Hysteresis Error Research Articles

Sensor-Less Grasping Force Control of a Pneumatic Underactuated Robotic Gripper

Abstract The primary motivation of this study is to develop a sensor-less, easily controlled, and passively adaptive robotic gripper. A back-drivable pneumatic underactuated robotic gripper (PURG), based on the pneumatic cylinder and underactuated finger mechanism, is presented to accomplish the above goals. A feedforward grasping force control method, based on the learned kinematics of the underactuated finger mechanism, is proposed to achieve sensor-less grasping force control. To enhance the grasping force control accuracy, a state-based actuating force modeling method is presented to compensate the hysteresis error which exists in the transmission mechanism. Actuating force control experiment is performed to validate the effectiveness of the state-based actuating pressure modeling method. Results reveal that compared with the non-state-based modeling method, the proposed state-based actuating force modeling method could reduce the modeling error and control error by about 37.0% and 77.2%, respectively. Results of grasping experiments further reveal that grasping force could be accurately controlled by the state-based feedforward control model in a sensor-less approach. Adaptive grasping experiments are performed to exhibit the effectiveness of the sensor-less grasping force control approach.

Facile and Economical Fabrication of Superhydrophobic Flexible Resistive Strain Sensors for Human Motion Detection

Superhydrophobic flexible strain sensors have great application value in the fields of personal health monitoring, human motion detection, and soft robotics due to their good flexibility and high sensitivity. However, complicated preparation processes and costly processing procedures have limited their development. To overcome these limitations, in this work we develop a facile and low-cost method for fabricating superhydrophobic flexible strain sensor via spraying carbon black (CB) nanoparticles dispersed in a thermoplastic elastomer (SEBS) solution on a polydimethylsiloxane (PDMS) flexible substrate. The prepared strain sensor had a large water contact angle of 153 ± 2.83° and a small rolling angle of 8.5 ± 1.04°, and exhibited excellent self-cleaning property. Due to the excellent superhydrophobicity, aqueous acid, salt, and alkali could quickly roll off the flexible strain sensor. In addition, the sensor showed excellent sensitivity (gauge factor (GF) of 5.4–7.35), wide sensing ranges (stretching: over 70%), good linearity (three linear regions), low hysteresis (hysteresis error of 4.8%), and a stable response over 100 stretching-releasing cycles. Moreover, the sensor was also capable of effectively detecting human motion signals like finger bending and wrist bending, showing promising application prospects in wearable electronic devices, personalized health monitoring, etc.

An FBG Temperature–Pressure Sensor Based on Diaphragm and Special-Shaped Bracket Structure

A fiber Bragg grating (FBG) sensor capable of simultaneous temperature–pressure measurement is presented and experimentally verified, which consists of a diaphragm, a special-shaped bracket, dual FBGs, and protective housing. The principle of simultaneous temperature and pressure measurement with dual FBGs is theoretically illustrated and simulated by a finite-element analysis. The experimentally investigated results demonstrate that the sensor can be employed to measure temperature and pressure in environments where the temperature ranges from 50 °C to 200 °C and the pressure ranges from 0 to 40 MPa. The temperature sensitivity of the sensor is 31.8 pm/°C with a linear correlation coefficient of 0.9997; the pressure sensitivity is 50.6 pm/MPa, the linearity is 0.21%, and the repeatability and hysteresis error are 0.024% and 0.16%, respectively. The sensor exhibits a large measuring range, high-temperature resistance, miniaturized structure, and easily multiplexed, which allows it for temperature and pressure dual parametric measurements in high-temperature and high-pressure environments such as oil and gas wells.

