Suppression of period doubling chetter in high-speed milling by spindle speed variation

Spindle speed variation is a well known technique to suppress regenerative machine tool vibra- tions, but it is usually considered to be effective only for low spindle speeds. In the current paper, spindle speed variation is applied to the high speed milling process, at the spindle speeds where the constant speed cutting results in period doubling chatter. The stability analysis of triangular and sinusoidal shape variations is made numerically with the semi-discretization method. It is shown that the milling process can be stabilized by increasing the amplitude of the spindle speed variation, while the frequency of the variation has no significant effect on the dynamic behaviour. The results are validated by experiments. Based on the analysis of the machined workpieces, it is shown that the surface roughness can also be decreased by the spindle speed variation technique

Continuous-Time and Companding Digital Signal Processors Using Adaptivity and Asynchronous Techniques

The fully synchronous approach has been the norm for digital signal processors (DSPs) for many decades. Due to its simplicity, the classical DSP structure has been used in many applications. However, due to its rigid discrete-time operation, a classical DSP has limited efficiency or inadequate resolution for some emerging applications, such as processing of multimedia and biological signals. This thesis proposes fundamentally new approaches to designing DSPs, which are different from the classical scheme. The defining characteristic of all new DSPs examined in this thesis is the notion of "adaptivity" or "adaptability." Adaptive DSPs dynamically change their behavior to adjust to some property of their input stream, for example the rate of change of the input. This thesis presents both enhancements to existing adaptive DSPs, as well as new adaptive DSPs. The main class of DSPs that are examined throughout the thesis are continuous-time (CT) DSPs. CT DSPs are clock-less and event-driven; they naturally adapt their activity and power consumption to the rate of their inputs. The absence of a clock also provides a complete avoidance of aliasing in the frequency domain, hence improved signal fidelity. The core of this thesis deals with the complete and systematic design of a truly general-purpose CT DSP. A scalable design methodology for CT DSPs is presented. This leads to the main contribution of this thesis, namely a new CT DSP chip. This chip is the first general-purpose CT DSP chip, able to process many different classes of CT and synchronous signals. The chip has the property of handling various types of signals, i.e. various different digital modulations, both synchronous and asynchronous, without requiring any reconfiguration; such property is presented for the first time CT DSPs and is impossible for classical DSPs. As opposed to previous CT DSPs, which were limited to using only one type of digital format, and whose design was hard to scale for different bandwidths and bit-widths, this chip has a formal, robust and scalable design, due to the systematic usage of asynchronous design techniques. The second contribution of this thesis is a complete methodology to design adaptive delay lines. In particular, it is shown how to make the granularity, i.e. the number of stages, adaptive in a real-time delay line. Adaptive granularity brings about a significant improvement in the line's power consumption, up to 70% as reported by simulations on two design examples. This enhancement can have a direct large power impact on any CT DSP, since a delay line consumes the majority of a CT DSP's power. The robust methodology presented in this thesis allows safe dynamic reconfiguration of the line's granularity, on-the-fly and according to the input traffic. As a final contribution, the thesis also examines two additional DSPs: one operating the CT domain and one using the companding technique. The former operates only on level-crossing samples; the proposed methodology shows a potential for high-quality outputs by using a complex interpolation function. Finally, a companding DSP is presented for MPEG audio. Companding DSPs adapt their dynamic range to the amplitude of their input; the resulting can offer high-quality outputs even for small inputs. By applying companding to MPEG DSPs, it is shown how the DSP distortion can be made almost inaudible, without requiring complex arithmetic hardware

Measurements, Models, Systems and Design

531 s.

