A Hybrid, Encompassing, Three-Fingered Robotic Gripper Combining Pneumatic Telescopic Mechanisms and Rigid Claws Lucas Gerez * , Che-Ming Chang * , and Minas Liarokapis Abstract— Unstructured and uncertain environments that are encountered in search and rescue applications require complex interactions that involve a wide range of grasps. These grasps are needed in order to handle unpredictable types of objects of various shapes, stiffnesses, and dimensions. Traditionally, the robotic end-effectors used in such situations are rigid and their operation requires sophisticated sensing elements and complicated control algorithms to manipulate delicate and fragile objects. Over the last decade, considerable research effort has been put into the development of adaptive, underactuated, and soft robots that facilitate robust interactions with dynamic environments. In this paper, we propose a three- fingered robotic gripper that combines pneumatic telescopic mechanisms and rigid claws. The gripper uses three large, rigid fingers to accomplish the execution of all the tasks required by a traditional robot gripper, while three inflatable, telescopic fingers provide soft interaction with objects. This synergistic combination of soft and rigid structures allows the gripper to cage / trap and firmly hold heavy and irregular objects. The experiments demonstrate that the gripper can successfully grasp a plethora of objects exerting up to 60 N of clench force. I. I NTRODUCTION Operations in dynamic and unstructured search and rescue environments require good grasping and manipulation capa- bilities that allow the robot to efficiently adapt to radically changing situations. In search and rescue robotic systems, end-effectors are traditionally designed as two fingered, rigid grippers or as simple, task-specific tools such as excavators. Such end-effectors can exert significant forces without sus- taining damage from interacting with the environment but they require sophisticated sensing and complicated control laws to perform more versatile object handling [1], especially when interacting with fragile or delicate objects. Recently, over the last decade, a plethora of robotic grippers and hands have been proposed employing compliant structures and underactuated designs in order to achieve efficient and stable grasps with simple and intuitive control. The addition of compliant elements into traditionally rigid robot hands allows for the successful execution of a variety of tasks under object pose uncertainties [2] and with a plethora of objects [3]. These design strategies increase the area of the contact patches between the object and the end-effectors, resulting to a balanced distribution of the grasping forces and enabling an efficient interaction with various soft, compliant objects [4], [5]. * These authors contributed equally to this work. Lucas Gerez, Che-Ming Chang, and Minas Liarokapis are with the New Dexterity research group, Department of Mechanical Engineering, The University of Auckland, New Zealand. E-mails: lger871@aucklanduni.ac.nz, ccha425@aucklanduni.ac.nz, minas.liarokapis@auckland.ac.nz Fig. 1. The proposed hybrid, encompassing, three-fingered robotic gripper which is equipped with telescopic, soft fingers and rigid claws is depicted in two different configurations: deflated (top) and inflated (bottom). In this paper, we propose a hybrid, encompassing, three- fingered robotic gripper that combines curved rigid fingers / claws with pneumatically actuated telescopic mechanisms. Such a design choice allows the gripper to employ: i) the rigid or the soft structures depending on the task speci- fications, or ii) both of them in a synergistic manner to handle heavy and highly irregular objects using caging grasps (Fig. 1). Grasping is robust without relying on sophisticated sensors or control schemes. Finally, although this gripper focuses on objects designed for the human hand, the design can be easily scaled up and down in order to be used with larger and smaller machinery and with multiple objects.