Protective Hood Locking Mechanism for Angle Grinders

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Solution Overview

Problem

Existing hand-held power tools, such as angle grinders, face damage issues when the protective hood is torsionally rigid, leading to potential damage during tool malfunctions like a bursting grinding wheel or workpiece jamming, as the hood and locking mechanism can be compromised.

Innovation Solution

A locking arrangement using a U-shaped torsion spring with a locking leg and fastening leg, where the spring plane is either transverse or parallel to the drive spindle axis, providing elastic support to allow the protective hood to pivot within a defined range, reducing the risk of damage by allowing flexibility during torque loads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the protective hood is designed with a torsionally rigid locking mechanism, then the hood is securely fixed in rotational positions, but the hood and locking mechanism are susceptible to damage during tool malfunctions such as bursting grinding wheels or workpiece jamming

Engineering Contradiction:
Improvesecure fixation of protective hoodVSAvoiddamage resistance of hood and locking mechanism
Core Design Contradiction:
ReliabilityVSStrength

Solution Approach 1:

The locking mechanism is designed to be dynamically adjustable between a locked state (for secure fixation) and an unlocked state (for damage protection). The actuating button enables the user to switch between these states, allowing the system to adapt to different operational conditions and avoid damage during malfunctions.

Inventive Principle:
Principle #15Dynamics

Solution Approach 2:

The torsional stiffness of the locking mechanism is made variable through the actuating button, which can change the engagement state of the locking elements. When unlocked, the mechanism allows rotational movement to absorb impact forces; when locked, it provides secure fixation for normal operation.

Inventive Principle:
Principle #35Parameter changes

2Stability of the object's composition

If the protective hood is made torsionally rigid for secure positioning, then the hood remains stable during operation, but it cannot accommodate sudden torque loads without risking damage to the hood or locking mechanism

Engineering Contradiction:
Improvestability of protective hood positionVSAvoiddamage from sudden torque loads
Core Design Contradiction:
Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The locking mechanism is designed with the capability to be unlocked beforehand, allowing the protective hood to rotate freely and absorb sudden torque loads without causing damage. This preventive measure enables the system to withstand unexpected forces during malfunctions such as bursting wheels or jamming workpieces.

Inventive Principle:
Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If a complex locking device with multiple components is used to secure the protective hood, then reliable fixation is achieved, but the device complexity increases

Engineering Contradiction:
Improvefixation reliability of protective hoodVSAvoidcomplexity of locking mechanism
Core Design Contradiction:
ReliabilityVSDevice complexity

Solution Approach 1:

Multiple locking elements are integrated into a unified locking mechanism that operates through a single actuating button. The locking elements are arranged to engage with corresponding recesses in the hub part, creating a coordinated system that achieves reliable fixation while minimizing the number of separate control components.

Inventive Principle:
Principle #5Merging (Combining)

Solution Approach 2:

The locking mechanism serves multiple functions: securing the protective hood in rotational positions, allowing controlled rotation for adjustment, and providing damage protection during malfunctions. The actuating button controls all these functions, simplifying the user interface despite the complexity of the underlying mechanism.

Inventive Principle:
Principle #6Universality (Multi-functionality)

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

This design enhances the protective hood's resilience and reduces the likelihood of damage during tool malfunctions by allowing elastic movement within predetermined locking positions, ensuring the hood and locking mechanism remain intact, thus minimizing repair needs.

Implementation Method 1

A locking arrangement using a U-shaped torsion spring with a locking leg and fastening leg, where the spring plane is either transverse or parallel to the drive spindle axis, providing elastic support to allow the protective hood to pivot within a defined range

Methodology Applied
Scientific EffectElasticity: Elasticity

Implementation Method 2

A locking arrangement using a U-shaped torsion spring with a locking leg and fastening leg

Methodology Applied
Scientific EffectTorsion Spring: Torsion Spring

Data Source

PatentEP2252430B1Hand-held power tool, in particular hand-guided grinding machine
Publication Date: 2015.04.29 ROBERT BOSCH GMBH
  • EP2252430B1 patent drawingFigure 1
  • EP2252430B1 patent drawingFigure 2
  • EP2252430B1 patent drawingFigure 3

AI summary

A protective hood is provided for a hand-held power tool, in particular a hand-guided grinding machine, the tool of which is at least partially covered by said protective hood for which protective layers, which support the protective hood in an elastically compliant manner in the direction of rotation, can be adjusted by locking positions of a locking arrangement.