Variable stiffness control has emerged as a key technology for enabling robots to adapt their interaction forces to diverse environments. From locomotion systems that navigate irregular terrains to manipulation tasks requiring delicate force regulation, the ability to dynamically modulate structural compliance enhances performance, stability, and versatility. This paper focuses on an elastic force modulation (EFM) mechanism that actively adjusts structural stiffness in response to environmental changes. The concept is demonstrated using a cylindrical flexible elastic crawler (FLEC) for in-pipe locomotion. The FLEC employs elastically deformable belts to conform to varying pipe geometries, but fixed stiffness leads to a trade-off: in large pipes, normal force and traction are insufficient, while in narrow pipes, excessive normal force increases friction. The proposed EFM mechanism resolves this issue by increasing stiffness in large-diameter pipes and reducing it in narrow pipes, thereby improving traction while minimizing internal friction. Beyond pipe inspection, the same principle—actively tuning structural stiffness to optimize interaction forces—is directly applicable to robotic hands. In particular, variable joint stiffness is essential for replicating human-like "relaxation" in piano-playing robots, enabling nuanced control of key touch and tone color for expressive performance. Theoretical analysis and experimental validation confirm the feasibility of the proposed mechanism, highlighting its potential as a foundational technology for both industrial mobility and artistic manipulation.

This paper presents a soft manipulator which mimics the muscle structure of an octopus arm and its operation by the master-slave method by using a wearable interface. The soft manipulator consists of a rubber structure and McKibben artificial muscles arranged in axial and oblique directions. This manipulator has high safety and shape adaptability and realizes smooth and continuous movement like the octopus arm such as bending and twisting. For the intuitive operation of the manipulator, the wearable interface using flexible strain sensors is developed. It is easy to wear on the human arm with high comfortability because it consists only of soft materials and stretches easily with following the arm motion. We can operate the soft manipulator by using the motions of the wrist and forearm as an operation input. The soft manipulator can move following the arm motion of the operator, and it shows the high possibility to conduct actual tasks.

An octopus arm has no rigid structure, it is mostly composed of muscles aligned in various directions and the nerves. The muscles are roughly aligned in three directions, and by driving the muscles selectively, the octopus arm can perform multiple functions such as the contracting, bending, torsion and stiffness alteration. This study aims at the development of a new flexible robotic arm using thin McKibben actuators mimicking the muscle structure of an octopus arm. The McKibben actuator is a well-known pneumatic artificial muscle, and we have developed extremely thin McKibben actuators by using a braiding machine. In this paper, configuration of the flexible arm is proposed. The developed mechanism consists of thirty two thin McKibben actuators arranged in three directions, axial, radial and oblique, imitating the muscle structure of an actual octopus arm. The fundamental motion of the flexible arm is investigated experimentally. The proposed mechanism performs bending, contracting, torsion movements and stiffness alteration like an octopus arm.

The aim of this research is to realize a functional adhesive robot skin with integrated micro suction cups, which has two new functions involving adaptive adhesion to rough/curved surfaces and anisotropic adhesion. This skin can be applied to various robot mechanisms such as robot hands, wall climbing robot feet and so on. In this report, the robot skins have been successfully developed to realize the higher adaptive adhesion by modifying materials and integration density of suction cups. The suction cups on 10mm × 10mm area realize the adhesion to surfaces with 145μm RMS roughness and with gap of 900μm in height.

This study aims at development of a multi-directional bending mechanism with thin and long body driven by fluidic rubber actuators. Generally bending mechanisms with fluidic rubber actuators can have advantages of smooth and continuous motion, however because of their low stiffness it is difficult to generate high output force. To solve this problem, we have proposed a novel bending mechanism combined with contracting and extending rubber actuators. By bundling rubber actuators with different types, the developed bending mechanism can have the high stiffness. In this report, optimized extending and contracting rubber actuators are made basis on a McKibben actuator, then they are combined to be the bending mechanism. Experimentally stiffness of the mechanism is measured and is compared with a bending mechanism bundled with same motion type actuators. Resulting high stiffness can be recognized by the proposed mechanism. Additionally, a very long bending mechanism, which is 7m in length, is developed and its motion is demonstrated.

