Orientador: Paulo Roberto de Aguiar / Resumo: O chatter corresponde a movimentos instáveis e caóticos no sistema de usinagem, resultando em flutuação das forças de corte e na impressão de ondulações na superficie da peça usinada. É um fenômeno indesejável ao processo de usinagem, especialmente ao processo de retificação, pois a sua ocorrência acentuada resulta em um produto acabado com tolerâncias dimensionais e geométricas fora dos padrões, ou até mesmo em danos irreversíveis, como por exemplo, alteração na dureza, alta rugosidade e queima superficial da peça usinada. Na literatura, poucos trabalhos tratam da análise e monitoramento do chatter com técnicas de processamento digital de sinais, especialmente de aceleração. O objetivo desse trabalho é propor uma nova técnica de processamento digital utilizando os sinais de aceleração baseados no cálculo da STFT - Short Time Fourier Transform (Transformada de Fourier de curta duração) e na estatística Relação de Potência (ROP – ratio of power), com a finalidade de detecção do fenômeno de chatter na retificação tangencial plana com rebolo superabrasivo de nitreto cúbico de boro (CBN) e óxido de alumínio. Para tanto, ensaios de retificação foram realizados em corpos de prova de aço ABNT 1045. Um acelerômetro piezelétrico foi acoplado ao suporte das peças e sinais de aceleração foram coletados à uma frequência de amostragem de 2MHz. Dentre as variáveis de saída, obteve-se a dureza Vickers (HV), rugosidade média (Ra) e a análise microestrutural das peças retificadas. Os sinais d... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Chatter corresponds to unstable and chaotic movements in the machining system, resulting in fluctuation of the cutting forces. It is a serious and undesired physical phenomenon that occurs in the grinding process during parts manufacturing. The intense occurrence of this phenomenon during machining can generate a finished part outside the dimensional and geometric tolerances or even cause irreversible damage, such as: changes to the hardness, high surface roughness, and thermal damages to the ground part. Few vibration signal processing techniques have been proposed for monitoring chatter during grinding. Thus, the objective of this study is to propose and validate a new vibration signal processing technique based on the short-time Fourier transform (STFT) and the ratio of power (ROP) statistic for the detection of chatter during the tangential surface grinding of ABNT 1045 steel with different grinding wheels. Experimental grinding tests were conducted, and the vibration signals were recorded at 2 MHz. The Vickers hardness (HV), roughness (Ra) and metallography of the ground workpiece surfaces were performed. Subsequently, a digital processing technique based on the STFT and ROP was applied to the vibration signals to extract the characteristics of the chatter in the grinding process. The results show that this technique can be used to characterize over time the spectral patterns of a frequency band related to chatter. The observed patterns have a strong relationship with th... (Complete abstract click electronic access below) / Doutor

Kognitive Kontrolle bezieht sich auf eine Vielzahl mentaler Fähigkeiten, die es uns erlauben im täglichen Leben zielgerichtete Entscheidungen zu treffen und sich flexibel an sich ständig ändernde Umweltanforderungen anzupassen. Das Ziel der vorliegenden Dissertation war es heraus zu finden, ob Kernfunktionen im Bereich der Konfliktüberwachung, Konfliktkontrolle, Fehlerverarbeitung und die daraus resultierenden Verhaltensanpassungen durch ein einheitliches Kontrollnetzwerk geleistet werden, oder ob spezifische Mechanismen die möglicherweise durch unabhängige neuronale Kontrollschleifen realisiert sind, die Flexibilität unserer Anpassungsfähigkeit steuern. Studie 1 und Studie 2 untersuchen sowohl generelle aus auch spezifische Aspekte der Konflikt- und Fehlerverarbeitung mit Hilfe klassischer Konfliktparadigmen und dem Einsatz von Zeit-Frequenz-analytischen Auswertungsmethoden. Studie 1 untersucht anhand 3 verschiedener Konfliktparadigmen (Simon, Flanker, NoGo) die Modulation der Theta Aktivität (4-8 Hz) und verortet diese grob innerhalb des medial frontalen Cortex (MFC), einer Struktur die durch eine Vielzahl von Studien als entscheidend bei der Konfliktverarbeitung angesehen wird. Die gefundene Theta Aktivität wurde in Studie 2 genutzt, um auch dynamische Netzwerkaktivierungen bei der Bearbeitung von Reiz- und Reaktionskonflikten zu beobachten. Es konnte gezeigt werden, dass ein vermutetes Netzwerk bestehend aus MFC, lateralen präfrontalen Cortices und motorischen Arealen bei der Lösung von Reaktionskonflikten beteiligt ist. In Studie 3 wird eine Simon-Aufgabe, die innerhalb von belohnenden oder bestrafenden Kontexten durchgeführt wurde, genutzt um zu zeigen, dass Konflikt- und Fehlerverarbeitung differentiell durch die Kontextmanipulation beeinflusst werden. Entgegen voriger Annahmen scheinen mehrere neuronale Kontrollsysteme an der Lösung von Konflikten und daraus resultierenden Verhaltensanpassungen beteiligt zu sein. / Cognitive control refers to a set of mental abilities that allow us goal-directed behavior in everyday life and to flexibly adapt to permanently changing environmental demands. The goal of the present dissertation was to investigate whether core functions in the area of conflict monitoring, conflict control, error processing and behavioral adjustments caused by these processes are enabled via a unitary control network or whether specific mechanisms that are possibly realized via independent control loops are responsible for the flexibility of our adaptability. Study 1 and 2 investigate general as well as specific aspects of conflict and error processing by using classic conflict paradigms and time-frequency-analytic methods. Study 1 compares the modulation of theta activity (4-8 Hz) across 3 conflict paradigms (Simon, Flanker, NoGo) and roughly situates it within medial frontal cortex (MFC), a structure which has been characterized as crucial for conflict processing in manifold studies. The found theta activity has been used in study 2, to observe dynamic network activations during processing of stimulus and response conflicts. Data confirmed that a hypothesized network consisting of MFC, lateral prefrontal cortices and motor areas is involved in conflict resolution. In study 3 we used a Simon task which was executed either during a rewarding or a punishing context assessing the influence of motivational contexts on conflict adaptation revealing that conflict and error processing were influenced differentially by the context manipulation. Against previous assumptions, several neuronal control systems seem to be engaged during conflict resolution and resulting behavioral adjustments.