Imbalanced data constitute a significant challenge in intelligent fault diagnosis cases because they can result in degraded diagnosis accuracy, which can in turn jeopardize the safety and reliability of industrial equipment. Generative adversarial networks (GANs) have been effectively used as common data augmentation methods to address this issue. However, their training process is difficult to perform and prone to mode collapse. Therefore, this article proposes a novel data augmentation method grounded in a diffusion model. The proposed method generates samples through physical simulation rather than adversarial training, which avoids the instability and mode collapse issues faced by GANs, leading to a more stable training process. Moreover, the proposed method utilizes the characteristics of gradual diffusion and random sampling to enhance the authenticity and diversity of sample generation. In addition, in terms of evaluating generation models, most existing works do not have a unified and thorough evaluation framework. Therefore, a comprehensive evaluation framework is proposed to effectively and comprehensively evaluate the performance of data augmentation models. Finally, the proposed method is evaluated using an open-source dataset and two actual testbeds to validate its effectiveness. The experimental results show that our method can generate higher quality and more diverse pseudosamples, and achieve superior fault diagnosis performance under imbalanced data. Specifically, our approach achieves diagnosis accuracies of 97.00%, 96.48%, and 98.30% on the three different datasets, all of which are superior to those of the compared state-of-the-art data augmentation algorithms.

The fault diagnosis of rolling bearings is vital for the safe and reliable operation of mechanical equipment. However, the imbalanced data collected from the real engineering scenario bring great challenges to the deep learning-based diagnosis methods. For this purpose, this article proposes a methodology called full attention Wasserstein generative adversarial network (WGAN) with gradient normalization (FAWGAN-GN) for data augmentation and uses a shallow 1-D convolutional neural network (CNN) to perform fault diagnosis. First, a gradient normalization (GN) is introduced into the discriminator as a model-wise constraint to make it more flexible in setting the structure of the network, which leads to a more stable and faster training process. Second, the full attention (FA) mechanism is utilized to let the generator pay more attention to learning the discriminative features of the original data and generate high-quality samples. Third, to more thoroughly and deeply evaluate the data generation performance of generative adversarial networks (GANs), a more comprehensive multiple indicator-based evaluation framework is developed to avoid the one-sidedness and superficiality of using one or two simple indicators. Based on two widely applied fault diagnosis datasets and a real rolling bearing fault diagnosis testbed, extensive comparative fault diagnosis experiments are conducted to validate the effectiveness of the proposed method. Experimental results reveal that the proposed FAWGAN-GN can effectively solve the sample imbalance problem and outperforms the state-of-the-art imbalanced fault diagnosis methods.

Most current state-of-the-art simultaneous localization and mapping (SLAM) algorithms perform well in static environments. However, their applications in real-world scenarios are limited by the assumption that environments are static because their performance becomes unstable in complex dynamic environments. To enhance system stability and localization accuracy in complex dynamic scenes, this article presents a novel visual-inertial SLAM system called DGM-VINS. In DGM-VINS, a joint geometric dynamic feature extraction module (JGDFE) is designed that can combine the advantages of multiple geometric constraints and effectively reduce the limitations of a single geometric constraint in the application process. In addition, a temporal instance segmentation module (TISM) is presented to establish the temporal correlation of instance objects in consecutive frames, which effectively addresses the instance segmentation issue in complex environments. The inertial measurement unit (IMU) is utilized for motion prediction and consistency detection to improve localization accuracy in challenging environments with weak textures. The proposed methodology is tested in various public datasets and actual scenarios, and the results demonstrate superior accuracy and robustness than existing methods in complex dynamic scenarios.

The critical issue of wheeled robot fault diagnosis is to comprehensively evaluate its health condition using multi-sensor data, but traditional deep learning-based methods are hard to model the relationships among sensor measurements. Unlike these methods, the graph convolutional network (GCN), which uses the graph-structured data along with the association graph as input, is more efficient for relationship modeling. However, existing GCN-based fault diagnosis methods suffer from the following weaknesses: 1) the association graphs are obtained according to the similarity of data samples or their features, which cannot guarantee accuracy; 2) these models are focused on spatial correlations and neglect temporal correlations. To address these problems, we propose to construct the association graph based on prior knowledge, i.e., a simplified mathematical model of the wheeled robot. Moreover, we develop a spatial-temporal difference graph convolutional network (STDGCN) for wheeled robot fault diagnosis. This network contains a difference layer that utilizes localized difference properties for feature enhancement, and the spatial-temporal graph convolutional modules are introduced to jointly capture the spatial-temporal correlations. To verify the effectiveness of STDGCN for fault diagnosis, experiments are carried out, and the results show that STDGCN achieves superior performance.