Scotch Yoke Actuator Side Loading Cancellation
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Solution Overview
Problem
Scotch yoke actuators experience side loading issues due to non-perpendicular force application, leading to wear, misalignment, and failure of support bushings and shafts, which affects smooth movement and torque distribution, especially in high-torque applications like large valves.
Innovation Solution
A dual yoke design with symmetric ends and opposing pushing shafts that apply equal and opposing forces to cancel out end loading forces on the rotatable shaft, reducing friction and wear through balanced weight distribution and diagonal symmetry, and utilizing yoke pins with rollers or bearings to minimize friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a traditional Scotch yoke design with a single push rod and yoke is used, then the actuator can convert linear motion to rotary motion with high torque at the ends of travel, but side loading forces cause wear, misalignment, and failure of support bushings and shafts
Solution Approach 1:
The single push rod and yoke are segmented into two symmetric push rods and a dual yoke structure. Each push rod is supported by its own support bushing, dividing the side loading forces into two separate paths that cancel each other out, preventing cumulative wear on a single shaft and bushing assembly
Solution Approach 2:
The dual yoke design with symmetric push rods creates counterbalancing side loading forces that oppose each other. The support bushings for the two push rods generate equal and opposite reactions that cancel the end loading forces on the rotatable shaft, eliminating the net harmful side loading effect
2Stability of the object's composition
If push rod support bushings are used to counteract side loading effects, then the orientation of the push rod is maintained, but the bushings wear and fail due to significant side loading force combined with constant sliding
Solution Approach 1:
The support function is segmented into two separate support bushings, one for each push rod. This segmentation distributes the side loading wear across two components rather than one, extending the service life of the support system while maintaining push rod orientation through the combined effect of both bushings
3Manufacturing precision
If a single push rod with a hole through it is used to hold the yoke pin in proper alignment, then the yoke pin alignment is maintained, but rotational tendencies of the push rod cause wear to the yoke pin and hole
Solution Approach 1:
The alignment function is segmented into two separate push rods with their own support bushings, eliminating the need for a single hole through the push rod. The support bushings maintain proper alignment of the yoke pins while preventing rotational tendencies, thereby preventing wear on the yoke pins and their mounting structures
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 dual yoke design effectively eliminates side loading forces, reducing wear and misalignment, ensuring smooth and controllable movement, and facilitating easy maintenance by allowing for balanced force application and reduced friction.
Implementation Method 1
A pair of pushing devices is able respectively to apply equal and opposing forces to the two pushing shafts, thereby applying equal and opposing forces respectively to the two ends of the dual yoke, causing end loading forces applied to the rotatable shaft to be cancelled and eliminated
Implementation Method 2
utilizing yoke pins with rollers or bearings to minimize friction
Data Source
AI summary
A Scotch yoke actuator is disclosed with a dual yoke and a diagonally symmetric design. A pair of shafts and pushing devices apply equal, opposing forces to the yoke, causing end loading forces applied to a rotatable shaft attached to the center of the yoke to be cancelled. In embodiments, the weight of the pushing devices is balanced about the yoke, each shaft extends in only one direction from the yoke, and/or the shafts are supported only by the yoke and the pushing devices. In embodiments that use yoke pins, the yoke pins include rollers or bearings to reduce friction, and/or two pair of yoke pin slots support protruding ends of the yoke pins. The yoke pin slots can extend to edges of a yoke housing face, allowing easy shaft removal and reinstallation, and each shaft can include a split end with extensions on opposing sides of the yoke.