Aerial work platform
Encyclopedia
They are generally used for temporary, flexible access purposes such as maintenance
Maintenance, Repair and Operations
Maintenance, repair, and operations or maintenance, repair, and overhaul involves fixing any sort of mechanical or electrical device should it become out of order or broken...
and construction
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...
work or by firefighters for emergency
Emergency
An emergency is a situation that poses an immediate risk to health, life, property or environment. Most emergencies require urgent intervention to prevent a worsening of the situation, although in some situations, mitigation may not be possible and agencies may only be able to offer palliative...
access, which distinguishes them from permanent access equipment such as elevator
Elevator
An elevator is a type of vertical transport equipment that efficiently moves people or goods between floors of a building, vessel or other structures...
s. They are designed to lift limited weights (usually less than a ton, although some have a higher safe working load (SWL)), distinguishing them from most types of crane
Crane (machine)
A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...
s. They are usually capable of being fully operated (including setup) by a single person.
Regardless of the task they are used for, aerial work platforms may provide additional features beyond transport and access, including being equipped with electrical outlets or compressed air
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...
connectors for power tool
Power tool
A power tool is a tool that is actuated by an additional power source and mechanism other than the solely manual labour used with hand tools. The most common types of power tools use electric motors. Internal combustion engines and compressed air are also commonly used...
s. They may also be equipped with specialist equipment, such as carrying frames for window glass.
Lifting mechanisms
There are several distinct types of aerial work platforms, which all have specific features which make them more or less desirable for different applications. The key difference is in the drive mechanism which propels the working platform to the desired location. Most are powered by either hydraulicsHydraulic machinery
Hydraulic machines are machinery and tools that use liquid fluid power to do simple work. Heavy equipment is a common example.In this type of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and which becomes pressurised according to...
or possibly pneumatics
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...
. The different techniques also reflect in the pricing and availability of each type.
Aerial Device
Aerial devices were once exclusively operated by hydraulic pistons, powered by diesel or gasoline motors on the base unit. Lightweight electrically powered units are gaining popularity for window-cleaning or other maintenance operations, especially indoors and in isolated courtyards, where heavier hydraulic equipment cannot be used. Aerial devices are the closest in appearance to a crane- consisting of a number of jointed sections, which can be controlled to extend the lift in a number of different directions, which can often include 'up and over' applications.
Orchard
An orchard is an intentional planting of trees or shrubs that is maintained for food production. Orchards comprise fruit or nut-producing trees which are grown for commercial production. Orchards are also sometimes a feature of large gardens, where they serve an aesthetic as well as a productive...
s (though not just cherry
Cherry
The cherry is the fruit of many plants of the genus Prunus, and is a fleshy stone fruit. The cherry fruits of commerce are usually obtained from a limited number of species, including especially cultivars of the wild cherry, Prunus avium....
orchards). It lets the picker standing in the transport basket pick fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
high in a tree with relative ease (with the jointed design ensuring minimum damage to the tree). The term 'cherry picker' has become generic, and is commonly used to describe articulated lifts (and more rarely all AWPs).
This type of AWP is now widely used for maintenance and construction of all types, including extensively in the power and telecommunications industries to service overhead lines
Electricity distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...
, and in arboriculture
Arboriculture
Arboriculture is the cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants. It is both a practice and a science....
to provide an independent work platform on difficult or dangerous trees. A specialist type of the articulated lift is the type of fire apparatus used by firefighter
Firefighter
Firefighters are rescuers extensively trained primarily to put out hazardous fires that threaten civilian populations and property, to rescue people from car incidents, collapsed and burning buildings and other such situations...
s worldwide as a vehicle to provide high level or difficult access. These types of platforms often have additional features such as a piped water supply and water cannon
Water cannon
A water cannon is a device that shoots a high-pressure stream of water. Typically, a water cannon can deliver a large volume of water, often over dozens of metres / hundreds of feet. They are used in firefighting and riot control. Most water cannon fall under the category of a fire...
to aid firefighters in their task.
Some articulated lifts are limited to only the distance accessible by the length of each boom arm, however, by the use of telescoping
Telescoping (mechanics)
Telescoping in mechanics describes the movement of one part sliding out from another, lengthening an object from its rest state. In modern equipment, this is often done by hydraulics....
sections, the range can be vastly increased. Some large hydraulic platforms mounted on a lorry
Truck
A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...
can reach heights of over 100 metres.
