Absolute Position Sensing Based on a Robust Differential Capacitive Sensor with a Grounded Shield Window

Bai, Yang; Lu, Yunfeng; Hu, Pengcheng; Wang, Gang; Xu, Jinxin; Zeng, Tao; Li, Zhengkun; Zhang, Zhonghua; Tan, Jiubin

doi:10.3390/s16050680

Cited by 19 publications

(20 citation statements)

References 22 publications

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“…Basically, their behavior can be simply described as a planar capacitor (i.e., C = ε·A/d, being ε the relative dielectric constant, A the active surface, and d the distance between capacitor metal plates) whose mechanical features (i.e., A and/or d) are temporarily changed by the physical phenomena to be detected. Furthermore, in several sensory systems, differential capacitive sensing configurations also provide a suitable reduction of the common-mode noise and the parasitic component effects [4][5][6][7][8][9][10][11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

A Capacitance-to-Time Converter-Based Electronic Interface for Differential Capacitive Sensors

2019

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In this paper we present an oscillating conditioning circuit, operating a capacitance-to-time conversion, which is suitable for the readout of differential capacitive sensors. The simple architecture, based on a multiple-feedbacks structure that avoids ground noise disturbs and system calibrations, employs only three Operational Amplifiers (OAs) and a mixer implementing a square wave oscillator that provides an AC sensor excitation voltage. It performs a Period Modulation (PM) and a Pulse Width Modulation (PWM) of the output signal proportionally to the sensor differential capacitance values. The sensor variation range and the detection sensitivity can be easily set through the additional resistors. Preliminary PSpice simulation results have shown a good agreement with theoretical calculations as well as a linear response with a high detection sensitivity of differential capacitive sensors having a baseline in the range [2.2 ÷ 180 pF]. Moreover, different experimental measurements have been also performed by implementing the circuit on a laboratory breadboard using commercial discrete components so validating the idea and providing the circuit performances with different kind of differential capacitive sensors achieving detection resolutions of about 0.1 fF in an overall differential capacitive variation range that is equal to ±15.8 pF. The achieved results demonstrate that the proposed interface solution is suitable for on-chip integration with different kinds of differential capacitive sensing devices, such as Micro-Electro-Mechanical-System (MEMS), force/position, and humidity sensors in biomedical and robotics applications.

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Section: Introductionmentioning

confidence: 99%

A Capacitance-to-Time Converter-Based Electronic Interface for Differential Capacitive Sensors

2019

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“…Absolute position displacement measurement sensors play an irreplaceable role in the field of high-precision measurements and as a component in the closed loop feedback control of computer numerical control (CNC) machine tool systems. The rapid development of high-precision positioning technology in CNC machine tool systems has generated an increasing demand for robust absolute displacement measurement sensors with high positioning accuracy and excellent repetitive positioning precision in harsh environments, such as under the conditions of electromagnetic interference, mechanical vibration, extreme temperature variation, and dust contamination [1][2][3][4][5][6][7]. Meanwhile, many types of absolute grating displacement measurement sensors with high precision and high resolution have been developed, including capacitive grating sensors [1,2], magnetic grating sensors [8], and optical grating sensors [9].…”

Section: Introductionmentioning

confidence: 99%

“…In contrast to AOG sensors, both magnetic and capacitive grating sensors have high tolerance for mechanical vibration and contamination due to dust and oil and, therefore, are commonly employed in servo drive systems [2,8,15]. The measurement error of absolute magnetic grating sensors can achieve values as low as ±5 µm over a 1000 mm range and can obtain a measurement resolution of 0.75 µm [15][16][17].…”

Section: Introductionmentioning

confidence: 99%

“…However, the large size of the magnetic head and poor resistance to electromagnetic interference restrict the use of such sensors for high accuracy applications. In comparison, capacitive grating sensors provide a fuller range of environmental advantages, which make them ideally suited to harsh machining environments [2,[18][19][20][21]. Moreover, the measurement error of absolute capacitive grating sensors can achieve values as low as ±0.3 µm over a 6 mm range, with an error of less than 0.01% over the full measurement range [2].…”

Section: Introductionmentioning

confidence: 99%

“…In comparison, capacitive grating sensors provide a fuller range of environmental advantages, which make them ideally suited to harsh machining environments [2,[18][19][20][21]. Moreover, the measurement error of absolute capacitive grating sensors can achieve values as low as ±0.3 µm over a 6 mm range, with an error of less than 0.01% over the full measurement range [2]. However, the measurement range of absolute capacitive grating sensors is limited, which restricts their use in practical applications [2].…”

