This paper presents a real-time collision avoidance method with simultaneous control of both translational and rotational motion with consideration of a robot width for an autonomous omni-directional mobile robot. In the method, to take into consideration the robot's size, a wide robot is regarded as a capsule-shaped case not a circle. With the proposed method, the wide robot can decide the direction of translational motion to avoid obstacles safely. In addition, the robot can decide the direction of the rotational motion in real time according to the situation to perform smooth motion. As an example of design method of the proposed method, novel control method based on the fuzzy potential method is proposed. To verify its effectiveness, several experiments using a real robot are carried out.