A Criteria-Based Approach to Grasp Synthesis

This study introduces a criteria-based methodology for grasp synthesis. The method allows using multiple performance criteria both at the finger and the hand levels, which are used to generate a preliminary grasp and an optimum grasp, respectively. The approach offers reduced complexity by decomposing grasp synthesis into manageable phases. A case study using a physical hand demonstrates the effectiveness of the method. 1.0 Introduction Grasp synthesis can be defined as constructing a set of contact locations and a corresponding hand configuration for a given set of task attributes associated with a target object. Grasp synthesis, also known as grasp planning, has enjoyed the attention of researchers. The approaches to grasp planning can be classified as empirical and analytical depending on the procedure used to construct a target grasp. The viability of these approaches has been tested in a number of cases with the physical hands designed and popularized in grasp research [11],[14]. Figure 1 NASA-JSC Robonaut Hand Recently, NASA-JSC designed a robotic hand to be used as the end-effector of the Robonaut, a dual arm robot to be used in space station extra-vehicular activities. The Robonaut Hand [13] is a 12-degrees of freedom (dof), five-fingered, anthropomorphic grasping device based on the 95th percentile man's hand. The Robonaut Hand design includes a forearm, wrist with pitch and yaw capability, palm, palm dof, two primary fingers, two secondary fingers and a thumb finger (See Figure 1). Robotics Research Group (RRG) at UT Austin was asked to study the grasp synthesis problem for the NASA-JSC hand. This paper presents the approach developed and applied for the grasp synthesis problem of the NASA-JSC hand. In Section 2, the common definitions used in grasp synthesis are introduced and the previous studies in grasp planning are surveyed with an emphasis on analytical approaches. In Section 3, the approach to the grasp synthesis problem is explained. Although the approach presented was applied only to the NASA-JSC hand, it is general and should apply to any arbitrary dof robotic hand. In Section 4, a case study is introduced and the results are discussed. Section 5 contains the summary and conclusions for future work. 2.0 Preliminaries The study of grasps can be categorized into two broad groups. Empirical approaches mimic human grasping by using heuristics to select one of a set of standard hand shapes that best conforms to task requirements and the target object geometry [4][8][12]. Analytical approaches, on the other hand, determine the contact locations on the object and the hand configuration that satisfy task requirements through kinematic and dynamic formulations. The method discussed in this paper is an analytical approach and the remainder of this section reviews analytical approaches to grasping. 2.1 Definitions This section introduces various definitions used in the rest of the paper. Most of these definitions can 1 National Aeronautics and Space Administration – Johnson Space Center