Studies Of Haptic Bilateral Teleoperation Minimally Invasive Surgery System Based On Hybrid Control

In biomedical engineering,one application of bilateral teleoperation system is the design and development of romote minimally invasive surgery(MIS)system.While the stability is a requisite for operation of the system,transparency is the ability of the system to transmit forces and positions from one end to the other end without distortion.Therefore,in order to obtain the realistic and real-time performance of the information feedback,the design of controllers in a bilateral teleoperation system must satisfy two important indicators,that is,stability and transparency.So far,studies on factors that influence teleoperation system performance are mainly focuses on the communication delay,whether the terminal satisfy passivity,and ignore the effect brought by the controller discretization.The reason why a discretization procedure has the potential to jeopardize the transparency of a bilateral teleoperation system,is that,in order to keep the digital system stable,as reported in the literature,there exist a upper bound for the product of the sampling period and control gain.When the sampling period has chosen its minimum value,if the control gain with its maximum value still cannot provide small enough position error/force error,or high enough impedance transmitted from salve robot to the master robot,the transparency of the bilateral teleoperation system is not idea.By analysing the transparency of analog control in bilateral teleoperation system,the target of this paper,is to reduce the effect of the controller discretization on the bilateral teleoperation control system,to improve transparency when keeping the system stable with the help of the field programmable analog array(FPAA).Main contents of this thesis are presented as follows:An analog controlled bilateral teleoperation system is designed and its transparency is analyzed.After given the system's stable region,by measuring and comparing the hybrid matrix parameters with parameters in the digital controller,both system are mathematically and experimentally studied and analyzed.The result show that under stability conditions,analog controlled teleoperation system have hybrid matrix parameters that are closer to their ideal values than their digital controlled counterpart.This means better force tracking and position tracking performance under analog control,which lead to better system transparency and task performance.A FPAA based bilateral teleoperation system is developed.In the analysis experiment for system transparency,if the slave robot do not have load and do not contact any environment,the position error of FPAA based bilateral teleoperation is lower than the digital controlled system;In the teleoperated switch task which requiring high impedance feedback,with the FPAA-based controlled system,the task success rate of operators can be improved to 90%,while the rate with digital system is 20%~40%.Both results of the experiments suggests that,FPAA-based bilateral teleoperation system have samll enough position error,can offer good enough impedance feedback to fulfill the task,reduce the constraints from the controller discretizatin on transparency and validate its advantages in improving transparency of the bilateral teleoperation systems.Considering the constraints brought by analog control,such as op-amp saturation and hard to implement complex algorithm,the FPAA-based controller and digital controller are combined.This combination expands the application scope of the bilateral teleoperation.The stability conditions for proposed hybrid control bilateral teleoperation system is deduced,considering whether the system has communication delay or the terminal are passivity.In stable region,the hybrid controller improves the maximum control gain from 30 N ?m rad to 40 N ?m rad;In the switched task,the position error under hybrid method controlled teleoperation system is 0.05 cm,while the position error of the pure analog/digital system is 0.09/0.21 cm.When analyze the force feedback transparency,the success rate of object stiffness discrimination is 90%,while the rate is only 40% in digital system.As a complementary to haptic bilateral teleoperation system,the stability and transparency of hybrid FPAA/digital controlled haptic virtual environment(HVE)system.A major application of HVE is minimally invasive surgery simulation system.This chapter combined the proposed hybrid controller to a lab self-developed surgery simulation platform,in order to derive the system stability condition and stable range for further research.By simulation,stability region of digital control on the non-delayed and delayed single-user HVE system have been obtained.The proposed FPAA based hybrid conrol method,can be used both in bilateral teleoperation systems and the virtual haptic teleoperatoin systems.The stability conditions derived in this paper considering four different conditions(the system is positive or not,and the effect of time delay exists or not)have never been proposed before.Study the application of FPAA based hybrid control method in a bilateral teleoperation system has provided a new thought not only for improving the stability and transparency simultaneously,but also for increasing the reality of information feedback in romote minimally invasive systems.