Bending Sensor Research Articles

Driving Signal and Geometry Analysis of a Magnetoelastic Bending Mode Pressductor Type Sensor.

The paper deals with a brief overview of magnetoelastic sensors and magnetoelastic sensors used in general for sensing bending forces, either directly or sensing bent structures, and defines the current state of the art. Bulk magnetoelastic force sensors are usually manufactured from transformer sheets or amorphous alloys. In praxis, usually, a compressive force is sensed by bulk magnetoelastic sensors; however, in this paper, the sensor is used for the measurement of bending forces, one reason being that the effect of such forces is easily experimentally tested, whereas compressive forces acting on a single sheet make buckling prevention a challenge. The measurement of the material characteristics that served as inputs into a FEM simulation model of the sensor is presented and described. The used material was considered to be mechanically and magnetically isotropic and magnetically nonlinear, even though the real sheet showed anisotropic behavior to some degree. A sinusoidal magnetizing current waveform was used in the experimental part of this paper, which was created by a current source. The effects of various frequencies, amplitudes, and sensor geometries were tested. The experimental part of this paper studies the sensors' RMS voltage changes to different loadings that bend the sheet out of its plane. The output voltage was the induced voltage in the secondary coil and was further analyzed to compute the linearity and sensitivity of the sensor at the specific current characteristic. It was found that for the given material, the most favorable operating conditions are obtained with higher frequency signals and higher excitation current amplitudes. The linearity of the sensor can be improved by placing the holes of the windings at different angles than 90° and by placing them further apart along the sheet's length. The current source was created by a simple op-amp voltage-to-current source controlled by a signal generator, which created a stable waveform. It was found that transformer sheet bending sensors with the dimensions described in this paper are suitable for the measurement of small forces in the range of up to 2 N for the shorter sensors and approximately 0.2 N for the longer sensors.

Flexible Bending Sensors Fabricated with Interdigitated Electrode Structures Cross-Linked by Transition Metal Doped ZnO Nanorods

Bending strain sensors based on one-dimensional ZnO nanorod (NR) arrays cross-linked with interdigitated electrodes were fabricated on polyethylene terephthalate (PET) substrates. ZnO NRs were grown using the hydrothermal method through the dopings with different transition metals, such as Co, Ni, or Co-plus-Ni, on PET substrates, and their microstructural morphology and crystalline properties were examined by a variety of surface analysis methods. Ultraviolet photoresponse and normalized resistance change were measured according to the bending strains to concave and convex directions, and the highest gauge factors of 175 and 83 were achieved in the convex and concave directions, respectively, at a bending strain of 1.75%, when Co-plus-Ni was doped to the NRs.

Modeling and Control of a 5-DOF Parallel Continuum Haptic Device

In this article, we propose a new continuum robotics approach for haptic rendering and comanipulation. This approach is illustrated using a robotic interface with six motorized fixed axes connected by deformable beams, in parallel, to an end effector with 5 degrees of freedom. Apart from the rotation of the motors, this design has no articulation, and the motion of the end effector is achieved by deformation of the beams. The flexible beams are equipped with bending sensors, and the motors have encoders. We use a nonlinear finite element mechanical model of the robot based on a mesh of beam elements that is computed in real time at 20 Hz. The bending sensors are incorporated into the model, which allows us to obtain an accurate estimate of the force exerted by the user on the end effector. The model enables a new methodology for calculating the workspace of the continuum haptic device. The model also is propagated to a higher frequency loop (500 Hz), which performs sensing and control of the robot at high rates, using an admittance-type control to command new positions of the actuators. We show that this control methodology allows haptic rendering of virtual walls that are stiffer than the natural stiffness of the robot. Finally, we demonstrate the use of the device for simple comanipulation tasks.

