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21 pages, 12324 KB

Open AccessArticle

Wireless Instrumented Ankle Foot Orthosis (AFO) for Gait Cycle Monitoring

by Soufiane Mahraoui and Mauro Serpelloni

Instruments 2026, 10(2), 23; https://doi.org/10.3390/instruments10020023 - 22 Apr 2026

Viewed by 310

Abstract

Ankle–foot orthoses (AFOs) are widely used in the rehabilitation of patients with neurological or musculoskeletal disorders. However, treatment outcomes may be influenced by incorrect use of the device or by inappropriate orthosis selection. Since many types of AFOs are available, differing in materials, [...] Read more.

Ankle–foot orthoses (AFOs) are widely used in the rehabilitation of patients with neurological or musculoskeletal disorders. However, treatment outcomes may be influenced by incorrect use of the device or by inappropriate orthosis selection. Since many types of AFOs are available, differing in materials, stiffness, and geometry, an objective evaluation tool can support clinical decision-making. This work presents the design, development, and characterization of an instrumented AFO able to quantify relevant gait parameters in an objective way. The proposed device integrates three measurement modalities in a compact wearable structure. Two longitudinal strain gauges estimate ankle plantar- and dorsiflexion angles. Two force-sensitive elements detect foot–ground contact and allow identification of stance and swing phases of the gait cycle. A single inertial measurement unit (IMU) is used to measure lateral shank inclination. The strain-gauge-based angle estimation was validated against a gold-standard motion capture system, achieving a root mean square error of approximately 1.6 degrees and showing higher accuracy than the IMU for plantar/dorsiflexion measurement, while maintaining a simple electronic architecture. The force sensors were validated using a force platform and demonstrated reliable detection of loading and unloading events. Monitoring lateral inclination through the single IMU provides additional information related to balance and potential fall risk. Data are transmitted via Bluetooth Low Energy (BLE) to a custom Python-based application for real-time visualization and recording. Overall, the results validate the electronic instrumentation and demonstrate reliable system performance, indicating that the proposed instrumented AFO represents a promising platform for objective gait assessment and future clinical applications. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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16 pages, 12735 KB

Open AccessArticle

Smartphone-Based Quantitative Measurement of Capillary Refill Time

by Chiho Miyazawa, Masayoshi Shinozaki, Yayoi Miwa, Satoshi Karasawa, Taka-aki Nakada, Yukihiro Nomura and Toshiya Nakaguchi

Instruments 2026, 10(1), 15; https://doi.org/10.3390/instruments10010015 - 3 Mar 2026

Viewed by 879

Abstract

Capillary refill time (CRT) is widely used in pediatric and emergency medicine as an indicator of peripheral circulation. CRT is defined as the time required for the skin to return to its original color after external compression is applied and then released. In [...] Read more.

Capillary refill time (CRT) is widely used in pediatric and emergency medicine as an indicator of peripheral circulation. CRT is defined as the time required for the skin to return to its original color after external compression is applied and then released. In current clinical practice, however, CRT assessment remains qualitative and relies heavily on the magnitude and consistency of compression applied by the measurer, as well as on subjective visual color perception, which together result in limited measurement reliability. To improve measurement reliability, several quantitative CRT measurement devices have been developed. Nevertheless, these devices are dedicated specifically to CRT measurement, which limits their versatility and complicates clinical implementation. In this study, we developed a simple and quantitative CRT measurement method using a smartphone. Based on skin color changes captured by the rear camera, we proposed a method to assess the adequacy of the applied compression force and implemented an application to calculate CRT. In addition, we investigated an algorithm to reduce the influence of pulse waves observed in the post-release waveform, enabling more stable CRT estimation. Furthermore, a dedicated smartphone case was designed to immobilize the finger during measurement, thereby improving measurement reliability. The feasibility of the proposed method was evaluated by examining agreement with a previously developed CRT measurement device and by assessing intraexaminer reliability, confirming its effectiveness. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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16 pages, 2752 KB

Open AccessArticle

Evaluation of Gap and Flush Inspection Algorithms in a Portable Laser Line Triangulation System Through Measurement System Analysis (MSA)

by Guerino Gianfranco Paolini, Sara Casaccia, Matteo Nisi, Cristina Cristalli and Nicola Paone

Instruments 2026, 10(1), 7; https://doi.org/10.3390/instruments10010007 - 26 Jan 2026

Viewed by 1055

Abstract

The shift toward Industry 5.0 places human-centred and digitally integrated metrology at the core of modern manufacturing, particularly in the automotive sector, where portable Laser Line Triangulation (LLT) systems must combine accuracy with operator usability. This study addresses the challenge of operator-induced variability [...] Read more.

