J.T. Wen

J.T. Wen
Rensselaer Polytechnic Institute | RPI · Department of Electrical, Computer, and Systems Engineering

PhD

About

431
Publications
61,818
Reads
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10,626
Citations
Citations since 2016
69 Research Items
3479 Citations
20162017201820192020202120220100200300400500
20162017201820192020202120220100200300400500
20162017201820192020202120220100200300400500
20162017201820192020202120220100200300400500
Additional affiliations
July 2013 - December 2018
Rensselaer Polytechnic Institute
Position
  • Head of Department
July 2005 - December 2013
Rensselaer Polytechnic Institute
Position
  • Managing Director
June 1995 - present
Rensselaer Polytechnic Institute
Position
  • Professor
Education
January 1983 - May 1985
Rensselaer Polytechnic Institute
Field of study
  • Electrical Engineering
January 1980 - May 1981
University of Illinois, Urbana-Champaign
Field of study
  • Electrical Engineering
September 1979 - December 1979
University of Toronto
Field of study
  • Electrical Engineering

Publications

Publications (431)
Article
Full-text available
Circadian rhythm is an important biological process for humans as it modulates a wide range of physiological processes, including body temperature, sleep-wake cycle, and cognitive performance. As the most powerful external stimulus of circadian rhythm, light has been studied as a zeitgeber to regulate the circadian phase and sleep. This paper addre...
Article
Full-text available
Space manipulator arms often exhibit significant joint flexibility and limited motor torque. Future space missions, including satellite servicing and large structure assembly, may involve the manipulation of massive objects, which will accentuate these limitations. Currently, astronauts use visual feedback on-orbit to mitigate oscillations and traj...
Article
Microchannel evaporator cooling systems are widely studied for their ability to remove high heat fluxes. However, flow instabilities during microchannel boiling, like pressure drop oscillation and flow maldistribution, can cause an uneven temperature variation and deteriorate the cooling performance. This study analyzes the effect of using an oscil...
Article
Flow boiling in microchannel evaporators is widely recognized and promising for its compact structure, lower coolant usage, high heat transfer coefficient, ability to provide higher heat fluxes, and better temperature uniformity than single-phase liquid cooling. However, critical heat flux, local dry-outs, and flow instabilities can be significant...
Article
This study quantitatively compares the finite element and lumped modeling techniques to analyze phase-change and multiphase flow in a microchannel evaporator. We compare the one-zone and two-zone models in the lumped modeling approach by considering both pressure drop and phase change in the evaporator. The study investigates the deviation in resul...
Article
Full-text available
The circadian rhythm, called Process C, regulates a wide range of biological processes in humans including sleep, metabolism, body temperature, and hormone secretion. Light is the dominant synchronizer of the circadian rhythm—it has been used to regulate the circadian phase to cope with jet-lag, shift work, and sleep disorder. The homeostatic oscil...
Article
Full-text available
Sleep schedule and circadian phase irregularity are associated with some health problems and diseases, e.g., narcolepsy, circadian disorder, and concussion. Actigraphy has been widely used in the study of sleep and circadian rhythms. This paper presents a method for estimating the sleep/wake state based on the minute-by-minute actigraphy data measu...
Article
Full-text available
Fast and precise robot motion is needed in many industrial applications. Most industrial robot motion controllers allow externally commanded motion profiles, but the trajectory tracking performance is affected by the robot dynamics and joint servo controllers, to which users have no direct access and about which they have little information. The pe...
Article
Full-text available
This paper presents a robotic assembly methodology for the manufacturing of large segmented composite structures. The approach addresses three key steps in the assembly process: panel localization and pick-up, panel transport, and panel placement. Multiple stationary and robot-mounted cameras provide information for localization and alignment. A ro...
Article
Technologies utilizing flow boiling in microchannel evaporators promise high heat fluxes and system efficiencies. However, boiling in microchannels also face significant challenges due to the occurrence of critical heat flux and flow instabilities, such as pressure drop oscillations. Since several system parameters can cause these issues in a two-p...
