How to Select a Vertical Storage and Retrieval System

January 16, 2010
Remstar International
Feature

Summary

By Ed Romaine, KardexRemstarMaterial handling in a typical machining or manufacturing operation can account for a large percentage of production time, and the movement and storage of tooling and dies can represent a significant portion of the cost of production.A solution to more efficient storing, handling and retrieval of materials is the installation of a vertical storage and retrieval system as an alternative to conventional drawer, shelving and rack systems. Vertical systems, when properly planned and integrated into daily operations, can solve many of the problems associated with poor utilization of floor space, throughput restrictions, centralized stockrooms, information and inventory management, lean manufacturing and quick response/JIT disciplines. In the process, they can significantly reduce operating costs.Vertical storage and retrieval systems consist of two primary devices. One is called a vertical carousel that uses rotating carriers, or shelves, that move on a track (like a Ferris wheel) in response to operator commands. The other vertical device is a VLM (Vertical Lift Module). VLMs consist of a series of trays that are mounted on both sides of an inserter/extractor device. With both the vertical carousel and VLM, items are automatically delivered to the operator at an ergonomically positioned work counter, eliminating walking, searching, bending and stooping. These systems come in a wide range of capacities and configurations and can be used for a number of storage and retrieval requirements. There are vertical systems that can easily handle tools, dies and pallets with each carrier able to accommodate up to 11,025 pounds. Some of these units are available with up to 210 shelf levels for a total unit capacity of 2,315,250 pounds. Other vertical storage and retrieval systems are designed specifically to store small tooling and consumable safety items. “Standard” vertical storage and retrieval systems can hold items as large as heavy tooling and sub-assemblies and as small as screws and other fasteners. Defining System Performance RequirementsInstalling a vertical system means first considering a specific set of factors ranging from discrete performance to equipment design code requirements to arrive at the best solution to meet financial and operating objectives.A key consideration is the nature of the load to be stored. Since vertical systems can be equipped with many variations of shelf configurations, load data are used to custom engineer the application to the need. For example, are the products to be stored odd-shaped or standard vendor carton sizes? Are they loose, requiring a container or a tote? With the help of a storage specialist, categorize storage load quantities into groups based on similar length, width and height characteristics. This way, each group can be assigned the best shelf configuration to maximize storage density within the unit. Weight is also a consideration. When defining system requirements, average weight density information is calculated to determine shelf loading requirements.Once information on load configurations has been determined and grouped by size and weight, it can be used to determine optimum shelf vertical spacing, depth and width. In most cases, the maximum load clearance needed above load heights for access need only be between 1/4 inch and 3/4 inch. Therefore, the pitch, which is the point-to-point shelf distance for a given model, can be estimated by adding the load height plus load clearance and hardware level thickness, approximately 1 inch to 1.5 inches in industrial applications. This estimate can then be confirmed against vendor data to determine exact pitch and clear load access distance between levels.Vendor information is also available on clearances for multi-tier shelf configurations when intermediate shelves are needed to accommodate load height variability. Load data are then used to establish desired shelf width, depth and quantity. Various accessories are also available such as wire or solid dividers, component reel inserts, different front lip heights, drawers, and security locks to accommodate special needs.Average weight load data, either in the form of discrete load weight ranges or density factors can now be used to establish carrier load weight configurations.System ThroughputSystem throughput is defined as the rate of transaction per period of time. Calculation of system throughput should include not only the standard “receipt to” and “pick from” inventory usage transactions, but also those associated with returns to stock, cycle counts and “hot” picks. Statistical information such as the average number of orders per day per shift, average number of line items per order, average pieces per line pick, average receipt of line items per day, and average miscellaneous transactions per day are common ways of expressing this performance requirement.The method of inventory movement to and from the vertical system can also affect throughput. Load parameters may necessitate a conveyor interface, or heavy load demands may require a manipulator in front of the unit. Double floor level operations may require dual top and bottom access points on the unit.The quantity of units also affects throughput. Inside building height along with vendor information concerning the number of shelves per given height are used to establish the number of loads per a given vertical unit. A simple division of total loads required to store by loads per unit results in the total quantity needed. Future growth and expansion capacity can be factored into this quantity.Another key consideration when configuring a system is the location of the access. The access opening of an industrial vertical storage and retrieval system is normally configured for either a standing or seated operation. Multiple access locations can also be provided. Access openings located at the top and bottom and front and back are most common. Consideration must also be given to the physical layout of the installation site. The clear height of the building interior will determine the height of the units and the total number of shelves at a given spacing allowed in each unit. In most cases, the top clearance from the unit to the building’s lowest obstruction above the unit can be as little as 8/10ths of an inch. It is possible to estimate space savings in square feet and percentage using general formulas developed by automated storage and retrieval system manufacturers. For example, in a facility with a ceiling height of 40 feet, a vertical storage and retrieval system eliminates up to 100 shelving sections with a resulting space savings of up to 929 square feet, or 91 percent. With a ceiling height of 30 feet, a vertical solution can eliminate 46 drawer-type cabinets for a space savings of 311 square feet, or 80 percent. Individual fire insurer’s requirements regarding ceiling clearance can also be a determining factor in unit height. Some insurers may require at least 18 inches clearance between the top of the unit and sprinkler heads. Requirements vary, so it’s worth a check. Industrial buildings with at least 4-6 inches of reinforced concrete over a solid, compacted base