Multi-axis Force Sensor Research Articles

Optical Micro/Nanofiber Enabled Multiaxial Force Sensor for Tactile Visualization and Human-Machine Interface.

Tactile sensors with capability of multiaxial force perception play a vital role in robotics and human-machine interfaces. Flexible optical waveguide sensors have been an emerging paradigm in tactile sensing due to their high sensitivity, fast response, and antielectromagnetic interference. Herein, a flexible multiaxial force sensor enabled by U-shaped optical micro/nanofibers (MNFs) is reported. The MNF is embedded within an elastomer film topped with a dome-shaped protrusion. When the protrusion is subjected to vector forces, the embedded MNF undergoes anisotropic deformations, yielding time-resolved variations in light transmission. Detection of both normal and shear forces is achieved with sensitivities reaching 50.7dB N-1 (14% kPa-1) and 82.2dB N-1 (21% kPa-1), respectively. Notably, the structural asymmetry of the MNF induces asymmetrical optical modes, granting the sensor directional responses to four-directional shear forces. As proof-of-concept applications, tactile visualizations for texture and relief pattern recognition are realized with a spatial resolution of 160µm. Moreover, a dual U-shaped MNF configuration is demonstrated as a human-machine interface for cursor manipulation. This work represents a step towards advanced multiaxial tactile sensing.

Design selection of experimental test rig for static thrust on micro size propeller using Pugh method

This paper aims to propose a simple, straightforward, yet robust test rig design to measure the static thrust magnitude for small propellers. Although there were advanced tools like multi-axis force or torque sensors, sophisticated equipment and complex mechanisms were required to capture the accurate thrust magnitude. Therefore, providing simple and effective test rig design for small-sized propellers is quite challenging. In this work, Pugh matrix analysis was used to evaluate three new designs of Propeller Thrust Measurement Rig (PMTR) and compare the designs against a benchmark model. The evaluation covered important design criteria during test operation, such as measurement accuracy, stability, ease of development, assembly, maintenance, versatility, electronic integration, airflow interference, adaptability for tilt angle studies, and resemblance to multicopter flight conditions. The results reveal that the PMTR-1 design scored the highest in the analysis and emerged as the most suitable candidate among the proposed designs. It showed potential superior performance in stability, ease of development and assembly, versatility, simplicity, airflow management, and adaptability for future studies. PMTR-3 demonstrated some potential but needs more enhancement in electronic integration and structural development. However, PMTR-2 faces significant potential challenges in providing stability, versatility, electronic integration, and adaptability for effective and safe operations.

Novel static decoupling algorithm for the multi-axis wheel force sensor based on the Informer network

Ensuring the stability of heavy multi-axle vehicles necessitates the accurate calibration and decoupling of Multi-axis Wheel Force Sensors (MWFS). Traditional methods often neglect the temporal coupling present in MWFS output data, leading to reduced accuracy. This paper introduces an Improved Decoupling Algorithm (IDI) based on the Informer network, designed to temporally decouple MWFS and enhance precision. The Decoupling embedding layer (DE) performs linear decoupling of the MWFS, while the Token embedding layer (TE) and Informer encoder extract timing coupling features. The highway network and linear fully-connected layer then provide nonlinear decoupling compensation. Experimental results demonstrate that the IDI algorithm significantly outperforms traditional methods like Extreme Learning Machine (ELM) and Back Propagation Network (BPNN), achieving at least a 41.12% improvement in accuracy in the highly coupled Mz channel. In conclusion, the IDI algorithm not only achieves high-precision decoupling of MWFS but also presents a robust framework for modeling various sensor types.

An Intuitively Derived Decoupling and Calibration Model to the Multiaxis Force Sensor Using Polynomials Basis

An Intuitively Derived Decoupling and Calibration Model to the Multiaxis Force Sensor Using Polynomials Basis

Centralized load decoupling of a rotational multi-axis force sensor for measuring wheel-terrain interaction forces

For ensuring the safe mobility of off-road wheeled mobile robots (WMRs), the rotational multi-axis force sensor (RMFS) plays an important role in measuring the wheel-terrain interaction forces. However, the existing decoupling models cannot fully describe the coupling process of the RMFS when it is subjected to centralized loads, which is a common condition for off-road WMRs. A corrected decoupling model is proposed by taking elastic strains as the intermediate variable such that the coupling errors caused by centralized loads can be avoided. The proposed decoupling model replaces the original rotation matrix with a corrected matrix whose elements are odd harmonic functions. The calibration experiments indicate that the corrected model can reduce the variance of calibration error rate from 1.95% to 0.054% compared with another representative machine learning-based decoupling model. A set of simulation and physical tests also demonstrate that the decoupling model have good repeatability, accuracy and anti-vibration capability.

