Absolute Sensor Research Articles

Design and optimization of large-range absolute linear displacement sensors based on splicing technology

This paper proposes a high-resolution absolute time-grating displacement sensor, which can splice multiple ruler segments to expand the measurement range. The single-segment range of a ruler using a vernier structure for absolute measurement is 400 mm, through which the method of remodulation (i.e., the output signal of the first-level unit) is used as the excitation signal of the second- and third-level units to increase the measurement period and realize the passive design of the mover. To make a smooth transition of the signal near the joint, we set two independent sets of sensing structures on the mover. We obtain the state judgment coding signal and displacement value through the traveling wave signal received on the ruler and the absolute position judgment is realized by combining the position state and displacement value. The use results indicate that the measurement range of the sensor increases to 1200 mm after splicing, and the measurement accuracy reaches ± 5 μm.

A Long-Range 6-DOF Absolute Displacement Sensor for Magnetic Levitation Stage Based on the Coding Principle

A Long-Range 6-DOF Absolute Displacement Sensor for Magnetic Levitation Stage Based on the Coding Principle

Single-Track Magnetic Tape Absolute Position Sensor with Self-Adaptivity.

In this study, we demonstrate a single-track magnetic code tape-based absolute position sensor system. Unlike traditional dual-track systems, our method simplifies manufacturing and avoids crosstalk between tracks, offering higher tolerance to alignment errors. The sensing system employs an array of magnetic field sensing elements that recognize the bit sequence encoded on the tape. This approach allows for accurate position determination even when the number of sensing elements is fewer than the number of bits covered, and without the need for specific spacing between sensing elements and bit length. We demonstrate the system's ability to learn and adapt to various magnetic code patterns, including those that are irregular or have been altered. Our method can identify and localize the sensed magnetic field pattern directly within a self-learned magnetic field map, providing robust performance in diverse conditions. This self-adaptive capability enhances operational safety and reliability, as the system can continue functioning even when the magnetic tape is misaligned or has undergone changes.

An integrated high precision absolute angular displacement sensor

Abstract This paper proposed a high precision absolute angular displacement time grating sensor, and was assembled into an integrated encoder. This absolute angle sensor contains two incremental sensors, namely, N1 measurement period fine measurement component and N2 measurement period coarse measurement component, N1 and N2 are mutually prime, and N1 > N2. The induction electrodes of the fine measurement component adopt differential design to minimize the effects of external electromagnetic interference and common mode interference between different sensing units so as to achieve high precision displacement measurement, the phase difference between two incremental sensor is used for absolute positioning. The reflecting ring design simplifies the structure of the encoder and facilitates sensor integration. The induction output signals of different components are cross connected through leads to the reflecting ring far away from the measurement component to the first harmonic error during the measurement period. The reading heads adopt a round, uniformly distributed design scheme, and the average effect of the whole circumference closed ring sampling scheme is beneficial for improving measurement accuracy and eliminating harmonic errors. A sensor prototype with a diameter of 83mm was manufactured and assembled into an integrated encoder. Experimental results show that the sensor achieve a precision of 12" over a full 360° measurement range and a resolution of 0.5", and it can realize absolute positioning.

Construction and Experimental Research of Active Vibration Control System of Voice Coil Motor with Integral Acceleration Feedback

Abstract The skyhook control technology is widely used in active vibration isolation and has proven effective. However, the absolute speed sensor used in the skyhook control technology is easily affected by external factors and may be easily damaged. There are few application scenarios for the skyhook control technology. To overcome this limitation, a brand-new approach is proposed for the design of an isolator that involves a voice coil motor (VCM) and an accelerometer. First of all, the proposed structure is introduced, and the dynamic model is established to achieve an analytical solution. Then, an integral acceleration feedback (IAF) algorithm is introduced and simulations are carried out. Finally, a prototype is constructed to verify its vibration isolation performance. From the experimental results, it can be concluded that the proposed active vibration control system (AVCS) can effectively reduce the peak value near the natural frequency, with a peak value reduction of 14.77 dB. Compared with the simulation results, the peak change rate at 12.5 Hz is 3.92%. AVCS with IAF can be applied to more application scenarios with a similar isolation effect to skyhook control technology.

