Variable Torque Pulley for Window Blind Slat Adjustment
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Solution Overview
Problem
Conventional horizontal window blind slat angle adjustment mechanisms using worm gears require excessive torque to close slats completely, leading to slow operation and inconvenience due to high friction and large gear ratios, which also result in incomplete closure due to back-drive from slat weight.
Innovation Solution
A slat angle adjustment mechanism utilizing a gear assembly with bevel gears and a pulley system, where the gear assembly includes a rod with one end coupled to a wand and a shaft, and a pulley with arced portions that provide varying torque and speed based on slat position, allowing faster slat rotation with lower torque when open and higher torque when closing, thus overcoming the limitations of worm gear systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a worm gear is used to provide high torque to close slats completely, then the slats can be closed against back-drive, but the operation becomes slow and requires many turns
Solution Approach 1:
The patent applies a variable ratio transmission mechanism where the effective gear ratio changes during operation. When slats are open, the mechanism provides lower gear ratio for faster adjustment. When slats approach closed position, the mechanism automatically increases gear ratio to provide higher torque for complete closure against back-drive from slat weight.
Solution Approach 2:
The transmission mechanism changes its mechanical parameters (gear ratio) dynamically during operation. The system transitions from a high-speed low-torque state when slats are open to a low-speed high-torque state when closing, optimizing both speed and torque delivery at different operational phases.
2Reliability
If a worm gear with high friction is used to resist back-drive, then slats remain closed, but the friction causes slow operation and requires excessive torque
Solution Approach 1:
The mechanism dynamically adjusts its mechanical advantage during operation. During the majority of the rotation when closing slats, it operates in a high-speed low-torque mode for ease of operation. Only in the final position near complete closure does it engage the high-torque mode needed to overcome back-drive, minimizing the time spent in high-friction operation.
Solution Approach 2:
The closing operation is segmented into two phases: a primary phase using low gear ratio for speed and ease of operation, and a final phase using high gear ratio for torque and back-drive resistance. This segmentation allows the system to optimize for different requirements at different stages of the same operation.
3Force
If a large gear ratio is used to provide torque for closing, then torque is sufficient, but the number of turns required increases making operation inconvenient
Solution Approach 1:
The variable ratio transmission allows the system to spend most of the adjustment time in a low gear ratio state for rapid movement, then automatically shifts to high gear ratio only when needed for final closure. This dynamic adjustment dramatically reduces the total time and number of turns required compared to a constant high gear ratio system.
Solution Approach 2:
The mechanical parameter of gear ratio is changed during operation based on the slat position. The system transitions from a parameter state optimized for speed (low gear ratio) to a parameter state optimized for torque (high gear ratio), minimizing the time spent in each state while achieving both speed and torque requirements.
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 mechanism achieves faster and more convenient slat adjustment, reducing the number of turns required by up to 5-10 times compared to conventional worm gear systems, while resisting back-drive to ensure complete closure.
Implementation Method 1
a first bevel gear coupled with the rod and a second bevel gear in mechanical communication with the first bevel gear and coupled with the shaft. A rotation of the wand causes a corresponding rotation of the shaft to adjust the tilt angle of the slats.
Implementation Method 2
The pulley causes adjustment of the tilt angle of the slats in response to rotation of the shaft, provides a first torque at a first position corresponding to an open position of the slats and a second torque at a second position corresponding to an approximately closed position of the slats, where the second torque is greater than the first torque.
Data Source
AI summary
An apparatus for adjusting a tilt angle of a plurality of slats in a window blind. The window blind includes a headrail having disposed therein a shaft that rotates responsive to rotation of an externally accessible angle adjustment wand. The apparatus includes a pulley coupled with the shaft and the slats. The pulley causes adjustment of the tilt angle of the slats in response to rotation of the shaft, provides a first torque at a first position corresponding to an open position of the slats and a second torque at a second position corresponding to an approximately closed position of the slats, where the second torque is greater than the first torque.