Three-axis Force Sensor Research Articles

Design of a Three-Axis Force Sensor Using Decoupled Compliant Parallel Mechanisms

Design of a Three-Axis Force Sensor Using Decoupled Compliant Parallel Mechanisms

A three-dimensional fiber Bragg grating wrist force sensor with separation elastic 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.

Hybrid 3D printed three-axis force sensor aided by machine learning decoupling

ABSTRACT Identification of magnitude and orientation for spatially applied loading is highly desired in the fields of not only the machinery components but also human-machine interaction. Despite the fact that the 3-axis force sensor with different structures has been proposed to measure the spatial force, there are still some common limitations including the multi-step manufacturing-assembly processes and complicated testing of decoupling calibration. Here, we propose a rapid fabrication strategy with low-cost to achieve high-precision 3-axis force sensors. The sensor is designed to compose of structural Maltese cross base and sensing units. It is directly fabricated within one step by a hybrid 3D printing technology combining deposition modeling (FDM) with direct-ink-writing (DIW). In particular, a machine learning (ML) model is used to convert the strain signal to the force components. Instead of a mount of calibration tests, this ML model is trained by sufficient simulation data based on programmed batch finite element modeling. This sensor is capable of continuously identifying a spatial force with varying magnitude and orientation, which successfully quantify the applied force of traditional Chinese medicine physiotherapy including Gua Sha and massage. This work provides insight for design and rapid fabrication of multi-axis force sensors, as well as potential applications.

A wearable three-axis force sensor based on deep learning technology for plantar measurement

A challenge in the measurement of plantar shear stress measurement is the absence of wearable and comfortable monitoring devices. In this paper, a wearable three-axis force sensor based on end-to-end deep learning technology is developed for plantar shear stress monitoring. The sensor can convert the three-axis stress it experiences into image signals through the deformation of the pattern layer embedded in the elastomeric probe. These images and three-axis stresses are fed into a convolution neural network for training, establishing a mapping relationship between images and three-axis forces. The prepared sensor has the advantages of small size (1.62 cm3), light weight (1.68 g), and flexibility, which make it possible to form a sensor array in the shoe without affecting the comfort of the wearer. By synchronizing with an action camera, the sensor array can provide real-time three-axis stress in different plantar regions for each frame of motions such as walking, running, playing football or basketball. This work contributes to the advancement of gait analysis, the clinical diagnosis of foot diseases, and the evaluation of athletic training.

Soft Three-Axis Capacitive Force Sensor for Robotic E-Skin on Curved Surfaces

Soft Three-Axis Capacitive Force Sensor for Robotic E-Skin on Curved Surfaces

Spatial and Temporal Analysis of Normal and Shear Forces During Grasping, Manipulation and Social Activities.

Extensive research has established and widely acknowledged the important contribution of human hand sensory receptors in providing tactile feedback. The absence of these receptors results in a poor perception of the environment, impairing our efficient manipulation skills. Although the literature emphasizes the significance of normal forces in human grasping, further investigations should point toward the role of shear forces in this process. This paper presents an analysis of human everyday grasping activities through the use of 20 three-axis magnetic soft skin force sensors, in the form of rings and bands, that measure both normal and shear forces. Our study includes twelve tasks that cover various grasping requirements. Results highlight the importance of spatial information and the usefulness of shear forces in the prediction of unexpected changes that can not be always observed in normal forces. Tactile sensing can ultimately be integrated into prosthetic and rehabilitation devices for improved control and potentially provide sensory feedback to the user.

A Compliant Three-Axis Force Sensor With Solid–Liquid Hybrid Cover for Prosthetic Fingertip

A Compliant Three-Axis Force Sensor With Solid–Liquid Hybrid Cover for Prosthetic Fingertip

Forces and moments generated during extrusion of a maxillary central incisor with clear aligners: an in vitro study

