Polylactic Acid Piezoelectric Sensor for Twist Detection
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Solution Overview
Problem
Existing displacement sensors using PVDF struggle to accurately detect twist and bending without temperature-dependent pyroelectricity, leading to complex configurations and limited directional sensitivity.
Innovation Solution
A displacement sensor employing a flat-film-shaped piezoelectric element made of polylactic acid, stretched uniaxially to enhance piezoelectricity in specific directions, allowing for effective detection of bending and twist by matching the stretch axis with the displacement direction, and using a dual-element configuration to increase sensitivity and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PVDF is used as the piezoelectric material, then the sensor can detect displacement, but the sensor structure becomes complicated due to temperature control requirements
Solution Approach 1:
The patent changes the piezoelectric material parameter from PVDF to polylactic acid, which fundamentally alters the material's response characteristics. This material substitution eliminates pyroelectricity while maintaining piezoelectricity, allowing the sensor to function without temperature control mechanisms, thus reducing device complexity while preserving measurement precision
Solution Approach 2:
The patent extracts and removes the temperature control system from the sensor configuration by selecting a material (polylactic acid) that does not exhibit pyroelectric effects. This extraction eliminates the need for complex temperature stabilization structures while maintaining the core displacement detection function
2Device complexity
If a single PVDF film is used, then the sensor structure is simple, but the sensor cannot detect twist effectively due to limited directional sensitivity
Solution Approach 1:
The patent segments the detection function by using multiple piezoelectric films with different orientations (0° and 90° relative to the elastic member's long side). Each film detects displacement in its specific direction, allowing the system to distinguish between bending and twist by analyzing the differential response of the segmented detection channels
Solution Approach 2:
The patent introduces asymmetric orientation of piezoelectric films at 0° and 90° angles relative to the elastic member's long side. This asymmetric arrangement creates directionally sensitive detection channels that can differentiate between displacement types (bending vs. twist) based on which orientation experiences the greatest stress, enabling twist detection while maintaining structural simplicity
3Reliability
If PVDF is used, then the sensor responds to displacement, but pyroelectricity causes temperature-dependent measurement errors
Solution Approach 1:
The patent changes the material parameter from PVDF to polylactic acid, which fundamentally alters the piezoelectric response characteristics. This material substitution eliminates pyroelectricity while maintaining piezoelectricity, allowing the sensor to function without temperature control mechanisms, thus reducing device complexity while preserving measurement precision
Solution Approach 2:
The patent converts the potential harm of temperature sensitivity into a benefit by selecting a material (polylactic acid) that is inherently resistant to temperature-induced pyroelectric effects. This material choice transforms the operating environment from temperature-critical to temperature-tolerant, improving reliability without requiring active temperature compensation
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 sensor achieves high-sensitivity, temperature-independent detection of bending and twist, enabling reliable and accurate displacement measurement without the need for complex temperature control, and can be integrated into various devices for efficient operation.
Implementation Method 1
the piezoelectric sheet is displaced by a displacement in the elastic member and, by the piezoelectric effect, an output voltage according to the displacement amount is output from the electrodes formed on both faces of the piezoelectric sheet
Data Source
AI summary
A displacement sensor having a rectangular shaped elastic member. A piezoelectric element is attached to a first main face of the elastic member. The piezoelectric element has a rectangular-shaped piezoelectric sheet and electrodes on both main faces of the piezoelectric sheet. The piezoelectric sheet is made of poly-L-lactic acid and is at least uniaxially-stretched. The piezoelectric element is attached so that the uniaxial-stretching direction of the piezoelectric sheet is 45° relative to a long-side direction of the elastic member. When the elastic member is bent along the long-side direction, the piezoelectric sheet is stretched along the long-side direction, and the piezoelectric element generates voltage of predetermined level.