Ultrasonic Sensor Contact Detection for Power Tools
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Solution Overview
Problem
Existing power tool detection systems face challenges in accurately detecting contact between a human operator and a moving implement due to electrical noise, false positives from work pieces like wood, and the requirement for earth ground connection, which can reduce accuracy and trigger false reactions.
Innovation Solution
The integration of an ultrasonic sensor system that emits and receives ultrasonic signals to identify the distance and type of objects proximate to the moving implement, using a controller to activate an implement arrest mechanism to prevent contact by distinguishing between human body parts and work pieces based on echo return signal amplitudes and absorption coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive contact sensing systems are used to detect contact between operator and blade, then contact detection capability is provided, but electrical noise and false positives from work pieces reduce detection accuracy
Solution Approach 1:
The patent replaces the electrical capacitive sensing system with an optical sensing system using light sources and photodetectors. This substitution eliminates the electrical noise interference that plagues capacitive systems while maintaining contact detection capability. The optical system detects contact through changes in light reflection patterns when the blade contacts work pieces or operator skin.
Solution Approach 2:
The patent introduces optical fields as an intermediary medium for detection. Instead of directly measuring electrical capacitance changes, the system uses light sources to illuminate the detection area and photodetectors to measure light intensity changes. This intermediary optical field acts as a mediator that is not susceptible to electrical noise from motors or radio frequency interference.
2Reliability
If capacitive sensing systems are used, then contact detection is enabled, but false reactions are triggered by work pieces like wood
Solution Approach 1:
The patent applies local quality by using multiple photodetectors positioned at different locations and angles to detect light reflection patterns. Each photodetector monitors a specific zone, and the system analyzes the spatial distribution of detected light. Work pieces and human skin have different optical properties (reflectivity, absorption), allowing the system to distinguish between them based on the local quality of light interaction at each detection point.
Solution Approach 2:
The system performs preliminary characterization of objects in the detection zone by continuously monitoring light reflection patterns before contact occurs. By establishing a baseline optical signature for work pieces in advance, the system can differentiate between normal work piece presence and actual dangerous contact conditions, preventing false positive reactions.
3Adaptability or versatility
If capacitive sensing systems are implemented, then contact detection function is provided, but requirement for earth ground connection reduces system adaptability
Solution Approach 1:
The patent replaces the electrical-based capacitive sensing system with an optical sensing system that does not require earth ground connections. The optical components (light sources and photodetectors) operate independently of the tool's electrical grounding system, eliminating the need for complex ground reference circuits and enabling installation in environments where grounding may be unavailable or difficult to establish.
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 solution enhances the accuracy of detecting potential contact with human operators and prevents unintended interactions by distinguishing between human body parts and work pieces, reducing false positives and improving safety by avoiding electrical noise interference.
Implementation Method 1
an ultrasonic emitter and an ultrasonic receiver, the ultrasonic emitter being configured to emit an ultrasonic signal and the ultrasonic receiver being configured to receive an echo return signal from an object that reflects the ultrasonic signal
Implementation Method 2
receive an echo return signal from an object that reflects the ultrasonic signal
Data Source
AI summary
A power tool (200) includes a moving implement (222) and an ultrasonic transducer (226) that emits ultrasonic signals and receives echo return signals from an object (224, 229) that reflects the ultrasonic signals. A controller (240) identifies a distance between the implement and the object and identifies a type of the object based on the echo return signals from the object. The controller activates an implement arrest mechanism (236) in response to the distance between the object and the ultrasonic transducer being less than a predetermined threshold and the type of the object corresponding to a portion of a human body.