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Real-Time Nonlinear Programming by Amplitude Modulation
공경철,Masayoshi Tomizuka 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.4
The nonlinear programming (NLP) is an optimization technique that minimizes arbitrary nonlinear cost functions. To apply the NLP to real-time applications, however, the estimation of the gradient of the cost function is remained as a challenge. The extremum-seeking control (ESC) optimizes the cost functions in real-time, but it involves the complicated design of filters for simultaneous estimation of the gradient. In this paper, a complementary method that optimizes an arbitrary multi-variable cost function in real-time is proposed. Taking the advantages of both NLP and ESC, the variables are updated by the steepest descent method of NLP, while the gradient of the cost function is continuously estimated by the amplitude modulation as in ESC. Unlike the ESC, the proposed method does not require the design of complicated filters. The optimization performance is verified by simulations on time-varying and noisy cost functions, as well as automatic controller tuning applications.
공경철,Masayoshi Tomizuka 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.1
Disturbance observer-based control systems often encounter the stability problem due to modeling un-certainties. In such cases, the disturbance observer (DOB) may have to be re-designed by narrowing the bandwidth of the Q-filter to enhance stability robustness, but this approach to stability enhancement deteriorates the performance of DOB. In order to improve robust stability while main-taining the performance of DOB, this paper proposes a method that manipulates the nominal plant model in the DOB; the parameters of the discretized nominal model are optimized to improve robust stability in the discrete time domain. For the optimization of nominal model, it is assumed that the closed-loop poles of DOB are subjected to multiplicative uncertainties, and the maximum allowable magnitude of uncertainties is utilized as the measure of stability robustness. Then, the proposed method changes the location of closed-loop poles to maximize the robustness margin. This paper pro-vides a case study that includes experimental results.
Network-Based Rehabilitation System for Improved Mobility and Tele-Rehabilitation
Joonbum Bae,Wenlong Zhang,Tomizuka, Masayoshi IEEE 2013 IEEE transactions on control systems technology Vol.21 No.5
<P>In this brief, a network-based rehabilitation system, which takes advantage of the Internet, wireless communication, and control, is proposed to increase the mobility of a rehabilitation system and to enable tele-rehabilitation. In the proposed system, control algorithms and rehabilitation strategies are distributed at the central location (physiotherapist) and the local site (patient) by communicating over the Internet, and the rehabilitation device is controlled wirelessly by the controller at the local site. In order to deal with possible packet losses over the local wireless network, a modified linear quadratic Gaussian controller and a disturbance observer are applied. The simulation and experimental results with an actual knee rehabilitation system show that the proposed network-based rehabilitation system can generate the desired assistive torque accurately in a network environment.</P>
Won, Daehee,Kim, Wonhee,Tomizuka, Masayoshi IEEE 2017 IEEE/ASME transactions on mechatronics Vol.22 No.6
<P>Although previous control methods improve control performance in electrohydraulic servo system (EHSS), they require full-state feedback information and/or the derivative of the measured signals so that noise may be amplified. In this paper, we propose a high-gain-observer-based integral sliding mode control to improve the position tracking performance of the EHSSs while solving the previous problems. The proposed method consists of a high-gain observer and an integral sliding mode controller. The high-gain observer is designed to estimate the velocity and load pressure using the position feedback. The stability is proven without the approximation of the model in EHSS. The integral sliding mode controller is proposed to improve the position tracking performance using the flatness property of the system. In the controller, the required derivatives of the state variables are obtained using the flatness property without employing the derivative of the measured signal.</P>
Modified Preview Control for a Wireless Tracking Control System With Packet Loss
Wenlong Zhang,Joonbum Bae,Tomizuka, Masayoshi IEEE 2015 IEEE/ASME transactions on mechatronics Vol.20 No.1
<P>In this paper, a modified preview control technique is proposed to compensate packet loss in a wireless tracking control system, where future reference signals over a finite horizon can be previewed. In order to utilize future reference information for the controller design, the system model is augmented with a reference generator whose states are the future reference signals. As a response to the packet loss that occurs in the wireless network, the preview control technique is modified by employing Bernoulli variables to represent packet loss in both controller-actuator and sensor-controller channels. The Bernoulli packet loss model, along with tracking errors and control inputs, is included in a quadratic cost function, and the optimal controller gain that minimizes the cost function is obtained by dynamic programming. A modified Kalman filter considering packet loss is utilized for full-state estimation and state feedback control. The choice of preview horizon is discussed and the performance of the proposed controller is verified by simulation and experimental results.</P>
Challenges and opportunities in the engineering of intelligent systems
Liu, Shi-Chi,Tomizuka, Masayoshi,Ulsoy, A. Galip Techno-Press 2005 Smart Structures and Systems, An International Jou Vol.1 No.1
This paper describes the area of intelligent systems research as funded by the Civil and Mechanical Systems (CMS) Division of the National Science Foundation (NSF). With developments in computer science, information technology, sensing and control the design of typical machines and structures by civil and mechanical engineers is evolving toward intelligent systems that can sense, decide and act. This trend toward electro-mechanical design is well-established in modern machines (e.g. vehicles, robots, disk drives) and often referred to as mechatronics. More recently intelligent systems design is becoming an important aspect of structures, such as buildings and bridges. We briefly review recent developments in structural control, including the role that NSF has played in their development, and discuss on-going CMS activities in this area. In particular, we highlight the interdisciplinary initiative on Sensors and Sensor Networks and the Network for Earthquake Engineering Simulation (NEES). NEES is a distributed cyberinfrastructure to support earthquake engineering research, and provides the pioneering NEES grid computing environment for simulation, teleoperation, data collection and archiving, etc.