Proposition of water meter for buildings based on a thin-film resistive sensor: electromechanical and thermal characterizations

Notoriously, measurement proves to be essential to encourage water conservation. Thus, this work characterizes two thin-film resistive sensors (bend sensors) with different coatings aiming at their application to measure water consumption. For this, the individual water measurement system is presented and discussed briefly. Then, resistive sensor parameters and operating principles are detailed, as well as the mathematical formulation of the correlation of the sensor resistance with the flow velocity. Methodologically, the system developed for the electromechanical and thermal characterization of the sensor is presented. The results allowed obtaining a quadratic relationship between the sensor deflection angle and the resistance. Furthermore, it was observed that the polyester-coated sensor presented a low hysteresis value when subjected to temperature variation, obtaining a negative linear relationship between the sensor resistance and temperature. In turn, the polyimide-coated sensor did not show low hysteresis when exposed to temperature change and flexed at 50° and 70° angles. Finally, it is proposed for future work computer simulations and experimental tests to confirm the applicability of the sensor for water measurement.

Bend Sensors Based on Nanocellulose Composites: Influence of Configuration of Resistive Strain Gauge

Bend Sensors Based on Nanocellulose Composites: Influence of Configuration of Resistive Strain Gauge

Intelligent fiber optic integrated sensing system for human motion monitoring

In recent years, the development of flexible bend sensors and their detection devices has attracted great interest. In this paper, an intelligent wearable plastic optical fiber (POF) integrated sensing system for human motion detection is presented. The system consists of POF bend sensors and a wearable fiber bend detection meter (WFBDM). By capturing the POF array image from the video stream, it realizes a sampling frequency of 91.7 times/s. It also greatly increases the integration of multiple sensors, with an integrated sensing area of only 0.35*0.35 mm2 for a single sensor. POF bending sensors with a diameter of 0.25 mm were tested using this system with a linear range of −40° to 90°, an accuracy of up to 0.4°, and a response time of 26.2 ms. The system has been successfully applied to human joint and muscle motion monitoring, and combined with machine learning to realize the intelligent recognition of human motion state. The sensing system is small in size, large in sensing range, high in sensitivity and good in stability, and has the ability of intelligent recognition and highly integrated multi-channel bend signals sensing.

Instrumented Flexible Glass Structure: A Bragg Grating Inscribed with Femtosecond Laser Used as a Bending Sensor.

Fused silica glass is a material with outstanding mechanical, thermal and optical properties. Being a brittle material, it is challenging to shape. In the last decade, the manufacturing of monolithic flexible mechanisms in fused silica has evolved with the femtosecond-laser-assisted etching process. However, instrumenting those structures is demanding. To address this obstacle, this article proposes to inscribe a Bragg Grating sensor inside a flexure and interface it with an optical fibre to record the strain using a spectrum analyser. The strain sensitivity of this Bragg Grating sensor is characterized at 1.2 pm/μϵ (1 μϵ = 1 microstrain). Among other applications, deformation sensing can be used to record a force. Its use as a micro-force sensor is estimated. The sensor resolution is limited by our recording equipment to 30 μN over a measurement range above 10 mN. This technology can offer opportunities for surgery applications or others where precision and stability in harsh environments are required.

Sustainable Collagen Composites with Graphene Oxide for Bending Resistive Sensing.

This work reports on the development of collagen films with graphene oxide nanoparticles (GO NPs), aiming toward the development of a new generation of functional sustainable sensors. For this purpose, different GO NP contents up to 3 wt % were incorporated into a collagen matrix, and morphological, thermal, mechanical and electrical properties were evaluated. Independently of the GO NP content, all films display an increase in thermal stability as a result of the increase in the structural order of collagen, as revealed by XRD analysis. Further, the inclusion of GO NPs into collagen promotes an increase in the intensity of oxygen characteristic absorption bands in FTIR spectra, due to the abundant oxygen-containing functional groups, which lead to an increase in the hydrophilic character of the surface. GO NPs also influence the mechanical properties of the composites, increasing the tensile strength from 33.2 ± 2.4 MPa (collagen) to 44.1 ± 1.0 MPa (collagen with 3 wt % GO NPs). Finally, the electrical conductivity also increases slightly with GO NP content, allowing the development of resistive bending sensors.

