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A New Synchronous Error Control Method for CNC Machine Tools with Dual-Driving Systems
Shih-Ming Wang,Ren-Jeng Wang,Shambaljamts Tsooj 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
Driving an object along one axis with two driving systems is a common method for obtaining high acceleration and high trust force for a large CNC machine tool. However, if large synchronous movement error exists between the two driving systems, the machine will not be able to achieve high acceleration. Moreover, it may also cause serious structure deformation and damage to the machine. To solve this problem, a new control method integrating the model reference adaptive control and variable structure control was developed and verified in this study. The proposed method can determine and compensate on-line the synchronous movement errors between two driving systems so that the master driving unit and the slave driving unit of a dual-driving system can synchronously move with no large drag force and reach the desired acceleration. Experiments were performed on a gantry-type two-axis platform with a sliding 5-Kg metal block attached on the X-axis. The experimental results showed that the maximum and the average synchronous movement errors were reduced from 0.061 mm to 0.040 mm and from 0.032 mm to 0.013 mm, respectively.
Shih-Ming Wang,Ji-Jun Lin,Zhe-Zhi Ye,Shambaljamts Tsooj,Chun-Chieh Wang 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.
To perform an accurate micro machining process, accurate alignment of the micro cutter with respect to the local coordinate frame for machining is essential. Due to the fragility of the micro tool, traditional cutter alignment method used in industry is no longer proper for micro machining. Utilizing machine vision technology with 2 CCDs, a micro tool positioning error measurement and auto-compensation method and system were proposed. In the measurement method, Power Law Method was first used to enhance the image taken by a CCD. Canny Edge Method and image projection method were then used to identify the contours of the cutter and the workpiece from the image. Finally, the position errors of the cutter were determined through calculating the number of pixels between the cutter and the workpiece. The proposed error compensation system can automatically generate NC codes which will accurately re-locate the cutter based on the measured position errors . Experiments were conducted on a micro machine tool, and the results have shown that the y-dir. positioning error of the cutter was significantly improved from -0.025 mm to 0.001 mm, and the total machining error was reduced from -0.02 mm to -0.001 mm.