Digital Theses Archive


Tesi etd-01022018-191118

Type of thesis
Soft Robotics Technologies for Exploration and Manipulation Tasks
Scientific disciplinary sector
INGEGNERIA - Biorobotics
relatore Prof.ssa LASCHI, CECILIA
  • continuum manipulator
  • foam actuator
  • light guide soft sensor
  • modular soft manipulator
  • multi-material 3D printed hydrogel actuator
  • Plant-inspired robot
  • root morphology
  • root-inspired probe
  • soft reconfigurable gripper
  • soft robotics
  • zea mays
Exam session start date
Soft robotics has exhibited its extreme potential through softness, mimicking the property of natural tissue, human muscle and plant-like movements, adaptability, safe interaction etc. Moreover, combining soft robotic technologies bio-inspiration could revolutionize the field of robotics and will bring the new era of robots and it could be a driving force for science or science could be leading the soft robotics. In addition, this thesis work is dedicated harvest the soft robotic potential to develop a technology for exploration and manipulation. In particular, this work includes developing soft exploratory robot inspired by plant roots, soft modular manipulator for manipulation and hydrogel actuators, soft sensors and foam actuator for manipulation and exploration both. <br>Developing a robot for exploration task, a plant could be an ideal model for inspiration. The plant represents almost 99.9% of the biomass of our planet. They are one of the most efficient soil explorers amongst all the fossorial creatures and survive in highly complex and abrasive environment. Amongst fossorial organisms, plants are particularly efficient in terms of perforation performance (3MPa axial stress) and are able to reach considerable depths (up to 100 m). The key features that make plant roots so efficient and able to compete in the highly unstructured environment are (i) release of sloughing cells and mucus; (ii) growth from the tip; (iii) lateral expansion; (iv) solid anchorage; and (v) ad hoc morphology. The (i-iii) strategies allow plants creating low friction channels to compete with high frictional and abrasion resistance and change soil impedance. The solid anchorage (iv) represents another crucial aspect of plant efficiency and it is obtained by development of hairy structures and lateral roots. Plants show, in addition, great ability to modify their own morphology (v) based on ecological variation.<br><br>Particularly, this work includes investigation of the plant root shape, development of plant-inspired probe, mimicry of root shape, an artificial design of sloughing and lateral growth mechanism and a growing robot with integrated all plant features. Moreover, my work firstly started with root morphology which describes the first translation of plant root morphology into a bioinspired artificial probe for soil exploration. Specifically, we propose a method to translate morphological features of Zea mays roots in an artificial probe. We selected Z. mays roots because of their fast growth and germination diversity in different ecological conditions. The proposed method relies on image processing and curve-fittings techniques to extract the profile of Z. mays primary root. We implemented an analytic translation of the root profile in a 3D model (CAD) to fabricate root-like probes by means of 3D printing technology. Then, we carried out a comparative analysis among the artificial root-like probe and probes with different tip shapes (cylindrical, conical, elliptical, and parabolic) and diameters (11, 9, 7, 5, and 3 mm). The results showed that the energy consumption and the penetration force of the bioinspired probe are better with respect to the other shapes for all the diameters of the developed probes. For example, 100 mm of penetration depth and 7 mm of probe diameter, the energy consumption of the bioinspired probe is 89% lesser with respect to the cylindrical probe and 26% lesser with respect to the conical probe We also performed numerical simulation with all different types of tip shapes to verify our experimental results and we found good agreements between them. An additional approach for investigations on plant root morphology is done through new methodology, to mimic the root shape closer, we developed a platform which mimics the exactly the shape and texture of the root. This work presents an image scanning method (Photogrammetry) to mimic the root shape of an aerial plant (the moth orchid). Here, we have developed an image scanning system and protocols for 3d reconstruction. The objective of this work is to mimic the morphology and colored texture of the species, develop 3D models and 3D print them by using additive manufacturing. This method will lead us to understand the root shape variation under different ecological conditions. Although, shape variations will also help to design a robotic penetration mechanism based on its ecology. <br>After finding the best penetration performance by the root shape, we investigated the several other features such as sloughing mechanism, mucus exudation, soft tip with morphology change and radial &amp; axial growth. In particular, we first realized soft hyperelastic probe, developed the artificial mucus exudation mechanism (its property close to real plant). Results suggested that softest tip has better performance amongst other stiffer soft tips and artificial mucus with closer viscosity to real mucus has better energy efficiency in the real soil. Moreover, after this study, we focused