F3Hand

What it does

Problems of many five-fingered prostheses are its weight and flexible grasps. F3Hand is a five-fingered prosthetic hand that achieves lightweight and flexible grasps by using curved pneumatic artificial muscles as a skeleton and an actuator of the fingers.

Your inspiration

Many five-fingered electric prosthetic hands have been commercialized to support daily living of forearm amputees. Though they can grasp objects with electric actuators, they have some problems. A general five-fingered electric prosthetic hand including a socket is more than 900g because of many actuators and complicated mechanisms in the hand. The heavy prosthetic hand causes users to give up it. In addition, fingers with high rigidity are difficult to fit the object to be grasped. Therefore, we solve these problems by developing a prosthetic hand driven with curved pneumatic artificial muscles.

How it works

The F3Hand has five fingers arranged similarly to the human hand. Each finger has double joints that flex and extend with curved pneumatic artificial muscles. The artificial muscle has a structure in which a rubber tube is sandwiched between two types of cloth with different elasticity. When air is sent to the artificial muscle through the polyurethane tube, the artificial muscle bend to one side because of the characteristics of the high-elastic cloth and the low-elastic cloth. The drive unit includes a small CO2 cylinder, a regulator, and a solenoid valve. Pressing the control switch opens the solenoid valve and sends air to the artificial muscle. By using the curved pneumatic artificial muscles as a skeleton and an actuator of the finger, lightweight, flexible grasps, and natural motions were achieved.

Design process

First, we surveyed papers and products related to the five-fingered hand and interviewed users. As a result, we found the problem of them is weight and flexible grasp. After the survey, we ideated the prosthetic hand which uses curved pneumatic artificial muscles as a skeleton and an actuator of the fingers. Next, we have developed prototypes. Prototypes were made with a 3D CAD and a 3D printer. In a primary prototype, the joint of the finger did not follow the curved pneumatic artificial muscle. Therefore, in a second prototype, we made double joints of the finger and it allows the finger following the movement of the artificial muscle. In addition, we developed a two-DOF passive CM joint so that various grasping postures can be taken. As a result, the F3Hand achieved lightweight (255g) and flexible grasp. Finally, we conducted a user test with a forearm amputee. A forearm amputee performed a hand function test (SHAP) and the grasping test of daily objects. The results showed that the F3Hand can grasp various daily objects. We've been upgrading the F3Hand in order to further improve the grasping performance by the result of the test.

How it is different

A general five-fingered electric prosthetic hand is more than 900 g. The F3Hand achieved 255g by using a lightweight curved pneumatic artificial muscle as an actuator. The F3Hand achieved flexible grasps compared to conventional five-fingered electric prosthetic hands which have fingers with high rigidity. By making the artificial muscle part of the exterior, the hand realizes a stylish appearance without covering a cosmetic glove.

Future plans

In the future, users can control the F3Hand by an operating system based on a muscle-bulge sensor. Also, we want to make each finger move independently in order to take various grasping postures. We would like to commercialize the F3Hand.

Awards