AGV, also known as an automatic guided vehicle, can be used to move materials along a predetermined path. In this process, the construction of automatic logistics system needs to fully reflect the automation and flexibility of AGV robot guided vehicle, and reasonably expand the application scope of AGV robot.
1.AGV robot with dual drive and bidirectional
The so-called AGV robot, also known as automated guided vehicle, belongs to a wheeled mobile robot. With the rapid development of intelligence and automation technology, more and more robots are used in various fields, which has become an important direction of technology research and development in China. Advanced manufacturing technology and factory logistics technology are the research hotspots, and the research on flexible processing and flexible equipment is becoming more and more extensive. Among them, AGV system is an important equipment and component unit, such as intelligent warehouse, workshop flexible manufacturing and logistics system
The AGV AGV system consists of production line control management system, LAN, dispatching control equipment, remote I / O, ground navigation system, wireless access point, charging station and guided vehicle. In the actual operation of AGV automatic guidance planning system, some auxiliary devices, conveying system and communication system are needed. (Figure 1)
2.Motion model of 2-drive bidirectional AGV robot
2.1 3D model
The dual drive bidirectional AGV robot is composed of guiding body, driving module, traction module and motion module. The model is constructed by UI group building, and the three-dimensional model of AGV is built. AGV motion system consists of four universal wheels and two driving modules. These system modules are set in a central symmetrical way, that is, one driving module drives two universal wheels. Driven by the driving module, the AGV robot can carry out linear motion and steering motion. The AGV robot can move and work according to the established trajectory, complete the factory handling task, and adapt to various complex working conditions.
2.2 operation model
In the design of dual drive bidirectional AGV robot, kinematics modeling is needed
Hypothesis 1, AGV robot is composed of rigid material structure;
Suppose 2, the working plane of AGV robot is smooth and smooth. When the AGV robot moves, only the roller moves, and no sliding motion is carried out;
Suppose 3, the friction between the universal wheel and the ground is very small, which will not affect the motion of the universal wheel according to the rotation axis.
In the structural design of dual drive bidirectional AGV robot, the distance between universal wheels driven by two driving modules should be reasonably adjusted. This study assumes that the distance between driving modules is 650mm, the distance between driving wheels under each driving module is 237mm, and the radius of each universal wheel used is 75mm. The velocity of four universal wheels, the velocity of middle point between universal wheels and the angular velocity of universal wheel are calculated. Assuming that the AGV robot moves in a straight line according to the established line, the velocity of the universal wheel driven by the two driving modules is the same; when the AGV robot moves in a curve according to the established line, the two driving modules need to coordinate with each other and rely on the AGV robot to carry out automatic tracking motion .
3.Kinematics simulation of 3-drive bidirectional AGV robot
3.1 formulation of kinematic simulation scheme
Based on the above discussion, the three-dimensional model is established by UG software, and the three-dimensional model is imported into Adams for automatic dynamic analysis of mechanical system. The data information obtained from the motion model is analyzed mathematically by using Matlab mathematical software, and the kinematic model is established. The kinematics equation is compiled under the MATLAB software environment, and the kinematic model curve is drawn The simulation analysis results are refined, the analysis results are compared with the matlab calculation results, and the technical route is determined.
3.2 building virtual prototype
In the design of dual drive bidirectional AGV guidance vehicle, it is necessary to consider its complex structure and complex parts. In kinematics simulation, if Adams is directly used to import the 3D model drawing, the workload will be increased and the simulation difficulty will be increased, which is very easy to make mistakes. Based on this, based on the consideration of simulation performance, this paper can simplify and transform the three-dimensional model of dual drive bidirectional AGV robot into Parasolid format, and then use Adams for simulation processing to form a virtual prototype.
After the 3D model is imported, the AGV parts which do not need to be simulated are fixed to avoid the relative motion of these parts in the actual motion. Then, the four driving wheels and the supporting wheels are created with the rotating pair, and the remaining parts are connected by the kinematic pair, and the contact between each wheel and the ground is established.
After each part of the virtual prototype is connected, the drive wheel is added. A spring is installed on the drive module to increase positive pressure on the drive module. The spring can be installed at the position between the driving module and the workshop to determine the spring coefficient setting, determine the technical parameter of 15N · mm, and increase the preload between the drive module and the frame. After a series of operations, the virtual prototype of AGV robot can run smoothly on the specified line .
3.3 kinematics simulation analysis
In order to simulate the walking characteristics of AGV robot, the trajectory of AGV robot is set as follows: linear motion → left turn → linear motion → left turn, and cycle. In motion, the robot makes four left turns. Therefore, in kinematics simulation analysis, the specific simulation process can be divided into four parts, each part contains a linear motion, a left turn movement and a steering walk, so the specific motion stage includes 16 links. In the kinematic simulation analysis, 16 functions should be written for each driving wheel, and the function should be determined based on the instantaneous speed of the driving wheel of the robot The critical point velocity is calculated and the step function of four driving wheels is compiled. In this study, UG software is used to create the three-dimensional model of the AGV robot guided vehicle. The differential speed principle between the wheels is used to build the kinematics model of the steering motion of the robot guided vehicle, and the minimum steering radius of the AGV robot is determined.
In kinematics simulation analysis, the center points of the two driving modules are set on the marker to realize the trajectory projection on the ground. The trajectory of the robot and the displacement curves of the two driving modules in X and Z directions are determined. Through simulation, it can be determined that the displacement curve of each driving module will produce curve displacement in X and Z directions, which fully reflects the simulated walking state of AGV robot. The displacement curve size and change trend of the two driving modules of the robot can be seen that there is no deviation between the displacement curve and the change trend. In the actual movement, the AGV is driven The module has a repeated running track, and there is no magnetic stripe separation problem.
3.4 comparison of theoretical calculation and simulation analysis results
The kinematics model of AGV robot is deduced. According to the specific derivation results, the instantaneous speed and critical speed of the initial driving wheel are determined through ADAMS simulation. MATLAB software is used for programming. The displacement of the center points of two driving modules of AGV robot in X and Z directions is analyzed, and the data information is extracted. The simulation results are combined with ADAMS software The simulation curve and theoretical curve of the two driving modules in two directions are determined respectively. Comparing the simulation results of the two software with the theoretical curve, it is confirmed that the displacement curve of AGV robot has deviation. The reason is that AGV robot will be disturbed by many factors when steering. Under the interference and influence of yaw rate, roll force and other factors, the steering of the steering car's universal wheel has uncertainty. Although there is a deviation in the displacement curve of AGV robot guided vehicle, the deviation is small, the average deviation is less than 0.14m, and the deviation degree is reasonable.
In the design and construction of dual drive bidirectional AGV robot guidance vehicle, the three-dimensional model and kinematics model should be constructed based on UG software. In the motion of this kind of guided vehicle, the kinematics model of steering motion will be constructed by using the principle of wheel differential speed, and its minimum turning radius will be determined. Then, the advanced ADAMS software will be used for simulation analysis to obtain the simulation curve. Comparing the simulation curve with the theoretical curve, the smaller average deviation is determined, which can prove the rationality of the theoretical analysis of robot motion.
 Liu Kuiyang, Wang Dianjun, Liu Zhanmin, et al. Kinematics analysis and Simulation of single drive unidirectional AGV robot [J]. New technology and new technology, 2015 (10): 45-48
 Wang Dianjun, Wu Chao, Chen ya, et al. Design of dual drive bidirectional AGV control system [J]. Machine tool and hydraulic, 2017 (5): 16-19, 22