Design and Fabrication of Four Bar Crane Mechanism Report PDF Download
A crane structure for hoisting, holding and/or towing heavy loads is provided. The crane structure includes a frame, for example a wrecker truck chassis, a boom support assembly, and a pair of booms each having a first member pivotally mounted to the boom support assembly so that the first boom and the second boom are pivotal in parallel vertical planes. Each of the first boom and the second boom also has a fluid operable second member slidably received by the first member. A control system is in operative communication with the first boom, the second boom and a winch assembly to independently activate each second member to extend from and retract to its corresponding first member, to pivotally position each boom with respect to the frame, and to activate the winch assembly to retract and extend cables about free ends of the respective second members.
WORKING OF FOUR BAR CRANE MECHANISM
A four-bar linkage or simply a 4-bar or four-bar is the simplest movable linkage. It consists of four rigid bodies (called bars or links), each attached to two others by single joints or pivots to form a closed loop.
Four-bars are simple mechanisms common in mechanical engineering machine design and fall under the study of kinematics. If each joint has one rotational degree of freedom (i.e., it is a pivot), then the mechanism is usually planar, and the 4-bar is determinate if the positions of any two bodies are known (although there may be two solutions). One body typically does not move (called the ground link, fixed link, or the frame), so the position of only one other body is needed to find all positions.
The two links connected to the ground link are called grounded links. The remaining link, not directly connected to the ground link, is called the coupler link. In terms of mechanical action, one of the grounded links is selected to be the input link, i.e., the link to which an external force is applied to rotate it. The second grounded link is called the follower link, since its motion is completely determined by the motion of the input link.
Planar four-bar linkages perform a wide variety of motions with a few simple parts. They were also popular in the past due to the ease of calculations, prior to computers, compared to more complicated mechanisms.
Couple curve for crane mechanism:
A modern crawler type derrick crane with. The lattice boom is fitted with a jib. An old manual crane with a pivoted boom. The incline of the boom is controlled by means of chains, sprockets and gear.A crane is a lifting machine, generally equipped with a winder (also called a wire rope drum), 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 a human. Cranes are
commonly employed in the transport industry for the loading and unloading of freight, in the construction industry for the movement of materials and in the manufacturing industry for the assembling of heavy equipment.
WORKING OF FOUR BAR LINKAGE:
Single treadwheel crane working from top of the building . The medieval treadwheel was a large wooden wheel turning around a central shaft with a treadway wide enough for two workers walking side by side. While the earlier ‘compass-arm’ wheel had spokes directly driven into the central shaft, the more advanced ‘clasp-arm’ type featured arms arranged as chords to the wheel rim, giving the possibility of using a thinner shaft and providing thus a greater mechanical advantage.Contrary to a popularly held belief, cranes on medieval building sites were neither placed on the extremely lightweight scaffolding used at the time nor on the thin walls of the Gothic churches which were incapable of supporting the weight of both hoisting machine and load. Rather, cranes were placed in the initial stages of construction on the ground, often within the building. When a new floor was completed, and massive tie beams of the roof connected the walls, the crane was dismantled and reassembled on the roof beams from where it was moved from bay to bay during construction of the vaults. Thus, the crane ‘grew’ and ‘wandered’ with the building with the result that today all extant construction.
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