Control model for the STIFF-FLOP arm

simulator image

The motions capacities and reachable positions of the STIFF-FLOP arm are clearly depending on the bending capacities of the flexible modules and on the number of flexible and controllable modules embedded within the STIFF-FLOP arm. Adding more flexible modules can be considered as a mean of increasing the reachable space by the arm. Nevertheless the addition of modules is not the only solution for doing so.

Indeed, we can consider that the flexible stiff-flop arm is mounted at the end effector of a regular robotic arm. This way, the overall system can not only bend any flexible module, but can also move the base of the flexible STIFF-FLOP arm, increasing thus significantly the reachable space. With such setup, we can furthermore imagine a nice collaboration in between the rigid robot (the regular arm) and the flexible one (based on the STIFF-FLOP modules), in which the bending capacities of the STIFF-FLOP components are mainly activated and used when the surgeon requests a motion that is not feasible by a standard and rigid robotic arm.


The bending capabili-ties can thus be used to complement the motion capabilities of a more conventional surgical robot. We have been working in that direction, by taking into consideration the STIFF-FLOP base motion in the Inverse Kinematics model (responsible of computing the appropriate system configuration to reach a specified pose in the working frame). In addition to the bending of each STIFF-FLOP module, the location of the STIFF-FLOP base becomes a set of parameters to control as well (as if it was mounted onto a robotic arm and thus able to move through the control of such an robotic arm). We have been considering two types of control mode of the STIFF-FLOP base, the “free-flying” mode, and the constraint one. In the “free-flying” mode, we suppose the base can move and rotate in any direction. Such mode is useful to benchmark the behavior of the Inverse Kinematics when adding the base parameters (three for the position and three for the orientation) in the control system. Nevertheless in a realistic setup the base motions are likely to be constraint. Indeed the STIFF-FLOP flexible arm is to be inserted into the human body through a trocar, and thus the motion of the standard robotic arm, providing the base motion capabilities, should respect the trocar constraint, main-taining the fulcrum point at the in-sertion location.

The second control mode is maintaining such constraint using a spherical description of the STIFF-FLOP base location, which enforces directly within the model of this trocar constraint, since all positions and motions defined are expressed with respect to this fulcrum point. The figure illustrates the combined use of the flexible modules bending and the STIFF-FLOP arm base motions to reach a target tip location provided by the surgeons. On that simulation image, the mo-tion of the STIFF-FLOP base are constrained so that the rigid support of the arm (in green) respect the fulcrum point or single point insertion represented in red. The extension of the control model to permit the control of the system base (and the underlying standard surgical robotic arm) significantly extends the STIFF-FLOP concept capabilities and potential uses.



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