James R. Morrison

Automatic Battery Replacement System for UAVs: Analysis and Design

Future Unmanned Aircraft Systems (UASs) are expected to be nearly autonomous and composed of heterogeneous Unmanned Aerial Vehicles (UAVs). While most of the current research focuses on UAV avionics and control algorithms, ground task automation has come to the attention of researchers during the past few years. Ground task automation not only relieves human operators, but may also expand the UAS operation area, improve system coverage and enable operation in risky environments without posing a threat to humans. We propose a model to evaluate the coverage of a given UAS. We also compare different solutions for various modules of an automated battery replacement system for UAVs. In addition, we propose a ground station capable of swapping a UAV’s batteries, followed by a discussion of prototype components and tests of some of the prototype modules. The proposed platform is well-suited for high-coverage requirements and is capable of handling a heterogeneous UAV fleet.

New linear program performance bounds for queueing networks

We obtain new linear programs for bounding the performance and proving the stability of queueing networks. They exploit the key facts that the transition probabilities of queueing networks are shift invariant on the relative interiors of faces and the cost functions of interest are linear in the state. A systematic procedure for choosing different quadratic functions on the relative interiors of faces to serve as surrogates of the differential costs in an inequality relaxation of the average cost function leads to linear program bounds. These bounds are probably better than earlier known bounds. It is also shown how to incorporate additional features, such as the presence of virtual multi-server stations to further improve the bounds. The approach also extends to provide functional bounds valid for all arrival rates.

Practical Extensions to Cycle Time Approximations for the

Approximate closed form expressions for the mean cycle time in a G/G/m-queue often serve as practical and intuitive alternatives to more exact but less tractable analyses. However, the G/G/m-queue model may not fully address issues that arise in practical manufacturing systems. Such issues include tools with production parallelism, tools that are idle with work in process, travel to the queue, and the tendency of lots to defect from a failed server and return to the queue even after they have entered production. In this paper, we extend popular approximate mean cycle time formulae to address these practical manufacturing issues. Employing automated data extraction algorithms embedded in software, we test the approximations using parameters gleaned from production tool groups in IBMs 200 mm semiconductor wafer fabricator.

G/G/m

A key requirement for the complete autonomy of an unmanned aerial vehicle (UAV) is the replenishment of its energy source and other consumables. Such processes are typically overseen and conducted by a human operator, may be time consuming and effectively reduce the operating range of the system. To satisfy the requirements of UAV customers such as military surveillance networks, that seek faster, broader and more fully autonomous systems, and hobbyists, who seek to avoid the hassle associated with changing the fuel source, we develop automated energy recharging systems. Focusing on battery operated remote control helicopters, we employ the Axiomatic Design methodology to develop design concepts of platforms to act as automatic service stations. We propose three station designs for refilling platforms and one concept for battery exchange platforms. In addition, we analyze the economic feasibility of automatic consumable replenishment stations, consider two types of station (container refilling and container exchange) and discuss the application of these systems. Refilling platforms better suit low coverage unmanned aerial systems (UAS) while exchange stations allow high coverage with fewer UAVs.

-Queue With Applications

The duration of missions that can be accomplished by a system of unmanned aerial vehicles (UAVs) is limited by the battery or fuel capacity of its constituent UAVs. However, a system of UAVs that is supported by automated refueling stations may support long term or even indefinite duration missions. We develop a mixed integer linear program (MILP) model to formalize the problem of scheduling a system of UAVs and multiple shared bases in disparate geographic locations. There are mission trajectories that must be followed by at least one UAV. A UAV may hand off the mission to another in order to return to base for fuel. To address the computational complexity of the MILP formulation, we develop a genetic algorithm to find feasible solutions when a state-of-the-art solver such as CPLEX cannot. In practice, the approach allows for a long-term mission to receive uninterrupted UAV service by successively handing off the task to replacement UAVs served by geographically distributed shared bases.

