Situation guided AGV technology research and development trends

????? Introduction

??????AGV (automated guided vehicle, AGV) having a flexible manufacturing, logistics and warehousing automation broad application prospects, usually battery powered and equipped with non-contact guide apparatus in computer control and guide means assisted, can accurately reach their destinations. Guided AGV technology is one of the core technologies, AGV guide techniques such as laser guidance, inertial guidance, image recognition guide, GPS / GIS pilot and aviation, aerospace, marine, missiles and other military technology related or similar, There are certain technical level. Research guided AGV technology must grasp the correct trends and mainstream technology roadmap technology, the paper made a more detailed description and analysis of existing AGV guidance technology, it introduces the development at home and abroad guided AGV technology, research and use case, and from the perspective of engineering practice, analyzing the advantages and disadvantages of various guidance techniques proposed research direction guided AGV technology.

??????1 Research Status

??????AGV guidance technologies include electromagnetic induction guidance, laser guidance, visual guidance, inertial guidance, ultrasound and magnetic nail guide, these guide way according to whether the guide route is divided into three kinds: a gyroscope fixed way guide-line, semi-fixed route system and free route system.

??????1.1 Electromagnetic induction guide

??????Electromagnetic induction is the most widely used guide the most mature way, belongs to the fixed route system. It is embedded in the AGV's travel route specialized cables, and low-load, low-pressure guide current to generate a magnetic field around the cable, electromagnetic induction sensors detect the magnetic field strength on the AGV and AGV sent out when walking along the path of induction magnetic field intensity differential signal, vehicle control system correction control based on the signal, AGV guide.

??????Branch path convergence and recognition generally have the following methods: by switching the operating frequency electromagnetic induction sensors for characterization of the branch and convergence of information (generally parallel buried many different frequency current through the cables); signal from the console source switch to a different cable lines to guide the route; electromagnetic lock guide and encode pulse method. The first two methods because of the need to switch the sensor group or cables current frequency to correspond to different frequencies, need the appropriate organs and subsidiary equipment electrical aspects, will increase the complexity and failure rate of the system, but also increased the system cost. Electromagnetic lock guide method, also known as time division multiplexing frequency selecion method, namely laying multiple cables on a path guiding device at a time can receive a signal of a certain frequency, if the frequency of the signal to be received, the sampling, otherwise, continue testing, but the number of frequencies is limited, because the frequency of the number, the more long polling cycle, AGV easily lead to loss of control. Frequency division multiplexing selection method enables circuit design guidance system greatly simplified, improving the ease of implementation and the reliability of the system. Coded pulse method using only a single frequency signal source, with only one guide cable to indicate the run path, road intersections information generated by the encoder pulse device, when powered trolley along the wire, differential electromagnetic induction sensor system is used only for detect whether the car deviated from the wire path near the road intersection to set a suitable encoder pulse generating means, when the car entered the signal is effective, the receiving device can receive the encoded information, which simplifies the complexity of the system and improve the reliability, reducing system cost.

??????In addition to frequency electromagnetic induction embedding guide, there is a fixed magnetic field strength and the magnetic tape nail guide way, its guiding principle is to guide the degree of deviation by the AGV symmetrical set of two opposite electromagnetic induction sensors detect the vehicle running path vehicle. The main advantage is that electromagnetic induction guide wire hidden and difficult to pollution and damage, guiding principle is simple, reliable, easy to control and communications, silent light interference, lower manufacturing costs; its main drawback is the complexity of the path is limited, and expand or change the path very troublesome, induction coil surrounding a ferromagnetic material is more sensitive, vulnerable to interference.

??????1.2 laser guidance

??????Laser guidance is arranged around the travel path of the AGV accurate reflection plate mounting position, the laser beam emitted by a laser scanner on the AGV, and the simultaneous acquisition of signals from different angles of the reflecting plate reflected, to determine the current position and orientation and through continuous triangular geometric operations to achieve AGV guide, a semi-fixed route system.

