BIOROBOTICS LABORATORY
SEOUL NATIONAL UNIVERSITY
Soft Robots
We have been developing soft, biologically inspired mechanisms and robots, especially with the goal of creating innovative methods for generating lifelike motion, without relying on rigid joints and links. Leveraging novel fabrication techniques and soft materials, we have developed soft grippers, actuators, and manipulators for real-world applications.
Hyperelastic Torque-Reversal Mechanism
Snap-through, a rapid transition of a system from an equilibrium state to a nonadjacent equilibrium state, is a valuable design element of soft devices for converting a monolithic stimulus into systematic responses with impulsive motions. A common way to benefit from snap-through is to embody it within structures and materials, such as bistable structures. Torque-reversal mechanisms discovered in nature, which harness snap-through instability via muscular forces, may have comparative advantages. However, the current intricacy of artificial torque-reversal mechanisms, which require sophisticated kinematics/kinetics, constrains design possibilities for soft joints and devices. Here, we harnessed hyperelasticity to implement a torque-reversal mechanism in a soft joint, generating repetitive cilia-like beating motions through an embedded tendon. The developed hyperelastic torque-reversal mechanism (HeTRM) exhibits transient bistability under a specific compressive displacement/force threshold, with snap-through occurring at the point where the transience ends. To validate the effectiveness of this design principle, we explored the functionalities of HeTRM in energy storage and release, dual modes for impulsive and continuous motion, mechanical fuse, and rapid three-dimensional motions, through proof-of-concept soft machines. We expect that this design principle provides insight into incorporating snap-through behavior in soft machines and may aid in understanding the relationship between torque-reversal mechanisms and bistability.
Keywords : #Soft robot #Soft Actuator
Related papers and patents
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Woo-Young Choi, Woongbae Kim, Jae-Ryeong Choi, Sung Yol Yu, Seunguk Moon, and Kyu-Jin Cho, "A hyperelastic torque-reversal mechanism for soft joints with compression-responsive transient bistability", Science Robotics, 2025. [PDF]
Deployable Suction Gripper
Applying suction grippers in unstructured environments is a challenging task because of depth and tilt errors in vision systems, requiring additional costs in elaborate sensing and control. To reduce additional costs, suction grippers with compliant bodies or mechanisms have been proposed; however, their bulkiness and limited allowable error hinder their use in complex environments with large errors. Here, we propose a compact suction gripper that can pick objects over a wide range of distances and tilt angles without elaborate sensing and control. The spring-inserted gripper body deploys and conforms to distant and tilted objects until the suction cup completely seals with the object and retracts immediately after, while holding the object. This seamless deployment and retraction is enabled by connecting the gripper body and suction cup to the same vacuum source, which couples the vacuum picking and retraction of the gripper body. Experimental results validated that the proposed gripper can pick objects within 79 mm, which is 1.4 times the initial length, and can pick objects with tilt angles up to 60◦. The feasibility of the gripper was verified by demonstrations, including picking objects of different heights from the same picking height and the bin picking of transparent objects.
Keywords : #Soft robot #Gripper
Related papers and patents
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Yuna Yoo, Jaemin Eom, MinJo Park, and Kyu-Jin Cho, "Compliant Suction Gripper with Seamless Deployment and Retraction for Robust Picking against Depth and Tilt Errors," IEEE Robotics and Automation Letters, vol.8, no.3, 2023. [PDF]
Deployable Soft Robotic Arm
Robots that share activity spaces or physically interact with humans typically benefit from appropriate payload capacity, extensible workspace, low weight, safety, and space efficiency. The soft origami design and mechanism can meet many of these beneficial factors; however, achieving a high payload capacity remains challenging. In this letter, we developed a soft origami arm module with high variable stiffness (x300) and spatial efficiency (compressed x3.1). The buckling of facets into a cylindrical tube followed by its pressurization enables the arm to be highly stiffened. High-pressure capacity was obtained via the sewing-heat press fabrication process. We used a pneumatic pressure–tendon pair and utilized the frictional force between origami and tendon to prevent unintentional gravity-induced deformation while deploying. An analytical model was developed and compared to the experimental results. With our modular design, we could easily build functional robotic structures. Two robotic demonstrations were performed to examine the expandability of the modules. A variable-length robotic arm that mimics a human arm was built to manipulate typical objects. Additionally, a soft rover, which could carry 14 kg of weight and change its volume 29 times for improved spatial efficiency, was developed. This research suggests a new design methodology for practical soft robotic systems.
