A Multifunctional Hybrid Hip Joint for Improved Adaptability in Miniature Climbing Robots Satya P. Krosuri and Mark A. Minor Department of Mechanical Engineering University of Utah Salt Lake City, UT 84112, U.S.A Email: minor@mech.utah.edu Abstract - The subject of this paper is a hybrid hip biped climbing robot. The hybrid hip provides both prismatic and revolute motion, discretely, to the robot, using a single actuator. This is intended to improve its adaptability in confined environments and its capability to maneuver over and around obstacles. Optimization of the hybrid hip relative to robot size, weight, and actuation limits is considered while maximizing range of motion. The mechanical structure of the robot is discussed, as well as forward and inverse kinematics for motion planning. Workspace analysis indicates that the hip provides an appreciable improvement in foot placement capability when compared to a purely prismatic or revolute hip movement. 1. INTRODUCTION The subject of this paper is a new type of kinematic structure for climbing robots based upon a hybrid hip joint capable of performing multiple functions with a single actuator. Namely, the hip of the biped can operate as either a prismatic joint or revolute joint, discretely, depending on joint position, Figure 1. As each of these types of joints has its own specialization, the intended purpose of the hybrid joint is to provide increased adaptability and functionality by allowing both of these types of motion. Similar to a prismatic joint, the robot should operate well in confined environments, and similar to the revolute joint the robot should perform well while crossing between surfaces with a wide range of relative inclinations. The subject of this paper is the optimal design, kinematics, and resulting workspace of a hybrid hip climbing robot. In Section 2, we examine existing climbing robots in the literature and compare the hybrid hip to several of the most similar systems. The mechanical design of the hybrid hip robot is explained in Section 3, and its optimization is considered in Section 4 with a special emphasis on range of motion, force minimization, and small robot size. Section 5 describes the kinematics of this unique structure and Section 6 studies the resulting workspace of the system while in each of the discrete hybrid modes and examines the cumulative affect of the joint. Concluding remarks and future work are presented in Section 7. 2. BACKGROUND Most climbing robots in the literature are intended for maintenance or inspection in environments such as the exterior of buildings, storage tanks, nuclear facilities, or surveillance and reconnaissance within buildings [1], [2]. Thus, numerous wall-climbing robots have been developed for these purposes. Most of the climbing robots in literature are large and are intended for maintenance and inspection purposes. Legged structures with two to eight limbs are predominant. Typically, more than two legs provide redundant support and often increase load capacity and safety. However, these benefits are achieved at the cost of increased complexity, size, and weight. For small robots, however, limited ability to grasp the climbing surface restricts the system to be much more lightweight. In the case of miniature climbing robots, size is limited by the capability of the foot, which for suction is typically in the range of 590gr 80mm from the surface and 365 grams 120 mm from the surface for a 45mm Figure 1. Hybrid hip motion. Proceedings of the 2003 IEEE International Conference on Robotics & Automation Taipei, Taiwan, September 14-19, 2003 0-7803-7736-2/03/$17.00 ©2003 IEEE 312