Soft Gripper using Variable Stiffness Mechanism and Its Application

  • KiBeom Ham
  • Jiho Han
  • Yong-Jai Park
Regular Paper


Soft robots have advantages such as low weight and compact size compared to rigid robots. Variable stiffness is one of the key methods of improving the performance of a soft robot. The soft gripper grasps objects of various shapes or sizes based on the variable stiffness. In a previous study, we validated the variable stiffness mechanism where flexible and rigid segments were connected alternately in series. This paper presents a soft variable stiffness gripper that can be used to control the stiffness by pulling tendons. The soft gripper has three variable stiffness structures acting as fingers and the stiffness can be controlled using two motors by winding tendons. To understand the tendency of the stiffness variation and determine the design parameters, a compliant mechanism was developed using a pseudo-rigid-body model (PRBM). The experimental results show that the difference between the lowest and highest stiffness values of the fabricated variable stiffness gripper was 5.6 times the original. Similarly, the difference in the gripping weight was 19 times. Using the experimental results, the variable stiffness gripper can be designed and manufactured based on the required stiffness and used to grip various types of objects.


Variable stiffness Adaptable structure Adjustable mechanism Soft robotics Gripper 



Young’s Modulus


Shear Modulus


second moment of inertia


shape factor


radius of cylinder


compressed length


length of flexible segment


length of rigid segment


length of ith segment


characteristic radius factor due to bending force


characteristic radius factor due to moment


pseudo torsional spring constant of ith flexible segment


parametric angle coefficient by bending force


parametric angle coefficient by moment


effective bending stiffness of bonded cylindrical layer


deflection angle of ith flexible segment


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© Korean Society for Precision Engineering and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.School of Mechanical EngineeringSunmoon UniversityChungcheongnam-doRepublic of Korea

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