Douglas A. Bristow

Missouri University of Science and Technology

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Robert G. Landers

University of Notre Dame

Edward C. Kinzel

University of Notre Dame

Ben Brown

National Nuclear Security Administration

Andrew G. Alleyne

University of Illinois Urbana-Champaign

Cody Lough

National Nuclear Security Administration

Patrick M. Sammons

University of Michigan–Ann Arbor

Troy Hartwig

Kansas City National Security Campus

Jonathan T. Goldstein

United States Air Force Research Laboratory

Jason Blough

Michigan Technological University

Mitchell R. Woodside

Missouri University of Science and Technology

Cooperative Institutions

Missouri University of Science and Technology

University of Illinois Urbana-Champaign

Chinese Academy of Sciences

University of Michigan–Ann Arbor

Purdue University West Lafayette

National Nuclear Security Administration

Kansas City National Security Campus

Michigan Technological University

United States Air Force Research Laboratory

Zhejiang University

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Frequency Domain Measurements of Melt Pool Recoil Force Using Modal Analysis

Research Square (Research Square) (2020)

Tristan Cullom Cody Lough Nicholas Altese Douglas A. Bristow Robert G. Landers

Abstract Recoil pressure is a critical factor affecting the melt pool dynamics during Laser Powder Bed Fusion (LPBF) processes. Recoil pressure depresses the melt pool, providing layer-to-layer fusion without introducing porosity. If the recoil pressure is too low, the process operates in a conduction mode where layers will not properly fuse, while excessive recoil pressure leads to a keyhole mode, which results in gas porosity. Direct recoil pressure measurements are challenging because it is localized over an area proportionate to the laser spot size producing a force in the mN range. This paper reports a vibration-based approach to quantify the recoil force exerted on a part in a commercial LPBF machine. The measured recoil force is consistent with estimates from high speed synchrotron imaging of entrained particles, and the results show that the recoil force scales with applied laser power and is inversely related to the laser scan speed. These results facilitate further studies of melt pool dynamics and have the potential to aid process development for new materials.

Recoil

Elastic recoil

10.21203/rs.3.rs-126149/v1

Cite

Citations (1)

Weighting matrix design for robust monotonic convergence in Norm Optimal iterative learning control

American Control Conference (2008)

Douglas A. Bristow

In this paper we examine the robustness of norm optimal ILC with quadratic cost criterion for discrete-time, linear time-invariant, single-input single-output systems. A bounded multiplicative uncertainty model is used to describe the uncertain system and a sufficient condition for robust monotonic convergence is developed. We find that, for sufficiently large uncertainty, the performance weighting can not be selected arbitrarily large, and thus overall performance is limited. To maximize available performance, a time-frequency design methodology is presented to shape the weighting matrix based on the initial tracking error. The design is applied to a nanopositioning system and simulation results are presented.

Robustness

Iterative Learning Control

Tracking error

10.1109/acc.2008.4587213

Cite

Citations (36)

Experiment-Based Superposition Thermal Modeling of Laser Powder Bed Fusion

Additive manufacturing (2025)

Cody Lough Tao Liu Robert G. Landers Douglas A. Bristow J. A. Drallmeier

10.1016/j.addma.2025.104708

Cite

Citations (0)

A manufacturing system for microscale robotic deposition

Douglas A. Bristow Andrew G. Alleyne

This paper presents initial results in the development of a fabrication system capable of producing prototype parts with feature sizes on both the meso- and micro-scale using a technique known as robocasting. A dual-stage design is proposed, but the work presented here focuses on individual control of the first or coarse stage. This stage suffers from several known position-dependent disturbances, and a technique for identifying and compensating for them through an inverse-mapping is presented. A loop-shaped feedback controller and iterative learning feedforward controller are designed. Experimental results show the controller to be extremely effective in tracking repeated trajectories. In many cases contour error is on the order of the feedback resolution.