An Absolute Displacement Sensor Based on SNAP Microresonator and Similarity Matching Method

An Absolute Displacement Sensor Based on SNAP Microresonator and Similarity Matching Method

Practical RGB-to-XYZ Color Transformation Matrix Estimation under Different Lighting Conditions for Graffiti Documentation.

Color data are often required for cultural heritage documentation. These data are typically acquired via standard digital cameras since they facilitate a quick and cost-effective way to extract RGB values from photos. However, cameras' absolute sensor responses are device-dependent and thus not colorimetric. One way to still achieve relatively accurate color data is via camera characterization, a procedure which computes a bespoke RGB-to-XYZ matrix to transform camera-dependent RGB values into the device-independent CIE XYZ color space. This article applies and assesses camera characterization techniques in heritage documentation, particularly graffiti photographed in the academic project INDIGO. To this end, this paper presents COOLPI (COlor Operations Library for Processing Images), a novel Python-based toolbox for colorimetric and spectral work, including white-point-preserving camera characterization from photos captured under diverse, real-world lighting conditions. The results highlight the colorimetric accuracy achievable through COOLPI's color-processing pipelines, affirming their suitability for heritage documentation.

Design, Fabrication, and Characterization of a PTAT Sensor Using CMOS Technology

This paper presents the design of an integrated temperature sensor. The sensor was manufactured using the 3 µm CMOS technology. The proportional to absolute temperature sensor output signal was produced by two MOS transistors with biasing and buffering circuits. The sensor output voltage was linearly proportional to the absolute temperature in a wide range of temperature values. The measurement results coincide very well with the results of the process corner analysis. Certain non-linearities occurring at high temperature values are investigated in this paper in more detail. Additionally, the influence of neighboring circuits present in the manufactured integrated circuit on the sensor temperature response is studied.

Absolute planar two-dimensional time-grating displacement sensor with multi-frequency magnetic field coupling

Absolute planar two-dimensional time-grating displacement sensor with multi-frequency magnetic field coupling

Thermal Conductivity Absolute Humidity Sensor Adapted in Ambient Temperature and Pressure Fluctuations

Thermal Conductivity Absolute Humidity Sensor Adapted in Ambient Temperature and Pressure Fluctuations

Feasibility Investigation on Sinusoidal-Reluctance Rotor Contour in Variable Reluctance Resolver

Variable reluctance (VR) resolvers are universally employed as the absolute position sensor in motor control systems. In this paper, a 4-pole 16-tooth VR resolver is proposed with the novel sinusoidal-reluctance rotor contour, and its operation feasibility is evaluated via the analytical investigation and finite element (FE) analysis. Considering the slot and air-gap flux leakage, the original third-order harmonic from the sinusoidal-reluctance rotor contour can be compensated to suppress the total harmonic distortion (THD) in the envelope. And the magnitude of the compensation third-order harmonic can be regulated by adjusting the tooth width. Under 4 mm tooth width, the THD of the cosine envelope with the proposed rotor contour can be limited to only 0.54%, and the angle error can also be restricted to only 0.012 degree (0.72 arc min).

A Collaborative Graph-based SLAM Framework Using a Computationally Effective Measurement Algebra

Simultaneous localization and mapping (SLAM) is an essential task for autonomous rover navigation in an unknown environment, especially if no absolute location information is available. This paper presents a computationally lightweight framework to enable agents with limited processing power to carry out the SLAM cooperatively and without absolute onboard localization sensors in a 2D environment. The proposed solution is built on a graph-based map representation, where nodes (resp. edges) represent landmarks (resp. odometry-based relative measurements), a measurement algebra with embedded uncertainty, and a compact database format that could be stored on a server in a centralized manner. The operations required by the agents to insert a new landmark in the graph, update landmark positions and combine measurements as a loop is closed in the graph are detailed. The resulting framework was tested in a laboratory environment and on a public dataset with encouraging results; hence our method can be used for cost-effective indoor mobile agents with limited computational resources and onboard sensors to achieve a mapping while keeping track of the agent's position. The method can also be easily generalized for a 3D scenario.

