Passively compliant underactuated mechanisms are one way to obtain the finger which could accommodate to any irregular shaped and sensitive grasping object. The purpose of the underactuation is to use the power of one actuator to drive the open and close motion of the gripper. The fully compliant mechanism has multiple degrees of freedom and can be considered as an underactuated mechanism. This paper presents design of the adaptive underactuated compliant multi-fingered gripper with distributed compliance. The optimal topology of the finger structure was obtained by an iterative optimization procedure. It was proven that for real robotic applications multi-fingered grippers with three or more fingers were more suitable for stable and safe grasping.Passiven nachgiebigen unteraktuierten Mechanismen bieten die Möglichkeit solche Robotergreifer zu entwerfen die anpassfähig an irgendeine unregelmäßig geformte und empfindliche Greifobjekt sind. Der Zweck der Unteraktuierung ist nur ein Aktor für die Greifer-öffnen/schließen-Funktionen zu benutzen. Völlig nachgiebige Mechanismus hat grosse Anzahl der Freiheitsgrade und man kann als unteraktuierte Mechanismus betrachtet werden. In diesem Beitrag wird ein adaptive unteraktuierte nachgiebige Multifinger-Greifer mit verteilten Nachgiebigkeit entworfen. Die optimale Topologie der Fingerstruktur wurde durch ein iteratives Optimisationverfahren bekommen. Es wurde bewährt dass für die realen Anwendungen der Multifinger-Greifer mit drei und mehr Fingern für stabile und sichere Greifen besser geeignet ist

Pavlović, Nenad D.

Petković, Dalibor

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Universitätsverlag Ilmenau, 2013 http://www.tu-ilmenau.de/universitaetsverlag/ Petković, Dalibor; Pavlović, Nenad D.: Compliant multi-fingered adaptive robotic gripper URN: urn:nbn:de:gbv:ilm1-2013100033-409-1 URL: http://nbn-resolving.de/urn:nbn:de:gbv:ilm1-2013100033-409-1 Erschienen in: 10. Kolloquium Getriebetechnik : Technische Universität Ilmenau, 11. - 13.September 2013. - Ilmenau : Univ.-Verl. Ilmenau, 2013. - S. 409-418. (Berichte der Ilmenauer Mechanismentechnik ; 2) ISSN: 2194-9476 ISBN: 978-3-86360-065-5 [Druckausgabe] URN: urn:nbn:de:gbv:ilm1-2013100033 URL: http://nbn-resolving.de/urn:nbn:de:gbv:ilm1-2013100033 COMPLIANT MULTI-FINGERED ADAPTIVE ROBOTIC GRIPPER Dalibor Petković*, Nenad D. Pavlović** *Faculty of Mechanical Engineering, Department of Mechatronics, Aleksandra Medvedeva 14, 18000 Niš, Serbia Telefon/E-Mail: dalibortc@gmail.com / 381643283048  ** Faculty of Mechanical Engineering, Department of Mechatronics, Aleksandra Medvedeva 14, 18000 Niš, Serbia Abstract Passively compliant underactuated mechanisms are one way to obtain the finger which could accommodate to any irregular shaped and sensitive grasping object. The purpose of the underactuation is to use the power of one actuator to drive the open and close motion of the gripper. The fully compliant mechanism has multiple degrees of freedom and can be considered as an underactuated mechanism. This paper presents design of the adaptive underactuated compliant multi-fingered gripper with distributed compliance. The optimal topology of the finger structure was obtained by an iterative optimization procedure. It was proven that for real robotic applications multi-fingered grippers with three or more fingers were more suitable for stable and safe grasping.  Passiven nachgiebigen unteraktuierten Mechanismen bieten die Möglichkeit solche Robotergreifer zu entwerfen die anpassfähig an irgendeine unregelmäßig geformte und empfindliche Greifobjekt sind. Der Zweck der Unteraktuierung ist nur ein Aktor für die Greifer-öffnen/schließen-Funktionen zu benutzen. Völlig nachgiebige Mechanismus hat grosse Anzahl der Freiheitsgrade und man kann als unteraktuierte Mechanismus betrachtet werden. In diesem Beitrag wird ein adaptive unteraktuierte nachgiebige Multifinger-Greifer mit verteilten Nachgiebigkeit entworfen. Die optimale Topologie der Fingerstruktur wurde durch ein iteratives Optimisation-verfahren bekommen. Es wurde bewährt dass für die realen Anwendungen _____________________________________________________________________10. Kolloquium Getriebetechnik – Ilmenau 2013 409der Multifinger-Greifer mit drei und mehr Fingern für stabile und sichere Greifen besser geeignet ist. 1 Introduction Multi-fingered robotic grippers offer great advantages compared with traditional tools mounted at the end of a