Design Of Force Sensor Research Articles

A novel sensor using photo-interrupter for measuring static friction coefficient

A force sensor design utilizing a photo-interrupter is presented for measuring the static coefficient of friction (COF). The measurement of ice friction on polymer surfaces, a process that requires detecting forces in the sub-Newton range, is chosen for the study. The photo-interrupter is coupled with a specially designed sensitive flexure, with structural parameters validated through finite element methods, to detect the small forces. The static properties of the sensor are characterized by calibration techniques. An accompanying rotary table is constructed to measure the COF of ice on polymethylmethacrylate (PMMA) and polyester specimens under refrigeration conditions. The experimental results indicate that the device can be utilized to predict the COF. The designed portable and miniature friction measurement setup can be a compact and cost-efficient alternative to bulky tribo-rheometer equipment.

Structural Features Guiding the Design of Liquid-Crystalline Elastomeric Fluorescent Force Sensors

Liquid single crystal elastomers (LSCEs) containing carbazole fluorogenic components alter their luminescence when they are stretched along the director direction. The differential luminescent behavior arises from the distinct interaction between the carbazole fluorophores and their local environment before and after the application of the mechanical input. Indeed, the uniaxial deformation of the material, along its anisotropic direction, forces a closer mesogen–fluorophore interaction, which leads to the quenching of the carbazole luminescence. Importantly, this intermolecular interaction is intimately related to the intrinsic order present in the LSCE. As a result, the amount of light emitted by the material in the form of fluorescence diminishes upon deformation. Thus, the application of mechanical stimuli to liquid-crystalline elastomers furnishes to two interconvertible states for the system with distinct optical properties (with either different emission color or fluorescence intensity). The initial state of the material is completely restored once the applied force is removed. In this way, this kind of macromolecular system can transduce mechanical events into detectable and processable optical signals, thus, having great potential as optical force sensors. In this context, the realization of the distinct structural factors that govern the interactions established between the mesogenic and fluorogenic units at the supramolecular level upon deformation is essential for the development of efficient LSCE-based force sensors. In fact, not only the density of carbazole units and their connection to the main polymer backbone, but also the presence of long range molecular order in the system and the type of mesophase exhibited by the LSCE are key factors for the conception of efficient force sensors based on these self-organized polymer networks. In this review, we present a comprehensive and systematic description of the different features that control the mechanoluminescent behavior of fluorescent liquid-crystalline elastomers and will guide the future design of LSCE-based force sensors with improved performances.

Creating a Soft Tactile Skin Employing Fluorescence Based Optical Sensing

Currently, optical tactile sensors propose solutions to measure contact forces at the tip of flexible medical instruments. However, the sensing capability of normal pressures applied to the surface along the tool body is still an open challenge. To deal with this challenge, this letter proposes a sensor design employing an angled tip optical fiber to measure the intensity modulation of a fluorescence signal proportional to the applied force. The fiber is used as both emitter of the excitation light and receiver of the fluorescence signal. This configuration allows to (i) halve the number of optical fibers and (ii) improve the signal to noise ratio thanks to the wavelength shift between excitation and fluorescence emission. The proposed design makes use of soft and flexible materials only, avoiding the size constraints given by rigid optical components and facilitating further miniaturization. The employed materials are bio-compatible and guarantee chemical inertness and non-toxicity for medical uses. In this work, the sensing principle is validated using a single optical fiber. Then, a soft stretchable skin pad, containing four tactile sensing elements, is presented to demonstrate the feasibility of this new force sensor design.

Optimization of internal thread structure of force sensor considering fatigue performance

Purpose Fatigue damage of internal threads has gradually become the main failure mode of force sensor. To make the internal thread structure of force sensor meet the fatigue performance requirements, the design criteria of static strength and fatigue life are comprehensively considered in this paper. Design/methodology/approach The variation of static stress and fatigue life with the size of the main structure is obtained by simulation. By changing the number of thread turns, the hub height and outer diameter of the hub, the optimized design of the spoke force sensor is determined. Findings The experiment was carried out based on the determined optimized structure, and the results showed that the fatigue life meets the design requirements. Originality/value This research has certain guiding significance for the design and developments of high-cycle fatigue force sensors.

