Abstract: This paper briefly introduces the program implementation and process of billet loading, walking beam movement, and positioning in the heating furnace in the small and medium-sized workshops of Laiwu Steel. The program is written in ABB AMPL programming language and realizes the loading, walking beam movement, positioning, and tracking of billets in three modes: normal rolling, billet turning, and furnace cleaning. Keywords: Pusher; Final back plate; Billet tracking; Moving beam; Data register ABSTRACTION: This article will briefly introduce the billet entering the furnace, the step-by-step and localization procedure realization, and the technological process of the Laigang zhongxiaoxing scale workshop. The procedure is compiled in ABB AMPL programming language. It realizes the furnace entering, step-by-step, localization, and tracking of the billet during normal rolling, under the semi-finished product, and in the clearing furnace. KEYWORDS: Pusher; Final back plate; Billet tracking; Moving beam; Data register 1. Process Equipment and Functions The heating furnace in the Laigang zhongxiaoxing scale workshop is a walking beam type with a production capacity of 120 t/h. It uses a mixture of blast furnace and coke oven gas as fuel. The furnace body consists of a fixed beam, a moving beam, a pusher, a final back plate, front and rear furnace doors, and inlet and outlet roller conveyors. During the furnace loading process, the position of the billet is controlled by the speed of the loading rollers and the final baffle to ensure the billet stops in the correct position and avoids scraping the furnace wall. The billet is then pushed onto the fixed beam by a pusher. Since there are no digital detection elements on the unloading side to check the billet's position, precise billet tracking must be achieved during the moving beam's movement to ensure the billet is safely delivered out of the furnace. To achieve full-process tracking during the billet's movement on the moving beam, the furnace has 100 tracking positions, denoted as P1, P2, P3…P100. P1, P2…P93 are located on the moving beam inside the furnace; P94 is merely a logical storage position with no mechanical location on the moving beam; P98 is located on the loading rollers outside the furnace; P95 is located on the unloading rollers outside the furnace; P99 is a virtual storage position; and P100 is a zeroed position. Billet tracking information includes the furnace number, weight, length, and position on the moving beam. Figure 1 shows the tracking positions of some mechanical equipment and billets inside and outside the furnace. After the billet is measured and weighed on the furnace feed rollers, it reaches position P1 inside the furnace after passing the final baffle and the pusher. The movement speed and stroke of the cylinders are controlled by position transmitters of the translational hydraulic cylinder and the lifting hydraulic cylinder installed on the movable beam, realizing the stepping of the billet inside the furnace. [align=center] Figure 1 Schematic diagram of billet tracking position[/align] 2 System Configuration This automatic control system for the heating furnace was introduced from ABB of Sweden in 1996 and represented the world's advanced level at that time. The entire system mainly consists of three parts: the operator station, the PLC controller, and the field detection and control equipment. The operator station and the controller communicate via Master Bus 300 and are connected to the rolling line control system through this network to form the first-level system of the entire small and medium-sized automatic control system, as shown in Figure 2. [align=center]Figure 2 System Configuration Diagram[/align] The Advant 500 operator station and the Master control station communicate and transfer data via the MB300 bus. The tape drive can reinstall the operator station's system software and application software. The printer can print events and alarms from the operator station at any time. Field detection equipment, acting as input points, is processed by the Master control station program and outputs signals to control field electrical equipment. In emergencies, the operator can forcibly intervene in the actuators using a backup handheld device. 3 Software Implementation The electric control system of the heating furnace has three control states: manual, semi-automatic, and automatic. The software implementation of the heating furnace electrical control system can be divided into three parts: the furnace feeding section, the billet walking section, and the billet tracking section. 3.1 Furnace Feeding Section The field mechanical equipment controlled by this part mainly includes the furnace feeding roller conveyor, the steel pusher, and the final baffle. Each piece of equipment can be manually operated under certain conditions or in emergencies. In automatic mode, the feed rollers initially move at high speed, then slow down after a delay. Upon contacting the final baffle, the rollers stop rotating, and the baffle moves backward in the direction the billet is moving. After the final baffle detects a signal from the proximity switch, it moves forward a short distance. Due to inertia, the billet continues to move forward, and the baffle moves with the billet until it reaches the zero position, at which point it stops, completing the billet feeding process. The pusher then moves again, pushing the billet onto the fixed beam and returning to its original position. Finally, the baffle returns to its original position, awaiting the arrival of the next billet. 3.2 Billet Walking Section To achieve the functions of billet feeding and unloading, steel feeding and unloading, and furnace cleaning in the heating furnace, the furnace operation is mainly divided into three working cycles: normal cycle, feeding-only cycle, and unloading-only cycle. To achieve these control cycles, the moving walking beam has three types of movement cycles: forward cycle, reverse cycle, and stepping cycle. 