A Novel All-Digital Resolver-to-Digital Conversion System Based on Numerical Synchronous Integration

Resolvers are universally employed as absolute angle sensors in motor control systems. Detecting the synchronous envelopes is an essential step during the Resolver-to-Digital Conversion (RDC) process when calculating the angle. However, conventional filter-based envelope detection could introduce enormous angle delay and peak capturing-based detection could lead to apparent quantization angle error. A novel all-digital RDC system is proposed in this paper with the synchronous envelopes detected based on numerical synchronous integration method. The sine and cosine signals are oversampled and then multiplied by the excitation signal before integration to derive the envelopes. The angle delay and quantization errors could thus be largely reduced compared with RDC systems based on conventional envelop detections. In the experiment, angle error is limited to less than 30 arc min at the angular speed of 1000 rpm.

Synthesis and photoluminescence characterizations of Zn2+ and Tb3+ codoped CeO2 phosphors for temperature sensing applications

Cyan light-emitting Ce0.985-xZnxO2:0.015 Tb3+ (x = 0 to 0.2) phosphors were synthesized using the ethylenediaminetetraacetic acid-assisted hydrothermal method. The X-ray diffraction and refinement analyses of the prepared phosphors indicated that the formed face-centered cubic structure remained intact even after the doping of large quantities of Zn2+ ions. However, the incorporation of Zn2+ ions increased the Ce3+/Ce4+ ratio, resulting in the enhancement of oxygen vacancies in the prepared phosphors. The generation of oxygen vacancies caused the evolution of a broad photoluminescence emission band ranging from 400 to 525 nm with a characteristic Tb3+ emission of approximately 543 nm. Two-emission regions in Ce0.885Zn0.1O2:0.015 Tb3+ phosphors were utilized for measuring the fluorescence intensity ratio (FIR) as a function of temperature ranging from 303 to 523 K. At 523 K, the FIR values dropped to approximately 40% of the starting temperature value. The variation of FIR values followed the Boltzmann behavior. The Boltzmann fitting demonstrated the feasibility of the present phosphors for temperature sensor applications. The optimum absolute sensor sensitivity of Ce0.885Zn0.1O2:0.015 Tb3+ phosphors was measured to be 0.0043 K−1 at 398 K with a resolution of approximately 1 K−1. Moderate temperature sensitivity, negligible hysteresis loop, and excellent reversibility revealed the suitability of Ce0.885Zn0.1O2:0.015 Tb3+ phosphors for sensing the temperature in various electronic devices.

Use of Different Types of Magnetic Field Sensors in Diagnosing the State of Ferromagnetic Elements Based on Residual Magnetic Field Measurements.

The early identification of micro-defects in ferromagnetic elements such as steel wire ropes significantly impacts structures' in-service reliability and safety. This work investigated the possibility of detecting mechanically introduced discontinuities using different magnetic sensors without magnetization of the tested object with a strong external field. This is called the passive magnetic testing method, and it is becoming increasingly popular. This research used differential sensors (measuring differences in field values at the nanotesla level) and absolute sensors (enabling the measurement of the magnetic field vector module or its components at the microtesla level). Each measurement result obtained from the sensors allowed for detecting discontinuities in the line. The problem to be solved is the quantitative identification of changes in the metallic cross-section of a rope.

Interference, diffraction, and diode effects in superconducting array based on bismuth antimony telluride topological insulator

It is well-known in optics that the spectroscopic resolution of a diffraction grating is much better compared to an interference device having just two slits, as in Young’s famous double-slit experiment. On the other hand, it is well known that a classical superconducting quantum interference device (SQUID) is analogous to the optical double-slit experiment. Here we report experiments and present a model describing a superconducting analogue to the diffraction grating, namely an array of superconducting islands positioned on a topological insulator film Bi0.8Sb1.2Te3. In the limit of an extremely weak field, of the order of one vortex per the entire array, such devices exhibit a critical current peak that is much sharper than the analogous peak of an ordinary SQUID. Therefore, such arrays can be used as sensitive absolute magnetic field sensors. A key finding is that the device acts as a superconducting diode, controlled by magnetic field.

