Conceptual design of additive manufactured capacitive displacement sensors for adaptive pin array grippers

In order to solve the problems of high error rate and long time in the traditional signal error compensation method, a new nonlinear compensation method for the signal error of capacitance micro displacement sensor is designed. The structure of the capacitive micro displacement sensor is optimized. The signal acquisition module is used to collect the optimized capacitive micro displacement sensor signal, and the collected signal is processed by adding window interpolation FFT. According to the signal processing results, the RBF neural network model is used to realize the nonlinear compensation of the signal error of the capacitive micro displacement sensor. The experimental results show that the method has the advantages of less noise, lower compensation error rate and time consuming, and better practical application effect.

High-precision displacement sensors, which can measure large displacements with nanometer resolution, are key components in many ultra-precision fabrication machines. In this paper, a new capacitive nanometer displacement sensor with differential sensing structure is proposed for long-range linear displacement measurements based on an approach denoted time grating. Analytical models established using electric field coupling theory and an area integral method indicate that common-mode interference will result in a first-harmonic error in the measurement results. To reduce the common-mode interference, the proposed sensor design employs a differential sensing structure, which adopts a second group of induction electrodes spatially separated from the first group of induction electrodes by a half-pitch length. Experimental results based on a prototype sensor demonstrate that the measurement accuracy and the stability of the sensor are substantially improved after adopting the differential sensing structure. Finally, a prototype sensor achieves a measurement accuracy of ±200 nm over the full 200 mm measurement range of the sensor.

Electrode configuration method with surface profile effect in a contact-type area-varying capacitive displacement sensor

The performance of the metering device of aeronautical vehicle can not be carried out without the feedback of displacement sensor. In order to control the engine accurately, the metering device for controlling the fuel oil quantity in the aeronautical vehicle needs accurate displacement feedback. In order to realize more lightweight and integrated aviation metering device, the measuring principle of capacitive grating displacement sensor is introduced. According to the principle of capacitive grating displacement sensor, an integrated displacement sensing structure is proposed, and the displacement sensing layer is integrated on the surface of the structure. Realize the integration of sensing and structure. The structure and material of integrated sensing layer are studied, and the influence of material on sensing precision is found. The integrated displacement sensing metering device is designed, and the method for acquiring the stable signal is obtained. The testing platform of micrometer-level displacement feedback is built, the resolution of the integrated displacement sensing device is 1 µm, the measuring range is 15 mm, and the integrated displacement sensing structure replaces the original separated displacement sensor, thereby reducing the structure volume and the weight of the aviation metering device.

A four horn monopulse tracking feed is used to generate tracking signal in a C-band tracking application. Choke flanges are incorporated at the aperture of array of pyramidal horns in order to achieve better pattern symmetry and reduction in sidelobes. An in-line polarizer is used against each horn to achieve multiple polarization i.e. VP, HP, RHCP and LHCP. The polarizer consists of an in-line waveguide structure - one fixed and one rotating waveguide sections to generate all four polarizations. Monopulse comparator is used to generate sum and difference signal. In order to realize the feed in a compact form factor, complex shapes, e.g. diagonal bends, have been used and manufacturing of these complex shapes would have been possible using additive manufacturing technology (Metallic 3D Printing). This made the feed very compact and light weight. Processes have been evolved to overcome the challenges with additive manufacturing for achieving desired accuracies. The feed assembly has been tested in a standard Antenna Test Range. Return loss of the system is achieved as better than −15dB and null depth of difference pattern is also better than −35dB. There has been a close agreement observed between the simulated and measured results.