Tactile Sensing for Soft Robotic Manipulators in 50 MPa Hydrostatic Pressure Environments

Deep‐sea exploration remains a challenging task as the extreme hydrostatic pressure environment, darkness, and suspended sediment launch severely hinder the capability of deep‐sea vehicles. As a complement to underwater camera, tactile perception becomes especially important in situations where machine vision is limited. However, tactile sensors utilized in deep sea, which should be able to detect pressure changes of only hundreds of pascals under high hydrostatic pressure, are still lacking. To tackle the challenge imposed by hydrostatic pressure, a simulated deep‐sea environment flexible sensor (SDEFS) is proposed, consisting of a force sensor array and a bending sensor based on hydrogels for tactile sensing in 50 MPa hydrostatic pressure environments. The force sensor is unaffected by the hydrostatic pressure and achieves high sensitivity of 82.62 N−1 under 100 MPa hydrostatic pressure. The SDEFS is utilized to classify objects based on the difference in hardness. It can accurately classify seven objects on the ground, and three objects in an underwater environment with hydrostatic pressure of 50 MPa, with total recognition accuracies of 98.3% and 96%, respectively. With high force measurement sensitivity and accurate recognition ability under water, the SDEFS is expected to provide very valuable haptic sensing and feedback in deep‐sea exploration.

Machine-learning-assisted omnidirectional bending sensor based on a cascaded asymmetric dual-core PCF sensor.

An omnidirectional bending sensor comprising cascaded asymmetric dual-core photonic crystal fibers (ADCPCFs) is designed and demonstrated experimentally. Upon cascading and splicing two ADCPCFs at a lateral rotation angle, the transmission spectrum of the sensor becomes highly dependent on the bending direction. Machine learning (ML) is employed to predict the curvature and bending orientation of the bending sensor for the first time, to the best of our knowledge. The experimental results demonstrate that the ADCPCF sensor used in combination with machine learning can predict the curvature and omnidirectional bending orientation within 360° without requiring any post-processing fabrication steps. The prediction accuracy is 99.85% with a mean absolute error (MAE) of 2.7° for bending direction measurement and 98.08% with an MAE of 0.03 m-1 for the curvature measurement. This promising strategy utilizes the global features (full spectra) in combination with machine learning to overcome the dependence of the sensor on high-quality transmission spectra, the wavelength range, and a special wavelength dip in the conventional dip tracking method. This excellent omnidirectional bending sensor has large potential for structural health monitoring, robotic arms, medical instruments, and wearable devices.

Temperature and Surrounding Refractive Index Insensitive Bending Sensor Based on a Novel Cascaded All-Fiber Structure

Temperature and Surrounding Refractive Index Insensitive Bending Sensor Based on a Novel Cascaded All-Fiber Structure

Effect of fluid viscosity on the biomechanical sequence of oropharyngeal swallowing in healthy males

