Gripper Tool Designed for a Surgical Collaborative Robot

University essay from KTH/Medicinteknik och hälsosystem

Abstract: In surgery, suturing is the use of needle and thread to join cut and/or damaged anatomical structures together. This repair strategy is highly versatile and is universal for all types of surgery as the goal is to restore, repair or improve function and/or appearance. The needles are almost always curved in shape, and it is handled and maneuvered by surgeons with a special tool called: needle driver. The versatility of this setup has proven its worth over time as needle drivers are one of the indispensable instruments in all types of surgery. We are entering a future where robots can be programmed to execute tasks with much higher level of precision and speed compared to humans. Medical robotics in surgery has gained ground over the past decades due to promising clinical results. A straightforward step in this direction would be to create a solution that enables the robot to grip needle driver. The purpose of this study was to develop a gripper tool that enables a collaborative robot to perform suturing with one of the most common types of needle drivers used in surgery. The Double Diamond design framework was employed. The selected content in the predefined four phases were: 1) Discover: Observation, MoSCoW Prioritization, Brainstorming, Choosing a Sample, Fast Visualisation, 2) Define: Assessment criteria, 3) Develop: Physical prototyping 4) Deliver: Final testing and Evaluation. In the first phase, Discover, clinical and technical demands were formulated. In the second phase, Define, numerous design ideas were generated and drafted on paper whereof the one with highest assessment score was chosen for physical prototyping. In phase three, Develop, the selected design idea was modelled in cardboard, clay and silicon, and 3D printed. Multiple design iterations were guided by feedback from clinical and technical experts and resulted in a final prototype design that was accepted by the experts. In phase four, Deliver, the final prototype was subjected to final testing and evaluation. Observation of five live and one video recording of surgical procedures on real patients were made. The insights gained were confirmed with the lead and co-surgeons of each procedure and were summarized in 24 clinically important observations relevant for the gripper tool design. Careful analysis of the previously designed gripper tool, live observation of the robot’s motion pattern and range, and interview with robotic engineer were summarized in ten technically important observations. The observations were then used to formulate the clinical and technical demands that the gripper tool design aims to fulfill, followed by prioritizing the demands and design features according by MoSCoW method and brainstorming on how to improve previous gripper tool design. To limit the scope of the design challenge, one of the five types of needle drivers used in pediatric heart surgery in Lund was selected in the method Choosing a Sample. To further characterize the clinical and technical demands, a test bench was set up to Define and measure force vectors applied on the needle driver when held by a surgeon during suturing. The radial forces vectors in six directions perpendicular to the tip of the needle driver ranged from 1.6 N to 3.8 N. The axial force along the length of the needle driver was 7.6 N towards the tip and 8.4 N towards the back end. The clockwise and counterclockwise torque along the length axis of the needle driver was 0.2 Nm and 0.18 Nm, respectively. The set of defined demands were sufficient to sketch numerous ideas of gripper tool designs according to the Fast Visualization method. These designs were then used in the Define phase to communicate the design ideas with surgeons, robotic and product development engineers. The most promising idea was advanced to the Develop phase where physical prototypes were produced in cardboard, clay and silicon and 3D printed. Inadequacies were found during design feedback with interviews and testing together with clinical and technical experts, and design actions were taken to arrive at the final prototype. The final prototype was brought into the Deliver phase for final testing and evaluation. The gripper tool could handle lager force loads than the human surgeon in all the stability tests. However, deflection of the needle driver occurred with the gripper tool unlike when the surgeon was subject to stability testing. One pediatric heart surgeon and one robotic engineer was asked to generate a composite score of fulfillment rate from 1–5, where 1 is bad, 3 satisfactory, and 5 excellent after final testing of the gripper tool was carried out. The final prototype of the gripper tool fulfills all clinical and technical demands at the level of 4, and 3–5, respectively. In conclusion, the design methodology used in this study was useful in the development of a gripper tool design that respects both clinical and technical demands. This suggest that the methodology may be used in similar setting of design challenges in the field between medical and technical innovation. The gripper tool fulfilled the demands, although further refinement in the choice of material, further testing and investigation of regulatory aspects are required before it can be implemented in the operating room.

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