AGV (automatic guided transport vehicle) is the key equipment in modern industrial automation logistics system. With the rapid development of the Internet of things, cloud computing, big data, mobile Internet and other new generation of information technology, intelligent logistics has gradually become the development direction of logistics information in the future. As the core equipment of intelligent logistics, the design and research of composite AGV is the only way to upgrade the application of traditional AGV equipment, which can greatly improve the overall level of domestic AGV application, which is conducive to the improvement AGV industry competitiveness; can greatly improve the production efficiency and quality of automatic logistics system, broaden the application ability and application field of AGV.
2. AGV Technology Foundation
In recent years, with the concept of intelligent logistics and investment in AGV technology research and development, the development speed of AGV equipment has been steadily improved, but there is still an obvious gap with the international level. It is necessary for research institutions and enterprise R & D departments to strengthen independent research and development, introduce and digest foreign advanced technology [1-2]. At present, there are many kinds of AGV products in China, such as assembly type AGV, handling type AGV and large load AGV; the core technology is special AGV control software and embedded can bus master controller; deficiency: AGV equipment has single function and can only complete the transportation function under intelligent logistics. The market competition at home and abroad intensifies, so it is urgent to design and optimize the main structure of AGV AGV transformation and upgrading of the key technology research. Therefore, it is necessary to completely change the application mode of traditional AGV, increase the complex functions of robot handling and sorting, reduce the operation cost, shorten the production rhythm, and improve the production efficiency; deeply integrate the robot mechanism system and AGV technology, integrate multiple composite functions such as handling and sorting with the traditional logistics system, and realize the intelligent upgrading of automatic logistics.
3. Overall composition of compound AGV equipment
The compound AGV equipment consists of two parts: the whole vehicle of magnetic strip guided AGV and the composite manipulator , as shown in Fig. 1.
4. Structure design of AGV guided by magnetic stripe
AGV It adapts to various environments (routine, pollution, radiation, noise, danger, etc.) with specific navigation mode (magnetic stripe navigation) and specific movement mode (spin, detour, tracking, blind walking, obstacle crossing, etc.) and specific loading form (roller docking, lifting, hooking, forking, clamping, monitoring and measuring, etc.) to adapt to various environments (routine, pollution, radiation, noise, danger, etc.) to achieve multiple tasks (high precision) better than human operation Intelligent mobile robot or intelligent integrated system. Schematic diagram 2 is as follows:
The overall system of automatic guided vehicle (AGV) is divided into mechanical part and control part, and combined with power part to supply power for each device . The mechanical system is mainly composed of walking, operation, body, control, power supply, safety device, etc., as shown in Fig. 3
4.1 walking part
The walking part is composed of wheel, motor, brake, driving device, speed detector (code plate, etc.) and reduction gear. The contact material between the wheel and the ground shall be wear-resistant soft material. The motor and reducer cooperate to ensure the rated walking speed within the allowable load. The brake shall function during emergency stop and power cut-off.
4.2 operation part
The operation part is the interactive operation unit of AGV to perform manual or automatic tasks. AGV must have the function of manual operation. According to the different power supply modes of AGV, the auxiliary power supply can be connected manually, but the connection mode must be fast and reliable, and it is not necessary to cut off the control power supply of AGV when connecting or disconnecting the auxiliary power supply. AGV must be able to switch to manual operation mode by simple operation. In manual operation mode, AGV shall be able to conduct manual control movement on the ground meeting the requirements. Manual operation shall use the operation panel or special manual control device provided by AGV, and the manual control device must be able to operate independently without communication network. The operating device must have the braking function when stopping, and ensure the normal operation under the allowable load. The operation part of AGV must provide complete display function. The display content should be adjusted according to the running state of AGV. It can display status data in the process of movement and component parameters in the maintenance process
AGV must provide an off-line automatic operation mode separated from the communication network. In this mode, the AGV takes a single machine as the running unit. A simple manual operation on the AGV can perform fixed tasks along the set route.
The automatic working mode of AGV is that AGV operates as an integral part of the system. AGV is operated according to the instructions of external transportation environment. Under the automatic working mode, AGV should obey the management and instruction distribution of external equipment and execute tasks according to the specified route.
4.3 body part
AGV body must ensure that the distortion and deformation generated during normal operation is small enough to avoid dysfunction. The body cover avoids possible dangerous shape, and the cover has a solid structure. In order to prevent functional failure when colliding with other objects.
4.4 control part
The control device has anti vibration function to avoid damage to equipment or functional failure caused by vibration generated during walking. The operation panel shall be easy to observe and operate to avoid misoperation by operators.
