Patrick J. Starr

An investigation of dynamic group scheduling heuristics in a job shop manufacturing cell

SUMMARY The objective of this study is to develop dynamic scheduling heuristics for cellular manufacturing environments (group scheduling or family heuristics) and compare them with existing family heuristics under various shop floor conditions. The proposed family heuristics stress good due date performance while reducing overall set-up time. Computer simulation is used to test three queue selection rules in conjunction with three dispatching rules under eight experimental conditions in a job shop cell. The results indicate that several of the proposed heuristics substantially improve the performance of the cell over the best previously suggested family heuristic under all experimental conditions.

Dynamics of Narrow Tilting Vehicles

Narrow commuter vehicles can address many congestion, parking and pollution issues associated with urban transportation. In making narrow vehicles safe, comfortable and acceptable to the public, active tilt control systems are likely to play a crucial role. This paper concentrates on developing a dynamic model for narrow vehicles that can be used for the design and evaluation of active tilt control systems. The model has four degrees of freedom including lateral and tilt dynamics. The influence of gyroscopic forces due to rotating wheels and the influence of front wheel trail are included but secondary coupling effects are ignored so as to keep the model tractable. The model is used in this paper to understand the influence of vehicle tilt on the steering angle required for cornering, the desired tilt angle for any specified cornering maneuver and the influence of gyroscopic moments on transient tilting/cornering maneuvers. A study of the model equations also provides insight into how narrow vehicles can be designed so as to be self-stabilizing.

A fundamental investigation of tilt control systems for narrow commuter vehicles

One way of addressing traffic congestion is by efficiently utilizing the existing highway infrastructure. Narrow tilting vehicles that need a reduced width lane can be part of the solution if they can be designed to be safe, stable, and easy to operate. In this paper, a control system that stabilizes the tilt mode of such a vehicle without affecting the handling of the vehicle is proposed. This control system is a combination of two different types of control schemes known as steering tilt control (STC) and direct tilt control (DTC) systems. First, different existing variations of both STC and DTC systems are considered and their shortcomings analysed. Modified control schemes are then suggested to overcome the deficiencies. Then a new method of integrating these two control schemes that guarantees smooth switchover between the controllers as a function of vehicle velocity is proposed. The performance of the proposed STC, DTC, and integrated systems is evaluated by carrying out simulations for different operating conditions and some experimental work. The design of a second-generation narrow tilting vehicle on which the developed control system has been implemented is presented.

Road bank angle considerations in modeling and tilt stability controller design for narrow commuter vehicles

Narrow tilting vehicles that occupy a half width lane can play a big role in addressing traffic congestion problems by effectively doubling the capacity of existing highway lanes. In designing the tilt stability control system of such a vehicle consideration of the road bank angle is crucial since it plays a big role in minimizing the torque requirement of the tilt actuation system. In this paper the dynamic model of a tilting vehicle that takes into account the road bank angle is first developed. Then the design of a direct tilt control scheme that stabilizes the tilt mode of such a vehicle is outlined. Since the controller designed makes use of current road bank angle data, a method is outlined on how to determine the road bank angle from accelerometer readings. Finally simulation results are presented and discussion of the results is given

Development and Experimental Evaluation of a Tilt Stability Control System for Narrow Commuter Vehicles

This paper concentrates on development and experimental investigation of a compound control system designed for tilt stability of a narrow commuter vehicle. The control system is a combination of three different types of control schemes: Steering Tilt Control (STC) system, Direct Tilt Control (DTC) system and Tilt Brake system. These schemes utilize different types of actuators and offer complementary advantages over different ranges of operating speeds. The design of the control system is discussed. Then the combined STC-DTC system is first validated by running standard vehicle maneuver experiments such as turns and lane changes. The performance of the Tilt Brake algorithm is then verified for different low speed maneuvers. The feasibility of a stand alone DTC system is also experimentally investigated. Finally different experimental results are presented to demonstrate the effect of desired tilt angle definition on the handling of a narrow tilting vehicle.

