“With the continuous changes in social lifestyles and the continuous advancement of technology, people demand more humane and intelligent living conditions. You don’t need to do everything yourself, and let intelligent systems replace manual methods as much as possible for effective management and execution. The current increasingly complex traffic conditions, such as difficulty in driving and parking, have greatly reduced the efficiency of work and life in the city, forcing us to find a convenient solution to the problem.
With the continuous changes in social lifestyles and the continuous advancement of technology, people demand more humane and intelligent living conditions. You don’t need to do everything yourself, and let intelligent systems replace manual methods as much as possible for effective management and execution. The current increasingly complex traffic conditions, such as difficulty in driving and parking, have greatly reduced the efficiency of work and life in the city, forcing us to find a convenient solution to the problem.
The intelligent parking lot came into being under this background. The emergence of smart parking lots not only standardizes the level of urban traffic management and vehicle management, but also expands the capacity of the city. It also has a huge guarantee in terms of safety and protection. At the same time, it can easily interface with other smart systems (such as smart buildings, smart communities, etc.) , To form a more complete logistics and equipment management system.
The status quo of smart parking lot communication
At present, parking lots have different levels of intelligence, lack of orderly management, and poor versatility among facilities, resulting in fewer types of equipment for system integrators and users, incomplete functions, and unclear system characteristics. Wait for insufficient.
According to the analysis of the communication mode of the intelligent parking lot, some early manufacturers adopted the serial RS-485 bus or RS-232 bus as the communication method between the devices; at the same time, some advanced manufacturers have adopted the CAN-bus bus or EtherNet is used as the network communication method.
The parking lot system that adopts RS-232 communication has very big limitations, it can only realize point-to-point operation, the central processing unit has a heavy burden, it is not convenient for system expansion, the communication distance is very short, and it is not suitable for remote operation; moreover, the system higher cost. The overall performance of the system using the RS-485 bus is better than that of the RS-232 system. Because it is a bus form, it is convenient to expand. However, as the parking lot system requires more and more intelligent degree, the function becomes stronger and stronger. With more and more nodes, RS-485 has low bus efficiency, poor system real-time performance, low communication reliability, high post-maintenance costs, complex network engineering debugging, unsatisfactory transmission distance, and single bus can be connected Shortcomings and shortcomings such as fewer nodes and inflexible applications are gradually manifesting; the system expansion of the intelligent parking lot is also restricted by the RS-485 itself, and it is increasingly unable to adapt to the control needs of large and medium-sized intelligent parking lots.
The advanced CAN-bus communication system is the mainstream development direction of smart parking lots. Using this industrial-grade communication method can ensure the reliability and real-time performance of communication data; and, in actual construction, the cost of CAN-bus is roughly equivalent to that of RS-485, even in larger parking systems. , The overall cost of the CAN bus is slightly lower than that of the RS-485 system. Because the CAN bus has good fault tolerance, it can greatly reduce the maintenance, repair, and expansion costs in the later period. However, most of the current smart parking lots adopt the mixed use of CAN-bus bus and RS-232 and RS-485 communication, which will cause network load imbalance to a certain extent, which limits the maximum performance of CAN-bus bus. Advantage.
The following will take the parking lot charging and management system formed by CAN-bus bus as an example to introduce a complete set of intelligent parking lot improvement schemes, thus reflecting the overall advantages of CAN-bus bus.
Smart parking lot CAN-bus solution
1: Introduction to CAN-bus
The CAN (Controller Area Network) bus was first proposed by the German BOSCH company and is mainly used for data communication between the internal measurement and control center of the car. Because of its good performance, it is widely used in other fields around the world, such as industrial automation, automotive electronics, building construction, elevator networks, power communications, security and fire protection and many other fields, and gradually become the main communication means of these industries.
The characteristics of fieldbus CAN-bus:
1. International standard industrial-grade fieldbus, reliable transmission and high real-time performance;
2. Long transmission distance (maximum 10KM), fast transmission rate (maximum 1Mbps);
3. A single bus can connect up to 110 nodes, and the number of nodes can be easily expanded;
3. The status of each node on the bus is equal, regardless of master and slave, burst data can be transmitted in real time;
4. Non-destructive bus arbitration technology, multiple nodes can send data to the bus at the same time, and the bus utilization rate is high;
5. The CAN node in error will automatically shut down and cut off the connection with the bus, without affecting the communication of the bus;
6. The message has a short frame structure and has a hardware CRC check. The probability of interference is small, and the data error rate is extremely low;
7. For unsuccessfully sent messages, the hardware has an automatic sending function, and the transmission reliability is very high;
8. With hardware address filtering function, it can simplify the compilation of software protocol;
9. The communication medium can be ordinary twisted pair, coaxial cable or optical fiber, etc.;
10. The CAN-bus bus system is simple in structure and extremely cost-effective.
2: General introduction
The communication scheme involves almost all the control functions of the parking lot, including import and export control, remote control, parking lot guidance, automatic parking space detection, and parking lot intelligent lighting control. The program does not include the transmission of audio and video, because the transmission of audio and video is generally separated from the control bus.
