A compact continuum tubular robotic system for transnasal procedures


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Project Goals

Nasopharynx cancer, or nasopharyngeal carcinoma (NPC), is a tumor that originates in the nasopharynx, the uppermost region of the pharynx where the nasal passage and the throat join. It is a common disease occurring to ethnic Chinese people living in or emigrating from southern China; it is also the eighth most frequently occurred cancer among Singaporean men. Traditional posterior nasopharyngeal biopsy using a flexible nasal endoscope has the risks of abrasion and injury to the nasal mucosa and thus causing trauma to the patient. Therefore, the goal of this project is to develop a compact continuum tubular robotic system to achieve collision free nasopharyngeal biopsy.


Fig.1  Illustration of the proposed CTR for nasopharyngeal biopsy.


We developed a compact CTR which is 35 cm in total length, 10 cm in diameter, 2.15 kg in weight, and easy to be integrated with a robotic arm to perform more complicated operations.


Fig.2 The proposed continuum tubular robot


Fig.3 Compact and light weight CTR integrated with a positioning arm for
better conducting surgery

We also developed a 3D printed biopsy needle to equip our robot for transnasal biopsy procedure.

Fig.4  3D printed biopsy needle for transnasal biopsy

The workspace of the robot was analyzed to determine optimized tube parameters.


Fig.5 Workspace comparison for 3-DOF CTR with three initial configurations.
Top: all the outstretched part of the inner tube exposes; Middle: the outstretched part of the inner tube is partially covered by the outer tube; Bottom: the outstretched part of the inner tube is totally covered by the outer tube.

Further more, by using an electromagnetic tracking system, we are able to build a navigation system with shape reconstruction for the tubes.


Fig.6  Shape reconstruction using 3-order Bézier curve fitting


Fig.7 Sensing by EM tracker


Fig.8 Navigation interface


Three groups of experiments were carried out. The first group is to tele-operate the robot to follow a linear path and a circular path. We found that the path following accuracy was about 2 mm.


Fig.9 Tele-operating the robot to follow a linear path and a circular path


Fig.10 Accuracy of the robot following the predefined paths

The second group is to validate the shape reconstruction algorithm. The accuracy of the results is about 1 mm.


Fig.11 Reconstruction setup


Fig.12 Reconstruction error

In the last group of experiments, the robot was tested in a biopsy procedure on a cadaver. The feasibility of the proposed robotic system was validated.


Fig.13  Cadaver experiment setup


Fig.14 Cadaver experiment process

People Involved

Research Fellow: Liao Wu
PhD Student: Keyu Wu
FYP Student: Li Ting Lynette Teo
Intern Student: Jan Feiling and Xin Liu
Project Investigator: Hongliang Ren


[1] Liao Wu, Shuang Song, Keyu Wu, Chwee Ming Lim, Hongliang Ren. Development of a compact continuum tubular robotic system for nasopharyngeal biopsy. Medical & Biological Engineering & Computing. 2016.
[2] Keyu Wu, Liao Wu, Hongliang Ren. Motion planning of continuum tubular robots based on features extracted from statistical atlas. In: Proceedings of 2015 IEEE International Conference on Intelligent Robots and Systems (IROS 2015).
[3] Keyu Wu, Liao Wu, Chwee Ming Lim, Hongliang Ren. Model-free image guidance for intelligent tubular robots with pre-clinical feasibility study: towards minimally invasive trans-orifice surgery. In: Proceedings of 2015 IEEE International Conference on Information and Automation (ICIA 2015). ( best paper finalist)
[4] Benedict Tan, Liao Wu, Hongliang Ren. Prototype development of a handheld tubular curvilinear robot for minimally invasive surgery. In: The 11th Asian Conference on Computer Aided Surgery (ACCAS 2015).
[5] Keyu Wu†, Liao Wu†, Hongliang Ren. An image based targeting method to guide a curvilinear concentric tube robot. In: Proceedings of 2014 IEEE International Conference on Robotics and Biomimetics (ROBIO 2014). Bali, Indonesia, 2014: 386-391 († equally contributed author).

ETH Image Based Visual Servoing to Guide Flexible Robots

Video Demo

Eye-To-Hand Image Based Visual Servoing to Guide Flexible Robots

Project goals

Flexible robots including active cannula or cable driven continuum robots are typically suitable for such minimally invasive surgeries because they are able to present various flexible shapes with great dexterity, which strengthens the ability of collision avoidance and enlarges the reachability of operation tools. Using model based control method will lead to artificial singularities and even inverted mapping in many situations because the models are usually developed in free space and cannot perform effectively in constrained environments. Therefore, the goal of this project is control the motion of a tentacle-like curvilinear concentric tube robot by model-less visual servoing.


A two-dimensional planar manipulator is constructed by enabling only the three translation inputs of a six DOF concentric tube robot. As shown in Fig. 1, the concentric tube manipulator is controlled using a PID controller and the images captured by an uncalibrated camera are used as visual feedback.

Fig. 1. The experimental setup includes a concentric tube robot, a camera, a laptop, a marker and a target.

The visual tracking of the concentric tube robot is based on shape detection. The circular marker is attached to the tip of the concentric tube robot and a square target is given for the tip to trace. During the experiments, the coordinates of the marker centroid and target centroid are calculated while the next target position is calculated at the same time as shown in Fig. 2.

Fig. 2. Working mechanism of the system. Top: translations of the three tubes. Bottom: marker, final target and the next target position on the image plane.


Fig. 3. Overview of the control algorithm. The Jacobian matrix is estimated based on the measurements of each incremental movement detected from the camera.

The framework of the controlling the robot is shown in Fig. 3. The initial Jacobian matrix is acquired by running each individual motor separately and measuring the change of tip position of the robot in the image space. Then the optimal control is achieved by solving a typical redundant inverse kinematics. And finally the Jacobian matrix is continuously estimated based on the measured displacements.


To evaluate the proposed model-less algorithm, a simulation was carried out on MATLAB first. The desired and actual trajectory was shown in Fig. 4, from which it could be seen that the robot succeeded in following the reference trajectory and reaching the target position.

Fig. 4. Simulation of using the proposed algorithm to control a concentric tube robot.

The proposed algorithm was also implemented on a physical concentric tube robot in free space. It was found the robot was able to reach goal with zero steady state error in all trials as shown in Fig. 5.

Fig. 5. The concentric tube robot is able to reach a desired goal using the proposed method. Top: the motion of the robot. Bottom: the reference and actual trajectories of two experiments.

People involved

Staff: Keyu WU, Liao WU
PI: Hongliang REN


1. Keyu Wu, Liao Wu and Hongliang Ren, “An Image Based Targeting Method to Guide a Tentacle-like Curvilinear Concentric Tube Robot”, ROBIO 2014, IEEE International Conference on Robotics and Biomimetics, 2014.