introduction
The PLC -frequency converter speed regulation in the lifting industry has been gradually promoted and popularized in recent years, especially in large lifting equipment, PLC program control is used to replace the traditional relay-contactor control; frequency conversion speed regulation is used to replace the winding motor Rotor string resistance speed regulation; replace the winding motor with variable frequency motor or asynchronous motor, and then cooperate with advanced field bus technology and human-machine interface system, improve the equipment control accuracy and stability, reduce the failure rate, and the energy saving effect is remarkable Overhaul and maintenance has become a good way to improve the production efficiency of enterprises.
Control plan
A heavy machinery manufacturing large parts branch, which undertakes the tasks of assembly, positioning and docking of all large parts equipment, has high requirements for crane performance. The QD250 / 50t bridge crane used Siemens S7-400 PLC and ABB frequency converter , Touch screen and other high-performance configurations, the application of advanced Profibus field bus technology, direct torque control with encoder feedback, and advanced man-machine interface system.
The bridge crane is divided into four parts: main hook, auxiliary hook, cart and trolley. Because the main lifting mechanism is the most typical in crane application and the control is also the most complicated, this chapter takes the main lifting as an example to introduce its control method in detail.
1. PLC
The entire system takes S7-400 PLC as the core of electric control, mainly composed of power supply module, CPU, input and output module and interface module. The input module collects the signal status of devices such as limit switches, thermistors, inverter fault feedback, etc .; receives the control commands issued by the main controller and the button switch, concentrates on the CPU for operation, and passes the program operation results through the output module And Profibus field bus is transmitted to the contactor and inverter and other execution equipment, so as to drive the motor, hydraulic brake, cooling fan, etc. to complete various production tasks.
2. Profibus serial communication field bus system
Profibus is an open serial communication standard that allows data to be exchanged between various types of automation components. In this system, the S7-400 is used as the master station, and the inverters of various institutions are used as slave stations. Data is exchanged in real time quickly through the DP interface module and RS485 shielded twisted pair.
Set the inverter communication parameters:
98.02 = fieldbus activate communication module
51.01 = Profibus-DP selects the fieldbus type
51.02 = 3 Set the main inverter station address
51.03 = 1500 select the communication transmission rate is 1.5Mbit / s
51.04 = PPO4 select data transmission type 4 (6 process data is a standard block)
The PLC central processor as the master station reads various input status information from the slave station, that is, reads the main rising status word and actual value from the inverter, including the inverter is ready, power-on response, operation, torque verification OK, Inverter failure, actual motor speed, etc .; write various output information to the slave, that is, write control word and speed reference to the inverter. Including communication detection position, Drive on of PLC system from field bus, start signal from upper system, fault reset signal and actual frequency setting, etc. The complex signal conversion, monitoring and feedback processes are all easily realized through the data transmission of the Profibus chain and the rapid centralized processing of the CPU.
3. Advanced human-machine interface system
The Profibus bus is also used for data transmission and exchange between the TP270 touch screen and the PLC, real-time display and monitoring of the operating status and operating parameters of each organization, such as voltage, current, torque, speed, etc., and can use its own fault real-time diagnosis system Make judgments and record various parameters at the time of failure, so that operators and maintenance personnel can fully and timely understand the status of the system, and can check and repair according to the prompted failure information to achieve accurate and rapid troubleshooting. Realized the human-machine intelligence.
4. Frequency control system
1) Lifting conditions and requirements
The hoisting mechanism requires a larger speed ratio and harder mechanical characteristics to meet the precise lifting requirements of heavy objects; it requires a large starting torque and excellent dynamic torque response capability to adapt to sudden load changes to ensure heavy loads The ability of secondary lifting; the energy feedback and processing of the regenerative braking state must be solved to shorten the deceleration stop time; the problem of slippage must be solved.
2) Application of frequency conversion function
According to the characteristics and technical requirements of the hoisting mechanism, the inverter adopts 800 series inverters with speed measurement feedback interface, cooperates with ACC 7.2 special lifting software to form closed-loop direct torque control, and the motor is started by the pre-excitation function and starting torque setting The instantaneous torque can be up to 300%, which achieves excellent starting characteristics. The built-in brake chopper and external braking resistor enable the regenerative energy generated during the braking process to be released through the braking resistor to achieve the purpose of rapid braking . Using the mechanical brake control function, the motor torque release and the brake are closely matched, which improves the safety of the equipment, and the ability and reliability to withstand frequent starting shocks are greatly increased.
Description
-Contact Resistance:≤50mΩ
-Insulation Resistance:≥100mΩ
-Dielectric Strength:1,500V,
-1min Electronic Life:10,000 cycles
-Operating temperature:T120
-Rating current/voltage:6A 250V AC
Features
â—† Small Compact Size, high reliability
â—† Micro contact gap,high speed operation,high sensitirity,Micro operatizon travel.
â—† Long life & high reliability
Rotary Switch,Rotary Limit Switch,Car Rotary Switch,Rotary Snap Switch
Ningbo Jialin Electronics Co.,Ltd , https://www.donghai-switch.com