Gerard McVicker

A remote center of motion robotic arm for computer assisted surgery

We have designed a robotic arm based on a double parallel four bar linkage to act as an assistant in minimally invasive surgical procedures. The remote center of motion (RCM) geometry of the robot arm kinematically constraints the robot motion such that minimal translation of an instrument held by the robot takes place at the entry portal into the patientApos;s body. In addition to the two rotational degrees of freedom comprising the RCM arm, distal translation and rotation are provided to manoeuver the instrument within the patients body about an axis coincident with the RCM. An XYZ translation stage located proximal to the RCM arm provides positioning capability to establish the RCM location relative to the patients anatomy. An electronics set capable of controlling the system, as well as performing a series of safety checks to verify correct system operation, has also been designed and constructed. The robot is capable of precise positional motion. Repeatability in the ±10 micron range is demonstrated. The complete robotic system consists of the robot hardware and an IBM PC-AT based servo controller connected via a custom shared memory link to a host IBM PS/2. For laparoscopic applications, the PS/2 includes an image capture board to capture and process video camera images. A camera rotation stage has also been designed for this application. We have successfully demonstrated this system as an assistant in a laparoscopic cholecystectomy. Further applications for this system involving active tissue manipulation are under development.

The Hummingbird minipositioner-providing three-axis motion at 50 g's with low reactions

The Hummingbird minipositioner is a three-axis servo-mechanism designed to provide fast and accurate positioning of a low-mass probe tip on or above a nearly planar object. Peak XYZ accelerations in excess of 500 m/s/sup 2/ (50 g) are obtained, with positioning resolution under 1 mu m and a workspace of 13 by 13 by 1 mm. The system weighs 950 g and is nearly reactionless during X-Y motion to simplify integration with large-area positioners. The design of the dynamically balanced five-bar linkage assembly and the Z-actuator is presented, along with data on in-plane linkage resonances (shown to be >1 kHz) and the torque cancellation effectiveness. A typical incremental move of 5 mm with 50 g peak acceleration and a move time of 8 ms is also presented.<<ETX>>

Thermal Characterization of Non-Raised Floor Air Cooled Data Centers Using Numerical Modeling

Data center equipment almost always represents a high expenditure capital investment to the customer, and is often operated without any down time. Data com equipment is typically designed to operate at a rack air inlet temperature of between 10 and 35°C, and a violation of this specification can diminish electronic device reliability and even lead to failure in the field. Thus, it is of paramount importance, from a reliability perspective, to sufficiently understand these systems. A representative non-raised floor data center system was numerically modeled and the data generated from a parametric study was analyzed. The model constitutes a half symmetry section of a 40 rack data center that is arranged in a cold aisle-hot aisle fashion. The effect of several input variables, namely, rack heat load, rack flow rate, rack temperature rise, diffuser flow rate, diffuser location, diffuser height, diffuser pitch, ceiling height, hot exhaust air return vent location, and non-uniformity in rack heat load, was studied. Temperature data was collected at several locations at the inlet to the racks. Statistical analysis was carried out to describe trends in the data.Copyright

Effect of Joule heating on electromigration reliability of Pb-free interconnect

Temperature and current are two major parameters that impact electromigration reliability. Due to the large current used in the accelerated electromigration test, the Joule self-heating associated with the stress current can be significant. The paper presents a study of electromigration fails in Pb-free interconnect from the point of view of localized Joule heating. The Joule heating effect in two types of packages, a fully assembled flip chip module with standard C4s and a silicon to silicon assembly with microbumps, is considered. A thermal FEM model is used as a guide to interpret the experimental observations.

Thermal model for embedded two-phase liquid cooled microprocessor

Chip embedded two phase evaporative cooling is an enabling technology to provide intra-chip cooling of high power chips and interlayer cooling for 3D chip stacks. Utilizing an interconnect-compatible dielectric fluid provides a cooling solution compatible with chip to chip interconnects for future high power 3D chip stacks. However, lack of high fidelity and computationally manageable conjugate thermal models limits the development of this technology. To address that, a thermal model for fast and accurate prediction of thermal and electrical behavior of an embedded two-phase liquid cooled micro-processor module is described in this paper. This model consists of a state-of-the-art conjugate heat transfer model for two-phase flow boiling through chip embedded micron-scale channels and a physics-based empirically tuned electrical model of the microprocessor. Extensive model validation using data from several experiments was performed to quantify the accuracy of this model under different operating conditions (including various chip operating frequencies and coolant mass flow rates). Results showed that this model can predict the electrical behavior as well as two-phase flow and heat transfer characteristics with very good accuracy. Overall, the chip junction temperature predictions were within two degrees of the experimental data and the temperature-dependent chip power predictions were within 10%.