Synthesis and spectroscopic characterization of Ce0.90Eu0.07Sm0.03O2 phosphors for luminescence-based thermometry applications

Uniform nanoparticles of Eu3+/Sm3+ co-doped CeO2 phosphors were prepared through a hydrothermal method assisted with ethylenediaminetetraacetic acid (EDTA) as a chelating agent. The pH values of the precursor solution were varied to obtain uniform morphology of Eu3+/Sm3+ co-doped CeO2 phosphors and the most uniform morphology of Eu3+/Sm3+ co-doped CeO2 phosphors was obtained at pH 10. The maximum photoluminescence efficiency was observed at 7 mol% of Eu3+ and 3 mol% of Sm3+ ions of Eu3+/Sm3+ co-doped CeO2 phosphors. The emission spectra for Ce0.9Eu0.07Sm0.03O2-δ phosphors consisted of a host (450–560 nm) and dopant (570–700 nm) emissions. The ratio between the intensity of host and dopant emissions showed strong temperature dependence and the variation of intensity ratio was utilized for temperature sensing. Within the studied temperature range (298–523 K), the value of absolute sensor sensitivity for Ce0.9Eu0.07Sm0.03O2-δ phosphors was elevated from 0.0026 to 0.025 K−1. The maximum relative sensor sensitivity of Ce0.9Eu0.07Sm0.03O2-δ phosphors was 2.8% K−1 at 373 K. The high sensor sensitivity and uniform morphology of Ce0.9Eu0.07Sm0.03O2-δ phosphors could be used for luminescence-based thermometry applications.

Feature-Based Scanning LiDAR-Inertial Odometry Using Factor Graph Optimization

Localization of a mobile robot in the absence of an absolute position sensor often relies on techniques such as visual or lidar-inertial odometry. While lidar has many advantages, the most capable sensors use scanning mechanisms, leading to motion-distorted scans. Previous strategies used to account for robot motion when performing state estimation and outlier rejection have drawbacks for use on highly dynamic, resource-constrained robots such as spacecraft during descent and landing. In this paper we develop a novel probabilistic factor for the inclusion of scanning lidar features, and an accompanying outlier rejection methodology. By using well-established, efficient feature tracking techniques, our image processing front end is both reliable and amenable to FPGA implementation, both of which are critical for operation on a spacecraft. We demonstrate our technique on a dataset from simulated planetary descent and landing. The results show that our system can be used to perform accurate lidar-inertial odometry, even in highly dynamic scenarios.

Review of Atom Chips for Absolute Gravity Sensors

As a powerful tool in scientific research and industrial technologies, the cold atom absolute gravity sensor (CAGS) based on cold atom interferometry has been proven to be the most promising new generation high-precision absolute gravity sensor. However, large size, heavy weight, and high–power consumption are still the main restriction factors of CAGS being applied for practical applications on mobile platforms. Combined with cold atom chips, it is possible to drastically reduce the complexity, weight, and size of CAGS. In this review, we started from the basic theory of atom chips to chart a clear development path to related technologies. Several related technologies including micro-magnetic traps, micro magneto–optical traps, material selection, fabrication, and packaging methods have been discussed. This review gives an overview of the current developments in a variety of cold atom chips, and some actual CAGS systems based on atom chips are also discussed. We summarize by listing some of the challenges and possible directions for further development in this area.

Reactive synthesis for relay-explorer consensus with intermittent communication

A distributed multi-agent system architecture is explored to reach approximate consensus with intermittent communication. The multi-agent system is cast as a relay-explorer problem, where a relay agent intermittently provides navigational feedback to multiple explorer agents that do not have on-board absolute navigational sensors in a pre-defined sub-region. Within each sub-region, there is one relay agent responsible for servicing the corresponding explorer agents, and the estimated trajectory of an explorer agent can cross the boundary and enter another sub-region. We develop a reactive synthesis approach to formulate the mission specifications, while the state–space system dynamics provide real-time information for state corrections. Specifically, we pre-synthesize a set of planning strategies corresponding to candidate instantiations (i.e., pre-specified representative information scenarios) to dynamically switch among the explorers, and the planning strategies enable transfer of the servicing responsibility between relay agents. To guarantee stability of the switching strategies and the approximate consensus of the explorer agents, we develop maximum dwell-time conditions using a Lyapunov-based analysis to allow the explorer agents to drift for a pre-defined period without requiring servicing from the relay agents. Finally, we include a simulation study to demonstrate the performance of the developed method.