Ⅰ. Origami
Deformation of the Miura-ori patterned sheet
The Miura-ori pattern possesses intriguing mechanical features, namely, the one Degree Of Freedom mobility, auxetic in-plane behavior and energy absorption capability, for applications such as core to sandwich structure, shock absorber, airless tire, etc. To realize the folding mechanism of Miura-ori, in this paper a Miura-ori patterned sheet was made from copolymer Elvaloy by compression molding, and then its deformation behavior was investigated experimentally and by using finite element analysis. The intrinsic mechanical properties of Elvaloy were obtained by tensile and four-point-bending tests, respectively, and subsequently used in the finite element (FE) simulation. For utilizing the sheet in all the principal directions, three types of tests were conducted: out-of-plane compression, three-point-bending and in-plane compressions. FE simulations using Abaqus/Explicit were carried out to analyze the deformations of the patterned sheet under the same loading as that in the tests. The simulation results were then compared with the tests, which show good agreements. Based on the simulation results, the deformation patterns of the patterned sheet under different loading conditions were examined, as well as the energy absorption capacity.
Deployable Prismatic Structures With Rigid Origami Patterns
Rigid origami inspires new design technology in deployable structures with large deployable ratio due to the property of flat foldability. In this paper, we present a general kinematic model of rigid origami pattern and obtain a family of deployable prismatic structures. Basically, a four-crease vertex rigid origami pattern can be presented as a spherical 4R linkage, and the multivertex patterns are the assemblies of spherical linkages. Thus, this prismatic origami structure is modeled as a closed loop of spherical 4R linkages, which includes all the possible prismatic deployable structures consisting of quadrilateral facets and four-crease vertices. By solving the compatibility of the kinematic model, a new group of 2n-sided deployable prismatic structures with plane symmetric intersections is derived with multilayer, straight and curvy variations. The general design method for the 2n-sided multilayer deployable prismatic structures is proposed. All the deployable structures constructed with this method have single degree-of-freedom (DOF), can be deployed and folded without stretching or twisting the facets, and have the compactly flat-folded configuration, which makes it to have great potential in engineering applications.
Ⅱ. Soft Robotics
Small-strain folding of semi-rigid elastomer derives high-performance 3D-printable soft origami actuators
Elastomers with hyperelastic deformation bring prosperity to soft robotics, especially in constituting fluidic actuators, largely due to the merit of large deformation and airtightness. However, the large (typically 0.5–1.5 strain) in-plane stretching of such materials concurrent to motion generation inevitably causes energy loss, hinders force output and accuracy. Particularly, the high nonlinearity of the low-durometer (typically 10A to 30A Shore) hyperelastic elastomers makes the modeling and control of actuators a well-known challenge. In this work, we proposed an alternative approach of using semi-rigid elastomer of significantly larger durometer (70 A–100 A) to create the typical fluidic soft actuator with axial translation, by utilizing small-strain folding to generate motion. Deformation constraints and property programming are combined into a single-piece body, enabling easy fabrication by Selective Laser Sintering 3D-printing and post-treatment for origami patterned structure. Systematic analyses on the principles, modeling and design are presented. The long lifespan (over 1 million cycles), superior output linearity, high energy efficiency (more than 60% increase), and drastically improved force output (more than 98% increase) were validated experimentally, showing high potentials in enabling high-performance soft actuators that are easy to design, fabricate and drive, strong to use, and accurate to control, towards even wider applications.
A High-Payload Proprioceptive Hybrid Robotic Gripper With Soft Origamic Actuators
Proprioception is the ability to perceive environmental stimulations through internal sensory organs. Enabling proprioception is critical for robots to be aware of the environmental interactions and respond appropriately, particularly for high-payload grippers to ensure safety when handling delicate objects. State-of-the-art robotic grippers with soft actuators are typically equipped with pressure sensors for pneumatic regulation and control, but very few utilized them for proprioceptive purposes. This lack of environmental awareness was largely compensated by their inherent compliance and conformity, but also due to the generally limited force capabilities. Targeting at this gap, this work proposes a novel Proprioceptive Origamic Soft Actuator (POSA) joint, and a corresponding hybrid robotic gripper design with high-payload soft origamic actuators and rigid supporting frames, achieving up to 564.5 N actuator output force or 302.4 N finger gripping force at 150 kPa low pneumatic pressure and 3.2 kg self-weight. Despite the substantially higher force capability over state-of-the-art soft grippers, the proposed hybrid gripper could retain the excellent inherent compliance thanks to the novel soft origamic actuators. Moreover, a novel scheme of multi-actuator proprioception is proposed by only using the embedded pneumatic pressure sensors, to enable the hybrid gripper with environmental awareness, achieving real-time position and force estimations of errors at <; 1% and 5.6%, respectively. The principles, design, prototyping, and experiments of the proposed hybrid high-payload gripper were presented in this letter. Combining soft robotic compliance, high payload, and proprioception, the gripper could both hold a pealed grape and crack a walnut, with position and force signals being measured without requiring dedicated sensors.