Reaction Force-Based Position Sensing for Magnetic Levitation Platform with Exceptionally Large Hovering Distance

This work introduces a novel sensing concept based on reaction forces for determining the position of the levitating magnet (mover) for magnetic levitation platforms (MLPs). Besides being effective in conventional magnetic bearings, the applied approach enables operation in systems where the mover is completely isolated from the actuating electromagnets (EMs) of the stator (e.g., located inside a sealed process chamber) while levitating at an extreme levitation height. To achieve active position control of the levitating mover by properly controlling the stator’s EM currents, it is necessary to employ a dynamic model of the complete MLP, including the reaction force sensor, and implement an observer that extracts the position from the force-dependent signals, given that the position is not directly tied to the measured forces. Furthermore, two possible controller implementations are discussed in detail: a basic PID controller and a more sophisticated state-space controller that can be chosen depending on the characteristics of the MLP and the accuracy of the employed sensing method. To show the effectiveness of the proposed position-sensing and control concept, a hardware demonstrator employing a 207 mm outer-diameter (characteristic dimension, CD) stator with permanent magnets, a set of electromagnets, and a commercial multi-axis force sensor is built, where a 0.36 kg mover is stably levitated at an extreme air gap of 104 mm.

High-Precision Integration of Optical Sensors into Metallic Tubes Using Rotary Swaging: Process Phenomena in Joint Formation

A novel process design for the damage-free and highly accurate positional integration of an optical multi-axial force sensor into a hollow tube by means of rotary swaging is introduced. Numerical simulations reveal the relevant process phenomena of thin disc joining inside a pre-toothed hollow tube and help us to find an optimal process design. Experimental trials show the significant effect of the axial material flow and the number of tools on the rotary swaging process. By taking these effects into account, successful form- and force-fit joining of the sensor carrying discs into the tube can be achieved. Successful joining of an optical sensor for bending force and torque measurement shows hysteresis-free sensory behavior and thus backlash-free joining of the sensor carrier discs. The paper concludes with a presentation of the results of a numerical study on a potential closed-loop approach to the joining process.

Increased Posterior Tibial Slope Increases Force on the Posterior Medial Meniscus Root

Background: Posterior medial meniscus root (PMMR) tears have been associated with increased posterior tibial slope, but this has not been fully evaluated biomechanically. In addition, the effects of knee flexion and rotation on the PMMR are not well understood biomechanically because of technological testing limitations. A novel multiaxial force sensor has made it possible to elucidate answers to these questions. Purpose: (1) To determine if increased posterior tibial slope results in increased posterior shear force and compression on the PMMR, (2) to evaluate how knee flexion angle affects PMMR forces, and (3) to assess how internal and external rotation affects force at the PMMR. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen cadaveric knees were tested in all combinations of 3 posterior tibial slopes and 4 flexion angles. A multiaxial force sensor was connected to the PMMR and installed below the posterior tibial plateau maintaining anatomic position. The specimen underwent a 500-N compression load followed by a 5-N·m internal torque and a 5-N·m external torque. The magnitude and direction of the forces acting on the PMMR were measured. Results: Under joint compression, an increased tibial slope significantly reduced the tension on the PMMR between 5° and 10° (from 13.5 N to 6.4 N), after which it transitioned to a significant increase in PMMR compression, reaching 7.6 N at 15°. Under internal torque, increased tibial slope resulted in 4.7 N of posterior shear at 5° significantly changed to 2.0 N of anterior shear at 10° and then 8.2 N of anterior shear at 15°. Under external torque, increased tibial slope significantly decreased PMMR compression (5°: 8.9 N; 10°: 4.3 N; 15°: 1.1 N). Under joint compression, increased flexion angle significantly increased medial shear forces of the PMMR (0°, 3.8 N; 30°, 6.2 N; 60°, 7.3 N; 90°, 8.4 N). Under internal torque, 90° of flexion significantly increased PMMR tension from 2.3 N to 7.5 N. Under external torque, 30° of flexion significantly increased PMMR compression from 4.7 N to 12.2 N. Conclusion: An increased posterior tibial slope affects compression and anterior shear forces at the PMMR. An increased flexion angle affects compression, tension, and medial shear forces at the PMMR. Clinical Relevance: The increase in compression and posterior shear force when the knee is loaded in compression may place the PMMR under increased stress and risk potential failure after repair. This study provides clinicians with information to create safer protocols and improve repair techniques to minimize the forces experienced at the PMMR.

