With the development of intelligent manufacturing, factory intelligence has become an inevitable trend. Automated Guided Vehicle (AGV) as an important tool for automated transportation and handling has become more and more widely used in recent years. Many manufacturing and warehousing logistics consider the use of AGV trolleys, but they are not particularly familiar with it, and do not know which type of AGV products to choose, and then they will worry about the various problems of AGV. As one of the core technologies of AGV, navigation and guidance technology is undoubtedly the key to choice. Today we introduce 8 different navigation methods commonly used in the market, so that more users have a simple understanding.
1. Magnetic nail navigation: This navigation method still uses the magnetic navigation sensor to detect the magnetic signal of the magnetic nail to find the travel path. It only changes the continuous induction of the magnetic strip when the magnetic strip navigation is used to intermittent induction. The distance between the two magnetic nails cannot be too large, and the AGV between the two magnetic nails is in a state of distance measurement. In this state, the encoder is required to measure the distance traveled. Secondly, the control module used for magnetic nail navigation is the same as the magnetic stripe navigation control module.
The advantages of magnetic nail navigation: low cost, mature and reliable technology. The navigation has good privacy and aesthetics, which means that the magnetic nails are pre-embedded and drilled and buried under the ground, and there are no other navigation aids above the ground in the entire factory. Magnetic nails have strong anti-interference, strong abrasion resistance, acid and alkali resistance, and oil pollution. Use the user outside, indoor, rain, etc.
Disadvantages of magnetic nail navigation: AGV navigation ground needs to meet technical requirements, that is, there can be no other magnetic materials in the AGV navigation route; AGV navigation lines cannot have demagnetization or diamagnetic materials, which affects the magnetism of AGV magnetic nails. The AGV magnetic nail navigation line is laid once, and the subsequent modification of the line must perform a second operation. Compared with the laser navigation technology, the magnetic nail navigation increases the cost and construction time for the later modification of the line. The AGV magnetic nail navigation construction will have a certain destructive function on the ground, that is, make a hole in the ground and then backfill it. The construction technology is strictly required to restore the original ground aesthetic requirements.
2. Magnetic stripe navigation: Magnetic stripe navigation is considered to be a very mature technology, mainly by measuring the magnetic field signal on the path to obtain the position deviation of the vehicle itself relative to the target tracking path, so as to realize the control and navigation of the vehicle. Magnetic stripe navigation has high measurement accuracy and good repeatability. Magnetic navigation is not easily affected by changes in light. During operation, the magnetic sensor system has high reliability and robustness. Once the magnetic strip is laid, the maintenance cost is very low, the service life is long, and it is easy to add and change the path.
Advantages of magnetic stripe navigation: simple on-site construction. Low cost, mature and reliable technology. No interference to sound and light. The obviousness of the AGV operating line. The second line change is easy, the change cost is low, and the change cycle is short. Low technical requirements for construction personnel
Disadvantages of magnetic stripe navigation: the magnetic stripe is easy to be damaged; because the magnetic stripe is laid on the ground, the overall aesthetics decreases. The magnetic stripe cannot be coherent. Because the AGV turns over the magnetic stripe, some of the magnetic stripe will be cut off and not laid. The magnetic strip will attract metal materials, causing AGV equipment failure and so on. Other sensors are needed to realize the function of positioning the site.
3. Laser navigation: Laser navigation is to install a laser reflector around the AGV's path. The AGV emits a laser beam and collects the laser beam reflected by the reflector at the same time to determine its current position and direction, and through continuous triangular geometry Operation to realize the navigation of AGV.
Advantages of laser navigation technology: AGV positioning is accurate. The ground does not require other positioning facilities, the driving path can be flexible and changeable, and can be suitable for a variety of on-site environments. It is currently the advanced navigation method preferred by many domestic and foreign AGV manufacturers.
Disadvantages of laser navigation technology: high cost, relatively harsh environmental requirements (external light, ground requirements, visibility requirements, etc.). Laser navigation equipment is expensive. Laser navigation equipment is suitable for unobstructed environments. The reflector is expensive.
At present, laser navigation technology has become the mainstream solution of domestic and foreign AGV manufacturers. Due to its high positioning accuracy, flexible route changes, and mature navigation technology, laser navigation has become popular.
4. Electromagnetic navigation: Electromagnetic navigation is one of the more traditional navigation methods, and it is still used. It embeds metal wires on the driving path of the AGV, and loads the guide frequency on the metal wires, and recognizes the guide frequency. Realize the navigation function of AGV. The navigation technology is similar to the magnetic stripe navigation. Due to the lack of beauty of the navigation technology and the difficulty of changing the route, the technical solution is gradually abandoned by the AGV manufacturer. However, the navigation technology is more suitable for certain occasions, depending on the requirements of the AGV working environment. For example, under high temperature environment, strict requirements such as line straightness are required.