UAV Consumable Replenishment: Design Concepts for Automated Service Stations

The photolithography cluster tool is typically the most expensive tool set utilized in the production of semiconductor wafers and is often selected as a fabricator bottleneck. Modeling such a tool as a serial processing cluster tool, we deduce measures of tool performance. Queueing models reveal that the mean cycle time in the presence of a Poisson arrival process is related to the parallelism inherent in the system configuration. As a consequence, the normalized mean cycle time behavior has a different form than that of the standard single server queue. The process time of a lot and the throughput are evaluated in the presence of disruptions common in practical manufacturing environments. For multiple products with different process rates, it is shown that the throughput is not influenced by the order in which the lots are sequenced.

On the Scheduling of Systems of UAVs and Fuel Service Stations for Long-Term Mission Fulfillment

The flight duration of unmanned aerial vehicles (UAVs) is limited by their battery or fuel capacity. As a consequence, the duration of missions that can be pursued by UAVs without supporting logistics is restricted. However, a system of UAVs that is supported by automated logistics structures, such as fuel service stations and orchestration algorithms, may pursue missions of conceivably indefinite duration. This may be accomplished by handing off the mission tasks to fully fueled replacement UAVs when the current fleet grows weary. The drained UAVs then seek replenishment from nearby logistics support facilities. To support the vision of a persistent fleet of UAVs pursuing missions across a field of operations, we develop an improved mixed integer linear programming (MILP) model that can serve to support the system’s efforts to orchestrate the operations of numerous UAVs, missions and logistics facilities. Further, we look toward the future implementation of such a persistent fleet outdoors and develop prototype components required for such a system. In particular, we develop and demonstrate the concerted operation of a scheduling model, UAV onboard vision-based guidance system and replenishment stations.

Performance evaluation of photolithography cluster tools

We demonstrate that flow line models with deterministic service times and an arbitrary arrival process may be exactly decomposed into segments that each exhibit similar behavior. We call the segments channels and demonstrate that this decomposition leads to a recursion for the delay experienced by customers within the system. The consequence, in addition to clearly elucidating the manner in which customers advance, is that the state of a flow line at any time can be completely characterized by a handful of parameters per channel. The recursions and channel decomposition allow us to model a class of state dependent failures that are common in certain cluster tools in semiconductor wafer manufacturing. Using the fact that wafers are typically grouped into batches, we are able to reduce the computation required to simulate the wafer advancement by about 50 times. The models have been tested with data from a clustered photolithography tool in production and provide throughput and process time predictions within 0.5% and 3% of the actual performance, respectively.

Persistent UAV Service: An Improved Scheduling Formulation and Prototypes of System Components

For multiclass flow line models, we identify a class of service times that allow a decomposition of the system into subsets of servers called channels. In each channel, the customer delay is well structured and we develop a recursion to calculate it. The recursions provide an alternative to the elementary evolution equations. By considering batch arrivals and restricting the structure of the model, the recursions can require nearly one order of magnitude less computation than is otherwise possible. Flow lines can be used as models for semiconductor manufacturing equipment such as multicluster or clustered photolithography tools. The models allow for internal wafer buffers and setups that are wafer location dependent. The models have shown to be very accurate in tests with data from clustered photolithography tools in production. As such, the models may serve as good candidates to improve the fidelity of existing equipment models in fab level simulation.

Deterministic Flow Lines With Applications

A cluster tool consists of a collection of wafer processing chambers housed in a chassis about a wafer transport robot. Cluster tools are of increasing importance in semiconductor wafer manufacturing. While much effort has been focused on the modeling and optimization of such tools in steady state, less attention has been paid to transient modeling. It is anticipated that there will be smaller lot sizes, more product changeovers and an increase in setups brought about by the transition to 450mm wafer diameters and product customization. As such, transient behavior may become the norm rather than the exception. In this paper we conduct a rigorous analysis of the cycle time of wafers that includes transient behavior, diverse process times and robot movement. The results extend existing analyzes, provide justification of existing approximations and allow us to develop more expressive and simple approximations for the cycle time. The models, which include the robot as a resource, can be used to replace the common affine Ax+B tool model in fab level simulations. A study of the quality and computational complexity of various transient models is conducted.