robot arm. Like human hands they are capable of handling both parts and tools. With a minimum of three contact points they offer a greater stability and mobility of the grasp [1,2]. Dexterous, multi-fingered grippers have been the subject of considerable research [3,4,5], with the kinematics and force control issues being investigated in [6,7]. Significant efforts have been made to find gripper designs simple enough to be easily built and controlled, in order to obtain practical systems. To overcome the limited success of the early designs due to the cost of the control architecture a special emphasis has been placed on the reduction of the number of degrees of freedom, thereby decreasing the number of actuators [8,9]. The strategy for reducing the number of actuators while keeping the hand capability to adapt its shape to the grasped object is referred to as underactuation [10,11]. Papers [12,13] show that underactuation allows reproducing most of the grasping behaviors of the human hand, without augmenting the mechanical and control complexity.  A mechanism is said to be underactuated when it has fewer actuators than degrees of freedom. In order to achieve this goal, passive elastic elements are used. The transmission mechanism used to achieve such a property must be adaptive, i.e. when one or more fingers are blocked, the remaining finger(s) should continue to move. When all the fingers are blocked, the force should be well-distributed among the fingers and it should be possible to apply large grasping forces while maintaining a stable grasp.  Due to the multiple degrees of freedom of a single compliant joint, any compliant mechanism [14,15,16,17] can be considered as an underactuated mechanism. Finger compliance allows the gripper to passively conform to a wide range of objects while minimizing contact forces. Passive compliance offers additional benefits, particularly in impacts, where control loop delays may lead to poor control of contact forces. Compliance allows lower implementation costs by reducing the sensing and actuation required for the gripper.  The proposed design of the finger in this article is able to flex inwards and _____________________________________________________________________410 10. Kolloquium Getriebetechnik – Ilmenau 2013outwards while closing around the grasping object. It means the gripper can accommodate to convex and concave grasping shapes. The optimal topology structure of the finger is obtained by iterative FEM optimization procedure. The obtained finger structure is also verified by optimality criteria method [18,19,20,21]. In this article, design and analysis of a multi-fingered robotic gripper is presented too; the single-actuated two-, three- and four-fingered grippers are analyzed.  2 Finger structure topology Finger structure topology was obtained by FEM iterative optimization procedure [22,23]. The main target grasping curvatures were concave and convex grasping shape.            (a)       (b)                            (c)                        (d)                       (e) Fig. 1:  (a) Slider crank mechanism, (b) finger design domain, (c) optimized finger topology, (e) convex grasping shape and (d) concave grasping shape [22] Figure 1 shows the input mechanism principle for one finger. As it is shown in Figure 1(a) the basic input mechanism for the finger can be presented as an slider crank mechanism. Figure 1(b) shows the slider crank mechanism with addition of the finger design domain. Finally, Figure 1(c) shows the optimized structure of the compliant adaptive finger. Figure 1(d) and 1(e) show the finger accomodation to convex and concave grasping shape. _____________________________________________________________________10. Kolloquium Getriebetechnik – Ilmenau 2013 4113 Two-fingered gripper To investigate the behavior of the fully compliant underactuated adaptive finger, many FEM simulations of the different gripper designs with two fingers were performed. By the way, the two-fingered gripper design is not practicle for real grasping applications especially for cylindrical grasping objects (Figure 2).   