Overview
The 4-ways shuttle of pallet is a new logistics technology developed in the past 10 years, and its creativity is based on shuttle board and satellite car, and has now become a widely accepted logistics technology.
Pallet four-way shuttles have many advantages, such as being particularly suitable for retrofitting old warehouses, no matter how high or low the warehouse is, or how strange the shape (plane shapes are tortuous and varied, space height changes, etc.), four-way shuttles can be adapted, so they are very popular. For example, the four-way shuttle has a very good flexibility, which can be adapted to the occasions with a high frequency of entry and exit, and is also suitable for occasions with a very low frequency of entry and exit, which can be said to be the best supplement to the AS RS system. In addition, the four-way shuttle system has a good dense storage capacity, which is much better than the traditional AS RS, and it is especially suitable for scenarios with low warehouse space (generally less than 15 meters, AS RS is not suitable), so it is quite popular in cold chain systems.
Pallet four-way shuttle garage case.
Of course, four-way shuttles aren't flawless. Due to the need to increase the tracks, the cost of the system is relatively high, which cannot be compensated for by its flexibility and adaptability, especially in larger warehouses. In addition, the scheduling of large four-way shuttle garages is more difficult, which raises the technical threshold for many enterprises and further increases the cost of the system.
Four-way shuttle technology offers a new option for the design of logistics and warehousing systems and is the first choice in specific situations, which is what makes sense. This article will preliminarily lead to the construction of a four-way shuttle system, as well as the matters to be paid attention to in the design.
System composition and core technology
A typical four-way shuttle system mainly includes racks, shuttles, hoists, conveyors and software systems, as well as some auxiliary facilities such as maintenance platforms and equipment.
1.shelves
Racking is one of the key equipment of the pallet four-way cart system. On the one hand, unlike traditional beam shelves, the shelves of the four-way car system have a fundamental change in structure with more tracks for shuttles to travel. On the other hand, its requirements for shelf rigidity and accuracy have been greatly improved. Therefore, the processing difficulty and installation difficulty of the shelf are greatly improved. This kind of precision improvement, the shelf production and manufacturing also put forward higher requirements, the traditional rolling mill has been difficult to meet the requirements, automatic punching and rolling technology has become a necessary condition, at present, an imported automatic rolling mill line often exceeds 10 million yuan, is difficult for many shelf enterprises to bear. In addition, due to the large error of the spraying process, it has become a trend to use galvanized sheet material for shelves. At present, only a few enterprises in China have production capacity.
2.Pallet four-way shuttle
Pallet four-way shuttles generally use two sets of wheel trains: one is responsible for the operation in the X direction, and the other is responsible for the operation in the Y direction. In the steering link, the steering is completed by changing the wheel train (height difference), and the pallet itself does not turn (there are also units developing turnable shuttles, but there are no application cases yet, and the prospects are not promising). The shuttle pick-up and unloading are completed by the jacking mechanism. When picking up the goods, the shuttle enters the bottom of the pallet, and the lifting mechanism rises after alignment, and the pallet is jacked up, and the bottom leaves the L-beam of the shelf or the surface of the conveyor chain, and then the shuttle and the pallet can run out of the shelf; In the release link, after the shuttle transports the pallet to the designated cargo position, the lifting mechanism descends after alignment, and the pallet will be placed on the L-beam or conveyor, so that the shuttle has completed a release operation. This is the basic principle of a four-way shuttle.
Pallet four-way shuttle
For pallet four-way shuttles, the reliability of positioning technology and wireless communication technology is its key technology; Battery selection and charging management are also important, and battery technology is even a major factor influencing the development of four-way shuttles; In addition, when multiple shuttles are running simultaneously in an area, the vehicle avoidance technology is a key factor affecting the efficiency of the system. These are important reference indicators for choosing a shuttle.
The control of the shuttle can use PLC or integrated circuit board, which has the best advantages, so it is adopted by more and more enterprises.
3.Hoist
The hoist is located at both ends of the three-dimensional warehouse, and its function is twofold: one is to send the pallet from the storage layer to the destination layer, and the other is to complete the shuttle layer change. In many cases, the shuttle needs to be replaced.
The hoist is important because it is one of the bottlenecks that affect the efficiency of the system. In a relatively large system, it is quite difficult to match the number of hoists and shuttles. This problem is not only related to its own parameters (such as acceleration, velocity, transfer time, etc.), but also related to the process design and strategy of the system. For example, if each operation is a shuttle with a pallet to complete the lifting operation (each shuttle carries goods to change layers), it is very different from the shuttle without layer change. None of these can be answered with simple calculations, and usually a computer is required.
4.Conveyors
Conveyors also play a very important role in the shuttle system, mainly for the transportation of pallets at the inbound and outbound ends. It is closely related to process design, affecting the overall efficiency of the system, and even has a great impact on the cost of the system.