ObjectiveTo assess the possibility of extrusion of a maxillary central incisor with the use of buccal and lingual pressure columns in the absence of attachments, and to evaluate the forces and moments experienced by the teeth using both thermoformed and 3D-printed clear aligners.Materials and methodsA three-axis force and moment sensor (Aidin Robotics, Anyang, South Korea) was used to measure the forces and moments during extrusion of an upper left central incisor (UL1) and any forces experienced by the upper right central incisor (UR1) using thermoformed aligners and 3D-printed aligners. For the thermoformed aligners, the materials used were ATMOS® (American Orthodontics, Sheboygan, WI) and Zendura FLX® (Bay Materials LLC, Fremont, CA). 3D-printed aligners were fabricated using TC-85 clear photocurable resin (Graphy Inc., Seoul, South Korea). For each material type, three conditions were tested: Group 1: No attachment or pressure columns (control); Group 2: Attachment only; and Group 3: Pressure columns only. Each group was planned for 0.5 mm of extrusion on the UL1.ResultsAll force readings collected demonstrated statistically significant differences when compared by materials and when compared by groups, with a P value of < 0.001. In the absence of attachment or pressure columns (Group 1), ATMOS® and TC-85 groups exerted extrusive force on the UL1. However, significantly lower forces and moments were exerted by the TC-85 group in comparison to the ATMOS® and Zendura FLX® groups. In the presence of attachment (Group 2), all three ATMOS®, Zendura FLX® and TC-85 groups exerted extrusive force on the UL1, with the TA group showing different directions of faciolingual force, mesiodistal force and faciolingual inclination on the UR1 when compared to the other two thermoformed groups. Whereas in the presence of pressure columns (Group 3), only the TC-85 3D-printed aligner group exerted extrusive force. Thermoformed aligners generated significantly higher mean forces and moments than 3D-printed aligners. Significant levels of unintended forces and moments were present in all groups.ConclusionsForce levels generated during extrusion with clear aligners are significantly lower with those 3D-printed using TC-85 than with those thermoformed using ATMOS® or Zendura FLX®. Attachments consistently generated extrusive forces, and may be an effective adjunct in achieving extrusion of incisors. Extrusion may be achieved without the use of attachments by utilizing pressure columns in 3D-printed aligners using TC-85. While different strategies can generate extrusive forces, there are significant unintended forces and moments.

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.

An RNN-LSTM Enhanced Compact and Affordable Micro Force Sensing System for Interventional Continuum Robots With Interchangeable End-Effector Instruments

Micro force sensing in various clinical scenarios is a challenging issue to be addressed. It is highly difficult to trade off the size, cost, and measurement accuracy of a micro force sensing system. In this paper, a compact and affordable micro force sensing system enhanced by deep neural network is proposed. A three-axis force sensor is designed and fabricated with a footprint of only 14 mm and is employed to transform the force on the material structure into more accurate distance information. Such a sensor configuration can be seamlessly interfaced with the distal end of our in-house compliant and flexible continuum robot. On top of that, the RNN-LSTM network is exploited to augment the micro force sensing capability of the distal end-effector of the robot, which addresses the limitation on the nonlinear force issue of the continuum robot and the material itself. The RNN-LSTM network alone can be employed to perform force curve fitting for specific interventional tasks. The results indicate that more than 90% accuracy has been achieved, and the network can be applied to large-scale continuum robot-assisted interventional scenario deployment and teleoperation force perception.

Experimental Analysis of Handcart Pushing and Pulling Safety in an Industrial Environment by Using IoT Force and EMG Sensors: Relationship with Operators’ Psychological Status and Pain Syndromes

Non-ergonomic execution of repetitive physical tasks represents a major cause of work-related musculoskeletal disorders (WMSD). This study was focused on the pushing and pulling (P&P) of an industrial handcart (which is a generic physical task present across many industries), with the aim to investigate the dependence of P&P execution on the operators’ psychological status and the presence of pain syndromes of the upper limbs and spine. The developed acquisition system integrated two three-axis force sensors (placed on the left and right arm) and six electromyography (EMG) electrodes (placed on the chest, back, and hand flexor muscles). The conducted experiment involved two groups of participants (with and without increased psychological scores and pain syndromes). Ten force parameters (for both left and right side), one EMG parameter (for three different muscles, both left and right side), and two time-domain parameters were extracted from the acquired signals. Data analysis showed intergroup differences in the examined parameters, especially in force integral values and EMG mean absolute values. To the best of our knowledge, this is the first study that evaluated the composite effects of pain syndromes, spine mobility, and psychological status of the participants on the execution of P&P tasks—concluding that they have a significant impact on the P&P task execution and potentially on the risk of WMSD. The future work will be directed towards the development of a personalized risk assessment system by considering more muscle groups, supplementary data derived from operators’ poses (extracted with computer vision algorithms), and cognitive parameters (extracted with EEG sensors).

