In physical human-robot interaction (pHRI) enabled by admittance control, delay-induced oscillations arising from both the neuromuscular time-delays of the human and electromechanical delays of the robot can cause unsafe instability in the system. This study presents and evaluates rate-limiting as a means to overcome such instability, and provides a new perspective on how rate-limiting can benefit pHRI. Specifically, a rate-limited and time-delayed human-in-the-loop (HITL) model is analyzed to show not only how the rate-limiter can transform an unstable equilibrium (due to time-delay) into a stable limit-cycle, but also how a desired upper-bound on the range of persistent oscillations can be achieved by appropriately setting the rate-limiter threshold. In addition, a study involving 10 subjects and the EXO-UL8 upper-limb exoskeleton, and consisting of 16 trials - 4 rate-limiter thresholds by 4 time-delays - is performed to: (1) validate the relationships between time-delays, rate-limits, and position bounds on persistent oscillations, and (2) demonstrate the effectiveness of rate-limiting for recovery from delay-induced oscillations without interfering with regular operation. Agreement of experimental results with the theoretical developments supports the feasibility of incorporating rate-limiting in admittance-controlled pHRI systems as a safety mechanism.

Suturing is required in almost all surgeries but it is challenging to perform with surgical robots due to limited vision and/or haptic feedback. To tackle this problem, we present an autonomous suturing framework that encompasses a novel needle path planner, as well as an accurate needle pose estimator and a six degrees-of-freedom controller. A novel needle grasper is developed that enables needle pose estimation both inside and outside the tissue. The framework was evaluated experimentally using the Raven IV surgical system and important suture parameters were quantified. The experiment results confirmed a needle pose estimation accuracy of°in orientation across all directions. Moreover, the results revealed that using the proposed framework enabled following the reference needle trajectories with errors of 2.07 mm in position and 4.29°in orientation. These are drastic improvements of more than 10× in position and 5× in orientation compared to the Raven IV kinematic controller. Additionally, the results verified that our framework delivered the desired clinical suture parameters successfully across tissue phantom environments with different mechanical properties and under various needle trajectories. A supplementary video can be found at: http://bionics.seas.ucla.edu/research/surgeryproject18.htmlhttp://bionics.seas.ucla.edu/research/surgeryproject18

Tissue manipulation is a frequently used fundamental subtask of any surgical procedures, and in some cases it may require the involvement of a surgeon's assistant. The complex dynamics of soft tissue as an unstructured environment is one of the main challenges in any attempt to automate the manipulation of it via a surgical robotic system. Two AI learning based model predictive control algorithms using vision strategies are proposed and studied: (1) reinforcement learning and (2) learning from demonstration. Comparison of the performance of these AI algorithms in a simulation setting indicated that the learning from demonstration algorithm can boost the learning policy by initializing the predicted dynamics with given demonstrations. Furthermore, the learning from demonstration algorithm is implemented on a Raven IV surgical robotic system and successfully demonstrated feasibility of the proposed algorithm using an experimental approach. This study is part of a profound vision in which the role of a surgeon will be redefined as a pure decision maker whereas the vast majority of the manipulation will be conducted autonomously by a surgical robotic system. A supplementary video can be found at: http://bionics.seas.ucla.edu/research/surgeryproject17.html.

In autonomous suturing with a surgical robot, needle shape, diameter, and path are critical parameters that directly affect suture depth and tissue trauma. This paper presents an optimization-based approach to specify these parameters. Given clinical suturing guidelines, a kinematic model of needle-tissue interaction was developed to quantify suture parameters and constraints. The model was further used to formulate constant curvature needle path planning as a nonlinear optimization problem. The inputs of the optimization include the tissue geometry, surgeon defined entry/exit points, and optimization weighting factors. The outputs are the needle geometry and suggested path. Off-line simulations were used to evaluate the accuracy and performance of the proposed model, and to determine optimized needle geometry and path for several clinically relevant input sets. The output and the optimization results were confirmed experimentally with the Raven II surgical system. The proposed needle path planning algorithm guarantees minimal tissue trauma and complies with a wide range of suturing requirements.