Rack storage – Storage and racking systems – Automatic storage and retrieval systems

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The automated rack storage stacker cranes are designed for the automatic storage and retrieval of parts and items in manufacturing, sales, retail, wholesale and institutions. They emerged in the 1960s and initially focused on heavy pallet loads, but as technology has advanced the loads to be handled have become smaller. The systems are computer controlled and keep an inventory of the stored items. Items are removed by specifying the item type and quantity to be removed. The computer determines where in the storage area the item can be removed and plans the removal. It directs the appropriate automated stacker crane to the location where the item is stored and instructs the device to place the item at a location where it is to be picked up. A system of conveyors and/or driverless transport systems is sometimes part of the stacker crane. These move the loads in and out of the storage area and transport them to the production floor or to the loading docks. To store items, the pallet or tray is placed at an input station for the system, inventory information is entered into a computer terminal, and the stacker crane moves the load into the storage area, determines an appropriate location for the item, and stores the load . As items are added to or removed from the shelves, the computer updates its inventory accordingly.

The benefits of a stacker crane include reduced labor to move items in and out of the warehouse, reduced inventory levels, more accurate inventory tracking, and space savings. Items are often stored more densely than in systems where items are moved in and out manually.

Within the warehouse, items may be placed on shelves or hung from bars attached to chains/drives to move up and down. The equipment of a storage and retrieval machine includes a storage and retrieval machine (RBG), which is used for the quick storage and retrieval of material. SRM (storage and retrieval machine) is used to move loads vertically or horizontally, and can also move laterally to place objects in the correct storage location.

The trend towards just-in-time production often requires availability of production resources at the sub-pallet level, and the storage and retrieval system is a much faster way to organize the storage of smaller items next to the production lines.

The Material Handling Institute of America (MHIA), the non-profit trade association for the material handling world, and its members have divided AS/RS into two primary segments:

• Fixed aisle and
• Carousels/lift

Both technologies enable the automatic storage and retrieval of parts and objects, but use different technologies. Each technology has its own advantages and disadvantages. Fixed Aisle Systems are typically larger systems, while Carousels and Vertical Lift Modules are used individually or in groups but in small to medium sized applications.

A fixed aisle stacker crane comes in two main styles:

• single mast or
• two-masted

Most rely on a track and the ceiling guided by guide rails or channels at the top to ensure accurate vertical alignment, but some are also suspended from the ceiling. The “shuttles” that make up the system travel between fixed storage racks to load or retrieve a requested load (ranging from a single book in a library system to a multi-ton pallet of goods in a warehouse system). The entire unit moves horizontally within an aisle, while the shuttles are able to raise to the required height to reach the load and extend and retract to load or unload loads located in multiple positions located deep on the shelf. A semi-automated system can be achieved by using only specialized shuttles within an existing racking system.

Another stacker crane technology is the so-called shuttle technology. With this technology, the horizontal movement is carried out by independent shuttles, each operating on one level of the rack, while a lift at a fixed position in the rack is responsible for the vertical movement. By using two separate machines for these two axes, shuttle technology is able to achieve higher throughput rates than stacker cranes.

Storage and retrieval machines pick up loads at specific stations or deliver them to the rest of the supporting transportation system, where incoming and outgoing loads are precisely positioned for proper handling.

In addition, there are different types of automatic storage and retrieval machines called

• Unit-load stacker crane, mid-load stacker crane
• Mini-load stacker crane, vertical buffer system / modules
• Vertical Lift Module (VLM)
• Vertical carousel, automated circulation rack or paternoster
• Horizontal carousel

be referred to. These systems are used either as stand-alone units or in integrated workstations called pods or systems. These units are typically integrated with various types of pick-to-light systems and use either microprocessor control for basic use or inventory management software.

These systems are ideal for increasing space utilization by up to 90%, productivity by 90%, accuracy to 99.9%+, and throughput up to 750 lines per hour/per operator or more, depending on the configuration of the systems.

With the advent of mass production in industry, the demands on internal material flow and thus on storage technology became ever greater. The demand to be able to store more and more in a small area gave rise to block storage in the 1950s. The block warehouses were served with stacking cranes, which required significantly less space for the aisles and reached heights that were not possible with a forklift or reach truck.

