A level-luffing crane is a crane mechanism where the hook remains at the same level while luffing; moving the jib up and down, so as to move the hook inwards and outwards relative to the base. [1]
Usually the description is only applied to those with a luffing jib that have some additional mechanism applied to keep the hook level when luffing.
Level-luffing is most important when careful movement of a load near ground level is required, such as in construction or shipbuilding. This partially explains the popularity of fixed horizontal jibs in these fields.
An early form of level-luffing gear was the "Toplis" design, invented by a Stothert & Pitt engineer in 1914. [2] [3] The crane jibs luffs as for a conventional crane, with the end of the jib rising and falling. The crane's hook is kept level by automatically paying out enough extra cable to compensate for this. This is also a purely mechanical linkage, arranged by the reeving of the hoist cables to the jib over a number of pulleys at the crane's apex above the cab, so that luffing the jib upwards allows more free cable and lowers the hook to compensate.
The usual mechanism for level-luffing in modern cranes is to add an additional "horse head" section to the top of the jib. By careful design of the geometry, this keeps level merely by the linked action of the pivots. [4]
As cranes and their control systems became more sophisticated, it became possible to control the level of luffing directly, by winching the hoist cable in and out as needed. The first of these systems used mechanical clutches between luffing and hoist drums, giving simplicity and a "near level" result. [5]
Later systems have used modern electronic controls and quickly reversible motors with good slow-speed control to the hoist winch motors, so as to give a positioning accuracy of inches. Some early systems used controllable hydraulic gearboxes to achieve the same result, but these added complexity and cost and so were only popular where high accuracy was needed, such as for shipbuilding.
Luffing mechanisms have also been applied to the driver's cab being mounted on its own jib, following the movement of the crane's main jib. [6] These are used for tasks such as ship unloading, where the view from the driver's cab is greatly improved by cantilevering it forwards and over the ship.
A winch is a mechanical device that is used to pull in or let out or otherwise adjust the tension of a rope or wire rope.
An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
A crane is a type of machine, generally equipped with a hoist rope, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It is mainly used for lifting heavy things and transporting them to other places. The device uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of a human. Cranes are commonly employed in transportation for the loading and unloading of freight, in construction for the movement of materials, and in manufacturing for the assembling of heavy equipment.
A dragline excavator is a piece of heavy equipment used in civil engineering and surface mining.
A railroad crane is a type of crane used on a railroad for one of three primary purposes: freight handling in goods yards, permanent way (PW) maintenance, and accident recovery work. Although the design differs according to the type of work, the basic configuration is similar in all cases: a rotating crane body is mounted on a sturdy chassis fitted with flanged wheels. The body supports the jib and provides all the lifting and operating mechanisms; on larger cranes, an operator's cabin is usually provided. The chassis is fitted with buffing (UK) and/or coupling gear to allow the crane to be moved by a locomotive, although many are also self-propelled to allow limited movement about a work site.
A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as disk drives and printers, in valves and dampers, and in many other places where linear motion is required. Hydraulic or pneumatic cylinders inherently produce linear motion. Many other mechanisms are used to generate linear motion from a rotating motor.
A fly system, or theatrical rigging system, is a system of rope lines, blocks (pulleys), counterweights and related devices within a theater that enables a stage crew to fly (hoist) quickly, quietly and safely components such as curtains, lights, scenery, stage effects and, sometimes, people. Systems are typically designed to fly components between clear view of the audience and out of view, into the large opening, known as the fly loft, above the stage.
A shiplift is a modern alternative for a slipway, a floating dry dock or a graving dry dock. A shiplift is used to dry dock and launch ships. It consists of a structural platform that is lifted and lowered exactly vertically, synchronously by a number of hoists. First, the platform is lowered underwater, then the ship is floated above the support, and finally the platform with support and ship is lifted and the ship is brought to the level of the quay.
An overhead crane, commonly called a bridge crane, is a type of crane found in industrial environments. An overhead crane consists of two parallel rails seated on longitudinal I-beams attached to opposite steel columns by means of brackets. The traveling bridge spans the gap. A hoist, the lifting component of a crane, travels along the bridge. If the bridge is rigidly supported on two or more legs running on two fixed rails at ground level, the crane is called a gantry crane or a goliath crane.
A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium. The most familiar form is an elevator, the car of which is raised and lowered by a hoist mechanism. Most hoists couple to their loads using a lifting hook. Today, there are a few governing bodies for the North American overhead hoist industry which include the Hoist Manufactures Institute, ASME, and the Occupational Safety and Health Administration. HMI is a product counsel of the Material Handling Industry of America consisting of hoist manufacturers promoting safe use of their products.
Hydraulic hooklift hoists are mounted on heavy duty trucks to enable hauliers to change out flatbeds, dumpster bodies, and similar containers. Primarily used in conjunction with tilt frame bodies and specialised roller containers, generally designed for the transportation of materials in the waste, recycling, scrap and demolition industries, as well as for disposal of construction debris.
Stothert & Pitt was a British engineering company founded in 1855 in Bath, England. It was the builder of various engineering products ranging from Dock cranes to construction plant and household cast iron items. It went out of business in 1989. The name and intellectual property became part of Clarke Chapman.
A Fairbairn crane is a type of crane of an 'improved design', patented in 1850 by Sir William Fairbairn. There are numerous hand-powered versions around the world and one surviving steam-powered example in Bristol Docks, England.
A bulk-handlingcrane is one that, instead of a simple hook that can handle a range of slung loads, has an integral grab for lifting bulk cargoes such as coal, mineral ore etc.
Active heave compensation (AHC) is a technique used on lifting equipment to reduce the influence of waves upon offshore operations. AHC differs from Passive Heave Compensation by having a control system that actively tries to compensate for any movement at a specific point, using power to gain accuracy.
Wire rope spooling technology is the technology to prevent wire rope getting snagged when spooled, especially in multiple layers on a drum.
The Beardmore Crane was a giant cantilever crane at the William Beardmore and Company yard.
A hydraulic jigger is a hydraulically-powered mechanical winch.
A block-setting crane is a form of crane. They were used for installing the large stone blocks used to build breakwaters, moles and stone piers.
A Hercules crane was a form of block-setting crane, developed in the 1870s. They were characterised by a wheeled, mobile gantry running on rails, surmounted by a slewing horizontal jib, held up by a kingpost.
Wikimedia Commons has media related to Level-luffing cranes . |