Stiffness Control With Shape Memory Polymer in Underactuated Robotic Origamis

Underactuated systems offer compact design with easy actuation and control but at the cost of limited stable con- figurations and reduced dexterity compared to the directly driven and fully actuated systems. Here, we propose a compact origamibased design in which we can modulate the material stiffness of the joints and thereby control the stable configurations and the overall stiffness in an underactuated robot. The robotic origami, robogami, design uses multiple functional layers in nominally twodimensional robots to achieve the desired functionality. To control the stiffness of the structure, we adjust the elastic modulus of a shape memory polymer using an embedded customized stretchable heater. We study the actuation of a robogami finger with three joints and determine its stable configurations and contact forces at different stiffness settings. We monitor the configuration of the finger using feedback from customized curvature sensors embedded in each joint. A scaled down version of the design is used in a two-fingered gripper and different grasp modes are achieved by activating different sets of joints

Soft actuation and sensing towards robot-assisted facial rehabilitation

Continuing research efforts in robot-assisted rehabilitation demand more adaptable and inherently soft wearable devices. A wearable rehabilitative device is required to follow the motion of the body and to provide assistive or corrective motions to restore natural movements. Providing the required level of fluidity in wearable devices becomes a challenge for rehabilitation of more sensitive and fragile body parts, such as the face. To address this challenge, we propose a soft actuation method based on a tendon-driven robotic origami (robogami) and a soft sensing method based on a strain gauge with customized stretchable mesh design. The proposed actuation and sensing methods are compatible with the requirements in a facial rehabilitative device. The conformity of robogamis originates from their multiple and redundant degrees of freedom and the controllability of the joint stiffness, which is provided by adjusting the elasticity modulus of an embedded shape memory polymer (SMP) layer. The reconfiguration of the robogami and the trajectory and directional compliance of its end-effector are controlled by modulating the temperatures, hence the stiffness, of the SMP layers. Here we demonstrate this correlation using simulation and experimental results. In this paper, we introduce a thin and highly compliant sensing method for measuring facial movements with a minimal effect on the natural motions. The measurements of the sensors on the healthy side can be used to calculate the required tendon displacement for replicating the natural motion on the paralyzed side of the face in patients suffering from facial palsy

Stiffness Control of Deformable Robots Using Finite Element Modeling

International audienceDue to the complexity of modeling deformable materials and infinite degrees of freedom, the rich background of rigid robot control has not been transferred to soft robots. Thus, most model-based control techniques developed for soft robots and soft haptic interfaces are specific to the particular device. In this paper, we develop a general method for stiffness control of soft robots suitable for arbitrary robot geometry and many types of actuation. Extending previous work that uses finite element modeling for position control, we determine the relationship between end-effector and actuator compliance, including the inherent device compliance, and use this to determine the appropriate controlled actuator stiffness for a desired stiffness of the end-effector. Such stiffness control, as the first component of impedance control, can be used to compensate for the natural stiffness of the deformable device and to control the robot's interaction with the environment or a user. We validate the stiffness projection on a deformable robot and include this stiffness projection in a haptic control loop to render a virtual fixture

Practical considerations on proprioceptive tactile sensing for underactuated fingers

