High-Precision FBG 3-D Force Sensor Based on Spatial Hierarchical Sensing Structure

PurposeThe use of a force sensor to estimate the external force of manipulator not only needs to deal with the signal noise of the sensor itself but also needs to solve the coupling interference of the sensor itself, especially the axial force. The purpose of this paper is to develop a three-dimensional fiber Bragg grating (FBG) wrist force sensor, which has a simple structure and reduces the coupling influence between several axes.Design/methodology/approachA particular separation elastic structure with four FBGs is devised for the three-axial force sensor. One FBG is suspended on the profile of central cylinder and the other three FBGs are pasted on the elastic beam surface of the over and under measuring bodies, respectively. Finite element analysis (FEA) simulation has been implemented to the strain distribution characteristics, the output characteristics of each direction and the coupling effects of the structure. Furthermore, theoretical derivation and experimental results are used to compare, which have a good consistency.FindingsThe experiment results show that the maximum repeatability error of the sensor is 6.75%, the maximum nonlinear error is 5.36%, the maximum coupling interference is 4.73% and the minimum sensitivity is 1.58 pm/N.Originality/valueA three-dimensional force sensor based on FBG adopts a particular separation elastic structure. The sensor can reduce the coupling influence between several axes, especially the coupling interference in the z-direction is 0.

This paper presents the development of a novel and high-precision Fiber Bragg Grating (FBG)-based sensor for the measurement of insertion forces during the needle puncture procedure. The proposed sensor mainly comprises two compact orthogonal planar springs connected in a parallel arrangement, one suspended FBG optical fiber and a hand-held sensor frame. Two orthogonal planar springs with curved limbs have been utilized to design the force-sensitive flexure with an excellent linear force-displacement relationship along the axial direction. The employed optical fiber has been arranged along the flexure’s central line, and it is tightly suspended under a pre-tension force with its two ends glued. This two-point pasting configuration can attain improved sensitivity and resolution and avoid the drawbacks of chirping and low repeatability. Finite element modeling (FEM)-enabled simulation has been implemented for design optimization to further advance the sensor sensitivity and performance investigation. The sensor’s axial sensitivity has been increased in the condition when the radial crosstalk decreased. The proposed sensor has been prototyped and calibrated to achieve a high resolution of 1.5mN within [0, 6N] and an excellent linearity with a small linearity error of 0.5%. This design can be conveniently customized to achieve adjustable measurement range and force sensitivity, which has been validated by the further simulation sensor version with a resolution of 4.9mN within [0, 20N]. In-vitro puncture experiments on silicone phantoms, artificial venipuncture simulation module and eggshell membrane, and ex-vivo puncture experiments on porcine liver and porcine aorta have been implemented to validate the effectiveness of the presented sensor design.

This work presents a fiber Bragg grating (FBG) wide-range tilt sensor based on a cam structure. Two FBGs are fixed on a specially-designed sensor shell. When one FBG is stretched by the rotating cam driven by tilt, the other FBG moves along a standard semicircle with a constant radius, and compensates for temperature variations of the stretched FBG. By detecting the difference of the central wavelength shifts of two FBGs, variations of the tilt angle can be measured. The detailed mechanical structure design and measurement theory of the sensor is presented, and the sensor prototype is discussed. Testing results of comprehensive performance show that there is a good linear relationship between the tilt angle and the central wavelength of the FBG over three intervals from -90° to 90°. The repeatability and creep resistance of the FBG tilt sensor are good, the measuring accuracy is 1.516°, and the measuring resolution is 0.003°. The measurement range is much larger than comparable existing sensors, and it avoids cross-sensitivity between temperature and strain for FBG. The sensitivity of the sensor can be easily adjusted by changing the outline of the cam, or the length of the optical fiber between two fixed points.

