Monitoring and intelligent control for complex curvature friction stir welding
- Hua, Tao
- Authors: Hua, Tao
- Date: 2006
- Subjects: Friction welding , Fuzzy systems
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9612 , http://hdl.handle.net/10948/420 , Friction welding , Fuzzy systems
- Description: A multi-input multi-output system to implement on-line process monitoring and intelligent control of complex curvature friction stir welding was proposed. An extra rotation axis was added to the existing three translation axes to perform friction stir welding of complex curvature other than straight welding line. A clamping system was designed for locating and holding the workpieces to bear the large force involved in the process between the welding tool and workpieces. Process parameters (feed rate, spindle speed, tilt angle and plunge depth), and process conditions (parent material and curvature), were used as factors for the orthogonal array experiments to collect sensor data of force, torque and tool temperature using multiple sensors and telemetry system. Using statistic analysis of the experimental data, sensitive signal features were selected to train the feed-forward neural networks, which were used for mapping the relationships between process parameters, process conditions and sensor data. A fuzzy controller with initial input/output membership functions and fuzzy rules generated on-line from the trained neural network was applied to perceive process condition changes and make adjustment of process parameters to maintain tool/workpiece contact and energy input. Input/output scaling factors of the fuzzy controller were tuned on-line to improve output response to the amount and trend of control variable deviation from the reference value. Simulation results showed that the presented neuro-fuzzy control scheme has adaptability to process conditions such as parent material and curvature changes, and that the control variables were well regulated. The presented neuro-fuzzy control scheme can be also expected to be applied in other multi-input multi-output machining processes.
- Full Text:
- Date Issued: 2006
- Authors: Hua, Tao
- Date: 2006
- Subjects: Friction welding , Fuzzy systems
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9612 , http://hdl.handle.net/10948/420 , Friction welding , Fuzzy systems
- Description: A multi-input multi-output system to implement on-line process monitoring and intelligent control of complex curvature friction stir welding was proposed. An extra rotation axis was added to the existing three translation axes to perform friction stir welding of complex curvature other than straight welding line. A clamping system was designed for locating and holding the workpieces to bear the large force involved in the process between the welding tool and workpieces. Process parameters (feed rate, spindle speed, tilt angle and plunge depth), and process conditions (parent material and curvature), were used as factors for the orthogonal array experiments to collect sensor data of force, torque and tool temperature using multiple sensors and telemetry system. Using statistic analysis of the experimental data, sensitive signal features were selected to train the feed-forward neural networks, which were used for mapping the relationships between process parameters, process conditions and sensor data. A fuzzy controller with initial input/output membership functions and fuzzy rules generated on-line from the trained neural network was applied to perceive process condition changes and make adjustment of process parameters to maintain tool/workpiece contact and energy input. Input/output scaling factors of the fuzzy controller were tuned on-line to improve output response to the amount and trend of control variable deviation from the reference value. Simulation results showed that the presented neuro-fuzzy control scheme has adaptability to process conditions such as parent material and curvature changes, and that the control variables were well regulated. The presented neuro-fuzzy control scheme can be also expected to be applied in other multi-input multi-output machining processes.
- Full Text:
- Date Issued: 2006
Restoring trust by verifying information integrity through continuous auditing
- Authors: Flowerday, Stephen
- Date: 2006
- Subjects: Auditing, Internal , Corporate governance
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9796 , http://hdl.handle.net/10948/504 , http://hdl.handle.net/10948/d1011920 , Auditing, Internal , Corporate governance
- Description: Corporate scandals such as Enron, WorldCom and Parmalat, have focused recent governance efforts in the domain of financial reporting due to fraudulent and/or erroneous accounting practices. In addition, the ineffectiveness of the current system of controls has been highlighted, including that some directors have been weak and ineffective monitors of managers. This board of director ‘weakness’ has called for additional mechanisms for monitoring and controlling of management, focusing on financial reporting. This problem intensifies in that today companies function in real-time, and decisions are based on available realtime financial information. However, the assurances provided by traditional auditing take place months after the transactions have occurred and therefore, a trust problem arises because information is not verified in real-time. Consequently, the errors and fraud concealed within the financial information is not discovered until months later. To address this trust problem a conceptual causal model is proposed in this study based on the principles of systems theory. The emergent property of the causal model is increased trust and control. This study establishes that mutual assurances assist in building trust and that information security assists in safeguarding trust. Subsequently, in order to have a positive relationship between the company directors and various stakeholders, uncertainty needs to be contained, and the level of trust needs to surpass the perceived risks. The study concludes that assurances need to be provided in real-time to restore stakeholder confidence and trust in the domain of financial reporting. In order to provide assurances in real-time, continuous auditing is required to verify the integrity of financial information when it becomes available, and not months later. A continuous auditing process has its foundations grounded in information technology and attends to the challenges in real-time by addressing the standardisation of data to enable effective analysis, the validation of the accuracy of the data and the reliability of the system.
- Full Text:
- Date Issued: 2006
- Authors: Flowerday, Stephen
- Date: 2006
- Subjects: Auditing, Internal , Corporate governance
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9796 , http://hdl.handle.net/10948/504 , http://hdl.handle.net/10948/d1011920 , Auditing, Internal , Corporate governance
- Description: Corporate scandals such as Enron, WorldCom and Parmalat, have focused recent governance efforts in the domain of financial reporting due to fraudulent and/or erroneous accounting practices. In addition, the ineffectiveness of the current system of controls has been highlighted, including that some directors have been weak and ineffective monitors of managers. This board of director ‘weakness’ has called for additional mechanisms for monitoring and controlling of management, focusing on financial reporting. This problem intensifies in that today companies function in real-time, and decisions are based on available realtime financial information. However, the assurances provided by traditional auditing take place months after the transactions have occurred and therefore, a trust problem arises because information is not verified in real-time. Consequently, the errors and fraud concealed within the financial information is not discovered until months later. To address this trust problem a conceptual causal model is proposed in this study based on the principles of systems theory. The emergent property of the causal model is increased trust and control. This study establishes that mutual assurances assist in building trust and that information security assists in safeguarding trust. Subsequently, in order to have a positive relationship between the company directors and various stakeholders, uncertainty needs to be contained, and the level of trust needs to surpass the perceived risks. The study concludes that assurances need to be provided in real-time to restore stakeholder confidence and trust in the domain of financial reporting. In order to provide assurances in real-time, continuous auditing is required to verify the integrity of financial information when it becomes available, and not months later. A continuous auditing process has its foundations grounded in information technology and attends to the challenges in real-time by addressing the standardisation of data to enable effective analysis, the validation of the accuracy of the data and the reliability of the system.
- Full Text:
- Date Issued: 2006
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