Detailed PLC control hardware design (elevator as an example)

At present, there are hundreds of PLCs produced by PLC manufacturers at home and abroad, and their performances have their own characteristics, and the prices are not the same. Therefore, in design, we must first consider the principle of uniformity of the model, and consider using the same series of PLC machines that the company is using as much as possible, so as to facilitate the learning, mastery and maintenance, and the versatility of spare parts. And can reduce the investment in programming.

This paper mainly studies the composition of the elevator, the key technology of the elevator control system, and the design of the electrical control system.

PLC is a new generation of industrial control device formed by introducing microelectronic technology, computer technology, automatic control technology and communication technology based on the traditional sequential controller. The purpose is to replace the relay, execution logic, timing, counting and other sequences. Control functions to build a flexible program control system. The International Electrotechnical Commission (IEC) has enacted the regulations for PLCs: programmable controllers are digital operating electronic systems designed for industrial applications. They use programmable memory for It internally stores instructions that perform operations such as logic operations, sequence control, timing, counting, and arithmetic operations, and controls various types of mechanical or production processes through digital, analog inputs and outputs. The programmable controller and its related equipment should be designed in such a way that it is easy to integrate with the industrial control system and easily expand its functions.

The RS-485 bus interface is a commonly used serial port, which has the advantages of convenient network connection, good anti-interference performance and long transmission distance. The RS-485 transceiver uses balanced transmission and differential reception, so it has the ability to reject common-mode interference. The transceiver has high sensitivity and can detect voltages as low as 200mV. The reliable communication distance can reach several kilometers. With RS-485 bus networking, a multi-system networking can be used to form a distributed system with only one pair of twisted pairs, which is simple in equipment, low in price and long in communication distance.

The concept of "configuration" is beginning to be familiar to a wide range of production process automation technicians with the advent of distributed control systems. In the continuous development and application of industrial control technology, PCs (including industrial computers) have increasingly obvious advantages over previous dedicated systems. These advantages are mainly reflected in: PC technology has maintained a relatively fast development speed, various related technologies have matured; industrial control systems built by PC have relatively low cost of ownership; PC software resources and hardware resources are abundant, software Interoperability is strong; PC-based control systems are easy to learn and use, and can be easily supported by technology. The paper was published. In the penetration of PC technology into the field of industrial control, configuration software occupies a very special and important position.

The configuration software refers to some special software for data acquisition and process control. They are the software platform and development environment at the level of the monitoring layer of the automatic control system. Using flexible configuration methods, users can quickly build monitoring functions of industrial automatic control systems. , general-level software tools. The configuration software supports a variety of industrial equipment and common communication protocols, and usually provides distributed data management and network functions. Corresponding to the original HMI concept, the configuration software is a software tool or development environment that enables users to quickly build their own HMIs. Before the emergence of the configuration software, users in the industrial control field can write HMI applications by hand or by a third party, which has long development time, low efficiency and poor reliability. Or purchase a dedicated industrial control system, usually a closed system. To meet the demand, it is difficult to interact with the outside world, and upgrades and added functions are severely limited. The emergence of configuration software frees users from these dilemmas, and can use the functions of configuration software to build a set of application systems that are most suitable for them. With its rapid development, real-time database, real-time control, SCADA, communication and networking, open data interface, and extensive support for I/O devices have become its main content. With the development of technology, the monitoring configuration software will also Will continue to be given new content.

The elevator system consists of a body and a controller. The body includes a base, a column, a car, and an inner and outer selection control panel; the controller includes a PLC, a frequency converter, and a switching power supply. The elevator is divided into eight floors, each floor has a digital display of the number of floors on which the car is located, an outbound button, and an outbound registration instruction. The car inner call panel includes 1 to 8 layers of internal call buttons, open and close buttons, internal call registration display, elevator up and down operation instructions.

