In this paper, we propose and develop an electro-conjugate fluid (ECF) finger with bidirectional motion and its application to a flexible hand. The finger is composed of a finger tube (5 mm in diameter) and a unit of ECF jet generators (5 × 7 × 8 mm3). The ECF is a kind of functional and dielectric fluid. Its jet flow is generated between two electrodes surrounded by the ECF under the high DC voltage. The ECF jet generator can be utilized as a hydraulic pressure source for the flexible finger tube and embedded in the finger. The flexible finger tube consists of two silicone rubber chambers whose cross-section is the shape of semi-circle along its axis. In the unit, there are two ECF jet generators, each of which has two pairs of needle-ring electrodes in parallel and which are connected to each other through the common line and placed to the opposite direction for the bidirectional motion of the ECF finger. One chamber of the finger expands due to the inner pressure generated by the ECF jet and the other one as an ECF container shrinks, causing the ECF finger to bend. The suitable parameters of the flexible finger tube are obtained by optimizing the cross-sectional shapes, the thickness of the partition and the fiber interval of the finger tube. Besides, the characteristics of the ECF finger including the displacement and self-generating force are investigated by experiments. The experimental results indicate that the proposed ECF finger can realize bidirectional motions with 9.2 mm in left-displacement and 6.4 mm in right-displacement and generate the maximum force: 6.6 mN. The final application of the ECF finger to a flexible hand also clearly shows the fingers are capable of grasping and releasing the object.
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