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Design and Implementation of an Auto-Grasping Algorithm for a Robotic Laparoscopic Instrument

Amirkhani, Golchehr | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56621 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farahmand, Farzam
  7. Abstract:
  8. The main goal of this project is to design and implementation of the tissue auto-grasping algorithm for a wristed laparoscopic instrument. In this algorithm, the difference between the pinch forces of two jaws was taken into account when the pull force direction corresponding to the rod instrument direction was changed. The term ‘Tissue auto-grasping’ means automatic adjustment of the pinch force corresponding to the pull force exerted on the tissue by the robotic surgical instrument, so that slip and exerting excessive force on the tissue are prevented. In this study, obtaining the pinch force is based on the proximal force-sensing technique. For this reason, the force model of wristed laparoscopic instrument was obtained. In this force model, the relationship between the trigger force and the pinch force at each jaw in terms of the wrist angle and the jaw angle was obtained by using a kinematic submodel and a friction submodel. In order to verify the validity of the instrument force model, two experiments at wrist angles 20 and 70 degree were performed. The root mean squared of the pinch forces, obtained by using the experimental data and the instrument force model at wrist angles 20 and 70 degree were 0.17 N and 0.11 N respectively. In order to find the pinch forces for grasping tissue in the safe area (corresponding to the magnitude and direction of the pull force), the three-zone model, including slip, damage and safe grasp was obtained for the sheep’s stomach sample empirically. Then an algorithm for tissue auto-grasping was designed. In this algorithm for grasping tissue in the safe area, the safe trigger force was determined by using the three-zone model, the force model and the magnitude and direction of the pull force. Finally, the Tissue auto-grasping algorithm was implemented on the laparoscopic instrument by a P controller. In order to examine the accuracy of the designed controller, two experiments at 0 and 40 degree between the pull force direction and the rod instrument direction were performed. Although the difference between the desired pinch force and the actual pinch force, measured by strain gages was in the range 0f 0.2 N to 0.35 N, the designed algorithm was able to adjust the pinch forces against the variable pull force in the safe area
  9. Keywords:
  10. Robotic Surgery ; Laparoscopic Surgery ; Robotic Laparascopic Instrument ; Force Control ; Tissue Auto-Grasping ; Minimally Invasive Procedures

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