Design and testing of a new microinjector with FBG force sensor for robot-assisted single cell microinjection

The lack of force information in surgical robots introduces new risks, such as injuries caused by too much force. This article presents a novel real-time temperature-compensated force sensor for surgical robot, which can provide real-time multidimensional force information without changing the structure of the surgical tool, but only installing one sensing fiber with four fiber Bragg gratings (FBGs). The finite element simulation shows that each FBG is subjected to different temperature changes under the influence of heat source. In order to achieve more accurate temperature compensation (TC), the sensitivity of reflectivity of FBG to strain and temperature is analyzed by theory and experiment, and TC is also realized with the dual parameter of reflectivity and wavelength shift. In addition, a zero-phase filter based on single-sided extension of fitting point is further designed to process the force signals, which eliminates the time delay introduced by traditional filters while filtering out interference signals. Finally, the effectiveness of this study is demonstrated by comparing the results with commercial force sensor.

Thermoacoustic Imaging (TAI) combines the high contrast of microwave imaging with the high resolution of ultrasound imaging, establishing itself as a novel, non-invasive medical diagnostic technique. However, the high-power (peak power: 5∼100kW; pulse width: 10∼1000ns) used in TAI often cause remarkable interference with thermoacoustic signal acquisition systems and traditional piezoelectric ultrasound transducers. This interference leads to degraded thermoacoustic image quality and a pronounced "near-field dead zone" (NFDZ), which severely restricts the clinical application and development of TAI. To address these challenges, this paper proposes using fiber Bragg grating (FBG) for thermoacoustic signal detection. The high sensitivity and strong resistance to electromagnetic interference offered by FBG are leveraged to achieve interference-resistant signal acquisition. Additionally, a photoelectric conversion synchronous triggering method is adopted to prevent strong coupling of spatially distributed pulse microwave signals to the data acquisition system due to excessively long coaxial cables. This approach ensures more reliable and interference-resistant data acquisition for TAI. Utilizing FBG with their high sensitivity and electromagnetic interference resistance, the system replaces traditional piezoelectric transducers for thermoacoustic signal detection. Additionally, a photoelectric conversion triggering method was implemented to avoid microwave pulse coupling interference caused by long coaxial cables. Experimental validation included comparisons between FBGs and traditional transducers in terms of signal-to-noise ratio (SNR), as well as noise measurements using both coaxial bayonet nut connector (BNC) cable and photoelectric trigger configurations to contrast test noise levels. Furthermore, the distance between the microwave antenna and data acquisition system was adjusted to validate the attenuation pattern of electromagnetic interference. TAI experiments used soy sauce tubes for their controllable composition/morphology. Systems imaging the tube also apply to human arms and ex vivo porcine liver (similar microwave absorption to tumors). This standardized, cost-efficient, and ethical approach provides a reliable basis for biological tissue imaging research. Experimental results show FBG with photoelectric triggering achieves SNR values of 28.32 (70.2% improvement) and 30.74dB (66.3% improvement) compared to traditional transducers at 16.64 and 18.48dB, respectively, representing an overall SNR enhancement of 64.0%∼88.0%. Furthermore, the photoelectric conversion triggering method reduces noise levels, which means shortening the NFDZ, leading to improved imaging quality and an extended effective detection range. Additionally, it was found that increasing the distance between the microwave antenna and the data acquisition system effectively reduced the noise amplitude, with the attenuation of direct spatial coupling interference conforming to the electric field intensity attenuation law (1/r attenuation). This study establishes that the FBG-based thermoacoustic imaging system, leveraging FBG's high sensitivity and electromagnetic interference resistance combined with photoelectric triggering, enhances signal quality and effectively suppresses near-field artifacts, enabling reliable clinical imaging. Validation through noise, signal, and spatial analyses confirms FBG's utility in advancing TAI. In summary, the method proposed in this article can be used for thermoacoustic endoscopy (especially for intravascular thermoacoustic endoscopy), thyroid and breast ablation TAI monitoring, as well as multimodal imaging combined with MRI and TAI.

