Sensor-based guidance control of a continuum robot for a semi-autonomous colonoscopy

Abstract

Due to their compliance and high dexterity, biologically-inspired continuum robots have attracted much interest for applications such as medical surgery, urban search and rescue, de-mining etc. In this paper, we will present an application to medical surgery-colonoscopy by designing a pneumatic-driven flexible robotic manipulator, called ColoBot. The focus of this paper lies in the sensor-based position control of the ColoBot for guiding the advancement in a tubular, compliant and slippery environment. The kinematic model related the position of the distal end of the ColoBot to the actuator inputs which is firstly developed and formulated to control the shape of the ColoBot through position control of the distal tip. To achieve safe guidance, the ideal position of the tip should be in the central axis of the colon. A method based on a circumscribed circle is proposed to approximate the central position in real-time based on three sensor readings. This position will be used as reference position for the tip to adjust its shape in real time to avoid the contact with tube wall. This proposed approach can be extended to the control of continuum robots in the conditions of a dynamically confined space. The simulation results and experimental results with a curved tube will be presented in order to validate the proposed control strategy.

Introduction

Robotics has increasingly become accepted in the past 20 years as a viable solution to many applications in surgery, particularly in the field of computer assisted surgery (CAS), Minimally Invasive Surgery and Therapy (MIS and MIT) [1]. Among them, surgical robotic instruments for MIS are assumed to be the most promising and technically challenging, needing integrated design, real-time sensing, actuation and control, power supply and some degree of autonomy [2]. Colonoscopy is a typical MIT procedure for observation, diagnostics and therapy of the lower gastrointestinal tract including the colon, where the second frequent malignant tumor is found in industrialized countries [3]. This procedure is accomplished through the insertion of an endoscope (also called the colonoscope) into the human colon. At present, however, the existing colonoscopy procedure is very technically demanding for doctors and tends to be unpopular with patients [2]. The main reason lies in the characteristics of current colonoscopes, which are quite rigid and require the doctor to perform difficult manoeuvres for long insertion with minimal damage of the colon wall [4], [5].

Since the human colon is a tortuous “tube” with several sharp bends, the insertion of the colonoscope requires the doctor to exert forces and rotations at shaft outside of the patient, thus causing discomfort to the patient. The complexity of the procedure for doctors and the discomfort experienced by the patient of current colonoscopies lead many researchers to choose the automated colonoscopy method. In [6], the authors proposed the concept of automated colonoscopy (also called robotic colonoscopy) from two aspects: locomotion and steering of the distal end, which are the two main actions during a colonoscopy. In order to facilitate the operation of colonoscopy, some studies on the robotic colonoscopy have been carried out from these two aspects. Most current research on autonomous colonoscopies have been focused on the self-propelled robots which utilize various locomotion mechanisms [7], [8], [9], [10], [11], [12]. Among them, inchworm-like locomotion attracted much more attention [8], [9]. However, most of the current inchworm-based robotic systems [8], [9], [10], [11] showed low efficiency of locomotion for exploring the colon because of the structure of the colon wall: slippery and different diameters at each section.

Another aspect work that could improve the performance of current colonoscopies is to design an autonomous steering robot for guidance inside the colon during the colonoscopy. Several robotic colonoscopy systems are also comprised of a flexible steering tip, but they did not focus on how to control this special robot to endow it with a capability for autonomous guidance [10], [13], [11], [14].

Our previous work [15] has been focused on a semi-autonomous robotic colonoscopy based on a biologically-inspired robotic manipulator-ColoBot. The ColoBot will replace the distal-end of an actual colonoscope and provide for the ability of autonomous steering inside the colon during the colonoscopy. This paper will present our work on the steering control of the ColoBot for a semi-autonomous robotic colonoscopy.