The MCP joint has two DOFs, abduction/adduction and
flexion/extension. The range of motion (ROM) of
abduction/adduction for an average adult is up to 45 deg, and
the ROM of flexion/extension is about 90 deg [12]. The
actuation for the abduction/adduction can be archived by a
pair of spur gear sets, in which the axis of the output gear
coincides with the axis of abduction/adduction of the MCP
joint. However, the same choice is not suitable for the
flexion/extension motion. Since the MCP joints of the four
fingers are separated from each other with the skin cleft, no
external components can be inserted in between. A logical
choice is to place the actuation mechanism on the back of
the hand and on top of MCP joint. To deliver the force fromhe actuator to the joint, an articulated mechanism can be
used. For safety reasons, only orthogonal force should be
applied to the phalanx without having the phalanx pulling
away from the joint. Among different articulated
mechanisms with one DOF, the Revolute-PrismaticRevolute-Prismatic (RPRP) configuration meets such
requirement. Therefore, it has been implemented in the
design. Fig 3 shows the side view of the MCP module.