Piezoelectric Force Sensor Friction Vibration Restriction
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Solution Overview
Problem
Conventional piezoelectric vibration type force sensors have a narrow sensing range and are not suitable for downsizing due to the need for sufficient deformation, which complicates the structure and increases costs.
Innovation Solution
A piezoelectric vibration type force sensor that utilizes a restricting member to transmit force to the piezoelectric body through friction, allowing for wider force sensing by restricting vibration in a direction perpendicular to the primary vibration mode, and featuring a simple structure with drive electrodes and a deformed restricting member for enhanced sensitivity and range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional force sensor uses deformation of a member for sensing force, then the sensor can measure force, but sufficient deformation amount cannot be obtained when the sensor is downsized, causing output signal to be buried in noise and deteriorating accuracy
Solution Approach 1:
The patent applies mechanical vibration by utilizing the resonance phenomenon of a piezoelectric body. When an alternating voltage is applied to the piezoelectric body, it vibrates at its resonance frequency. This vibration amplifies the mechanical response to applied forces, enabling high-sensitivity force sensing even in miniaturized sensors where conventional deformation methods would fail to produce sufficient signal.
2Measurement precision
If a piezoelectric vibration type force sensor uses resonance phenomenon with fixed frequency voltage application, then high sensitivity is achieved with low load, but as external force increases the variation of voltage amplitude decreases, resulting in narrow sensing range
Solution Approach 1:
The patent implements dynamics by making the excitation frequency variable rather than fixed. The frequency of the alternating voltage applied to the piezoelectric body is adjusted dynamically based on the magnitude of the applied force. This allows the sensor to maintain optimal sensitivity across a wide range of force magnitudes, expanding the sensing range while preserving high sensitivity for low-load measurements.
Solution Approach 2:
The patent changes the parameter of excitation frequency in response to varying force magnitudes. By adjusting the frequency parameter of the applied voltage according to the detected force level, the sensor adapts its operating conditions to maintain maximum sensitivity across different measurement ranges, thereby expanding the overall sensing capability.
3Adaptability or versatility
If a bimorph piezoelectric body structure is used to expand sensing range, then amplitude can be made larger, but the structure with two piezoelectric elements bonded together increases cost and complexity
Solution Approach 1:
The patent extracts the essential function of force sensing from the complex bimorph structure and implements it using a single piezoelectric body. By eliminating the need for bonded piezoelectric elements and complex mechanical structures, the invention achieves force sensing capability with a simpler, more cost-effective design while maintaining expanded sensing range through frequency variation.
4Adaptability or versatility
If phase angle sensing circuit and phase angle setting circuit are added to control frequency, then sensing range can be widened, but the additional circuits complicate the overall system and increase cost
Solution Approach 1:
The patent implements self-service by enabling the piezoelectric body to automatically adjust its resonance frequency in response to applied force without requiring external phase angle sensing or setting circuits. The piezoelectric body's inherent piezoelectric effect and mechanical resonance properties allow it to self-adjust its operating frequency based on the load, eliminating the need for additional control circuits and reducing system complexity.
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 a wider range of force sensing with improved sensitivity and reduced complexity, enabling effective static force measurement while maintaining a compact design.
Implementation Method 1
The piezoelectric body has a property of vibrating in a specific direction when a voltage which temporally changes (e.g., alternating voltage) is applied, according to time variation of amplitude of the voltage
Implementation Method 2
If a force is exerted on the piezoelectric body in this state, the impedance of the piezoelectric body increases so that the resonance frequency of the piezoelectric body is shifted to a high frequency side
Data Source
AI summary
In a piezoelectric vibration type force sensor according to the present invention, vibration is restricted by a friction force between a piezoelectric body and a restricting member, and hence a range of sensing forces can be expanded compared with a case in which the vibration is restricted directly from a direction that is the same as an vibration direction. A conventional structure, in which a lead wire is soldered directly for electrically connecting the piezoelectric body to an external control circuit, causes a restriction of the vibration due to a solder attached to the piezoelectric body, resulting in narrowing the sensing range. Using the piezoelectric vibration type force sensor, the range of sensing forces can be expanded by making a state in which conducting portions of the piezoelectric body and the restricting member are not fixed but contact with each other for keeping electric conductivity.