KIT-5-Assisted Synthesis of Mesoporous SnO2 for High-Performance Humidity Sensors with a Swift Response/Recovery Speed

Developing highly efficient semiconductor metal oxide (SMOX) sensors capable of accurate and fast responses to environmental humidity is still a challenging task. In addition to a not so pronounced sensitivity to relative humidity change, most of the SMOXs cannot meet the criteria of real-time humidity sensing due to their long response/recovery time. The way to tackle this problem is to control adsorption/desorption processes, i.e., water-vapor molecular dynamics, over the sensor's active layer through the powder and pore morphology design. With this in mind, a KIT-5-mediated synthesis was used to achieve mesoporous tin (IV) oxide replica (SnO2-R) with controlled pore size and ordering through template inversion and compared with a sol-gel synthesized powder (SnO2-SG). Unlike SnO2-SG, SnO2-R possessed a high specific surface area and quite an open pore structure, similar to the KIT-5, as observed by TEM, BET and SWAXS analyses. According to TEM, SnO2-R consisted of fine-grained globular particles and some percent of exaggerated, grown twinned crystals. The distinctive morphology of the SnO2-R-based sensor, with its specific pore structure and an increased number of oxygen-related defects associated with the powder preparation process and detected at the sensor surface by XPS analysis, contributed to excellent humidity sensing performances at room temperature, comprised of a low hysteresis error (3.7%), sensitivity of 406.8 kΩ/RH% and swift response/recovery speed (4 s/6 s).

A Highly Sensitive Multimodal Tactile Sensing Module with Planar Structure for Dexterous Manipulation of Robots

Herein, a multimodal tactile sensing module that can improve the dexterous manipulation capabilities of robots with parallel grippers is reported. The tactile sensor consists of a 4 × 4 matrix 3‐axis force sensor array (with spacings of 2 mm) and a single‐temperature sensor. The tactile sensor uses inorganic silicon and gold as materials for the detection of strain and temperature and a polymer‐based elastomer to encapsulate the sensing layer. The sensing module is equipped with a readout circuitry for signal processing. Within the measurable force range (≈1.5 N) of the sensor cell, a prototype module exhibits a repeatability error within 2%, a hysteresis error within 3%, and a resolution as small as 10 mN. Furthermore, each sensor cell independently measures 3‐axis forces with a cross‐talk error of approximately 3%. The temperature sensor exhibits linear output properties in the approximate range of 5–75 °C. Experiments are performed by mounting the module on a parallel gripper to grasp a paper cup and a reflex hammer toy. According to the experimental results, the sensor can accurately detect the state of contact with an object by analyzing three tactile modalities (i.e., 3‐axis force distribution, vibration, and temperature).

Temperature-compensated fiber Bragg grating sensor based on curvature sensing for bidirectional displacements measurement

Measurement of displacement, deformation, curvature, and other physical parameters is of great importance for adequate Structural Health Monitoring (SHM) of large surfaces. Fiber Bragg Grating (FBG) sensors have become a focus of research in academia and engineering for structural monitoring applications. This paper presents the study and characterization of a displacement FBG sensor based on curvature sensing of an array of 4 FBGs, as well as possible applications for structural monitoring, developing the sensing part, and analyzing the signals obtained to develop a sensor with good sensitivity and resolution, capable of measuring bidirectional displacements. The sensor prototype is presented to measure displacements in a range of ±30 mm with a single grating, with a sensitivity of up to 74 pm/mm, linearity to R2 = 0.999, and hysteresis error up to 1.27 %, with temperature compensation for displacement monitoring in case of temperature variations.

Diabot: Development of a Diabetic Foot Pressure Tracking Device

Foot-related problems are prevalent across the globe, and this issue is aggravated by the presence of diabetes mellitus. Diabetic-foot-related issues include extreme foot pain, plantar corns, and diabetic foot ulcers. To assess these conditions, accurate characterization of plantar pressure is required. In this work, an in-shoe, low-cost, and multi-material pressure measuring insole, based on a piezoresistive material, was developed. The device has a high number of sensors, and was tested on 25 healthy volunteers and 25 patients with different degrees of diabetes. The working range of the device was observed to be 5 kPa to 900 kPa, with an average hysteresis error of 3.25%. Plantar pressure was found to increase from healthy to diabetic volunteers, in terms of both standing and walking. In the case of the diabetic group, the-high pressure contact area was found to strongly and positively correlate (R2 = 0.78) with the peak plantar pressure. During the heel strike phase, the diabetic volunteers showed high plantar pressure on the medial heel region. In regard to the toe-off phase, the central forefoot was found to be a prevalent site for high plantar pressure across the diabetic volunteers. The developed device is expected not only to assist in the prediction of diabetic ulceration or re-ulceration, but also to provide strategies and suggestions for foot pressure alleviation and pain mitigation.

