A comprehensive grasp taxonomy Thomas Feix and Roland Pawlik Otto Bock Healtcare Gmbh 1070 Vienna, Austria Email: thomas.feix@ottobock.com roland.pawlik@ottobock.com Heinz-Bodo Schmiedmayer Vienna University of Technology Inst. for Mechanics and Mechatronics 1040 Vienna, Austria Email: hschmied@mail.tuwien.ac.at Javier Romero and Danica Kragi´ c Comp. Vision and Active Perception Lab Centre for Autonomous Systems School of Comp. Science and Communication KTH, SE-100 44 Stockholm, Sweden Email: jrgn,dani@kth.se Abstract—The goal of this work is to overview and summarize the grasping taxonomies reported in the literature. Our long term goal is to understand how to reduce mechanical complexity of anthropomorphic hands and still preserve their dexterity. On the basis of a literature survey, 33 different grasp types are taken into account. They were then arranged in a hierarchical manner, resulting in 17 grasp types. I. I NTRODUCTION The design of an anthropomorphic hand is always a compro- mise between hand complexity and the tasks it is supposed to accomplish. In general, sophisticated hands with many degrees of freedom are dexterous but pose significant requirements in terms of control. Many of the reported taxonomies have been made with the goal of understanding what types of grasps humans commonly use in everyday tasks and use this as an inspiration for designing robotic and prosthetic hands. The goal of our research is in the same direction: understanding how to minimize the complexity and maximize the dexterity of a mechanical hand. Since there is little consensus in the existing literature on the grasp types humans use, the first step was to review the existing literature. The goal was to find the maximal number of grasp types, which will act as basis for further research. II. METHOD A. Definition of a grasp Since grasping in humans is a very broad area, it was necessary to find a definition of a grasp relevant to our work. We thus propose the following: “A grasp is every static hand posture with which an object can be held securely with one hand.” The definition also implies that the grasp stability has to be guaranteed irrespective of the relative force direction between hand and object. Therefore, intrinsic movements are excluded because the object is not in a constant relationship to the hand. Bimanual tasks are not relevant because they use both hands. Gravity dependent grasps are ruled out, because the hand orientation is vital to the grasp stability. If one turns the hand, the object may fall down, which shows that it is not independent of the force direction. Thus grasps being excluded are the Hook Grasp and the Flat Hand Grasp. B. Comparison of Taxonomies To develop the comprehensive taxonomy, several literature sources were compared. They range from the field of robotics, developmental medicine, occupational therapy to biomechan- ics [1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14]. An excerpt of the comparison table is shown in Fig. 1. Columns store equal grasps, whereas rows store all grasps defined by an author. Grasps that are defined by the author as power, precision or intermediate, are marked with a color code. Yellow is denoting a power grasp, green a precision grasp and yellow/green an intermediate grasp as defined in [15],[16],[17]. Red is marking grasps that are not conforming to our definition of a grasp. п´³ п´³ п´³ п´³ п´³ п¼ п¼ п¼ п¼ п´ ÊÚïæ Ð ÊÚïæ Ð ÊÚïæ Ð ÊÚïæ Ð ÊÚïæ Ð ÊÚïæ ï ÊÚïæ ï ÊÚïæ ï ÊÚïæ ï ÊÚï ÊÚîæ îóë ÊÚîæ îóë ÊÚîæ îóë ÊÚîæ îóë ÊÚîæ îóë ÊÚîæ îóë ÊÚîæ îóì ÊÚîæ îóí ÊÚîæ î ÊÚî ÊÚíæ ÊÚíæ ÊÚíæ ÊÚíæ ï ÊÚíæ øï÷ ÊÚíæ ÊÚíæ ÊÚíæ ÊÚíæ ÊÚí Ò¿³» Ô¿®¹» Ü·¿³»¬»® ͳ¿´´ Ü·¿³»¬»® Ó»¼·«³ É®¿° ß¼¼«½¬»¼ ̸«³¾ Ô·¹¸¬ ̱±´ Ю· ³¿¬·½ ì Ú·²¹»® Ю· ³¿¬·½ í Ú·²¹»® Ю· ³¿¬·½ î Ú·²¹»® п´³¿® з²½¸ Ð Ù®¿ ° Ò«³¾»® ï î í ì ë ê é è ç Ѭ¬± Þ±½µ ̸±³¿ Ú»·¨ ðëòïîòîððè Ù®¿ ° Ò«³¾»® ï î í ì ë ê é è ç Û²¬®·» ïð í ê î î ì ì î ïî Ô¿®¹» Ü·¿³»¬»® ͳ¿´´ Ü·¿³»¬»® Ó»¼·«³ É®¿° ß¼¼«½¬»¼ ̸«³¾ Ô·¹¸¬ ̱±´ ̸«³¾óì Ú·²¹»® ̸«³¾óí Ú·²¹»® ̸«³¾óî Ú·²¹»® ̸«³¾óײ¼»¨ Ú·²¹»® Ý«¬µ± µ§ ïçèê ïçèç ͬ¿²¼¿®¼ ̧°» п®¿´´»´ Ó·´¼ Ú´»¨·±² Ù®·° Ì·° Ю»¸»² ·±² Õ¿³¿µ«®¿ ïçè𠦧´·²¼®· ½¸» Ù»¹»² ¬<²¼» ¦§´·²¼®· ½¸» Ù»¹»² ¬<²¼» þ̸«³¾ í Ú·²¹»®þ Ú·²¹»®¾»»®»²¹®·ºº Fig. 1. The sheet used for comparison of different grasp taxonomies. This is just a small excerpt of the whole sheet, the complete table can be downloaded via the Human Grasping Database, [18]. III. RESULTS A. The Taxonomy In total, we have found 147 grasp examples in the consid- ered literature sources. Out of those 147 examples, we have detected only 45 different grasp types. A further classification based on our grasp definition has revealed only 33 valid grasp types. The grasps were then arranged in a taxonomy depicted in Fig. 2. The classification in the columns is done by the power/precision requirements. The next finer differentiation is done, depending on whether the opposition type is Palm, Pad or Side Opposition. The opposition type is also defining the