Abstract: Metal surface coloring plays a crucial role in various aspects of metal engineering such as improving metal oxidation resistance, corrosion prevention, insulation, decoration, and surface performance. An automatic trajectory planning algorithm is proposed to achieve droplet uniform coloring of special-shaped zones on metal surface. Considering contact angle, surface tension, and droplet mass, the coloring technology is analyzed and the control equation of the distance between two neighboring droplets is established. For coloring pattern image, the binary image processing method, canny edge detection and contour point sorting algorithms are used to extract the target special-shaped zones, and the contour points are saved in order. The extracted zone contours are offset and interpolated by using the rational cubic Bézier curve. Taking the distance between two neighboring droplets into consideration, the equal chord length discretization algorithm is used to determine the droplet locations. Experimental results show that the proposed algorithm can achieve automatic region extraction, automatic coloring trajectory planning and special-shaped regions uniform coloring.

Key words: metal surface coloring, coloring zones extraction, Bézier curve interpolation, trajectory planning