Abstract: The intelligent control system for automated parking garages is the core of the garage control system, controlled by a Siemens 1200 PLC. It includes two processes: card recognition and loading bin movement. A contactless card reader is installed at the garage entrance (which is also the exit). When a user enters the garage, they swipe their card at the door. The card reader automatically transmits the data to the PLC. The PLC system automatically determines whether the card is valid. If valid, the garage door opens, and the system moves the loading bin to the handover position between the user and the vehicle, thereby shortening the time for parking and retrieval.
Keywords: automated parking system; automation; PLC
Foreword
Traffic congestion has become a major social problem of concern to local governments in cities. Traffic and parking management within urban areas are becoming increasingly difficult, especially in densely populated areas such as upscale hotels, guesthouses, and large department stores. Limited by existing land area, the inability to add parking spaces exacerbates parking difficulties and traffic congestion. Statistics show that in Beijing, over 500,000 cars are parked on both sides of the road every day; while in Shanghai, over 800,000 cars have nowhere to park daily. These problems will hinder the rapid development of the automotive industry.
Traditional underground parking garages require ample driving lanes, with each car occupying approximately 40 square meters of space. Double-layered multi-level parking garages can increase ground space utilization by nearly 90%. Multi-level above-ground parking garages can accommodate at least 40 cars on 50 square meters of land. This saves limited land resources and reduces construction costs. Secondly, multi-level parking garages are more effective at ensuring the safety of people and vehicles compared to underground garages. Electronically controlled systems will not operate if people are in the garage or if a car cannot be parked. Multi-level parking systems can park a large number of cars in a small area, eliminating the need for ramp design in traditional parking garages. This transforms the architectural space issues in parking garage design into mechanical solutions, employing new technologies to address parking problems. Computer control and unmanned parking areas effectively prevent theft and damage. Due to their space-saving design, flexibility, and ability to be used in both large and small areas, as well as their combination with surface and underground parking garages, mechanical parking systems have become one of the most effective means of solving urban parking difficulties and are an essential path for the development of the parking industry. In a sense, multi-level parking garages have completely achieved the separation of people and vehicles in terms of management.
With economic development and the gradual improvement of people's living standards, the number of cars has increased rapidly, and the demand for parking spaces is also rising. Since the vast majority of cars are concentrated in large and medium-sized cities, the significant increase in the number of cars in cities will inevitably lead to an increase in the demand for parking spaces. It is estimated that in the next five years, Chinese cities will need at least 2.5 million parking garages to meet the demand. The annual demand for garage doors is as high as 3 million sets, while the actual production is 1.5 million sets. The demand for automatic doors and industrial doors is 4.6 million square meters, of which the demand for automatic doors is 2.5 million square meters.
There are many types of mechanical automated parking systems. Based on different principles and structures, they can be divided into various types such as lift-and-slide, vertical circulation, vertical lift, planar movement, lane stacking, and horizontal circulation. Among them, lift-and-slide automated parking systems have a small footprint, and their scale can be flexibly changed according to site conditions and needs. This paper takes a 3-story, 10-space lift-and-slide automated parking system as the research object, designs a PLC-based control system, and implements it on an S7-1200. As electrical engineering technicians, we should strive to incorporate current high-tech achievements into the design of automatic parking doors, designing a low-cost, high-efficiency, highly reliable, and user-friendly automatic parking door to gain a competitive edge in the market. Automated parking systems have a wide range of applications, including commercial parking garages and residential parking garages. Their widespread application has significant socio-economic benefits and is of great importance to improving the urban landscape.
1. Structure and working principle of automated parking garages
The automated parking system control system includes a vehicle storage and retrieval system, a vehicle management system (vehicle identification, parking fee collection, etc.), and a monitoring and security system. The automated storage and retrieval system is the core of the automated parking system control, controlled by a PLC. It includes two processes: card recognition and loading bin movement. A contactless card reader is installed at the parking garage entrance (which is also the exit). When a user enters the parking garage, they swipe their card at the door. The card reader automatically transmits the data to the PLC. The PLC system automatically determines whether the card is valid. If valid, the parking garage door opens, and the system moves the loading bin to the handover position between the user and the vehicle, thereby shortening the storage and retrieval time.
