pallet conveying system
How to Configure the Pallet Conveying System in An Automated Warehouse?
The pallet conveying system is an indispensable component of the automated warehouse. The traditional pallet conveying system is mainly composed of roller conveyors, chain conveyors, rotary tables, lifting and transplanting machines and other equipment. This article will refer to the system composed of these equipment as the “traditional pallet conveying system”.
In addition, the pallet conveying systems that are widely used at present also include self-propelled trolley suspension conveying systems and automatic guided vehicle systems.
Usually, when designing a high-bay warehouse, the storage capacity of the aisle stacker is used as the key technical indicator of the high-bay warehouse. The pallet conveying system, an important link in the warehousing and warehousing process, must also be given high attention during design. Because when designing an automated warehousing system, the transportation capacity and storage capacity of each link must be comprehensively studied. Otherwise, it will cause an unbalanced logistics bottleneck and affect the system’s capabilities.
Limitations of traditional pallet conveyor systems
Traditional pallet conveyor systems are usually used for straight-line transportation of goods. If the direction of goods transportation needs to be changed, a lifting and transfer unit is required.
The lifting and transporting unit, under the joint action of the roller conveyor, chain conveyor and lifting mechanism, realizes the longitudinal and transverse reciprocating transportation and right-angle transfer of goods. After turning, the operation of the goods changes to the longitudinal and transverse mode of transmission.
Since the lifting and transporting unit requires multiple steps to realize its function, the processing capacity of the lifting and transporting unit limits the processing capacity of the entire traditional pallet conveying system.
According to experience, the processing capacity of a lifting and transplanting unit is about 180~200 pallets/h. For an automated warehouse with an inbound/outbound capacity of more than 200 pallets/h, the use of a traditional pallet conveying system is obviously a big challenge.
Perhaps, we can split a single (inbound/outbound) conveyor system into multiple independent ring conveyor systems, and the processing capacity of each ring conveyor system is about 180~200 pallets/h. According to this design, the inbound/outbound capacity is greatly improved.
However, each ring conveyor system only corresponds to a few fixed lanes, which brings many disadvantages to the entire automated warehouse.
For example, finished goods of various types can only be stored in the shelves of several specific aisles according to the set routes when entering the warehouse, resulting in an imbalance in the storage efficiency and utilization rate of storage equipment in the entire warehouse.
The in-and-out volume of goods is pre-set at the beginning of engineering design, but the fact is that the output (in-and-out volume) and out-and-out volume of each type of goods are constantly changing according to market conditions.
From the perspective of equipment redundancy, the principle of automated warehouse design should be to store each type of goods in each aisle as much as possible.
On the contrary, if a certain type of goods is stored in a specific aisle or area, if the corresponding storage equipment such as stackers fails, the in and out processing capacity of such goods will be more severely affected.
Similarly, if a certain type of goods has a peak in outbound or inbound traffic, the processing capacity is also limited because all storage equipment cannot be fully utilized to handle such goods at the same time.
As another form of transfer equipment, the turntable is different from the jacking and transfer unit in that the turntable uses a slewing mechanism to rotate the roller conveyor 90° forward and reverse, thereby changing the direction of cargo transportation, but the vertical and horizontal transmission of the cargo after the turn does not change.
However, its processing capacity is similar to or lower than that of the jacking and transfer mechanism. Therefore, the use of the turntable does not improve the limitations of the entire traditional pallet conveying system.
Advantages of self-propelled trolley suspension conveying system
The self-propelled trolley suspension conveying system is mainly represented by the electric rail trolley suspension conveying system, and typical products include monorail suspension conveying system, multi-rail heavy-duty suspension conveying system, etc.
The monorail suspension conveying system is an intelligent conveying equipment system suitable for flexible automated production. It is characterized by the optimal realization of linear aerial transportation of materials from a technical and economic point of view. Since all components such as straight rails, curved rails, turnouts, steering wheels, lifting platforms, etc. can be arbitrarily combined together, the track direction can be flexibly arranged according to the requirements of the building to meet the special requirements of products and jobs in production and processing.