Human-Delivered Brushstroke Characterization using an Instrumented Brush Focused on Torque.

Pleasant brush therapies may benefit those with autism, trauma, and anxiety. While studies monitor brushing velocity, hand-delivery of brush strokes introduces variability. Detailed measurements of human-delivered brushing physics may help understand such variability and subsequent impact on receivers' perceived pleasantness. Herein, we instrument a brush with multi-axis force and displacement sensors to measure their physics as 12 participants pleasantly stroke a receiver's forearm. Algorithmic procedures identify skin contact, and define four stages of arrival, stroke, departure, and airtime between strokes. Torque magnitude, rather than force, is evaluated as a metric to minimize inertial noise, as it registers brush bend and orientation. Overall, the results of the naturally delivered brushing experiments indicate force and velocity values in the range of 0.4 N and 3-10 cm/s, in alignment with prior work. However, we observe significant variance between brushers across velocity, force, torque, and brushstroke length. Upon further analysis, torque and force measures are correlated, yet torque provides distinct information from velocity. In evaluating the receiver's response to individual differences between brushers of the preliminary case study, higher pleasantness is tied to lower mean torque, and lower instantaneous variance over the stroke duration. Torque magnitude appears to complement velocity's influence on perceived pleasantness.

Motor controlled system development with force-assistance using force/torque sensor for four-axis ceiling suspension system

Multi-axis force and torque sensors are type of transducers. They can measure force and torque in three dimensions. These sensors have multiple applications in robotic systems. The majority of these type of sensors use the strain measurement in any elastic structure. There are multiple approaches for strain measurement which include resistive strain gauge, piezo-electric and capacitive technologies. The evaluation of such a system can be done on various parameters, maximizing the acceptable sensing range while minimizing measurement errors/crosstalk is the main design challenge. In future, because force and torque sensors are necessary for service machines to interact with people in different situations, they will be widely deployed. However, it is challenging to find an appropriate force/torque sensor, and the cost is very high, because of certain design concerns and needs. This paper discusses an application based on the multi-axis force/torque sensor. A force-assisted control system has been proposed with simultaneous motorized action using force as feedback. The sensor needs and machine performance are reviewed after a thorough analysis of relevant data. This thorough investigation will benefit in the interfacing of specialized force/torque sensors to reduce crosstalk and aid in broadening the scope of service machines in which they can be used.

A high sensitivity and multi-axis fringing electric field based capacitive tactile force sensor for robot assisted surgery

This paper presents a design of multi-axis tactile force sensor using the fringe effect of an electric field between stationary patterned electrodes. The unique configuration of the electrodes consisting of four separate square-shaped sensing electrodes, with each encircled by excitation electrodes, allows to achieve enhanced fringe field effect and hence sensitivity. The proposed sensor can decouple the normal, shear and angular shear applied forces. The sensor is fabricated using low-cost rapid prototyping techniques with flexible Ecoflex 00–30 and silicone rubber RTV-528 as the elastomers for contact with the environment. An analytical model is developed that correlates the nominal capacitance of the sensor with that of the geometric dimensions of the stationary electrodes and air cavity height between the electrodes and elastomer. The force measurement ranges in the normal, shear, and angular axis are 5 N, 1.5 N, and 1 N respectively. The sensor shows a perfectly linear response, repeatability, and a low hysteresis error, thermal stability and robustness to the environmental interferences that makes it suitable to be used for force feedback in minimally invasive robotic surgery.

