Controlling a Finger-arm Robot to Emulate the Motion of the Human Upper Limb by Regulating Finger Manipulability

The human upper limb possesses a high degree of freedom (DOF) and its redundant structure permits greater flexibility in various dexterous manipulations. The simplest structure of a multifingered robot arm is constructed by fixing a robot finger onto the end effector of a robot arm. A robot with such a structure is also called a macro-micro manipulator (Nagai & Yoshigawa, 1994, 1995; Yoshikawa, et al. 1993). Similar to the human upper limb, the fingerarm robot exhibits a high redundancy. The movement of the robots with such high redundancies creates the problem of how to determine the numerous DOFs of its joints. Controlling a robot with a high degree of redundancy is a fundamental problem in the field of robotics. A large number of studies have been published on the methodology for determining the redundant DOFs of a robot. Avoidance control of kinematics singularity (Nakamura & Hanafusa, 1986; Furusho & Usui 1989) and obstacle collision avoidance (Khatib, 1986; Maciejewski & Klein, 1985; Loeff & Soni, 1975; Guo & Hsia, 1993; Glass et. Al, 1995) by using redundant DOFs has been mostly investigated. In order to realize desired solutions for the above mentioned problems, methods involving null space (Vannoy & Xiao, 2004) and the criterion function (Kim & Kholsa, 1992; Ma & Nechev, 1995; Ma et al, 1996) have been typically applied. The finger-arm robot is unlike conventional redundant manipulators. The finger is usually lightweight and has a small link size as compared to the arm. Therefore, it is inappropriate to directly apply the methods developed for controlling a redundant manipulator to the finger-arm robot. To achieve the dexterity like the human hand-arm, a lightweight finger should be actively moved whereas the arm cooperate the movement of the finger, which will greatly improve the performance of a robot (Khatib, 1995; Melchiorri & Salisbury, 1995). The human hand-arm system exhibits similar features. The human hand is obviously lighter, smaller and more sensitive as compared to the arm. The hand-arm coordination is well organized by the central nervous system so as to generate a natural motion. The motivation of this study is to develop a control method emulating a natural movement similar to that of a human upper limb.