The introduction of collaborative robots is expected as one of the solutions for the labor shortage. To implement the collaborative robot in an industrial line, real-time motion planning is necessary to determine a robot's trajectory in order to consider the moving workers. In this paper, we propose a real-time trajectory planning method for co-worker robot based on the RRT in configuration-time space. Motion planning in configuration-time space is effective to avoid moving obstacles while considering robot dynamics and target reach time. In order to consider the dynamics of a robot in a time augmented configuration space, it is necessary to smoothly connect the robot velocities. The proposed method set the velocity of the sampling points depending on the initial condition in configuration-time space. In the simulation, we found that the proposed method has a higher success rate than the method without considering the velocity of the sampling points. Experiments using PaDY that we have developed show the effectiveness of the proposed method in an environment with two moving workers.