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Conventional industrial grippers that grip a flat object generally hold objects by using suction or electrostatic force. However, these grippers have limitations when gripping thin, flat, and flexible objects, such as films and flexible printed circuit boards (FPCBs), due to their undefined shape and high flexibility. This paper proposes a soft gripper that can grip flexible and thin objects by utilizing directional adhesives and a compliant mechanism. The directional adhesive pad is fabricated by a three-dimensional (3D) printing process for cost-effective and environment-friendly manufacturing. However, fabrication by 3D printing has disadvantages in terms of the quality of the adhesive surface. An additional coating process presented in this study compensates for the low resolution of 3D printing by improving smoothness. Moreover, an additional coating process is a simple approach for developing directional adhesives with enhanced adhesion strength by deforming the tip shape without a sophisticated fabrication process. The adhesion of adhesives with curved pillars is enhanced compared to adhesives with simple wedge-shaped pillars. The maximum normal adhesion force of the gripper is measured to be 0.47 N (1.57 kPa), and 95% of the initial adhesion is retained after ten thousand attachment/detachment cycles. The adhesion force can be recovered by the cleaning process when the contaminant is attached to the adhesive. The final demonstration shows that the gripper can handle various objects for potential applications such as in green-environmental industries.

Stiffness transition of a soft continuum body is an essential feature for dexterous interaction with an unstructured environment. Softness ensures safe interaction, whereas rigidness generates high force for movement or manipulation. Vacuum-based granular jamming is a widely used technique for on-line stiffness transition because of its high reconfigurability and intuitive driving method. However, vacuum driving method produces limited force levels, and the heavy weight and bulky size are unfavorable for portable applications. In this work, we propose a tendon-driven jamming mechanism for configurable variable stiffness. Compared with a vacuum system, an electric motor-tendon drive system has the benefits of force, bandwidth, size, and weight, but has different force characteristics for distribution, directionality, and transmissibility. In this study, a long snake-like shape is chosen instead of a lump shape for compatibility with tendon-drive characteristics. The snake-like shape is likely to cause buckling under the tendon force as the length increases, making the system extremely unstable. Implanting skeletal disk nodes in the structure is our solution to the buckling phenomenon by maintaining the tendon path in the desired position and for distributing the force evenly, thereby achieving stable stiffness transition capabilities for long free-curved shapes. As a proof of concept, a soft wearable device for wrist support is presented using the proposed variable stiffness mechanism. The weight of the device is 184 g, including the actuators, and it can support 2 kgf. Furthermore, the stiffness transition is completed within 2 s, thus achieving quick responses.

Soft robots have advantages such as low weight and compact size compared to rigid robots. Variable stiffness is one of the key methods of improving the performance of a soft robot. The soft gripper grasps objects of various shapes or sizes based on the variable stiffness. In a previous study, we validated the variable stiffness mechanism where flexible and rigid segments were connected alternately in series. This paper presents a soft variable stiffness gripper that can be used to control the stiffness by pulling tendons. The soft gripper has three variable stiffness structures acting as fingers and the stiffness can be controlled using two motors by winding tendons. To understand the tendency of the stiffness variation and determine the design parameters, a compliant mechanism was developed using a pseudo-rigid-body model (PRBM). The experimental results show that the difference between the lowest and highest stiffness values of the fabricated variable stiffness gripper was 5.6 times the original. Similarly, the difference in the gripping weight was 19 times. Using the experimental results, the variable stiffness gripper can be designed and manufactured based on the required stiffness and used to grip various types of objects.

A high aspect-ratio foil is known to be advantageous in terms of both thrust and efficiency in flapping propulsion. However, many species of fish have evolved a low aspect-ratio hydrofoil, which naturally leads one to search for its physical advantages in locomotion. Here we study the flow physics of a hydrofoil in angular reciprocating motion with negligible free-stream velocity to reveal the effects of an aspect ratio on hydrodynamic performance. By establishing a scaling law for the thrust of a foil of general shapes and corroborating it experimentally, we find that the thrust of an angularly reciprocating foil is maximized at a low aspect ratio of 0.7 while hydromechanical efficiency continuously increases with an aspect ratio. This result suggests that a low aspect-ratio foil can improve thrust produced by the foil when they start from rest, but at the expense of efficiency.

With the Fourth Industrial Revolution, many factories aim for efficient mass production, and robots are being used to reduce human workloads. In recent years, the field of gripper robots with a soft structure that can grip and move objects without damaging them has attracted considerable attention. This paper proposes a variable-stiffness soft gripper, based on previous designs, with an added silicone coating for increased friction and an EGaIn soft sensor for monitoring grip forces. The variable-stiffness structure used in this study was constructed by connecting soft structures to rigid structures and using tendons fixed to the rigid structures. Furthermore, a more responsive EGaIn soft sensor compared to existing sensors was designed by adding bumps to the path traced by the alloy. After selecting the appropriate fingertip shape, changes in the output of the EGaIn soft sensor corresponding to the object held by the soft gripper were observed, confirming that the strength of the device could be changed according to the intended purpose.