In terms of layout, the design of the conveyor is unpredictable and needs to be carefully considered according to the flow requirements, and many beginners are at a loss for it.
5.Software systems
The software in the pallet four-way shuttle system is mainly WMS and WCS, which are not significantly different from the traditional ASRS, but the difference is about the shuttle scheduling system, which is not available in ASRS.
One of the major problems with four-way shuttle systems is the uneven distribution of tasks, which leads to practical efficiencies that are far from theoretical, which is easy to think of. To solve this problem, we need to start from many aspects. For example, set up inventory ABC distribution strategy, adjust inventory structure in advance, and actively control the address allocation of return pallets. It is particularly important to choose the corresponding strategy for each project according to the specific situation, and avoid wearing a crown and wearing a crown, in order to achieve better results.
6.Ancillary Equipment
In addition to the above, the service platform and maintenance equipment of the four-way shuttle system are also essential, and the location and number of charging units are often a problem for designers. In the large four-way vehicle system, due to the movement of a large number of shuttles in the opposite direction, its resonance with the shelves is also a big problem, and effective measures need to be taken to prevent it.
How to do a good job in system planning and design
To do a good job in the planning and design of a pallet four-way shuttle system, there are many similarities with other three-dimensional warehouse systems, such as data analysis, demand analysis, determine the overall plan, do a good job in process analysis, select appropriate equipment parameters, etc. But there are also some special features: when the four-way shuttle is applied to the old warehouse, how to achieve the smooth operation process in and out of the warehouse is very important. In addition, due to some characteristics of the shuttle itself, such as the pre-warehouse conveying and goods-to-person picking area, the shuttle can be used to complete the pre-warehouse conveying operation, making the entire logistics system design more compact and integrated.
Integrated warehousing and warehousing system.
The design of the four-way shuttle garage should pay special attention to the design of pallets, shelves and floor heights. Generally speaking, in the shuttle garage, the orientation of the pallet is different from that of the ASRS, and many beginners are prone to mistakes. For the shelves, because of the shuttle, it is necessary to add tracks and charging devices, etc., and its design is much more complex than the beam shelves of AS RSHow to design shuttle tracks and shelves has become one of the key contents of the design of four-way shuttle three-dimensional warehouse。An unreasonable design will not only lead to the shelves not meeting the requirements of use (including strength, stiffness, stability, noise, resonance, etc.), but also greatly increase the cost (in general, the cost of four-way shuttle shelves is 2 times or more than that of AS RS beam shelves). The floor height of the shuttle garage is higher than that of the traditional beam shelves (the specific data is related to the structure and load of the shuttle, but also to the products of different brands). This makes it possible to use a four-way shuttle solution with one less layer than an AS RS rack in some cases due to space height limitations, thus affecting the final cost-effectiveness of the system.
Doing a good job in the design of the hoist is another key to the design of the shuttle system。In the design of the shuttle garage, if the pallet on the first floor does not enter the cargo location storage through the hoist, but directly uses the shuttle to complete the warehousing and outbound operations, the operation volume of the hoist will be greatly reduced, thereby reducing the number of hoists, which is a small trick of the shuttle garage design. For example, for a shuttle garage with only 2 floors, the effect of this is that the workload of the hoist will be reduced by more than 50% (considering the distribution of inventory ABC, it may be greater than 50%); For a 3-layer system, it will be reduced by more than 33%; Even for a 10-story shuttle garage, the amount of work can be reduced by more than 10%. Therefore, the design of the hoist tends to become a little more complicated. This is something that should be paid special attention to in the design of the four-way shuttle system.
There is another issue that is easily overlookedRepair issuesThis is the most common mistake most design engineers make, and one that users often don't care about. But for an automated system, the problem of maintenance is a big problem. Maintenance equipment includes maintenance of stairs, platforms and auxiliary tools, such as portable cranes. This is indispensable for the shuttle garage. Sometimes, the repair platform affects the overall system design and of course increases the expense, but these are unavoidable.
Finally, it is important to note that although a four-way shuttle system can be built very high, but:Fire issuesis another difficulty. This is also an important reason why the scale of the four-way shuttle garage currently in use is generally not large and the height is not high. Solving this problem requires more ingenuity and time from designers, as well as developing corresponding standards.
Key evaluation indicators of the system
To evaluate a four-way shuttle system, there are actually many indicators, including the following:
Shuttle garage that connects seamlessly to the ground.
1.The fluency of the job
It mainly includes: vehicle route planning, platform planning, pallet planning, receiving operation area planning, picking operation area planning, three-dimensional warehouse planning (layout, route, hoist layout, import and export layout, picking operation area planning, etc.), delivery operation area planning, etc. An excellent system in which the route of operation is smooth, its layout is reasonable, and its overall indicators are coordinated.
