In order to accurately reach a target position while executing a task which imposes occlusion or constraints of the posture, a humanoid robot requires an adaptive locomotion system, which can comprehensively integrate localization, environmental mapping, global locomotion planning and local error correction. In this paper, we propose a method of constructing a perception based locomotion system for a humanoid robot. The major contribution of this paper is solving a problem of the locomotion error caused by the task constraints, by locally compensating footsteps and assessing the need for global footstep re-planning online based on environmental measurements. The proposed system provides an accurate and dense ground point cloud, called HeightField, using plane estimation and space interpolation, and obstacle point cloud for frequent collision avoidance by accumulating laser scans. This environmental perception enables a humanoid robot to plan footsteps globally even in the situation where the sight of the robot is limited and compensate footsteps while estimating landing state during locomotion online with the localization result. We evaluated the practicality of the proposed system by applying it to our humanoid robot carrying a heavy object in a construction site and confirmed that the proposed system contributed to improved locomotion abilities of a humanoid robot engaging in heavy-duty or dangerous tasks.

For heavy duty tasks which are needed in field or rough terrain, we developed a hydrostatically actuated anthropomorphic hand. The hand is specifically designed for the humanoid robot HYDRA, whose 40 joints are driven by back-drivable electro-hydrostatic actuators (EHA). Each designed hand has four fingers with a total of five DOF. Each finger has three joints underactuated by one tendon. Opposition/reposition of the thumb joint is also driven by one tendon. The five tendons are pulled by a miniature linear cluster EHA mounted in the forearm. The cluster EHA consists of a light weight tie-rod cylinder cluster with five pistons, and five low friction trochoid pumps with a crescent separator. Its 300 N nominal tension generates 1.5 Nm joint torque on each of the finger joints. Design of the cylinder and pump, with results of evaluation experiments is shown in this paper. Forearm structure with a mechanism to measure the tendon tension, low friction tendon routing in the forearm, low friction wire guiding link for the wrist, and parallel link wrist driving mechanism with two EHAs are also described.

Underactuated hands usually have high adaptability in power grasping but they are limited in pinching task with fingertip. In this paper, we propose the design of a tendon-driven underactuated hand that is capable of fingertip pinching by utilizing our proposed coupling mechanism. To reduce the friction resulting from tendon routing, we introduce the carpal tunnel mechanism that replace all sliding-contact tendon routing with the pulley system allocated in 3-dimensional space. The prototype of 11-DOF anthropomorphic robot hand is fabricated using rapid prototyping. Experiments are done to prove the effectiveness of our proposed coupling mechanism and low-friction tendon-driven system for underactuated robot hand.

This paper proposes a new torque sensing method, Cr-N alloy strain sensitive thin-film based torque sensors and distributed joint torque servo systems that enable human support robots to have capabilities to make physical interaction in adaptive and safe operation tasks. Stiffer torque sensing with stable and high-resolution sensing to meet practical level of the developed torque sensors have been achieved. We have developed the joint torque control based 4-DOF arm models in order to verify practical effectiveness of the proposed joint torque servo systems. We also demonstrated the joint torque control based bilateral master slave system exploring future applications.

The importance of force measurement and back-drivability in realizing force sensitive actuator is widely acknowledged. There are studies on fidelity of torque sensors and backdrivability individually, but limited study are made on investigating effect of torque fidelity and backdrivability on force sensitivity of the actuation system. In this paper, we developed backdrivable electro-hydrostatic actuator equipped with torque sensor to analyze the effect of torque fidelity and backdrivability on force sensitive control system. We implemented friction compensation controller and evaluated force sensitivity of the actuator by residual friction torque after the friction compensation. Method using pressure sensor and torque sensor were compared. Effect of backdrivability was performed by comparing friction torque of Harmonic Drive joint and joint with developed actuator.

It is widely acknowledged that the actuator's intrinsic backdrivability is important in realizing a force sensitive behavior. It is desirable to realize such actuator with electric motor that is advantageous from power-to-weight ratio and controllability point of view. Electro-Hydrostatic Actuator is a type of hydraulic actuators that can realize high backdrivability by reducing transmission friction and by providing dynamics decoupling with an implicit serial damper. To farther enhance the backdrivability of a EHA, a pump with minimum static and Coulomb friction is necessary. In this paper, we introduce an EHA with viscous screw pump that minimizes static and Coulomb friction by eliminating the mechanical contact between pump components. Viscous screw pumps also have the advantage that there is no pulsation in pressure due to the continuity of the force transmission from the rotor to the fluid. The property of the actuator, including pulsation performance and impedance control performance were evaluated on a prototype of EHA with a viscous screw pump.

Realization of rigid and sensitive torque sensor is one of the key factors for the success of robots. With the conventional detectors as strain gauges, poor S/N (signal to noise) ratio has been the limitation of torque sensor sensitivity. Torque Encoder uses a linear encoder as a detector and significantly enhanced the S/N ratio, and realized stiff and sensitive torque sensor. However, the crosstalk in torque measurement was still an open problem as in other sensing methods. In this paper, we analyzed the cause of the crosstalk and proposed the mechanism to suppress the crosstalk using selectively compliant suspension mechanism. Design methodology, implementation to minimize crosstalk with minimal sensitivity loss are presented. Evaluation on a prototype of the mechanism is carried out to show the effectiveness of the mechanism.

Although backdrivability is recognized as an important property of actuators, this term is often used without clear definition. In order to design mechanisms with advanced controllability, it is important to understand the fundamental mechanism of backdrivability. In this paper, we introduced idea of series elasticity and series dissipation of actuators. Based on this idea, total/output backdrivability and their fundamental properties are stated. EHA was shown to be series dissipative and it was confirmed from the model of the actuator. Utilizing the backdrivability of EHA, position based impedance control was implemented and evaluated. Application of this EHA in a robot hand is also reported.

When robots cooperate with humans it is necessary for robots to move safely on sudden impact. Joint torque sensing is vital for robots to realize safe behavior and enhance physical performance. Firstly, this paper describes a new torque sensor with linear encoders which demonstrates electro magnetic noise immunity and is unaffected temperature changes. Secondly, we propose a friction compensation method using a disturbance observer to improve the positioning accuracy. In addition, we describe a torque feedback control method which scales down the motor inertia and enhances the joint flexibility. Experimental results of the proposed controller are presented.

Backdrivability is a keyword with rising importance, not only in humanoid robots, but also to wearable robots. Power assist robots, namely exoskeletons are expected to provide mobility and independence to elderly and people with disability. In such robots, without backdrivability, error between human and robot motion can be painful; sometimes dangerous. In this research, we apply a type of hydraulic actuator, specially designed to realize backdrivability, to exoskeletal robot to improve backdrivability. We present the basic methodology to apply such hydraulic actuator to wearable robots. We developed prototype of knee joint power assist exoskeleton and performed fundamental tests to verify the design method validity.

Robots must have similar mechanical impedance characteristics to humans in order to make safe and efficient contact. This impedance requirement applies not only to the surface but also to the actuation mechanisms. The objective of this research is to develop inherently flexible actuator by realizing backdrivability. A class of hydraulic actuation called electro-hydrostatic actuator was applied to knee joint in humanoid robots to satisfy flexibility and large torque output simultaneously. This paper explains the methodology of performance evaluation of actuators and design concept of joint mechanism. Mathematical model of electro-hydrostatic transmission is also presented. Evaluation of backdrivability, inertia modification control, and compliance control of developed mechanism are performed.