Electronic steel coil scales are specifically used for the measurement of metal materials such as steel coils, aluminum materials, and precious metals during production, processing, storage, and logistics. Due to the characteristic of underground transportation of steel coils, it is necessary to design an electronic steel coil scale that can perform weighing during underground transportation. The main production line at the site mainly produces finished steel coils, and each steel coil production line is equipped with an independent lifting transportation mechanism. This mechanism consists of a walking cart and a V-shaped transfer workpiece. The walking track of the walking cart is located in the underground, while the upper V-shaped transfer workpiece is above the ground. After the steel coil is bundled, it is moved to the V-shaped transfer workpiece of the lifting transportation mechanism, and then the lifting transportation mechanism transports the steel coil along the fixed route of the underground to the warehouse. Due to the layout modification of the production line in the workshop, the weighing process needs to be completed during the transfer process.
1 
Overall System Introduction
Due to the characteristic of the lifting transportation mechanism moving in the underground, two independent carriers need to be designed at the designated weighing position on both sides of the underground. Each carrier requires four weighing sensors for support, and each is equipped with a four-wire terminal box and a six-wire terminal box. The two terminal boxes are connected through overhead cables. The distance between the two carriers is a safe distance that can accommodate the transfer workpiece. After the lifting transportation mechanism with the steel coil and the V-shaped transfer workpiece reaches the weighing position, it will descend onto the carriers and separate from the lifting structure. After the steel coil and the transfer workpiece remain stable, the weighing process begins. This product requires a maximum weighing capacity of Max = 30t, a minimum weighing capacity of Min = 200kg, an accuracy grade of grade III, a verification division value of e = 10kg, a verification division number of n = 3000, and the maximum relative deformation of the carrier should meet the requirements of GB/T 7723-2017 "Fixed-type Electronic Weighing Instruments" for the maximum relative deformation of the weighing instrument. The A/D conversion rate is 360 times/second. It has a profibus-DP communication interface and profibus-DP bus interface. The working temperature is -10℃ to 40℃, and the relative humidity is 10% to 95%. The digital weighing sensor accuracy grade should at least meet C3, and it can also meet the signal exchange with the PLC of existing equipment and the control of the weighing equipment at the site.
At the same time, this steel coil scale is composed of two independent carriers. Each carrier requires four weighing sensors for support, and each set of four weighing sensors requires a terminal box. 2 
Design Process of SCS-30 Special Electronic Steel Coil Scale
Based on the above description, the author will briefly introduce the selection and design process of the SCS-30 special electronic steel coil scale from the selection of weighing sensors, terminal boxes, weighing indicators, and carriers.
(1) Selection of Weighing Sensors
This electronic steel coil scale has a large weighing load, high weighing accuracy requirements, and long-term stable weighing requirements. The accuracy grade is grade III. According to the maximum weighing capacity Max = 30t and the verification division value e = 10kg, the structure characteristics of the carrier require the selection of 8 weighing sensors. The static load DL of the carrier is 1160kg, there is no lever R = 1, the initial value zero range IZSR = 600kg, and the correction of unevenly distributed load is according to 50% of Max. The correction coefficient Q = (Max + DL + IZSR + NUD + T+) / Max = (30000 + 1160 + 600 + 30000 × 50% + 0) / 30000 = 1.558 > 1
The maximum weighing capacity of the weighing sensor Emax ≥ Q × Max × R / N = 1.558 × 30000 × (1/8) = 5842.5 Kg = 5.8425 t. The largest scale is selected as the CZL-YB-10SG type column-type weighing sensor with a maximum scale of 10t. This type of weighing sensor has a fully sealed double-ball head column structure, using a metal diaphragm welding sealing process. Its waterproof and dustproof ability meets the IP68 level requirements stipulated in GB4208. It is equipped with an analog-to-digital conversion module and a CPU processor, and outputs as a digital signal. At the same time, this type of weighing sensor has strong overload resistance, is easy to install, and is convenient to use.
(2) Selection of the junction box
A four-wire digital junction box and a six-wire digital junction box are selected. The four-wire digital junction box is connected to the four weighing sensors of the load-bearing component installed on the side far from the weighing indicator. The six-wire digital junction box is connected to the four weighing sensors of the load-bearing component installed on the same side as the weighing indicator, as well as the four-wire digital junction box. The wire cables of the four-wire digital junction box are laid overhead and connected to the six-wire digital junction box after crossing the underground trench. Both digital junction boxes are made of cast aluminum shells with high protection levels. They adopt an upper concave and lower convex imported sealing strip structure to ensure the sealing of the box body. At the same time, they are assembled using combination screws, which is convenient for disassembly.
