Mr. Richard Ellingham Profile

Richard Ellingham

at Univ of Canterbury

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Proceedings Article | 10 May 2024 Presentation + Paper

Deformation mapping in dielectric elastomer actuators using electrical impedance tomography

Richie Ellingham, Yeni Choi, Timothy Giffney

Proceedings Volume 12945, 129450P (2024) https://doi.org/10.1117/12.3010073

KEYWORDS: Electrodes, Dielectric elastomer actuators, Compliance, Piezoresistivity, Composites, Muscles, Deformation, Fabrication, Tomography, Video

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Dielectric elastomer actuators commonly use flexible conductive electrodes to apply an electric potential for actuation. Depending on the material used, these electrodes often possess predictable piezo-resistive properties. Combining electrical impedance tomography (EIT) with a dielectric elastomer actuator (DEA) is investigated in this work to map compressive forces occurring throughout the electrode surfaces. This technology could allow for enhanced closed-loop control of electroactive actuators, extending their already extensive set of applications. This deformation mapping system also has the potential to be used with other piezoresistive materials, opening up more applications requiring a large hardness range and pressure sensitivity. With the material used in this work, the DEA-EIT device has an inherent trade-off between actuation and pressure mapping accuracy driven by the compliant electrode thickness of the DEA. The DEA-EIT device exhibited actuation strains of 2.5 % with a mean centre-of-mass error from a range of loads applied were 7.9 ± 0.7mm for 2mm thick DEA electrodes. It is proposed that future work on custom hardware could be devised for the DEA-EIT system so the sensing and actuation can occur concurrently in real-time. Real-time control mean that applications requiring human-like manipulation can be designed, ranging from biomedical implant devices to agricultural processing equipment.

Proceedings Article | 20 April 2022 Paper

Carbon black silicone piezoresistive electrical impedance tomography stress sensor device

Richard Ellingham, Tim Giffney

Proceedings Volume 12042, 120420L (2022) https://doi.org/10.1117/12.2610694

KEYWORDS: Sensors, Composites, Electrodes, Resistors, Resistance, Tomography, Carbon, Tissues, Reconstruction algorithms

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Carbon black/silicone rubber composite is a desirable material for highly flexible strain sensors due to its repeatable piezoresistive characteristics, low cost, and simple fabrication process. By customising the conductivity and elastic modulus of the composite, the material can easily be adapted for many human physiological sensing applications. For applications such weight distribution sensors for wheelchair users, it is desirable to have not just a single sensor reading but instead a 2D map of pressure or strain. In this work, after demonstrating that the material can be modelled to give estimated strain value, we have developed a system to give a 2D map of pressure applied to the sensor using Electrical Impedance Tomography (EIT). This method has the advantage that a 2D pressure map can be obtained from a sensor using a homogeneous cast sheet of composite with electrodes around the perimeter only, without requiring complex patterning or a sensor array. Although the design is scalable, our demonstration system was fabricated using a 100 mm diameter pressure pad of carbon black (CB) silicone composite with electrodes evenly spaced around its perimeter. A low-cost circuit was developed to apply current to the material and measure the voltage between electrodes. The voltage measurements were then reconstructed into maps of resistivity and indications of compressive stress. Testing demonstrates that the fabricated pressure sensor can sense localised pressure within the pressure pad. The positional accuracy of the sensor was found to be on average 3.6 mm for the 100 mm diameter circular domain under test.

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