The goal of this research is to develop a functional adhesive robot skin with micro suction cups, which realizes two new functions: adaptive adhesion to rough/curved surfaces and anisotropic adhesion. Both functions are realized by integration of asymmetric micro cups. This skin can be applied to various robot mechanisms such as robot hands, wall-climbing robot feet and so on as a kind of robot skins. This paper especially reports the concept of this adhesive robot skin and its fundamental characteristics. The experiments show the developed skin realizes novel characteristics, high adhesion even on rough surface and anisotropic adhesion.

There are many big challenges for manipulation in ultimate temperature environments. Examples of these are in material sciences and industries. For example, steel industries desire new methods for direct handling of materials in temperature higher than 1000 degree Celsius while material scientists desire new method for handling specimen in helium temperature, where higher-quality analysis can be carried out with very low thermal noises. However, conventional actuators don't work in such environments because of their low thermo-stability and more essential reason of the loss of the magnetic and piezoelectric properties of actuator materials. It us well known that magnetism and piezoelectricity completely disappear in temperature higher than Curie-Point, for example. This report proposes a new working principle of actuators for the uses in very wide temperature range. It is driven by volume change associated with phase transition of working fluid. We propose the principle of this actuator and show the possibilities of the actuator design including the possible selections of temperature-resistant materials and working fluids in various temperatures. In addition, as the first step of this research, we designs the first prototype actuator, working successfully at 180 degree Celsius utilizing liquid-vapor transition of water and the basic experiments results, which shows the great possibility of this actuator.

Recently, colonoscopy has become much more important with increasing number of colonic diseases. However, the inspection time depends on the doctor's skill strongly. In this research, we aim at development of a tube type rubber pneumatic actuator for assisting insertion of a large intestine endoscope. This actuator can be wound around endoscopes in a spiral configuration. In previous paper, two types of actuator were developed and some experiments were conducted. However, there were drawbacks, one actuator could not generate enough output, and the other one was difficult to mount on endoscopes. In this paper, novel actuator has been designed by non-linear FEM (Finite Element Method) to realize high mountability and drivability. The actuator is configured with three air chambers, and by applying pneumatic pressure to each chamber in proper sequence, elliptical motion of the actuator has been confirmed by non-linear FEM analysis and experiments using motion capture system. Moreover the self propelling velocity and the traction force have been increased compared to previous actuators and effectiveness of this actuator has been confirmed from the phantom experiments.

Our research group has investigated various kinds of soft mechanisms for many years. Through these researches, several soft rubber actuators driven pneumatically have been developed. The typical one is FMA (Flexible Microactuator), which realizes continuous bending motions like a human finger. In addition, we are recently interested in several novel functions appeared on soft mechanism surfaces such as repellency, hydrophily, friction, structural color, and adhesiveness, which are realized with micro scale soft structures fabricated on the surfaces. We believe novel additional functions can be realized by utilizing the deformability of the soft structures. In this paper, micro grating structures made from silicone rubber are reported. Because of its elastic property, it can realize changing structural color. The experimental results show that beautiful color change can be observed. We fabricate a soft micro grating structure on FMA and confirm the appearance of structural color, which changes in following FMA's motion. This color change indicates distributed information of the strain of FMA, which may be used for servo control of FMA in the future.

We have developed a hydraulic McKibben artificial muscle which realizes great force density approximately ten times larger than the other conventional actuators. In this paper, we have applied this muscle to a power robot hand. The hand finger consists of metal links and the muscles. The contraction of the muscles generates the bending motion of the fingers. This hand has large holding capacity and shape adaptability to grasp objects. The experiments show that maximum holding force of the hand is 5000N. It can hold three types of different shaped objects; cylindrical objects of φ 267mm and φ 165mm in diameter and a square cross section of width 200mm in side. This hand can be applied to various applications, for example rescue robots in disaster area and forestry industry.

Colonoscopy is an important medical action to detect disorders like colon cancer. However generally it is difficult to insert a scope into the colon, because the colon is flexible and complex shape. This study aims at development of an actuator which can add propelling ability to a colonoscope. We focused on rubber pneumatic actuators, because advantages of them, for example, high compliance, low cost, water proof, and so on, agree with the required properties of medical devices. In previous paper, we designed a novel rubber actuator consisting multi air chambers by using nonlinear FEM (finite element method). In this research, we fabricated the actuator employing the design; whose cross section is about 5mm × 5mm and length is over 100m, by extrusion molding method successfully. The deformation characteristics of the actuator were clarified by a motion capture system. As a result, elliptic trajectory which leads propelling motion was confirmed. In addition, transportation of a dummy scope was achieved by winding two actuators.