Fig. 2:  Two-figered gripper desing The entire FEM analysis was performed in ABAQUS software with following parameters and characteristics: x grasping object as explicit discrete rigid element, x finite element type for grasping object R3D4: a 4-node 3-D bilinear rigid quadrilateral, 1mm size, x gripper material: ABS plastic (mass density 1250g/mm3, Young’s modulus: 2.3GPa, Poisson’s ratio: 0.37), x solid and homogeneous section for the gripper, x gripper as explicit 3D stress element, x finite element type for the gripper C3D8R: an 8-node linear brick, reduced integration, hourglass control, 1mm size. _____________________________________________________________________412 10. Kolloquium Getriebetechnik – Ilmenau 20134 Multi-fingered gripper Although two-fingered gripper structure can be useful for experimental analysis, for real grasping applications in robotics (especially for cylindrical grasping objects (Figure 2)) it is useful to model multi-fingered grippers with three or more fingers. Figure 3(a) shows the three-fingered gripper design principle. The fingers of the gripper are positioned 120 degrees relate to each other. Afterwards the four-fingered gripper was designed (Figure 3(b)). It can be noticed that the fingers of the gripper are positioned 90 degrees relate to each other.                                    (a)                                                           (b)                                   Fig. 3:  Multi-fingered gripper designs principles: (a) three-fingered and (b) four-fingered gripper Figure 4(a) shows three-fingered gripper accommodation to the cylindrical object (convex grasping shape). Figure 4(b) shows four-fingered gripper accommodation to the cylindrical grasping object. In both cases, single actuation principle was used. It means that with one actuator and without any control procedure the gripper should provide safe and fully accommodation to the object. This is the main advantage of the passive mechanisms with underactuation.  _____________________________________________________________________10. Kolloquium Getriebetechnik – Ilmenau 2013 413  (a)   (b) Fig. 4:  (a) Three-fingered and (b) four-fingered gripper design   _____________________________________________________________________414 10. Kolloquium Getriebetechnik – Ilmenau 2013Figure 5 shows four-fingered gripper behaviour for three different grasping objects: (a) cylindrical, (b) convex and (c) parallepopipedical grasping object. It can be noticed fully adaptation of the gripper in the all three cases.                          (a)                                            (b)                                        (c)                  Fig. 5:  Four-fingered gripper grasping of cylindrical object (a), concave object (b) and parallepopipedical object (c) 5 Conclusion The handling of irregular, unpredictably shaped and sensitive objects introduces demands on gripper flexibility and dexterity. Reaching the dexterity and adaptation capabilities require the control of a lot of actuators and sensors. The dexterity can also be obtained by underactuation, which consists in equipping the finger with fewer actuators than the number of degrees of freedom. The flexibility can be reached by introducing compliant mechanisms with distributed compliance, i.e. fully compliant mechanisms. The combination of the underactuation and the compliant mechanisms leads to a gripper with high adaptability and sensibility. Another characteristic of compliant underactuated grippers is the elasticity of the gripper structure which ensures a soft contact between the gripper and the grasped object, e.g. sensitive grasping. The main advantages of the compliant underactuated gripper are in its distributed compliance, simple manufacturing process, low cost and easy to adaptation to any irregular object.  The design and behavior of a novel multi-fingered compliant passive adaptive gripper was introduced. The adaptability of the proposed gripper in this article is passive and each finger of the gripper has many degrees of _____________________________________________________________________10. Kolloquium Getriebetechnik – Ilmenau 2013 415freedom. There are no sensors, or computers within this design to actively coordinate finger motion. Instead, the adaptive mechanism adaptive function relies on the physical contact force of the fingers with an object, to adjust the position of the fingers relative to each other. This allows simple design that can fit within a small space and is low in weight.  