Japanese

Development of flexible actuator


1.Introduction

2.Prototype

　 2.1 fiscal 2010　　　　　2.2 fiscal 2009

3. Acknowledgment














1. Introduction

　 Recently, several researchers propose to use humanoids as simulator of human beings. For example, some bipedal humanoids have been developed for father understanding of walking, and some upper body humanoids have been developed for use in training of medical doctors. These humanoids are well designed to mimic human functions such as walking or reflex behavior. However, these humanoids consist of electrical motors which has different mechanical properties from human muscles. Humanoids for simulation of human functions should be consisted of muscle like actuators for deeper understanding. However, there are a few muscle like actuators and each of them has some limitations to implement into humanoids. Therefore the purpose of this study is to develop a new muscle like actuator for humanoids.

Fig.1 Background

2 Prototype

2.1 Prototype developed in 2010

2.1.1 Hardware of the actuator

　 We developed a muscle like actuator which consists of two modules: a force generator and a nonlinear viscoelastic module. The force generator generates contractile force like muscle fiber. The nonlinear viscoelastic module changes its viscoelasticity with increase of applied force. The details of a force generator and a nonlinear visoelastic modules are described below.

2.1.1.1 Force generator

We use a SMA(Shape Memory Alloy) wire for the force generator because its generative force is much higher than that of human muscle and response time for contraction is enough fast. However, contraction displacement is much smaller than that of human muscle. Therefore, we developed displacement amplification mechanism as shown in figure 5. This mechanism consists of the SMA wire and some pulleys. Half of the pulleys are set on a shaft, and the others are set on another shaft. These two shafts are set parallel. The SMA wire is put on these pulleys. Therefore, total length of the SMA is several times longer than the distance of two shafts.

MOVIE

Lifting load(130gf) MPEG 1.3 MB

2.1.1.2 Nonlinear viscoelastic module

Human muscle increases its viscoelasticity with increase of applied force. We then developed a nonlinear viscoelastic module to represent it. We designed a mechanical link with elastic polymer (SEPTON, Kyraray Co. Ltd) for this aim. Its muscle like property is verified through a experiment as shown below.

2.1.2 Development of controller

　 We developed controller with a neural network to accelerate response time and stability. Response to the step input after learning is shown in figure.9.

2.1.3 Application

We developed an application, arthorisis model of human, to demonstrate the performance of the muscle like actuator. Four muscle like actuators are implemented in it. It is flexible when none of the actuators is actuated while it is bended when only one of the actuators is actuated.

Fig.10 Arthrosis model

　

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Arthrosis model MPEG 1.0 MB

2.2 fiscal 2009

2.2.1 Hardware of flexible actuator

　 We developed a flexible actuator which consists of three modules: a force generator, a nonlinear viscoelastic module and a lock-release mechanism. These three modules are connected each other via flexible wire hence the actuator has much flexibility. The force generator generates contractile force like muscle fiber. The nonlinear viscoelastic module changes its viscoelasticity with increase of applied force. The lock-release mechanism is implemented to represent relaxation of muscle. The details of a force generator and a nonlinear visoelastic modules are described below.

Fig.11 Hardware（2009-2010）

2.2.1.1 Force generator

Its characteristics are shown below;

・High holding force

・Low sound noise

・Robustness for magnetic field

・Few effects on magnetic field

MOVIE

UltrasonicMotor MPEG 353 KB

Lifting load(50gf) MPEG 1.3 MB

Flexibility MPEG 1.3 MB

2.2.1.2 Nonlinear viscoelastic module

Human muscle increases its viscoelasticity with increase of applied force. We then developed a nonlinear viscoelastic module to represent it. We designed a mechanical link with elastic polymer (SEPTON, Kyraray Co. Ltd) for this aim. Its muscle like property is verified through a experiment as shown below.

2.2.2 Automatic exploration method

　 Motion of the ultrasonic actuator can be controlled by PWM power consumption. Its response has nonlinear characteristics to frequency of PWM. In addition, the optimal frequency for an actuator can be changed depending on the load. The load on the actuator can be changed according to the application. Therefore, an adaptive controller which automatically finds optimal frequency should be developed. We then developed an automatic parameter exploration algorithm using the Genetic Algorithm. It was also verified through an experiment. 　

Fig.14 Flowchart

2.2.3 Application

We developed a demonstration model to show advantage of our flexible actuators. As a first prototype, we developed a tongue model. Four flexible actuators and the automatic parameter exploration algorithm are implemented in it. As you can see in the movie, its motion is very human like.

Fig.15 Tongue model

　

MOVIE

Before tuning MPEG 1.0 MB

After tuning MPEG 1.2 MB

3. Acknowledgment

　 We would like to express our thanks to all co-researchers ,Kuraray Co, Ltd, DYDEN Corporation, Chukoh Chemical Industries, Ltd, and SolidWorks Japan K. K. for the 3D-CAD contribution, Furukawa Techno Material for the SMA contribution, Nikki Fron for the pulleys contribution.

			Nikki Fron Corporation
			Furukawa Techno Material Corporation
			SolidWorks Japan K. K.
			DYDEN Corporation
	Kuraray Co, Ltd		SEPTON
	Chukoh Chemical Industries, Ltd

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