RÉSUMÉ: Les mécanismes sous-actionnés sont de plus en plus répandus dans les nouvelles mains robotisées, en raison notamment du désir de réduire la complexité et les coûts associés aux systèmes conventionnels pleinement actionnés. Avec le même objectif de réduire les coûts des composants nécessaires pour assurer un retour sensoriel, de nombreux auteurs ont travaillé sur la recherche de solutions de rechange aux capteurs tactiles externes. Cet article traite de l’une de ces méthodes, à savoir, la mesure tactile proprioceptive, spécifiquement conçue pour les doigts sous-actionnés. Une attention particulière est portée sur certaines considérations pratiques telles que l’impact de la courbure de l’objet saisi et la reconfiguration du doigt après le contact. En outre, l’analyse de leur influence sur la précision de l’algorithme est proposée. À cette fin, des simulations et des données expérimentales sont présentées pour différents scénarios de saisie. On montre que l’effet de la courbure locale reste limité par rapport à d’autres causes d’imprécision telles que le frottement dans le système. Il est également démontré que la reconfiguration, si elle se fait à l’intérieur de limites raisonnables, n’entraîne pas de variation significative sur l’estimation du point de contact. ---------- ABSTRACT: Underactuated mechanisms are becoming more prevalent in new robotic graspers, partly because of the desire to reduce the complexity and associated costs of conventional fully actuated systems. With the same objective of reducing the costs of the components needed to provide a sensory feedback, several authors have worked on finding alternatives to external tactile sensors. This paper is about one of these methods, namely proprioceptive tactile sensing, especially designed for underactuated fingers. It focuses on certain practical considerations, such as the impact of the curvature of the grasped object and the reconfiguration of the finger after the contact, and proposes the analysis of their influence on the precision of the algorithm. To this aim, simulations and experimental data are provided for different grasping scenarios. It is shown that the effect of local curvature remains limited compared with other causes of imprecision such as friction in the system. It is also demonstrated that the reconfiguration, if within reasonable limits, does not cause significant variations on the estimation of the contact location

Controllable and reversible tuning of material rigidity for robot applications

Tunable rigidity materials have potentially widespread implications in robotic technologies. They enable morphological shape change while maintaining structural strength, and can reversibly alternate between rigid, load bearing and compliant, flexible states capable of deformation within unstructured environments. In this review, we cover a range of materials with mechanical rigidity that can be reversibly tuned using one of several stimuli (e.g. heat, electrical current, electric field, magnetism, etc.). We explain the mechanisms by which these materials change rigidity and how they have been used for robot tasks. We quantitatively assess the performance in terms of the magnitude of rigidity, variation ratio, response time, and energy consumption, and explore the correlations between these desired characteristics as principles for material design and usage

