A Controller for Continuum Robot in Medical Application

Shen Treratanakulchai

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Most of the common surgical procedures carried out today require a large cut in the operation area. Surgeons then use a variety of tools to operate within the area and seal it with stitches after completing the procedure. Aiming to reduce the long recovery time caused by the cut, researchers have developed a new method called minimally invasive surgery. This method requires small or no incisions for operation (in case of natural orifice transluminal endoscopic surgery). Because of the limited operation area, normal tools cannot be used hence a flexible robotic tool is required, which are generally continuum robots.

Shen Treratanakulchai along with the team of researchers at the Hamlyn Centre is currently developing a continuum robot for transanal surgery. Controlling it is challenging as it must bend to navigate through the body's passages; change its orientation in tri-dimensional space to operate on specific areas and provide feedback to the operator to ensure optimal force is used. Shen is working on a new type of controller for this robot, which alleviates some of these issues.

The master controller can be manipulated in 3D space and matches the degrees of freedom with the continuum robot's instruments. A virtual-reality headset is worn by the operator to get the 3D perspective of the robot's view. Additionally, the controller is able to provide haptic feedback, transmitted from the capacitive plates on the continuum robot.  An algorithm is used to scale the force received by the controller, this ensures that the operator will not apply excessive pressure on the bodily tissues. This controller designed by Shen aims to provide enhanced control to the operator and improve the surgical process.

Continuum Robot

Continuum robots, also known as “snake-arm” or even “elephant trunk” robots are long, flexible robots capable of avoiding obstacles; following sinuous and exiguous paths thanks to their structure. The first robot of this kind, the Scripps Tensor Arm (1968), was a spine-like elephant trunk arm controlled by nylon microfilaments. Since then, the field has evolved to the point where robots capable of performing Minimal Impact Cardiac Surgery (MICS) now exist. These robots have several industrial applications: maintenance of nuclear-related infrastructures, aerospace, bomb disposal, search and rescue, and of course robotic surgery.

Snake-arm robots are formed by a base comprised of motors controlling the body. This body is a collection of vertebra-like patented links held together by groups of cables. The robot's head usually contains lamps, a camera to help the operator guide the robot and its tools according to its application (sensors, water hose, laser, etc.). Groups of cables have different lengths, dividing the robot into individually controlled segments. The number and size of segments/links depend on the length of the robot, how flexible it needs to be and the load it must carry. To make the robot move or bend in a certain direction, the motors either retract or release the cables of the needed segment. The force generated will bend certain links. In order to stabilise the structure, the robot is equipped with springs. These are bent during movement, and unloaded when straightened out to help it remain stable.

The use of continuum robots in surgery is revolutionary. It replaces rigid endoscope instruments, which due to their structure, had limited abilities. Continuum robots are used in what is called Natural Orifice Transluminal Endoscopic Surgery (NOTES), which includes transoral and transanal surgery. One of the most popular FDA approved transurgical continuum robots is the Flex robot, conceived by Medrobotics, which is used to access confined body areas.

Continuum robots are ground-breaking for both patients and surgeons. Since the robot is very agile and can access body parts through extremely sinuous and narrow paths, the doctors do not need to perform open surgery. Therefore, the patients undergo less pain, the operation and recovery time is shorter, infection risks as well as blood loss are reduced. For the surgeon, the use of a robot is very practical, as they can observe the surgical area in detail thanks to the camera-equipped robot. Also, its tools are extremely precise and adjustable, enhancing the surgeon’s dexterity and avoiding the risk of shaky hands. This allows them to operate faster and more safely.

Controller Arm By Shen TreratanakulchaiModelo »


The controlling device of the continuum robot is crucial for the success of medical procedures. The controller should ideally provide not only smooth, accurate and natural control of the robot but also information, feedback, and assistive tools. These allow the human operator to perform surgeries with unprecedented accuracy. The controlling device can be of many forms – from the most basic ones such as mouse, keyboard or joystick to highly sophisticated apparatuses suitable for the full 3D control. Such specialised devices are called master controllers while the controlled robot is usually labeled as a slave robot.

In traditional operations, surgeons typically use rigid instruments and hence easily feel contact with tissues in the operated area or even recognize the texture of the surface. Although some of the commercially available master controller devices provide haptic feedback, they are usually designed for robots with a rigid body and are thus unsuitable for the full control of the continuum robots. Such robots commonly allow many degrees of freedom, which poses a considerable technical challenge for the design of the controller. Commonly this results in a mismatch between the robot and the controller, which is addressed by switching between the control of various parts of the robot.