In the entire system, the communication backbone is only a twisted pair, and the controllers of each communication terminal are directly connected to the bus; and the status of each controller in the network can be equal, that is, there is no “master” and “slave”. With the concept of “machine”, any node can start data transmission, avoiding the use of RS-485 host polling, thereby ensuring the real-time nature of data. On the CAN-bus bus, both point-to-point communication can be realized, and multi-point broadcast communication can also be realized. Both real-time and flexibility can be well guaranteed.
For example, the parking space detector can directly transmit the number of vacancies to the parking space Display according to the changes in the entry and exit of the car in the parking lot; it does not need to be transmitted to the management machine first, and then transmitted from the management machine to the parking space display. Of course, the management machine can also receive this information for database recording.
The communication distance of the intelligent parking lot is restricted by the baud rate of the CAN-bus bus; at a communication rate of 20Kbps, it can reach a communication distance of 3KM (using the same twisted pair), which can meet most of the needs.
In this scheme, the parking lot system is divided into two parts according to different locations: vehicle entrance and exit control, and parking lot internal control.
3: Import and export control of vehicles
The main functions of the vehicle entrance and exit control part are the management, charging, ticket issuance and display of the vehicle entrance and exit. The wiring structure of the system is shown in Figure 1.
The CAN-bus network in the system adopts a linear topology, and each device node is connected to the CAN-bus main line through branch lines. At the entrance of the parking lot, when the sense of locality detects that there is a vehicle passing by, the entrance controller sends a signal to the computer management node, requesting to start the entire management system (before the system was in a dormant state to save energy), so that the system immediately enters the working mode. The entrance controller reads the Electronic card information of the vehicle through radio frequency or GPRS, and transmits it to the management computer through the CAN-bus bus, and compares it with the vehicle information (model, license plate, etc.) obtained by the camera, if it is a “legal” user Open the barriers, light up the green traffic lights, and allow vehicles to pass. When the ground sensor at the barrier detects that the vehicle has passed, and the ground sensor at the entrance does not detect that a new vehicle enters, the entrance controller still reports that the system is idle to the computer management node and can enter the sleep mode. Other functions, such as export controllers, charging functions, etc., can be managed in the same way.
In the system, the management node adopts a general PC equipped with a PC-CAN interface card to communicate with terminal function devices installed in various locations. Commonly used PC-CAN interface cards are: PCI-CAN interface card, ISA-CAN interface card, USBCAN interface card, PC104-CAN interface card, EtherNet-CAN interface card or parallel CAN interface card, etc., which can be changed according to the communication requirements of the system Make a reasonable choice.
4: Internal control of the parking lot
The main functions of the internal control part of the parking lot are vehicle guidance, empty space detection and lighting control.
As shown in Figure 2, the parking lot is divided into 4 parking areas: A zone, B zone, C zone and D zone. The location guidance systems of the 4 areas are uniformly placed at the entrance of the parking lot, indicating the direction of the area and the number of vacancies currently left. The location guidance system is controlled by a controller with a CAN-bus bus interface.
When a vehicle or vehicle owner enters or exits a related area, the lighting in that area is turned on. After the vehicle or vehicle owner leaves, the lights are automatically turned off, and the lights in areas that are not related to the current entry and exit will not light up, so that you can Save energy to the greatest extent and extend the life of equipment, which will play a more prominent role in larger parking lots.
After the vehicle enters and exits, the number of parking in the parking lot changes. The system can detect this change in time and report it to the main controller and location guidance signs to refresh the current record and display.
In this system, the CAN-bus bus mode is used for communication, and the network appears very simple and reliable, as shown in Figure 2. Each parking zone has a separate zone controller, all with CAN-bus interface, used to manage the zone’s lighting and parking space detection. As shown in the figure, the red line is the lighting line, and the zone controller directly controls the lighting of the zone lights. The green line is a single bus used to communicate with the parking detector. Together with the CAN-bus bus, it forms a convenient secondary data communication network. Of course, the network construction of parking detectors can also be implemented using CAN-bus, which is basically not restricted by the number of parking spaces, and can easily implement many specific functions such as equipment management and fault location.
The above two parts are connected to form a complete intelligent parking system. In the whole system, not only can be unattended, but also can be connected with other CAN-bus systems, such as the property management center, the community dispatch center, etc., to facilitate the management of the entire system.
The use of CAN-bus bus also provides very obvious advantages for custom communication protocols and design software, which improves the overall performance of the system. At the same time, the use of CAN-bus can greatly reduce the cost of equipment expansion, system upgrades, and terminal maintenance for the entire intelligent parking lot. Moreover, the more large-scale intelligent parking system, the more obvious the advantages of using CAN-bus bus will be better DD function, low cost, and save management and maintenance costs.
Practice has proved that the use of CAN-bus can obtain good social and economic benefits in the operation of intelligent parking lots.
CAN-bus bus has been successfully used in many domestic intelligent parking lots, garage equipment networks, vehicle management offices, vehicle toll stations and other occasions. This is also the development direction for many domestic communication control networks to achieve reliable, automated operation and unattended operation.