Motion Planning of Mobile Manipulator for Navigation Including Door Traversal

Door traversal is an essential task for a mobile manipulator to achieve autonomous navigation in indoor environment. However, it remains challenging since it requires the coupled motion of the robot and door and is composed of several sub-problems such as approaching, opening, passing through, and closing the door. This letter proposes a planning framework that formulates these sub-problems as a single problem and computes a path for the mobile manipulator to navigate from the initial position, traverse through the door, and arrive at the target position. The proposed framework obtains the path of the whole-body configuration in two steps. First, the path for the pose of the mobile robot and the path for the door angle are computed by using the graph search algorithm. In graph search, an integer variable called area indicator is defined as an element of state, which indicates where the robot is located relative to the door. Especially, the area indicator expresses a process of door traversal. In the second step, the configuration of the manipulator is computed by the Inverse Kinematics (IK) solver from the path of the mobile robot and door angle. The proposed framework has a distinct advantage over the existing methods that manually determine several parameters such as which direction to approach the door and the angle of the door required for passage. The effectiveness of the proposed framework was validated through experiments with a mobile manipulator.

I. Introduction

Mobile manipulators have the extended workspace compared to fixed-base manipulators. In this respect, mobile manipulators can help people by performing various tasks such as delivery, household chores, etc. Since the chances of successfully executing such tasks depend on whether the target object is reachable or not, mobile manipulators need the ability to open and traverse doors which connect spaces. However, the problem of generating the motion of mobile manipulator is not simple because the mobile manipulator is a unified system and the door is an articulated object. This letter addresses the motion planning problem of traversing through the door and reaching the goal position for the mobile manipulator.