Development of a linear axis system to extend the reach of surgical robot arms

The project was fulfilled as part of the Minimally Invasive Robot-Assisted Computer-guided LaserosteotomE (MIRACLE) project at the Department of Biomedical Engineering (DBE) at the University of Basel. Briefly, the aim of the project is to perform minimally invasive bone cutting with the assistance of robotic-guided system. For this reason, a collaborative surgical robot GG-1 was designed to hold a flexible endoscope and guide it into the target zone to perform laser osteotomy. To extend the workspace of the robotic system in the operating room and increase autonomy, a new concept was introduced in the development of GG-1 platform. A linear axis system using linear servo motor technology was implemented to the robotic system. The first prototype of the linear axis was developed and built in 3D printed parts with a magnetic encoder system. Due to the poor mechanical structure, the system was operating with a limited low/high speeds and lacking positioning accuracy in addition to the calibration needed at start-up. In this thesis, a new reliable linear axis system was designed and developed. Based on the defects detected in the old system and issues we had in the positioning system, the components of the previously existing prototype were revised and a literature review of different mechanisms was conducted. Several measurements were performed for the characterization of the newly developed system after the successful commissioning and controller tuning. The new linear axis system showed better positioning accuracy and smooth motion. In addition, different test movements were performed to determine system performance. The minimum velocity the system can reach and still responds smoothly was determined. A demonstration trajectory was created showing the ability of the linear axis system in responding to different motion paths. Also, the system was tested with a load of 25 kg to verify its capability in a loaded case. Although, all the tests were performed with a limited velocity. The results showed an improvement in mechanical structure and functionality. The last task of the thesis was the implementation of admittance control concept to the linear axis system. The concept was evaluated and showed good behavior with the simple control algorithm used. However, the controller parameters of the linear axis were tuned to operate with no additional load to the linear axis system. Further fine-tuning might be necessary for the full functionality of the complete robot mounted to the linear axis due to the variation in weight and inertia.