Proximal force signals are widely used benefiting from the advantage of easy collection and are critical for enhancing the safety of the catheter surgical robot. This article presented two kinds of 3-D printable fiber Bragg grating (FBG)-based sensors for clamping force and axial force sensing. The clamping force sensor can realize the clamping–sensing function integration based on a 45° inclined rod and an arc hinge, while the axial force sensor adopts two symmetrical lamina emergent torsional (LET) joints to enhance the sensitivity and hysteresis characteristic. A data and theoretical model-driven method has been proposed to derive sensitivity models of sensors, and the relative errors compared with the experimental sensitivities are all within 10%. The calibration experiment results demonstrate that the designed sensor has obvious benefits in resolution (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 2.5 \text {mN}$ </tex-math></inline-formula>) and sensitivity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$480 \text {pm/N}$ </tex-math></inline-formula>) compared with other similar sensors. In addition, dynamic and durability experiments have been implemented to validate the reliability of the designed sensors. To achieve direct measurement of proximal force and reduce the influence of parasitic movement, the integration mode of two sensors is also carefully considered. A wireless technology-based primary–secondary control system and a fuzzy proportional–integral–derivative (PID) control strategy with overshoot compensation have been constructed, leading to the achievement of automatic adjustment of catheter movement and clamping force. Furthermore, several in vitro experiments have been implemented to verify the vascular protection, primary–secondary hand switching, and grading force control functions of the system. Such merits indicate that the designed proximal force sensors have huge potential in the field of catheter surgical robots.

Short cavity fiber grating lasers (FGLs) based on fiber Bragg grating (FBG) written on rare-earth doped fibers are attractive alternatives compared to semiconductor lasers for DWDM applications because of their wide tuning range, single mode output, as well as the ease to fabricate FBG with highly accurate wavelength that matches the ITU wavelength grids. However, the FGL wavelength is highly sensitive to operating conditions, and it is also subject to large frequency fluctuation and wavelength drift under strong pumping conditions. In this paper, the frequency fluctuation characteristics of a DBR FGL with a single FBG as the output reflector was investigated by employing an all-fiber unbalanced-arm scanning Michelson interferometer. A possible stabilization scheme using the error signal generated by the pseudo-heterodyne detection method is also demonstrated.

Piezo-electrical transducer (PZT) driven Fabry-Perot filter (F-P) filters are widely employed to implement a fast speed and high-resolution wavelength interrogation. Under a certain voltage, the transmission band of FFP can be tuned by changing the voltage applied on PZT. For the ideal design of the tunable filter actuation, the displacement–voltage relationship of PZT is assumed to be linear. However, temperature changes make the piezoelectric constant and dielectric constant of the material gradually change, and temperature drift leads to deterioration of the demodulation performance of tunable FabryPerot filters. Traditional calibration approaches are mainly based on F-P etalon and absorption lines of inert gas, but these approaches dramatically increase system cost and complexity. Considering the time series characteristics of temperature drift data, this paper proposes long and short-term memory (LSTM) neural network to compensate temperature drift of FP filters. During the cooling process of the F-P filter, the temperature and the drift of the reference fiber Bragg grating (FBG) are employed as the features of the LSTM model to characterize the wavelength drift of the sensing FBG. The experiment results show that after the wavelength is compensated with LSTM, the wavelength drift is reduced to 8.45 pm, while the compensated wavelength drift with the least square support vector machine (LSSVM) is 15.51 pm. Compared with LSSVM, LSTM is more suitable in long-term temperature-changing environments. Additionally, no additional hardware is required and the whole C band is covered in the proposed method.

During last decades, sensor elements based on the fiber Bragg grating (FBG) have been widely studied and developed due to the advantages of immunity to electromagnetic interference, compact size, high precision, and so on. The FBG itself is sensitive to axial strain and temperature variation directly and can indirectly measure these complex physical parameters, such as pressure, displacement, and vibration, by using some specially designed elastic structures to convert them into the axial strain of the FBG. Whether the FBG is fixed on the measured object to measure the strain directly or fixed on an elastic structure body to measure other physical quantities, these types of FBGs could be collectively called as strain sensing FBGs. The packaging of the FBG has important influence on FBG characteristics that directly affect the measurement accuracy, such as strain transfer, temperature characteristic, and spectral shape. This paper summarizes the packaging methods and corresponding temperature compensation methods of the currently reported strain sensing FBGs, focusing especially on fully pasted FBG, pre-stretched FBG with double-end fixed, and metallic packaging. Furthermore, the advantages and drawbacks of different packaging methods have been analyzed, which can provide a reference for future researches.

A new walk-in high precision fiber Bragg grating temperature sensor encapsulated with ultra-fine stainless steel tube was designed. The temperature resolution of the fiber sensor is 0.01 °C and the Bragg wavelength of the grating responses linearly with the temperature in the range of room temperature to 175 °C, meanwhile, the response time is less than 108 ms, which can satisfy the rapid response need of oil temperature profile. In addition, the resistance of the temperature sensor to pressure can be high up to 100 MPa.