형상기억고분자 복합재료의 3D 프린팅 공정 개발

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 재료공학부, 2021. 2. 유웅열.4D 프린팅은 3D 프린팅된 물체가 시간이 지남에 따라 자신의 모양이나 성질을 변화시킬 수 있는 첨단기술이다. 형상기억고분자는 4D 프린팅의 대표적인 소재이다. 이 연구에서는 기존의 형상기억고분자 프린팅 기술들의 단점을 개선하는 새로운 3D 프린팅 방법이 개발되었다. 3D 프린팅된 형상기억고분자의 3차원 형상 변화를 분석하기 위해 3차원의 특성화 방법이 제시되었다. 3차원 형상기술자를 활용하여 형상기억고분자의 3차원 전개 거동이 정량적으로 분석되었다. 형상기술자란 주어진 3차원 물체의 형상 정보를 대표할 수 있는 수치로 표현되는 값이다. 3차원 형상 변형 거동을 분석하기 위해 에폭시 기반의 형상기억고분자를 이용하여 우주 전개용 안테나를 제조하였다. 우선, 안테나가 전개하는 동안의 3차원 형상을 스캔하고, 2차원과 3차원 형상기술자를 이용하여 이를 분석하여 어떤 형상기술자가 안테나의 전개거동을 기술하는 데 적합한지 조사하였다. 3차원 형상기술자는 2차원 형상 정보에 더해 높이 정보를 제공하기 때문에 접힘-전개 거동에서 나타나는 형상의 변화를 보다 정확하고 민감하게 반영할 수 있다. 그 중에서도 3차원 Compactness가 안테나의 접힙-전개 거동을 기술하는 데 가장 적합한 것으로 나타났다. 에폭시 기반의 형상기억고분자의 1차원 형상기억성능은 고정률이 98%, 회복률이 79%이지만, Compactness를 이용하여 3차원 전개 거동을 분석했을 때에는 고정률이 100%, 회복률이 99.5% 를 나타냈다. 이것은 3차원 분석 기술의 필요성과 적절성을 보여준다. 형상기억고분자의 약한 기계적 강도를 보완하기 위해, 연속섬유강화 열가소성 형상기억고분자의 새로운 3D 프린팅 시스템이 개발되었다. 연속섬유강화 열가소성 고분자는 가볍고, 강하기 때문에 널리 사용되지만, 일반적으로 무겁고 비싼 장비를 사용하여 제조된다. 최근에는 소형, 소량의 연속섬유강화 복합재료를 제조하기 위해 3D 프린팅 기술이 도입되었다. 이 연구에서는 핀보조 용융 함침 방법을 활용하여, 함침과 프린팅 공정이 동시에 진행될 수 있는 3D 프린팅 시스템을 개발하였다. 이 장비의 프린터빌러티와 함침도를 평가하여 프린팅 조건을 결정하였고, 인장 시험을 위한 시편이 프린팅 되었다. 이 시스템을 활용하여 프린팅한 인장 시편의 기계적 물성과 다른 프린팅 시스템으로 프린팅한 시편들의 기계적 물성이 비교되었다. 이 연구에서 개발된 3D 프린팅 시스템으로 만들어진 시편은 함침도가 우수했고, 결과적으로 우수한 기계적 물성을 보였다. 최종적으로 연속섬유강화 형상기억고분자 복합재료로 만든 안테나가 3D 프린팅되었고, 형상기술자를 이용하여 안테나의 형상기억거동을 분석하였다. 4D 프린팅용 재료 중에서 열경화성 고분자는 강한 기계적 물성, 화학적 안정성, 내용제성 등으로 인해 매우 유망한 재료이다. 정면 중합이 가능한 열경화성 재료를 사용하면, 형상의 복잡성을 높일 수 있는 프리스탠딩 구조를 3D 프린팅할 수 있다. 이 연구에서는 poly(dicyclooctene) 네트워크에 스위칭 세그먼트를 만들 수 있는 cyclooctene을 추가하여 정면 중합이 가능한 열경화성 형상기억고분자를 합성하였다. 열기계적 분석 결과 이 재료는 형상기억거동을 보이는 것으로 확인되었다. 프리스탠딩 구조를 프린팅할 수 있는 effective homogeneous shear modulus 를 가질 수 있도록 이 재료의 유변학적 성질이 조절되었다. 이 재료의 유변학적 성질과 정면 중합 속도를 바탕으로 프린팅 조건을 결정하고, 프리스탠딩 구조의 육각 나선 물체가 성공적으로 프린팅되었다. 프린팅된 육각 나선은 훌륭한 형상기억성질을 보였다.Four-dimensional (4D) printing is a cutting edge technology in which the three-dimensionally printed objects change their shapes or properties over time. Shape memory polymer (SMP) is a representative material for 4D printing. New three-dimensional (3D) printing systems for SMPs are developed to improve and overcome the drawbacks of the existing 3D printing methods. To characterize the 3D shape change of a 3D printed SMP, 3D characterization methods are suggested. The 3D deployment behavior of an SMP was quantitatively characterized using 3D shape descriptors. 3D shape descriptor is a numerical value which represents and analyzes the shape information of a given 3D shape. A 3D deployable antenna was designed and fabricated using an epoxy-based SMP. First, the folding behavior of the antenna was observed during deployment in a device. At this time, its entire shape was scanned, processed, and converted into surface data. Two-dimensional (2D) (area and circularity) and 3D (compactness and cubeness) shape descriptors were calculated from the surface data and compared to determine if the 3D folding behavior of an SMP antenna could be adequately described by 3D compactness, which represents how compactly the SMP antenna was able to fold. In addition to 2D shape information, these data provide height information, resulting in a more accurate and sensitive characterization of the folding process. Finally, the 3D deployment behavior (folding-unfolding) of the SMP antenna was analyzed using a 3D descriptor. The shape fixation and recovery ratios of the SMP antenna according to the 3D descriptor were 100% and 99.5%, respectively, whereas those values evaluated with a one-dimensional descriptor, such as uniaxial strain, were 98.0% and 79.1%, respectively. These results demonstrate that a 3D descriptor (compactness) can adequately assess shape memory performance. An SMP has poor mechanical