sloughing and radial growth using root-like tip shape. For example, we present an innovative probe for soil penetration inspired by the strategies of the radial expansion and sloughing mechanisms exploited by plants at the level of their root apical regions (i.e., apexes). We imitated these natural features developing four different probes endowed with spheres and ball bearings in their tips. These solutions produced a sliding effect of the probe while it moves into the soil with an improvement in terms of penetration energy consumption by 13.0% and penetration force by 13.4% respect to the probe without sloughing strategy. The prototype that got the best performance required 0.4 J energy consumption, 7.1 N penetration force for 150 mm penetration depth. Additionally, we mimicked the root apex radial expansion strategy via multi-chamber soft actuators and we observed a reduction of soil impedance by 91% at 120 mm depth. Moreover, we measured a total energy saved by the probe with radial expansion by 11% in comparison with the same system without a radial expansion. We tested the bioinspired probes in a granular soil (POM, polyoxymethylene beads), in controlled environmental conditions. <br>We believe that the development of these artefacts can be useful for engineering applications where low frictional passage and crack propagation are needed, or in geotechnical studies, space exploration and earth exploration to reduce energy consumption and protect the device from damage. From the other side, these digging bio-inspired robots can allow a better understanding of plant roots phenomena related to soil interaction and penetration, which are still quite unknown and difficult to investigate in the natural counterpart.<br>Apart from plant-inspired designs, in this thesis work, we have also explored soft robotic technologies and developed some actuators, sensors and a manipulator. In this work, we describe the conceptual design and implementation of the SIMBA manipulator. In our novel design, we have proposed: 1) a modular continuum arm with independent actuation units for each module; 2) a soft reconfigurable hand, for a better adaptation of the fingers to objects of different shapes and size; 3) a moving base for increasing the workspace. We used a hybrid approach in designing and manufacturing by mixing soft and hard components, in both materials and actuation, providing variable stiffness in the arm through flat springs, soft joints in fingers for more compliance and tendon-motor actuation mechanism providing flexibility but at the same time precision and speed. The SIMBA manipulator has demonstrated excellent grasping and manipulation capabilities by being able to grasp objects with different fragility, geometry, and size; and by lifting objects with up to 2Kg of weight it demonstrates also to be robust and reliable. We characterize a single module and developed a mathematical model, moreover, the module is characterized in a three-dimensional workspace with a constant radius around its rotation axis, large and highly repeatable bending, complete rotation and passive stiffness. We present an extensive analysis and characterization of the basic module of the SIMBA arm in terms of design, fabrication, kinematic model, stiffness, and bending behavior. All the theoretical models presented were validated with empirical results. Our findings show a positional typical error of less than ~6 % in module diameter (highly repeatable) with a passive stiffness of 0.8 N/mm (~ 1 kg load). <br>Our aim is to demonstrate that this kind of robotic element can be exploited as an elementary module of a more complex structure, which can be used in any application requiring high directional stiffness but without the need for an active stiffness mechanism, as is the case in daily activities (e.g. door opening, water pouring, obstacle avoidance, and manipulation tasks. For instance, alternative applications of the module could be as a leg for alligator-inspired robots where stiffness is required in the plane perpendicular to the motion, and the inherent compliance of the module could be exploited for unstructured terrains. Similarly, the module could be adopted for snake-inspired robots, where directional stiffness and axis rotation can be exploited for different snake locomotion modalities (sidewinding, corkscrewing and strafing).<br>This thesis also draws an attention, to develop new material for 3D printing of hydrogel using novel photochemistry of hydrogel. In addition, our work is focused on the development of soft gripper or hand to handle hot object using hydrogel actuator. In this regard, we proposed a multi-material 3D printed soft hydrogel actuator which contains micro texture for faster cooling, has the capability to change the stiffness, color, and its size. The printed actuated characterized and show the bending more 150 and strain ~ 80%. The hydrogel photochemistry depicts fast getting using our NPs and it can show hydrophobic and hydrophilic property just by changing the temperature. <br> Apart from the hydrogel actuator, we also worked on the development of a light guided optical sensor and foam based soft actuator. The objective was to develop soft optical sensor integrated soft actuator which will help measure the curvature, touch of the actuator. These actuators are made up of silicon coated foams to produce high impulse for making walking robot. The integrated sensor-based actuator was assembled on octopod chassis to build an eight-legged robot.<br>