Luffing Jib Crane Locking Device for Raised Configuration
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Solution Overview
Problem
Luffing jib cranes face issues with maintaining the jib in a raised configuration without human supervision, especially in high winds, due to hydraulic fluid leakages and expansion leading to uncontrolled lowering, which can result in overflying prohibited areas.
Innovation Solution
A locking device with a pivoting spacer and bearing device that mechanically locks the movable rod in a deployed holding position, aligning forces with the cylinder body to prevent bending and ensure the jib remains raised, using a ball joint connection and mechanical setting system to correct misalignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the lifting cylinder is used to hold the jib in a raised configuration without supervision, then the jib can remain in position for long periods, but hydraulic fluid leakages and expansion may cause compression of the cylinder leading to uncontrolled lowering
Solution Approach 1:
The locking device is activated before the jib is left unattended, preemptively preventing any potential lowering that could result from hydraulic fluid leakages or expansion during the period of no supervision. The lock engages the stop on the spacer with the cylinder body in advance, so that even if hydraulic issues occur later, the jib cannot lower.
Solution Approach 2:
The locking device acts as an intermediary mechanical element between the lifting cylinder and the jib. When engaged, it provides a direct mechanical constraint that bypasses the hydraulic system, preventing uncontrolled lowering due to hydraulic fluid issues while allowing the hydraulic cylinder to continue holding the jib in position.
2Extent of automation
If the jib is allowed to weathervane freely in strong winds, then the crane can operate automatically without supervision, but the wind forces may cause the lifting cylinder to deform or compress, risking jib lowering
Solution Approach 1:
The locking device applies a preliminary counter-action to the potential harmful effect of wind forces. By mechanically locking the movable rod in its extended position, it prevents the cylinder from compressing under wind-loaded weathervaning conditions, thereby protecting against the harmful deformation while allowing automatic operation.
3Measurement precision
If the lifting cylinder continuously controls the jib movement in both directions, then the jib can be precisely positioned, but the cylinder is susceptible to hydraulic fluid issues that may cause uncontrolled lowering
Solution Approach 1:
The control function is segmented into two independent systems: the hydraulic lifting cylinder for active positioning and control during operation, and the mechanical locking device for passive position holding during unattended periods. This segmentation allows the precision function to remain with the hydraulic system while the reliability function is transferred to the mechanical lock that is immune to hydraulic fluid issues.
Data Source
AI summary
A crane includes a luffing jib and a lifting cylinder having a cylinder body and a movable rod hinged on the jib to displace the jib in lifting motion and in lowering motion, and a locking device adapted to cooperate with the lifting cylinder to mechanically lock the rod in a deployed holding position and block the jib in a raised holding configuration. The crane further includes a spacer hinged on the jib and supporting a stop, the spacer pivotable between a release position in which the spacer is shifted, allowing the movable rod to be freely displaced, and a locking position in which the spacer is folded so that the stop is capable of abutting on a bearing surface in a ball jointed connection with the cylinder body, to fixedly hold the movable rod in the deployed holding position.