Manufacturers across various industries, both domestically and internationally, have always prioritized safety and protection during the manufacturing process. With continuously increasing production capacity, manufacturers are demanding higher levels of automation from their equipment, resulting in more complex and faster machines and equipment. Consequently, manufacturers are placing increasingly higher demands on the safety of these machines. We must ensure safety and reliability while also guaranteeing flexibility and ease of maintenance. This places certain requirements on the correct and reasonable design and selection of safety components. The use of safety functions in industrial equipment is widespread in developed countries. For example, Europe has mandatory safety standards, and equipment that does not meet the corresponding safety levels cannot be put into production; in the United States, high accident compensation is used to enforce equipment safety. Typically, we can refer to the following European standards for equipment design: EN 1050-1996 Safety risk assessment of machinery; EN 292-1:1991 Basic concepts and general design principles for machine safety; EN 954-1 Safety of machinery - Part 1: General design principles for safety components related to control systems; EN/IEC 60204 Safety of machinery - Electrical equipment for machinery; EN/ISO 13894 Safety of machinery - Safety components related to control systems; EN/IEC 61508 Functional safety mainly covering electrical/electronic/programmable electronic systems; EN 418 Emergency braking devices; EN 1088 Design and selection principles for interlocking devices related to protective devices; EN 12415 Machine tool safety - Small CNC lathes and turning centers; EN 12417 Machine tool safety - Machining centers; EN 12478 Machine tool safety - Large CNC lathes and turning centers; EN 692:1996 Safety of machinery - Presses; EN 693:2000 Machine tool safety - Hydraulic presses; EN 1550:1997 The safety requirements for the design and manufacture of machine tool workpiece clamping chucks are still in their infancy in my country. Many potentially dangerous pieces of equipment lack any safety protection measures, which is a significant reason for frequent factory accidents. However, with increasing national emphasis and the growing acceptance of a people-centered approach, equipment safety is receiving more and more attention. Equipment safety performance consists of two aspects: mechanical safety protection and electrical safety control. Mechanical safety protection will not be discussed in detail here; instead, the principles and applications of electrical safety control will be explained in detail. A safety control system must provide a highly reliable means of safety protection to minimize unsafe machine conditions, protect production equipment and personnel, prevent serious accidents, and reduce losses. This system provides safety protection for machinery and equipment during start-up, shutdown, process disturbances, and normal maintenance operations. Once a hazard arises in the machinery itself or due to human error, the system reacts immediately and outputs the correct signal to safely stop the machine, preventing the occurrence of danger or the spread of an accident. A safety control system consists of three parts: safety input signals (i.e., safety functions, such as emergency stop signals, safety door signals, etc.), safety control modules (such as safety relays, safety PLCs), and controlled output components (such as main contactors, valves, etc.). To achieve the corresponding safety level, necessary safety components and circuits are indispensable. Common safety components include emergency stop buttons, two-hand buttons, safety door switches, and safety light curtains. These components are connected to the core of the safety control system via circuits (usually dual circuits). This core is not an ordinary PLC, as it does not possess safety functions. In machines with safety requirements, ordinary relays or PLCs are widely used as control modules to monitor safety functions. Superficially, such machines can guarantee safety under certain conditions. However, when ordinary relays and PLCs malfunction due to inherent defects or external factors (such as contact welding, electrical short circuits, processor malfunctions, etc.), they lose their safety protection functions, leading to accidents. As for the safety control module, due to its redundant and diverse structure, coupled with safety measures such as self-detection and monitoring, reliable electrical components, and feedback loops, it ensures that safety functions are maintained even in the event of inherent defects or external faults, and can detect faults in a timely manner. This maximizes the normal operation of the entire safety control system, protecting the safety of people and machines. Electrical safety control methods can be broadly categorized as follows : 1. Using ordinary relays to build a dual-circuit line with self-locking and interlocking functions. This is the most primitive safety control method, achieving a relatively low safety level. Its advantage is low cost, but its disadvantages are complex maintenance and modification, and lack of monitoring capabilities. 2. Using safety relays to build a safety circuit. With the advent of safety relays in the last century, they have been increasingly used in various industrial equipment. They can be used to control a single safety function and are suitable for small safety control systems. Their safety outputs are typically relay contact outputs or transistor outputs. Regardless of the output structure used, safety relays can guarantee control from at least two channels. If one output channel fails, the other redundant channel can still ensure the safety function of the safety relay and detect the faulty channel in a timely manner. Common safety relay brands include Pilz and Schmersal, and now system integrators such as Siemens and Omron have also launched their own safety relay products. This control method is moderately priced and can achieve a high level of safety, but if there are many safety components, the circuit is still relatively complex and not suitable for large production lines. 