Soft continuum manipulators integrating a shape sensing modality using optoelectronic sensors

Over previous years, many soft continuum manipulators have been developed and adapted for medical use, including procedures such as minimally invasive surgery (MIS), endoscopy and colonoscopy. These soft continuum manipulators are often small and flexible, with a large workspace, allowing access through small passages and incisions, as well as to safely manoeuvre through the body, minimising excessive force on soft tissue and organs in surgery.

One of the main challenges that face the use of these manipulators for medical procedures is that of position control. It is important to have a sense of the position and shape of the manipulator inside the body, to ensure accuracy and safety in use. This is done through closed loop position feedback control, using different shape sensing techniques.

A vision approach (camera/video) is very simple, however, during surgical procedures, organs or objects might block the manipulator, resulting the camera being unable to determine position. There exists a soft continuum manipulator successfully integrating a shape sensing modality based on Fibre Bragg gratings (FBG); their sensing performances are accurate. Despite this, its calibration method is very complicated. The device called "interrogator" which can detect strain values from the FBGs attached on the soft material body costs around £20,000 and manufacturing the shape sensor is complex. Other methods in the literature included issues with miniaturisation, errors due to drift, slow update rate, and inability to accurately measure over a larger range of curvatures.

For this reason, the following solution is proposed for this project. This is a novel shape sensing method for soft continuum manipulators, that utilises optoelectronic sensors. This solution addresses the issues outlined previously, and it has the advantage of being potentially miniaturised, accurate, computationally inexpensive, easily integrated, as well as having a low cost, allowing such a device to be easily adopted within the healthcare industry. These sensors are to be integrated into a series of circular disks that are rigidly linked to form the body of the flexible manipulator. They measure the distances (or deformations) in each of the flexible mechanical structures, based in the amount of reflection on consecutive surfaces. From the measured deformation values, two to three orientations can be estimated (roll, pitch and yaw). Therefore, all of the estimated orientations in each of the serially connected mechanical flexures can be simplified by the rigid-link model, and the overall manipulator's shape can be visualised.

The methods that form part of this project firstly include the structural design of the manipulator that is able to house a number of these sensors. Next will involve developing software that enables the measuring of data from the sensors and carrying out a set of calibration experiments to obtain the optoelectronic sensor's data to physical orientation values, using a various modelling and computational techniques. The next step will be testing the application, by integrating this shape sensing method in to a flexible manipulator with motorised actuators with a chosen driving mechanism (tendon, hydraulic, or pneumatic). This can be tested on phantoms and a simulation can be built to visualise the manipulator shape in three dimensions. The final aim is to miniaturise and devise a design on how to combine the serially connected internal rigid structure with with an outer cover consisting of soft material.