Automated Guided Vehicle (AGV), as an important tool for automated transportation, has become more and more widely used in recent years. As one of the core technologies of AGV, navigation guidance technology plays a vital role in the development of AGV technology. There is even a saying that “the development history of AGV technology is the evolution history of navigation guidance methods”. In the process of working, AGV can only carry out operations effectively by accurately positioning itself.
The key technology of AGV navigation guidance
The AGV navigation guidance refers to the process in which the AGV controls the speed and steering angle according to the path offset, thereby ensuring that the AGV accurately drives to the position and course of the target point. Three main technical points are involved:
1. Positioning
Positioning is to determine the position and course of the AGV relative to the global coordinates in the working environment, and is the most basic link of the AGV navigation guidance.
2. Environmental perception and modeling
In order to realize AGV autonomous movement, it is necessary to recognize various environmental information based on various sensors: such as road boundaries, ground conditions, obstacles, etc. AGV determines the reachable and unreachable areas in the direction of travel through environmental perception, determines the relative position in the environment, and predicts the motion of dynamic obstacles to provide a basis for local path planning.
3. Path planning
According to the different degrees of AGV’s grasp of environmental information, it can be divided into two types: one is global path planning based on known environmental information, and the other is local path planning based on sensor information. The latter environment is unknown or partially unknown, namely Information such as the size, shape, and position of obstacles must be obtained through sensors.
Common AGV navigation guidance methods
1. Electromagnetic Guidance (Wire Guidance)
Electromagnetic guidance is one of the early AGV navigation guidance methods, and the technology is relatively mature. The technology is to bury the metal wire underground, AGV through the vehicle-mounted electromagnetic sensor to sense the magnetic signal emitted by the metal wire to achieve guidance. The advantage of this kind of guidance technology is that the principle is simple, it is not interfered by sound and light, the manufacturing cost is low, and the buried metal wire is not easy to damage. But the shortcomings are also obvious. First of all, it is difficult to expand and change the route in the later period, and the task cannot be changed in real time during the work process, which is easily interfered by magnetic substances such as metals.
Applicable scenarios: manufacturing routes with simple routes (eg, automobile manufacturing)
2. Tape Guide (Magnetic Tape Guidance)
The principle of magnetic tape guidance is similar to electromagnetic guidance. Guidance is achieved by laying magnetic tape on the ground, which is more flexible than electromagnetic guidance. It is also easier to re-lay the magnetic tape for secondary changes. However, the task cannot be changed in real time, and the AGV can only walk along the magnetic tape, which is also susceptible to interference from magnetic substances. The tape is also susceptible to damage when it is laid on the ground and requires regular maintenance.
Applicable scenarios: manufacturing routes with simple routes. In places where there is a forklift driving, tape navigation should not be used.
3. QR code Guidance
The two-dimensional code guidance method is to discretely lay QR two-dimensional codes, and scan and analyze the two-dimensional codes through the AGV car camera to obtain real-time coordinates. The two-dimensional code guidance method is also the most common AGV guidance method on the market. The composite navigation method of two-dimensional code guidance + inertial navigation is also widely used. Amazon’s KIVA robot realizes autonomous movement through this navigation method. This method is relatively flexible, and it is more convenient to lay and change the path. The disadvantage is that the QR code is easy to wear and requires regular maintenance.
Applicable scenarios: warehouse with better environment
4. Inertial Navigation
Inertial navigation is to install a gyroscope on the AGV. The gyroscope can be used to obtain the three-axis angular velocity and acceleration of the AGV. The integral positioning can be used to navigate the AGV. The advantages of inertial navigation are low cost and high accuracy in a short time, but this navigation method The shortcomings are also particularly obvious. As the gyroscope itself grows over time, the error will increase cumulatively until it loses its position, which is called an “absolute flaw”. Therefore, inertial navigation is usually used as an aid to other navigation methods. As mentioned above, the two-dimensional code guidance + inertial navigation method is to use inertial navigation in the blind area between two two-dimensional codes, and re-correct the position when passing the two-dimensional code.
5. Laser Navigation
The principle of traditional laser navigation is to install a reflective plate with an accurate position on the AGV driving route. The AGV’s on-board laser sensor will emit a laser beam while walking. The laser beam is reflected by multiple sets of reflective plates. The receiver receives the reflected laser and records it. The angle value can be calculated by combining the position of the reflector and the accurate coordinates of the AGV. Its advantage is that it does not require ground positioning facilities, and it has high flexibility. The disadvantage is that the manufacturing cost is high and the environmental requirements are more stringent.
Applicable scenarios: scenarios where the path needs to be changed frequently. The open air environment and the environment with more complicated light are not suitable for laser navigation.
6. SLAM Laser Navigation (Natural Navigation)
SLAM laser navigation is a natural way of navigation without the use of reflectors. It no longer needs to use auxiliary navigation signs (QR code, reflector, etc.), but through the natural environment of the work scene, such as: pillars in the warehouse , Walls, etc. as positioning reference objects to achieve positioning navigation. Compared with traditional laser navigation, its advantage is lower manufacturing cost. According to the editor, there are also manufacturers (such as: SICK) who have developed laser sensors suitable for AGV outdoor operations.
7. Visual Navigation (Visual Navigation)
Visual navigation is also a navigation method based on the SLAM algorithm. This navigation method is to collect image information of the operating area through the vehicle-mounted visual camera, and perform positioning and navigation through the processing of the image information. Visual navigation has the advantages of high flexibility, wide application range, and low cost. However, the current technology is generally mature, and the technology of using vehicle-mounted vision systems to quickly and accurately achieve road sign recognition is still in the bottleneck stage.
AGV navigation guidance technology has been developing in the direction of higher flexibility, higher precision and greater adaptability , and its dependence on auxiliary navigation signs is getting lower and lower . The free path navigation method like instant positioning and map construction like SLAM is undoubtedly the future development trend. It is believed that in the future, the interactive fusion of 5G, AI, cloud computing, IoT and other technologies and intelligent robots will bring about earth-shaking changes to the AGV industry, and the SLAM navigation method with higher flexibility, higher precision and greater adaptability It will be more suitable for complex and changing dynamic operating environment.
