Abstract
BackgroundIn a deforming anatomic environment, the motion of an instrument suffers from complex geometrical and dynamic constraints, robot assisted minimally invasive surgery therefore requires more sophisticated skills for surgeons. This paper proposes a novel dynamic virtual fixture (DVF) to enhance the surgical operation accuracy of admittance-type medical robotics in the deforming environment.MethodsA framework for DVF on the Euclidean Group SE(3) is presented, which unites rotation and translation in a compact form. First, we constructed the holonomic/non-holonomic constraints, and then searched for the corresponded reference to make a distinction between preferred and non-preferred directions. Second, different control strategies are employed to deal with the tasks along the distinguished directions. The desired spatial compliance matrix is synthesized from an allowable motion screw set to filter out the task unrelated components from manual input, the operator has complete control over the preferred directions; while the relative motion between the surgical instrument and the anatomy structures is actively tracked and cancelled, the deviation relative to the reference is compensated jointly by the operator and DVF controllers. The operator, haptic device, admittance-type proxy and virtual deforming environment are involved in a hardware-in-the-loop experiment, human-robot cooperation with the assistance of DVF controller is carried out on a deforming sphere to simulate beating heart surgery, performance of the proposed DVF on admittance-type proxy is evaluated, and both human factors and control parameters are analyzed.ResultsThe DVF can improve the dynamic properties of human-robot cooperation in a low-frequency (0 ~ 40 rad/sec) deforming environment, and maintain synergy of orientation and translation during the operation. Statistical analysis reveals that the operator has intuitive control over the preferred directions, human and the DVF controller jointly control the motion along the non-preferred directions, the target deformation is tracked actively.ConclusionsThe proposed DVF for an admittance-type manipulator is capable of assisting the operator to deal with skilled operations in a deforming environment.
Highlights
In a deforming anatomic environment, the motion of an instrument suffers from complex geometrical and dynamic constraints, robot assisted minimally invasive surgery requires more sophisticated skills for surgeons
The proposed virtual fixtures (VF) could not effectively eliminate the tracking error drifts over the deforming frequency growth, we hope to improve the dynamic performance of the VF for admittance controlled device
This paper described a novel framework of dynamic virtual fixture (DVF) for admittance-type manipulators on the Euclidean Group SE(3) to assist the surgeons to deal with the dynamic tasks, which
Summary
The configuration space of a robotic system is defined on the special Euclidean group. The following index is defined as the cross-correlation coefficient of manual force Fb = (mb, fb) and corresponded velocity acted on the proxy VbC = (ωCb , vCb ), which consists of the admittance controller output and the logarithmic error feedback in Eq (22). The RTE is suppressed by linear logarithm error compensation, and is independent of deforming frequency This is due to the fact that orientation of reference remained constant while translation along the radial direction, translational deviation along the same direction is compensated autonomously; the proxy is actuated manually along tangent directions, the referred orientation varied . The trajectories of the operator driving the proxy along straight line and circle on the deforming sphere are illustrated in Figure 7, the complicated behaviors of dynamic task is beyond human control, making a distinction between the preferred and nonpreferred directions and employed different control strategy helps reduce operation burden of surgeons and improve their skills in dynamic tasks
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