Abstract: Bionic inspiration from human thumb and index finger was the drive to design a high-performance two-finger dexterous hand. The size of each phalanx and the motion range of each joint in the human thumb and index finger were summarized, and the features of three grasping patterns were described in detail. Subsequently, a two-finger dexterous bionic hand with 6 Degrees of Freedom (DoFs) was developed. Both the mechanical thumb and index finger were made up of three rigid phalanx links and three mechanical rotation joints. Some grasp-release tests validated that the bionic hand can perform three grasping patterns: power grasp, precision pinch and lateral pinch. The grasping success rates were high under the following cases:  (1) when power grasping was used to grasp a ring with external diameter 
20 mm – 140 mm, a cylinder with mass < 500 g, or objects with cylinder, sphere or ellipsoid shape; (2) when the precision pinch was used to grasp thin or small objects; (3) when the lateral pinch was used to grasp low length-to-width ratio of objects. The work provided a method for developing two-finger bionic hand with three grasping patterns, and further revealed the linkage between the difference in finger structure and size and the hand manipulation dexterity.

Key words: dexterous bionic hand, mechanical finger, power grasp, precision pinch, lateral pinch