1. Control principle
The common point of the two control principles is that they both use distributed control: the main control unit and related components are arranged in the ground control cabinet, and the interior of the vehicle body also contains relatively independent control units and related components. The difference is that: RGV uses PLC as the control unit, and conducts information exchange between mobile power acquisition and PLC through sliding contact lines; a single trolley also uses PLC as the logic control unit, and uses the inverter as the power control device.
Compared with RGV, the control system of AGV is much more complicated. It belongs to the category of wheeled robots. The whole system takes an industrial computer as the central control unit, and integrates two I/O boards as the information acquisition unit and one relay output board as the output unit; each car has a main control unit. controller VCU100. In addition to communicating with the central control unit through the wireless local area network, the VCU100 also uses a 104-bus CAN communication card PCM3680 to realize the data exchange between the central processing unit and each signal acquisition unit.
2. Implementation of core functions
For the chassis assembly equipment, its core functions are guidance, positioning and synchronization.
In the implementation of the above-mentioned core functions, RGV is relatively simple and intuitive. The RGV is track-oriented, and only needs a variable frequency motor as a walking drive device without direction control; the positioning signal is obtained through a group of trolley lines, which are divided into several sections according to the task, and the brushes are used for sliding with each section. The contact between the contact wires obtains the position signal; and the synchronization with the large chain of the production line is to set the frequency converter to make the linear speed of the trolley driving wheel the same as the linear speed of the large chain. Therefore, when the line speed of the large chain changes, the track The settings of the bicycle inverter need to be changed accordingly.
The AGV uses navigation sensors, landmark sensors, and tracking sensors as the information collection unit to realize this part of the function. They acquire guidance, positioning and synchronization signals through induction with navigation magnetic strips, landmark magnetic strips and light targets respectively. Magnetic navigation technology is the core technology of AGV. Since the magnetic strip itself has a constant magnetic field signal, no additional signal generator is required. The navigation sensor is installed in front of the vehicle body, and the deviation and distance between the AGV and the magnetic strip are calculated by detecting the difference in the signal strength of the magnetic field of the navigation magnetic strip; landmarks The sensor is located on one side of the vehicle body, and determines its own position by detecting the landmark magnetic strip; the two feedback the required signal to the main controller VCU100 through the CAN bus to control the AGV to walk along the track.
The walking execution unit of AGV is a set of servo control system. The walking servo system of AGV adopts double closed-loop feedback of speed loop and position loop. Therefore, in terms of speed and accuracy, its function is better than that of inverters running in open-loop control. much more powerful. The power supply of the servo drive is a DC power supply. The loop gain, maximum operating current, input gain and offset can be adjusted by adjusting the potentiometer on the servo amplifier. Since there are more large chain speed feedbacks than the track bicycle, when the large chain speed changes, the realization of AGV synchronization does not require additional settings.
3. Communication method
Since the rail bicycle uses the sliding contact line as the communication method, only a few digital signals can be exchanged between PLCs; while the AGV realizes powerful communication functions by building a wireless local area network; the local area network is composed of a IEEE 802.11a/IEEE 802.11 b/IEEE 802.11g network standard CISCOAP radio and several Siemens SA radios, whose transmission rate and propagation distance can reach 2.4 GHz, 54 Mbps and 290 m respectively; the rear axle AGV loop line and engine AGV loop line pass through SSID The different settings of the AGV are divided into two local area networks; based on the wireless local area network, the AGV realizes task assignment, collision avoidance management and all information exchange between all industrial computers and each AGV.
4. How to get electricity
In the automobile assembly line, the chassis assembly equipment is in a moving state as a whole and moves frequently, which makes the power extraction method a technical focus and the focus of equipment failures in on-site maintenance. The track bicycle uses the sliding contact method to obtain power (220 V) through the wiring of two carbon brushes and the sliding contact wire; while the AGV uses a vehicle battery pack, which is charged at two points in the running loop. Because the battery pack It is DC, so this method needs to prepare another charging motor.
