欠驱动指爪机构具有抓取不同目标物的自适应性，可满足操作任务的多样化需求。其欠驱动特性使得被动弹性元件的参数对抓取性能的稳定性和自适应能力有很大影响。若弹簧刚度选择过小，欠驱动指爪的稳定性会降低；若弹簧刚度选择过大，指爪的自适应能力会下降。因此，本文基于抓取状态平面法，对欠驱动指爪的被动弹性元件参数进行优化设计。首先，在欠驱动指爪静力学分析的基础上，建立弹簧刚度与驱动力的平衡方程。然后，通过对不同抓取模式拓扑转换的定量分析，获得欠驱动指爪与目标物之间不同的接触状态；同时为了保证稳定抓取，考虑了不同抓取模式下指爪弹性元件刚度与驱动力矩的参数匹配关系。在此基础上，基于抓取状态平面法建立被动弹性元件刚度与机构稳定区域关系的解析表达，并基于稳定区域面积最大化的思想，进行弹簧刚度的最优设计。最后，基于不同的抓取状态模型对弹簧刚度进行了优化设计，为后续欠驱动指爪机构设计和控制应用奠定理论和技术基础。
The underactuated gripper is adaptive to different objects, and is expected to satisfy diverse operation tasks. Its underactuated characteristic determines that the design of passive elastic elements has a great impact on stability and adaptability of the gripper. If the spring becomes compliant, stability of the underactuated gripper will be reduced. On the other hand, if the spring becomes too stiff, adaptability of the gripper will decrease. This paper proposes a metric to design the spring stiffness for the underactuated gripper based on the grasp-state plane method. The equation for the equilibrium between spring stiffness and the driving force is established based on statics analysis. Through the transition between various grasp types, the different contact states between the underactuated finger and the object are obtained, and the matching relationship between the spring stiffness and the driving torque is considered to ensure the stable grab of different grasp types. A stable region is defined based on the grasp-state plane method, and spring stiffness is chosen by maximizing the area of the stable region. Several grasp models are given to demonstrate the effectiveness of the proposed method, providing foundation for the design and control of the underactuated gripper in future study.
[1] DOLLAR A M. Analyzing dexterous hands using a parallel robots framework[J]. Autonomous Robots, 2014, 36(1-2):169-180.[2] MASON M T, RODRIGUEZ A, SRINIVASA S S, et al. Autonomous manipulation with a general-purpose simple hand[J]. International Journal of Robotics Research, 2012, 31(31):688-703.[3] CARROZZA M C, SUPPO C, SEBASTIANI F, et al. The SPRING hand:development of a self-adaptive prosthesis for restoring natural grasping[J]. Autonomous Robots, 2004, 16:125-141.[4] WU L C, CARBONE G, CECCARELLI M. A numerical simulation for design and operation of an underactuated finger mechanism for LARM hand[J]. Mechanics Based Design of Structures and Machines, 2009, 37(1):86-112.[5] CABAS R, CABAS L M, BALAGUER C. Optimized design of the underactuated robotic hand[C]//2006 IEEE International Conference on Robotics and Automation. Piscataway, NJ:IEEE Press, 2006:982-987.[6] WU L C, CARBONE G, CECCARELLI M. Designing an underactuated mechanism for a 1 active DOF finger operation[J]. Mechanism & Machine Theory, 2009, 44(2):336-348.[7] ZHANG W, CHEN Q, SUN Z, et al. Passive adaptive grasp multi-fingered humanoid robot hand with high under-actuated function[C]//2004 IEEE International Conference on Robotics and Automation. Piscataway, NJ:IEEE Press, 2004:2216-2221.[8] ODHNER L U, JENTOFT L P, CLAFFEE M R, et al. A compliant, underactuated hand for robust manipulation[J]. International Journal of Robotics Research, 2014, 33(5):736-752.[9] AUKES D M, HEYNEMAN B, ULMEN J, et al. Design and testing of a selectively compliant underactuated hand[J]. International Journal of Robotics Research, 2014, 33(5):721-735.[10] ODHNER L U, DOLLAR A M. Stable, open-loop precision manipulation with underactuated hands[J]. International Journal of Robotics Research, 2015, 34(11):1347-1360.[11] KRAGTEN G A, HELM F C T V D, HERDER J L. A planar geometric design approach for a large grasp range in underactuated hands[J]. Mechanism & Machine Theory, 2011, 46(8):1121-1136.[12] PRATTICHIZZO D, MALVEZZI M, GABICCINI M, et al. On the manipulability ellipsoids of underactuated robotic hands with compliance[J]. Robotics & Autonomous Systems, 2012, 60(3):337-346.[13] DOLLA A M, HOWE R D. The highly adaptive SDM hand:Design and performance evaluation[J]. International Journal of Robotics Research, 2010, 29(5):585-597.[14] BIRGLEN L, LALIBERTE T, GOSSELIN C. Underactuated robotic hands[J]. Berlin:Springer Berlin, 2008:40.[15] KRUT S, BEGOC V, PIERROT F, et al. Extension of the form-closure property to underactuated hands[J]. IEEE Transactions on Robotics, 2010, 26(5):853-866.[16] 楚中毅, 周苗, 胡健, 等. 主被动复合驱动自适应指爪机构的抓取模式分析[J]. 航空学报, 2014, 35(12):3451-3458. CHU Z Y, ZHOU M,HU J, et al. Gripping mode analysis of an active-passive composited driving self-adaptive gripper mechanism[J]. Acta Aeronautica et Astronautica Sinica, 2014, 35(12):3451-3458(in Chinese).[17] JUNG G P, KOH J S, CHO K J. Underactuated adaptive gripper using flexural buckling[J]. IEEE Transactions on Robotics, 2013, 29(6):1396-1407.[18] ODHNER L U, DOLLAR A M. Dexterous manipulation with underactuated elastic hands[C]//2011 IEEE International Conference on Robotics and Automation. Piscataway, NJ:IEEE Press, 2011:5254-5260.[19] 刘菲, 何广平, 陆震. 弹性欠驱动四指灵巧手设计与试验[J]. 机械工程学报, 2014, 50(15):53-59. LIU F, HE G P, LU Z. Research anddesign of a novel tendon driven underactuated multi-fingered hand[J]. Journal of Mechanical Engineering, 2014,50(15):53-59(in Chinese).[20] KO H K, CHO C H, KWON H C, et al. Design of an underactuated robot hand based on displacement-force conversion mechanism[J]. International Journal of Precision Engineering and Manufacturing, 2012, 13(4):509-516.
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