The majority of articulated lifts require a wide supportive base to operate safely, and most models have extending legs/struts to help accomplish this. These legs can be manual or hydraulic (usually depending on size and price of the machine). Some AWPS are classified as 'spiders' due to the appearance of these legs. Spiders are also available in especially compact form, to fit through doorways for use inside buildings.
Scissor Lift
A scissor lift is a type of platform which can usually only move vertically. The mechanism to achieve this is the use of linked, folding supports in a criss-cross 'X' pattern, known as a pantographPantograph
A pantograph is a mechanical linkage connected in a special manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen...
. The upward motion is achieved by the application of pressure to the outside of the lowest set of supports, elongating the crossing pattern, and propelling the work platform vertically. The platform may also have an extending 'bridge' to allow closer access to the work area (because of the inherent limits of vertical only movement).
The contraction of the scissor action can be hydraulic, pneumatic or mechanical (via a leadscrew
Leadscrew
A leadscrew , also known as a power screw or translation screw, is a screw designed to translate turning motion into linear motion...
or rack and pinion
Rack and pinion
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby...
system). Depending on the power system employed on the lift, it may require no power to enter 'descent' mode, but rather a simple release of hydraulic or pneumatic pressure. This is the main reason that these methods of powering the lifts are preferred, as it allows a fail-safe
Fail-safe
A fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel....
option of returning the platform to the ground by release of a manual valve.
“Hotel Lift”
There are a number of smaller lifts which use mechanical devices such as rack and pinionRack and pinion
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby...
or screw
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...
threads to extend. These often have juxtaposed sections which move past each other in order to create the movement, usually in a vertical direction only. This lifts usually have limited capability in terms of weight and extension, and are most often used for internal maintenance tasks such as changing lightbulbs.
Motive mechanisms
AWPs, by their nature, are designed for temporary works and therefore frequently require transportation between sites, or simply around a single site (often as part of the same job). For this reason, they are almost all designed for easy movement.Unpowered
These usually smaller units have no motive drive and require external force to move them. Dependent on size and whether they are wheeled or otherwise supported, this may be possible by hand, or may require a vehicle for towing or transport. Small non-powered AWPs can be light enough to be transported in a pickup truck bed, and can usually be moved through a standard doorway.Self propelled
These units are able to drive themselves (on wheelWheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...
s or track
Caterpillar track
Continuous tracks or caterpillar tracks are a system of vehicle propulsion in which modular metal plates linked into a continuous band are driven by two or more wheels...
s) around a site (they usually require to be transported to a site, for reasons of safety and economy). In some instances, these units will be able to move whilst the job is in progress, although this is not possible on units which require secure outriggers, and therefore most common on the scissor lift types. The power can be almost any form of standard mechanical drive system, including electric or gasoline powered, or in some cases, a hybrid (especially where it may be used both inside and outside).
Vehicle mounted
Some units are mounted on a vehicle, usually a truckTruck
A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...
or it can be mounted on a flat back pick up van known as a Self Drive), though other vehicles are possible, such as railway cars
Railroad car
A railroad car or railway vehicle , also known as a bogie in Indian English, is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives...
. This vehicle provides mobility, and may also help stabilize the unit - though outrigger stabilizers are still typical, especially as vehicle-mounted AWPs are amongst the largest of their kind. The vehicle may also increase functionality by serving as mobile workshop or store.
Control
The power assisted drive (if fitted) and lift functions of an AWP are controlled by an operator, who can be situated either on the work platform itself, or at a control panel at the base of the unit. Some models are fitted with a panel at both locations or with a remote controlRemote control
A remote control is a component of an electronics device, most commonly a television set, used for operating the television device wirelessly from a short line-of-sight distance.The remote control is usually contracted to remote...
, giving operator a choice of position. A control panel at the base can also function as a safety feature if for any reason the operator is at height and becomes unable to operate his controls. Even models not fitted with a control panel at the base are usually fitted with an emergency switch of some sort, which allows manual lowering of the lift (usually by the release of hydraulic or pneumatic pressure) in the event of an emergency or power failure.
Controls vary by model, but are frequently either buttons or a joystick
Joystick
A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Joysticks, also known as 'control columns', are the principal control in the cockpit of many civilian and military aircraft, either as a center stick or...
. The type and complexity of these will depend on the functions the platform is able to perform. The controls can control features such as:
- Vertical movement
- Lateral movement
- Rotational movement (cardinal directionCardinal directionThe four cardinal directions or cardinal points are the directions of north, east, south, and west, commonly denoted by their initials: N, E, S, W. East and west are at right angles to north and south, with east being in the direction of rotation and west being directly opposite. Intermediate...
