Design Of Defogging System In Laparoscope And Analysis

Minimally invasive surgery has been applied widely due to its advantages such as small trauma,less scarring,quick recovery,and low cost.Endoscope is a key apparatus for observation in minimally invasive surgery.However,the lens of endoscope may covered by fog caused by temperature difference in surgical procedure.It affects image clarity and even makes image blurred which may cause interruption of surgery.In this thesis,design of an anti-fog system for endoscope is discussed to improve the reliability of endoscopy as well as the safety and efficiency of minimally invasive surgery.Firstly,the causes of lens fogging in every stage of minimally invasive surgery are analyzed.The existing anti-fog methods have disadvantages like short lasting time and poor performance.A novel anti-fog method is proposed based on multi-step heating strategy,which is a solution for different fogging reasons and is effective during the whole surgery operation procedure.Secondly,the lens temperature control model is established based on the detailed analysis of laparoscopic system structure and the working environment.Three types of heating components and their models are discussed respectively.A fuzzy control system with TEC voltage controlled by PWM is designed to achieve constant temperature in various stages of operation procedure.The simulation results show that the performance of presented temperature control system can meet the requirements with small overshoot and good robustness.Thirdly,based on the analysis above,the design of hardware system is introduced,including the selection of anti-fog sensors and the design of related circuits.The development of the software is also described in detail,which includes the main program,current acquisition,temperature acquisition,temperatures control,and communication program.A simulation system of anti-fog system is developed on Matlab.Furthermore,in order to improve the safety of the system to meet requirements of medical equipment,a protection circuit is designed to cut off PWM power automatically as long as current in temperature circuit or temperature on lens is over limit,so as to ensure the safety of the system effectively.In conclusion,the presented anti-fog system in this thesis lays the foundation for the realization of anti-fog system which is effective in whole operation procedure of minimally invasive surgery and provides the basis for further design of anti-fog endoscope.