Section: Introductionmentioning

confidence: 99%

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A High Precision Capacitive Linear Displacement Sensor with Time-Grating that Provides Absolute Positioning Capability Based on a Vernier-Type Structure

et al. 2018

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Nanometer-scale measurement devices with high accuracy and absolute long-range positioning capability are increasingly demanded in the field of computer numerical control machining. To meet this demand, the present report proposes a capacitive absolute linear displacement sensor with time-grating that employs a vernier-type structure based on a previously proposed single-row capacitive sensing structure. The novel proposed vernier-type absolute time-grating (VATG) sensor employs two capacitor rows, each with an equivalent measurement range. The first capacitor row is designed with n periods to realize fine measurement, while the second capacitor row is designed with n − 1 periods, and the phase difference between the second row and the first row is employed to obtain absolute positioning information. A prototype VATG sensor with a total measurement range of 600 mm and n = 150 is fabricated using printed circuit board manufacturing technology, and its measurement performance is evaluated experimentally. Harmonic analysis demonstrates that the measurement error mainly consists of first-harmonic error, which is mostly caused by signal crosstalk. Accordingly, an optimized prototype VATG sensor is fabricated by adding a shielding layer between the two capacitor rows and designing a differential induction structure. Experimental results demonstrate that the measurement error of the optimized prototype sensor is ±1.25 μm over the full 600 mm range and ±0.25 μm over a single 4 mm period.

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Characterization of a segmented printed circuit board (PCB) as a standard for absorbed dose to water from alpha‐emitting radionuclides

Khan,

Radtke,

DeWerd

2024

Medical Physics

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BackgroundOur previous work introduced and evaluated a standard for surface absorbed dose rate per unit radioactivity to water from unsealed alpha‐emitting radionuclides used in targeted radionuclide therapy (TRT). An overall uncertainty over 4.0% at k = 1 was reported for the absorbed dose to air measurements, which was partially attributed to the rotational alignment uncertainty in the geometrical setup.PurposeA printed circuit board (PCB) with a segmented guard was constructed to align the extrapolation chamber (EC) and the source plates using a differential capacitance technique. The PCB EC aimed to enhance the repeatability of the ionization current measurements. The PCB EC was evaluated using a thin film 210Po source. The measured absorbed dose to air cavity was compared with the Monte Carlo (MC) calculations. Using the extrapolation method, the surface absorbed dose rate to water was calculated.MethodsThe PCB EC was constructed with a 4.50 mm diameter collector surrounded by four sectors and a guard electrode. The sectors were isolated for rotational alignment and later connected to the guard for ionization current measurements. A bridge circuit measured differential capacitance between opposing sectors, and a hexapod motion stage rotated the source substrate to minimize the differential capacitance. The EC was evaluated using a 210Po source with a 3.20 mm diameter and 1.253 μCi radioactivity. MC simulations were performed to calculate the , , and correction factors. Ionization current measurements were performed for air gaps in the 0.3–0.525 mm range and surface absorbed dose rate to water was calculated.ResultsRotational offsets of up to 3.0° were found and the current repeatability was found to increase with the absorbed dose to air uncertainty calculated to be ∼2.0%. Using the capacitance method, the effective EC diameter was measured to be 4.53 mm. The recombination, polarity, and electrometer corrections were reported to be within 1.00% across all measurement trials. The MC‐calculated correction factors were calculated to be much larger than the recombination and polarity correction factors. The average , , and corrections were calculated to be 1.063, 0.9402, and 2.136, respectively. The MC‐calculated absorbed dose to air was found to overestimate the absorbed dose by over 4.00% when compared with the measured absorbed dose to air. The surface absorbed dose rate to water was calculated to be Gy/s/Bq with an overall uncertainty of 4.07%.ConclusionsThe constructed PCB EC was deemed suitable as an absorbed dose standard. A repeatable rotational alignment was achieved using the differential capacitance technique. The metal electrodes on the PCB made a difference of < 1.00% on the backscatter correction when compared to the EC comprised of polystyrene‐equivalent collector. A 20% difference in the surface absorbed dose rate to water was found between the two ECs, which is attributed to the cavity diameter differences leading to different magnitudes of dose fall‐off along the lateral direction.

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Absolute Position Sensing Based on a Robust Differential Capacitive Sensor with a Grounded Shield Window

Cited by 19 publications

References 22 publications

A Capacitance-to-Time Converter-Based Electronic Interface for Differential Capacitive Sensors

A Capacitance-to-Time Converter-Based Electronic Interface for Differential Capacitive Sensors

A High Precision Capacitive Linear Displacement Sensor with Time-Grating that Provides Absolute Positioning Capability Based on a Vernier-Type Structure

Characterization of a segmented printed circuit board (PCB) as a standard for absorbed dose to water from alpha‐emitting radionuclides

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