Two-Stage Spring Retractable Leash for Reduced Jerk Retraction
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Solution Overview
Problem
Existing retractable leashes cause sudden jerks to animals and handlers due to insufficient shock absorption and can result in the leash being left on the ground when the handler holds the stop button, leading to dirtiness and potential damage.
Innovation Solution
A retractable leash device with a spring system that applies a first, moderate retraction force followed by a stronger force, using cascaded constant-force springs to signal the end of the leash, and includes mechanisms to automatically transition between unwinding paths and block further unwinding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single strong retraction force is applied to prevent leash from being left on ground, then reliability is improved, but the animal experiences sudden harmful jerks
Solution Approach 1:
The spring system is divided into two distinct segments: a first spring providing a first retraction force for normal operation, and a second spring providing a second retraction force for final retraction. This segmentation allows the system to provide different force levels at different stages, ensuring reliable retraction while avoiding harmful jerks during normal use.
Solution Approach 2:
Different parts of the retraction process are assigned different force characteristics. The first spring provides a gentler, more gradual retraction force during most of the unwinding path, while the second spring provides a stronger force only when needed for final retraction. This local differentiation of force quality resolves the contradiction between gentle operation and reliable retraction.
2Object-affected harmful factors
If a shock absorber extension is added to cushion the jerk, then the harmful effect is reduced, but the device complexity increases and the shock absorber must be kept short to maintain leash effectiveness
Solution Approach 1:
The shock absorption function is merged with the existing spring system by adding a second spring in series with the first spring. This integration allows the retraction mechanism itself to provide cushioning through the progressive engagement of two springs, rather than adding a separate shock absorber component. The merging reduces device complexity while maintaining the cushioning effect.
3Reliability
If the stop button is pressed to block the leash, then the animal is prevented from running away, but the rewind mechanism is blocked causing the leash to rest on the ground and become dirty
Solution Approach 1:
The system transitions from a static blocking mechanism to a dynamic two-stage retraction system. When the stop button is pressed, instead of completely blocking the leash, the system allows controlled retraction through the two-stage spring mechanism. This dynamic approach maintains leash control while preventing the leash from being left on the ground, as the springs continuously pull the leash onto the spool.
4Reliability
If the leash is made completely unwindable to prevent it being left on ground, then reliability is improved, but the animal loses freedom of movement
Solution Approach 1:
The system changes the force parameter progressively through two stages. The first spring allows free unwinding and gentle retraction, providing animal freedom. The second spring engages only when the first spring is fully extended, providing stronger retraction force to ensure complete retraction and prevent the leash from being left on the ground. This parameter change approach maintains freedom during normal use while ensuring reliability at the limit.
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 device reduces sudden jerks by training the animal to associate the stronger force with the leash end, prevents the leash from being left on the ground, and allows controlled unwinding through adjustable paths and manual overrides.
Implementation Method 1
a spring system which is designed to push back or retain the spool body into a winding position in which the animal leash is arranged wound on the spool body and which is designed with a return force
Data Source
Figure 1~4
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Figure 9~10
AI summary
The invention relates to a retractable leash device (1) for an animal leash (2), which comprises a housing (3), a spool body (9) which is rotatably mounted on the housing (3), and a spring system (10) which is designed to urge the spool body (9) back into a winding position in which the animal leash (2) is wound on the spool body (9), and which is designed with a first return force and with a second return force, wherein the spring system (10) is designed such that the spool body (9) is rotatable from the winding position against the first return force for a first unwinding path of the animal leash (2), which is defined by a fixed number of revolutions of the spool body (9), and that the spool body (9) is rotatable against the second return force, which is greater than the first return force, for a second unwinding path of the animal leash (2),which adjoins the first unwinding path and which is defined by a fixed number of revolutions of the coil body (9), is rotatable.,