Automated Guided Vehicle (AGV) is important equipment in the logistics system of modern manufacturing enterprises. It is mainly used to transport various materials and provides an important guarantee for the flexible, integrated, and efficient operation of the system.
The laser navigation AGV uses lidar as a sensor to detect the external surrounding environment for navigation and positioning. Compared with other navigation methods, laser navigation AGV has higher reliability and flexibility and is widely used in various fields of manufacturing.
The form and characteristics of navigation
1. Laser navigation based on reflective markers
A sufficient number of laser reflective markers are arranged around the driving path of the AGV, and the laser radar detects and recognizes the reflective markers for navigation. Generally, laser reflective markers exist in the form of reflectors and reflectors, as shown in Figures 1 and 2. This navigation method is stable and reliable, has high positioning accuracy, low algorithm complexity, low requirements on the external environment, and wide application.
2. Laser navigation based on the external natural environment
This kind of navigation is also called natural navigation, which uses the contour information detected by the AGV lidar as a reference for navigation. Compared with the laser navigation method that relies on reflective markers, although the accuracy and reliability of natural navigation are relatively low (especially in the case of relatively single environmental information, such as a long corridor), the algorithm complexity is relatively high, but there is no need to install laser reflective markers, which reduces the installation and debugging time of the AGV system and improves the flexibility of the AGV system.
3. Composite laser navigation based on reflective markers and natural environment
In composite navigation, on the one hand, it uses the surrounding natural environment information to locate the AGV. On the other hand, it arranges reflective markers to solve the real-time position of the AGV in the station area where the environment is poorly recognizable or requires precise positioning.
Compared with the first two navigation forms, the complex navigation algorithm has the highest complexity, and the problem of information fusion needs to be considered. The specific manifestation is the comprehensive solution of the real-time position of the AGV and the unified description of the map information.
Key issues of laser navigation
1. Location and map construction
Whether it is cargo sorting in logistics and warehousing, or material handling in manufacturing, for laser navigation AGVs, it is necessary to store complete map information during the commissioning stage, and then put it into operation, and the global map may not be modified or only Make appropriate modifications.
It is very important to obtain accurate map information, which directly affects the positioning and navigation accuracy in the operation phase. On the one hand, through multiple static detections, multiple local maps can be spliced together to obtain complete map information. On the other hand, a complete map can also be obtained by simultaneous positioning and mapping (slam).
2. Internal sensor for positioning
Through the internal sensors used for positioning (AGV steering wheel drive, steering encoder, or AGV inertial measurement unit, etc.), the AGV position can be solved. However, these internal sensors inevitably have certain deficiencies. In order to improve the positioning accuracy of fixed-point parking, the positioning algorithm needs to be improved, and more importantly, the positioning accuracy can be improved by enhancing the external environment information. The specific methods are as follows:
- Increase the number of reflectors;
- Construct a local specific contour near the parking location;
- Introduce navigation methods such as magnetic nails and QR codes;
- A visual sensor is added to the AGV to scan materials or pallets to achieve precise docking between the AGV and the target.
The development trend of laser navigation
1. Complex navigation
In most driving areas, the AGV conducts natural navigation and arranges laser reflective markers for navigation in local areas that require high positioning accuracy. Moreover, according to the needs of the application, navigation methods such as magnetic strips, magnetic nails, and two-dimensional codes can be introduced to improve the navigation accuracy and reliability of the AGV.
2. Flexible driving route
Factory-oriented AGVs need to be highly reliable and efficient. Therefore, they basically drive along a pre-designed fixed path. Just like a train must travel along the track, although the track can be selected, it cannot be derailed.
In this regard, the fixed trajectory of the AGV near the end of the branch of the pick-and-place cargo platform can be canceled, allowing the AGV to self-plan the path in the area near the end according to the current environmental information. In this way, on the one hand, it can reduce the workload of designing the driving route during the pre-commissioning period, on the other hand, it can also improve the flexibility of the system, and have a certain obstacle avoidance effect on obstacles near the endpoint.
3. Navigation information modularization
The basic function of lidar is to obtain the outline of the external environment by detecting the surrounding area, and get the map information in the form of the point cloud, as shown in Figure 3.
Laser navigation AGV has high reliability, accuracy, and flexibility, and can be applied to most production fields. The technology of laser navigation based on reflective markers is relatively mature. Natural navigation has greater development potential because of its better flexibility. The composite laser navigation based on the above two methods, while taking into account the reliability and flexibility, has extremely high research value.
Map construction is a very important content of laser navigation AGV. Laser navigation combined with AGV internal positioning sensor can achieve better navigation quality. On the basis of laser navigation, the introduction of new navigation methods to assist, with additional specific contours added by the external environment, can further improve the positioning accuracy and reliability.
Due to the large market demand and broader application scenarios of laser navigation AGV, the AGV laser navigation technology should be continuously improved and improved. The future laser navigation AGV has complex and diversified navigation methods, more flexible and free driving routes, and more convenient navigation information acquisition and use, which is convenient for development and debugging personnel and production operators to use and maintain.