Zeitschrift für Osteoporose und körperliche Aktivität
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Improvement of Fixing Method for the Surgical Assistance Robot and Optimization of Body-Mounted Robotic System

Akira Bekku, Yoshikazu Nakajima, Joonhwan Kim1 and Kazuo Yonenobu

Robotically-assisted surgical system is introduced to achieve safety and high accurate operation. However, its fixation to the patient’s bones requires bone stiffness and there are some problems to apply brittle or cracked bones such as in rheumatism. Metal pin screws are commonly used to connect a robot and a patient and not safe for brittle bones. In this research, we focus on the optimization of a body-mounted small robot system that assists spine puncture surgeries. The robot consists of a fixation part and a needle guide part. The fixing unit can be controlled the stiffness to contour the patient’s body surface tightly. At first, it deforms freely to conform to the surface of the target, and then transition to solid-like state to save the deformed shape by utilizing the jamming transition phenomenon. The guiding part employs a double 45˚ gear mechanism and designed to locate the three cylinder-shaped motors in parallel. It achieved 4-degree-of-freedom needle guidance, X-ray-transparent views in the surgical area and downsizing.

The fixing device is designed to be attached firmly to the human body with keeping the gravity center of the surgical assistance robot low. We designed tripod stand fixing device that can circumvent the unsuitableness area of the human back. The performance of the fixing device on a soft tissue is evaluated. The force to insert a needle into a porcine soft tissue was measured to evaluate the required strength for needle insertion. To penetrate the 30-mm-thick soft tissue, required force was 7.7 N in RMS (Root-mean-square). The fixing stability and the accuracy of needle guide was evaluated by measuring the displacement during needle inserting operation. The displacement to penetrate the 30-mmthick soft tissue was 1.13 mm and 0.38˚ in RMS. Finally, we evaluated the result of the fixing device on human shape target. The displacement of the fixing device on a soft tissue by the external force of needle inserting operation was measured. The displacement of the fixing device on a human shape phantom by the external force of needle inserting operation was 0.13 mm and 0.06˚ in RMS. The total displacement of needle guide was 0.73 mm and 0.59˚ in RMS.