Capacitive Safety Detector for Cutting Tools
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Solution Overview
Problem
Existing cutting tools, such as pruning shears, face challenges in reliably detecting contact between cutting elements and human body parts without connecting them to control electronics, especially in varying environmental conditions and amidst parasitic electromagnetic noise, while ensuring robustness and adaptability.
Innovation Solution
A portable electric tool with a safety device that measures electrical capacitance changes between the active cutting element and foreign bodies, generating a security signal when a threshold is exceeded, and includes filters to account for environmental changes and parasitic noise, allowing for secure operation without electrical connections to the control electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If capacitive detection system is used to detect contact between cutting elements and human body, then detection capability is improved, but reliability deteriorates due to parasitic electromagnetic noise from motor components
Solution Approach 1:
The patent introduces an intermediary capacitive coupling mechanism between the cutting element and detection circuitry, using a capacitor to transfer detection signals while blocking parasitic electromagnetic noise from the motor. This intermediary component allows contact detection to function reliably despite the noisy electromagnetic environment generated by motor-driven cutting elements.
Solution Approach 2:
The patent replaces direct electrical connection mechanisms with capacitive coupling, substituting a mechanical/electrical contact-based detection system with a field-based capacitive detection system. This substitution enables contact detection without direct electrical connection, thereby reducing susceptibility to parasitic electromagnetic noise while maintaining detection capability.
2Reliability
If safety devices requiring user action or wire connections are used, then safety is improved, but ease of operation deteriorates
Solution Approach 1:
The patent implements a self-service safety system where the capacitive detection circuit automatically monitors for contact between cutting elements and the user's body without requiring any action from the user. The system continuously measures capacitive coupling and autonomously triggers safety responses, eliminating the need for user intervention or manual safety checks.
Solution Approach 2:
The patent extracts the safety monitoring function from manual user actions and separate wire connection requirements, integrating it directly into the tool's operational circuitry. By embedding capacitive sensors in the cutting element itself, the safety function is extracted from external accessories and made intrinsic to the tool's operation, simplifying user interaction.
3Reliability
If detection system is made robust against environmental changes, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent employs parameter changes by adjusting the capacitance reference values dynamically based on environmental conditions such as humidity and temperature. The detection circuit compares measured capacitive coupling against adaptively adjusted thresholds, allowing the system to maintain reliable contact detection across varying environmental conditions without requiring complex sensor arrays or multiple detection modalities.
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 effectively detects contact between cutting elements and human body parts or conductive objects, adapting to environmental changes and reducing the risk of injury by securely limiting tool operation, even in adverse conditions like bad weather, while minimizing false positives from parasitic noise.
Implementation Method 1
measuring, at the first interface, a value depending on an electrical capacitance and on the contact of the active element with a foreign body
Data Source
AI summary
The invention relates to a cutting tool provided with at least one cutting element. It comprises a safety device coupled electrically to the cutting element via a first interface. The safety device also comprises a detector arranged in such way as to: periodically measure, on the first interface, a value that is a function of an electrical capacity and of the contact of the active element with a foreign body; compare the measured value with a reference value for an event; and deliver, to a second interface, a safety signal comprising information relating to said event, when the gap between the measured value and the reference value exceeds a threshold.