Numerical and experimental analysis of A novel origami robotics based hinge design

Robotics technology is a field of study that enables the design of high-performance products that have emerged from the common areas of electronics and mechanics. For this reason, it has become the basic element of large and small projects ranging from hobby design projects to industrial machines. Production technology is being shaped and is evolving day by day according to the needs of designers and the requirements of their designs. Some systems are not suitable for production by conventional production methods: The materials used cannot be formed by conventional production methods, or a more practical and rapid production method is required. There is a need for a production method to solve such problems in the field. Today's developing soft-based robots are innovative and they employ different production techniques and robotics aspects. As can be understood from its name, constructions produced using soft, flexible materials are highly preferred, especially in projects designed to mimic the mobility of living things. Soft-bodied robotics are preferred in grippers, which are used to transport objects of various sizes without damaging them, as well as many nature-inspired robotics products created with soft materials like silicone. Since the materials used are soft and flexible, as the density is reduced, soft robotics can produce lightweight and highly mobile structures. High mobility is a very useful feature for soft robotics, and robotic arms produced with soft robotics do a better job than robotic arms produced with rigid materials when used with the aim of avoiding obstacles or reaching the target position with minimum error. For this reason, soft robotics' flexibility and variability in size are important, and their low weight and maximum mobility are preferred attributes in constructions. However, controlling soft robots is more difficult than controlling rigid structures because there are no limits to their motion. Origami-based robotics, a subdivision of soft-based robotics, is an advanced application area for rapid and simple production. Origami-based robotics is a production technique inspired from the art of folding paper, which has been used in Japan since hundreds of years. Flexible and foldable materials are used as in soft robotics. Just as in the paper folding art, 2D fine materials are based on the principle of obtaining the desired 3D shape using the correct folding scheme. The designer draws the 2D folding diagram of the 3D model that will be used in the project, and shapes it easily by folding it. As production and design are made in 2 dimensions, quick and practical results can be obtained. Although origami based robotics is a new field of study, many applications have been created until present day. Origami-based robotics is preferred on the body of small- sized modular vehicles or on their moving elements. Moreover, in pop-up mechanisms, that is, in self-assembled structures, origami-based robotics applications can be found. In addition to small-sized projects, origami-based robotics is utilized during the folding of gigantic solar panels to gain room within the satellites that are transporting them into outer space. In origami-based robotics design, users aim to produce flexible and lightweight structures, using the minimum, most basic and accessible materials in the fastest and most practical way. However, since origami-based robotics is not suitable for heavy loads, it is not recommended for use in industrial applications. In this study, origami-based joints are the focal point of analysis. Rapid and practical production of origami-based robots in the design of joints provides many benefits. Hard robotic arms are difficult to design and costly to produce. For this reason, arms or multi-axis structures are generally preferred for multi-purpose applications. This saves time and money by reducing the need for a new robot arm. However, despite all of their benefits, these types of arms are costly and need frequent maintenance. Rigid robotic arms are not the preferred method of solution in small size applications. On the other hand, origami-based joints need to be designed only once, and the only prerequisite is the 2D diagram for serial production. It is easy to produce a brand-new design that you desire. There is no need to conduct frequent maintenance on it because doing a quick replacement will cause neither money nor time loss. Because of these features, origami-based joints production is a successful technique. Origami-based joints within the literature were examined and models were categorized into two groups according to their movements. These are rotation and hinge joints. Categorized joint models are compared and rated based on certain performance types such as load carrying capacity, mobility and ease of production. Thanks to the comparative analysis conducted, this study also serves as a roadmap for origami-based joints. As a result of our investigations, it has been found that rotational joints can successfully carry a load and have the ability to move up to 360 degrees. However, looking at hinge joints, it seems that there is no model that can fully meet the requirements. It has been found that bending joints in the literature are extremely flexible, therefore their load carrying capacities are low. Since the joint is too flexible, it gives a high motion output, but the spring coefficient is too low to measure, so it tilts against the slightest force. Since the spring coefficient of the origami-based hinge joint is close to zero, no dynamic approach has been found in previous publications. The main purpose of this study is to examine origami-based hinge joints and to design a practical model with a higher spring coefficient. An existing hinge joint model was selected and developed further. The model that provides the best mobility is chosen for development. The design started with the examination of the movements of non-origami based flexure joints. When flexure joints are examined, it is seen that the motion of the joint is provided by the spring elements located between the two bodies of the moving joint, and the joint spring coefficient is equal to the equivalent spring coefficient of these springs. As a result, a model consisting of two parallel-connected springs was developed as the hinge joint model. The parallel connection of the springs means that the equivalent spring coefficient of the joint is equal to the sum of the spring coefficients of each spring. The modified model is developed based on this hypothesis. By simply increasing the number of parallel-connected springs, a higher spring constant and more stable joint were obtained. In the first stage of comparative analysis, the improved joint has been shown to have better spring coefficients than the old one with practical experiments. It was seen that an end-to-end system designed with the old hinge joint cannot even hold itself straight, even under no load. Yet, the modified model has no such problem. Origami-based joints are essentially modeled based on their mobility. The measurements of the 2D schematic are based on the mobility of the joint, which is determined by the user. In this study, kinematic modeling for a robotic arm using only parallel placed hinge joints is shown, and generalized formulas are developed. With the help of the formulas derived, the two-dimensional diagrams of the joints can easily be obtained. When origami-based joints are used in robotics, the extraction of the mathematical model of the system is important for controlling the dynamic behavior. In this study, an approach has been proposed to create a mathematical model that has not been done before in any origami-based joint study. This approach makes it easy to select the engine to be used in the system. Similarly, 3D modelling and stress analysis have never been applied to origami-based joints, either. The old hinge joint and the modified one are compared with the help of the simplified 3D model. Furthermore, 3D models are used for testing the contribution of material selection and the size of the modified hinge model on the system's stiffness coefficient and stress values. In addition to analytical and numerical studies, the joints are experimentally tested and the two joints were compared to obtain the closest results to reality. At the same time, this experiment yields the most realistic spring coefficient values. Comparisons showed that the modified hinge joint collapses less under the same load without loss of mobility. This is evidence that the spring constant of the new joint is higher than the old joint's spring constant. To summarize, in this study, origami-based joints were investigated and developed from the bending joint models available in the literature, to develop a better joint with high mobility and better load carrying capacity. The new joint has been analytically and experimentally tested, and the results are reported in this thesis. The thesis also carries the unique aspect of being, to the best of our knowledge, the first study to develop a mathematical model and conduct a 3D stress analysis for origami-based joints.