Automatic measurement of hand dimensions using consumer 3D cameras

This article describes the metrological characterisation of two prototypes that use the point clouds acquired by consumer 3D cameras for the measurement of the human hand geometrical parameters. The initial part of the work is focused on the general description of algorithms that allow for the derivation of dimensional parameters of the hand. Algorithms were tested on data acquired using Microsoft Kinect v2 and Intel RealSense D400 series sensors. The accuracy of the proposed measurement methods has been evaluated in different tests aiming to identify bias errors deriving from point-cloud inaccuracy and at the identification of the effect of the hand pressure and the wrist flexion/extension. Results evidenced an accuracy better than 1 mm in the identification of the hand’s linear dimension and better than 20 cm3 for hand volume measurements. The relative uncertainty of linear dimensions, areas, and volumes was in the range of 1-10 %. Measurements performed with the Intel RealSense D400 were, on average, more repeatable than those performed with Microsoft Kinect. The uncertainty values limit the use of these devices to applications where the requested accuracy is larger than 5 % (volume measurements), 3 % (area measurements), and 1 mm (hands’ linear dimensions and thickness)

Measurement of the force exchanged by orthodontic masks and patients

One of the key factors for the success of the orthodontic treatments is the patients' compliance to the prescriptions of the doctors, especially when removable appliances are used. However, at the current state of the art, there are no standard techniques for measuring for how long the patients use the prescribed appliance. Moreover, also the force exerted by the orthodontic appliance on patient is not directly measured. This paper describes two different sensors prototypes, based on pressure resistive transducers and on strain gauges respectively, that measure the traction force in the range between 5 and 30 N. The two prototypes have been calibrated with a purposely designed experimental setup. Results show the higher accuracy of the strain-gauge device in force measurements, that has a standard uncertainty of 0,23 N in the case of half bridge configuration, against a value of 6,7 N for the force sensitive resistors. The time in which the orthodontic mask is worn can be successfully measured also with the pressure-based setup, although the location and the positioning of the setup must be carefully chosen

Vibration transmissibility and apparent mass changes from vertical whole-body vibration exposure during stationary and propelled walking

Whole-Body Vibration (WBV) is an occupational hazard affecting employees working with transportation, construction or heavy machinery. To minimize vibration-induced pathologies, ISO identified WBV exposure limits based on vibration transmissibility and apparent mass studies. The ISO guidelines do not account for variations in posture or movement. In our study, we measured the transmissibility and apparent mass at the mouth, lower back, and leg of participants during stationary and propelled walking. Stationary walking transmissibility was significantly higher at the lumbar spine and bite bar at 5 and 10 Hz compared to all higher frequencies while the distal tibia was lower at 5 Hz compared to 10 and 15 Hz. Propelled walking transmissibility was significantly higher at the bite bar and knee at 2 Hz than all higher frequencies. These results vary from previously published transmissibility values for static participants, showing that ISO standards should be adjusted for active workers

Position uncertainty of a system for the localization of a reciprocating drill for geological inspections

In this paper, we describe a system for the identification of the trajectory of a novel reciprocating drill for geological exploration. The entire system (drill + measurement system) must withstand the harsh environmental conditions typical of the deep underground inspections. The trajectory of the system is determined using the orientation with respect to the gravity (using two dual axis accelerometers) and with respect to the earth magnetic field (using a triaxial magnetometer). Performances of the trajectory measurement system have been studied using Monte Carlo simulations. The reliability of different algorithms for the identification of the trajectory is also discussed. Results of preliminary experiments performed on commercially available MEMS accelerometers evidenced the possibility of obtaining a position error in the order of tens of meters each 1000 m travelled

Design and testing of a 3-DOF robot for studying the human response to vibration

This work describes the design and validation of an electro-mechanical excitation system for characterization of the response of the human body to multiaxial vibrations. The presented system is based on the linear delta configuration and is designed to expose standing subjects to vibration along three perpendicular axes, with an excitation bandwidth of at least 30 Hz and a maximum vibration amplitude of ± 30mm along the vertical direction and ± 20mm along the horizontal directions. The shaker characteristic dimensions are the result of numerical optimization of the inverse manipulability index; the motors and transmissions have been selected using a multibody dynamic simulation. Finite element simulations were performed to ensure that the structural resonances were outside the excitation bandwidth. Once the shaker had been manufactured, experiments were performed to verify the capability of the system in real testing conditions. The mean quadratic error between the modulus of the imposed acceleration and the measured one is between 5.7 × 10-3 and 1.4 × 10-2 m/s2 in the frequency range between 1 and 50 Hz, proving the good outcome of the design process.

Development of a Wearable Sensors System to Monitor Foot-Transmitted Vibration

Exposure to mechanical vibration may lead to harmful effects on the human body if it does not occur within a controlled environment. ISO 2631-1 regulates how to measure the vibration exposure and provides safety limits. According to this standard, the acceleration signals should be measured at the interface between the vibrating surface and the human body for a time interval long enough to represent a whole working shift. This is impossible to achieve in the case of foot-transmitted vibration, as standard equipment cannot fit between the foot and the floor. For this reason, a new system of sensors has been developed to be small enough to fit inside a regular foot insole. This system is powered through batteries and transmits the data to a cellphone through the Bluetooth connection, thus enabling a precise and continuous measurement. After production, the system has been validated by comparing the vibration exposure measured with the insoles to the vibration measured by standard piezo-electric accelerometers. The validation process took place both in laboratory controlled conditions and in real, outdoor conditions. The experimental results show a root-mean-squared error in the evaluation of vibration exposure lower than 0.1 m/s2, thus proving the potential of the proposed system

Validation of smart insoles for the measurement of vibration exposure of workers and athletes

Wearable sensors are becoming increasingly common in daily life for medical care, athletic training, or even daily activity monitoring [1]-[3]. As these systems advance, so do their potential application, but their use for monitoring vibration exposure is limited or absent, despite the adverse effects of vibration on health being well known among the scientific community. To address this deficit, we propose a system of sensorized smart insoles capable of measuring triaxial vibration exposure according to ISO 2631-1. Each insole allows measurement of the vibration exposure and contact pressure at the forefoot and rearfoot, as well as the temperature inside the shoe. We used the insoles to measure the vibration exposure of five male subjects in three different testing conditions: 1) indoor condition (Politecnico di Milano laboratory, atop a triaxial shaker; 2) outdoor condition riding a mountain bike; and 3) skiing. The vibration exposure along the three mutually perpendicular axes was compared with that measured using instrumentation compliant with the current standards (ISO 8041). Results show that the proposed system allows direct monitoring of vibration exposure at the feet, also accounting for the vibration reduction provided by the shoe sole