Giant dielectric response, nonlinear characteristics, and humidity sensing properties of a novel perovskite: Na1/3Sr1/3Tb1/3Cu3Ti4O12.

In this study, we unveil a novel perovskite compound, Na1/3Sr1/3Tb1/3Cu3Ti4O12, synthesized through a solid-state reaction method, exhibiting remarkable giant dielectric response, nonlinear characteristics, and humidity sensing capabilities. This research highlights the emergence of a Cu-rich phase, the properties of which undergo significant alterations depending on the sintering conditions. The optimization of sintering parameters, encompassing a temperature range of 1040-1450 °C for 1-8 h, resulted in substantial dielectric permittivity (ε') values (∼2800-6000). The temperature dependence of ε' demonstrated relationship to the particular sintering conditions utilized. The acquired loss tangent values were situated within encouraging values, ranging from 0.06 to 0.16 at 1 kHz. Furthermore, the material revealed distinct nonlinear electrical characteristics at 25 °C, with the nonlinear coefficient values of 5-127, depending on ceramic microstructures. Additionally, we delved deeply into the humidity-sensing properties of the Na1/3Sr1/3Tb1/3Cu3Ti4O12 material, showing a considerable variation in ε' in response to fluctuations in relative humidity, thereby indicating its prospective application in humidity sensing technologies. The hysteresis error and response/recovery times were calculated, highlighting the versatility of this compound and its promising potential across multiple applications. The Na1/3Sr1/3Tb1/3Cu3Ti4O12 not only shows remarkable giant dielectric responses but also portrays significant promise for nonlinear and humidity sensing applications, marking it as a significant participant in the advancement of perovskite-based functional materials.

Design and Characterization of Three-Axis High-Range Inductive Tactile Force Sensor Utilizing Magnetorheological Elastomer for Robotic Surgical Applications

This article presents a three-axis inductive tactile force sensor utilizing a magnetorheological elastomer (MRE) marker for inducing inductance change in square-shaped coils, in response to an input force. The sensor consists of copper coils on a printed circuit board (PCB) and a patterned elastomer layer between the marker and coils. The proposed configuration of the coils reduces the mechanical crosstalk between the applied three-axis forces, thus decoupling the force axes. Finite-element method (FEM)-based analyses are carried out to optimize the sensing gap between the coils and the marker. To observe the effect of the elastomer material on the sensor performance, two types of silicone rubbers, Ecoflex-30 and RTV-528, are used to make the patterned elastomer and the marker. The sensor with Ecoflex-30 elastomer can measure forces up to 25 N in normal and 2.5 N in shear directions, whereas the sensor with RTV-528 elastomer has a higher force range of up to 30 N for normal and 6 N for shear directions but has a lower sensitivity. A resolution of 12.71, 7.96, and 6.61 mN is achieved with Ecoflex-30, whereas for RTV-528, the force resolution is 76.52, 11.7, and 23.98 mN for normal, shear, and angular shear directions, respectively. The hysteresis error for the proposed sensors is 7.2% and 5.3% for Ecoflex-30 and RTV-528 elastomers, respectively. The proposed inductive tactile force sensor can be used in a wide range of robotic surgical applications for sensing multidirectional forces with better resolution and low hysteresis error.