Keywords : #Soft actuator
Related papers and patents
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MinJo Park, Woongbae Kim, Sung-Yol Yu, Jungmin Cho, Wonkyeong Kang, Junghwan Byun, Useok Jeong, and Kyu-Jin Cho, "Deployable Soft Origami Modular Robotic Arm With Variable Stiffness Using Facet Buckling," IEEE Robotics and Automation Letters, vol.8, no.2, 2023. [PDF]
Underwater Soft Robot
Falling leaves flutter from side to side due to passive and intrinsic fluid-body coupling. Exploiting the dynamics of passive fluttering could lead to fresh perspectives for the locomotion and manipulation of thin, planar objects in fluid environments. Here, we show that the time-varying density distribution within a thin, planar body effectively elicits minimal momentum control to reorient the principal flutter axis and propel itself via directional fluttery motions. We validated the principle by developing a swimming leaf with a soft skin that can modulate local buoyancy distributions for active flutter dynamics. To show generality and field applicability, we demonstrated underwater maneuvering and manipulation of adhesive and oil-skimming sheets for environmental remediation. These findings could inspire future intelligent underwater robots and manipulation schemes.
Keywords : #Soft material, #Soft actuator
Related papers and patents
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Junghwan Byun, Minjo Park, Sang-min Baek, Jaeyoung Yoon, Woongbae Kim, Byeongmoon Lee, Yongtaek Hong, and Kyujin Cho, "Underwater maneuvering of robotic sheets through buoyancy-mediated active flutter", Science Robotics, 2021. [PDF]
Surgical Robot
Stent placement in the gastrointestinal tract has emerged
as an effective method of therapy for intestinal obstruction. In fluoroscopic guided stenting, clinicians first insert a hyper-elastic guidewire, and a stent introducer loaded with a compressed stent is passed along the guidewire to the desired deployment site. However, the high bending stiffness of the loaded stent introducer tends to straighten the inserted guidewire at the tortuous region. To overcome this issue, tubes of various stiffnesses are repeatedly inserted and removed. To optimize the mechanical properties of the devices for successful GI stenting, the interaction between the device and the environment should be considered as a key factor. In this study, conformability factor, a new index that abstracts the physical interaction for GI stenting was proposed. Based on the conformability factor, we proposed design requirements for variable stiffness continuum robots for GI stenting. The in vitro stent deployment experiment result shows that the proposed instrument can successfully deploy the loaded stent introducer without exchanging multiple tubes.
Keywords : #Soft material
Related papers and patents
Joonmyeong Choi, Se Hyeok Ahn, Chunwoo Kim, Jung-Hoon Park, Ho-Young Song, and Kyu-Jin Cho, "Design of Continuum Robot With Variable Stiffness for Gastrointestinal Stenting Using Conformability Factor," IEEE Transactions on Medical and Bionics, vol. 2, no. 4, 2020.[PDF]
4D Printing
4D printing can address time-evolving structural functions that are unattainable by conventional 3D printing. Despite the advance in materials and printing techniques, however, 4D printing of continuity of shape representation that generally characterizes 3D matters is still challenging, because the existing methodologies mostly rely on a few discrete levels of strain and their spatial distributions. Here, a 4D printing strategy of shape memory polymers (SMPs) that can program continuous levels of shape-recovery strain is proposed. It is found that the irrecoverable state of the SMP and the corresponding recovery strain can be controlled in a continuous and precise manner by a single printing parameter. Importantly, the continuity of strain programming provides an opportunity for the translation into mathematical function representation (F-rep), which allows the systematic derivation and implementation of 4D-printed bilayer strain functions that are matched to the continuously varying curvatures of the target geometry. Combined with the custom-built software, the F-rep 4D printing strategy can produce 4D-printed architectures that involve continuously varying strain profiles of almost any function type. The effectiveness of the framework is highlighted by a set of 3D face masks with facial feature transformation driven by a function operator.
Keywords : #Soft material
Related papers and patents
Woongbae Kim, Junghwan Byun, Jae-Kyeong Kim, Woo-Young Choi, Kirsten Jakobsen, Joachim Jakobsen, Dae-Young Lee, and Kyu-Jin Cho, “Bioinspired dual-morphing stretchable origami,” Science Robotics, 4, 2019. [PDF]
Bioinspired dual-morphing origami
We introduce pelican eel–inspired dual-morphing architectures that embody quasi-sequential behaviors of origami unfolding and skin stretching in response to fluid pressure. In the proposed system, fluid paths were enclosed and guided by a set of entirely stretchable origami units that imitate the morphing principle of the pelican eel’s stretchable and foldable frames. This geometric and elastomeric design of fluid networks, in which fluid pressure acts in the direction that the whole body deploys first, resulted in a quasi-sequential dual-morphing response. To verify the effectiveness of our design rule, we built an artificial creature mimicking a pelican eel and reproduced biomimetic dual-morphing behavior. By compositing the basic dual-morphing unit cells into conventional origami frames, we demonstrated architectures of soft machines that exhibit deployment-combined adaptive gripping, crawling, and large range of underwater motion. This design principle may provide guidance for designing bioinspired, adaptive, and extreme shape-morphing systems.
Keywords : #Soft material, #Soft actuator, #Gripper
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Related papers and patents
Woongbae Kim, Junghwan Byun, Jae-Kyeong Kim, Woo-Young Choi, Kirsten Jakobsen, Joachim Jakobsen, Dae-Young Lee, and Kyu-Jin Cho, “Bioinspired dual-morphing stretchable origami,” Science Robotics, 4, 2019. [PDF]