Wheelchair Platform Lift Product

Overview

A wheelchair platform lift, or vertical platform lift (VPL), raises a wheelchair user over a short level change — a porch, a stage edge, a split-level lobby — that a ramp cannot serve in the available space. A 1 m rise needs a 12 m ramp at the 1:12 accessibility gradient; the lift does it in a 1.5 m² footprint. Unlike a passenger elevator it has no car: the rider stands or sits on an open Platform that travels along a Mast & Carriage, protected by gates, sensing edges and constant-pressure controls rather than an enclosing cab. ASME A18.1 governs these machines in North America and EN 81-41 in Europe; both cap speed at 0.15 m/s, and most units run nearer 0.06–0.1 m/s.

Drives are screw, hydraulic or scissor type. The screw drive described here dominates the European market and is the simplest to maintain; hydraulic units swap the mast-top motor for a pump and ram and are common in North America.

Drive

The Screw Drive System runs a steel lead screw the full height of the mast — functionally the same element as a Ball Screw, though most VPLs use an acme thread with a polymer nut for self-locking. A 1.5 kW single-phase Drive Motor at the mast head turns the screw through a Drive Belt, chosen over a direct coupling for quietness. The Drive Nut rides the screw and carries the carriage; directly below it trails the Safety Nut, normally unloaded. If the drive nut's thread strips through wear, the platform settles a few millimetres onto the safety nut, which carries the full load and closes a wear switch that takes the lift out of service — a passive anti-fall device with no moving parts to test. The screw's shallow helix is inherently self-locking, so the platform cannot run down under load, and a spring-applied Motor Brake on the motor shaft provides the second, independent means of holding.

Mast, carriage and platform

The Mast Extrusion is a structural aluminium profile anchored to the slab, self-supporting to about 2 m of travel and wall-tied above that. Inside it, the Carriage runs on eight polymer-tyred Guide Rollers that react the large cantilever moment of a loaded platform hung off one side. The platform itself is a 900 × 1,400 mm Platform Deck rated for 300 kg, with a Grab Rail at 900 mm and a hinged Folding Ramp at the lower entry that folds up during travel to become a roll-off barrier. The whole underside is a hinged Underpan Sensor: if the descending platform meets a foot, a bin or any obstruction, the pan lifts relative to the deck and cuts downward travel immediately. Safety Edge strips along the exposed edges do the same on contact sideways.

No pit is required — the platform sills out at about 75 mm above grade, met by a short fixed ramp or a shallow recess, which is much of why VPLs can be retrofitted where an elevator cannot.

Gates and interlocks

Each landing has a Landing Gate. The lower gate is typically 1.1 m high; the upper gate is full-height (1.8 m) because when the platform is down, the upper landing opening is an unguarded drop. A Gate Closer returns each Gate Panel shut, and the Gate Interlock enforces the elevator rule in miniature: a gate opens only when the platform is at that landing, and the platform will not move while any gate is open.

Controls and power failure

Control is deliberately primitive. The Control System use constant-pressure logic: the platform moves only while the rider holds the up or down paddle on the Platform Control Panel, and stops the instant it is released — there is no registered-call automation to carry the platform somewhere the rider did not intend. Key-switched Landing Call Stations at the landings let an attendant call or send the empty platform. The control circuit runs at 24 V through a handful of Relay contactors under an Microcontroller supervisor, with a latching Emergency Stop and a Pressure Sensor-based overload cutout that blocks starting above rated load. An 12 V Battery pair floats across the supply; on a power cut the drive completes the trip to a landing at reduced speed, so an outdoor lift never strands its rider between levels. Limit Switches define the normal stops, with final limits above and below that kill power if a normal stop is overrun.