| 摘要: | 遮蔽金屬電弧焊接是一種最通用的熔化與接合的電弧焊接方法，但是相關的文獻研究卻是比遮蔽金屬電弧焊接與惰性鎢極電弧焊接還少。本論文所描述的自動遮蔽金屬電弧焊接控制系統可用來取代需要良好訓練技工的手動焊接操作，雖然機械人焊接在許多焊接工業應用上已經取代了手工焊接，但是在發展自動化焊接過程中，由於其複雜的過程而無法完全地開發。 首先，展開一個二階數學模型的焊接控制系統，它主要由一交流伺服馬達驅動之焊條進給控制機構所組成，此自動化焊接控制系統可以視為一個焊條進給速度控制系統。為了設計非線性控制器來針對這個自動遮蔽金屬電弧焊接控制系統和使用數值模擬來分析這工業上焊接的過程，我們推導二階動態焊接控制系統並且鑑別此系統的參數。在操作期間，針對我們所提出兩種強健控制器來控制以交流伺服馬達驅動的焊條進給控制機構，可以補賞熔掉的焊條部份，也可以穩定不必要的電弧長度變動。 適應性滑動模態控制器由等效控制部份與迫近控制部分所組成，從李雅普若夫函數(Lyapunov function)所推導的適應性法則可用來得到模糊控制器的參數值和近似順滑模態控制(sliding mode control)的等效控制部份，因此系統狀態可以強迫到零點狀態。並藉由三條規則的模糊控制器來確保迫近控制能滿足系統狀態可以維持在順滑面上的迫近條件。因此，可以保證適應性滑動模態控制器的穩定度和用來調節電焊條進給機構以控制SMAW焊接系統的電弧電流大小。以適應性滑動模態為基礎的模擬與實驗結果均顯示可以表現得很有效率。 在論文的最後，推導一個如有死區，焊接控制系統飽和摩差力的表徵的非線性數學模型並鑑別出其系統參數。設計一個新的可變結構模型控制法則來調節焊接調節電焊條進給機構以控制電弧電流大小，並且可以確保自動化焊接系統的全區接近條件的順滑模態。在此順滑模態中，在自動焊接機器與模型上的電弧電流誤差最後會趨近於零。此外，此焊接系統雖在有摩差力的狀況下也不會受不確定性與干擾的影響。在模擬與實驗的結果可證實基於所提出的模型追隨可變結構控制器可以成功地維持所需要焊接電流的大小和維持電弧長度的穩定度，因而確保得到出色的焊接性能。 Shield metal arc welding (SMAW) is the most common type of an arc welding process that melts and joins metals, but its research is less than inert gas metal arc welding (GMAW) or inert gas tungsten arc welding (GTAW). This thesis describes an automatic SMAW control system which has replaced manual operations required a well-trained technician. Robotic welders have replaced manual human operations in many welding applications, but the automated process control systems have not been fully developed due to the complexity of the process. A numerical procedure is first developed to derive a second-order mathematical model of the welding control system, which consists primarily of an electrode feed-rate mechanism driven by an AC servomotor. The automatic welding control system can be considered an electrode feed-rate velocity control system. To be able to develop nonlinear controllers for the SMAW system and also for enabling numerical simulation to analyze an industrial welding process, a second-order mathematical model of the welding control system has been derived and the parameters of the system have been identified. The electrode feed-rate mechanism for our proposed controllers is driven an AC servomotor that can both compensate for the molted part of the consumed electrode and for the undesirable fluctuations of the arc length during automated welding operation. An adaptive fuzzy sliding mode controller (AFSMC) consists of an equivalent control part and a hitting control part. An adaptive law derived from a Lyapunov function is used to obtain the FLC’s parameters, and is applied to approximate the equivalent control part of the sliding mode control (SMC), so that the system states can be forced to zero. By using three rules FLC, the hitting control part that satisfies the hitting conditions of the SMC can force the system’s states to reach and remain on the sliding surface. Therefore, the stability of the AFSMC can be guaranteed and can be used to modulate the rate of the electrode feeding mechanism that regulates the arc current of the SMAW. The simulation and the experimental results both show that this automatic welding control system, based on the AFSMC, can perform effectively. Finally, in this thesis, a nominal nonlinear mathematical model containing uncertainties such as dead-zone, welding control system saturation, and the identified system parameters is derived. A novel variable structure model reference control scheme is designed to modulate the rate of the electrode feed mechanism thereby regulating the arc current, the developed controller assures the global reaching condition of the sliding mode of the controlled welding system. In the sliding mode, the electric current error between the plant and the model approaches zero asymptotically. Moreover, the welding system remains insensitive to uncertainties and disturbance as the systems with friction. The simulation and experimental results confirm that the automatic welding control system, based on the proposed model-following variable structure controller, successfully maintains the magnitude of the arc current at the desired value and preserves the stability of the arc length, thereby ensuring an excellent welding performance. |