The inner call panel in the car includes eight floor call buttons and switch door buttons; eight floors call registration display and elevator uplink and downlink display. The outbound call panels of each layer include up and down call buttons and displays. The floor digital display circuit uses CD4511 as the seven-segment decoding, which can save 3 output points of PLC than direct decoding by PLC. The floor digital display, outbound call button and outbound call registration display of each floor of the elevator are designed on a long and narrow circuit board, and two boards are installed on eight floors.

The PLC selects Mitsubishi FX2N-80MR, the inverter selects FR-S520S-0.4K-CH(R), and the DC power supply selects the switching power supply with 5V5A and 24V1A two sets of DC voltage output. The 5V power supply is mainly used for power supply of the external call, the internal call circuit board and the small signal processing part of the voice report station circuit. The 24V power supply is used to power the switch door motor and the OTL power amplifier circuit of the voice report station circuit. The main control board has a power socket and a safety socket at the back. The fuse is 250V10A. The elevator model system power supply voltage is AC 220V50Hz, and a three-core single-phase socket with protective grounding is used.

(1) Position signal. The position signal is generated by eight sensors XK1 to XK8 installed at the parking position of the elevator. Normally OFF, ON when the elevator is running to this position.

(2) Command signal (internal call). There are eight command signals, which are generated by eight command buttons of "1 to 8" (K11 to K18). Press a button to indicate that the passengers in the elevator want to go to the corresponding floor.

(3) Call signal. The paper was published. There are 14 call signals, which are generated by 14 (K21 ~ K34) call buttons. Press the call button to indicate that the passenger outside the elevator wants to take the elevator. For example, press K23 to indicate that the second floor passengers want to go up, and press K24 to indicate that the third floor passengers want to go down.

(4) 2 open and close door control signals, 2 door open and closed door in place signals.

(5) Photoelectric encoder pulse signal.

(1) Running direction signal. There are two running direction signals, which are composed of two arrow indicators to indicate the running direction of the elevator.

(2) Command registration signal (internal call). There are 8 command registration signals, which are composed of 8 (L11 ~ L18) indicators, indicating that the corresponding command signal has been accepted (registered). After the instruction is executed, the signal disappears (cancel). For example, if the elevator is on the second floor, press "3" to indicate that the passenger in the elevator wants to go to the third floor, then L13 lights up to indicate that the call has been accepted. The elevator runs up to the third floor and stops at L13.

(3) Call registration signal. There are 14 call registration signals, which are composed of 14 (L21～L34) indicator lights, and their meanings are similar to the above-mentioned command registration signals.

(4) Floor digital display signal. The BCD code is outputted with 4 points, and after being decoded by CD4511, the seven-segment digital tube display is sent, indicating the floor position where the elevator is currently located. LEDa~LEDg respectively represent seven segments of digital display segments.

(5) Two door opening and closing action signals. 4 elevator rising and falling action signals, high speed and medium speed control signals are sent to the inverter.

(6) Voice station control signal.

(7) Alarm ringing output signal.

Allocate PLC input/output ports to all kinds of signals in the elevator system. Among them, X0 is the input signal of high-speed counting C235, and is connected to the pulse signal A phase of the rotary encoder. The control of the inverter in the wiring diagram adopts I/O control mode. Connect all power, signal lines, and input/output wiring. Check for power disconnection to ensure proper power-on check. Check whether all PLC input signals are normal: press the leveling switch to check whether the corresponding input indicator is lit; press the internal call and the external call button to check whether the corresponding input indicator is lit. Check that all PLC outputs are normal for the load driver: Write a simple check program to scan each output port to see if the controlled object is working properly. If there is a problem, find out the cause and correct it. In order to prevent the normal operating range beyond 1 to 8 layers, a limit switch is installed above the 8-layer leveling switch and below the 1 level leveling switch. When the elevator reaches the 8th floor and continues to rise due to a program error, it will continue to fall after reaching the 1st floor, and will encounter the limit switch to make the limit switch operate. Connect the normally closed contact of the limit switch to the control signal common terminal (SD) of the inverter. Once the limit is reached, the signal that controls the operation of the inverter is cut off and the inverter stops working. This ensures that the car will not be super-layered.

Four Digits LED Display

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