AGV作为轮式移动机器人（WMR-Wheeled Mobile Robot）的一个分支，自动导引是其主要的特征，也是企业在AGV选型是需要关注的一大问题。随着各类技术的发展，AGV的导引技术也不断提升。20世纪70年代，基本的导引技术是靠感应埋在地下的导线产生的电磁频率，通过名为“地面控制器”的设备打开或关闭导线中的电磁频率，从而指引AGV沿着预定的路径行驶。20世纪80年代末期，无线式导引技术被运用到AGV系统中，例如利用激光和惯性进行导引，这样提高了AGV系统的灵活性和准确性。当需要修改路径时，也不必改动地面或中断生产。这些导引方式的引入，使得导引方式更加多样化了。
AGV is a branch of wheeled mobile robot, and automatic guidance is its main feature, and it is also a major issue that enterprises need to pay attention to in AGV selection. With the development of various technologies, the guidance technology of AGVs has also been continuously improved. In the 1970s, basic guidance technology was based on sensing the electromagnetic frequencies generated by wires buried in the ground, and turning the electromagnetic frequencies in the wires on or off through a device called a "ground controller" to guide the AGV along a predetermined path. drive. In the late 1980s, wireless guidance technology was applied to the AGV system, such as the use of laser and inertial guidance, which improved the flexibility and accuracy of the AGV system. When the path needs to be modified, there is no need to change the ground or interrupt production. The introduction of these guiding methods makes the guiding methods more diverse.
At present, the commonly used guidance methods are: electromagnetic guidance, tape guidance, ribbon guidance, laser guidance, inertial guidance, visual guidance, GPS guidance, coordinate guidance and so on. Various guidance methods make it difficult for companies to start when choosing AGV products.
To choose the correct guidance technology, enterprises need to understand the principles and characteristics of various guidance technologies. Although there are various AGV guidance technologies, their essence can be divided into two categories: "fixed path guidance" and "free path guidance". The AGV in the "fixed path guidance" mode simply drives along a fixed physical line (such as electromagnetic guidance, tape guidance, ribbon guidance, etc.), and the guidance sensor on the AGV measures the AGV and the theoretical path (wire The offset of the AGV, tape, ribbon, etc.) controls the running direction of the AGV; and the AGV with "free path guidance" can automatically select a preset "logical line" to drive (such as laser navigation, inertial Navigation, etc.), in this way, the AGV navigation sensor obtains indirect signals. For example, laser navigation measures the angle and distance of the reflector through a laser scanner; inertial navigation measures angular acceleration through a gyroscope and matches the position of the ground label. At present, the principles and characteristics of the mainstream AGV guidance technology are as follows:
Electromagnetic guidance is a more traditional guidance method. By burying a metal wire on the driving path of the AGV and loading a current on the metal wire to generate a guiding frequency, the AGV determines the running route by identifying and tracking the guiding frequency. . The advantage of electromagnetic guidance is that the guide wire is hidden, not easy to be polluted and damaged, the guiding principle is simple and reliable, easy to control communication, no interference to sound and light, and low investment cost; the disadvantage is that it is not easy to expand or change the path, and it is limited for complex paths big.
The tape guidance is similar to the electromagnetic guidance, the difference is that the tape is laid on the ground instead of burying the metal wire under the ground, and the guidance is realized by the tape induction signal. The advantages of tape guiding are accurate positioning, better flexibility, easier to change or expand the path, simple and easy to lay, and low cost; the disadvantage is that it is easily interfered by metal substances around the loop, the tape is susceptible to mechanical damage, and The AGV intelligently follows the tape path, so the tape needs to be relaid when the path changes.
Paint or paste the ribbon on the driving path of the AGV, and collect the image of the ribbon through the camera that comes with the AGV and perform signal processing to achieve guidance. The advantage of optical guidance is that it is more flexible and the route setting is simple and easy; the disadvantage is that it is very sensitive to the dirt and mechanical wear of the ribbon, and the guidance reliability is poor and the accuracy is low.
Laser guidance is to install laser positioning Peugeot (a highly reflective laser reflector) on the driving path, and laser positioning Peugeot is usually installed on walls or pillars along the running path. The laser scanner on the AGV emits laser light, and at the same time collects the laser light reflected by the reflector and performs signal processing to achieve positioning and heading. The advantage is that the positioning is accurate, the path is flexible and changeable, and it can meet a variety of on-site environments; the disadvantage is that there are requirements for ambient light, the ground, and the reflective surface of the equipment, and there can be no obstacles between the reflector and the laser scanner of the AGV. Logistics affected occasions.
According to the same principle, if the laser scanner is replaced with an infrared transmitter or an ultrasonic transmitter, the laser-guided AGV can become an infrared-guided AGV and an ultrasonic-guided AGV.
Inertial guidance is to install a gyroscope on the AGV and install a positioning block on the ground in the driving area. The AGV can determine its own position and heading by calculating the gyroscope deviation signal and collecting the signal of the ground positioning block. The advantages of inertial guidance are high positioning accuracy, strong flexibility, and wide applicability; the disadvantage is that the cost is high, and the accuracy and reliability of guidance are closely related to the manufacturing accuracy and service life of the gyroscope.
The AGV is equipped with a visual sensing device (CCD camera or vision sensor), and an image database of the surrounding environment of the AGV's predetermined travel path is set in the on-board computer. During the driving process of the AGV, the camera dynamically obtains the image information of the surrounding environment of the vehicle and compares it with the image database, so as to determine the current position and make a decision on the next driving. The advantage of visual guidance is that there is no need to manually set a physical path, and it has strong flexibility. With the rapid development of computer image acquisition, storage and processing technology, the practicability of this kind of AGV will become stronger and stronger.
According to the analysis of various AGV guidance technologies, the comparison of various AGV guidance technologies can be obtained, as shown in the following table.
Table 1 Comparison of various AGV guidance technologies
Some companies believe that the most advanced guidance method is the best. In fact, it is not the case. Whether it is an old technology or a new technology, it has its advantages, disadvantages and limitations of use. A single guidance technology cannot cover all the application needs of enterprises. Enterprises need to choose different guidance according to different occasions and different use requirements. technology-driven products. For example, tape guidance should not be used on the road section where forklifts or people often come and go; if the path of the AGV changes frequently, the "free path guidance" technology should be considered; in the production site with high-altitude logistics, it is not suitable to use laser guidance The way of introduction... When enterprises choose, they need to comprehensively consider various factors such as application requirements, environmental factors, and costs, and adapt to local conditions and use them flexibly to maximize the benefits of investment.