Driven by the strategy of "Made in China 2025", AGV (Automated Guided Vehicle) has gradually developed into an indispensable important equipment for modern warehouse automation logistics. The chassis of the "elf storage robot" produced by Shenzhen Yifeng Robot Technology Co., Ltd. is the load-bearing part of the AGV, and the installation position of the AGV and the jacking mechanism must be guaranteed, so it must have sufficient strength and rigidity. Studies have shown that reducing the weight of the car body can significantly reduce the power requirements of the vehicle, and every 10% weight reduction can save 5% to 8% of fuel. This is especially true for warehouse robots that frequently start and stop, reducing the weight of the AGV chassis can reduce the energy consumption required for deceleration and braking. With the same power, the reduced weight of the chassis can effectively increase the payload of the AGV.
In this paper, taking the "elf storage robot" as an example, under the premise of ensuring the strength and rigidity of the chassis structure, the topology optimization method is applied to optimize the design of the chassis structure.
1. The whole vehicle structure of storage robot
The storage robot adopts a two-dimensional code navigation method. The chassis of the whole vehicle adopts a six-wheel structure, in which two universal casters are installed at the front and rear, and driving wheels are installed symmetrically on both sides of the front and rear center of the vehicle body. The two drive assemblies can realize differential drive and steering, so the whole vehicle can realize in-situ steering. The maximum load of the vehicle is 500kg, and the traveling speed is 1.5m/s. Its structure is shown in Figure 1, which is mainly composed of a lifting assembly, a housing, a laser obstacle avoidance sensor, a chassis, a contact type anti-collision strip and two drive assemblies. Among them, the chassis welding structure, as shown in Figure 2.
The total weight of the welding structure of the storage robot chassis is 70.5kg. In order to reduce the energy consumption of the storage robot's no-load operation and increase the effective load of the vehicle, it is necessary to optimize the topology and reduce weight of the chassis welding structure.
2. Finite element analysis of chassis structure
On the premise of not affecting the calculation results, in order to improve the quality of mesh generation and reduce the calculation time, the welding structure of chassis is simplified as follows:
1. Ignore the round hole whose diameter is less than 5mm;
2. Ignore the influence of weld on structure;
3. Ignore the chamfering less than 5mm.
Moreover, the multi zone method is used to grid the chassis welded structure, which is divided into 20559 nodes and 3065 elements. The average value of element distortion is 0.24, the maximum value is 0.8, and more than 97% of them are within 0.5. Therefore, the quality of grid generation of chassis welding structure is better, which ensures the correctness of the solution results. According to the maximum load of the elf storage robot is 500kg, load it, and consider the influence of gravity, according to the actual working conditions, support constraints are carried out in the chassis welding structure. The finite element analysis results of chassis are shown in Fig. 3 and Fig. 4.
It can be seen from Fig. 3 that the maximum deformation occurs at the front end of the chassis, which is about 0.07mm, and the overall deformation of the frame is very small. According to Fig. 4 stress nephogram of chassis welding structure, the maximum stress of chassis welding structure is about 58.9mpa, which is far less than 235mpa of material yield strength.
3、 Optimization analysis of chassis structure of storage robot
1. Topology optimization analysis of chassis welding structure
The chassis of ELF storage robot is the load-bearing part of the whole vehicle, and its structural optimization criterion is to reduce the weight of the chassis as much as possible on the premise of ensuring the strength and stiffness of the chassis structure; at the same time, considering the manufacturability of the chassis structure, it ensures that the production is simple and the cost is low. According to the criteria of chassis optimization design, topology optimization of chassis welding structure is carried out. The main purpose of topology optimization is to find the optimal material distribution in a given design area. Topology optimization is carried out for the chassis welding structure of the elf storage robot, and the optimization results are shown in Fig. 5.
It can be seen from Figure 5 that the red area indicates that this part of material can be removed without affecting the strength and stiffness of the chassis welding structure. Therefore, the welding structure of chassis can be optimized according to the topology optimization results.
2. Improved structure of chassis
According to the topology optimization results of the chassis welding structure of the storage robot, and considering the layout of the electrical components on the chassis, the chassis welding structure is improved, as shown in Fig. 6.
The total weight of the improved chassis welding structure is 56.3kg, which is 14.2kg less than that of 70.5kg before improvement, and the weight loss is about 20%.
3. Simulation analysis of improved structure
According to the improved chassis welding structure, the multi zone method is used to divide 28275 nodes and 3823 elements. The average value of element distortion is 0.27, the maximum value is 0.8, and more than 96% are within 0.5. Therefore, the quality of grid generation of chassis welding structure is better, which ensures the correctness of the solution results. And set the same load and constraint as before, and carry on the finite element simulation. The deformation nephogram and stress nephogram of the improved chassis welding structure are shown in Fig. 7 and Fig. 8 respectively.
According to figure 7, the maximum deformation still occurs at the front end of the chassis, which is about 0.09mm. The overall deformation of the chassis welding structure is very small, which is basically the same as that of the chassis welding structure before improvement, so the stiffness of the chassis welding structure after improvement is basically unchanged. According to Fig. 8 stress nephogram of chassis welding structure after improvement, the maximum stress of chassis welding structure is 64mpa, which is 5.1mpa higher than the original, and the stress slightly increases, but it is still far less than the yield strength of the material. Therefore, the improved chassis welding structure meets the requirements of weight reduction design.
The topology optimization method is applied to optimize the welding structure of the chassis, and according to the optimization results, the design of the chassis welding structure is improved. Compared with the original chassis welding structure, the weight is reduced by about 20% under the condition that the stiffness is basically unchanged and the strength meets the use requirements. The optimization design goal of chassis welding structure is achieved, the performance and safety of AGV are improved, the manufacturing cost is reduced, and the development trend of energy saving and emission reduction is complied with.