The optimization design of thin piezoelectric force sensor and theoretical analysis of static loading estimation

In the development of automation industry, external force detection/monitoring is essential for the safety of human and machines. To detect or measure these forces easily, a static loading sensor is required. However, commercially available sensors are too bulky and cause installation difficulties in automated machines. A piezoelectric element is an electro-mechanical component wildly used for actuator sensing or harvesting applications. In this paper, a 10 N capacity thin piezoelectric force sensor is designed and tested for external static load detection. This paper considers that larger strain made by an external force on a proposed piezoelectric sensor generates higher voltage, thereby increasing its force estimation accuracy. Meanwhile, in most piezoelectric force sensors, a cantilever beam mechanism is usually adopted for its simple structure; however, large deformations seen in cantilever piezoelectric sensors are not proportional to its measuring accuracy nor force bearing capacity. Therefore, in this paper, an amplified trapezoidal shape mechanism is designed to convert external vertical load into horizontal displacement deformation in order to obtain higher voltage generation. The Taguchi optimization design method is proposed to analyze the key factors that affect the amplified mechanism design of the piezoelectric sensor. Moreover, static loading force applied on a piezoelectric component generates constant voltage that eventually decreases with time. This is because of its internal electric impedance property, which causes difficulty in static loading force estimation. To represent the theoretical model of the static force estimation in this paper, a chain scattering description matrix of a two-port network was proposed to represent the electric impedance in relation to the mechanical properties’ variation. The measured results demonstrate the accuracy of the proposed theoretical method which implies that the external force can be estimated by measuring its electric impedance variation, particularly the shift in resonance frequency Therefore, based on the developed theoretical model, a driving voltage with fixed frequency can measure its electric current in the same time, thereby achieving the external force monitoring technology.

On the Design of Force Sensors Based on Frustrated Total Internal Reflection

Frustrated total internal reflection (FTIR) of light is a physical phenomenon which can be used to accomplish several measurement tasks. This paper deals with the design and modeling of pressure field or force sensors based on FTIR. In fact, it is possible to convert the value of contact pressure into a light intensity signal, owing to the frustration of reflection of a dedicated medium. In this sense, it is possible to measure pressure/forces with a camera system or a photosensitive sensor. In this paper, the physical principles of the technique are recalled. Then, an experiment will document the behavior of FTIR at micromechanical level. Consequently, a Greenwood–Williamson (GW) model is proposed as a tool to predict the response of the FTIR-based pressure sensor. Experimental data and uncertainty analysis show that the design methodology is able to predict the behavior of the sensor with an uncertainty that is about ±10% of the actual specimen response, thus providing an effective tool to optimize the FTIR experiments.

Architecture and design of a robotic mastication simulator for interactive load testing of dental implants and the mandible

Statement of problemDetermination of interactive loading between a dental prosthesis and the host mandible is essential for implant prosthodontics and to preserve bone. PurposeThe purpose of this study was to develop and evaluate a robotic mastication simulator to replicate the human mastication force cycle to record the required interactive loading using specifically designed force sensors. Material and methodsThis robotic mastication simulator incorporated a Stewart parallel kinematic mechanism (PKM) controlled in the force-control loop. The hydraulically operated PKM executed the wrench operation, which consisted of the combined effect of forces and moments exhibited by the mastication process. Principal design features of this robotic simulator included PKM kinematic modeling, static force analysis to realize the masticatory wrench characteristics, and the architecture of its hydraulic system. Additionally, the design of a load-sensing element for the mandible and implant interaction was also incorporated. This element facilitated the quantification of the load distribution between implants and the host bone during the masticatory operation produced by the PKM. These loading tests were patient-specific and required separate artificial mandibular models for each patient. ResultsThe simulation results demonstrated that the robotic PKM could replicate human mastication. These results validated the hydraulic system modeling for the required range of masticatory movements and effective forces of the PKM end-effector. The overall structural design of the robotic mastication simulator presented the integration of the PKM and its hydraulic system with the premeditated load-recording mechanism. ConclusionsThe developed system facilitated the teeth-replacement procedure. The PKM accomplished the execution of mastication cycle involving 6 degrees of freedom, enabling any translation and rotation in sagittal, horizontal, and vertical planes. The mechanism can simulate the human mastication cycle and has a force application range of up to 2000 N. The designed load-sensing element can record interactive forces within the range of 200 N to 2000 N with fast response and high sensitivity to produce a robotic mastication simulator with custom-made modules.

