Data-driven Learning Intelligent Control for Flexible Surgical Manipulators


Automate Surgical Tasks for A Flexible Serpentine Manipulator via Learning Actuation Space Trajectory from Demonstration

Background: Accurate motion control of flexible surgical manipulators is crucial in tissue manipulation tasks. Tendon-driven serpentine manipulator (TSM) is one of the most widely adopted flexible mechanisms in MIS for its enhanced maneuverability in torturous environment. TSM, however, exhibits high nonlinearities and conventional analytical kinematics model is insufficient to achieve high accuracy.
Methods: To account for the system nonlinearities, we applied data driven approach to encode the system inverse kinematics. Three regression methods: Extreme Learning Machine (ELM), Gaussian Mixture Regression (GMR) and K-Nearest Neighbors Regression (KNNR) were implemented to learn a nonlinear mapping from the robot 3D position state to the control inputs.
Results: The performance of the three algorithms were evaluated both in simulation and physical trajectory tracking experiments. KNNR performs the best in the tracking experiments with the lowest RMSE of 2.1275mm.
Conclusions: The proposed inverse kinematics learning methods provide an alternative and efficient way to accurately model the challenging tendon driven flexible manipulator.
Keywords: Tendon-driven serpentine manipulator; surgical robotics; Inverse kinematics; Heuristic Methods

Demo video at:


  • W. Xu; J. Chen; H. Y. Lau & H. Ren Data-driven Methods towards Learning the Highly Nonlinear Inverse Kinematics of Tendon-driven Surgical Manipulators International Journal of Medical Robotics and Computer Assisted Surgery , 2016, 1-13
  • W. Xu; J. Chen; H. Y. Lau & H. Ren Automate Surgical Tasks for A Flexible Serpentine Manipulator via Learning Actuation Space Trajectory from Demonstration ICRA2016, IEEE International Conference on Robotics and Automation, 2016, –



We present a novel flexible endoscope (FE) which is well suited to minimally invasive cardiac surgery (MICS). It is named the cardioscope. The cardioscope is composed of a handle, a rigid shaft, a steerable flexible section, and the imaging system. The flexible section is composed of an elastic tube, a number of spacing disks, a constraint tube, and four wires. It employs the constrained wire-driven flexible mechanism (CWFM) with a continuum backbone, which enables the control of both the angulation and the length of the flexible section. Compared to other endoscopes, e.g., rigid endoscope (RE) and fixed-length FE, the cardioscope is much more dexterous. The cardioscope can bend over 180 deg in all directions, and the bending is decoupled from the distal tip position. Ex vivo tests show that the cardioscope is well suited to MICS. It provides much wider scope of vision than REs and provides good manipulation inside confined environments. In our tests, the cardioscope successfully explored the full heart through a single hole, which shows that the design is promising. Despite being designed for MICS, the cardioscope can also be applied to other minimally invasive surgeries (MISs), such as laparoscopy, neurosurgery, transnasal surgery, and transoral surgery.

Demo video


  • Z. Li; M. Zin Oo; V. Nalam; V. Duc Thang; H. Ren; T. Kofidis & H. Yu Design of a Novel Flexible Endoscope- Cardioscope Journal of Mechanisms and Robotics, ASME, 2016, 8, 051014-051014
  • Z. Li; M. Z. Oo; V. D. Thang; V. Nalam; T. Kofidis; H. Yu & H. Ren Design of a Novel Flexible Endoscope – Cardioscope 2015 IDETC: ASME 2015 International Design Engineering Technical Conferences , 2015

Shape Morphing Microscale Soft Robotic Actuators


The micro actuator has been studied for its application in micro operations such as manipulating cellular aggregate, the tissues or drug delivery. The traditional actuation methods include thermo-mechanical actuation, electromagnetic actuation, electrostatic actuation and pneumatic actuation. Among these actuation methods, pneumatic actuation has the advantage of not generating heat and current during actuation.
We investigate
1) a streamlined and standardized fabrication procedure to make sub-millimeter scale soft pneumatic actuators (SPA) with customizable bending modalities achieved by shape engineering. Preliminary models are also given to interpret width-based shape engineering for customization and to compare the bending angle and radius of curvature measured from the characterization experiments.
2) a new micro pneumatic actuator consisting of two biocompatible materials is designed, fabricated and tested. The actuator has one bending degree of freedom and the largest bending deformation is about 115°.


  • X. Liang; Y. Sun & H. Ren A Flexible Fabrication Approach towards the Shape Engineering of Microscale Soft Pneumatic Actuators IEEE Robotics and Automation Letters, 2016, 1-6
  • X. Liang; C. Lee & H. Ren Towards a Micro Pneumatic Actuator with Large Bending Deformation for Medical Interventions 7th WACBE World Congress on Bioengineering, 6th to 8th July, 2015, Singapore, Springer International Publishing, 2015, 52, 76-79
  • P. M. Khin; J. H. Low; S. Kukreja; H. Ren & R. Yeow Soft Haptics Using Soft Actuator and Soft Sensor BioRob2016, 6th IEEE RAS/EMBS International Conference on Biomedical Robotics and Biomechatronics, June 26-29, 2016, Singapore, 2016

Soft Robotic Manipulators: fabrication & applications


Flexible robotic manipulators have been widely used in minimally invasive surgery (MIS) and many other applications requiring closer inspection and operation. Although a variety of manipulators enabled by different mechanism have been developed, few of them can preserve softness, thinness and decent bending capability simultaneously. We develop miniature soft robotic manipulators made of hyper-elastic silicone rubber. Along with the manipulator design, novel fabrication methods are proposed and elaborated. Detailed characterizations are specified to show the bending capability of the manipulator given different air pressure. Specifically, our manipulator, as thin as 6 mm, is able to achieve 360° directional bending, and, when given pressure over 70kPa, it can reach 180° bending angle and around 5mm bending radius easily. Due to its innate compliance and small dimension, this type of robotic manipulator can deliver safe and comfortable interactions with the subjects. More significantly, the novel fabrications in this paper diversify the fabrication methods for soft pneumatic robots and actuators (SPRA) and further scale down their sizes.
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