Elevators are a primary means of transporting people and goods. Modern people have increasingly higher demands for quality of life, requiring elevators to be aesthetically pleasing, safe, comfortable, and stable. With the development of advanced technology, programmable logic controllers (PLCs) have emerged on the market. Due to their advantages such as high programming flexibility, strong anti-interference capabilities, high reliability, comprehensive functions, wide applicability, small size, light weight, and low energy consumption, their application in elevator control systems can meet the high demands placed on elevators today.
A programmable logic controller (PLC) is a digital electronic system specifically designed for industrial applications. It employs a programmable memory that stores instructions for performing logical operations, sequential control, timing, counting, and arithmetic operations, controlling various types of machinery or production processes through digital or analog inputs and outputs.
Programmable logic controllers (PLCs) are a new type of general-purpose automatic control device developed by combining computer technology and automation control technology, suitable for industrial environments. They emerged as a replacement for traditional relays. With the rapid development of microelectronics and computer technology, PLCs have acquired more computer functions, not only performing logic control but also data processing, communication, and networking. Because the control process can be modified through software, and because they are characterized by small size, convenient assembly and maintenance, simple programming, high reliability, and strong anti-interference capabilities, they have been widely used in various fields of industrial control, greatly advancing the process of mechatronics.
Elevators are indispensable transportation tools in high-rise buildings, used to vertically transport passengers and goods. Traditional elevator control systems mainly use relays and contactors, which have disadvantages such as numerous contacts, high failure rate, poor reliability, and heavy maintenance workload. PLC-based control systems can effectively solve these problems, making elevator operation safer, more convenient, and more comfortable. They are now widely used in the elevator industry. PLC control is particularly advantageous in situations with a limited number of floors and control functions.
1. Programmable Logic Controller (PLC)
A programmable logic controller (PLC) is a small, programmable device capable of logic operations, sequential control, counting, timing, etc., controlling various expected processes or results through digital or analog inputs and outputs. A PLC is a combination of relay and computer control, effectively integrating automation, computer, and communication technologies into a new type of industrial automation control device. It is currently widely used in automated processes for detection, monitoring, and control in various applications, and can also be used in various large-scale, complex mechatronic equipment, including escalators, elevators, machine tools, civil facilities, and environmental protection facilities.
2. Advantages of PLC control systems
PLC control systems have the following advantages:
(1) The structure is compact and simple, reducing the mathematical operation part, strengthening the logic operation function and timing function required for direct control, and standardizing the input and output signals, combining them with each controller, and applying them to the control of various modern equipment.
(2) It has high reliability, good stability, strong anti-interference ability and multiple protection functions. Once a fault occurs, it can quickly stop the elevator.
(3) The programming is simple, easy to use, and highly operable. The PLC is programmed using ladder diagrams, which is easily accepted by elevator operators. In addition, it can be monitored. By displaying the circuit operation status in the programming software, faults that occur in reality can be easily identified. It also has write and print functions.
(4) Convenient maintenance. PLCs have comprehensive monitoring and diagnostic functions, clearly displaying their working status, communication I/O status, and abnormal conditions. Currently, with the adoption of intelligent I/O modules, PLCs can diagnose and detect machine faults, greatly improving equipment maintenance efficiency.
(5) It adopts a modular structure, which is easy to expand and flexible to modify.
3. Advantages of PLC-controlled elevators
(1) PLC control is used in the elevator control system to control the operation of the elevator with software, which greatly improves the safety of elevator operation.
(2) A large number of relays were eliminated, improving the space utilization of the control system and simplifying the wiring of the system.
(3) PLC can be used to control complex elevator systems, and can easily add and change the control functions of the system.
(4) The PLC can automatically detect faults and display alarms, which improves the safety of the elevator, facilitates maintenance, and improves the operating efficiency of the elevator.
(5) When changing the control function, only the control program needs to be changed, and the wiring of the hardware circuit does not need to be changed.
4. PLC application in elevator real-time simulation
The structure of a PLC is basically the same as that of a microcomputer control system. Users can achieve their expected control requirements through programming, and the programmed instructions are stored in ROM memory. Periodic cyclic scanning can be performed, with the PLC outputs transmitting signals to the actuators to complete the entire scanning process. PLC input signals for elevators include floor selection, floor calls, various safety switches, and leveling position signals. Its output actuators include the traction machine, car lighting, communication facilities, and car door system. Using a PLC for elevator control enables the elevator to have comprehensive automatic detection, automatic diagnosis, and automatic protection functions, greatly improving the safety of elevator operation. Furthermore, the elevator operates according to an ideal running curve, with precise adjustment of the motor through vector control software, ensuring smooth, comfortable, safe, and reliable elevator operation.
