrodes is zero) the membrane is inflated as is shown in fig. 2b. A vacuum (50 kPa absolute pressure) permits to deflate and then clamp the membrane electrostatically by applying electrical potential to the electrodes (see fig. 2c). From this moment the increase of the pressure up to 200 kPa will not inflate the dot anymore as it is presented in fig 2d. The top view of the first version of the ceramic actuator is presented in fig. 3a.


TACMON2 actuator conceptFig. 1. Actuator concept

 

a)

TACMON2 actuating principle initial stage b) TACMON2 actuating principle dot deflected
c) TACMON2 actuating principle dot clamping d) TACMON2 actuating principle clamped dot

Fig. 2. Actuating principle, a) initial stage, b) dot deflected, c) dot clamping, d) clamped dot


a) TACMON2 actuator matrix b) TACMON2 single electrode

Fig. 3. Demonstrator of LTCC actuator, a) whole top view, b) zoomed single electrode


The electrical representation of each actuator dot is a capacitance, hence, the tactile display is a large number of capacitance matrix in row-column arrangement from the electronics point of view. The main purpose of the control circuit is to provide the clamping voltage for the dots. The clamping voltage is the potential difference between two electrodes of the dot which is sufficient to generate the electrostatic force which will hold the dot in position (flat) against the pneumatic pressure. The dot matrix is controlled appropriately if every dot in the matrix can be clamped or popped out independently of any other dots on the display. The clamping voltage is one of the key parameters in the application, as this voltage has a large influence on the selected control method. The cell capacitor, shown in fig. 4, can be charged/discharged through the Q1 cell transistor. The cells in the same row are selected by the row-driver, which is a simple N-channel MOSFET. It switches the gate of the cell transistors between the common (high) voltage and a lower voltage level which opens the cell transistors securely. The opened Q1 transistor allows the C1 cell capacitor to charge or discharge according to the state of the column driver. To charge the capacitor, the N-channel should be opened to connect the capacitor to the ground. To discharge the cap, the upper transistor should be opened to connect the two plate of the capacitor together and to discharge it. The discharge current has to be limited. The upper P-channel FET could be replaced with a simple resistor. Discharging the capacitors can be a default state of the column driver, as the capacitors will be discharged anyway within 2.14 milliseconds.


Active switch in the cell Fig. 4. Active switch in the cell (time multiplexed driving)

The pneumatic base board, which is presented in fig. 5, contains the pneumatic generation and control circuitry. It has a motorized miniature pressure pump to provide a pressure of 100 kPa, a motorized miniature vacuum pump to provide a vacuum of 50 kPa, two storage tanks, eight miniature electrovalves, three absolute pressure electronic sensors (pressure tank, vacuum tank and MEMS pressure) and a pneumatic circuit in a compact block (which replaces a series of flexible hoses which would require much more space). There is a filter between the output of the pump and its storage tank. The filter serves two purposes: it traps any dust particles that could hinder the operation of the LTCC MEMS chips and it acts as a shock absorber that dampens the pulses of the diaphragm pumps. The input of this pneumatic base board is connected to the normal atmosphere. The output of this pneumatic base board is connected to the air distribution manifold with the help of a flexible hose. This is the only hose in the system.


TACMON2 design pneumatic supply systemFig. 5. General view of the design pneumatic supply system

Conclusions

The proof of concept of the hybrid PDMS/LTCC based Interactive Graphical Tactile Display for blind people is under investigation. Each part of the system was verified according to SME partners specifications.

References

1. Jurków, D., Bechtold, F., Baborowski, J., Fazekas, S., Ágoston, A., Leung Ki, Y., Cuesta Mingorance, D., Mateos-Aparicio, L.M., Colina De Vivero, M., DorczyƄski, M., Golonka, L., Grotz, U. (2013). Low temperature Co-fired Ceramic/PDMS hybrid actuator for Interactive Graphical Tactile Display for people with visual impairments, Deutsche IMAPS-Konferenz München.