Comprehensive Guide: Building a Complete AGV Control System with S7-1200

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1.1 Types of Onboard Controllers

The onboard controller is the core of the control system and the entire AGV. Which type of controller should be chosen? Based on the author’s experience, the onboard controllers used in AGVs can be categorized into the following three types:

1. PLC: Representative products include Siemens’ S7-1200 and 1500 series, used by AGV manufacturers such as Jiasun and Jiateng. PLCs are known for their good stability and high reliability, but they excel in logic control and can generally only perform simple motion control. The price of Siemens PLCs ranges from around 2000 to 12000 yuan.

2. Industrial PC: Representative products include Beckhoff’s CX5130, used by manufacturers such as Kunchuan and Robert. An industrial PC is essentially a computer, but it is designed to have strong anti-interference capabilities and can be used in harsh industrial environments such as vibration and electromagnetic radiation. Industrial PCs are compact and can run general operating systems like Windows and Linux. For example, after installing Beckhoff’s TwinCAT control software, it inserts a real-time kernel into the Windows operating system, turning the computer into a real-time control system suitable for industrial applications. The price of Beckhoff industrial PCs ranges from about 5000 to 30000 yuan.

3. Microcontroller: Representative products include STM32, used by manufacturers such as Haitong and Jike. Compared to the first two, microcontrollers are inexpensive, and the cost of peripheral components is usually no more than a thousand yuan. One downside of using microcontrollers is that if you want to develop a mature product, you need to invest a lot of effort in designing external circuits and various low-level algorithms. The software development environment may not be as robust.

The above classifications do not imply that the three are distinctly separate; for example, the core chip of a PLC might actually be a microcontroller, and the programming languages used in industrial PCs might include ladder diagrams and structured text common in the PLC field. Microcontrollers can also run operating systems, forming a complete controller. Therefore, while each has its applicable fields, they can complement each other, evolving into a situation where one contains elements of the other.

Of course, there are now specialized AGV controllers on the market, such as the CVC600 from NDC in the USA, ANT from BlueBotics in Switzerland, MRC5000 from Kecong Intelligent in Zhejiang, and SRC from Xianzhihui Robotics in Shanghai. Compared to general industrial motion controllers or PLCs, these controllers integrate mature navigation and motion control algorithms, saving users a lot of work, and they have higher stability and protection levels, but their prices are also higher (20,000 to 60,000 yuan).

1.1 Siemens S7-1200 PLC

I chose Siemens’ S7-1215C PLC as the onboard controller for the AGV (hereinafter referred to as S1200), as shown in the figure below. Due to the wide variety of Siemens’ product models, each model has slight differences in interface types, performance, etc. To accurately describe which model to purchase, it is best to use the order number. Each Siemens product has a unique order number, and when procuring, you only need to provide this number. You can also find the corresponding model in Siemens’ programming software based on the order number. Of course, there are some drawbacks to using Siemens products, such as their PLCs being general products not specifically designed for vehicle control. A 100 yuan ARM development board on Taobao already has RS485, CAN, and Ethernet interfaces, while Siemens products come with a high price tag for these features, and their product openness is poor. Therefore, future AGVs will gradually phase out Siemens products.

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Some devices can access other devices, such as reading data from memory and writing data to memory. These devices have higher authority and status, hence they are called upper-level machines. Some devices can only be accessed by other devices and do not have the authority to access other devices; these are called lower-level machines. In this article, the PLC is the lower-level machine, while the programming computer is its upper-level machine.

To configure or program the PLC, you need to connect the S1200 to the upper-level machine using a network cable, ensuring that the IP address of the upper-level machine is set to the same subnet as the PLC. The default IP address of the S1200 is generally 192.168.0.1, so you can set your computer’s IP to 192.168.0.2. For mobile devices like AGVs, wireless communication is usually adopted, such as receiving control commands from the scheduling system. Wireless communication methods include WIFI, ZigBee, etc. Since WIFI is widely used in practice, I will introduce its configuration method. Connecting to Siemens PLC via WIFI is very convenient; you only need to connect the PLC’s Ethernet port to the LAN port of a wireless router with a network cable, then search for the corresponding WIFI on your laptop and connect to access the PLC. The wireless router used can be any brand, even a home router.