Hiroshi Kaminaga

Development of backdrivable hydraulic joint mechanism for knee joint of humanoid robots

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.

High-fidelity joint drive system by torque feedback control using high precision linear encoder

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 analysis of Electro-Hydrostatic Actuator and series dissipative actuation model

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.

Development of knee power assist using backdrivable electro-hydrostatic actuator

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.

Backdrivable miniature hydrostatic transmission for actuation of anthropomorphic robot hands

Humanoid robots demand high performance on actuators, such as power-to-weight ratio, durability, occupation volume, and freedom of placement. Also, for robots to interact with unknown objects, flexibility is necessary. Backdrivability is effective when both flexibility and high output torque needs to be realized, which were often contradicting requirement. In this paper, backdrivable hydrostatic transmission is proposed to satisfy requirements above. First, development of hydrostatic actuator including conditions of backdrivability is explained. Second design of backdrivable pump, hydraulic motor and manifold design is explained. Next, design of an anthropomorphic robot hand using developed hydrostatic transmission is discussed. Finally, developed hand is presented and experiments on backdrivability, force sensing, and grasping were performed.

Electro-hydrostatic actuators with Series Dissipative property and their application to power assist devices

The actuators used in wearable robots must behave compliant. This, however, is not easy mainly due to two reasons: lack of force measurement capability and lack of backdrivability. Both of above needs to be realized, but the latter issue lies in the actuation principle of conventional robot actuators. We have been investigating in the electro-hydrostatic actuators to realize backdrivability by minimizing friction due to the reduction. Still, the way to design actuator, considering backdrivability, including the one due to the internal leakage, was an open problem. We introduced the actuator model “Series Dissipative Actuator” to explain the actuator behavior. This model enables us to understand the roll of internal leakage in the hydraulic system and it shows the design guideline considering the backdrivability. In this paper, we show the method to apply SDA (Series Dissipative Actuator)concept on EHAs (Electro-Hydrostatic Actuators). Development of the actuator prototype targeted for use in lower limb is also presented and preliminary results in backdrivability evaluation is performed.

Low-friction tendon-driven robot hand with carpal tunnel mechanism in the palm by optimal 3D allocation of pulleys

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.

Mechanism and Control of Whole-Body Electro-Hydrostatic Actuator Driven Humanoid Robot Hydra

Field robots are gaining attentions that they can perform the tasks where human cannot reach. Improvement on physical performance of robots is a fundamental issue. Backdrivability is a key mechanical feature of actuators that enables robust and stable interaction of robots with environment. We developed a humanoid robot HYDRA with backdrivable hydraulic actuators. Parallel mechanism is used extensively in multi-DOF joints to efficiently use actuator force. In this paper, mechanical structure of Hydra with backdrivability and mechanical strength is treated. Also, realtime control of hydraulic actuators that utilize backdrivability, and realtime control of robot joint systems with parallel kinematic chains are explained.

Development of high-power and backdrivable linear electro-hydrostatic actuator

Actuator with high power output and durability is a important factor in developing humanoid robots with high mobility. Development of such actuator with force sensitivity is a challenge. We developed linear electro-hydrostatic actuator (EHA) to realize high-power output, high durability, and backdrivability. This paper presents mechanical design of a linear EHA that reduces friction. Low friction piston seal was employed to significantly improve volumetric efficiency while keeping loss of backdrivability minimum. To test this device, a testing device with reaction mass is proposed. This device can be used to give external force to actuator under dynamic movement with high repeatability. Backdrivability, maximum cylinder force, and frequency response were evaluated to show the efficacy of the proposed actuator.

A method of single camera robocup humanoid robot localization using cooperation with walking control

The target of robocup soccer is to beat humans world cup champion by 2050. Many kinds of technologies must be studied and developed for this purpose. In case of humanoid soccer league, the required technology level becomes higher and higher in every year. Besides, situations become closer to the practical use of humanoid robots for house, office, nursing and so on. The ideology of robocup is realized with the rules of each league. That is, there are many limitations for robocup kid-size soccer humanoid, such as robot height, foot size, and restrictions on sensors. We think that the most challenging subject under these limitations is the harmony of cost, mobility and intelligence. Our robot thus consists of single camera and small computers. In other words, our robot must estimate its field location with a costless equipment. In this paper, a method with single camera robot localization is presented. The maximum field of view is limited to 180 degrees (in 2008.) The camera can catch 2 landmarks (corner pole and goal) in usual cases. The global position information of each landmark can be used, so that the robot can get its field location by triangular surveying. The robot localization informed by two object distances is not so accurate, because the object distance from local vision system includes significant noises. Also, humanoid is not so suitable for camera carrier due to the vibrations occurred on high speed walking in actual matches. As a result, the cooperation of localization with walking control must be needed. We proposed here a method using error vector between estimation and command. In this method, the robot location can be estimated within 40 cm in most cases, with very small calculation cost.