In the 1960s, the first storage and retrieval machines were created, which, in contrast to stacking cranes, were aisle-bound and therefore did not require a portal to drive over the entire hall. This not only increased the storage capacity through increased use of space, but also the performance, as a separate SRM was now available for each aisle. Initially, the RBGs moved like small gantry cranes on the hall ceiling and were guided on the floor. However, they soon switched to transmitting the force not via the shelves or the hall ceiling, but via the hall floor, as this was much easier to control mechanically. The single-lane RBGs on the ground were now able to achieve ever higher performance.

While the RBGs were previously operated manually by a driver, the development of information technology in the 1980s made it possible to largely automate the storage and retrieval machines.

This led to strong growth in the industry from the 1990s. In the following years, the development of software (LSR (warehouse control computer) and LVR (warehouse management computer), see high-bay warehouse) became increasingly important. Mechanically, the RBGs were challenged by ever-increasing performance, but the basic concept remained the same to this day.

The stacker crane is not a combination of an industrial truck and a hoist, but because of the guidance at the top and bottom, it is a typical hoist, which moves itself in the direction of travel (X-axis) and the lifting carriage in the lifting direction (Y-axis). The stacker crane never operates alone, but always in combination with a so-called load handling device, which manipulates the load directly or the so-called loading aids, which act as carriers of the load (in the Z direction).

As a rule, a stacker crane is installed for each rack aisle. Changing the shelf aisle would require a significantly more complex construction and would significantly increase the access times to a shelf compartment; nevertheless they are manufactured (usually referred to as 'curved' RBG). If storage and retrieval are separated by side, pairs of storage and retrieval machines are also useful for each rack aisle. The choice of solutions is determined not only by the desired operating time, but also by payloads, building heights, storage strategies, etc.

landing gear

The single-track chassis connects the two wheels to the mast or frame. The wheels are guided on rails and are rotatably mounted on curved RBGs. Depending on the rail type (hot-rolled profiles such as U-profiles, I-profiles and railway rails) and wheel load, steel, plastic or Vulkollan wheels (steel hub with cast-on elastomer tread) are used in single or double wheel arches. Depending on the power requirement, one or both wheels are powered.

mast

The mast (column) connects the chassis with the head beam. Depending on the application, one-mast or two-mast versions (frame devices) are possible. The lifting carriage is guided along the mast. The mast also contains other components such as the hoist with the cable or chain drive, the main control cabinet, platforms and ladders with personal protective equipment (PPE), power supply to the main control cabinet and to the lifting carriage via conductor lines or cable chains.

lifting carriage

The lifting carriage primarily carries the load to be transported and is equipped with devices for picking up and delivering the load, the so-called load-carrying device.

With automatic RBG there is usually an emergency control position on the lifting carriage (for troubleshooting). Manual SRMs often have a cabin with more or less extensive equipment (PPE, seat, shelves, PC, scanner, fire extinguisher, etc.). Another important issue here is the design of the escape route.

The lifting movement takes place via a cable, belt or chain drive. To ensure that the lifting movement is automatically switched off in the event of a mechanical blockage of the lifting carriage, safety switches are installed in the suspensions to detect slack rope or overload. There are devices on the lifting carriage to prevent falls if the rope or chain breaks. This safety gear is particularly important if people can ride with the RBG.

head crossbar

The head traverse contains the upper chassis and, if necessary, connects the two masts. The upper chassis consists of guide rollers that are guided in a rail on the rack yoke (upper connecting structure of the rack rows). For single-mast machines that do not have curves, the head crossbar can even be omitted.

The head crosshead is particularly important when there are several curved RBGs in a rail system. In this case, a collision must be prevented. The anti-impact devices are built into the head crossbar, which also serves as a buffer.

Drive and power requirements

The travel and lifting drives are now predominantly speed-controlled electric motors, with driving performance becoming ever higher in order to reduce access times and increase system performance. Hydraulic drives are hardly used anymore because of the high risk of contamination, especially for the goods.

Manual control

With manual control, all movement axes are controlled by the operator using a joystick or button. With this type of control, logical and electrical interlocks must prevent all movements from being possible at any time during normal operation. Due to the constantly increasing level of automation, manually operated SRMs no longer play a significant role today. However, man-operated devices are still used, especially for picking work.

Semi-automatic control

With this type of control, certain movement sequences are automated. It is very helpful, for example: B. the so-called fork cycle, in which the operator approaches the relevant compartment and starts the following cycle by pressing a button:

Extend telescopic fork → raise telescopic fork → retract telescopic fork

Automatic control

With automatic control, all movements of the RBG are controlled and monitored autonomously on the storage and retrieval machine. The movement is coordinated by the order data from the warehouse management system. The data transmission between the functional units can e.g. B. via cable, light paths (infrared) or via radio.

