Steering of Multisegment Continuum Manipulators Using Rigid-Link Modeling and FBG-Based Shape Sensing

Abstract

Accurate closed-loop control of continuum manipulators requires integration of both models that describe their motion and methods to evaluate manipulator shape. This work presents a model that approximates the continuous shape of a continuum manipulator by a serial chain of rigid links, connected by flexible rotational joints. This rigid-link model permits a description of manipulator shape under different loading conditions. A kinematic controller, based on the manipulator Jacobian of the proposed rigid-link model, is implemented and realizes trajectory tracking, while using the kinematic redundancy of the manipulator to perform a secondary task of avoiding obstacles. The controller is evaluated on an experimental testbed, consisting of a planar tendon-driven continuum manipulator with two bending segments. Fiber Bragg grating (FBG) sensors are used to reconstruct 3-D manipulator shape, and is used as feedback for closed-loop control of the manipulator. Manipulator steering is evaluated for two cases: the first case involving steering around a static obstacle and the second case involving steering along a straight path while avoiding a moving obstacle. Mean trajectory tracking errors are 0.24 and 0.09 mm with maximum errors of 1.37 and 0.52 mm for the first and second cases, respectively. Finally, we demonstrate the possibility of FBG sensors to measure interaction forces, while simultaneously using them for shape sensing.

Online Disturbance Estimation for Improving Kinematic Accuracy in Continuum Manipulators

“…where τ i ∈ R 3 is a vector representing the internal bending moment and K i is the stiffness matrix of joint i with components in x, y and z directions. The effective torsional spring constant can be found in terms of the elastic material properties by comparing spring energy and strain energy due to bending, as explained in [20]:…”

“…This approach, however, is not suitable for all types of continuum manipulators, as these sensors do not scale down well to small designs and require precise alignment, complicating the fabrication process. Another common method is to use fiber optic shape sensors [19], [20]. However, this method begins to lose accuracy at high curvatures due to propagation losses, and cannot be implemented for many lowstiffness designs, as the fiber optic sensor is often stiffer than the manipulator itself.…”

Development and Experimental Evaluation of Concurrent Control of a Robotic Arm and Continuum Manipulator for Osteolytic Lesion Treatment

“…In the surgical scenario outlined in section I, FBGs [17–19] will be used for real time closed-loop control and occasional x-ray images [20] will be taken to correct for errors and reconfirm relation of the snake to the anatomy. Since real-time sensing with FBGs was still under investigation during this work, we chose to instead track an optical marker mounted to the tip of the CDM using a Polaris optical tracker (Northern Digital Inc., Waterloo, Canada).…”

Unified Tracking and Shape Estimation for Concentric Tube Robots

“…Optical fibres fabricated with FBGs have gained interest for shape sensing in recent years. Although FBG shape sensors can provide accurate and fast shape measurements of continuum robots, their integration with small flexible robots remains a challenge and adds significant cost [17], [18], [19], [20], [21].…”