Objective: To confirm the effect of fluid with different viscosity on the normal biomechanical sequence of oropharyngeal swallowing in healthy males. Methods: Fifteen healthy male subjects [(27.7±1.8) years old] were recruited from November 2011 to February 2012 and instructed to swallow 15 ml of water (W), nectar-like fluid (N), and honey-like fluid (H) in an upright sitting position. The sensing system was consisted of tongue pressure sensor sheet, bend sensor, surface electrodes and microphone. They were used to monitor tongue pressure, hyoid activity, surface electromyography (EMG) of swallowing-related muscles and swallowing sound, respectively. The swallowing sound was chosen as the reference time. The significance of biomechanical sequence of structural events was determined by repeated-measures analysis of variance (ANOVA). Results: When swallowing liquid of any consistency, hyoid premotor and suprahyoid muscle electromyography (EMG) appeared synchronously (P>0.05), followed by the simultaneous appearances of hyoid rapid movement, peak time of suprahyoid muscle EMG, onset of infrahyoid muscle EMG, and anterior tongue pressure production (P>0.05). The peak time of infrahyoid muscle EMG was very close to the peak time of anterior tongue pressure (P>0.05), and both of them were earlier than the time that the hyoid reaching the highest position (P<0.05). At last, the time that the hyoid departing the highest position was synchronized with the disappearances of suprahyoid muscle EMG, infrahyoid muscle EMG, and tongue pressure (P>0.05). The tongue pressure production and peak time of tongue pressure arose from anterior to posterior along the midline of hard palate during normal swallowing, with the significances for tongue pressure production between the anterior site and the middle site (W: P=0.035, N: P=0.027, H: P=0.013) as well as the anterior site and the posterior site (W: P<0.001, N: P<0.001, H: P<0.001), while the appearance and peak time of the circumferential tongue pressure were very close (P>0.05). The increase of fluid viscosity did not affect the biomechanical sequence of the above structural physiological movements during normal swallowing. There were statistically significant differences between the hyoid premotor and the onset of suprahyoid muscle EMG when swallowing the honey-like liquid [(-1.03±0.47) and (-0.90±0.50) s] and water[(-0.87±0.32) and (-0.74±0.31) s] (P<0.001). Among the delayed structural events, except for the onset of infrahyoid muscle EMG and the tongue pressure production on the anterior site (P>0.05), the occurrences of all the parameters in swallowing honey-like fluid were significantly later than those in swallowing water (onset of hyoid rapid movement, P=0.007; time of hyoid reaching the highest position, P=0.034; time of hyoid departing the highest position, P=0.041; offset of hyoid movement, P=0.035; peak time of suprahyoid muscle EMG: P=0.040; offset of suprahyoid muscle EMG, P=0.014; peak time of infrahyoid muscle EMG: P=0.042; offset of infrahyoid muscle EMG, P=0.028; peak time of Ch.1: P=0.045; offset of Ch.1: P=0.012; onset of Ch.2: P=0.038; peak time of Ch.2: P=0.009; offset of Ch.2: P=0.034; onset of Ch.3: P=0.043; peak time of Ch.3: P=0.011; offset of Ch.3: P=0.026;onset of Ch.4: P=0.040; peak time of Ch.4: P=0.038; offset of Ch.4: P=0.033; onset of Ch.5: P=0.046; peak time of Ch.5:P=0.028; offset of Ch.5: P<0.001), but not for those between nectar-like fluid and honey-like fluid (P>0.05). Conclusions: The alteration of fluid viscosity did not affect healthy male biomechanical sequence of tongue, hyoid and swallowing-related muscles during normal swallowing. The biomechanics of the oropharyngeal structures is physiologically regulated with the alteration of fluid viscosity to ensure swallowing safely and smoothly.

Dual-dip long-period fiber gratings for directional bending measurement

A high-sensitivity bending sensor based on dual-dip long period fiber gratings (LPFGs) in a single-mode fiber is proposed. The length of the gratings is very short only 7.2 mm. The asymmetric perturbation in fiber is generated during the fabrication, which makes the dual-dip LPFGs show different bending sensing characteristics at opposite directions. Meanwhile, the highest bending sensitivity of −35.91 nm/m−1 and −20.74 dB/m−1 can be obtained at bending directions of 0° and 180°, respectively. Furthermore, the torsion and temperature sensing characteristics are investigated experimentally. The torsion sensitivities follow sine function showing potential for directional sensing. The temperature sensitivities are 41.9 p.m./°C and 45.1 p.m./°C are close, which can eliminate the cross-sensitivity to temperature.

7-Core Fiber-Based High-Resolution Omnidirectional Vector Bending Sensor Enabled by Microwave Photonics Filter