The shift toward Industry 5.0 places human-centred and digitally integrated metrology at the core of modern manufacturing, particularly in the automotive sector, where portable Laser Line Triangulation (LLT) systems must combine accuracy with operator usability. This study addresses the challenge of operator-induced variability by evaluating how algorithmic strategies and mechanical support features jointly influence the performance of a portable LLT device derived from the G3F sensor. A comprehensive Measurement System Analysis was performed to compare three feature extraction algorithms—GC, FIR, and Steger—and to assess the effect of a masking device designed to improve mechanical alignment during manual measurements. The results highlight distinct algorithm-dependent behaviours in terms of repeatability, reproducibility, and computational efficiency. More sophisticated algorithms demonstrate improved sensitivity and feature localisation under controlled conditions, whereas simpler gradient-based strategies provide more stable performance and shorter processing times when measurement conditions deviate from the ideal. These differences indicate a trade-off between algorithmic complexity and operational robustness that is particularly relevant for portable, operator-assisted metrology. The presence of mechanical alignment aids was found to contribute to improved measurement consistency across all algorithms. Overall, the findings highlight the need for an integrated co-design of algorithms, calibration procedures, and ergonomic aids to enhance repeatability and support operator-friendly LLT systems aligned with Industry 5.0 principles. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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22 pages, 4689 KB

Open AccessArticle

A Procedure for Performing Reproducibility Assessment of the Accuracy of Impact Area Classification for Structural Health Monitoring in Aerospace Structures

by Luciano Chiominto, Giulio D’Emilia, Antonella Gaspari, Emanuela Natale, Francesco Nicassio and Gennaro Scarselli

Instruments 2026, 10(1), 6; https://doi.org/10.3390/instruments10010006 - 26 Jan 2026

Viewed by 581

Abstract

The principal objective of this work is to develop an optimized procedure that guarantees the reproducibility of results across different applications and laboratories, facilitating potential field applications of methodologies for Structural Health Monitoring in aerospace structures. The focus is to accurately detect and [...] Read more.

The principal objective of this work is to develop an optimized procedure that guarantees the reproducibility of results across different applications and laboratories, facilitating potential field applications of methodologies for Structural Health Monitoring in aerospace structures. The focus is to accurately detect and localize impact areas on planar structures using in situ transducers and Machine Learning (ML) techniques. The research concentrates on an aluminum plate where impacts are generated by metal spheres of different masses dropped from a fixed height. The resulting Lamb waves are detected by PZT sensors glued on the surface. Various data processing and feature extraction algorithms are implemented and compared to extract the differences in Time of Flight (ΔToF). The obtained features are used for training ML classification models. Then, the influence of various parameters in signal acquisition and data processing are assessed along with the reproducibility of the results. For this reason, an interlaboratory comparison is conducted in which the trained models are applied to data collected under varying conditions. The experimental results show that the most influencing factors for impact area classification are the algorithm for ΔToF estimation, the number of training points used in ML models, the type of classification model, the distribution of the impact points on the component, and their balance in the classification area. This evidence suggests approaches for reducing both issues, therefore improving the reproducibility of results. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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14 pages, 1296 KB

Open AccessArticle

Shoulder Muscle Strength Assessment: A Comparative Study of Hand-Held Dynamometers and Load Cell Measurements

by Carla Antonacci, Arianna Carnevale, Letizia Mancini, Alessandro de Sire, Pieter D’Hooghe, Michele Mercurio, Rocco Papalia, Emiliano Schena and Umile Giuseppe Longo

Instruments 2026, 10(1), 2; https://doi.org/10.3390/instruments10010002 - 20 Dec 2025

Viewed by 1378

Abstract

Accurate measurement of shoulder muscle strength is important for diagnosis, treatment planning, and monitoring recovery. Hand-held dynamometers (HHDs) are widely used in clinical practice but are affected by operator strength, patient positioning, and device stabilization, particularly under high-load conditions. No previous study has [...] Read more.

Accurate measurement of shoulder muscle strength is important for diagnosis, treatment planning, and monitoring recovery. Hand-held dynamometers (HHDs) are widely used in clinical practice but are affected by operator strength, patient positioning, and device stabilization, particularly under high-load conditions. No previous study has directly compared HHD measurements with a reference load cell in a rigid serial configuration or evaluated the effect of different load cell signal processing strategies on the final strength value. The aim of this study was to compare HHD measurements with those obtained from a reference load cell in a rigid serial configuration and to assess how different signal processing strategies applied to load cell data influence the final outcomes. A custom 3D-printed support was developed to align a commercial HHD and a load cell in series, ensuring identical loading conditions. Measurements were performed under two conditions: (i) application of known weights (9.81–98.10 N) and (ii) standardized strength tasks in five healthy volunteers. Agreement between instruments was evaluated using Bland–Altman analysis and Root Mean Square Error (RMSE). In static validation (i.e., experiments applying know weights), the load cell demonstrated stable performance, with standard deviations below 1% of the applied load. HHD variability increased with load, with RMSE rising from 0.55 N at 9.81 N to 5.06 N at 98.10 N. In human testing, the HHD consistently underestimated muscle strength compared with the load cell, with mean differences ranging from −15 N to −19 N, over exerted force ranges of approximately 20–90 N. Overall, the load cell provided stable reference measurements, while the choice of signal processing strategy influenced the results: plateau-phase analysis tended to reduce systematic bias but did not consistently narrow the limits of agreement. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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21 pages, 2306 KB

Open AccessArticle

Deep-Learning-Based Bearing Fault Classification Using Vibration Signals Under Variable-Speed Conditions

by Luca Martiri, Parisa Esmaili, Andrea Moschetti and Loredana Cristaldi

Instruments 2025, 9(4), 33; https://doi.org/10.3390/instruments9040033 - 4 Dec 2025

Viewed by 2154

Abstract

Predictive maintenance in industrial machinery relies on the timely detection of component faults to prevent costly downtime. Rolling bearings, being critical elements, are particularly prone to defects such as outer race faults and ball spin defects, which manifest as characteristic vibration patterns. In [...] Read more.

