Piezoelectric Actuator Drive Circuit with Dynamic Feedback
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Solution Overview
Problem
The existing self-oscillating piezoelectric actuator drive circuits face a trade-off between stable oscillation at the primary resonant frequency and increased oscillation amount, where reducing the sense resistor value enhances resonant current but increases the likelihood of oscillation at higher-order frequencies, compromising desired frequency stability.
Innovation Solution
Incorporating a switching device that alters the resistance values of the sense resistor and feedback resistors between startup and operating states, using a combination of inverters and a counter to manage frequency characteristics, ensuring primary resonant frequency oscillation while minimizing higher-order resonant frequency effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the sense resistor value is reduced to increase resonant current, then the oscillation amount increases, but the loop gain at primary resonant frequency decreases causing oscillation to occur at higher-order frequencies
Solution Approach 1:
The patent applies dynamics by making the feedback resistor values changeable between startup and operating states. During startup, a first feedback resistor with higher resistance is used to ensure stable primary resonant frequency oscillation. During operation, a second feedback resistor with lower resistance is used to increase oscillation amount. This dynamic adjustment resolves the contradiction between frequency stability and oscillation amount.
Solution Approach 2:
The patent changes the resistance parameter of the feedback resistor between two discrete values depending on the operational state. The first feedback resistor has a first resistance value optimized for startup stability, while the second feedback resistor has a second resistance value optimized for operating oscillation strength. This parameter change approach allows the system to achieve both frequency stability and increased oscillation amount at different times.
2Power
If the sense resistor value is reduced to increase resonant current, then the oscillation intensity increases, but the effect of higher-order resonant frequency increases
Solution Approach 1:
The patent dynamically adjusts the feedback resistor value based on the operational state. During startup, the first feedback resistor with higher resistance suppresses higher-order resonant frequency effects while establishing primary resonant oscillation. During operation, the second feedback resistor with lower resistance allows increased resonant current while maintaining frequency stability through the established oscillation pattern.
Solution Approach 2:
The patent performs preliminary action by establishing stable primary resonant frequency oscillation during the startup phase using the first feedback resistor before transitioning to the operation phase. This preliminary establishment of correct oscillation frequency prevents the system from locking into higher-order resonant frequencies even when the sense resistor value is reduced for increased power output.
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 approach eliminates the trade-off between stable primary resonant frequency oscillation and increased oscillation amount, maintaining predominant primary resonant current and reducing integration costs by adding a minimal number of circuits.
Implementation Method 1
An oscillating body using a piezoelectric actuator can realize lower power consumption and smaller size
Implementation Method 2
an integrating circuit that integrates a signal obtained in which a negative feedback signal is subtracted from a positive feedback signal
Implementation Method 3
a first inverter that inverts an output signal of the integrating circuit; a second inverter that inverts an output signal of the first inverter
Data Source
AI summary
A self-oscillating piezoelectric actuator drive circuit includes a integrating circuit; an inverter (INV1), inverters (INV2 and INV3) inverting an output signal of the inverter (INV1), sense resistors (Rs1 and Rs2) connected to output sides of the inverters (INV2 and INV3), a positive feedback resistor (Rfb2) feeding back an output signal of the inverters (INV2 and INV3) to the integrating circuit; and a negative feedback resistor (Rfb1) feeding back a voltage generated from the sense resistors (Rs1 and Rs2, Rs1<Rs2 in terms of a resistance value) to the integrating circuit. In a startup state, the sense resistor (Rs2) and the inverter (INV3) are selected, and in an operating state after the startup state, the sense resistor (Rs1) and the inverter (INV2) are selected.