Smart Mattress Based on Multipoint Fiber Bragg Gratings for Respiratory Rate Monitoring

Long-term monitoring of respiratory rate (RR) is of great importance in people suffering from sleep-related breathing disorders (SBDs). Instrumented mattresses are gaining the attention of several research groups to monitor this vital sign. Among the existing sensing techniques, fiber Bragg grating sensors (FBGs) show promise in this arena. In this article, we presented a novel FBG-based smart mattress to monitor RR over time. The proposed measuring system consisted of 13 sensing elements (SEs) based on FBGs encapsulated in soft biocompatible rubber, totally embedded in multiple silicone layers. Compactness, robustness, and user comfort are the main advantages of our solution. The mattress size and the arrangement of the 13 SEs were chosen to allow monitoring subjects with different anthropometric parameters and taking up different sleeping postures. Before the overall system integration, each SE was subjected to static and dynamic metrological characterization, a process often overlooked in fiber-optic-based mattresses. Results showed a mean sensitivity to force equal to 14 pm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \,\,\text{N}^{-1}$ </tex-math></inline-formula> and a mean percentage hysteresis error always lower than 18%. The feasibility assessment of the system in RR monitoring was carried out on five healthy volunteers taking up common sleeping postures (i.e., supine -S-, right side -RS-, left side -LS-, and prone -P-) under two breathing conditions (i.e., quiet breathing -QB-, and tachypnea -T-). RR estimation showed a mean absolute error (MAE) always lower than 0.65 breaths/min. The promising findings proved the capability of our smart mattress in monitoring RR over time, encouraging the investigation of its performance in real-world scenarios.

Research and Development of Intelligent Drying Detection Technology for Machine-Made Sand

This paper aims to develop a high precision variable dielectric constant capacitor detector for mechanical sand water content testing. The non-contact on-line test method can effectively solve the problems of low repeatability of test data, large hysteresis error and poor linearity due to the non-uniform water content. In terms of hardware, CAV444 is a high-precision integrated chip, which matches the corresponding test circuit. The system communicates with PC through serial interface and implements the man-machine interface of PC system based on VS. Secondly, the distribution map method is used to measure the water content of machine-made sand, and the error analysis is carried out. The test shows that the output of the capacitive hygrometer is 0-5 V. The delay time should not exceed 0.15%. The repetition rate was within 0.33%. The measurement accuracy of this method is less than 3.52%.

Inkjet-Printed Temperature Sensors Characterized according to Standards.

This paper describes the characterization of inkjet-printed resistive temperature sensors according to the international standard IEC 61928-2. The goal is to evaluate such sensors comprehensively, to identify important manufacturing processes, and to generate data for inkjet-printed temperature sensors according to the mentioned standard for the first time, which will enable future comparisons across different publications. Temperature sensors were printed with a silver nanoparticle ink on injection-molded parts. After printing, the sensors were sintered with different parameters to investigate their influences on the performance. Temperature sensors were characterized in a temperature range from 10 °C to 85 °C at 60% RH. It turned out that the highest tested sintering temperature of 200 °C, the longest dwell time of 24 h, and a coating with fluoropolymer resulted in the best sensor properties, which are a high temperature coefficient of resistance, low hysteresis, low non-repeatability, and low maximum error. The determined hysteresis, non-repeatability, and maximum error are below 1.4% of the full-scale output (FSO), and the temperature coefficient of resistance is 1.23-1.31 × 10-3 K-1. These results show that inkjet printing is a capable technology for the manufacturing of temperature sensors for applications up to 85 °C, such as lab-on-a-chip devices.

Evaluation of Additively Manufactured Parts in Disruptive Manner as Deformation Elements for Structural Integrated Force Sensors

Laser-based powder bed fusion (LPBF) as an additive manufacturing (AM) process allows the integration of sensors at any location within the manufactured part. This allows for manufacturing smart parts that can be integrated into complex structures for monitoring applications, as they can perform in situ measurements. Especially, monitoring of force and torque is gaining increasing interest. However, a proper strain transmission from the mechanically loaded part to the embedded strain sensing element must be ensured, as the performance of such sensors is strongly dependent on it. In this work, we present an approach for additively manufactured deformation elements in a disruptive manner with integrated strain gauges using a steel plate as a measuring element carrier. To evaluate the strain transmission, and, thus, the performance of the additively manufactured deformation elements, we compare them to a conventionally manufactured deformation element with identical geometry. The strain gauges are applied after manufacturing at locations with a proper strain, which are determined by finite-element analysis (FEA). Loading these additively and conventionally manufactured prototypes with 15N results in only 0.1% linearity and 0.2% hysteresis error. Furthermore, a nearly linear temperature behavior of manufactured prototypes with a TK 0 of up to 0.3%/10K and a TK C of up to 0.6%/10K is achieved. These results confirm that a proper strain transmission is ensured within the additively manufactured deformation elements, making them competitive with conventionally manufactured deformation elements. Thus, the disruptive manufacturing process introduced is suitable for fabricating structurally integrated force sensors based on strain gauges.

