Vibration based diagnostics on rolling contact fatigue test bench

The paper presents the first results of a study on vibrations associated with a rolling contact fatigue test bench and how this mechanical behavior may be correlated to the fatigue damage of the specimens. In particular, the aim of this study was to evaluate the possibility to detect and quantify, thanks to vibration analysis, the damage on two discs subjected to rolling contact fatigue. The first part of this work regards a description of the bench with a focus on the results acquired by its static and modal fem analyses. Then, some pure rolling and sliding condition tests were carried out and a procedure to monitor both the specimens damage state and to record accelerometric data was implemented by placing a set of piezoaccelerometers on the machine and developing a virtual instrument for automatic data handling and analysis. Tests were also periodically stoppedand the rolling contact surface profile was acquired by means of a linear video camera in order to evaluate its progressive damage. Data acquired were analyzed, considering also the results from the first part of work, both using a standard approach, such as a spectral analysis (FFT, PSD and waterfall), and by implementing custom digital weighting filters for a windowed RMS in order to estimate, realtime during the measurement, a good estimator for the specimen damage state development

Instrumented crutches for gait parameters evaluation

Most of the prototypes of instrumented crutches available in the literature require external motion capture devices to perform a gait analysis and to report the load applied on the crutches with respect to the gait cycle. Motion capture systems with markers require a controlled laboratory with cameras, instead IMU-based systems are more transportable, but the user must be instrumented. A new version of instrumented crutches, previously developed by the authors, allows one to measure the axial forces and to detect the gait phases during two-point assisted walking thanks to the cameras mounted on the lower part of the crutches

Relationship between measurement uncertainty and verifiability of geometric specifications: the case study of drilled hole orthogonality

In mechanical design, geometrical specifications and dimensional tolerances are commonly used to avoid final product malfunction and to allow for assembly integration. Geometric specification usage, in particular, has many manufacturing and durability implications, the feasibility of their measurement and verification, however, is often neglected and the influence of measurement uncertainty in their evaluation underestimated. Often geometrical specifications are defined without considering measurement uncertainties, or measurability at all: it is not uncommon to find approved specifications prescribing unverifiable geometry, or dimension tolerances that exceed state-of-art measurements. This article explores the case study of orthogonality between a circular hole and the plane on which it is drilled, evaluated using a Coordinate Measuring Machine. Such specification is defined, according to ISO 14253, as the angle between the plane normal and cylinder axis. Uncertainty of points coordinates obtained can, however small, play a key role in the final evaluation of orthogonality: if the specified tolerance is thigh enough it is also possible to have misalignment uncertainty higher than the tolerance itself. The authors propose the results of a mathematical and numerical model, meant to help the designer to define specification to assess the relationship between cylinder-plane misalignment measurability, CMM uncertainty and features dimensions

Biomechanics in crunch assisted walking

Crutch-assisted walking is very common among patients with a temporary or permanent impairment affecting lower limb biomechanics. Correct crutches’ handling is the way to avoid undesired side effects in lower limbs recovery or, in chronic users, upper limbs joints diseases. Active exoskeletons for spinal cord injured patients are commonly crutch assisted. In such cases, in which upper limbs must be preserved, specific training in crutch use is mandatory. A walking test setup was prepared to monitor healthy volunteers during crunch use as a first step. Measurements were performed by using both a motion capture system and instrumented crutches measuring load distribution. In this paper, we present preliminary tests results based on different subjects - having a variety of anthropometrical characteristics - during walking with parallel or alternate crutches, the so-called three and two-points strategies. Tests results present inter and intra subject variabilities and, as a first goal, influencing factors affecting crutch loads have been identified. In the future we aim to address crutch use errors that could lead to delayed recovery or upper limbs suffering in patients, giving valuable information to physicians and therapists to improve user’s training

Body measurement estimations using 3D scanner for individuals with severe motor impairments

In biomechanics, a still unresolved question is how to estimate with enough accuracy the volume and mass of each body segment of a subject. This is important for several applications ranging from the rehabilitation of injured subjects to the study of athletic performances via the analysis of the dynamic inertia of each body segment. However, traditionally this evaluation is done by referring to anthropometric tables or by approximating the volumes using manual measurements. We propose a novel method based on the 3D reconstruction of the subject’s body using the commercial low-cost camera Kinect v2. The software developed performs body segment separation in a few minutes leveraging alpha shape approximation of 3D polyhedrons to quickly compute a Montecarlo volume estimation. The procedure was evaluated on a total of 30 healthy subjects and the resulting segments’ lengths and masses were compared with the literature

Biomechanics in crutch assisted walking

Crutch-assisted walking is very common among patients with a temporary or permanent impairment affecting lower limb biomechanics. Correct crutches' handling is the way to avoid undesired side effects in lower limbs recovery or, in chronic users, upper limbs joints diseases. Active exoskeletons for spinal cord injured patients are commonly crutch assisted. In such cases, in which upper limbs must be preserved, specific training in crutch use is mandatory. A walking test setup was prepared to monitor healthy volunteers during crunch use as a first step. Measurements were performed by using both a motion capture system and instrumented crutches measuring load distribution. In this paper, we present preliminary tests results based on different subjects - having a variety of anthropometrical characteristics - during walking with parallel or alternate crutches, the so-called three and two-points strategies. Tests results present inter and intra subject variabilities and, as a first goal, influencing factors affecting crutch loads have been identified. In the future we aim to address crutch use errors that could lead to delayed recovery or upper limbs suffering in patients, giving valuable information to physicians and therapists to improve user's training

Experimental Procedure for the Metrological Characterization of Time-of-Flight Cameras for Human Body 3D Measurements

Time-of-flight cameras are widely adopted in a variety of indoor applications ranging from industrial object measurement to human activity recognition. However, the available products may differ in terms of the quality of the acquired point cloud, and the datasheet provided by the constructors may not be enough to guide researchers in the choice of the perfect device for their application. Hence, this work details the experimental procedure to assess time-of-flight cameras' error sources that should be considered when designing an application involving time-of-flight technology, such as the bias correction and the temperature influence on the point cloud stability. This is the first step towards a standardization of the metrological characterization procedure that could ensure the robustness and comparability of the results among tests and different devices. The procedure was conducted on Kinect Azure, Basler Blaze 101, and Basler ToF 640 cameras. Moreover, we compared the devices in the task of 3D reconstruction following a procedure involving the measure of both an object and a human upper-body-shaped mannequin. The experiment highlighted that, despite the results of the previously conducted metrological characterization, some devices showed evident difficulties in reconstructing the target objects. Thus, we proved that performing a rigorous evaluation procedure similar to the one proposed in this paper is always necessary when choosing the right device