5. Development Trends of Elevator Technology
In recent years, the domestic elevator industry has developed rapidly. Its elevator products are now largely in line with international standards in terms of technology, performance, and quality, and offer a significant price advantage compared to imported elevators. Internationally, as the elevator market approaches saturation, green, intelligent, information-based, and high-speed elevators will become the new direction for the industry's development.
5.1 Ultra-high-speed elevator
Elevators will evolve towards multi-purpose, full-function, and ultra-high-speed development in the future. Ultra-high-speed elevators will continue to utilize ultra-large capacity variable frequency motors, high-performance controllers, vibration reduction measures, new roller guide shoes and safety clamps, ultra-high-speed motors, communication and rescue facilities, and noise cancellation systems, significantly improving the comfort, stability, and safety of future ultra-high-speed elevators.
5.2 Bluetooth technology
Bluetooth technology is a globally open, short-range wireless communication standard. It can connect various electronic devices in an elevator via short-range wireless communication, eliminating the need for tangled cables and enabling wireless networking. Applying this technology to elevators can significantly reduce installation time, improve installation and control precision, and better solve wiring problems during elevator installation.
5.3 Green Elevator
The successful hosting of the 2008 Olympics and the 2010 World Expo has spurred the development of elevators towards environmental protection and energy conservation, which has become a major trend in elevator development in recent years. As one expert stated, "Whoever launches green products first and seizes the market will gain the initiative in market competition." Future new elevator products must align with environmental protection and energy conservation, thus intensifying in-depth research into these technologies by industry professionals both domestically and internationally. Green elevators require energy efficiency, low oil pollution, low noise, long lifespan, and the use of green materials.
With the rapid development of microelectronics and computer technologies, PLCs (Programmable Logic Controllers) have been widely used in industrial control. A PLC is an electronic control device based on digital computer technology, specifically designed for industrial environments. It uses a programmable memory to store user instructions and performs a series of defined functions such as logic, sequence, timing, counting, and arithmetic through digital or analog inputs/outputs to control various types of mechatronic equipment and production processes. This paper introduces a five-story elevator control system written using a programmable logic controller (PLC) and tests the operation of the elevator PLC control system. Practice has proven that the combination of a PLC and MCGS configuration software is beneficial for the design and testing of PLC control systems and has good application value.
Elevators are a type of vertical transportation tool that developed with the construction of high-rise buildings. Multi-story factories and warehouses need freight elevators; high-rise residential buildings need residential elevators; department stores and hotels need passenger elevators, escalators, etc. In modern society, elevators, like cars and ships, have become an indispensable means of transportation. Statistics show that in the United States, the number of people using elevators daily exceeds the number of people using other modes of transportation. In today's world, the usage of elevators has become one of the indicators of modernization. Tracing the history of this lifting device, it is said to have originated in ancient Greece in 236 BC. At that time, a man named Archimedes designed a manually driven drum-type winch.
Steam-powered passenger elevators appeared in the United States in 1858, followed by hydraulic elevators in Britain. In 1889, the Otis Elevator Company in the United States first used an electric motor as the power source for elevators, marking the emergence of a true elevator and making it more practical. The first escalator appeared in 1900. Group-controlled elevators appeared in 1949, with the first 4-6 group-controlled elevators used in the United Nations Headquarters in New York. In 1955, elevators controlled by minicomputers (vacuum tubes) appeared. In 1962, the United States saw the development of ultra-high-speed elevators with speeds reaching 8 meters per second. In 1963, some advanced industrialized countries only developed contactless semiconductor logic-controlled elevators. In 1967, thyristors were applied to elevators, simplifying the elevator drive system and improving performance. In 1971, integrated circuits were applied to elevators. The following year, numerically controlled elevators appeared. In 1976, microprocessors began to be used in elevators, ushering in a new era of development for elevator electrical control.
AC elevators use AC asynchronous motors for traction, which fall into four categories:
(1) AC single-speed elevator: The traction motor is an AC single-speed asynchronous motor, and the elevator speed V≤0.4M/S. For example, it is used for dumbwaiters, etc.
(2) AC dual-speed elevator: The traction motor is a special AC asynchronous motor with variable pole pairs, with a speed V≤1M/S and a lifting height h≤50M.
