Piezoelectric Displacement Sensor Voltage Conversion Circuit
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Solution Overview
Problem
Conventional displacement sensors using piezoelectric sheets face challenges in precisely detecting displacement due to the instantaneous change in voltage followed by a return to reference voltage, making it difficult to measure charges generated by the piezoelectric sensor effectively.
Innovation Solution
A displacement sensor configuration that includes a piezoelectric element generating charge proportional to displacement, a voltage converting unit with specific resistor and amplifier circuit connections to produce a stable temporal voltage change, and a detecting unit that integrates voltages to accurately measure displacement, using a piezoelectric film made of uniaxially stretched polylactic acid for high sensitivity and translucency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a piezoelectric sheet is used to detect displacement, then the sensor can generate charge proportional to displacement, but the output voltage changes instantaneously and returns to reference voltage without maintaining a fixed voltage, making precise measurement difficult
Solution Approach 1:
The patent introduces a capacitor as an intermediary element between the piezoelectric element and the measurement circuit. This capacitor holds the charge generated by the piezoelectric element and releases it gradually, transforming the instantaneous voltage spike into a stable, maintainable voltage signal that can be accurately measured and correlated to displacement magnitude.
Solution Approach 2:
The patent changes the temporal parameter of the voltage signal by using the capacitor to extend the duration of the voltage signal. Instead of an instantaneous spike that returns to reference voltage, the capacitor maintains a elevated voltage level for a measurable period, allowing precise displacement measurement while maintaining voltage stability during the measurement window.
2Reliability
If conventional piezoelectric sensors are used, then displacement detection is possible, but the voltage returns to reference voltage quickly making it hard to maintain fixed voltage for measurement
Solution Approach 1:
The capacitor serves as a charge storage intermediary that decouples the brief charge generation event from the measurement requirement. It captures the instantaneous charge from the piezoelectric element and provides a sustained voltage output, extending the duration during which reliable displacement detection can occur.
Solution Approach 2:
The capacitor performs preliminary charge storage action immediately after the piezoelectric element generates charge. By pre-storing the charge in the capacitor, the system prepares a stable voltage signal in advance, ensuring sufficient duration for accurate measurement before the voltage would naturally decay.
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
Enables precise measurement of displacement with stable output voltage, suppressing the influence of charge variations and body temperature, and effectively detecting pressing force as a touch sensor.
Implementation Method 1
a piezoelectric element which generates a charge proportional to an amount of displacement
Data Source
AI summary
There is provided a displacement sensor which can precisely detect the amount of displacement given by an operator. A touch sensor which is a type of the displacement sensor has a piezoelectric element, a voltage converting unit and a detecting unit. The piezoelectric element instantaneously generates a voltage proportional to a pressing force (the amount of pressing). The voltage converting unit converts the voltage generated by the piezoelectric element, into a voltage proportional to a transition determined based on a predetermined time constant determined by an impedance of a resistor of the voltage converting unit and capacitances of a capacitor and the piezoelectric element, and a pressing force. The detecting unit integrates output voltages of the voltage converting unit, and calculates the pressing force (the amount of pressing) based on an integration value.