We proposed and experimentally demonstrated a high-resolution omnidirectional vector bending sensor based on 7-core fiber Mach-Zehnder interferometers (MZIs), which is interrogated by the microwave photonics technique. The sensor is composed of three MZIs in the 7-core fiber, and each MZI consists of two symmetric outer cores. Instead of using the traditional wavelength demodulation method, which has the drawback of very limited resolution due to the used optical spectrum analysis devices, e.g., optical spectrum analyzer (OSA), the proposed sensor is interrogated by high-resolution microwave photonics filter (MPF) system, which is capable of offering up to KHz level measurement resolution. As a result, curvature measurement with resolution of 0.0213 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is demonstrated when the used resolution of vector network analyzer (VNA) is 500 kHz. Thanks to the ultra-high measurement resolution of VNA (∼KHz), the curvature resolution can achieve 4.27 х 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in theory, which is 2 orders of magnitude higher than the traditional wavelength demodulation-based fiber bending sensors. The measured curvature sensitivity of the MZI exhibits highly bending direction dependence, attributed to different strain variation under distinct bending angle. In addition, owing to the different angular positions of cores of the MZI in the 7-core fiber, the MZIs have differential response to fiber bending. This feature has been used to develop vector bending sensing, which is manage to determine the bending direction by using any two MZIs, and the obtained average relative errors for the retrieved curvature and bending direction are 2.57% and 0.86%, respectively. The proposed sensor possesses the unique advantages of high sensitivity and high resolution over the state-of-the-art technology, which is very promising for omnidirectional vector bending sensing in the future.

Soft pneumatic actuators with integrated resistive sensors enabled by multi-material 3D printing

The concept of soft robots has garnered significant attention in recent studies due to their unique capability to interact effectively with the surrounding environment. However, as the number of innovative soft pneumatic actuators (SPAs) continues to rise, integrating traditional sensors becomes challenging due to the complex and unrestricted movements exhibited by SPA during their operation. This article explores the importance of utilising one-shot multi-material 3D printing to integrate soft force and bending sensors into SPAs. It highlights the necessity of a well-tuned and robust low-cost fabrication process to ensure the functionality of these sensors over an extended period. Fused deposition modelling (FDM) offers a cost-effective solution for embedding sensors in soft robots, directly addressing such necessity. Also, a finite element method (FEM) based on the nonlinear hyper-elastic constitutive model equipped with experimental input is developed to precisely predict the deformation and tip force of the actuators measured in experiments. The dynamic mechanical test is conducted to observe and analyse the behaviour and resistance changes of conductive thermoplastic polyurethane (CTPU) and varioShore TPU (VTPU) during a cyclic test. The flexible sensor can detect deformations in SPAs through the application of air pressure. Similarly, the force sensor exhibits the ability to detect grasping objects by detecting changes in resistance. These findings suggest that the resistance change corresponds directly to the magnitude of the mechanical stimuli applied. Thus, the device shows potential for functioning as a resistive sensor for soft actuation. Furthermore, these findings highlight the significant potential of 3D and 4D printing technology in one-shot fabrication of soft sensor-actuator robotic systems, suggesting promising applications in various fields like grippers with sensors and rehabilitation devices.

Multimodal E-Textile Enabled by One-Step Maskless Patterning of Femtosecond-Laser-Induced Graphene on Nonwoven, Knit, and Woven Textiles.

Personal wearable devices are considered important in advanced healthcare, military, and sports applications. Among them, e-textiles are the best candidates because of their intrinsic conformability without any additional device installation. However, e-textile manufacturing to date has a high process complexity and low design flexibility. Here, we report the direct laser writing of e-textiles by converting raw Kevlar textiles to electrically conductive laser-induced graphene (LIG) via femtosecond laser pulses in ambient air. The resulting LIG has high electrical conductivity and chemical reliability with a low sheet resistance of 2.86 Ω/□. Wearable multimodal e-textile sensors and supercapacitors are realized on different types of Kevlar textiles, including nonwoven, knit, and woven structures, by considering their structural textile characteristics. The nonwoven textile exhibits high mechanical stability, making it suitable for applications in temperature sensors and micro-supercapacitors. On the other hand, the knit textile possesses inherent spring-like stretchability, enabling its use in the fabrication of strain sensors for human motion detection. Additionally, the woven textile offers special sensitive pressure-sensing networks between the warp and weft parts, making it suitable for the fabrication of bending sensors used in detecting human voices. This direct laser synthesis of arbitrarily patterned LIGs from various textile structures could result in the facile realization of wearable electronic sensors and energy storage.

