Motoji Yamamoto

Canes are commonly used for support and balance by people with mobility issues. However, falls occur among cane users owing to the lack of quantitative guidelines for cane usage. Therefore, this study proposes a guidance map that provides instructions on effective cane use to prevent falls. The map is constructed based on two factors: walking stability and physical burden. Walking stability is measured by the margin of stability (MoS), and physical burden is measured by the shoulder and elbow joint torques.We focus on the cane tip position and cane force as factors that significantly contribute to these two indicators. The increase in MoS per increase in joint torque is calculated to determine whether the cane tip position or cane force should be increased. Specifically, the joint torques and MoS are partially differentiated at the tip position, and the ratio of the partial differentiation coefficients is calculated. This calculation is also performed for partial differentiation by the cane force. By comparing the calculated values, it is possible to determine whether the appropriate technique is to adjust the cane tip position or the cane force. The calculation results are output in the form of a map. To verify the validity of the proposed map, we conducted an experiment with young, healthy individuals. The usefulness of the map was confirmed for participants A-C, suggesting the effectiveness of the proposed method. The proposed map can significantly reduce the burden on physical therapists by assisting them in guiding cane users.

Bio-inspired multi-joint snake robots offer the advantages of terrain adaptability due to their limbless structure and high flexibility. However, a series of dozens of motor units in typical multiple-joint snake robots results in a heavy body structure and hundreds of watts of high power consumption. This paper presents a joint-repositionable, inner-wireless snake robot that enables multi-joint-like locomotion using a low-powered underactuated mechanism. The snake robot, consisting of a series of flexible passive links, can dynamically change its joint coupling configuration by repositioning motor-driven joint units along rack gears inside the robot. Additionally, a soft robot skin wirelessly powers the internal joint units, avoiding the risk of wire tangling and disconnection caused by the movable joint units. The combination of the joint-repositionable mechanism and the wireless-charging-enabled soft skin achieves a high degree of bending, along with a lightweight structure of 1.3 kg and energy-efficient wireless power transmission of 7.6 watts.

T-cane is a primary method used to prevent falls. Although canes effectively increase stability and reduce load, the specific position of the cane tip that maximizes these effects is not yet clear. Furthermore, the cane tip position that enhances effectiveness may also increase the burden on the user. In this study, we used the center of pressure (CoP) as an indicator of stability and shoulder joint adduction torque as an indicator of burden. In this study, we propose a cane tip position that increases the stability of the cane user, but does not increase the burden, through experiment. The experiment involved healthy young male participants. The results confirmed that the CoP increased with the cane tip position. The shoulder joint adduction torque increased with the cane tip position and then remained constant. The results suggest that the participants can walk with higher stability per load when the cane tip was positioned 30 cm in front of the right foot on the ground.

To improve motion accuracy through functional electrical stimulation (FES) of forearm muscles, feedback control laws are applied to the index finger’s metacarpophalangeal (MP) joint. This paper introduces a proxy-based super-twisting algorithm (PSTA) for precise servo control of MP joints via FES. The PSTA combines first-order sliding mode control with a second-order super-twisting algorithm, effectively preventing windup during FES saturation and ensuring robust, accurate control. An implicit Euler method minimizes numerical chattering in the digital implementation. Experiments with Arduino and volunteers confirm the algorithm’s effectiveness.

Continuum robot arms that can access confined spaces are useful in many applications, such as invasive surgery, search and rescue, and inspection. However, their reach is often limited because their extension mechanism relies on elastic deformation or folding structures. To address this challenge, we propose a continuum robot with a novel extension mechanism inspired by the impressive ability of woodpeckers to extend and bend their long tongues to catch insects in tree holes. The proposed mechanism can change the effective length of the robot from almost zero to any length by moving the robot's body back and forth. Our prototype robot demonstrated a maximum extension of 450 mm and a minimum bending radius of 125 mm. In addition, we developed a Gaussian process regression model to predict an external force applied to the robot's tip using inertial measurement units. This enabled us to determine the magnitude and direction of the force with an error rate of 4.8 percent and 11.1 percent, even when the robot's length was varied between the training and test data. The unrestricted extension capability of the proposed approach has the potential to increase the application prospects of continuum robots.

The application of vibration stimulation to muscles, via the skin surface, can generate the sensation of movement, when actually there is no motion. This phenomenon is called kinesthetic illusion. Recently, in the fields of rehabilitation and virtual-reality technology, research has been conducted to utilize kinesthetic illusions to feel body movements, when there are none. To apply kinesthetic illusions in the above fields, it is necessary to develop techniques to improve the occurrence rates of the kinesthetic illusions and shorten the latency, which is the time lag from the onset of stimulation to the occurrence of the illusion. In a previous study, the authors reported that the occurrence rate of kinesthetic illusion could be improved by simultaneously applying vibration and electrical stimulations to the antagonistic muscles. In this study, the influence of this technique on the latency of the generated kinesthetic illusion is investigated by applying a combination of vibration and electrical stimulations. Three different electrical-stimulation voltages are used in the combined stimulation to induce the kinesthetic illusion, and the latency is studied for each voltage condition and the vibration-only condition. The effects of the voltage change on latency are evaluated from a regression analysis performed using the generalized linear mixed model. The results suggest that the change in the electrical stimulation voltage can shorten the latency of kinesthetic illusion.

Woodpeckers have flexible and extendable tongues that they use to reach their prey through tiny openings in trees and insect burrows. This unique capability of their tongue represents a promising design for a tool for picking up and handling objects in unstructured environments. Although continuum robots can produce dexterous movements because of their few shape constraints, the lack of structural stiffness has restricted their deployment in real-world environments. Inspired by the characteristics of woodpeckers, we designed a robot manipulator that can substantially extend its length and bend its shape in 2D space. This behavior is enabled by a backbone consisting of a chain of rigid joints and two flexible rack gears. The joints increase the payload by structurally supporting the robot. The proposed structure is 4.7 times stronger in vertical bending and 6.2 times stronger in torsion than without rigid links. Feeding the rack gears at the same and different speeds allows the robot to elongate and bend, respectively. We developed a geometric model based on a constant curvature model for motion planning. Experiments show that the robot can follow an arbitrary trajectory at an arbitrary tip angle. Lastly, we showcase various demonstrations, including deployment and storage for the backbone, follow-the-leader (FTL) motion, and whole-arm grasping in the horizontal plane.

Parallel elastic actuators (PEA) find a growing interest in many research areas ranging from rehabilitation devices to industrial robots on account of their ability to save energy as well as providing passive impact absorption. PEAs are actuators with elements of compliance, such as springs connected in parallel between the actuator and the load. The majority of these PEA mechanisms rely on clutches that require a high amount of power in a short amount of time. Furthermore, these PEA can only switch between a state of complete rigidity to constant stiffness. We consider the emerging design of rigid parallel series elastic actuators (RPSEA) which, in addition to the advantages provided by parallel elastic actuators, uses a motor instead of a clutch-based mechanism to manipulate the stiffness. We develop an experimental setup of the RPSEA and compare an Energy-based control method with a conventional PID control. The response of the two controllers is evaluated under disturbance and presented in this paper.