Ratchet Brake Mechanism With Alternating Teeth for Reverse Rotation Blocking
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Solution Overview
Problem
In lever hoists, accidental switching of the switching knob to the lowering direction can cause the brake mechanism to fail, allowing the ratchet wheel to powerfully rotate uncontrollably due to the load of the cargo, as the pawl member cannot effectively engage with the ratchet teeth to stop the rotation.
Innovation Solution
A brake device is implemented with a ratchet wheel featuring tall and short teeth, paired pawl members, and a brake plate system that ensures the pawl members engage with the valley parts between teeth to prevent reverse rotation, using a flange part, female screw member, and brake plates to control the rotation direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching knob is switched to the lowering direction by mistake in a state where the tip of the pawl member is in contact with the tip of the ratchet tooth, then the brake mechanism fails to stop reverse rotation, but the ratchet wheel starts to powerfully rotate uncontrollably
Solution Approach 1:
The ratchet teeth are designed with different heights (tall teeth and short teeth) to create local variations in the engagement characteristics. This local quality difference ensures that when the pawl member contacts a tall tooth tip, the subsequent short tooth provides a controlled engagement path that prevents uncontrolled rotation, thereby resolving the reliability issue while maintaining safety.
Solution Approach 2:
The alternating arrangement of tall and short teeth creates a pre-prepared engagement path. When the pawl member is in contact with a tall tooth tip and reverse rotation occurs, the next short tooth is positioned to provide a controlled engagement, cushioning the impact and preventing the pawl from bouncing off uncontrollably. This beforehand preparation ensures the brake mechanism remains reliable even during accidental switching.
2Ease of operation
If the pawl member tip contacts the ratchet tooth tip during accidental switching, then the brake mechanism cannot engage properly, but providing only uniform teeth height fails to prevent uncontrolled rotation
Solution Approach 1:
The ratchet wheel employs asymmetric tooth heights with alternating tall and short teeth. This asymmetry creates different engagement characteristics: tall teeth provide robust engagement points, while short teeth provide controlled engagement paths. This asymmetric design ensures that even when the pawl contacts a tall tooth tip during accidental switching, the subsequent short tooth guides the pawl into proper engagement, preventing uncontrolled rotation while maintaining ease of operation.
Solution Approach 2:
The ratchet teeth are segmented into two distinct types (tall and short) arranged alternately around the circumference. This segmentation creates a periodic pattern of engagement characteristics that ensures at least one short tooth will be encountered after any tall tooth, providing a reliable controlled engagement path regardless of the starting position, thereby resolving the reliability contradiction.
Data Source
AI summary
A brake device comprising: a brake receiver pivotally supported in a non-rotatable manner on the drive shaft and including a flange part and a boss part; a female screw member pivotally supported in a rotatable manner on the drive shaft and screwed to a male screw part; a ratchet wheel including ratchet teeth provided on an outer peripheral side and configured to restrict a rotation direction to one direction; a brake plate arranged between the ratchet wheel and at least one of the flange part and the female screw member; and at least one pawl member engaging, on a tip side, with a valley part located between adjacent ratchet teeth, and meshing with the ratchet tooth, wherein the ratchet teeth include tall teeth and short teeth lower in projection height from a rotation center of the ratchet wheel than the tall teeth.