Pneumatic actuators have several advantages such as light weight, safety, low cost and high compliance. They have been used in many areas such as industrial robots, rehabilitation tools, haptic devices, and medical/welfare robots. Pneumatic actuators are generally used in multi-DOF pneumatic system and have complicated systems that include a compressor, air tubes, and pneumatic valves with electrical wires. This research proposes a new control method for a multiplex pneumatic transmission constructed with special resonant valves and driven independently with air vibration in air supply tube without electrical wires. The control method simplifies the driving system and is effective for pneumatic systems having many degrees of freedom. In this paper, the development of a prototype model of the resonant valve is described. In addition, two control methods, which are a superimposing method and a time-sharing method for multi-valve control, are proposed and evaluated. Independent control of four pneumatic cylinders is realized.

In medical and biotechnology fields, soft devices are required because of their high safety from low mechanical impedance. FMA (Flexible Microactuator) is one of the typical soft actuators. It consists of fiber-reinforced rubber structure with multi air chambers and realizes bending motion pneumatically. It has been applied to robot hands, robot legs and so on. High potential of FMA has been confirmed by many experiments reported in several papers. However in fabrication process of the actuator, it is difficult to embed the reinforced fiber in the rubber structure. In this study, we aim at development of a fiber less FMA realizing quite large motion, which can be said curling motion, and a soft hand using the actuators. We design the actuator without fiber using nonlinear FEM (Finite Element Method) and derived efficient shape. The actuator is fabricated through micro rubber casting process including micro machining process for molds, micro vacuum rubber molding process and rubber bonding process with surface improvement by excimer light. Basic driving experiments of the actuator showed that it realized curling motion which agreed well with FEM results. And the actuator could grasp a fish egg without breaking. Additionally, we made a soft hand consisting of three curling actuators. This hand also could be manufactured by simple casting process. The developed hand works opening and closing motions well.

Recently, a variety of soft actuators have been developed. However, applicable sensors such as potentiometers and optical encoders generally have high stiffness and when they are used in a soft actuator, the actuator loses its compliance. To solve this problem, a flexible displacement sensor has been developed. This sensor was fabricated by depositing a conductive paste onto a rubber seat. Paste injection was utilized in the fabrication process of the sensor, and precise control of thickness, width and pattern of the conductive film and deposition onto a curved surface was realized by this system. Firstly, an experiment on a flat-type flexible displacement sensor was conducted to evaluate and improve the sensor. The experimental results showed sufficient linearity and detecting range. Then, an intelligent FMA (Flexible Microactuator) was fabricated by depositing the conductive paste onto the surface of an FMA. A servo control system for the intelligent FMA was set up, and high positioning accuracy was confirmed by a servo driving experiment.�

The aim of this study is to develop an intelligent McKibben actuator with an integrated soft displacement sensor inside, so that displacement of this actuator can be controlled without having any extra devices attached. In addition, the high compliance which is a positive feature of the McKibben actuator is still conserved. This paper consists of four main parts. First of all, different types of soft displacement sensors made out of rubber were composed, and tested for their functional characteristics. Secondly, the intelligent McKibben actuator was developed with the soft displacement sensor incorporated within. Then, experiments of the position servo control with a single intelligent McKibben actuator were carried out. At last a robot arm mechanism was designed with two intelligent McKibben actuators, and those experimental results showed a great potential for its future applications.

The purpose of this research is to realize a small robot which can negotiate pipes whose diameter varies widely during the robot's course. A new in-pipe locomotion mechanism named "snaking drive" is proposed in this paper and its potential and fundamental characteristics are shown with experimental data of the prototype model. First, in the sections 2 to 5, the basic traveling characteristics of the snaking drive mechanism are discussed: a theoretical formula of the fundamental characteristics and control algorithm are derived, the motions of the robot are simulated on a PC, and the prototype model was designed, developed, and tested. Next, in the sections 6 and 7, additional control algorithms for the front link are derived. They are necessary for steering at T-branches and L-bends of pipes, and also for camera view stabilization. Their performances are also shown by software simulation and experiments. The prototype robots moved in pipes whose diameter varies between 55 mm to 331 mm with the maximum speed of 22 mm/s. The paper also shows that the prototype negotiates T-branches and L-bends of pipes with inspection capability through a camera mounted on the robot.