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

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

Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third Edition - Comments and Statistics

The Catalogue, available at the Centre de Donn\'ees Stellaires de Strasbourg, consists of 13573 records concerning the results obtained from different methods for 7778 stars, reported in the literature. The following data are listed for each star: identifications, apparent magnitude, spectral type, apparent diameter in arcsec, absolute radius in solar units, method of determination, reference, remarks. Comments and statistics obtained from CADARS are given.Comment: A&A, in pres

A gesture-based robot program building software

With the advent of intelligent systems, industrial workstations and working areas have undergone a revolution. The increased need for automation is satisfied using high-performance industrial robots in fully automated workstations. In the manufacturing industry, sophisticated tasks still require human intervention in completely manual workstations, even if at a slower production rate. To improve the efficiency of manual workstations, Collaborative Robots (Co-Bots) have been designed as part of the Industry 4.0 paradigm. These robots collaborate with humans in safe environments to support the workers in their tasks, thus achieving higher production rates compared to completely manual workstations. The key factor is that their adoption relieves humans from stressful and heavy operations, decreasing job-related health issues. The drawback of Co-Bots stands in their design: to work side-by-side with humans they must guarantee safety; thus, they have very strict limitations on their forces and velocities, which limits their efficiency, especially when performing non-trivial tasks. To overcome these limitations, our idea is to design Meta-Collaborative workstations (MCWs), where the robot can operate behind a safety cage, either physical or virtual, and the operator can interact with the robot, either industrial or Collaborative, by means of the same communication channel. Our proposed system has been developed to easily build robot programs purposely designed for MCWs, based on (i) the recognition of hand gestures (using a vision-based communication channel) and (ii) ROS to carry out communication with the robot

A vision-based teleoperation system for robotic systems

Despite advances in robotic perception are increasing autonomous capabilities, human intelligence is still considered a necessity in unstructured or unpredictable environments. Hence, also according to the Industry 4.0 paradigm, humans and robots are encouraged to achieve mutual Human-Robot Interaction (HRI). HRI can be physical (pHRI) or not, depending on the assigned task. For example, when the robot is constrained in a dangerous environment or must handle hazardous materials, pHRI is not recommended. In these cases, robot teleoperation may be necessary. A teleoperation system concerns with the exploration and exploitation of spaces where the user presence is not allowed. Therefore, the operator needs to move the robot remotely. Although plenty of human-machine interfaces for teleoperation have been developed considering a mechanical device, vision-based interfaces do not require physical contact with external devices. This grants a more natural and intuitive interaction, which is reflected in task performance. Our proposed system is a novel robot teleoperation system that exploits RGB cameras, which are easy to use and commonly available on the market at a reduced price. A ROS-based framework has been developed to supply hand tracking and hand-gesture recognition features, exploiting the OpenPose software based on the Deep Learning framework Caffe. This, in combination with the ease of availability of an RGB camera, leads the framework to be strongly open-source-oriented and highly replicable on all ROS-based platforms. It is worth noting that the system does not include the Z-axis control in this first version. This is due to the high precision and sensitivity required to robustly control the third axis, a precision that 3D vision systems are not able to provide unless very expensive devices are adopted. Our aim is to further develop the system to include the third axis control in a future release

Standard and inverse site percolation of straight rigid rods on triangular lattices: Isotropic and nematic deposition/removal

Numerical simulations and finite-size scaling analysis have been carried out to study standard and inverse percolation of straight rigid rods on triangular lattices. In the case of standard (inverse) percolation, the lattice is initially empty(occupied) and linear $k$-mers ($k$ linear consecutive sites) are randomly and sequentially deposited on(removed from) the lattice, considering an isotropic and nematic scheme. The study is conducted by following the behavior of four critical concentrations with the size $k$, determined for a wide range of $k$ : $(i)$[$(ii)$] standard isotropic[nematic] percolation threshold $\theta_{c,k}$[$\vartheta_{c,k}$], and $(iii)$[$(iv)$] inverse isotropic[nematic] percolation threshold $\theta^i_{c,k}$[$\vartheta^i_{c,k}$]. The obtained results indicate that: $(1)$ $\theta_{c,k}$[$\theta^i_{c,k}$] exhibits a non-monotonous dependence with $k$. It decreases[increases], goes through a minimum[maximum] around $k = 11$, then increases and asymptotically converges towards a definite value for large $k$ $\theta_{c,k \rightarrow \infty}=0.500(2)$[$\theta^i_{c,k \rightarrow \infty}=0.500(1)$]; $(2)$ $\vartheta_{c,k}$[$\vartheta^i_{c,k}$] rapidly increases[decreases] and asymptotically converges towards a definite value for infinitely long $k$-mers $\vartheta_{c,k \rightarrow \infty}=0.5334(6)$[$\vartheta^i_{c,k \rightarrow \infty}=0.4666(6)$]; $(3)$ for both models, the curves of standard and inverse percolation thresholds are symmetric with respect to $\theta = 0.5$. Thus, a complementary property is found $\theta_{c,k} + \theta^i_{c,k} = 1$ (and $\vartheta_{c,k} + \vartheta^i_{c,k} = 1$), which has not been observed in other regular lattices. This condition is analytically validated by using exact enumeration of configurations for small systems; and $(4)$ in all cases, the model presents percolation transition for the whole range of $k$

Validation of a smart mirror for gesture recognition in gym training performed by a vision-based deep learning system

This paper illustrates the development and validation of a smart mirror for sports training. The application is based on the skeletonization algorithm MediaPipe and runs on an embedded device Nvidia Jetson Nano equipped with two fisheye cameras. The software has been evaluated considering the exercise biceps curl. The elbow angle has been measured by both MediaPipe and the motion capture system BTS (ground truth), and the resulting values have been compared to determine angle uncertainty, residual errors, and intra-subject and inter-subject repeatability. The uncertainty of the joints’ estimation and the quality of the image captured by the cameras reflect on the final uncertainty of the indicator over time, highlighting the areas of improvement for further development

Monte Carlo-based 3D surface point cloud volume estimation by exploding local cubes faces

This article proposes a state-of-the-art algorithm for estimating the 3D volume enclosed in a surface point cloud via a modified extension of the Monte Carlo integration approach. The algorithm consists of a pre-processing of the surface point cloud, a sequential generation of points managed by an affiliation criterion, and the final computation of the volume. The pre-processing phase allows a spatial reorientation of the original point cloud, the evaluation of the homogeneity of its points distribution, and its enclosure inside a rectangular parallelepiped of known volume. The affiliation criterion using the explosion of cube faces is the core of the algorithm, handles the sequential generation of points, and proposes the effective extension of the traditional Monte Carlo method by introducing its applicability to the discrete domains. Finally, the final computation estimates the volume as a function of the total amount of generated points, the portion enclosed within the surface point cloud, and the parallelepiped volume. The developed method proves to be accurate with surface point clouds of both convex and concave solids reporting an average percentage error of less than 7 %. It also shows considerable versatility in handling clouds with sparse, homogeneous, and sometimes even missing points distributions. A performance analysis is presented by testing the algorithm on both surface point clouds obtained from meshes of virtual objects as well as from real objects reconstructed using reverse engineering techniques