Fig. 5.
The forbidden-region virtual-fixture control algorithm requires computation of the distance d between the tool tip resting position (prest) and the 3D vessel point (pclosest) closest to prest. prest is the position Micron takes when no control is triggered. To understand if the control command has to be triggered, first, (left image) the closest point Cī on the 3D vessel centerline Ci, i ∈ [0, I − 1], with I equal to the number of centerline points) is found. Then, (central image) pclosest is found among the points on the circumferences [Cī−2, Cī+2]. Finally (right image) if d is lower than a predefined threshold (dsafety), the Micron control is activated and the new Micron tip position (pcontrol) is defined, which lays on the line passing through pclosest and the current prest and is at a safety distance (dsafety) from pclosest.