Vertical Lift Module

What is a Vertical Lift Module

A vertical lift module is an enclosed automated storage cabinet built around three functional groups: two stationary columns of horizontal trays facing each other, a central inserter-extractor (the "lift" or "elevator") that travels vertically in the gap between the columns, and one or more access openings at operator height where requested trays are presented. When a worker calls a part, the controller commands the extractor to travel to the stored tray, pull it from its column, carry it to the access opening, and lock it level with the picking window. After picking or replenishment, the tray returns to a column slot. Because the operator never walks the aisle, a VLM is classed as a goods-to-person system, in contrast to person-to-goods shelving where the worker travels to fixed locations.

The defining engineering advantage is vertical density. A VLM exploits the full clear height of a building, commonly 7 m to 10 m and up to about 30 m on the tallest machines, whereas static shelving rarely uses more than the 2 m a person can reach without a ladder. By stacking trays in fine increments and presenting any tray in seconds, the machine compresses the floor area required to store a given volume of goods by up to roughly 85 percent according to manufacturer figures, with typical real-world recovery of 60 to 70 percent of the original shelving floor area depending on SKU mix and ceiling height.

VLMs belong to the broader automated storage and retrieval systems (AS/RS) family, which also includes vertical carousels, horizontal carousels, unit-load and mini-load stacker cranes, and shuttle systems. Within that family the VLM occupies the small-to-medium-load, mixed-height, slow-to-medium-velocity niche: hand tools, electronic components, spare parts, surgical instruments, jewelry, e-commerce fulfillment items, and document archives. The technology matured in Europe during the 1980s and 1990s and is now supplied worldwide by Kardex (Shuttle), Modula (Lift), Hanel (Lean-Lift), SSI Schaefer (Logimat), Ferretto (Vertimag), and several regional builders.

Beyond density, the second value driver is ergonomics and accuracy. Trays arrive in the golden zone, an ergonomic picking band roughly 37 to 40 inches (0.95 m to 1.0 m) above the floor, eliminating bending, climbing, and overhead reaching, which reduces strain injuries and supports an aging or mixed-ability workforce. Paired with barcode scanning or pick-to-light, VLM operations report inventory and pick accuracy of 99.9 percent or better and picking productivity two to three times faster than manual shelving, with operator travel cut by roughly 80 percent. Security is inherent: the cabinet is fully enclosed with controlled, badge-based access, so high-value or controlled goods are protected without separate cages.

It is worth being precise about where a VLM sits among automated storage and retrieval systems, because the catalog terms overlap. A VLM and a vertical carousel both present goods at one window, but the carousel rotates every carrier to reach one bin and forces a single fixed pitch, while the VLM moves only the requested tray and packs mixed heights. A mini-load stacker crane stores totes in a racking aisle and outperforms a VLM on raw throughput and capacity, but needs aisle length, taller building envelope, and a larger capital outlay; it is the right answer above a few thousand totes and high line rates, where a VLM bay would become the bottleneck. The VLM is the efficient middle ground for a few hundred to a few thousand small-to-medium SKUs of varied height.

The four engineering metrics that determine whether a VLM fits an application are tray payload class, machine height (and therefore stored volume), tray presentation throughput, and environmental rating. These four, together with serviceability, set the total cost of ownership across a 15-to-20-year asset life. The chapters below take each in turn.

VLM Types and Classification

VLMs are classified along three practical axes that buyers actually specify: delivery configuration (single versus dual), payload class (standard versus heavy or oversized), and environment (ambient, cold store, cleanroom, or hazardous area). It is also useful to place the VLM against its nearest goods-to-person alternatives, because a wrong choice between a VLM and a vertical carousel or stacker crane is the most expensive selection error in this category. The table below compares the VLM with the two systems most often confused with it.

Delivery configuration is the first split. A single-delivery VLM has one extractor and one active bay: the lift fetches a tray, the operator picks, the lift returns it, then fetches the next. Wait time between trays caps throughput at roughly 50 to 100 tray presentations per hour. A dual-delivery or twin-extractor VLM stages the next tray behind the access opening while the operator works the current one, so presentation is near-continuous and throughput rises to about 130 trays per hour, with some twin designs exceeding 100 presentations per hour at far higher line rates. Dual delivery costs more and is justified only when picking demand approaches the single-bay ceiling.

Payload class is the second split. Standard VLMs handle tray net loads from roughly 250 kg to 700 kg and cover the great majority of MRO, spare-part, and small-item applications. Heavy and oversized variants such as the Kardex Shuttle 1000 (up to 1,000 kg per tray) or Modula Lift 990 kg class, and dedicated wide-tray or reinforced models, serve dies, molds, fixtures, aerospace panels, and bulky components. Heavy units use stronger extractors, wider trays (up to about 4.1 m), and reinforced frames, and they trade some throughput for capacity.

