6,074 research outputs found
Beyond the Waterbed Effect: Development of Fractional Order CRONE Control with Non-Linear Reset
In this paper a novel reset control synthesis method is proposed: CRONE reset
control, combining a robust fractional CRONE controller with non-linear reset
control to overcome waterbed effect. In CRONE control, robustness is achieved
by creation of constant phase behaviour around bandwidth with the use of
fractional operators, also allowing more freedom in shaping the open-loop
frequency response. However, being a linear controller it suffers from the
inevitable trade-off between robustness and performance as a result of the
waterbed effect. Here reset control is introduced in the CRONE design to
overcome the fundamental limitations. In the new controller design, reset phase
advantage is approximated using describing function analysis and used to
achieve better open-loop shape. Sufficient quadratic stability conditions are
shown for the designed CRONE reset controllers and the control design is
validated on a Lorentz-actuated nanometre precision stage. It is shown that for
similar phase margin, better performance in terms of reference-tracking and
noise attenuation can be achieved.Comment: American Control Conference 201
No More Differentiator in PID:Development of Nonlinear Lead for Precision Mechatronics
Industrial PID consists of three elements: Lag (integrator), Lead
(Differentiator) and Low Pass Filters (LPF). PID being a linear control method
is inherently bounded by the waterbed effect due to which there exists a
trade-off between precision \& tracking, provided by Lag and LPF on one side
and stability \& robustness, provided by Lead on the other side. Nonlinear
reset strategies applied in Lag and LPF elements have been very effective in
reducing this trade-off. However, there is lack of study in developing a reset
Lead element. In this paper, we develop a novel lead element which provides
higher precision and stability compared to the linear lead filter and can be
used as a replacement for the same. The concept is presented and validated on a
Lorentz-actuated nanometer precision stage. Improvements in precision, tracking
and bandwidth are shown through two separate designs. Performance is validated
in both time and frequency domain to ensure that phase margin achieved on the
practical setup matches design theories.Comment: European Control Conference 201
'Constant in gain Lead in phase' element - Application in precision motion control
This work presents a novel 'Constant in gain Lead in phase' (CgLp) element
using nonlinear reset technique. PID is the industrial workhorse even to this
day in high-tech precision positioning applications. However, Bode's gain phase
relationship and waterbed effect fundamentally limit performance of PID and
other linear controllers. This paper presents CgLp as a controlled nonlinear
element which can be introduced within the framework of PID allowing for wide
applicability and overcoming linear control limitations. Design of CgLp with
generalized first order reset element (GFORE) and generalized second order
reset element (GSORE) (introduced in this work) is presented using describing
function analysis. A more detailed analysis of reset elements in frequency
domain compared to existing literature is first carried out for this purpose.
Finally, CgLp is integrated with PID and tested on one of the DOFs of a planar
precision positioning stage. Performance improvement is shown in terms of
tracking, steady-state precision and bandwidth
Complex order control for improved loop-shaping in precision positioning
This paper presents a complex order filter developed and subsequently
integrated into a PID-based controller design. The nonlinear filter is designed
with reset elements to have describing function based frequency response
similar to that of a linear (practically non-implementable) complex order
filter. This allows for a design which has a negative gain slope and a
corresponding positive phase slope as desired from a loop-shaping
controller-design perspective. This approach enables improvement in precision
tracking without compromising the bandwidth or stability requirements. The
proposed designs are tested on a planar precision positioning stage and
performance compared with PID and other state-of-the-art reset based
controllers to showcase the advantages of this filter
Dynamic load balancing based on live migration of virtual machines: Security threats and effects
Live migration of virtual machines (VMs) is the process of transitioning a VM from one virtual machine monitor (VMM) to another without halting the guest operating system, often between distinct physical machines, has opened new opportunities in computing. It allows a clean separation between hardware and software, and facilitates fault management, load balancing, and low-level system maintenance. Implemented by several existing virtualization products, live migration also aids in aspects such as high availability services, transparent mobility and consolidated management. While virtualization and live migration enable important new functionality, the combination introduces novel security challenges. A virtual machine monitor that incorporates a vulnerable implementation of live migration functionality may expose both the guest and host operating system to attack and result in a compromise of integrity. Given the large and increasing market for virtualization technology, a comprehensive understanding of virtual machine migration security is essential. So the main idea behind this thesis is to create a test environment that is suitable for experimenting and analyzing the security implications in case of exploitation of Live Migration of Virtual Machines. Using Live VM migration for dynamic load balancing or scheduling, this study determines workload hotspots in physical environment and through use of effective Live Migration process; tries to carry out resource profiling. By carrying out effective profiling, this thesis research is able to determine how much of each resource needs to be allocated to a VM. To understand exactly why process migration would not work in such scenarios and better understand Live VM Migration, this thesis tries to provide requisite incites as to which model is most appropriate for automatic load balancing for virtual machine infrastructure based on resource consumption. The security implications of exploiting the process of migration may end in unexpected results or results that are not noticeable. The scope of this thesis research is identifying these results and the causes for them
Computer control of an HF chirp radar
This thesis describes the interfacing of an IBM compatible microcomputer to a BR Communications chirp sounder. The need for this is twofold: Firstly for control of the sounder including automatic scheduling of operations, and secondly for data capture. A signal processing card inside the computer performs a Fast Fourier Transform on the sampled data from two phase matched receivers. The transformed data is then transferred to the host computer for further processing, display and storage on hard disk or magnetic tape, all in real time. Critical timing functions are provided by another card in the microcomputer, the timing controller. Built by the author, the design and operation of this sub-system is discussed in detail. Additional circuitry is required to perform antenna and filter switching, and a possible design thereof is also presented by the author. The completed system, comprising the chirp sounder, the PC environment, and the signal switching circuitry, has a dual purpose. It can operate as either a meteor radar, using a fixed frequency (currently 27,99 MHz), or as an advanced chirp ionosonde allowing frequency sweeps from 1,6 to 30 MHz. In the latter case fixed frequency doppler soundings are also possible. Examples of data recorded in the various modes are given
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