SAW Scale Recalibration Using Push Oscillator Frequency Shift
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Solution Overview
Problem
Existing electronic weighing devices face challenges in achieving high accuracy, expanded range, and low cost, with surface acoustic wave (SAW) scales experiencing issues with zero stability, span parameter stability, and temperature sensitivity, leading to measurement errors and linearity distortions.
Innovation Solution
The method involves recalibrating the auxiliary sensor of a SAW scale by storing frequency differences between adjacent resonance modes during initial calibration and determining the operating oscillation frequency upon power-up, allowing for precise weight calculation and elimination of drift, while using a push oscillator to enhance phase linearity and temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic force restoration technology is used to achieve high accuracy weighing, then measurement precision is improved, but device cost increases and temperature sensitivity worsens
Solution Approach 1:
The patent replaces magnetic force restoration technology with surface acoustic wave technology. Instead of using electromagnets to counterbalance weight, the invention uses piezoelectric transducers to generate and detect surface acoustic waves on a substrate. The weight measurement is achieved by measuring changes in the acoustic wave properties caused by substrate deformation, thereby eliminating the need for magnetic components and their associated temperature sensitivity issues.
Solution Approach 2:
The patent changes the fundamental measurement parameter from electrical current (in magnetic scales) to acoustic wave frequency and phase characteristics. By measuring the frequency shift and phase change of surface acoustic waves as the substrate deforms under load, the system achieves high accuracy while being less sensitive to temperature variations, as acoustic wave measurements are inherently more stable across temperature ranges.
2Weight of stationary object
If load cell technology with strain gauges is used to expand weighing range, then capacity is improved, but measurement precision deteriorates
Solution Approach 1:
The patent segments the weighing measurement into multiple acoustic wave modes (fundamental mode and higher-order modes). Each mode provides a different sensitivity range, allowing the system to maintain high resolution across a broad capacity range. By utilizing multiple resonant modes of the substrate, the system can accurately measure both small and large weights without sacrificing precision.
Solution Approach 2:
The patent transitions from one-dimensional strain gauge measurements to multi-dimensional acoustic wave analysis. By measuring frequency, phase, and amplitude characteristics of surface acoustic waves across different modes, the system extracts multiple measurement dimensions from a single substrate, enabling both high capacity and high resolution simultaneously.
3Ease of manufacture
If surface acoustic wave technology is used to achieve low cost and expanded range, then device cost is reduced and capacity is improved, but zero stability and span parameter stability worsen
Solution Approach 1:
The patent implements preliminary calibration procedures that store reference frequency and phase values for different weight conditions. During operation, the system compares real-time acoustic wave measurements against these pre-stored calibration data to compensate for drift in zero stability and span parameters. This preliminary calibration approach allows the system to maintain stability without requiring expensive environmental control mechanisms.
Solution Approach 2:
The patent employs feedback mechanisms where the measured acoustic wave parameters are continuously monitored and used to adjust and recalibrate the measurement system. By feeding back the actual frequency and phase measurements to the control system, the patent compensates for zero drift and span parameter changes, maintaining long-term stability without increasing device complexity or cost.
4Measurement precision
If auxiliary sensor recalibration is implemented to eliminate drift, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent makes the surface acoustic wave substrate serve multiple functions: it acts as both the sensing element for weight measurement and the reference element for calibration. The same substrate that measures weight also provides the reference frequency and phase signals needed for recalibration, eliminating the need for separate auxiliary sensors and reducing overall system complexity while maintaining high precision.
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 significantly reduces span drift, enhances linearity, and maintains high accuracy across varying temperatures, improving the overall performance of SAW scales by automatically recalibrating the auxiliary sensor and compensating for temperature effects.
Implementation Method 1
Each transducer includes a substantially rectangular piezoelectric substrate and a pair of electrodes imprinted on the substrate
Implementation Method 2
The output of the amplifier causes the first transducer to emit a surface acoustic wave which propagates along the surface of the first transducer substrate
Implementation Method 3
The propagating waves in the first transducer induce an oscillating electric field in the substrate which in turn induces similar SAW waves on the surface of the second transducer substrate
Implementation Method 4
the applied weight bends an elastic member which has strain gauges bonded to its surface
Implementation Method 5
When a load is applied to the load platform, the free end of the cantilevered elastic member moves and causes the first transducer to move relative to the second transducer. The movement of the first transducer relative to the second transducer causes a change in the frequency at the output of the amplifier.
Data Source
AI summary
Apparatus and related methods are provided in a surface acoustic wave (SAW) scale for measuring weight of a load. A processor reads a first frequency of a SAW delay line operating in a first mode. A push oscillator injects a frequency similar to but different than the first frequency in order to cause the SAW delay line to operate in a second mode, and the processor reads a second frequency of the SAW delay line operating in the second mode. A difference between the frequencies is calculated and compared to values in a stored table to determine the first mode at which the SAW delay line was operating. Based on a determination of the first mode and the first frequency, the weight of the load is determined. This determined weight can be used to recalibrate an auxiliary weight sensor.