Pneumatic valve-controlled micro-droplet ejection is a printing technique that has potential applications in many fields, especially in the field of bio-printing. The ejection is controlled by a solenoid valve being briefly turned on, so that high pressure gas enters the liquid reservoir, forming a gas pressure pulse, forcing the liquid out through a tiny nozzle to form a micro-droplet. For bio-printing applications, the bio-inks are typically non-standard. The difficulties are not only that the initial working parameters are difficult to set, but also the working conditions change over time in many cases. In order to maintain a stable single-drop ejection state, a machine vision based ejection monitoring was designed to obtain the number, positions and sizes of the droplets for each ejection, and a feedback control is realized by adjusting the conduction time of the solenoid valve or the gas pressure at the front end of the solenoid valve.
Vehicle classification is vital to an intelligent transport system. To obtain a high accuracy, it is the most crucial process to extract reliable and distinguishable features of vehicles. A feature extraction method using a lightweight convolutional network for vehicle classification is proposed. The main contributions are threefold: (1) a lightweight network named LWNet with two convolution layers is proposed to extract the features of the vehicles; (2) Hu moment is integrated with spatial location information to improve its own describing and distinguishing ability; and (3) histogram of oriented gradient (HOG) feature is extracted from the complete image, and then the above two kinds of features are combined with HOG to form the vector. And then, a support vector machine is trained to obtain the classification model. Vehicles are classified into six categories, i.e., large bus, car, motorcycle, minibus, truck, and van. The experimental results have demonstrated that the classification accuracy can achieve 97.39%, which is 3.81% higher than that obtained from the conventional methods. In addition, for this vehicle classification task, the proposed lightweight convolutional network can achieve comparable or even higher performance compared to the deep convolutional neural networks, while the proposed method does not need the support of a graphics processing unit and has much lower complexity without the training process.
Vehicle color recognition is easily affected by subtle environmental changes. The existing recognition methods cannot achieve an accurate result. A high-accuracy vehicle color recognition method using a hierarchical fine-tuning strategy for urban surveillance videos is proposed. Different from the conventional convolutional neural networks-based methods, which usually obtain a single classification model, the proposed method combines pretraining and hierarchical fine-tunings to obtain different classification models that can adapt to the change of illumination conditions. First, the GoogLeNet is pretrained using the ILSVRC-2012 dataset to obtain the initial weight parameters of the network. During the first stage of fine-tuning, the whole vehicle color dataset is used to fine-tune the pretrained results to get the initial classification model. Then, an image quality assessment method is proposed to evaluate the illumination conditions of the image. The whole vehicle color dataset is divided into some subdatasets according to the evaluation results. The second stage of fine-tuning is performed on the initial classification model using each subdataset. Thus, the final classification models for the subdatasets are obtained. The experimental results on different databases demonstrate that the recognition accuracy of the proposed method can achieve superior performance over the state-of-the-art methods.