Design of a Hydraulic Dexterous Manipulator for Minimally Invasive Surgery
The research described here identifies the limitations of existing robotic surgical platforms, which include the balance between the scale of the robot and its manipulability in terms of range of motion, load capacity, and tool capability, then develops a means of overcoming them by taking advantage of fluid power as an enabling technology with its inherent power density and controllability. The approach described here differs significantly from conventional surgical robots in that the robot is embedded within the surgical device itself, whereas in the conventional system, a general-purpose robot is used to manipulate various surgical tools. This is done in order to demonstrate that fluid power can be used advantageously for the design of embedded surgical robotic systems for minimally invasive surgery.
To enable the design of a fluid powered surgical robot, it was first necessary to identify the design requirements for a robot of this nature as well as the considerations unique to this approach. To this end, a quantification of the necessary load capacity for natural orifice robots was conducted. Further, through a review of the literature in the fields of surgery and robotics, considerations of necessary workspace and limitations for the prevention of tissue damage were explored. The results of these analyses are presented.
The technologies that comprise this novel surgical robotic system include a hydraulic control valve, actuation units, and an enabling structure. The intended application of these technologies introduced numerous limitations and challenges to the design process. The most stringent of these limitations was that of overall size, due to the realities of patient anatomy, which prevented the use of commercially available hydraulic components. An assemblage of components to achieve the aforementioned design requirements is described including the design of a novel hydraulic control valve to enable manipulation of three actuators using a single valve sized to fit within the working channel of a surgical endoscope.
The advantage of the described approach is that the device enables greater miniaturization, improves cost effectiveness, and has better ease of mobility. The mobility and the relaxed requirements for operating room cleanliness can be potentially useful for mobile clinics, out-patient clinical settings, and on the battlefield. Being more cost effective and having a small overall size, the robotic assisted surgical devices can be widely deployed, even in rural or other less technology intensive environments. Through careful review of the literature and analytical evaluation of the various proposed concepts, it was possible to arrive at a design that meets the needs of modern surgical interventions while addressing the perceived limitations of existing surgical robotics.
Through the efforts described in this dissertation, much new information was produced and developments resulted. The considerations of hydraulic power for surgical robots were evaluated and are applicable to other surgical tasks where hydraulic power may be used advantageously. A quantification of the load requirements for surgical robots performing abdominal procedures was produced which will provide a guide for other researchers developing surgical robots. These values are difficult to find in the literature and are a valuable resource for the field. An alternative, simplified model for predicting the behavior of continuum beams under load was developed to provide an inverse formulation for computing beam shape and end loads. This is useful as continuum beams are widely used for minimally invasive surgical manipulators as well as in a wide variety of other applications. Finally, a novel valve concept and two possible designs realizing this concept were developed. These valve designs facilitate control over the three actuators in an antagonistic arrangement. Further, the valve designs enable proportional control of the three actuators at a size scale not commercially available. In summary, the design of a novel hydraulic surgical manipulator as a summation of its parts has been performed. This design demonstrates the feasibility of the fluid power approach to embedded minimally invasive surgical robotics. The pursuit of this research has provided many unique challenges and the work presented here has addressed many of them, as well as laid the foundation for future developments in the application of hydraulic power to the growing field of surgical robotics for minimally invasive surgery.
University of Minnesota, September 2013