III. Experiments and Results
We have performed five in vivo porcine animal tests with our device. A laparoscopic surgeon (Fowler) used this device to perform a number of surgical procedures, including cholecystectomy, appendectomy, running (measuring) the bowel, suturing, and nephrectomy (kidney removal). Since this test animal species does not have an appendix as a human, resecting part of the colon was used to simulate an appendectomy. We present results from two of the tests below.
[Some details are omitted]
IV. Conclusions and future work
This paper describes a new fully insertable robotic surgical imaging device. The device is part of an effort to create totally insertable surgical imaging systems which do not require a dedicated surgical port, and allow more flexibility and DOF's for viewing. The device has controllable pan/tilt axes, and has been used in-vivo animal experiments which included cholecystectomy, appendectomy, running the bowel, suturing, and nephrectomy. The results suggest that the device is:
- Easier and more intuitive to use than a standard laparoscope.
- Joystick operation requires no specialized operator training.
- Field of view and access to relevant regions of the body superior to a standard laparoscope using a single port.
Time to perform procedures was better or equivalent to a standard laparoscope.
We believe these insertable platforms will be an integral part of future surgical systems. The platforms can be used with tooling as well as imaging systems, allowing many surgical procedures to be done using such a platform. The system can be extended to a multi-functional surgical robot with detachable end-effectors (grasper, cutting, dissection and scissor). Because the systems are insertable, a single surgical port can be used to introduce multiple imaging and tooling platforms into a patient. In addition, we have built our camera/lens/lighting package in a modular manner, allowing us to design a 2 camera system that can provide stereo 3D views of the site.
One of our design goals is to simplify the operation and control of the imaging system. One possible approach to controlling the cameras would be to use a hybrid controller, which allows the surgeon to control some of the degrees-of-freedom (DOF) of the device and an autonomous system, which controls the remaining DOF. For example, the autonomous system can control pan/tilt on the camera to keep a surgeon-identified organ in view, while the surgeon simultaneously may translate the camera to obtain a better viewing angle - all the while keeping the organ centered in the viewing field. We have developed hybrid controllers and mechanisms similar to this for robotic work-cell inspection [27] and believe we can transfer these methods for use with this device.
References
[1] R. H. Taylor, etl, ComputerIntegrated Surgery: Technology and Clinical Applications Cambrisge, MA: The MIT Press; 1996.
[2] Mark Vierra, "Minimally Invasive Surgery,"Annu.Rev.Med.,vol.46, pp147-58,1995.
[3] P.Dario, C. Paggetti, N.Troisfontaine, E. Papa, T.Ciucci, M.C.Carrozza,and M.Marcacci,"A Miniature Steerable End-Effector for application in an integrated system for computer-assisted arthroscopy,"ICRA 97, Albuquerque, New Mexico, 1997.
[References 4 – 28 are omitted]
Instability of pump-turbines during start-up in turbine mode
Thomas Staubli, Florian Senn, Manfred Sallaberger
Introduction
During the last decade the deregulation in the European electricity market has resulted in rapidly changing conditions on the market. Due to the growing demand for balancing power and frequency control an investment in increased pumped storage capacity became economically feasible. Reversible pump-turbines seem to be in many cases the most cost-effective solution. Occasionally torque fluctuations of reversible pump-turbines are encountered in power plants during start-up in turbine mode operation. Such fluctuations can slow down the process of synchronization what is highly undesirable when fast peak power production is required. During start up there is practically no load on the turbine shaft and the turbine operates close to the runaway characteristic. The guide vanes are opened only a few degrees during this phase.
A first case study of such oscillations on a model pump-turbine was presented by Yamabe [1] and [2]. He observed oscillations with pronounced hysteretic behavior which interacted with unsteady cavitation patterns. A case study and a simple cure of the problem by detuning some guide vanes are given by Klemm [3]. A linear stability analysis to predict the occurrence of the oscillations was successfully introduced by Martin [4] and [5]. Also Doerfler [6] presented a case study on how stable operation could be achieved in spite of the instability at no load.
Recent experiences with single stage reversible pump turbines are published by Billdal and Wedmark [7]. They propagandize multiflow guide vanes (MGV) to overcome difficulties with synchronization and to obtain stable speed after load rejection. All authors agree that the so-called S-shape of the four quadrant characteristic of the pump turbines is responsible for the oscillations at no load operation.
[Some details are omitted]
In the following a numerical study will be presented which focuses on the prediction of the characteristic near runaway and on the flow phenomena leading to the instability. To do so, tools were developed to analyze local and time-dependent flow, momentum and energy exchange in each of the runner and guide vane channels and in the vaneless spaces. For validation of a model of a reversible pump-turbine with a known unstable behavior and well documented model test data was chosen.
Numerical flow simulation
The flow near the no load operation of turbines becomes very complex in a sense that the flow is dominated by backflow regions and vortex formations in all parts of the turbine. Furthermore, partial pumping flows start to build up in some or all runner channels. Additionally, the flow becomes vigorously unsteady. Recirculation zones build up and disappear, vortical flows are swept away. To predict such flows - at least qualitatively correct - grid generation must be carried out carefully. The grids used in this study were generated using only hexaedra elements. Grid generation was done with the commercial software ICEMCFD v11.0.
Validation
For validation the numerical flow simulations for operation near the runaway point experimental data from model test were used. The validation was carried out in two steps. In a first step stationary simulations were performed. The demand with respect to computational power is much lower for stationary simulations compared to unsteady, transient simulations. However, the expectations in the accuracy of the results of the stationary simulations are low, since the flow is certainly not stationary near runaway.
[Some details are omitted]