2.Reasonableness of the number of devices and parameters
It mainly refers to whether the number and parameters of hoists and shuttles are reasonable and match each other.
Regarding the number of hoists, it is necessary to carefully calculate the compliance between the operation flow rate and the system requirements, too much and too little are bad designs; In addition, the location and layout of the hoist is the focus of the design, and a good design should reasonably arrange the hoist position. The number of shuttles is generally more than the calculated value, that is, there is a certain redundancy.
3.Value for money
The issue of cost performance is often overlooked, but it is one of the most important parameters for judging the rationality of a system design. Generally speaking, the cost performance should be compared in the same caliber, such as storage capacity, storage capacity, storage and storage capacity, etc., otherwise it will lose meaning. Of course, we often encounter some special projects that can only be solved by four-way shuttles, and the comparison is not very meaningful, but it is still necessary to compare.
4.Stability of the system
As an important evaluation index of the system, stability is also a basic requirement for equipment and system selection. From the perspective of system design, the ability of the system to cope with failures can be improved through some redundant design. In this regard, in addition to hardware equipment, system process design and system software also play a very important role.
5.The flexibility of the system
For four-way shuttle systems, flexibility is usually reflected in the system's ability to cope with peak operations, including the addition of hardware equipment to increase the processing capacity of the system, and how to effectively improve the efficiency of the system when more equipment is used. Sometimes, in order to meet the needs of flexibility, some equipment can be arranged in advance, such as hoists, etc., and sometimes it is required that there should be room for additional equipment in the future.
Factors that affect the effectiveness of the system
There are many factors that affect the operation effect of the four-way shuttle system, which are mainly divided into the following parts:
1.Rationality of the design
System design is the most basic factor in the operation of a logistics center. The design process is divided into many parts, among which the accuracy of the first class, the rationality of the design index, the rationality of the overall scheme, the rationality of the process design, the rationality of the equipment selection, and the rationality of the software selection are more important aspects. Many companies tend to ignore the importance of design because they don't know much about the nature of logistics. As everyone knows, if there is a major problem in the design solution, even the best equipment and software will not work. If we want to make an assessment of the importance of design, it is no exaggeration to say that design plays a fundamental and decisive role in the operation of the system, much more important than both equipment and software.
In actual projects, due to different perspectives on the problem, users tend to attach importance to hardware investment and despise software investment. Some users would rather spend tens of millions of yuan more on civil engineering and equipment investment than spend appropriate money on software and design. This is also the root cause of many system designs that are not reasonable or even fail.
2.Reliability of the system
The reliability of the system is one of the key indicators that affect the operational efficiency of the system. If the equipment and software in one system are unreliable, it can affect overall operational efficiency at least and cause the entire system to be unable to function properly.
The hardware of a four-way shuttle system, whether it is a rack, a shuttle, a hoist, or a conveyor, is required to be reliable enough to meet the design requirements. The reliability of the system can be expressed in terms of the availability of the system [1], and for general occasions, the availability of the logistics system should reach more than 97%; For special occasions, the availability should reach more than 99%.
There are many ways to improve system reliability, mainly in terms of stand-alone devices and software. With higher quality and reliable equipment, the reliability of the system will inevitably increase, but at the cost of higher procurement costs. Finding a balance between reliability and cost is both a design requirement and a challenge for users. In practice, the tendency to over-rely on equipment reliability and neglect system reliability needs to be avoided. The reliability of the system depends not only on the reliability of the equipment, but also on many other factors, such as redundant design, spare parts, etc.
3.Timeliness of maintenance
Any complex automation system, in the process of long-term use, will inevitably have failures and problems, which requires the system to be maintained in a timely and reasonable manner for a long time. On the one hand, the daily maintenance and repair work, especially the fault monitoring work, should be perfected in place; On the other hand, if a system fails, it is important to ensure that it can be repaired quickly. At this time, a professional team and sufficient spare parts are indispensable.
In the design, on the one hand, the key equipment should be redundantly designed, so that it can switch to a new mode of operation in the event of a failure, such as a hoist, a plurality of hoists can be used to back up each other, and there is a certain ability to redundancy, so that any hoist fails, and the system can continue to work, but the efficiency is affected. The same goes for shuttles. For mobile equipment such as shuttles, once there is a failure, there must be equipment that can be quickly replaced, so as not to delay the normal operation of the entire system, in the design, it is particularly necessary to maintain a certain amount of redundancy. Of course, for very small systems, hardware backup is not necessary or difficult to achieve, and it is necessary to seek higher quality equipment and systems.
References: 1] Yin Junqi, "Modern Logistics System Integration-Methods, Practice and Speculation", China Fortune Press, October 2020.
Editing and typesetting: Rodin.
This article is from:Logistics Technology and Application, Issue 10, 2023
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