Development of a Three-Axis Monolithic Flexure-Based Ground Reaction Force Sensor for Various Gait Analysis

In this letter, we developed a monolithic flexure-based three-axis ground reaction force (GRF) sensor to analyze various gaits, including walking, running, and jumping. The GRF sensor requires different force capacities on each axis. In order to satisfy the force range requirements, a simple circular cross-section flexure was designed. The use of a monolithic flexure allows the sensor to have broad measurement range with enhanced durability in a compact, simple and lightweight structure. The proposed sensor can measure vertical force up to 2400 N and shear force up to 240 N that can measure wide range of GRF for walking, running and jumping. The deformation of the flexure under applied force is measured through capacitance changes and these values are converted into the three-axis force. The performance of the sensor was evaluated through several experiments. An outsole GRF measurement system was designed by embedding two developed sensors. The resultant GRF data during several in-place motions were measured with the developed system.

A Low-Cost Three-Axis Force Sensor for Wearable Gait Analysis Systems

Abstract This paper presents the design, analysis, and fabrication of a capacitive-based three-axis force sensor as the building block of a wearable sensing system to directly measure all the components of three-dimensional (3D) ground reaction forces (GRFs) during walking. The proposed sensor is low-cost and easy to fabricate with high accuracy, which promotes its accessibility and usability for gait analysis in clinical and research settings. The sensor is comprised of three parallel capacitors that enable three-axial force measurement while significantly reducing the complexity of fabrication and maintenance associated with three-axis force sensors. Comprehensive experiments were conducted to rigorously quantify different aspects of the sensor's performance. The static and dynamic errors along the three axes were less than 2.28%, which is well within the acceptable range for the intended application. The force sensor could decouple three-axial forces with a cross-sensitivity of less than 2%. The developed sensor also demonstrated desirable repeatability and hysteresis behaviors with almost no drift over long periods of usage.

一种新型三维力传感器结构设计与优化

一种新型三维力传感器结构设计与优化

A Three-Axial Force Sensor Based on Fiber Bragg Gratings for Surgical Robots

Haptic feedback is absent in flexible endoscopic surgical robots due to the size constraint of installing sensors on the small robotic arms. Besides, inherent hysteresis caused by the nonlinear friction between tendons and sheaths makes it hard to estimate the distal force by modeling. In this work, we addressed this challenge by proposing a new three-axial force sensor. This standalone device can be seamlessly integrated into the endoscopic robotic arm. Three optical fibers with fiber Bragg gratings (FBGs) are embedded in the sensing structure, where one is located at the center hole of the structure (ø 1.4 mm) and the other two are eccentrically placed around the structure at 90° apart from each other. This device can measure the pulling force and lateral forces of an articulated surgical instrument. Mechanics analysis has been studied to reveal the link between FBGs’ wavelength shifts and forces caused by the elongation and the bending with a temperature-compensation feature. The sensor has a lateral force sensitivity of 838.386 pm/N, with a measurement resolution of 1.19 mN. Performance comparison with a commercial force sensor Nano17 was made, with measurement errors from 4.50% to 6.18%. In the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex vivo</i> tests, we teleoperated the sensorized grasper to pull, steer, and lift a piece of pig colon tissue. The tool–tissue interaction forces measured by the force sensor were displayed on the computer screen in real time. In addition to the endoscopic robots, the force sensor can also be integrated with other surgical robots such as laparoscopic robots and catheters.

Wearable Artificial Fingers With Skin Vibration and Multi-Axis Force Sensors.

Tactile sensations are based on stimulation elicited on the skin through mechanical interactions between the skin and an object. Hence, it is important to consider skin properties as well as objects. In this article, we aim to develop wearable artificial fingers for quantitative evaluations reflecting individual differences in human fingers. In a previous study, a wearable skin vibration sensor was attached to artificial fingers and it was demonstrated that the skin vibrations differed according to the dimension of surface ridge and the artificial finger is useful for roughness evaluation. This article improved the artificial finger to measure the contact force and friction in addition to the skin vibration. A small three-axis force sensor was embedded into the base of the finger, and normal and friction forces were estimated via a multi-regression method. Furthermore, artificial fingers with different hardness were prepared and six different textures were used to investigate tactile evaluation. Experimental results showed that the artificial fingers could measure normal and friction forces along with the skin vibration and were useful to evaluate textures. Resulting distributions of the vibration intensity and friction coefficient were different for the soft and hard artificial fingers, indicating the complex influence of skin properties on tactile sensations.