Elastomer Encapsulated Pressure Sensor With Engineered Air Cavity for Force Sensing

Ground contact and force detection sensors are of critical technical importance in the realization of articulated robots capable of navigating unknown or challenging terrains. Current force sensors for robotic ground contact have limitations, including being too heavy, vulnerability to inertial noise, and lacking robustness and redundancy against failure. In this paper, we present the design, laboratory testing, and flight testing of a novel force sensor which addresses the aforementioned difficulties. The force sensor presented here is based on a custom elastomer dome with an engineered air cavity adhered to a barometric pressure sensor. Uniquely, we may tailor the sensitivity and range of the sensor by engineering the elastomer shape and the air cavity within it. Further, the large deformations incurred by the sensor are exploited to design a sensor enclosure which transfers large loads to structural members rather than onto the force sensor itself. An experimentally validated finite element model is developed to numerically predict the response of the sensor under an applied load. The model is used to perform trade studies on the geometry and material properties of the elastomer dome with a focus on developing design rules for this new type of sensor. With these simple design rules and finite element model, we design, manufacture, and test these new sensors as individuals and within arrays specifically for use on a rotorcraft robotic landing gear.

Design of By-Pass Excitation Cable Force Sensor

With the continuous progress of bridge technology and the requirements for bridge aesthetics, cable technology is increasingly widely used in long-span bridges. Due to the long-term environment of alternating stress, corrosion and wind-induced vibration, it is easy to cause local fatigue and damage of the cables, which endangers the safety of the entire bridge structure. The sleeve cable force sensor based on magnetic flux method is widely used in practical engineering among many measurement methods. Existing sleeve cable force sensors need to be installed at the beginning of construction, so it is difficult to reinstall them in the follow-up, and its long-term performance is also difficult to evaluate and measure online. To solve this problem, this paper introduces the design of a kind of magnetic flux cable force sensor with by-pass excitation, and presents its measuring principle and design structure. The designed by-pass excitation cable force sensor is expected to solve the problem of the existing sleeve sensor.

Design and analysis of three-axis cantilever type force sensor

PurposeThe force sensing is used in robotic assembly tasks. The sensors developed are much advanced and costly. The force transducers are generally configured and deployed at the wrist of the robotic arm. The purpose of this paper is to describe the concept of an elastic transducer to make available cost-effective force sensor with simple construction and analysis.Design/methodology/approachThe analytical formulation is developed herewith for one-, two- and three-axis elastic cantilever configuration. The force to be measured can be calculated analytically using derived strain expressions. The strains are estimated using proposed formulation, further crosschecked through FEA approach. The analytical method for strain estimation using moment equations is presented along with validation using finite element method (FEM) tool (ANSYS 15.0) with the case study.FindingsThe derivation of expressions for force components from strains is developed. The resulting formulation found to confirm the estimated strains from analytical methods closely to the FEM results. Theoretically, it is possible to find contact forces and angle of force on stationary force platform. It is found that the magnitude of estimated contact forces is within 1 per cent deviations.Research limitations/implicationsThe mathematical modeling and FEA simulation of the three-axis force sensor under elastic (no deformation) conditions.Originality/valueThese sensors are ranging from simple crossbar structure to Stewart platform type. The subsequent development in this field pertains to performance enhancement such as accuracy and cross-sensitivity. The basic structure of the sensor has not changed drastically. The major problem, as discussed by many authors, is a complex interdependence of six components and intricate geometrical structure. Derivation of expressions for force components from strains is a breakthrough contribution by the authors. The analytical treatment for finding the strains is aimed in this paper.