Manual movement of each RBG is possible via an emergency control station that can be used to override the connection to the warehouse management system.

The costs for an SRB depend heavily on the level of automation, dimensions, number of units and performance data. A smaller automatic RBG is in the range of 100,000 euros, for an RBG like the example above the investment is in the range of 300,000 euros.

An effective automated storage and retrieval system offers several benefits to supply chain management:

• An efficient storage and retrieval system helps companies reduce costs by minimizing the amount of unnecessary parts and products in the warehouse and improving the organization of warehouse contents. Automated processes also create more storage space through high-density storage, narrower aisles, etc.
• Automation reduces labor costs while reducing staffing requirements and increasing safety.
• Modeling and managing the logical representation of physical storage facilities (e.g. shelves, etc.). If e.g. For example, if certain products are often sold together or are more popular than others, these products can be grouped or placed near the delivery area to speed up the process of picking, packing and shipping to customers.
• Enabling seamless connection with order processing and logistics management to pick, pack and ship products from the factory.
• Tracking where products are stored, which suppliers they come from and how long they are stored. By analyzing such data, companies can control inventory levels and maximize the use of warehouse space. In addition, companies are better prepared for market demand and supply, especially in special circumstances such as: B. a peak season in a particular month. Through the reports generated by an AS/RS system, companies are also able to collect important data that can be inserted into a model and analyzed.

A horizontal carousel is a series of bins that rotate on an oval track. Each container has compartments that are adjustable and can be configured for a variety of standard and specialty applications. The operator simply enters the container number, part number or cell location and the carousel rotates along the shortest path. Multiple horizontal carousels integrated with pick-to-light technology and warehouse management software (a carousel pod) are used for order fulfillment.

The quantity of orders is sent to the pod. A group of orders is selected to create a batch. The operator simply follows the lights and selects the carousels and places the items into a batch station behind them. Each carousel is pre-positioned and rotates during removal. By applying the product-to-person principle, the operator does not have to move from his position to prepare the job.

When the batch is complete, a new batch is fed and the process repeats. Horizontal carousels can save up to 75% of floor space, increase productivity by 2/3, achieve 99.9%+ accuracy, and achieve throughput of up to 750 lines per hour per operator.

Horizontal carousel systems generally outperform robotic systems for a fraction of the cost. Horizontal carousels are the most cost-effective stacker crane available.

Robotic in/out transfer devices can also be used for horizontal carousels. The robotic device is positioned at the front or back of up to three horizontal carousels at floor level. The robot grabs the container needed in the order and often refills at the same time to speed up throughput. The container or containers are then transferred to a conveyor belt that directs them to a work station for picking or refilling. Up to eight transactions can be carried out per minute per unit. Containers up to 36″ x 36″ x 36″ can be used in one system.

To put it simply, horizontal carousels are often used as “revolving shelves”. With a simple “Get” command, items are brought to the operator, eliminating otherwise wasted space.

AS/RS Applications: Most applications of stacker crane technology are associated with warehousing and distribution operations. A storage and retrieval machine can also be used to store raw materials and unfinished products in production.

Three areas of application for stacker cranes can be distinguished:

• General cargo storage and handling,
• picking and
• Storage of goods in progress.

General cargo storage and storage and retrieval machines are represented by storage and retrieval machines and storage and retrieval machines with deep aisles. These types of applications are commonly found in finished goods warehousing in a distribution center, rarely in manufacturing. Underground systems are used in the food industry. As described above, picking involves removing materials in less than the full package quantity. Miniload, man-on-board and item retrieval systems are used for this second area of ​​application.

A newer application of automated warehouse technology is the work-in-process warehouse. Although it is desirable to minimize the amount of work in progress, WIP (Work in Process) is unavoidable and must be managed effectively. Automated storage systems, either automatic storage and retrieval systems or carousel systems, provide an efficient way to store materials between processing steps, especially in batch and job shop production. In large-scale production, goods in progress are often transported between work steps using conveyor systems that perform both storage and transport functions.

Work in process / goods in progress – inventory in circulation

In business administration, circulating inventory refers to the amount of inventory that is tied up by released orders in the individual stages of ongoing production. This includes materials that are in progress as well as those lying in queues or buffers. As a takeover of the English term “work in process”, the term “ware-in-work” is also increasingly becoming established in German.

