With the depletion of global energy resources，saving energy has become an important aspect in design of energy consuming equipment. Hence，this paper deals with the determination of the optimal trajectory which can minimize the dissipated energy in an articulated manipulator.
In a horizontally articulated manipulator without friction, the optimal trajectory is found out globally. It is proved that the dissipated energy is monotonously decreased against the operating time in case of zero non-linear-fnction，therefore the optimal operating time does not exist. Since a vertically articulated manipulator system is highly non-linear due to gravity and an analytical solution can not be found. Therefore，the system is first linearized around various equilibrium points and the existence of an optimal time is investigated theoretically. The theoretical results and smulations show that an optimal operating time exists when the first link of the manipulator traverses the stable equilibrium point and that it does not exist when the firstlink traverses the unstable equilibrium point. Finally，the optimal trajectory of the manipulator constrained by an obstacle is obtained.