Research On Tactile Sensor For Minimally Invasive Surgical Instruments

Minimally invasive surgery(MIS)has been widely accepted for many advantages such as minimal trauma,short recovery time and low risk.However,surgeons can’t acquire comprehensive tactile information in MIS comparing with traditional surgery because of the minimal trauma,leading to several problems,which limits the development of MIS.In this paper,a novel tactile sensor was designed for the minimally invasive surgical instruments,providing tactile perception system for MIS.Both hardness and contact force measurement can be realized by using this sensor.The structure of this sensor is simple and can be easily miniaturized,which means it’s suitable for MIS.This research can effectively make the lack of tactile information in MIS up and improve the safety of MIS,which will be helpful for the further development of MIS.In this paper,the requirements of the sensor were analyzed and the design of the tactile sensing system was finished first.Then,several principles of measuring hardness and force were compared.Lead zirconate titanate(PZT)and piezoresistor were chosen to be the sensitive material for hardness and force measurement respectively,then the design of the tactile sensor was finished.The theoretical model of hardness measurement part contacting to the tissue was established based on the Hertz static contact theory and dynamic contact theory.Then,the feasibility of the hardness measurement sensor was verified by finite element analysis method and the calibration was finished in ANSYS.The deformation of hardness measurement sensor and tissue was acquired by static structural analysis.Natural frequency of the hardness measurement sensor was acquired by modal analysis and was the reference for the next step.Based on the results of static structural analysis,the impedance curves of the hardness measurement sensor corresponding to tissues with different hardness were acquired in harmonic response analysis,which verified the feasibility of the sensor.Several samples with different hardness were set to calibrate this sensor.After that,factors affect the measurement sensitivity and range of the sensor were analyzed in order to improve the scope of application of this sensor.Three parts of the hardness measurement sensor were chosen to be analyzed,they were the PZT,the spiral metal plate and the probe.Main factors affect the measurement sensitivity and range of the sensor were chosen from the theoretical contacting model.Contacting models of different sizes for each factor were designed and calibrated.The effects brought by each factor were analyzed by comparing the calibration curve of each contacting model,which can provide basis for selecting size of the sensor.Finally,experiments were carried out to test and calibrate the sensor.Parts of the sensor for hardness and contact force measurement were fabricated.Experimental platform was designed and the data acquisition and analysis system was established.Several silicone samples were used to test the sensor’s abilities of distinguishing hardness,lump detection and modify the simulating calibration curve,then the elasticity modulus of a pig’s heart was measured.The calibrations of four piezoresistors were carried out by a set of weights.After that,the whole assembly of the tactile sensor was finished and the real-time tactile display system was wrote,based on the calibration curves of the sensor,contributing to the establishment of tactile sensing system for MIS.