External force compensation in a tendon-driven flexible robotic endoscope using Cosserat Rod modeling

Willem B. Hoitzing, Yoeko Xavier Mak, Momen Abayazid

Research output: Contribution to conferenceAbstractAcademic


Tendon-actuated endoscopic camera is used extensively in minimally invasive surgery and can be robotically controlled to improve its positioning accuracy. Numerous studies have been conducted to develop and investigate the feasibility of flexible endoscopic tool for laparoscopy procedures. While long and slender flexible endoscope has advantage to safely maneuver and reach difficult targets compared to the rigid scopes, it lacks stiffness and can easily deform due to external loads such as gravity and interaction forces. This deformation of flexible endoscopes can be estimated using a Cosserat based model. This will enable the system to compensate for such deformations and thus achieve reliable positioning during minimally invasive procedures. A prototype of a flexible tendon-actuated endoscopic system that can be robotically controlled while compensating for external load is developed in this study. The prototype uses 2 pairs of antagonistic tendon actuation mechanism with force measurement on the tendon. The position of endoscope tip is measured using an electromagnetic tracker. The designed actuation system shows good tracking performance according to the design goal, using PD position controller on each tendon. Secondly, the deformation prediction due to external loads was validated by comparing the simulated Cosserat-rod based model to the experimental result using the developed prototype. Identification of stiffness and mass parameters of the prototype with movable tip length of 110 mm were performed and the difference in deformation between simulated model and physical case were measured at 6 different bending, 12 axial rotation and loading amount m ε {0, 5, 10} grams. Significant prediction errors were observed for model-based compensation: 12.2 ± 6.4 mm error norm for case of 10 grams of loading. This is due to the unmodeled friction between tendons and the endoscope’s spacer disks. In conclusion, the design and modeling of flexible endoscope were successfully achieved in this study, while the deformation prediction has on average 14.6 mm (13.3% of the endoscope length) error over all tested configurations. Further work in improving the accuracy of the prediction is required to progress towards clinical use.
Original languageEnglish
Publication statusPublished - 28 Jan 2021
Event8th Dutch Bio-Medical Engineering Conference, BME 2021 - Virtual Conference
Duration: 28 Jan 202129 Jan 2021
Conference number: 8


Conference8th Dutch Bio-Medical Engineering Conference, BME 2021
Abbreviated titleBME 2021
CityVirtual Conference
Internet address


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