Two-Wire Magnetostrictive Driver Eliminates Feedback Wire
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Solution Overview
Problem
Existing ultrasonic dental scalers require a feedback wire for maintaining optimal operational frequency, leading to increased cable weight and inefficiency, which complicates the circuitry and generates excess heat, limiting the device's compactness and efficiency.
Innovation Solution
A two-wire approach using a full bridge synchronous class D amplifier and a power control circuit that measures current and voltage outputs through quadrature sampling, eliminating the need for a feedback wire by generating a pulse width modulated signal to drive the transducer at its optimal operational frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedback wire is used to maintain optimal operational frequency, then frequency control precision is improved, but cable weight increases
Solution Approach 1:
The patent extracts the frequency sensing function from the handpiece by using the existing energizing coil as a feedback coil, eliminating the need for a separate feedback wire. The sensing function is obtained by measuring the voltage induced in the energizing coil during the off-period of the class D amplifier, thereby achieving frequency control without adding cable weight.
Solution Approach 2:
The energizing coil serves dual functions: it acts as both the excitation coil for driving the magnetostrictive stack and as the feedback sensing coil for detecting operational frequency. This multi-functionality eliminates the need for a separate feedback wire, reducing cable weight while maintaining frequency control precision.
2Stability of the object's composition
If traditional feedback control circuitry is used, then frequency stability is improved, but device complexity increases
Solution Approach 1:
The patent combines the frequency sensing function with the existing drive circuitry by using the energizing coil as both excitation and feedback coil. The feedback voltage is obtained during the off-period of the class D amplifier without requiring separate sensing circuits, thereby reducing device complexity while maintaining frequency stability through automatic frequency tuning.
Solution Approach 2:
The system uses its own energizing coil to generate the feedback signal needed for frequency control, rather than requiring external sensing coils or complex feedback circuits. The class D amplifier's off-period is utilized to measure the induced voltage, allowing the system to self-regulate frequency without additional complexity.
3Speed
If conventional amplifier circuits are used, then frequency control is achieved, but heat generation increases
Solution Approach 1:
The patent replaces conventional linear amplifier circuits with a class D synchronous amplifier, which uses pulse-width modulation and switching transistors instead of continuous analog signal processing. This substitution dramatically reduces heat generation while maintaining fast frequency control response through efficient switching operation and resonant circuit tuning.
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 solution allows for efficient operation of the magnetostrictive transducer at optimal frequency without a feedback wire, reducing cable weight, heat generation, and enhancing the device's compactness and efficiency.
Implementation Method 1
a stack of plates of magnetostrictive material that expands and contracts when subjected to a time-varying electro-magnetic field generated by the energizing coil
Implementation Method 2
generating a pulse width modulated signal from the quadrature sampled sensed current and voltage that represents a pulse train approximation of a sine wave of the drive signal
Implementation Method 3
generating a resonant drive signal for a resonant circuit, the electrical signal output by the resonant circuit drives an excitation coil
Data Source
Figure 1~2b
Figure 3a~4
Figure 5~6
AI summary
A method for controlling a magnetostrictive ultrasonic transducer of the type used in a magnetostrictive ultrasonic dental scaler includes generating a drive signal for a resonant circuit using a full bridge synchronous class D amplifier. The electrical signal output by the resonant circuit drives an excitation coil that generates an electromagnetic field that causes the magnetostrictive ultrasonic transducer to vibrate. A feedback wire is rendered unnecessary by measuring current and voltage outputs of the resonant circuit and quadrature sampling the measured current and voltage outputs at the same sampling rate as used for the generation of the electrical signal by the resonant circuit. A pulse width modulated signal is generated from the quadrature sampled sensed current and voltage that represents a pulse train approximation of a sine wave of the drive signal for, in turn, being applied to the full bridge synchronous class D amplifier to generate the drive signal for the resonant circuit. Changes in the pulse widths of the pulse train change the amplitude of the drive signal.