property so that an SMP composite (SMPC) has been studied and used in various applications. Continuous carbon fiber is the most effective reinforcing material to give great mechanical properties. In order to print the continuous carbon fiber-reinforced thermoplastic (CCFRTP) SMP three-dimensionally, a new 3D printing system was developed. CCFRTPs, which are popular due to their light weight and high strength, are typically fabricated using heavy and expensive equipment. Recently, 3D printing has been used for efficient production of small CCFRTPs. In this study, the 3D printing system was developed based on in situ pin-assisted melt impregnation in the printing head, i.e., melt impregnation and printing processes in one pot. Printing conditions were investigated by evaluating the printability and degree of impregnation. The tensile strength of specimens printed using the new printing system was compared with that of specimens printed using other printing methods. The uniformly impregnated CCFRTP printed case specimens had superior mechanical properties. Finally, an SMPC antenna was 3D printed and its 3D shape memory properties were characterized by 3D deployment test. Among 4D printing materials, thermosetting polymers are useful for various applications due to their high mechanical properties, thermodynamic stability, excellent chemical resistance, and solvent resistance. Using a thermosetting material capable of frontal polymerization, a free-standing structure could be 3D printed which can enlarge the complexity of the shape. In this study, an SMP capable of frontal polymerization was synthesized by adding cyclooctene as a monomer to form switching segments in a poly(dicyclo-pentadiene) network. As a result of thermomechanical analysis of the material, it was confirmed that it shows shape memory behavior. The rheological properties of the material was controlled to have an effective homogeneous shear modulus for printing a free-standing structure. A hexagonal spiral with free-standing structure was successfully printed using the 3D printing system. The printed product showed good shape memory performance.1. Introduction 1 1.1. Shape memory polymers 1 1.2. 4D printing: 3D printing of shape memory polymers 3 1.3. 3D printing methods of shape memory polymers 4 1.4. Research objectives 7 2. 3D characterization of 3D deployable shape memory polymer composites 9 2.1. Preparation of 3D deployable SMPC 12 2.1.1. Preparation and 1D shape memory test of SMP 12 2.1.2. Multi-dimensional deployment test of SMP 18 2.2. 3D characterization via 3D shape descriptors 21 2.3. Multi-dimensional shape memory properties of SMP 24 2.3.1. Thermomechanical properties of SMP 24 2.3.2. Multi-dimensional shape memory properties 30 2.3.3. Shape memory properties of deployable SMP 37 2.5. Summary 41 3. 3D printing process of thermoplastic shape memory polymer composites 42 3.1. Preparation of a new 3D printing system 43 3.1.1. Design of the new printing system 43 3.1.2. Materials and printed samples 47 3.1.3. Characterization 48 3.2. 3D printing of CCFRTPs 49 3.2.1. Printability of the new printing system 49 3.2.2. Degree of impregnation of the CCFRTPs 55 3.2.3. Mechanical properties of the CCFRTPs 59 3.3. 3D printing and 3D characterization of SMPCs 64 3.4. Summary 68 4. 3D printing process of thermosetting shape memory polymers 69 4.1. Preparation of a new 3D printing system 71 4.1.1. Materials and sample preparation 71 4.1.2. Characterization 72 4.1.3. 3D printing process 74 4.2. 3D printing of the thermosetting SMP 74 4.2.1. Thermomechanical and shape memory properties 74 4.2.2. Rheological properties and frontal velocity 79 4.2.3. 3D printing and the shape memory properties of SMP 86 4.3. Summary 90 5. Conclusions 91 Reference 93 Korean abstract 104Docto

