The safety brake is a very mature and reliable product. What kind of control mode is used to ensure the accurate and unmistakable action of the safety brake, so that it does play a safe and protective role in the state of the accident, and puts forward higher requirements for the electrical control, that is, the reliability and accuracy of the control are very important.

　　The role of 1 safety brakes on the casting crane

　　The foundry crane is used in metallurgical industry. Its task is to transport molten steel for smelting furnace. There are generally 5 main institutions: main hoisting, vice lift, cart, main car and auxiliary trolley. The motor is installed on the high speed shaft, the reel is installed on the low speed shaft, and the high speed shaft and the low speed shaft are connected by a reducer. The traditional lifting mechanism brake is located on the high speed shaft and is called the working brake. In this case, if a transmission link between the high speed shaft and the low speed shaft fails, the main lifting brake will lose its function on the drum. In view of this situation, a brake is installed on the drum, which is called a safety brake. When the transmission link fault and overspeed fault occur, the brake is acted first and the safety brake is delayed. Ensure that the ladle of liquid metal steel can be protected and safely and reliably protected in case of accident.

　　2 control mode of safety brake

　　(1) an overspeed switch is installed on the drum, and the safety brake moves when the lifting mechanism fails and the drum is overspeeding. The advantage is that the control principle is simple and easy to debug. The drawback is that the reel works only when overspeed occurs, and the action of the safety brake destroys the mechanical structure.

　　(2) the transmission ratio of high and low speed is constant, and the constant is detected by the device. When this constant changes, it means that the mechanical transmission links are damaged, and the safety brakes move immediately. The advantage is that it can be judged at the beginning of the failure, so that the safety brake moves, and the safety brake action has little damage to the mechanical structure. The disadvantage is that the control principle is more complex, debugging requires professional electrical technicians.

　　Control hardware composition of 3 safety brake

　　(1) the 2 encoders installed on the 2 reel.

　　(2) 2 encoders installed on 2 main lifting motors.

　　(3) safety brake control panel (or cabinet) (installed: programmable controller, circuit breaker, relay, contactor, voltage stable power supply, terminal terminal, etc.).

　　(4) shielded cables that control the screen to 4 encoders.

　　(5) emergency stop button and failure reset button installed on the operation platform, safety brake light indicator, encoder fault indicator, etc.

　　4 electrical installation and component selection

　　The incorrect operation of the safety brakes affects the normal use of the crane, which may cause greater losses. If the safety brake is frequently misused, the user will doubt and lose confidence in the function of the safety brakes. In order to ensure that the safety brake can not be misoperated, the selection of the components and the electrical installation are particularly important in the case that the program of the programmable controller is completely unmistakable and can work properly.

　　4.1 electrical installation

　　(1) there is no breakpoint between the control screen and the shielded cable of the 4 encoders. If breakpoints are broken, the breakpoints should be screened.

　　(2) the shielding layer of the shielded cable from the control panel to the 4 encoders needs 2 terminal grounding and is guaranteed to be the same. In order to ensure the same place, the grounding device should be installed on the main car. Make the main car and the big car in the same place.

　　(3) calculate the length of the shielded cable, confirm that the transmission distance of the encoder pulse signal is in the effective range.

　　(4) different shielded cables are used for the signal lines and power lines of the 4 encoders. The signal line and the various power lines on the crane should be separately arranged.

　　(5) the regulated power supply is installed near the PLC and is grounded.

　　(6) the signal line is not connected to the terminal, and is directly connected to the programmable controller input module.

　　(7) if a crane is equipped with a frequency converter or other equipment with strong interference, there should be an inlet and outlet reactor or other devices to minimize the interference to the control system of the safety brake.

　　Selection of 4.2 elements

　　(1) encoder selection should match the programmable controller. The output mode is to choose the push-pull output mode. The environment of the steelmaking plant is relatively poor, and the iron dust is very large. The output voltage of the encoder matches the value of the supply voltage.

　　(2) programmable logic controller has 4 independent high-speed counters, and the high speed counting ability of high-speed counters should meet the requirements. This needs to be determined by calculation. In actual use, it is found that the high-speed counting ability of the high speed counter is best to reach 1.5 to 2 times the actual need counting ability, in order to ensure the normal work of the programmable controller.

　　The principle of 5PLC control system

　　(1) PLC control system

　　The system is controlled by SIEMENS s 7 - 200 PLC. It has high performance price ratio, high reliability, rich instruction, good real-time communication ability, easy to master, easy to operate, rich built-in integration function and expansion module. The principle block diagram of the PLC control system is shown in Figure 1.

　　(2) PLC programming

　　A program structured programming with a control task decomposed into a process, a function, or a small task that can be used repeatedly. These tasks are represented by the corresponding part of the program, that is, the known block, the user program works, the block of the user program must be called, and the block call instruction can only be written in the logic and in the logic. Start. In order to allow