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This article proposes a compact ankle exoskeleton with a multiaxis parallel linkage mechanism. By applying torques to the ankle joint, it can generate dorsi- and plantar-flexion motions. The design variables of the mechanism were analyzed and optimized to accommodate up to 12 N·m of torque within a thickness constraint of 40 mm. The parallel linkage structure of the proposed mechanism requires that moving mechanical parts must be thin and located at the front of the shank. Using the data from foot pressure sensors, the device can recognize the gait phases. The output torque and angle data were collected to evaluate the performance of the device.

This letter proposes a multifunctional ankle exoskeleton to safely expand the mobility. By applying torque to the ankle in dorsiflexion and plantarflexion, the exoskeleton prevents foot drop and foot slip and helps the ankle to push off the ground. The exoskeleton includes a remote center-of-motion (RCM) mechanism, a linear actuation module, and fastening modules. The RCM mechanism, which has two degrees of freedom, is designed to be aligned with the talocrural and subtalar axes of the ankle. A key feature of the RCM mechanism is a three-dimensional combination of two four-bar linkage mechanisms that have the linear motion and rotational motion, respectively. Only the talocrural axis is actively actuated for dorsiflexion and plantarflexion of the ankle, whereas the subtalar axis is passively released to allow the unconstrained motion by the user. The active axis is driven by a linear actuation mechanism comprising a ball-screw and a brushless dc motor. The device can be separated into fastening modules and actuation module and weighs only 869 g/leg without the battery. The results of ground and treadmill tests indicate that the peak torque and average positive mechanical power delivered by the exoskeleton are approximately 20 N·m and 6.21 W, respectively.

Several research groups have developed and studied powered ankle exoskeletons to improve energetics of healthy subjects and the mobility of elderly subjects, or to reduce asymmetry in gaits induced by strokes. To achieve optimal effect, the timing of assistive torque has been proved to be of crucial importance. Previous studies estimated the onset timings mostly by extrapolating the time horizon from past gait events observed with sensors. Such methods have inherently limited performance when subjects are not walking at steady frequencies. To overcome such limitation and allow the use of exoskeletons in various scenarios in a daily life, we propose to estimate the gait phase as a continuous variable progressing over a gait cycle, hence allowing immediate response to frequency changes rather than iteratively correcting it after each cycle. Our method uses recurrent neural networks to estimate gait phases out of an inertial measurement unit (IMU) every 10 ms. By replacing foot sensors with an IMU we can obtain rich enough information to estimate gait phase continuously as well as avoid physical damage in sensors from ground impacts. Our preliminary tests with 2 healthy subjects showed qualitatively positive outcomes regarding the gait phase estimation and the assistive torque control.

There are many important factors in developing an exoskeleton for assisting human locomotion. For example, the weight should be sufficiently light, the assist torque should be high enough to assist joint motion, and the assistance timing should be just right. Understanding how these design parameters affect overall performance of a complex human-machine system is critical for the development of these types of systems. The present study introduces an assistance timing controller that regulates assistance timing such that peak joint velocity and peak assistance power are offset by a reference value for our hip-type exoskeleton. This is followed by measuring the manner in which various assistance timing references affect an important metric for performance, namely metabolic cost. The results indicate that net metabolic cost exhibits a concave up pattern with the most reduction of 21%, when compared to walking without the exoskeleton, at 0% assistance timing reference. The study also examines assistance timing's effect on gait parameters; increase in assistance timing reference increases step length, decreases cadence, and increases walk ratio (i.e. step length/cadence ratio) during treadmill walking.

This paper presents a novel flexible sliding thigh frame for a gait enhancing mechatronic system. With its two-layered unique structure, the frame is flexible in certain locations and directions, and stiff at certain other locations, so that it can fît well to the wearer's thigh and transmit the assisting torque without joint loading. The paper describes the basic mechanics of this 3D flexible frame and its stiffness characteristics. We implemented the 3D flexible frame on a gait enhancing mechatronic system and conducted experiments. The performance of the proposed mechanism is verified by simulation and experiments.

