Simultaneous Time-Frequency Control of Multi-Dimensional Micro-Milling Instability

2012 ◽  
Author(s):  
Meng-Kun Liu ◽  
Eric B. Halfmann ◽  
C. Steve Suh
Keyword(s):  
Frequency Response ◽  
High Speed ◽  
Frequency Control ◽  
External Perturbation ◽  
Micro Milling ◽  
Time Frequency ◽  
System A ◽  
Control Concept ◽  
The Time Domain ◽  
Tool Damage

A novel control concept is presented for the online control of a high-speed micro-milling model system in the time and frequency domains concurrently. Micro-milling response at high-speed is highly sensitive to machining condition and external perturbation, easily deteriorating from bifurcation to chaos. When losing stability, milling time response is no longer periodic and the frequency response becomes broadband, rendering aberrational tool chatter and probable tool damage. The controller effectively mitigates the nonlinear vibration of the tool in the time domain and at the same time confines the frequency response from expanding and becoming chaotically broadband. The simultaneous time-frequency control is achieved through manipulating wavelet coefficients, thus not limited by the increasing bandwidth of the chaotic system — a fundamental restraint that deprives contemporary controller designs of validity and effectiveness. The feedforward feature of the control concept prevents errors from re-entering the control loop and inadvertently perturbing the sensitive micro-milling system. Because neither closed-form nor linearization is required, the innate, genuine features of the micro-milling response are faithfully retained.

Simultaneous Time-Frequency Synchronization of Non-Autonomous Chaotic Systems

2013 ◽  
Author(s):  
Meng-Kun Liu ◽  
C. Steve Suh
Keyword(s):  
Chaotic System ◽  
Initial Conditions ◽  
Frequency Control ◽  
Frequency Synchronization ◽  
Time Frequency ◽  
System A ◽  
Frequency Domains ◽  
Control Concept ◽  
On Line ◽  
The Time Domain

A novel chaos control concept is presented for the synchronization of a non-autonomous chaotic circuit system in the time and frequency domains concurrently. The controller effectively eliminates the differences between two chaotic circuits in the time domain and at the same time restores the characteristics of the driving response in the frequency domain. The simultaneous time-frequency control is achieved through manipulating wavelet coefficients, thus not limited by the increasing bandwidth of the chaotic system — a fundamental restraint that deprives contemporary controller designs of validity and effectiveness. The feedforward feature of the control concept prevents errors from re-entering the control loop and inadvertently perturbing the sensitive chaotic system. Because neither closed-form nor linearization is required, the innate, genuine features of the chaotic response are faithfully retained. The on-line identification feature allows the response system to start at arbitrary initial conditions and to be driven by the sinusoidal forcing term of different amplitudes and phases requiring no knowledge of the system parameters.

Frequency Response Bandwidth Calibration of High Speed Photodetector Using Frequency-Stabilized Laser by Optical Heterodyne Technique

2014 ◽  
Vol 644-650 ◽  
pp. 1031-1034
Author(s):  
Nan Xu ◽  
Jian Wei Li ◽  
Jian Li ◽  
Zhi Xin Zhang
Keyword(s):  
Frequency Response ◽  
High Speed ◽  
Beat Frequency ◽  
Tunable Laser ◽  
Laser Source ◽  
Response Measurement ◽  
System A ◽  
Response Bandwidth ◽  
Heterodyne Technique ◽  
Frequency Stabilized Laser

In this paper, frequency-stabilized laser technology is introduced into photodetector frequency response measurement system. A 1531nm frequency-stabilized laser fulfilled by acetylene saturated absorption is employed to produce coherent light with a tunable laser source, gaining stable beat frequency light that reaches as high as several hundred ghz, fulfilling measurement of 40ghz high-speed photodetector frequency response bandwidth, and lowering impacts caused by instability of light frequency. In addition, measurement uncertainty analysis is conducted, which is better than 7 %(k=2).

Control of a Wheeled Inverted Pendulum: A Nonlinear Time-Frequency Approach

2016 ◽  
Author(s):  
Tanja Baumann ◽  
Steve Suh
Keyword(s):  
Inverted Pendulum ◽  
Discrete Wavelet ◽  
Least Mean Square ◽  
Time Frequency ◽  
Feed Forward Control ◽  
Online Identification ◽  
Wheeled Inverted Pendulum ◽  
Frequency Domains ◽  
Control Concept ◽  
The Time Domain

The wheeled inverted pendulum shown in Fig. 1 is a typical nonlinear system that is both nonholonomic and complex in dynamics. In this paper a novel control concept is applied to stabilize a wheeled inverted pendulum. The suggested controller requires no mathematical simplification or linearization of the system. Online identification and feed-forward control are realized by an adapted filtered-x least mean square algorithm (FXLMS). Using discrete wavelet transform (DWT), control can be exerted in both the time and frequency domains simultaneously. The results show that the proposed controller is robust even when the system is perturbed. The system can also be partially stabilized at positions out of the upper equilibrium. In this case the time domain error is small though the system stays broadband in the frequency domain.