It has been agreed that a proper level of flexibility in moving appendages like a fin of swimming animals enhances their propulsive performance. However, a few efforts have been spent to characterize the criterion, as a simple guideline for designing a biomimetic propulsor, at which the beneficial effect of compliance is maximized. Recently, it was reported that a sinusoidally pitching panel produces the enhanced thrust when the passively bending angle of a trailing edge lags behind its pitching angle by around π / 2 due to its compliance. To understand its mechanism, we perform a series of particle image velocimetry measurements around a panel pitching in quiescent water, while varying its compliance, planform shape and pitching frequency. For all the planform shapes and frequencies considered, with a phase delay of about π / 2 , the region of high streamwise velocity with thrust-generating momentum is retained farther (in the streamwise direction) in the wake, caused by the large effective pitching angle during the accelerating stage of pitching rotation. When the panel is stiffer (or the phase delay is smaller than π / 2 ) than the optimal condition, however, a strong interaction between the trailing-edge vortices (TEVs) formed successively at each half strokes pushes the surrounding fluid into the transverse direction, thereby accelerating the decay of thrust-generating streamwise velocity. This interaction between TEVs is weak for the case of optimal compliance. On the other hand, in the case of over-compliance, the trailing edge of the panel rotates opposite to the pitching direction, which indicates that the inertial work required to rotate the panel during the stroke-reversal becomes excessive at the expense of rotational circulation which eventually weakens the thrust.

To improve the multi-functionality of a structure, a foldable or deployable structure with variable stiffness is needed. This article presents dual-stiffness structures with two stiffness states: a stiff state and a flexible state for a multi-mission capability. This dual-stiffness structure is based on a hybrid structure that combines rigid and flexible segments; when the rigid segments are rearranged, the bending motion of the compliant material is constrained by the rigid segments, which varies the stiffness of the structure. Instead of continuously changing the stiffness, the dual-stiffness structure abruptly changes the stiffness state with a simple reconfiguring mechanism. We developed two reconfiguring mechanisms: a sliding mechanism and a folding mechanism. Using a layering process, the dual-stiffness structure with a two-dimensional multi-layer design was manufactured. To verify the behavior of the structure, a simplified structure with no sliding mechanism was designed and simulated using a finite element method. The ratio of the length of a rigid segment to the length of a compliant segment determined the stiffness of the structure. This dual-stiffness structure with the reconfiguring mechanism can be effective for applications that require a big change in stiffness, such as for a deployable solar panel, or flexible display.

Fish generates thrust with a compliant fin which is known to increase the efficiency. In this paper, the performance of a robotic dolphin, the velocity and the stability, was improved using an optimal compliant caudal fin under certain oscillating frequency. Optimal compliance of the caudal fin exists that maximizes the thrust at a certain oscillating frequency. Four different compliant fins were used to find the optimal compliance of the caudal fin at a certain frequency using the half-pi phase delay condition. The swimming results show that the optimal compliant fin increases the velocity of the robotic fish. The compliance of the caudal fin was also shown to improve the stability of the robotic fish. A reactive motion at the head of the robotic dolphin causes fluctuation of the caudal fin. This phenomenon increases with the oscillating frequency. However, compliant fin reduced this fluctuation and increased the stability.

As one of the most important force production mechanisms of swimming and flying animals, the fluid dynamics of flapping has been intensively studied. However, these efforts have been mainly directed toward animals in forward motion or locomotive appendages undergoing linear translation. Here we seek to complement the existing knowledge of the flapping mechanism by studying angularly reciprocating flat plates without a free stream velocity, under a so-called ‘bollard pull’ condition. We visualize the flow field around the flat plate to find that two independent vortical structures are formed per half-cycle, resulting in the separation of two distinct vortex pairs at sharp edges rather than a single vortex loop which is typical of a starting–stopping vortex paradigm in flows with free streams. Based on our observations, we derive a scaling law to predict the thrust of the flapping plate; this is the first experimentally validated theoretical model for the thrust of angularly reciprocating plates without a prescribed background flow.

The compliance of a fin affects the thrust of underwater vehicles mimicking the undulatory motion of fish. Determining the optimal compliance of a fin to maximize thrust is an important issue in designing robotic fish using a compliant fin. We present a simple method to identify the condition for maximizing the thrust generated by a compliant fin propulsion system. When a fin oscillates in a sinusoidal manner, it also bends in a sinusoidal manner. We focus on a particular kinematic parameter of this motion: the phase difference between the sinusoidal motion of the driving angle and the fin-bending angle. By observing the relationship between the thrust and phase difference, we conclude that while satisfying the zero velocity condition, the maximum thrust is obtained when a compliance creates a phase difference of approximately π/2 at a certain undulation frequency. This half-pi phase delay condition is supported by thrust measurements from different compliant fins (four caudal-shaped fins with different aspect ratios) and a beam bending model of the compliant fin. This condition can be used as a guideline to select the proper compliance of a fin when designing a robotic fish.

