In current research on soft grippers, pneumatically actuated soft grippers are generally fabricated using fully soft materials, which have the advantage of flexibility as well as the disadvantages of a small gripping force and slow response speed. To improve these characteristics, a novel pneumatic soft gripper with a jointed endoskeleton structure (E-Gripper) is developed, in which the muscle actuating function has been separated from the force bearing function. The soft action of an E-Gripper finger is performed by some air chambers surrounded by multilayer rubber embedded in the restraining fiber. The gripping force is borne and transferred by the rigid endoskeleton within the E-Gripper finger. Thus, the gripping force and action response speed can be increased while the flexibility is maintained. Through experiments, the bending angle of each finger segment, response time, and gripping force of the E-Gripper have been measured, which provides a basis for designing and controlling the soft gripper. The test results have shown that the maximum gripping force of the E-Gripper can be 35 N, which is three times greater than that of a fully soft gripper (FS-Gripper) of the same size. At the maximum charging pressure of 150 kPa, the response time is 1.123 s faster than that of the FS-Gripper. The research results indicate that the flexibility of a pneumatic soft gripper is not only maintained in the case of the E-Gripper, but its gripping force is also obviously increased, and the response time is reduced. The E-Gripper thus shows great potential for future development and applications.
[1] C Majidi. Soft robotics:a perspective-current trends and prospects for the future. Soft Robotics, 2014, 1(1):5-11.
[2] R Deimel, O Brock. A compliant hand based on a novel pneumatic actuator. IEEE International Conference on Robotics and Automation, Karlsruhe, Germany, May 6-10, 2013:2047-2053.
[3] R Deimel, O Brock. A novel type of compliant and underactuated robotic hand for dexterous grasping. Thousand Oaks:Sage Publications, Inc., 2016.
[4] M E Giannaccini, I Georgilas, I Horsfield, et al. A variable compliance, soft gripper. Autonomous Robots, 2014, 36(1-2):93-107.
[5] S Wakimoto, K Ogura, K Suzumori, et al. Miniature soft hand with curling rubber pneumatic actuators. IEEE International Conference on Robotics and Automation, Kobe, Japan, May 12-17, 2009:556-561.
[6] Z Wang Z, D S Chathuranga, S Hirai. 3D printed soft gripper for automatic lunch box packing. IEEE International Conference on Robotics and Biomimetics, Qingdao, China, December, 2017:503-508.
[7] J R Amend, E Brown, N Rodenberg, et al. A positive pressure universal gripper based on the jamming of granular material. IEEE Transactions on Robotics, 2012, 28(2):341-350.
[8] T Matsuno, Z Wang, S Hirai. Grasping state estimation of printable soft gripper using electro-conductive yarn. Robotics & Biomimetics, 2017, 4(1):13.
[9] F Ilievski F, A D Mazzeo, R F Shepherd, et al. Soft robotics for chemists. Angewandte Chemie International Edition, 2011, 50(8):1890-5.
[10] B S Homberg, R K Katzschmann, M R Dogar, et al. Haptic identification of objects using a modular soft robotic gripper. IEEE/RSJ International Conference on Intelligent Robots and Systems, Hamburg, Germany, September 28-October 2, 2015:1698-1705.
[11] P Polygerinos, K C Galloway, S Sanan, et al. EMG controlled soft robotic glove for assistance during activities of daily living. IEEE International Conference on Rehabilitation Robotics, Singapore, August 11-14, 2015:55-60.
[12] P Polygerinos, Z Wang, J T B Overvelde, et al. Modeling of Soft Fiber-Reinforced Bending Actuators. IEEE Transactions on Robotics, 2015, 31(3):778-789.
[13] C T Loh, H Tsukagoshi. Pneumatic Big-hand gripper with slip-in tip aimed for the transfer support of the human body. IEEE International Conference on Robotics and Automation, Hong Kong, China, May 31-June 7, 2014:475-481.
[14] R V Martinez, J L Branch, C R Fish, et al. Robotic tentacles with three-dimensional mobility based on flexible elastomers. Advanced Materials, 2013, 25(2):153-153.
[15] L Margheri, C Laschi, B Mazzolai. Soft robotic arm inspired by the octopus:Ⅰ. From biological functions to artificial requirements. Bioinspiration & Biomimetics, 2012, 7(2):025004.
[16] D Rus, M T Tolley. Design, fabrication and control of soft robots. Nature, 2015, 521(7553):467.
[17] F J Chen, S Dirven, W L Xu, et al. Soft actuator mimicking human esophageal peristalsis for a swallowing robot. IEEE/ASME Transactions on Mechatronics, 2014, 19(4):1300-1308.
[18] X Liu, Y Wang, D Geng, et al. Mechanical characteristics analysis on PAM with elongation and torsion. International Conference on Mechatronic Science, Electric Engineering and Computer, Jilin, China, Aug 19-22, 2011:613-616.
[19] Z Wang, S Hirai. Soft gripper dynamics using a line-segment model with an optimization-based parameter identification method. IEEE Robotics & Automation Letters, 2017, 2(2):624-631.
[20] Y Kamel, B Hocine. A new hyper-elastic model for predicting multi-axial behaviour of rubber-like materials:formulation and computational aspects. Mechanics of Time-Dependent Material, 2017(7):1-20.
[21] B Kim, S B Lee, S Cho, et al. A comparison among Neo-Hookean model, Mooney-Rivlin model, and Ogden model for chloroprene rubber. International Journal of Precision Engineering & Manufacturing, 2012, 13(5):759-764.
[22] J L Huang, G J Xie, Z W Liu. Finite element analysis of super-elastic rubber materials based on the Mooney-Rivlin and Yeoh model. China Rubber/Plastics Technology and Equipment, 2008, 34(12):22-26. (in Chinese)
[23] Y L Xiong. Fundamentals of robotics. Wuhan:Huazhong University of Science & Technology Press, 1996. (in Chinese)
[24] J F Li. Pneumatic transmission system dynamics.Guangzhou:South China University of Technology Press, 1991. (in Chinese)
[25] A D Marchese, R Tedrake, D Rus. Dynamics and trajectory optimization for a soft spatial fluidic elastomer manipulator. IEEE International Conference on Robotics and Automation, Seattle, USA, May 26-30, 2015:2528-2535.
[26] J C Trinkle. The mechanics and planning of enveloping grasp. USA:University of Pennsylvania, 1987.
[27] K Harada, M Kaneko. Enveloping grasp for multiple objects. Proc. of IEEE Int. Conf. on Robotics & Automation, 2010, 16(6):860-867.
[28] S Qian, L Zhang, Q Yang, et al. Research on output force of flexible pneumatic bending joint. International Conference on Control, Automation, Robotics and Vision, Hanoi, Vietnam, December 17-20, 2009:144-148.
[29] S H Li, H M Jia, et al. Theory and testing method of hyperelastic material constitutive model. China Elastomerics, 2011, 21(1):58-64. (in Chinese)
