Abstract: This paper studies the design method of the electrical control system of a fully digital and intelligent pliers-type hoist, and designs a control scheme with PLC and MENTOR II as the core. This scheme greatly improves the working efficiency, reliability and control accuracy of the pliers-type hoist, and reduces energy consumption. Experimental results prove the effectiveness of this scheme. Keywords: all-digital; intelligent; pliers-type hoist; MENTOR II . Introduction : Currently, some large steel plants in China use pliers-type hoists to lift hot and cold steel billets above soaking furnaces. The temperature is high, there is a lot of metal dust, the load is heavy, and the vibration is large, so the requirements for electrical control equipment are high. Currently, most clamp-type cranes in China use DC slide rails with series resistance speed regulation. Although the control circuit is relatively simple, the frequent switching of the resistors leads to a high failure rate, high energy consumption, and non-smooth speed regulation, resulting in unstable operation. In the 1990s, many manufacturers attempted to upgrade clamp-type cranes using direct thyristor control, but these methods failed to achieve the desired results due to harsh on-site environments. Based on in-depth research on clamp-type crane equipment, we conducted a fully digital intelligent control upgrade experiment on the electrical equipment of clamp-type cranes, and the results have achieved the expected goals so far. This technology is feasible for the complete transformation of clamp-type cranes. Through a survey of major steel enterprises across the country, this technology is the first of its kind in China and is at the leading level domestically. I. Full Digital Upgrade Scheme for Clamp-Type Cranes 1. Overall Planning The clamp-type cranes in the rolling mill of Wuyang Iron and Steel Company originally used 6KV/170V, which was rectified to 220V DC and fed onto the slide rail before being sent to the clamp-type crane control cabinet. Each mechanism is speed-regulated in segments by series resistors. The forward and reverse directions of the motor and the speed of each segment are controlled by the master controller in the driver's cab, which drives the main contactors and relays of each segment. This method involves many contactors and resistors, and the frequent operation of the contactors results in a high failure rate and high energy consumption, which has seriously affected production. The overall idea of ​​the full digital transformation is to directly install a DC speed control device on the clamp-type crane, and all logic control is completed by the PLC. The specific overall plan is as follows: (1) Replace the rectifier transformer with a 6KV/380V rectifier transformer with a capacity of 1000KVA calculated by calculation, and use two units as before, one for use and one for standby. (2) Increase the number of slide rails from two to three, and send the three-phase 380V power supply to the busbar of the control cabinet through the main switch in the control cabinet. (3) Remove all the original contactors, speed control resistors, and braking resistors. Adjust the speed by adjusting the output voltage of the full digital DC speed control device. (4) All the master control switch signals of each mechanism in the driver's cab are directly sent to the PLC, and then the PLC is programmed to directly control the DC device through the PLC output point. (5) Set an emergency lifting function on the main hook. When the main hook controller fails or the main power supply fails, the emergency lifting switch is activated from the driver's cab. The emergency lifting device lifts the main hook. The emergency lifting device is powered by the auxiliary sliding rail. (6) The master switch installed in the driver's cab and various function switches are kept as they are. The trolley accident travel is changed to the main hook emergency lifting. All other switches are connected to the PLC. 2. Selection of digital DC speed control device Because the clamp-type hoist is used to hoist hot and cold steel billets above the soaking furnace, the temperature is high, the metal dust is large, the load is heavy, and the vibration is large. Therefore, the requirements for electrical control equipment are high. We selected the Mentor II fully digital DC speed control device from Control Techniques (CT) in the UK. It adopts a microprocessor core. The operation instructions and running parameters can be input, set and modified by the panel or serial port. It is protected by a three-level security word. All analog inputs and most digital inputs can be programmed by the user. The serial port uses RS485, facilitating multi-machine networking and forming an automated network with a host computer and other devices. It also offers various optional components to enhance system functionality, such as a field control module with automatic field weakening for constant power applications, a microcontroller processing module programmed