Modeling embedded two-phase liquid cooled high power 3D compatible electronic devices

Interlayer cooling utilizing pumped two-phase flow of a chip-to-chip interconnect-compatible dielectric fluid is an enabling technology for future high power 3D (three-dimensional) chip stacks. Development of this approach requires high fidelity and computationally manageable conjugate thermal models. In this paper, a conjugate heat transfer model developed for simulating two-phase flow boiling through chip embedded micron-scale channels is described. This model uses a novel hybrid approach where governing equations for flow-field and convection in the single-phase flow regions (e.g. inlet plenum) as well as that for heat conduction in solids is solved in detail (i.e., full-physics) while in the two-phase flow regions (e.g. micro-channels), a reduced-physics approach is used. Extensive model validation using data from several experiments was performed to quantify the accuracy of this model under different operating conditions.

Microfluidic two-phase cooling of a high power microprocessor part A: Design and fabrication

The effective use of embedded radial expanding micro-channels with micro-pin fields for two phase cooling of a microprocessor die has been demonstrated. In this first part of a two part paper, the integration of this approach into a functional high performance server is presented. Modeling was conducted to design radial micro-channels, micro-pin fields, and orifices to properly distribute flow according to the anticipated maximum work load distribution of power across the processor chip. This design incorporates modeling of two-phase pressure drop under power, allowing for a tight distribution of exit vapor quality across the radial channels. Integrating this technology into a functioning server requires a packaging design and assembly approach compatible with an originally lidded fully functional organic single chip processor module. Processes for de-lidding, channel etching, and packaging for desired coolant flow and thermal behavior through the chip-embedded channels were developed. The resulting processor modules were re-installed in a commercial server and the fluidic performance was measured. In the second part, the functional performance experiments and results are detailed.

Boiling sensitivity analysis of asymmetrically heated micro-scale devices

Thermal challenges in 3D ICs have driven the need for embedded chip cooling. In this paper, we measured the thermal performance of a two-phase system employing flow boiling in chip-embedded micro-channels utilizing the latent heat of vaporization of dielectric refrigerants (such as R-1234ze) In the present study, an investigation was performed on a 20 mm × 20 mm thermal test vehicle having a heater layer to simulate the heat generation from a state-of-the-art 8-core microprocessor chip and a sensor layer to measure temperature at key locations within the test vehicle. Fluidic channels in the form of radial expanding micro-scale cavities with micro-pin fields were etched into the test vehicle. The micro-pin fields represent the through-silicon-via (TSV) interconnects present in multi-die stacks. The heaters are used to simulate a background heat flux of 20 W/cm2 and individual core heat fluxes of up to 210 W/cm2. This heat generation capability corresponds anywhere from a processor low-power idle mode to a high-power super-turbo mode and beyond. Since the flow resistance in a microchannel for two-phase cooling depends on in-situ heat generation, asymmetric power dissipation due to different power levels in various cores and non-core areas may unbalance the overall flow distribution. Furthermore, it may reduce the local heat transfer rate and even lead to premature failure of working cores. This study aims at understanding the effects of asymmetric heat flux profiles on flow resistance and boiling heat transfer.

Integration and Packaging of Embedded Radial Micro-Channels for 3D Chip Cooling

This paper reports on the integration and packaging of embedded radial micro-channels for 3D chip cooling. A thermal demonstration vehicle (TDV) has been designed, fabricated and assembled. Radial micro-channels based on deep Si etching was integrated with a manifold chip to form a 2-layer chip stack, which has been assembled using a ceramic substrate and a Cu manifold. A test vehicle with an effective critical heat flux of 340 W/cm2 and uniform cooling has been successfully demonstrated using a dielectric coolant (R1234ze).