Article
This study presents a control strategy for electronic cooling systems incorporating microchannel evaporators that experience unanticipated and significant heat load variations. It complements prior studies that focus primarily on the steady operation of two-phase systems facing static heat loads. This study's overall objective is to maintain a fixe...
Article
Robotic manipulators used in space applications are often lightweight, exhibit significant joint flexibility, and have limited joint torques. Many applications of space manipulation involve the transport of massive objects, e.g., a captured satellite, well beyond the 1 g capability of these robots. This may cause challenges during manipulation, suc...
Article
Two-phase systems comprising of a single pump or compressor, a condenser, and multiple microchannel evaporators can provide the unique advantage of handling multiple heat sources while being compact and lightweight. Such systems also present challenges with regards to handling asynchronous transient heat loads, maintaining fixed evaporator temperat...
Article
Microchannel evaporators are capable of removing large heat fluxes by taking advantage of the latent heat of phase-change. However, flow maldistribution in the parallel channels of the evaporator can cause a considerable variation in the cooling performance of each channel. Such variations in performance are undesirable and present a significant ch...
Article
Full-text available
We report herein the application of an adaptive notch filter (ANF) algorithm to minute-by-minute actigraphy data to estimate the continuous circadian phase of eight healthy adults. As the adaptation rates and damping factor of the ANF algorithm have large impacts on the ANF states and circadian phase estimation results, we propose a method for opti...
Article
Large industrial robots offer an attractive option for deep rolling in terms of cost and flexibility. These robots are typically designed for fast and precise motion, but may be commanded to perform force control by adjusting the position setpoint based on the measurements from a wrist-mounted force/torque sensor. Contact force during deep rolling...
Article
Full-text available
Temperature control is essential for regulating material properties in laser-based manufacturing. Motion and power of the scanning laser affect local temperature evolution, which in turn determines the a posteriori microstructure. This paper addresses the problem of adjusting the laser speed and power to achieve the desired values of key process pa...
Preprint
Full-text available
Collaborative robots and space manipulators contain significant joint flexibility. It complicates the control design, compromises the control bandwidth, and limits the tracking accuracy. The imprecise knowledge of the flexible joint dynamics compounds the challenge. In this paper, we present a new control architecture for controlling flexible-joint...
Article
While microchannel evaporator based cooling systems are efficient in removing high heat fluxes they are prone to the instability mechanism called pressure drop oscillation. The instability can lead to poor cooling performance, system fatigue and even mechanical failure of the cooling system. To address this challenge, a system level approach with d...
Article
Full-text available
The circadian rhythm functions as a master clock that regulates many physiological processes in humans including sleep, metabolism, hormone secretion, and neurobehavioral processes. Disruption of the circadian rhythm is known to have negative impacts on health. Light is the strongest circadian stimulus that can be used to regulate the circadian pha...
Article
Microstructure affects the physical properties and behavior of materials. While metallurgists have long studied microstructure characterization and evolution, thermo-mechanical material processing to achieve a desired microstructure remains largely experience-based. This paper presents a distributed thermal control methodology for the microstructur...
Article
We seek a methodological approach to assess circadian processes in subjects who have recently experienced traumatic brain injury, using regularly gathered intracranial temperature data. The health effects of circadian regulation are profound, yet assessments of circadian processes are often infeasible in the neurotrauma intensive care unit (ICU). W...
Preprint
Full-text available
Fast and precise motion control is important for industrial robots in manufacturing applications. However, some collaborative robots sacrifice precision for safety, particular for high motion speed. The performance degradation is caused by the inability of the joint servo controller to address the uncertain nonlinear dynamics of the robot arm, e.g....
Article
This study analyzes instability due to pressure drop oscillation occurring in a closed system comprising of a vapor compression cycle. The system includes a microchannel evaporator, a condenser, an accumulator, an electronic expansion valve and a compressor. Using a spatially lumped dynamic model, this study investigates how various system paramete...
