Variable Guying for Mobile Crane Jib Bending Relief
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Solution Overview
Problem
Mobile cranes with long main jibs experience high bending moments during raising and lowering due to the combination of compressive and normal forces, which are exacerbated by existing guying arrangements, leading to sagging and reduced bearing load capacity.
Innovation Solution
A mobile crane design incorporating a combination of first and second secondary tensile connectors, where the second connector is variable in length, optimally adjusting to counteract sagging and bending loads by varying its length during operation, raising, and lowering phases, particularly for jibs between 150 m to 250 m.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If additional guying arrangements (secondary tensile means) are used between the main guying arrangement and the main jib to reduce bending moment, then the bending moment on the main jib is reduced, but the structural outlay and weight increase
Solution Approach 1:
The patent applies the dynamics principle by making the second secondary tensile connector variable in length while keeping the first secondary tensile connector of fixed length. This allows the guying arrangement to adapt dynamically to different operational phases (raising, lowering, operation) and optimize the bending moment resistance without requiring multiple fixed-length connectors for each scenario, thereby reducing overall structural complexity while maintaining strength.
Solution Approach 2:
The patent changes the parameter of the second secondary tensile connector from fixed length to variable length. This parameter change enables the connector to adjust its tension and geometry according to the main jib's position and load conditions, effectively reducing bending moments across different operational states without requiring additional connectors, thus simplifying the overall guying arrangement.
2Productivity
If the main jib is raised to an almost horizontal mounting position, then the operational reach is maximized, but high bending moments act upon the main jib due to compressive and normal forces
Solution Approach 1:
The variable length of the second secondary tensile connector allows it to dynamically adjust during the raising operation. As the main jib approaches horizontal position, the connector can lengthen to maintain optimal tension geometry, distributing forces more effectively and reducing the peak bending moments that would otherwise occur at extreme positions, thereby enabling safe operation at maximum reach.
Solution Approach 2:
The second secondary tensile connector is designed to counteract the bending moment in advance by applying a normal force that opposes the compressive force from the main guying arrangement. This preliminary anti-action prevents the excessive sagging and bending that would occur when the main jib is raised to horizontal position, allowing the crane to achieve maximum operational reach safely.
3Device complexity
If fixed length secondary tensile connectors are used, then structural outlay and weight are reduced, but the load capacity is reduced when the main jib is positioned steeply
Solution Approach 1:
The patent combines one fixed-length secondary tensile connector with one variable-length secondary tensile connector. The variable-length connector specifically addresses the adaptability requirement by adjusting its length according to the main jib's position, maintaining optimal load capacity at steep positions, while the fixed-length connector provides structural simplicity. This hybrid approach balances both requirements effectively.
Solution Approach 2:
By changing the length parameter of the second secondary tensile connector based on the main jib's position, the system maintains high load capacity at steep positions. The variable connector can shorten when the jib is steep to increase tension and support, while the fixed connector maintains structural simplicity. This selective parameter change resolves the contradiction between simplicity and adaptability.
Data Source
AI summary
A mobile crane having a main jib that can be raised and lowered but not telescoped by means of at least one main tensile connector, and a counter jib, where the main tensile connector extends between a first connection point in the region of a head of the main jib and a second connection point in the region of a head of the counter jib, a first secondary tensile connector and a second secondary tensile connector are arranged between the main tensile connector and the main jib, and the first secondary tensile connector has a fixed length. In order to further reduce the loads acting upon the main jib, such as during raising and lowering, and to increase its overall bearing load, at least portions of the second secondary tensile connector can be varied in length.