With the continuous development of intelligent manufacturing and the improvement of inherent safety in modern industrial production, AGV vehicles are increasingly widely used in material handling and circulation in industrial production. For special industries with flammable and explosive hazardous locations, explosion-proof AGV vehicles are required. Besides intelligently, efficiently, and accurately completing material handling and circulation, these vehicles must not generate ignition sources during operation, eliminating the risk of fire and explosion accidents. In the early stages of the development of explosion-proof AGV vehicles, the electromagnetic and ultrasonic ignition hazards of their guidance, safety, and wireless communication systems were a major challenge for manufacturers. Initially, the explosion-proof performance testing of explosion-proof AGV vehicles mainly referred to GB19854-2005 "General Technical Rules for Explosion-proof Industrial Vehicles for Explosive Atmospheres". Following the release and implementation of GB/T37669-2019, "Safety Specifications for Automated Guided Vehicles (AGVs) in Hazardous Production Environments," systematic regulations were established for electrical explosion-proof, mechanical explosion-proof, electromagnetic radiation and light radiation safety performance, as well as electrostatic safety performance. However, detailed guidelines and reference methods were not provided regarding the identification of ignition hazards in explosion-proof AGV vehicles, the assessment of non-electrical ignition hazards, and explosion-proof performance certification models. European explosion-proof AGV vehicles, as complete sets of explosion-proof industrial equipment, must undergo overall testing and conformity assessment according to the IEC60079 series of explosion-proof standards and comply with the EU CE certification requirements of the ATEX Directive (2014/34/EU). Currently, my country's explosion-proof AGV vehicles are only subject to explosion-proof certificate inspections based on GB/T37669-2019, GB/T19854-2018 "General Technical Rules for Explosion-proof Industrial Vehicles for Explosive Atmospheres" and the GB/T3836 series of explosion-proof basic standards, which are equivalent to type tests. This does not yet cover the factory quality assurance capabilities of explosion-proof AGV vehicle manufacturers. Therefore, systematically analyzing the ignition hazards of explosion-proof AGV vehicles in conjunction with their structural characteristics and conducting corresponding explosion-proof design and conformity assessment is of great significance for improving the explosion-proof safety performance of explosion-proof AGV vehicles. I. Identification of Ignition Hazards and Explosion-proof Technology for Explosion-proof AGV Vehicles 1.1 Identification of Main Structure and Ignition Sources AGV vehicles are classified into load-bearing AGVs, towing AGVs, and forklift AGVs according to their structure and purpose. Generally, the main structure of explosion-proof AGV vehicles includes the walking drive system, control and guidance system, power system, safety system, wireless communication system, and vehicle body. Based on the ignition source categories in GB/T25285.1-2021 "Explosive Atmospheres - Prevention and Protection from Explosions - Part 1: Basic Principles and Methods", and considering the structural and operational characteristics of explosion-proof AGV vehicles, the potential ignition hazards during their operation are analyzed in Table 1.
Table 1. Analysis of Main Structure and Ignition Sources of Explosion-Proof AGV Vehicles
1.2 Ignition Source Prevention and Explosion-Proof Technical Measures
1.2.1 Basic Principles of Ignition Source Prevention
Based on the correspondence between the EPL protection level of explosion-proof equipment and the prevention of ignition sources under different working conditions, the different ignition source types in Table 1 can be further analyzed and evaluated according to the explosion-proof level of explosion-proof AGV vehicles in different areas. Corresponding explosion-proof technical measures can be proposed to eliminate the ignition hazard or minimize it, thereby meeting the corresponding explosion-proof category and level in hazardous locations. The basic principles and procedures of ignition source prevention measures for explosion-proof AGV vehicles in different hazardous areas are shown in Figure 1. Currently, the explosion-proof battery pack technology and the non-electrical explosion-proof technology for mechanical collision and friction of the walking drive system in Zone 0/20 AGV vehicles are not yet mature, and their application scenarios are relatively rare. Therefore, explosion-proof AGV vehicles are currently limited to use in Zone 1/21 and Zone 2/22.
Figure 1. Basic Principles and Procedures for Ignition Source Prevention Measures for AGV Vehicles of Different Explosion-Proof Levels
1-No ignition source will appear during normal operation; 2-No ignition source will appear under expected fault conditions; 3-No ignition source will appear under rare fault conditions; 4-Redundant systems or fail-safe systems are used to avoid ignition sources under expected and rare fault conditions; 5-A single system is used to avoid ignition sources under rare fault conditions; 6-A single system is used to avoid ignition sources under expected fault conditions; 7-No measures are required
1.2.2 Main Explosion-Proof Technical Measures
According to Table 1, the main ignition sources for explosion-proof AGV vehicles include sparks and high temperatures generated by electrical equipment and components, frictional sparks and hot surfaces generated by mechanical movement, radio frequency electromagnetic waves, optical radiation electromagnetic waves, ultrasonic waves, and static electricity. Based on the basic principles and requirements of ignition source prevention measures shown in Figure 1, and combined with the latest IEC 60079 series and GB/T 3836 series explosion-proof basic standards, as well as GB/T 19854–2018 and GB/T 37669–2019 explosion-proof vehicle professional standards, the explosion-proof technology analysis and summary applicable to Zone 1/21 and Zone 2/22 explosion-proof AGV vehicles are summarized as follows: 1) Sparks and high temperatures generated by electrical equipment and components. The sparks and high temperatures generated by the electrical equipment and components of explosion-proof AGV vehicles can be addressed by designing or selecting motors, switches, control instruments, battery packs, lighting, alarms, sensors, and communication components as type d, e, i/iD, n, m/mD, t, or other explosion-proof electrical components that conform to the corresponding explosion-proof types, according to the IEC60079 series and GB/T3836 series. After different explosion-proof electrical components are designed or selected, the explosion-proof level and temperature group of the electrical component section are determined by the lowest explosion-proof level and temperature group corresponding to all components. For explosion-proof battery packs, they are generally designed as flameproof, increased safety, or dust explosion-proof type T. The type of battery should comply with Clause 23.3 of GB/T3836.1-2021 "Explosive Atmospheres - Part 1: Equipment - General Requirements" and Appendix E of GB/T3836.2-2021 "Explosive Atmospheres - Part 2: Equipment Protected by Flameproof Enclosures". For dust explosion-proof type T batteries, sealed battery elements should be selected. 2) Frictional sparks and hot surfaces generated by mechanical movement. The frictional sparks and hot surfaces generated by the mechanical movement of explosion-proof AGV vehicles mainly involve non-electrical explosion-proof technologies, which mainly adopt the following three prevention technologies. ① Prevention measure 1: Do not form an ignition source. The contact surfaces of transmission gears and load devices are made of stainless steel, copper, copper alloys, or similar non-sparking materials. The brake's mechanical structure is designed as either explosion-proof housing type ("d") or structurally safe type ("c"). Rolling friction bearings are kept well lubricated and sealed. ②Prevention Measure 2: Prevent the formation of an effective ignition source. For example, control the AGV vehicle's speed, such as ensuring the vehicle's speed does not exceed 1 m/s; design the clearance between rotating mechanical parts and other parts to be no less than 1/100 mm of the moving part's diameter, and at least 1 mm; install temperature monitoring and protection devices, placing temperature monitoring and control devices on surfaces that generate high frictional temperatures, such as gearbox bearings and brakes, to control the formation of dangerous high temperatures. ③Prevention Measure 3: Isolate the explosive atmosphere from the ignition source. Design the brake as liquid-immersed type ("k") and the gearbox as a current-limiting housing type ("fr") according to non-electrical explosion-proof technology.
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