Research Of 3Dof Minimally Invasive Surgery Tissue Clamp And The Force Estimation Of Clamping Jaws

With the same treatment effect as traditional open surgery,abdominal minimally invasive surgery has the advantages of small scar,small pain,quick recovery,and has been accepted by the public.It has been developed faster and faster,and is gradually replacing the traditional open surgery.In the minimally invasive surgery,the quality of the operation is directly determined by the performance of the surgical instruments which are directly contacted with the tissue.The traditional minimally invasive surgical instruments have few degrees of freedom and poor flexibility.The surgical instruments used by the minimally invasive surgical robot represented by Da Vinci are flexible enough,but there is motion coupling between the wrist and the gripper,which is not conducive to position control.Moreover,most of the current surgical robots lack the ability of force feedback,which increases the difficulty of doctors' surgical operation,and the force detection at the end of surgical instruments is the key to achieve the force feedback of the surgical robot.In this paper,aiming at the problem of the low degree of freedom of the minimally invasive surgical instruments,the movement coupling of the wrist and the jaws and the lack of force feedback,a decoupled three degree of freedom tissue clamp is designed and its force estimation is studied.According to the characteristics of minimally invasive surgery,the design requirements of surgical instruments were studied,and an overall configuration of three degrees of freedom tissue grasping forceps was proposed.In order to solve the problem of motion coupling between wrist and gripper,a decoupled structure based on planetary gear principle is designed by mechanical decoupling method.The gripper can realize the deflection of the wrist,the pitch of the claw and the movement of the opening and closing.Each degree of freedom is independent of each other and is driven separately by the motor.Using wire rope transmission mode and friction wheel preload principle,the power is effectively transmitted from the drive end to the end of each degree of freedom.A decoupling method based on the principle of planetary gear is put forward,and the decoupling structure of wrist and claw is designed based on theoretical deduction.According to the whole structure of the grasping clamp,the motor type is selected for each degree of freedom.Finally,the whole physical model of the three degree of freedom tissue grasping clamp is obtained.According to the designed gripper,one claw was taken as the research object to study the force estimation.In order to minimize the influence of friction on force estimation,an experimental platform corresponding to the structure of the gripper is built,and a friction model consistent with the claw structure is obtained by experiments.Based on the Lagrange equation,the dynamic model of the system is established.Considering the effect of friction and external load force,the estimation equation of the external load force based on the dynamic model is derived.The friction terms in force estimation equation are studied by fixed parameter compensation and adaptive parameter compensation method respectively.The feasibility of the two methods is verified by Simulink simulation.The three degrees of freedom of the tissue clamp are tested by single movement and combined movement test,which verifies the rationality of the designed structure and the flexibility of the movement.The decoupling experiment between the wrist and the jaw proves that the coupling problem between the wrist and the jaw is solved,which lays the foundation for improving the position control precision and the force estimation.According to the existing experimental conditions,the force estimation experiment is carried out through the motor current and the motor position,speed and acceleration information collected by the driver.The experimental results show that the estimated value follows the true value,and the steady-state error is about 0.25N(10%),which proves the effectiveness of the force estimation method.