Synthetic fiber ropes are widely used for robots because of their advantages such as lightweight, high tensile strength and flexibility. However, there is limited information on the physical properties of synthetic fiber ropes when used for robots. This study focuses on repetitive twisting of synthetic fiber ropes and provides information for selecting them for robots based on durability. To this end, we conducted repetitive twisting experiments on five types of ropes made from different fibers; we revealed that Dyneema has higher durability against repetitive twisting than the other ropes when a single rope is twisted. In addition, we conducted experiments on Dyneema by applying torsion to two ropes in parallel like a twisted string actuator. The result indicated that two Dyneema ropes in parallel have higher durability than a single rope; however, we revealed that the the tensile strength decreases sharply with an increase in the angle of twist.

A hydraulic drive system can generate a large force and is impact resistant. Thus, robots that utilize hydraulic drive systems have been developed for use in disaster areas. In a hydraulic drive system, it is necessary to design the motion of the robot within the capacity of the pump unit, but it is generally difficult to predict the required flow rate and pressure. Especially for hydraulically driven legged robots, the periodic significant changes in the required flow rate and pressure can make it difficult to select a pump and design the leg operation within pump capacity. Therefore, most operations are not designed in full consideration of the characteristics of the pump. By designing the operation of the robot considering the characteristics of the pump, improvements in energy efficiency and working speed can be expected. In this study, we theoretically derive the relationship between the leg motion of the hydraulic leg robot and the required pressure and flow rate. Based on the results, a method for designing the operation considering the characteristics of the pump is proposed, and its validity is experimentally confirmed.

Ionic polymer-metal composites (IPMC) actuators are popular because they can be driven at a low voltage, possess excellent responsiveness, and can perform soft motions similar to that of living creatures. Conventional IPMC soft robots are manufactured by cutting and assembling IPMC sheets. However, using this conventional process to stably manufacture three-dimensional (3D)-shaped soft robots is difficult. To mitigate this problem, we propose a new method for fabricating 3D IPMC actuators in which several surface electrodes are separately fabricated from a single ion-exchange membrane. We refer to our proposal as the simultaneous 3D forming and patterning (SFP) method. Unlike the conventional IPMC fabrication process, the SFP method requires only one step to fix the ion-exchange membrane to contact masks. First, we briefly describe IPMC actuators, before introducing the proposed SFP method in detail. Next, we describe our investigations of the patterning resolution for the surface electrode using the proposed method. We fabricated two soft robot prototypes using the proposed method. The first robot is a starfish-type soft robot. Its surface electrode can be patterned in a plane using the proposed method, and independent driving is possible by applying voltage individually to the divided electrodes. The second prototype is a sea anemone-type soft robot, wherein surface electrodes can be patterned on a 3D curved surface to form a 3D shape.

Among the various pneumatic actuators, thin McKibben muscles are particularly attractive owing to their high performance in terms of high contraction ratio, high flexibility, and productivity. One of the challenges for thin McKibben muscles and other pneumatic actuators is the fact that they generally need air hoses and air sources like compressors. This necessarily leads to bulky systems. To solve this problem, we propose and study a new approach to driving pneumatic actuators that exploits electrolysis/synthesis of water by a polymer electrolyte fuel cell (PEFC). This method could in-principle have high applicability to thin McKibben muscles. However, one challenge must still be addressed for the realization of an electrically driven thin McKibben muscle: the development of a tube-shaped soft PEFC. This paper proposes an electrically driven thin McKibben muscle with a tube-shaped soft PEFC realized through a flowing non-electrolytic plating method. First, the proposed thin McKibben muscle is briefly described. Then, a novel method for plating a tube-shaped soft PEFC using reflux is introduced, and its fundamental operation is tested. After the evaluation of the PEFC, we report a prototype realization of the proposed thin McKibben muscle. The developed prototype has a length of over 170 mm, a diameter of 4 mm, and high flexibility for bending. Finally, we elaborate on a driving experiment through which fundamental characteristics were experimentally evaluated. The prototype thin McKibben muscle succeeded in electrically controlling contraction and expansion motion with a flexible and bendable structure.