Feed forward

Iterative Learning Control

Microscale chemistry

Feature (linguistics)

Feedback loop

10.1109/acc.2003.1243472

Cite

Citations (35)

Frequency Response Inspection of Additively Manufactured Parts for Defect Identification

Kevin Johnson Jason Blough Andrew Barnard Troy Hartwig Ben Brown

Identification

10.26153/tsw/17230

Cite

Citations (2)

Modeling of Absolute Distance Meter Shift Inside a Laser Tracker

He Li Robert G. Landers Douglas A. Bristow

In the measurement of machine tool and robot geometric errors, one of the most extensively used instruments is the Laser Tracker (LT). Errors in the LT measurements will decrease the effectiveness of the error modeling and compensation methods that utilize these measurements. When the LT’s Absolute Distance Meter (ADM) is used without frequent referencing to a home position, large and long-term shifts occur. The ADM shift directly introduces errors in the radial component of every measurement in spherical coordinates, which will result in measurement errors in the Cartesian coordinates. Although the ADM shift is addressed in newer LT designs using internal referencing hardware, this paper presents a pragmatic and efficient software solution to ADM shift for LTs in which the internal referencing hardware is not embedded. The LT was measured for 22 hr in a temperature-constant room to examine the ADM shift effects on measurements. An ADM shift model was then proposed by assuming that the ADM shift equally affects radial components of all measurements wherever the target is, as long as it is within the measurement range. Another experiment was then performed to test the validity of the proposed model. After the model was identified and errors were corrected, the maximum temporal variation in the radial distance measurement is reduced by 80–86%.

Laser tracker

Distance measurement

Accuracy and precision

Constant (computer programming)

Tracking (education)

10.1115/msec2017-3028

Cite

Citations (1)

A High Precision Motion Control System With Application to Microscale Robotic Deposition

IEEE Transactions on Control Systems Technology (2006)

Douglas A. Bristow Andrew G. Alleyne

Decreasing the minimum feature size of solid free-form (SFF) fabrication techniques requires advancements in both the SFF process and the actuating hardware. Microscale robotic deposition (mu-RD) is an ink-deposition SFF process where recent advances in ink design coupled with a high-precision motion system can lead to the fabrication of parts with microscale-sized features. This paper presents a control algorithm that combines nonlinearity compensation and a learning feedforward approach to achieve high-precision tracking with a standard, off-the-shelf motion system. The off-the-shelf motion system is affected by several nonlinear disturbances that severely inhibit the accuracy of linear models for small motions. Iterative learning control (ILC) is used in an inverse identification procedure to obtain accurate maps of the disturbances. These maps are used in the controller to yield a linear system after nonlinearity cancellation. As a further improvement, ILC is used to increase accuracy in tracking the repetitive portion of specific part trajectories. The combined approach yields extremely low contour tracking errors and is used to fabricate two types of periodic parts demonstrating high aspect ratios and spanning elements. Although high-precision tracking can also be achieved with an expensive, customized system, the off-the-shelf system combined with the control technique presented here provides a more cost-effective solution. The proposed control technique is effective for improving performance of repeatable, but uncertain nonlinear systems

Microscale chemistry

Feed forward

Iterative Learning Control

Motion system

Tracking (education)

10.1109/tcst.2006.880189

Cite

Citations (74)

Towards Defect Detection in Metal SLM Parts Using Modal Analysis "Fingerprinting"

James S. Urban Nick E. Capps Brian West Troy Hartwig Ben Brown

10.26153/tsw/16969

Cite

Citations (1)

Model Predictive Height Control for Direct Energy Deposition

Michelle L. Gegel Douglas A. Bristow Robert G. Landers

Model Predictive Control

Deposition

10.1115/dscc2019-9217

Cite

Citations (2)

Optimizing Learning Convergence Speed and Converged Error for Precision Motion Control

Journal of Dynamic Systems Measurement and Control (2008)

Douglas A. Bristow Andrew G. Alleyne Marina Tharayil

This brief paper considers iterative learning control (ILC) for precision motion control (PMC) applications. This work develops a methodology to design a low pass filter, called the Q-filter, that is used to limit the bandwidth of the ILC to prevent the propagation of high frequencies in the learning. A time-varying bandwidth Q-filter is considered because PMC reference trajectories can exhibit rapid changes in acceleration that may require high bandwidth for short periods of time. Time-frequency analysis of the initial error signal is used to generate a shape function for the bandwidth profile. Key parameters of the bandwidth profile are numerically optimized to obtain the best tradeoff in converged error and convergence speed. Simulation and experimental results for a permanent-magnet linear motor are included. Results show that the optimal time-varying Q-filter bandwidth provides faster convergence to lower error than the optimal time-invariant bandwidth.

Iterative Learning Control

10.1115/1.2936844

Cite

Citations (11)