Fringe field sensors based on piezo dielectrics offer opportunities in under water sensing as they are solid state, incompressible and robust. Questions remain regarding their susceptibility to noise. Specifically, we refer to anomalous outputs when the sensor is brought in close proximity to or just touching a conductive object. One solution involves isolation through a flexible Faraday cage. We have investigated two approaches for such a Faraday cage. One approach utilizes a conductive fabric while the other is based on a carbon filled dielectric. We compared the performance of both shielding approaches regarding noise suppression and their influence on sensitivity. The anomalous effects upon contact with conductive objects leading to inconsistent measurements were overcome. Furthermore, their response to salinity levels and submersion time were investigated and the influence of design parameters on the performance of the sensor determined in a Design of Experiment study. Varied parameters include overall footprint alongside electrode spacing and width. Performing a full factorial design plan enabled us to quantify the relations between the parameters. This investigation improved signal stability in the piezo dielectric fringe field sensors, making it possible to design a broader range of sensory systems able to withstand the harsh marine environment. The sensor will assist fish robots in their exploration of the ‘Silent World’.
Sensor arrays are ubiquitous. They capture images in digital cameras, record the swipes of our fingers on the screens of our phones and tablets, or map pressure distribution over an area. Soft capacitive sensors have long been proposed to make electronic pressure-sensing skins. However, although different designs of entirely soft capacitive sensors have been proposed, large arrays of those sensors are challenging to produce. Indeed, arrays require high-resolution patterning of electrodes, and routing of long and thin electrical connections. These two tasks remain difficult or costly for the high-resistivity compliant electrodes of dielectric elastomer sensors. Instead of relying on the complex patterning of arrays to provide location resolution, we propose to use a plain, unstructured sensor with a single pair of electrodes but rely on computing power to infer pressure location and amplitude from clever sensing signals. Here, we propose a new machine-learning-based approach, which enables us to identify pressure location on a continuous 1D sensor split into 5 sensing zones with an accuracy greater than 98 %. We also demonstrate that we can identify pressure location and qualitative pressure magnitude (soft, medium, hard) on a 3-zone sensor with 99% accuracy.
We have developed a diver-robot empathetic communication system that allows the diver to feel the disturbance around the robot and control the robot remotely using hand gestures. The underwater robot is embedded with soft dielectric elastomer (DE) sensors to sense the direction and amplitude of the disturbance around its surroundings, defined as the physical indentation of the eye sensors. The direction and intensity of the disturbance communicate to the user remotely via an array of vibrotactile actuators in the form of a bracelet. Wears of the glove will feel what the robot is going through, represented by different vibration intensities and patterns. The smart glove employs five dielectric elastomer sensors to capture finger motion and implements a machine-learning classifier in the onboard electronics to recognize gestures. Hence allowing the wearer to send commands in the form of hand gestures for correcting the underwater robot’s posture. The system will be tested in a user study to determine performance improvement over the traditional robotic control interface. Our work has demonstrated the capability of DE sensing for advanced human-machine interaction.
Capacitive dielectric elastomer sensors (DES) are well-known in robotic sensing applications due to their sensitivity and stability under tensile strain. These sensors rely on changes in geometry to detect deformation. Since DES are thin, they are resistant to out-of-plane compression and this is made more difficult if they are bonded to a rigid surface. Here, we present a new type of DES that detects changes in the fringe field between interdigitated electrodes (IDEs). This is made possible using a compression sensitive silicone/carbon black composite that sits atop the electrodes. The IDEs create a fringing field extending into the composite whose relative permittivity can change by 250% when compressed. As a result, there is no longer any design challenges brought on by the incompressibility of elastomers. Additionally, since compliant electrodes are not required in this configuration, and the electrodes are kept in a single plane on a commercial PCB, the fabrication process is simple. This sensor is convenient to be used as a tactile sensor for either conventional rigid or soft robotic grippers, allowing the safe manipulation of soft and delicate objects.
For long-range swimming fish, low cost of transportation is a critical requirement. This also applies to autonomous fishlike robots (AFR). As with their biological cohorts, AFR require sensory input that characterizes the flow of the water surrounding them. Thus, there is a need for low power hydrodynamic sensors that can be deployed on a fish-like robot, and which can provide flow information from open water conditions. Electroactive polymers offer opportunities for flow sensing on soft and flexible AFR. We developed and evaluated an approach for capacitive electroactive polymer flow sensing. This uses dielectric elastomer sensor membranes mounted on a liquid-filled cavity protruding into the flow. Flow speed and incident angle on a hydrofoil standing in for the fish are registered through electrical capacitance changes resulting from deformation of its 350μm thick membrane. Through its triple-electrode design, measurements are largely shielded against the influence of the surrounding water on the capacitor. Differences in flow speed along the sensor can be detected with high reproducibility for extended durations of time. The developed sensors were assessed regarding accuracy, reliability, and durability. For performance and long-term testing, an automated tabletop water tunnel test rig was created. This setup enables sensor testing for flows up to 1 m/s with automated incident angle control and data logging. We are thus presenting further steps towards robust ocean-faring hydrodynamic sensory systems by demonstrating advances in electroactive sensory technology and testing facilities.
Biomimetics Laboratory, Auckland Bioengineering Institute, University of Auckland, New Zealand
Soft compassion sensors provide a sense of touch for robots which plays a crucial role in safe interaction between robots and their environment. Here we report on Carbon black/dimethylsiloxane (PDMS) composite at the top of an interdigitated electrode (IDE) patterned on a printed circuit board (PCB). The sensor's response only depends on the change in relative permittivity of the composite. Any deformation causes a decrease in permittivity due to a change in the filler's network shape. The sensor shows an excellent sensitivity of 7.1%N-1, which is 35 times more than a composite made with insulating particles (BaTiO3). Our sensor combines high sensitivity with a simple fabrication, thus making it ideal for manipulating fragile objects.
Soft compression sensors represent a promising approach to provide proprioceptive feedback for robotic manipulators. However, dielectric elastomer sensors work well as stretch sensors, their sensitivity is low when used as com- pression sensors, due to the incompressibility of elastomers. Therefore, the simple electrode/membrane/electrode sensor configuration is not sensitive enough to a low range of force. Here, we report on the use of a patterned silicone layer (it is considered as pillars) to produce a compressible dielectric elastomer sensor to detect deformation and pressure. Interdigitated electrodes (IDEs) are patterned on the backside of the sensor to generate a fringing electric field into the dielectric material. The deformation of the silicone pillars causes changes in the relative permittivity due to changes in the air-volume fraction of each component. By using IDEs on the backside of the sensor, there is no need for compliant electrodes, and a simple printed circuit board (PCB) can be used. This simplifies the fabrication process and takes advantage of the good conductivity and reliability of the PCB copper electrodes. We optimized different parameters of the sensor such as the pillar’s dimension which affects the stiffness and electrical sensitivity of the sensor. Using our optimization process, we demonstrate sensors that exhibit a capacitance change of more than 36% for an input force of 60N. Our sensor combines high sensitivity with a simple fabrication and assembly, thus making it ideal for applications like the manipulation of fragile objects.
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