A lift-and-slide automated parking system stores and retrieves vehicles by lifting or sliding car carriers. It mainly consists of six parts: the main frame, car carriers, the transmission system, the control system, and safety protection measures. The main frame is the supporting structure of the automated parking system and is typically made of steel. The car carriers hold the vehicles and are equipped with lateral movement motors that drive the entire car carrier to move laterally. The transporters on the car carriers are connected to the frame by four steel cables and can be raised and lowered. The transmission system of the lift-and-slide automated parking system is divided into a lifting transmission system and a lateral movement transmission system, and is the core of the entire parking system. The control system of the lift-and-slide automated parking system can use hardware such as microcontrollers and programmable logic controllers (PLCs) to control the states of relays and contactors to complete the lifting and lateral movement actions. Safety protection measures are the safety guarantee of the automated parking system and generally include emergency stop switches, over-limit devices, vehicle length detection, vehicle blocking devices, fall prevention devices, and warning devices.
2. Design of Intelligent Control System for Automated Parking Garage
This design is based on Siemens PLC, which processes the data and then controls the operation of field equipment to achieve automated, efficient, and accurate operation of the urban drainage pumping station monitoring and control system.
The control system in this design is fully automatic. After starting the simulation software WINCC, simply press start, and the PLC will control the automated parking system through the corresponding program written in the TIA Portal software.
In the control system of a lift-and-slide automated parking garage, the majority of signals are switching signals such as motor start/stop signals and sensor detection signals. The control modes are logic control and sequential control; therefore, a PLC is selected as the main control unit for the control system design. This control system uses a Siemens S7-200 PLC as the main control unit. Various sensor detection signals from the lift-and-slide automated parking garage are input to the PLC controller through digital input channels. The PLC processes the signals and outputs them to the automated parking garage through output channels, completing the control actions of the lift motor, slide motor, and other actuators. The flowchart of the automated parking garage control system is shown in Figure 1.
Figure 1. Flowchart of the automated parking system
3. Control System Hardware Configuration
3.1 Main Circuit Design
The main drive motor is a 22kW AC dual-speed motor. KM1 is connected to the rising contactor, KM2 to the falling contactor, KM3 to energize the low-speed winding, and KM4 to energize the high-speed winding. KM4 is short-circuited to disconnect the high-speed starting reactor, and KM31 is short-circuited to disconnect the low-speed reactor. L is a smoothing reactor for limiting current. During starting (braking), in order to limit the starting (braking) current, reduce the voltage surge of the power grid, and reduce the acceleration during starting (braking), a series reactor is connected in series with the stator winding to gradually reduce the voltage for starting (braking).
The storage floor sensing circuit. Storage floor sensing is achieved by switching the main leveling limit switches at the four corners of each floor on and off, generating a storage floor signal for functions such as floor pointing, direction selection, floor selection, and deactivation of lobby calls. The sensing signal must be continuous, disappearing only when the load-bearing box moves to the upper or lower floor.
② In-car or lobby call circuit. This circuit differs from the elevator control system. In the in-car and lobby call circuits of the automated parking garage, the in-car call button is located on the control panel inside the loading compartment. It is not used normally, but only when maintenance personnel or administrators need to enter a designated parking area, making it convenient to operate.
③ Lateral movement circuit. The lateral movement circuit refers to the control circuit that pushes (or pulls out) the vehicle into the left or right parking space after the load box is moved to the designated floor and leveled. This action is issued by the signal after leveling (solenoid valve unlocking) and terminates with the action of the solenoid valve latch (load box upper limit switch).
④ Load box starting speed change and leveling circuit. The AC dual-speed motor has two sets of windings: a high-speed winding and a low-speed winding. The high-speed winding has 4 poles and the low-speed winding has 16 poles, with a speed ratio of 4:1.
3.2 PLC Selection
This system requires 74 digital inputs and 36 digital outputs, necessitating a certain margin in configuration. The basic unit cannot meet the input/output requirements, necessitating the addition of expansion modules. Considering various factors, this design utilizes a Siemens S7-1200 PLC, a 1214C CPU, 5 digital input modules, and 2 digital output modules, which satisfies the design requirements of the automated parking system.
3.3 Analysis of Control System I/O Points
(1) Control box. The control box is the operating interface of the control system and should be equipped with control buttons such as parking space selection, start/stop, emergency stop, reset, and automatic/jog switching.
