This paper presents direct methods for vision-based control for the application of industrial inkjet printing. In this, visual control is designed with a direct coupling between camera measurements and joint motion. Traditional visual servoing commonly has a slow visual update rate and needs an additional local joint controller to guarantee stability. By only using the product as reference and sampling with a high update rate, direct visual measurements are sufficient for controlled positioning. The proposed method is simpler and more reliable than standard motor encoders, despite the tight real-time constraints. This direct visual control method is experimentally verified with a 2D planar motion stage for micrometer positioning. To achieve accurate and fast motion, a balance is found between frame rate and image size. With a frame rate of 1600 fps and an image size of 160 100 pixels we show the effectiveness of the approach. Note to Practitioners-This method of visual control is motivated by the current state-of-the-art in display manufacturing. Traditional solutions for the manufacturing of displays assumes that the transformation between production head and control reference (e.g., kinematic or dynamic model) is known with high accuracy and that the display itself is rigid (i.e., fixed pitch between pixel centers). For flexible displays, this latter assumption is not the case. A method is proposed that takes these issues into account. A camera measures directly where the center of each display cell is located and generates online a trajectory for velocity motion control.This velocity reference is based on a smooth profile with a fixed velocity on cell centers and a higher velocity in between cell centers. This enables a higher overall velocity while ensuring a similar quality of printing compared to a constant velocity reference. Visual control and trajectory generation is executed at 1600 [Hz] with an image size of 160 100 pixels. Feedback is obtained only from visual input, the encoders present in the motors are not used.
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