For new robot applications, as medical robots, safety has became a major concern. The human sharing the working area with the robot led to integrate the field of human factors in the development. Hence, the human component has to be integrated in the early steps of the development process. Regards to the complexity of today's robotic application, and to the requirements of a teamwork, we choose UML as the language. This paper focuses on the UML modeling contribution to the human factors analysis of a medical robot. A first section presents the function allocation and task analysis step, and a second section deals with human error. Each section is illustrated by a case study of a system for robotic tele-echography (ultrasound scan examination).