??????Laser scanner is usually installed in a high position of the AGV, and the height of the reflection plate matches, which uses a pulsed laser emits a laser and an internal mirror through a certain rotational speed, constantly scans the surrounding environment, when scanning the traveling path around When predefined reflecting plate that reflects light will be AGV own laser sensor to "see." AGV moving process, as long as the scan to three or three more reflective plate, you can according to their coordinate values ??and each reflective plate relative to the distance and angle of the vehicle body. AGV current coordinates (X, Y) and the angle between the current direction of travel, and the coordinate system of the X-axis in the global coordinate system is calculated by the positioning computer, to achieve accurate positioning and orientation to guide AGV to run along the lines set in advance.

??????In recent years, laser guidance sensors have been industrialization, laser guidance means Sweden NDC Electronics Co., Ltd. employs GaAs pulsed lasers, rotating scanning rate of 10r / s, registration marks visible distance is usually greater than 30m. Rotation rate LS5 Navigator United States Danaher Motion is 20r / s that is the absolute position coordinates every 50ms measured and calculated once the AGV, positioning accuracy within 2cm. Germany SICK company also introduced a laser navigation system NAV200.

??????The biggest advantage is laser guided AGV positioning accuracy, positioning the ground without additional facilities, be able to adapt to the complex path conditions and working environment, can quickly change the travel route and modify operating parameters, is concerned about the many domestic and foreign manufacturers use AGV guide manner; disadvantage is more expensive, China is still not complete this civilian technology.

??????1.3 visual guide

??????Visual guide mainly using CCD / CMOS image sensors to obtain an image around AGV through real-time machine vision processing to determine the AGV sport, and this way there is a fixed route and guide route two kinds of freedom. Fixed line approach is generally the case wher the image sensor will be mounted to the top of the AGV and AGV vision of the ground in front, and on the travel path painted or pasted ribbon, AGV real time image recognition according to a guide wire, and along it The road ahead. In this way a high precision, and low price image sensor, do not ask for the venue, ideal for special occasions. But the way fixed routes painted on the ground guide line must be a standard form, otherwise, the visual guidance system may not recognize. If AGV want to change the path, you must re-draw the wire on the ground, poor flexibility.

??????Freedom trail travel area of ??environmental AGV image recognition, to achieve intelligent driving without a fixed route. Currently, the world are studying the use of multi-image sensor, to obtain images from different angles, using machine vision to integrate a three-dimensional image by image recognition guidance, not only can recognize the surrounding environment, but also can measure the distance to the object. This is a technique with a long-term development potential, at present, only a handful of countries in the military trial, which was applied to the general AGV there is a long distance.

??????Visual guide with a wide detection range, large-capacity information (structured or unstructured road environment can provide a wealth of information), similar to the manned decision and many other advantages, with the rapid development of image sensors and a microprocessor, visual guide a low price, high accuracy and flexibility, by the high degree of attention, become more research guide technology. The inadequacies of the visual guide that changes in light of the impact of a large machine vision in poorly lit or no light situations can not be guaranteed simply rely on visual detection and reliable guide.

??????1.4 inertial guidance

??????Inertial guidance and aerospace, inertial navigation guidance system used in the works, is a free route guide mode. AGV inertial guidance system by an inertial measurement unit (IMU) and global positioning system (GPS), thus achieving the purpose of the guide. In theory, the use of GPS can be absolutely precise position of the AGV, can achieve outdoor AGV guide. However, in the warehouse, workshop, since the block of buildings, GPS signal is not good often occur, and even to be lost, then you need to continue to AGV IMU guide; on the other hand, IMU by a plurality of sets of gyro and accelerometers constitute, respectively, can measure the angular rotation of the vehicle body and translational acceleration, wherby the car can be calculated from the reference point of the distance and attitude. This method requires each acceleration double integral, but because the relationship between the cost of the AGV can not use high-precision accelerometers and gyroscopes, so positioning error of this approach will also run with increasing distance from the car becomes large, a certain distance must be separated, it updates its position and orientation information with absolute positioning methods (such as GPS).

