Friction Dog Prepositioning for Skewed Engagement
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Solution Overview
Problem
Existing methods fail to reliably preposition friction dogs for engagement with supported members and allow for free lateral movement after engagement, especially in sensitive applications like subsea umbilicals, without damaging the equipment.
Innovation Solution
The use of inclined surfaces and leaf springs to preposition friction dogs before engagement, allowing for wedging action and amplification of friction, while ensuring they can return to the prepositioned state from either direction, utilizing a system of carriers, actuator plates, and guide pins to maintain alignment and allow sliding movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If friction dogs use sharp teeth to bite into the supported member, then the coefficient of friction increases to provide dependable grip, but the supported member may be damaged
Solution Approach 1:
The invention changes the interaction mechanism from mechanical interlocking (sharp teeth biting) to friction-based gripping through wedging action. The friction dogs use a skewed surface angle (typically 8 degrees) to create wedging action that amplifies the normal force, achieving high friction coefficients without damaging the supported member. This parameter change transforms the gripping mechanism from aggressive mechanical engagement to controlled frictional contact.
Solution Approach 2:
The invention replaces the mechanical interlocking system (sharp teeth) with a friction-based system utilizing wedging action. Instead of relying on tooth engagement, the friction dogs use the inclined surface geometry to convert axial load into radial clamping force, thereby achieving secure grip through friction alone and eliminating the need for damaging sharp teeth.
2Ease of manufacture
If friction dogs are prepositioned by hand or without control, then the process is simple, but the prepositioning reliability is insufficient
Solution Approach 1:
The invention implements self-service prepositioning where the friction dogs automatically position themselves onto the supported member without manual intervention. The skewed surface geometry and carrier design enable the friction dogs to self-align and self-position during the engagement process, ensuring reliable prepositioning while maintaining operational simplicity. The system uses the inherent geometry of the components to achieve automatic positioning.
3Stability of the object's composition
If friction dogs are constrained to prevent lateral movement, then prepositioning is maintained, but the wedging action cannot be achieved
Solution Approach 1:
The invention introduces dynamic behavior to the friction dog system, allowing lateral movement along the skewed surface after initial engagement. The carrier design permits controlled sliding of friction dogs relative to the supported member, enabling the wedging action to develop fully. This dynamic capability transforms the system from a static constrained position to a dynamic engagement process where friction amplification occurs through controlled lateral motion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures dependable grip and safe support of tubular members like subsea umbilicals by enhancing friction without damaging them, enabling precise prepositioning and flexible movement post-engagement, effectively addressing the limitations of prior manual or uncontrolled prepositioning methods.
Implementation Method 1
placing a resilient member in both said first groove and said second groove, said leaf spring having a preload when said first groove and said second groove are aligned, such that if said friction dog is displaced from said predetermined position it is urged back towards said predetermined position
Implementation Method 2
The coefficient of friction on the back side of the slip is enhanced by the typical eight degree taper of the supporting surface. The coefficient of friction against the supported member must be enhanced more by the wedging action of that invention for the supported member to be safely supported.
Implementation Method 3
the force against the supported member is amplified by the wedging action of a surface on the back side of the friction dog which is at a skewed angle relative to the direction of approach of the friction dog to the supported member
Data Source
AI summary
The method of using friction dogs for the skewed force amplifying gripping engagement of a circular member including positively prepositioning the friction dog in a predetermined position on a force wedging angled surface before the engagement with the circular member and the freedom to move along a skewed surface after the engagement to allow the force amplifying wedging action to occur.