The length of the bars is regarded as the restrict condition to obtain the unconstrained optimization model for rigid-body guidance approximate kinematc synthesis of hinged 4-bar linkages and this optimal problem is solved by means of the particle swarm optimization （PSO） algorithm. All approximate solutions of the mechanism is difficultly obtained

using directly the PSO algorithm to solve this problem in its whole space of solutions. Aimed at this weakness

the improved PSO algorithm

the Escape PSO Based on the interval search （EPSObIS）

is presented to make the optimal problem for rigid-body guidance synthesis of hinged 4-bar linkages. Numerical examples show that the EPSObIS can solve to hinged 4-bar linkages to satisfy approximately the requirement of rigid-body guidancing.