Environment is the third split. Ambient units are the catalog default. Cold-store builds add low-temperature lubricants, heated cabinets, and condensation control and can run to roughly -30 degrees Celsius for food and pharma cold chains. Cleanroom variants use sealed enclosures and compatible surfaces for ISO-class environments in electronics and life sciences. Hazardous-area units require ATEX or IECEx rated components and are special-engineering orders. Each environment option changes lead time, price, and the maintenance regime, so it must be fixed at the specification stage, not retrofitted.

Mechanism and Drive Technology

Understanding the drive and control chain explains where speed, accuracy, and reliability come from. The VLM mechanism breaks into four subsystems: the extractor carriage and its vertical drive, the tray transfer (insert and extract) mechanism, the height-sensing and dynamic-allocation logic, and the safety and control electronics. The table below summarizes the four subsystems and the engineering metric each controls.

Vertical drive. The extractor is hoisted by a toothed belt or chain driven through a gearbox by an AC motor with a variable-frequency drive (VFD). Soft-start control with a frequency converter ramps acceleration so loose loads do not shift; on the Hanel Lean-Lift the loaded extractor travels vertically at about 1 m/s. Closed-loop position feedback (encoder or absolute measuring system) lets the controller stop any tray repeatably level with the access window within a few millimetres, which is what guarantees the tray edge lands in the ergonomic golden zone every cycle.

Tray transfer. At the target slot the extractor extends a fork or roller bed under the tray, lifts it a few millimetres off its rails, withdraws it onto the carriage, then reverses the motion at the access opening. This horizontal transfer runs slower than the hoist, around 0.5 m/s and jolt-free, because it is the step most likely to disturb a loaded tray. Transfer reliability over millions of cycles is the main mechanical-wear concern and the reason extractor belts, chains, and rollers are scheduled wear parts.

Height sensing and dynamic allocation. The single most important density feature is automatic tray-height measurement. As a tray is loaded, a laser or photoelectric measurement reads the height of its contents; the controller then stores the tray in the smallest slot that fits, packing the columns in fine increments rather than wasting a fixed shelf pitch. Kardex Shuttle uses a 100 mm height grid; Modula Lift stores on a 25 mm pitch. Because trays do not return to a fixed home but to the best available slot, the system continuously re-optimizes density and balances load between the two columns. This is the core reason a VLM out-stores both fixed shelving and a same-pitch carousel.

Safety and control electronics. A PLC coordinates motion, inventory, and the human interface (touchscreen console, barcode, pick-to-light). Functional safety of the access opening, light curtains, and maintenance doors follows ISO 13849-1 and IEC 62061, commonly to performance level PLd / category 3, so the extractor cannot move while a hand is in the bay. Electrical builds follow IEC 60204-1, with UL 508A control panels in North America. Modern units expose data to ERP, WMS, or MES through software such as Modula WMS or White Systems MILO, enabling pick lists, replenishment tasks, and real-time inventory reporting.

Stored Goods, Trays, and Standards

What a VLM stores well, and badly, is decided by tray dimensions, payload distribution, and the standards that govern the steel structure and its anchoring. Trays are flat steel pans, typically 25.75 inches (654 mm) or 33.74 inches (857 mm) deep on Modula Lift, in widths from 59 to 161 inches (1,500 mm to 4,100 mm). Dividers, bins, and partitions subdivide a tray into compartments, so one tray can carry dozens of distinct SKUs. The right fit is small-to-medium parts of mixed height that move at slow-to-medium velocity; the wrong fit is very high-velocity uniform fast movers (a carousel or pick-to-light shelf beats a VLM there) or single items heavier than the tray class.

Tray payload distribution. A tray rating assumes the load is spread, not point-loaded at one corner; concentrated loads can exceed local deflection limits even below the nominal tray weight. For heavy, dense goods such as dies or castings, confirm both the per-tray net payload and the maximum point load with the manufacturer, and verify that the total of all loaded trays stays under the machine gross capacity (Modula Lift quotes a gross total payload of roughly 35,000 to 90,000 kg). A tall unit can reach its structural ceiling before every tray is full of heavy parts.

Structural and seismic standards. A loaded VLM is a tall steel storage structure and must be designed and anchored accordingly. In North America the reference is ANSI MH16.1, the Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks, whose AS/RS provisions use current USGS seismic Ss and S1 values; the Rack Manufacturers Institute (RMI) maintains it. In Europe, EN 528 covers the safety of rail-dependent storage and retrieval equipment and the FEM 9.xxx series covers S/R machine design, both under the Machinery Directive 2006/42/EC with CE marking. Seismic design category must be confirmed against the local building code for the install site.

The table below maps common stored-goods profiles to the VLM attributes that matter for each, as an initial screening aid. Before engineering, always confirm tray payload, point load, and any environmental rating against the manufacturer datasheet.

Key Specification Parameters

Reading a VLM datasheet means separating the few parameters that drive selection from the many that are derived. Eight parameters truly matter: tray net payload, machine gross payload, machine height, tray width and depth, storage pitch (height grid), throughput, positioning and access height, and environmental rating. The comparison table below shows representative published values for three mainstream platforms; treat these as catalog ranges, not a single configuration, and confirm against the live datasheet before purchase.