Preprint
Full-text available
Temperature control is essential for regulating material properties in laser-based manufacturing. Motion and power of the scanning laser affect local temperature evolution, which in turn determines the a posteriori microstructure. This paper addresses the problem of adjusting the laser speed and power to achieve the desired values of key process pa...
Article
Building interior temperatures are affected by the outdoor air temperature. Note that outdoor weather patterns are somewhat repetitive in nature and historical records of outdoor temperature are readily accessible; we present a data-driven iterative learning approach to improve the room temperature tracking performance over time. By comparing the s...
Preprint
Fast and precise robot motion is needed in certain applications such as electronic manufacturing, additive manufacturing and assembly. Most industrial robot motion controllers allow externally commanded motion profile, but the trajectory tracking performance is affected by the robot dynamics and joint servo controllers which users have no direct ac...
Preprint
Circadian rhythm is usually represented by the 24-hour biological cycles which are mainly driven by the daily light-dark cycle on earth. Light stimulus is widely used as the control input of the circadian system entrainment. In this paper, we study the light-based minimum-time circadian entrainment problem of mammals, Neurospora, and Drosophila bas...
Article
We consider asymptotic synchronization of multiple phase oscillators represented by first order reduced dynamics with a phase response curve (PRC) function. A single control input is employed to synchronize the oscillators. We design a feedback control that achieves asymptotic synchronization of the oscillators. We also show that the undesired equi...
Conference Paper
This paper presents the design and initial results of a project involving the robotic assembly of a large segmented structure. This project aims to develop an operator-guided semi-autonomous assembly process using industrial robots integrated with multiple sensors. The goal is to demonstrate the potential of robotic technology to reduce cycle time,...
Article
Full-text available
This paper presents the control strategy and experimental results of multiple dual-arm robots cooperatively manipulating an object whose load and size is beyond the capability of a single robot. The multi-robot system is required to stably grasp and transport the load through frictional contacts. The human operator provides motion guidance by direc...
Article
Full-text available
Actigraphy has been widely used for the analysis of circadian rhythm. Current practice applies regression analysis to data from multiple days to estimate the circadian phase. This paper presents a filtering method for online processing of biometric data to estimate the circadian phase. We apply the proposed method on actigraphy data of fruit flies...
Chapter
The built environment is an integral part of modern human society. Buildings offer shelter from the elements, security from predators, privacy from intrusion, and space for work, entertainment, and storage.
Book
Readers of this book will be shown how, with the adoption of ubiquituous sensing, extensive data-gathering and forecasting, and building-embedded advanced actuation, intelligent building systems with the ability to respond to occupant preferences in a safe and energy-efficient manner are becoming a reality. The articles collected present a holistic...
Article
Energy inefficiency and underlying occupant discomfort associated with building thermal management systems have led to the development of a human-in-the-loop control system. Minimizing total energy use and maximizing comfort of all the occupants present is the major objective of such system based on human comfort feedback. However, the approaches p...
Article
Full-text available
This paper presents a modeling and control method for the thermohygrometric condition (temperature and humidity) in a multizone building. The interconnection between the zones is captured through an undirected graph. Employing an electrical circuit analogy, rooms represent capacitances, and walls and doors/windows are resistances. This model charac...
Article
In this work we propose a framework for incorporating occupant feedback towards temperature control of multi-occupant spaces, and analyze it using singular perturbation theory. Such a system would typically have to accommodate occupants with different temperature preferences, and incorporate that with thermal correlation among multiple zones to obt...
Article
Full-text available
This paper presents the design of a passivity-based iterative learning control (ILC) algorithm for coupled temperature and humidity in buildings. Since buildings are subjected to repeating diurnal patterns of disturbances, ILC algorithms can significantly improve performance. Moreover, since it is a feedforward control scheme, it can be used in con...