??????Inertial guidance mode flexibility is very strong, easy to mix and compatibility, without prior fixed routes, and radio frequency identification (RFID) tag technology combines greater prospects; its disadvantage is the higher manufacturing cost, accuracy and guided Reliability is closely related to manufacturing precision gyroscopes and life.

??????1.5 Ultrasonic guide

??????Ultrasound guidance is similar to laser guidance, except that does not need to set up a special reflector plate, but the use of general wall or similar object can be guided, therefore, under certain circumstances provides greater flexibility and cost effective solution, they are free route system, but due to the large reflective surface, at the manufacturing workshop environment applications often have difficulties. Ultrasound is used to guide more container terminals, container utilization rules placed the ultrasonic reflection, may very well achieve the purpose of automatic guided, and that the price is very cheap, positioning accuracy of ± 100mm.

??????1.6 Magnetic nail a gyro guide

??????Magnetic nail guide exploit a gyro magnetic sensor detects a magnetic nail installed on the ground, and then use the gyroscope technology continuously control the direction of the AGV, the guide mode requires every 5-10m installed on the ground along the guide path pair Magnetic nail. The magnetic sensor is microprocessor-based, the use of the Hall element detects a magnetic field sensor, when the coordinates (X, Y) AGV when on the road surface by a magnetic nail sensor AGV is given; the gyroscope is a solid state angular rate sensor six-axis , speed is proportional to the output voltage to its sensitive axis thereof, thereby determining the direction of the AGV. If using high-quality components, magnetic nail a gyro guidance system with high precision. Using standard components can significantly reduce costs, the cost is much lower than the guided electromagnetic induction, this guide method is applicable to the case can not be embedded in the guide cable.

??????2 trends

??????2.1 low-cost, miniaturization and high reliability technology guide

??????The development of cost-effective guidance sensor will be an important research direction in order to improve the level of guidance from the Component reliability. As for visual guidance, should be developed to adapt to the large dynamic range of light CCD, in order to meet the requirements of outdoor road environment, in order to ensure real-time visual guidance and robust, high-performance hardware devices can be used, but the study efficient recognition algorithm is also essential. For inertial guidance, in recent years, with the rapid development of micro-electromechanical systems (MEMS) technology, in-depth study of low-cost silicon micro-gyroscope, accelerometer and silicon micro-miniature inertial measurement unit, etc., to continuously improve performance and reliability, Car inertial guidance in the field to meet the huge demand.

??????2.2 Integrated Guidance

??????Different ways of guiding the information provided on the forms, the sampling frequency and the temporal characteristics are different, reflecting the state of AGV guidance from different aspects, such as: GPS AGV can provide two-dimensional spatial position and speed information, visual guide capable of measuring the position of the center of the vehicle relative to the road, to make these complementary guide or redundancy approach has been to maximize the utilization, to avoid a single way of working blind guide, it requires in-depth study of the various guide technology working mechanism, thereby establishing an appropriate multi-sensor combination model guide, the guide system with system-level fault diagnosis, isolation and fault tolerance to meet the reliability requirements of complex environment guide.

??????2.3 Information Fusion Method

??????Currently, in the field of research and information guide fusion applications are mainly Kalman filtering, Bayesian estimation and DS evidential reasoning, of which the most widely Kalman filtering. Kalman filter has a good real-time, but it is built on the basis of strict mathematical model, when there is a big guide model modeling errors or system characteristics change often leads to filter divergence. To improve the filtering algorithm robustness and adaptability, can guide the requirements for the AGV and characteristics, research appropriate adaptive Kalman filter algorithm, robust filtering algorithm (eg, H∞ filtering) or intelligent filtering (such as fuzzy reasoning , neural networks and expert systems) methods.

??????3 Conclusion

??????Low cost, high reliability technology is the guiding premise and basis of the AGV, has been a research focus and difficulty AGV manufacturers and researchers, guide research technology must grasp the trend of the world mainstream technology development. This paper summarizes the characteristics and shortcomings of the various existing guidance technology, to explore the future direction of AGV guidance technology and main contents.