At present, there are hundreds of PLCs available from both domestic and international manufacturers, each with unique performance characteristics and varying price points. Therefore, in the design phase, it is essential to prioritize model uniformity. It is recommended to use a consistent series of PLCs that the company already employs, as this facilitates learning, mastering, and maintaining the system, while also ensuring the availability of spare parts. This approach can also reduce programming costs and improve overall efficiency.
This paper primarily focuses on the composition of elevators, key technologies in elevator control systems, and the design of the electrical control system.
**First, the key technology of the elevator control system**
**1. PLC Control Technology**
PLC (Programmable Logic Controller) is a modern industrial control device that integrates microelectronics, computer technology, automatic control, and communication. It replaces traditional relay-based logic, timing, and counting functions, enabling flexible program-controlled systems. According to the International Electrotechnical Commission (IEC), a PLC is a digital electronic system designed for industrial applications. It uses programmable memory to store instructions for performing logical operations, sequence control, timing, counting, and arithmetic functions. These systems control various mechanical or production processes through digital and analog inputs and outputs. The design of PLCs ensures compatibility with industrial control systems and allows for easy expansion of functionality.
**2. Communication Technology Based on RS-485**
The RS-485 bus interface is a widely used serial communication standard known for its ease of network integration, strong anti-interference capabilities, and long transmission distances. It uses balanced transmission and differential reception, which helps reject common-mode interference. With high sensitivity, it can detect voltages as low as 200mV, allowing reliable communication over several kilometers. Using an RS-485 bus, multiple systems can be connected in a distributed configuration using just one pair of twisted wires, offering cost-effective and simple networking solutions.
**3. Configuration Technology**
The concept of "configuration" has become increasingly familiar to automation engineers with the rise of distributed control systems. As industrial control technology continues to evolve, PCs—especially industrial computers—have shown significant advantages over previous dedicated systems. These include faster development speeds, mature supporting technologies, lower total cost of ownership, abundant software and hardware resources, strong interoperability, and ease of learning and use. In the context of PC technology entering industrial control, configuration software plays a vital role. It serves as a platform for data acquisition and process control, enabling users to quickly build monitoring systems for industrial automation. With features like real-time databases, SCADA support, and open data interfaces, configuration software has become an essential tool in modern control systems.
**Second, the Components of the Elevator System**
The elevator system consists of two main parts: the physical structure and the controller. The physical structure includes the base, column, car, and inner and outer call panels. The controller comprises a PLC, a frequency inverter, and a switching power supply. The elevator is divided into eight floors, each equipped with a floor number display, an external call button, and a registration panel. The internal call panel inside the car includes buttons for all eight floors, door opening/closing controls, and indicators for call registration and direction signals.
**Third, the Design of the Elevator Electrical Control System**
The internal call panel contains eight floor selection buttons, door operation switches, and indicators for call registration and direction. Each floor's external call panel includes up and down buttons along with display screens. The floor display circuit uses the CD4511 IC for seven-segment decoding, reducing the number of PLC output points compared to direct decoding. All floor displays, external call buttons, and registration indicators are mounted on compact PCBs, with two boards installed across the eight floors.
The PLC selected is the Mitsubishi FX2N-80MR, the inverter is the FR-S520S-0.4K-CH(R), and the power supply is a switching power supply providing 5V/5A and 24V/1A outputs. The 5V supply powers the external and internal call circuits and small signal processing sections, while the 24V supply powers the door motor and voice station amplifier. The main control board includes a power socket and safety socket, with a 250V/10A fuse. The elevator system operates on AC 220V, 50Hz, using a three-core single-phase socket with protective grounding.
**1. Input Signals and Their Significance**
(1) Position signal: Generated by eight sensors (XK1–XK8) at each floor. They switch ON when the elevator reaches that floor.
(2) Internal call signal: Activated by eight buttons (K11–K18), indicating the desired floor.
(3) External call signal: Triggered by 14 buttons (K21–K34), signaling passengers outside the elevator.
(4) Door control signals: Two signals for door opening/closing and two for detecting whether the doors are fully opened or closed.
(5) Encoder pulse signal: Used for position tracking.
**2. Output Signals and Their Significance**
(1) Direction signal: Indicated by two arrow lights showing the elevator’s movement direction.
(2) Internal call registration: Eight LEDs (L11–L18) indicate accepted internal calls.
(3) External call registration: Fourteen LEDs (L21–L34) show accepted external calls.
(4) Floor display: BCD code is decoded via CD4511 to drive a seven-segment display.
(5) Door action and speed control signals: Sent to the inverter for high/medium speed operation.
(6) Voice station control signal.
(7) Alarm signal.
**3. PLC I/O Assignment and External Wiring**
All input and output signals are assigned to specific PLC ports. For example, X0 is connected to the encoder’s A-phase pulse signal. The inverter is controlled via I/O mode. All wiring is checked for proper connections, and power-on tests are conducted. Input signals are verified by pressing switches and checking indicator lights. Output signals are tested by running a basic check program to ensure proper operation. To prevent overtravel, limit switches are installed above the 8th floor and below the 1st floor. If the elevator exceeds these limits, the inverter is stopped via the limit switch contact, preventing damage and ensuring safe operation.
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