Cone Roller Lock Bi-Directional Stiffness
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Solution Overview
Problem
Existing bi-directional locking mechanisms in applications like electric wheelchairs and power-assist manipulators face challenges in maintaining high stiffness and preventing 'backlash' under reversing loads, while minimizing deflection and release force.
Innovation Solution
A roller lock device with frusto-conical rollers and a housing featuring ramps with a twisted and curved surface ensures uniform contact and alignment, allowing bi-directional locking with independent release force, minimizing free play and maximizing stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bi-directional dual wrap spring devices are used for locking, then locking function is achieved, but backlash or low system stiffness occurs under reversing load
Solution Approach 1:
The patent employs curved ramps instead of straight ramps to guide the rollers. The curvature of the ramps ensures that the rollers maintain optimal contact angles during bidirectional movement, eliminating the zone of reduced torque that causes backlash. This curved geometry allows the locking mechanism to maintain high stiffness and consistent locking force in both directions of movement.
Solution Approach 2:
The patent changes the geometric parameters of the ramp surfaces, specifically using a curved profile with optimized radius and angle. This parameter change transforms the torque output characteristic from one with a reduced torque zone to one that maintains consistent torque throughout the bidirectional movement, thereby eliminating backlash while preserving locking reliability.
2Stability of the object's composition
If opposed straight roller ramp locks are used, then system stiffness is improved, but large release forces are required after load removal
Solution Approach 1:
The curved ramp geometry creates a more favorable force distribution during the release phase. As the roller traverses the curved ramp during release, the normal force component gradually decreases, allowing the spring force to more effectively overcome the locking force. This reduces the peak release force required compared to straight ramp configurations.
Solution Approach 2:
The ramp profile is designed with asymmetric curvature that optimizes both engagement and release characteristics. The curvature is tailored so that during engagement the roller follows a path that maintains stiffness, while during release the same curved path reduces the force required to break the locking condition, creating asymmetric performance optimized for both phases.
3Ease of manufacture
If straight rollers on a straight shaft are used, then ease of manufacture is improved, but self-locking occurs requiring large release forces
Solution Approach 1:
While maintaining relatively simple manufacturing, the patent introduces curvature to the ramp surfaces. This curvature can be achieved through standard machining or forming processes, balancing manufacturing ease with the critical function of reducing self-locking effects. The curved geometry prevents the roller from digging into the ramp surface, reducing the adhesion and friction forces that cause self-locking.
Solution Approach 2:
The patent optimizes the geometric parameters of the curved ramps, including radius of curvature and ramp angle, to achieve the right balance between manufacturing simplicity and functional performance. These parameter changes reduce the tendency toward self-locking while maintaining a design that can be manufactured with conventional processes.
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
The roller lock device achieves high stiffness and bi-directional locking with reduced deflection and consistent release force, maintaining load support without premature locking or high release forces.
Implementation Method 1
A roller lock device with frusto-conical rollers and a housing featuring ramps with a twisted and curved surface ensures uniform contact and alignment
Data Source
AI summary
A roller lock device has a shaft and a housing configured over the shaft for selective relative movement thereto. A plurality of rollers is configured between the housing and the shaft, at least some of which are substantially conically shaped. A cage is configured between the housing and the shaft and adjacent the rollers such that the rollers are at least partially constrained from movement by the cage. A control is configured to move the rollers axially thereby engaging and disengaging the roller lock. The housing has ramps configured to receive the rollers, the ramps having a curved contour.