Comprehensive Indicators for Evaluating and Seeking Elasto-Magnetic Parameters for High-Performance Cable Force Monitoring

The elasto-magnetic method is a promising pathway for cable force monitoring in cable-stayed bridges. Under the action of an externally applied pulsed magnetic field, both the variation in the main flux recorded by the induction coil and the localized surface magnetic field measured by the packaged magnetic sensor are typical signals for observing the elasto-magnetic effect in tensioned cables. However, the performances of the parameters extracted from the two types of elasto-magnetic signals are never strictly compared in the experiment. Meanwhile, comprehensive indicators for evaluating the ability of elasto-magnetic parameters on cable force characterization are seldom discussed. As a result, it is difficult to compare the performances of elasto-magnetic devices developed by different teams, and the pathway of seeking new parameters for cable force monitoring is obstructed. In this study, elasto-magnetic calibration experiments were performed on a cable of seven-wire steel strands to simultaneously measure the variation in the main flux and the localized surface magnetic field. Comprehensive indicators considering sensitivity, hysteresis error, and cable force resolution are proposed to examine the performances of classic elasto-magnetic parameters and new candidate ones. Through comparative study, two new parameters demonstrated outstanding ability for cable force measurement, and they are the minimum amplitude of the induced voltage and the area under the curve between two points of 3 dB height of the voltage measured by a Hall sensor. The latter is recommended for high-performance cable force monitoring from the perspective of simplicity in sensor configuration.

A Double FBGs Temperature Self-Compensating Displacement Sensor and Its Application in Subway Monitoring.

In order to ensure the effective vibration–reduction and vibration–isolation of the steel spring floating plate rail and meet the safe operation requirements of the subway, a Fiber Bragg Grating (FBG) displacement sensor for the deformation monitoring of the subway floating plate is proposed. The sensor adopts double FBGs to realize temperature self-compensation. The elastic ring is used as the elastic conversion structure after the fiber grating is pre-stretched; the two ends are pasted and fixed in the groove in the diameter direction of the ring, which avoids the waveform distortion caused by the full pasting of the fiber grating. The combination of linear bearing and displacement probe rods can increase stability and reduce friction loss so that the sensor has the advantages of high sensitivity and accurate measurement results. The test results and error analysis show that in the range of 0~20 mm, the sensitivity of the sensor is 164.2 pm/mm, the accuracy reaches 0.09% F.S, and the repeatability error and hysteresis error are only 1.86% and 0.99%, respectively. The thermal displacement coupling experiment proves that the sensor has good temperature self-compensation performance. It provides a new technical scheme for the effective monitoring and condition assessment of the built-in steel spring floating plate rail.

Calibrating a double aluminium bar with electrotensometric strain gauge attached

The transducers which are used for measuring force or weight are also called load cells. Most of those transducers use strain gauges to measure the applied force. In this paper, a calibration of a double aluminium bar with strain gauges attached is conducted in order to determine the major sources of error in the measurement process. The authors explain the entire process of calibration for a single load cell. The purpose is to determine the main measurement errors. The sensor was calibrated at maximum of 10 kg and loading were made by manual application of weights. The results of calibration reveal a very small hysteresis and linearity error which makes the sensor a reliable choice to measure force, weight, or load.