References [1] Dechev H, Cleghorn W.L, Naumann S. (2001), ''Multiple finger, passive adaptive grasp prosthetic hand'', Mechanism and Machine Theory 36, pp. 1157-1173. [2] Yang J, Pitarch E.P, Abdul-Malek K, Patrick A, Lindkvist L. (2004), ''A multi-fingered hand prosthesis'', Mechanism and Machine Theory 39, pp. 555-581. [3] Osswald D, Martin J, Burghart C, Mikut R, Worn H, Bretthauer G. (2004), ''Integrating a flexible anthropomorphic, robot hand into the control, system of a humanoid robot'', Robotics and Autonomous Systems 48, 2004, pp.213-221.  [4] Arimoto S. (2004), ''Intelligent control of multi-fingered hands'', Annual Reviews in Control 28, 2004, pp.75-85. [5] Panwar V, Kumar N, Sukavanam N, Borm J.-H. (2012), ''Adaptive neural controller for cooperative multiple robot manipulator system manipulating a single rigid object'', Applied Soft Computing 12, pp.216–227. [6] Kudoh S, Ogawara K, Ruchanurucks M, Ikeuchi K. (2009), ''Painting robot with multi-fingered hands and stereo vision'', Robotics and Autonomous Systems 57, pp.279-288. [7] Giachritsis C. D, Ferre M, Barrio J, Wing A. M. (2011), ''Unimanual and bimanual weight perception of virtual objects with a new multi-finger haptic interface'', Brain Research Bulletin 85, pp.271–275. [8] Boughdiri R, Nasser H, Bezine H, M’Sirdi N. K, Alimi A.M, Naamane A. (2012), ''Dynamic Modeling and Control of a Multi-Fingered Robot Hand for  Grasping Task'', Procedia Engineering 41, pp.923–931.  [9] Lehmann A, Mikut R, Osswald D. (2005), ''Low-Level Finger Coordination for Compliant Anthropomorphic Robot Grippers'', in _____________________________________________________________________416 10. Kolloquium Getriebetechnik – Ilmenau 2013Proceedings of the 44th IEEE Conference on Decision and Control, and the European Control Conference 2005, Seville, Spain, December 12-15, pp.8319-8324.  [10] Carrozza M.C, Suppo C, Sebastiani F, Massa B, Vecchi F, Lazzarini R, Cutkosky M.R, Dario P. (2004), ''The SPRING Hand: Development of a Self-Adaptive Prosthesis for Restoring Natural Grasping'', Autonomous Robots, 16, pp. 125- 141.  [11] Montambault S, Gosselin C.M. (2001), ''Analysis of Underactuated Mechanical Grippers'', Journal of Mechanical Design 123, 367-345.   [12] Birglen L. (2011), ''The kinematic preshaping of triggered self-adaptive linkage-driven robotic fingers'', Mechanical Science 2, pp. 41-49 [13] Daniel A, Barrett H, Vincent D, Mark R.C. (2011), ''Varying spring preloads to select grasp strategies in an adaptive hand'', in IEEE IROS 2011, San Francisco, September, pp. 1-6  [14] Lu, K.-J., Kota, S. (2003), ''Parametrization strategy for optimization of shape morphing compliant  mechanisms using load path representation'', in Proceedings of DETC’03 ASME 2003 Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Chicago, Illinois USA, pp. 693-702 [15] Lu, K.-J., Kota, S. (2005), ''An effective method of synthesizing compliant adaptive structures using load path representation'', J. of Intelligent Material Syst. And Struct. 16, pp. 307-317.  [16] Lu, K.-J., Kota, S. (2002), ''Compliant mechanism synthesis for shape-change applications:  preliminary results'', Smart Struct. And Materials. 4693, pp. 161-172.  [17] Lu, K.-J., Kota, S. (2003), ''Design of compliant mechanisms for morphing structural shapes'', J. of Intelligent Material and Struct. 14, pp. 379-391.  [18] Bendsoe M. P, Sigmund 0. (2003), ''Topology optimization, theory, methods and applications'', Springer-Verlag Berlin Heidelberg. [19] Sigmund 0. (2001), ''A 99 line topology optimization code written in matlab'', Struct. Multidisc. Optim. 21:12&127. _____________________________________________________________________10. Kolloquium Getriebetechnik – Ilmenau 2013 417[20] Sigmund 0. (1994), ''Design of material structures using topology optimization'', PhD thesis, Technical University of Denmark.  [21] Sigmund 0. (1997), ''On the design of compliant mechanisms using topology optimization'', Mech. Struct. Mach., 25, pp.495-526. [22] Petković, D, Issa, M, Pavlović, N.D, Zentner, L, Passively Adaptive Compliant Gripper, Mechanisms, Mechanical Transmissions and Robotics, Applied Mechanics and Materials, Vol. 162, 2012, Trans Tech Publications, ISBN 978-3-03785-395-5, 316-325. [23] Petković, D., Pavlović, N.D.: Development of a new type of passively adaptive compliant gripper, Industrial Robot, Volume 40, Issue 6, (2013). _____________________________________________________________________418 10. Kolloquium Getriebetechnik – Ilmenau 2013

Compliant multi-fingered adaptive robotic gripper

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Compliant multi-fingered adaptive robotic gripper

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