Insights into the Discrepancy between Single Molecule Experiments**Supported by the National Natural Science Foundation of China under Grant Nos. 11204045, 11464004, and 11864006, the State Scholarship Fund (20173015), and Guizhou Scientific and Technological Program (20185781)

Sharp bending as one of the mechanical properties of double-stranded DNA (dsDNA) on the nanoscale is essential for biological functions and processes. Force sensors with optical readout have been designed to measure the forces inside short, strained loops composed of both dsDNA and single-stranded DNA (ssDNA). Recent FRET single-molecule experiments were carried out based on the same force sensor design, but provided totally contrary results. In the current work, Monte Carlo simulations were performed under three conditions to clarify the discrepancy between the two experiments. The criterion that the work done by the force exerted on dsDNA by ssDNA should be larger than the nearest-neighbor (NN) stacking interaction energy is used to identify the generation of the fork at the junction of dsDNA and ssDNA. When the contour length of dsDNA in the sensor is larger than its critical length, the fork begins to generate at the junction of dsDNA and ssDNA, even with a kink in dsDNA. The forces inferred from simulations under three conditions are consistent with the ones inferred from experiments, including extra large force and can be grouped into two different states, namely, fork states and kink states. The phase diagrams constructed in the phase space of the NN stacking interaction energy and excited energy indicate that the transition between the fork state and kink state is difficult to identify in the phase space with an ultra small or large number of forks, but it can be detected in the phase space with a medium number of forks and kinks.

Spatio-temporal deep learning models for tip force estimation during needle insertion

PurposePrecise placement of needles is a challenge in a number of clinical applications such as brachytherapy or biopsy. Forces acting at the needle cause tissue deformation and needle deflection which in turn may lead to misplacement or injury. Hence, a number of approaches to estimate the forces at the needle have been proposed. Yet, integrating sensors into the needle tip is challenging and a careful calibration is required to obtain good force estimates.MethodsWe describe a fiber-optic needle tip force sensor design using a single OCT fiber for measurement. The fiber images the deformation of an epoxy layer placed below the needle tip which results in a stream of 1D depth profiles. We study different deep learning approaches to facilitate calibration between this spatio-temporal image data and the related forces. In particular, we propose a novel convGRU-CNN architecture for simultaneous spatial and temporal data processing.ResultsThe needle can be adapted to different operating ranges by changing the stiffness of the epoxy layer. Likewise, calibration can be adapted by training the deep learning models. Our novel convGRU-CNN architecture results in the lowest mean absolute error of 1.59 pm 1.3,hbox {mN} and a cross-correlation coefficient of 0.9997 and clearly outperforms the other methods. Ex vivo experiments in human prostate tissue demonstrate the needle’s application.ConclusionsOur OCT-based fiber-optic sensor presents a viable alternative for needle tip force estimation. The results indicate that the rich spatio-temporal information included in the stream of images showing the deformation throughout the epoxy layer can be effectively used by deep learning models. Particularly, we demonstrate that the convGRU-CNN architecture performs favorably, making it a promising approach for other spatio-temporal learning problems.

Clip-brazing for the design and fabrication of micronewton-resolution millimeter-scale force sensors