Active Roll Mode Control Implementation on a Narrow Tilting Vehicle

This paper describes work carried out on the development of a narrow tilting vehicle at the University of Minnesota. The project had two objectives. One objective was to better understand the dynamics of two-passenger leaning vehicles. The other was to use this understanding to design and implement leaning control on such a vehicle. The desire was to make a tilting vehicle as easy, in some sense, to drive as a non-leaning vehicle. The scope of this work was fourfold. First, a model of such a system was developed and linearized to obtain a fourth-order linear model. Second, a tilt controller was designed to stabilize a tilting vehicles unstable rolling mode. Third, the system and controller were simulated using both Simulink and a real time simulator written with Visual Basic. Fourth, and most importantly, an experimental vehicle was built and used for implementation. Comparisons were made between the simulated system and the experimental vehicle. This illustrated the limitations encountered in the simulations but also showed similarities that validated the model. Also, experimental results showed that the vehicle was stabilized well by the controller within the limitations of our hardware.

An evaluation of order releasing and due date assignment heuristics in a cellular manufacturing system

Abstract The presence of an order release function, where dispatchers can release or hold jobs from the first work center, has yielded beneficial results in practice but inconsistent results in research. Previous research results contradict the notion that shop floor information should be used to trigger the release mechanism. At the same time, such information has been effectively used to assign realistic due dates to released jobs. This study extends previous work on order releasing and due date assignment by providing a controlled comparison of three order releasing and two due date assignment heuristics in conjunction with six scheduling heuristics in a cellular manufacturing environment. Results show that controlled release deteriorates flow time, lateness, and tardiness performance and is inferior to both immediate and interval release. Controlled release appears to work best in situations of low load and tight due dates. Analysis of different dispatching rules shows the relative performance remains unchanged by the presence of different order release mechanisms. Comparisons of internally and externally set due date mechanisms indicate simpler, non-due date oriented heuristics demonstrate as good a performance as the more complex due date oriented heuristics when shop information is utilized to assign job due dates. Finally, results indicate that in a manufacturing cell, the use of shop floor information is effective for due date assignment, but is not worthwhile for order releasing.

Integration of simulation and analytical submodels for supporting manufacturing decisions

This work describes the concept and prototype software to assist in parameter adjustments when engaged in the trial and error search process of tuning a manufacturing simulation. The concept uses simple analytical models of the simulation which are amenable to optimization schemes and can provide ‘good’ initial parameter values. The menu-driven prototype is illustrated with four decision situations in operations planning that would normally be resolved by successive simulations. The work shows that analytical models and optimization schemes can be integrated with simulation to accelerate the search process, and thereby shows an avenue where expert systems and simulation can meet.

The development of tilt-controlled narrow ground vehicles

Narrow commuter vehicles can address congestion, parking and pollution issues associated with urban transportation. In order for narrow commuter vehicles to become acceptable to the driving public, they must be easy to drive and perceptibly provide the same level of safety as bigger passenger vehicles. This requires that they be relatively tall in spite of being narrow. Tall vehicles tend to overturn during tight cornering. The driver of a narrow vehicle such as a motorcycle must tilt the vehicle into the curve to compensate for the tilting moment due to the lateral acceleration generated by the tires. The use of an active tilt control system to assist the driver in balancing the vehicle (as well as in automatic tilting while cornering) is expected to greatly enhance the acceptability of narrow vehicles. This paper concentrates on the development of a prototype narrow commuter vehicle with automatic tilt control. The prototype narrow vehicle built at the University of Minnesota is presented. A dynamic model for the prototype vehicle is developed. The challenges in the development of a reliable tilt control system are discussed and control system design for control with two different types of actuators is analyzed.

Experimental Investigation of a Narrow Leaning Vehicle Tilt Stability Control System

One way of addressing traffic congestion is by more efficiently utilizing existing highway infrastructure. Narrow tilting vehicles that need reduced-width lanes can be part of the solution if they can be designed to be safe, stable and easy to operate. In this paper implementation and experimental investigation of a tilt stability control system for such a vehicle is presented. This control system is a combination of three different types of control schemes: steering tilt control (STC) system, direct tilt control (DTC) system and Tilt Brake system. The combined STC + DTC (SDTC) system is validated by running standard vehicle maneuver experiments such as turns and lane changes. The performance of the Tilt Brake algorithm is also verified for different brake switchover scenarios. Finally different experiment results are presented to demonstrate the effect of desired tilt angle definition on the handling of a narrow tilting vehicle.