Abstract：Based on the principle of Rong-Cha, a novel control method is proposed, which can work effectively within a certain range without precise perception. The working principle of how to use the same control input to achieve different grasping tasks by the Rong-Cha based grasping method is analyzed. Based on this principle, the grasping method can cope with a large class of grasping tasks without knowing the specific parameters of the objects, only the boundary conditions of this large class of objects are needed to know. The applicability of the Rong-Cha based grasping method to underactuated grippers is analyzed, and limitations of underactuated grippers are unveiled. The experiments show that by the Rong-Cha based grasping method and with the unchanged control inputs, the soft gripper can grasp the soft tofu without damage within the width range of 5～ 45 mm, and can successfully grasp the rigid cuboid within the width range of 5～ 60 mm. The spring-jointed underactuated gripper can grasp soft tofu within the width range of 20～ 40 mm without damage, and can successfully grasp the hard cuboid within the width range of 5～ 60 mm. The results demonstrate the versatility of the Rong-Cha based grasping method and the limitations of the underactuated gripper in grasping soft objects. Finally, it is shown that the soft gripper uses the Rong-Cha based grasping method to successfully grasp objects of different shapes and materials with a simple control strategy in a desktop grasping application. This fully demonstrates that the Rong-Cha based grasping method doesn't rely on the accurate object perception and the corresponding object model, and can simplify the control strategy.
 Liarokapis M, Dollar A M. Learning the post-contact reconfiguration of the hand object system for adaptive grasping mechanisms[C]//IEEE/RSJ International Conference on Intelligent Robots and Systems. Piscataway USA: IEEE, 2017: 293-299.  Laschi C, Mazzolai B, Mattoli V, et al. Design of a biomimetic robotic octopus arm[J]. Bioinspiration & Biomimetics, 2009,4(1). DOI: 10.1088/1748-3182/4/1/015006.  Hao Y F, Wang T M, Ren Z Y, et al. Modeling and experiments of a soft robotic gripper in amphibious environments[J]. International Journal of Advanced Robotic Systems, 2017, 14(3). DOI: 10.1177/1729881417707148.  Yang Y, Chen Y H, Li Y T, et al. Novel variable-stiffness robotic fingers with built-in position feedback[J]. Soft Robotics, 2017, 4(4): 338-352.  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(4): 736-752.  Deimel R, Brock O. A novel type of compliant and underactuated robotic hand for dexterous grasping[J]. International Journal of Robotics Research, 2016, 35(1-3): 161-185.  Krahn J M, Fabbro F, Menon C. A soft-touch gripper for grasping delicate objects[J]. IEEE/ASME Transactions on Mechatronics, 2017, 22(3): 1276-1286.  Craig J. Introduction to robotics: Mechanics and control[M]. 4th ed. New York, USA: Pearson, 2017.  Odhner L U, Dollar A M. The smooth curvature flexure model: An accurate, low-dimensional approach for robot analysis[C]// Robotics: Science and Systems VI. Cambridge, USA: MIT, 2010. DOI: 10.15607/RSS.2010.VI.018.  Odhner L U, Dollar A M. The smooth curvature model: An efficient representation of Euler-Bernoulli flexures as robot joints [J]. IEEE Transactions on Robotics, 2012, 28(4): 761-772.  Webster III R J, Jones B A. Design and kinematic modeling of constant curvature continuum robots: A review[J]. International Journal of Robotics Research, 2010, 29(13): 1661-1683.  Ciocarlie M, Allen P. A constrained optimization framework for compliant underactuated grasping[J]. Mechanical Sciences, 2011, 2(1): 17-26.  Wang L, DelPreto J, Bhattacharyya S, et al. A highlyunderactuated robotic hand with force and joint angle sensors [C]//IEEE/RSJ International Conference on Intelligent Robots and Systems. Piscataway, USA: IEEE, 2011: 1380-1385.  王晶晶，刘玉庆．基于力封闭的虚拟手静抓持规则[J]．机械科学与技术， 2011， 30(5)： 778-784. Wang J J, Liu Y Q. Virtual hand grasp rule based on force closure[J]. Mechanical Science and Technology for Aerospace Engineering, 2011, 30(5): 778-784.  苏建华，刘传凯，王智伟，等．面向3 维物体的三指机械手“包笼抓取”方法[J]．机器人， 2021， 43(2)： 129-139. Su J H, Liu C K, Wang Z W, et al. Caging grasp of 3D objects with a three-finger gripper[J]. Robot, 2021, 43(2): 129-139.  王宁扬，孙昊，姜皓，等．一种基于蜂巢气动网络的软体夹持器抓取策略研究[J]．机器人， 2016， 38(3)： 371-377, 384. Wang N Y, Sun H, Jiang H, et al. On grasp strategy of honeycomb PneuNets soft gripper[J]. Robot, 2016, 38(3): 371-377, 384.  Wu P C, Lin N, Duan Y F, et al. An automatic grasp system with sensor feedback based on soft gripper[C]//WRC Symposium on Advanced Robotics and Automation. Piscataway, USA: IEEE, 2018. DOI: 10.1109/WRC-SARA.2018.8584250.  胡寿松．自动控制原理[M]． 6版．北京：科学出版社， 2013： 5-6. Hu S S. Principle of automatic control[M]． 6th ed. Beijing: Science Press, 2013: 5-6.  Wang L, DelPreto J, Bhattacharyya S, et al. A highlyunderactuated robotic hand with force and joint angle sensors [C]//IEEE/RSJ International Conference on Intelligent Robots and Systems. Piscataway, USA: IEEE, 2011: 1380-1385.  Ueda J, Ikeda A, Ogasawara T. Grip-force control of an elastic object by vision-based slip-margin feedback during the incipient slip[J]. IEEE Transactions on Robotics, 2005, 21(6): 1139- 1147.  Adachi R, Fujihira Y, Watanabe T. Identification of danger state for grasping delicate tofu with fingertips containing viscoelastic fluid[C]//IEEE/RSJ International Conference on Intelligent Robots and Systems. Piscataway, USA: IEEE, 2015: 497-503.  Nishimura T, Fujihira Y, Adachi R, et al. New condition for tofu stable grasping with fluid fingertips[C]//IEEE International Conference on Automation Science and Engineering. Piscataway, USA: IEEE, 2016: 335-341.  陈小平．人工智能伦理导引[M]． 1版．合肥：中国科学技术大学出版社， 2021： 7-50. Chen X P. Ethical guidance of artificial intelligence[M]． 1st ed. Hefei: University of Science and Technology of China Press, 2021: 7-50.  Lin N, Wu P C, Tan X, et al. Design and analysis of a novel sucked-type underactuated hand with multiple grasping modes[C]//International Conference on Robot Intelligence Technology and Applications. Cham, Switzerland: Springer, 2017: 299-312.  Wu P C, Lin N, Lei T, el al. A new grasping mode based on a sucked-type underactuated hand[J]. Chinese Journal of Mechanical Engineering, 2018, 31(6): 15-23.  Hawkes E W, Majidi C, Tolley M T. Hard questions for soft robotics[J]. Science Robotics, 2021, 6(53). DOI: 10.1126/sci robotics.abg6049.