(3) AC speed-regulating elevator: The traction elevator uses a single-speed or multi-speed AC asynchronous motor dedicated to elevators. The drive control system of the motor adopts voltage regulation speed regulation, eddy current brake speed regulation, or frequency conversion and voltage regulation during the elevator's starting acceleration-speed stabilization-braking deceleration (or only braking deceleration). The elevator speed V≤2M/S and the lifting height h≤50M.
(4) High-speed AC elevator: The traction motor is a low-speed AC asynchronous motor specifically designed for elevators. Its drive control system is a variable frequency, variable voltage, and vectoring VVVF system. Its elevator speed V > 2 m/s, and the typical lifting height h ≤ 120 m.
DC elevators use dedicated DC traction motors, which fall into two categories:
(1) DC high-speed elevator: The traction motor drives the elevator after powering the gearbox, with a speed V ≤ 2.0 m/s. Current DC high-speed elevators powered by DC generators to DC motors are obsolete. Future DC high-speed elevators will be powered by thyristors. The typical lifting height h ≤ 50 m.
(2) DC high-speed elevator: The traction motor is a low-speed DC motor specifically designed for elevators. The motor is powered by either a DC generator set or a thyristor power supply. Its speed V>2.0M/S, and the typical lifting height h≤120 m.
Hydraulic elevators, which rely on hydraulic transmission for lifting and lowering, fall into two categories:
(1) Plunger Direct-Actuation Type: The hydraulic cylinder plunger is directly supported at the bottom of the car. The car is raised and lowered by the lifting of the plunger. Elevator speed V≤1M/S, typical lifting height h≤20M.
(2) Plunger side-mounted type: ( commonly known as "backpack type") The hydraulic cylinder plunger is set on both sides of the car. The car is raised and lowered by the plunger. The speed of the elevator V≤0.63. The general lifting height h≤15M.
In the 1990s, variable voltage and frequency (VVVF) speed-regulating elevators began to dominate the market. The speed regulation method of VVVF elevators involves adjusting the amplitude and frequency of the supply voltage to the stator windings of the motor. The VVVF elevator drive system extensively utilizes microcomputer control technology and pulse width modulation (PWM) technology. The PWM controller ensures that the stator voltage waveform delivered from the inverter to the three-phase asynchronous motor is an equivalent sine wave. Vector transformation technology is also widely used in the VVVF elevator drive system, making the control of the AC motor speed similar to that of a DC motor. Due to its small size, light weight, high operating efficiency, and energy saving, the VVVF elevator incorporates almost all the advantages of previous elevators. Combined with its highly refined speed regulation performance, its application is almost entirely comparable to that of DC elevators. AC motors are known for their compact structure and simple maintenance. Single and dual-speed AC motor drive systems use open-loop control, resulting in simple circuitry and lower prices, and are therefore still widely used in elevators. However, their disadvantage is poor comfort, so they are generally used in freight elevators. This system controls elevators with speeds below 1 meter per second.
AC motor stator voltage regulation and speed control drive systems are widely used in elevators abroad. This system employs thyristor closed-loop speed control, combined with energy-saving or eddy current braking methods, enabling it to largely replace DC high-speed and AC dual-speed elevators in the low-to-medium speed range. It offers superior comfort, high leveling accuracy, and lower cost than DC elevators. It also features a simpler structure, easier maintenance, and is commonly used in elevators with speeds below 2 meters per second.
DC motors are characterized by good speed regulation performance and a wide speed range, so they have long been used in elevators, driven by generator-motor sets. They can control elevator speeds up to 4 meters per second. However, the units are large in size, consume a lot of electricity, require significant maintenance, and are expensive. Therefore, they are typically used in buildings where speed and comfort are paramount.
While thyristor-controlled direct-powered drive systems have long been used in industry, their application in elevators (especially at low speeds) presented a challenge in terms of comfort. This led to their later adoption, almost simultaneously with the development of microcomputer-based systems. Compared to DC elevators using a motor-generator configuration, they offer numerous advantages, such as a 35% reduction in machine room space, a 40% weight reduction, and 25% to 35% energy savings. The world's fastest elevator, operating at 10 meters per second, utilizes this system, achieving a speed ratio of 1:1200.
In the early 1980s, elevators controlled by VVVF variable frequency and voltage systems were introduced. Driven by an AC motor, it achieves the performance of a DC motor, with current control speeds reaching 6 meters per second. Its small size, light weight, high efficiency, and energy savings encompass almost all the advantages of previous elevators. It is currently the most advanced elevator drive system.
In short, theoretically speaking, elevators are vertical transportation tools that do not require a rotating mechanism to drive them. The newer elevator drive system is actually a linear motor drive system.