) - Platform / basket movement – Normally, the system automatically levels the platform regardless of boom position, but some allow overrides, tilting up to 90 degrees for work in difficult locations.
- Ground movement (in self propelled models)
Safety
Work platforms are fitted with safety or guard rails around the platform itself to contain operators and passengers. This is supplemented in most models by a restraining point, designed to secure a harness
Safety harness
A safety harness is a form of protective equipment designed to protect a person, animal, or object from injury or damage. The harness is an attachment between a stationary and non-stationary object and is usually fabricated from rope, cable or webbing and locking hardware...
or fall arrestor. Some work platforms also have a lip around the floor of the platform itself to avoid tools or supplies being accidentally kicked off the platform. Some protocols require all equipment to be attached to the structure by its own lanyard.
Extreme caution must be taken when using AWPs in the vicinity of overhead power line
Overhead power line
An overhead power line is an electric power transmission line suspended by towers or utility poles. Since most of the insulation is provided by air, overhead power lines are generally the lowest-cost method of transmission for large quantities of electric energy...
s as electrocution
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
may result if the lift comes in contact with energized wiring. Non-conductive
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
materials, such as fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
, may be used to reduce this hazard.
AWPs often come equipped with a variety of tilt sensors. The most commonly activated sensor (especially with two people on a lift), will cause the machine to refuse to raise the platform beyond a certain height. Sensors within the machine detect that weight on the platform is off balance to such a point as to risk a possible tip-over if the platform is raised further. Another sensor will refuse to extend the platform if the machine is on a significant incline. Some models of AWPs additionally feature counterweight
Counterweight
A counterweight is an equivalent counterbalancing weight that balances a load.-Uses:A counterweight is often used in traction lifts , cranes and funfair rides...
s, which extend in order to offset the danger of tipping the machine inherent in extending items like booms or bridges. Some lifts are also fitted with sensors which will prevent operation if the weight on the platform exceeds the safe working load.
As with most dangerous mechanical devices, all AWPs are fitted with an emergency stop button or buttons for use in the event of a malfunction or danger. Best practice dicates fitting of emergency stop buttons on the platform and at the base as a minimum. Other safety features include automatic self checking of the AWPs working parts, including a voltmeter, which detects if the lift has insufficient power to complete its tasks (which will result in it refusing to operate for safety). Some AWPs provide manual lowering levers at the base of the machine, allowing operators to lower the platform to the ground in the event of a power or control failure or deliberate use of the machine (e.g. by unauthorized persons).
Business model
AWPs are often bought by equipment rental companies, who then rent them out to construction companies or individuals needing these specialised machines. The market for these machines is known to be marked by especially strong boom and bustBoom and bust
A credit boom-bust cycle is an episode characterized by a sustained increase in several economics indicators followed by a sharp and rapid contraction. Commonly the boom is driven by a rapid expansion of credit to the private sector accompanied with rising prices of commodities and stock market index...
cycles, and after a great demand in the 1990s (with up to 70,000 AWPs sold per year in the US) the market crashed in the early 2000s, leading to a strong contraction amongst the manufacturers.
See also
- Cherry pickerCherry pickerA cherry picker , is a type of aerial work platform that consists of a platform or bucket at the end of a hydraulic lifting system.- Design :...
- CraneCrane (machine)A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...
- Fire apparatusFire apparatusA fire apparatus, fire engine, fire truck, or fire appliance is a vehicle designed to assist in fighting fires by transporting firefighters to the scene and providing them with access to the fire, along with water or other equipment...
- Forklift truckForklift truckA forklift is a powered industrial truck used to lift and transport materials. The modern forklift was developed in the 1920s by various companies including the transmission manufacturing company Clark and the hoist company Yale & Towne Manufacturing...
- Lift tableLift tableA lift table is a device that employs a scissors mechanism to raise or lower goods and / or persons. Typically they are used to raise large, heavy loads through relatively small distances. Common applications include pallet handling, vehicle loading and work positioning...
has scissor like supports underneath - Long reach excavatorLong reach excavatorThe long reach excavator or high reach excavator is a development of the excavator with an especially long boom arm, that is primarily used for demolition. Instead of excavating ditches, the long reach excavator is designed to reach the upper stories of buildings that are being demolished and pull...
External links
- International Powered Access Federation
- Aerial Work Platform Training (a website of the IPAFInternational Powered Access FederationThe International Powered Access Federation is a not-for-profit member organization in the field of powered access, i.e. part of or associated with the industry of elevating work platforms, which is the general term, or aerial work platforms , as they are commonly referred to in North America...
) - Aerial Lift Trucks Information