The common requirements of rough terrain mobile robots are long-term operation and high mobility in rough terrain to perform difficult tasks. In rough terrain, excessive wheel slip could cause an increase in the amount of dissipated energy at the contact point between the wheel and ground or, even more seriously, the robot could lose all mobility and become trapped. This paper proposes a traction control algorithm that can be independently implemented to each wheel without requiring extra sensors and devices compared with standard velocity control methods. The proposed traction algorithm is analogous to the stick-slip friction mechanism. The algorithm estimates the slippage of wheels by angular acceleration change, and controls the increase or decrease state of torque applied to wheels Simulations are performed to validate the algorithm. The proposed traction control algorithm yielded a 65.4% reduction of total slip distance and 70.6% reduction of power consumption compared with the standard velocity control method.

Mobile robots are being developed for building inspection and security, military reconnaissance, and planetary exploration. In such applications, the robot is expected to encounter rough terrain. In rough terrain, it is important for mobile robots to maintain adequate traction as excessive wheel slip causes the robot to lose mobility or even be trapped. This paper proposes a traction control algorithm that can be independently implemented to each wheel without requiring extra sensors and devices compared with standard velocity control methods. The algorithm estimates the stick-slip of the wheels based on estimation of angular acceleration. Thus, the traction force induced by torque of wheel converses between the maximum static friction and kinetic friction. Simulations and experiments are performed to validate the algorithm. The proposed traction control algorithm yielded a 40.5% reduction of total slip distance and 25.6% reduction of power consumption compared with the standard velocity control method. Furthermore, the algorithm does not require a complex wheel-soil interaction model or optimization of robot kinematics.

This paper proposes a linkage-driven manipulator having linear ultrasonic motors inside of an elongated shaft. The manipulator can be divided into a driving rod module and wrist joint module. The driving rod module consists of several ultrasonic motors and driving rods. Flexible leaf springs between the ultrasonic motors and the driving rods enable synchronized motion of the driving rod by compensating mechanical clearance and different characteristics of ultrasonic motors. Two driving rods operate 2-DOF wrist module by linear motion. The wrist joint module is composed by two non-closing rotation joints, serially connected sliders and intermediate linkages, and designed to rotate from +60° to −60° in yaw and pitch directions respectively. The wrist parameters are determined by parametric studies of the motion range and torque characteristic, and the effect of the flexible leaf spring is studied by simulation. Experiments are performed in order to evaluate the velocity-force characteristic of the rod module.

This paper proposes a traction control algorithm which can be independently implemented to each wheel without extra sensors and devices compared with standard speed control. The algorithm estimates stick-slip of wheels based on estimation of angular acceleration so that the traction force induced by torque of wheel converses between maximum static friction and kinetic friction. Simulations are performed to verify the validity of the algorithm. The proposed traction control algorithm obtained 40.5% reduction of total slip distance and 48.4% reduction of dissipated work on the contact point compared with standard speed control. Furthermore, the algorithm does not require complex wheel-soil interaction model and optimization of robot kinematics.

Piezoelectric motors have been used in many applications where excellent controllability and fine position resolution are required or magnetic field noise should be eliminated. However, the piezoelectric motor has two major drawbacks. One is difficulty in maintaining constant vibration amplitude with temperature rise and wear, and the other is heat generation induced by dielectric and mechanical losses. A piezoelectric motor that can overcome these problems is proposed. It is operated using momentum exchange between a bimorph and a rotor. To maximize the motor's steady state velocity and static torque, a guideline is established using two bimorph models. The guideline is then partially validated by comparison between simulation and experiment results. There was no heat generation in several hours of testing.

Piezoelectric motors have been used in many applications where excellent controllability and fine position resolution are required and/or magnetic-field noise should be eliminated. However, the piezoelectric motor has two major drawbacks, difficulty in maintaining vibration amplitude constantly with temperature rise and wear and heat generation induced by dielectric and mechanical losses. In this article, a new piezoelectric motor that can overcome these problems is proposed. The proposed piezoelectric motor is operated using momentum exchange between four bimorphs and a rotor. In order to maximize the steady-state velocity and static torque of the proposed motor, a guideline is established using two bimorph models. The guideline is partially verified by comparison between simulations and experiments. There was no heat generation in a few hours of operation in experiments.