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Open and closed-loop control systems

Open and closed-loop control systems

Control systems are foundational elements in automation and engineering. They are broadly categorized into open-loop and closed-loop systems. These classifications hinge on the presence or absence of feedback mechanisms, significantly influencing the system's performance, complexity, and application.
An open-loop control system operates without feedback from the output. It consists of two primary elements: the controller and the controlled process. The controller receives an input signal and...

Phase-lead and Phase-lag Controllers

Phase-lead and Phase-lag Controllers

Understanding the working function of different types of controllers can be illustrated with practical analogies, such as adjusting a stereo's volume equalizer. Cranking up the bass involves a phase-lead controller, which functions as a high-pass filter, while increasing the treble uses a phase-lag controller, which acts as a low-pass filter. PD controllers, similar to high-pass filters, enhance the system's response to high-frequency components. PI controllers, akin to low-pass filters, manage...

Time and frequency -Domain Interpretation of Phase-lead Control

Time and frequency -Domain Interpretation of Phase-lead Control

Phase-lead controllers are commonly used in various control systems to enhance response speed and stability. Adjusting the brightness on a television screen offers a practical example of phase-lead control. When contrast is enhanced, a phase-lead controller is employed. Mathematically, phase-lead control is identified when the first parameter is smaller than the second.
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Frequency-Domain Interpretation of PD Control

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Design Example

Design Example

The innovation of touch-tone telephony revolutionized the telecommunications industry by replacing the traditional rotary dial with a dual-tone multi-frequency (DTMF) signaling system. This system uses a matrix-style keypad with buttons arranged in four rows and three columns, creating 12 distinct signals each assigned to a pair of frequencies. Each button press results in a simultaneous generation of two sinusoidal tones – one from a low-frequency group (697 to 941 Hz) and one from a...

Feedback control systems

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Related Experiment Video

Updated: Jun 7, 2026

Bringing the Visible Universe into Focus with Robo-AO

Bringing the Visible Universe into Focus with Robo-AO

Published on: February 12, 2013

Closed-loop control of a woofer-tweeter adaptive optics system using wavelet-based phase reconstruction.

Peter J Hampton¹, Pan Agathoklis, Rodolphe Conan

¹Department of Electrical & Computer Engineering, University of Victoria, PO Box 3055 STN CSC, Victoria, BC, Canada V8W 3P6. peterjhampton@ieee.org

Journal of the Optical Society of America. A, Optics, Image Science, and Vision

|November 4, 2010

Summary

This study introduces a fast, wavelet-based adaptive optics (AO) control technique using a woofer-tweeter controller. It achieves high speed and accuracy in correcting atmospheric turbulence aberrations.

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Characterization of SiN Integrated Optical Phased Arrays on a Wafer-Scale Test Station

Characterization of SiN Integrated Optical Phased Arrays on a Wafer-Scale Test Station

Published on: April 1, 2020

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Last Updated: Jun 7, 2026

Bringing the Visible Universe into Focus with Robo-AO

Bringing the Visible Universe into Focus with Robo-AO

Published on: February 12, 2013

Characterization of SiN Integrated Optical Phased Arrays on a Wafer-Scale Test Station

Characterization of SiN Integrated Optical Phased Arrays on a Wafer-Scale Test Station

Published on: April 1, 2020

Area of Science:

Optics
Signal Processing
Computational Science

Background:

Adaptive optics (AO) systems correct wavefront distortions.
Efficient phase reconstruction is crucial for AO system performance.
Controlling low- and high-spatial-frequency aberrations requires specialized methods.

Purpose of the Study:

To present a novel closed-loop control technique for AO systems.
To develop a fast and accurate wavelet-based phase reconstruction method.
To integrate this method with a woofer-tweeter controller for aberration correction.

Main Methods:

Utilized a wavelet-based phase reconstruction technique employing Haar decomposition of the phase screen from gradient measurements.
Extended the wavelet method with a Poisson solver for enhanced performance.
Implemented a woofer-tweeter controller for managing low- and high-spatial-frequency aberrations.
Developed an efficient signal separation method based on low-resolution reconstruction during wavelet synthesis.

Main Results:

The proposed wavelet-based reconstruction achieves O(N) linear computational cost, outperforming existing O(N) techniques in speed.
The integrated system demonstrated high accuracy and speed in correcting simulated atmospheric turbulence.
The woofer-tweeter controller effectively separated and managed different spatial frequencies of aberrations.

Conclusions:

The novel closed-loop control technique combining wavelet-based reconstruction and a woofer-tweeter controller offers significant speed and accuracy improvements for AO systems.
This approach provides an efficient solution for real-time aberration correction in dynamic environments.
The method is particularly effective for correcting atmospheric turbulence in optical systems.