The physical quantities involved in a triaxial testing device have mostly been monitored with electric sensors. These sensors are currently subject to short circuit when submerged under water and electromagnetic interference (EMI). Waterproofing and EMI noise filtration have often been a challenge to the triaxial test set-up. These drawbacks can be substantially minimized when using optic fiber sensors. The optic fiber Bragg grating (FBG) sensors have the additional advantage of being partially distributive where multiple sensors can share the same signal transmission line. Taking advantage of these unique capabilities, the authors explored the possibility of converting all pressure/force and linear displacement transducers in a triaxial testing device into FBG based sensors. A series of shearing tests on unsaturated and saturated soil specimens were carried out using the new FBG sensored triaxial testing device. In most cases, the measurement of physical quantities was paired with electric sensors so that the results can be compared. This paper describes the principles of the individual FBG sensor designs and demonstrates their applications in triaxial testing.

Fiber Bragg Grating (FBG) technology is very attractive to develop sensors for the measurement of thermal and mechanical parameters in biological applications, particularly in presence of electromagnetic interferences. This work presents the design, working principle and experimental characterization of a force sensor based on two FBGs, with the feature of being compatible with Magnetic Resonance. Two prototypes based on different designs are considered and characterized: 1) the fiber with the FBGs is encapsulated in a polydimethylsiloxane (PDMS) sheet; 2) the fiber with the FBGs is free without the employment of any polymeric layer. Results show that the prototype which adopts the polymeric sheet has a wider range of measurement (4200 mN vs 250 mN) and good linearity; although it has lower sensitivity (≈0.1 nm-N(1) vs 7 nm-N(1)). The sensor without polymeric layer is also characterized by employing a differential configuration which allows neglecting the influence of temperature. This solution improves the linearity of the sensor, on the other hand the sensitivity decreases. The resulting good metrological properties of the prototypes here tested make them attractive for the intended application and in general for force measurement during biomedical applications in presence of electromagnetic interferences.

We demonstrate a simple fiber-optic sensor for the measurement of transverse force, where a fiber Bragg grating (FBG) is used as a sensing element as well as a wavelength-selection element for a self-seeded Fabry-Pe/spl acute/rot laser diode (FP-LD). When a transverse force is applied on the FBG, the birefringence induced in the fiber causes the FP-LD to emit short pulses at two close wavelengths. The wavelength separation of the pulses is converted into a time difference between the two pulse trains by using a dispersive single-mode fiber, so that wavelength measurement is replaced by the much less expensive time-difference measurement. To extend the measurement range, the laser is made to emit at the two wavelengths alternately by using a polarization-switching technique. The sensor also allows compensation for any isotropic drift on the Bragg wavelength of the FBG.

Tension force sensing of driving cables is essential for continuum surgical robots to ensure operational safety and enhance surgical quality and outcomes. This article presents a fiber Bragg grating (FBG)-based force sensor with high sensitivity and accuracy for cable tension measurement in continuum robots. The proposed sensor comprises a force-sensitive flexure with a trapezoidal-shaped beam and a suspended optical fiber inscribed with an FBG element. The force-sensing flexure is developed from a conceptual lever displacement amplification model, and its specific shape is determined by topology optimization to achieve high stiffness and compactness. It transforms the tension input into the flexure deformation, which is further amplified to stretch the FBG optical fiber. The optical fiber adopts a two-point suspended configuration to avoid chirping failure and enhance sensitivity, taking advantage of the flexure’s lever amplification capability. Finite element method (FEM)-based simulation has been implemented to investigate the proposed sensor’s performance, and structural size optimization has been conducted for optimal design parameters and enhanced sensitivity. The sensor prototype has been calibrated to demonstrate a high resolution of 10.1 mN within [0, 50 N] and excellent linearity with a slight error of 0.25% FS. Dynamic loading experiments have been conducted to verify the prototype’s high accuracy with a root-mean-square error (RMSE) of 0.33% FS. The cable tension measurement experiment integrated into a continuum robot has been implemented to validate the effectiveness of the proposed sensor.