Three-axis force sensor miniaturized by 3D microstructuring using high-temperature punch creep-forming process

This study developed a small, three-axis force sensor with a 3D microstructure for installation into a robot gripper. The sensor was manufactured by high-temperature punch creep-forming of 5 μm thick single-crystal silicon (Si) cantilevers during an impurity diffusion process for piezoresistors. The punch creep-forming could achieve a large out-of-plane deformation of the Si cantilevers within a small area. The punch creep-forming simulations were conducted for designing the 3D formed force sensor based on the creep constitutive equation for a 5 μm thick Si film at 1050 °C. Consequently, this study succeeded in fabricating a 3D formed force sensor with a 320 μm diameter hemispheric structure by punch creep-forming without breaking the structure. The force sensor was set on a printed circuit board and packaged using urethane resin. The viscoelastic response of the resin-packaged sensor was evaluated by conducting stress-relaxation (SR) tests and dynamic mechanical analysis, and characterized by a five-element generalized Maxwell model (GMM). In the SR tests, the sensor output signal in the vertical direction showed a strong correlation with the displacement applied to the test, whereas that in the lateral direction was closely related to the load acting on the sensor. Numerical analyses based on the GMM could estimate the load and displacement acting on the sensor from its output signal.

Ultrathin Three-Axis FBG Wrist Force Sensor for Collaborative Robots

Collaborative robots equipped with multicomponent force-sensing systems at the human-robot-environment interaction interface provides competitive advantages, such as collaboration, flexibility, and reliability. Most wrist force sensors use the cross-beam structures with electrical strain gauge measurement technologies. This article proposes an approach to develop a new ultrathin three-axis fiber Bragg grating (FBG) force sensor. First, an appropriate elastomer with embedded floating beams in ultrathin dimensions to measure three-axis force is designed using a finite-element method (FEM). A temperature-compensated extreme learning machine (TC-ELM) network is proposed to achieve the characteristics of low coupling and temperature compensation (TC). Calibration and experiment on the UR5 robot are conducted, and results illustrate that the highest sensitivity of the sensor can reach 34.07 pm/N, the repetition error is less than 5%, and the maximum coupling error is less than 0.21%. The maximum temperature drift after compensation is less than 20 pm. The proposed sensor has identical output as a commercial sensor and performs well in dynamic loading and unloading operations. Finally, comparison results from commercial and academic alternatives demonstrate the interest of the proposed approach to develop high-performance and integrated force-sensing solutions.

Functional Evaluation of a Force Sensor-Controlled Upper-Limb Power-Assisted Exoskeleton with High Backdrivability.

A power-assisted exoskeleton should be capable of reducing the burden on the wearer’s body or rendering his or her work improved and efficient. More specifically, the exoskeleton should be easy to wear, be simple to use, and provide power assistance without hindering the wearer’s movement. Therefore, it is necessary to evaluate the backdrivability, range of motion, and power-assist capability of such an exoskeleton. This evaluation identifies the pros and cons of the exoskeleton, and it serves as the basis for its subsequent development. In this study, a lightweight upper-limb power-assisted exoskeleton with high backdrivability was developed. Moreover, a motion capture system was adopted to measure and analyze the workspace of the wearer’s upper limb after the exoskeleton was worn. The results were used to evaluate the exoskeleton’s ability to support the wearer’s movement. Furthermore, a small and compact three-axis force sensor was used for power assistance, and the effect of the power assistance was evaluated by means of measuring the wearer’s surface electromyography, force, and joint angle signals. Overall, the study showed that the exoskeleton could achieve power assistance and did not affect the wearer’s movements.

Control of vortex shedding from two side-by-side cylinders using a pair of tangential jets

The active control of two side-by-side cylinder wakes by tangential jets with a Reynolds number of 3900 and a pitch ratio of 1.1 was studied experimentally and numerically. The particle image velocimetry technique was used to obtain the flow around side-by-side cylinders in a wind tunnel, and the dynamic lift on the cylinder was measured by a three-axis force-sensor. A numerical model was set up for comparison with the experimental data. The effects of the jet angles and jet intensities on the wake control were discussed. It was found that the flow structure was bistable biased flow and that the gap flow led to an asymmetry of the flow field. Tangential jets with angles smaller than 20° were ineffective in controlling the wake and suppressing the vortex-induced vibrations of the cylinders. Tangential jets with angles larger than 45° induced a reverse vortex and were not suitable to be applied. The vortex flow region became smaller with an increase in the jet momentum coefficient but needed additional power supply. A moderate jet angle of 45° with a jet momentum coefficient of 0.218 demonstrated the best control effect in which the shedding vortex could be controlled in a small triangle region behind the cylinders (X ≦ 1.5D). The peak amplitude of the cylinder lift power spectral density (PSD) can be reduced to ∼8.7% of the PSD without the control. Effective control via the use of tangential jets provides a theoretical basis for subsequent active closed-loop control.