Redundant Parallel Beam Multiaxis Force Sensor—Stress Correlation Coefficient

The stress nonuniformity on the loading neck is an important factor that leads to the local force error of an individual multiaxis force sensor (MAFS) in a distributed multiaxis force sensing system (DMAFSS). The stress correlation coefficient is used to characterize the stress nonuniformity. The stress correlation coefficient decreases with the increase of the loading offset. A full-constrained high-relative-stiffness-ratio structure is important for an MAFS to obtain a good stress correlation coefficient on its loading neck under various external loads. An individual MAFS with two loading necks is employed in the sensing system to increase the relative stiffness ratio. A thin loading neck, a long loading neck distance, and a high stiffness loading frame are important for the high-relative-stiffness-ratio structure. A local high-relative-stiffness-ratio structure is valuable for a large-scale DMAFSS. The mechanical hinge on the loading neck is useful to realize a large-scale lightweight DMAFSS. The extreme load including the load outside the reference loading zone and the concentrated torque affects the stress correlation coefficient apparently which should be specified in future standards.

A Decoupling Method of Multiaxis Accelerometers Based on Segmentation Surface Fitting

The coupling of a multiaxis accelerometer mainly depends on two input variables: acceleration and its frequency, which is different from a multiaxis force sensor with a single input variable and changes the coupling function from 2-D to 3-D. As a result, new challenges arise in the decoupling process. In view of this situation, a decoupling method of multiaxis accelerometers suitable for unknown input variables is proposed in this article. The method uses calibration data as input variables to deduce a coupling model. In the process of decoupling, based on a segmentation surface fitting method, two solving methods of the coupling model are proposed: the direct surface fitting and the point-line surface distribution fitting. The two fitting methods are used to solve the coupling function of a triaxial MEMS accelerometer. The experimental results show that the two fitting methods can reduce coupling error without increasing the highest order of the fitting function. In cases of strong coupling, the decoupling method proposed can reduce the coupling error to 1.47% of that before decoupling, the coupling interference was reduced significantly. The coupling error can be reduced to less than 0.005 g, and the decoupling effect is stable. Compared with the decoupling method based on backpropagation (BP) neural network, the decoupling effect is also improved. In addition, the single-decoupling time of the decoupling method is less than 0.561 ms.

A Multiaxis Force Sensor Based on Pre-Strained Piezoresistive Film Strips

A Multiaxis Force Sensor Based on Pre-Strained Piezoresistive Film Strips

Analysis of Force Sensor Using Polymer Optical Fiber Based on Twisting Structure

This article highlights an intensity variation-based force sensor for polymer optical fiber (POF) that relies on the twisting structure. The sensing phenomena of the sensor rely on cladding mode frustrated total internal reflection (CMFTIR). A portion of two POFs is twisted in the middle where the light source is connected with illuminating fiber, and the power meter is connected with the forward end of the second fiber. Thus, the force measurement is taken from the second fiber by observing the variation of coupled intensity in which the applied force is up to 0–20 N. The sensor is analyzed on straight fiber, twisted fiber with bend, and without bend (considering the sensor’s sensitivity). The experimental results show that the sensor has higher sensitivity in the twisted with-bend structure, and the bending radius also affects the sensor sensitivity. Moreover, a multipoint and multiaxis force sensor is also presented. The POF is twisted up to 100 cm for multipoint sensing, and force is applied at five different points, whereas the cascading scheme is adopted for multiaxis to achieve the individual response of each axis. This study provides an alternative way to measure force based on intensity changes and has an additional advantage of being cheaper than fiber Bragg gratings and other systems.

Easy-to-Deploy Combined Nasal/Throat Swab Robot With Sampling Dexterity and Resistance to External Interference

Robots have been used extensively in the battle against the COVID-19 pandemic since its outbreak. One prominent direction is the use of robots for swab sampling, which not only solves the shortage of medical staffs, but also prevents them from being infected during face-to-face sampling. However, a massive deployment of sampling robots is still not achievable due to their high costs, safety concerns, deployment complexity, and so on. In this letter, we propose a flexible, safe, and easy-to-deploy swab robot in a compact bench-top system. The robot can perform nasal/throat swab sampling tasks as dexterous as a human manual operation. The bio-mimetic rigid interior and soft exterior design guarantee the sampling robot with both flexibility and safety. Furthermore, the integration of 3-D fiber Bragg grating (FBG) based shape sensor and multi-axis force sensor may enhance the control performance. A dedicated constrained compliance control (CCC) algorithm was developed to tackle the unexpected interactions during sampling, which ensures the validity and safety of the sampling under disturbance. Various experiments are conducted to validate our system and prove its feasibility, flexibility, high safety, and efficiency for both nasal/throat swab sampling tasks. The proposed system is promising to be massive duplicated for robotic swab sampling.

