# Mini-Crack Detection of Conveyor Belt Based on Laser Excited Thermography
## 1 Introduction
To reduce the poor visibility impact on IBVD, a dual-band infrared detection (DBID) technique is proposed by analyzing mid-infrared and long infrared images to meet the requirement of real-time online detection [22]. Concerning the feature of normal, wear and tear of conveyor belt, [PERSON] et al. [23] propose a multispectral visual detection method to distinguish the different feature state of the conveyor belt. However, infrared imaging equipment is susceptible to external radiation. When the amount of infrared radiation in the target area is equal to that in the environment, the quality of infrared images will be affected [24]. Therefore, the defect detection method based on infrared imaging needs to further enhance the infrared characteristics of the target region. Benefitting from the recent advances in structural health monitoring (SHM) [25; 26] and nondestructive testing (NDT) [27; 28], many different methods, such as thermography [29; 30], ultrasonics [31; 32], have been developed, and some of them have been applied to detection/monitoring of cracks on conveyor belts. [PERSON] et al. [33] used a CW laser to scan the surface of stainless steel samples with constant motion for submicron crack detection. [PERSON] et al. [34] studied a CO\({}_{2}\) laser scanning device for scanning carbon fiber reinforced plastic (CFRP) samples at a distance and determining the crack zone by analyzing the temperature of the defect surface. [PERSON] et al. [35] proposes the impact damage detection of polymer composites (aircraft components) based on remote line scanning thermal Imager. [PERSON] et al. [36] used the continuous laser scanning of metal fiber laminates (FMLs) to analyze the interlaminar peeling defects of metal fiber laminates (FMLs) by thermal image. [PERSON] et al. [37] used a semiconductor laser to heating the multi-layer carbon composite material, which was composed of carbon fiber fabric and thin epoxy resin (CFRP). The temperature field changes on the sample surface were recorded and used to detect the delamination defects. [PERSON] et al. [38] proposesa nondestructive testing method based on flying spot thermography, which is used to measure thermal diffusivity and crack width. The method of laser excited thermography is an active thermography method. Compared with the passive thermography method (which uses an infrared camera to collect the thermal wave generated in the process of conveyor belt friction heating), the laser excited thermography does not rely on the local heating characteristics caused by conveyor belt friction and can detect mini-cracks before the occurrence of a large tear. In order to meet the needs of industrial development, a mini-crack detection method on conveyor belt based on laser excited thermography is proposed in this paper. The surface of the conveyor belt is heated by a laser beam, then the frame difference method is used to extract the image to quickly record the temperature change of the mini-crack under laser heating. The image features are extracted and fused by mini-crack feature imaging algorithm. At the same time, the power function image enhancement algorithm based on thermal signals further reveals the features of mini-cracks. Finally, the threshold segmentation and Hough transform algorithm are used to determine the size of the mini-cracks. The rest of the paper is organized as follows. Section 2 reviews the basics about mini-crack detection using laser excited thermography. Section 3 proposes the detailed method with algorithms for the mini-crack detection based on the laser excited thermography. Section 4 presents the experimental methods, results, and the discussion. Finally, Section 5 concludes the paper with recommendation for future work.