<title>Thermopneumatic actuator for tactile displays and smart actuation circuitry</title>

Abstract

This paper presents a thermopneumatic actuator to build large tactile displays as well as a smart activation circuitry to study and improve its performance. Since the main drawback of large tactile screens in the market is their cost (45000$ the device reported in [1]), this proposal is intended to reduce the price because of the simplicity of the actuator and the potential low cost assembling. A small display with 4 x 4 taxels and 2.54mm of distance between centres has been built to show the viability of the proposal. Furthermore, a smart actuation strategy is implemented where the heater element (a diode) is also used as sensor in a feedback control loop that improves the dynamic response. Such strategy consists in sensing the voltage drop in the diode to measure its temperature, thus it can be heated up quickly without being destroyed because power supply is decreased once the target temperature is reached. We have measured rise times around 2 seconds and fall times around 4 seconds, while the maximum force and stroke are above 10grams (0.1N) and 1mm respectively. The obtained results are good, specially to implement a large tactile screen. Power consumption is high, but it could be lower if latching mechanisms are used to keep the taxel active without power supply.

An innovative idea for low cost Braille e-reader

“…The Electromagnetic actuator may cost up to $8 per cell (17) . Thermo-pneumatic actuator (13) usage makes the device to be sold at $5000. EAP technology cost up to $5 for each cell (18) .…”

“…However, it consumes high electricity and slower (12) . The thermal expansion and phase transition property of thermo pneumatic actuator makes it very slower and consuming high power (13) . In general, the electromechanical devices are complicated and expensive and the difference between them is as listed in [ Table 1].…”

Actuator Design

“…Consequently, a large number of different designs have been tested till date. In [128], a thermopneumatic system is introduced ( Fig. 9.87) based on tubes filled with a fluid (methyl chloride) with a low boiling point.…”

“…When the material is heated up, its internal structure starts to change Fig. 9.87 Thermopneumatic actuation principle in a schematic sketch (a) and as actual realization (b) [128] and the materials forms back in its pre-deformed state. Due to the material intrinsic actuating effect, high-resolution tactile displays are achievable.…”

Optimization of a Pneumatic Balloon Tactile Display for Robot-Assisted Surgery Based on Human Perception

“…Various tactile display technologies, including electromagnetic, electrocutaneous, electrostatic, motor, piezoelectric, rheological fluid, and shape-memory alloy (SMA) actuators, have previously been explored [13]- [19]. Pneumatic tactile actuators are capable of producing high displacement and large output force [20]; however, those that have been developed are not practical for surgical robotics due to bulky size, awkward geometries for mounting, or slow dynamic response [21]- [24].…”