As a part of our research on several different types of Giacometti robots, a 20-m-long, considerably light, and simple robot arm, referred to as the Giacometti arm, is developed in this study. Even though the Giacometti arm is not suitable for precise positioning, rapid motion, and high load capacity, which are the aspects most conventional robots focus on, it is designed for extremely specific purposes such as the inspection of otherwise unreachable regions using a small camera at the arm's tip. In addition, it is designed to be essentially safe even if it falls down or hits an object. This aspect is realized using helium-filled balloon bodies and thin pneumatic muscles. In this paper, we designed new Giacometti arm which is 20-m-long, weighs 940 g, and has 20 degrees of freedom. To realize this long arm, we derived a kinematic model of the 20-m-long Giacometti arm, factoring in the air resistance. We verified the model using the arm, and its utility was confirmed at a mock-up facility.

Compressors and air hoses limit the mobility of mobile robots and the use of pneumatic actuators such that small pneumatic actuators, which can be driven without compressors, are strongly desired. We have been developing a new hose-free pneumatic actuator based on reversible gas/liquid chemical reactions. This novel pneumatic actuator neither requires compressors nor air hoses for its source of power because its pressure source is in the actuator itself. In this paper, we present a way to estimate gas generation speed from both theoretical and experimental aspects. We also present a new untethered soft robot, which has this actuator located internally. This robot has three hands and can move them up in 16 s and down in 35 s.

An amphibious all terrain mobile robot is required for disaster response tasks. In this paper, we propose “R-Crank”, which has a simple four wheels driving configuration with crank links, connecting to ipsilateral front and rear wheels so as to form parallel four-bar linkage systems. The crank links act as legs because their trajectory with respect to the ground become trochoid curve, which is commonly used as leg trajectories for a legged robot. These links achieve high terrain adaptability while maintaining simple structure of the wheeled robot. We developed a prototype model and carried out basic experiments. The robot achieved to climb 0.3 m of a step(76.9% of the wheel diameter), stairs and a snowy slope. In addition, we propose amphibious structure of crank links by installing multiple rigid paddles. The propulsive force generated by the crank links was measured and empirically derived the optimum parameters by using a small-sized experimental apparatus. Finally the robot equipped with the amphibious crank links achieved propulsion on water at 0.13 m/s. We also verified that the robot achieved going up and into water through stairs.

This paper introduces an approach for manipulating bodily self-consciousness, in particular, senses of body ownership and illusory self-touch by using a robotic/haptic technology. This study especially focuses on the rubber hand illusion (RHI). In the classic RHI paradigm, an invisible participant's hand and a visible fake rubber hand are manually stimulated by an experimenter. However, our approach, which is termed active self-touch, allows the participants to administrate the tactile stimulation with variable force feedback by using a robotic master-slave system. Three RHI experiments with active self-touch were performed to demonstrate the utility of the proposed approach for assessment of bodily self-consciousness. The embodiment of a fake hand was assessed with the classic RHI paradigm, and the RHI paradigm with somatic sensation was applied to examine the effect of variable force feedback on the sense of illusory self-touch. These experiments verified that active self-touch allows participants to experience the classic RHI. In addition, the results implied that the sense of illusory self-touch can be induced, even if force feedback is absent in the dynamic self-touch condition, and that illusory sensation is easily modulated by variable force feedback during quasi-static self-touch rather than during dynamic self-touch. These findings suggest that our proposed approach has the potential to reveal relationships between action/haptic perception and the sense of body ownership.

Our previous study has proposed a novel approach with a robotic/haptic technology to tactile rubber hand illusion (TRHI) paradigm in order to open new discussions about the manipulation of human body-parts ownership. The results demonstrated that the use of master-slave system can cause the TRHI, enabling a unique condition-active self-touch. As an advanced approach, this study examines the effect of force feedback on the TRHI under the active self-touch. We hypothesize that appropriate force feedback plays an important role to determine our body-parts ownership, people would not experience the TRHI if the force feedback from a fake hand largely differs from the contact force on a real hand. This paper, in particular, discusses how the force feedback affects the TRHI under the active self-touch by variously changing force rendering on the master device.