We present clip-brazing as a new method to construct millimeter-to-centimeter-scale metal structures with micron-scale precision that is fast, scalable and extremely low-cost. Small structures with demanding requirements on both dimensional tolerances and dynamic force responses to time-varying loads are difficult to fabricate and expensive to iteratively prototype. The technique introduced here enables precise placement of strong metallic brazed bonds to create 3D structures with micrometric accuracy, which in this work is exemplified through the design and construction of a broadband micronewton-resolution force-sensing device. The fabrication method uses tensioned clips made from a silver brazing alloy wire to accurately place and control the volume of the metal that joins and supports the pieces that compose the micro-structures. The use of clips also allows the simultaneous fusion of all the connections in the structure during a single heating sequence, reducing tolerance stack-up. To analyze the quality and strength of the brazes, we employed scanning electron microscopy (SEM) on cross-sections and tensile testing on dogbone-shaped sample pieces, respectively. After proper calibration, the functionality of the constructed micro-force-sensing system was analyzed and demonstrated using constant a priori known weights and the vertical periodic forces produced by an 83 mg flapping-wing microrobot (including a 3 mg attachment truss). The static tests, in combination with solid-mechanics analyses and simulations based on finite-element analysis (FEA), provide compelling evidence of the high accuracy and precision of the force sensing system for frequencies below 167.5 Hz. Furthermore, the shape characteristics and average values of the measured periodic signals are compared to computational fluid dynamics (CFD) simulations and validated for two sets of flapping angles across the frequency range from 55 to 100 Hz. These results validate the proposed approach as a viable tool for microrobotic design and fabrication.

The Design and Analysis of a Novel Micro Force Sensor Based on Depletion Type Movable Gate Field Effect Transistor

A novel micro force sensor based on depletion type vertically movable gate array field effect transistor (VMGAFET) was developed with cross-axis decoupling structure and eight gate arrays. This novel sensor is able to detect ultra-low force and exhibit high measuring sensitivity. An accurate electrical model was then proposed and compared with a long channel model, which is better adopted in small-sized devices to predict the electrical performance of this sensor. We also developed a mechanical model for the micro force sensor. Finite element method simulations were conducted, and the results were in accordance with the theoretical ones. Then, a feasible fabrication process was illustrated for the proposed sensor. The measuring sensitivity and nonlinearity of the micro force sensor with the proposed structure and dimension parameters are $12.528~\mu \text{A}$ /nN and <1.35%, respectively. These theoretical analyses provide insights into the design of depletion type VMAGFET-based sensor and other kinds of devices based on movable gate field effect transistor or with similar movable structures.

Multi-dimensional force sensor for haptic interaction: a review

Haptic interaction plays an important role in the virtual reality technology, which let a person not only view the 3D virtual environment but also realistically touch the virtual environment. As a key part of haptic interaction, force feedback has become an essential function for the haptic interaction. Therefore, multi-dimensional force sensors are widely used in the fields of virtual reality and augmented reality. In this paper, some conventional multi-dimensional force sensors based on different measurement principles, such as resistive, capacitive, piezoelectric, are briefly introduced. Then the mechanical structures of the elastic body of multi-dimensional force sensors are reviewed. It is obvious that the performance of the multi-dimensional force sensor is mainly dependent upon the mechanical structure of elastic body. Furthermore, the calibration process of the force sensor is analyzed, and problems in calibration are discussed. Interdimensional coupling error is one of the main factors affecting the measurement precision of the multi-dimensional force sensors. Therefore, reducing or even eliminating dimensional coupling error becomes a fundamental requirement in the design of multi-dimensional force sensors, and the decoupling state-of-art of the multi-dimensional force sensors are introduced in this paper. At last, the trends and current challenges of multi-dimensional force sensing technology are proposed.

Phantom study of a fiber optic force sensor design for biopsy needles under MRI.

Biopsy needles with embedded force sensors can eliminate the needle deflection and the needle targeting failure risks during MRI guided biopsy procedures. Fabry-Pérot interferometry (FPI) based sensors are small, compact and immune to electromagnetic and RF interferences, and therefore they are suitable for needle guidance under MRI. In this work, an FPI based fiber optic force sensor design and its integration to an 18-gauge MRI compatible biopsy needle are presented. The custom designed FPI sensor provides a force measurement range up to 13 N with a resolution of 0.1 N through benchtop experiments. The MRI compatibility of the sensor was evaluated using a commercially available prostate phantom under MRI.