High-end instrumentation such as optical systems for space science applications deal with challenging requirements on the dimensional stability not only for the employed materials but also for assembled structures. Advanced materials and connection techniques demand investigation of yet unknown properties and validation of medium to long-term if not-life time stability to the picometer level. Examples are C/SiC and CFRP materials and diffusion bonded junctions [1,2]. Furthermore, highest level position sensing and control may be in need of displacement sensors that not only do provide picometer-level sensitivity (resolution) and precision (stability) but also accuracy. This accuracy demands for calibration methodologies with appropriate statistical and systematic measurement uncertainty budget and with traceability to international standards. Examples are capacitive displacement sensors, available with very high sensitivity and excellent linearity. Optical displacement interferometry is a promising approach to meet these validation and calibration needs. Non-contact optical interfacing in heterodyne and homodyne interferometry minimizes the perturbation on the sample under test while providing high sensitivity in phase measurement as it scales with the optical wavelength. Also many possible configurations and large displacement range are supported. Even higher sensitivity and precision for displacement measurement is available by means of Fabry-Perot interferometry (FPI), facilitated by the high frequency selectivity of the optical cavity resonance. Given the versatility in choice of the translation-actuated measurement interface, e.g. an electrically conductive one for capacitive sensors, FPI is particularly useful for the calibration of ultra-precision displacement sensors. We report on progress in our research on (i) displacement interferometry for dimensional stability measurements of materials, connections and sensors, and on (ii) calibration methodologies for ultra-precision displacement sensors using FPI, both approaches (i) and (ii) aiming for sub-nanometer accuracy. The concept (i) for dimensional stability measurements is a double-ended optical heterodyne interferometer [3]. A particular challenge in achieving picometer-level measurement uncertainty over longer periods of time (seconds to days) is the discrimination on intrinsic sample instability from other effects such as thermal expansion of both sample and interferometer bench. A dedicated balanced optical configuration is chosen in order to reduce the sensitivity of the instrument to such perturbations. Furthermore, for practical use in industrial applications, an intrinsic compensation of air refractive index variations is considered by means of a refractometer in a twin-interferometer configuration. For both concepts (i) and (ii) the targeted measurement accuracy requires validated alignment methodologies and measurement and correction of ambient conditions. Highest level accuracy is facilitated by the direct traceability to the VSL primary optical frequency standards. This work receives funding from the European Union within the European Metrology Research Program (EMRP) and from the Dutch Ministry of Economic Affairs, Agriculture and Innovation.

Chapter 8 - Measurement of Mechanical Quantities

The maglev train suspension gap sensor will generate detection errors when passing through the rail gap, which will affect the stability and safety of the train operation. Based on the three-dimensional finite element simulation, the over-slit characteristics of the rectangular electrode capacitive displacement sensor passing through the track gap are analyzed. A capacitive displacement sensor with a grid electrode is proposed. The capacitance fluctuation and detection error of the gate capacitance sensor passing through the rail gap under the condition of constant total size are studied, and the over-slit characteristics of the rectangular capacitance sensor and the grid capacitance sensor are compared. The simulation results show that the grid capacitance sensor significantly reduces the capacitance fluctuation of the maglev train passing through the rail gap, and also reduces the detection error to a certain extent. When the rail length is 20mm, the detection error of the grid capacitance sensor is reduced to nearly 1mm.

Capacitive sensors enable non-contact displacement measurements in the micrometer range with sub-nanometer resolution. To achieve this, a proper alignment of capacitive sensors is necessary. In this work, a non-contact, automated and intrinsic adjustment procedure is presented which is based on determining the extrema of slope error and nonlinearity. After the final adjustment step, the remaining tilt is less than 1.5 mrad. A measurement routine is used to evaluate the adjustment procedure by applying tilt around the final adjustment position and measuring the global slope error and the global nonlinearity. The combination of adjustment procedure and measurement routine enables the investigation of capacitive displacement sensors with higher accuracy in order to establish a comprehensive uncertainty budget and to explore improvements in capacitive sensor technology.

This paper presents a review of the latest advances in the field of capacitive, inductive (eddy current), and magnetic sensors, for measurement of absolute displacement. The need for accurate displacement and position measurement in the micrometer, nanometer, and subnanometer scales has increased significantly over the last few years. Application examples can be found in high-tech industries, metrology, and space equipment. Besides measuring displacement as a primary quantity, absolute displacement sensors are also used when physical quantities such as pressure, acceleration, vibration, inertia, etc., have to be measured. A better understanding of the commonalities between capacitive, inductive, and magnetic displacement sensors, as well as the main performance differences and limitations, will help one make the best choice for a specific application. This review is based on both theoretical analysis and experimental results. The main performance criteria used are: sensitivity, resolution, compactness, long-term stability, thermal drift, and power efficiency.