An essential task of production planning and control (PPS) is to keep circulating stocks as low as possible. They tie up liquidity, capital and space, often cause additional transport and, unless they are being processed immediately, are generally considered waste (Muda). Due to the relationship between circulating inventory and lead time (Little's Law), circulating inventory also limits flexibility.

The counterpart to current inventories is current assets.

VLMs can be built quite tall to accommodate the available space in a facility. Multiple units can be placed in “gondolas,” where an operator can remove items from one unit while the other units move. Variants include width, height, load, speed and a control system.

The VLM is a board-controlled, automatic vertical lift module. Inventory within the VLM is stored on front and rear tray spaces or rails. When a tray is requested, either by entering a tray number into the built-in directional pad or by requesting a part through the software, an extractor travels vertically between the two tray columns and pulls the requested tray out of position and brings it to an access point. The operator then picks or replenishes inventory and the tray is returned to its location after confirmation.

VLM systems are sold in numerous configurations that can be used in various industries, logistics and office environments. The VLM systems can be adjusted to take full advantage of the height of the facility, even across multiple floors. With the ability to create multiple access openings on different floors, the VLM system can provide an innovative solution for storage and retrieval. The quick movement of the picking device as well as the inventory management software can dramatically increase the efficiency of the picking process. This is done by simultaneously removing and storing trays in several units. Unlike large stacker cranes that require a complete overhaul of the warehouse or production line, the vertical lift modules are modular and can be easily integrated into the existing system or introduced gradually in different phases.

Some of the most common applications include: MRO (Maintenance, Repair and Operations), order picking, consolidation, kitting, parts handling, buffering, inventory storage, WIP, buffer storage and many more.

VLMs offer space savings, increased labor productivity and picking accuracy, improved worker ergonomics and controlled processes.

Most VLMs offer dynamic space storage where the tray is measured each time it is returned to the device to optimize space, safety features include a tilting tray tray for better ergonomic accessibility, and laser pointers that indicate the exact item that is should be removed from each compartment.

Kitting

During kitting, all of the materials for a product are collected in advance, bundled into a set and prepared for the assembly line to be assembled from there.

Vertical Lift Storage Modules (VLSM)

These are also known as vertical-lift automatic storage/retrieval systems. All of the following stacker crane types are built around a horizontal aisle. The same principle of the central aisle is used to access the loads, with the difference that the aisle is vertical. Vertical lift storage modules, some with heights of 10 meters or more, are capable of accommodating large inventories while saving valuable factory floor space.

General cargo stacker

The general cargo stacker is typically a large automated system designed to handle general cargo stored on pallets or in other standard containers. The system is computer controlled and the stacker cranes are automated and designed to handle the general cargo containers.

RBG gantry robot

This is a type of automated stacker crane used in warehousing and logistics. They are often used in the tire industry to stack tire inventories. Most of these systems have a width of 50-60 feet and an average length of 200-300 feet. These systems use end effectors, also known as “end of arm tooling,” to pick and place the tire stacks of conveyor belts.

Man-on-board systems

A man-on-board system can provide significant space savings compared to manual or forklift operations, but is not a true stacker crane as the process is still manual. The height of the storage system is not limited by the picker's reach height, as the picker rides on the platform while being moved vertically or horizontally to the various storage locations. The shelves or storage cabinets can be stacked as high as floor loading, weight capacity, throughput requirements and/or ceiling heights allow. Man-board stacker cranes are by far the most expensive variant of order picking devices, but cheaper than a fully automatic system. Aisle stacker cranes that reach heights of up to 12 meters cost approximately $125,000. Therefore, there must be sufficient storage density and/or productivity improvement over cart and bin picking to justify the investment. Because vertical movement is slow compared to horizontal movement, typical picking rates for onboard picking are between 40 and 250 lines per person-hour. The range is wide because there is a wide variety of operating schemes for man-aboard systems. Man-board systems are typically suitable for slow-moving items where space is relatively expensive.

High rack warehouse (HLR)

More about it here:

• High-bay warehouse (HBW)

Automatic small parts warehouse (AKL)

More about it here:

• Automatic small parts warehouse (AKL) – Automatic mini-load system – Vertical Buffer System / Modules

Suitable for:

• Buffer storage: For e-commerce, retail and manufacturing industries