4.5 power supply
If the open AC magnetic field power supply mode is selected, it should be used in unmanned working environment in principle. For example, AGV must interact with people, and the manufacturer must provide users with relevant safety data of magnetic field generated by power supply. Ensure that there is no harm to personnel in the environment, and it is necessary to make clear marks within the open range of power supply.
If the battery charging mode is selected, the manufacturer must select the appropriate battery and charging equipment according to the delivery time demand of users.
It adopts fast charging from the pool and online charging mode. It can ensure a certain charging time in the running environment and can work for 24 hours continuously. The ratio of high current charging to average operation time of fast charging battery should reach 1:8.
Maintenance free slow charging battery shall be adopted. The battery shall work continuously for at least 8h every time it is fully charged.
4.6 safety devices
Contact obstacle buffer: to prevent injury or failure when the automatic guided vehicle collides with people or objects.
According to the actual situation of field application, users can choose laser ranging scanning, infrared region diffuse reflection, ultrasonic detection or not.
Warning device: the warning device uses sound or warning light to remind people around AGV to find the approaching AGV in time.
Stop button, when the button is pressed, AGV must stop running reliably and can quickly resume operation through simple manual operation.
5. Calculation of running resistance
When studying the driving dynamics of AGV, it is necessary to determine various external forces acting on AGV, including driving force and running resistance . AGV must overcome the rolling resistance from the ground and the air resistance from the air when driving at constant speed on the horizontal road. However, the friction force corresponding to the sliding state of the wheel when AGV is just started is sliding friction. Before starting, the static friction force must be overcome first, because the static friction coefficient is the largest among the three, and the corresponding static friction force is also the largest. Therefore, as long as the AGV can be started, the rolling resistance is always much smaller than the static friction force. Therefore, the calculation of AGV is necessary Starting resistance is enough.
The maximum static friction force is represented by the symbol FF, and the air resistance is represented by the symbol FW.
When the AGV is running on a ramp, it must also overcome the component force of gravity along the ramp, which is called slope resistance, and is represented by the symbol fi. The resistance that AGV needs to overcome when accelerating is called acceleration resistance, which is represented by the symbol FJ. Therefore, the total resistance of vehicle operation  is:
5.1 calculation of AGV static friction
Where: μ - the maximum static friction coefficient, i.e. the ratio of the thrust required when the wheel just rolls to the positive pressure on the ground, that is, the thrust just required by unit vehicle gravity. The maximum static friction coefficient is determined by experiment. It is related to the type of road surface, driving speed and the structure and material of wheels. According to the relevant reference materials, the static friction coefficient increases with the increase of the positive pressure in a certain range, and is related to the degree of dryness and wetness of the ground. For example, under the positive pressure of 24kg, the static friction coefficient μ is between 0.4 and 0.6, and the static friction coefficient μ = 0.7 is taken into account for calculation under certain allowance
5.2 calculation of acceleration resistance
In the process of accelerating, AGV needs to overcome the inertia force of mass acceleration, namely acceleration resistance FJ; when the displacement S = LM, and the vehicle speed reaches VT = 0.4m/s, the acceleration of AGV is: a = (VT? - VO 2) / 2 = 0.16 / 2 = 0.08m? / s
Therefore, the acceleration resistance is:
5.3 calculation of slope resistance
The road condition of AGV working field is generally good, the slope is small, and the slope angle is α = 2 °, then the slope resistance is:
5.4 calculation of air resistance
Since the air resistance f = - kV, K is the air resistance coefficient, the calculation formula is: k = ρ v? CDA / 2; where ρ is the air density, V is the speed, CD is the aerodynamic resistance coefficient, and a is the windward area of the car; then the air resistance is proportional to the third power of the speed, and the AGV car is different from the high-speed vehicles on the road, the maximum speed of AGV is 0.4m/s and the windward area of AGV
Therefore, the influence of air resistance on AGV driving can be ignored.
So FW = 0n; (6)
According to the AGV total running resistance formula:
6. Structure design of end tool of compound manipulator
According to the requirements of practical application, a special robot end tool is designed. In this case, the flexible grabbing device is used. Under the drive of the cylinder, the length of the gripper can be changed. A variety of auxiliary tools, such as V-shaped block and suction cup, can be replaced on the gripper to grasp parts of different shapes and specifications, as shown in the following figure:
Under the concept of intelligent logistics, this type of compound AGV equipment is designed, which not only includes traditional AGV At the same time, the robot and end tool structure with multiple functions, sorting, handling and other complex functions are added, the production efficiency is improved, the degree of intelligence is improved, and the intelligent upgrading and transformation of automatic logistics is realized.
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