Active Magnetic Bearings for High Speed Spindle Design With Nonlinear Time-Frequency Control

2015 ◽  
Author(s):  
Mengke Liu ◽  
C. Steve Suh
Keyword(s):  
High Speed ◽  
Frequency Control ◽  
Air Gap ◽  
Magnetic Bearings ◽  
Lms Algorithm ◽  
Significant Implication ◽  
Active Magnetic Bearings ◽  
Gyroscopic Effect ◽  
Electromagnetic Actuators ◽  
Time Frequency

A novel concept applicable to the control of spindles at high speed is developed by using active magnetic bearings (AMBs) that are non-contact and of low vibration. Though former studies are abundant and demonstrating promising potentials, however, two major issues hamper the broader application of AMBs. The first is the disregard for the gyroscopic effect and geometry coupling that influence the magnitude as well as distribution of the electromagnetic force in AMBs. Not considering the two has a significant implication for the proper control of AMBs. This paper considers the gyroscopic effect and explores the geometry coupling of the electromagnetic actuators to the formulation of a comprehensive nonlinear AMB-rotor model. The model provides the basis for the creation of a novel time-frequency control algorithm whose derivation requires no linearization or mathematical simplification of any kind, thus allowing the model system to retain its true fundamental characteristics. Unlike proportional-integral-derivative (PID) controllers that are dominant in most if not all AMB configurations, the controller developed for the research is inspired by the wavelet-based nonlinear time-frequency control methodology that incorporates the basic notions of online system identification and adaptive control. Due to the fact that dynamic instability is characterized by time-varying frequency and non-stationary spectrum, the control of AMBs needs be executed in the time and frequency-domain concurrently to ensure stability and performance at high speed. Wavelet filter banks and filtered-x least-mean-square (LMS) algorithm are two of the major salient physical features of the controller design, with the former providing concurrent temporal and spectral resolutions needed for identifying the nonlinear state of motion and the latter ensuring the dynamic stability of the AMB-rotor system at extremely high speed. It is shown that the vibration of the rotor is unconditionally controlled by maintaining a mandatory 0.55 mm air gap at 187,500 rpm subject to a tight spatial constraint (tolerance) of the order of 0.1375mm, which is the 25% of the air gap.

Simultaneous Time-Frequency Control of Active Magnetic Bearing

2013 ◽  
Author(s):  
Meng-Kun Liu ◽  
C. Steve Suh
Keyword(s):  
Control Theory ◽  
High Speed ◽  
Frequency Control ◽  
Dynamic Stiffness ◽  
Magnetic Bearing ◽  
Active Magnetic Bearing ◽  
Time Frequency ◽  
Highly Nonlinear ◽  
Nonlinear Character ◽  
On Line

Active magnetic bearings enable greater spindle dynamic stiffness through higher attainable bearing surface speeds. However, the active magnetic bearing system is highly nonlinear due to the interaction between electromagnetic field and rotor dynamics. Its nonlinear character becomes prominent when rotating in high speed. The operation undergoes route-to-chaos and is vulnerable to external excitation, which eventually leads to detrimental failure. A novel simultaneous time-frequency control theory is developed for controlling the active magnetic bearing at high speed. The control theory is able to tolerate the uncertainties in the system due to on-line identification and the deterioration in both time and frequency domain can be restrained.

Multi-dimensional time-frequency control of micro-milling instability

2012 ◽  
Vol 20 (5) ◽  
pp. 643-660 ◽  
Author(s):  
Meng-Kun Liu ◽  
Eric B Halfmann ◽  
C Steve Suh
Keyword(s):  
Frequency Control ◽  
Micro Milling ◽  
Time Frequency

scholarly journals Vibration Measurements by Tracking Laser Doppler Vibrometer on Automotive Components

2002 ◽  
Vol 9 (1-2) ◽  
pp. 67-89 ◽  
Author(s):  
P. Castellini
Keyword(s):  
High Speed ◽  
Assessment Tool ◽  
Traditional Approach ◽  
Laser Doppler Vibrometer ◽  
Laser Doppler ◽  
Automotive Component ◽  
Time Frequency ◽  
Noise Rejection ◽  
Timing Belt ◽  
The Time Domain

This paper describes the application of a Tracking Laser Doppler Vibrometer (TLDV) to the measurement of vibration of some typical automotive component.After a presentation and discussion of the measurement technique, the attention is focused on the development of specific version optimised for each application.The first component analysed is the sidewall of a tire during its rotation in a typical drum test-bench. An optimised version of the TLDV was developed for the specific application adding a trajectory assessment tool based on image analysis, in order to fulfil the accuracy specifications imposed by tire manufacturer.The second automotive component is a timing belt.This application presents problems related to the high-speed linear motion and to data processing for noise rejection. The third application is on windscreen wipers. In this case the tracking approach fully demonstrate his capabilities, representing the only technique able to give information in the time domain on the dynamic behaviour of the rubber blade in operative conditions.All the application shows as the TLDV allows to obtain realistic results on the dynamic characteristics under simulated operative conditions.A Lagrangian approach was adopted: data were acquired with the target in continuously changing conditions and that impose a not traditional approach on LDV data such as a joint time-frequency analysis.

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