金屬積層製造生產過程中，使用相同製程參數，以目前開迴路製程的機台而言，其所產製的品質也會有所差異，例如當風場穩定度、鋪粉均勻度、與粉粒尺寸和積層過程有所變異時，上述製程變異將導致的成品瑕疵，將造成時間與材料的浪費。因此，如何對此種機台進行上述的製程變異偵測與補償，並達到即時控制的目標，為本研究的挑戰。
本研究針對開迴路粉床式金屬積層製造機台進行補償控制，包含風場、鋪粉、與拋光補償等三大閉迴路控制。在風場補償上，透過風場流速回授與控制，可在不擾動金屬粉層下有效排出腔體內的煙霧顆粒。在鋪粉補償上，透過全域相機以光學檢測鋪粉均勻度之回授，以重鋪或補粉方式控制鋪粉品質。在拋光補償上，藉由同軸相機以即時檢測熔池變化，並應用全自動虛擬量測方法以估測列印品質之回授，並參考積層製造模擬之建議，逐層調整雷射參數以進行拋光補償，以控制逐層粗糙度的穩定度。
研究結果顯示，當應用本研究所開發的閉迴路控制系統，相對開迴路而言，風場可減少92.5 %之變異，鋪粉均勻度可提改善37%，而列印品質包含粗糙度、密度、拉力等指標有提升。因此，本研究所開發的閉迴路補償功能，實可大幅改善製程變異所造成的成品瑕疵情況。

When using a metal additive manufacturing (AM) machine with open-loop control, the built qualities of parts are varying while using the identical process conditions. Due to variations of air flowing stability, powder spreading homogeneity, powder-size uniformity, and building stability, time and materials costs will be increased when defects existed in finished parts. Hence, the challenge of this research is how to detect and compensate the variations to achieve the goal of real-time control of the AM process.
This research aims at compensation control of an open-loop powder-bed metal AM machine with close-loop controls of air flowing, powder spreading, and part building compensation. In air flowing compensation, without disturbing powder layers, the discharge smoke and particles can be effectively exhausted from the chamber by using the air-speed feedback control. For spreading powder compensation, the feedback of spreading powder uniformity is optically detected through a global camera, and the spreading quality is controlled by means of spreading or re-filling powder. In part building compensation, the coaxial camera is used to detect the change of the molt-pool in real time, and the automatic virtual metrology system is used to estimate printing quality, and refer to recommendations of AM simulation to adjust the laser parameters layer by layer. Polishing compensation is performed to control the stability of roughness layer by layer.
The research results show that when the close-loop control system developed by this research is applied, the flow rate variation can be reduced by 92.5%, and the homogeneity of powder spreading can be improved by 37%, and the printing quality includes indexes such as roughness, density, and tensile have been improved. Therefore, the close-loop compensation functions developed by this research can greatly improve defects of a built part caused by the process variations.

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