3.2.1 Forward Cycle: In manual mode, as long as the pusher and walking beam meet the conditions, and there is no steel on the furnace feed and discharge sides, selecting the forward cycle button will start the forward cycle of the walking beam. When the heating furnace is in automatic or semi-automatic mode, during the normal cycle or discharge cycle of the heating furnace, if the rolling mill needs steel and the billet is ready on the discharge side, the forward cycle of the walking beam can be started when the start auto cycle fwd condition is met; during the furnace feed cycle, if there is steel at position P1 in Figure 1 and no steel at position P94, the forward cycle of the walking beam can be started when the start auto cycle fwd condition is met. The software flowchart for the forward cycle is shown in Figure 3. In the flowchart, startfwdcycle represents the condition for starting the forward cycle of the walking beam. The four judgment conditions are the upper position of the walking beam, the last position of the walking beam, the bottom position of the walking beam, the foremost position of the walking beam, and the original position of the walking beam. 3.2.2 Reverse Cycle: In this program, the reverse cycle of the walking beam can only be started under manual control. The following conditions must be met to start the reverse cycle: there is no steel on the furnace inlet side, the pusher is in the last position, the walking beam is in the initial position, and there is no steel on the furnace outlet side. After these safety conditions are met, select the back button to start the walking beam reverse cycle. The flowchart of the reverse cycle is shown in Figure 4. In the flowchart of the reverse cycle, StartReverseCycle is the condition for starting the walking beam reverse cycle, and the other judgment conditions are the same as those in the comment in the forward cycle. 3.2.3 Stepping Cycle The stepping cycle of the walking beam can only be selected in the automatic and semi-automatic states of the heating furnace. When the safety conditions are met, after setting a delay, select the lift button, and the walking beam will start the stepping cycle until the delay ends. The flowchart is shown in Figure 5. In the flowchart of the reverse cycle, StartUpDownCycle is the condition for starting the walking beam stepping cycle, and the other judgment conditions are the same as those in the comment in the forward cycle. [align=center]Figure 5 Reverse Loop Flowchart[/align] 3.2 Billet Tracking Section To achieve billet tracking, the furnace number, length, weight, and billet position in the furnace are stored in the DAT\QP data memory. Taking the billet at position P2 as an example, these data are stored in the P2:TEXT, LP2, P2:REAL, and QP2 data memories. During normal rolling, the tracking signal StartChaBilTra=1 is activated, and data is transferred according to the MOVE element as shown in Figure 6. [align=center]Figure 6 Normal Rolling Tracking[/align] When a defective billet is detected in the furnace and needs to be removed, StepTraking2=1 is activated, and the billet data is transferred as shown in Figure 7. [align=center]Figure 7 Billet Tracking[/align] When the billet is under furnace cleaning control, the billet only exits and does not enter. StepTraking=1 is activated. Since there is no billet entering the furnace at this time, the pusher does not generate an action signal. After the billet on the moving beam moves forward, the data in the data register at position P1 is supplemented by all zero bits of P100. The furnace number of the billet at position P98 is manually entered by the operator in the human-machine interface of the Advant500 operating station. The weight is automatically stored in the P98:TEXT register after being weighed by the weighing system in front of the furnace. The length is calculated by setting the speed of the roller conveyor entering the furnace and detecting it through the photoelectric tube in front of the furnace. The length is obtained by the length integration element LINT and written into the LP98 register. Once these values ​​are obtained, they will not change due to changes in the position of the billet in the furnace. When the billet moves from position P97 to P1 in the furnace, the QP1 data is obtained from the position transmitter of the pusher at position P1, i.e., QP1 = AOC147 (the detection value of the position transmitter at position P1). During normal rolling, the position of the billet in the furnace is calculated according to formulas ① and ②: QPn = QPn + WB Step Done Formula ① QP(n+1) = QPn Formula ② When pouring steel from the furnace, the position of the billet in the furnace is calculated according to formulas ③ and ④: QPn = QPn - WB Step Done Formula ③ QP(n-1) = QPn Formula ④ QP(n-1), QPn, and QP(n+1) represent the tracking values ​​of positions P(n-1), Pn, and P(n+1) in the furnace, respectively. WB Step Done represents the difference between the backward and forward positions of the position transmitter installed on the moving beam, i.e., the detected forward stroke of the moving beam. To prevent the deviation between the set execution step distance of the moving beam and the actual step distance detected by the position transmitter from accumulating in the next step cycle, and to ensure that the billet can be smoothly tapped when it reaches the tapping side, the execution step distance of the moving beam needs to be compensated. The flowchart of the error compensation procedure for the moving beam is shown in Figure 8. The error compensation and the calculation formula for the next step distance of the moving beam are: WBTrasERROR = StepWBDone - StepWBToDo (previous cycle) Equation ⑤ StepToDo (next cycle) = StepWBSet - WBTrasError Equation ⑥ In the formula, WBTrasERROR is the step error, StepWBDone is the step value of the previous step, StepWBToDo is the step value of the next step, and StepWBSet is the step setting value. [align=center]Figure 8 Error Compensation Flowchart[/align] In the flowchart, PosTrasBmmBwd is the translation value of the ZT4 walking beam taken in WBBackwardPosition, and PosTrasBmmFwd is the translation value of the ZT4 walking beam taken in WBForwardPosition. The presence of billets on the moving beam and the furnace number, length, weight, and furnace position of the billets to be unloaded can be directly observed in the HMI dialog box of the Advant500 operator station, i.e., P94. When creating the HMI dialog box, the position QPn of each billet on the moving beam is compared with L2=1 and H2=21920. If QPn>L2, it indicates that there is a billet at this position, and the furnace number, length, weight, and furnace position of the billet are displayed, flashing continuously. Otherwise, a black box is used to indicate that there is no billet at this position. The flowchart of the billet tracking section is shown in Figure 9. [align=center]Figure 9 Flowchart of the billet tracking program[/align] 4 Conclusion After being put into operation in the small and medium-sized workshops of Laiwu Steel in 1997, this system has stable performance and can fire both large and small billets. It achieves full-process tracking of the furnace number, length, weight, and position of each billet from the furnace inlet roller conveyor to the furnace outlet roller conveyor, ensuring normal steel rolling production. At the same time, it provides convenience for operators.