in BASIC, and an intelligent multi-language user interface. The design is compact and highly reliable. The selected driver is the M550R all-digital DC motor driver from Control Techniques (UK), with an output current range of 25A to 1850A. It is available in single-quadrant and four-quadrant configurations. The single-quadrant driver can only achieve forward operation, while the four-quadrant driver is fully reversible. Both configurations provide comprehensive control over the motor's speed and torque, with the four-quadrant driver offering comprehensive control over both forward and reverse operation. Its basic working principle is to control the armature terminal voltage to control the current supplied to the motor, thereby achieving speed regulation. 3. PLC Selection PLCs outperform relay control logic in performance. They offer high reliability and strong anti-interference capabilities. Both hardware and software incorporate shielding, filtering, isolation, fault diagnosis, and automatic recovery measures, achieving a mean time between failures (MTBF) of over (3-5) × 10⁴ hours. PLC programming is intuitive and simple, employing a ladder diagram language oriented towards the control process. PLCs are highly adaptable, implementing control through programs. In this design, the Mitsubishi FX2N-128MR micro programmable controller is used. II. Control Method Due to the complexity of the working components of the clamp-type crane, including the main hook, auxiliary hook, trolley, gantry, clamp rotation, and opening/closing mechanisms, these motors require four speed levels and forward/reverse switching. Taking the main hook system as an example, the control method to achieve these requirements is explained. Figure 1 is a speed setting selection diagram for the Mentor II DC speed controller. In Figure 1, 01.17 is speed setting 1; 01.18 is speed setting 2; 01.19 is speed setting 3; 01.20 is speed setting 4 (the four set speeds are set on the Mentor II menu); and 01.12 is for forward and reverse selection. [align=center] Figure 1: Speed ​​setting selection diagram of Mentor II[/align] We use PLC output control, as shown in Figure 2 [align=center] Figure 2: PLC output control[/align] In Figure 2, Y20 is for forward and reverse switching, and Y21 and Y22 are for speed switching. The speed table is shown in Table 1: Table 1 Main hook speed table In Figure 2, M26, M27, and M28 correspond to the TB3-26, TB3-27, and TB3-28 terminals of the DC speed control device Mentor II, respectively. TB3-26, TB3-27, and TB3-28 correspond to the digital input terminals 08.16, 08.17, and 08.18, respectively. By setting 08.16=01.12, 08.17=01.14, and 08.18=01.15, we can use the PLC output to control the forward and reverse direction and speed switching of the motor. In addition, when the main hook controller malfunctions or the main power supply fails, the emergency lifting switch is activated from the driver's cab. The emergency lifting device lifts the main hook, and the emergency lifting device is powered by the auxiliary sliding rail. III. Transformer Selection Table 2 shows the power equipment used by the clamp-type crane in the Wuyang Iron and Steel Company's rolling mill. The total capacity Pe of one clamp-type crane motor is 565KW. According to the power supply manual, the demand factor for the rolling mill crane is Kx=0.35, =0.5; =1.73. The maximum active calculated load P30 is 197.8kW. Therefore, the maximum apparent calculated load S30 is 395.6kV·A. Considering a 2.5 times overload, we select two 1000kV·A transformers, one as a backup and one as a standby. The transformers are 6KV/380V rectifier transformers. The two high-voltage switches remain unchanged, and the transformers are installed in the original transformer locations. Conclusion: After nearly a year of equipment operation, the expected goals have been achieved so far. This system is a digital system; it has a simple hardware structure, stable performance, and is resistant to high temperatures, dust, and vibration. It offers smooth adjustment and stable operation. Equipment developed based on this technology is currently applying for a national patent. The author's innovations include: energy saving and improved operational efficiency. Its direct economic benefits are considerable. This technology can not only be applied to clamp-type cranes nationwide but can also be extended to other large cranes, indicating a very broad market prospect. References: [1] Huang Jun, Wang Zhaoan. Power Electronic Converter Technology. Beijing: Machinery Industry Press. 1999 [2] Yu Qingguang. Programmable Controller Principles and System Design. Beijing: Tsinghua University Press. 2004 [3] Mitsubishi Electric Corporation. FX2N Series Micro Programmable Controller, 1999 [4] Control Techniques. User Guide MENTORⅡ, 1999 [5] Chen Boshi. Automatic Control System for Electric Drive. Beijing: Machinery Industry Press, 1991 [F] Yang Binfeng. Control System for Anti-Runaway in Mine Inclined Shaft Based on PLC. Microcomputer Information. 2005. 10-1: 14-15