A practically applicable collision-free trajectory planning technique for two robot systems is proposed. The robot trajectories considered in this work are composed of many segments between which the robots stop to assemble, weld, or do other jobs by end-effector. The proposed method is based on the planning-coordination decomposition approach in which planning finds the trajectory of each robot independently according to their tasks and coordination finds velocity modification to avoid collision with each other. To fully utilize the convenience of independent trajectory planning and to ensure no geometrical path change after coordination, a simple technique avoiding collision by adding least delay-time in the local sense before moving along the next path-segment is developed. The least delay time is determined by a graphical method on the space called co-ordination space where collision between two robots and coordination of two robots are easily visualized.