Ichiro Okumura

Tendon-Driven Continuum Robot for Endoscopic Surgery: Preclinical Development and Validation of a Tension Propagation Model

In this paper, we present a tendon-driven continuum robot for endoscopic surgery. The robot has two sections for articulation actuated by tendon wires. By actuating the two sections independently, the robot can generate a variety of tip positions while maintaining the tip direction. This feature offers more flexibility in positioning the tip for large viewing angles of up to 180° than does a conventional endoscope. To accurately estimate the tip position at large viewing angles, we employed kinematic mapping with a tension propagation model including friction between the tendon wires and the robot body. In a simulation study using this kinematic mapping, the two-section robot at a target scale (outer diameter 1.7 mm and length 60 mm) produced a variety of tip positions within 50-mm ranges at the 180° angle view. In the experimental validation, a 10:1 scale prototype performed three salient postures with different tip positions at the 180° angle view. The proposed forward kinematic mapping (FKM) predicted the tip position within a tip-to-tip error of 6 mm over the 208-mm articulating length. The tip-to-tip error by FKM was significantly less than the one by conventional piecewise-constant-curvature approximation (FKM: 5.9 ± 2.9 mm versus PCCA: 23.7 ± 3.6 mm, n = 15, P <; 0.01).

Tendon-driven continuum robot for neuroendoscopy: validation of extended kinematic mapping for hysteresis operation

PurposeThe hysteresis operation is an outstanding issue in tendon-driven actuation—which is used in robot-assisted surgery—as it is incompatible with kinematic mapping for control and trajectory planning. Here, a new tendon-driven continuum robot, designed to fit existing neuroendoscopes, is presented with kinematic mapping for hysteresis operation.MethodsWith attention to tension in tendons as a salient factor of the hysteresis operation, extended forward kinematic mapping (FKM) has been developed. In the experiment, the significance of every component in the robot for the hysteresis operation has been investigated. Moreover, the prediction accuracy of postures by the extended FKM has been determined experimentally and compared with piecewise constant curvature assumption.ResultsThe tendons were the most predominant factor affecting the hysteresis operation of the robot. The extended FKM including friction in tendons predicted the postures in the hysteresis operation with improved accuracy (2.89 and 3.87 mm for the single and the antagonistic-tendons layouts, respectively). The measured accuracy was within the target value of 5 mm for planning of neuroendoscopic resection of intraventricle tumors.ConclusionThe friction in tendons was the most predominant factor for the hysteresis operation in the robot. The extended FKM including this factor can improve prediction accuracy of the postures in the hysteresis operation. The trajectory of the new robot can be planned within target value for the neuroendoscopic procedure by using the extended FKM.

Extended kinematic mapping of tendon-driven continuum robot for neuroendoscopy

We have developed and validated a new tendon-driven continuum robot for neuroendoscopy. The tendon-driven continuum robot has the outer diameter of 3.4 mm and two bending sections. We have also newly introduced an extended forward kinematic mapping (FKM) with attention to the hysteresis operation of the robot. The extended FKM maps tension in tendons to the posture of the robot as time discrete valuables, and evolves the previous posture to the present posture. Through this computation process, the extended FKM performs mapping with the hysteresis. We conducted articulation experiments with the tendon-driven continuum robot to test the extended FKM. We measured the postures reached from two different initial postures as the hysteresis operation, and assessed the prediction accuracy of the postures in comparison to the FKM in our previous study. In the experimental results, the extended FKM predicted the postures in the hysteresis operation with improved accuracy (the maximum position error: 1.6 mm by the extended FKM vs. 3.5 mm by the FKM over 60 mm articulation length).