A Mechanism for Moving and Rotating Fingers in Robotic Hand Minzhou Luo 1 , Giuseppe Carbone 2 , Marco Ceccarelli 2 , Tao Li 1 1 Institute of Intelligent Machines, Chinese Academy of Sciences, P.O.BOX 1130, Hefei, 230031, china 2 LARM Laboratory of Robotics and Mechatronics, DiMSAT-University of Cassino Via Di Biasio 43, 03043 Cassino (Fr), Italy e-mail: lmz@iim.ac.cn, carbone@unicas.it, ceccarelli@unicas.it Abstract- Many robotic hands have few configurations to achieve versatile grasp or the proper grasp force wrench, which is necessary for stable grasp. In this paper, design considerations are reported for improving the grasping capabilities of a low-cost easy-operation three-finger robotic hand. A special planetary gear mechanism has been designed for adjusting the position and orientation of the two fingers in robotics hand. This novel solution significantly improves the flexibility of a robotic hand in terms of sizes and shapes of objects that can be grasped. Furthermore, both pinching and enveloping grasp configurations can be achieved similarly to human hands. Simulations are performed in Adams environment to show the effectiveness of the proposed mechanism design in terms of both kinematic and dynamic performance. I. INTRODUCTION There has been a growing interest in multi-fingered robotic hands. Several researchers have investigated different types of devices for achieving the grasping and handling of objects. Mechanical grippers having more than two fingers are widely used in practical applications, [1, 2]. However, multi-fingered robotic devices and hands have been also widely investigated, as reported for example in [3, 4]. This type of devices tries to mimic the performances of human hands in order to have high flexibility multi-purpose operation. Nevertheless, most of the available multi-fingered prototypes have a high number of degrees of freedom, a complex control and a high cost. Moreover, they are still not able to fully reproduce all grasping capabilities of a human hand. In this paper, attention is addressed to improve the grasping capabilities of a low-cost and easy-operation three-finger robotic hand by means of a novel mechanism. In particular, this mechanism can adjust position and orientation of two fingers in robotic hand. Thus, it can provide much more human-like behaviors, since both pinching and enveloping grasp configurations can be achieved. Simulations are performed in Adams environment to show the effectiveness of the proposed mechanism design. II. ATTACHED PROBLEM A. Grasp Modes of Human Hands Human hands can achieve different grasp modes and configurations because of the flexibility of fingers and palm. Grasp taxonomy of human hand has been given for example in [5], which provides a classification according to the degree of precision of the task and geometrical characteristics of the objects. Usually, there are two main kinds of grasp modes: pinching grasp and enveloping grasp as shown in figure 1. Thin objects commonly require dexterous operations. Thus, they should be grasped with pinching grasp mode. Voluminous or massive objects need to resist wrenches in any direction, so they should be grasped with enveloping mode. a) b) c) d) e) f) g) h) Figure.1 A grasp taxonomy of human hand: a) pinching grasp; b) grasp a pen; c) grasp a sphere; d) grasp circle; e) Enveloping grasp; f) grasp a spanner; g) grasp a sphere; h)grasp a book