The monorail suspension conveyor system is mainly composed of suspended running tracks, power supply system, cargo trolley, turnout and electrical control system. The system adopts modular design, and each trolley has independent drive and data communication functions, which is convenient for flexible expansion.
Since the running track is suspended, the equipment’s demand for ground space is reduced, and floor cleaning becomes very convenient. This gives it a huge advantage in the food, medicine and other industries.
In the monorail suspension conveyor system, the load trolley can be designed to transport one or two pallets of goods at a time as needed. Combined with factors such as the specific running track length and the trolley running speed, the processing capacity of a monorail suspension conveyor system conveying loop can reach 400~800 pallets/h.
The running speed of the load trolley can usually reach 1.5~2.0m/s, which is a significant improvement compared to the roller (chain) conveying equipment of 0.2~0.35m/s. Therefore, the monorail suspension conveyor system is usually used in systems that require long-distance transportation or high outbound and inbound capacity requirements.
Therefore, finished goods of different varieties can be evenly distributed throughout the stereoscopic warehouse, effectively improving the utilization rate of storage space and storage equipment.
Similarly, for the outbound end, if the market needs it, all stackers can handle the same kind of goods at the same time, which greatly enhances the flexibility of the system in handling different varieties of goods or dispatching plans.
When individual storage equipment fails, the impact on the entire storage system will be minimal. In addition, the advantage of the monorail suspension conveyor system is that the number of trolleys in the system can be appropriately increased to improve the processing capacity of the entire system. This is also not available in traditional pallet conveyor systems.
It is worth noting that the performance of the monorail suspension conveyor system is affected by many factors, such as the number of trolleys, running speed, acceleration, number of turnouts, number of input/output points, and control strategy.
In areas with many input/output points, it is particularly easy to cause congestion of the cargo trolleys. The system performance bottleneck caused by congestion cannot be improved simply by increasing the number of cargo trolleys.
Therefore, when designing a monorail suspension conveyor system, especially when there are many cargo trolleys and input/output points in the loop, it is very necessary to establish a model for the entire system for dynamic simulation, and continuously study and optimize the design.
Relatively speaking, the traditional pallet conveyor system is relatively mature and easy in terms of processing capacity calculation.
In addition, since the pallet enters the loading trolley, the relative position of the pallet and the loading trolley remains stationary. Compared with traditional pallet conveying equipment, the monorail suspended conveying system also has greater advantages in reducing pallet loss.
Similar to the monorail suspended conveyor system, the circular shuttle system does not have significant advantages in saving floor space. The entire system is similar to the monorail suspended conveyor system in terms of flexibility, scalability, and redundancy.
The circular shuttle can run at a speed of up to 3.0m/s and is usually used in pallet conveying systems for short-distance transportation.
Automatic Guided Vehicle System
Automated Guided Vehicle (AGV) is equipped with electromagnetic or optical automatic guidance devices. When working, the AGV car travels along the specified guidance route without the need for a driver.
AGV car uses rechargeable batteries as a power source, and its route and operation are usually controlled by a computer. In an automated warehouse with high storage and warehousing performance requirements, the function of the AGV car is similar to that of a self-propelled car suspension conveying system. Each AGV car can be regarded as a cargo car in an EMS.
The difference is that the AGV does not need a suspended running track, and relies on its automatic guidance device and anti-collision device, so it does not need corresponding maintenance structures to ensure the safety of personnel in the operating area, reducing the equipment footprint.
In terms of running speed, the AGV is generally between traditional pallet conveying equipment and suspended self-propelled trolleys, about 1~1.5m/s.
Although the AGV is slightly inferior in terms of engineering investment, its huge advantages in system flexibility and scalability make the AGV still widely used.
Generally, the type of conveying device used in an automated warehouse depends on the type of goods, shipping conditions, warehouse structure, etc.
For automated warehouses with high requirements for inbound and outbound performance, inbound and outbound capacity is a very important design consideration when choosing the type of conveying system.
Although the capacity of traditional pallet conveying systems can be confirmed through optimized layout and quantitative calculation. However, we should also qualitatively analyze whether the design of the entire system is reasonable through aspects such as system flexibility, scalability, and redundancy.