In this paper, biomimetic underwater robots built using smart actuators, e.g., a shape memory alloy (SMA), an ionic polymer metal composite (IPMC), lead zirconate titanate (PZT), or a hybrid SMA and IPMC actuator, are reviewed. The effects of underwater environment were also considered because smart actuators are often affected by their external environment. The characteristics of smart actuators are described based on their actuating conditions and motion types. Underwater robots are classified based on different swimming modes. We expanded our classification to non-fish creatures based on their swimming modes. The five swimming modes are body/caudal actuation oscillatory (BCA-O), body/caudal actuation undulatory (BCA-U), median/paired actuation oscillatory (MPA-O), median/paired actuation undulatory (MPA-U), and jet propulsion (JET). The trends of biomimetic underwater robots were analyzed based on robot speed (body length per second, BL/s). For speed per body length, robots using an SMA as an actuator are faster than robots using an IPMC when considering a similar length or weight. Robots using a DC motor are longer while their speeds per body length are similar, which means that robots using smart actuators have an advantage of compactness. Finally, robots (using smart actuators or a motor) were compared with underwater animals according to their speed and different swimming modes. This review will help in setting guidelines for the development of future biomimetic underwater robots, especially those that use smart actuators.

In this paper, we present a novel stiffness adjustable structure that changes its stiffness by pulling a tendon. It adopts an endoskeleton structure where rigid segments and compliant segments are alternately connected in series. The stiffness of this structure is controlled by compressing the compliant segments with an axial force. A tendon that runs through the endoskeleton and is fixed at the tip provides the axial compression force when pulled. We analyze the structure using the cylindrical isolation bearing model. The bending stiffness of the proposed structure was simulated and compared with experimental results. The structure can be stiffened approximately fifty-times the original stiffness. This stiffness adjustable structure can be used to increase the efficiency of a system that uses compliance, e.g., a robotic fish that uses a compliant fin for its propulsion system.

Fish generates large thrust through an oscillating motion with a compliant joint of caudal fin. The compliance of caudal fin affects the thrust generated by the fish. Due to the flexibility of the fish, the fish can generate a travelling wave motion which is known to increase the efficiency of the fish. However, a detailed research on the relationship between the flexible joint and the thrust generation is needed. In this paper, the compliant joint of a caudal fin is implemented in the driving mechanism of a robotic fish. By varying the driving frequency and stiffness of the compliant joint, the relationship between the thrust generation and the stiffness of the flexible joint is investigated. In general, as the frequency increases, the thrust increases. When higher driving frequency is applied, higher stiffness of the flexible joint is needed to maximize the thrust. The bending angles between the compliant joint and the caudal fin are compared with the changes of the thrust in one cycle. This result can be used to design the robotic fish which can be operated at the maximum thrust condition using the appropriate stiffness of the compliant joint.

Robotic fish and dolphin have been studied to increase their dynamic performance, especially the velocity of a robotic dolphin. There are lots of parameters to increase the velocity of the robotic dolphin such as increasing an oscillating frequency, the area of a caudal fin, or the oscillatory amplitude and so on. The efficient and easy way to increase the thrust is to use a compliant caudal fin. Using the flexible caudal fin, the velocity of the robotic dolphin can increase. Furthermore, using a novel variable stiffness mechanism, the stiffness of the caudal fin can be varied depending on an oscillating frequency to maximize the thrust. We introduce the design and manufacturing of a robotic dolphin which has a variable stiffness mechanism.

Various oscillating parameters have been used to increase the velocity of a robotic dolphin. Among them, an efficient and easy way to increase the thrust is to increase an oscillating frequency of the robotic dolphin. However, there is a trade-off. If the oscillating frequency increases, the stability of the robotic dolphin decreases. Especially, a reactive motion is occurred in a head of the robotic dolphin due to the fluctuating motion of a caudal fin. The unsteady motion in the head position can be controlled using an additional actuator. However, the best solution is to reduce an undesired motion without adding the actuator. In this paper, to reduce the fluctuating problem, we consider the flexibility of the caudal fin. An oscillating amplitude of the caudal fin and head motion is changed with varying the stiffness of the caudal fin. Therefore, if we find the appropriate stiffness of the caudal fin, the head motion can be stabilized.

