The article describes the use of a modified ACO algorithm to optimize the trajectory of a planar 3RPR robot. The trajectories of the motion of agents of the first generation were obtained in accordance with the classical and modified algorithm. The efficiency of using the modified trajectory planning algorithm was demonstrated, which made it possible to reduce the length of the original trajectories and the time required to process them. At the same time, in order to save time, the trajectories of movement obtained during its operation can be subjected to discrete local optimization. The result of the work of the algorithms is a set of tasks reflecting the change in each of the input coordinates of the mechanism over time, which can be directly used during the operation of the robot control system. A detailed description of the algorithm and the results of mathematical modeling are presented.