The advantages of electromagnetic navigation: low cost, mature and reliable technology. The navigation has good privacy and aesthetics, which means that the magnetic nails are pre-embedded and drilled and buried under the ground, and there are no other navigation aids above the ground in the entire factory. Magnetic nails have strong anti-interference, strong abrasion resistance, acid and alkali resistance, and oil pollution. Use outside, indoor, etc.
The disadvantage of electromagnetic navigation: additional equipment is required to generate electromagnetic signals. Other sensors are needed to realize the site positioning function. The AGV electromagnetic navigation line is laid once, and the subsequent modification of the line must perform a second operation. Compared with laser navigation technology, electromagnetic navigation increases the cost and construction time for the later modification of the line. The AGV magnetic nail navigation construction will have a certain destructive function on the ground, that is, slotting in the ground and then backfilling. The construction technology requires strict requirements to restore the original ground aesthetic requirements.
5. Ranging navigation: This navigation technology is mainly applied to the laser two-position scanner to scan and measure its surrounding environment, obtain the measurement data and then combine the navigation algorithm to realize the AGV navigation. The navigation sensor is usually realized by a safety laser scanner with safety functions, because the safety laser scanner can realize the safety function as well as the navigation measurement function. The AGV with ranging navigation technology can realize the function of automatically picking up and delivering goods inside the container.
6. Contour navigation: Contour navigation is currently the most advanced navigation technology of AGV. This technology uses a two-dimensional laser scanner to measure and learn the on-site environment, and draw the navigation environment, and then how many measurements are performed, the map is corrected to realize the contour navigation function . Use the natural environment (walls, pillars and other fixed objects) for free ranging navigation and update the position according to the environmental measurement results. Contour navigation advantages: no need for reflectors or other artificial landmarks; reduce installation costs; reduce maintenance work; laser navigation alternatives
7. Hybrid navigation: Hybrid navigation is a collection of multiple navigations, and this navigation method is born according to the changes in the on-site environment. Due to changes in the on-site environment, a certain kind of navigation cannot meet the requirements temporarily, and then switch to another navigation method to continue to meet the continuous operation of AGV.
8. Optical navigation: Optical navigation actually uses industrial camera recognition. The navigation is divided into ribbon tracking navigation, QR code recognition and other functions.
Comparison of AGV navigation methods
Early AGVs mostly used magnetic tape or electromagnetic navigation. These two solutions have simple principles, mature technology, and low cost. However, changing or expanding paths and subsequent maintenance are more troublesome, and AGVs can only walk on a fixed route, which cannot achieve intelligent avoidance. Or change the task in real time through the control system.
At present, the mainstream navigation method of AGV is QR code + inertial navigation. This method is relatively flexible and easy to lay or change the path. However, the path needs to be maintained regularly. If the site is complex, the QR code must be replaced frequently. The accuracy and service life of the instrument are strictly required.
With the development of the SLAM algorithm, SLAM has become the preferred advanced navigation method of many AGV manufacturers. The SLAM method does not require other positioning facilities, the form path is flexible and changeable, and it can adapt to a variety of on-site environments. I believe that with the maturity of the algorithm and the compression of hardware costs, SLAM will undoubtedly become the mainstream navigation method for AGV in the future.
SLAM is roughly divided into two categories: laser SLAM (2D or 3D) and visual SLAM.
Visual SLAM is still in the stage of further research and development and application scenario expansion. Visual SLAM has received widespread attention because of its large amount of information and wide application range. However, the algorithm has higher requirements for the processor. Generally, a quasi-desktop CPU or even GPU is required. However, most AGVs use embedded processors, so they are short. Time is difficult to apply on a large scale on small AGV equipment.
Laser SLAM started earlier than visual SLAM, the theory and technology are relatively mature, stability and reliability have also been verified, and the performance requirements for the processor are much lower than visual SLAM, for example, mainstream laser SLAM can be real-time on an ordinary ARM CPU In operation, some AGV manufacturers have already launched products based on laser SLAM navigation. Undoubtedly, laser SLAM is still the mainstream SLAM solution for a period of time.
The AGV navigation and guidance technology has been developing in the direction of higher flexibility, higher precision and stronger adaptability, and its dependence on auxiliary navigation signs is getting lower and lower. The free route navigation method of instant positioning and map construction like SLAM is undoubtedly the future development trend. It is believed that in the near future, the interactive integration of 5G, AI, cloud computing, IoT and other technologies with intelligent robots will bring earth-shaking changes to the AGV industry, and the SLAM navigation method with higher flexibility, higher precision and stronger adaptability It will also be more adaptable to the complex and changeable dynamic operating environment.