Ⅲ. Bio-Inspired
Otariidae-Inspired Soft-Robotic Supernumerary Flippers by Fabric Kirigami and Origami
Wearable robotic devices are receiving rapidly growing attentions for human-centered scenarios from medical, rehabilitation, to industrial applications. Supernumerary robotic limbs have been widely investigated for the augmentation of human limb functions, both as fingers and manipulator arms. Soft robotics offers an alternative approach to conventional motor-driven robot limbs toward safer and lighter systems, while pioneering soft supernumerary limbs are strongly limited in payload and dexterity by the soft robotic design approach, as well as the fabrication techniques. In this article, we proposed a wearable supernumerary soft robot for the human forearm, inspired by the fore flippers of otariids (eared seals). A flat flipper design was adopted, differing from the finger- or arm-shaped state-of-the-art works, with multiple soft actuators embedded as different joints for manipulation dexterity. The soft actuators were designed following origami (paper folding) patterns, reinforced by kirigami (paper cutting) fabrics. With this new approach, the proposed soft flipper incorporated eight independent muscles, achieving over 20 times payload to self-weight ratio, while weighing less than 500 g. The versatility, dexterity, and payload capability were experimentally demonstrated using a fabricated prototype with proprietary actuation and control. This article demonstrates the feasibility and unique advantages of origami + kirigami soft robots as a new approach to strong, dexterous, and yet safe and lightweight wearable robotic devices.
3D Printed Multi-Cavity Soft Actuator with Integrated Motion and Sensing Functionalities via Bio-Inspired Interweaving Foldable Endomysium
The human muscle bundle generates versatile movements with synchronous neurosensory, enabling human to undertake complex tasks, which inspires researches into functional integration of motions and sensing in actuators for robots. Although soft actuators have developed diverse motion capabilities utilizing the inherent compliance, the simultaneous-sensing approaches typically involve adding sensing components or embedding certain-signal-field substrates, resulting in structural complexity and discrepant deformations between the actuation parts with high-dimensional motions and the sensing parts with heterogeneous stiffnesses. Inspired by the muscle-bundle multifiber mechanism, a multicavity functional integration (McFI) approach is proposed for soft pneumatic actuators to simultaneously realize multidimensional motions and sensing by separating and coordinating active and passive cavities. A bio-inspired interweaving foldable endomysium (BIFE) is introduced to construct and reinforce the multicavity chamber with optimized purposive foldability, enabling 3D printing single-material fabrication. Performing elongation, contraction, and bidirectional bending, the McFI actuator senses its spatial position, orientation, and axial force, based on the kinematic and sensing models built on multi-cavity pressures. Two McFI-actuator-driven robots are built: a soft crawling robot with path reconstruction and a narrow-maneuverable soft gripper with object exteroception, validating the practicality in stand-alone use of the actuator and the potential for intelligent soft robotic innovation of the McFI approach.
Ⅳ. Applications
Rhythm-based Power Allocation Strategy of Bionic Tail-Flapping for Propulsion Enhancement
With the vast demand in marine development, robotic fish show promising potential in underwater exploration for their high-performance propulsion ability. However, fish-inspired robots are yet to utilize the structural flexibility of rhythmic actuation such as bony fish (Osteichthyes). The Body and Caudal Fin (BCF) locomotion in fish optimizes the use of muscle power and body flexibility by synchronizing muscle activation with the undulating-oscillatory tail-flapping, such as Thunniform, while robotic fish are primarily designed as motion trackers rather than as efficient swimmers. In this paper, we propose a power allocation strategy (PAS) that imitates muscle rhythmic actuation, which increases the flapping amplitude by the coupling of the peduncle motion and the tail deformation. Inspired by this peduncle-tail mechanism, we developed a Direct-Drive Fish Robot (DDRFishBot). The DDRFishBot is enhanced by our developed PAS in Tail-Elastic Potential Energy (T-EPE) release by 228%, in propulsion by 45.6% and in efficiency coefficient by 16.3%. This study establishes the performance enhancement principle of exploiting tail flexibility through a simple scotch yoke mechanism, expanding the performance space of fish-inspired tail-flapping swimming robot.
Single Pump-Valve Pneumatic Actuation With Continuous Flow Rate Control for Soft Robots
Pneumatic actuated soft robots attract increasing interest of the researchers due to the availability and simplicity in actuation. The soft robots driven by soft pneumatic actuators (SPAs) of various active volumes demand pneumatic systems with various range of flow rate. However, the usually bulky and hard-to-carry pneumatic actuation systems restrict the portability, and the air pumps provide constant flow rate which constrained the applications such as soft wearable devices and scenarios require fine flow rate control. In this work, aiming for simplicity, high portability, continuous and small flow rate regulation, the pneumatic actuation system consists of identical integrated soft robotic drivers (iSoRD) modules is proposed, obtaining positive and negative pressure output (−53∼83 kPa) in each module using one-pump-one-valve (4-way/2-position solenoid) design. With the check valves installed and the modular design, pressure holding and flow independence are achieved in each pneumatic branch. The heat generation (37.7 °C) and power consumption (2.95 W per-channel) are measure to verify usability. The continuous and fine flow rate regulation (15 mL/s) is achieved by applying the PID controller on the pump motor, which shows superior performance in signal tracking in comparison with the non-continuous Bang-Bang and Varia-speed Bang-Bang algorithms. With the same control, the iSoRD system reduces the error by 37.5% in comparison to our previous two-pump system. The portability, versatility in wearing, practicality and adaptivity of the system are validated by driving three wearable soft robots, a small gripper and a pollination device. Comparing with the existing, the iSoRD is capable of fine flow rate regulation in both negative and positive pressure range with low power consumption, portability and versatility, which will benefit the pneumatic soft robotic systems with broadened application potential.
