The end-effector angle is defined as the angle between the end-effector axial axis and the hand axis (an axis from the wrist center to the end-effector reference point). Most industrial manipulators posses a zero end-effector angle. This paper shows that the dexterity of a manipulator, which is indexed by the volume of dexterous workspace, is affected by the end-effector angle. Three 6-d.o.f., anthropomorphic manipulators and three types of dexterous workspace are used to study this influence. The results show that, for all three manipulators, the volume of a dexterous workspace in general increases along with the end-effector angle and it reaches maximum value when the end-effector angle is 90 deg. This influence is very obvious with the reachably dexterous workspace and the 180 deg spinnably dexterous workspace and is less obvious with the 360 deg spinnably dexterous workspace. These results somewhat confirm the fact that the majority of human hand prehensions used in daily life operations apply a nonzero end-effector angle.

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