Fish generates large thrust through an oscillating motion with a fin. It is assumed that the flexibility of a fin affects the thrust generated by the fish. However, detailed investigation on the relationship between the flexibility of the fin and thrust generation is lacking. In this paper, the driving mechanism of a robotic fish is implemented using a compliant joint and caudal fin that is adapted from fish. The effect of the passive mechanism on the thrust generation with changes in the stiffness and frequency is investigated with this driving mechanism. The present research is carried out to understand the relationship among the compliance of the joint and caudal fin, the frequency of oscillating motion and the thrust which is generated by oscillating motion. The thrust is measured using a force transducer while varying the frequency and compliance. The bending angles between the compliant joint and caudal fin are also compared with the changes of the thrust in one cycle. The results show the appropriate stiffness of the compliant mechanism can be found in order to generate maximum thrust under the condition that the other parameters are not varied.

This paper proposes a new design concept of hybrid instrument for single-port laparoscopic surgery (SPLS) and a new method of verification using a scaled-up prototype based on the principle of elastic similarity. The proposed concept is a hand-held instrument that uses a tendon-gear mechanism for dexterous movement of its end-effector and servomotors with flexible tendon-sheath transmission to maintain the dexterity by compensating the loss of output angle from tendon elongation during the manual operation. The kinematic relationship of the tendon-gear mechanism was derived mathematically, and the ratio of external moment to resistive flexural stiffness of the articulating joint was matched between the real-sized model and the large-scale prototype. Our scale model tests have shown good agreement between their input–output relationships under the equivalent loading conditions, and thus verified the validity of similarity analysis. Also, the proof-of-concept experiments have demonstrated the functionality of output loss compensation of the hybrid instrument. Our methodology can be used to simplify and speed up the prototype development process for SPLS by avoiding miniaturization challenges such as high precision manufacturing, which is costly and time-consuming.

Compliance can increase the thrust generated by the fin of a bio-inspired underwater vehicle. To improve the performance of a compliant fin, the compliance should change with the operating conditions; a fin should become stiffer as the oscillating frequency increases. This paper presents a novel variable-stiffness flapping (VaSF) mechanism that can change its stiffness to maximize the thrust of a bio-inspired underwater robot. The mechanism is designed on the basis of an endoskeleton structure, composed of compliant and rigid segments alternately connected in series. To determine the attachment point of tendons, the anatomy of a dolphin's fluke is considered. Two tendons run through the mechanism to adjust the stiffness. The fluke becomes stiffer when the tendons are pulled to compress the structure. The thrust generated by a prototype mechanism is measured under different conditions to show that the thrust can be maximized by changing the stiffness. The thrust of the VaSF device can approximately triple at a certain frequency just by changing the stiffness. This VaSF mechanism can be used to improve the efficiency of a bio-inspired underwater robot that uses compliance.

Eosinophilic infiltration into skeletal muscles has been rarely reported in a variety of conditions such as parasite infection, sarcoidosis, rheumatoid arthritis, eosinophilia-myalgia syndrome, and idiopathic hypereosinophilic syndrome. Eosinophilic myositis (EM) is one of idiopathic inflammatory muscle diseases associated with muscle and/or blood eosiophilia. The case of EM complicated with hypercapnic respiratory failure has been extremely rarely reported. A 61-year-old woman was admitted with sudden-onset pain in both calves. She had elevated serum muscle enzymes and peripheral eosinophil count. Findings of electromyography were consistent with inflammatory myopathy. MRI showed diffuse hyperintensity of calf muscles on T2-weighted and enhanced T1 images. Muscle biopsy showed eosinophils' infiltration in the endomysium and perivascular area. During the diagnostic work-up, she presented with hypercapnic respiratory failure. She was successfully treated with mechanical ventilation and high doses of prednisolone. This case suggests EM can cause respiratory failure secondary to respiratory muscle involvement.

Oxaliplatin is a third-generation platinum compound that is used as a single agent and in combination with fluorouracil (5-FU) to treat colorectal and gastric carcinoma. The patients treated with oxaliplatin may develop hypersensitivity and idiosyncratic reactions, although these complications are known to be rare. We report here on two patients who suffered with metastatic colorectal cancer and who underwent palliative combination chemotherapy with oxaliplatin; they then developed hypersensitivity reactions to oxaliplatin. The first case had an anaphylatic reaction immediately after the beginning of the 7(th) to 8(th) cycle infusion of oxaliplatin. The second case developed repeated febrile episodes from the 4(th) to 8(th) cycles of oxaliplatin infusion. With the increasing use of oxaliplatin in clinical practice, we are now encountering an increasing incidence of suspected hypersensitivity reactions. Physicians should keep their eyes wide open and carefully observe for the clinical manifestations of these hypersensitivity reactions.

We apply SU(2/2) superalgebra to five dimensional supergravity. Pure supergravity multiplets, Maxwell multiplets and hypermultiplets are identified with either typical or atypical representations of SU(2/2). All possible representations describing supermultiplets are presented.