Article
This work investigated the development of a Monte Carlo (MC) simulation approach to modeling grain growth in the presence of non-uniform temperature field that may vary with time. We first scale the MC model to physical growth processes by fitting experimental data. Based on the scaling relationship, we derive a grid site selection probability (SSP...
Chapter
People with severe mobility impairment such as quadriplegia require help from human assistants to manage activities of daily living. Various assistive robotic devices have been proposed and some are commercially available, but they mostly have limited functionalities. We propose a cost-effective mobile robotic manipulator , BOW, or Baxter -on-Wheel...
Article
Full-text available
This paper considers the control of a mobile manipulator with the end-effector commanded by a human user. The motivation is to empower mobility impaired individuals to tackle certain activities of daily living. The prototype robotic system consists of a redundant articulated arm mounted on a mobile base. The human user specifies the desired motion...
Article
There are well established control methods to stabilize the vapor compression cycle (VCC) about a given operating point. However, it is challenging to design such local controllers to handle large transient heat flux disturbances, due to complex coupling and constraints, and potential violation of critical heat flux (CHF) which could lead to the da...
Article
Full-text available
This paper describes the simulation, fabrication and feedback control of a micro-heater array, designed for the implementation of real-time control during thermal evolution of microstructure. The ten-channel heating array was designed through finite element simulation and micro-fabricated to be compatible with in-situ imaging in a scanning electron...
Article
The traditional method of circadian rhythm estimation is based on a double actogram that provides phase estimation on a daily basis, but not continuously and also fails to effectively filter noise. Our goal is to develop a circadian rhythm estimator that accurately and continuously estimates circadian phase while filtering noise. The estimator is a...
Article
A non-linear inverse heat source identification problem is described and solved. The inverse problem analysis is used in the design of an embedded micro-heater array and to estimate the required control settings, which are the input currents to each heating element, to generate as close as possible to a prescribed temperature profile on the surface...
Article
Accurate estimation of circadian phase is critical to the assessment and treatment of circadian disruption. Direct measurements of circadian rhythm markers such as dim light melatonin onset and core body temperature are inconvenient and acquired at best at low rate. On the other hand, measurements of other circadian rhythm modulated signals such as...
Conference Paper
Full-text available
This paper presents a modeling and control strategy for comfort zone set-based control of temperature and humidity in buildings. We first propose a coupled model for humidity and temperature dynamics based on lumped parameter analysis. The interconnection of rooms/zones is captured through an undirected graph, with rooms represented as capacitances...
Article
Full-text available
Light is a strong synchronizer for circadian rhythm — the 24-h biological oscillation in plants, insects, and mammals. This paper considers the circadian entrainment problem for a popular circadian oscillation model (the Kronauer model) by using light intensity as the control input. This problem is commonly encountered by shift workers and internat...
Article
In this work we present an end-to-end framework designed for enabling occupant feedback collection and incorporating the feedback data towards energy efficient operation of a building. We have designed a mobile application that occupants can use on their smart phones to provide their thermal preference feedback. When relaying the occupant feedback...
Conference Paper
Two-phase cooling of electronics using vapor compression systems (VCS) is a promising approach for high heat flux removal. A challenge for multi-evaporator VCS is charge management during highly transient or peak/off-peak loads. We present a VCS architecture for direct cooling of multiple, high transient heat loads. This system utilizes a secondary...
Article
Full-text available
An integrated experimental – simulation – control theory approach designed to enable adaptive control of microstructural evolution in polycrystalline metals is described. A micro-heater array, containing ten addressable channels, is used to create desired temperature profiles across thin polycrystalline films in situ to a scanning electron microsco...
Article
Full-text available
First order phase reduced model is a good approximation of the dynamics of forced nonlinear oscillators near its limit cycle. The phase evolution is determined by the unforced frequency, the forcing term, and the phase response curve (PRC). Such models arise in biological oscillations such as in circadian rhythm, neural signaling, heart beat, etc....