The rapid expansion in the industrial revolution has been aroused to utilize of the robot arm in various high accuracy and productivity applications. For guiding the robot arm accurately, the path planning has been upgraded to optimize the robot arm movement. In this paper, 2-DOF robot navigation is analyzed and the free Cartesian spaces are constructed for detecting the free space that guarantee a collision-free path planning accordingly. The modified Ant Colony Optimization algorithm is proposed to obtain the optimal path planning that fulfils the aims of motion. The essential function of modified ACO algorithm is to generate an optimal path depending on the exact distance of D* algorithm. Fifth-order polynomial equations is applied to generate a smooth trajectory from initial to goal configurations. The observed detailed results of proposed implementation demonstrates the accuracy and efficiency of proposed method performance in achieving the optimal path and trajectory.