Applying Virtual Fixtures to the Distal End of a Minimally Invasive Surgery Instrument

Abstract

The comanipulation paradigm, in which a user and a robot simultaneously hold a tool, allows for gesture guidance. In particular, virtual fixtures, which are geometrical constraints imposed to the tool by the robot, have received a great interest in the domain of surgical applications. So far, this concept has been implemented in the context of open surgery. This paper explores the application of virtual fixtures for minimally invasive surgery, where the tool is inserted in the patient through a fulcrum. Here, a key issue is to return to the surgeon forces that are virtually applied at the instrument distal tip, while the robot is physically attached to the instrument proximal handle. To this aim, two approaches are investigated. A first approach consists in applying a full wrench at the proximal end of the instrument that is equal to the wrench constituted by a pure force applied to the instrument's distal tip. A second approach consists in applying a pure force to the instrument proximal end, thanks to a lever model about the fulcrum. The two approaches are compared through experiments during which naive subjects blindly perform virtual object palpation and robot guided movements. During experiments, indicators involving motion and force analysis are computed. The user capacity to distinguish between several virtual objects is evaluated as well. Although drastically different, the two approaches provide assistance with a similar level of efficiency.

Dynamic Active Constraints for Surgical Robots Using Vector-Field Inequalities

“…Using the same methodology of Section III-A, we redefine d safe to maintain the robot inside a safe region; that is, 5 The motion of the restricted zone takes into account the actual obstacle motion and the motion of the safe boundary (i.e., whenḋ safe = 0). with final solution, assuming the desired signed distance dynamics (16), given by…”

“…The first one is used to evaluate the effect of the parameter η d in the vector-field inequality in (16); the second one is used to evaluate the use of several simultaneous active constraints to avoid collisions with an anatomically correct head model while a pair of robots automatically track a prescribed trajectory; and the last one is used to evaluate the system behavior under teleoperation and tool-tissue interactions with a flexible tissue phantom. Both simulations and experiments used the same software implementation on a single computer running Ubuntu 16.04 x64 with a kernel patch to Linux called CON-FIG_PREEMPT_RT 9 from Ingo Molnar and Thomas Gleixner.…”

“…In the experiments, the tool-tip position with respect to the robot end effector was calibrated by using a visual tracking system (Polaris Spectra, NDI, Canada) through a pivoting process. 16 The visual tracking system was also used to calibrate one robot base with respect to the other.…”

“…1) Results and discussion: The performance for η d = 2 in terms of the trajectory tracking error and minimum separation 16 The pivoting process consists in adding a marker to the tool, then pivoting the tool tip about a divot and recording the marker coordinates to obtain the relative translation between marker and tool tip. This process is available in the manufacturer's software.…”

“…A thorough survey on active constraints was done by Bowyer et al [14]. More recent papers published after that survey presented the use of guidance virtual fixtures to assist with knot tying in robotic laparoscopy [15] and virtual fixtures to allow surgeons to feel the projected force feedback from the distal end of a tool to the proximal end of a tool in a comanipulation context [16].…”