Power Window Capacitance Sensing With Variable Detection Zones
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Solution Overview
Problem
Conventional entrapment prevention devices for vehicle power windows and automatic doors are either inaccurate in detecting foreign objects or overly sensitive, leading to false detections, such as mistaking raindrops for objects, and often require significant force to detect larger objects.
Innovation Solution
An object detection device with a variable sensitivity electric field measurement function, utilizing a plurality of electrodes on both the window glass and frame, and a control circuit that adjusts sensitivity by switching electrode pairs based on movement, allowing for accurate detection without false positives, especially in different detection zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a static capacitance sensor is used to detect foreign objects in a non-contact manner with high sensitivity, then foreign objects can be detected before entrapment occurs, but the device becomes overly sensitive to small objects like raindrops causing false detections
Solution Approach 1:
The detection space is divided into multiple detection zones (first detection zone, second detection zone, third detection zone) along the movement direction of the movable object. Each zone has different sensitivity thresholds and electrode configurations, allowing the system to differentiate between relevant foreign objects and irrelevant small objects like raindrops based on their position and capacitance characteristics.
Solution Approach 2:
Different detection zones have different sensitivity characteristics and reference capacitance values. The first detection zone uses higher sensitivity for early detection, while subsequent zones use progressively lower sensitivity thresholds. This local differentiation allows the system to maintain high detection accuracy in critical zones while reducing false alarms in less critical zones.
2Measurement precision
If the detection sensitivity is increased to detect small foreign objects early, then entrapment prevention is improved, but the device mistakes raindrops and small objects for foreign objects causing unnecessary window movement
Solution Approach 1:
The detection sensitivity and reference capacitance values are dynamically adjusted based on the movement state of the movable object and the detected zone. As the movable object approaches the frame, the system transitions between detection zones with different sensitivity thresholds, allowing early detection when needed while reducing sensitivity to prevent false alarms during normal operation.
Solution Approach 2:
The control circuit continuously monitors capacitance changes and compares them against zone-specific reference values. The system provides feedback by adjusting the detection threshold based on the current detection zone and movement state, enabling discrimination between actual entrapment risks and benign objects like raindrops.
3Device complexity
If a fixed reference static capacitance is used for entrapment detection, then the detection threshold is simple to set, but the device cannot appropriately detect entrapment across different detection zones and object sizes
Solution Approach 1:
Instead of using a fixed reference capacitance value, the system employs multiple reference capacitance values corresponding to different detection zones. The reference value is dynamically selected based on which detection zone the foreign object is currently in, allowing the detection threshold to adapt to the object's position and the specific detection requirements of each zone.
4Reliability
If the detection threshold is lowered to detect larger foreign objects with significant force applied, then detection sensitivity is improved, but entrapment is only detected after a large force is applied reducing safety
Solution Approach 1:
The detection process is segmented into multiple zones with progressively different sensitivity thresholds. The first detection zone uses high sensitivity to detect even small capacitance changes from large objects before significant force is applied. Subsequent zones use progressively lower thresholds, ensuring that large objects are detected early in their approach while still maintaining robust detection capability.
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 provides accurate detection of foreign objects near moving parts while avoiding over-sensitivity, preventing unnecessary window movement and ensuring safety without mistaking raindrops or small objects as entrapments.
Implementation Method 1
measures the static capacitance formed between the window glass and the sensor electrodes provided in the window frame
Implementation Method 2
varies the sensitivity of the electric field measurement unit by switching between two electrodes of the first plurality of electrodes in response to movement of the movable object
Data Source
AI summary
Three or more electrodes are arranged on either a window frame or window glass of an automobile. An electric field measurement unit measures the capacitance between various combinations of the electrodes to detect whether an object is located between the window frame and window glass. A control circuit varies the sensitivity of the electric field measurement unit by switching amongst the electrodes used for capacitance measurement based on the movement and position of the window glass.