There are many kinds of elevator control methods. The traditional relay control wiring is complicated and inconvenient to maintain, and it is difficult to meet the control requirements of modern elevators. Programmable controller (PLC) can overcome the above shortcomings, and now PLC is used to realize elevator control. In the design, firstly, the general situation of PLC and elevator is introduced, the requirements of elevator control system are analyzed, the block diagram of the system is drawn, and the control ladder diagram of each part of elevator is designed by using FX2—80MR PLC of Mitsubishi Company, and its working principle is briefly introduced, which realizes the function of centralized control of elevator well.
Centralized selection control of PLC elevator
Elevator is a vertical transportation tool developed with the construction of high-rise buildings, which is widely used in national economy and life. With the continuous development of urban and rural construction, elevators will enter our daily life at a faster speed. In modern society, elevators, like cars and ships, have become an indispensable means of transportation for human beings. In today's world, the use of elevators has become one of the symbols to measure the degree of modernization. In high-rise buildings, elevators are indispensable and important equipment. Early elevators used relay contact control system. However, due to the complexity of elevator control system, the wiring of relay contact control system is complicated. Hundreds of different relays may be used and connected by many wires in a complicated way. In this way, if a relay is damaged or has poor contact, the normal operation of the whole system will be affected, and it is very difficult to find and eliminate the fault, so the reliability of the relay control system is low. Programmable controller (PLC) has the characteristics of simple and easy-to-learn ladder diagram language, flexible and convenient control, strong anti-interference ability, stable and reliable operation, less maintenance workload and convenient maintenance. Now elevator control is mostly realized by programmable controller. Because the operation of the elevator is based on the call signal, travel signal and automatic control law of the floor and car, and the call of the floor and car is random, the elevator is actually a man-machine interaction control system, which can not meet the control requirements simply by sequential control or logical control, so the system adopts centralized control mode. This elevator has a highly automatic control function, with or without a driver. In addition to the functions of automatic floor leveling, automatic door opening, car instruction registration, elevator call registration outside the hall, automatic floor parking and forward parking, it also has the functions of automatic parking time, automatic elevator call service, automatic reversing and reverse elevator call outside the hall. Through comprehensive analysis and judgment, we can make up and down elevator call signals outside the hall, floor selection signals inside the car and various special signals.
Programmable controller is a new type of industrial control equipment based on microprocessor, and it is a brand-new product that applies computer technology to industrial control field. In 1985, the International Electrotechnical Commission (IEC) defines a programmable controller as an electronic system with digital operation, which is specially designed for application in industrial environment. It uses programmable memory to store instructions for performing logical operations, sequence control, timing, counting and arithmetic operations, and controls various types of machines or production processes through digital and analog inputs and outputs. Programmable controller and its related equipment should be designed according to the principle that it is easy to make the industrial control system form a whole and expand its functions.
Programmable controller adopts ladder diagram programming language, which is easy for factory electricians to master. It can realize the logical control of on-off value, and also has the functions of mathematical operation, data processing, motion control, analog PID control, networking communication and so on. Especially after the application of microprocessor and programmable controller, because of its small size, strong function and low price, the function of programmable controller is enhanced, the working speed is accelerated, the volume is reduced, the reliability is improved and the cost is reduced.
Characteristics of 1.2PLC
(1) has high reliability and strong anti-interference ability.
(2) The programming method is easy to learn and use.
(3) Perfect function and flexible application.
(4) low environmental requirements and strong adaptability,
(5) small volume, light weight and low energy consumption
(6) The maintenance workload is small and the maintenance is convenient.
(7) The workload of system design, installation and debugging is less.
Structure and working principle of 1.3PLC
Programmable controller is mainly composed of CPU module, input module, output module, programmer and power supply. As shown in the figure:
CPU module, also known as central processing unit or controller, is mainly composed of microprocessor (CPU) and memory.
Input/output module (I/O) module is the bridge between external field and CPU module. The input module is used to receive and collect input signals, and the programmable controller controls actuators such as contactors, solenoid valves and electromagnets and other external loads through the output module.
Programmable controller has two basic working states: running and stopping. In the running state, the programmable controller realizes the control function by executing the user program that reflects the control requirements. In order to make the output of the programmable controller respond to the input signal that changes at any time in time, the user program is not only executed once, but repeatedly executed until the programmable controller stops or switches to the stopped working state.
In addition to executing user programs, the programmable controller must also complete internal processing and communication processing in each cycle. A cycle can be divided into five stages, and this cycle of programmable controller is called scanning mode. Because of the high speed of computer executing instructions, the processing process is almost completed at the same time from the external input-output relationship.
In the internal processing stage, the programmable controller checks whether the hardware inside the CPU module is normal, resets the monitor, and completes some other internal work.
In the communication service stage, the programmable controller communicates with other intelligent devices with microprocessors and updates the display content of the programmer in response to the commands typed by the programmer.
When the programmable controller is in the stopped state, only the above operations are performed. In the running state, input processing, program execution, output processing and other stages are needed.
In the memory of programmable controller, there is an area for storing the states of input signal and output signal, which are called input image register and output image accumulator respectively. Other programming elements in the ladder diagram of programmable controller also have corresponding image storage areas, which are collectively called element image registers.
In the input processing stage, the programmable controller reads the on/off states of all external input circuits into the input image register.
In the program execution stage, even if the state of the external input signal changes, the state of the input image register will not change accordingly, and the changed state of the input signal can only be read in the input processing stage of the next scanning cycle.
In the output processing stage, the CPU transfers the 0/ 1 state of the output image register to the output latch. When the coil of an output relay in the ladder diagram is "energized", the corresponding output image register is "1". After the signal is isolated and power amplified by the output module, the coil of the corresponding hardware relay in the relay output module is electrified, and its normally open contact is closed, so that the external load is electrified to work.