Ultra-low bending and temperature crosstalk directional torsion sensor by few-mode fiber based Mach-Zehnder interferometer

In this paper, a few-mode-fiber based in-line Mach-Zehnder interferometer is proposed and completed for directional torsion sensing by core-offset splicing technique. The optimal offset and fiber length for fabrication are gained and the comprehensive tests are conducted in terms of torsion, bending and temperature. The experimental results show that our sensor has obvious intensity variation with the applied shear strain. The torsion sensitivity reaches ∼1.1 dB/(rad/m) in the range from −13.08 rad/m to 13.08 rad/m, but with the wavelength shift of 0.102 nm/(rad/m). In addition, thanks for the tiny bending and temperature responses of −0.055 dB/m−1 and 0.014 dB/℃, the ultra-low cross-sensitivities of 4.7 × 10−2 (rad/m)/m−1 and 1.2 × 10−2 (rad/m)/℃ are gained simultaneously, which dramatically improves the practicality of fiber-optic torsion sensor.

Vector Bending Sensor Based on Hole-Assisted Three-Core Fiber Mach-Zehnder Interferometer

A vector bending sensor based on hole-assisted three-core fiber (HATCF) Mach-Zehnder interferometer (MZI) is demonstrated. The sensor is composed of multi-mode fiber (MMF) - HATCF - MMF structure embedded between two single-mode fibers (SMFs). The bending curvature and direction can be identified by interrogating the wavelength of the interference peak, and the maximum bending sensitivity of -28.726 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is obtained at the 220° direction. In addition, the sensor has a temperature sensitivity of 44 pm/°C and is insensitive to the external refractive index (RI).

Shape perception of soft hand based on dual-signal comparison contact detection

PurposeThe structural adaptive ability of the soft robot is fully demonstrated in the grasping task of the soft hand. A soft hand can easily realize the envelope operation of the object without planning. With the continuous development of robot applications, researchers are no longer satisfied with the ability of the soft hand to grasp. The purpose of this paper is to perceive the object’s shape while grasping to provide a decision-making basis for more intelligent robot applications.Design/methodology/approachThis paper proposes a dual-signal comparison method to obtain the fingertip position. The dual signal includes the displacement calculated by the static model without considering the external load change and the displacement calculated by the bending sensor. The dual-signal comparison method can use the obvious change trend difference between the above two signals in the hover and contact states to identify the touch position. The authors make the soft hand scan around the object through touch operation to detect the object’s shape, and the tracks of every touch fingertip position can envelop the object’s shape.FindingsThe experimental results show that the dual-signal comparison method can accurately identify the contact moment of soft fingers. This detection method makes the soft hand develop the shape detection ability. The soft hand in the experiment can perceive squares, circles and a few other complex shapes.Originality/valueThe dual-signal comparison method proposed in this paper can detect a touch action by using the signal change trend when the working condition suddenly changes with the rough robotic model and sensing, thus improving the utilization value of the measured signal. The problems of large model errors and inaccurate sensors also negatively impact the use of other soft robots. It is generally difficult to achieve good results by directly using these models and sensors with the thinking of rigid robot analysis. The dual-signal comparison method in this paper can provide some reference for this aspect.

Intelligent soft robotic fingers with multi-modality perception ability

In the context of industry 4.0, automatic sorting is becoming prevalent in production lines. Herein, we developed a bionic sensing system to achieve real-time object recognition. The system consists of 9 single-layer triboelectric nanogenerators (SL-TENGs) as touch sensors and 3 comb-shaped TENGs (CS-TENGs) as bending sensors, with a sensitivity of 110 V/kPa and stable output after 20,000 press cycles. These sensors were attached to a manipulator composed of three soft actuators, serving as soft robotic fingers. An enhanced electrical output of these sensors was achieved successfully, demonstrating their feasibility in detecting grasping location, contact pressure, and bending curvature. A one-dimensional convolutional neural network (1D-CNN) with 98.96% accuracy extracted information from the sensors, enabling the manipulator to serve as an intelligent sensing system with multi-modality perception ability. This robotic manipulator successfully integrated TENG-based self-powered sensors, soft actuators, and artificial intelligence, demonstrating the potential for future digital twin applications, particularly in automatic component sorting.