The design of modern mechanical hands requires a choice for the kinematic structure of the finger. The typical finger is a planar manipulator with one, two, or three independently controllable joints. Each controllable joint requires a motor and sensor system which increases the weight of the hand. There is a desire to minimize the number of degrees of freedom in a mechanical hand because the payload capacity of a manipulator is limited. Two degrees of freedom provides the required positioning capability of a finger tip (though not the ability to control contact angle). Three joints are required to provide the ability to enclose grasped objects. This paper considers the design of fingers which are planar manipulators with three joints but only two degrees of freedom. In addition to the fully coupled design, twelve classes of finger designs with varying degrees of de-coupling are presented. It happens that one of these classes includes the human finger, a mechanical model of which is presented in detail.

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