A novel pose sensing model for soft manipulator based on helical FBG

[Display omitted] •The improved model removes the restriction that the conventional piecewise constant curvature is only suitable for the manipulator with the constant axial length.•The quantitative analysis between the FBG strain and coupled strain of the soft manipulator can reflect its internal deformation in real time.•The following deflection angle verified by the simulation and vision explains the additional passive deformation caused by the nonlinearity of the soft material.•The improved model provides the deformation parameters as the feedback signals and a new idea for the control modeling of the soft manipulator. Pose sensing is the key to realizing the closed-loop control for the soft manipulator with large deformation. However, few detection models of the flexible sensors based on fiber Bragg grating (FBG) consider the effect of the soft material on the actual deformation. In this paper, the FBG-based sensing principle suitable for the soft manipulator whose axial elongation/compression cannot be ignored is proposed. Besides, the improved kinematics model including the following deflection angle explains the influence of the nonlinear soft material on the modeling based on conventional piecewise constant curvature (CPCC). The experiments show that the maximum error of the end coordinates detected by the improved piecewise constant curvature (IPCC) is no more than 0.76 mm. The maximum error of the Euler angle β is less than 1 %. The study reveals that IPCC has higher accuracy in pose detection of the soft manipulator and potential to provide the reliable feedback data to realize the feedback control.