Redundant Parallel Beam Multiaxis Force Sensor—Accuracy Space

The principle of the redundant parallel beam multi-axis force sensor is a transformation from displacement domain to force domain. This paper proposed a general force error model of a distributed force measurement system with redundant multi-axis force sensors based on the measurement <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/$ </tex-math></inline-formula> surveying adjustment method to transform displacement sensor errors to force errors. The optimum accuracy space is defined according to the error model. According to the accuracy space, the torque error increase sharply when the measuring point is far away from the optimum accuracy space, but the force error remains constant. A long-distance arrangement of displacement sensors can increase the size of the optimum accuracy space and a high-precision displacement sensor can increase the measurement accuracy in the whole space. A deformation filter can minimize the affection of the loading platform deformation on the measurement accuracy. A dual-measurement system is recommended to increase both the force accuracy and the torque accuracy when the measuring point is far from the optimum accuracy space of the main multi-axis force sensing system. The error point cloud is used to verify the proposed error model.

Design and development of a multi-axis force sensor based on the hall effect with decouple structure

This paper investigates the design and development of a novel 3-axis force sensor for human–robot interaction purposes. Based on the characteristics of the sensing technologies proposed in the literature, the Hall effect sensor is chosen according to its linearity, low-cost and appropriate range for voltage output. Then, by properly positioning the hall effect sensors, an asymmetric structure for the force sensor is presented. The proposed structure is inspired by an gyroscope’s architecture which provides an independent output on the sensor’s axes. As a result, each axis of the sensor, independently, creates a relationship between force and displacement which is covered by a silicon structure. Therefore, the Jacobian matrix of the proposed structure becomes an identity matrix for which the least-squares estimation is used to identify the force/displacement relationship. The developed force sensor has the ability to measure the force along the three cartesian axes Xˆ, Yˆ, Zˆ with the resolution of 2 mN, 1.5 mN, and 0.2 N, respectively. In order to illustrate the performance of the proposed multi-axis force sensor, an interactive simple control is carried out which is performed by attaching the sensor to the end-effector of a parallel robot, the so-called Tripteron robot, and enable to have a safe reaction in the case of occurring a collision in an environment.

Resonant sensors for multi-axis force and torque estimation in collaborative robotics

This paper presents a complete design methodology for a multi-axis resonant force sensor. The proposed device has been designed to be useable in a context of physical interaction between robots and humans. The proposed solution allows the three force components and the three torque components to be measured simultaneously and can be inserted into an interface handle or a robot end-effector. The information on wrench can then be used to detect and control interactions for cooperative tasks between humans and robots. In the context of sensors for robotic co-manipulation, it is imperative to guarantee not only a certain level of performance (accuracy, dynamics, size) but also to guarantee certain non-functional specifications associated with safety, measurement redundancy or functional integration of the sensor into its environment. The consideration of all these design specifications, both functional and non-functional, led to the principles and technologies used to develop this sensor. Multi-axis resonant sensors have excellent performance and safety characteristics, two key elements for collaborative robotics, but the literature review did not reveal any significant previous work in this area. Thus, this paper proposes an original sensor based on a breakthrough technology in the crucial field of multi-axis force sensors. The performances obtained on our prototype are already close to the performances of the best existing 6-axis industrial sensors, which suggests very good prospects for this new technology. In addition, and compared to alternative technologies, resonance technology offers new possibilities in terms of sensor fault detection, thus improving the intrinsic safety of these devices.

A low cost 3-DOF force sensing unit design for wrist rehabilitation robots

In this study, a low cost and modular three degree-of-freedom force sensor design is developed for the purposes of wrist rehabilitation. The proposed sensor in this study and the existing sensors in the literature are compared to each other considering nine main topics namely, measurement capability, design purpose, measurement approach, force limits, dimensions, producing & assembly complexity, producing cost, modularity and electronics. The comparison results are given as a table. Considering the sensors developed especially for the purpose of wrist rehabilitation in the literature, the proposed sensor has some advantages as follows: The proposed sensor has i) modular structure, ii) less producing & assembly complexity, iii) low cost and iv) integrated electronic and mechanical structures. A specific experimental setup is also developed for both performing force measurements and control of flexion/extension movements. Linearity, hysteresis and repeatability errors of proposed multi-axis force sensor unit are given as table. A set of force measurements is carried out using this experimental setup. Measurements are illustrated as figures. It can be concluded that the proposed force sensor can be used for human-robot interaction in wrist rehabilitation.