| At present,in minimally invasive interventional surgery of cardiovascular disease,doctor can effectively improve operation accuracy by use of a robot assisted system.However,most of these assisted systems do not have force information feedback and the corresponding control function,for this reason,doctor in outer operating room can not feel the touch sense through this assisted system.Therefore,it is necessary to design a catheter operating system with a force reproduction.In this research,a force reproduction system is designed based on master-slave operating technique.Based on the force reproduction concept,three modules of force reproduction are established,the one is motion control module,the other is active module and the third is actual operation module.Motion control module is using the encoder pulse signal to realize the motion of the catheter;Based on the the simulation of the stress of the catheter,the active control module can realize a control method of the simulated force and master damping force;Based on the function relation between the damping force and system control current,actual operation module is established through detecting force of the front of catheter,so as to realize the real-time adjustment of master damping force and accumulate data for subsequent experiments.Accurate three-dimensional model of thoracic aorta is a precondition for simulating catheter stress.Therefore,a proper algorithm is adopted to segment the human body color slices,and moreover,the aortic model reconstruction is achieved.Transient simulations of model thoracic aorta are processed through FEA software such as ANSYS CFX,blood flow velocities in different positions are obtained,and then,the function equation between catheter’s force and its insert length is established under the condition of the catheter do not touch vessel wall.Consequently,the stress analysis is studied when collisions are happened between catheter and vessel wall at different angles,which provide a basis for the design of master operating mechanisms.Master operating mechanism provides the damping force for doctor,and at thesame time,magnetorheological fluid damping force within the mechanism must change with the external magnetic field.Based on this,the relationship between catheter actual force and master damping force is set up,and then the geometric parameter design about master operating mechanism is completed.Finally,the function equation between the system control current and the master damping force is obtained through calculating the magnetic circuit.Master-slave operation experimental platform is built and relevant experiments are carried out.Experimental results show that the output of master damping force is consistent with the designed control system,which means the basic function of force reproduction can be realized in this platform. |