Tray net payload and machine gross payload are two independent limits. Per-tray net payload is the weight one tray may carry, evenly distributed: 560, 725, and 1,000 kg classes on Kardex Shuttle; 250, 500, 750, and 990 kg net on Modula Lift. Machine gross payload is the total all loaded trays may impose on the structure and drive, roughly 35,000 to 90,000 kg on Modula Lift depending on height. Specify the tray class from your heaviest single tray, then check that the sum of all trays stays under the gross limit.

Machine height and tray dimensions together set stored volume. Heights run from about 2.5 m to 30 m (Kardex Shuttle), with Modula Lift in 200 mm height increments from 3.3 m to 20 m. Tray width spans roughly 1.5 m to 4.4 m and depth 654 mm or 857 mm on Modula. Wider and deeper trays store more per presentation but slow the transfer slightly and raise frame cost. Match height to the clear building height minus required service clearance.

Storage pitch (height grid) is the increment in which the machine packs trays vertically: 100 mm on Kardex Shuttle, 25 mm on Modula Lift. Combined with automatic height sensing, a finer pitch packs mixed-height goods more densely, which is the largest single lever on stored volume after machine height. Throughput is quoted as tray presentations per hour: up to about 130 on a dual-delivery Modula Lift, lower on single delivery. Convert to your real metric (order lines per hour) using your average SKUs per tray and picks per presentation.

A practical reading discipline helps: vendors quote best-case figures (maximum height, maximum tray width, peak throughput) that rarely coexist in one configuration. A unit at full 30 m height does not also hit peak presentation rate, because the extractor spends more time travelling; the widest 4.1 m tray slows the horizontal transfer; and the maximum gross machine payload assumes a height and column layout that may not match your tray class. When you compare two quotations, normalize them to the same configuration (same height, tray class, width, and delivery mode) before trusting any single headline number, and request the throughput figure at your actual average travel distance rather than the catalog maximum.

Positioning, access height, and environmental rating close the list. The access opening presents trays in the golden zone, about 0.95 m to 1.0 m above the floor, with repeatable positioning to a few millimetres. Environmental rating covers temperature range (ambient, cold store to -30 C), cleanroom class, and any hazardous-area certification. Control-cabinet ingress protection and seismic anchoring belong here too, because they are routinely under-specified and expensive to add later.

Selection Decision Factors

To convert the preceding five chapters into a model choice, follow the decision sequence below. Most selection mistakes are not single wrong numbers but decisions taken at the wrong level, for example fixing a tray width before profiling the SKU height histogram. These eight steps double as a fixed RFQ template.

1. Profile the inventory first: count SKUs, measure their height histogram, footprint, weight, and pick velocity (lines per day). The height distribution drives the storage-pitch benefit; velocity decides whether a VLM, a carousel, or pick-to-light shelving wins.
2. Set the throughput target: required order lines per hour at peak. Below the single-bay ceiling, choose single delivery; near or above it, choose dual delivery or a pod of multiple VLMs served by one operator with batch picking software.
3. Fix the height envelope: available clear building height minus service clearance and any sprinkler or seismic allowance sets the machine height, and therefore stored volume. Confirm floor loading can carry a fully loaded unit.
4. Choose tray class and dimensions: tray net payload from your heaviest single tray load, tray width and depth from part footprint. Verify point-load capacity for dense items and that total trays stay under machine gross payload.
5. Specify the environment: ambient, cold store (to -30 C), cleanroom (ISO class), or hazardous area (ATEX / IECEx). Fix control-cabinet ingress protection. These options must be set now, not retrofitted.
6. Confirm standards and seismic: ANSI MH16.1 (North America) or EN 528 and FEM 9.xxx with the Machinery Directive 2006/42/EC (Europe), functional safety to ISO 13849-1 / IEC 62061, and seismic design category against the local building code.
7. Plan software and integration: standalone touchscreen console, or full ERP / WMS / MES integration via the maker software (for example Modula WMS, White Systems MILO). Specify barcode, RFID, or badge access and whether pick-to-light is needed at the bay.
8. Model total cost of ownership: capital (roughly 60,000 to 250,000 US dollars per unit) plus install, two preventive-maintenance visits per year, wear parts, software support, and the value of labour and floor space recovered. Reported ROI is 12 to 18 months; confirm with your own labour rate and rent.

One last and commonly overlooked dimension is manufacturer serviceability: local spare-part stock, remote diagnostics, response time of the service network, and long-term PLC and software support. A VLM is a 15-to-20-year asset whose unplanned downtime can stall an entire picking line, and manufacturers report uptime above 99.5 percent only on properly maintained fleets. Kardex, Modula, Hanel, SSI Schaefer, and Ferretto all operate regional service and spare-part networks, which makes them safer choices for installations where the unit sits on the critical path of daily fulfillment.