| Robotic minimally invasive surgery(RMIS) overcomes drawbacks of the traditional minimally invasive surgery(MIS) in many aspects such as observation, ergonomics, manipulation, and dexterity. Therefore, it has a wide application in helping the surgeon to conduct surgical operations. However, existing RMIS system still lacks of force feedback. It can not provide the surgeon with interaciton forces between the surgical instruments and patient’s tissues. This causes difficulties in performing tissue palpation to identify tissue properties and abnormalities for the surgeon. It is very difficult for the surgeon to apply precise forces while conducting some delicate tasks. Therefore, force sensing in RMIS has become the hotspot and frontier in this research area. Recently, researchers in this area still suffer from many problems such as inadequate sensing dimensions, low sensing ranges and resolutions, poor compatibility with surgical instruments. It has already become a large obstacl e to improve the quality and efficiency of RMIS.In order to solve the problem of force sensing in RMIS, analysis of interation forces, miniature force sensors and sensorized surgical instrument are developed, technical efficiency of the sensors and instrument are verified by static calibration, test experiment, and ex-vivo experiment. Main contents of this thesis are presented as follows:The interaction forces between the surgical instrument and organ tissues are analyzed. Forces acting on the different parts of the surgical instrument during MIS are analyzed qualitatively. It is essential to sense interaction forces during typical operations such as tissue palpation and blunt dissection, etc. Sensing ranges of the interaction forces for the typical operations and resistive-based sensing method are summarized in order to provide design requirements for the miniature sensors.A miniature 3-axis force sensor for tissue palpation in MIS is developed. A novel tripod elastic structure is designed, strain gauges are used to discriminate the magnitudes and directions of the three orthogonal force components. Linear stiffness matrix and sensitivity matrix are derived to disclose the relationship between the forces, sensitivity and the geometric parameters of the structure. A geometric parameterized optimization method is proposed to provide the sensor structure with adequate stiffness and high sensitivity. Sensing ranges and resolutions are obtained by static calibration. The ex-vivo experiment shows that the sensor can be used to perform tissue palpation during MIS procedures.A miniature 6-axis force/torque sensor for typical operations is designed. A flexural-hinged Stewart platform is designed to measure all the six components of interaction forces. A novel straightforward optimization method considering the generalized force and sensitivity isotropy is proposed and a non-dominated sorting genetic algorithm(NSGA-ΙΙ) is applied to determine geometric parameters best suited for the given external loads. Sensing ranges and resolutions are obtained by static calibration.A novel surgical instrument with modular joints and 6-axis force sensing capability is developed. A grasper mechanism integrated with the miniature sensor is designed, a tension decomposition mechanism is introduced to alleviate disturbance of the grasper cable force to the sensor. Based on reconfigurable design method, a modularized wrist mechanism is designed to facilitate integration of the miniature sensor, provide the instrument with pitch and yaw motions, and effectively eliminate coupled motion of the wrist. Experimental test in motion aspects are discussed, and the technical indexes such as motion ranges and repeated position resolutions are obtained.Effect of force sensing for this instrument prototype is experimentally evaluated. Tissue palpation and blunt dissection experiments conducted in the master-slave manner show that it is feasible to apply this instrument prototype in RMIS for force sensing and force feedback. |
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