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The Underactuated Lightweight Tensegrity Robotic Assistive Spine (ULTRA Spine) project is an ongoing effort to create a compliant, cable-driven, 3-degree-of-freedom, underactuated tensegrity core for quadruped robots. This work presents simulations and preliminary mechanism designs of that robot. Design goals and the iterative design process for an ULTRA Spine prototype are discussed. Inverse kinematics simulations are used to develop engineering characteristics for the robot, and forward kinematics simulations are used to verify these parameters. Then, multiple novel mechanism designs are presented that address challenges for this structure, in the context of design for prototyping and assembly. These include the spine robot’s multiple-gear-ratio actuators, spine link structure, spine link assembly locks, and the multiple-spring cable compliance system.

Abstract-Tensegrity robots are a class of compliant robots that have many desirable traits when designing mass efficient systems that must interact with uncertain environments. Various promising control approaches have been proposed for tensegrity systems in simulation. Unfortunately, state estimation methods for tensegrity robots have not yet been thoroughly studied. In this paper, we present the design and evaluation of a state estimator for tensegrity robots. This state estimator will enable existing and future control algorithms to transfer from simulation to hardware. Our approach is based on the unscented Kalman filter (UKF) and combines inertial measurements, ultra wideband time-of-flight ranging measurements, and actuator state information. We evaluate the effectiveness of our method on the SUPERball, a tensegrity based planetary exploration robotic prototype. In particular, we conduct tests for evaluating both the robot's success in estimating global position in relation to fixed ranging base stations during rolling maneuvers as well as local behavior due to small-amplitude deformations induced by cable actuation.

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Extralevator abdominoperineal resection (E-APR) has been advocated as a superior procedure to achieve negative circumferential resection margins (CRMs) for sphincter-invading rectal cancers. An open total mesorectal excision is performed followed by perineal dissection with resection of the levators in the prone position. We describe a novel minimally invasive robotic approach carried out in the lithotomy position. Using the robotic arms to dissect the rectum and divide the levator fibers at their origin, the dissection is carried out in the ischiorectal space as distally as possible. From May to July 2011, six cases of robotic E-APR for rectal cancer were performed. The mean age was 54.5 years old. Mean operating time was 335 minutes. Mean estimated blood loss was 250 mL. There were no conversions to the open approach. A cylindrical specimen was obtained in all patients without perforation. All CRMs were negative. Mean hospital stay was 5 days. Two patients developed perineal wound infections and one developed a small bowel obstruction postoperatively. Robotic-assisted E-APR performed in the lithotomy position is safe and feasible. Future studies are needed to define the benefits of this technique.

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