Capacitive Grating Sensor Absolute Positioning Signal Processing
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Solution Overview
Problem
Existing absolute type capacitive grating displacement sensors face limitations such as static and spatially distributed drive signals, requiring complex signal processing, sine waveform electrodes, inefficient analog-to-digital conversion, and linear approximation, which hinder real-time processing and lead to measurement errors and convergence issues during rapid movements.
Innovation Solution
The design incorporates a capacitive grating displacement sensor with a transmission board and a reflection board that move relative to each other, using periodically arranged electrodes to generate measurement wavelengths, and a measurement circuit with a drive signal generator and signal processing unit that converts the sensor drive signal into a periodic waveform, allowing for zero-crossing detection and elimination of harmonic components, eliminating the need for complex signal processing and enabling independent determination of displacement in each wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a static and spatially distributed drive signal is used, then the sensor can perform absolute positioning, but the demodulated signal becomes a DC signal that cannot alleviate harmonic effects through signal processing
Solution Approach 1:
The patent transforms the static spatially distributed drive signal into a dynamic time-varying periodic signal. The drive signal now varies with time according to a periodic waveform, which allows the demodulated signal to be AC rather than DC, enabling harmonic effect alleviation through signal processing while maintaining absolute positioning capability
Solution Approach 2:
The patent changes the temporal parameter of the drive signal from static to dynamic periodic variation. By introducing time-varying characteristics with a specific period, the system enables frequency-based signal processing techniques to remove harmonic components while preserving the absolute position measurement function
2Measurement precision
If a sine waveform electrode is used to downsize harmonic component, then measurement accuracy improves, but the electrode becomes difficult to manufacture
Solution Approach 1:
The patent replaces the mechanical requirement of sine waveform electrodes with an electrical solution. Instead of physically shaping electrodes into complex sine waveforms, the system uses a periodically varying drive signal applied to simple rectangular electrodes, achieving harmonic reduction through signal processing rather than electrode geometry
Solution Approach 2:
The patent changes the approach from geometric parameter control (electrode shape) to signal parameter control (drive signal waveform). By varying the temporal characteristics of the drive signal rather than the spatial characteristics of the electrodes, the system achieves the same harmonic reduction effect with much simpler manufacturing requirements
3Measurement precision
If A/D conversion of two orthogonal signals is performed to determine displacement, then measurement capability is achieved, but processing load increases
Solution Approach 1:
The patent extracts and processes only the fundamental wave component of the received signal through synchronous demodulation, rather than performing full A/D conversion of multiple orthogonal signals. This selective extraction approach determines displacement from a single processed signal component, significantly reducing A/D conversion requirements and processing load
Solution Approach 2:
The patent introduces synchronous demodulation as an intermediary processing step that converts the received signal into a form where displacement can be determined without complex multi-signal A/D conversion. The synchronous demodulation process acts as a mediator that simplifies the measurement pathway while preserving accuracy
4Measurement precision
If arctg operation is performed to determine displacement, then accurate position measurement is achieved, but real-time processing capability is exceeded
Solution Approach 1:
The patent extracts the displacement information directly from the phase or amplitude characteristics of the synchronous demodulation output, avoiding the need for arctg operations. By formulating the measurement to directly yield displacement through simpler mathematical relationships, real-time processing capability is maintained while measurement accuracy is preserved
Solution Approach 2:
The patent replaces computationally expensive arctg operations with simpler, faster calculations that can be performed in real-time. The solution uses computationally lightweight methods that achieve the same measurement goal without the processing burden of transcendental functions
5Productivity
If linear approximation is adopted to reduce processing load, then real-time processing is enabled, but measurement accuracy decreases
Solution Approach 1:
The patent replaces the need for linear approximation with exact trigonometric relationships obtained through synchronous demodulation. The method directly calculates displacement using precise mathematical relationships from the modulated signal, eliminating approximation errors while maintaining real-time processing through efficient signal processing algorithms
6Measurement precision
If a small fine wavelength is used to reduce linear approximation error and harmonic component effect, then measurement accuracy improves, but measurement range is limited
Solution Approach 1:
The patent implements multi-wavelength segmentation, using multiple different wavelengths simultaneously in the capacitive grating system. Each wavelength provides measurement information for different ranges, with the combination enabling both high precision (through the fine wavelength component) and extended measurement range (through coarser wavelength components), avoiding the trade-off between the two
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 simplifies displacement measurement, reduces processing load, and increases measurement speed and accuracy, enabling efficient absolute position measurement without the need for complex MCU processing or sine waveform electrodes, facilitating low-power, compact, and cost-effective implementation suitable for handheld tools.
Implementation Method 1
The capacitive coupling between the transmission grating and the reflection grating changes accordingly with change of the relative position of the transmission board and the reflection board
Data Source
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AI summary
An absolute position measurement capacitive grating displacement measurement method, a sensor, and an operating method of the sensor are provided. In the measurement method, a drive signal having wave properties is used to excite a transmission grating, and displacement of a measured position in each wavelength is transformed into an initial phase of a time fundamental wave. The displacement of the measured position in each wavelength is acquired through an addition counter. A signal having wave properties output by a drive signal generator of the sensor is connected to a transmission grating, the master clock of an oscillator is connected to each circuit, an output of a reception grating is connected to a synchronous capture circuit through a signal selection switch and an analog processing circuit; and the synchronous capture circuit is connected to a controller, an addition counter, and a Random Access Memory (RAM). The controller is connected to all components. In the operating method of the sensor, an interface unit starts a measurement unit, a controller coordinates operation of all circuits, and after measurement of displacements in coarse, medium, and fine wavelengths is successively completed, the interface unit turns off the measurement unit, performs processing, and displays the measurement result. The circuits are simple, easy to control, and easy to be realized, and have high precision.