Autonomous mobile robot increasingly expands its functionality into various applications where the long-term autonomous capability is necessary. These applications, warehouse service, building inspection, exploration of unknown terrains and military reconnaissance, require the mobile robot to correspond with the command of remote operators or environments. To meet this requirement, automatic recharging station can be used for a robot not to be taken offline. However, the range of docking error is wide by various homing algorithms and kinds of sensors. This paper describes a new docking mechanism developed to compensate entry error of robot in homing and to maintain robust state in the process of recharging battery without actuators and sensors. The proposed mechanism is self-adjustable to position and orientation of robot and reconfigures its states by driving force of mobile robot without any active energy elements. The geometric parameters are determined to avoid mechanical interference in docking procedure and specifications of springs are obtained from optimization which maximizes the grip force with constraint induced at each docking process. The docking mechanism can compensate for ±5cm lateral offset error and ±30° orientation error of mobile robot and holds it over 20N load after docking is finished.