(3) Selection of the weighing indicator
Since the maximum scale Max = 30t, the verification graduation value e = 10kg, and the verification graduation number n = 30000/10 = 3000, the maximum verification graduation number nind of the weighing indicator is ≥ 3000. Therefore, the XK3200 type weighing indicator is selected according to the user's display graduation, resolution, A/D conversion rate, communication interface, bus interface, PLC signal exchange, etc. This weighing indicator has stable performance and powerful functions. It has multiple expansion interfaces and can be connected to various industrial equipment, providing users with the optimal solution for industrial weighing. It supports CAN bus and RS485 bus digital weighing sensors and analog weighing sensors. It has RS232/RS485 interfaces, printing interfaces, USB interfaces, Ethernet interfaces. It can upload weighing data in real time through the Ethernet interface, has data processing and automatic control functions, can replace the PLC + computer control mode, simplify the system network, reduce installation time, and reduce costs.
(4) Design of the load-bearing component
Due to the thick and wide flange of the I-beam and the large section moment of inertia, it can withstand large compressive stress and effectively resist bending deformation. Therefore, the structure of the main beam of the load-bearing component in contact with the transfer tooling adopts 20a I-beam. The overall size of the load-bearing component is 3000mm × 400mm × 490mm. After welding a frame with ribs, the I-beam is welded on the upper surface, and the installation positions of the weighing sensors are reserved at both ends, and corresponding strengthening is carried out at the weighing sensor installation positions. The ends of the ribs on the lower part of the load-bearing component are reserved for the wiring holes of the weighing sensors, and a wiring pipe is welded in the middle part. It is convenient for the leads of the two inner weighing sensors to be led to the junction box on the upper part of the load-bearing component. A limit structure for restricting the up and down, front and back, and left and right oscillation of the load-bearing component's main beam is reserved near the position of installing the weighing sensors on the load-bearing component. The pull rods are installed at both ends of each load-bearing component, on both sides of the center line of the main beam. One end of each pull rod is welded to the main beam, and the other end is welded to the installation base plate of the load-bearing component, used to limit the movement gap of the load-bearing component's main beam in the length direction.
The upper and lower limit positions are located outside the pull rod limit positions. The bottom of the screw rods of the upper and lower limit positions is fixed on the load-bearing component installation base plate. The upper end passes through the reserved hole of the main beam and is adjusted by a nut to limit the movement gap of the load-bearing component's main beam in the gravitational direction. The left and right limit positions are located outside the pull rod limit positions. The installation seat of the left and right limit positions is fixed on the load-bearing component installation base plate, and the width The direction restricts the movement gap of the main beam in the width direction by adjusting the gap between the adjusting bolts installed on the left and right limit seats and the main beam.
The limitations in three directions are concentratedly arranged, forming constraints in three directions within the limited space, ensuring the stability, measurement accuracy and equipment safety of the steel coil scale during the weighing process, and ensuring the equipment can operate stably and accurately for a long time and meet the requirements of cost-effectiveness. This structure is compact, easy to install, use and maintain, and has the advantage of impact resistance.
The steel coil and the transfer tooling fall onto the carrier, and the width of the transfer tooling trolley is 1000mm. The 1000mm area between the two carriers is the force-bearing area for the transfer tooling trolley. During the weighing process, the carrier is in a local uniformly distributed load force state, and the force-bearing model is established according to the local uniformly distributed load. Using the force analysis software for modeling analysis, according to the analysis results: the maximum deformation of the carrier is 1.47mm, which is the absolute deflection of 1.47mm, and the relative deflection is 1.47/3000 = 0.00049 < 1/2000, which is much smaller than the requirement of GB/T 7723-2017 "Fixed-type Electronic Weighing Instruments" for the maximum relative deformation of the weighing instrument ≤ 1/800, and can meet the structural strength requirements.
3 Conclusion
In the early stage, after the factory trench was built, the transportation route was fixed. If the production line was upgraded or the production layout was adjusted, the cost of reopening the trench was high. For the steel coil-specific electronic steel coil scale designed for the trench transportation method, without affecting the normal operation of the transportation system and without the need for extensive re-excavation of the trench, it solved the problem of steel coils needing to be weighed on the transportation route due to the adjustment of the production layout, improving the space utilization rate of the trench transportation method and making the environmental adaptability stronger. The equipment structure is stable, saving manpower and time costs, improving weighing efficiency, reducing downtime, reducing production costs, and improving economic benefits.