Optimized state feedback regulation of 3DOF helicopter system via extremum seeking

In this paper, an optimized state feedback regulation of a 3 degree of freedom (DOF) helicopter is designed via extremum seeking (ES) technique. Multi-parameter ES is applied to optimize the tracking performance via tuning State Vector Feedback with Integration of the Control Error (SVFBICE). Discrete multivariable version of ES is developed to minimize a cost function that measures the performance of the controller. The cost function is a function of the error between the actual and desired axis positions. The controller parameters are updated online as the optimization takes place. This method significantly decreases the time in obtaining optimal controller parameters. Simulations were conducted for the online optimization under both fixed and varying operating conditions. The results demonstrate the usefulness of using ES for preserving the maximum attainable performance

On the Stabilization through Linear Output Feedback of a Class of Linear Hybrid Time-Varying Systems with Coupled Continuous/Discrete and Delayed Dynamics with Eventually Unbounded Delay

This research studies a class of linear, hybrid, time-varying, continuous time-systems with time-varying delayed dynamics and non-necessarily bounded, time-varying, time-differentiable delay. The considered class of systems also involves a contribution to the whole delayed dynamics with respect to the last preceding sampled values of the solution according to a prefixed constant sampling period. Such systems are also subject to linear output-feedback time-varying control, which picks-up combined information on the output at the current time instant, the delayed one, and its discretized value at the preceding sampling instant. Closed-loop asymptotic stabilization is addressed through the analysis of two “ad hoc” Krasovskii–Lyapunov-type functional candidates, which involve quadratic forms of the state solution at the current time instant together with an integral-type contribution of the state solution along a time-varying previous time interval associated with the time-varying delay. An analytic method is proposed to synthesize the stabilizing output-feedback time-varying controller from the solution of an associated algebraic system, which has the objective of tracking prescribed suited reference closed-loop dynamics. If this is not possible—in the event that the mentioned algebraic system is not compatible—then a best approximation of such targeted closed-loop dynamics is made in an error-norm sense minimization. Sufficiency-type conditions for asymptotic stability of the closed-loop system are also derived based on the two mentioned Krasovskii–Lyapunov functional candidates, which involve evaluations of the contributions of the delay-free and delayed dynamics.This research was funded by the Spanish Government and the European Commission through Grant RTI2018-094336-B-I00 (MCIU/AEI/FEDER, UE)

Recent Advances in Robust Control

Robust control has been a topic of active research in the last three decades culminating in H_2/H_\infty and \mu design methods followed by research on parametric robustness, initially motivated by Kharitonov's theorem, the extension to non-linear time delay systems, and other more recent methods. The two volumes of Recent Advances in Robust Control give a selective overview of recent theoretical developments and present selected application examples. The volumes comprise 39 contributions covering various theoretical aspects as well as different application areas. The first volume covers selected problems in the theory of robust control and its application to robotic and electromechanical systems. The second volume is dedicated to special topics in robust control and problem specific solutions. Recent Advances in Robust Control will be a valuable reference for those interested in the recent theoretical advances and for researchers working in the broad field of robotics and mechatronics

SIRM 2017

This volume contains selected papers presented at the 12th International Conference on vibrations in rotating machines, SIRM, which took place February 15-17, 2017 at the campus of the Graz University of Technology. By all meaningful measures, SIRM was a great success, attracting about 120 participants (ranging from senior colleagues to graduate students) from 14 countries. Latest trends in theoretical research, development, design and machine maintenance have been discussed between machine manufacturers, machine operators and scientific representatives in the field of rotor dynamics. SIRM 2017 included thematic sessions on the following topics: Rotordynamics, Stability, Friction, Monitoring, Electrical Machines, Torsional Vibrations, Blade Vibrations, Balancing, Parametric Excitation, and Bearings. The papers struck an admirable balance between theory, analysis, computation and experiment, thus contributing a richly diverse set of perspectives and methods to the audience of the conference

Event-driven control in theory and practice : trade-offs in software and control performance