Embedded piezoresistive pressure sensitive pillars from piezoresistive carbon black composites towards a soft large-strain compressive load sensor

Soft robotics is a rapidly expanding field that aims at replacing rigid robotic components in a wide range of applications with more compliant, organic and functional components. The limited availability actuator-compatible sensors that can provide real-time feedback limits large scale implementation of these soft robots. A secondary sensing layer that encompasses the soft actuator or a sensor embedded soft actuator would enhance the suitability of soft robots in a wider range of applications. This article describes the design, fabrication and characterization of a carbon composite elastomeric force sensor, which aims to be a free standing film than can be cut into desired shape and embedded into soft robots while manufacturing for imparting self-sensing capabilities. Various concentrations of carbon black in the elastomer composite have been studied and the ideal concentration is derived. Carbon composite pillars as soft sensors with conductive tracks on top and bottom were fabricated and embedded in a soft elastomer matrix for analysing the sensor response under physical loading. The sensitivity of these sensors were identified and characterised, and were found to be capable of detecting forces as small as 0.1 N. The thin-film free-standing architecture of sensing element allows embedding the fabricated sensing element into any elastomer matrix improves the applicability of these sensors in a wide range of soft robotic applications.

Application of EMG and Force Signals of Elbow Joint on Robot-assisted Arm Training

Flexion-extension based on the system's robotic arm has the potential to increase the patient's elbow joint movement. The force sensor and electromyography signals can support the biomechanical system to detect electrical signals generated by the muscles of the biological. The purpose of this study is to implement the design of force sensor and EMG signals application on the elbow flexion motion of the upper arm. In this experiments, the movements of flexion at an angle of 45o, 90o and 135o is applied to identify the relationship between the amplitude of the EMG and force signals on every angle. The contribution of this research is for supporting the development of the Robot-Assisted Arm Training. The correlation between the force signal and the EMG signal from the subject studied in the elbow joint motion tests. The application of sensors tested by an experimental on healthy subjects to simulating arm movement. The experimental results show the relationship between the amplitude of the EMG and force signals on flexion angle of the joint mechanism for monitoring the angular displacement of the robotic arm. Further developments in the design of force sensor and EMG signals are potentially for open the way for the next researches based on the physiological condition of each patient.

Effect of elastomer characteristics on fiber optic force sensing performance in biomedical robotics applications

Miniaturized and “smart” sensors are required for research in biology, physiology, and biomechanics, and they have extremely important clinical applications for diagnostics and minimally invasive surgery. Fiber optic sensors have been proven to provide advantages compared to conventional sensors and high potential for biomechanical and biomedical applications. They are small, easy to operate, minimally invasive with low risk, more accurate, and inexpensive. This paper reports the design and modeling of a fiber optic force sensor that is capable of measuring compliance for a contact force of up to 1 N. The main objective of this study is to design and model a fiber optic sensor capable of measuring the total force applied on an object. A polydimethylsiloxane (PDMS) elastomer film with a thickness of 1.2 mm is placed between an optical fiber tip and an object, and it is used for measuring the force applied on a rigid element. The compliance of the fiber optic force sensor is measured by recording the response of PDMS elastomer films under different load conditions. We use finite element modeling results as a basis for comparing experimental data. The agreement between theoretical predictions and experimental data is reasonable and within an acceptable range.

Design and Calibration Experiment of a Novel Rigid-Flexible Hybrid Parallel Three-Dimensional Force Sensor With Deformability

To meet the requirement for multi-dimensional force sensor with flexibility in the field of human–robot interaction, a novel parallel 3-D force sensor with rigid–flexible hybrid component is proposed. The sensor can not only possess a high deformability, but also maintain constant transformation between the input and output forces in the whole deformable range. First, the static mathematical model of the sensor is established based on vector method. The isotropic performance of the sensor is then studied by using mathematical analytic approach, and the condition leading to isotropy is introduced. Furthermore, the influence of the main structural parameters on the sensor’s deformable range is analyzed. Based on that, a sensor prototype is fabricated. The calibration experiment and the moment effect experiment are performed. Experimental results prove the feasibility of the proposed sensor and the correctness of theoretical analysis. The study lays a foundation for the practical application of the novel 3-D force sensor.