Predictive maintenance in industrial machinery relies on the timely detection of component faults to prevent costly downtime. Rolling bearings, being critical elements, are particularly prone to defects such as outer race faults and ball spin defects, which manifest as characteristic vibration patterns. In this study, we introduce a novel bearing vibration dataset collected on a testbench under both constant and variable rotational speeds (0–5000 rpm), encompassing healthy and faulty conditions. The dataset was used for failure classification and further enriched through feature engineering, resulting in input features that include raw acceleration, signal envelopes, and time- and frequency-domain statistical descriptors, which capture fault-specific signatures. To quantify prediction uncertainty, two different approaches are applied, providing confidence measures alongside model outputs. Our results demonstrate the progressive improvement of classification accuracy from 87.2% using only raw acceleration data to 99.3% with a CNN-BiLSTM (Convolutional Neural Network–Bidirectional Long Short-Term Memory) ensemble and advanced features. Shapley Additive Explanation (SHAP)-based explainability further validates the relevance of frequency-domain features for distinguishing fault types. The proposed methodology offers a robust and interpretable framework for industrial fault diagnosis, capable of handling both stationary and non-stationary operating conditions. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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9 pages, 1500 KB

Open AccessCommunication

Conceptual Study on the Implementation of NRTA for Industrial Applications

by Melissa Azzoune, Ludovic Mathieu, Ngoc Duy Trinh, Mourad Aïche, Laurence Villatte, Fabrice Piquemal, Lionel Tondut and Sylvain Pelletier

Instruments 2025, 9(4), 30; https://doi.org/10.3390/instruments9040030 - 26 Nov 2025

Viewed by 810

Abstract

Neutron Resonance Transmission Analysis (NRTA) is a non-destructive technique allowing the elemental and isotopic characterization of materials and objects. This study represents a first step toward understanding the NRTA technique and developing a novel compact system adapted for industrial applications. The industrial feasibility [...] Read more.

Neutron Resonance Transmission Analysis (NRTA) is a non-destructive technique allowing the elemental and isotopic characterization of materials and objects. This study represents a first step toward understanding the NRTA technique and developing a novel compact system adapted for industrial applications. The industrial feasibility of the NRTA was assessed by simulating a compact system using the Monte Carlo code MCNP 6.1. Neutron transmission spectra were generated for various metallic samples, ranging from 0.1 mm to 1 cm in thickness, and analyzed using a home-developed quantification method that incorporates nuclear cross sections from the ENDF/B-VIII.0 library and accounts for instrumental resolution. For this first study, an idealized configuration was considered, with a 0 µs pulsed neutron source and a Gaussian resolution function, to validate the methodology under a simple controlled condition. The results demonstrate that the areal densities of isotopes of Uranium and Plutonium can be determined with relative deviations below 10%, even under compact measurement conditions. This study validates the characterization method and represents a first step toward the continued development of an industrial NRTA prototype for rapid, non-destructive isotopic control of nuclear materials. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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Review

Jump to: Research

31 pages, 2673 KB

Open AccessReview

Electrode Configurations for Electrical Bioimpedance-Based Pulse Wave Signal Acquisition: A Narrative Review

by Margus Metshein

Instruments 2026, 10(2), 26; https://doi.org/10.3390/instruments10020026 - 3 May 2026

Viewed by 188

Abstract

The pulsatile modulation of arterial blood carries essential information about the cardiovascular system and cardiac function—information that can be extracted through appropriate signal-processing algorithms. As wearable technologies are increasingly integrated into everyday life, measurement methods are required to be non-invasive and compact in [...] Read more.

The pulsatile modulation of arterial blood carries essential information about the cardiovascular system and cardiac function—information that can be extracted through appropriate signal-processing algorithms. As wearable technologies are increasingly integrated into everyday life, measurement methods are required to be non-invasive and compact in scale. Electrical bioimpedance (EBI) methods meet these wearability criteria well; however, they introduce uncertainties associated with the electrode–skin interface. This paper presents a targeted overview of electrode configurations for EBI-based pulse wave signal acquisition, focusing on non-invasive solutions suitable for wearable devices. Electrode configurations are examined with respect to major peripheral arteries in the human body that are accessible at the skin surface and suitable for regional impedance cardiography. The review includes a carefully selected set of references, drawing on both research literature and patent descriptions, and discusses the primary differences in how electrode configurations are presented across these sources. Full article

(This article belongs to the Special Issue Instrumentation and Measurement Methods for Industry 4.0 and IoT)

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