Shen's Current Project

Shen Treratanakulchai and the Hamlyn Centre are currently developing a controller for continuum robots that provides immediate haptic feedback for the operator. This ensures surgery with continuum robots is safer and more accessible to medical specialists, who are inexperienced in this area. Haptic perception can also help differentiate various types of human tissues including cancerous ones.

The full master controller will be composed of the console with virtual reality headset and two attached controlling devices, which control the corresponding arms of the robot.  The base of controlling arm is equipped with motors providing the haptic feedback. The device aims to allow smooth and natural control of the robot's translational and rotational movement as well as the gripping instrument placed at the robot's head. Prototypes of the controlling arms are currently being tested at the Hamlyn Centre.

The Future

It is expected that, by the end of the research project, a master controller will be used as an instinctive device with transparency properties used to control a continuum robot. The device should provide a realistic sensation through haptic feedback and intuitive control which can be used in different kinematic contexts. The controller should control the slave robot with smooth movement, exerting maximum force in a particular direction through the use of an auxiliary algorithm. The master controller should also have a shared control architecture enabling to be applied to different kinematics. Finally, the haptic feedback element of the continuum robot must be free of errors.

Once integrated into existing clinical procedures, both the patients and the surgeons will benefit from the use of a master controller. Patients will see better outcomes alongside faster recovery times predominantly due to minimally invasive surgery. Surgeons can use devices with increased dexterity, haptic feedback and overall provide better clinical care since the precision of such surgeries is greatly increased.

Future Research

The evolution of technology is encouraging surgeons to use robots as part of their surgical procedures. There are many ways to optimise robot-assisted surgeries. In this research project, haptic feedback was implemented as a method of detecting obstruction. Other features, such as visual feedback where the shade of the continuum robot changes colour, have yet to be implemented into master controllers in a meaningful way, opening up an opportunity for future research.

Further studies are also required to evaluate the strengths and weaknesses of using robots in clinical surgeries. Whilst initial data suggests that robotic-assisted surgeries produce similar results to conventional procedures, development must be rigorously tested in order to reduce risks. This opens up a discussion regarding the ethics of robotic-assisted surgery.

Ethical Aspects of Robotic Surgery

As expected, there are massive ethical repercussions caused by the use of robots within surgeries. For example, technology can be fallible and error-prone and this can cause serious injury to a patient. How can we ensure the safety of a new type of robotic-assisted surgery? Another aspect to consider is the training of surgeons in using continuum robots. An improperly trained surgeon wielding the master controller can be dangerous. How can we ensure that a surgeon is properly trained in robotic-assisted surgery? These issues must be highlighted and risk to human life must be minimised.

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About Shen

Shen Treratanakulchai attended Mahidol University in Thailand, receiving his bachelor’s degree with Distinction Program in Biomedical Engineering. The topic of his senior project was Simulation and Image Reconstruction for Magnetic Resonance Imaging. Following this Shen also received his master's degree in biomedical engineering where he wrote his Master Thesis: Fusion Sensory Schemes for Real-Time Survival Searching on Extreme-Terrain Rescue Robot. Currently, Shen is a Ph.D. student at Imperial College London where his research title is “A Controller for Continuum Robot in Medical Application”. He is doing his research under supervision from Prof. Guang-Zhong Yang at the Hamlyn Centre.

The Hamlyn Centre

The Hamlyn Centre, named after Lady Helen Hamlyn of the Helen Hamlyn Trust, is part of the Institute of Global Health Innovation (IGHI). It was founded for evolving safe, effective and accessible technologies that can reshape the future of healthcare for both developing and developed countries; focusing on research in imaging, sensing, and robotics for addressing global health challenges.

A particular area that the Hamlyn Centre is researching, is the design of lightweight, cost-effective, flexible manipulators with a minimal footprint in the operative theatre. These should augment the present surgical workflow, rather than modify it completely or become a hindrance to normal procedures. The researchers at the Hamlyn Centre are currently developing a new generation of miniaturised, intelligent mechatronic devices and robots for flexible access surgery. They are also investigating new techniques for providing a synergistic, more natural control interface between the surgeon and the robot.

With developments in smart materials and composites, the Hamlyn Centre has focussed on the improvement of continuum robots and their function in endoluminal procedures. Rather than using rigid links, these robots use new materials and typically bio-inspired mechanical design to offer more dynamic articulation and navigation.

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