Feedback control algorithms are indispensable for the proper functioning of many industrial high-tech systems like copiers, wafer steppers and so on. Most research in digital feedback control considers periodic or time-driven control systems, where continuous-time signals are represented by their sampled values at a fixed frequency. In most applications, these digital control algorithms are implemented in a real-time embedded software environment. As a consequence of the time-driven nature of controllers, control engineers pose strong, non-negotiable requirements on the real-time implementations of their algorithms as the required control performance can be guaranteed in this manner. This might lead to non-optimal solutions if the design problem is considered from a broader multi-disciplinary system perspective. As an example, time-driven controllers perform control calculations all the time at a fixed rate, so also when nothing significant has happened in the process. This is clearly an unnecessary waste of resources like processor load and communication bus load and thus not optimal if these aspects are considered as well. To reduce the severe real-time constraints imposed by the control engineer and the accompanying disadvantages, this thesis proposes to drop the strict requirement of equidistant sampling. This enables the designers to make better balanced multidisciplinary trade-offs resulting in a better overall system performance and reduced cost price. By not requiring equidistant sampling, one could for instance vary the sample frequency over time and dynamically schedule the control algorithms in order to optimize over processor load. Another option is to perform a control update when new measurement data arrives. In this manner quantization effects and latencies are reduced considerably, which can reduce the required sensor resolution and thus the system cost price. As it is now an event (e.g. the arrival of a new measurement), rather than the elapse of time, that triggers the controller to perform an update, this type of feedback controllers is called event-driven control. In this thesis, we present two different event-driven control structures. The first one is sensor-based event-driven control in the sense that the control update is triggered by the arrival of new sensor data. In particular, this control structure is applied to accurately control a motor, based on an (extremely) low resolution encoder. The control design is based on transforming the system equations from the time domain to the angular position (spatial) domain. As controller updates are synchronous with respect to the angular position of the motor, we can apply variations on classical control theory to design and tune the controller. As a result of the transformation, the typical control measures that we obtain from analysis, are formulated in the spatial domain. For instance, the bandwidth of the controller is not expressed in Hertz (s¡1) anymore, but in rad¡1 and settling time is replaced by settling distance. For many high-tech systems these spatial measures directly relate to the real performance requirements. Moreover, disturbances are often more easily formulated in terms of angular position than in terms of time, which has clear advantages from a modeling point of view. To validate the theory, the controller is implemented on a high speed document printing system, to accurately control a motor based on an encoder resolution of only 1 pulse per revolution. By means of analysis, simulation and measurements we show that the control performance is similar to the initially proposed industrial controller that is based on a much higher encoder resolution. Moreover, we show that the proposed event-driven controller involves a significant lower processor load and hence outperforms the time-driven controller from a system perspective. The aim of the second type of event-driven controllers is to reduce the resource utilization for the controller tasks, such as processor load and communication bus load. The main idea is to only update the controller when it is necessary from a control performance point of view. For instance, we propose event-driven controllers that do not update the control value when the tracking/stabilization error is below a certain threshold. By choosing this threshold, a trade-off can be made between control performance and processor load. To get insight in this trade-off, theory is presented to analyze the control performance of these event-driven control loops in terms of ultimate bounds on the tracking/stabilization error. The theory is based on inferring properties (like robust positive invariance, ultimate boundedness and convergence indices) for the event-driven controlled system from discrete-time linear systems and piecewise linear systems. Next to the theoretical analysis, simulations and experiments are carried out on a printer paper path test-setup. It is shown that for the particular application the average processing time, needed to execute the controller tasks, was reduced by a factor 2 without significant degradation of the control performance in comparison to a timedriven implementation. Moreover, we developed a method to accurately predict the processor load for different processing platforms. This method is based on simulation models and micro measurements on the processing platform, such that the processor load can be estimated prior to implementing the controller on the platform. Next to these contributions in the field of event-driven control, a system engineering technique called "threads of reasoning" is extended and applied to the printer case study to achieve a focus on the right issues and trade-offs in a design. In summary, two types of event-driven controllers are theoretically analyzed and experimentally validated on a prototype document printing system. The results clearly indicate the potential benefits of event-driven control with respect to the overall system performance and in making trade-offs between control performance, software performance and cost price