Showing papers by "James S. Freudenberg published in 1998"

Control-Oriented Model of a Dual Equal Variable Cam Timing Spark Ignition Engine

Abstract: A control-oriented engine model is developed to represent a spark ignited engine equipped with a variable cam timing mechanism over a wide range of operating conditions. Based upon laboratory measurements a continuous, nonlinear, low-frequency phenomenological engine model is developed. With respect to a fixed-cam timing engine, the VCT mechanism alters the mass air flow into the cylinders, the torque response, and the emissions of the engine. The developed model reflects all of these modifications and includes a representation of the breathing process, torque and emission generation, and sensor/actuator dynamics. The model has been validated with engine-dynamometer experimental data and can be used in powertrain controller design and development.

Control of variable geometry turbocharged diesel engines for reduced emissions

Abstract: A multivariable control scheme is designed to minimize emission of nitrogen oxides (NO/sub x/) and generation of smoke in a diesel engine equipped with a variable geometry turbocharger (VGT) and an external exhaust gas recirculation system (EGR). Steady-state optimization results in operating points where NO/sub x/ emissions and smoke generation are highly coupled and require joint management by VGT and EGR actuators.

L/sub 2/-induced norms and frequency gains of sampled-data sensitivity operators

Abstract: This paper develops exact, computable formulas for the frequency gain and L/sub 2/-induced norm of the sensitivity operator in a sampled-data control system. With sampled data, we refer to a system that combines both continuous-time and discrete time signals, which is studied in continuous time. The expressions are obtained using lifting techniques in the frequency domain and have application in performance and stability robustness analysis taking into account full intersample information.

Properties of single input, two output feedback systems

Abstract: We describe properties of multivariable feedback control systems for which the plant has a single input and two outputs. Of particular interest are "algebraic" design trade-offs that occur between different feedback properties at the same frequency. We define concepts of plant and controller direction and alignment, and show that the closed loop response depends upon the alignment between plant and controller. In particular, if alignment is poor, then using high gain will cause output sensitivity to be large and the closed loop system will exhibit large interactions. We also discuss alignment in the case where gain is not necessarily large, and show that alignment is not important beyond the closed loop bandwidth. Also, the closed loop properties are not sensitive to modest amounts of misalignment. Finally, we show there exists a class of controllers that are always poorly aligned with the plant independently of the scaling used for the system outputs.

Cheap control tracking performance for non-right-invertible systems

Abstract: A fundamental limitation exists in the achievable tracking performance of non-right-invertible systems. This limitation manifests itself in the cheap control tracking cost, which we show to be a function of the plant non-minimum phase zeros and of the variation with frequency of the plant direction. The cheap control tracking cost is further connected with an integral relation that constrains the performance of any stable closed-loop system where the plant has a single input and two outputs.

Optimal feedforward recipe adjustment for CD control in semiconductor patterning

Abstract: Acceptable yields for nanofabrication will require significant improvement in CD control. One method to achieve better run-to-run CD control is through inter-process feedforward control. The potential benefits of feedforward control include reduced run-to-run post-etch CD variance, rework, and scrap. However, measurement noise poses a significant threat to the success of feedforward control. Since the stakes are high, an incorrect control action is unacceptable. To answer this concern, this paper will focus on how to properly use the available sensor measurement in a run-to-run feedforward recipe adjustment controller. We have developed a methodology based in probability theory that detunes the controller based on the confidence in the sensor’s accuracy. Properly detuning the controller has the effect of filtering out the noise from the SEM. We will simulate this control strategy on industrial gate-etch data.

Feedforward recipe selection control design software

Abstract: One method to achieve lower process variance is through inter-process feedforward control. There are two problematic issues associated with feedforward recipe adjustment: (1) there is noise in the measurement tool and adjusting for inaccurate measurements could increase the variance; and (2) it is difficult to alter one parameter in a manufacturing process without worsening other key parameters. The first issue is addressed by integrating statistics theory into the controller design. One way to solve the second issue is to constrain the controller to select a recipe form a finite set of pre-qualified recipes. We call this feedforward recipe selection control (FRSC). Each recipe in FRSC has a unique adjustment and, by definition of pre-qualified, every recipe will give acceptable values for all other key characteristics. The goal of this paper is to guide the reader through a complete FRSC design. The modeling data set is from an industrial CD patterning processes. Simulation of FRSC implementation shows a standard deviation reduction of 16 percent. We also derive a re-centering methodology order to place more integrated circuits into the fastest speed grade. Our simulation doubled the number of ICs in this fastest speed grade.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.