title: Embedded sensing for advanced robotic applications
Creators: name: Ntagios, Markellos
Publisher: name: University of Glasgow
Year: 2022

description: The human skin has several sensors with different properties and responses to different stimuli, such as pressure, temperature, and pain. Tactile sensors are generally modelled after the biological sense of cutaneous touch; these are able to detect stimuli resulting from mechanical stimulation. Pressure sensors are the most common types of receptors that enable the manipulation of foreign objects. Their application in robotics is rapidly developing, mainly driven by the prospect of autonomous and intelligent robots that can interact with the environment. Robotic end-effectors, prosthesis and wearable devices benefit from the development of tactile technology. This tries to mimic the properties of human skin not only as a protective shell, but also to provide sensory information from the outside environment. Many attempts have been made to create tactile sensors with various techniques and materials, leading to a variety of devices. Most of these are based on the human skin’s functionality and appearance and resemble small patches of the skin with various degrees of flexibility and occasionally stretchability, such as electronic skin (Eskin). New manufacturing techniques such as Additive Manufacturing (AM) are currently used to develop complex structures via layer-by-layer deposition methods. Complex shapes are possible using 3D printing as deposition is controlled from the electronics. Antennas, interconnects and 3D printed circuit boards are now possible to be manufactured using this technology. Moreover, tactile sensing devices embedded in the core structure of robotic parts intrinsically can be made. This has the potential to produce a new generation of tactile sensors without the issues noted in Eskins. This thesis presents an investigation in the development of complex, smart and intelligent devices, particularly for robotic end-effectors. This new approach presented in this thesis developed complex three-dimensional (3D) intelligent structures using innovative designs and multi-material AM technology. It covers current 3D printing systems with the ability of past-like extruder mechanism and traditional filament deposition modelling (FDM), resulting in 3D printed structures with various materials for complex applications. The enhanced 3D printer can print a variety of materials from food-based materials (chocolate, condiment etc) to conductive materials and dielectrics. This methodology was used to produce distal phalanges for a 3D printed hand with inherent capacitive pressure sensors and embedded electronics. Materials such as thermoplastic polyurethane (TPU), silver paint, conductive polylactic acid composite, graphite ink, etc. are explored to develop different variants of the sensors using 3D printing. The best-performing 3D printed soft capacitive touch sensors, formed with silver paint and soft rubber (Ecoflex 00-30), are integrated on the distal phalanges of the 3D printed robotic hand. These sensors exhibit a stable response with sensitivity of 0.00348 kPa−1 for pressure &lt;10 kPa and 0.00134 kPa−1 for higher pressure. A 3D printed hand was designed, fabricated and integrated with the sensors. The robotic hand was also provided with harvesting generating devices for autonomous operation. As 3D printing provides design freedom for complex shapes, a soft, flexible and low-cost capacitive pressure-sensitive insole was developed using a single-step 3D printing method. Developed using elastomeric materials, the soft and robust sensory sole can bend and twist, without altering its performance. The sensors exhibit a sensitivity of 2.4MPa-1 for the range of 0-60kPa and 0.526MPa-1 for 60kPa and above while tested for forces up to 1000N. As capacitive sensors are slow to respond/read a piezoresistive sensor was embedded using 3D printing for faster response on dynamic conditions. The devices fabricated use graphite paste encapsulated in a two-part rubber material and embedded using a 3D printer in TPU. The devices are tested for their response in the time and frequency domain. While the above focuses on devices, fabrication difficulties arose. A novel closed-loop feedback 3D printer extruder was developed to expand 3D printers’ capabilities and eliminate current problems and short-comings of current state 3D printers. The system expands the range of materials that can be printed with the advantage of printing multi-part materials such as two-part polymers without preparation. Experimentation was done using various materials showing good flow control at high printing speeds.