Dispenser Screw Thread Chamfer Prevents Breakage
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Solution Overview
Problem
Screw-operated dispensers often break when users mistakenly rotate the screw in the wrong direction, especially when the elevator is in the lowermost repel position, leading to stress and pressure on the screw, resulting in breakage and rendering the dispenser inoperable.
Innovation Solution
The dispenser features a chamfered screw thread in the lowermost revolutions, allowing the elevator thread to override and slide past the screw thread when rotated incorrectly, preventing stress and pressure on the screw, and maintaining dispenser operability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional squared or straight angled thread is used on the screw shaft, then the dispenser can normally operate for propelling and repelling the elevator, but the screw breaks when the user rotates the base in the wrong direction while the elevator is in the lowermost position
Solution Approach 1:
The patent applies local quality by modifying only the lowermost 1 to 1.75 revolutions of the screw thread to have a chamfered edge, while the rest of the thread maintains its original squared or straight angled configuration. This localized modification provides stress relief exactly where needed (at the potential breakage point near the hub) without compromising the overall thread engagement and dispensing function throughout the rest of the screw length.
Solution Approach 2:
The chamfered edge acts as a beforehand cushioning feature that prepares the thread structure to absorb and distribute accidental reverse-direction forces. By pre-configuring the thread geometry with an inclined bottom edge at the vulnerable lowermost section, the design anticipates and mitigates the harmful stress concentration that would otherwise occur during incorrect operation, preventing breakage before it happens.
2Reliability
If the screw thread is modified to prevent breakage, then the dispenser maintains operability after incorrect rotation, but the thread structure becomes more complex
Solution Approach 1:
The complexity is minimized by applying the chamfered edge modification only to the lowermost 1 to 1.75 revolutions of the thread, rather than redesigning the entire thread structure. This localized approach maintains simplicity in the majority of the thread length while providing the necessary stress relief feature only where it is needed to prevent breakage.
Solution Approach 2:
The invention changes a single geometric parameter of the thread - the bottom edge angle - from a right angle (in conventional threads) to an inclined chamfered edge. This simple parameter change in the thread geometry provides the stress relief function without requiring complex additional components or fundamentally redesigning the thread form, thus maintaining manufacturing simplicity.
Data Source
AI summary
A screw-operated dispenser providing for prevention of breakage of an engaged screw when a user rotates a turn member in the wrong direction, i.e., repels rather than propels an elevator. A tubular body holds a supply of product, which is dispensed by action of the elevator along a threaded shaft upon turning a base to either propel or repel the elevator along the shaft which is threadably engaged with the elevator. Certain lowermost revolutions of the thread on the shaft are chamfered at the bottom edge thereof so that when the elevator is in a lowermost position on the screw shaft and a user mistakenly rotates the turn member in a repel direction, the thread of the elevator will not engage, i.e., will override, the thread of the screw shaft thereby eliminating stress and/or pressure between the threads which may result in breakage of the screw shaft and render the dispenser inoperable.