Chain Saw Brake Arrangement with Wrap Spring Clutch
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Solution Overview
Problem
Current chain saw braking systems, including both run-down and kick-back brakes, fail to effectively manage rotational inertia, leading to potential user safety risks due to slow chain stoppage and mechanical stress on the motor.
Innovation Solution
A wrap spring clutch assembly with a disengagable one-way directional drive mechanism, combined with a kick-back brake actuator, allows for quick disengagement of the motor from the chain sprocket, separating the motor's rotational inertia from the chain, enabling rapid chain stoppage and reducing motor stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a metal strip brake is used for both run-down and kick-back braking, then the braking system is simple in structure, but the chain stoppage time is too long during kick-back situations
Solution Approach 1:
The braking system is segmented into two distinct braking mechanisms: a run-down brake using a first metal strip for normal operation, and a kick-back brake using a second metal strip for emergency situations. This segmentation allows each brake to be optimized for its specific function, with the kick-back brake providing much faster stopping capability when needed.
Solution Approach 2:
Different braking characteristics are applied to different operational conditions through the use of two separate metal strips with different properties. The first metal strip is optimized for gradual run-down braking, while the second metal strip is optimized for rapid kick-back stopping, providing locally appropriate braking force for each situation.
2Reliability
If a stronger compression spring is used for kick-back actuation, then the kick-back brake becomes more effective, but the motor experiences greater mechanical stress
Solution Approach 1:
The braking function is segmented between two separate metal strips, allowing the kick-back brake to use a stronger second metal strip with a stronger compression spring for reliable emergency stopping, while the run-down brake continues to use the first metal strip that applies gentler braking during normal operation, protecting the motor from excessive stress.
Solution Approach 2:
The stronger compression spring and second metal strip are engaged only partially - specifically during kick-back emergencies when rapid stopping is absolutely necessary. During normal run-down operation, the weaker first metal strip handles the braking, avoiding the excessive mechanical stress that would result from continuously engaging the stronger brake components.
3Device complexity
If the motor remains connected to the chain sprocket during braking, then the drive mechanism remains simple, but the rotational inertia causes the chain to continue rotating and potentially contact the user
Solution Approach 1:
The motor's rotational inertia is extracted from the chain braking process through the one-way drive mechanism. When the kick-back brake applies braking force to the chain sprocket, the one-way mechanism allows the motor to be disengaged from the chain, removing the harmful rotational inertia that would otherwise cause the chain to continue rotating and potentially contact the user.
Solution Approach 2:
The one-way drive mechanism acts as an intermediary between the motor and the chain sprocket. It allows torque transmission during normal operation but permits disengagement during braking, serving as a protective mediator that prevents the motor's rotational inertia from contributing to dangerous chain movement during kick-back emergencies.
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 solution enables faster chain stoppage during kick-back situations and prolonged motor lifespan by disengaging the motor's rotational inertia from the chain, enhancing user safety and reducing mechanical stress on the motor.
Implementation Method 1
A wrap spring clutch assembly with a disengagable one-way directional drive mechanism
Implementation Method 2
a metal strip wound around and urged by means of spring bias into contact with a brake disc mounted on the driveshaft
Data Source
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AI summary
The present invention relates to improvements in or relating to chain saws (10). In particular, it relates to chain saw switching mechanisms. We describe a chain saw (10) comprising a run-down brake function and a kick-back brake function, wherein the kick-back brake function is provided by a switchable one-way directional drive assembly (33), characterised in that the switchable one-way directional drive assembly (33) also acts to provide the run-down brake function. A cutting chain (15) is carried on a chain bar (16) and driven by means of a chain sprocket (31) rotated by a prime mover (32) through the switchable one-way directional drive assembly (33). Suitably, the switchable one-way directional drive assembly (33) is a freewheel or clutch mechanism (33); preferably a wrap-spring clutch arrangement (33).