3. Using a safety PLC for safety control. The CPU of a safety programmable controller adopts a redundant multi-processor structure. Each processor monitors each other, and if any inconsistency occurs, the controller immediately enters a safe state and issues an alarm message; at the same time, the safety programmable controller monitors internal components such as RAM, EPROM, and input/output registers in real time, and uses special test pulses to detect input signals and output controlled components. If any safety hazard is found, the controller immediately switches to a safety protection state. Safety bus systems are suitable for large, discrete safety control systems. Their principle is based on existing industrial fieldbuses, employing a series of time detection, address detection, connection detection, and CRC redundancy checks to achieve a high level of safety. Safety PLCs are products that appeared at the end of the last century. Their advantages are powerful programmability and the ability to achieve high-requirement safety control using a safety bus, but their cost is relatively high. 4. Using programmable safety relays for safety control. Programmable safety relays are a relatively new safety product, falling between safety PLCs and safety relays in that they offer a degree of programmability at a lower price. A safety relay is a multi-functional, freely configurable modular safety system. Unlike other ordinary safety relays, the safety circuit of a programmable safety relay can be easily generated using graphical configuration tools on a personal computer. Programs can be directly written to the programmable safety relay via the RS232 interface on the basic module. The above briefly introduces several methods of safety control. So how do safety components, which are closely related to safety levels, achieve the purpose of safety control? The following is a categorized introduction: 1. Short-circuit protection. Safety circuits generally use dual-circuit control. Even if one circuit experiences a short circuit, it can still prevent the equipment from operating under unsuitable conditions. In addition, both safety relays and safety PLCs have short-circuit diagnostic functions. 2. Anti-sticking function. Unlike ordinary relays, which may experience contact sticking under prolonged arcing, safety relays, due to their special structure, can ensure that the contacts are forcibly disconnected if the circuit conditions are not met. 3. Safe zone function. The safety zone is defined by safety door locks and safety light curtains. Once someone enters a safety door or crosses the light curtain, the equipment can be forcibly stopped under safety control, ensuring the safety of production personnel. 4. Redundancy Function. Both the safety PLC and safety bus have redundancy functions to ensure that safety performance is not affected by external interference. For single equipment or production lines with fewer than four safety functions, we can use compact safety relays. For example, a single CNC machine tool in a power workshop typically includes several emergency stop buttons, one or two safety doors, and a safety level of 3 or higher. For such an application, we can use one compact safety relay to control all emergency stop buttons; and another 1/2 compact safety relay to control 1/2 of the safety doors. When any safety relay is triggered, the safety output must disconnect the relevant load (such as a frequency converter or servo controlling the axis movement). For equipment or production lines with 4 to 14 safety functions, we recommend using modular programmable safety relays for greater flexibility and lower cost. Taking an automated painting line as an example, this production area typically includes two pairs of safety light curtains installed at the entrance and exit of the painting area, four to eight safety doors, several emergency stop buttons, and two sets of shielded sensors, with a safety level of 3 or higher. We could certainly use compact safety relays to achieve these safety functions. However, this solution is costly, involves complex wiring, and is difficult to diagnose. The application of programmable safety relays not only reliably and efficiently performs safety functions but also reduces costs in design, purchase, and maintenance. For sites with dozens or more safety functions, or where most safety functions are discretely distributed, programmable safety PLC systems and safety bus systems can simplify and clarify complex safety control. Safety PLCs have successful application cases in large-scale stamping production lines. Typically, a stamping production line is 10m high and 50m long, divided into several work areas such as painting, stamping, and shearing. Each area has two stroke doors and several emergency stop buttons; the perimeter also requires safety light curtains to protect the die-changing area; furthermore, the stamping machinery has a large number of safety signals (such as top dead center, valve signals, etc.) that need to be connected to the safety control system, and these signals are interwoven with complex logic throughout the entire safety control loop. In this case, programmable safety relays and safety bus systems are the most suitable solutions. Safety PLCs can easily implement complex logic relationships. Through the safety bus, safety input signals scattered in the field can be centralized to the master station for control via a single cable. In my country's manufacturing industry, various safety control systems have been widely used. Taking the automotive industry as an example, joint ventures use imported equipment from Europe and the United States, which generally have a high level of safety, such as the production workshops of FAW-Volkswagen, Shanghai Volkswagen, and Shanghai General Motors. Most domestic automotive brands, such as Chery Automobile and Great Wall Motors, use domestic equipment extensively in their stamping, welding, and final assembly lines, and are mostly equipped with safety relays and safety PLCs, improving production safety. With the deepening implementation of the people-oriented concept, it is believed that safety control will be more widely used in future industrial production.