will support most loaded vertical systems.Defining Control RequirementsThe controller, software and computer interface are elements that can be combined in a number of ways to meet overall storage and retrieval objectives.Operator interface with the system is a critical consideration. For functional effectiveness, transaction information must be transmitted between the operator and the control system. A determination must be made concerning what data will be generated by the control system and how it will be displayed to the operator. For example, in a strictly manual system, the operator decides all location transactions and enters, via keypad, the shelf locations. This activity is followed by manual inventory adjustments. In a fully automated environment, all information requests from location selection, container type, inventory adjustment, activity analysis, and data transfers between the control computer and host system are accomplished transparently with no operator intervention.Vertical storage and retrieval systems can be controlled using PC software or hardware controls. The difference is in the graphic interface, or ease of use and the amount of information needed to track and manage materials in a specific application. A system can be configured for stand alone, single user operation or multi-user network use. The controls solution can be as simple as a piece of paper indicating the shelf level of each stored item. The operator simply enters the shelf number using the controls, and the shelf and its contents are delivered automatically.A single PC can control from one to 99 units. In this type of operation, bills of materials (BOM) could be generated on the host system. The BOM is downloaded and sent to the storage and retrieval system control PC. The operator can call up each order, or batch picks multiple orders, depending on the hardware configuration. Pick lights can be installed to direct the operator to the proper pick location for added accuracy. Inventory is tracked by the control software that processes all parts orders, adjusts inventory files based on transactions and monitors inventory re-order levels. Operator logins allow managers to track and monitor usage patterns to reduce shrinkage.A software system can be networked to manage multiple vertical units in high throughput applications. A multi-user system provides independent operation of each unit in the network while information accessed on workstations is shared on a common database and uploaded to a host WMS or ERP system. With a multi-user configuration, operators can process multiple bills of material orders, print status reports or store receipts.Why Vertical Systems?Conventional static storage systems like shelving require employees to spend up to 70 percent of their time traveling aisles searching for items. On average, in typical industrial applications, productivity throughput can increase by more than 2.5 times.One of the primary reasons for considering a vertical system is the improved space utilization they offer. Depending on useable building interior heights, a significant percentage of a conventional storage system’s occupied floor space can be recovered. The small unit footprint makes vertical systems especially valuable for point-of-use storage and JIT manufacturing applications. Recovered floor space can be re-allocated from cost-associated functions of inventory to value-increasing production operations. Improved space utilization can also extend the useful life of existing facilities, eliminating the need for expensive brick and mortar expansion to meet growth requirements.Redundant or non-essential handling can be reduced with vertical systems, especially in applications frequent reuse of tools and dies. The time saved results in less operating cost and usually improved customer service. Labor costs are reduced due to the system’s quick retrieval times and the capability to meet varying throughput requirements while not being bound by thresholds imposed by limited-access systems. Typically, an operator’s walk and search time is reversed from that of conventional systems to 70 percent picking and only 30 percent dwell time.The access area of vertical systems is ergonomically designed to present stored items at an ideal height for picking, usually about waist high. This location of the access area contributes to employee safety since this positioning design eliminates the bending, climbing and stretching associated with conventional shelving and rack systems. Throughput generally improves as well. Since vertical systems are totally enclosed and lockable to protect products from external hazards and reduce product damage and pilfering, inventories can be reduced in many operations. Stock rotation can be improved by utilizing computerized picking controls.Vertical storage and retrieval systems also offer increased picking speed and accuracy using microprocessor controls with position indicators, information displays, PC-based software, and overall system physical design.These systems can also be easily expanded since they are literally modular units. Re-programming of system controls is a simple matter of software configuration updates.Making the Right MoveVertical storage and retrieval systems are an important investment. However, they produce a verifiable positive return if they are properly configured for specific applications. Integrated vertical storage and retrieval systems often have a return on investment (ROI) of less than 18 months. However, as with any major investment, a comparison of the costs of the new system vs. the old system must be considered. For vertical storage and retrieval systems, the operative data are the amount of floor space occupied by current equipment, cost per square foot, the number of employees handling daily transactions, number of transactions performed daily, average labor cost and other information that affects system costs. Sitting down with an installation specialist and putting the numbers into a standard ROI/IRR (Return on Investment/Internal Rate of Return) formula is one way to do this. Another is to log on to the website and use a special ROI/IRR calculator that allows users to enter the appropriate data. It automatically computes the daily cost of the current system and the daily cost of the new system. The calculator also computes dollar savings from reduced space requirements, cost savings from improved employee productivity, depreciation savings, and total annualized savings. From this information, the calculator helps determine the payback schedule for the user’s specific installation.There are a number of important factors to consider when planning the installation of a vertical storage and retrieval system. A properly applied approach to planning and specifying can substantially enhance the benefits these systems offer. After you have determined what your particular storage and retrieval requirements are, using the planning approach outlined in this article, call in an expert to help you specify a system. KardexRemstar Inc., a company of the Kardex AG Group is a leading provider of automated storage and retrieval systems for manufacturing, distribution, warehousing, office and institutions. Learn More

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