(2) Vehicle presence detection. To determine whether a vehicle is present on each vehicle carrier, a sensor for detecting the presence of a vehicle should be installed on each vehicle carrier.
(3) Accurate positioning detection. In order to ensure that the vehicle platform has moved to the designated position, a detection device should be installed at the corresponding parking space to detect whether the vehicle platform has been raised, lowered or moved laterally into place.
(4) Vehicle overlength detection. To prevent overlength vehicles from entering parking spaces, a detection device for checking whether a vehicle is overlength is installed at the entrance of the garage.
(5) Lifting motor. Since the lifting of the vehicle platform requires a large amount of power, an AC motor is selected. The lifting of the transporter is controlled by the forward and reverse rotation of the motor.
(6) Transverse motor. A small AC motor is used to control the transverse movement of the vehicle platform by rotating the transverse motor in both directions.
(7) Anti-fall device. After the intermediate or top-level vehicle platform is parked, an anti-fall device is installed in the corresponding parking space to prevent the transporter from falling. The device is in the form of a hook and is driven to open and close by an electromagnet.
(8) Garage indicator equipment. Operation lights, alarm lights and alarm bells. When there is movement in a parking space in the garage, the operation lights will illuminate to alert personnel; in case of an emergency, the alarm lights will flash and the alarm bell will sound.
4. Software Design
The main function of the PLC control system for a lift-and-slide automated parking system is vehicle storage and retrieval. It offers two control modes: jog and automatic. Jog control uses the "up," "down," "left," and "right" keys to adjust the vehicle platform to a predetermined position, primarily for debugging, maintenance, or emergency handling. Automatic control is the normal operating mode of the automated parking system. When a parking space is selected for storage or retrieval, the system automatically determines the parking space movement plan and calls the corresponding parking space movement program to automatically complete the storage and retrieval operation.
The main problem in parking control is solving the problem of parking space movement. When a parking space is selected for parking or retrieval, all the parking spaces below it need to be moved to create a downward passage. The creation of the downward passage must follow the principle of efficiency, which includes two aspects: minimizing the time required to create the downward passage, i.e., minimizing the distance the parking spaces move; and minimizing the number of parking spaces that need to be moved to create the downward passage.
When selecting a ground-level parking space, vehicles can directly enter and exit, so the location of available spaces is not a concern, and the parking operation can proceed directly. When selecting a middle or top-level parking space, based on efficiency principles, the selected space is compared with available spaces on the levels below it. If an available space on a certain level is to the left of the selected space, the corresponding space on that level is moved to the left; if an available space on a certain level is to the right, the corresponding space on that level is moved to the right. Ultimately, a passageway is created beneath the selected parking space, facilitating its movement and enabling the parking operation to complete.
To ensure reliable and efficient parking control, parking space reset rules were established. The lateral parking space reset rule is as follows: Lateral parking spaces do not require row/column reset. During the establishment of the downlink channel, parking spaces on floors below the top floor require lateral movement. To ensure parking efficiency, it is stipulated that after parking is completed, the laterally moved parking spaces do not need to be reset and can directly participate in the next downlink channel establishment process. When the system performs a forced reset operation, each parking space returns to its initial position. The lifting parking space reset rule is as follows: Lifting parking spaces require floor reset. To ensure the reliability of parking control, it is stipulated that after parking is completed, without forced system stop, the lowered parking space should promptly rise after completing the parking operation, returning to the floor where the parking space is located.
Based on the aforementioned parking space reset rules, the parking space lifting and lowering actions for both parking and retrieval operations are consistent. That is, regardless of whether a parking or retrieval operation is performed, the parking space first descends from its current floor to the ground floor, and then promptly rises back to its original floor after the operation is completed. Therefore, the same control program can be used to control the parking space's access, improving the program's execution efficiency and saving storage space.
5. Summary
This paper mainly designs an intelligent control system for an automated parking garage based on a Siemens 1200 PLC. The use of soft-wiring PLC program control significantly improves the system's reliability. The PLC-based automated parking garage control system simplifies operation, ensures reliable operation, reduces maintenance costs, and achieves intelligent control. This system aims to perform some actions simultaneously in the parking and retrieval process, such as lifting and lowering the loading bins and moving them forward and backward, greatly saving parking and retrieval time. Furthermore, this system can be expanded to high-rise buildings and multi-bay parking spaces, making it suitable for densely populated car communities or parking lots.