This work presents a compact (125 mm diameter) wideband four-element antenna array with a high isolation level for Global Navigation Satellite System (GNSS) anti-jamming applications. The array consists of four identical right hand circularly polarized (RHCP) single feed rectangular patch antennas that can cover BeiDou B1 band (1559.05 – 1563.15 MHz), GPS L1 band (1563 – 1587 MHz), Galileo E1 band (1559 – 1591 MHz), and GLONASS G1 band (1593 – 1610 MHz). The proposed array has a wide frequency bandwidth of 100 MHz (1.55 – 1.65 GHz) with an axial ratio of less than 3 dB. The patch antenna elements are designed on a substrate that has a high dielectric constant to achieve a compact size. The size of each patch element is only 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 32\times5.08$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . These patches are placed along the circumference of a circular aluminium ground plane of 125 mm diameter and 1.5 mm thickness in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> symmetrical arrangement. The edge-to-edge distance between the opposite patch elements is only 48 mm while for the adjacent elements the separation is only 27 mm. A microwave absorber material is employed to achieve an extremely low mutual coupling level over a wide frequency range (1.55 – 1.65 GHz) within a compact form factor. The proposed design achieves a mutual coupling of less than −20 dB within a compact overall form factor of 125 mm diameter over the entire band of interest. The simulated and measured results of reflection coefficient, mutual coupling, null steering, null depth, and radiation pattern show that the proposed antenna array is an excellent choice for multiband GNSS applications.

In this paper, we propose a three-axis pneumatic tactile display that is precisely controlled by using integrated capacitive displacement sensors. The proposed tactile display consists of a core body with a 3 × 3 balloon array on its top surface, four lateral balloons made of latex rubber, and inner and outer frames that include capacitive displacement sensors based on a flexible printed circuit board. The 3 × 3 balloon array on the core body is designed to apply normal haptic stimulation to a human fingertip. In addition, the lateral motions of the core body and each frame produce haptic stimulation in a tangential direction. Precise control of lateral motion was achieved by feedback control using the capacitive displacement sensors. The size of the fabricated tactile display was 26 × 26 × 18 mm3. We experimentally performed manipulation of the proposed device with a custom control system, thereby demonstrating accurate control of displacement.

A totally implant cochlear hearing aids system, integrating an implant microphone, interface electronics, a speech processor, a stimulator, and cochlear electrodes, can overcome the uncomfortable, inconvenient, and stigma problems associated with the conventional and semi-implantable hearing aids. This paper presents a laboratory feasibility study on the use of an electret condenser microphone (ECM) displacement sensor, serving as an implant microphone, and combined with a spring coupler to directly sense the umbo acoustic vibration. The umbo vibration characteristics were extracted from literature to determine the coupler and sensor requirements. A laboratory model was built to simulate the vibration source and experimentally study the transmission coefficient. Experimental data demonstrate that by using a 5 N/m stiffness spring, the umbo vibration amplitude as high as 67% can be transmitted to the sensor. Measurement of the sensor system on the temporal bone was also made. The minimum detectable sound pressure level (SPL) at 1 kHz is 41 and 67 dB for laboratory and 38 and 64 dB for temporal bone measurement for 1 and 388 Hz bandwidth, respectively. Better performance was achieved in a higher frequency. Results and analysis of this study can be used as a guideline for the future design of displacement sensors as implant microphones.

Efforts to meet the demand for planar two-dimensional (2D) displacement measurement systems are limited by the difficulties of manufacturing 2D diffraction gratings with high precision over a large area. The present work addresses this issue by capitalizing on the high-precision of one-dimensional capacitive displacement sensors based on time-grating to develop a planar 2D capacitive displacement sensor technology composed of a large-area array of excitation electrodes positioned on a fixed ruler and a small-area array of induction electrodes assembled on a coplanar moving ruler that travels over the fixed ruler at a fixed separation gap. Firstly, the individual traveling wave signals of the induction electrodes on the moving ruler are analyzed theoretically to develop a method for decoupling information pertaining to the separate displacements in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> directions. Then, the feasibility of the proposed decoupling method is verified by simulations based on a three-dimensional electric field model. Finally, the proposed measurement technology is validated experimentally based on tests conducted using a prototype sensor manufactured using standard printed circuit board technology. The experimental results demonstrate that the prototype sensor achieves measurement errors of ±8.2 μm and ±6.8 μm in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> directions, respectively, over the full 200 mm × 200 mm measurement range of the sensor.

High frequency bandwidth cutting force measurement in milling using capacitance displacement sensors