Designing LMPA-Based Smart Materials for Soft Robotics Applications

This doctoral research, Designing LMPA (Low Melting Point Alloy) Based Smart Materials for Soft Robotics Applications, includes the following topics: (1) Introduction; (2) Robust Bicontinuous Metal-Elastomer Foam Composites with Highly Tunable Mechanical Stiffness; (3) Actively Morphing Drone Wing Design Enabled by Smart Materials for Green Unmanned Aerial Vehicles; (4) Dynamically Tunable Friction via Subsurface Stiffness Modulation; (5) LMPA Wool Sponge Based Smart Materials with Tunable Electrical Conductivity and Tunable Mechanical Stiffness for Soft Robotics; and (6) Contributions and Future Work.Soft robots are developed to interact safely with environments. Smart composites with tunable properties have found use in many soft robotics applications including robotic manipulators, locomotors, and haptics. The purpose of this work is to develop new smart materials with tunable properties (most importantly, mechanical stiffness) upon external stimuli, and integrate these novel smart materials in relevant soft robots. Stiffness tunable composites developed in previous studies have many drawbacks. For example, there is not enough stiffness change, or they are not robust enough. Here, we explore soft robotic mechanisms integrating stiffness tunable materials and innovate smart materials as needed to develop better versions of such soft robotic mechanisms. First, we develop a bicontinuous metal-elastomer foam composites with highly tunable mechanical stiffness. Second, we design and fabricate an actively morphing drone wing enabled by this smart composite, which is used as smart joints in the drone wing. Third, we explore composite pad-like structures with dynamically tunable friction achieved via subsurface stiffness modulation (SSM). We demonstrate that when these composite structures are properly integrated into soft crawling robots, the differences in friction of the two ends of these robots through SSM can be used to generate translational locomotion for untethered crawling robots. Also, we further develop a new class of smart composite based on LMPA wool sponge with tunable electrical conductivity and tunable stiffness for soft robotics applications. The implications of these studies on novel smart materials design are also discussed

Large Array of Shape Memory Polymer Actuators for Haptics and Microfluidics

My thesis advances the field of shape memory polymer (SMP) actuators by providing a versatile strategy to arbitrarily reconfigure large arrays of densely packed latching soft actuators. It exploits two key intrinsic characteristics of SMPs, which are their multistable nature and their drastic change in Young¿s modulus with temperature, to combine both actuation plus latching in a single actuator. The novel concept consists in individually and selectively addressing arrays of SMP actuators by synchronizing their local Joule heating with a single common air pneumatic supply. Stretchable heaters are integrated and patterned on thin SMP membranes in order to precisely define regions where the stiffness can be changed by over two orders of magnitude. By a timely synchronization of the thermal stimuli with the external air pressure, each actuator can be independently, reversibly, and rapidly latched into any positions. The potential of coupling local Joule heating with global air pneumatic actuation for large arrays of SMP actuators is demonstrated by a 32x24 flexible haptic display and by a 4x4 microfluidic platform. The active layer of the SMP actuator is made of a commercially available SMP material for the SMP membrane and a mixture of carbon black (CB) with soft polydimethylsiloxane (PDMS) for the stretchable heating electrodes. The final SMP actuator geometry corresponds to the best trade-off between displacement and holding force for both haptic and microfluidic applications. The 32x24 flexible haptic display is the first high resolution wearable sleeve capable to vary its surface topology. This device consists of a 40 µm thick SMP membrane, on which a matrix of 25 µm thick stretchable heaters on 4 mm pitch is integrated, interconnected by a 4-layers flexible printed circuit board (PCB) and bonded to a stretchable 3D-printed pneumatic chamber. Each tactile pixel (taxel) can be individually controlled via row/column addressing, requires 250 mW to heat up from 20 °C to 70 °C, and takes 2.5 s to latch to a different state. Each line (row or column) of taxels consumes at most 8 W and the entire haptic display is refreshed in under 1 min 30 s. The haptic display weighs only 55 g and is 2 mm thick. More than 99 % of the 768 taxels are fully functional, with a lifetime in excess of 20000 cycles. The perception tests conducted on the 4x4 tactile tablet with 15 blindfolded sighted users resulted in 98 % correct pattern recognition in less than 10 s exploration, confirming that my SMP actuators are a promising taxel technology. The 4x4 microfluidic platform is the first latching microfluidic array where each valve is directly controlled with a common air pneumatic supply. Its active layer consists of a 50 µm thick SMP membrane, a matrix of 25 µm thick stretchable heaters, and a 37.5 µm thick styrene ethylene butylene styrene (SEBS) membrane. The actuators are electrically interconnected and mechanically bonded to a PCB. On the bottom, a polymethyl methacrylate (PMMA) pneumatic chamber is sealed and, on the top, a micromachined polystyrene (PS) microfluidic chip is bonded. The similarity in design for both normally closed (NC) and normally open (NO) valves enables to implement them in the same chip. These 3 mm in diameter valves remain closed up to 70 mbar of pressure before opening, validating that my SMP actuators are an interesting valve-unit for micropumps, mixers, and multiplexers in microfluidic large scale integration (mLSI) systems