Soft Capacitive Force Sensors With Low Hysteresis Based on Folded and Rolled Structures

Force sensors made of a polymer material with soft characteristics have application potential in the fields of soft robotics, exoskeletons, and human motion measurement. However, the hysteresis of soft force sensors is generally large because their sensing materials are rubbers with large dynamic viscoelasticity. The problem of large hysteresis caused by this dynamic viscoelasticity needs to be solved to improve the dynamic measurement precision of these force sensors. In this article, we have tested and found that the hysteresis of silicone rubber is significantly reduced when it operates in a large strain range. Therefore, we propose a design idea to allow the silicone rubber to work at large strain ranges involving a folded and rolled capacitive sensor structure based on large prestretching. Compared with previously reported silicone rubber force sensors, this sensor has a lower hysteresis error of 4.73% and a lower repeatability error of 3.42%. In addition, the folded and rolled sensor exhibits quick response, long-term stability, and durability under periodic dynamic load.

Online capacitive detection method for moisture content of aggregate based on edge effect

The moisture content of aggregate has an important influence on the final mix proportion of concrete and the quality of finished products. The detection methods of moisture content include offline and online. At present, the offline oven-dried method which is inefficient is often used for measurement. The capacitance method is easy to implement, low cost, high precision, low power consumption and fast response. However, the traditional capacitance measurement method must ensure that the space inside the plate is full of medium, which is more suitable for offline measurement. In order to realize online measurement, a moisture content detection method of aggregate based on edge effect is proposed. The wear of the plate can be avoided effectively by using the coplanar scattering field capacitive plate combined with the striker plate. The signal processing circuit uses a single chip solution PCAP01 to effectively improve the anti-interference ability of the detection circuit. The developed sensor is suitable for inner water detection of aggregate. The experimental results show that the effective measurement range of the sensor is 0 ∼ 1.0%,the penetration depth is 10 mm, the resolution is 0.1%, the hysteresis error is 2.69%, and the repeatability error is 10.31%.

Design and experimental study of a fiber Bragg grating strain sensor with enhanced sensitivity.

A novel high-sensitivity fiber Bragg grating (FBG) strain sensor is reported, to the best of our knowledge. The sensitivity of the sensor is improved by fixing the FBG on an elastic substrate with a sensitization function. The sensitization principle of the designed sensor is introduced, and the mathematical model of the sensor is established. In the static and dynamic experiments of the sensor, the effect of adhesive between the sensor and the measured structure on the sensitivity of the FBG strain sensor is experimentally investigated. The experimental results show that the adhesive with high shear strength is beneficial to the realization of a high-sensitivity sensor. The sensor fixed with planting bar glue can achieve a sensitivity of 9.42 pm/µε, a repeatability error of 4.79%, and a hysteresis error of 3.36%, which is consistent with theoretical and simulation results. The designed high-sensitivity strain sensor has a simple structure, small size, and convenient installation, so it has a good application prospect in micro-strain monitoring.

High-temperature Pt–Al2O3 composite nano-thick interdigital electrodes for surface acoustic wave sensors

High-temperature stability of ultra-thin film electrodes is vital for surface acoustic wave (SAW) devices in harsh environments. This paper proposed the Pt–Al2O3 composite Nano-thick interdigital electrodes (IDEs) for langasite-based high-temperature SAW sensors. The sandwich structure of the IDEs was composed of Pt layers and Al2O3 armors. The armor consisting of barrier and coating layers was introduced to reduce the agglomeration, oxidation, and interdiffusion of IDEs at high temperatures. Capacitive bonding pads were proposed to transmit radiofrequency signals through the closed armor. The composite IDEs (226 nm thickness) had good structural stability and impurities concentration less than 1% at 1000 °C (3 h, air condition). Improved quality factors of 8805, and matched electrical impedance of 51 Ω and −16° were achieved through the electroacoustic optimized IDEs. Finally, multiple SAW temperature sensors using the composite IDEs presented fitting errors less than 1% and hysteresis errors below 4% in 80–1000 °C exceeded 9 h, which was 150 °C higher than existing ones. The proposed composite IDEs enable SAW devices to be applicated in 80–1000 °C.