Deployable soft robotics for minimally invasive surgery

Abstract

Several benefits have been brought about by using Minimally Invasive Surgery (MIS), including faster procedure times, reduction of patient pain, and reductions in complications intraoperatively and postoperatively. However, some new techniques in MIS for colon cancer are technically difficult to perform using currently available instruments. Robotic systems for treatment of cancer in the lower Gastrointestinal (GI) tract have not shown performance that has translated into regular adoption. This thesis describes the creation of soft parallel robots for MIS that provide a different approach to the devices in the literature. To the author’s knowledge, this is the first deployable, laser welded, soft, hybrid parallel robot designed for minimally invasive surgery. The field of soft robotics relies on soft materials for the construction of robotic devices and is a growing field of research. A keyword search of soft robotic devices for use in MIS was performed, revealing general trends in the current research. It was found that a majority of devices in research were of continuum type, were moulded with elastomeric materials, and were pneumatically actuated. The literature review helped to shape the manufacturing approach taken in this work, as it had been identified that few devices were low-profile, deployable, or could significantly change their volume when transitioning from an inactive to active state. A laser welding system was designed and built for this purpose, delivering a rapid, low-cost, and adaptable manufacturing method for low-profile, deployable structures and actuators. This thesis describes the first use of this manufacturing technique for creation of soft robotic devices for minimally invasive surgery. A deployable, bimanual, cable-driven parallel robot was manufactured using the laser welding system and showed maximum force exertion capabilities of 8.29 N. A programmatic design approach was used to design the structure of the robot, which highlights the ability to customise the design. The robot was used to successfully perform a procedure with similar steps to Endoscopic Submucosal Dissection (ESD) with an untrained, novice user. The estimated volume change from the undeployed to the deployed state of the robot was approximately 73%. Novel soft hydraulic actuators were designed for use with deployable soft robots and were tested in a variety of configurations, from one Degree Of Freedom (DOF) to three DOFs. This is the first time, to the author’s knowledge, that open loop position control, length estimation based on internal pressure, and collision detection have been demonstrated with this type of actuator. Open loop position control was demonstrated with the soft actuator, achieving RMSE values of 0.47 mm for a single actuator acting against gravity and 0.35 mm when used in an antagonistic configuration. The hysteresis values in each configuration were 0.71 mm and 0.51 mm respectively. The contraction of the soft actuators was estimated based on the internal pressure of the actuators. The RMSE between the estimated contraction and desired contraction was 0.98 mm when applied to the pressure data from the same configuration and 0.76 mm in the hybrid parallel configuration after a correctional offset was applied. The internal pressure in the actuators was used to demonstrate collision detection when the actuators were setup in a hybrid parallel mechanism. 100% of the simulated collisions were detected using a heuristic method that monitored changes in pressure over time and the angle at which the collisions were made could also be estimated. The RMSE between the estimated contact angle and the true angle at which contact was made was 8.22° over a 120° test range, and the method had an R-squared value of 0.95. Finally, a second deployable robot was manufactured that used three of the novel soft actuators to control its end effector. The robot was manufactured rapidly, at low-cost, with the only rigid components being the shaft assembly that delivered the instrument. A user was able to repeatedly trace a circle using the robot and the performance of the robot with a human-in-the-loop to correct its motion online even with the simple construction and control strategy of the robot.